Objective: To provide a practical guide to appropriate statistical analysis of a reliability study using real-time ultrasound for measuring muscle size as an example. Design: Inter-rater and intra-rater (between-scans and between-days) reliability. Subjects: Ten normal subjects (five male) aged 22–58 years. Method: The cross-sectional area (CSA) of the anterior tibial muscle group was measured using real-time ultrasonography. Main outcome measures: Intraclass correlation coefficients (ICCs) and the 95% confidence interval (CI) for the ICCs, and Bland and Altman method for assessing agreement, which includes calculation of the mean difference between measures ( d), the 95% CI for d, the standard deviation of the differences (SD diff), the 95% limits of agreement and a reliability coefficient. Results: Inter-rater reliability was high, ICC (3,1) was 0.92 with a 95% CI of 0.72 → 0.98. There was reasonable agreement between measures on the Bland and Altman test, as d was -0.63 cm², the 95% CI for d was -1.4 → 0.14 cm², the SD_diff was 1.08 cm², the 95% limits of agreement -2.73 → 1.53 cm² and the reliability coefficient was 2.4. Between-scans repeatability was high, ICCs (1,1) were 0.94 and 0.93 with 95% CIs of 0.8 → 0.99 and 0.75 → 0.98, for days 1 and 2 respectively. Measures showed good agreement on the Bland and Altman test: d for day 1 was 0.15 cm² and for day 2 it was -0.32 cm², the 95% CIs for d were -0.51 → 0.81 cm² for day 1 and -0.98 → 0.34 cm² for day 2; SD_diff was 0.93 cm² for both days, the 95% limits of agreement were -1.71 → 2.01 cm² for day 1 and -2.18 → 1.54 cm²for day 2; the reliability coefficient was 1.80 for day 1 and 1.88 for day 2. The between-days ICC (1,2) was 0.92 and the 95% CI 0.69 0.98. The d was -0.98 cm², the SD_diff was 1.25 cm² with 95% limits of agreement of -3.48 → 1.52 cm² and the reliability coefficient 2.8. The 95% CI for d(-1.88 → -0.08 cm²) and the distribution graph showed a bias towards a larger measurement on day 2. Conclusions: The ICC and Bland and Altman tests are appropriate for analysis of reliability studies of similar design to that described, but neither test alone provides sufficient information and it is recommended that both are used.

The effect of low back pain on the size of the lumbar multifidus muscle was examined using real-time ultrasound imaging. Bilateral scans were performed in 26 patients with acute unilateral low back pain (LBP) symptoms (aged 17-46 years) and 51 normal subjects (aged 19-32 years). In all patients, multifidus cross-sectional area (CSA) was measured from the 2nd to the 5th lumbar vertebrae (L2-5) and in six patients, that of S1 was also measured. In all normal subjects, CSA was measured at L4 and in 10 subjects measurements were made from L2-5. Marked asymmetry of multifidus CSA was seen in patients with the smaller muscle being on the side ipsilateral to symptoms (between-side difference 31 +/- 8%), but this was confined to one vertebral level. Above and below this level of wasting, mean CSA differences were < 6%. In normal subjects, the mean differences were < 5% at all vertebral levels. The site of wasting in patients corresponded to the clinically determined level of symptoms in 24 of the 26 patients, but there was no correlation between the degree of asymmetry and severity of symptoms. Patients had rounder muscles than normal subjects (measured by a shape ratio index), perhaps indicating muscle spasm. Linear measurements of multifidus cross-section were highly correlated with CSA in normal muscles but less so in wasted muscles, so CSA measurements are more accurate than linear dimensions. The fact that reduced CSA, i.e., wasting, was unilateral and isolated to one level suggests that the mechanism of wasting was not generalized disuse atrophy or spinal reflex inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

‘Arthrogenous muscle weakness’ is weakness of muscles acting about an injured or inflamed joint. The weakness may be due to loss of muscle or to inability to activate the muscle (Fig. 1). Weakness of the thigh muscles, and of the quadriceps in particular, is a common and important consequence of knee trauma, surgery or arthritis. Muscle weakness contributes significantly to disability and probably also renders the joint vulnerable to further damage (Fig. 1). This review starts with a brief discussion of the contribution of atrophy to weakness. It concentrates, however, on inhibition of quadriceps activation and suggests some therapeutic implications. It does not deal with the reduced oxidative capacity and increased fatiguability of disused muscle since, although important, these have not been part of our programme of work.