By Shreen Ahmed Lashien, Ahmed Omar Abdelnaeem, and Ebtessam Fawzy Gomaa

Dynamic knee valgus, a highly reliable measure of this alignment assessed in the frontal plane, is a valuable tool for identifying this pathomechanical dysfunction.

The purpose of this study was to investigate the effectiveness of functional hip abductor strength training on reducing contralateral pelvic drop angle (hip frontal plane projection angle (FPPA)), and dynamic knee valgus (knee frontal plane projection angle) in runners with medial tibial stress syndrome (MTSS)—shin splints.

Methods

The study cohort for this single-blind randomized controlled trial included 26 male and 14 female recreational runners (age 25–35 years; body mass index between 18.5 and 25 kg/m2) were diagnosed with MTSS for at least 1 month. Participants were randomized into 2 groups: a control group (Group A, n = 20) received a selected physical therapy exercise program, and an experimental group (Group B, n = 20) received the same program plus functional hip abductor strength training (Figure 1).

Both groups ceased running activity for 3 weeks during the exercise program, followed by a gradual return to running at < 50% of their previous training volume, with continuity practicing their exercise program. Dynamic knee valgus (FPPA) and contralateral pelvic drop angle were measured using 2D video and analyzed at baseline and after 8 weeks.

Results

After 8 weeks, Group B (intervention) demonstrated a significant decrease in FPPA, indicating improved knee alignment after treatment compared to baseline (P < 0.001). Conversely, Group A (control) exhibited a significant increase in FPPA, worsening knee alignment, post-treatment compared to baseline (P < 0.001). Both groups showed a significant decrease in contralateral pelvic drop angle (improved pelvic stability) post-treatment compared to baseline (P < 0.01). The percent change of FPPA and contralateral pelvic drop angle in group A was 28.41% and 19.42%, respectively, and that of group B was 42.05% and 49.85%, respectively.

Discussion

The significant decrease in dynamic knee valgus (FPPA) in group B represents the critical value of hip abductors’ added functional strength training, accurate clinical reasoning, and proper lower limb biomechanical assessment, taking into consideration the hip abductors’ weakness as the main reason for the dynamic knee valgus and contralateral pelvic drop.

The anatomical explanation of the study’s findings lies in the femur’s obliquity anatomical (longitudinal) axis, which angulation creates a physiological valgus of up to 5 degrees from the vertical line. In contrast, the lower limb’s mechanical axis (weight-bearing line) travels from the center of the hip joint to the center of the ankle joint, passing through the midpoint of the tibiofemoral joint. This mechanical axis represents the ground reaction force as it transmits up through the lower extremity. In a neutrally aligned limb, the weight-bearing forces distribute equally between the medial and lateral condyles of the knee joint.

However, during single-leg stance (the stance phase of gait and running), the mechanical axis shifts toward the medial part of the knee joint to accommodate the narrower base of support below the center of mass, amplifying the compressive stress on the medial compartment and the tensile stress on the lateral compartment. Thus, any altered or abnormal anatomical alignment increases the lateral compressive force as the weight-bearing line shifts onto the lateral compartment of the knee (genu valgus), increasing the lateral compressive force. Conversely, a medial shift of the weight-bearing line (genu varum) increases the medial compressive force. Furthermore, recent studies support that MTSS arises from an overload of the medial tibia.

The running cycle includes 2 phases: the stance phase accounts for 40%, while the swing phase accounts for 60%. During single-limb support in running, the hip abductors, particularly the gluteus medius contracts eccentrically to control contralateral pelvis drop, hip adduction, internal rotation, and knee abduction (dynamic knee valgus), which occurs as the ground reaction force falls medial to the hip and the hip abductor moment is less than the external adduction moment due to gravity and acceleration load. While in the propulsion phase, the gluteus medius contracts concentrically to abduct the hip and generate power. Weakness in the gluteus medius can lead to excessive hip adduction and contralateral pelvic drop.

To achieve sufficient strength improvements, functional training should target the gluteus medius with an intensity of at least 60% of its maximum voluntary contraction, which explains the importance of the 5 exercises in the study authors’ functional training.

After identifying the baseline repetition maximum (RM) for a particular training-induced adaptation in strength, a percentage of an exercise program ranges from 60–70% of the baseline RM for healthy, untrained adults, and > 80% of the baseline RM for highly trained athletes is needed.

Conclusions

This study demonstrates that 8 weeks of functional hip abductor strength training, combined with traditional physical therapy, effectively improves lower extremity kinematics in recreational runners with MTSS by reducing dynamic knee valgus and contralateral pelvic drop. This targeted approach likely addresses underlying muscle weakness and movement dysfunction, offering hope for potentially reducing MTSS recurrence.

Shreen Ahmed Lashien, Ahmed Omar Abdelnaeem, and Ebtessam Fawzy Gomaa are affiliated with the Department of Orthopedic Physical Therapy, Faculty of Physical Therapy, Cairo University, Egypt.