Although the biomechanics of ACL injuries is a popular research topic, precise descriptions of the motion involved is not available. We have therefore developed a model-based image-matching technique to reconstruct human motion from uncalibrated video sequences of actual injury situations. The method has been validated against traditional 3D motion analysis system with good results . The purpose of the present study was to test the applicability of the method on two different ACL injuries from different sports.
The first situation was a non-contact plant-and-cut injury with three different camera views (Fig. 1a). In situation two (Fig. 1b), a downhill skier suffers an ACL injury to the left leg as the right ski looses the grip, causing a wide snow-plough position. The 3D modelling program Poser provided the environment for the model matching procedure. A customized skeleton computer-model was built based on anthropometrical measurements which were obtained from each injured athlete. A computer model of the handball field was built and the Poser cameras were calibrated by adjusting the translation, orientation and focal length parameters for each time frame, until our field model matched the background video sequences. This was not possible with the same precision for the downhill video, since the positions of landmarks in the background were unknown. Finally, a frame-by-frame matching of the skeleton model to the athlete in the video was completed.
Fig. 1 a) The non-contact cutting ACL injury matching. b) Downhill skier and the matching at two time-points. c) Hip and knee joint angles (°) for the handball ACL injury. Time zero indicates initial contact. The shaded area indicates the assumed time of injury d) Hip and knee joint angles (°) for the alpine skiing ACL injury.
Team handball: At the initial contact (IC), the speed was 3.9 m/s, and hip and knee flexion was 25° and 13° respectively (Fig. 1c). A center of mass peak acceleration of 33 m/s2 was seen 100 ms after IC. Our validation study  showed that the limited 50Hz frame rate will cause a delay of initial force peaks in the range 0-60 ms, as indicated in the shaded area in Fig. 1c. During this period valgus motion and particularly external rotation was obvious at the knee. Downhill skiing: Large joint motions took place during the fall (Fig. 1d), until ultimately the left ski caught the edge and the skier was flipped over and thrown up into the air. Up to 24° of valgus and 39° internal rotation was seen at the knee.
Discussion / Conclusions
The new model-based image-matching method provides a means to reconstruct and analyse injury situations in three dimensions. Such information can potentially aid our understanding of how injuries occur (e.g. ACL injuries), and form the basis for preventive measures in sport.
© Copyright 2004 Pre-olympic Congress 2004. Thessaloniki, Grécia. de 6 a 11 de Agosto de 2004. Published by ICSSPE. All rights reserved.
|Subjects:||analysis knee injury accident downhill skiing connective tissue handball|
|Notations:||technical and natural sciences biological and medical sciences|
|Published in:||Pre-olympic Congress 2004. Thessaloniki, Grécia. de 6 a 11 de Agosto de 2004|
|Document types:||electronical publication