Hand Dislocation

background

Hand dislocation is a common damage in sports activities and in occupational settings, incessantly appearing to be minor. If the athlete, trainer, or show has already reduced the dislocation, it appears unimpressive when put next with an incredible knee damage or a shoulder dislocation.

however, hand dislocations have actual potential for long-time period incapacity in sports activities and other areas of existence if enough discount is not carried out, if associated injuries are not recognized and as it should be handled or referred, and if doable issues of the damage and its therapy aren't foreseen. The judgment of the initial treating medical doctor may also be crucial in determining the lengthy-time period outcome of these accidents.

Many hand dislocations will also be successfully handled with closed discount, traction, or each. Grossly unstable joints and people for which closed discount has failed most often require surgical intervention. physical and occupational therapy are key elements of therapy all through. Any long-term problems (usually involving stiffness or instability) that improve must be addressed.

NextAnatomyInterphalangeal joints

The bony anatomy of the proximal interphalangeal (PIP) joint includes medial and lateral condyles on the proximal phalanx, with matching concavities on the associated distal phalanx. The joint has a variety of motion (ROM) in flexion and extension but is moderately rigid in abduction and adduction; hence, it is a hinge (ginglymus) joint functionally. The bony anatomy of the distal interphalangeal (DIP) joint is an identical, but the surrounding soft tissue gives extra restriction in flexion.

The extrinsic flexors across each joints are as a minimum four occasions greater than the extensors, permitting flexion contractures to strengthen very abruptly, especially with immobilization in flexion. sufficient ROM, particularly at the PIP joint, is critical for normal hand function.

The PIP and DIP joints are both supported on all 4 sides by using an identical tender-tissue buildings, which embody the volar plate on the palmar side (the integrity of which is essential for a secure reduction), collateral ligaments on the radial and ulnar sides, and the extensor complicated (vital slip, lateral bands, and hood) dorsally (see the image under). These buildings connect to and beef up the joint tablet. For a dislocation to occur, at least 1, regularly 2, and sometimes 3 of those constructions have to be considerably injured.

Lateral view of relevant finger anatomy.

The volar plate is a roughly triangular structure with its base oriented distally, attaching to the volar base of the center phalanx with its tip attaching to the distal facet of the proximal phalanx. The volar plate features generally in limiting hyperextension. to that end, it's just about at all times injured in dorsal dislocations.

The collateral ligaments restrict the joint from opening to varus or valgus stress and are additionally commonly injured in dorsal dislocation. injury to the radial collateral ligament is about 6 occasions more fashionable than harm to the ulnar collateral ligament.

The extensor complex comprises the imperative slip, which attaches to the base of the middle phalanx; the lateral bands, which run dorsolaterally on each and every aspect; and the transverse retinacular ligament, which connects these buildings and extends laterally. It helps restrict volar movement of the base of the center phalanx and subsequently is frequently injured in volar dislocations at the PIP joint, with the center phalanx both tearing the principal slip from its insertion or buttonholing throughout the transverse retinacular ligament between the significant slip and a lateral band.

Metacarpophalangeal joint

The metacarpophalangeal (MCP) joint is regarded as an ellipsoid joint. the head of the metacarpal includes medial and lateral condyles and is narrower on its dorsal floor than on its palmar floor; it fits into the concavity of the bottom of the proximal phalanx. The true collateral ligament attaches to a recess created by the junction of the shoulder and head. The collateral ligament is composed of the next 2 elements:

A dorsally positioned twine portionA fan-formed volar portion or accessory collateral ligament, which extends from the metacarpal to the perimeters of the volar plate

to accomplish flexion and extension on the MCP joint, the anterior and posterior components of the tablet should be lax. When the joint is prolonged, the phalanges have substantial lateral play in abduction and adduction; in consequence, this joint shouldn't be regularly injured. on the other hand, if the ligament is torn, dislocation happens.

The MCP joint of the thumb has radial and ulnar collateral ligaments, which might be loose when the joint is prolonged and tight when flexed. When the joint is extended, the proximal phalanx has the lateral play finished by way of the motion of the interosseous muscles.

When the thumb is flexed and in a practical position, as in the case of many sports activities eventualities (eg, snowboarding, falls on a gloved hand), the ulnar collateral ligament is the structure in danger and will also be ruptured (see Skier’s Thumb). The ulnar collateral ligament can then be displaced in order that the adductor aponeurosis is interposed between the ruptured end of the ligament and its web page of bony attachment.

Carpometacarpal joint

The bony anatomy of the carpometacarpal (CMC) joint includes the 5 metacarpal bases that articulate with the trapezoid, trapezium, capitate, and hamate (in that order) from the radial side of the hand to its ulnar aspect. The CMC joint is a moderately fixed joint section because of the articular congruity of the joint surfaces, with the metacarpal bases acting like concave receptacles to the distal carpal row, and because of the strong interosseous and extrinsic ligament complicated.

The palmar and dorsal ligaments are dissimilar, with the palmar ligaments being better. The scaphoid acts as a link between the proximal and distal carpal rows. The extensor and flexor tendons move over this articular area but add no strength to the CMC joint because the bases of the metacarpals dislocate dorsally relative to the distal carpal row.

the first CMC joint (also referred to as the first metacarpotrapezoid joint) is a extremely mobile saddle joint, with articular surfaces that are reciprocally concavoconvex. crucial mushy-tissue toughen for this primary CMC joint is the deep ulnar or anterior indirect ligament, which runs from the volar beak of the metacarpal to the tubercle of the trapezium. This ligament may also be ruptured, but it tends to be avulsed with a bit of bone (Bennett fracture-dislocation).

PreviousNextPathophysiology

traumatic pressure applied to the hand can be transmitted to bone, gentle tissue, nerves, and vascular structures. for the reason that structures of the hand are on the subject of the surface and close to each different, damage regularly ends up in a combination of fractures, dislocations, and mushy tissue damage.

The DIP and PIP joints both have lateral ligaments and a fibrous volar plate. widespread dislocations are posterior or lateral. standard forces leading to DIP dislocations include a jamming blow to the tip of the finger. Forces that repeatedly result in PIP joint dislocation embody axial loading or hyperextension. Lateral dislocations may result from radial- or ulnar-directed force on the joint.

Dislocations of finger MCP joints are uncommon and frequently are trapped through the surrounding ligaments, during which case surgical relocation is necessary. MCP or palmar dislocations happen when a hyperextension motion occurs with rotation. The finger is bent again towards the top of the hand and is twisted all over the injury. The finger may have been pushed, or compressed, throughout the injury. MCP dislocations are most often related to fractures.

