Orthopedic Teaching Cases 2023, Jan, 17 | 12:00 am

Hand CASE 14

CASE                               14                               

A 22-year-old male was climbing a tree when he lost his hold and fell out onto an outstretched left upper limb. He presented to the emergency room with a small wound over the volar aspect of his left palm, minimal clinical deformity, difficulty with moving his index finger and with severe pain. Clinical appearance and radiographs are shown in Figure 4–12A to E.

 

 

 

Figure 4–12 A–D

 

 

 

Figure 4–12 E

 

The most likely diagnosis is:

  1. Sprain of the index finger metacarpophalangeal joint

  2. Complex dislocation of the metacarpophalangeal joint of the index finger

  3. Subluxation of the metacarpophalangeal joint of the index finger

  4. Laceration of flexor tendons of the index finger

  5. Contusion of index finger

 

Discussion

The correct answer is (B). The patient has an open wound over the index finger metacarpophalangeal joint volar aspect. He also has a minimal deformity of the left index finger. This appearance is classic in complex dislocations of the metacarpophalangeal joint of the index finger. These subluxations present with a much greater deformity with the index finger usually pointing dorsally and ulnarly. Compared to the extensive nature of a complex dislocation, counter-intuitively a subluxation, which is a much less significant injury, appears to have a much greater degree of deformity. The patient’s radiographs also show in the PA view that the degree of deformity is minimal. However, the metacarpal and the index of proximal phalanx are not collinear unlike the other three digits, which is the first clue to suggest that this joint is dislocated. Careful assessment of the lateral view shows the base of the proximal phalanx of the index finger lying dorsal to the metacarpal head of the index finger. This finding confirms the presence of a complex dislocation.

The components of complexity of an index metacarpophalangeal joint dislocation include which of the following?

  1. Injury to the volar plate

  2. Buttonholing of the metacarpal head between the flexor tendons and the lumbrical

  3. Dorsal entrapment of the volar plate

  4. All of the above

 

Discussion

The correct answer is (D). During the injury, as hyperextension of the metacarpophalangeal joint occurs, the volar plate, which is attached to the base of the proximal phalanx and the volar aspect of the neck of the metacarpal, is avulsed from its proximal attachment. As the deforming force continues, the collateral ligaments are also torn and the metacarpal head is now free to be displaced volarly as the proximal phalanx gets displaced dorsally. The metacarpal head then displaces volarly in the space between the lumbrical and the flexor tendons with the lumbrical lying radial and the flexor tendons lying ulnar. The volar plate then gets trapped dorsally making this a complex dislocation.

The most appropriate treatment of a complex dislocation at this time is which of the following?

  1. Sustained longitudinal traction with flexion

  2. Gentle traction with a milking over the base of the proximal phalanx as the finger is flexed slowly

  3. Placement of the digit in finger traps for 20 minutes followed by attempt at reduction

  4. Primary open reduction of the metacarpophalangeal joint

 

Discussion

The correct answer is (D). Complex dislocations are, in most if not all circumstances, irreducible by closed means. The pathophysiology described above suggests that the head of the metacarpal is trapped in a so-called “noose,” which is formed by the lumbrical on one side, the flexor tendons on the other side, and by the distal and dorsal entrapment of the volar plate. The noose is completed by the deep transverse metacarpal ligament. Therefore, the metacarpal head is essentially trapped within these four structures. Any attempt at closed reduction by providing traction, almost inevitably tightens this “noose” making a closed manipulative reduction impossible. Therefore, if a single judicious and gentle attempt at closed reduction is unsuccessful, further manipulative trauma is best avoided and the

patient is scheduled for open treatment.

 

Open reduction of the metacarpophalangeal joint dislocation of the index finger can be attempted by:

  1. Volar approach

  2. Dorsal approach

  3. Either approach

 

Discussion

The correct answer is (C). Open reduction of a dislocated MP joint of the index finger has been described using both volar as well as dorsal approaches. The volar approach has been traditionally described. However, it places the radial digital nerve of the index finger at risk. This is contiguous with the lumbrical and is tented over the head of the metacarpal which inevitably lies below the open wound as seen in this patient’s palm. Therefore, any incisions made in this area have to be made carefully so as to avoid an iatrogenic injury to the index radial digital nerve. To facilitate reduction, it is usually necessary to release the A1 pulley thereby creating some degree of slack within the flexor tendons, which are then retracted and the volar plate is then extracted from behind the metacarpal head allowing the phalanx to be reduced upon the metacarpal head. Proponents of the dorsal approach suggest simple splitting of the extensor mechanism between the EDC and EIP, approaching the base of the phalanx dorsally. This allows direct visualization of the dorsally displaced volar plate, which is then split longitudinally, thereby allowing for a safer reduction of the phalanx on the metacarpal head. The dorsal technique does not endanger the radial digital nerve of the index finger.

 

Objectives: Did you learn...?

 

 

Identify the clinical and radiographic appearance of MCP joint dislocation? Describe the pathoanatomy of the injury?

 

 

Select surgical approaches for open reduction and internal fixation? Treat these injuries?