C-38 Free Communication/Poster - Posture/Balance: JUNE 2, 2011 7:30 AM - 12:30 PM: ROOM: Hall B
Knee osteoarthritis (OA) is a leading cause of disability in the population. A powerful risk factor for knee OA is frontal plane knee alignment. The measurement of frontal plane tibial mechanical axis (TMA) has been reported to be a valid clinical alternative to gold-standard radiographic assessment. However, more information is needed, including the normal distribution and reliability of this measure. In addition, males are often thought to exhibit more genu varum and thus may exhibit larger TMA values. Finally, the effect of foot position on TMA measurement has not been examined.
PURPOSE: Therefore, we tested the hypotheses that 1) both inter-rater and intra-rater reliability would be high, 2) males would have higher TMA values than females, and 3) tandem stance measurement would decrease population standard deviations compared to natural stance.
METHODS: Normative data were derived from 72 subjects (42 females), and independent t-tests were used to compare means between gender, using an alpha level of 0.05. Thirty individuals were assessed by a single tester (Examiner 1) in both natural and tandem stance, and standard deviations were compared between test positions. The same 30 subjects were also assessed the following day in tandem stance to determine intra-rater reliability. Fifteen different individuals were assessed by Examiners 2 and 3 to determine inter-rater reliability. Intraclass correlation coefficients (2,k) were calculated for the reliability analyses.
RESULTS: Intra-rater and inter-rater reliability were excellent (ICC 0.94 and 0.93, respectively). On average, males were nearly a degree more varus (8 degrees) than females (7 degrees) (p=0.10). Finally, compared to natural stance, tandem stance positioning resulted in a more inclined TMA by 4 degrees, and reduced the standard deviation of the measure by half a degree.
CONCLUSIONS: In summary, TMA is highly reliable as a measure of frontal plane knee alignment, both within and between raters. Normal TMA appears to be between 7 and 8 degrees, with males presenting with slightly more varum. Measuring TMA in tandem stance results in a less variable measure of alignment. Future studies assessing frontal plane knee alignment may consider using TMA as a valid and reliable alternative to full-limb radiography.