Quantitative Assessment of the Pivot-Shift Test in an Awake and an Asleep State
Researchers have accurately quantified the Pivot-Shift Test of anterior cruciate ligament (ACL) injury over the past decade using navigation systems, electromagnetic sensors and inertial sensors. However, these tests have been conducted under anesthetic, which negate the contribution of muscular guarding from structures surrounding the knee that could make it difficult to generalize the measures for a pre-operative diagnosis. Therefore, the purpose of this study was to determine if the quantification of the Pivot-Shift Test differed between a non- anesthetized and anesthetized state (intra-operatively where no muscle activity is possible), and if the difference could be attributed to muscular guarding. To achieve this, 12 patients who had acquired a unilateral ACL-injury were tested on the day of their ACL reconstructive surgery. Acceleration and muscle activity were recorded over 10 consecutive Pivot-shift tests on their injured and uninjured knee pre-operatively and intra-operatively from 8 Delsys Trigno wireless EMG electrodes and 2 Delsys accelerometers. From the results, the slope of net tibial acceleration could differentiate between the injured and uninjured knee (mean difference, 2.14 g/s, p<0.05). Furthermore, the slope was larger in intra-operatively than in pre-operatively (mean difference, 1.92 g/s, p<0.05) indicating that a difference between conditions. Non- normalized semitendinosus muscle activity explained a proportion of the difference in slope between the pre-op and intra-op (b = 0.6, p<0.05), suggesting hamstring muscular guarding was at play. However, comparing muscle activity during the Pivot-Shift Test to the participant’s maximum voluntary isometric contraction (MVIC) produced results over 100%, suggesting that maximums were taken incorrectly. Thus, without normalizing, the generalizability of the muscular activity results is limited. Finally, no correlation between the slope and the clinical grade in either pre-op or intra-op was found. As a result, the objective quantification of the clinical grade was not possible. The lack of a correlation was speculated to be, in-part, due to the subjective grading scale that was the reference measurement for the grade of injury. Future research should consider changing the method by which MVICs are taken and the grade of injury should be based on diagnostic imaging.
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