Subacromial impingement syndrome is the most common shoulder disorder. Abnormal superior translation of the humeral head is believed to be a major cause of this pathology. The first purpose of the study was to examine the effects of suprascapular nerve block on superior translation of the humeral head and scapular upward rotation during dynamic shoulder elevation. The secondary purpose was to assess muscle activation patterns during these motions. Twenty healthy subjects participated in the study. Using fluoroscopy and electromyography, humeral head translation and muscle activation were measured before and after a suprascapular nerve block. The humeral head was superiorly located at 60 degrees of humeral elevation, and the scapula was more upwardly rotated from 30 to 90 degrees of humeral elevation after the block. The differences were observed during midrange of motion. In addition, the deltoid muscle group demonstrated increased muscle activation after the nerve block. The study’s results showed a compensatory increase in humeral head translation, scapular upward rotation, and deltoid muscle activation due to the nerve block. These outcomes suggest that increasing muscular strength and endurance of the supraspinatus and infraspinatus muscles could prevent any increased superior humeral head translation. This may be beneficial in reducing shoulder impingement or rotator cuff tears over time.
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Humeral Head Translation After a Suprascapular Nerve Block
Jun G. San Juan, Peter Kosek, and Andrew R. Karduna
Individuals With Knee Osteoarthritis Demonstrate Interlimb Asymmetry in Pedaling Power During Stationary Cycling
Harsh H. Buddhadev, Daniel L. Crisafulli, David N. Suprak, and Jun G. San Juan
Cycling is commonly prescribed for physical rehabilitation of individuals with knee osteoarthritis (OA). Despite the known therapeutic benefits, no research has examined interlimb symmetry of power output during cycling in these individuals. We investigated the effects of external workload and cadence on interlimb symmetry of crank power output in individuals with knee OA versus healthy controls. A total of 12 older participants with knee OA and 12 healthy sex- and age-matched controls were recruited. Participants performed 2-minute bouts of stationary cycling at 4 workload-cadence conditions (75 W at 60 rpm, 75 W at 90 rpm, 100 W at 60 rpm, and 100 W at 90 rpm). Power output contribution of each limb toward total crank power output was computed over 60 crank cycles from the effective component of pedal force, which was perpendicular to the crank arm. Across the workload-cadence conditions, the knee OA group generated significantly higher power output with the severely affected leg compared with the less affected leg (10% difference; P = .02). Healthy controls did not show interlimb asymmetry in power output (0.1% difference; P > .99). For both groups, interlimb asymmetry was unaffected by external workload and cadence. Our results indicate that individuals with knee OA demonstrate interlimb asymmetry in crank power output during stationary cycling.
Effects of Changing Hip Position on Scapular Kinematics
Sarah E. Schlittler, David N. Suprak, Lorrie R. Brilla, and Jun G. San Juan
The effects of hip position and posture on scapular kinematics have yet to be explored. The purpose of this study was to measure differences in scapular kinematics with changing hip position. Scapular kinematics were measured during scapular plane humeral elevation. Twenty-four subjects were required to elevate the dominant arm up to 120° in the following randomized conditions: standing, seated, seated ipsilateral hip flexion, and seated contralateral hip flexion. Two-way analyses of variance were used to evaluate effects of shoulder elevation and hip position on scapular upward rotation, posterior tilt (PT), and external rotation. For external rotation, there was no significant interaction (P = .714) and no main effect of elevation (P = .618) or condition (P = .390). For PT, there was no significant interaction (P = .693) but significant main effects of elevation (P < .001) and condition (P < .001), with the greatest PT in standing. For upward rotation, there was no significant interaction (P = .698), a significant main effect of elevation (P < .001), and no significant effect of condition (P = .726). The effect on PT may not be clinically significant. These results may serve as a baseline measurement of healthy scapular kinematics across hip positions.