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Tuesday, June 6, 2023

Hip and Abdominal Strengthening May Improve Postural Stability in Females with Patellofemoral Pain Syndrome

Brent Brookbush

Brent Brookbush


Research Review: Hip and Abdominal Strengthening May Improve Postural Stability in Females with Patellofemoral Pain Syndrome

By Tristan J. Rodik, M.AT, ATC

Edited By Brent Brookbush, DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Carry, P. M., Gala, R., Worster, K., Kanai, S., Miller, N. H., James, D., Provance, A. J. and Carollo, J. J. (2017) Postural stability and kinetic change in subjects with patellofemoral pain after a nine-week hip and core strengthening intervention. The International Journal of Sports Medicine, 12(3), 314-323 FULL ARTICLE

Introduction: Patellofemoral Pain Syndrome (PFPS) has been correlated with gluteus maximus and gluteus medius  (glute complex ) weakness, and patients often respond favorably to specific exercise for strengthening these muscles (1-14). Human movement professionals and researchers often use the single-leg squat as a functional task to identify movement impairments, including glute complex weakness (15-18). This study by Carry et al. (2017) demonstrated improvements in patient reported pain, foot center of pressure (balance) during a single leg squat, peak knee power and peak knee flexion angles, after a 9 week, progressive hip and abdominal strengthening program. Human movement professionals may consider movement assessment, abdominal strengthening and hip strengthening programs for patients/clients exhibiting signs of PFPS.

Prone hip extension
Caption: Prone hip extension

Study Summary

Study Design Cross-sectional intervention study
Level of Evidence IIA Evidence from at least one controlled study without randomization
Participant Characteristics Demographics: Patellofemoral Pain Syndrome (PFPS) Group
  • Age: 14.20 +/- 0.75
  • Body Mass Index: 17.40 +/- 2.87 (kg/m²)
  • Gender: Female
  • Number of participants: 7
  • Tegner Activity Level: 6.43 +/- 2.99

Demographics: Control Group

  • Age: 14.12 +/- 0.86
  • Body Mass Index: 18.40 +/- 3.21  (kg/m²)
  • Gender: Female
  • Number of Participants:7
  • Tegner Activity Level: 7.43 +/- 1.51

Inclusion Criteria: PFPS Group

  • Unilateral or bilateral PFPS
  • Insidious onset of activity-related knee pain for 1-6 months
  • Pain with at least two of the following activities:
    • exercise
    • sitting for greater than 1 hour
    • climbing stairs
    • squatting
    • kneeling

Inclusion Criteria: Control Group

  • No history of knee pathology and/or pain

Exclusion Criteria: PFPS Group

  • History of knee trauma

Exclusion Criteria: Control Group

  • N/A
Methodology Self-Reported Symptom Severity
  • For symptom severity the following self-reported questionnaires were used:
    • Anterior Knee Pain Symptom Scale (AKPS)
    • Visual Analogue Scale for Worst pain (VAS-W)
    • Visual Analog Scale for Usual pain (VAS-U)

Lower-Extremity Function

  • Prior to testing, retroreflective markers were placed on 10 bony landmarks
  • The single-leg squat (SLS) was chosen for functional testing
  • Participants performed the SLS with self-selected arm position, tempo, and knee flexion
    • The torso was to remain vertical
    • The foot was to remain flat on the platform
    • No external assistance was allowed for balance

  • 5-practice trials were provided followed by 5-tested trials for the SLS
  • The Center of Pressure (CoP) measured each participant's ability to maintain balance

Physical Therapy Intervention

  • Participants with PFPS were assigned to report to one of two physical therapists (Sports Certified Specialists)
  • The PFPS group received individualized exercises and formal instructions for an at-home program
  • Exercises were performed 3-4x/week with the following progression:
    • Open kinetic chain (3 weeks)
    • Closed kinetic chain (3 weeks)
    • Functional exercise (3 weeks)

  • The intervention lasted 9-weeks.
  • Repetitions, tempo's, sets, and frequency were individually prescribed.
  • Each participant saw their respective physical therapist once per week.
  • Upon completion of the intervention, participants were then re-tested for self-reported symptom severity and lower-extremity testing.
Data Collection and Analysis
  • Bertec strain gage force platforms (Model 4060-10) were used for the SLS
  • Retroreflective markers were a modified version of the Helen Hayes marker set
  • Marker trajectory data was recorded at 120 Hz using a 13-camera Vicon MX motion capture system
  • Vicon Nexus™ processed all motion capture data
  • Vicon Plug-in-Gait™ was used to generate kinematics, kinetics and CoP
    • Kinetic measures were normalized to each participant's body weight

  • Data was then imported to a Matlab (The MathWorks Inc., Natwick, MA, USA) program to extract peak knee flexion, peak power absorption, peak power generation, and CoP for the SLS
  • All CoP measures were quantified using MatLab
  • The average of 5-trials was used for CoP variables
  • Paired, two-tailed, t-tests were used to compare demographics as well as self-reported symptom severity measures
  • Generalized linear regression analysis was used to compare within group and between group measures
  • For participants with both limbs tested, random intercept models were used
  • All statistical analyses were performed using SAS version 9.3 (SAS Institute, Inc., Cary, NC, USA)
Outcome Measures
  • The following CoP measures were collected:
    • Mean distance
    • Average distance from the mean CoP
    • Root-mean-square distance
    • Root-mean-square distance from mean CoP
    • Range
    • Maximum distance between two CoP locations
    • 95% confidence interval circle area

  • Pre and post self-reported symptom severity results
  • Pre and post functional testing results
Results Demographics
  • No statistical difference in age, activity level or BMI was noted between groups.

