ANTERIOR CRUCIATE LIGAMENT INJURIES
Pivot Shift | Graft Selection | Tunnel Placement | Return to Sport
GRAFT OPTIONS
Critical Must-Knows
- ACL is PRIMARY restraint to anterior tibial translation
- Pivot shift is most specific clinical test
- Wait 3+ weeks post-injury to reduce arthrofibrosis risk
- Anatomic tunnel placement critical - avoid high noon position
- BTB autograft remains gold standard for young athletes
Examiner's Pearls
- "Segond fracture = pathognomonic for ACL tear
- "Associated meniscal tears in 50%+ of acute injuries
- "Allograft failure 4x higher in patients under 25
- "STABILITY trial: LET reduces graft failure in high-risk
Critical Exam Concepts
Pivot Shift is KEY
Pivot shift test is most specific for ACL deficiency. Demonstrates rotational instability. Grade correlates with functional disability.
Tunnel Position Critical
Anatomic femoral tunnel at center of native footprint. Old high noon position is NON-ANATOMIC. Use anteromedial portal technique.
Graft Selection
BTB autograft = gold standard for young athletes. Fastest bone-to-bone healing. Avoid allograft in under 25 years old.
Timing Matters
Wait 3+ weeks before surgery. Regain full ROM first. Early surgery = arthrofibrosis risk.
Graft Selection Quick Guide
| Graft | Advantages | Disadvantages | Best For |
|---|---|---|---|
| BTB Autograft | Fastest integration | Anterior knee pain | Young athletes, contact sports |
| Hamstring | Less knee pain | Slower integration | Non-contact sports |
| Quadriceps | Strong graft | Quad weakness | Revision surgery |
| Allograft | No donor morbidity | 4x failure in young | Low-demand older than 35 |
PIVOTACL Injury Mechanism
Memory Hook:PIVOT mechanism causes ACL tears - pivot shift tests for it!
GRAFTACL Reconstruction Principles
Memory Hook:Get the GRAFT right for successful reconstruction!
LAPClinical Tests for ACL
Memory Hook:LAP up the ACL tests!
Overview and Epidemiology
Female ACL Injury Risk
Females have 2-8x higher ACL injury rate than males in same sports. Factors: narrower notch, hormonal, neuromuscular patterns. Prevention programs reduce risk by 50%.
Epidemiology
- Incidence: 68/100,000/year
- Peak age: 15-25 years
- Female greater than male (same sport)
- High-risk: soccer, basketball, skiing
- 70% non-contact injuries
Associated Injuries
- Meniscal tears: 50%+ acute
- MCL injury: contact mechanism
- Bone bruise pattern: posterolateral tibia
- Segond fracture: pathognomonic
- Lateral meniscus root tears
Pathophysiology and Mechanisms
ACL Anatomy
Origin: Posteromedial lateral femoral condyle in intercondylar notch.
Insertion: Anterior intercondylar tibia, anterolateral to medial tibial spine.
Two bundles:
- Anteromedial (AM): tight in flexion
- Posterolateral (PL): tight in extension
Blood supply: Middle genicular artery. Poor vascularity limits healing.
Length: 30-35mm. Width: 10-12mm.
Two-Bundle Anatomy
Understanding AM and PL bundles is important for anatomic reconstruction. Aim to recreate center of native footprint - double-bundle reconstruction has not shown superiority in most studies.
Classification Systems
ACL Injury Grading
| Grade | Pathology | Clinical Finding | Treatment |
|---|---|---|---|
| I Sprain | Microscopic tears | Firm endpoint | Conservative |
| II Partial | Partial macroscopic | Endpoint present | Variable |
| III Complete | Complete rupture | No endpoint, positive pivot | Reconstruction |
Most presentations are Grade III (complete tears).
