Beyond guesswork: how accurate are surgeons at determining the degree of glenoid bone loss in instability surgery?

Abstract

Background: Accurate measurement of glenoid bone loss (GBL) is critical to preoperative planning in cases of recurrent shoulder instability. The concept of critical bone loss has been established with a value of GBL >13.5% being associated with higher failure rate following arthroscopic Bankart Repair. Advanced imaging, such as magnetic resonance imaging (MRI) scans, can be used to quantify GBL prior to surgery using the best-fit circle technique. Surgeons have traditionally relied on visual inspection of the MRI scan preoperatively or on visual inspection of the glenoid at the time of arthroscopy to determine whether GBL is present. The purpose of this study is to determine if 3 fellowship-trained shoulder surgeons could adequately quantify GBL without using best-fit circle measurements on MRI.

Methods: A retrospective review was performed which included 122 patients over an 8-year period that had an arthroscopic Bankart repair performed by 3 fellowship-trained surgeons. In all patients, preoperative MRI scans were retrospectively measured using best-fit circle technique to determine true GBL and compare that to the surgeons' preoperative and intraoperative estimation of GBL.

Results: GBL was correctly identified in only 36% (18/50) of patients when the preoperative best-fit circle measurements were not made. Critical bone loss was missed in 9.8% (12/122) of patients in the study group. The estimated mean bone loss in that group by visual inspection was 11.3% compared to 16% true bone loss measured on MRI. Even in the 18 patients with some identified bone loss prior to surgery, critical bone loss was missed in 6 patients when using visual inspection of the MRI or intraoperative inspection alone.

Conclusion: Simple visual inspection of glenoid images on MRI scan and visual inspection of the glenoid at the time of surgery are inaccurate in determining the true extent of GBL especially in cases of subtle bone deficiency. Preoperative planning is dependent on the exact degree of bone deficiency and measurement on the MRI scan using the best-fit circle technique is recommended in all cases of instability surgery.

Keywords: Bankart repair; Best fit circle; Critical bone loss; Glenoid bone loss; Remplissage; Traumatic anterior shoulder instability.

Figure 1

The normal glenoid. (A) The long axis of the glenoid is defined by the line A1B1. (B) The widest portion of the inferior glenoid is line C1D1, which is perpendicular to the line A1B1. (C) The intersection of lines A1B1 and C1D1 is labeled O1, and it represents the geometric Center of the inferior glenoid circle (D). Image courtesy of Chuang et al.

Figure 2

Calculating the glenoid track (GT) and and Hill-Sachs interval for determining on-track and off-track lesions, as described by Di Giacomo et al (A), a circle is superimposed over sagittal view of the glenoid, using the inferior border of the glenoid as a reference. The diameter of the best fit circle (D) and the width of the glenoid defect (d) are measured and entered into the above equation to calculate the GT. (B) The HSI is measured adding the width of the bony bridge between the insertion of the rotator cuff and the width of the HS lesion. HSI, Hill-Sachs interval. Image provided courtesy of Makhni et al.