Chapter 77: Phalangeal Dislocations

When assessing the stability of the small joints of the hand, stress testing should be performed in both flexion and extension to ensure that the collateral ligaments and volar plate are independently and accurately tested. For example, the proximal interphalangeal (PIP) joint can remain stable in extension despite a collateral ligament tear because of volar plate stability. Flexion of the joint relaxes the volar plate and facilitates assessment of the collateral ligaments. Local anesthetic blocks are often required to perform this assessment. Collateral ligament injuries are graded I through III, according to increasing instability. A grade I injury is grossly stable with only a microscopic tear. A grade II injury results in relative instability in lateral stress testing (around 20 degrees), but with a definite endpoint. A grade III injury results in gross instability with no firm endpoint. Only grade III injuries (complete) lead to a Stener lesion which is specific to the thumb metacarpophalangeal (MCP) joint.1,2 Dislocations are described according to the position of the distal bone (not proximal) relative to normal joint alignment. While the joints proximal and distal to the injury must be imaged, this must be in three (not two) views.

2. Stener B. Skeletal injuries associated with rupture of the ulnar collateral ligament of the metacarpophalangeal joint of the thumb. A clinical and anatomical study. Acta Chir Scand 1963;125:583–586 All of the listed options contribute to the stability of the MCP joint, but during flexion it is particularly stable from the cam effect of the joint. A cam effect converts a rotational motion into a linear one (Fig. 77.1). The metacarpal head is nonspherical, and when flexion occurs the collateral ligaments are placed on stretch. This explains why splints are designed to maintain the joint in flexion, and why Dupuytren’s contractures can be left longer before treatment when involving this joint. There is also more stable bony contact when the MCP joint is placed in 70 degrees or more of flexion, which also contributes to overall stability.1–3

Fig. 77.1 The cam effect is created by eccentric movement of the proximal phalanx on the metacarpal head, causing a dynamic change in collateral ligament length. The head of the metacarpal is commonly found to be trapped between the lumbrical radially and the flexor tendons ulnarly and this is often a reason why reduction is challenging. Closed reduction is most likely to be successful if the wrist is flexed, because this will slacken off the long flexors. This is a fairly high-energy injury and the radial collateral ligament may have been avulsed. A volar approach provides the best access to the key structures during open reduction. Either the radial digital nerve to the index finger or the lumbrical may lie very superficially over the metacarpal head; so, care must be taken when elevating the skin flaps and exploring the joint to avoid damage. Dividing the A1 pulley is sometimes used to slacken off the flexor pull and give more flexibility to the volar joint structures during reduction. Loss of this pulley would not have any negative functional consequences. Dorsal subluxations may also be complicated by the volar plate becoming trapped within the joint. In these circumstances, this must be removed from the joint intraoperatively and followed up with joint immobilization in flexion for the first few weeks.1

injuries? Grade II RCL/UCL injuries of the thumb are treated similarly, with cast immobilization for 4 weeks then protected mobilization for a further 2 weeks. This is because there remains some continuity of the ligaments and in each scenario there will be the potential for adequate healing. In contrast, grade III injuries are treated differently due the risk of a Stener lesion. A Stener lesion is where the adductor aponeurosis becomes interposed between the distal UCL and base of the proximal phalanx. In this situation, primary repair of the ligament cannot occur. Stener lesions occur only at the UCL, since on the radial side the abductor insertion is too wide to become interposed between the RCL fragments. Failure to recognize and treat a Stener lesion of the UCL may result in chronic instability and degenerative changes at the MCP joint. Surgical repair of RCL injures will need repair only if there is volar subluxation.1 UCL injuries of the thumb are 10 times more common than RCL injuries. UCL tears are five times more likely to occur distally at the insertion into the proximal phalanx than at the proximal site. Avulsion fractures of the proximal phalanx can occur with UCL tears. Typically, they are small fracture fragments that do not involve the articular surface and are managed with cast immobilization. Large fracture fragments with more than 2 mm of displacement require intervention.

