Anterior Cruciate Ligament (ACL) Reconstruction
Anterior Cruciate Ligament (ACL) Reconstruction
What is the aim of an anterior cruciate ligament (ACL) reconstruction?
  • The aim of an ACL reconstruction is to: 
    • Restore knee stability
    • Enable a safe and early return to work and sporting activities
    • Restore, repair, or reconstruct other structures that have been damaged such as meniscus, cartilage and other ligaments 
    • Restore full range of pain free movement in the knee

How is an ACL reconstruction performed?
  • A general anaesthetic and a regional block around the knee is administered to provide additional pain relief
  • Once the patient is fully anaesthetised the knee is examined by the orthopaedic surgeon to assess presence and degree of:
    • ACL laxity
    • Knee rotational instability
    • Any additional ligament injury
    • Range of motion
  • Findings of the clinical examination whilst the patient is anaesthetised provide helpful information that guides and confirms the surgical plan
  • A tight inflatable belt called a tourniquet is inflated around the upper end of the thigh in order to prevent bleeding and provide a clear view inside the knee during the operation
  • The graft to be used to reconstruct the new ACL is harvested:
    • The graft is most commonly hamstrings or the middle third of the patella tendon
  • Knee arthroscopy is performed through two small cuts (portals) either side of the patella through which the following structures can be seen, assessed and appropriately treated:
    • Articular cartilage surface throughout the knee i.e. femur, tibia and patella
    • Medial and lateral meniscus
    • ACL and PCL
  • The torn ACL is surgically cleared from the femur to enable better visibility of where to drill on the femur
  • Accurate drilling of the bone tunnels in the femur and tibia is carried out
  • The ACL graft is passed through the tibia and femoral tunnels
  • There are surgical techniques to try and preserve the ACL stump on the tibia or an uninjured bundle and augment it, which helps improve vascularity and healing of the ACL reconstruction 
  • The ACL graft is secured on the femur and tibia with screws or suspensory device after first cycling the knee through a full range of motion to ensure this is achieved:
    • The devices used to fix the graft are left permanently in the knee and do not require removal
  • Other soft tissue injuries are addressed such as articular cartilage, meniscus or ligament
  • For some patients an extraarticular tenodesis will be performed to provide additional stability (rotational in particular) which reduces by almost a half the risk of reinjury to the ACL
  • Local anaesthetic is injected into the wounds for extra pain relief
  • Dressings are applied on the wounds and the knee is wrapped up in bandages to reduce postoperative knee swelling
What should you expect from an ACL reconstruction?
  • ACL reconstruction is the gold standard treatment for most active patients with an ACL injury:
    • 90% of patients are able to return to sport at the same level of competition as before the injury
    • 98% of patients would undergo surgery again
    • 85% of patients are satisfied with their outcome

What are the advantages of an ACL reconstruction?
  • ACL reconstruction provides the best way to restore optimal knee stability
  • Permits a safe return to competitive sports
  • Helps prevent instability episodes with the knee giving way, which would cause further damage inside the knee especially to the menisci and articular cartilage and lead to subsequent early osteoarthritis
  • Allows for a more normal feeling of knee movement and stability