Clinical Assessment
History
- Mechanism: Non-contact pivot, pop heard
- Immediate swelling: Hemarthrosis
- Instability: Giving way with pivoting
- Sport level: Determines treatment
- Previous injuries: Contralateral ACL
Examination
- Lachman test: Most sensitive (85-95%)
- Anterior drawer: Less sensitive
- Pivot shift: Most specific
- Associated injuries: MCL, meniscus
- Effusion: Hemarthrosis acute
Lachman Test Technique
Knee 20-30 degrees flexion. Stabilize femur. Translate tibia anteriorly. Positive: Increased translation AND soft/absent endpoint. Compare to contralateral side.
Key Clinical Pearls
Pivot shift: Best with patient relaxed (EUA). Demonstrates functional rotational instability causing giving way.
Associated injuries: Always check MCL, menisci, posterolateral corner.
Investigations
Standard Views
AP weight-bearing: Alignment, fractures.
Lateral: Segond fracture, tibial plateau.
Key findings:
- Segond fracture: Pathognomonic for ACL tear
- Tibial spine fracture: Common in children
- Deep lateral notch sign: Greater than 1.5mm
These radiographic signs should prompt further evaluation with MRI.
Segond Fracture
Segond fracture = small avulsion lateral tibial plateau = anterolateral ligament avulsion. Pathognomonic for ACL injury. Associated with high-grade pivot shift.
Management Algorithm
Management Pathway
ACL Injury Management
RICE, aspiration for comfort, brace, physiotherapy for ROM.
Consider: age, activity, sports demands, instability, associated injuries.
Low-demand, willing to avoid pivoting, no giving way, older patient.
Young active, pivoting sports, recurrent instability, repairable meniscus.
Surgical Technique
Anatomic Tunnel Position
Femoral tunnel:
- Center of native ACL footprint
- NOT high noon (non-anatomic)
- Use anteromedial portal technique
- Resident ridge as posterior landmark
Tibial tunnel:
- Anterolateral to medial tibial spine
- 1:30 (right) or 10:30 (left) position
Anatomic placement is essential for restoring rotational stability.
Avoid High Noon
Old transtibial technique placed femoral tunnel too vertically. This is non-anatomic with poor rotational control. Use anteromedial portal for anatomic placement (10:30 right knee).
Complications
| Complication | Risk Factors | Prevention | Management |
|---|---|---|---|
| Arthrofibrosis | Early surgery, poor ROM | Wait 3+ weeks, restore ROM | Aggressive PT, lysis |
| Graft failure | Allograft young, malposition | Autograft, anatomic tunnels | Revision ACLR |
| Anterior knee pain | BTB graft | Hamstring/quad graft | Usually settles |
| Infection | Any surgery | Aseptic technique | Washout, antibiotics |
Graft Failure Risk Factors
Highest failure risk: Allograft in under 25 (4x), RTS before 9 months, non-anatomic tunnels. BTB autograft + anatomic tunnels + delayed RTS minimizes failure.
Postoperative Care
Rehabilitation Protocol
Brace locked extension. WBAT with crutches. ROM 0-90 degrees. Quad sets, SLR.
Unlock brace. Progressive ROM. Stationary bike. Patellar mobilization.
Wean crutches. Pool running. Closed chain exercises. Proprioception.
Running program (straight). Progressive resistance. Late agility.
Cutting/pivoting. Sport drills. Psychological readiness.
Full competition after functional tests. Hop tests, strength greater than 90%.
Return to Sport Criteria
Before RTS: Hop test LSI greater than 90%, quad strength greater than 90%, no effusion, full ROM, ACL-RSI passed, minimum 9 months. Each month delay reduces re-injury risk.
Outcomes and Prognosis
Outcome Factors
Good: Anatomic reconstruction, appropriate graft, compliant rehab, adequate time, isolated injury.
Poor: Malposition, early RTS, cartilage injury, meniscectomy, non-compliance.
Long-Term
OA: 50% develop radiographic OA by 10-15 years regardless of treatment. Higher if meniscectomy.
Contralateral ACL: 10-25% lifetime risk, especially young females.
