Is there an association between plantar fasciitis and knee osteoarthritis?

Background: Knee osteoarthritis (OA) and plantar fasciitis share similar risk factors including ageing, occupation, obesity, and inappropriate shoe wear. However, the association between knee OA and heel pain caused by plantar fasciitis has received limited attention to date.

Aim: We aimed to assess the prevalence of plantar fasciitis using ultrasound in patients with knee OA and to identify factors associated with plantar fasciitis in these patients.

Patients and methods: We conducted a cross-sectional study including patients with Knee OA, fulfiling the European League Against Rheumatism criteria. The Western Ontario and McMaster Universities Osteoarthritis (WOMAC) and the Lequesne indexes were used to evaluate pain and function of the knees. The Manchester Foot Pain and Disability Index (MFPDI) was used to estimate foot pain and disability. Each patient underwent a physical examination, plain radiographs of the knees and the heels, and an ultrasound examination of both heels to find signs of plantar fasciitis. Statistical analysis was performed using SPSS.

Results: We included 40 knee OA patients, with a mean age of 59.85 ± 9.65 years [32-74] and a male-to-female ratio of 0.17. The mean WOMAC was 34.03 ± 19.9 [4-75]. The mean Lequesne for knees was 9.62 ± 4.57 [3-16.5]. Among our patients, 52% (n = 21) experienced heel pain. The heel pain was severe in 19% (n = 4). The mean MFPDI was 4.67 ± 4.16 [0-8]. Limited ankle dorsiflexion and plantar flexion were noted in 47% of patients (n = 17) each. High and low arch deformities were seen in 23% (n = 9) and 40% (n = 16) of patients. Ultrasound revealed a thickened plantar fascia in 62% (n = 25). An abnormal hypoechoic plantar fascia was noted in 47% (n = 19), with the loss of normal fibrillar architecture in 12 cases (30%). No Doppler signal was exhibited. Patients with plantar fasciitis had significantly limited dorsiflexion (n = 2 (13%) versus n = 15 (60%), p = 0.004) and plantar flexion (n = 3 (20%) versus n = 14 (56%), p = 0.026). The range of supination was also less important in the plantar fasciitis group (17.73 ± 4.1 vs. 12.8 ± 6.46, p = 0.027). The low arch was statistically more present in patients with plantar fasciitis (G1: 36% [n = 9] vs. G0: 0% [n = 0], p = 0.015). However, the high arch deformity was statistically more present in patients without plantar fasciitis (G1: 28% [n = 7] vs. G0: 60% [n = 9], p = 0.046). Multivariate analysis showed that the risk factor for plantar fasciitis in knee OA patients was limited dorsiflexion (OR = 3.889, 95% CI [0.017-0.987], p = 0.049).

Conclusion: In conclusion, our work showed that plantar fasciitis is frequent in knee OA patients, with reduced ankle dorsiflexion being the main risk factor for plantar fasciitis in these patients.