High-yield overview
Avulsion of Cartilaginous Pole | Extensor Mechanism Injury
8-12 yoPeak Age
InferiorMost Common Pole
CartilageAvulsed Component
ORIFDisplaced Needs Surgery
Patella Sleeve Fracture
Inferior Pole (Common)
PatternAvulsion of inferior pole with cartilage sleeve.
TreatmentORIF if displaced
Superior Pole
PatternAvulsion of superior pole. Less common.
TreatmentORIF if displaced
Critical Must-Knows
- Definition: Avulsion fracture of the patellar pole where the bony fragment pulls off a 'sleeve' of articular cartilage.
- Age Group: Children (8-12 years). Cartilage is weaker than bone.
- Injury Mechanism: Eccentric quadriceps contraction (jumping, landing).
- Key Point: The small bony fragment underestimates the size of the cartilage avulsion.
- Treatment: Non-displaced = Cylinder cast. Displaced (greater than 2mm) = ORIF.
Clinical Pearls
- "The X-ray underestimates the injury - the cartilage sleeve is not visible.
- "Patella Alta on lateral X-ray indicates extensor mechanism disruption.
- "Loss of active knee extension = Surgical indication.
- "MRI shows the true extent of the cartilage avulsion.
Patella Sleeve Pitfalls
X-ray Underestimates
Cartilage is Invisible. The small bony fragment on X-ray hides a large cartilage sleeve avulsion. Don't underestimate.
Loss of Extension
Extensor Mechanism Injury. If the child cannot actively extend the knee, the extensor mechanism is disrupted. Surgery needed.
Patella Alta
Look for High Patella. On lateral X-ray, a high-riding patella suggests the patellar tendon has pulled the bony fragment distally.
Missed Diagnosis
Delay = Poor Outcome. Delayed diagnosis leads to difficult repair, quadriceps retraction, and poor function.
At a Glance: Sleeve vs Adult Patella Fractures
| Feature | Sleeve Fracture (Pediatric) | Adult Patella Fracture |
|---|---|---|
| Age | 8-12 years | Adults |
| Avulsed Material | Bony fragment + Cartilage 'Sleeve' | Bone only |
| X-ray Appearance | Small fragment (Underestimates) | Fracture visible |
| Location | Inferior or Superior Pole | Transverse, Stellate, etc. |
| Treatment | ORIF with Sutures/Anchors | ORIF with Wires/Screws |
Mnemonic
SLEEVESleeve Fracture Features
| S | Small Bone Small bony fragment on X-ray |
| L | Large Cartilage Large cartilage avulsion (invisible) |
| E | Extensor Loss Loss of active knee extension |
| E | Eccentric Load Mechanism: Eccentric quadriceps |
| V | Very Young Pediatric age (8-12 yo) |
| E | Early Surgery Early ORIF for displaced |
| S | Small Bone Small bony fragment on X-ray | E | Extensor Loss Loss of active knee extension | V | Very Young Pediatric age (8-12 yo) |
| L | Large Cartilage Large cartilage avulsion (invisible) | E | Eccentric Load Mechanism: Eccentric quadriceps | E | Early Surgery Early ORIF for displaced |
Hook:Key features of Sleeve Fracture.
Mnemonic
JUMPMechanism
| J | Jumping Landing from a jump |
| U | Unexpected Force Sudden eccentric load |
| M | Muscle Contraction Quadriceps contracts |
| P | Pole Avulses Patellar pole pulled off |
| J | Jumping Landing from a jump | M | Muscle Contraction Quadriceps contracts |
| U | Unexpected Force Sudden eccentric load | P | Pole Avulses Patellar pole pulled off |
Hook:Mechanism of injury.
Mnemonic
2-ExSurgical Criteria
| 2 | 2mm Displacement Greater than 2mm = Surgery |
| - | Minus OR... |
| E | Extension Loss of active extension |
| x | X-ray Alta Patella Alta on lateral X-ray |
| 2 | 2mm Displacement Greater than 2mm = Surgery | E | Extension Loss of active extension |
| - | Minus OR... | x | X-ray Alta Patella Alta on lateral X-ray |
Hook:Surgical indications.
