Full length articlePosture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis
Introduction
Kneeosteoarthritis (OA) is one of the representatives of the multi-causation disease model. It is not only contributed by the biochemical factors in the human body, but also related to the mechanical properties of the adjacent joints including the hip and the ankle [1].
The biomechanical factors mostly work by altering the knee adduction moment, which forces the knee to adduction position during gait. Adduction moment is the leading factor that affects the mediolateral force distribution inside the knee joint [2,3]. Theoretically, increase in the adduction moment can give a rise to medial tibiofemoral OA, can also make contribution to the radiologic and clinical progression of knee OA [4,5]. Along the kinetic chain of the lower limb, the adjacent joints including the ankle work together with the knee joint in order to properly align the extremity. Therefore, postural deformities of the ankle/foot might serve as potential determinants of adduction moment, thus knee OA. The mechanism for the impact of foot posture on knee adduction moment might be explained partially with the change in the centre of ground reaction force. Particular foot alignments are likely to exert greater knee adduction moments, whilst some certain types such as increased rearfoot eversion, rearfoot internal rotation and forefoot inversion can reduce the knee adduction moment. Differences in foot alignments make differences on the ground reaction force vector. The longer the perpendicular distance of the vector from the knee joint, the greater the adduction moment would be [6]. Foot posture in knee OA/knee pain was studied by a number of researchers in the literature [[7], [8], [9], [10]]. Gross et al. [8], in their cross-sectional study, highlighted the association of planus arch deformity with the higher frequency of knee pain and medial tibiofemoral cartilage damage in older adults. On the other hand, Levinger and colleagues [7] found that patients with medial tibiofemoral OA had higher frequency of pronated foot than 28 asymptomatic age-matched controls.
All in all, there are several studies evaluating the association of foot posture with the frequency of knee OA, along with the parameters such as knee pain and cartilage damage. However, the potential interaction of foot posture with the clinical and the radiological parameters in patients with knee OA is scarce [11]. Taken as a whole, a comprehensive look identifying the relation of foot posture with the objective clinical measures of knee OA, as well as with the radiologic indicators of knee loading/alignment seems necessary.
In the light of the above-mentioned knowledge, the present study aimed to evaluate the relation of foot posture with i) the radiologic severity of knee OA, ii) the varus alignment of the knee and iii) the clinical severity in patients with medial tibiofemoral knee OA.
Section snippets
Patients
The study included patients with symptomatic and radiographic signs of knee OA according to the American Collage of Rheumatology Criteria for knee OA [12]. The exclusion criteria were as follows: i) presence of any known inflammatory rheumatic disease/arthritis, ii) concomitant neurologic diseases including stroke, spinal cord injury, multiple sclerosis, polyneuropathy and drop foot, iii) presence of lower limb length discrepancy/deformity, iv) history of lower extremity fracture/surgery, v)
Results
The study included 150 patients (150 knees and feet at one side) with symptomatic and radiographic knee OA. Characteristics of the study population were summarized in Table 1. Accordingly, mean values for age, BMI and symptom duration of the study participants were 61.2 ± 10.1 years, 33.7 ± 5.3 kg/m2 and 6.0 ± 4.1 months, respectively.
Of the 150 feet evaluated; 34 (22.66%), 103 (68.66%) and 13 (8.66%) were at supinated (FPI < 0), neutral (FPI = 0 to +5) and pronated (FPI ≥ +6) posture,
Discussion
The present study has two emerging findings to discuss:
- i)
Both the radiologic and the clinical severity of knee OA is associated with supinated foot posture.
- ii)
Varus alignment in knee OA is related to pronated foot posture.
Supination/pronation of the foot is a complex entity. Supination of the foot is a combination of three movements: inversion in the frontal plane, plantar flexion in the sagittal plane and adduction in the horizontal plane. On the other hand, pronation of the foot refers to the
Conflicts of interest
The authors declare no conflicts of interest.
Acknowledgement
None to declare.
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