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. 2024 Feb 16;103(7):e37102. doi: 10.1097/MD.0000000000037102

Effects of hip abductor with external rotator strengthening versus proprioceptive training on pain and functions in patients with patellofemoral pain syndrome: A randomized controlled trial

Aiswarya Raju a, Kavitha Jayaraman a, Shibili Nuhmani b, Salbin Sebastian a, Masood Khan c,*, Ahmad H Alghadir c
PMCID: PMC10869081  PMID: 38363950

Abstract

Background:

Strengthening the hip muscles, particularly the abductors and rotators, has been reported beneficial for treating Patellofemoral pain syndrome (PFPS). Proprioceptive training (PT) is also shown to improve musculoskeletal pain and function in PFPS. The most appropriate treatment from these 2 is unclear. This study aimed to compare the effects of hip abductors and external rotator strengthening exercises along with conventional physical therapy (CPT) vs the proprioceptive training of the knee along with CPT in patients with PFPS.

Methods:

Forty-five participants were divided into 3 groups, experimental group 1 (EG 1), experimental group 2 (EG 2), and control group (CG), with fifteen participants in each group. EG 1 received hip abductor and external rotator strengthening exercises in addition to CPT. EG 2 received proprioceptive training and CPT. CG received CPT alone. Intervention programs lasted for 4 weeks. The pain was measured by Kujala Anterior Knee Pain Scale (AKPS). The study was registered retrospectively in the protocol registration and results system (clinicaltrials.gov, ID: NCT05698797 on 26/01/2023).

Results:

AKPS scores significantly (P < .001) improved in all 3 groups. A significant (P < .05) difference was also observed between all 3 groups. The greatest improvement was observed in EG 1, followed by EG 2 and CG.

Conclusion:

The addition of hip abductor and external rotator strengthening exercises to a 4-week CPT program showed a more significant improvement in AKPS scores than the addition of proprioceptive training in patients with PFPS.

Keywords: conventional physical therapy, exercises, knee, Kujala anterior knee pain scale

1. Introduction

Patellofemoral pain syndrome (PFPS) is a common musculoskeletal condition characterized by an insidious onset of pain in the knee anterior/retro-patellar/peripatellar region. The pain worsens with loading activities of the lower limb, such as squatting, stair climbing, uphill running, and prolonged sitting, which may severely affect the ADLs in the general population and sports participation in athletes.[1] PFPS is considered one of the most prevalent knee pain diagnoses in sports injury clinics, accounting for around one-fourth of all medical consultations for knee pain, with an annual prevalence of 22.7% in the general population and 29.2% in females and 15.5% in males.[2] A conservative treatment approach which includes relative rest, quadriceps strengthening, hip muscle strengthening, proprioceptive training, neuromuscular electrical stimulation, manual therapy, and electrotherapy modalities, is the first line of treatment for PFPS.[3]

There is considerable evidence that impaired hip muscle control can alter the kinematics and kinetics of the patellofemoral joint in multiple planes.[4] Powers (2010)[4] reported that an imbalance in the muscle strength in the trunk and hip region could alter the biomechanics of the patellofemoral joint during various activities. According to Rothermich et al,[5] PFPS is caused by a varying combination of lower extremity malalignment and hip and knee muscle imbalance. PFPS could be caused by dynamic valgus, involving hip medial rotation and adduction. It has been demonstrated that excessive medial femoral rotation reduces patellofemoral contact area and increases patellofemoral joint stress.

According to previous studies, strengthening the hip muscles, particularly the abductors and rotators, is beneficial for treating PFPS. In a systematic review, Nascimento et al[6] documented the beneficial effects of hip strengthening exercises compared to knee strengthening alone to relieve pain and improve function in PFPS patients. Santos et al[7] reported similar findings in PFPS patients. According to Dolak et al,[8] early hip strengthening may allow patients with patellofemoral pain to experience faster pain relief than quadriceps-focused exercises. Khayambashi et al[9] reported that an isolated strengthening of the hip abductor and external rotator muscles is more beneficial in improving patient condition than the no-exercise control group in females diagnosed with PFPS. The authors recommended incorporating hip strengthening as an important part of the rehabilitation of female patients with PFPS. A recent study by Alammari et al[10] also reported that hip abductors and lateral rotator strengthening have greater long-term and short-term benefits than traditional knee exercises for alleviating PFPS symptoms.