Overview and Epidemiology
Definition: A patella sleeve fracture is an avulsion injury of the inferior or superior pole of the patella in which the bony fragment pulls off a 'sleeve' of articular and periarticular cartilage. The cartilage injury is much larger than the visible bone fragment.
Epidemiology:
- Age: 8-12 years (before skeletal maturity).
- Sex: Males greater than Females.
- Sports: Basketball, Soccer, Gymnastics.
Why This Age?
- In children, the cartilage at the patellar poles is weaker than the bone or tendon.
- In adults, the bone or tendon fails (transverse fracture or tendon rupture).
Pathophysiology and Mechanisms
Anatomy:
- Patella: Largest sesamoid bone. Embedded in quadriceps/patellar tendon mechanism.
- Inferior Pole: Attachment of patellar tendon.
- Superior Pole: Attachment of quadriceps tendon.
- Articular Surface: Thick hyaline cartilage.
Pathophysiology:
- Mechanism: Eccentric quadriceps contraction (landing from jump, forceful extension).
- Failure Point: In children, the cartilaginous pole is the weak link.
- Avulsion: The bony pole avulses, taking a 'sleeve' of articular cartilage with it.
- Result: Extensor mechanism disruption. Loss of active knee extension.
Why X-ray Underestimates:
- Only the small ossified bone fragment is visible.
- The large cartilage sleeve is radiolucent.
Classification
By Location
- Inferior Pole Sleeve Fracture: Most common. Patellar tendon attachment.
- Superior Pole Sleeve Fracture: Less common. Quadriceps tendon attachment.
Inferior pole is more common.
Clinical Assessment
History:
- Mechanism: Jumping/Landing. Direct blow rare.
- Pain: Anterior knee. Immediate swelling.
- Function: Cannot straighten knee? Cannot walk?
Physical Examination:
- Swelling: Hemarthrosis.
- Tenderness: Over inferior (or superior) pole.
- Palpable Gap: May feel defect at inferior pole.
- Extensor Mechanism Test: Can the child actively extend the knee against gravity? (Key test).
- If NO = Disrupted mechanism = Needs surgery.
- Straight Leg Raise: Can they lift the leg off the bed with knee extended?
Investigations
Imaging:
- X-ray (AP and Lateral): Lateral is key.
- Small Shell of Bone: At inferior pole.
- Patella Alta: Insall-Salvati ratio greater than 1.2 (Patella is high - tendon has pulled fragment distally).
- Joint Effusion: Hemarthrosis.
- MRI: If diagnosis unclear. Shows full extent of cartilage avulsion.
- Ultrasound: Can assess extensor mechanism if available.
Key Point:
- The X-ray severely UNDERESTIMATES the injury. A small bone chip = Large cartilage avulsion.
Differential Diagnosis
The three inferior-pole pathologies of the immature knee are frequently confused. Clinical function (straight-leg raise, weight-bearing) and patellar height discriminate them far better than fragment size. Figures below are from the 125-patient comparative cohort of Devana et al (Am J Sports Med 2022).
Sleeve Fracture vs Inferior-Pole Fracture vs Sinding-Larsen-Johansson
| Feature | Sleeve Fracture | Inferior-Pole Fracture (IPF) | Sinding-Larsen-Johansson (SLJS) |
|---|---|---|---|
| Onset | Acute trauma (forceful quadriceps) | Acute trauma | Insidious overuse (only ~24% acute) |
| Intact straight-leg raise | ~38% (often lost) | ~94% | ~98% |
| Able to weight-bear | 0% (cannot) | ~12% | ~88% |
| Knee effusion present | ~81% | ~37% | ~3% |
| Mean fragment displacement | ~13.3mm (large) | ~1.45mm | ~1.1mm |
| Mean Insall-Salvati ratio | ~1.92 (marked alta) | ~1.22 | ~1.10 (normal) |
| Default management | ORIF if displaced / no extension | Often non-op; ORIF if extensor loss | Activity modification, rest |
One-line discriminator
A child who cannot straight-leg raise or bear weight, with a tense effusion and patella alta, has a sleeve fracture until proven otherwise — even if the radiograph looks almost normal. SLJS children walk in and lift the leg.
