Fifth metacarpals were potted with plaster of Paris in a polyvinyl chloride pipe. The potted fifth metarcarpals were secured and the hamate was loaded on the volar surface at 0.01 mm/s until failure in extension with an MTS machine (Eden Prairie, MN) (Fig. 3).
SPSS 20 (IBM, Armonk, NY) was used for statistical analysis. The Student t test was used to compare the 2 groups. α was set at 0.05.
The stiffness was 15.0±7.2 N/mm for the K-wire group and 14.7±6.0 N/mm (mean±SD) for the plate group (P=0.9366, Fig. 4). The peak loads were 62.5±40.0 and 64.6±24.8 N for K-wire and plate groups, respectively (P=0.9181, Fig. 5). The energy to peak load was 294±281 N mm for the K-wire group and 418±190 N mm for the plate group (P=0.3904, Fig. 6). All specimens in the plate group failed by bending of the plate. All specimens in the K-wire group failed by bending of K-wires.
Stability is essential for a successful fusion of a joint. K-wires are widely used in arthrodeses in hand surgery. The purpose of this study was to determine if low-profile plates provide similar biomechanical stability as K-wires when applied to the fifth CMC arthrodesis.
Low-profile plates with locking holes present an attractive alternative to K-wires as they avoid possible complications such as pin migration, pin site infection, and necessity for pin removal. Furthermore, because plates do not need to be routinely removed, they may also offer the theoretical advantage of continued stabilization the fifth CMC fusion site. This longer period of stabilization may be an advantage particularly in patients with risk factors for slower bone union, such as smoking or diabetes mellitus.
The surgical technique involves preparation of the joint, which is similar to arthrodesis with K-wires. A key difference is that the dorsal longitudinal incision is extended 2 to 3 cm distally beyond the fifth CMC proper. This allows visualization of the fifth metacarpal shaft for plate application. Using a chisel, curette, or a small burr, the articular surfaces of the fifth CMC joint are decorticated while protecting the insertion of the extensor carpi ulnaris tendon. Once the 2 surfaces are denuded of cartilage and are congruent, a plate is applied. If desired, autologous cancellous bone graft can be harvested from the Lister tubercle and applied to the fusion site.
Some surgeons favor other procedures that preserve motion at the fifth CMC joint, including resection arthroplasty, which can be performed alone6 or supplemented with tendon interposition,7 suspensionplasty,8 silastic prosthesis,9,10 or fusion of the fifth metacarpal to the fourth metacarpal.11 However, Clendenin et al2 report no clinically apparent loss of motion after fifth CMC fusion, and our experience has been similar. Patients have full motion at the metacarpophalangeal and wrist joints, and triquetrum-hamate articulation also allows motion at the midcarpal joint.12 Furthermore, Clendenin et al2 report that patients also regained grip strength to 93% of the contralateral, uninjured hand. Thus, fifth CMC fusion remains an effective treatment, especially for patients with more severe arthritis or for heavy laborers who need to preserve grip strength.
The results of the current biomechanical study show that arthrodeses with K-wires versus a small dorsal plate have similar stability. However, the study has several limitations. First, it is a cadaveric study, which does not account for biological responses and healing that occur after surgery. Second, the stability of the construct was tested only in a single mode of failure. We elected to test failure in extension because the fifth CMC joint extends in power grip. Furthermore, plates would have been at significant advantage over K-wires if failure to flexion had been tested; flexion force on a dorsally applied plate would have generated a stabilizing, compressive force at the fusion site. The loading parameter (0.01 mm/s) was chosen based on a previous study by Capo et al13 comparing various fixation methods for proximal interphalangeal joint arthrodesis.
Fifth CMC fusion using either K-wires or a plate and screws showed no significant difference in stiffness, peak load, and energy to peak load. These data suggest that a low-profile dorsal plate provides stability similar to K-wires for arthrodesis of fifth CMC. Further research is warranted to determine which technique is associated with superior clinical outcomes.
The orthopedic implants for this study were borrowed from Medartis.
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Keywords:Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved
fifth carpometacarpal joint; arthritis; arthrodesis; fusion