Biomechanical Analysis of the Trapeziometacarpal Joint After Surface Replacement Arthroplasty Shigeharu Uchiyama, MD, PhD, William P. Cooney, MD, Glen Niebur, MS, Kai-Nan An, PhD, Ronald L. Linscheid, MD, Rochester, MN A biomechanical analysis of the trapeziometacarpal joint was performed in 7 fresh-frozen normal human cadaveric hands to compare the kinematics of the trapeziometacarpal joint before and after surface total joint replacement. Using a 3-space magnetic Isotrak system (Polhemus, Colchester, VT), which provides a 3-dimensional analysis of motion of joints as well as translation, we found that kinematics and stability of the trapeziometacarpal joint could be duplicated by joint surface replacement arthroplasty provided that normal ligament tensionswere present. (JHand Surg 1999;24A:483–490. Copyright © 1999 by the American Society for Surgery of the Hand.) Key words: Trapeziometacarpal joint, kinematics, surface replacement arthroplasty. The trapeziometacarpal (TMC) joint is as a bicon- cave saddle joint. 1,2 It has 2 reciprocal, saddle- shaped articular surfaces that define the range and direction of joint motion constrained by 5 supporting ligaments. The thumb TMC joint is a common site for osteoarthritis. Wear of the articular surface is a consequence of ligament attenuation and joint insta- bility. Classic regions of arthritic deformity and wear result from compression loading and shear forces at the TMC joint. 3,4 Nonoperative treatment of osteoarthritis consists of abduction splinting, nonsteroidal anti-inflamma- tory drugs, and rest. When pain and instability per- sist, surgical options can be considered. These options include soft tissue interposition, joint re- placement arthroplasty, and surgical fusion. Many soft tissue arthroplasties have assumed a simple con- dylar surface for the thumb TMC joint and replace the joint surfaces with silicone, fascia, or tendon. 5–12 Alternatively, investigators have attempted to dupli- cate the TMC joint kinematics with a ball–socket joint of articulated polyethylene and metal. 13–18 Problems associated with implant loosening, 17,18 however, suggest that this approach will not be suc- cessful. The TMC joint with a universal (saddle joint) design may not be adequately substituted by a ball–socket configuration as the centers of rotation are different. 19,20 To date, normal kinematics of the TMC joint have not been accurately incorporated into any joint re- placement design. Failure of single-axis joint im- plants is based on incorrect assumptions regarding a fixed center of joint rotation. Better definition of the complex normal motion of the TMC joint can clari- fied by examining joint motion throughout the entire range of motion using an electromagnetic tracking device. 19,20 Studies have confirmed that there is no single center of rotation; rather, instantaneous mo- tion occurs between the centers of rotation for flexion From the Division of Orthopedic Research, Biomechanics Labora- tory, Mayo Clinic/Mayo Foundation, Rochester, MN. Received for publication January 26, 1998; accepted in revised form December 29, 1998. Although the author or authors have not received or will not receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article, benefits have been or will be received but are directed solely to a research fund, foundation, educational institution, or other non-profit organization with which one or more of the authors are associated. Reprint requests: William P. Cooney, MD, Division of Orthopedic Research, Biomechanics Laboratory, Mayo Clinic/Mayo Foundation, 200 First St, SW, Rochester, MN 55905. Copyright © 1999 by the American Society for Surgery of the Hand 0363-5023/99/24A03-0024$3.00/0 The Journal of Hand Surgery 483