An investigation into the reliability and methodology of the Linburg-Comstock anomaly clinical test.

STUDY DESIGN: This is a cross-sectional study. INTRODUCTION: An intertendinous connection between the flexor pollicis longus (FPL) and index flexor digitorum profundus (IFDP) tendons causes involuntary index flexion during active thumb flexion and has been named the Linburg-Comstock anomaly (LCA). It may become symptomatic or cause functional limitations. Literature has documented the prevalence to range from 13% to 70%. Cadaver studies have reported an anatomical connection in 5% to 25%. PURPOSE: This study aimed to examine the methodology and reliability of the LCA clinical diagnostic test and to explore the wide range of reported incidence and the discrepancy between cadaver and subject prevalence. METHODS: Two examiners observed for the presence of involuntary index flexion during 3 separate variations of thumb flexion in 67 subjects (134 limbs); results were considered positive if involuntary flexion occurred at either index interphalangeal joint. Intertester reliability was assessed using Cohen's kappa coefficient. The volar forearm and wrist of 53 cadavers (106 limbs) were dissected and assessed for an observable and mechanical tendinous connection between the FPL and IFDP tendons. RESULTS: Prevalence for subjects (5%-32%) was at the lower end of the range of previously reported values; results differed with altering thumb flexion motion. Observation for the presence of an intertendinous connection between the FPL and IFDP tendons in cadaver specimens (23%) fell within previously reported ranges. Intertester reliability coefficients ranged from no to weak agreement and varied according to specific thumb flexion motion performed during the test. CONCLUSIONS: The identification of index finger flexion during thumb flexion varied both with thumb flexion motions and with whether flexion was assessed at the index proximal interphalangeal or distal interphalangeal joint. Intertester reliability was low for all variations of the LCA clinical test performed. The wide range in previously reported LCA incidence may be due to variability in testing procedure, and there is a need to establish a reliable and valid clinical test for this potentially symptomatic anatomic anomaly.

Linburg-Comstock anomaly: A comparison of the prevalence in women with and without clinical carpal tunnel syndrome.

We aimed to compare the prevalence of the Linburg-Comstock anomaly in women with and without a clinical diagnosis of carpal tunnel syndrome. The prevalence of the Linburg-Comstock anomaly was evaluated in 400 hands from 200 women over 40 years of age who were diagnosed clinically with carpal tunnel syndrome (CTS), designated as the CTS group. The volunteer group consisted of 400 hands from 200 healthy women over 40 years of age. The women from both groups were asked to carry out the clinical flexion and pain tests described by Linburg and Comstock (1979) as a basis for the clinical diagnosis. CTS patient ages ranged from 40 to 90 (mean 55.8) years, while volunteer group ages ranged from 40 to 93 (mean 55) years. The flexion test was positive in 305 (76%) hands in the CTS group and 242 (60%) hands in the volunteer group. The pain test was positive in 261 (65%) hands in the CTS group and 108 (27%) hands in the volunteer group. Both tests were positive in 244 (61%) hands in the CTS group and 98 (24%) hands in the volunteer group. All these differences were statistically significant. Based on clinical examination using the flexion and pain tests, the prevalence of Linburg-Comstock anomaly was statistically higher in the group of women with carpal tunnel syndrome than in healthy volunteers.