Department of Orthopaedics, Division of Hand, Shoulder and Elbow Surgery, University of Rochester Medical Center, 601 Elmwood Avenue, Box 665, Rochester, NY 14642, USA
The normal ligamentous anatomy of the thumb basal joint provides extraordinary stability without sacrificing motion . In providing a fixed pivot point at the thumb trapeziometacarpal (TM) joint, substantial cantilever bending forces are resisted, and large loads are accommodated during pinch and grip without subluxation or pain [2,3]. When ligamentous restraint is compromised, however, functional grip and pinch may result in painful synovitis and hypermobility at the TM joint long before the development of cartilage wear and arthritis .
This article describes the rationale and results of a "biomechanical" strategy to restore TM stability when symptomatic Eaton Stage I disease exists. Though the author has performed TM arthros-copy, synovectomy, and capsular shrinkage for such cases in 10 patients, I have been dissatisfied with the outcomes, particularly pain relief, and currently rely exclusively on extension osteotomy as treatment for this subset of patients.
Radiographs are typically normal, or the TM joint may appear widened, from synovitis. This stage reflects Stage I of the classic Eaton classification of basal joint arthritis. Physical examination may reveal only pain with TM stress and tenderness to palpation beneath the thenar cone (Fig. 1). Deformity, frank instability, subluxation, or crepitance are unusual. It is critical to evaluate the entire hand for signs and symptoms of carpal tunnel syndrome, stenosing flexor tenosynovitis,
DeQuervain's disease, flexor carpi radialis tendonitis, and subsesamoid arthritis. Indeed, when the radiograph is normal and tenderness exists on palpation of the thenar muscles at the level of the TM joint, Stage I disease effectively becomes a diagnosis of exclusion [4,5].
Functional incompetence of the basal joint's palmar oblique ligament (POL) results in pathologic laxity, abnormal translation of the meta-carpal on the trapezium, and generation of excessive shear forces between the joint surfaces, particularly within the palmar portion of the joint during grip and pinch activity [6,7]. Histologic study has shown that attritional changes in the POL at its attachment to the palmar lip of the metacarpal precede degeneration of cartilage .
Cadaveric investigation of acute dislocation of the thumb TM joint has shown that the primary restraint was the dorsoradial (DRL) ligament . Thus the POL and DRL ligament are critical stabilizers of the TM joint during lateral pinch, and when either or both are attenuated or incompetent, some degree of dorsal translation of the metacarpal may cause symptoms of pain. Indeed, though Eaton and Littler  recommended ligament reconstruction in 1973 to restore thumb stability in cases of end-stage osteoarthritis, subsequent reports have confirmed its efficacy for early stage disease—the hypermobile TM joint—as well [10,11].
Rationale for osteotomy
Pellegrini and colleagues  were the first to evaluate the biomechanical efficacy of extension
osteotomy (Fig. 2). Palmar contact area was unloaded with a concomitant shift in contact more dorsally so long as arthrosis did not extend more dorsal than the midpoint of the trapezium. Shrivastava and coworkers  studied the effect of a simulated osteotomy on TM joint laxity by flexing the metacarpal base 30°, thus placing the joint in the relationship it would assume if an extension osteotomy was performed (Fig. 3). The simulated extension osteotomy reduced laxity in all directions tested: dorsal-volar (40% reduction), radial-ulnar (23% reduction), distraction (15% reduction), and pronation-supination (29% reduction). They hypothesized that the beneficial clinical effects of a thumb metacarpal extension osteotomy may be partially caused by tightening of the DRL, which might reduce dorsal translation.
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