Several studies have proven that proprioceptive training effectively reduces musculoskeletal pain and function and should be included in rehabilitation programs.[11,12] It has been reported that the proprioceptive quality of the knee is diminished in PFPS. Akseki et al[13] reported that patients with PFPS have impaired proprioception in the affected knee compared to the contralateral side. Boitrago et al[14] noted that resisted exercise and proprioceptive training improved pain and lower limb function in females with PFPS more effectively than behavioral, cognitive, and educational guidance. Some authors recommended including knee proprioceptive training in the rehabilitation program for PFPS. Boitrago et al[14] stated that concurrent application of the hip abductor along with external rotator strengthening and proprioceptive training could improve pain and function in PFPS.

Even though various rehabilitation approaches, including hip strengthening and proprioceptive training, are being considered for managing PFPS, the most appropriate treatment from these 2 is still unclear. Therefore, this study aimed to compare the effects of a program consisting of hip abductors and external rotator strengthening exercises along with conventional physical therapy (CPT) versus a program composed of proprioceptive training of the knee along with CPT on pain and functions in patients with PFPS. This study will identify the most effective rehabilitation approach for patients suffering from PFPS. This study hypothesized a significant difference between the effects of both exercise programs on pain and functions.

2. Methods

2.1. Sample size

Sample size was calculated using the G*power software version 3.1.9.4 (Heinrich-Heine-Universitat Dusseldorf, Germany; https://www.gpower.hhu.de/). VAS post-intervention mean and standard deviation values were used for sample size calculation from a similar study by Khayambashi et al, which gave a minimum total sample size of 12.[9]

2.2. Ethics approval and consent to participate

The institutional ethics committee, Association for Welfare of the Handicapped (AWH)Special College, approved the study (ID: AWH/EC/03/2021; approved on 11/11/2021), and “The Declaration of Helsinki” (The World Medical Association Code of Ethics) were adhered to. Before inclusion into the study, the study advantages and disadvantages were discussed with each participant and written informed consent was obtained.

2.3. Study design

A randomized clinical trial with 3 parallel arms pretest-post-test design was used in our study.

2.4. Participants and setting

The participants were patients from various government and private hospitals in and around Calicut, India, who were between 18 and 35 years and had recently been diagnosed with PFPS by an orthopedic surgeon. Forty-five participants (19 males and 26 females) were included. The study was conducted at the physical therapy laboratory of AWH Special College. All methods were performed in accordance with the relevant guidelines and regulations.

2.5. Inclusion and exclusion criteria

Participants were screened by the principal investigator using specific criteria for inclusion and exclusion. To be included in the study, the patient should experience anterior/retro patellar knee pain during activities, with insidious onset of symptoms not linked to trauma, pain persisting for no less than 4 weeks, pain on patellar facets palpation, as well as pain upon descending a 25-cm step or while performing a double-legged squat.[15–17] Patients with recent lower limb fractures or dislocations, knee/hip joint surgery, signs, symptoms, or radiological findings of intra-articular pathologies, such as effusion, ligamentous or meniscal involvement, were excluded from the study. Those with indications of patellar apprehension, referred pain from the hip, back, or sacroiliac joint, acute knee strain or sprain, patients on medication such as NSAIDs or corticosteroids, and those with degenerative and infectious arthritis were also excluded.

2.6. Recruitment period and clinical trial registration

The recruitment and follow-up period were from February 6, 2022 to May 6, 2022. The study was registered retrospectively in the protocol registration and results system (clinicaltrials.gov, ID: NCT05698797 on 26/01/2023).

2.7. Randomization and procedure

A familiarization session was conducted before the beginning of the study to ensure that the participants were acquainted with the procedures. An independent researcher unaffiliated with the current study randomly assigned the participants to 3 groups experimental group 1 (EG 1), experimental group 2 (EG 2), and control group (CG), with fifteen participants in each group. IBM SPSS (version 26) software and the lottery method were used for randomization. EG 1 received hip abductor and external rotator strengthening exercises in addition to CPT. EG 2 received proprioceptive training and CPT. CG received CPT alone. Figure 1 shows the number of recruited, randomized, and analyzed participants in both groups. Before starting the intervention, a pretest/baseline measurement was taken on the first day of treatment. The post-test assessment was performed after 4 weeks of treatment sessions. An expert physical therapist supervised all the exercise sessions in all 3 groups. The outcome assessor was kept blind to the allocation of participants.

