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Evaluation of an examination maneuver for ulnocarpal instability: a biomechanical study
Christopher J. Dy1, Arianna Trionfo, MD2, Anna-Lena Makowski3, Edward Milne, BS4, Loren Latta, PhD, PE4, E. Anne Ouellette3
1Hospital for Special Surgery, New York, 2UMDNJ, Camden, 3Physicians For The Hand/The Hand Place, Coral Gables, FL, 4 Max Biedermann Institute for Biomechanics, Miami Beach, FL

Introduction:The supination test (ST), performed by stabilizing the DRUJ with a firm grasp while stressing the carpus in dorsal and volar excursion is validated as a diagnostic tool for ulnocarpal instability (UCI).

Materials & Methods:The ST was performed on 20 cadaver forearms and divided in stable and unstable groups. ST was captured on fluoroscopic videos, the length of the triquetrum measured in mm using Image Pro software while in the extreme positions of the ST. The difference in length is the triquetral rotational index (TRI). Mechanical testing compared the ulnocarpal motion with the ST grade and the TRI. The specimens were held with the elbow in 90° flexion, forearm in pronation, wrist in neutral on a servo-hydraulic loading machine. A screw in the distal ulna was fixed to the loading ram and a vertical load was cycled at ¼ Hz while the vertical movement was measurement. The dorsal/volar excursion (D/VE) between ST end points were measured on the load-displacement curve. Slope of the end points was termed ulnocarpal stiffness.

A 3mm lesion of the ulnar-sided peripheral TFCC was created with a #15 scalpel blade under direct arthroscopic visualization. The ST, TRI and mechanical measures were repeated and again after surgical repair of the UCI. In total, 47 ST were conducted before and after the pTFCC tear and repair. After sorting the data in groups of stable vs unstable ulnocarpal joints based on the ST, statistical comparison was made with a student’s t-test.

Results:The examiner rated 11 ST stable, 36 unstable. Wrists judged stable by ST had an average D/VE length of 2.47 ±0.89mm and wrists judged unstable had an average D/VE length of 3.58±1.26mm. There was a statistically significant difference between the D/VE's of the "stable" vs. "unstable" wrists.

Conclusions:

  • TRI and biomechanic evaluation were able to distinguish stable and unstable ulnocarpal joints as judged by the subjective clinical ST
  • The correlation of D/VE measures with the TRI validates the objective ST
  • TRI may provide a tool that can help the novice examiner to make accurate clinical assessments with ST

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