A Biomechanical and Evolutionary Perspective on the Function of the Lumbrical Muscle

Abstract

The lumbrical muscles of the hand originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons. Owing to these movable attachments, the function of this muscle is difficult to visualize. To better determine the function of this muscle, we took a novel approach by considering its relative anatomy, biomechanical characteristics, and evolution. With the smallest physiological cross-sectional area in the upper extremity, the lumbrical muscles have weak motor function, which is only 1/10 of the interosseous muscle. Because it is spindle-rich, the lumbrical muscles play an important role in the sensory feedback of the distal interphalangeal, proximal interphalangeal and metacarpalphalangeal joints of the fingers. The first two lumbrical muscles have lower variation in anatomy and higher density of muscle spindles compared to the ulnar two lumbricals. Additionally, the index and long finger lumbrical muscles are innervated by the median nerve, which also innervates the thenar muscles of the thumb. Therefore, it is possible that the first two lumbricals are functionally more important than the two ulnar lumbricals, specifically for precision pinch movements.

A Novel Grip-Type Microsurgical Needle Holder: Introduction and Electromyographic Evaluation

“…Among them, the lumbrical muscles have the greatest number of muscle spindles among upper limb muscles; therefore, although their biomechanical contribution is secondary due to their small size, they are considered to factor prominently in proprioceptive monitoring for precision movements of the fingers. 8,9 We considered that the efficient use of these intrinsic muscles enabled the grip-type holder to spare forearm muscle movement by contributing principally to stable microsurgical suturing. Releasing the needle with the grip-type needle holder requires flexion of the middle finger to pull on the trigger with the extrinsic forearm flexors of the flexor digitorum superficialis and profundus.…”

MRI of the Intrinsic Muscles of the Hand

“…Some believe that the lumbricals contribute to the radial deviation and abduction of the digits. 2 The function of the lumbricals is determined by their origin and insertion. The lumbricals arise from the radiovolar surface of the flexor tendons at the level of the wrist and proximal palm, and, as such, they have a variable location.…”

“…The thenar muscles control the motion of the thumb, and the hypothenar muscles control the motion of the little finger. 1,2 The intrinsic muscles of the hand have not received much attention in the radiologic literature, despite their importance in moving the hand. [3][4][5][6][7] Prospective studies on magnetic resonance (MR) imaging of the intrinsic muscles of the hand are rare, especially with a focus on new imaging techniques.…”

New insights into the origin of the lumbrical muscles of the foot: tendinous slip of the flexor hallucis longus muscle

“…This information is essential for the coordination of movement [25], and it has been suggested that the sensory function of the lumbricals in the hand is more important than its motor function. Furthermore, the concentration of muscle spindles in the second and third lumbricals of primates, such as marmosets (Callithrux genus) and the Gray Langur, may reflect the importance of these digits during locomotion, whereas the high concentrations of muscle spindles in the first and second lumbricals in humans enable us to perform precision pinch movements [21]. Evolutionary considerations support that the lumbricals may have more of a sensory role than a motor function.…”

“…Evolutionary considerations support that the lumbricals may have more of a sensory role than a motor function. The decrease in size of the lumbricals and the increase in the number of spindle fibers in the lumbricals could be related to the change in the use of the forelimbs from primarily locomotion in nonprimate mammals, toward feeding in some primates, and finally to tool use and precision manipulation of objects in humans [21].…”