Pre-Intervention (PFPS Group verse Control Group)

  • Differences between groups were noted for the following measures during the SLS:
    • Peak knee power absorption was greater for the control group (p = 0.0029)
    • Peak knee power generation was greater for the control group (p = 0.0081)
    • CoP Range was greater for the control group (p = 0.0403)
    • No difference was noted for peak knee flexion angle (p = 0.8114)

Pre- verse Post-Intervention Changes for the PFPS Group

  • The PFPS group noted significant improvements in the following:
    • AKPS (p = 0.0056)
    • VAS-W (p = 0.0098)
    • VAS-U (p < 0.0001)
    • 95% confidence interval circle area (p < 0.05)
    • Mean distance (p <0.05)
    • Root-mean-square distance (p < 0.05)
    • Range (p < 0.05)
    • Peak knee flexion (p < 0.05)
    • Peak knee power generation (p < 0.05)
    • Peak knee power absorption (p < 0.05)

Post-Intervention (PFPS Group verse Control Group)

  • No differences were noted for the following measures:
    • Peak knee power absorption (p = 0.1019)
    • Peak knee power generation (p = 0.3324)
    • CoP range (p = 0.3708)

Our Conclusions This study demonstrates that a progressive glute complex and abdominal strengthening program can improve reported pain, balance, peak knee power absorption, and peak knee power generation in individuals with PFPS. This study is congruent with the methodology used by the Brookbush Institute which includes glute complex and abdominals activation for those individuals exhibiting Lower Extremity Dysfunctions (LEDs), such as PFPS.
Researchers' Conclusions

Participants with PFPS noted improvements in CoP range, peak knee power absorption, and peak knee power generation after a 9-week physical therapy intervention. Upon completion of the intervention, self-reported symptoms also significantly improved. CoP measures may be an effective tool for evaluating progression during an intervention in those with PFPS.

Dr. Brookbush instructs model, Melissa Ruiz, on proper form during a Kneeling Chop
Caption: Dr. Brookbush instructs model, Melissa Ruiz, on proper form during a Kneeling Chop

Kneeling Chop

How This Study Contributes to the Body of Research:

This study contributes to a body of research investigating glute complex and core strength and patellofemoral pain syndrome (PFPS) (5, 6, 10, 11, 13, ). A relatively unique combination of outcome measures was evaluated in this study including pain, strength, balance, peak knee power generation, and peak knee power absorption, and the PFPS group was compared to a group of pain-free controls. Although this study did not evaluate electromyographic or kinematic variables (ex. knee valgus, contralateral pelvic drop), it does demonstrate that glute complex core strength , and the resolution of PFPS symptoms has a significant impact on key performance variables.

How the Findings Apply to Practice:

This study supports the implementation of functional assessment and progressive glute complex and core strengthening  for those exhibiting signs of PFPS. The exercises used in this study are similar to exercises commonly seen in practice, and the programs were individualized for volume (reps, sets, tempo, load) (19-22). Human movement professionals should consider integrating functional assessment and progressive glute complex and core strengthening  into routines for individuals with PFPS looking to reduce pain and increase performance.

This study had many methodological strengths, including:

  1. Exercise volume (sets, reps, tempo) was tailored to each participant's needs in accordance with an assessment; similar to the program design commonly used by human movement professionals.
  2. The single-leg squat assessment was used for functional testing which is widely used and easily implemented by human movement professionals. Further, the use of the single-leg squat assessment in this study aids in validating the use of functional movement assessments in practice.
  3. The exercises selected used minimal equipment (resistance band) improving replicability for future researchers and applicability for human movement professionals.

Weaknesses that should be noted prior to clinical integration:

  1. A cohort of 7 participants is extremely small; any changes in practice implied by the study should be carefully assessed and re-assessed.
  2. The tests selected by the physical therapists in the study were not well described; therefore, it is uncertain the specific tests used for range of motion  and manual muscle testing .
  3. EMG analysis was not included in the study which makes it difficult to compare the results of this study to previous studies.

How this Study Relates to Brookbush Institute Content:

The findings of this study are consistent with the Brookbush Institutes' (BI) predictive models of Lower-Extremity Dysfunction (LED) , Lumbopelvic Hip Complex Dysfunction (LPHCD) and Sacroiliac Joint Dysfunction (SIJD) . These models of movement impairment imply that functional testing , range of motion testing and manual muscle testing for the muscles discussed in this study may be beneficial. Further, glute complex and core strengthening are also implied by the models. BI always recommends an integrated approach to assessment and intervention, and has suggested in prior studies that addressing dysfunction is not only beneficial for rehabilitation but performance as well. The improvements in balance, peak knee power generation, and peak knee power absorption may support this assertion.

Sample Videos Related to the Research Content:

Gluteus Medius Manual Muscle Testing

Gluteus Medius Activation Circuit

Side Stepping for Gluteus Medius Reactive Activation

Recommended Readings:

  1. Introduction to Activation Exercises
  2. Manual Muscle Testing: Lower Body


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