Article
Biomechanical Analysis of Thumb Ulnar Collateral Ligament Tear Kinematics
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Authors
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Steven Shin
- Cedars-Sinai Kerlan-Jobe Institute, Los Angeles, CA, United States
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Charles Lin
- Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, CA, United States
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Nilay Patel
- Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, CA, United States
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Yasuo Itami
- Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, CA, United States
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Michelle McGarry
- Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, CA, United States
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Thay Lee
- Orthopaedic Biomechanics Laboratory, Long Beach VA Healthcare System, Long Beach, CA, United States
| Published: | February 6, 2020 |
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Outline
Text
Objectives/Interrogation: Although thumb ulnar collateral ligament (UCL) injuries are common, the kinematics of thumb UCL injuries have not been extensively described. The purpose of this study was to assess the kinematic changes of the thumb MCP joint with progressive UCL injury.
Methods: Eleven cadaveric specimens were utilized for this study. Thumbs were dissected of soft tissue while taking care to leave the UCL, volar plate and dorsal capsule intact along with the EPL, EPB and FPL tendons. Each specimen was potted in plaster of Paris and placed in a custom jig for kinematic testing of the thumb. Each thumb underwent kinematic testing in four conditions: intact, partial tear (50%) of the proper UCL, full tear of the proper UCL and complete tear of both the proper and accessory UCL. Kinematic testing parameters included varus / valgus stress, pronation / supination and volar / dorsal translation. Each testing parameter was assessed at -10, 0, 15, 30° of MCP flexion.
Results and Conclusions: Partial tear of the proper UCL did not result in any significant increase in varus / valgus angulation, pronation / supination or volar / dorsal translation (Figure 4) at any degree of flexion. Full tear of the proper UCL resulted in a significant increase in valgus angulation (intact: 11.5 ± 1.5 degrees vs. full tear: 18.8 ± 1.7 degrees; p = 0.024) and pronation at 30 degrees of flexion relative to intact (intact: 12.6 ± 2.3 degrees vs. full tear: 15.4 ± 2.5 degrees; p = 0.034). Complete tear of the proper and accessory UCLs resulted in increased valgus angulation compared to intact at all degrees of flexion (p < 0.001). It also resulted in a significant increase in total pronation / supination relative to intact at all degrees of flexion (p < 0.004). Furthermore, complete tear resulted in significant volar translation at 0, 15 and 30 degrees of flexion (p < 0.016).
Sequential tearing of the thumb UCL leads to progressive instability of the MCP. Partial tear of the proper UCL does not significantly affect the stability of the joint, but full tear of the proper UCL increases valgus instability at 30 degrees of flexion. Complete tear of the UCL is necessary for increased varus / valgus instability at all degrees of flexion and also results in significant increases in pronation/supination and volar translation.
