In vivo kinematics of the thumb during flexion and adduction motion: Evidence for a screw-home mechanism

Abstract

The thumb plays a crucial role in basic hand function. However, the kinematics of its entire articular chain have not yet been quantified. Such investigation is essential to improve our understanding of thumb function and to develop better strategies to treat thumb joint pathologies. The primary objective of this study is to quantify the in vivo kinematics of the trapeziometacarpal (TMC) and scaphotrapezial (ST) joints during flexion and adduction of the thumb. In addition, we want to evaluate the potential coupling between the TMC and ST joints during these tasks. The hand of 16 asymptomatic women without signs of thumb osteoarthritis were CT scanned in positions of maximal thumb extension, flexion, abduction, and adduction. The CT images were segmented and three-dimensional surface models of the radius, scaphoid, trapezium, and the first metacarpal were created for each thumb motion. The corresponding rotations angles, translations, and helical axes were calculated for each sequence. The analysis shows that flexion and adduction of the thumb result in a three-dimensional rotation and translation of the entire articular chain, including the trapezium and scaphoid. A wider range of motion is observed for the first metacarpal, which displays a clear axial rotation. The coupling of axial rotation of the first metacarpal with flexion and abduction during thumb flexion supports the existence of a screw-home mechanism in the TMC joint. In addition, our results point to a potential motion coupling between the TMC and ST joints and underline the complexity of thumb kinematics. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1556-1564, 2017.

Trabecular variation in the first metacarpal and manipulation in hominids

“…Therefore, we predict flexion will be the dominant habitual movement in these grips, rather than adduction, reflected by the trabecular distribution in the nonhuman primate TMc joint (Figure b, bottom). In humans we predict RBV/TV and DA will be greater in the radiopalmar aspect of the Mc1 base ( H2c ; Figure a), due to habitual abduction and flexion during precision grasping (D'Agostino, Dourthe, Kerkhof, Stockmans, et al, ; Feix et al, ; Napier, ) as has been demonstrated before for RBV/TV (Stephens et al, ).…”

“…While values average DA values for this species were highest in the radiopalmar region (Figure b) consistent with opposition of the thumb these were only significantly higher than those of bonobos (Figure ) and DA were also higher at some ulnar landmarks (Figure b). Conversely, humans displayed the highest RBV/TV values at the radial and less extreme palmar region of Mc1 base landmarks, consistent with a habitually and forcefully abducted thumb, flexed in opposition ( H2c ; Napier, ; Halilaj, Rainbow, et al, ; Feix et al, ; D'Agostino, Dourthe, Kerkhof, Stockmans, et al, , Marchi et al, ). These results agree with other studies that have found a palmar concentration of Mc1 base BV/TV in comparison to other apes (Skinner et al, , ) and other metacarpals (Wong et al, ).…”

“…This pattern may be interpreted as habitual loading of the human TMc joint in a less flexed position than in other extant hominids. This may be a result of the “screw‐home” mechanism of the TMc joint during human opposition where axial rotation of the Mc1 causes the tip of the palmar beak to enter a recess on the trapezium (D'Agostino, Dourthe, Kerkhof, Stockmans, et al, ; Edmunds, ). In this position, the majority of the Mc1 base is in compression and stabilizes the joint without the need of a taut palmar peak ligament but the tip of the beak no longer articulates with the trapezium as it moves ulnarly into this recess (Edmunds, ).…”

“…The rounded palmar beak at the Mc1 base in nonhuman great apes, relative to humans, is also thought to restrict axial rotation of the Mc1, and thus adduction (Marzke et al, ; van Leeuwen, Vanneste, et al, ). When similar pad‐to‐side grips are experimentally performed in humans, the contact area of the TMc surfaces is larger ulnarly but the closest point between them is at the palmar beak of the Mc1 (D'Agostino, Dourthe, Kerkhof, Stockmans, et al, ; Figure b). Therefore, we predict flexion will be the dominant habitual movement in these grips, rather than adduction, reflected by the trabecular distribution in the nonhuman primate TMc joint (Figure b, bottom).…”

“…Whether in extension or flexion forceful precision grips are achieved through high potential torques of human musculature compared to great apes (Marzke et al, ). During finger opposition, large human thenar muscles allow a forceful compound movement of axial rotation, flexion, and abduction of the human thumb (D'Agostino, Dourthe, Kerkhof, Stockmans, & Vereecke, ; Feix, Romero, Schmiedmayer, Dollar, & Kragic, ; Halilaj, Rainbow, et al, ; Napier, ). The larger and flatter sellar–facet (Marzke et al, ; Tocheri, Razdan, Williams, & Marzke, ), as well as a less curved proximal Mc1 and a shorter palmar beak (Marchi, Proctor, Huston, Nicholas, & Fischer, ; Niewoehner, ), are associated with greater TMc joint mobility in humans compared to other great apes (Cooney, Lucca, Chao, & Linscheid, ; Rose, ).…”