¶ … HIP MUSCLE STRENGTH & KNEE VALGUS DURING a SINGLE LEG SQUAT Relationship between Hip Muscle Strength & Knee Valgus in a Single Leg Squat

In the research paper entitled, "Physical Therapy Alters Recruitment of the Vasti in Patellofemoral Pain Syndrome," author Cowan et al. Of the Centre for Sports Medicine Research and Education at the University of Melbourne outlined a study of the effects of physical therapy on patients suffering from Patellofemoral Pain Syndrome (PFPS), manifesting as pain in the knee valgus. More specifically, the purpose of the study was to "investigate the effect of physical therapy treatment on the timing of electromyography (EMG) activity of the vasti" in patients with PFPS, with a particular focus on the influence of increased motor control [COWAN et al. 2002].

PFPS is a condition defined by pain in the anterior or retropatellar regions of the knee; this pain is often made worse by repetitive exercises such as squatting and stair climbing, in addition to long periods of sitting or kneeling. For the purposes of this study, PFPS was required to exist independently of additional knee conditions and/or complaints. The test group consisted of 42 female and 23 male participants between the ages of 29 and 40. These participants were divided into two groups, active and placebo. The mean age of the active group was 29.1; the mean age of the placebo group was 25.6. In regards to size, the weight and body mass index (BMI) of the active group was 68.7 k and 23.4 BMI, while the placebo group had a mean weight of 72.0 k and a mean BMI of 24.6.

Treatment for the active group consisted of six physical therapy sessions over a six-week time-frame, in addition to patellar taping. The focus of these sessions was the retraining of the vastus medialis oblique (VMO) via exercises designed to increase gluteal strength, in addition to light stretching of soft tissue areas. Meanwhile, the placebo group received treatment in the form of patellar taping only.

Prior to treatment, participants were asked to perform a simple stair climbing exercise, during and after which pain and functionality levels were measured. The custom built stair apparatus consisted of two ascending stairs and two descending stairs of 20 cm in height, separated by a platform of 60 cm in width. Participants started at a distance of 1.8 m from the ascending steps and ascended and descended the apparatus at a rate of 96 steps per minute.

Prior to the administration of treatment EMG onset timing was similar between the active and placebo groups, however a marked difference in EMG onset timing was observed in the physical therapy group after treatment, resulting in decreased pain levels and improved functionality post activity. Specifically speaking, "In the physical therapy group, this change resulted in simultaneous onset of VMO and VL EMG during the concentric phase (P=0.07). In the eccentric phase, the onset of VMO EMG actually preceded that of VL (P= < 0.001)" [COWAN et al. 2002]. Conversely, in the placebo group, only a slight improvement was observed in the eccentric phase, with no improvement observed in the concentric phase. What the groups had in common was that no difference in pain or functionality was observed while performing the stair stepping exercise.

Nonetheless, the physical therapy group demonstrated a significant change in average and worst pain experienced by the last week of treatment, which in turn supports the claim that "a comprehensive physical therapy program incorporating VMO retraining with biofeedback results in a change in the onset of VMO EMG relative to that of VL in participants with PFPS" [COWAN et al. 2002].

While the multi-faced nature of the treatment program -- to include VMO retraining with biofeedback, gluteus medius retraining, soft tissue stretching, patellar taping, patellar mobilization, and a home exercise program -- made it impossible to isolate the component most responsible for the change, that a large part of the physical therapy exercises aimed at strengthening the gluteal and hip muscles nonetheless suggests that improved strength in these areas results in decreased knee valgus pain and improved functionality in PFPS patients.

A study conducted by Stephen. J. Nicholas et al. Of the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital directly supports the notion that hip strength is related to knee valgus flexion in persons with PFPS. The study, outlined in the research paper entitled "The Role of Hip Muscle Function in the Treatment of Patellofemoral Pain Syndrome" consisted of 35 PFPS participants, too include 29 women and 6 men of the mean age of 33. As in the Cowan et al. study, participants received physical therapy treatment...

