EXTENSOR MECHANISM RUPTURES
Quadriceps Tendon | Patellar Tendon | Primary Repair vs Allograft
RUPTURE TYPES
Critical Must-Knows
- Acute rupture (under 6 weeks): Primary repair with Krackow weave - 85-95% success rate
- Chronic rupture (over 6 weeks): Achilles allograft reconstruction - 60-80% success rate
- Gap size threshold: Under 2cm = primary repair, over 2cm = allograft reconstruction
- Patellar height critical: Insall-Salvati ratio 0.8-1.2 - overtightening causes patella baja and stiffness
- Tension setting: Knee in full extension, confirm patellar height on image intensifier
Examiner's Pearls
- "Extensor mechanism rupture = inability to perform straight leg raise (pathognomonic)
- "Quadriceps rupture more common in older patients (over 40), patellar tendon in younger (under 40)
- "Primary repair for acute ruptures (under 6 weeks, gap under 2cm) - excellent outcomes
- "Achilles allograft for chronic ruptures (over 6 weeks, gap over 2cm) - good outcomes but lower than primary repair
Clinical Imaging
Imaging Gallery
Critical Extensor Mechanism Rupture Exam Points
Pathognomonic Sign
Inability to perform straight leg raise = complete extensor mechanism rupture. This is pathognomonic. Partial ruptures may have extensor lag (10-90 degrees). Always test straight leg raise in suspected cases.
Acute vs Chronic
Acute (under 6 weeks, gap under 2cm): Primary repair with Krackow weave - 85-95% success. Chronic (over 6 weeks, gap over 2cm): Achilles allograft reconstruction - 60-80% success. Timing and gap size determine treatment.
Patellar Height Critical
Insall-Salvati ratio 0.8-1.2 - must restore normal patellar height. Overtightening causes patella baja and stiffness. Undertightening causes patella alta and weakness. Set tension with knee in full extension.
Allograft Selection
Achilles allograft is gold standard - provides calcaneal bone block for tibial tubercle fixation (bone-to-bone healing) and adequate length (15-18cm). Alternative: extensor mechanism allograft for massive defects.
Extensor Mechanism Ruptures - Quick Decision Guide
| Type | Location | Age Group | Treatment |
|---|---|---|---|
| Quadriceps tendon | Superior to patella | Over 40 years | Primary repair (acute) or allograft (chronic) |
| Patellar tendon | Inferior to patella | Under 40 years | Primary repair (acute) or allograft (chronic) |
| Acute rupture | Under 6 weeks, gap under 2cm | Any age | Primary repair with Krackow weave |
| Chronic rupture | Over 6 weeks, gap over 2cm | Any age | Achilles allograft reconstruction |
RUPTUREExtensor Mechanism Rupture Features
Memory Hook:RUPTURE: Cannot Raise leg (pathognomonic), Urgent repair better, Patellar height critical, Tension in Extension, Under 2cm gap = repair, Reconstruction for chronic!
ACUTEPrimary Repair Indications
Memory Hook:ACUTE repair for Acute injury, Close gap, Uncomplicated case, good Tissue quality, Early timing!
CHRONICAllograft Reconstruction Indications
Memory Hook:CHRONIC cases need allograft: Chronic injury, Huge gap, Revision, Old tissue, No length, Insufficient tissue, Complex case!
Overview and Epidemiology
Extensor mechanism ruptures involve disruption of the quadriceps tendon, patellar tendon, or both, resulting in loss of active knee extension. These injuries can be acute traumatic ruptures or chronic degenerative failures. Treatment depends on timing (acute vs chronic), gap size, and tissue quality.
Mechanism of Injury
Quadriceps tendon rupture:
- Eccentric contraction: Sudden quadriceps contraction against resistance (falling, jumping)
- Age factor: More common in patients over 40 (tendon degeneration)
- Risk factors: Steroids, diabetes, renal disease, quinolone antibiotics
- Location: Usually at insertion on superior pole of patella
Patellar tendon rupture:
- Eccentric contraction: Sudden quadriceps contraction with knee flexion
- Age factor: More common in patients under 40 (athletic activity)
- Risk factors: Previous patellar tendonitis, Osgood-Schlatter disease, steroids
- Location: Usually at insertion on inferior pole of patella or tibial tubercle
Pathognomonic Sign
Inability to perform straight leg raise = complete extensor mechanism rupture. This is pathognomonic. Partial ruptures may have extensor lag (10-90 degrees). Always test straight leg raise in suspected cases - if patient cannot lift heel off bed, rupture is complete.
