The 10% Solution to Patellofemoral Pain

Patellofemoral pain (PFP) is a common injury in runners that is often caused by aberrant frontal-plane hip and/or pelvis kinematics. Gait training has been proven to be helpful, but it often can only occur in a clinical or laboratory setting.

A new study, “A 10% Increase in Step Rate Improves Running Kinematics and Clinical Outcomes in Runners With Patellofemoral Pain at 4 Weeks and 3 Months,” however suggests that a simple change in step rate may be all that is needed to improve clinical outcomes. The study was recently published in the American Journal of Sports Medicine.

Running Kinematics

According to previous research, incidence rates of patellofemoral pain have been as high as 20.8% while prevalence rates as high as 22.7%. Common characteristics of runners with PFP include increased hip adduction (HADD), hip internal rotation and contralateral pelvic drop (CPD). One theory is that the aberrant frontal- and transverse-plane running kinematics causes lateral tracking of the patella which puts more stress on the patellofemoral joint.

The researchers explained in their study, “When exposed to repeat loading cycles during running, the knee may experience damage to the underlying chondral surface, stress within the subchondral bone, and excitation of nociceptors, leading to pain and injury.”

Studies have shown improvements in the rehabilitation of PFP with mirror retraining, real-time feedback and transitioning to a forefoot contact.

However, because mirror retraining and real-time feedback can only occur in clinical and laboratory settings and transitioning to a forefoot strike can increase Achilles tendon and ankle joint loading, there is need for a more practical option like a change in step rate which can be done more independently.

Only three studies so far have looked at the effects of increasing the step rate among runners with PFP. One study did find improved frontal-plane hip and pelvis kinematics and a reduction in pain, but it did not include a long follow-up. Another study did not find it any more effective than education on load management while a third study found only small improvements after two weeks of retraining.

Chris Bramah, MCSP, Msc, with the School of Health Sciences at the University of Salford in the United Kingdom talked to OTW about why gait retraining is so effective for patellofemoral pain. He said:

“I think one reason for its effectiveness is that it can target biomechanical parameters that may be contributing to PFP. Certain kinematic patterns have been prospectively linked to PFP (increased hip adduction for example), it is generally thought that kinematics such as hip adduction and contralateral pelvic drop, may affect the arthrokinematics at the patellofemoral joint leading to elevated patellofemoral joint stress.”

“Therefore, gait retraining could reduce this joint stress by correcting the underlying mechanical contributors to this injury. This is what we hypothesize as a potential explanation for such positive clinical outcomes in our paper.”

He added, “However, it is important for us as clinicians to remember patellofemoral pain can often be due to multiple different factors and therefore targeting the appropriate injury or pain driver is necessary to improve clinical outcomes. In those who biomechanics may be the cause, gait retraining seems to work really well. However, this may not be the case for those where biomechanics are not the underlying driver.”

Study Findings

The researchers conducted 3-dimensional gait analysis on runners with PFP and those with aberrant frontal-plane hip and/or pelvis kinematics at baseline were invited to go through gait retraining. In total 12 runners were asked to participate. Data on running kinematics and clinical outcomes of pain and functional outcomes were recorded at baseline, four weeks after retraining and at three months.

The gait retraining took place in one session where the runner’s step rate was increased by 10% using an audible metronome. Then participants were asked to continue their typical running routine while self-monitoring their step rate which they were able to do with a global positioning system smartwatch and audible metronome.

According to the data collected, both running kinematics and clinical outcomes improved at the four-week and three-month follow-ups.

In particular, there were reductions in peak contralateral pelvic drop (mean difference [MD], 3.12˚ [95% CI, 1.88˚-4.37˚], hip adduction (MD, 3.99˚ [95% CI, 2.01˚-5.96˚]), knee flexion (MD, 4.09˚ [95% CI, 0.04˚-8.15˚]), increases in self-reported weekly running volume (MD, 13.78 km [95% CI, 4.62-22.93 km]) and longest run pain-free (MD, 6.84 km [95% CI, 3.05-10.62 km]).

