Abstract
The concept of non-anatomic reversed arthroplasty is becoming increasingly popular. The design medializes and stabilizes the center of rotation, and lowers the humerus relative to the acromion, and lengthens the deltoid muscle up to 18%. Such a surgically created global distraction of muscles is likely to affect nervous structures. When nerves are stretched up to 5–10%, axonal transport and nerve conduction starts to be impaired. At 8% of elongation, venous blood flow starts to diminish and at 15% all circulation in and out of the nerve is obstructed. [1] To understand nerve dynamics following reversed arthroplasty, we investigated nerve strain and excursion in a cadaver model.
In a formalin-embalmed female cadaver specimen, the brachial plexus en peripheral upper limb nerves were carefully dissected and injected with an iodine containing contrast medium. At the same time 1.2 mm-diameter leaded markers were implanted at topographically crucial via points for later enhanced recognition on CT reconstructions. After the first session of CT scanning a plastic replica of the Delta reversed shoulder prosthesis® was surgically placed followed by re-injection of the plexus with the same solution. The preoperative and the postoperative specimen were studied using a helical CT scan with a 0,5 mm slice increment. The Mimics® (Materialise NV, Belgium) software package was used for visualization and segmentation of CT images and 3D rendering of the brachial plexus and peripheral nerves.
After surgery, there was an average increase in nerve strain below physiologically relevant amplitudes. In a few local segments of the brachial plexus an increase in nerve strain exceeding 5–10 % was calculated. The largest increase in strain (up to 19%) was observed in a segment of the medial cord. These results suggest there might be a clinically relevant increase in nerve strain following reversed shoulder arthroplasty.
Correspondence should be addressed to EORS Secretariat Mag. Gerlinde M. Jahn, c/o Vienna Medical Academy, Alserstrasse 4, 1090 Vienna, Austria. Fax: +43-1-4078274. Email: eors@medacad.org
1 Ogata, K. and Naito, M. Blood flow of peripheral nerve effects of dissection, stretching and compression. J Hand Surg [Br].11(1):10–4, 1986. Google Scholar
