MSK: Trauma and Overuse, Hip/Femur/Sacrum Flashcards
What is the classic location for a femoral neck stress fracture?
The medial (compressive) side
Stress fracture of the femoral shaft
Note: The medial side is common for classic stress fractures. If on the lateral side, think bisphosphonate fracture.
Think bisphosphonate fracture
Note: Stress fracture on the lateral aspect of the femoral shaft.
Think bisphosphonate fracture
Note: Horizontal, transverse fracture of the femoral shaft.
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Anterior acetabular wall
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Posterior acetabular wall
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Acetabular roof
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Iliopectineal line
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Ilioischial line
What is the most common type of hip dislocation?
Posterior
Note: This is usually due to dashboard injuries and almost always associated with an acetabular fracture.
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Radiographic U (tear drop)
Right posterior hip dislocation
What are the two columns referring to in a “both column” acetabular fracture?
The anterior (iliopectineal) and posterior (ilioischial) columns that support the acetabulum
What bone do you sit on when in a chair?
The ischium (ischial tuberosity)
Corona mortis
Variant anastomotic vessels between the internal and external iliac vessels that are located near the superior pubic ramus (and can be injured during the lateral dissection portion of a hip fracture repair)
Note: This anastomosis is often between the obturator vessels (from the internal iliac) and the inferior epigastric vessels (from the external iliac).
Light blue
Corona mortis
Arterial supply to the femoral head is from the…
Circumflex femoral arteries
Note: This is why displaced, intracapsular femoral neck fractures can lead to avascular necrosis.
Which type of proximal femoral fractures are at increased risk for avascular necrosis of the femoral head?
Intracapsular femoral neck fractures
Note: Degree of fracture displacement corresponds with risk of avascular necrosis.
68 y/o M
Lesser trochanter avulsion fracture
Note: In an adult, this is likely a pathologic fracture and you should look for an underlying lesion.
Which muscle got avulsed?
Iliopsoas muscle
Note: Lesser trochanter avulsion fracture.
Which muscle got avulsed?
Abdominal muscles
Note: Iliac crest avulsion fracture.
Which muscle got avulsed?
Sartorius and tensor fascia lata
Note: ASIS (anterior superior iliac spine) avulsion fracture.
Which muscle got avulsed?
Rectus femoris
Note: AIIS (anterior inferior iliac spine) avulsion fracture
Which muscle got avulsed?
Gluteal muscles
Note: Left greater trochanter avulsion fracture.
Which muscle got avulsed?
Hamstrings
Note: Left ischial tuberosity avulsion fracture.
Which muscle got avulsed?
Adductor group
Note: These are secondary changes due to a prior pubic symphysis avulsion fracture.
These pelvic injuries most likely resulted from what injury force pattern?
Lateral compression
Note: Pubic symphysis intact and no vertical shifting.
These pelvic injuries most likely resulted from what injury force pattern?
AP compression
Note: Diastasis of the pubic symphysis.
These pelvic injuries most likely resulted from what injury force pattern?
Vertical sheer
Note: There is vertical shifting of the fracture fragments.
Is an isolated acetabular fracture considered stable?
Yes
Is an isolated pubic ramus fracture considered stable?
Yes
Is an isolated iliac wing fracture considered stable?
Yes
Are pelvic avulsion fractures considered stable?
Yes
Snapping hip syndrome
A clinical sensation of snapping or clicking with hip flexion/extension
Common causes of snapping hip syndrome
- External (IT band snapping over the greater trochanter)
- Internal (iliopsoas snapping over the iliopectineal eminence or femoral head)
- Intra-articular (due to labral tears or loose bodies)
What is the typical workup for snapping hip syndrome?
- Clinical evaluation (can identify external/iliotibial band type)
- Radiographs (hip degeneration/loose bodies suggests intra-articular type)
- Dynamic ultrasound (to look for internal/iliopsoas type)
- MRI arthrogram (to look for intra-articular labral tears)
Which cause of snapping hip syndrome is identified on clinical exam?
External (iliotibial band snapping over the greater trochanter)
Note: This is the most common type.
You are shown an ultrasound cine of the hip for snapping hip syndrome…
Think internal type (due to the iliopsoas snapping over the iliopectineal eminence or femoral head)
Which cause of snapping hip syndrome can be identified on radiographs?
Intra-articular (due to hip degeneration or intraarticular loose bodies)
Think IT band syndrome
Think IT band syndrome
IT band syndrome
A repetitive stress syndrome due to rubbing of the iliotibial band against the lateral knee (classically seen in runners)
What is the most common type of acetabular labral tear?
Anterior-superior tears
Paralabral cyst, suspicious for a labral tear
Acetabular labral tear (anterior superior, most common)
What is the largest bursa?
Iliopsoas bursa
Iliopsoas bursitis
Ultrasound anterior to the femoral head
Think iliopsoas bursitis
Iliopsoas bursitis
Does the iliopsoas bursa communicate with the hip joint?
Usually not, but it does in 15% of the population
Iliopsoas bursitis is often associated with…
- Osteoarthritis of the hip
- Rheumatoid arthritis
- Post hip arthroplasty
Snapping hip syndrome
Iliopsoas tendinopathy (think internal snapping hip due to iliopsoas snapping over the iliopectineal eminence or femoral head)
Note: The iliopsoas tendon can mimic a labral tear because it runs directly anterior to the labrum on axial images.
What are the two major types of femoroacetabular impingement?
- Cam-type
- Pincer-type
Cam-type femoroacetabular impingement
Note: A convex bump (yellow arrowheads) is present at the anterior femoral head-neck junction. An area of chondral loss (red arrows) is present on the acetabular side of the joint. Subtle subchondral degenerative changes (red arrowhead) are located on the corresponding femoral side of the joint.
