The influence of orthotic devices and vastus medialis strength and timing on patellofemoral loads during running
Introduction
Running is a popular form of recreation and fitness and is central to many sports. However, running is also associated with a high injury rate for both younger (32%) and older (41%) age populations [1]. Depending on the study cited, the overall yearly incidence rate for running injuries is between 37% and 56% [2] with 42% of these injuries related to the knee and 26% of knee injuries associated with patellofemoral pain (PFP) [3]. PFP includes all disorders associated with discomfort on the anterior side of the knee joint. Two of the more common, conservative PFP treatments are exercise programs and the prescription of orthoses [4]. Although conservative treatments have been reported to be successful, the effectiveness is often based on subjective or empirical data [5]. Therefore, there is considerable disagreement within the scientific community on the mechanisms causing PFP and consequently, it is not clear which treatment is the most effective for specific patients [5], [6], [7]. Further, running mechanics and musculoskeletal properties vary among individuals and may play an important role in the effectiveness of individual treatments.
Studies have suggested that differences in relative muscle forces exerted on the patella between the vastus medialis (VM) and vastus lateralis (VL) contribute to lateral patellar tracking and malalignment, which have been linked to PFP [4], [5], [6], [7]. The lateral tracking and malalignment occurs when the lateral pull of VL is not adequately balanced by pull of the vastus medialis longus (VML) and vastus medialis oblique (VMO). This imbalance can lead to altered patellofemoral contact forces and pressures that may lead to PFP. The VMO is deemed the primary medial patellar stabilizer due to the anatomical differences between the VML and VMO [8]. Therefore, much effort has been directed towards identifying techniques to selectively strengthen the VMO to improve the force balance on the patella [4], [5], [7], although the effectiveness and feasibility of selective VMO strengthening have been widely questioned [6], [7], [9], [10]. Much of the controversy regarding the effectiveness of VMO strengthening is caused by the difficulty of isolating the treatment effect in patients. Electrical stimulation may be the only way to strengthen the VMO selectively [11], but should not be recommended unless its effect on patellofemoral joint mechanics is shown to be significant. Therefore, a theoretical analysis is needed to quantify the effect of VMO strengthening on patellofemoral joint loads to justify further studies seeking to identify techniques to selectively strengthen the VMO.
From a neuromechanical perspective, selective VMO activation can also reduce the lateral dominance of VL by either increasing the intensity of VMO relative to VL, or by initiating VMO activity prior to VL [6]. In patients with PFP, it is speculated that VL is activated earlier than VMO [6], [12] and at a higher relative intensity [13]. But studies examining this dynamic imbalance theory have provided conflicting results [7], [12], [13], [14], [15], [16], and the functional significance of the identified timing differences, on the order of 5 ms, has been questioned [6], [7]. Methodological differences between studies and the inherent difficulty identifying muscle excitation onset and offset make reconciling differences difficult, but these studies suggest a theoretical investigation into the influence of vasti timing and intensity is warranted.
Another conservative treatment for PFP has been the prescription of foot orthoses [4]. Eng and Pierrynowski [17] found that foot orthoses combined with an exercise program can be an effective method to reduce PFP in young females. Bahlsen [18] examined the relationship between excessive foot pronation and PFP and found a significant association. The mechanism behind the pain is speculated to be a kinematic coupling between excessive foot pronation and prolonged tibial rotation [18], [19], [20]. Tiberio [20] used a theoretical model to examine the relationship between excessive pronation and lateral patellofemoral joint compression. Tiberio [20] suggested that during gait, the prolonged tibial rotation prevents the knee from extending freely. To compensate for this, the femur rotates internally relative to the tibia causing changes to the patella contact force and pressure patterns. This biomechanical explanation was termed compensatory internal rotation of the femur, although other studies have provided alternative explanations of the relationship between excessive foot pronation and PFP [5]. These studies suggest that further research is needed to understand the biomechanical relationship between excessive pronation and PFP before the effectiveness of foot orthoses verses exercise programs can be evaluated.
Running is a highly dynamic and complex movement that makes it difficult to predict the effect of these treatments on musculoskeletal loading during movement. Changes in the movement caused by these mechanical treatments (e.g., orthoses, [21]) result in changes in the muscle kinematics and therefore the muscle forces through the intrinsic muscle force, length and velocity relationships. The dynamic interaction within the musculoskeletal system makes such changes difficult to predict and interpret and are often counterintuitive [22]. Thus, the mechanisms behind the changes in patellofemoral joint loading are difficult to identify.
Forward dynamic simulations of running have been developed that allow for the precise identification of muscle forces and joint loading and have contributed to the understanding of mechanisms involved in loading the leg during running (e.g., [23], [24], [25]). These models were, however, limited to the initial impact phase (0–50 ms). Since the etiology and mechanics of PFP and the effectiveness of conservative treatments are not well understood, a theoretical model and simulation approach may contribute to our understanding and provide the information necessary to design effective rehabilitation protocols. Therefore, the goal of this study was to use a three-dimensional forward dynamic simulation of running to investigate the effectiveness of selective VMO strength and activation and the prescription of orthoses on patellofemoral loads.
Section snippets
Musculoskeletal model
A forward dynamic musculoskeletal model was used to produce simulations of heel–toe running. The model was previously described in detail [26] and will be described briefly here. The musculoskeletal model was developed using DADS 8.5 software (CADSI, Coralville, IA, USA) and consisted of rigid segments representing the foot, talus, shank, patella, thigh of the support leg, pelvis, and a rest-of-body segment. The model was dimensioned to represent a male subject with a height of 180 cm and a
Results
The optimization was able to find the muscle controls (excitation onset, offset and magnitude) to reproduce the salient features of the experimentally collected data for the nine subjects. Typical simulation results have been previously reported [26]. The major joint angles and ground reaction forces were almost always within 2 S.D. of the subject’s data, and the muscle stimulation patterns compared well with the collected EMG data.
Typical medio-lateral patellofemoral loading patterns are shown
Discussion
The goal of this work was to examine the influence of two commonly prescribed treatments (vastus medialis strengthening and orthoses) for PFP and the functional significance of timing deficits between VMO and VL on lateral patellofemoral joint forces. The forward dynamic simulation model used in the present study had been shown to closely replicate experimentally collected kinetic, kinematic and EMG data during the same running conditions as the present study [26]. The close agreement between
Acknowledgements
This research was supported by NSERC of Canada, The Whitaker Foundation and Adidas America. We are thankful to Trisha Bellchamber and Phuong Ngo for collecting the experimental data.
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2016, Manual TherapyCitation Excerpt :Although not statistically significant, the amount of change was considerably large (30 ms). Neptune et al. suggested that a 5 ms timing delay or advance between the VLO and VM could lead to a biomechanical imbalance at the patellofemoral joint (Neptune et al., 2000). Therefore, the observed change of 30 ms can be considered clinically significant.