Apophyseal Avulsion Fracture

The apophysis is a secondary ossification center found on non-weight-bearing segments of bones. The apophysis is also the site of ligament or tendon insertion and is involved in the peripheral growth of the bone. These secondary growth centers are generally open in late childhood and may not close until early adulthood. With overuse, the apophysis may become inflamed and painful, becoming vulnerable to tearing and avulsion. An acute apophyseal avulsion fracture occurs when a portion of the apophysis is pulled off by the ligament, usually secondary to explosive movements and eccentric muscular contractions. Apophyseal avulsion fractures are primarily treated conservatively, but may require surgical repair if the avulsed fragment is large or significantly displaced.

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An avulsion fracture occurs when part of an apophysis is ripped off by the ligament due to a sudden forceful eccentric or concentric contraction of the muscle attached to it.


Apophyses exist on many bones and are the insertion site of a number of ligaments. Avulsion fractures can occur at any of these sites.

  • Tibial tuberosity: attachment of patellar ligament on proximal tibia
  • Anterior superior iliac spine (ASIS): attachment of sartorius muscle; seen most commonly in adolescent sprinters
  • Anterior inferior iliac spine (AIIS): attachment of rectus femoris muscle
  • Distal pole of patella: patella sleeve fracture; rare injury characterized by separation of cartilage sleeve from ossified patella; may require surgery
  • Ischial tuberosity apophysis: hamstring insertion avulsion seen in adolescent sprinters; frequently misdiagnosed as acute hamstring tendon or muscle injury 
  • Iliac crest: insertion of oblique muscles 
  • Medial epicondyle of humerus: insertion of many muscles including the flexors of the forearm; variant of “little league elbow”
  • Olecranon: insertion of tricep tendon
Sites of pelvic apophyseal avulsion fractures

Most frequent sites of pelvic apophyseal avulsion fractures:
a: iliac crest (attachment of the obliques and rectus abdominis muscles)
b: anterior superior iliac spine (attachment of sartorius muscle; seen most commonly in adolescent sprinters)
c: anterior inferior iliac spine (attachment of rectus femoris)
d: superior aspect of the symphysis pubis (insertion of rectus abdominis muscle)
e: ischial tuberosity (hamstring insertion avulsion seen in adolescent sprinters; frequently misdiagnosed as acute hamstring tendon or muscle injury)
f: lesser trochanter of the femur (insertion of iliopsoas muscle, rarely injured in adolescents during traumatic injury)

Image by Lecturio.

Clinical Presentation and Diagnosis

Acute apophyseal injuries are generally non-contact related, but rather due to a sudden explosive eccentric muscle contraction.

History and physical exam

Patients present with:

  • Severe pain
  • Swelling
  • Point tenderness
  • Ecchymosis
  • Sometimes, history of a “popping noise or feeling” precedes injury

Exam can reveal:

  • Deformity of interested area
  • Decreased range of motion
  • Difficulty weight-bearing 
  • Abnormally high patella in cases of tibial tubercle avulsion fracture
  • Acute injury leads to swelling, which limits examination; re-examination after 10–14 days may be necessary.


  • Plain X-rays:
    • Soft tissue swelling and joint effusion are non-specific findings often seen.
    • Avulsed bone fragments may be visible in acute injuries.
    • Subacute injuries may reveal areas of sclerosis.
    • Calcifications due to previous trauma may be visible.
  • Computed tomography (CT) scan: 
    • May be used to assess size of fragment and amount of displacement
    • Can assist in perioperative planning
  • Magnetic resonance imaging (MRI) scan: may be used to assess associated soft tissue injury


Management of most acute avulsion injuries is non-surgical and based on the location and amount of displacement of the avulsed bone.

  • Non-displaced or minimally displaced apophyseal avulsion fractures: 
    • Rest
    • Protected motion, including partial weight-bearing
    • Appropriately staged physical therapy
  • For displaced fractures: Amount of displacement, size of fragment, and demands of athlete are important factors in surgical decision.
Stress avulsion of the tibial tuberosity

Surgical refixation of avulsion fracture of the tibial tuberosity: postoperative anteroposterior and lateral radiographs of left knee after refixation of avulsion fracture of the tibial tuberosity

Image: “Radiographs of left knee” by Department of Orthopaedic Surgery and Traumatology, Kantonsspital Bruderholz, CH-4101 Bruderholz, Switzerland. License: CC BY 2.0

Clinical Relevance

Additional important pediatric skeletal injuries:

  • Greenstick fracture: partial-thickness fracture involving a complete break of cortex and periosteum on only 1 side of the bone. Termed “greenstick” as it resembles a break in a live, “green” twig, where 1 side of the stick remains intact. High risk for refracture and should be completely immobilized. Rarely requires reduction, but should be managed cautiously to prevent malunion or angulation deformities, and often should be referred for orthopedic follow-up.
  • Supracondylar fracture: complete fracture affecting distal humerus after falling on outstretched hand (FOOSH). Commonly fractures of the elbow in children. Requires immediate orthopedic consultation as many cases are associated with neurovascular injury and require surgical intervention. 
  • Buckle or Torus fracture: fracture affecting growing metaphyseal bone secondary to compression load, where bone buckles or compresses. Generally considered a stable fracture. Treated by immobilization, and has a good prognosis.


  1. Calderazzi F, Nosenzo A, Galavotti C, Menozzi M, Pogliacomi F, Ceccarelli F. (2018). Apophyseal avulsion fractures of the pelvis. A review. Acta Biomed. 2018;89(4):470-476. doi:10.23750/abm.v89i4.7632
  2. Porr J, Lucaciu C, Birkett S. (2011). Avulsion fractures of the pelvis – a qualitative systematic review of the literature. J Can Chiropr Assoc. PMID: 22131561; PMCID: PMC3222700.
  3. George MS. (2007). Fractures of the greater tuberosity of the humerus. J Am Acad Orthop Surg. doi: 10.5435/00124635-200710000-00005. PMID: 17916784.
  4. Schiller J, DeFroda S, Blood T. (2017). Lower Extremity Avulsion Fractures in the Pediatric and Adolescent Athlete. J Am Acad Orthop Surg. doi: 10.5435/JAAOS-D-15-00328. PMID: 28291142.

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