Inter- and intra-tester reliability of clinical measurement to determine medio-lateral patellar position using a pachymeter or visual assessment.

The aim was to investigate inter-tester and intra-tester reliability and parallel reliability between a visual assessment method and a method using a pachymeter for locating the mid-point of the patella in determining the medial/lateral patella orientation. Fifteen asymptomatic subjects were assessed and the mid-point of the patella was determined by both methods on two separate occasions two weeks apart. Inter-tester reliability was obtained by ANOVA and by intraclass correlation coefficient (ICC); intra-tester reliability was obtained by a paired t-test and ICC; and parallel reliability was obtained by Pearson's Correlation and ICC, for the measurement on the first and second evaluations. There was acceptable inter-tester agreement (p=0.490) and reliability for the visual inspection (ICC=0.747) and for the pachymeter (ICC=0.716) at the second evaluation. The inter-tester reliability in the first evaluation was unacceptable (visual ICC=0.604; pachymeter ICC=0.612). Although there was statistical similarity between measurements for the first and second evaluations for all testers, intra-tester reliability was not acceptable for both methods: visual (examiner 1 ICC=0.175; examiner 2 ICC=0.189; examiner 3 ICC=0.155) and pachymeter (examiner 1 ICC=0.214; examiner 2 ICC=0.246; examiner 3 ICC=0.069). Parallel reliability gave a perfect correlation at the first evaluation (r=0.828; p<0.001) and at the second (r=0.756; p<0.001) and reliability was between acceptable and very good (ICC=[0.748-0.813]). Both visual and pachymeter methods provide reliable and similar medial/lateral patella orientation and are reliable between different examiners, but the results between the two assessments at 2 weeks' interval demonstrated an unacceptable reliability.