Interexaminer reliability of the prone leg length analysis procedure

The purpose of this study was to perform an interexaminer reliability evaluation of the prone leg length analysis procedure.

Two chiropractors each examined a series of 45 patients with a history of low back pain. Patients were in the prone position, with the knees in both extended and flexed positions, and with the head rotated right and left. The clinicians were asked to determine the side of the short leg with knees extended and if a change in leg length occurred with head rotation or when the knees were flexed. They were also asked to visually judge the amount of leg length differential by categorizing the difference as either less than 0.25, 0.25 to 0.5, 0.5 to 0.75, or more than 0.75 in. The head rotation portion of the test was performed only with patients (n = 22) in whom the leg length differential was determined to be less than 0.25 in.

kappa statistics and frequency distributions were calculated for each of the respective observations. Reliability of determining the side of the short leg with knees extended was good at 82% agreement (kappa = 0.65) but fair for determining the amount of leg length difference at 67% agreement (kappa = 0.28). Reliability of the head rotation testing procedure was extremely poor, with only 50% and 45% agreement about the observed change in leg length with the head rotated left and right, respectively (kappa = 0.04, kappa = -0.195). There was no significant correlation found between the side of reported pain by the patient and the side of the short leg as noted by either clinician (chi2 = 0.55, P = .91, and chi2 = 1.55, P = .67). All of the patients (100%) were judged to have a leg length difference by both clinicians. When the knees were flexed, there was 93% agreement that the short leg became longer (43/45 cases), with no reported cases of the short leg getting shorter. Calculation of kappa statistics was confounded for these last 2 observations because of extremely high prevalence bias.

The results indicate that 2 clinicians show good reliability in determining the side of the short leg in the prone position with knees extended but show poor reliability when determining the precise amount of that leg length difference. The head rotation test for assessing changes in leg length was unreliable in this sample of patients. There does not appear to be any correlation between the side of pain noted by the patient and the side of the short leg as observed by the clinicians; all 45 patients in this sample were found to have a short leg by both clinicians.