Answer:
1.) strenuous flexion of the hip in adolescent athletes
2.) pathologic fracture associated with a metastatic lesion

Discussion: In patients who have open epiphyses, an avulsion fracture of the lesser trochanter is usually secondary to vigorous activity. This type of fracture typically occurs during adolescence. It usually is seen between the ages of seven and sixteen years(2,6-8) and most commonly occurs at the age of fourteen years. Theoretically, the upper age-limit for an avulsion fracture of the lesser trochanter secondary to vigorous activity is eighteen or nineteen years, by which time there is fusion of the lesser trochanteric apophysis(17). The literature is replete with reports of this mechanism of injury(2,5-9,11,15,16).

To the best of our knowledge, only two groups of authors have explicitly discussed fracture of the lesser trochanter in conjunction with neoplasm, and in all patients the fracture was the first sign of metastatic disease. Bertin et al.(3) and Phillips et al.(14) both described four patients who had a fracture of the lesser trochanter and previously undiagnosed metastatic disease involving the proximal aspect of the femur. In those two small series, no particular neoplasm appeared to be more prone than any other lesion to cause an avulsion of the lesser trochanter. Although breast cancer is the most common neoplasm to metastasize to bone and has been reported to cause approximately one-half of all neoplastic pathological fractures(1,18), it has not been identified as the underlying cause of a pathological avulsion fracture of the lesser trochanter, to our knowledge.

As far as we know, we are the first to describe avulsion of the lesser trochanter as the presenting symptom leading to the diagnosis of a primary malignant tumor. The present report describes four patients who had an avulsion fracture of the lesser trochanter secondary to a primary malignant bone tumor (a sarcoma in three patients and a solitary plasmacytoma in one). However, it is well known that a pathological fracture through a primary malignant tumor may be the presenting symptom or may occur during the course of preoperative neoadjuvant treatment(21). These fractures tend to occur in the metaphysis or diaphysis of the humerus or femur rather than presenting as avulsion fractures of the lesser trochanter.

Plasmacytoma is a primary malignant bone tumor that is histologically identical to multiple myeloma(10). Knowling et al. considered the solitary plasmacytoma to be an early form of multiple myeloma, with eventual progression to multiple-site involvement being the rule(12). This understanding of the natural progression of plasmacytoma to multiple myeloma is shared by orthopaedic oncologists and pathologists(4,13,19). In the present report, the patient who had a solitary plasmacytoma of the intertrochanteric area of the femur did not have progression to multiple myeloma during the thirteen-year period of postoperative observation.

Close scrutiny of the initial radiographs of all of the patients in the present report demonstrated a destructive lesion or pathological process that involved the proximal part of the femur in addition to the more obvious fracture of the lesser trochanter. The presenting symptoms of a fracture of the lesser trochanter, regardless of etiology, include pain in the groin and pain-induced weakness of flexion of the hip when tested with the patient in the supine or standing position. When there is no history of trauma, the presence of a destructive lesion on radiographs should lead to suspicion of an underlying pathological process but cannot be assumed to be evidence of metastatic disease. Appropriate diagnostic studies include plain radiography, technetium-99 bone-scanning, and magnetic resonance imaging or computed tomography, or both. If myeloma or plasmacytoma is considered in the differential diagnosis before the biopsy, immunoprotein electrophoresis should be performed along with the usual chemistry panels, hematological studies, and measurement of the erythrocyte sedimentation rate. A carefully planned open biopsy or a closed biopsy performed under the guidance of computed tomography should be done by an individual who is knowledgeable in the treatment of primary malignant bone tumors in order to avoid delaying the diagnosis or complicating a possible limb-salvage procedure. Two of the four patients in the present report had inappropriate and premature operative procedures. In the first patient (Case 2), the assumption that the fracture was due to metastatic disease led to a conventional open reduction and internal fixation procedure. The diagnosis of primary chondrosarcoma was established only after the fact. Extensive contamination of the surrounding tissues placed the patient at increased risk for local recurrence, which did in fact occur. In the second patient (Case 3), failure to adequately assess the cause of the lesser trochanteric avulsion resulted in an aborted attempt to fix the fracture through an inappropriate incision and, consequently, a delay in the proper diagnosis.

In contrast to traumatic or exercise-induced avulsion fractures, pathological fractures secondary to metastatic disease have been reported to occur over a wide range of ages (eighteen to seventy years(3,14)). The patients in the present report were nineteen, thirty-six, forty-four, and sixty-nine years old. In all four patients, the clinical presentation of the lesion was similar to that of a metastatic tumor in that it was characterized by a sudden or insidious onset of pain in the groin without antecedent acute trauma or strenuous exercise. The history is therefore critical in the differentiation between traumatic and pathological avulsion fractures of the lesser trochanter. As both conditions are associated with similar clinical findings, including pain and weakness with attempted flexion of the hip, radiographs must be carefully scrutinized to determine if there is an underlying pathological process. A full workup, including a carefully planned biopsy, is necessary to differentiate a metastatic malignant tumor from a primary malignant tumor. Accurate distinction between these two conditions is critical because the methods of operative treatment are drastically different.

In conclusion, one must be wary of several factors when evaluating a patient who has separation of the lesser trochanter from the proximal aspect of the femur. Distinction between apophyseal avulsion of the lesser trochanter and pathological fracture through the lesser trochanter entails a detailed workup that must include consideration of age, medical history, the mechanism of injury, and the shape of the lesser trochanteric fragment on radiographs. Additional ancillary studies should be performed, when appropriate, to detect the presence of a neoplasm. If the fracture is atraumatic and has occurred in an adult, the physician must include the possibility of a primary or metastatic tumor in the differential diagnosis. In addition to a pathological fracture through an existing metastatic lesion, one must consider the possibility of a primary malignant bone tumor. To avoid an inappropriate operative procedure, a pathological diagnosis must be made by means of a biopsy before internal fixation is attempted.

Reference:
Afra, R.; Boardman, D.L.; Kabo, J.M.; and Ekardt, J.J.: Avulsion fracture of the lesser trochanter as a result of a primary malignant tumor of bone. J. Bone and Joint Surg., 81-A: 1299-304, September 1999.