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.