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Posture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis
Accepted Manuscript Title: Posture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis Authors: Zainb Al-Bayati, Ilke Coskun Benlidayi, Neslihan Gokcen PII: DOI: Reference:
S0966-6362(18)30146-2 https://doi.org/10.1016/j.gaitpost.2018.08.036 GAIPOS 6492
To appear in:
Gait & Posture
Received date: Revised date: Accepted date:
4-4-2018 30-7-2018 27-8-2018
Please cite this article as: Al-Bayati Z, Benlidayi IC, Gokcen N, Posture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis, Gait and amp; Posture (2018), https://doi.org/10.1016/j.gaitpost.2018.08.036 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Posture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis Zainb Al-Bayati, M.D. Cukurova University Faculty of Medicine, Department of Physical Medicine and Rehabilitation, AdanaTurkey
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Ilke Coskun Benlidayi, M.D. Associate Professor, Cukurova University Faculty of Medicine, Department of Physical Medicine and Rehabilitation, AdanaTurkey
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Neslihan Gokcen, M.D.
Cukurova University Faculty of Medicine, Department of Physical Medicine and Rehabilitation,
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Division of Rheumatology, Adana-Turkey
Ilke COSKUN BENLIDAYI, MD. Associate Professor,
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Department of Physical Medicine and Rehabilitation,
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Corresponding Author:
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Faculty of Medicine, Cukurova University, Adana-TURKEY Mobile phone number : + 90 538 545 39 37
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Fax number : + 90 322 338 64 29 e-mail : [email protected]
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Highlights:
Radiologic severity of knee OA is associated with supinated foot posture.
Varus alignment in knee OA is related to pronated foot posture.
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Clinical severity in knee OA is associated with supinated foot posture.
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ABSTRACT
Background: There are many contributors of knee osteoarthritis including the postural abnormalities of the adjacent joints. The relationship between foot posture and the clinical-radiological parameters of knee osteoarthritis is poorly understood. Research question: Is foot posture related to the clinical and radiological parameters in patients with knee osteoarthritis? Methods: Patients diagnosed with primary clinical and radiographic medial tibiofemoral knee
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osteoarthritis were included in the study. Anteroposterior knee radiographs were staged by using the
Kellgren-Lawrence grading system. Computer-based measurements of the medial joint space width
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(mJSW), condylar angle, anatomical axis angle, tibial plateau angle and condylar plateau angle were performed on digital anteroposterior knee radiographs. The Western Ontario and Mc Master University Osteoarthritis Index (WOMAC) questionnaire was used to assess pain and the functional status of the
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patients. Foot posture was assessed by the Foot Posture Index (FPI) system and feet were categorized into three (pronated, neutral and supinated).
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Results: The study included 150 patients (150 knees and feet at one side) with a mean age of 61.2±10.1
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years. In terms of foot posture groups; percentages for supination, neutral and pronation were 22.66%,
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68.66% and 8.66%, respectively. In the group with supinated FPI; WOMAC total score, pain and function subscale scores were higher (p<0.001), mJSW was narrowed (p=0.038) and the condylar plateau
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angle was increased (p=0.009). In the FPI pronation group; anatomic axis angle values were found to change in the varus direction (p=0.012).
Significance: The potential postural dysfunction of the foot should be taken into consideration during
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the assessment and/or management of a patient with knee osteoarthritis. Keywords: foot posture index; foot posture; knee osteoarthritis.
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Introduction:
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Knee osteoarthritis (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 center of ground reaction force. Particular foot
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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
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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
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researchers in the literature [7-10]. Gross et al. [8], in their cross-sectional study, highlighted the
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association of planus arch deformity with the higher frequency of knee pain and medial tibiofemoral
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cartilage damage in older adults. On the other hand, Levinger and colleagues [7] found that patients
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with medial tibiofemoral OA had higher frequency of pronated foot than 28 asymptomatic agematched controls.
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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
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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
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loading/alignment seems necessary.
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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. Methods: 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) knee
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prosthesis. Study Protocol;
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The study was conducted at the Department of Physical Medicine and Rehabilitation in
Cukurova University Faculty of Medicine between October 2016 and February 2017. Ethical approval was obtained from the Local Ethics Committee of Cukurova University (Approval date: 7-Oct-2016,
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number: 57). Written informed consent was taken from each study participant. Demographic variables
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(age, gender), symptom duration (month), anthropometric measures including body weight (kg), height
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(m) and body mass index (kg/m2) were noted.
