3-D CT Scans Detect Glenoid Shifts Earlier
Glenoid component loosening after total shoulder arthroplasty is not easy to predict. We looked at 3-D computed tomography (CT) to see if could identify changes that standard imaging methods could not.
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One of the most common complications following total shoulder arthroplasty (TSA) is glenoid component loosening. Yet routine imaging can be insufficient to predict when loosening will occur and to determine a precise and accurate component position over time. To solve this problem, we tested whether using 3-D computed tomography (CT) analysis would identify changes in glenoid component position over time that standard imaging methods cannot detect.
We enrolled 41 patients who had undergone TSA with a polyethylene anchor peg glenoid component for sequential CT scanning and analysis. Each enrollee had a preoperative study (CT1), an early postoperative study within three months of surgery (CT2), and a postoperative study performed at a minimum of two years after surgery (CT3) (see figure). They also had routine plain radiographs and Penn Shoulder Scores at the two-year follow-up visit.
We performed the postoperative CTs using metal artifact reduction techniques. We used a custom 3-D image analysis software to detect the location of the glenoid and humeral head components based on four metal markers embedded in the pegs of the glenoid component and a volumetric center fit to the humeral head component. This technique allowed us to determine glenoid component version, inclination and joint line position. It also allowed us to determine humeral head alignment.
We measured humeral-glenoid alignment and humeral-scapular alignment in the anteroposterior and superoinferior dimensions based on the relationship of the center of the humeral head to the glenoid and scapular planes, respectively. On the postoperative CT scans, we also assessed backside seating of the glenoid component and presence of peg radiolucencies, including evidence of osteolysis versus bone integration of the central anchor peg. We compared those CT scans to findings on plain radiographs.
We found that 27 percent of patients (11 of 41) showed evidence of glenoid component shift, which we defined as a change in component position of 5 degrees or more in version and/or inclination from CT2 to CT3. Importantly, the patients’ plain radiographs showed no obvious evidence of component shift, and patients with and without component shift did not have significantly different Penn Shoulder Scores.
Our findings demonstrate that glenoid component shift can occur without obvious implant loosening at short-term follow-up and suggest that component deformation or bone remodeling may occur over time. Improved backside seating of the glenoid component can also occur over time in stable implants due to bone remodeling. While radiostereometric analysis studies have shown evidence of component shift over time, they cannot be used to assess for bony integration of the implant. We believe follow-up investigations using larger patient cohorts are needed to clarify our findings and determine their long-term clinical impact.