Ischial tuberosity avulsion fracture
Muscular insertion and Mechanism of injury:
· The semimembranosus,
semitendinosus adductor magnus and the long head of the biceps femoris tendons originate at the ischial tuberosity.
· This is the most common avulsion injury of the pelvis.
The mechanism of avulsion is from a violent contraction of the hamstring muscles,
which is associated with activities such as sprinting,
cheerleading or gymnastics.
Imaging Findings:
• Radiographs demonstrate avulsed fragments.
Large avulsed fragments may cause fibrous union and in some cases open reduction and internal fixation in severely displaced fragments.
• MRI helps identify extent of injury of proximal hamstring fibers and surrounding edema/fluid.
• Prominence of the ischial tuberosity is associated with an old ischial tuberosity avulsion injury.• Proximity of the ischial tuberosity to the sciatic nerve warrants clinical suspicion for sciatic nerve injuries.• Pitfall: Callus formation or heterotopic bone formation adjacent to chronic avulsion injuries do not represent an aggressive lesion.
Anterosuperior iliac spine avulsion fracture
Muscular insertion and Mechanism of injury:
• The Sartorius tendon and the tensor muscle of the fascia lata originate at the anterior superior iliac spine
• This injury occurs in sprinters during forceful extension of the hip with the knee in flexion.
• Patients with this injury present with point tenderness and edema over the avulsion site.
Symptoms are less severe than in avulsions of the ischial tuberosity.
Imaging Findings:
• Radiographs demonstrate a triangular-appearing cortical avulsion fracture of the anterior superior iliac spine which are usually smaller than ischial tuberosity avulsion fragments.• MRI helps define the retraction of the Sartorius tendon and CT can aid in demonstrate displacement of the apophysis.• Pitfall: Minimally displaced or nondisplaced avulsion fractures can be subtle and missed on pelvic AP films.• Prominence or deformity of the anterior superior iliac spine represents an old avulsion fracture.
Anteroinferior iliac spine avulsion fracture
Muscular insertion and mechanism of injury:
• The rectus femoris tendon originates at the anterior inferior iliac spine.
• The mechanism of injury of is a forceful extension of the hip.
Clinically,
there is point tenderness and edema overlying the avulsion site.
•
Imaging findings:
• Displacement of the apophysis or an avulsion fragment can be seen proximal and lateral to the acetabular rim.• Avulsion fragments smaller than 2 cm may be overlooked in AP views,
for which oblique views can aid in demonstrate a minimally displaced or nondisplaced fracture.• Chronic injuries may demonstrate surrounding heterotopic bone formation.• Pitfall: A significantly retracted bone fragment resulting from an avulsion injury of the anterior superior iliac spine may mimic radiographically an avulsion fracture of the anterior inferior iliac spine.
Iliac Crest Avulsion
Muscular insertion and mechanism of injury:
• The site of attachment of the anterior abdominal wall musculature is the anterior iliac crest.• This apophysis starts ossifying by 15 years of age and closes by 18 years of age.• Iliac crest avulsions commonly occur along its most anterior aspect with displacement of the anterior aspect of the apophysis.
Imaging Findings:
• Radiographs demonstrate separation and displacement of the apophysis.• MR demonstrates soft tissue edema overlying the apophysis with associated strain of the abdominal musculature.
Pitfalls:
• Segmentation of the apophysis which is a developmental variant can be a mimic.• Comparison with contralateral iliac crest must be made since patients may uncommonly present with bilateral avulsion injuries.
Pubic ramus avulsion
Muscular insertion and Mechanism of injury:
• The site of origin for the adductor muscles of the hip (adductor longus,
brevis,
gracilis and rectus abdominis muscle) are the symphysis pubis and inferior pubic ramus.• This injury is caused by chronic repetitive stress from rotational movements of the abdomen and pelvis.• Groin pain resulting from injury to the muscle attachments of the pubic ramus is referred to as athletic pubalgia.• In this avulsion injury,
usually there is an isolated soft tissue injury with no displaced bone fragment.
Imaging Findings:
• On radiographs,
sclerosis of the pubic symphysis may indicate chronic repetitive stress.• MR imaging can demonstrate a muscle strain,
partial or full thickness avulsion,
or marrow edema adjacent to the site of adductor attachment injury.
Lesser Trochanter
Muscular insertion and mechanism of injury:
• The insertion of the iliopsoas muscle is the lesser trochanter.• This injury occurs mostly in adolescent soccer players with unfused apophysis caused by violent contraction of the iliopsoas muscle while the thigh is extended.
In adults this same type of injury results in strain or tear of the iliopsoas at the distal musculotendinous junction.• In adults,
this type of injury without history of trauma is suspicious for a pathological fracture.
Imaging Findings:
• Injury to an unfused apophysis on radiographs may demonstrate separation of the aphophysis and widening of the growth plate.
Heterotopic bone formation may be seen in an old injury.• MR demonstrates marrow edema of the apophyisis and edema within the growth plate.
Strain or tear of the distal tendon of the iliopsoas with associated edema may also be seen.
Greater Trochanter
Muscular insertion and mechanism of injury:
• This is the attachment site for the internal obturator,
gemellus,
piriform,
gluteus medius and minimus.• This injury occurs with abrupt directional changes.
Imaging findings:
• Radiographs demonstrates displacement of the greater trochanter.• MR imaging is not usually required.
On MR,
this type of injury may have an aggressive appearance such as a neoplastic or infectious process.