The inverted pear glenoid: an indicator of significant glenoid bone loss

Abstract

Purpose The purpose of this study was to determine the amount of glenoid bone loss required to produce an inverted pear glenoid. Type of study Two-part anatomic study involving live subjects and cadaveric specimens. Methods From June 2000 to April 2002, 53 patients (mean age, 30 ± 13 years) underwent arthroscopic evaluation and treatment with a diagnosis of anterior instability by the senior author (S.S.B.). Each of these patients underwent a 3-portal diagnostic arthroscopy to determine the morphology of the glenoid. Glenoids were classified as either inverted pear or non-inverted pear glenoids based on the visual appearance. The amount of glenoid bone loss was then quantified arthroscopically using a validated methodology. In addition, 6 fresh-frozen cadaveric specimens (mean age, 74.1 ± 7.4 years) were dissected and evaluated to determine the minimum amount of bone loss required to produce an inverted pear glenoid. Results Forty-two patients were classified as having non-inverted pear glenoids and 11 patients were classified as having inverted pear glenoids. The mean amount of bone loss anteriorly was significantly more ( P < .000006) in the inverted pear glenoid group (mean, 8.6 mm; range, 6 to 12 mm) than the non-inverted pear glenoid group (mean, 1.5 mm; range, 0 to 3.0 mm). The percentage of loss of glenoid width was also significantly different (inverted pear mean, 36%; range, 25% to 45% versus non-inverted pear mean, 6.2%; range, 0% to 12.5%; P < .000006). The mean amount of bone loss required in cadaveric specimens to convert a normal pear-shaped glenoid into an inverted pear glenoid was 7.5 mm (range, 6.5 to 9.0 mm), representing 28.8% of the glenoid width (range, 27% to 30%). Conclusions The results of this study show that the majority of patients with the diagnosis of anterior instability show some bone loss anteriorly. However, the inverted pear glenoid represents a significant amount of bone loss, at least 25% to 27% of the width of the inferior glenoid. In patients with an inverted pear glenoid, a bone grafting procedure to restore the normal articular arc of the glenoid should be strongly considered to re-establish normal stability to the shoulder.