What are the disadvantages of ACL reconstruction?
  • Surgery is not 100% effective 
  • Exposure to the risks of an operation 
  • Studies have shown that when an ACL reconstruction is performed by a non-specialist surgeon there is an increased risk of:
    • Retearing the ACL mainly due to suboptimal positioning of the tunnels in the femur and tibia
    • Inadequate restoration of rotational stability to the knee despite an intact ACL graft
    • Meniscectomy rather than saving the meniscus through a successful repair
    • Not addressing adequately articular cartilage injuries 
    • Not addressing other ligamentous injury in addition to the ACL
Who should have an ACL reconstruction?
  • Active individuals who wish to get back to competitive sport:
    • Especially pivoting sports such as football, basketball, tennis, skiing
  • Patients who continue to have ongoing instability, despite trying conservative measures, and have engaged fully in an ACL rehabilitation programme
  • Patients who have additional injuries (such as meniscus, cartilage and other ligaments) as they have the highest risk of osteoarthritis without surgical intervention
  • Children and adolescents: 
    • They should have ACL reconstructed promptly to prevent further injury inside the knee
    • It is difficult for this age group to abstain from sporting activities 
    • Without an ACL, recurrent instability episodes occur that put at risk cartilage and menisci with disastrous consequences leading to rapid onset osteoarthritis
    • Surgery should not be delayed by more than 5 months in children and adolescents with an ACL injury as this doubles the risk of requiring medial meniscal surgery and the risk increases to 6 times if delayed by more than a year
When should an ACL reconstruction be carried out?
  • The timing of an ACL reconstruction can have many consequences on outcome
  • If the ACL reconstruction is delayed for too long and patient has recurrent episodes of instability, there will be increased risk of more damage inside the knee and subsequent early osteoarthritis
  • However, rushing to have the operation too early if the knee isn’t ready, will increase the risk of postoperative knee stiffness and incorrect placement of ACL tunnels which will then increase the risk of ACL graft failure
  • Guidance for when the timing is right to proceed with surgery and in order to avoid stiffness after surgery the patient should have: 
    • Full range of motion
    • No swelling
    • Good active quadriceps muscle
  • Even with a large initial swelling the above criteria can be achieved within 2-3 weeks so long as a careful ACL rehabilitation programme is carried out before surgery and there is no joint injury that would limit progress such as a displaced bucket handle tear of the meniscus
Can the ACL be repaired?
  • ACL repair involves stitching back together the torn ACL ligament
  • In contrast, ACL reconstruction involves using tissue from elsewhere to provide a new ACL ligament
  • Historically ACL repair has had appalling results (40-100% failure rate)
  • ACL repair sounds appealing since there is no need to harvest tissue from elsewhere as is required for an ACL reconstruction
  • However, the ACL has a low capacity to heal due to:
    • Poor blood supply to the ACL ligament
    • Presence of synovial fluid prevents normal healing processes of injured tissue to occur and the initial requirement for a haematoma to form is repeatedly washed away by the synovial fluid
    • Too much motion and stresses on the ACL ligament for healing process to succeed
  • There has been a recent resurgence for ACL repair with new techniques and instruments:
    • ACL repair has a very narrow spectrum of when it might be suitable:
      • Healthy young patients especially children
      • Operation is performed shortly after injury (within 2 weeks ideally)
      • ACL has detached very close to the femur with the remaining ligament being well preserved
    • Even with this very select group of patients the failure rate is around 5-10 times greater than ACL reconstruction 
  • As with anything in medicine not all new things are the solution to the problem and evidence is needed to support the use of new interventions
  • Currently the evidence isn’t there yet to support satisfactory success rate for ACL repair

What is the failure rate of an ACL reconstruction?
  • About 5% of patients undergo revision ACL reconstruction following their primary procedure 
  • However, there is a large variability in the reported failure rates from under 2% in the hands of a specialist to more than 40% failure in the hands of a non-specialist

