Linburg-Comstock variation: histoanatomy and classification of the connection between flexor pollicis longus and flexor digitorum profundus to the index finger.

PURPOSE: The aim of the study was to investigate the anatomy and histology of Linburg-Comstock variation, or the anomalous connection between flexor pollicis longus and flexor digitorum profundus to the index finger, in Thai population.

METHODS: One hundred and thirty cadaveric upper limbs were dissected. Skin and superficial fascia on the anterior distal forearm and hand were removed. The tendons of the flexor pollicis longus and flexor digitorum profundus to the index finger were identified for the possible occurrence of the intertendinous connection. For histological analysis, selected specimens were sampled, and were stained with hematoxylin and eosin.

RESULTS: Out of 130 dissected upper limbs, interconnection between the two tendons was found in 32 limbs (25%). The connection was classified into three types including fibrous, tendinous, and musculotendinous. In 29 cases (22%), the connection was simply the thickening of synovial sheath between the two tendons. In two cases (1%) the connection was found as an additional tendinous slip of dense regular collagen bundles running from the flexor pollicis longus to flexor digitorum profundus of the index. In one case (1%), there was an aberrant reversed musculotendinous unit running from flexor pollicis longus, and later joined the first lumbrical.

CONCLUSIONS: This study provides a detailed anatomo-histological description of the interconnection between flexor pollicis longus and flexor digitorum profundus to the index finger. Its etiology could either be congenital or secondarily acquired. Surgeons should be aware of this connection for better diagnosis, surgical planning and treatment of diseased hands.