Also consider: acute patellar dislocation with osteochondral fragment, bipartite patella (smooth corticated margin, usually superolateral, often bilateral and asymptomatic), and patellar/quadriceps tendon avulsion in older adolescents.
Controversies & Areas of Uncertainty
- Operative threshold. The widely quoted "greater than 2mm displacement" cut-off is pragmatic rather than trial-derived. The functional test (loss of active extension / straight-leg raise) arguably matters more than any millimetre figure, and current-concept reviews list the non-operative versus operative threshold as genuinely unresolved (Turati et al, J Child Orthop 2025).
- Imaging strategy. Ultrasound (Hunt & Somashekar) and MRI (Bates et al) both reveal the radiolucent cartilage sleeve, but neither is universally available acutely. Whether every suspected case needs cross-sectional imaging, or whether clinical extensor-mechanism failure alone justifies surgery, varies by centre and resources.
- Fixation construct. Transosseous non-absorbable sutures, suture anchors and (in larger ossified fragments) tension-band or screw constructs are all reported; no comparative trial establishes superiority. Choice is guided by fragment ossification and surgeon preference.
- The neglected sleeve. Because the periosteal sleeve continues to ossify, a missed injury can enlarge or duplicate the patella, complicating late reconstruction — a strong argument for early recognition but based on case-level evidence only.
- Evidence ceiling. The entire literature is Level III–V (small retrospective cohorts and reviews); there are no randomised data, so most "rules" are consensus and mechanism-based.
Management Algorithm
Algorithm
Non-Displaced (less than 2mm)
Extensor Mechanism Intact.
- Immobilization: Cylinder cast or Knee Immobilizer in extension for 4-6 weeks.
- Weight-Bearing: WBAT in brace.
- Follow-up: X-ray at 2 weeks (ensure no displacement).
- Rehabilitation: After cast removal - ROM, Quad strengthening.
Must confirm active extension is intact before choosing non-op.
Surgical Technique
Positioning and Exposure
Positioning: Supine with bump under knee for slight flexion. Tourniquet on thigh.
Incision: Midline longitudinal or medial parapatellar approach.
Exposure: Identify the retracted proximal fragment (often flipped superiorly). Irrigate hematoma to visualize the fracture bed.
Standard pediatric knee approach provides excellent access.
Complications
Complications
| Complication | Risk Factor | Management |
|---|---|---|
| Extensor Lag | Inadequate repair | Revision / PT |
| Re-rupture | Early activity | Re-operate |
| Patellofemoral OA | Articular incongruity | Surveillance / Later intervention |
| Stiffness | Prolonged immobilization | PT |
| Missed Diagnosis | Delay in treatment | Early recognition is key |
Postoperative Care
- Immobilization: Cylinder cast or Knee Immobilizer in extension 4-6 weeks.
- Weight-Bearing: WBAT in brace.
- ROM: Start at 4-6 weeks. Gentle.
- Strengthening: Quad strengthening after 6 weeks.
- Return to Sport: 4-6 months (when full strength and ROM).
Outcomes
- Good Outcomes: Expected with early diagnosis and anatomic repair.
- Poor Outcomes: Delayed diagnosis, Articular incongruity, Missed injury.
Evidence Base
Original Description of the Sleeve Fracture
Key Findings:
- Series of 3 children that named and characterised the 'sleeve' avulsion of the patella.
- Warned that the distal bony fragment may be so small it is undetectable on radiographs, while a large fragment of articular cartilage separates with it.
