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INTRODUCTION
Partial carpal fusion is a useful and proven method of treating specific carpal disorders. Selective intercarpal arthrodesis is used as a means of maximizing postoperative wrist motion and strength while eliminating pain and instability. This form of arthrodesis therefore has remained an important tool for the reconstructive hand surgeon.
We discuss here the current principles, indications, and contraindications of partial carpal fusions for scapholunate advanced collapse (SLAC) and scaphoid nonunion advanced collapse (SNAC) wrists and the current operative techniques with expected outcomes for these common limited wrist fusions.
SCAPHOLUNATE ADVANCED COLLAPSE WRIST
SLAC wrist is the most common pattern of degenerative disease of the wrist. This accounts for 57% of all periscaphoid arthritis. The most common cause of SLAC wrist is rotary subluxation of the scaphoid (RSS) followed by scaphoid nonunion. Other conditions include Preiser’s disease, midcarpal instability, intra-articular fractures involving the radioscaphoid (RS) joint or capitolunate joints, Kienböck’s disease, and secondary rotary subluxation of the scaphoid. These etiologies involve the scaphoid or the periscaphoid ligaments and supports. In the wrist, the scaphoid is the fragile link with regard to degenerative disease, and the radioscaphoid joint is particularly susceptible. When this weak link is injured or its supporting system deranged, a collapse pattern on the radial side is produced ultimately leading to SLAC wrist degeneration. Both dynamic and static rotatory subluxation of the scaphoid can lead to degenerative wear and tear of the radioscaphoid joint over a period of time, and in later stages can affect the capitolunate (CL) joint owing to the shear loading of the joint. Invariably, the radiolunate (RL) joint is preserved in all stages of SLAC wrist involvement and represents the key to preserving a reasonable range of motion.
Stage I of SLAC degeneration occurs first between the radial styloid and the scaphoid. Progression of degeneration leads to complete destruction of the radioscaphoid joint and collapse of the articular space (stage II). Once the collapse occurs, the capitolunate joint is then unable to bear loads normally, and the capitate is then driven off the radial or dorsal radial portion of the lunate articular surface, causing shear stress with eventual destruction of the capitolunate joint and leading to SLAC stage III ( Fig. 34-1 A–C).
SLAC reconstruction relies on the radiolunate joint because of its resistance to degenerative processes, and it is preserved in the initial three stages of SLAC progression. The reason for this is that the lunate fossa in the distal radius is spherical; therefore, the lunate can be rotated volarly or dorsally, radially or ulnarly, and the radiolunate joint remains congruent and still has perpendicular loading even with significant displacement of the lunate into volar intercalated segment instability (VISI) or dorsal intercalated segment instability (DISI).
SCAPHOID NONUNION ADVANCED COLLAPSE WRIST
It has been shown that scaphoid nonunion leads to progressive osteoarthritis of the radioscaphoid joint. The natural history of symptomatic nonunions is well documented. Ruby and colleagues showed a 97% incidence of osteoarthritis in patients with nonunions for at least 5 years and an overall incidence of 55%. Also, in a study by Mack and colleagues in which they studied 47 patients with scaphoid nonunions, the authors concluded that all patients developed osteoarthritis if the nonunion had existed for more than 10 years. This is supported by Inoue and Sakuma, who looked retrospectively at a radiographic and clinical analysis of 102 symptomatic patients with 104 scaphoid nonunions. In their conclusion, osteoarthritis occurred in 22% of scaphoid nonunions within a 5-year period. Seventy-five percent of scaphoid nonunions between 5 years and 9 years old and 100% of nonunions had osteoarthritis if they were over 10 years old. The overall incidence of DISI deformity in their series was 56%. Arthritic changes in a SNAC wrist initially appear in the radioscaphoid joint as radial styloid beaking and dorsal scaphoid osteophyte formation. Later changes are arthritis of the scaphocapitate, midcarpal arthritis, and finally pan-wrist arthritis ( Fig. 34-2 A–C).
The pattern of degeneration is similar to the SLAC degeneration process; however, with SNAC degeneration, the radial fossa that articulates with the proximal pole of the scaphoid escapes degeneration until late in the disease process. The four stages of SNAC degeneration are similar to those of SLAC degeneration and are described in Table 34-1 along with recommended modalities of treatment.
| Stage | SLAC–Anatomical Area Effected | SNAC–Anatomical Area Effected | Treatment Option |
|---|---|---|---|
| I | Radial styloid | Radial styloid |
|
| II | Scaphoid fossa (and radial styloid) | Scaphocapitate articulation (and radial styloid) |
|
| III | Lunate/Capitate articulation (and radial styloid and scaphoid fossa) | Lunate/Capitate articulation (and radial styloid and scaphocapitate articulation) | Scaphoid excision and partial carpal fusion (LC, LCH, LCHT) |
| IV | Pan wrist arthritis | Pan wrist arthritis | Total wrist arthrodesis |
PRINCIPLES OF INTERCARPAL ARTHRODESIS
Various principles of intercarpal arthrodesis have evolved that apply to limited wrist arthrodesis.