Figure 1.

Figure 1.

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The Consolidated Standards of Reporting Trials (CONSORT) chart shows the number of recruited, randomized, and analyzed participants in both groups.

Outcome measurement:

The physical limitations and severity of symptoms were assessed using the Kujala Anterior Knee Pain Scale (AKPS). This questionnaire has thirteen items regarding specific activities, pain intensity, and clinical symptoms. It is self-administered by patients. The maximum achievable score is 100; a higher score indicates greater pain and disability. The reliability and validity of the scale to measure pain and function in PFPS have been documented in previous studies.[18]

2.8. Intervention

  • 1.

    Experimental group 1 (EG 1): Participants in this group performed 4 weeks of hip strengthening exercises along with CPT. The CERT checklist for hip strengthening exercises provided to experimental group 1 has been given in supplementary table 1, http://links.lww.com/MD/L382 The hip strengthening exercises consisted of the following 3 exercises:

    • a.

      Isolated hip abductor strengthening: To perform hip abductor strengthening, the participants were in a side-lying position with the hip and knees extended and an elastic band tied proximal to the ankle joint. The participants performed hip abduction (up to approximately 30°) against the resistance.[9]

    • b.

      Hip abductor with lateral rotator strengthening: The participants were in a side-lying position with the feet together, the hip and knee flexed nearly 45°, and elastic resistance strapped across the knees. The participants were instructed to keep their feet together and perform an abduction against the resistance of the elastic band. The physical therapist positioned themselves behind the patient so that no compensation occurred.[15]

    • c.

      Hip lateral rotator strengthening: The participants sat at the edge of a treatment table with 90° knee flexion. A strap was applied to stabilize the thigh to avoid sagittal and frontal plane hip motion. An Elastic band was tied around the ankle and fastened to a rigid pole. The band length was customized based on the thigh length. The distance between the exercising limb and the pole was adjusted to avoid slack in the tubing. The exercise was carried out by doing an external rotation of the hip to nearly 30°.[9]

The participants performed ten repetitions and 3 sets of each exercise, with 30-second breaks in between 2 sets. The treatment duration for hip strengthening was approximately 20 minutes.

  • 2.

    Experimental group 2 (EG 2): Participants in this group performed 4 weeks of proprioceptive training of the affected knee joint along with CPT. The CERT checklist for proprioceptive training provided to experimental group 2 has been given in supplementary table 2, http://links.lww.com/MD/L385 This proprioceptive training consisted of 8 exercises which included

    • a.

      Exercise for balance on 1 leg on a stable surface (duration—10 sec. with 300 knee flexion)

    • b.

      Exercise for balance on 1 leg on a stable surface (bilateral arm movement in flexion, abduction, duration—10 sec. with 300 knee flexion)

    • c.

      Exercise for balance on 1 leg on a stable surface (eyes closed, duration—10 sec. with 300 knee flexion)

    • d.

      Exercise for balance on 1 leg on an unstable surface (duration—10 sec. with 300 knee flexion)

    • e.

      Exercise for balance on 1 leg on an unstable surface (bilateral arm movement in flexion, abduction, duration—10 sec. with 300 knee flexion)

    • f.

      Exercise for balance on 1 leg on an unstable surface (eyes closed, duration—10 sec. with 30° knee flexion)

    • g.

      Exercise for balance on 1 leg on an unstable surface (300 knee flexion, partner ball throw—10 repetitions)

    • h.

      Stair-up and -down a regular 3 steps staircase

The participants did each exercise with ten repetitions and 3 sets. The approximate time taken for proprioceptive training was 20 minutes.[14]

  • 3

    Control group (CG): Participants in this group performed 4 weeks of CPT. This CPT included interferential therapy (IFT) and 2 types of knee-strengthening exercises.[19–21] For IFT, 2 electrodes were secured with Velcro straps on either side of the patellofemoral joint. Amplitude modulated frequency of 80 Hz was selected and generated by 4 KHz sinusoidal waves. The knee strengthening exercises included quadriceps setting exercises and straight leg raising (SLR).[20,21] The participants did each exercise with ten repetitions and 3 sets. The approximate time taken for CPT was 20 minutes.

