High Yield Overview
Pelvic Avulsion Fractures
Adolescent Sports Injuries | Apophyseal Avulsions
ASIS/AIISCommon Sites
14-17Peak Age (Years)
SprintingCommon Mechanism
ConservativeMost Treatment
Avulsion Sites
ASIS
PatternSartorius origin. Sprinting/Kicking.
TreatmentConservative
AIIS
PatternRectus Femoris origin. Kicking.
TreatmentConservative
Ischial Tuberosity
PatternHamstrings origin. Hurdling/Splits.
TreatmentConservative / ORIF if displaced greater than 2cm
Iliac Crest
PatternAbdominal muscles. Twisting.
TreatmentConservative
Lesser Trochanter
PatternIliopsoas insertion. Rare.
TreatmentConservative
Critical Must-Knows
- Population: Adolescent athletes (open apophyses). Apophysis is weaker than muscle/tendon.
- Mechanism: Sudden forceful muscle contraction against resistance.
- Imaging: X-ray (compare to contralateral). CT if unclear.
- Treatment: Most are conservative. ORIF for Ischial Tuberosity greater than 2cm displacement.
- Prognosis: Excellent. Return to sport 6-12 weeks.
Examiner's Pearls
- "Avulsions occur because the APOPHYSIS is weaker than the muscle-tendon unit in adolescents.
- "ASIS avulsion is from Sartorius (sprinting). AIIS is from Rectus Femoris (kicking).
- "Ischial Tuberosity is the one that may need surgery (greater than 2cm displacement).
- "Always compare to the contralateral side on X-ray (apophyses can look irregular).
Pelvic Avulsion Pitfalls
Missed Diagnosis
Compare Sides. Apophyses look irregular normally. Compare to contralateral to avoid missing avulsion.
Ischial Tuberosity Displacement
May Need Surgery. If greater than 2cm displaced, consider ORIF. Chronic pain/weakness if missed.
Tumor Mimics
Callus Formation. Exuberant callus can mimic osteosarcoma on imaging. Know the history.
Recurrence
Return Too Early. Athletes want to return quickly. Ensure healed before full sport.
At a Glance: Avulsion Sites
| Site | Muscle | Mechanism | Surgery |
|---|---|---|---|
| ASIS | Sartorius | Sprinting | Rare |
| AIIS | Rectus Femoris | Kicking | Rare |
| Ischial Tuberosity | Hamstrings | Hurdles/Splits | If greater than 2cm |
| Iliac Crest | Abdominals | Twisting | Rare |
| Lesser Trochanter | Iliopsoas | Hip Flexion | Rare |
Mnemonic
AIILAvulsion Sites
A
ASIS
Sartorius origin
A
AIIS
Rectus Femoris origin
I
Ischial Tuberosity
Hamstrings origin
I
Iliac Crest
Abdominal muscles
L
Lesser Trochanter
Iliopsoas insertion
Memory Hook:Apophyseal Avulsion Sites.
Mnemonic
S-R-H-AMuscles by Site
S
Sartorius
ASIS
R
Rectus Femoris
AIIS (Straight head)
H
Hamstrings
Ischial Tuberosity
A
Abdominals
Iliac Crest (EO, IO, TA)
Memory Hook:Match muscle to site.
Mnemonic
2cm ITSurgical Indication
2
2 centimeters
Displacement threshold
c
Consider
Consider surgery if greater than 2cm
m
Matters
Only IT commonly needs surgery
I
Ischial
Ischial Tuberosity
T
Tuberosity
Hamstring avulsion
Memory Hook:IT greater than 2cm = Surgery.
Overview and Epidemiology
Definition: Pelvic avulsion fractures are injuries where a muscle-tendon unit avulses its apophyseal attachment from the pelvis. They occur almost exclusively in adolescents due to the relative weakness of the unfused apophysis compared to the muscle-tendon unit.
Epidemiology:
- Age: 14-17 years (before apophyseal closure).
- Sex: Males greater than Females.
