This study is based on forty cases of osteochondroma observed at the Mayo Clinic from 1910 to 1943, inclusive. In each case, the diagnosis was verified by microseopic examination. A total of sixty-nine operations were performed on these patients. Nine of the patients are known to have died, and eight are known to have had one or more recurrences. In two cases, not all of the tumor was removed at the time of operation. In fifteen cases, there was no evidence of recurrence when the last follow-up data were obtained. No follow-up data were obtained in six cases.

In four of the forty patients, definite malignant changes were later found in the lesions. In sixteen patients (not included among the forty), microscopic examination revealed that the lesions were malignant at the time the patients were first operated upon at the Clinic.

From the foregoing review, the complexity of this problem is obvious. Chondromata of the pelvis must always be considered as serious surgical lesions. This is particularly true of those that are not well pedunculated, and of those in the more remote and inaccessible parts of the pelvis. When the tumor is purely cartilaginous in nature, the diagnosis may be extremely difficult. We have seen at least two cases in which the symptoms were referable to the hip, and, in spite of biopsies with negative findings, the symptoms continued and ultimately a chondroma was revealed. If the tumor is on the inner side of the innominate bone, particularly if it is within the true pelvis, its complete local removal is often difficult or impossible.

The idea is prevalent that these tumors may go from a benign to a malignant status, and in many cases this would seem to be true. However, in some of the cases described this change has not taken place, in spite of several recurrences and operations. In other instances, the presence of both benign and malignant regions in the same tumor may explain the apparent discrepancy.

The importance of complete surgical removal is evident to any one who has seen one or two of these patients in the late stage, when the tumor has reached a huge size, with a great deal of pain and discomfort, and there is little to offer in the way of relief. In those instances in which such removal cannot be accomplished by local excision, interinnomino-abdominal (hindquarter) amputations may be indicated.