Saturday, March 18, 2000
The result of this positioning will likely increase impact forces, knee loads and anterior cruciate ligament (ACL) strain. Whether these factors contribute to the high rate of noncontact ACL injuries in women's jumping sports remains to be proven, say researchers in scientific paper 248, presented Thursday.
One of the most frequent noncontact mechanisms of ACL injury, especially in women, is landing from a jump. A survey of injuries to female basketball players reported that 58 percent of all injured players were landing from a jump at the time of their injury. Results of a volleyball participant survey showed that the jump-land sequence during typical game play was associated with 63 percent of all reported injuries, including 61 percent of knee joint injuries.
Researchers said factors that might contribute to the frequency and severity of such injuries includes torso and lower extremity position and contact at landing, lower extremity strength, landing surface and athletic shoe surface.
Twenty-eight healthy, height matched subjects (10 males and 10 females, mean age 28 years) asked to perform three unconstrained jumps from three different heights -20, 40, and 60 cm-onto a concrete floor.
Reflective markers were placed on the right side of their body at six sites: the head of the fifth metatarsal, the lateral malleolus, the lateral femoral condyle, the greater trochanter, the posterior superior iliac spine and the anterior superior iliac spine.Reflective markers were placed on the right side of their body at six sites: the head of the fifth metatarsal, the lateral malleolus, the lateral femoral condyle, the greater trochanter, the posterior superior iliac spine and the anterior superior iliac spine.
Ankle, knee and hip ankles were measured using a 2-D motion analysis system.
The largest gender difference in knee angle occurred when landing from a height of 60 cm. Men landed with 16 degrees of knee flexion while women landed with a significantly straighter knee angle of 7 degrees. A similar gender difference was found when landing from the medium jump height of 40 cm. There were no significant differences when landing from the 20 cm height.
The researchers said theoretical analyses suggest that the greater the angle of knee extension at impact, the larger the ground impact force. Therefore, in these drop landings the women systematically placed larger loads on their knees, relative to their body weight, than did the men.
Co-authors of the study, all of MedSport section of orthopaedic surgery, University of Michigan, Ann Arbor, are Laura J. Huston, MS; Brady Vibert, BS; and Edward M. Wojtys, MD, professor of surgery; and James A. Ashton-Miller, PhD, department of mechanical engineering and applied mechanics department of biomedical engineering, University of Michigan, Ann Arbor, Mich.
|2000 Academy News March 18 Index B|
Last modified 18/March/2000 by IS