Tuesday, February 13, 2018

Glenoid component loosening

Sequential 3-dimensional computed tomography analysis of implant position following total shoulder arthroplasty

These authors used  3-dimensional computed tomography (CT) to evaluate glenoid component position over time in 20 patients with minimum 2-year follow-up. They obtained scans (1) before surgery, (2) within two weeks after surgery and (3) at a minimum of 2-years after surgery.

Glenoids with evidence of component shift and/or central peg osteolysis were considered at risk of loosening. 

Of the patients, 7 (35%) showed evidence of glenoid components at risk of loosening, 6 with component shift (3 with increased inclination alone, 1 with increased retroversion alone, and 2 with both increased inclination and retroversion). 

Significantly more patients with glenoid component shift had central peg osteolysis compared with those without shift (83% vs 7%, P = .002).

Comment: It is surely of concern that more than one third of these patients having total shoulder arthroplasty were characterized as being at risk for glenoid component loosening.

Some of the findings in the Table S1 were interesting:
Type A glenoids tended to be at increased risk for loosening:
    Of 11 type A glenoids, 4 were at risk for loosening.
    Of 7 type B or C glenoids, only 1 was at risk for loosening.

Posteriorly augmented glenoid components tended to be at increased risk for loosening:
    Of 14 standard glenoid components, 4 were at risk for loosening
    Of 6 posteriorly augmented glenoid components, 3 were at risk for loosening.

Retroverted glenoids tended to at lower risk for loosening.

While these differences did not attain statistical significance with the small number of cases, these trends merit further observation in that they challenge some of the commonly held tenets.

The increases in inclination noted are of interest as well. Perhaps they were related to cuff failure allowing the humeral head to migrate upwards resulting in the rocking horse phenomenon. Loading of the superior glenoid can also result from superior positioning of the humeral component.

Here are some of their findings as seen on plain films. Note the narrowed acromiohumeral interval on the 'at risk glenoid' on the left.

Finally, this study requires each patient to have three CT scans, imaging that comes at a cost in terms of dollars and in terms of radiation exposure to the patient.

The reader may also be interested in these posts:

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