Abstract
Introduction
Humeral head subluxation in patients with cuff tear arthropathy (CTA) and in patients with primary arthrosis has been classified by Hamada and by Walch (type B). These classifications are based on 2D evaluation techniques (AP X-ray view, axial CT images). To our knowledge no 3D evaluation of the direction of humeral head subluxation has been described
Aim
To describe a reproducible 3D measuring technique to evaluate the direction of the humeral head subluxation in shoulder arthropathy
Methods
72 shoulders with arthrosis type B, 51 nonoperated CTA patients and 151 normal shoulders were 3D reconstructed using Mimics®. The center of rotation on the glenoid was determined using 3-matic® 6.1 with a published technique. Next best fitting sphere of the humeral head and its center was determined. Finally the direction of migration was quantified. The reproducibility of this technique was evaluated using inter- and intra-observer reliability.
Results
This technique showed a good inter and intra-observer reliability (p = 0.9). In patients with CTA the humeral head is subluxed in the superoposterior direction (p=0.006) (94°:X-axis; 94° Y-axis versus 92°:X-axis; 92° Y-axis) regardless the type of rotator cuff tear (anterosuperior or superoposterior). In patients with arthrosis type B, the humeral head is subluxed posteriorly (p=0.005) (112°: X-axis; 92° Y-axis versus 92°: X-axis; 92° Y-axis) regardless the type (B1 or B2).
Conclusion
With the use of this new developed reproducible measuring technique, the direction of humeral head migration can be evaluated in 3D. In CTA the direction of the migration is superoposterior and in arthrosis type B posteriorly regardless sub-classifications.
