The Pathophysiology of the Osteoarthritis of the Thumb

Abstract

Introduction: More than 16 ligaments around the joint have been described by Bettinger et al. (1999); four ligaments and the joint capsule are the main stabilizers of the trapeziometacarpal (TM) joint. These ligaments are the dorsoradial (DRL), intermetacarpal (IML), anterior oblique (AOL), and posterior oblique ligaments (POL). The importance of each of these ligaments in the stability of the TM joint is debatable. The purpose of the study was (1) to describe the anatomy and dimension of the thumb carpometacarpal (CMC) joint ligaments, (2) to assess the ligament lesions and the degree of subluxation of the CMC joint, and (3) to measure cartilage thickness in the trapezium and metacarpal and pattern of chondromalacia and osteoarthritis (OA). We investigated the role that these ligament ruptures play in the pathophysiology of the OA. Methods: Twenty-five fresh-frozen cadaver hands were dissected of all soft tissue to expose the joint capsule and ligaments of the TM joint. There were 14 male and 11 female with mean age of 67 years (range, 51-94 years). The dissection was performed under ×4.5 loupe magnification. We showed the main ligaments and also the ligament ruptures in IML, AOL or beak ligament, dorsal oblique ligament (DOL), and DRL. We described the location of the ligament tears and whether these ruptures were partial or total. The ligament ruptures and the metacarpal translation associated with these ruptures were measured (mm). Cartilage thickness in the trapezium and metacarpal of specimens was assessed. We described the degree of degenerative changes using the stanging protocol to describe visual degeneration by Koff et al. (2003). We investigated the relationship between the ligament ruptures and the area of chondromalacia and OA. Statistical analysis of data was performed with the chi-square test, and the level of significance was P < .05. Results: Seven principal ligaments of the thumb CMC joint were identified using Berger’s principles (200s1). Ligament lesions were found in all 25 specimens. Isolated rupture of the AOL was found in 7 (28%), isolated rupture of the DRL was found in 10 (40%), isolated rupture of the IML was found in 2 (8%). Combined rupture of the AOL and IML was found in 2 (8%) and combined rupture of the DRL and IML in 4 (16%) joints. The mean metacarpal displacement due to isolated rupture of the ligaments was DRL 17 mm ( P = .006), AOL 11 mm, POL 0.5 mm, and IML 0.4 mm. We found 2 cases OA stage I, 7 cases OA stage II (1 IIa, 3 lib, and 3 IIc), 9 OA stage III, and 7 OA stage IV. There was a relationship between the presence of a tear in the DRL and the presence of OA in the radial quadrants ( P = .032). Conclusion: These observations suggest a translation of metacarpal on trapezium in the production of arthritic lesions and support a hypothesis that pathologic joint instability could be a cause of CMC OA. This study suggests that repairing the DRL during ligament reconstruction of the CMC joint should be considered.