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Biomechanical Stability of Button Suspension for Thumb Metacarpophalangeal Joint Ulnar Collateral Ligament Reconstruction in a Cadaveric Osteolysis Model
Riley Hart Kahan, MBS
1, Dylan R Rakowski, MD
1, Evan Herbert Richman, MD
1, Adam Peszek, MD
1, Todd H. Baldini, MS
1, Matthew Belton, MD
1; Alexander Lauder, MD
2(1)University of Colorado, Aurora, CO, (2)University of Colorado Anschutz Medical Campus, Aurora, CO
Introduction: Injury to the ulnar collateral ligament (UCL) of the thumb results in pain, metacarpophalangeal (MP) joint instability, and loss of grip and pinch strength. The use of polyetheretherketone (PEEK) suture anchors for UCL repair or reconstruction may have associated osteolysis-related construct failure in up to 27%. This study utilized a cadaveric osteolysis model to evaluate the biomechanical integrity of button suspension UCL reconstruction previously described for revision reconstruction in the setting of osteolysis.
Materials & Methods: Twelve cadaveric specimen thumb MP joints were loaded to failure by applying valgus force across the MP joint to produce a UCL injury. One specimen fractured during this testing and was excluded. Osseus tunnels (5mm diameter x 10mm depth) were drilled at the ligament origin and insertions to simulate osteolysis in remaining specimens (11/12). The UCL was then reconstructed using a button suspension technique using palmaris longus (PL) autograft and suture augmentation. UCL reconstruction strength was tested by repeating the valgus force across the MP joint until construct failure. Primary outcomes included force (N) necessary to elicit 30 degrees of angular displacement or 11.5 mm of vertical displacement across the MP joint (clinical failure) and maximum force (N) applied before a decrease in resistance was observed (mechanical failure). Anatomical location and mode of construct failure were recorded (ligament reconstruction construct failure vs. fracture). The experimental group was compared to intrinsic controls using paired T tests (significance p<0.05).
Results: Eleven specimens had complete data for biomechanical comparison of the reconstruction to the native ligament strength. Native ligaments exhibited clinical and mechanical failure with 112 +/- 38 N and 169 +/- 75 N of valgus force, respectively. Reconstructed ligaments exhibited clinical and mechanical failure with 26 +/- 12 N and 68 +/- 37 N of valgus force, respectively. Paired T tests (N=22) demonstrated that reconstructed UCLs with 5mm of osteolysis failed under less force both clinically (mean difference of 86.9 N [95%CI(62.2-111.5), p<0.05]) and mechanically (mean difference of 100.8 N [95%CI(48.9-152.8), p<0.05]). All reconstructed UCL constructs failed by fracture; 73% (8/11) at the proximal phalanx and 27% (3/11) at the metacarpal.
Conclusion: The button suspension UCL technique is a feasible reconstructive option; however, reconstruction in the setting of osteolysis produced a weaker construct than the native UCL, likely due to bone loss increasing fracture risk. These findings help guide post-operative rehabilitation for this patient cohort.
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