- Best results came from reconstituting the extensor apparatus by internal fixation with repair of the quadriceps expansion.
Clinical Implication: The eponymous paper: radiographs underestimate the injury, so suspect it clinically and repair the extensor mechanism.
Limitation: Three-case report; no comparator and no long-term outcome data.
Avulsion Fractures of the Patella in the Immature Knee
Key Findings:
- 47 skeletally immature patients with marginal patellar avulsions (superior, inferior and medial margins).
- Fractures separate through subchondral bone along the margin of chondro-osseous transformation of the ossification centre.
- Small osseous fragment belies the larger peripheral radiolucent cartilaginous component; treatment is conservative or operative depending on separation and extensor-mechanism integrity.
Clinical Implication: Establishes the anatomic basis for the injury and that displacement plus extensor function — not fragment size — drive the decision to operate.
Limitation: Retrospective case series, single institution, pre-MRI imaging.
MRI Demonstration of the Cartilaginous Avulsion
Key Findings:
- Three children with suspected sleeve fractures; radiographs showed a small bone fragment in two and were normal in one.
- MRI demonstrated separation of most of the cartilaginous lower patella in all three, with definite intra-articular extension in one.
- MRI can determine the need for surgery by depicting the extent of cartilage injury and fragment displacement.
Clinical Implication: When radiographs are equivocal, MRI reveals the true cartilage avulsion and intra-articular extension — use it to make the operative call.
Limitation: Three patients; the journal is Radiology (not Pediatric Radiology, a frequently mis-cited detail).
Sleeve Fractures of the Patella: A Review
Key Findings:
- Synthesises that the sleeve fracture is the most common patella fracture in children and is caused by rapid quadriceps contraction.
- Patella alta is described as the best radiographic sign and ultrasound is highlighted as very helpful when radiographs look normal.
- Untreated, the periosteal 'sleeve' continues to form bone and can enlarge or even duplicate the patella — an argument for prompt reduction and fixation.
Clinical Implication: Awareness is everything: patella alta and ultrasound rescue the diagnosis, and the bone-forming periosteal sleeve is a reason to treat promptly.
Limitation: Narrative review without pooled quantitative outcomes.
Differentiating Sleeve Fracture from IPF and SLJS
Key Findings:
- 125 skeletally immature patients (16 sleeve fractures, 51 inferior-pole fractures, 58 Sinding-Larsen-Johansson) compared clinically and radiographically.
- No sleeve-fracture patient could bear weight and only 38% had an intact straight-leg raise, versus 88% weight-bearing and 98% intact SLR in SLJS.
- Sleeve fractures had the largest fragment displacement (mean 13.3mm) and highest Insall-Salvati ratio (mean 1.92) versus 1.22 (IPF) and 1.10 (SLJS).
Clinical Implication: Loss of straight-leg raise, inability to weight-bear, large fragment displacement and marked patella alta separate a true sleeve fracture from its mimics.
Limitation: Retrospective single-centre cohort; small sleeve-fracture subgroup (n=16).
Paediatric Knee Fractures: Current Concepts
Key Findings:
- Contemporary review grouping patella sleeve and tibial apophyseal fractures as forceful-quadriceps-contraction injuries of the immature knee.
- Highlights ongoing controversies in non-operative versus operative thresholds and fixation choice.
- Stresses careful detection of chondral and sleeve injuries that are easily missed on plain films.
Clinical Implication: Frames sleeve fractures within the spectrum of paediatric extensor-mechanism injuries and flags the unresolved operative-threshold debate.
Limitation: Narrative current-concept review (Level V), no primary outcome data.
AO / Paediatric Trauma Principles
Key Findings:
- Reserve non-operative care (cylinder cast in extension) for non-displaced fractures with a documented intact active extension / straight-leg raise.
- Operative indication: displacement over 2mm, articular incongruity, or loss of active extension.
- Anatomic restoration of the articular surface and extensor mechanism, with retinacular repair, is the surgical goal.