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Evaluation of the foot posture;
Posture of the foot was evaluated by using the Foot Posture Index-6 (FPI-6) designed by
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Redmond et al. [13]. This tool is a valid static clinical measure comprises 6 components including; i) talar head palpation, ii) supra and infra lateral malleolar curvature, iii) calcaneal frontal plane position, iv) prominence in the region of the talonavicular joint, v) congruence of the medial longitudinal arch,
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vi) abduction/adduction of the forefoot on the rearfoot. The foot posture was assessed while the patient standing barefoot on double limb in a relaxed position. Each FPI component is scored from -2
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to +2, where -2 represents clear signs of supination and +2 addresses positive signs for pronation. The
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total score ranged from -12 to +12. Each foot was scored according to the above-mentioned explanation. Total scores between 0
to +5 represented the normal/neutral foot posture. Values ≥ +6 were regarded as pronated foot, whereas values below 0 were accepted as supinated foot posture. Evaluation of the radiologic severity of knee OA;
Radiologic severity was assessed by i) using the Kellgren-Lawrence (KL) grading system of knee OA, ii) the assessment of the medial tibiofemoral joint space width (mJSW) and iii) measuring the condylar plateau angle. Each patient was undergone standardized weight-bearing anteroposterior xray evaluation of both knees. The beam was aligned parallel to the floor and positioned relative to the tibiofemoral joint, while knees were in extension position.
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Radiographic severity of knee OA was classified by using the KL grading system of knee OA on digitalized images (Enlil PACS System 2.5) [14]. Knees were then categorized into two as mild OA (KL grade 1-2) and severe OA (KL grade 3-4). The severity of knee OA was also evaluated by the assessment
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of medial tibiofemoral joint space narrowing [15,16]. The minimum vertical distance between the
medial femoral condyle and the medial tibial plateau was taken as the mJSW (Figure 1). Condylar
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plateau angle was measured on the digitized anteroposterior knee radiographs. This angle was defined as the angle between the line tangent to the femoral condyles and the line tangent to the tibial plateaus
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Evaluation of the varus alignment of the knee;
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[17,18] (Figure 1).
Varus alignment of the knee joint was evaluated by digitalized measurement of the anatomic
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axis angle, the condylar angle, and the tibial plateau angle on anteroposterior knee radiographs as follows [17,18] (Figure 1):
i) Anatomic axis angle: The angle between the femoral anatomic axis (the line drawn from the
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midpoint of the femoral shaft to the midpoint of tibial eminences) and the tibial anatomic axis (the line
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drawn from the midpoint of the tibial eminences to the midpoint of the tibia). ii) Condylar angle: The angle between the femoral anatomic axis (the line drawn from the
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midpoint of the femoral shaft to the midpoint of tibial eminences) and the line tangent to the femoral condyles. Condylar angle was recorded in degrees form 90°. iii) Tibial plateau angle: The angle between the tibial anatomic axis (the line drawn from the midpoint of the tibial eminences to the midpoint of the tibia) and the line tangent to the tibia plateaus. Tibial plateau angle was recorded in degrees form 90°.
Clinical evaluation; The clinical evaluation was based on the validated 3.1 form of Western Ontario and Mc Master Universities Osteoarthritis Index (WOMAC) for the target population [19-21]. This form evaluates the patients’ symptoms by 24 questions in three categories including pain (5 questions), stiffness (2 questions) and physical function (17 questions). In this 5-point Likert (0-4) form of WOMAC 3.1, scale
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lengths for pain, stiffness and physical function vary between 0-20, 0-8 and 0-68, respectively. The following correction factors were used to normalize the index to 0-10 scales; 0.5 for pain score, 1.25
for stiffness score and 0.147 for physical function score. Thus, each subscale score ranged between 0-
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10, where the total score ranged 0-30 and higher scores indicated the higher intensity of the related symptom.
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Statistical analysis;
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Statistical analysis of the study was performed by using IBM SPSS version 20.0. Descriptive
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statistics was used for the analysis of the demographic data. Continuous characteristics of the study
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population were checked for normality. Between-group comparison of the categorical variables was performed by chi-square test. Kruskall-Wallis test was used to compare continuous variables among
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foot posture groups. If statistical significance was found, a post hoc analysis was performed to analyze differences among pairs of groups. P values below 0.05 were considered as statistically significant.
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Results:
The study included 150 patients (150 knees and feet at one side) with symptomatic and
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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,
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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, respectively. Of the 150 knees evaluated; 43(28.7%), 53(35.3%), 35 (23.3%) and 19 (12.7%) were graded as KL grade 1, 2, 3 and 4, respectively. Accordingly, 64.0% (n=96) were assigned to the mild OA (KL grade 1-2) group, whereas 36.0% (n=54)
were assigned to the severe OA (KL grade 3-4) group. Median and minimum-maximum values for the radiographic knee alignment measures and WOMAC scores were given in Table 1. When FPI was compared according to the KL radiologic severity of knee OA; foot posture differed significantly between mild (KL grade 1-2) and severe OA (KL grade 3-4) groups (x2=0.045). Severe OA group showed a more supinated foot posture (27.8%) than the mild OA group (19.8%). The
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percentage of neutral foot posture was also lower (57.4%) in the severe OA group than the mild OA group (72.0%). In accordance with this finding, mJSW and condylar plateau angle, which are other
representatives of radiologic severity, also differed among groups of FPI (p=0.038 and p=0.009,
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respectively). The post-hoc pairwise comparative analysis exhibited that mJSW of the supinated foot
posture group is significantly narrower than that of the neutral FPI group (p=0.040). In addition, post-
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hoc analysis for condylar plateau angle revealed that, this angle-which also represents the narrowing of the medial tibiofemoral joint space-is significantly wider in the supinated FPI group than that
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observed in the neutral FPI group (p=0.009).
