These authors aimed to identify arm positions and maneuvers that may risk causing nerve injury during shoulder joint replacement arthroplasty.
They measured the tensions in the cords of the brachial plexuses of 6 human cadavers while the limb was placed in different arm positions during shoulder arthroplasty.
They measured the tensions in the cords of the brachial plexuses of 6 human cadavers while the limb was placed in different arm positions during shoulder arthroplasty.
The four key findings were:
1. Strain in the cords of the brachial plexus sufficient to cause neurologic injury (10%) occurs during shoulder abduction greater than 70°, the combination of 70° shoulder abduction with external rotation, and the combination of shoulder external rotation greater than 60° with extension greater than 50°.
2. During shoulder hemiarthroplasty, tensions in the medial cord of the brachial plexus increased compared with baseline tension during sounder insertion to size the medullary canal, humeral head prosthesis implantation and impaction, and retractor removal and humeral head reduction.
3. Supporting the upper limb from under the elbow reduced medial cord tensions during these surgical steps.
Comment: There is no question that the nerves of the upper extremity experience major and unaccustomed tension during shoulder arthroplasty - tension sufficient to disrupt their function either briefly or for a long time. This is especially the case for shoulders that have been stiff for a protracted period before surgery. Retractors, extreme positions while removing osteophytes or seeking to optimize glenoid exposure can further increase the tension on the nerves. Medications, such as methotrexate, or diagnoses, such as diabetes, or additional interventions, such a brachial plexus block injections, can increase the risk of nerve injury.
In all cases, but especially in those with increased risk, we seek to minimize the amount of time the shoulder is held in positions other than the neutral position, in which position tension on the nerves is minimized.
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