Michael R. Boland

The Function of Brachioradialis

PURPOSE The function of the brachioradialis muscle is controversial. The objective of this study was to determine primary and secondary functions of the brachioradialis under various loading tasks as measured by EMG. METHODS Ten healthy individuals (9 men, 1 woman; average age, 34 years +/- 10; average height, 175 cm +/- 7; average weight, 76 kg +/- 13) performed elbow flexion with the forearm in 1 of 3 positions (neutral, pronation, and supination) with 4 different loads (0, 22, 45, and 67 N). The elbow was flexed to 90 degrees as the volunteers performed 2 separate movements: (1) from full supination to neutral and (2) from full pronation to neutral using 4 different loads (0, 9, 18, and 27 N). Each movement started and ended in supination and pronation, respectively. Fine-wire EMG electrodes were placed in the brachioradialis, and kinematic data were collected using an electromagnetic motion analysis system. The EMG data were reported as a percentage of maximal voluntary isometric contraction and were ensemble averaged from 5 trials of each exercise condition for statistical analysis. RESULTS No difference in muscular activation was found during elbow flexion tasks in the 3 forearm positions. Significantly greater activation was found during concentric (23% maximal voluntary isometric contractions +/- 5% maximal voluntary isometric contractions) than during eccentric (11% maximal voluntary isometric contractions +/- 5% maximal voluntary isometric contractions) phases during elbow flexion. Brachioradialis mean activity during concentric pronation and eccentric supination with the heaviest loads 18 and 27 N was significantly greater than activity during concentric supination and eccentric pronation. CONCLUSIONS The greatest EMG activity recorded from the brachioradialis occurs during elbow flexion tasks regardless of forearm position indicating that the primary function of the brachioradialis is as a consistent elbow stabilizer during flexion tasks. During rotational tasks, more EMG activity was recorded during pronation compared with that during supination tasks indicating a secondary function of the brachioradialis as a pronator.

Proximal Sciatic Nerve Intraneural Ganglion Cyst

Intraneural ganglion cysts are nonneoplastic, mucinous cysts within the epineurium of peripheral nerves which usually involve the peroneal nerve at the knee. A 37-year-old female presented with progressive left buttock and posterior thigh pain. Magnetic resonance imaging revealed a sciatic nerve mass at the sacral notch which was subsequently revealed to be an intraneural ganglion cyst. An intraneural ganglion cyst confined to the proximal sciatic nerve has only been reported once prior to 2009.

Ultrasound imaging of the distal radioulnar joint: a new method to assess ulnar radial translation in forearm rotation.

A cross-sectional reliability study was conducted with 23 normal participants to establish normal values, and the repeatability and validity of distal radioulnar joint translation measurements using ultrasound imaging. Static transverse images of maximal supination, neutral and maximal pronation were examined to assess translation, using a method consistent with the rheumatoid arthritis subluxation ratio. Translation while gripping a 1 kg weight in supinated and pronated positions was then compared with non-gripping translation. There was significantly more ulnar radial translation found with pronation than supination, when compared with neutral. Gripping in pronation did not produce statistically significant changes in translation, whereas the changes produced by gripping in supination were significant. Internal consistency was deemed very high and the rheumatoid arthritis subluxation ratio values measured using ultrasound imaging were consistent with previously documented values measured by computerized tomography. This study demonstrated that translational movement of the distal radioulnar joint can be reliably detected in healthy participants using ultrasound imaging. This may reduce dependency on other imaging modalities to diagnose distal radioulnar joint instability. Level of Evidence: 2.

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 joints 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.

Ulnar neuropathy with abnormal non-localizing electrophysiology: Clinical, electrophysiological and ultrasound findings

OBJECTIVE To systematically study demographic, clinical, electrophysiological and nerve ultrasound characteristics of ulnar neuropathy with abnormal non-localizing electrophysiology (NL-UN) and further define the utility of ultrasound over and above the conventional electro-diagnostic approach. METHOD NL-UNs were prospectively identified from 113 consecutive referrals with suspected ulnar neuropathy. All received electro-diagnostic tests and ulnar nerve ultrasound. NL-UN severity was graded using clinical and electrophysiological scales. RESULTS In 64 of 113 referrals, an ulnar mono- neuropathy was confirmed by electrophysiology. Sixteen of these 64 (25%) had NL-UN, predominantly males (14 out of 16 patients) with severe or moderate clinical and electrophysiological ratings. Ultrasound showed focal ulnar neuropathy at the elbow in 13 out of 16, and diffuse ulnar nerve abnormality in three, and identified a likely or possible causative mechanism in 11. CONCLUSION A significant proportion (a quarter) of ulnar neuropathies with abnormal electrophysiology were NL-UN, of heterogeneous etiology; the majority were males with significant disability and axonal loss. Ultrasound had a significant role in localization and classification that facilitated management. SIGNIFICANCE To our knowledge, this is the first systematic prospective study that analyzes the demographic, clinical, electrophysiological and ultrasound characteristics of NL-UN in a routine clinical neurophysiology setting.

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 (µ = 52.1%, SD = 17.5%) than pronating (µ = 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

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

External neurolysis may result in early return of function in some muscle groups following brachial plexus surgery.

A retrospective chart review, of those individuals seen and operated on by the Multidisciplinary Brachial Plexus Clinic team at the University of Kentucky Chandler Medical Center, was undertaken to determine those individuals who had early return-of-function following surgery for BPI. Seven patients met our criteria, with four of them having substantial improvement of two or more points gained on the MRC rating scale, in one or more muscle groups within six to eight weeks after surgery. Those patients with return-of-function earlier than expected for axonal regrowth from nerve transfer or grafting, had evidence for continuity but no significant reinnervation before surgery in the muscle groups that improved. We theorize that this early improvement is related to a compression-induced dysfunction which inhibited reinnervation and was relieved by performing external neurolysis.