Development and Verification of a Protocol to Quantify Hip Joint Kinematics

Abstract

Background: The butterfly save technique is commonly used by ice hockey goaltenders and has recently been identified as a potential mechanism for hip joint injuries due to the extreme body positions involved. Unfortunately, commonly used kinematic marker sets that determine these body positions are heavily influenced by skin motion artifact and are obscured by protective equipment, making it difficult to obtain reliable measures of hip motion. Purpose: To create a new kinematic protocol that could be used when protective equipment prevents typical marker placements and to use this protocol to quantify hip kinematics and butterfly performance in 4 different goalie pad conditions. Study Design: Controlled laboratory study. Methods: A new marker set consisting of marker clusters attached to the lateral thigh and posterior leg was developed. This marker set was verified by evaluating the root mean square (RMS) difference between the developed testing marker set and the calibrated anatomic systems technique marker set during passive range of motion (ROM) tests. The testing marker set was then used in a repeated-measures study in which 12 junior goaltenders performed 5 butterfly movements on synthetic ice, in 4 different goalie pad conditions (control, flexible-wide leg channel, flexible-tight leg channel, and stiff-wide leg channel). Results: The grouped RMS differences and SDs calculated during verification were 1.43° ± 0.41°, 1.0° ± 0.39°, and 3.32° ± 1.32° for hip flexion-extension, abduction-adduction, and internal-external rotation, respectively. There was no significant main effect of goal pad condition on the peak amount of hip internal rotation; however, there was a significant main effect of goal pad condition on the butterfly width (P = .022). Post hoc comparisons revealed that the butterfly width was significantly smaller in the control pad condition compared with the flexible-tight pad condition (P = .03). Conclusion: The new marker set enabled measurements of hip joint kinematics while subjects are wearing protective equipment that are not possible with other marker sets. Interindividual variations in performance of the butterfly technique influenced the amount of hip internal rotation achieved; however, on average, goaltenders exceeded their active internal ROM during butterfly movements. Clinical Relevance: Exceeding internal rotation range of hip motion may make goaltenders susceptible to hip injuries such as femoral acetabular impingement.