Effects of Clamshell Exercises in Addition to Standardized Physical Therapy in the Management of Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) is one of the most common causes of anterior knee pain, affecting both physically active individuals and the general population. The condition is associated with pain during activities that increase patellofemoral joint loading, including squatting, stair climbing, running, jumping, and prolonged sitting. Altered lower-limb biomechanics, particularly weakness of the hip abductors and external rotators, may contribute to excessive femoral internal rotation and dynamic knee valgus, thereby increasing patellofemoral joint stress.

Conventional physiotherapy for PFPS typically includes stretching, quadriceps strengthening, and functional rehabilitation. Although these interventions are beneficial, many patients continue to experience persistent symptoms or recurrence. Recent evidence suggests that strengthening the hip musculature, particularly the gluteus medius, may improve lower-limb alignment and reduce patellofemoral joint stress. The clamshell exercise is a simple, low-cost exercise designed to activate the hip abductors and external rotators and may provide additional clinical benefit when combined with standard physiotherapy.

The purpose of this randomized controlled trial is to determine whether adding clamshell exercises to standardized physical therapy results in greater reductions in pain and improvements in knee function compared with standardized physical therapy alone in patients with PFPS.

Participants aged 18-45 years who meet the American Physical Therapy Association clinical diagnostic criteria for PFPS and have symptoms lasting at least three months with a pain score of 3 or higher on the Numeric Pain Rating Scale (NPRS) will be recruited. Participants with previous knee surgery, significant ligament or meniscal injuries, patellar dislocation, osteoarthritis, lumbar radiculopathy, hip pathology, systemic inflammatory arthritis, recent corticosteroid injection or surgery, neuromuscular disorders, pregnancy, or other exclusion criteria will not be eligible.

Approximately 40 participants will be enrolled using purposive sampling after accounting for potential loss to follow-up. Participants will be randomly allocated into one of two treatment groups:

Control Group: Standardized physical therapy. Experimental Group: Standardized physical therapy plus clamshell exercises.

Both groups will receive equal treatment duration of approximately 45 minutes per session, three sessions per week for four weeks. Standardized physical therapy includes warm-up activities, stretching of the hamstrings, quadriceps, gastrocnemius-soleus complex, and iliotibial band, quadriceps and lower-limb strengthening exercises, and cool-down stretching. The experimental group will additionally perform side-lying clamshell exercises (3 sets of 12-15 repetitions) during each treatment session.

Outcome assessments will be performed at baseline and after completion of the intervention. Pain intensity will be evaluated using the Numeric Pain Rating Scale (NPRS), while knee function will be assessed using the Kujala Anterior Knee Pain Scale. Statistical analyses will be conducted using SPSS version 27. Appropriate parametric or non-parametric tests will be selected based on data distribution, with statistical significance established at p < 0.05.

Ethical approval will be obtained from the Research Ethics Review Committee of Ibadat International University, Islamabad, and permission will be obtained from Alkhidmat Hospital, Peshawar. Written informed consent will be obtained from all participants before enrollment. Participant confidentiality will be maintained throughout the study, and participation will be voluntary with the right to withdraw at any stage without penalty.

Inclusion criteria

• Adults aged 18 to 45 years. Male or female participants. Clinically diagnosed with patellofemoral pain syndrome (PFPS) according to the American Physical Therapy Association (APTA) clinical practice guidelines.

Presence of retropatellar or peripatellar pain. Reproduction of retropatellar or peripatellar pain during squatting or other functional activities that load the patellofemoral joint in knee flexion.

Symptoms present for at least 3 months. Pain intensity of ≥3 on the Numeric Pain Rating Scale (NPRS) during aggravating activities.

Able and willing to provide written informed consent and comply with the study procedures.

Exclusion criteria

• History of knee surgery, ligament injury, meniscal tear, patellar dislocation, or knee osteoarthritis.

Lumbar radiculopathy, hip pathology, or systemic inflammatory arthritis (e.g., rheumatoid arthritis).

Corticosteroid injection or knee surgery within the previous 3 months. Neuromuscular disorders affecting muscle function (e.g., stroke or Parkinson's disease).

Pregnancy or within 6 months postpartum. Family history of early degenerative joint disease. Any condition that, in the investigator's opinion, would interfere with safe participation or completion of the study.