Estimation of anterior glenoid bone loss area using the ratio of bone defect length to the distance from posterior glenoid rim to the centre of the glenoid.

PURPOSE

Estimation of anterior glenoid bone loss is important for surgical decision-making. The purpose of this study was to describe a method for estimating anterior glenoid bone loss.

METHODS

Thirty-nine cadaveric glenoids were digitized to obtain glenoid geometry. Glenoid bare spot centre, arthroscopic centre, and centre of the inferior glenoid circle relative to the geometric centre were measured. To simulate anterior glenoid bone loss, imaginary sequential osteotomies were created 0°, 22.5°, and 45° to the superior-inferior line in a 3D digitizing programme. Per cent of anterior glenoid bone loss area was calculated as the percentage of defect area relative to the entire area of the glenoid. The relationship between area loss and ratio of bone defect length to the distance from posterior glenoid to various centres was determined.

RESULTS

As the ratio of bone defect length to the distance from posterior glenoid to all three centres increased, the per cent area of bone loss increased exponentially. The ratio using the inferior circle centre and arthroscopic centre was highly correlated to the actual glenoid bone loss in all osteotomies (R  > 0.90). The ratio using the centre of bare area had the lowest correlation. The ratio of defect length to distance from posterior glenoid to arthroscopic centre greater than 2.4 for 0° and 2.0 for 45° osteotomies results in bone loss area greater than 25 %. The bare area centre had the largest variation. Average bone loss was overestimated when the centre of bare spot was used compared to other centre locations.

CONCLUSION

Per cent of anterior glenoid bone loss can be estimated using the ratio of bone defect length to the distance from posterior glenoid rim to the centre of inferior glenoid circle or arthroscopic centre either preoperatively using 3D CT or arthroscopically which can be useful for determining surgical treatment.