Pediatric Patella Sleeve Fractures
Avulsion of Cartilaginous Pole | Extensor Mechanism Injury
Patella Sleeve Fracture
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.
Examiner's 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 |
SLEEVESleeve Fracture Features
Memory Hook:Key features of Sleeve Fracture.
JUMPMechanism
Memory Hook:Mechanism of injury.
2-ExSurgical Criteria
Memory 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.
Management 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
Sleeve Fracture Description
- Described the 'sleeve' avulsion of cartilage.
- Emphasized X-ray underestimation.
- Recommended early surgical repair.
Pediatric Patella Fractures
- Reviewed patella fractures in children.
- Sleeve fractures are unique to pediatrics.
- Good outcomes with ORIF.
Surgical Outcomes
- ORIF with transosseous sutures effective.
- Good restoration of extensor mechanism.
- Early diagnosis is key.
MRI for Sleeve Fractures
- MRI shows the full extent of cartilage avulsion.
- Useful when X-ray is inconclusive.
Patella Alta in Sleeve Fractures
- Patella Alta on lateral X-ray is a key sign.
- Indicates extensor mechanism disruption.
Viva Scenarios
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
The Jumping Kid
"What is your diagnosis and management?"
The Small Fragment
"What is the injury and why is X-ray misleading?"
The Surgical Plan
"Outline the surgical technique."
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.
Australian Context
- Pediatric Emergency: Common presentation to pediatric hospitals.
- Early Referral: Important to recognize and refer early.
- Sports Medicine: Seen in basketball, soccer, gymnastics.
High-Yield Exam 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