2.9. Statistical analysis

Data from a total of 45 participants were analyzed. IBM SPSS (version 26) software (SPSS Inc., Chicago, IL) was used for data analysis. The Shapiro–Wilk test of Normality was used to determine whether the baseline values of the dependent variables had a normal distribution. The Shapiro–Wilk test of Normality P values indicated that the distribution was normal, as shown in Table 1. Therefore, for with-in-group analyses, paired t-test was used. One-way ANOVA was used to see if there were any significant differences between the groups, and multiple comparisons were made using the Tukey HSD test. A 0.05 level of significance was employed for the comparisons, and a difference was considered significant with a P value ≤ .05. 95% was chosen as the value of the confidence interval. In addition, Cohen d was used for effect size estimation.

Table 1.

Descriptive statistics (mean ± SD), dependent variables data (n = 15 each group), and P values for the Shapiro–Wilk test of normality.

EG 1 P value EG 2 P value CG P value
Age (yr) 25.47 ± 4.27 26.00 ± 4.12 25.27 ± 4.48
Gender
Male (n)
Female (n)
5
10
8
7
6
9
Height (cm) 162.13 ± 7.96 164.07 ± 6.19 163.07 ± 7.91
Weight (kg) 62.27 ± 13.33 66.79 ± 14.59 64.73 ± 15.57
BMI (kg./m2) 23.49 ± 3.64 24.59 ± 4.10 24.12 ± 4.41
AKPS_Pre (points) 41.67 ± 15.28 .42 39.33 ± 17.00 .29 40.07 ± 16.68 .21
AKPS_Post (points) 92.87 ± 4.82 78.13 ± 10.00 48.33 ± 15.25
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AKPS = Kujala Anterior Knee Pain Scale, BMI = Body Mass Index, CG = Control Group, EG 1 = Experimental Group 1, EG 2 = Experimental Group 2, SD = Standard Deviation.

3. Results

Participants’ demographic data, including age, height, weight, and BMI for all 3 groups, is descriptively summarized in Table 1. Baseline and post-intervention values of the dependent variable, that is, AKPS, are also presented in Table 1. Data from 45 participants was analyzed with 15 participants from each group.

3.1. With-in group results

These results are presented in Table 2.

Table 2.

With-in-group results (Paired samples t test), P value, and effect size (Cohen d).

Groups AKPS_Post - AKPS_Pre
(MD ± SD)		 P value Cohen d
EG 1 51.200 ± 11.977 <.001* 4.275
EG 2 38.800 ± 8.291 <.001* 4.680
CG 8.267 ± 3.515 <.001* 2.352
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AKPS = Kujala Anterior Knee Pain Scale, CG = Control Group, EG 1 = Experimental Group 1, EG 2 = Experimental Group 2, MD = Mean Difference, SD = Standard Deviation

*

Significant.

EG 1 (hip abductor and external rotator strengthening in addition to CPT): AKPS significantly (P < .001) increased by 122.87 % with a large effect size (Cohen d = 4.275).

EG 2 (proprioceptive training and CPT): AKPS significantly (P < .001) increased by 98.65% with a large effect size (Cohen d = 4.680).

CG (CPT): AKPS significantly (P < .001) increased by 20.61% with a large effect size (Cohen d = 2.352).

3.2. Between-group results

These results are presented in Tables 3 and 4. A significant (P < .001) difference was found in post-intervention values of AKPS between all 3 groups, as shown in Table 3. The greatest improvement was observed in EG 1, followed by EG 2 and CG.

Table 3.

Between-group results (one-way ANOVA) for comparison of 3 groups.

Variable df F P value Effect size (Eta-squared)
AKPS_Post 2 61.476 <.001* 0.745
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AKPS = Kujala Anterior Knee Pain Scale, Df = Degree of Freedom.

*

Significant.

Table 4.

Group-wise, between-group results (Tukey HSD test).