- Sports: Sprinting, Soccer, Gymnastics, Hurdling, Baseball.
- Bilaterality: Rare.
Common Sites:
- ASIS (Anterior Superior Iliac Spine): Sartorius.
- AIIS (Anterior Inferior Iliac Spine): Rectus Femoris (Straight head).
- Ischial Tuberosity: Hamstrings (Semimembranosus, Semitendinosus, Biceps Femoris long head).
- Iliac Crest: External Oblique, Internal Oblique, Transversus Abdominis.
- Lesser Trochanter: Iliopsoas.
Anatomy and Pathophysiology
Apophyseal Anatomy:
- Apophysis: Secondary ossification center for muscle attachment.
- Weakness: Cartilaginous growth plate is weaker than bone, muscle, or tendon.
- Closure: Apophyses fuse in late adolescence (17-25 years).
Mechanism:
- Sudden Contraction: Explosive muscle contraction against resistance.
- Eccentric Load: Muscle lengthening under load (e.g., hurdle).
- Result: Apophysis avulses before muscle or tendon fails.
Site-Specific Mechanisms:
- ASIS (Sartorius): Sprinting (hip extension with knee flexion).
- AIIS (Rectus Femoris): Kicking (hip flexion with knee extension).
- Ischial Tuberosity (Hamstrings): Hurdles, Splits, Waterskiing.
- Iliac Crest: Twisting, Throwing.
Classification
By Site
| Site | Muscle | Sport | Surgery |
|---|---|---|---|
| ASIS | Sartorius | Sprinting | Rare |
| AIIS | Rectus Femoris | Kicking | Rare |
| Ischial Tuberosity | Hamstrings | Hurdles | If greater than 2cm |
| Iliac Crest | Abdominals | Twisting | Rare |
| Lesser Trochanter | Iliopsoas | Flexion | Rare |
| Pubic Symphysis | Adductors | Adduction | Rare |
Ischial Tuberosity is the most important to recognize for surgical consideration.
Clinical Assessment
History:
- Mechanism: Sudden pop/pain during sprinting, kicking, or jumping.
- Sport: Sprinting, Soccer, Gymnastics.
- Age: Adolescent (13-17).
Physical Examination:
- Tenderness: Point tenderness over avulsion site (ASIS, AIIS, IT, Iliac Crest).
- Swelling/Bruising: Variable.
- Weakness: Weakness of the involved muscle (Hip flexion, Hamstrings).
- Gait: Antalgic.
- ROM: Painful with stretch of involved muscle.
Investigations
Imaging:
- X-ray (AP Pelvis): Compare to contralateral side. Look for displaced fragment.
- CT: If X-ray unclear. Quantify displacement.
- MRI: Rarely needed. For soft tissue assessment or chronic cases.
Key Findings:
- ASIS Avulsion: Fragment displaced inferolaterally.
- AIIS Avulsion: Fragment displaced inferiorly.
- Ischial Tuberosity: Fragment displaced inferiorly (by hamstrings).
- Iliac Crest: Multiple small fragments (apophysis strips).
Differential Diagnosis:
- Normal apophyseal irregularity (compare sides).
- Osteosarcoma (callus mimics tumor).
- Osteomyelitis.
Management Algorithm
📊 Management Algorithm
Click to expand
Conservative Management (Most Cases)
- Rest: Crutches for comfort (1-2 weeks).
- Ice: 20 minutes, 3-4 times daily.
- Analgesia: NSAIDs, Paracetamol.
- Physiotherapy:
- Week 1-2: Gentle ROM.
- Week 2-6: Progressive strengthening.
- Week 6-12: Sport-specific training.
- Return to Sport: 6-12 weeks (when pain-free and full strength).
Most avulsions heal well without surgery.
Surgical Technique
Ischial Tuberosity ORIF
- Positioning: Prone or Lateral.
- Incision: Gluteal crease incision (cosmetically hidden).
- Dissection: Identify sciatic nerve (protect). Identify hamstring origin.
