Revisiting the Critical Pathology of Primary Thumb Trapeziometacarpal Osteoarthritis: Volar Beak Ligament Degeneration

Abstract

Purpose: Volar and dorsal capsular contributions to trapeziometacarpal joint stability have been extensively studied in laboratory models. We investigated the less-understood relationship between trapeziometacarpal joint osteoarthritis and capsuloligamentous integrity in human thumbs.

Methods: Eighty thumb trapeziometacarpal joints from two distinct groups of 20 anatomical donors were prospectively specified for dissection through either a dorsal (20 men, 20 women; mean age 83 (72-100) years) or volar (24 men, 16 women; mean age 90 (76-100) years) arthrotomy. One thumb evidenced prior anatomical dissection, another underwent surgical arthrodesis, and 78 were anatomically undisturbed. Seven joints exhibited inflammatory arthritis, leaving 71 available for study. Capsuloligamentous structures were characterized through an opposite side arthrotomy, and articular surfaces were stained with methylene blue. Trapezium/metacarpal surface eburnation ratios were calculated using ImageJ analysis and digitally summed to display aggregate topographical wear pattern heat maps by arthritis stage.

Results: Osteoarthritic eburnation was similar in both arthrotomy groups. Twenty (28%) joints contained no surface eburnation, 15 (21%) early osteoarthritis, 17 (24%) advanced osteoarthritis, and 19 (27%) end-stage osteoarthritis. Early arthritis specimens exhibited greater trapezial than metacarpal eburnation; Trapezium/metacarpal ratios were 1.22, 1.07, and 0.98 for early, advanced, and end-stage, respectively. Through a dorsal arthrotomy, complete beak ligament detachment from the metacarpal was observed in 8 of 8 end-stage, 7 of 8 advanced, and 6 of 7 early osteoarthritis specimens. Eleven of 12 thumbs without eburnation exhibited no beak ligament degeneration. Through a volar arthrotomy, none of 36 specimens exhibited dorsal capsuloligamentous degeneration irrespective of articular surface eburnation.

Conclusions: Volar beak ligament detachment from the thumb metacarpal, not dorsal capsular degeneration, is strongly associated with trapeziometacarpal osteoarthritis in elderly cadaveric thumbs. Greater trapezial eburnation in early-stage osteoarthritis suggests translational metacarpal instability.

Clinical relevance: Volar beak ligament degeneration and trapeziometacarpal instability represent the primary pathology associated with age-related osteoarthritis and should inform surgical treatment.

Keywords: Basal joint osteoarthritis; beak ligament; eburnation; trapeziometacarpal instability; trapeziometacarpal wear patterns.