Hip extensor weakness and its association with reduced physical activity in children surgically treated for DDH

Introduction:
Developmental dysplasia of the hip (DDH) may lead to persistent functional limitations despite surgical treatment. Beyond anatomical correction, residual impairments in hip joint mobility and muscle strength may affect children’s participation in daily physical activity. However, the relationship between these functional deficits and physical activity level remains insufficiently documented in operated children.

Objectives:
To compare hip joint range of motion and muscle strength between children operated on for DDH and healthy controls, and to explore their association with physical activity level.

Methodology:
A case-control study was conducted from January to May 2025 at the Department of Pediatric Orthopedic Surgery, Mohammed VI University Hospital, Marrakech, including 20 children surgically treated for DDH between 2020 and 2024 and 20 healthy controls. Children with DDH were assessed at least 3 months after surgery. Hip range of motion and manual muscle strength were assessed bilaterally. Physical activity was evaluated using the PAQ-C. Between-group comparisons and Spearman correlations were performed (p<0.05).

Results:
Median age was 9.5 years in both groups (DDH: IQR 8.25–12; controls: 9–11.75), with 17 girls and 3 boys per group. The groups were comparable in weight, height, and BMI (all p>0.05). DDH was right-sided in 3 (15%), left-sided in 6 (30%), and bilateral in 11 (55%) children. Median age at first surgery was 48 months (IQR 30.5–81), with 2 surgical procedures (IQR 1–4). Median time from the most recent surgery to assessment was 27 months (IQR 16.25–43). Children with DDH showed reduced bilateral hip flexion (both p<0.001), left medial rotation (p=0.016), and left lateral rotation (p<0.001). Muscle strength was significantly lower for hip flexors, extensors, abductors, adductors, and medial and lateral rotators. Lower PAQ-C scores were associated with lower left hip extensor strength (ρ=0.319, p=0.045).

Conclusion:
Children operated on for DDH demonstrated persistent deficits in hip mobility and muscle strength compared with healthy controls. Lower physical activity was associated with lower hip extensor strength, supporting consideration of muscle function and physical activity in postoperative rehabilitation.