Partial Trapezoid Excision in Thumb CMC Arthroplasty for STT Arthritis: A Cadaveric Study

Abstract

Thumb carpometacarpal (CMC) joint arthroplasty is one of the most commonly performed surgeries by hand surgeons. A large portion of these patients also have scaphotrapezoidal (ST) arthritis in addition to CMC arthritis. The purposes of this study were to quantify the amount of transverse trapezoid resection necessary to prevent ST impingement and to compare an oblique with a transverse osteotomy of the trapezoid. A total of 9 cadaveric specimens were used and were randomly placed into 2 groups. Group 1 had sequential transverse osteotomies and the space between the scaphoid and trapezoid was measured in various wrist positions. Group 2 had oblique osteotomies and the ST distance was measured in multiple wrist positions. In group 1, there was no contact between the scaphoid and trapezoid in neutral wrist position after any resection. The half and two-thirds transverse osteotomies did not have contact at 20° radial deviation (RD) and 30° wrist flexion (WF). In 1 of the 5 specimens, there was contact at one-third resection in either isolated RD or WF. In 3 specimens, there was contact at one-third resection with 20° of radial deviation combined with 30° WF. In group 2, there was no contact in any specimen in any wrist position tested. At neutral, there was 3.7 mm of space between the scaphoid and trapezoid measured at the radial side. In 20° RD and 0° WF, an average space remaining was 2.8 mm. In 0° RD and 30° WF, there was an average space of 2.3 mm remaining. At 20° RD and 30° WF, there was an average space remaining of 1.8 mm. At the extreme of RD and WF, there was an average space remaining of 1.4 mm. An oblique osteotomy of the trapezoid did not have any ST contact in 20° RD and 30° WF. The transverse osteotomies had contact with only one-third resection. Therefore, if a transverse osteotomy of the trapezoid is performed, more than one-third of the bone should be resected to minimize the risk for bony impingement in positions of WF, RD, or both. In ST arthritis, an oblique osteotomy of the trapezoid may prevent impingement while allowing for less overall bony resection compared with a transverse osteotomy.