CT MEASUREMENT OF GLENOID EROSION IN ARTHRITIS

We studied serial CT scans of 45 arthritic shoulders (34 rheumatoid, 1 1 osteoarthritic) and 19 normal shoulders, making measurements at thre e levels on axial images. The maximum anteroposterior diameter of the glenoid was increased in rheumatoid glenoids at the upper and middle l evels by 6 mm and in osteoarthritic glenoids at all levels by 5 to 8 m m as compared with normal. In rheumatoid cases, nearly half the availa ble surface of the glenoid was of unsupported bone, mainly posteriorly at the upper and middle levels. In osteoarthritic glenoids, the best supported bone was anterior at the upper level and central at the midd le and lower levels. The depth of the rheumatoid glenoid was reduced b y a mean of 6 mm at the upper and middle levels and by 3 mm at the low er level. This inclined the surface of the glenoid superiorly. The dep th at the middle level in osteoarthritis was reduced by a mean of 5 mm , suggesting central protrusion. Osteoarthritic glenoids were retrover ted by a mean of 12.5 degrees, but of rheumatoid glenoids two-thirds w ere retroverted (mean 15.1 degrees) and one-third anteverted (mean 8.2 degrees). Our findings have important implications for the planning a nd placement of the glenoid component of total shoulder replacements; CT can provide useful information.