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Biomechanics of 2nd Metacarpal Suture-Button-Suspensionplasty: A Cadaveric Hand Model
Ian D Kretzmann, BA
1, Emma Judge, BA
2, Jonathan Tueting, MD
3, Fraser J. Leversedge, MD
1, Todd H. Baldini, MS
1; Louis W. Catalano, MD
4(1)University of Colorado, Aurora, CO, (2)University of Colorado, Centennial, CO, (3)Rush University, Chicago, IL, (4)University of Colorado Anschutz Medical Campus, Aurora, CO
IntroductionSuture button suspensionplasty (SBS) using the Mini TightRope (Arthrex, Naples, FL) has become a widely used technique for treating thumb carpometacarpal (CMC) arthritis, offering several advantages over traditional procedures, including shorter immobilization periods and preservation of thumb height. However, complications such as fractures of the second metacarpal (MC) have been reported in both clinical and cadaveric settings. These fractures may result from the drill trajectory, cortical breach patterns, or altered load transfer across the suspension construct. While prior research has examined the effect of drill angle on first MC stability, the biomechanical consequences of drill trajectory on second MC integrity remain poorly understood. The purpose of this study was to evaluate the effect of three different K-wire trajectories on the structural strength of the second MC following SBS placement.
Materials & MethodsThirty-three fresh-frozen cadaveric hands (mean age: 74.5 years) were randomized into three experimental groups (n = 11 per group). Each group received a different K-wire trajectory during Mini TightRope SBS placement: (1) a single central bicortical pass, (2) a dorsal unicortical pass followed by a central bicortical pass, or (3) a volar unicortical pass followed by a central bicortical pass. The K-wire was inserted in the midaxial dorsal-volar plane, at a 20° angle, confirmed using a goniometer. Following device placement, all specimens underwent biomechanical testing using a custom cantilever bending apparatus. Force was applied in a volar-to-dorsal direction to simulate physiologic loading. Peak force-to-failure and corresponding stress values were recorded.
ResultsComparison of max load (N) and peak stress (MPa) are shown below.
| Groups | Max Load (N), SD | Peak Stress (MPa), SD |
| Bicortical (BC) | 359 (141) | 168 (54.5) |
| Bicortical + Dorsal Unicortical (DUC) | 359 (223) | 135 (50.6) |
| Bicortical + Volar Unicortical (VUC) | 375 (160) | 169 (28.7) |
A summary figure of the statistical analysis is attached.
A Bayesian analysis yielded a Baye's factor of 1.42 between volar and dorsal approaches.
Conclusions
No significant differences were appreciated in maximum load to fracture between groups. Bayes analysis demonstrates evidence favoring a volar approach over a dorsal approach (BF = 1.42) with differences in peak stress of 34 MPa; whereas the 33 MPa difference between BC and DUC was not statistically significant. Clinically, these data suggest surgeons performing SBS should aim for a central bicortical hole, but error volarly, not dorsally, to minimize the risk of subsequent second metacarpal fracture.
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