An Aberrant Pronator Quadratus with Possible Flexor Function at the Wrist

Hand specialists rely on anatomical knowledge to properly assess and treat patients. Our study sought to describe clinically relevant variations that may facilitate accurate diagnoses and effective treatment and management of hand disorders. Forearms from 21 embalmed cadavers (n=42, ages 55‐97, mean 80) were dissected and observed for anomalous attachment points, innervations, muscle shape, and fascicle orientation. Here we report a bilateral aberrant pronator quadratus (PQ) in a single cadaver, whose features suggest its role as a wrist flexor. Typically, the PQ, a flat quadrilateral muscle spanning the distal quarter of the forearm, initiates pronation. Its superficial fibers traverse the anterior surfaces of the radius and ulna, while its deep fibers bind them together. The aberrant PQ has both superficial and deep bellies originating on the lateral surfaces of these bones with the muscle fascicles oriented obliquely (pennation=80° for radial bellies, bilaterally; 60° for left, 48° for right ulnar bellies). Each PQ has tendons from the radial (1 from right, 2 from left) and ulnar bellies (2 from right, 1 from left). In both forearms, these form a common tendon that travels distally across the radioulnar joint, through the carpal tunnel floor, and inserts onto the capitate. Collectively, these features suggest an additional function of wrist flexion, similar to a rare flexor carpi radialis brevis. Thus, the aberrant PQ may not have been the typical initiator of forearm pronation, and perhaps other muscles compensated, i.e., pronator teres, brachioradialis, and/or flexor carpi radialis . To conclude, awareness of diverse hand anatomy is critical for clinical examination and management of hand disorders.