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Using Dynamic Biplane Radiography to Characterize Pre- and Post-Trapeziectomy First Metacarpal Subsidence and Strength During Key Pinch
Maria A Munsch, MD
1; Edward D Godbold, BS
1; Joshua C Setliff, BA
2; William J Anderst, PhD
1; John R Fowler, MD
11Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, PA; 2School of Medicine, University of Pittsburgh, Pittsburgh, PA
HYPOTHESIS: The thumb carpometacarpal (TCMC) joint is the most common site of osteoarthritis in the upper extremity. Trapeziectomy with TCMC joint reconstruction is currently utilized to treat osteoarthritis and prevent instability secondary to first metacarpal (MTC1) subsidence. However, there are no
in vivo biomechanical data to characterize relationships between postoperative static and dynamic subsidence and strength. This interim work aims to identify relationships between three-dimensional (3D) static and dynamic MTC1 subsidence, and between dynamic MTC1 subsidence and thumb strength during key pinch.
MATERIALS & METHODS: Participants scheduled for unilateral trapeziectomy and reconstruction via ligament reconstruction with tendon interposition or suture suspensionplasty were recruited. Synchronized dynamic biplane radiographs of the TCMC joint were collected at 100 images per second preoperatively and six months postoperatively while participants performed three trials of key pinch, with continuous force measurement. Preoperative computed tomography scans of each participant's hands and wrists were collected and segmented to create 3D, subject-specific bone models. A validated volumetric model-based tracking technique was used to track the bones, and
3D-kinematics software was used to measure and visualize trapezial height. Change in peak force pre- to postoperatively was calculated and compared with the change in trapezial height and the minimum trapezial height during the postoperative trials.
RESULTS: Data from 10 participants from this ongoing study are included. The minimum trapezial heights decreased postoperatively. During key pinch, better maintenance of peak force postoperatively correlated with greater minimum trapezial height (r2=0.3498) (Figure 1), but changes in peak force generation postoperatively showed negligible correlation with dynamic change in trapezial height (r2=0.06387) (Figure 2). CONCLUSIONS: Plain radiographs may not characterize the full extent of dynamic MTC1 subsidence. Across participants, better maintenance of peak force postoperatively was associated with maintenance of minimum trapezial height but not with dynamic change in trapezial height during key pinch. Thus, subsidence-related weakness may correlate with absolute loss of trapezial height, but not dynamic instability during functional tasks. Ultimately, this study seeks to relate force, subsidence, and location of minimum trapezial space to clinical outcomes and reconstructive technique. ACKNOWLEDGMENT: This ongoing research is sponsored by the National Institutes of Health, grant R21AR081556.
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