Regarding the varus alignment measures of the knee; the anatomic axis angle differed among
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FPI groups (p=0.012), where the pronated FPI group had the lowest anatomic axis angle value (Table
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2). Post-hoc analysis for anatomic axis angle showed that pronated FPI group had significantly decreased anatomic axis angle than that in the neutral foot posture group (p=0.009). Although the pronated foot posture group revealed also the lowest condylar and tibial plateau angles, the difference
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among FPI groups did not reach significance (Table 2). With regard to the clinical variables; WOMAC total score and subscores of pain and physical
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function showed significant difference among foot posture groups (p<0.001 for pain and total score; p=0.001 for physical function score). The supinated FPI group revealed the highest total and subscale
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scores, although the difference did not reach significance for the WOMAC stiffness subscore (Table 2). 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 eversion, dorsiflexion and abduction of the ankle complex [22]. As a matter of fact, any postural abnormalities (either as
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supination or pronation) in the ankle joint would not only affect the ankle joint complex, but also have an impact on the force distribution inside the knee joint. Foot posture kinematic patterns would
definitely change the centre of pressure, thus the vertical direction of the ground reaction force and in
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turn, loading of the knee. This biomechanical perspective was the cornerstone of the hypothesis that
the present study was based on. Accordingly, results derived from the study showed that postural
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the misalignment of the knee joint in patients with knee OA.
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abnormalities of the foot are associated with both the clinical and radiologic severity, as well as with
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In the current study, radiologic severity, which was found to be associated with the supinated foot posture, was assessed by the evaluation of KL grade, mJSW and condylar plateau angle. All three
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measures, in their nature, directly (mJSW) or indirectly (KL grade and condylar plateau angle) evaluate
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the narrowing of the medial tibiofemoral joint space, which is one of the most important indicators of the cartilage loss-thus progression-in knee OA [23]. Uncontrolled dynamic mechanic loading on the medial compartment in an arthritic knee is one of the leading factors for cartilage defects and mJSW
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narrowing [24]. This dynamic mechanical loading occurs several times during a normal gait cycle [25]. External knee adduction moment is the major determinant of the dynamic mechanic loading in knee
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joint. A higher magnitude of this moment deteriorates the medial-to-lateral loading and contributes to medial tibiofemoral knee OA [25]. Knee adduction moment is highly affected by the ground reaction
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force occurs during the stance phase of gait. A greater moment arm between the knee axis and the ground reaction force leads to a greater knee adduction moment [26]. In an individual with a supinated foot posture, midpoint of the ground reaction force line would pass relatively more medially from the knee and the moment arm would increase, thus would the knee adduction moment. The misaligned foot posture would increase the medial tibiofemoral loading, joint space narrowing and progression of knee OA. The afore-mentioned domino-like mechanism might also give an explanation to the other
main finding of this study, which is the relation of supinated foot posture with the clinical disease severity in knee OA. Patients with supinated FPI revealed the highest total WOMAC score, as well as the highest pain and physical function subscores, which would be a consequence of increased mechanic loading and cartilage degeneration due to the increased moment of adduction. The other main finding of the present study was the relationship between the pronated foot
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posture and the loss of physiologic valgus alignment of the knee. Results of this study revealed that, as the anatomic axis angle gets narrower-in other words-as the physiologic tibiofemoral valgus disappears; the foot starts to misalign from neutral towards pronation. When the anatomic axis angle
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turns to negative values, which represent varus alignment, the foot shows an apparent pronated posture. Loss of valgus alignment is a common consequence of knee OA. It is related with an increase
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in knee adduction moment and is a contributor of accelerated loading on the medial tibiofemoral knee joint. Messier et al. [27] found that varus alignment in a degenerative knee was associated with greater
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peak external knee adduction moments, independent of body mass index of a patient. On the other
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hand, they determined that patients with valgus alignment had adduction moments that were 10 Nm
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less than those in patients with neutral knee alignment [27]. Therefore, loss of the physiologic valgus alignment might lead to a compensatory pronated foot posture in order to shorten the knee adduction
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moment arm and to decrease the mechanic loading on the medial tibiofemoral compartment of the knee joint. In a study by van Gheluwe et al. [28], simulated genu varum was shown to cause pronation at the subtalar joint during the contact phase of walking. In line with this finding, Levinger et al. [7]
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found that patients with medial tibiofemoral knee OA revealed a more pronated foot posture when compared to controls. Levinger et al. [6], in their subsequent study, determined that kinematic
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parameters indicative of a pronated foot posture were related with a decreased knee adduction
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moment during the stance phase of gait. The present study has a number of limitations: firstly the cross-sectional design of the study
did not allow us to determine the impact of foot posture on knee OA, or vice versa, through a longitudinal perspective. Therefore the association between two entities still remained as a “chicken and egg” issue. Secondly, foot posture was evaluated only by FPI, which is a clinical instrument. Supporting this evaluation by kinetic/kinematic analysis of the foot-ankle complex would increase the
degree of evidence. Lastly, the foot posture was not distributed normally, with a relatively low number of pronated foots. Also there are some strengths of this study: i) the multidimensional evaluation of the patients not only revealed the interaction of foot posture with the radiologic and clinical severity, but also with the alignment-related measures of the knee joint and ii) the study sample size allowed us to perform multi-group comparisons.
