High Yield Overview
MENISCAL ROOT TEARS
The Silent Meniscectomy
Extrusiongreater than 3mm
Pressure+200%
ConversionTKA Risk
SignGhost
LaPrade Classification
Type 1
PatternPartial tear (stable)
TreatmentObservation/Debridement
Type 2
PatternComplete radial tear less than 9mm from root
TreatmentRepair
Type 4
PatternComplex oblique tear into root
TreatmentRepair vs Partial Meiscectomy
Critical Must-Knows
- A root tear is biomechanically equivalent to a total meniscectomy.
- Hoop stress is lost, leading to peak contact pressure increase.
- Medial root tears are more common (degenerative/deep flexion).
- Lateral root tears are associated with ACL tears.
- The 'Ghost Sign' on Sagittal MRI is pathognomonic.
Examiner's Pearls
- "Always look for the root tea in patients with a 'pop' during deep squatting.
- "Extrusion greater than 3mm indicates incompetence of the meniscus.
- "Spontaneous Osteonecrosis of the Knee (SONK) is often secondary to a missed root tear.
Clinical Imaging
Imaging Gallery
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High Yield Concept
The Biomechanical Disaste
Loss of Hoop Stress. The meniscus functions to convert axial load into hoop stress. When the root tears, this mechanism fails completely. The femur articulates directly with the tibia (bone-on-bone forces).
Association
Lateral vs Medial.
- Medial: Degenerative, Middle-aged, Deep Flexion (Squatting/Gardening).
- Lateral: Acute, Young, ACL Tear association (10-15%).
| Feature | Medial Root | Lateral Root |
|---|---|---|
| Mechanism | Deep Flexion/Degenerative | Acute Trauma (ACL) |
| Patient Age | 50-60s | 20-30s |
| Arthritis Risk | High (Rapid Progression) | High (Lateral OA) |
| Repair Urgency | Semi-urgent (Prevent OA) | Acute (With ACL) |
Mnemonic
ROOTSIndications for Repair
R
Rotational
Control rotational stability
O
OA
Mild OA (Kellgren-Lawrence less than 3)
O
Outer
Outerbridge 1-2 only
T
Timing
Acute/Subacute preferred
S
Stable
Stable knee/alignment (Correct varus first)
Memory Hook:Plant the ROOTS to save the tree (knee).
Mnemonic
GHOSTMRI Signs
G
Ghost
Ghost Sign (Empty Sagittal view)
H
High
High signal at root
O
Out
Extrusion (Out of joint, greater than 3mm)
S
Subchondral
Subchondral edema (SONK-like)
T
Truncated
Truncated meniscus sign
Memory Hook:The meniscus is a GHOST.
Mnemonic
BAD KNEEContraindications
B
BMI
greater than 35 (Relative)
A
Arthritis
Severe OA (KL 3-4)
D
Dealignment
Severe Malalignment (uncorrected)
KNEE
Knee
Unstable knee (e.g. chronic ACL deficiency)
Memory Hook:Don't fix a BAD KNEE.
Overview
The Silent Epidemic
Meniscal root tears are often missed in primary care. Patients present with posterior knee pain after a minor event (squatting). X-rays are often normal or show mild OA. Without MRI, the diagnosis is missed, leading to rapid joint destruction (SONK).
A meniscal root tear is defined as an avulsion of the meniscal attachment (or tear within 1cm of the attachment). It results in the complete loss of the ability of the meniscus to withstand circumferential hoop tension, rendering the meniscus functionally incompetent.
This injury was historically under-recognized and often treated as a simple meniscal tear. However, modern biomechanical understanding has redefined it as a major structural failure requiring urgent attention. It represents a "silent" cause of rapid joint destruction.
Anatomy and Biomechanics
Insertion Sites
- Medial Root:
- Posterior to the medial tibial spine.
- 1cm posterior to the ACL connection.
- Located on the downslope of the retro-eminence.
- Approximately 9.6mm posterior and 0.7mm lateral to the apex of the medial tibial eminence.
- Close proximity to the PCL insertion.
- Lateral Root:
- Adjacent to the ACL footprints.
- Often torn with ACL avulsion.
The medial root is most vulnerable to shear in deep flexion.
