Sex differences in neck strength and head impact kinematics in university rugby union players.

Globally, over three million women participate in rugby union, yet injury prevention and training strategies are predominantly based on androcentric data. These strategies may have limited generalisability to females, given the cervical spine is more susceptible to whiplash and less adept at resisting inertial loading. A total of 53 university rugby union players (25 female, 28 male, 20.7 ± 1.8 years) had their isometric neck strength measured. Bespoke instrumented mouthguards were used to record the magnitude of head impact events in six female and seven male competitive matches. Mean female maximal isometric neck strength was 47% lower than male. Independent samples Mann-Whitney U tests showed no significant differences for peak linear head acceleration (female: median 11.7 g, IQR 7.9 g; male: median 12.5 g, IQR 7.0 g p=.23) or peak rotational head acceleration (female: median 800.2 rad·s-2, IQR 677.7 rad·s-2; male: median 849.4 rad·s-2, IQR 479.8 rad·s-2; p=.76), despite the mean male body mass being 24% greater than female. Coded video analysis revealed substantial differences in head-impact mechanisms; uncontrolled whiplash dominated >50% of all recorded female impact events and <0.5% in males. Direct head-to-ground impacts comprised 26.1% of female and 9.7% of male impacts, with whiplash occurring in 78.0% and 0.5%, respectively. Overall, the data provided in this study do not support the generalisation of male-derived training and injury-prevention data to female rugby athletes. These results suggest a considerable research effort is required to identify specific weakness of female rugby players and derive appropriate training, injury prevention and return to play protocols.Highlights Video analysis revealed substantial differences in head-impact mechanisms, with uncontrolled whiplash dominating >50% of all recorded female impact events but rarely in males.Isometric neck strength was 47% lower in female players than males.Direct head-to-ground impacts accounted for 26.1% and 9.7% of female and male impacts, with whiplash occurring in 78.0% and 0.5%, respectively.

Muscle activity during maximal isometric forearm rotation using a power grip.

This study aimed to provide quantitative activation data for muscles of the forearm during pronation and supination while using a power grip. Electromyographic data was collected from 15 forearm muscles in 11 subjects while they performed maximal isometric pronating and supinating efforts in nine positions of forearm rotation. Biceps brachii was the only muscle with substantial activation in only one effort direction. It was significantly more active when supinating (µâ€¯= 52.1%, SD = 17.5%) than pronating (µâ€¯= 5.1%, SD = 4.8%, p < .001). All other muscles showed considerable muscle activity during both pronation and supination. Brachioradialis, flexor carpi radialis, palmaris longus, pronator quadratus and pronator teres were significantly more active when pronating the forearm. Abductor pollicis longus and biceps brachii were significantly more active when supinating. This data highlights the importance of including muscles additional to the primary forearm rotators in a biomechanical analysis of forearm rotation. Doing so will further our understanding of forearm function and lead to the improved treatment of forearm fractures, trauma-induced muscle dysfunction and joint replacements.

A finite element model to investigate the effect of ulnar variance on distal radioulnar joint mechanics.

Ulnocarpal impaction syndrome involves excessive loading of the ulnocarpal joint. Ulnar shortening osteotomies are an effective way to reduce ulnocarpal loading but alter contact mechanics at the distal radioulnar joint (DRUJ). This study used a computational model to investigate the relationship between ulnar length and DRUJ mechanics. Detailed, finite element models of the radius and ulna bones were constructed from magnetic resonance imaging data. The length of the ulna bone model was increased and decreased up to 5 mm in 1 mm increments. A computational model was used to predict joint contact at the DRUJ for each ulnar length. Lengthening the ulna caused a slight decrease in DRUJ contact pressure, with a more substantial decrease in contact area. Shortening the ulna caused a substantial increase in contact area, with a smaller increase in DRUJ contact pressure. The location of contact on the radial sigmoid notch changed with 2 mm lengthening and 3 mm shortening. The results of this study demonstrate the sensitivity of DRUJ contact to ulnar length changes, which may explain the DRUJ cartilage degeneration that often follows ulnar osteotomies. The joint contact model implemented in this study allowed the relationship between ulnar length and DRUJ contact to be examined systematically, in a way that is difficult to achieve through cadaveric experimentation. The results confirmed published experimental data showing an increased DRUJ contact pressure with ulnar shortening. It is important that clinicians consider the influence of ulnar osteotomies, not only on ulnocarpal loading but also on DRUJ mechanics. Copyright © 2016 John Wiley & Sons, Ltd.

Vector-based forearm rotation moment arms - A sensitivity analysis.

All existing moment arm data for muscles of the forearm derive from tendon excursion experiments. Moment arms determined this way are only valid for movement about the same generalised coordinate system as was used during the tendon excursion, which makes their implementation in more complex or realistic joint models problematic. This study used a vector-based method to calculate muscle moment arms in a three dimensional model of forearm rotation. It also evaluated the sensitivity of this method to errors in the input data. There was reasonably close agreement between the moment arms calculated in this study and those published using tendon excursion methods. Six out of eight muscles had moment arms within the range of values reported previously. However, the vector-based method was sensitive to the accuracy of the input data. This sensitivity varied between muscles and input variables. Generally, the calculations were more robust to the point of force application than the muscle lines of action and the joint's axis of rotation. A small change in these variables could produce substantial changes in the calculated moment arms. Consequently, accurate input data is important when using the vector-based method in a joint model.

Examining the influence of distal radius orientation on distal radioulnar joint contact using a finite element model.

Distal radius malunion is a problem that is common to distal radius fractures and can affect the contact mechanics of the distal radioulnar joint (DRUJ). The goal of this study was to use a computational model of the DRUJ to investigate the influence distal radius orientation has on its contact mechanics. Detailed, finite element models of the radius and ulna bones were constructed from magnetic resonance imaging data. The orientation of the distal radius was rotated in 2° increments about three orthogonal axes representing dorsal-palmar rotation, radial-ulnar rotation and anteversion-retroversion. A computational model was used to predict joint contact at the DRUJ in each condition. Joint contact was found to be most sensitive to dorsal rotation of the distal radius, while radial and ulnar rotation did not substantially affect joint contact pressure. Slight retroversion was found to lower joint contact pressure. In most cases, more than 6° rotation in a given direction resulted in dislocation of the DRUJ, so that adaptation at the joint would be required to maintain articular contact. The joint contact model implemented in this study allowed the relationship between distal radius orientation and DRUJ contact to be examined systematically, in a way that is difficult to achieve using a cadaver-based approach. The results demonstrated the distal radius displacements most critical for maintaining healthy joint mechanics at the DRUJ. It is important that clinicians consider the influence of distal radius malunion and its treatment on DRUJ mechanics, in addition to its consequences for wrist function and forearm rotation. Copyright © 2016 John Wiley & Sons, Ltd.