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Longitudinal studies are needed in order to confirm the results and to highlight the initial trigger of this association among patients with knee OA.
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Conflicts of interest: The authors declare no conflicts of interest.
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Acknowledgements: None to report
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Table 1. Characteristics of the study population Age (years)a 61.2±10.1 BMI (kg/m2)a 33.7±5.3 Symptom duration (months)a 6.0±4.1 KL gradeb Grade 1 43 (28.7) Grade 2 53 (35.3) Grade 3 35 (23.3) Grade 4 19 (12.7) Mild OA 96 (64.0) Severe OA 54 (36.0) Knee measurementsc mJSW (mm) 4.0 (0.2-8.2) Condylar angle (°) 5.4 (-1.3-14.5) Anatomic axis angle (°) 1.7 (-16.3-10.1) Tibial plateau angle (°) -1.8 (-9.7-7.4) Condylar plateau angle (°) 2.9 (0.5-8.6) c WOMAC scores Pain 4.5 (0-8.0) Stiffness 1.9 (0-7.5) Physical function 4.7 (0-8.2) Total 11.5 (0.2-20.7) FPI (-12 to +12)b Supinated (FPI<0) 34 (22.66) Neutral (FPI=0 to +5) 103 (68.66) Pronated (FPI≥ +6) 13 (8.66) BMI: Body mass index; KL: Kellgren- Lawrence; OA: Osteoarthritis; mJSW: Medial tibiofemoral joint space width; WOMAC: Western Ontario and Mc Master Universities Osteoarthritis Index; FPI: Foot posture index; aValues represent mean±standard deviation; bValues represent n(%); cValues represent median (minimum-maximum)
Table 2. Comparison of the radiologic and clinical variables among foot posture groups
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Supinated Neutral Pronated p KL grade groups Mild OAa 19 (19.8) 72 (75) 5 (5.2) 0.045¶ Severe OAa 15 (27.8) 31 (57.4) 8 (14.8) mJSW (mm)b 3.3 (0.3-7.9) 4.2 (0.2-8.2) 3.6 (0.3-6.0) 0.038 Condylar plateau angle (°)b 3.7(0.7-8.6) 2.6 (0.5-7.5) 3.2 (1.4-7.5) 0.009 Anatomic axis angle (°)b 1.8 (-16.3-7.0) 2.0 (-6.7-10.1) -1.6 (-8.8-6.7) 0.012 Condylar angle (°)b 5.5 (1.3-14.5) 5.4 (-1.3-14.6) 5.0 (1.1-12.2) 0.996 Tibial plateau angle (°)b -2.3 (-9.7-5.6) -1.6 (-7.8-7.4) -2.8 (-7.3-2.2) 0.613 WOMAC scores b Pain (0-10) 5.5 (1.5-8.0) 4.0 (0-7.5) 4.0 (2.0-8.0) <0.001 Stiffness (0-10) 3.1 (0-7.5) 1.3 (0-6.3) 1.3 (0-6.3) 0.250 Physical function (0-10) 5.6 (2.2-7.6) 4.4 (0-8.2) 4.9 (1.9-8.2) 0.001 Total (0-30) 14.3 (4.0-20.5) 10.9 (0.2-20.6) 10.6 (3.9-19.0) <0.001 KL: Kellgren-Lawrence; OA: Osteoarthritis; mJSW: Medial joint space width; WOMAC: Western Ontario and Mc Master Universities Osteoarthritis Index; a Values represent n(%); b Values represent median (minimum-maximum); ¶ Represents the value of the chi-square test (x2).
Figure legends: Figure 1. Radiologic measurements on anteroposterior knee radiographs; a. Femoral anatomic axis, b. Tibial anatomic axis, c. Condylar line, d. Tibial plateau line, e. Medial tibiofemoral joint width, f. Condylar
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plateau angle, g. Anatomic axis angle, h. Condylar angle, i. Tibial plateau angle.
