Surgical Technique

Dorsal implantation is recommended by Péquignot. The capsular approach is between the tendons of the extensor pollicis longus on the radial side and the extensor carpi radialis brevis on the ulnar side. Capsular incision is made longitudinally and the distal portion of the scaphoid is exposed.

Palmar implantation is another option made with a longitudinal skin incision on the volar aspect between the flexor carpi radialis (FCR) tendon and the radial artery. ⁷ After reaching the plane of radiocarpal joint, a longitudinal incision is made on the STT joint distal to the radioscaphocapitate ligament.

Whatever the side of the approach chosen, about one-quarter of the scaphoid length (3 to 4 mm) is removed distally after a bone cut is made with an oscillating saw perpendicularly to the axis of the scaphoid.

The appropriate implant size is chosen using trial implants under fluoroscopic control to confirm that enough bone has been removed on the medial side and to check the absence of impingement of the implant especially on its radial side. The implant should be mobile and self-stabilizing.

After closure of the capsule, no ligamentoplasty is required.

Postoperative permanent splinting of the wrist does not exceed 2 to 3 weeks. After this time period passive and active motion exercises of the wrist and the thumb are allowed, and a removable splint is worn for protection for 3 weeks.

Arthroscopic implantation of the STPI spacer has been proposed after arthroscopic debridement and partial resection of the STT joint especially in case of instability of the scaphoid seen with DISI deformity. ^{8 , 9} The arthroscopic portals are located dorsally. One STT portal (ulnar to the tendons of the first compartment) is used as the working portal with a 2.5-mm shaver and burr and occasionally a 3.5-burr, and the second arthroscopic portal (radial to the tendons of the third compartment) is used as the viewing portal using a 1.9-mm arthroscope. A volar portal can be used as if there is difficulty visualizing the dorsoulnar portion of the STT joint. ¹⁰ Joint debridement, synovectomy, and resection of 3 to 4 mm of the distal scaphoid are performed. A small transverse incision can join the two dorsal arthroscopic portals for inserting the implant (Fig. 22.4). Postoperative protocol is same as the open procedure.

Results of the Literature

Several STPI interposition studies have been published ^{6 , 7 , 8 , 9 , 11} with small cohort and an average follow-up of 1.5 to over 6 years. Satisfactory short- and medium-term clinical results were achieved in all the studies; these studies found much improvement in pain and function.

Mobility was not significantly changed, and the grip strength was preserved or even improved. Implant instability was reported in two arthroscopy studies ^{8 , 9} and one open surgery study ⁷ at a rate of 20, 15.4, and 4%, respectively. These were attributed to technical errors related to insufficient medial scaphoid resection.

Pre-existing intracarpal misalignment was controlled or corrected in all series. No failure requiring conversion of this arthroplasty to another surgical solution has been reported in the literature.

Author’s Experience

Good clinical results were also achieved in our experience of 24 STPI interposition. However, two cases of implant luxation required reoperation for repositioning. We do not use the STPI implant anymore because we find this implant to be thick and potentially instable. We prefer to use a thinner and more stable pyrocarbon implant such as the Pyrocardan. ¹²

Surgical Technique (Fig. 22.7)

The approach is an anterior curved incision of about 4 cm centered on the scaphotrapezoid space, delimited by the FCR tendon, and the volar tubercles of the scaphoid and trapezium (Fig. 22.8A). ¹³ The FCR sheath is opened to treat tenosynovitis or to remove the synovial cysts often associated with arthritis. Partial detachment of the proximal insertions of the thenar muscles from the trapezium tubercle is required to access the STT joint, which is then opened longitudinally between the distal flange of the FCR tendon and the scaphoid and trapezium tubercles. Axial traction is placed on the thumb to expose the STT joint space. The aim of joint preparation is to spare the articular surface of the scaphoid and the ligament insertions at the distal pole, while removing the double concavity of the trapeziotrapezoid surface. Resection is performed using a thin oscillating saw, starting with the extremities of the lateral edge of the trapezium, followed by the medial edge, which is relative to the trapezoid (Fig. 22.8b). The articular trapeziotrapezoid surface is then remodeled using a reamer to obtain a slight mediolateral and anteroposterior convexity (Fig. 22.8c). The trial implant is then positioned along its long axis mediolaterally with its concavity facing the new trapeziotrapezoid surface. The size of the implant is chosen to ensure optimal trapeziotrapezoid articular coverage over the scaphoid. A majority of implants used in our practice range from size 14 to size 15. Fluoroscopic control is required to check the bone preparation, especially of the most medial part of the joint and the position of the trial implant during flexion–extension and ulnar and radial deviation movements of the wrist. Kinematics of the distal pole of the scaphoid on the implant surface is also evaluated under visual examination. The final implant is inserted and the articular capsule is closed with resorbable suture. No ligamentoplasty is required even in case the capsule is not closable.

Arthroscopic implantation of Pyrocardan implant in STT joint is also possible but has not yet been reported in the literature.

Postoperative permanent splinting of the wrist does not exceed 2 to 3 weeks. After this time period passive and active motion exercises of the wrist and the thumb are allowed, and a removable splint is worn for protection for 3 weeks.