Abstract (English)

Objectives

Osteoid osteoma (OO), described in 1935 by Jaffe, is a well-known disease entity, although its study has often shown disconcertingly peculiarities. Universally accepted as a benign bone tumor, some authors have expressed their doubts on the neoplastic nature of the disease. This work will present how current knowledge on OO and stress fractures (SF) has lead to question the neoplastic origin of OO and to propose a new etiopathogenic theory, which clarifies many of OO traits.

Methods

Based on two personal clinical cases for which the suspected diagnoses were OO and stress fracture (SF), we started studying the similarities between both lesions and found striking associations in some scientific publications.Further study of SF pathogenesis and its biomechanical aspects led us to consider the possibility of a concentric accumulation of overload-induced microcracks or microfractures, which resulted in a new hypothesis on OO formation. We conducted a thorough review of scientific journals on OO, evaluating all its related aspects.

Results

Abundant evidence has led us to rebut that OO is a neoplasm, and to propose a new etiological theory. As in the case of overload lesions, the alleged tumor starts forming from a microcrack or microfracture. However, with sustained mechanical stress and accumulation of new microcracks, instead of propagating or extending bidimensionally with a “planar” or linear topography, as SF do, this microfracture extends concentrically like a sphere. Around the created bone defect a repair process develops, which attempts to heal the fracture. The “activated” osteoblasts fill that spherical gap producing osteoid tissue in a concentric fashion. The biomechanical conditions of the lesion lead to its chronification, without growing, thus forming the OO nidus.

We can then explain many of the singularities which had not been clear until now, such as the presence of bilateral symmetrical OOs, post-traumatic OOs, spontaneous remission in some OO cases, or OO relapse years after an en bloc resection, which are not in fact new tumors but rather new spherical SFs. We also confirmed that OOs located in the upper limbs nearly always occur in the right or dominant side and in patients older than those with OOs in the lower limbs (difference averages 12 years), as happens with SFs.

OO’s consistent histology is also analyzed, as well as prostaglandin-induced pain, innervation and other aspects which point to the similarities between both lesions, OO and SF.

Conclusions

When Jaffe proposed his neoplasm theory for OO, very little was known about stress fractures. The new theory presented here implies a mentality change which may be difficult to assimilate, but this work provides enough evidence to support said change.

An OO should no longer be considered a tumor, but a specific type of overload fracture, in a spherical pattern, which becomes chronic and causes pain. Although surgical treatment will continue to be indicated for many cases, it will no longer involve the urgency and the connotations associated with tumor diseases, and conservative treatment could be considered instead. When administering surgical treatment, it will also be clear that it is not necessary to remove or necrose the whole nidus: it will be enough to open and partially undermine it to cure the lesion, which will then undergo remodeling, like any other fracture.