An examination of possible quadriceps force at the time of anterior cruciate ligament injury during landing: A simulation study.

Anterior cruciate ligament (ACL) rupture is a common and traumatic injury. Although, identifying the mechanism of ACL injury has received considerable research attention, there are still many unanswered questions. One proposed mechanism asserts that the ACL is injured due to an aggressive quadriceps muscle contraction. However, recently it has been questioned if the magnitude of quadriceps force needed to tear the ACL is physiologically realistic under the conditions where injury occurs during landing (e.g. near full knee extension and within 50ms after impact). To answer this question, a simple simulation model was developed to examine the upper bounds of quadriceps force that can be developed under these conditions. The model included force-length, and force-velocity properties as well as activation dynamics. Model parameters were chosen to provide a high estimate for possible quadriceps force in a young healthy man. The effects of varying quadriceps pre-activation levels were also examined. When using realistic pre-activation levels, the simulated quadriceps force was less than half of what has been shown to cause ACL injury. Even when using maximum pre-activation, the quadriceps force still did not reach close to the level shown to cause injury. Therefore, we conclude that quadriceps force alone seems to be an unlikely mechanism for ACL injury.

Influences of variation in force application on tibial displacement and strain in the anterior cruciate ligament during the Lachman test.

OBJECTIVE: The purpose of this study was to examine the influence of Lachman test performance technique on tibial displacement and strain in the anterior cruciate ligament. DESIGN: Model simulation of experimental Lachman test performance by trained clinicians. BACKGROUND: Differences in clinician hand placement during Lachman test performance have been observed. METHODS: A two-dimensional computer sagittal plane model of the knee was designed to simulate experimentally observed Lachman test performance, and determine anterior cruciate ligament strain and tibial translation that occurred during variation in clinician hand placement and force magnitude. RESULTS: Anterior cruciate ligament strain and tibial translation were greater under conditions mimicking clinician hand placement utilizing a more proximal force application on the tibia. CONCLUSIONS: Tibial translation and strain behavior of the anterior cruciate ligament during the Lachman test appear to be influenced by clinician hand position used in the application of force to the tibia.

Further evidence on the dynamics of self-injurious behaviors: impact forces and limb motions.

The dynamics of self-injurious behaviors (SIBs) were examined in 8 adults with mental retardation. The trajectories of the arm movements and the impact forces of the head blows were determined from a dynamic analysis of videotapes of discrete bouts of self-injury. The results revealed a high degree of cycle-to-cycle consistency in the qualitative dynamics of the limb motions, indicating that the motions involved in SIB are often stereotyped in nature. The resultant individual peak impact forces ranged from 50 to 1560 N. The impact forces of SIB as a percentage of body mass are either near or at the low end of forces generated in boxing blows and karate hits.