In thumb MCP joint dislocations, the mechanism encountered most often is hyperextension that results in volar dislocations. a significant lateral force can disrupt the collateral ligaments, leading to instability. Gamekeeper’s (skier’s) thumb often results from a fall onto the hand with the thumb in abduction (as when the hand grips a ski pole).[1]

CMC joint dislocation will not be all the time a excessive-power harm. Identification includes careful prognosis of delicate findings on radiographs and may just require additional radiographic views. overlooked diagnosis of carpometacarpal dislocation may end up in vital morbidity.

PreviousNextEtiology

Hand dislocation is caused by the next:

sports injuries (frequently involving contact sports activities or a ball forcefully hanging the tip of the finger)Occupational injuriesFallsTraffic collisionsSport-particular biomechanics

Dislocations of the PIP and DIP joints of the hand more than likely occur most frequently in basketball and football. In basketball, the usual mechanisms embrace being struck by means of the ball, catching a finger on the rim, or contact with another participant. In soccer, the finger is also caught on a jersey, slapped against a helmet, or crushed between some aggregate of gamers, gear, and the bottom. Linemen and protective avid gamers are at best chance. In both sports activities, return to play virtually always requires that the harm can also be splinted stably to allow a power grip.

Dislocations of the MCP and basilar CMC joints happen most repeatedly with falls on the outstretched hand (so-referred to as FOOSH harm) or the flexed supinated wrist. With this extension vector, the forces are transmitted up in the course of the carpus.

accidents and dislocations of the thumb, the MCP joint, and the CMC basilar joint repeatedly happen in falls with the thumb in abduction. Examples of this sort of harm embody a fall on the gloved hand in baseball or utility of an abduction drive to a flexed thumb whereas the hand is greedy an object—as in snowboarding injuries, when the pole influences the proximal phalanx tearing the radial collateral ligament. this happens when the wrist is extended at the time of the injury.

PreviousNextEpidemiology

The annual incidence of all types of dislocations within the hand is roughly 67,000 in the united states. Most hand dislocations are sports activities or occupational injuries, with a lesser number sustained in falls and traffic collisions (every so often associated with airbag deployment).[2, 3, 4, 5, 6]

a lot of these accidents are dislocations on the PIP joint, for the reason that better ROM of this joint makes it extra vulnerable to harm. Of the PIP dislocations, most are dorsal.[7] Volar dislocations of the PIP joint are a lot less in style, more difficult to cut back, and associated with more problems. DIP joint dislocations are also distinct, nearly all the time dorsal, and continuously open.

along with PIP and DIP joint dislocations, MCP and CMC joint dislocations also happen, though less often.[3, 8, 9] The MCP joint of the 4 fingers usually dislocates posteriorly (simple kind) but can, on rare occasions, turn into entrapped between the palmar fascia and the palmar plate and change into irreducibly dislocated.[10] CMC joint dislocation is a disabling injury, which is frequently dorsal and is also related to fractures of the bases of the metacarpals.

Transcarpal fractures in kids are uncommon, but the emergency medical doctor must be cognizant that they do happen.

PreviousNextPrognosis

Anatomic restoration of dislocated joints is imperative for achieving just right long-time period outcomes. correct and stable reduction, early fixation, and initiation of ROM exercise are essential. Dislocations can lead to osteoarthritis, compression neuropathies, and carpal tunnel syndrome. extra incapacity from chondrolysis, carpal instability, and annoying arthritis might also occur.

Median or ulnar neuropathy can happen from direct nerve compression or increased power within the median or ulnar nerve canals.[11] analysis of the patient’s nerve standing is mainly necessary in the early analysis of carpal dislocations.[12] Grip energy have to be tested prior to and after discount.

The prognosis is just right for simple PIP dislocations and most DIP dislocations, in addition to for volar dislocations with the significant slip intact (rotatory subluxations). incessantly, some lack of ROM happens, however with sufficient rehabilitation, a useful vary can also be maintained.

The prognosis is honest for volar dislocations with avulsion of the significant slip if the analysis is made on the time of preliminary evaluation and right kind treatment initiated; alternatively, the prognosis is truthful to negative for dorsal fracture-dislocations.

The prognosis is negative for any dislocation that is incompletely reduced for quite a lot of days and may be very poor for a dorsal fracture-dislocation or a volar dislocation with central slip harm if the analysis shouldn't be made and applicable remedy instituted early during the damage.

The prognosis is excellent in most MCP joint and CMC joint dislocations which can be treated early. lengthen in diagnosis and treatment may just progressively irritate the prognosis. lengthy-term sequelae of hand dislocations with damage to the joint surface embrace instability, ankylosis, and arthrosis.

PreviousNextPatient training

All athletes in excessive-possibility sports should be aware of to have vital finger accidents evaluated and handled with the aid of the staff health practitioner or coach at the time they happen. This helps to steer clear of one of the morbidity from fracture-dislocations, boutonniere accidents, and incompletely diminished dislocations. in addition, all athletes who sustain these injuries must be made aware of the significance of timely follow-up, of the expected length of immobilization, and of the rehabilitation plan, targets, and timetable.

For patient schooling instruments, see broken Hand, broken Finger, and Hand accidents.

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Shoulder Dislocation

Background

Shoulder dislocations may occur from a traumatic injury or from loose capsular ligaments. Different conditions may affect the stabilizing structures of the shoulder and, thus, negatively affect patients with shoulder dislocations.[1]

Note the images below.

Normal shoulder. Anterior dislocation.

This article focuses on glenohumeral joint dislocation. Although acromioclavicular (AC) joint separations are sometimes called shoulder dislocations by nonmedical persons, these are not true shoulder dislocations. Shoulder dislocations occur when the head of the humerus comes out of its socket, the glenoid.

For patient education resources, see the Breaks, Fractures, and Dislocations Center and Sports Injury Center, as well as Shoulder Dislocation and Shoulder Separation.

Related Medscape Reference topics include the following:

Acromioclavicular InjuryAcromioclavicular Joint SeparationsDislocation, ShoulderSuperior Labrum LesionsNextEpidemiologyFrequencyUnited States

The shoulder is the most commonly dislocated joint in the body.[1, 2, 3]

Although most shoulder dislocations occur anteriorly, they may also occur posteriorly, inferiorly, or anterior-superiorly.

Patients with a previous shoulder dislocation are more prone to redislocation.

Other factors that show a clear correlation to redislocation are the age of the patient and concomitant rotator cuff tears and fractures of the glenoid.

Younger patients (teenagers and those aged 20 years) have a much higher frequency of redislocation than patients in their 50s and 60s.[4] Many physicians believe that age is less of a predisposing risk factor for redislocation than activity level.

Patients who tear their rotator cuffs or fracture the glenoid during their shoulder dislocation have a higher incidence of redislocation than patients without these problems.

