Prevalence, Morphometric Characteristics of the Accessory Abductor Pollicis Longus Muscle and Clinical Implications: A Cadaveric Study

<b>Background/Objectives:</b> The abductor pollicis longus (APL) muscle exhibits a high degree of anatomical variation, particularly in the number and configuration of its tendons. Understanding these variants is crucial in surgical contexts, especially for tendon transfer and reconstruction procedures. This study aimed to determine the prevalence and morphometric characteristics of the accessory abductor pollicis longus (AAPL) muscle in a Bolivian cadaveric population. <b>Methods:</b> A descriptive, cross-sectional study was performed on 16 forearms from eight adult cadavers (six males and two females) preserved in 10% formalin. Cadaveric dissection was conducted following the AQUA guidelines, with measurements obtained for the AAPL proximal tendon length (PTL), distal tendon length (DTL), muscle length (ML), and transverse muscle length (TML) using a digital caliper. Statistical analysis was carried out using SPSS v26. <b>Results:</b> The AAPL muscle was present in 50% of forearms. Most were unilateral, with one bilateral case. The muscle exhibited a fusiform shape, with fibers aligned longitudinally. Morphometric analysis revealed a mean PTL of 1.20 ± 0.08 cm, DTL of 3.91 ± 0.52 cm, ML of 5.30 ± 0.45 cm, and TML of 0.55 ± 0.056 cm. One case (6.25%) exhibited a multicaudal APL with an additional tendon measuring 6.23 cm. No significant correlations were found between muscle and tendon measurements. <b>Conclusions:</b> AAPL muscles are relatively common and demonstrate notable morphometric variation. While the proximal tendon may be inadequate for grafting due to its short length, the distal tendon offers a viable alternative for reconstructive procedures. Recognition of such variants is clinically relevant, as they may contribute to pathologies like De Quervain's tenosynovitis or serve as graft sources in surgical interventions.