Chapter 5 Metacarpophalangeal Joint Arthroplasty
Anatomic and Surgical Overview
• Although arthrodesis may be indicated for deformities of the proximal and distal interphalangeal (IP) joints, arthrodesis is rarely indicated for MP joint deformities because it is so functionally limiting.
• Arthroplasty is the treatment of choice. Surgery consists of a replacement of the MP joint with an implant (typically made of silicone) and soft tissue rebalancing.
1 MP joint arthroplasty necessitates excision of the head of the metacarpal, the hypertrophied synovium, and the base of the proximal phalanx.
2 The medullary canals of the metacarpal and proximal phalanx are reamed and trial implants inserted to determine the best fit.
3 Soft tissue releases are performed to correct ulnar deviation, palmar subluxation, and ulnar intrinsic tightness.
• Many approaches to MP arthroplasty have been taken, including joint resurfacing and hinged, semiconstrained, and constrained implants.
• Awareness of the particular implant used is helpful to the therapist in setting goals for motion.
2 The Swanson (Dow Corning, Midland, MI), NeuFlex (Depuy Inc., Warsaw, IN), and Avanta (Avanta Orthopedics, San Diego, CA) MP implants are all one-piece, flexible prostheses of this type. However, differences between them may result in different, potential motion ranges.
3 Because the NeuFlex MP joint prosthesis rests in 30-degree flexion, greater flexion may result than with use of the Swanson MP implant, which rests in 0-degree extension.
Rehabilitation Overview
• The primary purpose of rehabilitation is to promote functional motion of the implanted MP joints while preserving correct alignment as healing occurs.
• Stability of the implanted MP joints depends on the formation of a fibrous pseudo-capsule around the implants, a process known as encapsulation.
• Protection is provided both through splinting and through patient education, in avoidance of deforming forces during exercises and functional activities.
• Lifelong adherence to joint protection principles is critical to preserve the implants and maximize joint stability.
• MP joint arthroplasty is widely considered to be effective in improving motion, cosmesis, function, and pain. However, implant fracture and deformation have been shown to be common with long-term follow-up, performed at an average of 14 years postoperatively.
