Effect of varying hamstring tension on anterior cruciate ligament strain during in vitro impulsive knee flexion and compression loading

Department of Mechanical Engineering, Vanderbilt University, VU Station B 351592, Nashville, TN 37235, USA.
The Journal of Bone and Joint Surgery (Impact Factor: 5.28). 05/2008; 90(4):815-23. DOI: 10.2106/JBJS.F.01352
Source: PubMed


The hamstring muscles are well positioned to limit both anterior tibial translation and anterior cruciate ligament strain during the knee flexion phase of a jump landing. We hypothesized that systematically increasing or decreasing hamstring tension during the knee flexion phase of a simulated jump landing would significantly affect peak relative strain in the anterior cruciate ligament.
Ten cadaveric knees from four male and six female donors (mean age [and standard deviation] at the time of death, 60.3 +/- 23.6 years) were mounted in a custom fixture to initially position the specimen in 25 degrees of knee flexion and simulate axial impulsive loading averaging 1700 N to cause an increase in knee flexion. Quadriceps, hamstring, and gastrocnemius muscle forces were simulated with use of pretensioned linear springs, with the tension in the hamstrings arranged to be increased, held constant, decreased, at "baseline," or absent during knee flexion. Impulsive loading applied along the tibia and femur was monitored with use of triaxial load transducers, while uniaxial load cells monitored quadriceps and medial and lateral hamstring forces. Relative strain in the anterior cruciate ligament was measured with use of a differential variable reluctance transducer, and tibiofemoral kinematics were measured optoelectronically. For each specimen, anterior cruciate ligament strains were recorded over eighty impact trials: ten preconditioning trials, ten "baseline" trials involving decreasing hamstring tension performed before and after three sets of ten trials conducted with increasing hamstring tension, constant hamstring tension, or no hamstring tension. Peak relative strains in the anterior cruciate ligament were normalized for comparison across specimens.
Increasing hamstring force during the knee flexion landing phase decreased the peak relative strain in the anterior cruciate ligament by >70% compared with the baseline condition (p = 0.005). Neither a constant hamstring muscle force nor the absence of a hamstring force significantly changed the peak strain in the anterior cruciate ligament relative to the baseline condition.
Increasing hamstring muscle force during the knee flexion phase of a simulated jump landing significantly reduces the peak relative strain in the anterior cruciate ligament in vitro.

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    • "Experimental strategies have been developed to replicate high-risk, potentially injurious conditions and reproduce ACL injury (DeMorat et al., 2004; Hashemi et al., 2010; Meyer and Haut, 2008; Oh et al., 2012; Wall et al., 2012; Withrow et al., 2006; Yeow et al., 2009). Such experiments have focused on a variety of causative factors including muscle loading (DeMorat et al., 2004; Hashemi et al., 2010; Wall et al., 2012; Withrow et al., 2008), axial compression (Meyer and Haut, 2008; Wall et al., 2012; Yeow et al., 2009), and off-axis external loads (Meyer and Haut, 2008; Oh et al., 2012; Withrow et al., 2006) to simulate landing. Yet, such models are primarily limited by non-physiologic simulation of dynamic loading conditions (i.e. "
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    • "This agrees with the generally accepted role of ankle plantarflexors in landing, which is to absorb impact loads (Devita and Skelly, 1992). Although greater landing heights showed increased Soleus forces, the Soleus/Hams force and activation ratios at peak GRF was approximately the same for both landing heights, with Soleus exerting up to 30% (Fig. 3) of the Hamsgenerated posterior force that is believed to help protect the ACL (Withrow et al., 2008). This indicates that a similar level of coactivation of Soleus and Hams was required regardless of the perceived risk of injury (Fig. 3). "
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    • "Anterior cruciate ligament (ACL) strain is reduced further however, when the hamstrings are cocontracted with the quadriceps (Withrow, Huston, Wojtys, & Ashton- Miller, 2008). The cocontraction of the quadriceps and hamstring muscle groups reduces ACL tension from 15 • –60 • of knee flexion by resisting the displacement of the tibia relative to the femur in all three planes of motion (Li et al., 1999; Withrow et al., 2008). Valgus and internal rotation knee moments can be supported with the activation of specified muscles crossing the knee joint (Lloyd, Buchanan, & Besier, 2005). "
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