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Research Review By Gary Maguire©


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Date Posted:

October 2011

Study Title:

A Proximal Strengthening Program Improves Pain, Function and Biomechanics in Women with Patellofemoral Pain Syndrome


Earl JE & Hoch AZ

Author's Affiliations:

University-Milwaukee and the Medical College of Wisconsin (Froedtert Memorial Lutheran Hospital), Milwaukee, Wisconsin, USA

Publication Information:

American Journal of Sports Medicine 2011; 39(1): 154-163

Background Information:

In theory, research and practice, the link between proximal function and distal dysfunction is finally receiving the attention it deserves. A primary example of this is the relationship between hip function and knee syndromes (see Related Reviews below). The focus of this study was to investigate whether patients with patellofemoral pain syndrome (PFPS) have hip and core muscle weakness contributing to dynamic misalignment of the lower extremity, and whether targeted rehabilitation focused on the hip and core improves function and symptomatology.

As you know, PFPS is a general term referring to an overuse syndrome in the knee, presenting with aching pain and altered functional capacity, particularly with running, squatting, stairs, prolonged sitting, and so on. The prevalence of PFPS is high, accounting for 25% of all athletic knee injuries seen in clinical settings. Further, it is the most common cause of knee pain in adolescents and has a much higher incidence in women than men (1).

Current research reveals that poor proximal neuromuscular control and/or weakness of the hip musculature may lead to limited control of transverse and frontal plane motions of the hip (especially during single-legged stance). Other evidence suggests such dysfunction can result in dynamic malalignment including components of femoral adduction and internal rotation, valgus collapse at the knee, tibial rotation and foot pronation. Findings of deficits in hip abduction, extension and external rotation strength has also been shown with patients with PFPS.

Further, multiple studies by Willson and colleagues demonstrate that there is an increased hip adduction angle in PFPS patients compared to healthy controls (2).

What is not yet clear from existing PFPS research is whether changes in biomechanics follow targeted rehabilitation programs. That was the focus of this study. The primary objective was to determine if a proximally focused rehabilitation program for women would:
  1. decrease pain and increase function;
  2. increase hip strength and core muscle endurance; and
  3. improve lower extremity biomechanics during running.

Pertinent Results:

  • Nineteen subjects participated in a rehabilitation program over an 8-week timeframe with a range of 8-15 sessions completed. Sessions were monitored by a physical therapist or athletic trainer and random follow-up phone calls were utilized to ensure compliance with home exercise programs.
  • Significant improvements in pain were measured and reported using the visual analog scale (VAS) pain rating score (Z = -3.823, P < 0.0005) and the Kujala anterior knee pain scale (AKPS) functional score (Z = -3.342, P = 0.001). Overall, 17 of 19 participants demonstrated successful outcome in pain, function, lateral core endurance, hip abduction, and hip external rotation strength.
  • More specifically, lateral core endurance was found to improve significantly (by 51%) although there was no significant change in anterior or posterior core endurance.
  • External rotation (16%) and hip abduction (12%) strength were also significantly increased.
  • Peak internal knee abduction moment was significantly reduced following the rehabilitation program, while there were no significant changes in joint moments or joint ROM.

Clinical Application & Conclusions:

This study supports the concept that rehabilitation of women with PFPS can be successfully augmented with a proximal stability program, significantly reducing pain and increasing functional ability. One important clinical application derived from the study is a reduction in knee abduction moment. This is important because high abduction moments have been prospectively related to the development of PFPS.

Developing improved PFPS pre/rehabilitation programs is necessary due to the recurrence rate of PFPS symptoms of 25% to 91%, with some patients reporting continuing symptoms several years post-rehabilitation.

The current study provides evidence for the benefits of implementing proximal rehabilitation on patient outcomes, strength, and lower extremity biomechanics in women with PFPS (EDITOR’S NOTE: although this study only included women, we all know that men get PFPS as well. Hip mechanics, by nature, are more of a challenge in women [wider pelvis etc.] but these concepts can and should be applied to men also). This creates a foundation for conducting clinical trials comparing proximal strengthening to other PFPS treatment protocols, or perhaps combining manual and rehab approaches. While pain was reduced with this protocol the magnitude of pain improvement measured is within the range of previously reported studies focusing on PFPS rehabilitation.

Runners with PFPS have previously been reported to have increased knee abduction impulse (the area under the joint moment-time curve) compared to healthy subjects, and as mentioned, high knee abduction impulse is predictive of developing PFPS symptoms in runners. The study produced a significant decrease in the knee abduction moment following rehabilitation and therefore this approach should be considered as a component of PFPS protocols.