In order to be included in the study, participants had to experience anterior or retropatellar knee pain after prolonged sitting, stair climbing, running, kneeling, squatting, hopping or jumping, unrelated to a particular injury and persisting for four weeks or more. Potential participants were excluded from the study if they presented the following:
(1) Signs or symptoms of meniscal or other intra-article injury conditions; (2) cruciate or collateral ligament involvement; (3) tenderness over the patellar tendon, iliotibial band, or pes anserinus tendons; (4) patellar apprehension sign; (5) Osgood-Schlatter or Sinding-Larsen-Johansson syndromes; (6) evidence of a knee joint effusion; (7) hip or lumbar referred pain; (8) a history of patellar dislocation; (9) previous surgery on the patellofemoral joint; or (10) evidence of a degenerative joint disease on radiographs. Patients taking nonsteroidal anti-inflammatory or corticosteroid medication were also excluded. [TYLER et al. 2006]

The physical therapy treatment consisted of three phases. The first phase consisted of seated hip flexion, adduction, abduction and extension exercises; stretching of the quadriceps, hip flexors, and iliotibial band; balance, squatting and stepping exercises. Clinical improvements observed during this phase included the patients' ability to perform 45-degree mini-squats and 4-inch step-ups without pain, in addition to improved balance and stability throughout exercises. The second phase consisted of much the same thing, but with a particular focus on the patient's weakest plane of motion, while the third phase incorporated more advanced exercises such as lunges, sports activities, and plyometric/agility exercises. Observed improvements over the second and third phases included the ability to perform step-downs with no pain, increased speed, and the passing of specific tests such as the Functional Hop Test, Vertical Jump Test, and Sport-Specific tests.

At the end of the six-week treatment session, 21 of the 35 patients reported a significant decrease in daily pain experienced, accounting for a clinical success rate of 60%. Clinical success was found to be related to an increase in hip muscle strength as related to knee flexion, which clinical failure corresponded with hip muscle strength stagnancy. The hypothesized reason for the relation has to do with the effect of hip muscle strength and flexibility on pelvic stability. As Nicholas et al. explains:

Increasing the flexibility of the hip flexors and ITB would allow the pelvis to rotate posteriorly, creating relative femoral external rotations and helping to align the patella in the trochlear groove of the femur. An additional improvement in hip flexor strength may provide a stable pelvis during gait and allow it to act eccentrically to prevent the pelvis from going into an anterior pelvic tilt and concomitant femoral internal rotation. [TYLER et al. 2006]

The conclusion of these studies and others like them is that "improvements in hip flexion strength combined with normalized iliotibial band and iliopsoas flexibility [are] associated with excellent results for patients with PFPS," and should therefore be incorporated into PFPS treatment programs [TYLER et al. 2006]. In turn, the results support the claim that hip muscle strength -- or lack thereof -- is directly related to pain in the knee valgus, as an increase in hip muscled strength resulted in a decrease of knee valgus pain. The evidence to support the correlation of hip muscle strength and knee valgus pain is particularly clear in the Nicholas et al. study, in which:

A combination of improved hip flexion strength as well as normal Ober and Thomas test results was seen in 93% (15/14 lower extremities) of successfully treat cases, compared with a 75% success rate (9/12 lower extremities) if 2 of the 3 factors improved, a 27% success rate (3/11 lower extremites) if only 1 factor improved, and 0% success (0/5 lower extremities) if there was no change in hip flexion strength (< 20%) and if both Ober and Thomas test results remained positive. [TYLER et al. 2006]

The Ober and Thomas tests were used to measure hip and knee flexibility. Prior to treatment, a positive Ober test result -- representing impaired flexibility -- was observed in 39 of 43 lower extremities, while a positive Thomas test result -- also representing impaired flexibility -- was observed in 31 of 43 lower extremities. Test normalization after treatment represented an 80% success rate in treatment of the lower extremities. That both average and worse pain decreased most when hip muscle strength in addition to hip and knee flexibility improved supports the combination of…