Complex, multidimensional thumb movements generated by individual extrinsic muscles

Abstract

The objective of this study was to investigate three-dimensional thumb joint movements produced by individual extrinsic thumb muscles. Ten cadaveric arms were dissected to expose the musculotendinous junctions of the flexor pollicis longus (FPL), abductor pollicis longus (APL), extensor pollicis brevis (EPB), and extensor pollicis longus (EPL). Each muscle/tendon was loaded to 10% of its maximal force capability whereas three-dimensional angular movements of the carpometacarpal (CMC), metacarpophalangeal (MCP), and interphalangeal (IP) joints were obtained simultaneously. We found that each extrinsic muscle produced unique joint angular trajectories in multiple directions. The FPL, APL, EBP, and EPL generated two, two, three, and six movements, respectively. The extrinsic muscles all together generated eight movements among the multiple thumb joints. High interjoint coordination was shown between the MCP joint flexion and IP joint flexion by FPL loading, as well as between the MCP joint extension and IP joint extension by EPL loading. High intrajoint coordination was observed between extension and supination at the CMC joint by the APL, EPL, and EPB. We concluded that each muscle produces movements in multiple joints and/or in multiple anatomical directions. The findings provide a novel insight into the biomechanical roles of the extrinsic muscles of the thumb. The human thumb is exceptionally mobile, strong, and dexterous partially due to its sophisticated musculature. Kinematically, thumb motion results from complicated combinations of flexion/extension, abduction/ adduction, and pronation/supination (i.e., axial rotation) at the carpometacarpal (CMC), metacarpophalangeal (MCP), and interphalangeal (IP) joints. 1,2 The movement capability of the thumb was previously determined by measuring the linear distance between the thumb tip and the fingertips or other anatomical landmarks, 3,4 but thumb pathology can be characterized by examining the angular motion at the individual joints. Manual goniometry is commonly used in the clinic to evaluate statically joint mobility in a single plane. Electrogoniometers can be used to monitor dynamic joint motion, 5 but they can be too bulky to record simultaneous movements from multiple joints within the thumb and can interfere with delicate thumb movements. X-rays, 1,6 and CT 7 have been used to study in vivo thumb kinematics, but the amount of kinematic information is limited. Recently, noninvasive, marker-based video methods have been used to study advanced kinematic features thus providing a more accurate representation of thumb motion. 2,[8][9][10][11] Marker-based motion analyses were applied to study thumb pathokinematics in individuals with cervical myelopathy 12 and lower median nerve block; 13 the authors reported aberrant thumb kinematics during pinch movements.Thus far, our understanding of thumb motion by each muscle remains dominated by basic functional anatomy using unidirectional, simplified nomenclature such as flexors or extensors. Therefore, this ...

Kinematic Analyses of the Thumb during Simulated Posteroanterior Glide Mobilization

“…This interjoint coordination may be attributable to the extrinsic muscles and torques created by the tensioned muscles on the joints it crosses [17]. Although tasks performed in this study were different from Li’s study [17], we suspected that the negative correlation between adjacent joints was a result of interjoint coordination for the PA glide technique requirements. Due to the different levels of experience, each group likely adapted to different control patterns in order to direct force more efficiently.…”

“…Novice participants appeared to respond to tip forces by controlling the IP joint without paying proper attention to the proximal joints while experienced participants controlled both the IP and CMC joints during the process of directing force to the target. Li et al [17] observed interjoint coordination, which was coordination among multiple thumb joints in a specific thumb movement direction. This interjoint coordination may be attributable to the extrinsic muscles and torques created by the tensioned muscles on the joints it crosses [17].…”

“…Li et al [17] observed interjoint coordination, which was coordination among multiple thumb joints in a specific thumb movement direction. This interjoint coordination may be attributable to the extrinsic muscles and torques created by the tensioned muscles on the joints it crosses [17]. Although tasks performed in this study were different from Li’s study [17], we suspected that the negative correlation between adjacent joints was a result of interjoint coordination for the PA glide technique requirements.…”

Rotation in the Interphalangeal Thumb Joint In Vivo

“…Our study confirmed variable pronation at the IP joint of the thumb previously demonstrated by these ex vivo studies. [1][2][3][4][5][6][7] Furthermore, we propose that, using accepted noninvasive photographic methodology, 10,11 preoperative IP joint pronation can be reliably measured and incorporated into thumb IP joint arthrodesis procedures. In cases with distorted thumb pathology, comparative measurements can be taken from the contralateral thumb IP joint.…”

“…5,6 Extension, valgus, and external rotation or supination is provided by the extensor expansion receiving fibers from abductor pollicis brevis, ulnar head of flexor pollicis brevis/1st palmar interosseous, and extensor pollicis longus, because the IP joint axis of rotation is not perpendicular to the proximal phalanx. 5,7 When performing a pollicization, arthrodesing or replacing the IP joint of the thumb, 8 this pronation can be lost.…”