AKPS_Post - AKPS_Post Mean difference Std. error P value
EG 1- EG 2 14.733 4.092 .002*
EG 1- CG 44.533 4.092 <.001*
EG 2- CG 29.800 4.092 <.001*
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AKPS = Kujala Anterior Knee Pain Scale, CG = Control Group, EG 1 = Experimental Group 1, EG 2 = Experimental Group 2.

*

Significant.

Between EG 1 and EG 2:

Significant (P = .002) difference was observed in post-intervention values of AKPS of EG 1 and EG 2 (Table 4). Greater improvement occurred in EG 1.

Between EG 1 and CG:

Significant (P < .001) difference was observed in post-intervention values of AKPS of EG 1 and CG (Table 4). Greater improvement occurred in EG 1.

Between EG 2 and CG:

Significant (P < .001) difference was observed in post-intervention values of AKPS of EG 2 and CG (Table 4). Greater improvement occurred in EG 2.

4. Discussion

The present study compared the efficacy of 3 programs on pain and functions in patients with PFPS. The first program included hip abductor and external rotator strengthening exercises along with CPT. The second program consisted of knee proprioceptive training and CPT, and the third program consisted of CPT alone. These interventions were performed for 4 weeks. Pain and functions were assessed using the AKPS. The study results revealed an improvement in AKPS scores in all the groups. However, the greatest improvement was observed in the group receiving hip abductor and external rotator strengthening exercises.

Although there was a significant improvement in AKPS scores in participants who underwent a hip strengthening program, the mechanism underlying this improvement cannot be determined based on this study. Weakness in the hip muscles, especially the hip abductors and external rotators, is well documented in patients with PFPS.[10,22] When engaging in dynamic activities, weak hip abductors and external rotators might not be able to adequately counteract hip internal rotation and adduction. This results in improper patellar tracking by increasing the lateral quadriceps muscle pulling force on the patella. Impaired hip muscle strength is associated with the knee joint excessive frontal plane motion, leading to increased Q-angle.[23] A significant negative correlation was reported between hip abduction and motion toward the valgus direction; the greater the hip abduction peak torque, the lesser the motion toward the valgus direction.[24] Resistance training showed a reduction in Q-angle and increased hip abductor strength. Therefore, hip strengthening exercise improves the knee joint kinematics and reduces the Q-angle, reducing patellofemoral joint load and improving symptoms. Strength training can also improve joint proprioception through muscle spindle activation.[25] Besides sending sensory information, muscle spindles receive information from efferent gamma motor neurons. Strength training improves gamma efferent activity, increasing joint position sense, which improves joint stability.

Our study findings support the suggestion of the previous researchers regarding the addition of hip-strengthening training in the rehabilitation of PFPS. Mascal et al[26] reported that a strengthening program aimed at hip and trunk muscles effectively reduced pain and improved function in PFPS. Nakagawa et al[15] reported that a combination of the hip abductor, external rotator, and knee extensor strengthening was more helpful than knee strengthening alone in females diagnosed with PFPS. Similarly, Dolak et al[8] reported that 4 weeks of hip strengthening exercise reduced self-reported symptoms in patients with PFPS.

In the present study, there was also a significant improvement in AKPS scores in patients who received proprioceptive training. Proprioceptive training improves sensory-motor control and joint stability and optimizes the functional task excursion in favor of synchronization and coordination in activating muscle groups. Somatosensory deficits are related to PFPS.[27] Patellofemoral pain patients have been reported to have impaired proprioception and postural imbalance.[27,28] Proprioceptive training improves physical function by alleviating pain and improving joint position sense, balance, and joint stability. The mechanism of pain reduction with proprioceptive training could be explained through the gait control theory of pain. Proprioceptive training activates afferent input from the muscle spindle and other mechanoreceptors of the joint, tendon, and capsule, which could prevent the spinal cord dorsal gray horn laminae from transmitting pain signals. Proprioceptive training improves balance and joint stability by stimulating the joint proprioceptors.[29,30] These receptors provide sensory signals to the gamma motor neurons. This provides efferent signals to the muscle that produce co-contraction of these muscles and provide joint stability and balance.

IFT, static quadriceps strengthening, and SLR were given to the participants in the control group as a CPT program. Analgesic effects of IFT have been explained by various physiological mechanisms, including the pain-gate theory, improved circulation, and the placebo effect.[31] The quadriceps-strengthening exercise was found to have significantly affected the pain, daily functions, and muscle performance of individuals with PFPS.[32] Therefore, static quadriceps and SLR exercises were performed to manage patients in the control group.