PreviousNextFunctional Anatomy

Shoulder stability is maintained by the glenohumeral ligaments, the joint capsule, the rotator cuff muscles, the negative intra-articular pressure, and the bony/cartilaginous anatomy.

The main stabilizers of the shoulder joint are the ligaments and the capsule complex. Multiple ligaments are present, but the inferior glenohumeral ligament is the most important and the one most commonly injured during an anterior shoulder dislocation. The injury may be a tear of the ligament/capsule off one of its bony attachments, and/or it may cause a stretch injury to these structures.

Tears in the rotator cuff muscles may also lead to shoulder instability. Four rotator cuff muscles are present in the shoulder. They are found superficial to the glenohumeral ligaments and the bones. Large tears may lead to shoulder instability, even with intact glenohumeral ligaments. Instability of the shoulder can also occur from injury to the nerves that control the shoulder muscles, specifically the axillary nerve.

PreviousNextSport-Specific Biomechanics

The shoulder is a very mobile joint; therefore, it is often placed in awkward positions during sports. Thus, the force from a fall or a blow may be sufficient to cause shoulder damage. If the force is strong enough, the athlete tears the ligaments/tendons, fractures the glenoid or humerus, and dislocates the shoulder.

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Elbow Dislocation

Background

Elbow dislocation is the most common dislocation in children; in adults, it is the second most common dislocation after that of the shoulder.[1, 2, 3, 4, 5] The elbow is amazingly stable, relying more on bony anatomy configuration for stability rather than ligaments. Considerable force is necessary to dislocate the elbow; sports activities account for up to 50% of elbow dislocations, and this type of injury is more commonly seen in adolescent and young adult populations (see the image below).

Posterior and lateral dislocation of the left elbow in a soccer goalie. A small avulsion fracture of the olecranon is present.

Posterior elbow dislocations comprise over 90% of elbow injuries. Early recognition of this injury is required due to the need for early reduction, given a higher likelihood for poor function and possible neurovascular compromise with delays in reduction.[1, 2, 3, 4, 6, 7] Associated fractures are not infrequent with elbow dislocations, given the force that is required to dislocate the elbow.

Anterior dislocations are seen much less commonly than posterior dislocations. Divergent dislocations, which result in the ulna and radius dislocating in opposite directions, are even more rare. In the pediatric population, radial head subluxation is the main cause of elbow dislocations.

For excellent patient education resources, visit eMedicineHealth's First Aid and Injuries Center. Also, see eMedicineHealth's patient education articles Elbow Dislocation and Broken Elbow.

NextEpidemiologyFrequencyUnited States

The rate of elbow dislocation is 6-13 cases per 100,000 people, and this injury occurs more frequently in males than in females. Of all elbow dislocations, 10-50% are sports related. More than 90% of elbow dislocations are posterior dislocations.

PreviousNextFunctional Anatomy

The elbow is primarily a flexion-extension hinge joint, which also allows for pronation and supination. Normal range of motion (ROM) at the elbow should be extension to 0° and flexion to 150°.[1, 2]

The humerus and ulna form a very stable unit, which is generally resistant to disruption unless considerable force is applied. This inherent stability also reduces the likelihood of redislocation. The primary bony stabilizers are the coronoid and radial head.

The medial collateral ligament (MCL) and lateral collateral ligament (LCL) comprise the ligamentous stability of the elbow and act as a back-up system to the elbow's natural bony stability. The MCL consists of 3 bands, the anterior oblique, posterior oblique, and the transverse. The anterior band provides most of the resistance to valgus stress. The LCL has 2 bands, the ulnar collateral and radial collateral.

The 2 main compartments of the elbow are the anterior and posterior compartments. The anterior compartment contains the brachial artery and the ulnar and median nerves. This compartment is more commonly affected by dislocations and is the reason for clinical concern regarding brachial artery disruption and median or ulnar nerve entrapment.[1, 2, 4, 8]

The ulnar nerve passes posteriorly to the medial epicondyle of the humerus, and then it travels deep in the forearm before becoming more superficial again at the wrist. The close proximity of the ulnar nerve to the medial epicondyle allows for the increased likelihood of entrapment when a dislocation occurs. The median nerve is also frequently affected and travels intimately with the brachial artery, which predisposes to simultaneous injury for both the artery and nerve. The posterior compartment contains the radial nerve and triceps brachii muscle.

Anatomically, the mechanism for elbow dislocations is believed to occur as a continuum of damaged/torn structures, beginning laterally with the ulnar portion of the LCL, followed by complete LCL disruption, then damage to the anterior and posterior compartments. The posterior MCL can then become damaged, leaving the anterior portion intact. Further force can allow the elbow to pivot about the anterior bundle of the MCL, potentially damaging it. The LCL, therefore, is considered to be the initial weak link in elbow dislocations.

In the pediatric population, the clinician should be aware of the 6 ossification centers of the elbow joint as well as the annular ligament. The capitellum, radial head, internal (medial) epicondyle, trochlea, olecranon, and external (lateral) epicondyle (CRITOE) is the order in which the ossification centers appear. These centers may often be mistaken for fractures on x-rays. NOTE: A general rule of thumb for the time of appearance of the ossification centers is "1-3-5-7-9-11," which are the ages in years, corresponding to the CRITOE pneumonic.

In cases in which there is radial head subluxation, the radial head slips under the annular ligament and becomes trapped.

PreviousNextSport-Specific Biomechanics

Biomechanically, no single sport definitively increases the risk of elbow dislocations; however, sports that increase the likelihood of a person falling onto an outstretched hand (ie, FOOSH injury) (eg, gymnastics, rollerblading, cycling) may theoretically increase the risk of elbow dislocation.

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Metacarpal Fracture and Dislocation

Background

For as much as we use our hands, it is surprising that they are not injured more frequently. Sports-related metacarpal fractures most commonly occur during participation in contact sports, such as football, rugby, or basketball, in which the hands are unprotected. A direct fall onto the hand (FOOSH injury) while cycling, running, or skiing may also result in a fracture.

See the images below.

Displaced fourth and fifth metacarpal fractures, anteroposterior view. Displaced fourth and fifth metacarpal fractures, lateral view. Fourth and fifth metacarpal fractures, oblique view.

For patient education resources, see the Fractures and Broken Bones Center, as well as Boxer's Fracture, Broken Hand, Cast Care, Finger Dislocation, Finger Injuries, and Human Bites.