Unaffected joints must be left unfused. This is to achieve maximal range of motion postoperatively. However, because of the relatively high nonunion rates of lunocapitate arthrodeses, the hamate and triquetrum are often included in the fusion mass after removal of the scaphoid in a four-corner fusion to maximize the surface area for bone graft consolidation and to improve fusion rates.
External dimensions of the carpal bones involved in the fusion must be preserved. This is to preserve a normal articulation with the adjacent bones and prevent impingement. An example is in the lunocapitate arthrodesis in which an interposition bone graft is used to preserve the length of the carpus. This prevents ulnocarpal (triquetral) impingement. Fusion of the capitate-lunate-hamate-triquetrum in the SLAC wrist reconstruction is an exception, since the scaphoid is removed and reduction of carpal length does not cause impingement.
Fixation is only for bones involved in the arthrodesis (the grid concept). Inadvertent fixation of other bones during fusion inhibits motion of other joints because carpal bones are arranged in a grid.
The Principle of Containment
Any removal of bone to improve range of motion should not be done at the expense of carpal stability. Containment should always be maintained.
FOUR-CORNER ARTHRODESIS
Indications
This procedure is indicated in patients with stages II and III SLAC/SNAC disease.
Contraindications
Because SLAC wrist reconstruction depends on a normal radiolunate joint, an absolute contraindication is any form of wrist arthropathy that may compromise the integrity of the radiolunate joint. Other contraindications include ulnar translation of the carpus and radiolunate pathology as observed intraoperatively or preoperatively. Trauma or generalized inflammatory conditions that lead to radiocarpal instability with ulnar translation are also contraindications for four-corner arthrodesis.
Surgical Technique
After administration of the anesthetic, the hand is placed on the table and a tourniquet is applied at the upper arm. An incision is made over the dorsum of the wrist, which is placed just ulnar to Lister’s tubercle. Subcutaneous fat is retracted, the third extensor compartment is visualized, and the fascia overlying this compartment is incised while protecting the extensor pollicis longus (EPL) tendon. The extensor pollicis longus is retracted radially and protected. The capsule is entered through a longitudinal incision and reflected to expose the proximal and distal rows.
Exposure of the radiolunate joint is made through longitudinal traction on the fingers. This is to confirm that it is well preserved. With confirmation, the midcarpal joint is decorticated. Articular cartilage and subchondral bone are removed from the adjacent surfaces of the capitate, lunate, hamate, and triquetrum until a broad cancellous surface is obtained. Bone graft is harvested from a window in the dorsal radius just proximal to Lister’s tubercle. It is not vital to maintain the original dimensions of the capitate-lunate-hamate-triquetrum joints.
Fixation Methods
Kirschner Wires
The 0.045-inch Kirschner (K) wires are percutaneously preset through the capitate, hamate, and triquetrum to line up with the more proximal lunate. Other wires are passed into the triquetrum directed toward the capitate. Cancellous graft is packed into the deep interval between the capitate and lunate.
Correction of the DISI deformity of the lunate is an important step in SLAC reconstruction. The capitate is volarly displaced onto the lunate for proper alignment. A buttress pin that is inserted through the dorsal edge of the radius can be used to maintain the lunate in a slight VISI position. A pin is driven perpendicularly into the lunate and used as a joystick, which is sometimes helpful in reducing the DISI deformity. It is important to bring the capitate ulnarly and align it centered on the lunate because it tightens ligaments such as the radioscaphocapitate ligament and maintains radial positioning of the lunate ( Fig. 34-3 A and B).
With the lunate reduced into neutral alignment or very slight flexion, the capitate is translated ulnarward to center it with the lunate. The preset pins are advanced into the lunate from the capitate, hamate, and triquetrum, followed by the K wire from the triquetrum into the capitate. Additional K wires can be placed, and extracancellous bone is packed into the intercarpal spaces using a curet or dental tamp. All pins are cut off below skin level, and the capsule is closed with 3-0 braided nylon. The skin is closed with subcuticular monofilament and Steri-Strips ( Fig. 34-4 A and B).
Staple Fixation
Stapling can also be used to fix the capitate-lunate-hamate-triquetrum during four-corner fusions. Power-driven staples have shown increased pullout strength compared with manually driven staples. For four-corner fusion, staples can be used in conjunction with K wires or by themselves. Stapling can be in either of two configuration. One configuration uses four staples in a “box” pattern ( Fig. 34-5 A) and spans the capitolunate, capitohamate, triquetrohamate and lunotriquetral joints. Care should be taken with the lunotriquetral staple because it may impinge on the dorsal lip of the radius. The second configuration is one in which three staples are placed to span the capitohamate, capitolunate, and triquetrohamate joints, as shown in Figure 34-5 B.
Related posts:
Ulnar Head and Styloid Fractures
Traumatic Extensor Carpi Ulnaris Disruption: Subluxation, Dislocation, Rupture
Management of Soft Tissue Contractures Around the Distal Radioulnar Joint
External Fixation of Distal Radius Fractures
Arthroscopic Trapeziometacarpal Arthroplasty
Bone Tumors of the Hand and Wrist
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