- Reduction: Reduce avulsed fragment to ischial tuberosity.
- Fixation: 2 x 4.5mm Cortical Screws or Cannulated Screws. Suture anchors if fragment small.
- Closure: Layered.
- Post-op: Crutches. NWB 2 weeks. Progressive PT.
Protect the Sciatic Nerve.
Complications
Complications
| Complication | Risk Factor | Management |
|---|---|---|
| Non-Union | Large displacement | ORIF / Excision |
| Chronic Weakness | IT greater than 2cm | Delayed ORIF |
| Exuberant Callus | Normal healing | Reassurance (Mimics tumor) |
| Recurrence | Early return to sport | Wait for healing |
| Sciatic Nerve Injury | IT surgery | Careful dissection |
Postoperative Care
- Crutches: 2-4 weeks.
- ROM: Early gentle ROM.
- Strengthening: Week 4-6 progressive.
- Return to Sport: 12-16 weeks (post-surgery).
Outcomes
- Conservative: 90%+ return to full sport.
- Surgical (IT): Good outcomes with ORIF.
- Long-term: No significant issues if managed appropriately.
Evidence Base
Ischial Tuberosity Threshold
Key Findings:
- Reviewed outcomes of Ischial Tuberosity avulsions.
- Displacement greater than 2cm associated with worse outcomes if non-op.
- Supports surgical threshold of 2cm.
Clinical Implication: Consider ORIF for IT greater than 2cm.
Limitation: Retrospective
Conservative Management
Key Findings:
- Most pelvic avulsions heal with conservative treatment.
- Return to sport at 6-12 weeks.
- Excellent outcomes.
Clinical Implication: Conservative is standard for most avulsions.
Limitation: Case series
AIIS Avulsion
Key Findings:
- Described AIIS avulsion as a cause of FAI.
- Exuberant callus can cause impingement.
- Arthroscopic resection may be needed.
Clinical Implication: Monitor for FAI if large AIIS callus.
Limitation: Case series
Comparison of Sites
Key Findings:
- Reviewed all pelvic avulsion sites.
- ASIS, AIIS, IT, Iliac Crest all described.
- Conservative management for most.
Clinical Implication: Know all sites and mechanisms.
Limitation: Review
Return to Sport
Key Findings:
- Most athletes return to full sport.
- Average 6-12 weeks for healing.
- IT may take longer.
Clinical Implication: Counsel athletes on expected timeline.
Limitation: Case series
Viva Scenarios
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
The Sprinter with Hip Pain
EXAMINER
"What is your working diagnosis and management?"
EXCEPTIONAL ANSWER
**Likely ASIS Avulsion (Sartorius).**
1. **History**: Sprinting, sudden pop, anterior hip/pelvis.
2. **Examination**:
- *Tenderness*: Point tenderness over ASIS.
- *Weakness*: Weak hip flexion.
- *ROM*: Painful with hip extension.
3. **Imaging**: X-ray AP Pelvis. Compare to contralateral. Look for avulsed fragment at ASIS.
4. **Diagnosis**: ASIS Avulsion (Sartorius origin).
5. **Management**:
- *Conservative*: Rest, Crutches, Ice, Analgesia.
- *Physiotherapy*: ROM then strengthening over 6-12 weeks.
6. **Return to Sport**: 6-12 weeks when pain-free and full strength.
KEY POINTS TO SCORE
ASIS = Sartorius
Sprinting mechanism
X-ray compare to contralateral
Conservative treatment
COMMON TRAPS
✗Missing the diagnosis (compare sides)
✗Operating (not needed)
LIKELY FOLLOW-UPS
"What is AIIS avulsion?"
"When would you operate on a pelvic avulsion?"
VIVA SCENARIOStandard
The Hurdler with Posterior Thigh Pain
EXAMINER
"What is your diagnosis and when would you operate?"
EXCEPTIONAL ANSWER
**Likely Ischial Tuberosity Avulsion (Hamstrings).**
1. **History**: Hurdling (eccentric hamstring load), sudden pain, posterior thigh.