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S0966-6362(18)30146-2 https://doi.org/10.1016/j.gaitpost.2018.08.036 GAIPOS 6492
To appear in:
Gait & Posture
Received date: Revised date: Accepted date:
4-4-2018 30-7-2018 27-8-2018
Please cite this article as: Al-Bayati Z, Benlidayi IC, Gokcen N, Posture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis, Gait and amp; Posture (2018), https://doi.org/10.1016/j.gaitpost.2018.08.036 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Posture of the foot: Don’t keep it out of sight, out of mind in knee osteoarthritis Zainb Al-Bayati, M.D. Cukurova University Faculty of Medicine, Department of Physical Medicine and Rehabilitation, AdanaTurkey
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Ilke Coskun Benlidayi, M.D. Associate Professor, Cukurova University Faculty of Medicine, Department of Physical Medicine and Rehabilitation, AdanaTurkey
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Neslihan Gokcen, M.D.
Cukurova University Faculty of Medicine, Department of Physical Medicine and Rehabilitation,
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Division of Rheumatology, Adana-Turkey
Ilke COSKUN BENLIDAYI, MD. Associate Professor,
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Department of Physical Medicine and Rehabilitation,
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Corresponding Author:
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Faculty of Medicine, Cukurova University, Adana-TURKEY Mobile phone number : + 90 538 545 39 37
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Fax number : + 90 322 338 64 29 e-mail : [email protected]
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Highlights:
Radiologic severity of knee OA is associated with supinated foot posture.
Varus alignment in knee OA is related to pronated foot posture.
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Clinical severity in knee OA is associated with supinated foot posture.
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ABSTRACT
Background: There are many contributors of knee osteoarthritis including the postural abnormalities of the adjacent joints. The relationship between foot posture and the clinical-radiological parameters of knee osteoarthritis is poorly understood. Research question: Is foot posture related to the clinical and radiological parameters in patients with knee osteoarthritis? Methods: Patients diagnosed with primary clinical and radiographic medial tibiofemoral knee
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osteoarthritis were included in the study. Anteroposterior knee radiographs were staged by using the
Kellgren-Lawrence grading system. Computer-based measurements of the medial joint space width
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(mJSW), condylar angle, anatomical axis angle, tibial plateau angle and condylar plateau angle were performed on digital anteroposterior knee radiographs. The Western Ontario and Mc Master University Osteoarthritis Index (WOMAC) questionnaire was used to assess pain and the functional status of the
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patients. Foot posture was assessed by the Foot Posture Index (FPI) system and feet were categorized into three (pronated, neutral and supinated).
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Results: The study included 150 patients (150 knees and feet at one side) with a mean age of 61.2±10.1
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years. In terms of foot posture groups; percentages for supination, neutral and pronation were 22.66%,
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68.66% and 8.66%, respectively. In the group with supinated FPI; WOMAC total score, pain and function subscale scores were higher (p<0.001), mJSW was narrowed (p=0.038) and the condylar plateau
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angle was increased (p=0.009). In the FPI pronation group; anatomic axis angle values were found to change in the varus direction (p=0.012).
Significance: The potential postural dysfunction of the foot should be taken into consideration during
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the assessment and/or management of a patient with knee osteoarthritis. Keywords: foot posture index; foot posture; knee osteoarthritis.
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Introduction:
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Knee osteoarthritis (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 center of ground reaction force. Particular foot
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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
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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
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researchers in the literature [7-10]. Gross et al. [8], in their cross-sectional study, highlighted the
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association of planus arch deformity with the higher frequency of knee pain and medial tibiofemoral
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cartilage damage in older adults. On the other hand, Levinger and colleagues [7] found that patients
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with medial tibiofemoral OA had higher frequency of pronated foot than 28 asymptomatic agematched controls.
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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
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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
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loading/alignment seems necessary.
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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. Methods: 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) knee
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prosthesis. Study Protocol;
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The study was conducted at the Department of Physical Medicine and Rehabilitation in
Cukurova University Faculty of Medicine between October 2016 and February 2017. Ethical approval was obtained from the Local Ethics Committee of Cukurova University (Approval date: 7-Oct-2016,
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number: 57). Written informed consent was taken from each study participant. Demographic variables
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(age, gender), symptom duration (month), anthropometric measures including body weight (kg), height
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(m) and body mass index (kg/m2) were noted.
