Swing limb mechanics and minimum toe clearance in people with knee osteoarthritis☆
Introduction
Osteoarthritis (OA) is one of the most prevalent musculoskeletal diseases in older people and a major source of pain and disability. Chronic knee pain has been shown to be a risk factor for falls [1], [2] with more than 50% of people with lower limb arthritis reporting one or more falls each year [3], [4]. This is a major concern, as it is considerably higher than the 33% incidence of falls in the general older population [5]. The increased risk of falls in people with OA may be attributed to disease symptoms such as chronic pain [1], [2] and the consequent deficiency in neuromuscular functioning. However the exact mechanisms remain unclear.
Most falls in older people occur when walking [6], [7]. Tripping over an obstacle has been reported to be one of the main causes of falls [7], [8], [9]. Changes in gait patterns due to ageing, including reduced speed, stride length and toe clearance, may increase the probability of tripping in older people [6], [10]. In particular, reductions in foot clearance (specifically minimum toe clearance, or MTC) during the swing phase of walking can cause a trip and potentially result in a fall, since the orientation of the swing limb at the critical time of MTC makes toe stubbing a potential cause of balance loss [11], [12]. Although MTC has been shown to be similar in healthy young and older people [13], recent studies have reported reduced MTC in elderly fallers compared to non-fallers [14].
Toe clearance is affected by swing limb joint angles and is therefore sensitive to changes in the angle of the knee joint [11]. Since patients with knee OA exhibit altered knee function [15], [16] it is possible that knee joint pain may lead to the adoption of different gait strategies. Recent studies investigating obstacle crossing in people with knee OA have reported increased MTC for the trailing limb and a range of biomechanical strategies to compensate for the compromised function of the affected knee [17], [18]. Moreover, pain associated with knee OA has been shown to increase the propensity to trip over an obstacle [19] and is also associated with physiological predictors of falls risk [20].
Foot clearance and associated limb shortening in walking requires a complex mechanism where rotation at one joint complements those at other joints to achieve the desired objective of clearing the foot safely when advancing it in front of the body. A limb angle sensitivity analysis has previously been developed to determine the influence of the swing leg hip, knee and ankle joints on foot clearance [11], [21]. This model determines the effect of incremental changes in the angle of the lower limb joints of the swing limb on foot clearance and effective leg length. This technique may therefore be useful in populations with increased risk of falls such as those with knee OA, where deficiencies in the painful joint may be compensated through other joints to obtain sufficient foot clearance.
Therefore, the purpose of this study was to examine swing phase mechanics in people with and without knee OA during level walking. More specifically, we examined the influence of the angular changes of the hip, knee and ankle of the swing leg on foot clearance using sensitivity analysis [21].
Section snippets
Methods
Two groups participated in the study: a knee OA group and an age-matched asymptomatic control group. The OA group included 50 participants diagnosed with knee OA, determined by a radiographic assessment. The severity of knee OA was based on the loss of joint space determined by an orthopaedic surgeon from radiographic images [22] and was graded as follows: 1 – less than a half of joint space loss (mild), 2 – more than a half of joint space loss; bone on bone (moderate) and 3 – bone
Instrumentation
A three dimensional motion analysis system (Vicon MX, Vicon Motion System Ltd., Oxford, England) was used with 10 cameras (8 MX3 and 2 MX40) to capture and analyse motion of the lower leg with a sampling frequency of 100 Hz. Two force plates (Kistler, type 9865B, Winterthur, Switzerland and AMTI, OR6, USA) (1000 Hz) were used to capture ground reaction forces and identify gait cycle events.
Joint motion
Joint angles and foot clearance of the symptomatic leg (or the most symptomatic leg in the case of bilateral involvement) in the knee OA group and the same corresponding leg of each age-matched control were assessed. Retro-reflective markers were attached on anatomical landmarks over the lower legs in accordance with the oxford foot model (OFM) marker set and Plug In Gait (PIG) as described by Stebbins et al. [23]. Prior to kinematic evaluation of the lower leg motion, a relaxed standing
Data analysis
All analyses were performed using SPSS 17.0 (SPSS Inc., Chicago, IL, USA). Differences in the joint angles at the time of MTC, the MTC height and the toe clearance sensitivity were compared between the groups using multivariate analyses. Due to the potential difference of gait velocity between the groups and its affect on joint angles, gait velocity was included as a covariate. Moreover, the height of MTC could be affected by stride length, and therefore stride length was also included as a
Results
Characteristics of both groups are summarised in Table 1. The knee OA group had a significantly greater body mass and body mass index. The severity of knee OA based on radiographic assessment ranged from 1 to 3, with four patients graded as mild, 19 moderate and 27 severe. The knee OA group walked significantly slower and with smaller stride length as indicated in Table 2. The knee OA group reported mild pain of 162.0 ± 109.4, function 528.4 ± 333.8 and stiffness 86.3 ± 50.9 with WOMAC total score of
Discussion
Recent studies have identified that knee OA, the most prevalent musculoskeletal condition, increases the risk of falling [5], [25]. The present study investigated swing phase mechanics in people with knee OA during level walking and asymptomatic age-matched healthy subjects and therefore provides further information about the gait pattern associated with the risk of tripping [13]. The study findings indicated that MTC height of people with knee OA is similar to asymptomatic controls. However
Conclusion
The MTC height was comparable between the groups, however different swing phase mechanisms were used by the knee OA group to achieve the same foot clearance, including greater knee flexion, greater hip abduction and less ankle adduction. Although adequate MTC is an important component of safe locomotion, it does not appear to be impaired in people with knee OA. Other risk factors may be responsible for the increased risk of falls in this group, such as tripping during obstacle crossing or
Conflict of interest statement
The authors declare no financial support or other benefits from commercial sources for the work reported on in the manuscript, or any other financial interests.
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This study was funded by the Clive and Vera Ramaciotti Foundation and the Arthritis Australia. HBM is currently a National Health and Medical Research Council fellow (Clinical Career Development Award, ID: 433049). The authors would like to thank Margaret Perrott for her assistance in the data collection and Mr. Barry Gavin for his assistance with patient recruitment.