Related Medscape Reference topics:

Fracture, Hand

Hand, Fracture and Dislocations: Metacarpal [in the Plastic Surgery section]

Hand, Fracture and Dislocations: Phalangeal

Metacarpal Fractures [in the Orthopedic Surgery section]

Related Medscape topics:

Resource Center Adolescent Medicine

Resource Center Exercise and Sports Medicine

Specialty Site Orthopaedics

Conservative Treatment for Closed Fifth (Small Finger) Metacarpal Neck Fractures

Until the early 20th century, metacarpal fractures were treated exclusively by nonoperative means. Surgery was first suggested as an alternative treatment for certain fracture patterns in the 1920s.[1, 2]

NextEpidemiologyFrequencyUnited States

Metacarpal and phalangeal fractures are the most common fractures of the upper extremity. They account for approximately 10% of all orthopedic fractures.[2, 3] Most occur in young adults, usually as a result of direct blunt trauma, axial loading, or throwing a punch during an altercation. The thumb and small finger are the most frequently injured.

PreviousNextFunctional Anatomy

The finger metacarpals describe a gentle arch in both the axial and coronal planes. Each bone is relatively straight along its dorsal cortex and concave along the palmar surface.

The carpometacarpal (CMC) joints consist of 5 metacarpal bases that articulate with the trapezoid, trapezium, capitate, and hamate. Articular congruity of the joint surfaces, in combination with the strong interosseous and extrinsic palmar and dorsal ligaments, provides stability to the CMC joint. The CMC joints of the index and long fingers are essentially fixed, whereas those of the ring and small fingers enjoy 20-30° of motion in flexion-extension. The thumb is extremely mobile at the CMC joint.

The opposing saddle shapes of the metacarpal base and the articulating trapezium allow for flexion, extension, abduction, and adduction. The joint capsule and ligaments permit a small degree of rotation. The most important soft-tissue support for the first CMC joint is the anterior oblique ligament, which runs from the tubercle of the trapezium to the volar beak of the metacarpal. This ligament may be ruptured in a dislocation, but it is most commonly avulsed by a fragment of bone from the ulnar corner of the metacarpal (Bennett fracture).[4]

PreviousNextSport-Specific Biomechanics

The anatomic relationships described above maintain proper rotational alignment of the fingers and allow for the smooth production of power grip and the ability to clench the fist, functions that are required in many sports. The high mobility of the thumb enables both pinching (squeezing small equipment or objects between the thumb and the forefinger) and grasping of large objects.

Bennett fractures are unstable because of the deforming forces of the intrinsic and extrinsic muscles. The anterior oblique ligament stabilizes the volar-ulnar fragment, but the thenar muscles and abductor pollicis longus displace the remaining metacarpal in the proximal, dorsal, and radial directions.[5]

An analogous situation exists with the reverse Bennett fracture of the small-finger metacarpal. Intermetacarpal ligaments stabilize the radial fragment. The hypothenar and the flexor and extensor carpi ulnaris muscles pull the remaining metacarpal proximally and dorsally.

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Patellar Injury and Dislocation

Background

Patellar pain is common in both athletic and nonathletic individuals. Among athletes, men tend to present with more patellofemoral injuries, including traumatic dislocations, than women. In the nonathletic population, women present more commonly with patellar disorders.

Anatomic morphology of patellar insertion into the intercondylar notch. Muscles influencing patellar biomechanics.

Patellofemoral problems are mainly diagnosed by obtaining a thorough history and performing a physical examination. Imaging studies help confirm the diagnosis. Plain radiography is not as sensitive as magnetic resonance imaging (MRI), but it is the least expensive and most readily available modality.

Patellofemoral syndromes are usually the result of biomechanical imbalances of the kinetic chain, with each individual having an optimal joint-loading limit that is dependent on his or her unique skeletal and muscular anatomy, combined with his or her unique neuromuscular patterning. As this limit is surpassed, the patient is at risk for either acute injury, such as patella dislocation, or chronic injury, such as patellofemoral pain syndrome. Therefore, the goal of a rehabilitative treatment program must be to guide the patient toward performing functional activities without surpassing his or her optimal joint-loading limit. Therapy techniques need to be designed around this principle.

In general, surgery is more effective in preventing recurrences of dislocation because skeletal and muscular components of the patellofemoral joint and extensor mechanism are realigned; however, surgery also has risks. In a patient with normal anatomy, surgery should be considered an option after all conservative treatment modalities are unsuccessful. Patients with anatomic abnormalities may benefit from earlier surgical consideration.

Traditionally, several different systems have been used to classify patellofemoral dysfunction. Some were developed from a functional perspective, whereas others were developed from an anatomic viewpoint. This latter perspective was held by Insall and Merchant, who classified patellofemoral dysfunction according to anatomy.

In 1972, Insall proposed a method of classification based on cartilage damage. The 3 categories in his system are normal, damaged, and variably damaged cartilage. In 1986, Fulkerson and Schutzer developed a system based on measuring arthralgias against joint instability to determine the necessity for surgical intervention. In 1988, Merchant created a system of 5 categories for patellofemoral dysfunction, which included acute trauma, dysplasia, idiopathic chondromalacia, osteochondritis dissecans, and synovial plicae.

No standardized and widely accepted method of patellofemoral dysfunction classification applicable for all specialties has been developed. However, for the purposes of rehabilitation medicine, patellofemoral disorders may be loosely divided into 3 categories. These are soft-tissue abnormalities, patellar instability due to subluxation and dislocation, and patellofemoral arthritis.

For excellent patient education resources, visit eMedicineHealth's First Aid and Injuries Center. Also, see eMedicineHealth's patient education articles Knee Pain and Knee Injury.

NextEpidemiologyFrequencyUnited States

Pain of the patellofemoral joint secondary to patellofemoral dysfunction is the most common disorder of the knee. A 5-year study published in 1984 revealed that 25% of all knee issues in a sports injury clinic were of patellofemoral origin. Another study similarly revealed that 1 in 4 runners is afflicted by patellofemoral pain. Whether related to sports or not, 1 of every 4 painful knees has been reported to be the result of patellofemoral dysfunction.

Patellar injury and dislocation are more prevalent in individuals who participate in certain sports and activities. Anterior knee pain is the most common initial manifestation. In order of descending prevalence, soccer players, weight lifters, runners, and shooters regularly report acute knee pain. In addition, studies show soccer players and weight lifters have the most potential for long-term knee pain.

One study reported 52% of 31 soccer players, 31% of 29 weightlifters, 21% of 28 long-distance runners, and 17% of 29 shooters reported knee pain at least once per month.[1] Thijs et al evaluated gait-related intrinsic risk factors for patellofemoral pain in 102 novice recreational runners.[2] The authors findings suggested an increased risk for patellofemoral pain may be due to excessive impact shock during heel strike and at the propulsion phase of running. In addition, Thijs et al believe their results do not support the theory that those at risk for this condition show an altered static foot posture relative to those who are unaffected.[2]

Swimming also places the athlete at risk for knee pain.[3] On the other hand, sports such as tennis are not associated with knee pain. In summary, factors that cause knee pain include the type, amount, and duration of sports activity.