Epidemiology
- Incidence: 1-2% of knee injuries
- Quadriceps tendon: Peak age 40-60 years, male predominance
- Patellar tendon: Peak age 20-40 years, male predominance
- Bilateral: Rare (5-10%), usually associated with systemic disease (renal failure, steroids)
- Associated injuries: Patellar fractures, tibial tubercle avulsions (pediatric)
Anatomy and Pathophysiology
Extensor Mechanism Anatomy
The extensor mechanism consists of:
- Quadriceps muscle: Vastus medialis, vastus lateralis, vastus intermedius, rectus femoris
- Quadriceps tendon: Inserts on superior pole of patella
- Patella: Sesamoid bone, improves mechanical advantage
- Patellar tendon: Inserts on tibial tubercle
- Medial/lateral retinaculum: Secondary extensors
Blood supply:
- Superior: Descending genicular artery (quadriceps tendon)
- Inferior: Anterior tibial recurrent artery (patellar tendon)
- Patella: Peripatellar plexus (vulnerable to injury)
Pathophysiology
Acute rupture:
- Traumatic: Sudden eccentric contraction
- Tissue quality: Usually good (healthy tendon)
- Gap size: Usually under 2cm (can be approximated)
- Healing potential: Excellent with primary repair
Chronic rupture:
- Degenerative: Progressive tendon weakening
- Tissue quality: Poor (degenerated, friable)
- Gap size: Usually over 2cm (cannot be approximated)
- Healing potential: Poor - requires allograft reconstruction
Risk factors for rupture:
- Systemic: Steroids, diabetes, renal disease, quinolone antibiotics
- Local: Previous tendonitis, Osgood-Schlatter disease, patellar tendinopathy
- Age: Quadriceps (over 40), patellar tendon (under 40)
Patellar Blood Supply
The patella has a tenuous blood supply through the peripatellar plexus. Extensive dissection or multiple surgeries can compromise blood supply, leading to avascular necrosis. Preserve retinaculum and minimize dissection when possible.
Classification Systems
Location-Based Classification
Quadriceps tendon rupture:
- Superior to patella
- More common in older patients (over 40)
- Usually at insertion on superior pole
- May extend into muscle belly (rare)
Patellar tendon rupture:
- Inferior to patella
- More common in younger patients (under 40)
- Usually at insertion on inferior pole or tibial tubercle
- May be midsubstance (rare)
Combined rupture:
- Both quadriceps and patellar tendon
- Usually high-energy trauma
- Requires extensive reconstruction
Location-based classification helps guide surgical approach and reconstruction strategy.
Clinical Assessment
History
Mechanism: Eccentric quadriceps contraction
- Falling with knee flexion
- Jumping/landing
- Sudden change in direction
- Direct trauma (rare)
Symptoms:
- Immediate pain and swelling
- Inability to extend knee actively
- "Pop" or "snap" sensation
- Inability to bear weight
- Knee "giving way"
Physical Examination
Inspection:
- Knee effusion (hemarthrosis)
- Visible/palpable defect (superior or inferior to patella)
- Patellar position: Alta (patellar tendon rupture) or baja (quadriceps rupture)
- Ecchymosis (acute ruptures)
- Previous surgical scars
Palpation:
- Quadriceps rupture: Gap superior to patella
- Patellar tendon rupture: Gap between patella and tibial tubercle
- Tenderness at rupture site
- Patellar position assessment
Range of Motion:
- Passive: Usually full (pain-limited)
- Active: Cannot extend (complete rupture) or extensor lag (partial rupture)
- Flexion: May be limited by pain
Special Tests:
- Straight leg raise: Pathognomonic - inability to perform = complete rupture
- Extensor lag: Measure angle of lag (10-90 degrees = partial rupture)
- Patellar height: Insall-Salvati ratio (normal 0.8-1.2)
Clinical Examination Key Point
Straight leg raise test is pathognomonic for complete extensor mechanism rupture. If patient cannot lift heel off bed, rupture is complete. Partial ruptures may have extensor lag (10-90 degrees). Always test straight leg raise in suspected cases.
Imaging
Radiographs:
- AP and lateral knee: Assess patellar height (Insall-Salvati ratio)
- Patella alta: Suggests patellar tendon rupture
- Patella baja: Suggests quadriceps rupture
- Avulsion fractures: May see bony avulsion at insertion sites
Ultrasound:
- Can visualize tendon discontinuity
- Assess gap size
- Evaluate tissue quality
- Useful for diagnosis but MRI preferred
MRI:
- Gold standard for diagnosis
- Shows exact location and extent of rupture
- Assesses gap size
- Evaluates tissue quality
- Identifies associated injuries
Imaging Gallery
Investigations
Standard X-ray Protocol
Views: AP and lateral knee.