Evidence Base and Key Studies
MOON Cohort - Graft Outcomes
- 2683 ACL reconstructions multicenter
- BTB: 3.4% revision at 6 years
- Hamstring: 4.5% revision
- Allograft: 6.9% revision
Timing of ACL Reconstruction
- RCT early (within 21 days) vs delayed
- Early: 12% arthrofibrosis
- Delayed: 1.8% arthrofibrosis
- No difference final outcomes
STABILITY Trial - LET
- RCT ACLR +/- lateral extra-articular tenodesis
- 618 patients randomized
- ACLR + LET: 4% graft rupture
- ACLR alone: 11% graft rupture
Return to Sport Timing
- 106 elite athletes prospective
- Each month delay = 51% reduced re-injury
- Less than 9 months RTS: higher failure
- Passing functional tests protective
Allograft Failure in Young
- MOON cohort analysis
- Under 25 with allograft: 4x failure vs autograft
- No difference in over 35
- Activity level also affects outcome
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Young Athlete ACL Injury
"A 20-year-old male soccer player presents 2 weeks after a non-contact pivoting injury. He heard a pop and had immediate swelling. Examination shows positive Lachman and pivot shift. MRI confirms complete ACL tear without meniscal injury. How would you manage this?"
Scenario 2: Graft Selection in Female
"A 30-year-old female recreational skier needs ACL reconstruction but is concerned about anterior knee pain as she kneels frequently for work. She asks about graft options. What would you discuss?"
Scenario 3: Failed ACL Reconstruction
"A 23-year-old presents 18 months after hamstring ACL reconstruction. He returned to soccer at 7 months and now has recurrent instability. MRI shows graft rupture. CT shows vertical femoral tunnel. How would you approach this?"
MCQ Practice Points
Primary ACL Function
Q: Primary function of ACL? A: Restraint to anterior tibial translation - 85% of restraint at 30 degrees. Also resists internal rotation and hyperextension.
Most Sensitive Test
Q: Most sensitive clinical test for ACL? A: Lachman test (85-95% sensitive). At 20-30 degrees flexion. Assess translation AND endpoint quality.
Most Specific Test
Q: Most specific clinical test for ACL? A: Pivot shift test. Demonstrates rotational instability causing functional giving way.
Segond Fracture
Q: What does Segond fracture indicate? A: ACL rupture (pathognomonic). Avulsion lateral tibial plateau. Associated high-grade pivot shift.
Allograft in Young
Q: Why avoid allograft in young athletes? A: 4x higher failure rate in under 25. Slower incorporation, remodeling issues.
Early Surgery Risk
Q: Primary risk of ACL surgery within 3 weeks? A: Arthrofibrosis. Wait for ROM recovery. Optimal timing 4-12 weeks.
Australian Context
Clinical Practice
- High ACL injury rates (sports culture)
- BTB and hamstring both common
- Anteromedial portal technique standard
- LET gaining popularity
- Strong rehab emphasis
Funding and Access
- ACL reconstruction covered under public system
- Variable public wait times
- Private insurance covers procedures
- Physiotherapy accessible
- Sports medicine multidisciplinary
Orthopaedic Exam Relevance
ACL injuries are extremely common viva topic. Know graft selection, surgical timing, tunnel placement, RTS criteria. Be prepared to discuss STABILITY trial and lateral extra-articular tenodesis.
ANTERIOR CRUCIATE LIGAMENT INJURIES
High-Yield Exam Summary
Clinical Tests (LAP)
- •Lachman: Most sensitive 85-95%
- •Anterior drawer: Less sensitive
- •Pivot shift: Most specific
- •Compare endpoint quality
Graft Selection
- •BTB: Gold standard young athletes
- •Hamstring: Less anterior knee pain
- •Quad: Growing popularity
- •Allograft: Over 35 only (4x failure young)
Surgical Timing
- •Wait 3+ weeks post-injury
- •Regain full ROM extension
- •Early surgery = arthrofibrosis
- •Optimal: 4-12 weeks
Tunnel Placement
- •Anatomic = center of footprint
- •Avoid high noon non-anatomic
- •Use anteromedial portal
- •10:30 right or 1:30 left
Return to Sport
- •Minimum 9 months post-op
- •Hop test LSI greater than 90%
- •Quad strength greater than 90%
- •Each month delay = 51% less re-injury