In addition, there were significant improvements in regard to pain in the Friedman test with a post hoc Wilcoxon signed-rank test. Overall, the step rate increased by an average of 11.2% at four weeks.

There were also observable reductions in pain scores on the Numerical Rating Scale (NRS) from an average of 6.2 out of 10 at baseline to 1.0 and 0.3 at four weeks and three months, respectively (X² = 21.38; p < .01) and on the Lower Extremity Functional Scale the improvement was from 62.3 at baseline to 76.6 at four weeks and 79.7 at three months (X² = 22.29; p ≤ .01)

Higher Step Rate Changes Hip Adduction, Internal Rotation and Contralateral Pelvic Drop

According to the research team, “After the step rate increase, we observed a 3.12˚ and 3.99˚ reduction in CPD and HADD, respectively, which may offer a mechanical explanation for the improved clinical outcomes seen in this study. These changes are greater than those observed in previous step rate studies, with this being the first study to highlight that kinematic adaptations are maintained at longer term follow-up.”

They added that “it is important to assess for aberrant running kinematics at baseline to ensure that gait interventions are targeted appropriately.”

“It is thought that CPD will give rise to an increase in iliotibial band tension, resulting in lateral displacement of the patella, while HADD would cause the femur to shift medially under the patella. This would result in elevated contact pressure between the patella and lateral facet, leading to elevated joint stress and potentially injury. Therefore, it is possible that the reductions in CPD and HADD after an increase in the step rate would contribute to reduced lateral displacement of the patella and a corresponding reduction in patellofemoral joint stress.”

Reduction in peak knee flexion and increased gluteus medius and maximus muscle activity in late swing phase just before initial foot contact may also reduce the pressure on the patellofemoral joint.

The researchers wrote, “Considering the role that the gluteus medius plays in frontal-plane stability of the hip and pelvis, it is likely that the earlier onset of the gluteal muscles would result in increased neuromuscular stability during the stance phase of gait. This would likely explain the mechanical improvements of reduced CPD and HADD observed in the present study.”

They noted how bigger the improvements were compared to previous step rate studies and how much easier it was for the runners to take control of their retraining. At the four-week follow-up, they all reported that they didn’t have to use the metronome past the first week and were able to easily monitor their step rate with just their GPS smartwatch.

Targeting Gait Intervention

On any data that surprised them, Bramah said, “The really interesting findings came from the individual data sets. Interestingly, one subject had relatively small hip adduction angles at baseline which did not change much following the intervention. This suggests that gait retraining may indeed be more effective in those with aberrant kinematics.”

He also emphasized that only one session of gait retraining was needed. He said, “No participant needed more than one session, they were all able to apply the retraining really well following the simple instructions for self-monitoring.”

“This is great for clinical practice where we may not be able to see our patients more than once every couple of weeks, as it shows gait retraining can be easily integrated into a runner’s normal routine. Interestingly though, there was a subtle trend for some participants to slip back into their previous mechanics at the three-month follow up point (increased hip adduction & contralateral pelvic drop), although not statistically significant.”

“This suggests that there may be a need for continued monitoring of gait changes and questions whether long term changes can be maintained without further input.”

He said, “I think the most important suggestion from the study is that clinical outcomes may be improved by specifically targeting gait interventions to those with aberrant running kinematics at baseline.”

“We selected only participants with aberrant kinematics at baseline in order to ensure the intervention was appropriately targeted to patients for whom kinematics may be the driver of their symptoms. As a result, we observed clinical outcomes greater than that of previous studies. It’s difficult to know for sure if that’s why the clinical outcomes were greater in this study, so future research should consider stratifying groups into those with aberrant kinematics at baseline and those without. This would allow direct comparison as to whether specifically targeted interventions does improve clinical outcomes.”