Background The intermalleolar distance (IMD) is one of the spinal mobility measures included in the BASMI as a measure of hip function. Another measure of hip function, which has been proposed for patients with Ankylosing Spondylitis, is the internal hip rotation (IHR) according to Maksymowych . However, the extent to which these measures are affected by height, age and gender has not been assessed, neither among patients, nor among healthy people.
Objectives To assess the effect of height, age, gender and weight on IMD and IHR among healthy people.
Methods A cross-sectional study (“MOBILITY study”) was conducted among healthy volunteers aged 20-69 years old. Recruitment was stratified by gender, age (10-year categories) and height (10cm categories). Participants were any Caucasian volunteering to be measured in the Netherlands and Portugal. Exclusion criteria were factors potentially influencing spinal mobility or hip function (eg. back surgery, hip or spine osteoarthritis). IMD was measured with the participant supine, straight knees, separating the legs as far as possible and the distance between the medial malleoli being measured. IHR was measured with the participant seated with the knees and hips flexed 90° and the knees together clasping a piece of paper. The participant moved the ankles apart as far as possible without releasing the paper and the distance between the medial malleoli was measured. Both assessments were measured in cm and the best of two tries was recorded. The effect of height, age, gender and weight was investigated through linear regression (univariable followed by multivariable). Interactions were tested.
Results A total of 393 volunteers were included. IMD had a mean value of 112 (SD 15) cm and IHR of 48 (SD 10) cm. Height had a positive effect on IMD (every increase in height of 10cm resulted in a 4.2cm increase in IMD) and age had an inverse effect (Table 1). There was a significant interaction between age and gender on IHR and therefore models were stratified by gender. In females, height had a positive effect on IHR, whereas age and weight had a negative effect on IHR. In males, height and weight had a significant positive and inverse association, respectively (Table 2).
Conclusions IMD and IHR are both dependent on height and age; and IHR in addition also depends on gender and weight. Therefore these measures need age, gender and height adjusted reference values.
Maksymowych et al. Arthritis & Rheumatism, 2006: 55, 575-582
Disclosure of Interest None Declared