CHAPTER 31 Trapeziometacarpal Arthritis
ANATOMY
The anatomy of the thumb basilar joint is complex. This biconcave-convex saddle-shaped joint has minimal bony constraints, permitting a wide arc of mobility and facilitating prehension. The ligamentous structures about the elbow promote stability, and the muscular forces about the thumb confer large forces on the thumb in pinch and grasp.1 Basilar joint arthritis at the thumb is related to a variety of factors, including age and use, genetics, and hormonal effects. Bettinger and colleagues described the complex ligamentous structure about the trapeziometacarpal joint and 16 ligaments that stabilize the joint.2 The important anterior oblique (beak) ligament is considered the primary stabilizer of the trapeziometacarpal joint.3 Bettinger and coworkers described superficial and deep components of the beak ligament.2 The superficial and deep anterior oblique ligament, the dorsoradial ligament, the posterior oblique ligament, the ulnar collateral ligament, the intermetacarpal ligament, and the dorsal intermetacarpal ligament stabilize the thumb carpometacarpal (CMC) joint; the other nine ligaments stabilize the trapezium.2 The degree of anterior oblique ligament degeneration corresponded with the extent of arthritis4 in a cadaveric study. Laxity of the beak ligament may alter the contact pressures and congruity of the joint, leading to joint subluxation and arthritic changes.5
PATIENT EVALUATION
History and Physical Examination
Examination may elicit the shoulder sign, in which the CMC joint is subluxated and the metacarpus adducted. The CMC grind test is performed by axial loading and circumduction of the metacarpal on the trapezium. Concomitant or alternative diagnoses should be ruled out; patients may have carpal tunnel syndrome (estimated to coexist in 43% of cases), deQuervain’s tendonitis, or hypermobility of the CMC joint.3,6 The status of the scaphotrapeziotrapeziod (STT) joint and arthritis in this joint should be assessed. Range of motion at the wrist and thumb should be documented, including thumb abduction and opposition (i.e., ability touch the base of the small finger) and metacarpophalangeal (MCP) motion. The MCP joint must be examined in hyperextension, which exacerbates metacarpal adduction. If MCP hyperextension is not addressed during ligament reconstruction, the stresses on the reconstruction may lead to failure. If hyperextension is greater than 30 degrees, the MCP joint should be treated with fusion, capsulodesis, or sesmoidectomy.7 If hyperextension is less than 30 degrees, the surgeon can consider pinning the MCP joint with a Kirschner wire for 4 to 6 weeks.
Diagnostic Imaging
Radiographs that should be obtained include posteroanterior, lateral, and Bett’s views. From plain film radiographs, the extent of disease may be staged according to the system described by Eaton.8 However, it is important to consider the patient’s radiographic stage and symptoms together. Radiographs often demonstrate severe arthritis in a patient with only minimal symptoms; conversely, some patients have minimal changes on radiographs but are quite symptomatic.
