29.1.1 Introduction

The Adaptive Proximal Scaphoid Implant (APSI) pyrocarbon implant, first developed by Péquignot and Allieu in 2000, ² has been reported to be a very useful solution for treating wrists affected by proximal scaphoid nonunion and scaphoid nonunion advanced collapse (SNAC) wrist. ² This ovoid-shaped implant (Fig. 29.1) is intended to replace the scaphoid’s proximal pole to maintain carpal height. The implant helps to restore even force distribution at the proximal carpal row and aims to reduce progression of degenerative (osteoarthritic) changes. ¹ When conservative treatment is no longer beneficial, the principle is to use a spacer to preserve mobility and maintain the radial column of the carpus limiting carpal collapse (Fig. 29.2a). This is an intervention that does not burn bridges other than excluding scaphoid bone union, i.e., other salvage procedures can still be undertaken if it fails.

29.1.2 Implant and Surgical Technique

The commonest approaches are radial or dorsal. A palmar approach has been used but much less commonly. We prefer the radial approach (Fig. 29.2b) which easily allows for a concomitant radial styloidectomy.

Via the radial approach we protect the branches of the radial nerve and dissect down to the radiocarpal joint between the first and the second extensor compartments. If a radial styloidectomy is performed, no more than 6 mm should be removed measuring from the tip to the styloid in order to respect the anterior radiocarpal ligaments and to avoid compromising the stability of the implant (Fig. 29.2c). The extent of the resection of the proximal pole of the scaphoid will depend on the initial damage: for a SNAC wrist, resection will be limited to pseudarthrosis (Fig. 29.2d); for a scapholunate advanced collapse (SLAC) wrist, we recommend excising as little as possible to allow the implant to be centered and to maintain the ligament insertions of the scaphoid. The proximal end of the remaining distal scaphoid is burred to match the shape of the implant (Fig. 29.2e); this aims to enhance implant stability. It is important to remove any posterior bone fragments that could generate a cam effect and cause anterior subluxation or dislocation of the implant. The implant size is based on the radiographic testing of the wrist (Fig. 29.3). The aim is for the implant to be stable through the full range of wrist movement and to avoid breaching the first arc of Gilula. If, in doubt, we recommend undersizing the implant. To avoid impingement, it is necessary to ensure that the proximal scaphoid bone surface lies parallel to the slope of the distal radius in the sagittal plane. We also recommend removing a little of the capitate head of the capitate with a motorized cutter to avoid impingement with the implant. After testing with a trial, the definitive implant is inserted (Fig. 29.4). The joint capsule is closed securely and if necessary the capsule can be sutured to bone (Fig. 29.5). The wrist is supported in a splint/plaster for 2 weeks in a neutral position and then in a removable splint with protected mobilization for the next 4 weeks. From 6 weeks postoperatively onward the patient is encouraged to move without restriction.

29.1.3 Indication and Contraindication

For scaphoid nonunions we recommend the APSI when the proximal pole of the scaphoid is no longer suitable for reconstruction, e.g., due to fragmentation or radioscaphoid arthritis, typically SNAC stages 1 and 2. For SLAC wrists the indication for an APSI is isolated radioscaphoid osteoarthritis without associated carpal collapse. We are very cautious and generally advise against the APSI implant when there is any carpal collapse, especially any dorsal subluxation of the capitate. Small and medium bone cysts are not contraindications for the APSI, as they can be filled during the operation with bone from the scaphoid proximal pole, the radial styloid process, or a bone substitute.

29.1.4 Results in Literature

Several studies have demonstrated its effectiveness in the short and medium terms, providing good pain relief without loss of wrist mobility or strength. ^{2 , 3 , 4 , 5 , 6 , 7 , 8 , 9} The main complication is dislocation. A retrospective analysis of these implants at 10 years has shown 12% early dislocation primarily due to technical errors; and 9% reoperation for implant removal and midcarpal arthrodesis between 3 and 9 years postoperatively. ¹⁰ There is a lack of long-term follow-up using this technique ¹¹ but the biocompatibility of pyrocarbon is well established ¹² and one study has suggested that it reduces the progression of osteoarthritis elsewhere in the wrist. ¹¹

29.1.5 Comparison with Other Techniques

Use of the APSI is a lesser intervention and burns fewer bridges than conventional treatment methods (fusion, proximal row carpectomy) and allows for various bailout options including other conventional treatments.

29.2.1 Introduction

When the capitolunate joint space is destroyed by primary osteoarthritis (OA), osteonecrosis of the capitate head or Fenton’s syndrome (scaphocapitate fracture), an unconstrained capitolunate interposition arthroplasty with a pyrocarbon implant, e.g., Pi2 (pyrocarbon interposition implant) or RCPI (resurfacing capitate pyrocarbon implant) is an option to avoid a partial wrist arthrodesis.

29.2.2 Pi2 and RCPI Implants

The Pi2 ellipsoidal implant is 9 mm thick and comes in two sizes (Fig. 29.6). It was originally intended for treatment of thumb carpometacarpal (CMC) joint arthritis. The RCPI is a one-piece hemiprosthesis for capitate head resurfacing (Fig. 29.7). The truncated spherical head is tilted by 15 degrees and mounted on an intramedullary stem; it is press-fitted into the capitate.

29.2.3 Surgical Technique and Indication

The implants are inserted by a posterior approach with transverse arthrotomy that aims to preserve the continuity of the dorsal intercarpal ligaments. The capitate head is resected by a few millimeters (no more than 5 mm to avoid damaging the extrinsic ligamentous system), and a trial implant is inserted. Similar to the APSI, care should be taken to maintain “normal” carpal alignment clinically and radiologically, particularly the medial carpal space. Typically, a smaller implant is used than for thumb CMC joint OA. The wrist is closed securely to help maintain implant stability especially for implants without a stem. The wrist is supported in a splint/plaster for 2 weeks in neutral and then a removable splint with protected mobilization for the next 4 weeks. From 6 weeks postoperatively the patient is encouraged to move without restriction.

29.2.4 Results in Literature and in Our Experience

The use of a pyrocarbon implant (RCPI) was first reported by Dereudre et al in 2010. ²⁸ They reported good clinical results at 22-month follow-up, but dorsal translation of the distal carpal row relative to the proximal carpal row was noted radiologically. A later study reported encouraging results in a 15-year-old patient followed-up for more than 4 years; he had regained a good range of motion and grip strength and had resumed sport. ²⁹ Our published experience is based on three cases, ³⁰ with a mean follow-up of 4.8 (range 1–8.2) years (Table 29.1). There were improvements in functional scores and pain but not in mobility. So far, we have performed this technique in patients (unpublished) with follow-up of 10 years in one case (Fig. 29.8). Resurfacing of the capitate head using a RCPI implant has been reported following trauma, i.e., Fenton’s syndrome ^{28 , 31} (Table 29.2). Although the functional results are good, there is little improvement in mobility.

Overall, the indications are more limited, but we believe there is a role in specific cases.