Though the history and the specific changes indicate the tuberculous nature of the joint affection, the histological examination leaves no doubt that the joint tumor was a squamous-cell carcinoma. The sequence of events would seem to indicate that in childhood this patient had suffered from a disseminated caseous glandular tuberculosis which eventuated in tuberculosis of the knee with chronic fistula formation. The extent of the influence of heliotherapy and roentgenotherapy on the development of the carcinoma cannot be appraised, but it is certain that under their influence the epithelium grew rapidly along the sinus tracts to the very center of the joint. This led to the formation of small islands of squamous epithelium, which under the constant irritation of the purulent secretion developed into a malignant tumor. Since the tumor arose from healthy tissue secondarily stimulated to malignancy by locally determined factors, it must be differentiated from a primary as well as from a metastatic tumor.

The continued effect of repeated heliotherapy and x-ray irradiation with the chronic irritation of tuberculous fistulae may account for malignant degeneration such as is seen in carcinomatous degeneration of skin lupus after roentgenotherapy. Beck, Küttner, Marsch, and others have suggested a possible relationship between the appearance of joint sarcoma and previous x-ray treatment of joint tuberculosis.

The clinical experience in this-case points to the conclusion that resection should be undertaken as soon as growth has ceased in all cases of chronic pyogenic joint disease with fistula formation. In older people with extensive involvement or in those in whom there is unsatisfactory healing, amputation should be undertaken at the very outset.