Introduction
The thumb ulnar collateral ligament is commonly injured, especially during sport, resulting in an acute injury that must be appropriately managed.
Purpose of Study
To evaluate the effectiveness of common stabilization techniques for the thumb UCL in fresh cadaveric specimens and to analyse the anatomical differences between male and female UCLs.
Methods
Eight, fresh cadaveric specimens (79 ± 8 years old) were evaluated in four conditions; stabilization, Spica tape job, abduction tape job, and an over-the-counter spica orthosis. The forearm was stabilized, positioning the thumb in neutral. The thumb was attached to a Teflon rail-guided drop tower using an impact load transfer system designed to abduct the thumb with 131 Newton (N) of force. TEMA motion analysis software was used to calculate the maximum abduction angles at impact. Following biomechanical testing, an incision was performed along the ulnar aspect of the thumb to expose the UCL for measurement.
Results
All stabilization conditions significantly limited thumb abduction. The thumb abduction tape job was most effective (8.3°), followed by the spica tape job (15.8°), and the spica orthosis (16.6°). Each specimen was dissected following testing and no ligament damage was identified. No statistically significant difference was found between the length and width of male and female thumb UCLs.
Conclusions
This is the first study to assess the efficacy of commonly used thumb stabilization methods. Bracing is often regarded as superior to taping, but these data suggest otherwise. This information may aid clinicians in understanding how to best protect the thumb UCL from sustaining initial injury and protection when returning to sport.
Discussion
The primary objective of this study was to evaluate the effectiveness of common stabilization techniques for the thumb UCL by measuring angular displacement in fresh cadaveric specimens. Results demonstrate that the AbdT and SpicaT were more effective at reducing mean abduction angles of the thumb at the CMC and MCP joints than the OTC orthosis, and all were better than no stabilization device at all. The Abd T reduced mean abduction angles by 78.8%, the Spica T condition reduced mean abduction angles by 59.9%, and the OTC orthosis reduced mean abduction angles by 57.7% when compared to Cont. The average abduction angles for the control (39.38O) are consistent with previous literature (32.6O). Our average abduction angles in the stabilization conditions can be compared to a custom orthosis described in the literature (24.0°) in up to 100 N of force applied. Our study offers insight into the thumb and UCL stability against valgus forces at a high rate of speed. Previous studies tested the UCL and thumb abduction at rates of 0.1 mm/s and 1 mm/s and mainly looked at load-to-failure ratios, pinch, and grip forces of the UCL. While these studies offer a great deal of information regarding the properties of the thumb UCL, it is difficult to apply this to a real-time injury mechanism of injury. We consistently abducted the thumb at rates of approximately 1 m/s, which is much higher than the rates of thumb abduction described in the literature. Our rationale for choosing 1 m/s was to make our rates of abduction considerably closer to real-life scenarios, whereas other studies applied abduction rates several magnitudes lower. Our study is more representative of the instantaneous mechanism of injury sustained by many athletes in contact and non-contact sports. Determining the necessary thumb abduction force was also difficult because of the wide range of UCL load to failure values reported in the literature, which ranged from 111 N to 156 N and 246 N to 513 N in two biomechanical studies with fresh cadaveric specimens. The force applied to the thumb in our study ranged from 111 N to 150 N. After dissection of the fresh cadaveric specimens, it was determined that there were no ligament failures. There was no preload applied to the thumb during the biomechanical testing because a small preload of 1 pound was able to almost fully abduct the thumb, which could be attributed to the increased flexibility of the fresh specimen tissue.
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