In the early 1970s the design for the metacarpophalangeal (MCP) silastic implant was modified to accommodate the smaller canal size of the distal proximal phalanx and the middle phalanx. These devices were made from a relatively strong, non-reactive rubber polymer. The hinged silastic spacer remains the most common implant for PIPJ reconstruction, particularly in the rheumatoid patient, in whom 90% 10-year survivorship has been reported [19,20]; however, silastic implant arthro-plasty is generally not recommended for the index or long fingers, particularly in active individuals [18,21]. The bony resection required for the proximal phalangeal head sacrifices the PIPJ radial and ulnar collateral ligaments, thereby causing the silastic to become vulnerable to the high loads seen during the pinching maneuver.
For silastic PIPJ arthroplasty, a volar approach is often used with a standard Brunner incision. The A-3 pulley is excised and the flexor tendons are retracted to expose the volar plate, which is detached proximally off the proximal phalanx. The collateral ligaments are released and the PIPJ hyperextended, much like a shotgun, to expose the articular surfaces of the proximal and middle phalanges. The proximal phalangeal head is excised with an oscillating saw. The base of the middle phalanx is not resected to avoid postoperative collapse deformity of the digit. The intramedullary canals are prepared with broaches. Rotational malalignment is specifically avoided.
Trial components are sized and a trial reduction performed. Once a satisfactory implant has been chosen, the permanent prosthesis is placed and the PIPJ reduced. Grommets are not used. The collateral ligaments are reattached to the proximal phalanx, if possible. This is not always feasible. The volar plate can be split longitudinally and used to reconstruct the collateral ligaments. Ideally, the volar plate should be repaired and the original collateral ligaments reattached. After the first week postoperative, the patient is placed in an extension outrigger splint, and active flexion and passive extension are initiated with a flexion block. The degree of flexion permitted is gradually increased, such that the extension outrigger splint is discontinued at 4 weeks postoperative. The operative digit is then buddy-taped to the adjacent digit for up to 3 months.
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