Full length articleRepeatability of the Oxford Foot Model in children with foot deformity☆
Introduction
Foot deformities are prevalent in children and can be either congenital or acquired. Clubfoot is the most common congenital musculoskeletal deformity in children occurring in 1–2 out of 1000 live births [1]. It can result in foot and ankle stiffness, pain and arthritis which tend to increase over the lifespan [2]. Other examples of congenital foot deformities include vertical talus, cavus and metatarsus adductus. Flat foot deformity can be acquired, first becoming obvious as a child begins to walk. In general it is noted that the majority of toddlers have flat feet [3,4] which improves as they mature such that the adult prevalence is nearer 20% [5]. Acquired foot deformity is also very common in children with neurological problems such as cerebral palsy. Cerebral palsy (CP) is the most common motor disability in childhood with international prevalence estimates ranging from 1.5 to more than 4 per 1000 live births [6]. At birth CP children’s feet have normal postures, but over time the effects of their abnormal neurology leads to increasing lower limb deformity [7].
Three-dimensional gait analysis is an assessment tool to measure dynamic deformity in the lower limbs. It is widely used to identify lower limb deformity in children with clubfoot [[8], [9], [10], [11], [12], [13], [14]] and cerebral palsy [15,16] to assist in treatment planning. Traditionally the foot has been measured as a single rigid segment in a two-dimensional kinematic model. More recently, three-dimensional multi-segment foot models have been developed to improve our understanding of foot motion during gait. Fifteen foot models have been reported in the literature [17] with up to 9 segments being proposed [18]. Baker [18] reports 3 or 4 segment foot models are gaining preference for use in clinical gait analysis. Despite numerous foot models being available in the literature, very few are being used in centres outside of where they were developed [18].
The Oxford Foot Model (OFM) is a multi-segment, three-dimensional kinematic model that assesses dynamic motion of the foot [19]. It was developed to measure tibia, hindfoot, forefoot and hallux motion in a clinical setting. It can identify the presence of dynamic deformity compared to a healthy population, monitor change of an individual’s foot posture over time, and measure change in foot motion before and after intervention. Published literature confirms the OFM is being used world-wide to evaluate various populations with foot deformity such as flat foot [20,21,22] clubfoot [23] and calcaneal fractures [24]. The OFM has already been shown to be repeatable in healthy populations (adults and children) for both intra-tester and inter-tester repeatability [19,25,26,27]; however to date there is no published literature of its repeatability in pathological conditions. The aim of this study was to assess the repeatability of the OFM in children with hemiplegic cerebral palsy and in children previously treated for clubfoot deformity, and compare it to a healthy population. Our hypothesis is that the repeatability of the OFM in children with foot deformity will be similar to previously reported values of the OFM’s repeatability in healthy populations in the literature. For the purpose of this study, repeatability is defined as the difference between two repetitions of testing.
Section snippets
Typically developing
Fifteen typically developing children (mean age 9.5 years, range 6–14 years; 10 female and 5 male) were assessed with the OFM during level walking at self-selected velocity using a 12 camera Vicon 612 system (sampling at 100 Hz) and 14 mm passive markers. Each child was measured on two occasions by the same tester with the visits spaced between two and four weeks apart. The typically developing children were recruited from friends and colleagues of the Oxford Gait Laboratory.
Hemiplegia
Fifteen children
Hemiplegia
Children with hemiplegic cerebral palsy were assessed for intra-rater repeatability across two sessions. The mean difference across all variables was 4.1° (Table 1). The largest difference was in hindfoot rotation (6.0°) and the smallest differences were seen in the sagittal plane.
Clubfoot
Children previously treated for clubfoot deformity were tested for intra-rater repeatability with a mean difference between visits of 2.9°, with a range between 1.8–3.5° for the fifteen kinematic variables (Fig. 1).
Discussion
This study shows the OFM has good intra-tester repeatability in typically developing children, as well as in children with cerebral palsy (hemiplegia) and in children with clubfoot deformity. The mean absolute difference in typically developing children was 4.8°, which improved to 4.1° in children with hemiplegia, and further improved to 2.9° in children with clubfoot. Overall the intra-tester variability of the clubfoot population was less than the hemiplegic and typically developing
Study limitations
As stated in the discussion, the main limitations of the study include a more experienced marker placer for the clubfoot data and the clubfoot data was collected more recently with an upgraded VICON system with more cameras and smaller markers. Both improved technology and clinician experience play an important role in improving repeatability. This is why the clubfoot data has the best reported repeatability, even better than the typically developing population. A third limitation is the
Conclusions
Three-dimensional gait analysis is widely used to guide the management of older children with congenital foot deformities such as clubfoot, and in children with acquired foot deformities such as flat foot and cerebral palsy. In order to measure the dynamic foot motion in detail, a multi-segment foot model must be used. The Oxford Foot Model was designed to be adaptable in its application to measure different types of foot deformity. In order to determine the reliability of the model for
Conflicts of interest
None.
Acknowledgements
We would like to acknowledge the team at the Oxford Gait Laboratory and in particular Julie Letherland, MCSP for assisting in the inter-tester repeatability data.
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We would like to acknowledge partial funding of this research from VICON.