Background Some people are particularly flexible and have Generalised Joint Hypermobility (GJH). However, others are similarly flexible but suffer with pain, joint instability, weakness and fatigue. People who have joint hypermobility and symptoms are classified as having Joint Hypermobility Syndrome (JHS (1)). It is unclear why some flexible people have symptoms and some do not. However, it may be due to impaired mechanisms of control (2). Surprisingly, no one has investigated these mechanisms of control thoroughly.

Objectives To assess the sample size required for an investigation comparing quadriceps corticospinal excitability between people with normal flexibility, people who are flexible without knee pain and people who have JHS with knee pain.

Methods With ethical approval and informed consent, the surface electromyography of Quadriceps were recorded from 3 cohorts of age matched people; individuals with normal flexibility without knee pain (Beighton score of 3 or less), individuals with JHS (classified using the Brighton criteria (1)) without knee pain and individuals with JHS with knee pain.

A figure of eight coil from a magnetic stimulator was positioned over the cortex upon the hotspot for Quadriceps, evoking a MEP in the muscle of the painful or dominant side. The stimulus strength was varied whilst the muscle was held at a constant, low level of contraction with the assistance of a feedback monitor. In addition, the maximum amplitude of the motor response (Mmax) to electrical stimulation of the femoral nerve was established. A recruitment plot was constructed of stimulus strength against MEP amplitude normalised to Mmax and a Boltzmann sigmoid curve was fitted. The threshold and latency of the MEP, the maximum amplitude of the normalised MEP, the slope of the recruitment curve and the stimulus required to evoke a response of 50% of the maximum amplitude (X₅₀) were recorded and compared across groups. Normality of distribution was tested using Shapiro-Wilk test. If normally distributed a one way ANOVA or where data was not normally distributed, a Kruskal-Wallis one way analysis of variance on ranks was used to compare between cohorts. Using the standard deviation of the results, sample size estimates were calculated using a power of 0.8 and a probability of 0.05.

Results 36 people were recruited aged 29.2yrs ±6.6 (mean ± standard deviation); 12 with normal flexibility (Beighton score 0.96±0.86), 11 with JHS without knee pain (6.37±1.54) and 13 with JHS and knee pain (6.04±1.67). Data was not normally distributed. No differences in threshold (p=0.33), latency of the MEP (p=0.45), maximum amplitude of the normalised MEP (p=0.58), slope of the recruitment curve (p=0.60) and the X₅₀ (p=0.22) were found. Taking into account the variability of the data, this pilot investigation suggests a sample size of 30 in each group is required in order to exclude the possibility that these results are due to random sampling variability.

Conclusions Differences to corticospinal excitability in JHS are yet to be elucidated; however differences may be subtle.

References

1. Grahame R, et al. J Rheumatol 2000 Jul;27(7):1777-9.

2. Rombaut L. Arthritis Care Res (Hoboken) 2013 Jun;65(6):1017-8.

Acknowledgements CMA is supported by the National Institute of Health Research. We gratefully acknowledge Louise Kiru for her assistance in some of the data collection as well as the participation of our volunteers.

Disclosure of Interest J. Kassam: None declared, C. Alexander Grant/research support: NIHR Senior Clinical Lectureship, Employee of: Imperial College Healthcare NHS Trust

DOI 10.1136/annrheumdis-2014-eular.1065