Volar plate avulsions and central slip avulsion fractures.
Volar plate avulsions
These painful injuries usually occur with forceful hyperextension of the finger, frequently a ‘ball versus finger’ during netball, basketball, cricket or other ball sports. There is a characteristic bruising over the palmar aspect of the PIP joint, with rapid swelling.
The volar plate is a thick ligament that spans the palmar aspect of each of the MCP and IP joints, providing a firm constraint to hyperextension. In volar plate fractures the avulsed chip of bone remains attached to the distal ligament insertion, and on Xray appears as an insignificant looking flake, volar to the PIP joint.
These injuries can be managed conservatively provided the fracture fragment is not large enough to make the joint unstable or is significantly displaced. Hand therapy management is likely to include a dorsal blocking splint, swelling control and exercises to maintain PIP joint flexion, tendon glide and protection for sport when soft tissue healing has resulted in a stable joint. This injury may occur concurrently with collateral ligament injury or in severe cases following dorsal PIP joint dislocation, when surgical review may be warranted.
Central slip avulsion fracture
The central slip forms part of the delicate extensor tendon mechanism that slides over the dorsal aspect of the PIP joint. Central slip avulsion injuries occur when adequate forces – usually a hyperflexion of the PIP (after a ball hits the end of the finger directly) or after a dorsal subluxation of the PIP joint. Both result in an avulsion of the insertion of the central slip at the base of the middle phalanx. The central slip portion of the extensor mechanism remains attached to the avulsed fragment.
These patients are likely to present with either an inability to fully straighten or at best very weak extension of the PIP joint, or a Boutonniere deformity with hyperextension of the DIP. Some ability to straighten the joint may remain due to the integrity of the lateral bands, though their action alone at the PIP joint will be inefficient.
Provided the fracture fragment is not so large as to affect joint stability and is not significantly displaced – these injuries can often be managed conservatively with extension splinting for a period of 6 to 8 weeks. Options can include small POP casts to assist in managing swelling, cylinder splinting and active DIP flexion exercises to assist in bringing the lateral bands dorsally. Failure to adequately manage this injury may result in Boutonniere deformity due to the altered balance of the extensor mechanism.