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Evaluation of the foot posture;
Posture of the foot was evaluated by using the Foot Posture Index-6 (FPI-6) designed by
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Redmond et al. [13]. This tool is a valid static clinical measure comprises 6 components including; i) talar head palpation, ii) supra and infra lateral malleolar curvature, iii) calcaneal frontal plane position, iv) prominence in the region of the talonavicular joint, v) congruence of the medial longitudinal arch,
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vi) abduction/adduction of the forefoot on the rearfoot. The foot posture was assessed while the patient standing barefoot on double limb in a relaxed position. Each FPI component is scored from -2
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to +2, where -2 represents clear signs of supination and +2 addresses positive signs for pronation. The
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total score ranged from -12 to +12. Each foot was scored according to the above-mentioned explanation. Total scores between 0
to +5 represented the normal/neutral foot posture. Values ≥ +6 were regarded as pronated foot, whereas values below 0 were accepted as supinated foot posture. Evaluation of the radiologic severity of knee OA;
Radiologic severity was assessed by i) using the Kellgren-Lawrence (KL) grading system of knee OA, ii) the assessment of the medial tibiofemoral joint space width (mJSW) and iii) measuring the condylar plateau angle. Each patient was undergone standardized weight-bearing anteroposterior xray evaluation of both knees. The beam was aligned parallel to the floor and positioned relative to the tibiofemoral joint, while knees were in extension position.
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Radiographic severity of knee OA was classified by using the KL grading system of knee OA on digitalized images (Enlil PACS System 2.5) [14]. Knees were then categorized into two as mild OA (KL grade 1-2) and severe OA (KL grade 3-4). The severity of knee OA was also evaluated by the assessment
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of medial tibiofemoral joint space narrowing [15,16]. The minimum vertical distance between the
medial femoral condyle and the medial tibial plateau was taken as the mJSW (Figure 1). Condylar
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plateau angle was measured on the digitized anteroposterior knee radiographs. This angle was defined as the angle between the line tangent to the femoral condyles and the line tangent to the tibial plateaus
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Evaluation of the varus alignment of the knee;
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[17,18] (Figure 1).
Varus alignment of the knee joint was evaluated by digitalized measurement of the anatomic
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axis angle, the condylar angle, and the tibial plateau angle on anteroposterior knee radiographs as follows [17,18] (Figure 1):
i) Anatomic axis angle: The angle between the femoral anatomic axis (the line drawn from the
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midpoint of the femoral shaft to the midpoint of tibial eminences) and the tibial anatomic axis (the line
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drawn from the midpoint of the tibial eminences to the midpoint of the tibia). ii) Condylar angle: The angle between the femoral anatomic axis (the line drawn from the
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midpoint of the femoral shaft to the midpoint of tibial eminences) and the line tangent to the femoral condyles. Condylar angle was recorded in degrees form 90°. iii) Tibial plateau angle: The angle between the tibial anatomic axis (the line drawn from the midpoint of the tibial eminences to the midpoint of the tibia) and the line tangent to the tibia plateaus. Tibial plateau angle was recorded in degrees form 90°.
Clinical evaluation; The clinical evaluation was based on the validated 3.1 form of Western Ontario and Mc Master Universities Osteoarthritis Index (WOMAC) for the target population [19-21]. This form evaluates the patients’ symptoms by 24 questions in three categories including pain (5 questions), stiffness (2 questions) and physical function (17 questions). In this 5-point Likert (0-4) form of WOMAC 3.1, scale
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lengths for pain, stiffness and physical function vary between 0-20, 0-8 and 0-68, respectively. The following correction factors were used to normalize the index to 0-10 scales; 0.5 for pain score, 1.25
for stiffness score and 0.147 for physical function score. Thus, each subscale score ranged between 0-
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10, where the total score ranged 0-30 and higher scores indicated the higher intensity of the related symptom.
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Statistical analysis;
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Statistical analysis of the study was performed by using IBM SPSS version 20.0. Descriptive
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statistics was used for the analysis of the demographic data. Continuous characteristics of the study
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population were checked for normality. Between-group comparison of the categorical variables was performed by chi-square test. Kruskall-Wallis test was used to compare continuous variables among
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foot posture groups. If statistical significance was found, a post hoc analysis was performed to analyze differences among pairs of groups. P values below 0.05 were considered as statistically significant.
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Results:
The study included 150 patients (150 knees and feet at one side) with symptomatic and
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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,
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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, respectively. Of the 150 knees evaluated; 43(28.7%), 53(35.3%), 35 (23.3%) and 19 (12.7%) were graded as KL grade 1, 2, 3 and 4, respectively. Accordingly, 64.0% (n=96) were assigned to the mild OA (KL grade 1-2) group, whereas 36.0% (n=54)
were assigned to the severe OA (KL grade 3-4) group. Median and minimum-maximum values for the radiographic knee alignment measures and WOMAC scores were given in Table 1. When FPI was compared according to the KL radiologic severity of knee OA; foot posture differed significantly between mild (KL grade 1-2) and severe OA (KL grade 3-4) groups (x2=0.045). Severe OA group showed a more supinated foot posture (27.8%) than the mild OA group (19.8%). The
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percentage of neutral foot posture was also lower (57.4%) in the severe OA group than the mild OA group (72.0%). In accordance with this finding, mJSW and condylar plateau angle, which are other
representatives of radiologic severity, also differed among groups of FPI (p=0.038 and p=0.009,
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respectively). The post-hoc pairwise comparative analysis exhibited that mJSW of the supinated foot
posture group is significantly narrower than that of the neutral FPI group (p=0.040). In addition, post-
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hoc analysis for condylar plateau angle revealed that, this angle-which also represents the narrowing of the medial tibiofemoral joint space-is significantly wider in the supinated FPI group than that
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observed in the neutral FPI group (p=0.009).