In addition to activity-specific variance, patellofemoral pain displays some variation between the sexes. A study revealed that in the general population, the female-to-male ratio for patellofemoral dysfunction is 2:1. However, in the athletic population, more men than women experience such syndromes. Further, the study revealed acute dislocation occurred more frequently in males and that recurrent dislocation may be more common in individuals whose initial dislocation occurred when they were younger than 15 years.

Patellofemoral disorders are more likely the result of inappropriate activity duration and type as opposed to genetic factors. Aoyagi et al examined the higher prevalence of joint pain of female Japanese individuals living in rural Japan versus female Americans of Japanese descent living in Hawaii.[4] Despite the similar genetic stock, significant differences in prevalence of joint pain were noted. The researchers postulated that environmental factors influencing activity levels and types were responsible.

Similarly, Zhang et al found that Chinese women in Beijing have a higher prevalence of knee osteoarthritis versus American women in Framingham, Massachusetts.[5] Again, this was thought to be the result of the lower activity levels of women living in the United States. In the same study, men from Beijing were found to have a similar incidence of knee osteoarthritis compared with their Framingham counterparts.

International

Nietosvaara et al studied the annual incidence of acute patellar dislocations in Finnish children younger than 16 years.[6] They found an annual incidence of 43 cases per 100,000 children. Over a 2-year period, 72 children revealed patellar dislocations. Of these, 28 (39%) of the knees had associated osteochondral fractures. Of the 28 osteochondral fractures, 15 had capsular avulsions of the medial patellar margin, and another 15 had intra-articular fragments from the patella and/or lateral femoral condyle.[6]

PreviousNextFunctional Anatomy

Soft-tissue elements that affect the patella are the stabilizing capsular and ligamentous structures within which the patella lies. Some ligaments of the knee are continuous with the fibrous capsule surrounding the patella. When injuries occur, all structures are simultaneously affected. These ligaments hold the patella in place during static and dynamic phases.

The synovial capsule, a separate structure, lies deep to the fibrous capsule and may often be damaged.

The regional anatomy of the knee soft tissues is as follows:

Anteriorly: The synovial capsule forms attachments around the peripheral margins of the patella.Laterally: The lateral or fibular collateral ligament is a tough, round cord that attaches proximally at the lateral epicondyle of the femur and distally at the head of the fibula. This ligament transects the tendon of the biceps femoris, and the popliteus tendon runs medial to it. The biceps femoris tendon is very strong, rarely tears, and protects the joint against varus forces. If torn, the biceps femoris tendon usually tears at the distal end, and the peroneal nerve may be injured, resulting in foot drop. In such cases, the head of the fibula is often fractured because the ligament is stronger than the bone. Increased tension from these lateral structures predisposes individuals for lateral patellar tracking and dislocation. Medially The medial or tibial collateral ligament is a flat band extending from the medial epicondyle of the femur to the medial condyle of the tibia. The medial collateral ligament is continuous with the medial meniscus and the capsule of the knee joint. Three medial ligamentous structures provide static restraint to lateral movement of the patella. These were further defined by a cadaveric study conducted by Andrikoula et al.[7] The medial patellofemoral ligament (MPFL) is a band of retinacular tissue that originates at the medial femoral condyle and attaches to the proximal two thirds of the medial border of the patella. This ligament is overlaid by the distal fibers of the vastus medialis obliquus (VMO) muscle, and the authors found that to a variable extent, its fibers merge into the deep aspect of this muscle. The medial patellomeniscal ligament (MPML) attaches the anterior horn of the medial meniscus to the inferior border of the medial patella. The medial patellotibial ligament (MPTL) connects the distal patella to the tibia.The MPFL has been found to be the major medial soft-tissue restraint to patellar lateral displacement. Studies indicate that up to 97% of acute lateral patella dislocations result in disruption of the MPFL. In studies examining in vitro patella subluxation, an isolated release of the MPTL resulted in a 50% increase in lateral displacement. The results of one study on pediatric patients noted that the zone of MPFL injury after primary patellar dislocation was predominantly isolated to the patellar attachment, which is in contrast to previously published literature. MRI findings showed that the anatomic insertion of the MPFL is distal to the physis in 93% of patients and that the MPFL is more likely to be injured at the patellar attachment. These data provide important evidence to assist in surgical reconstruction of the MPFL in pediatric or adolescent patients.[8] Finally, the 2 more distal structures, the MPML and MPTL, provide important secondary restraints.Posteriorly: The oblique popliteal ligament is broad and strengthens the synovial capsule posteriorly. The oblique popliteal ligament originates inferiorly from the medial condyle of the tibia, and it inserts superiorly and laterally to the posterior aspect of the capsule. The posterior capsule is supplemented by the arcuate popliteal ligament, which stretches from the fibular head and splits. Some fibers run medially to insert into the tibial intercondylar area, and other fibers run superiorly and medially to the posterior lateral epicondyle of the femur. Superiorly: The knee joint capsule inserts into the femur proximal to the condylar margins anteriorly and intercondylar line posteriorly. Inferiorly: The knee joint capsule attaches to the articular margin of the tibia and to the fibular head. The capsule opening for the popliteus is located here. The capsule has openings to the bursae and to the popliteus muscle and tendon.

Pain may develop in these periarticular soft-tissue structures as a result of patellofemoral dysfunction, or vice versa. All these structures operate as a functional unit to optimize weight-bearing capacity. These structures decrease joint-reaction forces (JRFs) and form a base of support for the upper body. If one of these structures is altered, a greater risk of patellar injury and dislocation can develop.

The patellofemoral mechanism is very complicated. Patellofemoral malalignment, abnormal patellar configuration, and a previous history of instability increase the risk for anterior knee pain, patellar dislocation, and recurrent dislocations. The risk for symptoms increases when a combination of factors exists.

PreviousNextSport-Specific Biomechanics

Excluding acute patellar trauma, patellar injury and dislocation are the end result of patellofemoral force imbalances. These force imbalances may also result in less dramatic presentations of patellofemoral pain. Deformities of cartilage resulting from arthritis; congenital variants of the patellofemoral joint; imbalances in lower extremity muscular strength and/or firing pattern; skeletal imbalances at the hip, knee, ankle, or foot; and changes of the patellar stabilizing capsular and ligamentous elements may also contribute to the development of patellofemoral pain and/or dislocations.

The patella is the largest sesamoid bone in the body, and it resides within the complex of the quadriceps and patellar tendons, superiorly and inferiorly, respectively. The patella assists in coordinating the forces of these tendons and functions as both a lever and a pulley. As a lever, the patella magnifies the force exerted by the quadriceps during knee extension. As a pulley, the patella redirects the quadriceps force as it undergoes normal lateral tracking during flexion.