The MCP joint sits in radial deviation, but there is an endpoint on radial stressing at 45 degrees. The radial Gamekeeper’s thumb is a term used for chronic thumb MCP joint UCL injuries. It may be the result of a missed grade III UCL rupture with a Stener lesion, or it may be caused by repeated minor injuries that culminate in gradual attrition of the ligament. Either way, direct delayed repair of the UCL is not usually possible. The joint should always be assessed for signs of osteoarthritis before considering UCL reconstruction. If arthritis is present, it is usually more appropriate to fuse the MCP joint instead of reconstructing the UCL. Fusion of this joint is well tolerated if there is good IP joint and carpometacarpal (CMC) joint function.1

The PIP joint is the most commonly dislocated small joint in the hand, and dorsal dislocation, because of hyperextension, is the most common mechanism. The joint is normally very stable because of the anatomy of the ligament box complex which comprises the volar plate as well as the proper and accessory collateral ligaments (Fig. 77.2). This ligament complex must be disrupted in at least two planes for dislocation to occur. The volar plate most commonly (80%) avulses distally from the middle phalanx, and when it avulses proximally it can become trapped within the joint necessitating open reduction. The collateral ligaments usually avulse proximally (85%). The normal range of PIP joint motion varies between digits, but is typically more than 100 degrees. The arc of rotation of the DIP joint is usually 90 degrees.1–3 Accessory collateral ligament Proper collateral ligament Volar plate Fig. 77.2 The ligament box complex provides joint stability to the proximal interphalangeal joint.

The classification system for dorsal dislocations of the PIP joint has three categories. The system is useful as it guides treatment. Injury types I and II are soft-tissue injuries only. Type III injuries have associated fractures. Types I and II differ in the degree of soft-tissue damage and joint congruity. Type I is a hyperextension injury with either partial or complete volar plate avulsion and partial articulation of the joint remains intact. Type II is also a hyperextension injury but results in complete dorsal dislocation of the middle phalanx. The volar plate must be completely divided for this to occur and the collateral ligaments must also be damaged.1–3

angle weekly. Following adequate reduction of a dorsal PIP joint dislocation, the size of any volar fragment at the middle phalanx base tends to indicate the degree of stability and subsequent treatment. Fragments less than 40% of the articular surface, as in this case, are often stable. This is because a portion of the true collateral ligament insertion to the base of the middle phalanx is preserved on each side. If the injury is stable with good alignment of the fragment, operative intervention is not required. A splint regimen should protect against recurrent dorsal dislocation, while mobilizing the joint early to reduce subsequent fibrosis and stiffness.1–3

Lateral dislocations of the PIP joint are relatively common and can usually be treated nonoperatively with buddy taping to the adjacent finger and early mobilization. Surgical intervention is not usually required. The main injury involves the RCL, but there will also be a degree of damage to the volar plate. Outcomes following PIP joint dislocation are generally poor, even with good compliance and physiotherapy. The range of movement may take several months to recover and may not return to normal. There is often some long-term residual thickening around the PIP joint because of fibrosis after an injury, which some patients find distressing. Lateral dislocations of the little finger PIP joint are more common than volar dislocations, which are rare.1

Trauma to the DIP joint can result in fractures, dislocations, and associated tendon injuries. For example, the flexor digitorum profundus (FDP) or flexor pollicis longus (FPL) tendons can be avulsed from the bone during dislocation or fractures of the distal phalanx and DIP joint. If these do become detached, then they must be reattached surgically with either a bone anchor or bone tunnel and a pull-out suture. Although the anatomy of the DIP joint shares characteristics with the PIP joint, and the fingertip is very commonly injured, the DIP joint is still less commonly injured than the PIP, especially with regard to dislocations. When DIP joint injuries do occur, they are frequently open injuries and when surgery is required, they usually are undertaken under local anesthetic rather than general anesthetic or regional block. After reduction, it is usual practice to immobilize the DIP joint in slight flexion for a number of weeks. It generally tolerates immobilization well.1