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Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Journal of Biomechanics, , Volume 40, Issue 5, 2007, Pages 1145-1152
Anterior cruciate ligament (ACL) injury commonly occurs during single limb landing or stopping from a run, yet the conditions that influence ACL strain are not well understood. The purpose of this study was to develop, test and apply a 3D specimen-specific dynamic simulation model of the knee designed to evaluate the influence of deceleration forces during running to a stop (single-leg landing) on ACL strain. This work tested the conceptual development of the model by simulating a physical experiment that provided direct measurements of ACL strain during vertical impact loading (peak value 1294 N) with the leg near full extension. The properties of the soft tissue structures were estimated by simulating previous experiments described in the literature. A key element of the model was obtaining precise anatomy from segmented MR images of the soft tissue structures and articular geometry for the tibiofemoral and patellofemoral joints of the knee used in the cadaver experiment. The model predictions were correlated (Pearson correlation coefficient 0.889) to the temporal and amplitude characteristic of the experimental strains. The simulation model was then used to test the balance between ACL strain produced by quadriceps contraction and the reductions in ACL strain associated with the posterior braking force. When posterior forces that replicated in vivo conditions were applied, the peak ACL strain was reduced. These results suggest that the typical deceleration force that occurs during running to a single limb landing can substantially reduce the strain in the ACL relative to conditions associated with an isolated single limb landing from a vertical jump.
Anterior cruciate ligament (ACL) injury is very common during sport activities and frequently occurs in the absence of contact with another player or object (Boden et al., 2000; Griffin et al., 2000). While it is reported that noncontact ACL injuries often occur during landing or deceleration prior to a change of direction (Boden et al., 2000), the mechanism of ACL injury is not well understood. Anterior forces on the tibia, internal/external rotational torque, and valgus torque contribute to strain in the ACL in controlled in vitro and in vivo studies with low-magnitude quasi-static loads (Markolf et al., 1995; Woo et al., 1999; Fleming et al., 2001). However, a recent study of individuals performing a single-leg run-to-stop revealed that anterior translation of the tibia may not occur during this activity (Chaudhari et al., 2004). Instead, posterior forces on the tibia were observed during the first 100 ms after foot strike, due to the deceleration forces acting at the foot. These forces caused posterior tibial translation in most subjects, which would seem to protect the ACL from injury. However, the effect of this observed combination of loads on ACL strain remains unknown. To understand the mechanism of ACL injuries, estimating the strain of the ACL is essential. ACL strain has mainly been measured using in vivo measurement with implanted displacement transducers (Beynnon et al., 1992; Fleming et al., 2001) or in vitro measurement using various techniques (Markolf et al., 1995; Woo et al., 2006). Computer simulations have also predicated ligament forces (Pandy and Shelburne, 1997; Song et al., 2004). Simulation studies have provided considerable insight into the biomechanics of the knee joint (Crowninshield et al., 1976; Andriacchi et al., 1983; Garg et al., 1990; Blankevoort et al., 1991; Shelburne and Pandy, 1997; Yu et al., 2001; Chen et al., 2001; Caruntu and Hefzy, 2004). However, most of these models use generic anatomical geometry and are designed only to predict static or quasi-static characteristics of the knee joint such as passive flexion and rotational stiffness. Predictions of ACL strain during dynamic landing motions have not been performed using a model validated for the estimation of ACL strain. Thus there is a need for a knee model that predicts ACL strain under dynamic loading conditions that occur in vivo during sports activities similar to those that result in ACL injuries. The purpose of this study was to develop, test, and apply a 3D specimen-specific dynamic simulation model of the knee designed to test the influence of deceleration forces on ACL strain during run-to-stop single-leg landing.
نتیجه گیری انگلیسی
This study demonstrated that the posterior deceleration force during a run-to-stop can protect the ACL by reducing the peak strain produced by quadriceps contraction. The external posterior force was caused by decelerating the body's forward momentum. The findings of this study suggest that excessive quadriceps force is an unlikely mechanism of ACL injury when an external posterior force is present, because for the quadriceps to cause an injury through anterior translation it first would have to overcome the sizable posterior forces. Thus, other mechanisms such as valgus rotation, internal rotation, or a combination of the two, which are not protected by external loading, may be more relevant to ACL injuries (Hewett et al., 2005; Olsen et al., 2004; McLean et al., 2004). In real activities such as a run-to-stop or a vertical landing, the total combined loading applied to the knee may include other forces or moments as well, such as externally applied valgus or tibial internal rotation moments. One main difference between run-to-stop and simple drop landing is the posterior force due to horizontal deceleration during a run-to-stop. Therefore, the results of this study should be considered in light of the fact that the complete complexity of loading during single limb landing was not simulated. The purpose of this study was to use a model simulation to isolate the influence of the posterior force on ACL strain since in many sports injuries occur during run-to-stop activities rather than in drop landings from a height. A number of assumptions were used to construct the model used in this study. The quadriceps, hamstrings, and gastrocnemius were assumed to be passively tensioned before the impact to simulate eccentric contraction in the quadriceps. The assumption was based on previous reports that peak tension in the ligament occurred within 40 ms of the initial impact (Fig. 8a), which is shorter than the time needed for an active response (Burke et al., 1991). In addition, quadriceps activity has been shown to increase slowly before landing, and during high deceleration or landing the quadriceps undergoes eccentric contraction (Colby et al., 2000). These studies support the assumption of constant activation with pretensioned muscles in this model. In such a situation, passive stretch of muscle fibers should account for most of the force generated. Other assumptions for the model included ligament material properties obtained from the literature rather than the specific material properties of the cadaver specimen, and an assumption that the contribution of the meniscus was negligible for the purposes of this study. Another assumption that should be considered carefully is that the model does not account for wrapping of the ACL around the intercondylar notch of the femur or the interaction between the bundles. However, since this study was conducted with the knee near 25° of flexion with no external rotation, no interference between the ACL and intercondylar notch is likely (Fung and Zhang, 2003; Withrow et al., 2006). Therefore, this assumption is unlikely to have affected the results of the study. Finally, the model was created using the anatomy of one average size knee specimen. Unlike previous simulation studies where a single generic model is generated from averaged anatomical data that may not represent any real specimen and whose results cannot be directly validated, this model represents a real individual of average size, and it has the distinct advantage of being directly validated against experimental results. While this approach permitted direct validation against experimental results, one must take care in generalizing these results to all knees. Even though some subtle differences may occur in anatomy and motions between individuals, the general trend of the influence of posterior force on ACL strain in this study should be preserved. In consideration of the assumptions noted above, the predicted and measured ACL strain matched quite well. ACL strain prediction of the model was validated with a specimen-specific simulation. The validation was achieved without any adjustment to model properties. The properties and assumption used in this model were developed based on previous efforts to build a stand-alone knee model, which includes passive flexion and rotational stiffness tests to ensure proper tibiofemoral behavior (Wilson et al., 2000; Pandy and Shelburne, 1997; Blankevoort et al., 1991; Andriacchi et al., 1983; Crowninshield et al., 1976). After generating this complete simulation model with both the knee and experimental apparatus, we merely compared the results in response to the same impact loading. Thus, the knee model appears to provide reliable results when applying various loading conditions which are difficult to set up in cadaver or in in vivo studies. In conclusion, the results of this study demonstrate that an external posterior force during landing reduces strain in the ACL, thus reducing ACL injury risk. The use of a specimen-specific computational model gives unique insight into the factors that affect ACL strain and may lead to ACL injuries