Elsevier

Gait & Posture

Volume 27, Issue 1, January 2008, Pages 60-69
Gait & Posture

Influence of thigh cluster configuration on the estimation of hip axial rotation

https://doi.org/10.1016/j.gaitpost.2007.01.002Get rights and content

Abstract

The non-invasive estimation of hip axial rotation is prone to error. Most of this is likely to originate from soft tissue artefact (STA) at the thigh. The purpose of this study was to evaluate the relative performance of four different thigh cluster configurations. Three were novel configurations whilst one represented the Helen Hayes convention. Twenty able-bodied adults performed two alternative motor tasks involving hip axial rotation: gait and an isolated longitudinal rotation task. Kinematic data were acquired using a three-dimensional motion analysis system (VICON 512, Oxford Metrics, Oxford, England). Indirect criteria were used to evaluate STA. Hip axial rotation kinematic profiles during gait were highly sensitive to thigh cluster configuration. For the longitudinal rotation task, the various thigh clusters were only capable of estimating, at best, up to 60% of the reference amount of movement. The Helen Hayes convention was associated with the greatest degree of STA. Whilst none of the clusters represented an optimal solution, a non-rigid configuration on the distal thigh provided a more favourable alternative. The main limitation associated with this study was the absence of a true gold standard measure of hip axial rotation. Until future work provides further insight, one must remain cautious when using estimates of hip axial rotation for purposes of research or clinical interpretation.

Introduction

Hip axial rotation during gait is of clinical significance. For example, children with cerebral palsy typically walk with increased hip internal rotation [1]. Hip axial rotation during gait is therefore a common outcome measure for studies evaluating the effects of surgical interventions in cerebral palsy [2], [3], [4]. This necessitates accurate measurement techniques for non-invasively estimating hip axial rotation.

Conceptually, there are two major sources of error associated with the non-invasive estimation of hip axial rotation. The first source concerns the process of defining the relevant anatomical frames (AF). Specifically, the procedure for identifying the femoral AF frontal plane (conventionally defined by the knee joint flexion–extension axis) can be prone to error [5]. As ‘neutral’ hip axial rotation is reliant upon the orientation of the knee flexion–extension axis, errors in defining this axis manifest as offsets in the hip axial rotation kinematic profile. Optimisation procedures designed to minimise this error have recently been proposed [6], [7], [8], [9]. The second source concerns soft tissue artefact (STA). In the context of hip axial rotation, it is STA at the thigh that is most critical. The thigh is surrounded by large amounts of soft tissue and contains few areas of subcutaneous bone. Hence, it is associated with the greatest degree of STA in the lower limb [10], [11], [12]. As the amplitude of hip axial rotation during gait is small [13], errors must be minimised. Quantification of thigh STA and its effect on the estimation of hip axial rotation is therefore necessary to be able to critically interpret results. This is especially important if results are to be used to aid clinical decision-making.

Despite the potential for the non-invasive estimation of hip axial rotation to be erroneous, few studies have investigated this issue. Of those that have, only simple non-daily living motor tasks have been considered. Lamoreux [14] evaluated the performance of several different thigh clusters for one subject using an isolated lower limb longitudinal rotation task. Hip axial rotation kinematic profiles generated from a known reference, obtained in this instance from shank markers, were compared with those generated from markers at different locations on the thigh. Thigh markers were found to be only capable of estimating, at best, up to 70% of the reference amount of movement. Cappozzo et al. [10] also utilised a longitudinal rotation task. The orientation of a femoral AF generated from a technical frame (TF) rigid with the bone (via an external fixator) was compared with that generated from a skin marker TF for two subjects. Depending upon thigh marker location, transverse plane orientation errors varied from 6° to 28° for rotations in the range of 45°. With respect to gait, several studies have compared joint kinematics generated from skin versus bone-mounted markers [12], [15], [16]. However, none of these studies inserted bone pins into the pelvis. Thus, the effect of STA on hip joint kinematics has not been considered. Limited knowledge therefore exists regarding the effect of STA at the thigh on the non-invasive estimation of hip axial rotation.

One way to evaluate the effect of STA at the thigh is to compare the performance of different cluster configurations. This is an attractive approach given the ethical constraints that may be associated with the use of bone pins or fluoroscopy [17], [18]. Furthermore, natural soft tissue movement is not impeded and results are readily transferable to clinical practice. The magnitude of STA at the thigh is known to be location specific [10], [14], [19]. This information can be used to devise thigh clusters comprising of markers overlying areas least susceptible to STA. In support of this approach, previous studies have shown that STA propagation to estimated knee joint kinematics is strongly dependent upon cluster configuration [10], [16], [19], [20], [21]. In the context of the current study, preliminary data from Lamoreux [14] and Cappozzo et al. [10] suggest that cluster configuration is also likely to be critical in minimising errors associated with the non-invasive estimation of hip axial rotation.

The purpose of this study was to compare the relative performance of four alternative thigh cluster configurations. It was hypothesised that: (a) the estimation of hip axial rotation would be sensitive to thigh cluster configuration [H1]; (b) a more favourable solution would be obtained from clusters overlying areas on the thigh that are least susceptible to STA [H2].

Section snippets

Subjects

Twenty able-bodied adults (five males; 15 females) with a mean height of 165.8 (S.D. 7.9) cm, body mass of 60.9 (S.D. 9.7) kg and age of 20.8 (S.D. 4.1) years were voluntarily recruited. Approval was obtained from the Royal Children's Hospital Ethics in Human Research Committee prior to commencement and subjects signed a consent form.

Instrumentation

Kinematic data were acquired using a three-dimensional (3D) motion analysis system (VICON 512, Oxford Metrics, Oxford, England) with six high-resolution M1 cameras

Estimating hip axial rotation during gait

Hip axial rotation kinematic profiles during gait were sensitive to thigh cluster configuration (Fig. 2). The overall similarity between profiles was quite poor, with a mean CMD value of 0.274 (Table 3). The paired comparisons demonstrated that the hip axial rotation kinematic profile for thigh cluster A was dissimilar to the profiles for all other thigh clusters (CMD < 0.2). In contrast, the hip axial rotation kinematic profiles for thigh clusters C and D were virtually identical. Thus, the

Estimating hip axial rotation during gait

The estimated hip axial rotation kinematic profile during gait was sensitive to thigh cluster configuration. The kinematic profile from thigh cluster A was distinctly different to the profiles from all other clusters. In contrast, the kinematic profiles from thigh clusters C and D were virtually identical (Fig. 2 and Table 3). The estimated hip axial rotation kinematic profile during gait is therefore more dependent on thigh cluster location than specific construction effects (e.g.,

Acknowledgment

This project was financially supported by a Health Professional Research Training Fellowship from the Australian National Health and Medical Research Council (Grant ID: 237153).

References (37)

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