The Impact of Pes Planus on Knee Function and Its Association with Medial Compartment Knee Osteoarthritis

Pes planus, commonly known as flat foot, is characterized by the lowering of the medial longitudinal arch of the foot, leading to alterations in lower limb biomechanics and potential pain and injury. This condition can affect the mechanical alignment and dynamic function of the lower limb, potentially contributing to the development and progression of knee osteoarthritis (OA). This study aims to investigate the association between pes planus and medial compartment knee OA as well as its impact on the knee functional score.

This cross-sectional study included 165 patients aged 20-72 years. Inclusion criteria were individuals with unilateral or bilateral flat feet, while exclusion criteria were other foot conditions, history of knee or ankle surgeries, rheumatoid arthritis, and limb length discrepancies. Clinical assessments included knee joint tenderness, foot arch measurement using the foot arch index, and radiographic evaluations of Meary's angle and tibiofemoral (TF) angle. The knee injury and osteoarthritis outcome score (KOOS) was used to assess knee function.

The study population had a mean age of 43.98 ± 13.17 years. Meary's angle ranged from 5 to 19° (mean 9.46), and the foot arch index ranged from 0.220 to 0.520 (mean 0.33). The TF angle ranged from 1.7 to 7.5° (mean 4.98). KOOS scores varied from 10 to 100 (mean 62.40). Patients with more severe flat feet (higher Meary's angle and foot arch index) had significantly lower KOOS scores, indicating worse knee function and greater pain. The correlations between foot arch index, Meary's angle, and KOOS scores were statistically significant (P = 0.001).

This study demonstrates a strong association between flat foot severity and knee OA. Increased Meary's angle and foot arch index were correlated with worsened knee function and increased pain, as measured by KOOS scores. These findings highlight the importance of assessing foot posture in patients with medial compartment OA and suggest that early intervention and orthotic management could be beneficial in mitigating the progression and severity of knee OA in patients with pes planus.