Case Analysis of Accessory Abductor Pollicis Longus Tendons and Brevis Muscles with Implications for Occupational Therapy

Abstract

INTRODUCTIONVariations in muscles to the pollex are relatively common. Abnormal cleavage of the thenar muscles during development can form accessory muscle bellies, and forearm muscles sending long tendons to the pollex can develop extra tendons. While these abnormalities are typically asymptomatic and often go undetected, serious sequelae can result that affect pollex function. Pollex abduction, generated primarily by the abductor pollicis longus (APL) and brevis (APB) muscles, is an essential movement for hand function. APL has been reported with accessory tendons, split muscle bellies, and abnormal attachments, but variations in APB are less common. The addition of an accessory APL (aAPL) tendon in the 1st extensor compartment may cause crowding of APL and extensor pollicis brevis (EPB) tendons and result in inflammation. This condition is known as de Quervain’s tenosynovitis and often generates pain during abduction and extension of the pollex – implications that are pertinent to Occupational Therapy (OT). The objective of this study is to analyze a unique case of bilateral aAPL tendons which distally attach to accessory APB (aAPB) muscles and discuss their implications for OT practice.METHODSBilateral aAPL tendons distally attaching to aAPB muscles were discovered during routine cadaver dissection at the University of Nebraska Medical Center. The aAPL tendons, aAPB muscles, and surrounding anatomy were cleaned of extraneous tissue to better view the course, structure, and attachments of the anomalies. The bilateral anomalies were comparable, so only the left aAPL tendon and aAPB muscle were photographed in situand post‐evisceration. Bilateral tendon measurements and maximal isometric forces (Fmax) for each muscle were used to determine comparability and thereafter discussed as means. The normal APL and APB were also analyzed bilaterally to gauge accessory muscle impact. A literature review was conducted to discuss rarity and clinical implications of these muscles for OT practice.RESULTSThe regular APL tendon displayed a normal insertion on the base of the 1st metacarpal. The aAPL tendon originated from the APL muscle belly and exhibited two distal attachments: the main tendon (137.5 mm length) to the aAPB muscle belly and a short distal branch of the main tendon to the trapezium. Compression of the aAPL tendon in the 1st extensor compartment was grossly visible. The literature consistently references de Quervain’s tenosynovitis as an expected result from similar cases, but no studies describe a distal bifurcation of the aAPL tendon that distinctly attaches to both aAPB and trapezium. Mean Fmax for APB, aAPB, and APL were 12.1 N, 8.2 N, and 40.8 N, respectfully.CONCLUSIONS & SIGNIFICANCEThe present study reports a unique case of an aAPL tendon with a distinct bifurcation to an aAPB and the trapezium. The short tendon to trapezium allows aAPB to use the aAPL tendon as an anchor (origin) but limits APL’s ability to abduct the pollex via pull on aAPB. This report may help OT providers better determine the presence of accessory abductor pollicis tendons and/or muscles when treating patients with de Quervain’s tenosynovitis, adapt treatment modalities, and note this in their medical record for possible future use in tendon transfer surgeries.