Abstract & Commentary
Synopsis: This study found that subjects with either genu valgus or genu varus at the knee compensate with a more rear-foot directed center of pressure and greater plantar forces. This suggests that subjects with greater valgus or varus rely more on the subtalar and midtarsal joint control function of the ankle plantar flexor muscle group for lower extremity postural control.
Source: Nyland J, et al. Med Sci Sports Exerc. 2002;34:1150-1157.
Athletes that are either positioned in genu valgus or genu varus must compensate with compensatory alignment changes at the ankle, subtalar and midtarsal, or hip joints. Either genu valgus or varus alters foot plant position and frontal plane sway during running. Genu valgus or varus alignment may alter the quadriceps’ effectiveness at stabilizing the joint and possibly altering strain on the anterior cruciate ligament.
Nyland and colleagues studied 56 male and female intercollegiate athletes with either neutral, varus, or valgus alignment. They monitored center of pressure (COP) of the foot using an insole foot pressure system and the measured knee alignment using a video camcorder. Nyland et al’s first hypothesis was that the COP of the foot in subjects with neutral tibiofemoral geometry would be more anterior and lateral than compared to subjects with greater genu valgus or genu varus. The hypothesis was founded on a second hypothesis that a forefoot shift in AP COP and a lateral shift in ML COP would be suggestive of increased ankle plantar flexor group function. They observed a posterior shift of the COP in subjects with greater than 5° of varus or valgus, but they did not observe a medial shift.
Comment by Timothy E. Hewett, PhD
Nyland et al observed a posterior shift in the COP in valgus or varus subjects and suggest that these observations demonstrate movement away from a plantarflexor ankle strategy of postural control. They suggest that these athletes use the plantar flexor musculature more for subtalar and midtarsal joint control than do athletes with more neutral alignment.
This was a very well done study. The testing methods were documented to be reliable and reproducible. The ideas were original. The study design was well thought out. Nyland et al did not present an analysis of their data with athletes grouped into valgus and varus subgroups. This may have proven very important for their analysis. Why did Nyland et al not observe the medial shift in COP that they postulated? Perhaps because the varus and valgus individuals shifted their weight in opposite directions and canceled each other out. Another problem with the study is that Nyland et al extended their conclusions too far from their findings. They use their findings to draw conclusions about plantar flexor control patterns that may or may not have been present. A more proximal strategy could underlie the observed posterior shift in COP.
In summary, it appears that increased knee angulation leads to altered strategies for postural sway control. Nyland et al suggest that this shift is more toward a subtalar or midtarsal joint control strategy. However, we cannot rule out a shift to a more proximal joint control strategy.
Dr. Hewett, Director, The Sports Medicine Biodynamics Center, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, is Associate Editor of Sports Medicine Reports.