34 Arthroscopic Distal Scaphoidectomy
▪ Treatment Rationale
In a scaphoid nonunion with advanced collapse (SNAC), the initial arthritic change is often due to the abnormal bone contact and stress concentration between the distal fragment of the nonunion and the radial styloid articulating surface. One three-dimensional computed tomographic (CT) study using proximity mapping revealed that when the nonunion site was distal to the dorsal scaphoid ridge (which is the attachment site for the dorsal intercarpal ligament) the distal fragment displaced volar relative to the proximal fragment and the inferred contact area shifted radially toward the radial styloid. When the nonunion site was proximal to the dorsal ridge the distal fragment displaced dorsal relative to the proximal fragment and the inferred contact area shifted toward the dorsal lip of the radius. In both cases the proximity map of the proximal fragment to the radius was unchanged.1 This produces typical arthritic change with thinning of cartilage between the distal fragment and the radius, subchondral sclerosis, provocation of traumatic synovitis, and osteophyte formation. The abnormal motion of the distal scaphoid fragment also leads to synovitis and chondral changes at the scaphotrapezial trapezoidal (STT) joint as well as the scaphocapitate joint. The larger proximal fragment is often capable of transmitting the normal loads across the wrist with preservation of the joint space; hence the arthritic changes surrounding the distal scaphoid fragment are responsible for the early signs and symptoms of the SNAC wrist condition, which includes a loss of both radial deviation and extension of the wrist. Resection of the distal scaphoid therefore can remove a primary source of mechanical impingement.
Removal of the distal scaphoid, however, is not without consequence. The carpal bones behave as a ring composed of two transverse segments (lunate and distal carpal row), both connected radially to the scaphoid and ulnarly to the triquetrum. The scaphoid under the axial load of trapezium tends to rotate in flexion because of its oblique alignment, whereas the triquetrum tends to extend dorsally when it is being pushed by the proximally loaded hamate at the dorsally inclined triquetrum–hamate articulation. Normal carpal stability is thus maintained by a stable equilibrium achieved through the balanced couple of the opposing forces. Marc Garcia-Elias has beautifully illustrated the concept by drawing an analogy of the system to a spring with two (radial and ulnar) ends prolonged distally with divergent directions2 (see Chapter 32). When being compressed by the distal carpal row against the distal radius, the angle between the two arms of the spring increases until the spring is blocked and maximal stability is reached. Shortening of the scaphoid arm due to excision of the distal scaphoid or through a fracture malunion implies a loss of balance between the two ends of the spring. The triquetral arm predominates and promotes a rotation of the entire proximal carpal row in extension until the shorter scaphoid arm reaches the distal row again so as to restore a new balanced status. Thus resection of a substantial portion of the distal scaphoid will reduce the influence of the scaphoid on the overall wrist stability and allows the ulnar column to take control of the entire proximal carpal row, leading to a dorsal intercalated segmental instability (DISI) pattern.3 Whether the wrist can cope with the anatomical malalignment and biomechanical change will also be dependent on several factors, including the volume of the scaphoid being removed; the status of the surrounding ligaments, including the scapholunate, STT, and scaphocapitate ligaments; and the functional status of the patient. The effect may also be influenced by the fracture pattern. In a recent biomechanical study on the wrist force analysis, Matsuki et al reconstructed a normal wrist model from CT images and performed a theoretical analysis utilizing a three-dimensional rigid body spring model.4 Two types of scaphoid fracture nonunion followed by distal fragment resection were simulated, the volar type and the dorsal type. The typing was first described by Nakamura et al in 1991.5 In the volar type, which is associated with a distally located scaphoid fracture, the distal fragment overhangs palmarly relative to the proximal fragment. Conversely, in the dorsal type, which is usually associated with a proximal scaphoid fracture, the distal fragment shifts dorsally with respect to the proximal fragment. It was shown in the study that in the distal fragment resection simulation for a volar type nonunion, the force transmission ratio in the radiocarpal joint resembled that of the normal joint. The pressure concentration in the dorsoulnar part of the scaphoid fossa disappeared, whereas there was minimal change at the midcarpal joint. However, in the dorsal type nonunion, the pressure concentration around the capitate head was aggravated with the simulated distal fragment resection, indicating a potential risk for worsening of any preexisting lunocapitate arthritis.