The greater the anteroposterior length of the patella, the greater the angle between the quadriceps and patellar tendons, thus decreasing the force generation needed by the quadriceps to support the upper body at any particular angle of knee flexion. One study demonstrated that the patella most significantly increases the moment arm of the quadriceps at 20° of knee flexion. After patellectomy, the moment arm of the quadriceps is obliterated. After patellectomy, one study demonstrated the effectiveness of the quadriceps-patellar moment arm to be reduced by 31% at 0° of flexion, 22% at 30°, 13% at 60°, 12% at 90°, and 10% at 120°.

The quadriceps tendon and the patellar tendon are continuous with each other and work in cooperation. Muscular forces are transmitted in differing proportions to each tendon over the changing angle of the knee as it flexes and extends. At different angles of knee flexion, the quadriceps and the patellar tendons appear to alternate the role of being the primary force transmitter. From 0-20° of knee flexion, the consensus among researchers is that tension in the patellar tendon is greater than in the quadriceps tendon. From 20-50° of flexion, which tendon has more tension is controversial among research findings. From 50° to full flexion, tension in the quadriceps tendon is greater than in the patellar tendon. Theoretically, isolated development of either the quadriceps tendon or the patellar tendon is accomplished by appropriately limiting knee flexion in exercise programs.

The chondral surface of the patella articulates with the trochlear surface of the distal femur, which forms a groove between the medial and lateral femoral condyles anteriorly. The trochlear surface is continuous with the intercondyloid fossa as it extends inferiorly and posteriorly. The lateral aspect of the trochlear surface is more prominent than the medial aspect, and it extends further anteriorly.

The chondral surface of the patella has several divisions. The 3 transverse ridges create 3 roughly equal-sized upper, middle, and lower groups. Two vertical ridges are found on the chondral surface of the patella. The prominent median vertical ridge separates the medial and lateral facets. The facets are at an acute angle to each other, with the prominent ridge acting as their adjoining corner.

These structures form a V-shaped wedge along the transverse plane for the purpose of better insertion into the depression formed by the trochlear groove. The lateral facet is larger in most individuals. The medial facet is further separated into medial and lateral surfaces by a less prominent vertical ridge. The medial surface of the medial facet is sagittally oriented and only makes contact with the femur when the knee is flexed past 90°. Pain at this range of motion (ROM) that is associated with a compressive mechanism, such as increased JRFs, is suggestive of lesions on the chondral surface.

In full extension, the patella does not fit into the trochlear groove but lies over the smooth synovial tissue that overlies the supratrochlear tubercle. The lateral aspect of the tubercle has a smooth, continuous transition with the trochlear groove. The medial aspect of the tubercle is sharply elevated in regard to the trochlear groove. In normal motion, the patella moves superolaterally, riding the lateral aspect of the supratrochlear tubercle so that it makes a smooth translation from the groove to the tubercle.

The cartilage of the patella contacts the trochlear cartilage of the femur to reduce friction during motion of the patellofemoral joint. Gross normal joint motion is along a sagittal plane. This is why examination of the joint at the transverse plane reveals a congruent articulation, whereas the joint along the sagittal plane is incongruent. Good contact at the transverse plane promotes medial/lateral stability, whereas the incongruent sagittal articulation provides more free space for superior/inferior movement.

Compared with the femoral cartilage, the patellar cartilage is thicker, more pliant, and more permeable. In fact, the cartilage of the inner patella at the prominent median vertical ridge is normally the thickest cartilaginous structure in the body, suggesting its role in counteracting tremendous JRFs. These characteristics of the patellar cartilage allow it to sit deeper in the trochlear groove and conform to its shape, allowing for better articulation and distribution of JRFs. However, these actions place a burden on the collagen-proteoglycan matrix of the patellar cartilage and may be the reason for the higher prevalence of patellar cartilaginous lesions compared with femoral trochlear cartilaginous lesions.

JRFs at the patellofemoral joint are directly related to the contraction of the quadriceps.

The stress at the patellofemoral joint can be mathematically defined as the sum JRF divided over the surface area of force distribution. From 0-60°, the surface area of the patella contacting the femur enlarges with increased knee flexion. This provides a larger contact surface area over which to distribute the load as the load is increasing. Beyond 60° of flexion, anatomic studies regarding the contact area have been inconclusive.

The location of contact for the patella and femur vary with different degrees of flexion and joint load. At 0°, no contact occurs; in early flexion, the distal patella contacts the proximal trochlea; at 90° of flexion, the superior aspect of the patella contacts the femur; when flexion is greater than 90°, the contact area returns to the center of the patella; and when the knee is fully flexed, the inner border of the medial femoral condyle is in contact with the small vertical ridge of the medial facet.

Lateral tracking of the patella leads to decreased efficiency of the quadriceps extensor mechanism and increased patellofemoral joint stress. A lateral patellar subluxation of only a few millimeters results in a decreased contact surface area between the patellar and trochlear surfaces as the lateral facet moves closer to the lateral side of the trochlear groove and the distance between the medial facet and the medial side of the trochlear groove increases. The total JRF, initially distributed over both patellar facets, is now completely transmitted to the lateral patellar facet. This increases lateral facet stress and may result in pain, chondromalacia, and the development of arthritic changes.

A summary of forces on the patellofemoral joint follows. They maintain the physiologic positioning of the patella dynamically within the trochlea and extensor mechanism and provide for patella stability and proper tracking.

Static stabilizers: These provide fixed inhibition to lateral translation of the patella and most notably include the MPFL but also include the MPML and MPTL. These 3 structures play a primary role in stabilization during the first 20-30° of knee flexion when the patella has not fully engaged the trochlea. At knee flexion greater than 30°, the geometry of the patella-trochlea interface combined with posteriorly directed force vectors provide most of the stabilization for the joint. Dynamic stabilizers: These are muscular structures and are primarily the quadriceps group. The VMO muscle has been noted to provide a medially directed dynamic stabilizing force on the patella during knee extension. Andrikoula et al's cadaveric study demonstrated that the VMO fibers are at approximately a 40° medially directed angle to the rectus tendon.[7] Weakness of the quadriceps in general, and specifically of the VMO, allows lateral tracking and deviation of the patella. With persistent lateral patellar deviation, lateral structures (eg, distal fibers of the iliotibial band) contract, resulting in further lateral deviation and greater lateral subluxation. Lateral deviation of the patella also results in altered VMO length and/or tension, which may diminish the medially directed force generation of the VMO muscle. The adductor magnus should also be noted with this group because the distal fibers of the VMO often attach to the adductor magnus tendon and strengthening of the adductor group may contribute to the ability of the VMO to provide active, dynamic restraint.