Pathophysiology
Mechanism of Injury
Traumatic root tears:
- Deep flexion during squat or kneeling activities
- Pivot mechanism with axial loading
- Posterior horn trapped between femoral condyle and tibial plateau
- More common in young active patients
Degenerative root tears:
- Chronic degeneration of root attachment
- Often associated with existing osteoarthritis
- Common in patients over 50 years
- May occur with minimal trauma ("pop while getting up from chair")
Loss of Hoop Stress - The Critical Concept
The meniscal root anchors circumferential collagen fibers that convert axial load into circumferential (hoop) stress. When the root is torn:
- Circumferential fibers lose their anchor point
- Axial load cannot be converted to hoop stress
- Meniscus extrudes radially
- Functionally equivalent to total meniscectomy
- 25% immediate loss of tibiofemoral contact area
- Rapid progression to medial compartment osteoarthritis
Natural History Without Treatment
Untreated medial meniscal root tears progress predictably:
- Meniscal extrusion of greater than 3mm within months
- Progressive cartilage degeneration
- Development of medial compartment OA within 2-5 years
- Eventual need for knee arthroplasty
Classification Systems
LaPrade Classification (Morphology)
- Type 1: Partial stable root tear.
- Type 2: Complete radial tear within 9mm of root. (Most common operative type).
- Type 3: Bucket-handle tear extending into root.
- Type 4: Complex oblique tear into root.
- Type 5: Avulsion fracture of the root attachment.
Type 2 and 4 are the classic "Root Tears" requiring repair.
Type 5 is essentially an avulsion fracture.
History
Patient History
- Mechanism: Usually non-contact. "Pop" felt while squatting, kneeling, or descending stairs.
- Pain: Posterior knee pain. Constant.
- Locking: Mechanical locking is UNCOMMON (unlike bucket handle tears).
The absence of locking often delays presentation.
Examination
Physical Exam
- Effusion: Mild to moderate.
- Joint Line Tenderness: Posterior medial joint line (highly sensitive).
- Seated McMurray: Pain with external rotation/varus.
- Deep Squat: Pain at maximum flexion.
A high index of suspicion is required to avoid missing this diagnosis.
Imaging: MRI
The Ghost Sign
Sagittal View is Key. On sagittal sequences, the posterior horn normally appears as a black triangle ("Bow tie"). In a root tear, this triangle is absent or replaced by fluid signal. This is the "Ghost Sign".
MRI Signs
- Ghost Sign: Absence of meniscus on sagittal cut.
- Cleft Sign: Fluid signal (vertical line) at the root on T2 Coronal.
- Radial Extrusion: Greater than 3mm extrusion of the medial meniscus body relative to the tibial plateau (Coronal view).
- Giraffe Neck Sign: Distortion of the meniscus.
Look for edema in the subchondral bone adjacent to the root.
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Management Algorithm
📊 Management Algorithm
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Decision Making
- Group A (Ideal): Age less than 65, BMI less than 35, KL Grade 0-2, Normal alignment. ACTION: REPAIR.
- Group B (Borderline): Mild varus, Age greater than 65 but active. ACTION: Consider HTO + Repair.
- Group C (Poor): Severe OA (KL 3-4), Fixed flexion deformity. ACTION: Non-operative / Total Knee.
Partial meniscectomy is reserved for failed repairs or symptomatic relief in poor candidates, but it accelerates OA.
Surgical Considerations
Transtibial Pull-out Repair
- Concept: Sutures passed through the root, pulled down a tibial tunnel, and fixed on the anterior tibia (Button).
- Pros: Strong restoration of footprint.
- Cons: "Bungee cord" effect (suture elongation), technically demanding.
- Steps:
- Debride root footprint to bleeding bone.
- Pass sutures (Luggagetag/Cinch) through meniscus.
- Drill tibial tunnel using ACL guide (aiming at footprint).
- Pass sutures down tunnel.
- Fix over button on anterior tibia.
Ensure the tunnel exit point doesn't compromise the PES attachment.
Complications
- Failure of Repair: Suture breakage or pull-through (10-15%).
- Progression of OA: Despite repair, some arthritis may progress.
- Arthrofibrosis: Stiffness due to immobilization.
- Posterior Neurovascular Injury: Risk during drilling or anchor placement (Popliteal vessels are directly posterior).
- Saphenous Nerve Injury: During tibial tunnel drilling/button placement.
- Meniscal Cyst Formation: Can occur at the repair site or due to fluid leak.
- Iatrogenic Cartilage Injury: During instrumentation in the tight posterior compartment.
Rehabilitation
-
Phase 1 (0-6 weeks):
- Non-weight bearing (or toe-touch) in brace in extension.
- Passive ROM 0-90 degrees.
- Avoid deep flexion (greater than 90) to protect repair.
-
Phase 2 (6-12 weeks):
- Progress to full weight bearing.
- Full ROM.
- Closed chain strengthening.
-
Phase 3 (3-6 months):
- Return to running.
