Arthroscopic treatment of scaphotrapeziotrapezoidal osteoarthritis

Relevant anatomy and pathomechanics

Isolated scaphotrapeziotrapezoidal (STT) osteoarthritis (OA) involves the distal scaphoid, trapezium, and trapezoid. The true incidence is uncertain because many patients with radiographic changes remain asymptomatic, but it is a common finding with advancing age. Bhatia et al. noted degenerative changes involving the STT joint in 61 out of 73 cadaver hands (average age, 84 yr). Moritomo et al. found similar STT changes in 64 out of 165 cadaver wrists (average age, 76 yr). In Watson’s series it affected 26% of patients who presented with painful degenerative arthritis involving the wrist. It has been reported to be a frequent finding in the presence of chondrocalcinosis. Although it may present as a primary form of arthritis, there is some evidence that STT OA is linked with carpal instability nondissociative (CIND) pattern. Ferris et al. surveyed the radiographs of 697 wrists in patients over 50 years old and found the combination of a dorsal intercalated segmental instability (DISI) deformity and STT OA in 16 wrists. Viegas et al. found a significant correlation between a membranous tear of the scapholunate interosseous ligament (SLIL) and the presence of cartilage erosion in the STT joint. Tay et al. also found that DISI was linked with STT OA in 26 patients.

Distal scaphoid excision for the treatment of STT arthritis is an appealing treatment alternative to fusion because STT motion is retained and it does not carry the risk of nonunion or radial styloid impingement that can occur after a fusion. The procedure is not without consequences, however. The proximal carpal row acts as an intercalated segment between the distal row and the radius and can be envisioned as a multilevel linkage that has the tendency to collapse in a Z -shaped manner. The distal row joint reactive forces are transmitted through the trapezium, which imparts a flexion moment to the long lever arm of the distal scaphoid. This is balanced by an equal and opposite extension moment, which is transmitted through the hamate to the triquetrum. Garcia-Elias and Lluch have likened the situation to a spring with a medial and lateral prong extending distally in divergent directions. Others have compared this to a twisted wash rag in which one end is twisted into flexion (the scaphoid) and the other end is twisted into extension (the triquetrum) with the lunate in between. In either event, if the distal scaphoid lever arm is shortened, the ulnar column takes control of the proximal row, causing the triquetrum to rotate into extension (taking the lunate with it) until a new equilibrium is reached. This produces a CIND pattern with a DISI deformity (CIND-DISI). In addition, the loads are shifted toward the capitolunate (CL) joint.

The scaphoid bridges the proximal and distal rows of the carpus and articulates with the distal radius, the lunate, capitate, trapezium, and trapezoid. Moritomo et al. found an interfacet ridge dividing the distal scaphoid into a dorsoulnar and radiopalmar facet in 140 out of 165 cadaver wrists ( Fig. 26.1 ). Wrists with scaphoids that have a wide dorsoulnar facet were more likely to have STT OA. The ulnar facet of the distal scaphoid was the most common location for degenerative changes as was the radial and central aspect of the trapezoid facet, more so than the trapezium. They also noted that the scaphoid axial plane is oriented in approximately 45 degrees of supination from the anteroposterior (AP) (a.k.a., coronal) plane of the wrist. The trapezium-trapezoid (TT) inclination represents the degree of bone coverage by the facets of the trapezium and the trapezoid over the distal pole of the scaphoid, which is defined as an angle between a line drawn over the distal scaphoid with a line drawn along the axis of the third metacarpal. It ranged from 55 to 90 degrees (ave., 68 deg) ( Fig. 26.2 ). An inclination of 70 degrees or more perpendicular relative to the third metacarpal axis had a significant correlation with the presence of degenerative changes in the STT joint.

These same authors identified three distinct ligaments around the STT joint ( Fig. 26.3 A). The scaphotrapezial (ST) ligament is a V -shaped ligament composed of a radial and ulnar limb that originate from the radiopalmar aspect of the scaphoid tuberosity and attach to the trapezium and the trapezial ridge, respectively, and work as a collateral ligament in STT motion. The scaphocapitate (SC) ligament is a short ligament that originates from the palmar aspect of the scaphoid at the ulnar aspect of the border between the trapezoid facet and the capitate facet of the scaphoid and inserts on the palmar waist of the capitate. The capitate-trapezium (C-Tm) ligament originates from the radiopalmar aspect of the trapezium and inserts directly onto the volar waist of the capitate without any attachment to the trapezoid. The C-Tm presumably acts as a labrum, which deepens the socket of the STT joint and serves to prevent palmar subluxation of the distal pole of the scaphoid ( Fig. 26.3 B). The authors observed that underdevelopment of the C-Tm ligament was associated with a higher incidence of degenerative changes, which may be due to higher shear forces in the STT joint. ^, Garcia-Elias et al. noted that removal of the C-Tm ligament also weakened the stability of the carpal arch.

Diagnosis

Because STT and trapeziometacarpal (TM) arthritis often coexist ( Fig. 26.4 ), patients frequently present with complaints of basilar thumb pain. In isolated STT arthritis, pain is often localized as more medial, within the thenar eminence, and is noted as a deep aching pain not necessarily associated with thumb motion. Palpation of the STT joint, which is located at the junction of the extensor pollicis longus (EPL) and extensor carpi radialis brevis (ECRB), may elicit pain. The Watson test may be painful but the carpometacarpal (CMC) grind test is negative. Gerald Blatt, M.D. introduced the shake test (personal communication) wherein the examiner grasps the patient’s wrist and then shakes the wrist up and down in a rapid fashion. This reproduces the pain. ST joint stress testing can also be performed by moving the wrist from full ulnar deviation to full radial deviation and back, to provoke pain at the STT joint. A diagnostic local anesthetic injection of the STT joint under fluoroscopy may help to localize the site of pain generation.

The definitive diagnosis is usually made radiographically. The STT joint is best seen by maintaining the hand in a half-pronated position and obtaining a pronated oblique view, or by fully supinating the forearm and obtaining an AP view. A lateral view should be performed to measure the SL and radiolunate angles, to rule out a preexisting DISI deformity. Radiographic and visual evaluations of the STT joint do not necessarily correlate with each other. Asymptomatic STT OA is common despite radiographic findings.

Treatment

Nonoperative treatment consists of a thumb spica splint, NSAIDs, and activity modification. Activity modification consists of avoiding forceful pinch and using adaptive equipment such as jar-top openers. Splinting can consist of either a long or short thumb spica splint, or both. Corticosteroid injections have not been studied specifically for STT arthritis but may provide temporary relief. Surgical treatment is indicated after a failure of response to conservative measures.

STT fusion is one method of treatment, though the recognized complications include nonunion, radial styloid impingement, and radioscaphoid OA. Distal scaphoid resection for STT OA is not a new concept, having been proposed more than three decades ago. In 1999, Garcia-Elias et al. reported encouraging results at the midterm follow-up in a series of patients who underwent this procedure. A disconcerting finding, however, was the development of a DISI in over half of the patients, which highlighted the integral role of the palmar ST ligaments in maintaining carpal stability. An arthroscopic distal scaphoid resection or a resection of the proximal trapezium have been proposed as less invasive techniques that have the potential of preserving these ligaments, which may reduce the risk of a DISI deformity, although there are no long-term studies as yet to substantiate this.