A summary of risk factors for patella subluxation and dislocation is as follows:

Disruption of either of the 2 groups of stabilizers noted abovePatella alta: This is an abnormally high-riding patella and is associated with a long patella tendon. In a healthy knee, the patella is roughly equal in length to the patella tendon. In patella alta, the ratio of the tendon length to the patella body length is increased, placing the patella in an elevated position that delays patella engagement of the trochlea until an increased angle of flexion. This greatly increases the risk for dislocation. Several different methods can be used to measure patellar instability on a true lateral radiograph of the knee. One such method is the Insall-Salvati index. Patella alta is defined as a ratio of patella tendon length divided by the greatest diagonal length of the patella equal to greater than 1.2. Escala et al found 78% sensitivity and 68% specificity for objective patella instability (OPI) for this parameter.[9] Patella tilt: This parameter may be measured on various axial views of the knee. For patella tilt greater than 11°, Escala et al found 93% sensitivity and an odds ratio of 8.7 for OPI.[9] They found this single parameter to be of the highest combined sensitivity and specificity for identifying patients with OPI. Hypoplastic trochlea: This may also be evaluated on a true lateral radiograph. A classification system was designed by Dejour et al and defined 4 grades of dysplasia.[10] Dejour et al also suggested that the so-called crossing sign they introduced was present on 96% of their patients with patella instability. Using a measurement of trochlear groove depth at the Roman arch level, Escala et al found 85% sensitivity and an odds ratio of 7.7 for OPI.[9] Elevated Q-angle: This represents an estimate of potential lateralizing forces on the patella and is affected by several skeletal features. It is the intersection of 2 lines on the anterior aspect of the lower extremity of a standing patient. One line is from the anterior superior iliac spine to the middle of the patella, and the second line is from the tibial tubercle to the middle of the patella; the Q-angle is the angle between these lines. A Q-angle greater than 15° may predispose an individual to lateral patellar tracking and possible dislocations, although some authors report as high as 20° within a patient’s normal range. This topic is explored in more detail in Physical. Genu valgum: This medially directed knee joint may be the result of a valgus femur, valgus tibia, or intra-articular height loss within the lateral compartment of the knee. Genu valgum may be evaluated on an anteroposterior radiograph. Increased valgum increases the tendency for valgus motion of the knee joint with loading and, as such, increases the potential for lateral motion of the patella. Increased femoral anteversion: This increases the internal rotation of the femur and increases the lateral displacement force vector affecting the patella. According to Post et al, this factor is additive when associated with concurrent genu valgum.[11] This factor may be clinically estimated by evaluating relative internal versus external rotation at the hip. However, accurate measurement is best obtained with computed tomography (CT) scanning of the hips. Coxa valga: This also increases the lateral displacement force vector acting on the patella. This skeletal factor increases valgus stress at the knee. Foot pronation: When present, this contributes to the lateral forces on the patella. It can be easily managed with in-shoe orthotics. Lateral tibial tubercle: This moves the pull of the extensor mechanism laterally and thus increases laterally directed forces on the patella. External tibial torsion: This contributes to the lateral placement of the tibial tubercle, thus increasing the effective Q-angle and increasing the lateral displacement vector acting on the patella. Family history of dislocation: This is reported in the literature and may represent a correlation with an underlying biomechanical anomaly preserved among family members. Other: Escala et al identified other radiographic measurements that are indicators of OPI. These include short patella nose ([9] Kinetic chain models

JRFs of the patellofemoral joint are different when studied under closed and open kinetic chain models. When the kinetic chain is closed (eg, leg press, squats), the JRF increases when the knee is flexed 0-90°. To counteract this load, a greater surface area of the patella comes into contact with the femur, effectively dissipating the forces. However, the contact area does not increase as much as the reaction force. Therefore, forces on the contact areas increase during flexion to 90°. Further flexion greater than 90° causes a leveling off or a decrease in the JRFs. After 90° of flexion, the contact of the quadriceps tendon with the trochlear groove further diffuses the load. Irrespective of the cause, JRFs decrease when the knee is flexed 90-120°.

The open-chain model encompasses lower extremity non – weight-bearing exercises such as leg curls and extensions. When the leg is at 0° flexion, the reaction forces of the patellofemoral joint are low because the patella does not contact the femur when the leg is in full extension. Studies have shown widely varying results from 5-25° of flexion. With the knee flexed to 90°, the JRFs increase and the contact area decreases, resulting in very high patellofemoral stress. A study of knee flexion-extension with a 0.9-kg ankle weight showed JRFs are greatest at 36° of flexion. JRFs are lowest at 90° of flexion.

Closed-chain exercises are most protective for the patellofemoral joint when performed at 0-45° of flexion. Open-chain exercises should be performed from 0-5° of flexion and from 90° to full flexion. JRFs should be limited as much as possible during repetitive motion to avoid chondrosis and chondromalacia. In strengthening or rehabilitative exercises for the quadriceps, programs should be designed with open and closed kinetic chain models in mind.

Anatomic variants

When evaluating patients with patellofemoral disorders, the physician needs to consider anatomic variants, which often manifest as bone deformities and would include bipartite patellae. Additionally, the knee joint may be affected by congenital anomalies. Many genetic syndromes involve the knee joint, including congenital patellar aplasia, nail patella syndrome, small patella syndrome, Meir-Gorlin syndrome, RAPADILINO syndrome (RA for radial, PA for absent/hypoplastic patellas and cleft/high-arched palate, DI for diarrhea/dislocated joints, LI for little size/limb malformations, NO for long, slender nose/normal intelligence), and genitopatellar syndrome. A 2005 article by Bongers et al reviews genetic anomalies in greater depth.[12]

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Elbow Dislocation

Background

Elbow dislocation is the most common dislocation in children; in adults, it is the second most common dislocation after that of the shoulder.[1, 2, 3, 4, 5] The elbow is amazingly stable, relying more on bony anatomy configuration for stability rather than ligaments. Considerable force is necessary to dislocate the elbow; sports activities account for up to 50% of elbow dislocations, and this type of injury is more commonly seen in adolescent and young adult populations (see the image below).

Posterior and lateral dislocation of the left elbow in a soccer goalie. A small avulsion fracture of the olecranon is present.

Posterior elbow dislocations comprise over 90% of elbow injuries. Early recognition of this injury is required due to the need for early reduction, given a higher likelihood for poor function and possible neurovascular compromise with delays in reduction.[1, 2, 3, 4, 6, 7] Associated fractures are not infrequent with elbow dislocations, given the force that is required to dislocate the elbow.

Anterior dislocations are seen much less commonly than posterior dislocations. Divergent dislocations, which result in the ulna and radius dislocating in opposite directions, are even more rare. In the pediatric population, radial head subluxation is the main cause of elbow dislocations.

