STT fusion is commonly indicated in stage 1 or II SLAC wrist, Kienbock disease stage 3a or 3b and STT joint arthritis [16–18]. It is frequently performed together with a radial styloidectomy, which can also be accomplished under an arthroscopic mean. The best indication for arthroscopic STT fusion is STT joint arthritis, with or without association with SLAC wrist. Under such circumstance, there is usually no scaphoid mal-alignment and hence no DISI deformity needed to be correct.

Radiocarpal joint arthroscopy should be routinely performed to look for arthritic changes over the radioscaphoid and radiolunate joints. Arthritic change in the former compartment may make the radial styloidectomy a necessary accompanying procedure while change in the latter compartment may constitute a contraindication of the procedure.

Arthroscopic STT fusion is then performed at the midcarpal joint. The STT portal is often required to provide a direct access to the STT joint. The arthroscope is inserted in the MCR portal and directed towards the STT joint by climbing up the slanting articular surface of the scaphoid over the waist portion opposing the capitate till the scapho-trapezoid-capitate junction is reached. The latter is signified by an inverted Y shaped joint interval which I call it as “Mercedes Benz” sign (Fig. 17.10). In STT arthritis condition, the joint is frequently obliterated by synovial overgrowth and joint debris (Fig. 17.11). They need to be cleared up with a shaver and/or radiofrequency probe before the articular cartilage condition can be verified. The joint space may also be contracted with the periarticular soft tissue fibrosis. Joint entry can be facilitated by using a smaller arthroscope such as 1.9 mm. Sometimes the joint space in the whole radial compartment of the midcarpal joint may be compromised and one should not hesitate to start the joint exploration through the ulnar midcarpal portal, which is always less affected under such circumstances. Nevertheless, joint space usually gets enlarged after a period of joint debridement procedure and manipulation to allow sufficient access for the subsequent grafting procedure with bigger instruments. The arthritic joint surface is then debrided of the remaining articular cartilage till subchondral bone is exposed. Initially the trapezium may be difficult to reach as it is situated in deeper space at the STT joint. As long as the cartilage surface of the distal scaphoid and trapezoid is removed with arthroscopic burr, there is progressively more space for the burr to reach the surface of the trapezium. Due to the relatively tight space, bleeding from bone ends may obscure the operative field and tourniquet may be required to control bleeding at this junction temporarily. The proximal part of the articular surface between the trapezium and trapezoid should also be denuded of cartilage with an arthroscopic burr. However complete take down of the articular surface is probably not necessary as normally the TT joint is very tight and stable.

Once the articular surface for fusion is well prepared, a percutaneous fixation of the STT joint can be performed. Fixation can be in ththe form of K wires transfixing scapho-trapezial, scapho-trapezoid, and trapezio-trapezoid joints. I prefer to employ rigid fixation using a cannulated screw with compression inserted from trapezium to scaphoid percutaneously. Fixation of the scapho-trapezoid and trapezio-trapezoid joints then becomes nonessential. With the hand placed horizontally in hand table, a guide pin is inserted through a small stab wound at junction between base of first metacarpal and the trapezium under an image guidance with the aim towards the proximal pole of the scaphoid (Fig. 17.12). Alignment should be confirmed by at least four radiological views of AP, lateral, semi-supinated AP, and semi-pronated PA view. If scaphoid is abnormally flexed and pronated due to scapholunate instability, a 1.6 mm K wire can be inserted percutaneously to be used as joystick to correct the alignment of scaphoid. With the arthroscope in MCR portal, a small probe can also be inserted through STT portal to assist the reduction of scaphoid alignment by hooking onto the distal part of the scaphoid to extend and derotate the scaphoid. The K wire inserted through trapezium can then be driven through to reach the proximal scaphoid.

The arthroscope is then inserted again into the joint through MCR portal to verify the position of K wire (Fig. 17.13). If the joint space at STT joint becomes too tight to allow bone grafting through an arthroscopic cannula, the K wire can be withdrawn from the scaphoid but remains attached to the trapezium. Autogenous bone graft or bone substitute can be inserted through a small cannula as described above to fill up the void (Fig. 17.14). The K wire is then driven back into the scaphoid till the subchondral surface of proximal scaphoid is reached. Length of the inserted portion of the K wire is measured. The screw length should be 2 mm short of the measured length to reduce the possibility of perforation of the proximal articular surface of scaphoid. The K wire is then driven further proximally, perforating the proximal pole of scaphoid and exiting outside skin near the 3/4 portal of radiocarpal joint. The tip of the K wire is grabbed with a hemostat. This trick helps to prevent accident pull off of the K wire during subsequent drilling process with the small cannulated drill. The bone is then drilled with a cannulated drill bit and finally the trapezio-scaphoid joint is transfixed with an appropriate cannulated screw with compression for added stability (Fig. 17.15). The guide wire can be removed afterward. Final alignment of the screw should be confirmed using an image intensifier. The midcarpal joint is then surveyed with an arthroscope to check for any spilled out graft material, which should be removed by using a mosquito grasper or flushed out from the canula with saline.

Wounds are closed with steri-strips and a comfortable bulky dressing is applied supported with a short arm plaster slab. The slab is changed to a removable scaphoid splint after the first week. Active mobilization of the wrist is allowed out of splint under supervision of a hand therapist. Passive wrist mobilization and strengthening exercise can be offered when radiological and clinical union is evidenced, usually around 10–12 weeks post-op (Fig. 17.16).