Key findings:
- Patellar height: Insall-Salvati ratio (normal 0.8-1.2)
- Patella alta: Suggests patellar tendon rupture
- Patella baja: Suggests quadriceps rupture
- Avulsion fractures: Bony avulsion at insertion sites
- Associated fractures: Patellar fractures, tibial tubercle avulsions
Lateral view is critical - shows patellar height and any avulsion fractures.
Management Algorithm
Management Pathway
Extensor Mechanism Rupture Management
Determine location (quadriceps vs patellar tendon), timing (acute vs chronic), gap size (under vs over 2cm), and tissue quality.
If gap under 2cm and good tissue quality, primary repair with Krackow weave. Excellent outcomes (85-95% success).
If gap over 2cm or poor tissue quality, Achilles allograft reconstruction. Good outcomes (60-80% success).
Immobilize in extension for 4-6 weeks. Begin ROM at 2-4 weeks. No active extension for 8-12 weeks. Progressive strengthening.
Surgical Technique
Primary Repair Technique
Indications:
- Acute rupture (under 6 weeks)
- Gap under 2cm after mobilization
- Good tissue quality
- First-time rupture
Patient Positioning:
- Supine on standard table
- Tourniquet on thigh
- Bump under ipsilateral hip
- Contralateral leg abducted
Incision:
- Midline anterior incision
- Extend as needed for exposure
- Full-thickness flaps
Exposure:
- Evacuate hematoma
- Identify rupture edges
- Assess tissue quality
- Mobilize tendon edges
Repair Technique:
- Krackow weave: No. 5 non-absorbable suture (Ethibond or Fiberwire)
- Quadriceps rupture: 3-4 throws each side, pass through patellar tunnels, tie over inferior pole
- Patellar tendon rupture: 3-4 throws each side, pass through patellar tunnels, tie over superior pole
- Augmentation: Side-to-side sutures, retinacular repair
- Tensioning: Knee in full extension, confirm Insall-Salvati ratio 0.8-1.2
Closure: Layered closure, hinged brace locked in extension.
Patellar Height is Critical
Insall-Salvati ratio must be 0.8-1.2 - this is critical for function. Overtightening causes patella baja and stiffness. Undertightening causes patella alta and weakness. Always set tension with knee in full extension and confirm patellar height on image intensifier before closing.
Complications
| Complication | Incidence | Risk Factors | Prevention/Management |
|---|---|---|---|
| Re-rupture | 5-10% | Inadequate fixation, early active extension | Secure fixation, protect for 8-12 weeks |
| Stiffness | 10-20% | Overtightening, prolonged immobilization | Proper tension, early ROM (2-4 weeks) |
| Weakness | 15-25% | Undertightening, incomplete rehabilitation | Proper tension, complete rehabilitation |
| Patella baja/alta | 5-10% | Improper tension setting | Confirm Insall-Salvati ratio 0.8-1.2 |
| Infection | 2-5% | Open injury, comorbidities | Aseptic technique, antibiotics |
| Nonunion | Less than 5% | Poor fixation, poor tissue quality | Secure fixation, good tissue apposition |
Re-rupture
5-10% incidence:
- Cause: Inadequate fixation, early active extension, poor tissue quality
- Prevention: Secure fixation, protect for 8-12 weeks (no active extension)
- Management: Revision repair or allograft reconstruction
Stiffness
10-20% incidence:
- Cause: Overtightening, prolonged immobilization, arthrofibrosis
- Prevention: Proper tension (Insall-Salvati 0.8-1.2), early ROM (2-4 weeks)
- Management: Manipulation under anesthesia, arthroscopic lysis of adhesions
Weakness
15-25% incidence:
- Cause: Undertightening, incomplete rehabilitation, muscle atrophy
- Prevention: Proper tension, complete rehabilitation program
- Management: Revision repair if undertightened, continued rehabilitation
Postoperative Care
Immediate Postoperative
- Immobilization: Hinged knee brace locked in extension (4-6 weeks)
- Weight bearing: Non-weight bearing initially (2-3 weeks)
- ROM: Begin passive ROM at 2-4 weeks (unlock brace)
- PT: Quadriceps sets, straight leg raises (immediate)
Rehabilitation Protocol
Weeks 0-2:
- Brace locked in extension
- Non-weight bearing
- Quadriceps sets, straight leg raises
- Ice and elevation
Weeks 2-4:
- Unlock brace for passive ROM (0-90 degrees)
- Progressive weight bearing (partial to full)
- Continue quadriceps strengthening
- No active extension (protect repair)
Weeks 4-6:
- Full passive ROM
- Full weight bearing
- Continue quadriceps strengthening
- No active extension (still protecting repair)
Weeks 6-8:
- Begin active extension (gradual)
- Progressive strengthening
- Balance and proprioception
Weeks 8-12:
- Full active extension
- Progressive resistance training
- Sport-specific training
- Return to sport (when strength adequate)
Return to Sport
Criteria:
- Full ROM (equal to contralateral)
- Quadriceps strength greater than 90% of contralateral
- No extensor lag
- Functional testing passed
Timeline: Usually 4-6 months postoperatively.
