Relationship between toe grip strength and osteoarthritis of the knee: a preliminary study

Abstract

Purpose: Toe flexor function is important for balancing and walking. However, we often encounter knee osteoarthritis (OA) patients who cannot touch their toes to the ground, and therefore, the toes do not function during walking. We hypothesised that toe function is affected with knee OA and investigated the relationship between knee OA and toe grip strength (TGS). Methods: Seventy-eight knee OA patients (12 men and 66 women; mean age, 73.5 ± 7.3 years; OA group) and 71 healthy community-dwelling individuals (13 men and 54 women; mean age, 72.5 ± 5.5 years; control group participated in the study. With regard to Kellgren-Lawrence grading in the OA group, 8 subjects had grade 2, 32 had grade 3, and 38 had grade 4. The control group comprised individuals without any pain and knee malalignment, who could walk without aid. The outcome measures were body mass index (BMI), TGS, and isometric knee extension strength (IKES). The TGS and IKES were measured twice using a toe grip dynamometer and hand-held dynamometer, respectively, and the mean values were calculated. Data were collected on the affected side in the OA group and non-dominant side in the control group. The dominant foot was identified as the one preferred for kicking a ball. Data were compared between the 2 groups using an unpaired t-test. Moreover, multiple logistic regression analysis was performed. The independent variable was the group and the dependent variables were age, sex, BMI, TGS, and IKES. The significance level was set at 5%. The local ethics committee approved the study, and all subjects provided written informed consent prior to study participation. This study was supported by JSPS KAKENHI Grant Number 25870971. Results: The BMI was significantly higher in the OA group (25.5 ± 3.5) compared to the control group (21.7 ± 2.6), whereas the TGS and IKES in the OA group (7.4 ± 4.2 kg and 15.3 ± 6.9 kg, respectively) were significantly lower than in the control group (11.6 ± 5.2 kg and 26.8 ± 7.5 kg, respectively). According to multiple logistic regression analysis, the sex (odds ratio [OR]: 0.05, 95% confidential interval [95%CI]: 0.01-0.32), BMI(OR: 1.98, 95% CI: 1.49-2.63) and IKES (OR: 0.71, 95% CI: 0.63-0.80) were associated with OA. Conclusions: The TGS in OA patients was significantly weaker than that in control subjects. Although our results cannot explain a causal relationship between TGS and knee OA, a reduced TGS may influence dynamic balance and force generation for propulsion, and thus increase the mechanical stress on the knee. Moreover, a reduction in activity with the progression of knee OA may also result in a reduced TGS. However, although the TGS was significantly different between the groups, it was not significantly associated with knee OA. The BMI was significantly higher and the IKES was significantly lower in the OA group relative to the control group. Furthermore, using multiple logistic regression analysis, the BMI and IKES were significantly associated with knee OA. These findings are similar to previously published reports. The current patient population included a large number of severe OA patients with 48.7% with grade 4 and only 10.3% with grade 2. In addition, 71 of the 78 participants were patients who were hospitalised for a total knee arthroplasty operation. Thus, it is likely that this patient group had a long history of OA, which may have resulted in marked weight gain and decrease in the IKES. Therefore, the BMI and IKES might have had a stronger effect than TGS. Moreover, the control group comprised individuals who attended a municipal sports event by themselves. It might have an effect on the result of this study. Future studies will need to include more patients with mild knee OA and verify the biomechanical aspects.