Documentation of dislocation arthropathy of the shoulder "area index": a better method to objectify the humeral osteophyte?

We suggest a method to validate the Samilson-Prieto classification system of dislocation arthropathy of the shoulder. Based on a mean standard sagital measure of the humeral head, we calculate an area index for the humeral osteophyte. The application of this method is done on a previous published series of 56 shoulders with a follow-up time of 15 years minimum after surgery with the Bankart or Bristow repairs. This technique of evaluation showed that the Bristow shoulders had a higher mean area index value on all radiological projections compared to the Bankart shoulders. The highest index was found on AP radiogrammes angulated 45 degrees from above with the arm in neutral rotation (subcoracoid view) followed by the AP view in inward rotation. Our observations indicate that the humeral osteophyte mostly has its largest size at 4 to 5 o'clock position, as visualized with its greatest index on the subcoracoid view. Mild arthropathy, according to Samilson-Prieto, had a mean osteophyte area index of 3.7 (standard deviation, 3.4) on the AP inward rotation view. The corresponding figures for moderate arthropathy were 10.6 (standard deviation, 13.3) and 30.3 for severe (standard deviation, 24.1), respectively. The use of this index, based on the AP view in inward and outward rotation, will make future comparisons between different series of patients more reliable than using just the Samilson-Prieto classification. The radiological change over time should also be more appropriately described. Furthermore, this paper emphasizes the importance of using the same radiological views when dislocation arthropathy of the shoulder is documented.