Clinical Implication: Standard reference framework for indications and operative principles across training curricula worldwide.
Limitation: Consensus / textbook guidance rather than trial evidence.
Viva Scenarios
Clinical Decision Scenarios
Use these scenarios to practise clinical reasoning and management decisions
CLINICAL SCENARIOStandard
The Jumping Kid
CLINICAL PROMPT
"What is your diagnosis and management?"
PRACTICAL APPROACH
**Likely Inferior Pole Patella Sleeve Fracture.**
1. **Key Findings**:
- Age 10 (Pediatric).
- Jumping mechanism (Eccentric quad load).
- Cannot straighten knee (Extensor mechanism disrupted).
2. **Examination**:
- Hemarthrosis.
- Tenderness inferior pole.
- Cannot actively extend knee.
3. **Imaging**:
- X-ray Lateral: Small bone chip at inferior pole. Patella Alta.
- (MRI if unclear: Shows cartilage avulsion).
4. **Diagnosis**: Sleeve fracture.
5. **Management**:
- *Displaced + Loss of Extension*: ORIF.
- *Technique*: Transosseous sutures or Anchors. Repair retinaculum.
6. **Post-op**: Cylinder cast 4-6 weeks. PT.
KEY CLINICAL POINTS
Loss of extension = Surgery
X-ray underestimates
Patella Alta = Disruption
ORIF with sutures
COMMON PITFALLS
Trusting the small X-ray fragment
Missing the diagnosis
FURTHER QUESTIONS
"Why does X-ray underestimate?"
"What is the Insall-Salvati ratio?"
CLINICAL SCENARIOStandard
The Small Fragment
CLINICAL PROMPT
"What is the injury and why is X-ray misleading?"
PRACTICAL APPROACH
**Patella Sleeve Fracture. X-ray Underestimates.**
1. **X-ray Finding**: Small bone chip at inferior pole.
2. **Hidden Injury**: The bone chip pulls off a LARGE 'SLEEVE' of articular cartilage. This cartilage is radiolucent (invisible on X-ray).
3. **Patella Alta**: The patella is high because the patellar tendon (attached to the fragment) has pulled the avulsed cartilage distally.
4. **True Injury**: Much larger than the bone chip suggests.
5. **Management Implication**:
- If you treat based on the small bone chip alone, you will undertreat.
- The cartilage sleeve needs anatomic reduction to restore the articular surface.
6. **MRI**: Would show the full extent of cartilage avulsion.
KEY CLINICAL POINTS
Small bone + Large cartilage sleeve
Cartilage is invisible on X-ray
Patella Alta = Extensor disruption
MRI shows true extent
COMMON PITFALLS
Assuming small fragment = Minor injury
Treating conservatively when surgery needed
FURTHER QUESTIONS
"How do you fix this surgically?"
"What if extension is intact?"
CLINICAL SCENARIOStandard
The Surgical Plan
CLINICAL PROMPT
"Outline the surgical technique."
PRACTICAL APPROACH
**ORIF for Inferior Pole Sleeve Fracture.**
1. **Position**: Supine. Tourniquet.
2. **Incision**: Midline longitudinal over patella.
3. **Identify**: Find the avulsed fragment (bone + cartilage sleeve). May be flipped.
4. **Washout**: Clear hematoma.
5. **Prepare Patella**: Freshen bone at inferior pole.
6. **Reduce**: Anatomically reduce cartilage to patella articular surface.
7. **Fixation**:
- *Transosseous Sutures*: Drill 2-3 tunnels in patella (2mm drill). Pass non-absorbable sutures (Ethibond) through tunnels and through cartilage/periosteum of fragment. Tie securely.
- *OR Suture Anchors*: Place anchors in patella pole. Sutures through fragment.
8. **Repair Retinaculum**: Suture medial and lateral retinacular tears.
9. **Check**: Confirm knee can extend. Confirm articular surface is congruent.
10. **Close**: Layered.