-
Phase 4 (greater than 6 months):
- Return to sport/squatting.
Note: Protocol is surprisingly slow compared to meniscectomy because root healing takes time.
Return to Sport Criteria
- Full pain-free range of motion.
- No effusion.
- Quadriceps strength greater than 90% of contralateral side.
- Hamstring strength greater than 90% of contralateral side.
- Successful completion of functional hop tests.
- Timeframe: Usually 6-9 months post-operatively.
Early return leads to failure of the repair construct.
Prognosis
Outcomes by Treatment
- Repair Survival: 5-year survival approximately 85% in ideal candidates.
- Extrusion Response: Rarely improves fully, but progression is halted with repair.
- OA Progression: Significantly slower than meniscectomy, but faster than normal knee.
- Meniscectomy: Rapid OA progression within 2-3 years in most patients.
Prognostic Factors
| Factor | Favorable | Unfavorable |
|---|---|---|
| Age | Less than 50 years | Greater than 65 years |
| BMI | Less than 30 | Greater than 35 |
| Cartilage | Outerbridge 0-2 | Outerbridge 3-4 |
| Alignment | Neutral | Varus greater than 5 degrees |
| Timing | Acute (less than 6 weeks) | Chronic (greater than 3 months) |
Long-Term Considerations
- Conversion to TKA: 30% at 5 years in non-operative management vs 10-15% with repair.
- Functional Outcomes: Significant improvement in IKDC and Lysholm scores with repair.
- Activity Level: Most patients return to recreational activities but may need to modify high-impact sports.
Evidence Base
Biomechanics of Root Repair
Allaire et al. • J Bone Joint Surg Am (2008)
Key Findings:
- Cadaveric study measuring contact pressures
- Root tear increased peak contact pressure by 25%
- Total meniscectomy increased it by 26% (Statistically indistinguishable)
- Repair restored pressures to normal
Clinical Implication: Root tear IS a functional meniscectomy.
Outcomes of Pull-out Repair
Chahla et al. • Am J Sports Med (2016)
Key Findings:
- Systematic review of 11 studies
- Significant improvement in Lysholm and IKDC scores
- Failures usually due to progression of OA in older patients
Clinical Implication: Repair is effective for symptoms and function.
SONK association
Robertson et al. • Knee (2009)
Key Findings:
- Review of SONK patients
- 80% had associated medial Meniscal Root Tear
- Suggests SONK is actually subchondral insufficiency fracture secondary to overload
Clinical Implication: Look for the root tear in SONK.
Classification System
LaPrade et al. • Am J Sports Med (2015)
Key Findings:
- Proposed the 5-type classification system
- Type 2 (Complete radial tear) most common
- Type 1 and 5 were stable in some patterns
Clinical Implication: Standardized reporting helps surgical planning.
Biomechanical Consequences
Bhatia et al. • Knee Surg Sports Traumatol Arthrosc (2014)
Key Findings:
- Finite element analysis of root tears
- Confirmed hoop stress loss hypothesis
- Demonstrated that extrusion is a secondary phenomenon to root failure
Clinical Implication: The root is the anchor of the meniscus.
Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Scenario 1: The Pop in the Garden
EXAMINER
"A 55-year-old female presents with acute posterior knee pain after squatting in the garden. She felt a pop. X-rays show mild OA. What is your differential?"
EXCEPTIONAL ANSWER
This is a classic presentation for a Medial Meniscal Root Tear. The mechanism of deep flexion in a middle-aged patient with 'pop' and posterior knee pain is pathognomonic. My differential would include: primary diagnosis of medial meniscal root tear, degenerative meniscal tear, spontaneous osteonecrosis of the knee (SONK which is often secondary to root tears), pes anserine bursitis, and posterior capsular strain. I would urgently arrange an MRI to assess for the Ghost Sign on sagittal sequences, meniscal extrusion greater than 3mm on coronal views, and the Cleft Sign at the root attachment. If confirmed, and she has Kellgren-Lawrence Grade 0-2 OA with acceptable alignment, I would recommend semi-urgent transtibial pull-out repair to prevent rapid progression to bone-on-bone arthritis. Early repair within 6 weeks gives the best outcomes for healing and preventing extrusion progression.
KEY POINTS TO SCORE
Mechanism: Deep Flexion
Age: Middle-aged female
Urgency: Semi-urgent MRI
COMMON TRAPS
✗Dismissing as 'just arthritis'
✗Ordering just X-rays
LIKELY FOLLOW-UPS
"What signs on MRI?"
"Ghost sign, Extrusion, Radial tear."
