Friday, February 28, 2014

Glenoid component fixation - does perforation of the bone matter?

Glenoid perforation does not affect the short-term outcomes of pegged all-polyethylene implants in total shoulder arthroplasty.

Because the bone of the glenoid may be thin due to erosion from arthritis or due to the small size of the patient, there has been some concern about the effect of penetration of the glenoid bone by the pegs used for fixation of the component in the conduct of total shoulder arthroplasty.

These authors identified 18 patients with known intraoperative glenoid perforations (identified using a 'sounder') compared them to 34 patients without penetration matched by age, gender, diagnosis, and arm dominance during the same period. Patients were evaluated with multiple outcome scores. Radiographs were evaluated for glenoid lucency immediately postoperatively and at final follow-up.

They found that the presence and number of perforations were not related to the American Shoulder and Elbow Surgeons score (P = .549), Constant score (P = .154), or radiographic lucency grade (P = .584) at an average of 2 years of follow-up.

Glenoid morphology was noted to have an effect on Constant scores. B2 glenoids showed worse scores compared with A1s. B1 glenoids showed lower scores than A2s, but glenoid morphology did not affect the presence of perforation.

Comment: The chances of perforation obviously depend on the distribution and length of the holes in relation to the amount of bone present where the holes are drilled.

We use the glenoid component shown below, similar in many respects to that used in this study.

One or more of the three peripheral pegs not infrequently penetrate slightly from the bone in smaller patients and in patients with glenoid erosion. In that these pegs are largely for rotational stability, we have no been concerned about penetration except that when the hole for the peg exits the bone one must be careful in cementing the hole to avoid extrusion of cement. This is especially important for the superior hole which is close to the suprascapular nerve. 
The central peg hole commonly penetrates the bone. Since it is not cemented, extrusion of cement is not a concern with this hole. There are no structures at risk from penetration of this peg. The only possible concern (which we have not encountered in thousands of total shoulder arthroplasties) would be if there was insufficient bone to grasp the flutes of the peg.
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