Anatomy of ACL
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- It is intra-articular but extra-synovial.
- Blood supply comes from the middle genicular artery.
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- The ACL consists of two bundles: the anteromedial (AM) and posterolateral (PL) bundles, named based on their tibial attachments.
- The AM bundle tightens during knee flexion and primarily resists anterior translation of the tibia.
- The PL bundle tightens during knee extension and primarily resists rotational forces.
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- On the femoral side, it attaches below the lateral intercondylar ridge.
- The lateral bifurcate ridge further divides it into two bundles.
- On the tibial side, it attaches medial to the anterior horn of the lateral meniscus and posterior to the anterior horn of the medial meniscus.
ACL injuries
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- Females have a higher risk, with a 4:1 ratio compared to males. This increased risk is multifactorial:
- Intrinsic factors: increased knee valgus, smaller intercondylar notch, and reduced ligament diameter
- Hormonal influences: linked to menstrual cycles
- Biomechanical factors: differences in landing mechanics
- Neuromuscular factors: variations in muscle activation patterns and control
OJSM menstrual cycle.pdf331.5KB
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- Pivoting injury: The foot is planted, the knee moves into valgus, and the femur externally rotates on the tibia (or Internal rotation of the tibia).
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- Lateral meniscus (LM)
- This is due to the injury mechanism. The valgus force applied during the injury is more likely to compress the lateral meniscus, potentially causing a tear.
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- In a chronic ACL-deficient knee, the medial meniscus becomes a crucial secondary stabilizer. It prevents excessive anterior tibial translation through its "doorstop" effect. As a result, the medial meniscus is more susceptible to tearing in chronic ACL injuries due to this increased stabilizing role.
- Mok 2018 found that longer time to surgery is associated with an increased prevalence of medial meniscus tears in ACL reconstruction.
Mok2018.pdf675.1KB
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- Segond fracture: A small avulsion fracture of the lateral tibial plateau, associated with injury to the Anterolateral Ligament (ALL)
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- The femur externally rotates on the tibia (or the tibia internally rotates). This motion forms the basis of the pivot shift test, which can demonstrate tibial subluxation.
- Bone edema typically appears on the anterior aspect of the lateral femoral condyle and the posterior aspect of the tibial plateau.
CONSERVATIVE MANAGEMENT OF ACL
CONSIDERATIONS for RECONSTRUCTION
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- Traditionally, we aim to reconstruct the ACL after 3 weeksto minimize the incidence of arthrofibrosis. This approach is based on the1991 landmark paper by Shelbourne, which compared three groups of patients with different surgery timings: < 1 week, < 3 weeks, and > 3 weeks.
- The incidence of arthrofibrosis was significantly higher in reconstructions performed at < 1 week.
- The group that had reconstruction done < 3 weeks showed results dependent on the rehabilitation program (accelerated program yielded better outcomes than conventional).
- The study concludes that the ideal timing for reconstruction is > 3 weeks post-injury.
- However, recent evidence suggests that ACL reconstruction (ACLR) performed within 10 days of the inciting injury does not increase the risk of postoperative arthrofibrosis and shows similar patient-reported outcomes compared to ACLR performed at or after the 3-week mark. (https://journals.sagepub.com/doi/abs/10.1177/03635465231192987)
- Personally, I ensure that the patient achieves full range of motion regardless of the time since injury. As the saying goes, "If the knee is not straight, wait."
- This approach is supported by Bertrand Sonnery-Cottet's study, which found that preoperative limited range of motion and typical bone bruises of the lateral femoral condyle and tibial plateau are major risk factors for difficult rehabilitation after anterior cruciate ligament reconstruction.
shelbourne1991.pdf473.0KB
Commentary - not straight, wait.pdf115.5KB
quelard2010.pdf161.8KB
Graft Choice Question
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- I will use autograft because Allograft has a higher failure rate – over 4 times higher than autograft.