4.1. Relevance to the clinical practice

The present study finding supports the inclusion of hip abductor and external rotator strengthening exercises in the CPT program for the treatment of PFPS patients.

4.2. Limitations of the study

There were a few potential limitations in the present study that deserve mention. Firstly, this study aimed to examine the intervention immediate effects on PFPS patients. So, generalization of the study is limited to the defined time frame of the current study. Further studies are recommended to determine the long-term effectiveness of these treatment techniques in patients with PFPS. Secondly, we assume that the improvement in the AKPS score in experimental groups may be due to an improvement in muscle strength, Q-angle, and proprioception. However, this study didn’t measure the participants’ muscle strength, Q-angle, and proprioception. Therefore, further studies are recommended to compare the strength, Q-angle, and proprioception changes following these training programs in the included 3 groups.

5. Conclusion

The present study compared the effects of 3 programs, each 4 weeks long, on pain and functions in PFPS patients. These patients were divided into 3 groups, i.e., EG 1, EG 2, and CG. EG 1 involved hip abductor and external rotator strengthening in addition to CPT; EG 2 involved proprioceptive training and CPT; CG involved CPT alone. This study concluded that AKPS scores significantly improved with all 3 interventions. However, the greatest improvement was observed with EG 1, followed by EG 2 and CG. Therefore, to improve pain and functions, the physical therapist should consider adding hip abductor and external rotator strengthening to the CPT program to treat PFPS patients.

Acknowledgments

The authors are grateful to the Researchers Supporting Project number (RSP2024R382), King Saud University, Riyadh, Saudi Arabia for funding this research.

Author contributions

Conceptualization: Aiswarya Raju, Salbin Sebastian.

Data curation: Aiswarya Raju, Salbin Sebastian.

Funding acquisition: Ahmad H. Alghadir.

Formal analysis: Aiswarya Raju, Masood Khan.

Investigation: Shibili Nuhmani, Salbin Sebastian, Masood Khan.

Methodology: Aiswarya Raju, Salbin Sebastian.

Project administration: Shibili Nuhmani, Ahmad H. Alghadir.

Resources: Kavitha Jayaraman, Shibili Nuhmani, Ahmad H. Alghadir.

Software: Ahmad H. Alghadir.

Supervision: Kavitha Jayaraman, Shibili Nuhmani, Ahmad H. Alghadir.

Validation: Kavitha Jayaraman, Shibili Nuhmani, Masood Khan.

Visualization: Kavitha Jayaraman, Shibili Nuhmani, Masood Khan.

Writing – original draft: Aiswarya Raju.

Writing – review & editing: Kavitha Jayaraman, Salbin Sebastian, Masood Khan.

Supplementary Material

medi-103-e37102-s001.docx (15.3KB, docx)
medi-103-e37102-s002.docx (16.3KB, docx)

Abbreviations:

AKPS
Kujala Anterior Knee Pain Scale
CG
control group
CPT
conventional physical therapy
IFT
interferential therapy
PFPS
patellofemoral pain syndrome
SLR
straight leg raising

All data generated or analyzed during this study are included in this published article [and its supplementary information files].

Supplemental Digital Content is available for this article.

The authors have no conflicts of interest to disclose.

Researchers Supporting Project number (RSP2024R382), King Saud University, Riyadh, Saudi Arabia.

How to cite this article: Raju A, Jayaraman K, Nuhmani S, Sebastian S, Khan M, Alghadir AH. Effects of hip abductor with external rotator strengthening versus proprioceptive training on pain and functions in patients with patellofemoral pain syndrome: A randomized controlled trial. Medicine 2024;103:7(e37102).

Contributor Information

Aiswarya Raju, Email: aiswaryaphysio2018@gmail.com.

Kavitha Jayaraman, Email: kavithajayaram7@gmail.com.

Shibili Nuhmani, Email: snuhmani@iau.edu.sa.

Salbin Sebastian, Email: salbinsebastian91@gmail.com.

Ahmad H. Alghadir, Email: aalghadir@hotmail.com.

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