2. **Examination**:
- *Tenderness*: Ischial Tuberosity.
- *Bruising*: Posterior thigh.
- *Weakness*: Hamstrings.
3. **Imaging**: X-ray AP Pelvis. CT if unclear. Quantify displacement.
4. **Diagnosis**: Ischial Tuberosity Avulsion.
5. **Surgical Decision**:
- *Displacement less than 2cm*: Conservative management.
- *Displacement greater than 2cm*: Consider ORIF.
6. **Rationale for Surgery**: Large displacement can lead to chronic hamstring weakness and painful non-union.
KEY POINTS TO SCORE
IT = Hamstrings
Hurdling mechanism
greater than 2cm = Consider Surgery
Rest do conservative
COMMON TRAPS
✗Missing large displacement
✗Not assessing displacement
LIKELY FOLLOW-UPS
"How do you fix an IT avulsion?"
"What nerve is at risk?"
VIVA SCENARIOStandard
The Concerning X-ray
EXAMINER
"What is your assessment?"
EXCEPTIONAL ANSWER
**Exuberant Callus from AIIS Avulsion (Not Tumor).**
1. **History is Key**: Known AIIS avulsion 4 weeks ago. This is healing callus.
2. **Exuberant Callus**: Common in adolescents. Can look aggressive on imaging.
3. **Differentiation from Tumor**:
- *History*: Clear mechanism at sport. Acute onset.
- *Clinical*: Improving symptoms (not worsening).
- *Imaging*: Localized to apophysis. No soft tissue mass. No periosteal reaction elsewhere.
4. **Management**: Reassurance. Continue conservative treatment.
5. **If Still Concerned**: MRI will show healing fracture, not tumor.
**Key Point**: Know the history. Callus mimics tumor but is benign.
KEY POINTS TO SCORE
Callus is normal healing
History differentiates from tumor
MRI if concerned
Reassurance
COMMON TRAPS
✗Ordering biopsy (not needed if history clear)
✗Alarming the family unnecessarily
LIKELY FOLLOW-UPS
"What if the callus causes impingement?"
"What is the typical healing time?"
MCQ Practice Points
ASIS Muscle
Q: Which muscle avulses from the ASIS? A: Sartorius.
AIIS Muscle
Q: Which muscle avulses from the AIIS? A: Rectus Femoris (straight head).
Surgical Threshold
Q: What is the surgical threshold for Ischial Tuberosity avulsion? A: Greater than 2cm displacement. Consider ORIF to prevent chronic hamstring weakness.
Population
Q: Why do pelvic avulsion fractures occur in adolescents? A: The apophysis (secondary ossification center) is weaker than the muscle-tendon unit in adolescents before skeletal maturity.
Ischial Tuberosity Mechanism
Q: What is the mechanism for Ischial Tuberosity avulsion? A: Forceful eccentric contraction of the hamstrings (e.g., hurdling, splits, waterskiing).
Australian Context
- Common in Adolescent Athletes: Football (soccer, AFL), Track and Field, Gymnastics.
- Sports Medicine Clinics: Many pelvic avulsions managed by sports medicine physicians.
- Return to Sport: Emphasis on graduated return to prevent recurrence.
High-Yield Exam Summary
Sites
- •ASIS: Sartorius
- •AIIS: Rectus Femoris
- •IT: Hamstrings
- •Iliac Crest: Abdominals
- •Lesser Troch: Iliopsoas
Surgery
- •IT displacement over 2cm: Consider ORIF
- •Excision for chronic nonunion/painful callus
- •Sciatic nerve at risk (IT approach)
- •Most conservative: Rest + Protected activity
Treatment
- •Rest, Ice, Analgesia initially
- •PT: ROM then Strength progression
- •Return to sport: 6-12 weeks
- •No contact until pain-free strength
Pitfalls
- •Compare sides on X-ray
- •Callus mimics tumor (biopsy risk)
- •Don't over-treat (most heal)
- •Consider apophyseal stage (MRI if needed)