- Failure rates are more pronounced in younger patients (< 20 years old)
- Kaeding 2011 found, based on the MOON cohort:
- Patients aged 10 to 19 years had the highest percentage of graft failures
- The odds of graft rupture with an allograft reconstruction are 4 times higher than those of autograft reconstructions
- For each 10-year decrease in age, the odds of graft rupture increase 2.3 times
Kaeding 2011.pdf213.7KB
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- I will be careful to use non-irradiated allografts because:
- On the basic science level, irradiation negatively affects biomechanical properties. This is shown in AJSM 1995 where increased radiation reduces maximum stress and strain on BPTB grafts
- Non irradiated grafts have better outcomes than irradiated grafts as shown in recent meta-analysis
- Thus, I will consider using a chemically sterilized grafts. Recent RCT have found no difference in addressing donor-to-recipient disease compared to radiation
Fideler AJSM 1995.pdf553.5 KB
Yan Liu et al.pdf2.2 MB
Peter et al. KSSTA.pdf255.4 KB
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- Load to failure in general of the tendon grafts are higher than the native ACL, dependent on the diameter of the graft with the highest documented in literature being the quadrapled hamstring graft.
- Native ACL load to failure ~ 2,100 N
- Quadruple hamstring: ~ 4,000 N
- Bone-patellar tendon-bone (BPTB): ~ 2,600 N
- Quadriceps tendon ~2100
- But recent cadaveric study of 3 grafts had similar loads to failure with a significant increase in stiffness when compared to the native ACL.
s40634-023-00601-3.pdf876.6 KB
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- Advantage: Better bone-to-bone healing and incorporation
- Disadvantage: Risk of anterior knee pain
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- I am aware no difference in functional outcomes among the autografts
- Recent Meta-analysis published in AJSM 2019 found all 3 graft types - BPTB, Hamstring and Quads tendon have comparable clinical and functional outcomes and graft survival rate
Dany AJSM 2019.pdf1.2 MB
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- I am aware no difference in retear rates among the autografts
- MARS Cohort 6 years study: No significant differences were found in graft re-rupture rates between BTB autograft and soft tissue autografts (p=0.87), nor between BTB autografts and soft tissue allografts (p=0.36)
MARS cohort 6 years.pdf285.6 KB
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- Journal of ISAKOS 2023 Sachin Tapasvi et al. Worldwide benchmark study
- Survey of 2,000 surgeons, with 50% from Asia and Oceania
- Hamstring grafts are most commonly used worldwide, except in North America
world wide bench mark.pdf1.3 MB
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- For this patient who is 19 years old
- I am inclined to choose an autograft over an allograft
- Despite knowing some countries like Korea use mainly allografts.
- Reason: higher retear rates especially in younger patients based on MOON data
- If patient still keen for allograft (no donor site morbidity) → Non irradiated, chemically treated graft (radiation affects stiffness and functional outcomes)
- I am aware of no difference in outcomes among the various types of autografts
- Stiffness and load to failure
- Functional outcomes
- Retear rates
- Worldwide, I am aware that 80% of surgeons use HT graft, while in North America, most use a BTPB.
- In my practice, I will use the ST- only Hamstring graft, prepared in a quadrupled manner
- Lead-in to next questions
- For this, I will use an all-inside reconstruction technique with dual suspensory technique.
- I will also add on a LET in patients who are at higher risk based on the STABILITY trial…
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- Graft diameter ≥8mm is associated with the lowest revision rates (Magnussen et al., Conte et al.)
- Odds ratio of 2.20 for graft rupture if diameter is <8mm
magnussen2012 .pdf175.1KB
Conte2014.pdf410.5KB
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- Positioning - break table or supine position
- Leg support
- Foot support - allows hyperflexion to prevent posterior blowout when drilling femoral tunnel
- Insertion points
- Tibia – "within footprint" just adjacent to lateral meniscus anterior horn; ensuring clearance from medial meniscus
- Femur – "anatomic center" below resident ridge (intercondylar ridge), at the lateral bifurcate ridge; ensure sufficient buffer using offset guide to prevent posterior blowout
- Transportal vs transtibial – transtibial creates more vertical tunnel, resulting in less rotational stability
- Single bundle vs double bundle – double bundle offers better biomechanical stability, but clinical significance is uncertain
- Notch plasty to remove osteophytes
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- Transtibial technique involves drilling the femur tunnel through the tibia tunnel.