11. **Post-op**: Cylinder cast in extension 4-6 weeks.
KEY CLINICAL POINTS
Anatomic cartilage reduction
Transosseous sutures or Anchors
Repair retinaculum
Cast in extension
COMMON PITFALLS
Not repairing retinacular tears
Leaving articular step-off
FURTHER QUESTIONS
"What suture do you use?"
"When do they start ROM?"
MCQ Practice Points
Age Group
Q: What age group typically gets patella sleeve fractures? A: Children aged 8-12 years. The cartilage at the patellar pole is weaker than bone/tendon at this age.
X-ray Appearance
Q: Why does X-ray underestimate patella sleeve fractures? A: Only the small bone fragment is visible. The large avulsed cartilage 'sleeve' is radiolucent and invisible on X-ray.
Clinical Test
Q: What is the key clinical test for patella sleeve fractures? A: Active knee extension test. If the child cannot actively extend the knee, the extensor mechanism is disrupted and surgery is needed.
X-ray Sign
Q: What X-ray sign indicates extensor mechanism disruption? A: Patella Alta (High-riding patella on lateral X-ray). Insall-Salvati ratio greater than 1.2.
Surgical Fixation
Q: How are patella sleeve fractures surgically fixed? A: Transosseous non-absorbable sutures through bone tunnels in the patella, or Suture anchors. The avulsed cartilage is reduced anatomically.
Guidelines, Registries & Global Practice
Global epidemiology
- Patella fractures are rare in children (roughly 1% of paediatric fractures), but among them the sleeve fracture is the most common pattern (Hunt & Somashekar, Knee 2005).
- Peak age 8–12 years, strongly male-predominant (82% male in the Devana et al cohort), reflecting the window of chondro-osseous transformation at the patellar poles.
- Mechanism is consistent worldwide: forceful eccentric quadriceps contraction during jumping/landing sports (basketball, football/soccer, gymnastics).
Side-by-side guidance
How Major Frameworks Approach the Injury
| Body | Emphasis | Practical recommendation |
|---|---|---|
| AO Foundation | Articular & extensor-mechanism restoration | ORIF for displacement over 2mm or extensor loss; anatomic reduction + retinacular repair |
| BOA / BOAST (UK paediatric) | Timely senior review of children's fractures | Urgent assessment of extensor mechanism; cross-sectional imaging when radiograph equivocal |
| AAOS / POSNA (US) | Recognition of the radiographically occult injury | Suspect on clinical grounds (alta, effusion, SLR loss); operative repair when displaced |
| EFORT / European paediatric consensus | Function-led decision-making | Active-extension failure drives surgery as much as millimetre displacement |
Registry note: Paediatric patella sleeve fractures are not tracked by arthroplasty/implant registries (NJR, AJRR, AOANJRR, SHAR) because no implant is registered — evidence remains single-centre cohorts and reviews rather than registry data.
High- vs limited-resource practice
- Well-resourced settings: ready access to MRI/ultrasound to confirm the cartilage sleeve and intra-articular extension; suture-anchor fixation common.
- Limited-resource settings: diagnosis is clinical (patella alta on lateral film, loss of straight-leg raise, tense effusion); transosseous sutures through drill holes are reliable and low-cost. Awareness of the entity is the single biggest determinant of outcome everywhere.
Clinical summary
Key Features
- •Age 8-12 years
- •Small bone + Large cartilage
- •X-ray underestimates
- •Loss of extension = Surgery
Mechanism
- •Eccentric quadriceps contraction
- •Jumping/Landing mechanism
- •Cartilage is weak link (8-12 yo)
- •Sports: Basketball, Soccer, Gymnastics
Treatment
- •Non-displaced: Cast
- •Displaced: ORIF
- •Sutures through bone tunnels
- •Repair retinaculum
Imaging
- •Lateral X-ray: Small bone chip at pole
- •Patella Alta (IS ratio greater than 1.2)
- •MRI shows full cartilage extent
- •Hemarthrosis on imaging