VIVA SCENARIOStandard
Scenario 2: The ACL Associated Tear
EXAMINER
"You are performing an ACL reconstruction. You inspect the lateral meniscus posterior horn. It looks mobile. How do you assess for root tear?"
EXCEPTIONAL ANSWER
During ACL reconstruction, I always systematically evaluate the lateral meniscus root as there is a 10-15% association with ACL ruptures. My assessment involves: First, I use a probe to assess the root attachment directly - I look for the 'lift-off sign' where the root elevates from its tibial footprint with gentle probing. Second, I assess translation - increased movement suggests root incompetence. Third, I inspect the root on MRI preoperatively for high signal or radial tear pattern. If I confirm a lateral root tear, it MUST be repaired concomitantly with ACL reconstruction. An unrepaired root increases stress on the ACL graft and accelerates lateral compartment degeneration. My technique would be transtibial pull-out repair using a separate tunnel posterior-lateral to the ACL tunnel, or an all-inside suture anchor if bone quality and access allow. Timing is critical - addressing both injuries at the same sitting prevents the biomechanical cascade that leads to graft failure and cartilage loss.
KEY POINTS TO SCORE
Lateral root association with ACL
Graft protection
Probing technique
COMMON TRAPS
✗Missing the pathology (Blind spot)
✗Assuming stability
LIKELY FOLLOW-UPS
"How do you fix it?"
"Usually transtibial pull-out or suture anchor."
VIVA SCENARIOStandard
Scenario 3: The Failed Repair
EXAMINER
"A patient 6 months post-root repair returns with pain. MRI shows pull-through of sutures. She has Grade 3 OA. Management?"
EXCEPTIONAL ANSWER
This represents a failed root repair with suture pull-through and progression to Grade 3 osteoarthritis - a challenging but definable clinical scenario. My management approach considers: First, patient symptoms and functional demands - is she symptomatic enough to require intervention? Second, I would assess the current state with weight-bearing X-rays showing alignment and joint space, MRI confirming the failed repair, and clinical examination for mechanical symptoms versus arthritic pain. Given Grade 3 OA (bone-on-bone in medial compartment with osteophytes), re-repair is contraindicated - the biological environment for healing is compromised and the cartilage is already damaged. My surgical options include: Total Knee Arthroplasty if pan-compartmental involvement or significant symptoms, or Unicompartmental Knee Arthroplasty if isolated medial disease with preserved lateral compartment and normal alignment. I would quote 85-90% survival at 5 years for appropriately selected initial repairs, but this patient has unfortunately progressed beyond salvage repair options. Conservative management with unloader brace and injections may temporize symptoms while awaiting arthroplasty.
KEY POINTS TO SCORE
Salvage options
OA progression
Arthroplasty indication
COMMON TRAPS
✗Attempting re-repair in OA
✗Ignoring the arthroplasty option
LIKELY FOLLOW-UPS
"What is the survival rate of repair?"
"Approximately 85% at 5 years in appropriately selected patients."
MCQ Practice Points
Biomechanics
Q: A meniscal root tear increases contact pressure equivalent to: A: Total Meniscectomy.
Imaging Sign
Q: The 'Ghost Sign' is seen on which MRI sequence? A: Sagittal T2.
Management
Q: Which factor is a relative contraindication to root repair? A: Kellgren-Lawrence Grade 3-4 OA.
Extrusion
Q: Significant meniscal extrusion is defined as: A: Greater than 3mm.
SONK Association
Q: What is the relationship between SONK and meniscal root tears? A: 80% of SONK patients have associated medial root tears - SONK is likely secondary subchondral insufficiency fracture from root-tear overload.
Surgical Technique
Q: What is the most common surgical technique for meniscal root repair? A: Transtibial pull-out repair - sutures through root, passed down tibial tunnel, fixed over button.
Australian Context
- Epidemiology: High incidence in netball (ACL associated) and gardening (degenerative) populations.
- Practice: High rate of pull-out repairs in public hospitals.
High-Yield Exam Summary
Diagnosis
- •Mechanism: Squatting 'pop'
- •Sign: Joint line tenderness
- •MRI: Ghost Sign
- •MRI: Cleft Sign
- •MRI: Extrusion over 3mm
Decision Making
- •Ideal: Young, No OA, Normal alignment
- •Contraindication: Severe OA (KL 3-4)
- •Contraindication: BMI over 35
- •Contraindication: Malalignment (unless corrected)
Surgical Steps
- •Assessment: Probe root
- •Debridement: Bleeding bone
- •Suture: Cinch/Locking
- •Tunnel: ACL guide aiming at footprint
- •Fixation: Button on tibia