Maltracking signals VMO involvement
By Jordana Bieze Foster
Research from Stanford University adds to the evidence that patellofemoral pain management may be most effective when tailored to subcategories of patients, and suggests that it’s too soon to give up on vastus medialis oblique activation as a contributing factor.
The findings were presented in early November at the annual meeting of the American Academy of Physical Medicine & Rehabilitation.
Investigators assessed 40 patients with patellofemoral pain longer than three months duration and 15 healthy control subjects. They used weight-bearing magnetic resonance imaging to quantify patellar maltracking in terms of tilt and bisect offset (the percentage of the patella that is lateral to the midline of the femur). Timing of VMO activation relative to vastus lateralis activation during the swing phase of walking gait was determined using electromyography.
The researchers found a significant relationship between VMO onset delay and patellar tilt, but only in patients who were categorized as abnormal for both maltracking variables.
This finding supports the concept that subcategories of patellofemoral pain patients differ in terms of contributing factors, which in turn suggests that interventions for PFP should be tailored to address the specific needs of each subcategory.
“If you focus on the timing issue in that subgroup of patients, you may be able to improve the maltracking,” said Michael Fredericson, MD, director of the PM&R sports medicine service at Stanford, who presented the findings at the AAPM&R meeting.
This type of classification-based approach to PFP has been gaining traction. Earlier this year, researchers from the National Institutes of Health reported a similar trend with regard to maltracking and response to patellar taping (see “Patellofemoral taping: Pain relief mechanisms,” August, page XX). An earlier Stanford study, also presented at the AAPM&R meeting, found that female patients with PFP were significantly more likely than male patients to demonstrate both patellar tilt and excessive bisect offset, suggesting that gender may be another factor to consider when subcategorizing PFP patients.
Such heterogeneity within the PFP patient population may help explain why findings in the medical literature have ranged from inconsistent to inconclusive with regard to the effectiveness of specific interventions.
Fredericson believes this may be particularly true of research on VMO onset delay, which was once a primary focus of PFP discussions but has faded into the background as new studies have drawn attention to the potential role of the hip.
“We used to talk a lot about strengthening the VMO, but that sort of died out,” Fredericson said. “To a certain extent I feel we may have gone too far. Not every patient is going to respond to hip strengthening.”
One of the next steps for the Stanford group will be to address the VMO using a new approach pioneered by researchers from the University of Western Australia, where Stanford team member Scott Delp, PhD, recently spent a sabbatical. The Australians have had success in treating patellofemoral pain with botulinum toxin injections to the vastus lateralis muscle as an adjunct to VMO strengthening.
In a paper e-published in August by the British Journal of Sports Medicine, the Western Australia group reported that this dual intervention led to a satisfactory outcome at 24 weeks in 16 of 19 PFP patients in the original experimental group and two of five controls who crossed over at week 12. All patients in that study had documented vastus lateralis activation dominance.
Now, considering the Western Australia findings in the context of their maltracking findings, the Stanford group wants to take things a step further by applying the same approach to a subcategory of patients with confirmed patellar maltracking in addition to VMO onset delay.