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Linburg-Comstock Anomaly: Prevalence in a Racially Diverse Population and Effect on Hand Strength
Nicholas Schraut, MD; David Mossad, BS; Olivia Wang, MD; Mark Gonzalez, MD, PhD
Orthopaedic Surgery, University of Illinois Chicago, Chicago, IL

Introduction: The Linburg-Comstock anomaly is an anomalous tendinous connection between the flexor pollicis longus (FPL) of the thumb and the flexor digitorum profundus (FDP) of the index finger resulting in the lack of independent flexion of the thumb and index finger. There are few studies describing the effect of the anomaly on grip, key, chuck and tip pinch strength in racially diverse patient populations. The purpose of this study was to determine if there is a difference in the prevalence of the Linburg-Comstock anomaly among ethnically diverse patients as well as to determine the effect this anomaly has on grip, key, chuck and tip pinch strength.

Methods: 184 patients were recruited to participate in the study. The subjects were patients in clinic being seen for orthopedic problems not relating to the hand. Exclusion criteria included previous or current hand, wrist, or forearm injury, contractures or history of extensive arthritis in the hand. Information including race, gender, and hand dominance was collected for each patient. Each patient underwent examination for the Linburg-Comstock anomaly bilaterally and subsequently tested for grip, key, chuck, and tip pinch strength in kilograms using grip and pinch dynanometers. Statistical comparisons were made using Student's t-test and chi-square analysis for proportions with a significance level of 0.05.

Results: The anomaly was present in 25 of 184 subjects (13.6%), with 16 presenting bilaterally and 9 presenting unilaterally. The Hispanic population had the highest prevalence overall at 34.5% (10/29), significantly higher than African Americans (9/102, 8.8%, p<0.01) and all races combined (25/184, 13.6%, p<0.01) but not significantly higher than the individual cohorts of Caucasians (6/43, 14.0%, p= 0.08) or Asians/Indians (0/10, 0%, p=0.08). The male to female ratio for the group with the anomaly was 2 to 3. Of the patients presenting with the anomaly unilaterally, 8/9 were present in the right forearm. There was no difference in average grip (34.8 vs 30.5, p=0.12), key (8.3 vs 8.0, p=0.50), chuck (7.2 vs 6.7, p=0.43), or tip pinch strength (5.9 vs 5.5, p=0.39) between the group with the anomaly and the group without it.

Conclusion: The Hispanic population showed a significantly higher prevalence of the Linburg-Comstock anomaly compared to African Americans, and a higher but insignificantly different prevalence compared to Caucasians, Asians, and Indians. For those with the anomaly, grip, key, chuck, and tip pinch strength were not significantly different, suggesting this anomaly does not have an effect on hand functionality.

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