Association between Popliteal Crease Obliquity Angle and Early Osteoarthritis Questionnaire: A Smartphone-Based Preliminary Study for Preclinical Knee Osteoarthritis

Background Osteoarthritis (OA) is a major public health concern, yet standard radiographic diagnosis faces limitations like radiation exposure, costs, and poor correlation with clinical symptoms. Accessible non-invasive indicators are needed. The popliteal crease obliquity angle (PCOA) has emerged as a promising tool reflecting lower limb alignment, while the Early Osteoarthritis Questionnaire Assessment (EOQA) provides critical subjective symptom data. Despite their individual utility, the relationship between PCOA and EOQA remains insufficiently explored. This study investigates their association to evaluate if PCOA can serve as a reliable, non-invasive surrogate to supplement or replace conventional imaging in OA evaluation. Purpose To investigate the association between the PCOA and the clinical features of the EOQA in individuals with preclinical knee osteoarthritis. By analyzing this relationship, this study evaluates whether PCOA can serve as a potential non-invasive clinical indicator for early screening and biomechanical assessment in primary care settings. Study design A comparative study Methods This study involved 43 manufacturing workers (86 legs) recruited from a cosmetic production facility. Participants were assigned to the experimental group (n=42 legs) and control group (n=44 legs). The PCOA was measured in a barefoot standing position under two conditions. Mann–Whitney U test to compare PCOA values between groups under two different conditions: shoulder-width apart and feet together. Results In the shoulder-width stance, the EOQA group exhibited significantly higher PCOA angles compared to the non-EOQA group. Similarly, in the feet-together stance, EOQA-positive limbs showed a significantly greater PCOA. For both positions, the differences were statistically highly significant (p<0.001), confirming a robust association between EOQA status and PCOA. Receiver operating characteristic analysis demonstrated an area under the curve of 0.888, and the optimal cutoff value of PCOA was 7.0°, yielding a sensitivity of 0.900. Conclusions This study demonstrates a significant association between the PCOA and the clinical features of the EOQA. Measuring PCOA, especially in a shoulder-width stance, provides a practical, radiation-free screening tool for preclinical knee OA. The high area under the curve and sensitivity indicate the practical utility of integrating objective PCOA with subjective EOQA assessments. This combined approach facilitates early detection and simplifies biomechanical evaluation in primary care and occupational health settings.