Four corners fusion is indicated when there is significant peri-scaphoid arthritis in the presence of a relatively intact radio-lunate joint (Fig. 17.17). Under these circumstances, the scaphoid is usually removed surgically as a concomitant procedure with the four corners fusion. Presence of severe arthritic change at the midcarpal joint will exclude the alternative option of proximal row carpectomy and makes the operation a procedure of choice [19, 20]. For pathology that does not involve radioscaphoid arthritis, the indications include midcarpal instability, isolated midcarpal arthritis, or lunotriquetral dissociation with fixed volar intercalated segmental instability alignment of the lunate. When performing four corners fusion in cases without radioscaphoid arthritis, Taleisnik favored scaphoid inclusion [21] and Weiss et al. preferred scaphoid retention [22]. In a cadaveric study carried out by Kobza et al., it was shown that simple four corners fusion with scaphoid retention led to a significant decrease in extension, radial deviation, and ulnar deviation [10]. Four corners fusion with scaphoid excision allowed significantly greater radial deviation but also led to significant increase in radiolunate contact area and the mean contact pressure. However the clinical impact was not known.

We reported four cases of arthroscopic four corners fusion with scaphoidectomy in 2008 [23]. The operation should begin with a surveillance of the radio-carpal joint to confirm an intact radio-lunate articulation and preferably an intact proximal articular surface of triquetrum. Arthroscopic scaphoidectomy is then performed from the midcarpal joint. The operation can be performed without a tourniquet provided that the portal sites and joint space are infiltrated with adrenaline solution in lignocaine. With the arthroscope introduced from the MCU portal, an arthroscopic burr of 2.9 mm is inserted into MCR portal and directed towards the proximal and mid-scaphoid region. The scaphoid is burred at high speed from the articular surface down to the core cancellous bone. Bone debris is removed by intermittently applied suction. To avoid accidental damage of the adjacent articular surfaces to be preserved, a shell of cartilage can be left intact until majority of the cancellous bone is removed. This shell of cartilage can help to separate the burr from the adjacent carpal bone during the burring process (Fig. 17.18). This can be removed piecemeal at the end of the scaphoidectomy procedure by using a small pituitary rongeur or an arthroscopic punch (Fig. 17.19). When taking out the larger piece of bone fragment, it is advisable not to use excessive violence in order to avoid damage to the attaching ligament and soft tissue structure. One trick is to firmly grip on the bone fragment with the small rongeur using both hands while to twist around its own axis and maintain a gentle pulling force. The fragment will gradually lose its connection to the soft tissue and can be delivered smoothly out of the joint. During the delivery process, the surgeon has to maintain a sustained and firm grip on the bony fragment or otherwise it may get lost in the juxta-articular or subcutaneous tissue plane. Under such situation, the surgeon may be forced to enlarge the surgical wound in order to remove the retained bony fragment, which is not desirable (Fig. 17.20). In order to speed up the process, an arthroscopic burr of progressive increase in size such as 3.5 mm and even 4.5 mm can be used when there is more space opened up after part of the scaphoid is removed (Fig. 17.21). The speed of scaphoid excision can often be doubled or even tripled. Alternatively a small osteotome can also be used to break the bone into piecemeal for easier removal. Extreme care has to be exercised during insertion of the larger burr or osteotome to avoid iatrogenic injury to the extensor tendon and cutaneous nerve. The distal few millimeters of the scaphoid can be left in situ so as to preserve the scapho-trapezial ligament. The distal scaphoid tubercle does not normally articulate with the radial styloid and hence its preservation will not cause impingement pain postoperatively.

Once scaphoid is cleared, attention can be paid to the fusion of the midcarpal joint at the four corners region. The arthroscope is now inserted through MCR portal while the MCU portal is reserved for the arthroscopic instruments. The articular surface between the capitate, lunate, triquetrum, and hamate is denuded of cartilage with 2.9 mm burr. The joint surface of the luno-triquetral joint is also burred. I do not routinely burr the articulation between hamate and capitate as the joint is very rigid normally.

After an adequate cartilage destruction, provisional fixation is performed under an image intensifier’s guide. If there is significant ulnar translocation and DISI deformity of the lunate and radial subluxation of the capitate off the lunate margin, the lunate is reduced by gentle flexion and radial translation of the wrist so as to restore the normal radio-lunate relationship. The aim is to have at least half of the lunate sitting over the distal radius. The lunate is then fixed to the radius with a percutaneous K wire of 1.1 or 1.6 mm inserted from the distal radius.

The capitate is then reduced by ulnar translation of the wrist so that it sits as much as possible on the distal lunate articular surface (Fig. 17.22). A percutaneous K wire is inserted from the dorsal surface of the capitate at the distal junction with the base of the third metacarpal under an image guide (Fig. 17.23). The mini-stab wound should be bluntly dissected to avoid iatrogenic injury to the extensor tendon. With the help of a lateral projection on the image guide, the K wire is driven across the capitolunate joint to anchor into the lunate. The angle of attack has to be acute enough in order to catch the central part of the lunate to have a better purchase of the bone. It is most crucial to obtain a good surface contact of the capitolunate joint as the key point of the operation is to achieve solid fusion of the CL joint to avoid late collapse of the midcarpal joint and hence loss of the carpal height.

If satisfactory alignment can be achieved, the K wire is withdrawn from lunate while still attaching to the capitate. This is then followed by the bone grafting procedure at the midcarpal joint as described in session before. With the arthroscope held at MCR portal, the cannula can be inserted through the MCU portal for bone graft or substitute delivery. If scaphoidectomy is included, a French size 6 Foley catheter is inserted via the 3/4 portal to completely obliterate the empty space left after the scaphoidectomy procedure. The balloon is inflated while bone graft or substitute is being delivered to the ulnar midcarpal space (Fig. 17.24). The catheter can be removed after the bone grafting procedure, or can be left in situ for a day or two to serve as a surgical drain.