Narrow Results

The objectives of this study were two-fold. Firstly we wished to investigate the segmental anatomy, geometry and gross innervation patterns of selected shoulder joint musculature (pectoralis major, latissimus dorsi and deltoid) to establish if these muscles could be anatomically subdivided according to predetermined criteria. We then wished to use this information to help determine if a segments activation pattern was reliant on an efficient line of action and a large moment arm for the intended movement. Surface electromyography was used for this purpose whilst manipulating the independent variable of contraction intensity (% MVC) during two shoulder joint flexion tasks.

For the anatomical portion of the study the dissection of ten cadaveric shoulders revealed the deltoid to consist of seven segments whilst the pectoralis major and the latissimus dorsi were both ascribed six segments according to predetermined anatomical/functional criteria. Primary nerve branching was evident in each muscle but no apparent relationship existed between the designated anatomical segments and the primary nerve branches. Differences were evident in the geometry of each segment in regard to moment arms and orientations of each segments line of action.

The functional portion of this study, which utilized miniature bipolar surface electrodes during the performance of a static shoulder joint flexion task at 75% and 25% MVC, showed significant differences (p<0.05) in the activation patterns of active segments between the two tasks. Specifically, a "drop out" of segments with smaller flexion moment arms and more diverging lines of action in comparison to the movement plane was evident for all subjects in the 25% MVC task in comparison to the 75% MVC task.

The purpose of the current study was to determine if the classically described triphasic EMG burst was applicable in describing the EMG patterns across the breadth of three large radiate muscles during the production of a rapid shoulder joint movement. Miniature (6.5 mm inter-electrode distance) bipolar surface electrodes were placed across the breadth of the pectoralis major (6 off), latissimus dorsi (6 off) and the deltoid (7 off). Subjects performed a series of rapid shoulder joint adduction movements (<400 ms) against the resistance of a free weight and pulley apparatus whilst seated in an experimental chair. EMG data sampled from the multiple recording sites of the three muscles identified four different types of EMG waveforms. This was based on the presence, or absence, of multiple bursts, the length of each burst and the level of the silent period between bursts from the same segment of a muscle. The four bursts included a one-burst pattern, a one-continuous burst pattern, a two-continuous burst pattern and a two non-continuous burst pattern. Upon further analysis it was established that a relationship existed between the type of burst displayed by a segment and the functional role of that segment (prime mover, synergist, primary or secondary antagonist), hence a uniform type of burst pattern was not apparent across the breadth of the agonist (pectoralis major and latissimus dorsi) and antagonist (deltoid) muscles. It was evident that the triphasic EMG burst was most applicable for the EMG patterns arising from the prime mover segments of the pectoralis major and the latissimus dorsi and the primary antagonist segment of the deltoid. In conclusion, these results suggest that caution is warranted if stating that popular motor control theories^{10, 11} based on EMG patterns produced by small agonist and antagonist muscles during rapid limb movement, apply to all segments of large radiate muscles.

The importance of core stabilization exercises for extremities associated with dynamic spinal stabilization prior to movement has been demonstrated. However, no previous studies have investigated the muscle-coordinated effects on the upper trapezius (UT), anterior deltoid (AD), pectoralis major (PM), bilateral transverse abdominis (TrA), bilateral internal oblique (IO), and bilateral external oblique (EO) in healthy adults. The purpose of this study was to compare the effects of the dynamic neuromuscular stabilization (DNS) breathing technique and the abdominal bracing (AB) technique on UT, AD, PM, bilateral IO/TrA, and bilateral EO motor control in healthy participants during horizontal shoulder adduction. Thirty-six participants, eight of whom were female, were randomized into an AB and a DNS group and performed horizontal shoulder adduction with loads (8 and 17 lb). The clinical outcomes were UT, AD, and PM muscle activation and TrA/IO and EO muscle activation. Paired t-tests were used to analyze electromyography (EMG) data to determine statistically significant differences in muscle activity between the two techniques. For the EMG analysis, the maximal voluntary isometric contraction was measured for normalization and then divided by the EMG amplitude value. The results showed that UT, AD, and PM muscle amplitudes were lower and TrA/IO and EO muscle amplitudes were higher with DNS than with AB ($P<0.05$). Our findings provide clinical evidence that core exercise with DNS is more effective in lessening UT, AD, and PM muscle activation and improving bilateral TrA/IO motor control than with AB.

One of the rarer manifestations of constriction band syndrome (CBS) is peripheral nerve palsy. We report a 6-year-old child presenting with motor deficits of the median, ulnar and radial nerves and atrophy of the biceps and brachialis atrophy due to CBS. We were unable to find any similar reports in the literature. He had a constriction ring at the upper arm that had undergone multiple z-plasty by another surgeon. On examination, he had medical research council (MRC) grade 1 elbow flexion, weak flexion of fingers and absent extension of fingers and wrist. We used a pedicled pectoralis major myocutaneous flap to restore elbow flexion and the patient achieved M4 flexion of the elbow.

Level of Evidence: Level V (Therapeutic)

Spontaneous neuronal recovery is an expected phenomenon in brachial plexus palsy patients. However, the spontaneous recovery owing to retrograde regeneration is an evolving phenomenon with dearth of adequate research on it. Pectoralis major contraction on stimulation of median nerve (in the arm) is an unexpected phenomenon, in the absence of any anomalous communication and with distal coaptation site of intraplexal nerve repair. We presumably attribute it to the retrograde regrowth of axons. The case described supports our hypothesis.

Level of Evidence: Level V (Therapeutic)