Regarding the varus alignment measures of the knee; the anatomic axis angle differed among
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FPI groups (p=0.012), where the pronated FPI group had the lowest anatomic axis angle value (Table
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2). Post-hoc analysis for anatomic axis angle showed that pronated FPI group had significantly decreased anatomic axis angle than that in the neutral foot posture group (p=0.009). Although the pronated foot posture group revealed also the lowest condylar and tibial plateau angles, the difference
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among FPI groups did not reach significance (Table 2). With regard to the clinical variables; WOMAC total score and subscores of pain and physical
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function showed significant difference among foot posture groups (p<0.001 for pain and total score; p=0.001 for physical function score). The supinated FPI group revealed the highest total and subscale
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scores, although the difference did not reach significance for the WOMAC stiffness subscore (Table 2). 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 eversion, dorsiflexion and abduction of the ankle complex [22]. As a matter of fact, any postural abnormalities (either as
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supination or pronation) in the ankle joint would not only affect the ankle joint complex, but also have an impact on the force distribution inside the knee joint. Foot posture kinematic patterns would
definitely change the centre of pressure, thus the vertical direction of the ground reaction force and in
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turn, loading of the knee. This biomechanical perspective was the cornerstone of the hypothesis that
the present study was based on. Accordingly, results derived from the study showed that postural
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the misalignment of the knee joint in patients with knee OA.
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abnormalities of the foot are associated with both the clinical and radiologic severity, as well as with
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In the current study, radiologic severity, which was found to be associated with the supinated foot posture, was assessed by the evaluation of KL grade, mJSW and condylar plateau angle. All three
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measures, in their nature, directly (mJSW) or indirectly (KL grade and condylar plateau angle) evaluate
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the narrowing of the medial tibiofemoral joint space, which is one of the most important indicators of the cartilage loss-thus progression-in knee OA [23]. Uncontrolled dynamic mechanic loading on the medial compartment in an arthritic knee is one of the leading factors for cartilage defects and mJSW
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narrowing [24]. This dynamic mechanical loading occurs several times during a normal gait cycle [25]. External knee adduction moment is the major determinant of the dynamic mechanic loading in knee
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joint. A higher magnitude of this moment deteriorates the medial-to-lateral loading and contributes to medial tibiofemoral knee OA [25]. Knee adduction moment is highly affected by the ground reaction
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force occurs during the stance phase of gait. A greater moment arm between the knee axis and the ground reaction force leads to a greater knee adduction moment [26]. In an individual with a supinated foot posture, midpoint of the ground reaction force line would pass relatively more medially from the knee and the moment arm would increase, thus would the knee adduction moment. The misaligned foot posture would increase the medial tibiofemoral loading, joint space narrowing and progression of knee OA. The afore-mentioned domino-like mechanism might also give an explanation to the other
main finding of this study, which is the relation of supinated foot posture with the clinical disease severity in knee OA. Patients with supinated FPI revealed the highest total WOMAC score, as well as the highest pain and physical function subscores, which would be a consequence of increased mechanic loading and cartilage degeneration due to the increased moment of adduction. The other main finding of the present study was the relationship between the pronated foot
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posture and the loss of physiologic valgus alignment of the knee. Results of this study revealed that, as the anatomic axis angle gets narrower-in other words-as the physiologic tibiofemoral valgus disappears; the foot starts to misalign from neutral towards pronation. When the anatomic axis angle
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turns to negative values, which represent varus alignment, the foot shows an apparent pronated posture. Loss of valgus alignment is a common consequence of knee OA. It is related with an increase
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in knee adduction moment and is a contributor of accelerated loading on the medial tibiofemoral knee joint. Messier et al. [27] found that varus alignment in a degenerative knee was associated with greater
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peak external knee adduction moments, independent of body mass index of a patient. On the other
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hand, they determined that patients with valgus alignment had adduction moments that were 10 Nm
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less than those in patients with neutral knee alignment [27]. Therefore, loss of the physiologic valgus alignment might lead to a compensatory pronated foot posture in order to shorten the knee adduction
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moment arm and to decrease the mechanic loading on the medial tibiofemoral compartment of the knee joint. In a study by van Gheluwe et al. [28], simulated genu varum was shown to cause pronation at the subtalar joint during the contact phase of walking. In line with this finding, Levinger et al. [7]
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found that patients with medial tibiofemoral knee OA revealed a more pronated foot posture when compared to controls. Levinger et al. [6], in their subsequent study, determined that kinematic
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parameters indicative of a pronated foot posture were related with a decreased knee adduction
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moment during the stance phase of gait. The present study has a number of limitations: firstly the cross-sectional design of the study
did not allow us to determine the impact of foot posture on knee OA, or vice versa, through a longitudinal perspective. Therefore the association between two entities still remained as a “chicken and egg” issue. Secondly, foot posture was evaluated only by FPI, which is a clinical instrument. Supporting this evaluation by kinetic/kinematic analysis of the foot-ankle complex would increase the
degree of evidence. Lastly, the foot posture was not distributed normally, with a relatively low number of pronated foots. Also there are some strengths of this study: i) the multidimensional evaluation of the patients not only revealed the interaction of foot posture with the radiologic and clinical severity, but also with the alignment-related measures of the knee joint and ii) the study sample size allowed us to perform multi-group comparisons.
