Abstract
PURPOSE: To quantitatively analyze the structural changes of the knee in patients with neglected developmental dysplasia of the hip (DDH). METHODS: PubMed, Embase, Web of Science, and Cochrane Library databases were searched to identify studies comparing the morphological parameters of the knee between DDH patients and healthy individuals. Data on rotational and mechanical parameters of the lower limb, rate of occasional anterior knee pain (AKP), and knee morphological parameters, were extracted. Review Manager and R statistic software were used to perform the statistical analysis. RESULTS: Nine studies with a total of 790 legs in 521 neglected DDH patients and 431 legs in 303 health subjects were included. Patients were predominantly female (88.3%). The Crowe classification is most commonly used to assess the severity of DDH. The total incidence of occasional AKP ranged from 8.6 to 20.6%, with an overall pooled rate of 14.4% (95%CI = 9.8-19.8%). In patients with neglected DDH, significant increases (P < 0.0001) were observed in femoral anteversion (weighted mean: 39.1° vs. 17.7°), knee torsion (weighted mean: 9.0° vs. 1.6°), and the vertical dimension of the medial femoral condyle (weighted mean: 13.8 mm vs. 11.6 mm), along with a significant decrease in the lateral distal femoral angle (weighted mean: 82.1° vs. 84.8°), which can lead to torsion deformity of the lower limb and valgus inclination of the distal femoral articular surface. Compared with the intact subjects, DDH knees demonstrated an increased sulcus angle (weighted mean: 144.9° vs. 137.5°; P < 0.0001), decreased trochlear depth (weighted mean: 3.1 mm vs. 4.5 mm; P < 0.0001), increased lateral shift of the patella (5.1 mm vs. 3.8 mm, P = 0.06), and increased patellar tilt angle (weighted mean: 18.2° vs. 13.2°; P < 0.0001). These findings were associated with developmental dysplasia of femoral trochlear and patellar instability. CONCLUSION: Developmental dysplasia of the hip leads to patellar malalignment and developmental changes in the bony anatomy of the knee joint, including the development of a valgus deformity of the lower extremity and trochlear dysplasia. These findings may be associated with patellar instability. LEVEL OF EVIDENCE: III, systematic review. REGISTRATION: This study was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42025640292).