The authors noted that PFPS is multifactorial in nature, meaning some participants could have had other factors causing knee pain (common in PFPS rehabilitation literature). Finally, future studies should investigate categorizing PFPS patients by etiological subgroup. This is necessary to examine a specific intervention in each subgroup to better identify the factors contributing to PFPS knee pain. As with other conditions such as low back pain, PFPS in a general diagnostic category that likely contains distinct subgroups.

EDITOR’S NOTE: You’ll notice that once again, the authors of a rehab study failed to include adequate descriptions of the exercises they used. Frustrating indeed, but for what it’s worth, I think the following exercises are reasonable choices for addressing hip stability, lower extremity mechanics and core stability [obviously this is not a comprehensive list]:
  • clam shells or other open chain hip abduction movements with external resistance, ankle weights, cables etc.
  • lateral band walks with a Theraband (straight leg and half squat)
  • Bowler’s squats or single leg squat variations
  • step ups or step-downs
  • directional lunges
  • for the core – start from McGill’s protocols and add external challenges and integration into other exercises

Study Methods:

Using a case series design, eligible subjects with a chief complaint of knee pain and meeting the inclusion criteria (used in similar PFPS studies) resulted in a selection of 19 women (age 22.68 ± 7.19 years, height, 1.64 ± 0.07m; mass, 60.2 ± 7.35kg). They had an average duration of symptoms of 17 months (participating in various athletic activities).

Three-dimensional joint angle data were collected using a 7-camera motion capture system while ground-reaction force (GRF) data were recorded by a force plate mounted in the center of a flush runway floor. Participants ran straight ahead down the runway (set speeds of 4.0-4.5 m/s) with several practice trials to ensure proper foot contact on the force plate. This resulted in five subsequent trials capturing 3-dimensional movement of the hip, knee and ankle plus GRF.

The protocol of Leetun et al. was used to test external hip rotation and abduction strength using a handheld dynamometer and straps to facilitate maximal isometric contraction (3). Hip strength and core endurance were counterbalanced to prevent fatigues. Various core muscle endurance (horizontal extension, posterior and lateral) was tested using Stu McGill’s techniques. This is defined as the duration of time a patient can hold a static position. This represented the dependent variable for analysis.

The rehabilitation intervention consisted of a “proximal stability program”, conducted over 8 weeks including 8-15 treatment sessions, each lasting 30-60 minutes. Phase I (weeks 1-2) consisted of improving volitional control of the hip and core muscles (transverse abdominus, gluteus medius and gluteus minimus). Phase II (weeks 3-5) involved restoring reflex contractions to perturbations (proper lower extremity alignment, maintaining proper alignment during exercises and progressing to maintaining joint stability). Phase III (weeks 6-8) focused on restoring pattern-generated movements (maintenance of posture and alignment to become subconscious allowing for increased complex functional tasks).

Analysis of the data consisted of paired t tests for comparison of the dependent variables for strength, joint ROM and joint moment variables between pre-rehabilitation and post-rehabilitation testing. Using the nonparametric Wilcoxon signed rank statistic compared the 2 subjective outcome variables of VAS and AKPS scores. The ? level was set a priori at .05 and effect size for variables was calculated with Cohen d (to give an indication of the magnitude of the effect of the exercise intervention).

Study Strengths / Weaknesses:

The authors noted that in addition to a small study sample, one of the primary limitations of the investigation was that no control group was part of the study design. The study does support that a proximal strengthening approach to treating PFPS can result in positive patient outcomes and positively change hip strength and lower extremity mechanics. Future study designs need to determine when improvement occurs and subsequently if 8 weeks is needed to achieve an improved functional outcome. The authors concluded that this was a limitation in the study as they only collected data at the beginning and conclusion of the protocol. Longer term follow-up would have been a plus. To build on the success of this study, future research should examine the effectiveness of the proximal stability program using a paradigm in which PFPS patients are included based on the cause of proximal weakness and dynamic malalignment. Another limitation that I would suspect contributes to PFPS that should be included in future research is adaptive shortening mechanisms of the hamstring and popliteus muscle groups and terminal knee extension (TKE). These often play a part in increased friction and patellar tracking dysfunction which is also noted to be a contributory factor with PFPS.

Additional References:

  1. Fulkerson JP, Arendt EA. Anterior knee pain in females. Clin Orthop. 2000; 372: 69-73.
  2. Wilson JD, Davis IS. Lower extremity strength and mechanics during jumping in women with patellofemoral pain. J Sport Rehabil. 2009; 18 (1): 76-90.
  3. Leetun D et al. Core stability measures as risk factors for lower extremity athletes. Med Sci Sports Exerc. 2004; 3 (6): 926-934.

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