Itoi and colleagues measured how anteroinferior glenoid rim defects of increasing size change stability and external rotation after Bankart repair.
Cadaveric study of 10 fresh‑frozen shoulders (mean donor age 79), each tested under 11 sequential conditions from intact capsule to a 46% glenoid defect.
Methods
Model
10 fresh‑frozen cadaveric shoulders
Mean donor age 79
All muscles removed, capsule preserved
Defect templates designed from the average glenoid shape of 16 dried scapulae
Constructs
Intact capsule
Simulated Bankart lesion
Bankart repair
Anteroinferior defect 9% of glenoid length (mean 2.8 mm)
Defect 21% of glenoid length (mean 6.8 mm)
Defect 34% of glenoid length (mean 10.8 mm)
Defect 46% of glenoid length (mean 14.8 mm)
Capsule repaired again after each defect
Loading
10 mm anteroinferior humeral head translation
Abduction with external rotation
Abduction with internal rotation
Constant 50 N axial force to center the head
Custom multiaxis machine with a six‑degree‑of‑freedom load cell
Outcome measures
Peak force to translate the humeral head at each condition
Range of external rotation
Key Findings
In abduction and internal rotation, repaired shoulders lost stability as the defect grew (p < 0.0001), with translation force significantly below that of shoulders without a defect once the width reached 21% of glenoid length (mean 6.8 mm).
In abduction and external rotation, stability after repair showed no significant change at any defect size (p = 0.106).
External rotation after repair was significantly reduced with defects of 21% or more (p < 0.0001), which the authors attributed to capsular pretensioning from closing the gap to the rim.
External rotation was lost at an average of 25° per centimeter of defect width.
In abduction and neutral rotation, 2 of 10 shoulders subluxated anteriorly after the 9% osteotomy and 5 after the 21% osteotomy, and all 10 were grossly unstable after the 34% osteotomy (8 dislocated, 2 subluxated).
By the conventional area estimate the critical 21% defect covered about one‑fifth of the glenoid surface, yet to the authors it looked like nearly one‑third.
Board pearl
Itoi's critical defect is a width measured against glenoid length (21%, mean 6.8 mm in these specimens), and it amounts to only about one‑fifth of the glenoid surface.
Authors' conclusion
An osseous defect with a width that is at least 21 percent of the glenoid length may cause instability and limit the range of motion of the shoulder after Bankart repair.
Itoi and colleagues measured how anteroinferior glenoid rim defects of increasing size change stability and external rotation after Bankart repair.
Cadaveric study of 10 fresh‑frozen shoulders (mean donor age 79), each tested under 11 sequential conditions from intact capsule to a 46% glenoid defect.
Methods
Model
10 fresh‑frozen cadaveric shoulders
Mean donor age 79
All muscles removed, capsule preserved
Defect templates designed from the average glenoid shape of 16 dried scapulae
Constructs
Intact capsule
Simulated Bankart lesion
Bankart repair
Anteroinferior defect 9% of glenoid length (mean 2.8 mm)
Defect 21% of glenoid length (mean 6.8 mm)
Defect 34% of glenoid length (mean 10.8 mm)
Defect 46% of glenoid length (mean 14.8 mm)
Capsule repaired again after each defect
Loading
10 mm anteroinferior humeral head translation
Abduction with external rotation
Abduction with internal rotation
Constant 50 N axial force to center the head
Custom multiaxis machine with a six‑degree‑of‑freedom load cell
Outcome measures
Peak force to translate the humeral head at each condition
Range of external rotation
Key Findings
In abduction and internal rotation, repaired shoulders lost stability as the defect grew (p < 0.0001), with translation force significantly below that of shoulders without a defect once the width reached 21% of glenoid length (mean 6.8 mm).
In abduction and external rotation, stability after repair showed no significant change at any defect size (p = 0.106).
External rotation after repair was significantly reduced with defects of 21% or more (p < 0.0001), which the authors attributed to capsular pretensioning from closing the gap to the rim.
External rotation was lost at an average of 25° per centimeter of defect width.
In abduction and neutral rotation, 2 of 10 shoulders subluxated anteriorly after the 9% osteotomy and 5 after the 21% osteotomy, and all 10 were grossly unstable after the 34% osteotomy (8 dislocated, 2 subluxated).
By the conventional area estimate the critical 21% defect covered about one‑fifth of the glenoid surface, yet to the authors it looked like nearly one‑third.
Board pearl
Itoi's critical defect is a width measured against glenoid length (21%, mean 6.8 mm in these specimens), and it amounts to only about one‑fifth of the glenoid surface.
Authors' conclusion
An osseous defect with a width that is at least 21 percent of the glenoid length may cause instability and limit the range of motion of the shoulder after Bankart repair.