Age / Sex : 62 / F

Age / Sex : 13 / M

Avulsion fracture of ischial tuberosity

Discussion

Findings:

1.     Plain AP radiograph; irregularity and bony protuberance of the left side of ischial tuberosity

2.     MRI; 1) Thickening and heterogenous signal change with contrast enhancement of left ischial tuberosity  2) Signal change and contrast enhancement of tendinous portion of left hamstrings  3) Signal change and contrast enhancement of bone marrow of left ischium

Diagnosis:  Avulsion fracture of left ischium

Discussion:

 Adolescent participants, because of the inherent weakness of the apophysis, are especially vulnerable to avulsion fractures. When eccentric muscular contraction occurs in adults as a result of landing after a jump or falling from a height, for example, the musculotendinous junction is particularly vulnerable to injury. In adolescents, muscles and tendons commonly insert on apophyses, which are more susceptible to injury until patients reach their middle twenties. Therefore, the age of the patient is an important factor in evaluation of the injury site.

In the pelvis, avulsion injuries primarily occur at six sites . The ischial tuberosity is the most common site. It is the insertion site of the hamstring muscle group, and avulsions usually occur before closure of the apophysis. Avulsion is caused by extreme active contraction of the hamstrings during, for example, sprinting by runners or sudden and excessive passive lengthening in cheerleaders or dancers. Patients typically present with pain in the buttock region, an antalgic gait, or inability to walk. In acute cases, a nondisplaced avulsion of the ischial tuberosity appears as a curved, sharply marginated piece of bone adjacent to its origin (ischial epiphysiolysis). Patients with injuries of this type tend to respond well to conservative treatment such as several days of bed rest, restricted activity, and a return to normal activity over the next 6–12 weeks. If the fragment is displaced more than 2 cm, however, fibrous union may occur, resulting in extended disability. Development of sciatica may be related to irritation of the sciatic nerve either when exuberant callus formation occurs during healing or when the avulsed fragment directly impinges on the nerve.

At radiography, healing avulsions can have an aggressive appearance, including lysis and destruction. These changes can mimic those seen with osteomyelitis or Ewing sarcoma. Chronic avulsion injuries frequently result in prominent bone formation. Sometimes only a remote history of minor trauma exists, which makes the clinical diagnosis difficult.

References:

1. Stevens MA, El-Khoury GY, Kathol MH, Brandser EA, Chow S. Imaging features of avulsion injuries. RadioGraphics1999; 19:655 -672

2.Brandser EA, El-Khoury GY, Kathol MH. Adolescent hamstring avulsions that simulate tumors. Emerg Radiol 1995; 2:273-278.

3.Combs JA. Hip and pelvis avulsion fractures in adolescents. Physician Sports Med 1994; 22:41-49.

4.El-Khoury GY, Daniel WW, Kathol MH. Acute and chronic avulsive injuries. Radiol Clin North Am 1997; 35:747-766.

5.Wootton JR, Cross MJ, Holt KWG. Avulsion of the ischial apophysis. J Bone Joint Surg [Br] 1990; 72:625-627.

6.Metzmaker JN, Pappas AM. Avulsion fractures of the pelvis. Am J Sports Med 1985; 13:349-358.