Outcomes and Prognosis
Overall Outcomes
Acute primary repair:
- Success rate: 85-95%
- Functional outcomes: 80-90% return to pre-injury level
- Complications: 10-20% (stiffness, weakness, re-rupture)
Chronic allograft reconstruction:
- Success rate: 60-80%
- Functional outcomes: 60-70% return to pre-injury level
- Complications: 20-30% (stiffness, weakness, re-rupture)
Functional Outcomes
Return to sport:
- Timeline: 4-6 months postoperatively
- Rate: 70-80% return to pre-injury level
- Factors: Age, sport level, rehabilitation compliance
Functional testing:
- Quadriceps strength: 90%+ of contralateral
- No extensor lag
- Full ROM
Long-Term Prognosis
Re-rupture risk:
- Acute repair: 5-10% (usually with inadequate fixation or early active extension)
- Allograft reconstruction: 10-15% (higher due to chronicity and tissue quality)
Stiffness risk:
- Acute repair: 10-15% (usually with overtightening)
- Allograft reconstruction: 15-20% (higher due to chronicity)
Weakness risk:
- Acute repair: 10-15% (usually with undertightening or incomplete rehabilitation)
- Allograft reconstruction: 20-25% (higher due to chronicity and muscle atrophy)
Factors Affecting Outcomes
Positive factors:
- Early repair (within 2 weeks)
- Good tissue quality
- Secure fixation
- Proper tension (Insall-Salvati 0.8-1.2)
- Complete rehabilitation
Negative factors:
- Delayed repair (over 6 weeks)
- Poor tissue quality
- Inadequate fixation
- Improper tension (patella baja/alta)
- Incomplete rehabilitation
Prevention and Return to Sport
Prevention
Primary prevention:
- Proper landing technique (knee flexion, not hyperextension)
- Strength training (quadriceps, hamstrings)
- Flexibility training
- Avoid sudden eccentric loading
Secondary prevention (after injury):
- Complete rehabilitation before return to sport
- Continued strength and conditioning
- Gradual return to activity
- Sport-specific training
Return to Sport Criteria
Clinical:
- Full ROM (equal to contralateral)
- Quadriceps strength greater than 90% of contralateral
- No extensor lag
- No effusion
Functional:
- Single-leg hop test (greater than 90% of contralateral)
- Agility testing passed
- Sport-specific drills completed
Timeline: Usually 4-6 months postoperatively, depending on sport and level.
Evidence Base
Primary Repair Outcomes
- Original description of primary repair technique
- Acute repairs (under 6 weeks) achieve 85-95% success rate
- Proper technique critical for outcomes
Allograft Reconstruction Outcomes
- Achilles allograft reconstruction for chronic ruptures: 60-80% success rate
- Good outcomes but lower than primary repair
- Patellar height critical for function
Gap Size Threshold
- Gap size under 2cm allows primary repair with good outcomes
- Gap over 2cm requires allograft reconstruction
- Gap size is key determinant of treatment
Patellar Height and Outcomes
- Insall-Salvati ratio 0.8-1.2 is normal
- Overtightening causes patella baja and stiffness
- Undertightening causes patella alta and weakness
Timing of Repair
- Early repair (within 2 weeks) has better outcomes than delayed repair
- Acute repairs (under 6 weeks) achieve 85-95% success
- Chronic repairs (over 6 weeks) achieve 60-80% success
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Acute Quadriceps Rupture
"A 55-year-old man presents to ED after falling down stairs. He cannot extend his knee or perform a straight leg raise. Examination shows a palpable defect superior to the patella and patella baja. X-ray shows patella baja. MRI shows complete quadriceps tendon rupture with a 1.5cm gap."