For excellent patient education resources, visit eMedicineHealth's First Aid and Injuries Center. Also, see eMedicineHealth's patient education articles Elbow Dislocation and Broken Elbow.

NextEpidemiologyFrequencyUnited States

The rate of elbow dislocation is 6-13 cases per 100,000 people, and this injury occurs more frequently in males than in females. Of all elbow dislocations, 10-50% are sports related. More than 90% of elbow dislocations are posterior dislocations.

PreviousNextFunctional Anatomy

The elbow is primarily a flexion-extension hinge joint, which also allows for pronation and supination. Normal range of motion (ROM) at the elbow should be extension to 0° and flexion to 150°.[1, 2]

The humerus and ulna form a very stable unit, which is generally resistant to disruption unless considerable force is applied. This inherent stability also reduces the likelihood of redislocation. The primary bony stabilizers are the coronoid and radial head.

The medial collateral ligament (MCL) and lateral collateral ligament (LCL) comprise the ligamentous stability of the elbow and act as a back-up system to the elbow's natural bony stability. The MCL consists of 3 bands, the anterior oblique, posterior oblique, and the transverse. The anterior band provides most of the resistance to valgus stress. The LCL has 2 bands, the ulnar collateral and radial collateral.

The 2 main compartments of the elbow are the anterior and posterior compartments. The anterior compartment contains the brachial artery and the ulnar and median nerves. This compartment is more commonly affected by dislocations and is the reason for clinical concern regarding brachial artery disruption and median or ulnar nerve entrapment.[1, 2, 4, 8]

The ulnar nerve passes posteriorly to the medial epicondyle of the humerus, and then it travels deep in the forearm before becoming more superficial again at the wrist. The close proximity of the ulnar nerve to the medial epicondyle allows for the increased likelihood of entrapment when a dislocation occurs. The median nerve is also frequently affected and travels intimately with the brachial artery, which predisposes to simultaneous injury for both the artery and nerve. The posterior compartment contains the radial nerve and triceps brachii muscle.

Anatomically, the mechanism for elbow dislocations is believed to occur as a continuum of damaged/torn structures, beginning laterally with the ulnar portion of the LCL, followed by complete LCL disruption, then damage to the anterior and posterior compartments. The posterior MCL can then become damaged, leaving the anterior portion intact. Further force can allow the elbow to pivot about the anterior bundle of the MCL, potentially damaging it. The LCL, therefore, is considered to be the initial weak link in elbow dislocations.

In the pediatric population, the clinician should be aware of the 6 ossification centers of the elbow joint as well as the annular ligament. The capitellum, radial head, internal (medial) epicondyle, trochlea, olecranon, and external (lateral) epicondyle (CRITOE) is the order in which the ossification centers appear. These centers may often be mistaken for fractures on x-rays. NOTE: A general rule of thumb for the time of appearance of the ossification centers is "1-3-5-7-9-11," which are the ages in years, corresponding to the CRITOE pneumonic.

In cases in which there is radial head subluxation, the radial head slips under the annular ligament and becomes trapped.

PreviousNextSport-Specific Biomechanics

Biomechanically, no single sport definitively increases the risk of elbow dislocations; however, sports that increase the likelihood of a person falling onto an outstretched hand (ie, FOOSH injury) (eg, gymnastics, rollerblading, cycling) may theoretically increase the risk of elbow dislocation.

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Metacarpophalangeal Joint Dislocation

Background

Sprains and dislocations of the metacarpophalangeal (MCP) joint of the finger are relatively rare due to the protected position of this joint in the hand.[1, 2, 3, 4] Injuries to the MCP joint of the thumb are more common, although these usually consist of collateral ligament injuries rather than dorsal or palmar dislocations.[5, 6]

MCP joint dislocation is seen in the image below.

Metacarpophalangeal joint dislocation of the small finger. Posteroanterior radiograph demonstrates loss of joint space.

For patient education resources, see the Bone, Joint, and Muscle Center and Breaks, Fractures, and Dislocations Center, as well as Finger Dislocation, Broken Finger, and Sprains and Strains.

NextFunctional Anatomy

The bony anatomy of the finger MCP joint provides greater laxity in extension, with the shallow articular surface of the proximal phalanx resting on the spherical metacarpal head. The metacarpal head is wider in palmar orientation, which leads to increasing bony stability as the joint approaches maximal flexion. Soft-tissue constraints, including the volar plate, accessory and true collateral ligaments, dorsal capsule, extensor tendon and sagittal band, and intrinsic tendons provide additional stability to the MCP joint. This results in an arc of motion from 30º of hyperextension to 120º of flexion, 30-40º of mediolateral laxity, and a small degree of rotational laxity.

The volar plate is a fibrocartilaginous structure firmly attached to the base of the proximal phalanx. Its origin, just proximal to the metacarpal head, is thin and diaphanous; this allows hyperextension of the MCP joint, but it is also the part of the joint most susceptible to injury during dislocations. The deep transverse metacarpal ligaments further stabilize the volar plates of the neighboring MCP joint.

The collateral ligaments originate from mediolateral depressions in the metacarpal head and travel in a distal-palmar direction to insert onto the base of the proximal phalanx. The elliptical shape of the metacarpal head causes these ligaments to loosen in extension and tighten in flexion. The accessory collateral ligament spans from the true collateral ligament to the volar plate, providing additional joint stability in extension. The central extensor tendon and sagittal band augment the thin dorsal capsule. The tendons of the palmar and dorsal interossei add a small degree of dynamic stability.

The MCP joint of the thumb is a condyloid (hinged) joint, with a quadrilateral rather than spherical metacarpal head. The capsule and ligaments of this joint are similar to those of the finger MCP joint. Additionally, the volar plate of the thumb MPJ usually contains 2 sesamoids that articulate with the metacarpal head. The insertion of the thenar muscles into the sesamoids contributes to joint stability. These bony and ligamentous constraints allow less motion than in the MCP joint of the fingers, especially in lateral motion and rotation; abduction and adduction average 10º and a slight amount of pronation occurs during flexion.

PreviousNextSport-Specific Biomechanics

Dorsal MCP joint dislocations have been described as simple or complex. Simple dislocations are those in which no soft tissue is interposed in the joint. These are usually reduced easily with an appropriate closed technique. In a classic article published in 1957, Kaplan elegantly described the anatomic features of the complex MCP joint dislocation.[7] A metacarpal head displaced in palmar orientation sits between the lumbrical muscle radially and the flexor tendons ulnarly. The volar plate, still firmly attached to the base of the proximal phalanx, is displaced into the MCP joint. Longitudinal traction only further tightens these already taut soft tissues, trapping the metacarpal head. Complex dislocations usually require open reduction.

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