Absorption of the bone fragment in shoulders with bony Bankart lesions caused by recurrent anterior dislocations or subluxations: when does it occur?

Background: Recently, bony defects of the glenoid in patients with traumatic anterior shoulder instability have been increasingly noticed. The bone fragment of a bony Bankart lesion is often utilized for Bankart repair, but the fragment is at times smaller than the glenoid defect. The reason for this mismatch in size is unknown.

Hypothesis: The bone fragment of a bony Bankart lesion might gradually be absorbed over time.

Study Design: Case series; Level of evidence, 4.

Methods: A total of 163 shoulders were prospectively examined by computed tomography. In shoulders with bony Bankart lesions, glenoid defects and bone fragment absorption were assessed, and findings were compared with the time elapsed after the primary traumatic episode. When a bone fragment was not detected despite loss of the normal contour of the glenoid rim, the findings were classified as erosions if the rim appeared round and slightly compressed and classified as complete bone fragment absorption if the rim appeared straight and sharp.

Results: There were no glenoid defects in 55 shoulders, erosions in 16 shoulders, and glenoid defects in 92 shoulders. The size of the glenoid defect was 0% to 10% in 15 shoulders, 10% to 20% in 44, 20% to 30% in 26, 30% to 40% in 6, and 40% to 50% in 1. The average defect size was 7.9% in shoulders scanned at <1 year, 10.7% between 1 and 2 years, and 11.3% at >2 years, indicating no relationship with time after trauma. Regarding bone fragment absorption, all 92 shoulders with glenoid defects showed absorption to some extent. The extent of absorption was <50% in 32 shoulders, >50% in 45, and 100% in 15. The average extent of absorption was 51.9% in shoulders scanned at <1 year, 65.3% between 1 and 2 years, and 70.0% at >2 years, indicating a significant relationship with time after trauma.

Conclusion: Bone fragment absorption was seen in all of the shoulders with bony Bankart lesions. Most bone fragments showed severe absorption within 1 year after the primary traumatic episode. Before arthroscopic Bankart repair, not only glenoid defects but also bone fragment absorption should be assessed.