Scenario 2: Chronic Patellar Tendon Rupture
"A 35-year-old athlete presents 3 months after a patellar tendon rupture that was initially missed. He has persistent extensor lag of 30 degrees and cannot return to sport. Examination shows a palpable defect between patella and tibial tubercle, patella alta, and quadriceps atrophy. MRI shows chronic patellar tendon rupture with a 4cm gap and poor tissue quality."
MCQ Practice Points
Pathognomonic Sign
Q: What is the pathognomonic sign of complete extensor mechanism rupture? A: Inability to perform straight leg raise - If patient cannot lift heel off bed, rupture is complete. Partial ruptures may have extensor lag (10-90 degrees).
Acute vs Chronic Treatment
Q: What is the treatment for an acute extensor mechanism rupture (under 6 weeks, gap under 2cm)? A: Primary repair with Krackow weave - Acute repairs achieve 85-95% success rate. Chronic ruptures (over 6 weeks, gap over 2cm) require allograft reconstruction (60-80% success).
Gap Size Threshold
Q: What gap size threshold determines primary repair vs allograft reconstruction? A: 2cm - Gap under 2cm allows primary repair. Gap over 2cm requires allograft reconstruction. Gap size is key determinant of treatment.
Patellar Height
Q: What is the normal Insall-Salvati ratio and why is it critical? A: 0.8-1.2 - Overtightening causes patella baja and stiffness. Undertightening causes patella alta and weakness. Patellar height is critical for function.
Allograft Selection
Q: What is the gold standard allograft for extensor mechanism reconstruction? A: Achilles allograft - Provides calcaneal bone block for tibial tubercle fixation (bone-to-bone healing) and adequate length (15-18cm) to bridge gaps.
Timing of Repair
Q: What is the optimal timing for acute extensor mechanism repair? A: Within 2 weeks - Early repair has better outcomes than delayed repair. Acute repairs (under 6 weeks) achieve 85-95% success vs 60-80% for chronic (over 6 weeks).
Australian Context
Clinical Practice
- Extensor mechanism ruptures common in trauma and sports
- Primary repair standard for acute cases
- Achilles allograft for chronic cases
- Early ROM and aggressive PT emphasized
Healthcare System
- Extensor mechanism repair covered under public system
- Public hospitals handle most cases
- Private insurance covers procedures
- Physiotherapy accessible through public/private
Orthopaedic Exam Relevance
Extensor mechanism ruptures are a common viva topic. Know the pathognomonic sign (inability to perform straight leg raise), acute vs chronic treatment (primary repair vs allograft), gap size threshold (2cm), patellar height (Insall-Salvati 0.8-1.2), and allograft selection (Achilles allograft). Be prepared to discuss surgical technique and complications.
EXTENSOR MECHANISM RUPTURES
High-Yield Exam Summary
Key Anatomy
- •Extensor mechanism: Quadriceps → quadriceps tendon → patella → patellar tendon → tibial tubercle
- •Insall-Salvati ratio: Normal 0.8-1.2 (patellar length / patellar tendon length)
- •Patella alta: Suggests patellar tendon rupture
- •Patella baja: Suggests quadriceps rupture
Classification
- •By location: Quadriceps tendon (over 40) vs patellar tendon (under 40)
- •By timing: Acute (under 6 weeks) vs chronic (over 6 weeks)
- •By gap size: Under 2cm (primary repair) vs over 2cm (allograft)
- •By tissue quality: Good (primary repair) vs poor/degenerated (allograft)
- •Subacute (4-8 weeks): Gray zone - assess gap and tissue quality
Treatment Algorithm
- •Acute (under 6 weeks, gap under 2cm): Primary repair with Krackow weave
- •Chronic (over 6 weeks, gap over 2cm): Achilles allograft reconstruction
- •Gap size threshold: 2cm (key determinant)
- •Timing: Early repair (within 2 weeks) has better outcomes
Surgical Pearls
- •Krackow weave: No. 5 non-absorbable suture, 3-4 throws each side
- •Patellar height critical: Insall-Salvati ratio 0.8-1.2
- •Tension setting: Knee in full extension, confirm on image intensifier
- •Achilles allograft: Bone block for tibial fixation, adequate length (15-18cm)
Complications
- •Re-rupture: 5-10% (prevent with secure fixation, protect 8-12 weeks)
- •Stiffness: 10-20% (prevent with proper tension, early ROM)
- •Weakness: 15-25% (prevent with proper tension, complete rehabilitation)
- •Patella baja/alta: 5-10% (prevent with proper tension setting)