- Transportal technique involves drilling the femoral tunnel independently of the tibial tunnel through the anteromedial portal
- Evidence:
- Meta-analysis by Riboh et al. (2013) found transportal technique resulted in better rotational stability and higher subjective scores
- Systematic review by Chalmers et al. (2013) showed transportal technique achieved more anatomic graft placement
- Yau et al. found that the the adoption of the transportal technique in single-bundle ACL reconstruction produced improved positions in both the femoral and tibial tunnels when compared with the transtibial technique.
- However, long-term clinical significance of these differences remains debated
riboh2013.pdf2302.1KB
Chalmers 2013.pdf857.8KB
yau2013.pdf717.2KB
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- Pre-tensioning – Performed statically on a board and dynamically through cycling, including final tightening (~30 cycles)
- Reduces the crimp in the tendon fibers, ensuring the graft is taut when inserted
- Stress relaxation: While held at constant length on the board, the stress in the tendon gradually decreases
- Creep: During cycling, a constant force is applied to the graft, causing it to elongate
- These processes aim to insert a taut graft, minimizing residual creep and stress relaxation post-implantation
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- Lemaire Lateral Extra-articular Tenodesis (LET)
- Technique: The iliotibial band (ITB) is harvested proximally while keeping its distal attachment at Gerdy's tubercle. It is then attached to the lateral femoral condyle.
Postoperative Considerations
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- Inflammatory – Partial necrosis occurs (0-6 weeks). This is the weakest phase.
- Proliferation – Angiogenesis and revascularization take place (6 weeks - 3 months).
- Number of myofibroblasts increases
- Type 3 collagen is deposited
- Ligamentization – Remodeling occurs (after 3 months)
- Collagen fibers regain organization with parallel alignment
- Graft reaches maximum properties at 1 year
Graft incorporation.pdf389.1KB
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- Bone block undergoes creeping substitution
- Cancellous bone integration occurs through creeping substitution (3 stages):
- 1: Vascular ingrowth
- 2: Osteoblasts lay new bone with simultaneous stochastic (random) resorption (creeping substitution)
- 3: Remodeling via cutting cones
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- Draw the ligamentization chart
- 0-6 weeks - Full weight-bearing, early range of motion, closed chain exercises (foot fixed on ground) [Inflammatory phase]
- 6 weeks - 3 months - Open chain exercises [Proliferation phase]
- 3+ months - Jogging [Ligamentization phase]
- 4-6 months - Sport-specific training
- 6-12 months - Return to sports
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- The 20-year graft survival rate is 86%. Salmon 2017
salmon2017.pdf791.9KB
Complications of ACL Reconstruction
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- Missed posterolateral corner injury
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- Tunnel placement issues
- Tibial tunnel: Too anterior (causing extension notch impingement and tightness in flexion), too posterior (impinging on PCL)
- Femoral tunnel: Too anterior (tight in flexion, lax in extension), too posterior (lax in flexion, tight in extension)
- Posterior blowout if knee isn't hyperflexed during femoral tunnel reaming
- Overly vertical tunnel (defined as femoral tunnel divergence < 30°)
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- Cyclops lesion
- Also known as localized anterior arthrofibrosis, it's a fibrous nodule in the intercondylar notch anterior to the ACL graft, causing extension blockage
- This is an infrapatellar nodule (distinct from the suprapatellar patellar clunk)
- Treatment: Arthroscopic debridement
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- Non-compliance with physical therapy
- Limb malalignment, increasing risk of graft retear
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- Perform a triple assessment: History, Physical Examination, and Investigations
- First, rule out infection through clinical evaluation and biochemical tests if necessary
- Next, determine if the stiffness was immediate or delayed onset:
- Immediate onset suggests: aberrant tunnel placement, overtensioning, or notch impingement
- Delayed onset indicates: arthrofibrosis or cyclops lesion
- Investigations: Order an MRI scan
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- The medial meniscus provides anteroposterior stability. If you don't repair it, you lose a secondary stabilizer that helps protect the ACL reconstruction.
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- Tibial tunnel:
- Too anterior: Impingement in extension
- Too posterior: Tightness in extension
- Femoral tunnel:
- Too anterior: Tightness in flexion; laxity in extension
- Too posterior: Tightness in extension; laxity in flexion
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For the Lord gives wisdom; from his mouth come knowledge and understanding. Proverbs 2:6