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Longitudinal studies are needed in order to confirm the results and to highlight the initial trigger of this association among patients with knee OA.
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Conflicts of interest: The authors declare no conflicts of interest.
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Acknowledgements: None to report
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Table 1. Characteristics of the study population Age (years)a 61.2±10.1 BMI (kg/m2)a 33.7±5.3 Symptom duration (months)a 6.0±4.1 KL gradeb Grade 1 43 (28.7) Grade 2 53 (35.3) Grade 3 35 (23.3) Grade 4 19 (12.7) Mild OA 96 (64.0) Severe OA 54 (36.0) Knee measurementsc mJSW (mm) 4.0 (0.2-8.2) Condylar angle (°) 5.4 (-1.3-14.5) Anatomic axis angle (°) 1.7 (-16.3-10.1) Tibial plateau angle (°) -1.8 (-9.7-7.4) Condylar plateau angle (°) 2.9 (0.5-8.6) c WOMAC scores Pain 4.5 (0-8.0) Stiffness 1.9 (0-7.5) Physical function 4.7 (0-8.2) Total 11.5 (0.2-20.7) FPI (-12 to +12)b Supinated (FPI<0) 34 (22.66) Neutral (FPI=0 to +5) 103 (68.66) Pronated (FPI≥ +6) 13 (8.66) BMI: Body mass index; KL: Kellgren- Lawrence; OA: Osteoarthritis; mJSW: Medial tibiofemoral joint space width; WOMAC: Western Ontario and Mc Master Universities Osteoarthritis Index; FPI: Foot posture index; aValues represent mean±standard deviation; bValues represent n(%); cValues represent median (minimum-maximum)
Table 2. Comparison of the radiologic and clinical variables among foot posture groups
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Supinated Neutral Pronated p KL grade groups Mild OAa 19 (19.8) 72 (75) 5 (5.2) 0.045¶ Severe OAa 15 (27.8) 31 (57.4) 8 (14.8) mJSW (mm)b 3.3 (0.3-7.9) 4.2 (0.2-8.2) 3.6 (0.3-6.0) 0.038 Condylar plateau angle (°)b 3.7(0.7-8.6) 2.6 (0.5-7.5) 3.2 (1.4-7.5) 0.009 Anatomic axis angle (°)b 1.8 (-16.3-7.0) 2.0 (-6.7-10.1) -1.6 (-8.8-6.7) 0.012 Condylar angle (°)b 5.5 (1.3-14.5) 5.4 (-1.3-14.6) 5.0 (1.1-12.2) 0.996 Tibial plateau angle (°)b -2.3 (-9.7-5.6) -1.6 (-7.8-7.4) -2.8 (-7.3-2.2) 0.613 WOMAC scores b Pain (0-10) 5.5 (1.5-8.0) 4.0 (0-7.5) 4.0 (2.0-8.0) <0.001 Stiffness (0-10) 3.1 (0-7.5) 1.3 (0-6.3) 1.3 (0-6.3) 0.250 Physical function (0-10) 5.6 (2.2-7.6) 4.4 (0-8.2) 4.9 (1.9-8.2) 0.001 Total (0-30) 14.3 (4.0-20.5) 10.9 (0.2-20.6) 10.6 (3.9-19.0) <0.001 KL: Kellgren-Lawrence; OA: Osteoarthritis; mJSW: Medial joint space width; WOMAC: Western Ontario and Mc Master Universities Osteoarthritis Index; a Values represent n(%); b Values represent median (minimum-maximum); ¶ Represents the value of the chi-square test (x2).
Figure legends: Figure 1. Radiologic measurements on anteroposterior knee radiographs; a. Femoral anatomic axis, b. Tibial anatomic axis, c. Condylar line, d. Tibial plateau line, e. Medial tibiofemoral joint width, f. Condylar
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plateau angle, g. Anatomic axis angle, h. Condylar angle, i. Tibial plateau angle.
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Figr-1