Saturday, March 19, 2016

How important is the humeral head-shaft (neck-shaft) angle in anatomic shoulder arthroplasty?

The rotation of the humeral head does not alter radiographic evaluation of the head-shaft angle.

These authors measured 18 cadaveric humeri. Radiographs were taken with the specimens initially placed in a true anteroposterior position and then subsequently positioned with internal and external rotations of 10°, 20°, and 30°.

For the humerus in the neutral position, the head-shaft angle was 137° ± 4°. With the anatomic specimen positioned with increasing external and internal rotations, there was a maximum difference of only 2° compared with the value observed in the neutral position. The authors concluded that th head-shaft angle did not change significantly with varying degrees of humeral rotation.

Comment: We note that there is substantial variability in the anatomy of the arthritic humerus; the 'anatomic' location of the previously normal articular surface is difficult to determine.

Some surgeons have attached major importance to the humeral head-shaft (neck-shaft) angle in anatomic shoulder arthroplasty. A number of implant systems allow variability in the inclination of the head; however, the effect on the center of rotation of the articular surface seems small.

We use a simpler approach of placing the humeral head at an angle of 45 degrees with the medullary axis of the shaft in all cases, irrespective of the appearance of the preoperative pathoanatomy.

The humeral neck cut is always made at 45 degrees with the orthopedic axis, regardless of whether the preoperative films suggest that the neck-shaft angle is


or "varus"

or "valgus"
A typical example is shown below.



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