▪ Historical Perspective
Excision of the distal fragment of the scaphoid in treatment of scaphoid nonunion was first reported by Downing in 1951.6 It was performed together with resection of the radial styloid as an adjunct treatment. It did not gain popularity until 48 years later when Malerich et al reported a similar open technique in a larger series of 19 patients with chronic scaphoid nonunion and associated degenerative arthritis between the distal scaphoid fragment and the radial styloid. Good results were obtained in 13 patients with stage I and early stage II SNAC wrist.7 The arthroscopic version was in fact first proposed by Ruch et al 1 year earlier in 1998.8 They described a technique of treating scaphoid nonunion with associated avascular necrosis consisting of an arthroscopic resection of the distal pole of the scaphoid combined with a radial styloidectomy in three patients, who obtained a complete relief of their mechanical pain and an improvement of wrist motion. An arthroscopic distal scaphoidectomy has the potential advantage of minimizing the surgical damage to the supporting ligaments of the scaphotrapezial joint and the capsular structures of the wrist. This allows for immediate wrist mobilization following operation. The simultaneous arthroscopic surveillance of the joint ensures a more accurate staging of the arthritis and facilitates the clinical decision making. There is also cosmetic benefit with a minimal surgical scar.
Distal scaphoid resection can be regarded as a temporizing procedure to remove a source of mechanical impingement in the painful scaphoid nonunion. The best indication is when the cartilage degeneration, osteophyte formation, and deformity are confined mainly to the distal scaphoid articular surface on both the radiocarpal and midcarpal joint surfaces, accompanied by severe degenerative change over the radial styloid articulation. The capitolunate joint should be intact, and there should preferably be no or minimal DISI deformity.
It is indicated in patients who have a poor prognosis for healing, such as those with severe avascular necrosis, repeated failed surgery, or advanced age, or in chronic smokers and patients with other significant comorbidities. It also has special value when the presence of severe arthritis or deformity may preclude a good result from a conventional scaphoid union procedure. Other factors such as volar type nonunion with a more distally situated fracture site, and the absence of a significant DISI deformity, are favorable considerations.
As recommended by Malerich, marked arthritis at the capitolunate joint can constitute a relative contraindication to the procedure,7 though Soejima et al did report satisfactory outcomes even in patients with late stage II and stage III SNAC wrist.9 Ruch and Papadonikolakis considered intact scapholunate and radioscaphocapitate ligaments as prerequisites to the procedure to minimize a progressive midcarpal collapse with DISI deformity in the long run.10
▪ Surgical Technique
Setup and Instrumentation
The procedure can be performed under local anesthesia or regional anesthesia. Essential instrumentation includes a motorized full-radius shaver and arthroscopic burrs ranging from 2.0 to 2.9 mm, a 2.5 mm suction punch, and a radiofrequency thermal ablation system.
The patient is placed in the supine position with the operated arm supported on a hand table. An arm tourniquet is applied but need not be inflated routinely. Most procedures can be done without the use of a tourniquet. Vertical traction of 4 to 6 kg force is applied through plastic finger trap devices to the middle three fingers for joint distraction via a wrist traction tower. We employ continuous saline irrigation and distension of the joint by using a 3 L bag of normal saline solution instilled with the aid of gravity. An infusion pump is not necessary and is potentially harmful in causing an extravasation of fluid.
We routinely use the technique of portal site local anesthesia (PSLA) in which 1% lignocaine with 1:200,000 adrenaline is injected through a 25 gauge needle into the various standard portal sites just down to the level of the capsule with or without intraarticular infiltration ( Fig. 34.1 ).11 For contingent use, a 22 gauge IV catheter is placed over the dorsum of the operated hand ( Fig. 34.2 ). If there is significant patient discomfort, a sterile pneumatic forearm tourniquet is applied and 20 to 25 mL of 0.5% plain lignocaine solution is injected after exsanguination for intravenous regional anesthesia (FIRA).