Cam-type femoroacetabular impingement (yellow arrow) and an acetabular labral tear (red arrowhead)
Is femoroacetabular impingement more common in males or females?
Cam-type is more common in males
Pincer-type is more common in females
How can you tell whether there is rotation on a frontal pelvic radiograph?
The coccyx should be lined up with the pubic symphysis, if its not then the pt is rotated
What acetabular malformation is present?
Pincer-type femoroacetabular impingement
Note: This is the “crossover sign” where the posterior rim crosses over the anterior rim, creating a figure 8.
Imaging findings of acetabular over coverage (associated with pincer-type femoroacetabular impingement)
- Coxa profunda
- Acetabular protrusion
- Prominent ischial spine
Acetabular “crossover sign”
Acetabular malformation where the posterior rim crosses over the anterior rim on an AP radiograph, creating a figure 8
Note: This is associated with pincer-type femoroacetabular impingement.
Which acetabular malformation is present on the left?
Coxa profunda
Note: The deepened acetabulum projects medial to the ilioischial line. This is a sign of acetabular over coverage and is associated with pincer-type femoroacetabular impingement.
Which acetabular malformation is present?
Acetabular protrusion
Note: The femoral head projects medial to the ilioischial line. This is a sign of acetabular over coverage and is associated with pincer-type femoroacetabular impingement.
Prominent ischial spine
Note: This is a sign of acetabular over coverage and is associated with pincer-type femoroacetabular impingement.
Femoroacetabular impingement predisposes to the development of…
- Os acetabuli (40%)
- Labral tears
- Early arthritis
Os acetabuli
Note: This is an unfused secondary ossification center associated with femoroacetabular impingement.
Os acetabuli
Note: This is an unfused secondary ossification center associated with femoroacetabular impingement. This pt also has hip dysplasia.
Normal bone remodeling/stress shielding (common in noncemented hip arthroplasties), increased risk for fractures
Note: The bone that is getting resorbed is not being used for weight bearing anymore (axial weight loading is transmitted through the metallic stem to the “pedestal” below the tip of the stem).
Imaging findings of stress shielding/stress loading in hip arthroplasties
Proximal femoral stress shielding results in greater tuberosity and calcar resorption
Distal femoral stress loading results in cortical thickening and pedestal formation
Note: This is more common in noncemented arthroplasties.
Why do pts with ankylosing spondylitis sometimes receive radiation prior to total hip arthroplasty?
Prophylaxis against heterotopic ossification
Note: Pts with ankylosing spondylitis are at very high risk for heterotypic ossification.
Heterotopic ossification
Note: This occurs in 15-50% of pts with total hip arthroplasties.
What is the most common symptom of heterotopic ossification following total hip arthroplasty?
Hip stiffness
What is the most common indication for revision of a total hip arthroplasty?
Aseptic loosening
Follow up imaging
Stress shielding (normal proximal femur resorption following arthroplasty)
Note: Progressive calcar resorption.
Follow up imaging
Septic loosening due to polyethylene wear
Note: Progressive Lucent zone surrounding the acetabular component (loosening) and subtle eccentric positioning of the femoral head (polyethylene wear).
These are common resorption patterns of what complications?
- Aseptic loosening (left)
- Particle disease (middle)
- Infection (right)
Imaging findings of aseptic loosening
- Widening of the periprosthetic Lucent zone to > 2 mm (suggestive)
- Component migration (diagnostic)
Follow up imaging
Progressive subsidence (diagnostic for loosening)
Note: The femoral component is sliding further down the femur.
How should you check for subsidence on postoperative radiographs of a total hip arthroplasty?
Measure the distance between the tip of the greater trochanter and the shoulder of the femoral component
Note: An increase in this distance by > 1 cm (or any progression after 2 years) indicates subsidence (diagnostic for loosening). A collared stem can help prevent this.
Acetabular component migration (diagnostic for loosening)
Note: The acetabular component is moving superior relative to the pelvic teardrop.
Particle disease
Note: Focal osteolysis without secondary bone response (no sclerosis). Likely secondary to polyethylene wear given the eccentric position of the femoral head within the acetabular cup.
Particle disease
Aggressive osteolytic lesions due to a granulomatous response to small particles (usually due to polyethylene wear releasing small particles)
Particle disease
Note: Focal osteolysis around the screws without a secondary bone response (no sclerosis). Likely secondary to polyethylene wear given the eccentric position of the femoral head within the acetabular cup.
How can you differentiate normal acetabular cup creep from acetabular polyethylene wear s/p total hip arthroplasty?
Normal prosthetic creep moves superomedially due to normal polyethylene thinning (at the weight bearing portion)
Polyethylene wear moves superolaterally
What type of hip arthroplasty is at a higher risk for particle disease?
Non-cemented
When does particle disease tend to occur s/p total hip arthroplasty?
1-5 years later (it is a late complication)
How can you distinguish particle disease from periprosthetic osteomyelitis?
In particle disease, lytic areas should have smooth endosteal scalloping
In osteomyelitis, the endosteal surface is more ill-defined
Note: You can also look at ESR and CRP, which will be normal in particle disease and elevated in osteomyelitis.
What should you consider?
CT angiography to look for bleeding vessels
Note: This is true for most pelvic fractures.
What is the most common cause of a sacral insufficiency fracture?
Postmenopausal osteoporosis
Sacral insufficiency fracture
Risk factors for sacral insufficiency fractures
- Osteoporosis
- Renal failure
- Rheumatoid arthritis
- Pelvic radiation
- Hip arthroplasty (due to mechanical changes)
- Extended steroid use
Think sacral insufficiency fracture
Note: This is the “Honda sign” on MRI.
Bone scan
Think sacral insufficiency fracture
Note: This is the “Honda sign”.
