The Falcon Test: An Observer Agreement Study in Subjects With and Without Anterior Knee Pain

INTRODUCTION: A shortened rectus femoris muscle has been associated with many different musculoskeletal problems. Assessing rectus femoris muscle length is commonly performed using the Modified Thomas Test. However, this test position is often difficult to assume and there are difficulties with reliably measuring rectus femoris length. A method that that uses an easier position to assume and could be more reliable would be beneficial to therapists. The purpose of this study was to determine observer agreement using a new test for assessment of rectus femoris length. A second purpose was to determine if those with anterior knee pain have different rectus femoris muscle length than those without anterior knee pain. METHOD: Fifty-three participants with and without anterior knee pain were enrolled. Rectus femoris muscle length was measured lying prone with the leg measured on the table while the non-measured leg was off the table in a position of 90° hip flexion. Rectus femoris muscle was lengthened by passively bending the knee until a firm end-feel. The angle of knee flexion was then measured. The process was then repeated after a brief rest period. RESULTS: Observer agreement assessing rectus femoris length using this method showed “almost perfect” reliability for both intra- and inter-rater testing: intra-rater: ICC = .99, [CI(95): .98-.99], inter-rater: ICC = .96, [CI(95): .92- .98]. Agreement for the sub-sample of those with anterior knee pain (N=16) showed “almost perfect” reliability for intra-rater (ICC 1,1 = .98); [CI(95): 0.94-.99] and inter-rater reliability (ICC 2,1 = 0.88); [CI(95): 0.70 -.95]. No differences were noted in rectus femoris length between those without and those with anterior knee pain (t= 0.82, p> 0.01); [CI(95): -7.8 -3.33]; (SEM = 1.3°; MDC=3.6°). CONCLUSION: This new method of assessing rectus femoris length is reliable between and within raters. No differences were noted in rectus femoris length between those with anterior knee pain and those without.