What is the clinical importance of radiographic changes around the humeral component in anatomic shoulder arthroplasty? A minimum 4-year follow-up study.

BACKGROUND

While stress shielding and adaptive bone changes around the humeral component are often observed after shoulder arthroplasty, the potential causative factors and clinical significance of these findings at midterm follow-up have not been well elucidated. The purpose of this study was to investigate the frequency, patterns, and clinical significance of radiographic findings around the humeral component of total shoulder arthroplasty (TSA) and hemiarthroplasty (HA) at minimum 4-year follow-up.

METHODS

The 6-week and minimum 4-year radiographs of patients who underwent HA and TSA were evaluated for filling ratios, changes in the humeral bone surrounding the component, and component shift or subsidence. All procedures were performed using a traditional-length, smooth stem fixed by impaction autografting with the goal of secure fixation with a relatively low filling ratio. Radiographs after TSA were evaluated for high-grade radiolucencies around the glenoid component. The clinical outcomes of interest were revision for humeral fixation failure and Simple Shoulder Test score.

RESULTS

A total of 170 patients met the study criteria (91 TSA and 79 HA). The mean radiographic and clinical follow-up was 7.0 years [interquartile range, 5.3-8.6 years]. No patients were revised for loose humeral components during the study period. For both HA and TSA, the most common zones of cortical thinning or resorption involved the medial calcar, greater tuberosity, and lateral humerus diaphysis. The mean metaphyseal filling ratio was higher in patients with bone changes in ≥3 zones (P < .001) and resorption of the calcar (P = .051). The frequency and degree of bone changes around the humeral component were higher in TSA patients with high-grade radiolucencies around the glenoid component. These findings in TSA patients with high-grade radiolucencies around the glenoid component had a stronger correlation with inferior Simple Shoulder Test scores than in patients who did not have high-grade radiolucencies around the glenoid component.

CONCLUSIONS

At minimum 4-year and mean 7-year follow-up, greater bone changes around the humeral component were associated with higher metaphyseal filling ratios. The association of glenoid component radiolucency with the degree and clinical impact of these bone changes should be considered when interpreting midterm radiographs after TSA and may represent the effects of other processes - such as osteolytic reaction to particulate debris - in addition to stress shielding.