Keywords

1 Definition

  • Avulsion injury is considered a special type of fracture.

  • Radiographically and histologically, the lesion may have a pseudosarcomatous appearance.

2 Synonyms

  • Cortical avulsion

  • Avulsion fracture

3 Etiology

  • Repetitive muscle contraction or a violent muscle contraction may pull off a fragment of cortical and medullary bone across the tendon insertion, which has a stronger tensile strength than the bone.

4 Epidemiology

  • Occurs more frequently in active young adolescents.

5 Sites of Involvement

  • Most commonly in the tibial tuberosity, at the insertion of the quadriceps (Osgood-Schlatter disease), and in the medial distal metaphysis of the femur, at the insertion of the adductor magnus tendon (distal femoral cortical syndrome or periosteal desmoid)

  • Around the pelvis:

    • Ischial tuberosity (ischial apophyseolysis), at the insertion of the hamstring muscles

    • Inferior pubic ramus, at the insertion of the adductor muscles

    • Iliac spine, at the insertion of the rectus femoris

    • Femoral greater trochanter, at the insertion of the gluteus

    • Femoral lesser trochanter, at the insertion of the psoas

    • Humerus, at the insertion of the pectoralis major or the subscapularis muscle

6 Clinical Symptoms and Signs

  • Usually sudden and severe pain.

  • Slight swelling in bones near the skin.

7 Imaging Features

7.1 Radiographic and CT Features

  • The radiographic picture commonly shows extensive reactive bone proliferation and may suggest malignant neoplasms.

  • In the ischium, iliac spine, and femoral greater trochanter, a portion of the cortex is pulled off by a violent muscle contraction or repetitive muscle contractions, and radiographs frequently show the apophysis loose in the soft tissue (Figs. 63.1 and 63.2).

  • Later, reactive bone formation appears, which in some patients may be exuberant.

Fig. 63.1
figure 1

Avulsion injury. (a, b) X-ray and CT scan showing an avulsion injury in the ischial tuberosity (ischial apophyseolysis), at the insertion of the hamstring muscles. Muscle contraction pulled off a portion of the cortex, and radiographs show the loose ischial apophysis in the soft tissue

Full size image
Fig. 63.2
figure 2

Avulsion injury. Roentgenogram (a) and CT scan (b) showing a cortical avulsion in the iliac spine at the insertion of the rectus femoris

Full size image

7.2 Bone Scan Features

  • Intense uptake of technetium.

8 Imaging Differential Diagnosis

8.1 Bone-Forming Benign and Malignant Neoplasms (e.g., Surface Osteosarcoma)

  • Avulsion injury has a limited growth potential and mineralizes early over time.

9 Pathology

9.1 Gross Features

  • Frequently the material is obtained by core needle biopsy (Fig. 63.3).

Fig. 63.3
figure 3

Microphotograph at low magnification of a core needle biopsy specimen from an avulsion injury

Full size image

9.2 Histological Features

  • The histological pattern is similar to a repairing fracture process (endosteal and periosteal callus) (Figs. 63.4, 63.5, and 63.6).

  • The osteoid trabeculae are lined by typical osteoblasts.

  • Reactive cartilage may be present, similar to a fracture callus.

  • Typical mitosis may be present, especially in the early phase of evolution.

Fig. 63.4
figure 4

Microphotograph showing peripheral muscle fibers and a chondroid fracture callus

Full size image
Fig. 63.5
figure 5

The histological pattern is similar to a repairing fracture process with endosteal and periosteal callus

Full size image
Fig. 63.6
figure 6

Avulsive fracture of a mineralized tendon insertion segment. (a) Radiograph showing fracture of the ossified tendon end (arrow). (b) Panoramic microphotograph of both ends of the fracture fragments. (c) Reactive fibro-chondro-osteoid proliferation

Full size image

10 Pathologic Differential Diagnosis

10.1 Osteosarcoma

  • The brisk mitotic activity and the osteoid production may result in a mistaken overdiagnosis of malignancy.

  • Atypical mitoses or cellular pleomorphism are never seen in an avulsion injury.

11 Prognosis

  • Benign lesion, with excellent prognosis.

12 Treatment

  • Lesions often can be confidently diagnosed on the basis of radiographic features and puncture needle or surgical biopsy, so that surgical treatment is not necessary; follow-up may be done by radiographic studies.