What are the potential complications of an ACL reconstruction?
  • ACL graft rupture:
    • The most common cause for ACL graft failure is traumatic 
    • The second most common cause for is incorrect tunnel placement at time of surgery:
      • The most important factor in correct placement of the bony tunnels is the expertise of the orthopaedic surgeon 
      • Errors made with tunnel positioning can lead to problems despite having an intact ACL graft:
        • Continued laxity 
        • Rotational instability
        • Reduced range of motion 
        • Increased risk of ACL rupture
    • Other causes of ACL graft failure:
      • Inadequate graft fixation into bone:
        • The graft itself is stronger than the native ACL but the weakest point is its attachment to the bone
        • The weak point of the ACL reconstruction is not the graft itself but its attachment points in the femur and tibia 
        • It takes around a year for the graft to solidify and anchor strongly to the bone 
        • This is one of the reasons why early return to competitive sport before one year has an increased risk of reinjury
      • Failure to identify and address other concomitant injuries such as:
        • Posterolateral corner:
          • This is a complex area of tendons and ligaments located at the back (posterior) and outer (lateral) corner of the knee
          • The posterolateral corner provides stability against laterally (outer) directed and external rotation (outer twist) forces
        • Medial collateral ligament injury:
          • This is the inner ligament of the knee, connecting the femur with the tibia 
          • The medial collateral ligament prevents the ankle from going outwards in relation to the knee
        • Meniscal root tear:
          • Meniscus root is the part of the meniscus that dives down into the tibia and anchors the meniscus
          • Meniscal root tear is a very significant meniscal injury and completely defunctions the whole meniscus as if it has been totally removed
        • Medial meniscocapsular tear (ramp lesion):
          • The posterior (back) part of the meniscus is attached to the capsule of the knee and is the second most important stabiliser of the meniscus that holds it in place (the most important stabiliser is the  meniscal root)
          • A meniscocapsular tear of the medial (inner) meniscus results in excessive front to back movement of the meniscus which ends up getting trashed by the impact of the femur and there is reduced front to back and rotational stability to the knee
        • Missed posterior cruciate ligament (PCL) injury:
          • The PCL connects the femur to the tibia in the centre of the knee and goes in the opposite direction to the ACL
          • A PCL tear results in excessive posterior (backward) movement of the tibia in relation to the femur
      • Failure to address excessive forces on the ACL graft:
        • Lower limb malalignment:
          • If the lower limb isn’t neutrally aligned it can lead to excessive stress on the ACL i.e. excessive varus or valgus malalignment
          • Forces are restored through corrective osteotomy to bring the mechanical axis in the middle of the knee such that the forces are distributed equally on the knee
        • Increased tibial slope:
          • The tibial slope is calculated from the side view of the knee joint and the angle the tibia joint surface makes with a line that is 90 degrees to the shaft of the tibia
          • If the tibial slope is too steep downhill as you go backwards, it results in the tibia being constantly forced anteriorly as you weight bear, thus increasing the forces on the ACL
          • This is rectified through corrective tibial slope changing osteotomy 
      • Failure to complete rehabilitation programme adequately:
        • Failure to comply with postoperative physiotherapy sessions and rehabilitation results in an unacceptably high failure rate so patients need to be aware they need to invest time and effort to carry this out, in order for the surgery to be successful long term
  • Ongoing knee instability despite an intact ACL graft:
    • About 1-20% of patients experience a feeling of knee instability despite having undergone an ACL reconstruction and the graft remaining in tact
  • Infection: 
    • This is reported to be <1% but the level of care in theatre can affect rates of infection
    • Symptoms that suggest deep infection in the knee joint:
      • Intense pain in the knee even with little movement
      • Acutely swollen knee 
      • Redness to the skin around the knee
      • Knee is warm to touch
      • Limited knee range of motion due to pain
      • Intermittent temperature (>38 degrees C)
      • Wound discharge: 
        • Fluid seeping out of the wound especially pus
      • If there is any concern for infection inside the knee then there is an urgent need for medical evaluation by an orthopaedic surgeon and arthroscopic washout of the knee
  • Knee stiffness:
    • It is of paramount importance that a full range of motion in the knee is achieved prior to an ACL reconstruction
    • If the knee is stiff just before the operation: 
      • It makes the operation much more difficult 
      • It increases the risk of incorrect placement of the tunnels in the knee for the graft which then leads to increased risk of graft rupture, ongoing instability and reduced range of motion 
      • It increases the risk of even greater stiffness following the operation with poor clinical outcomes and even inability to regain full range of motion in the knee
    • Cyclops lesion: 
      • This is where a lump of tissue from the ACL graft forms at the front of the knee which limits the ability to get the knee fully straight and it necessitates in arthroscopic debridement to achieve full extension 
  • Risks specific to patella tendon graft:
    • There are some specific risks when the patellar tendon is chosen for the ACL graft which are not present when the other ACL grafts are chosen
    • The patella tendon graft involves taking the middle third of the patella tendon together with the attached blocks of bone from the patella and the tibia
    • As a result of taking these blocks of bone the remaining patella tendon construct is weakened which can lead to:
      • Patella tendon rupture
      • Patella fracture
      • Permanent pain at the front of the knee especially when kneeling
  • Subsequent osteoarthritis:
    • Subsequent osteoarthritis following an ACL injury is directly linked to meniscal and articular cartilage damage at the time of the original injury and until the operation is performed
    • If at the time of ACL reconstruction, a meniscal tear is trimmed rather than repaired then the patient is exposed to risk of early osteoarthritis

Careful rehabilitation gets you further than rushing through it
  • During the postoperative rehabilitation phase, the graft which has been taken from elsewhere in the body loses its blood supply and the cells start to die off
  • The graft then becomes a biological scaffold for new blood vessels to grow into it (revascularisation) and graft starts to fuse with the bone
  • This revascularisation period, weakening of the graft, and timing of fusion with the bone are all critical and it means tailoring the exercises so as to not put unnecessarily excessive stresses on the graft
  • When the graft end is soft tissue (such as hamstrings) this typically takes around 8-12 weeks but if it is a bone block (such as from a patella tendon graft) this takes around 6 weeks
  • Hence the quicker rehabilitation in the first few months with grafts that have a block block (patella or quadriceps tendon) versus the soft tissue only grafts (hamstring tendons)

What are the phases of ACL graft healing and their impact on rehabilitation?
  • The ACL graft does not stay in the same condition as it is during the operation
  • It goes through three phases of remodelling following the operation
  • Early graft healing phase:
    • This occurs during the first 4 weeks and it is characterised by increasing death of cells in the graft particularly at its centre
    • During this phase the strength of the graft gradually declines
  • Proliferation phase:
    • This occurs during 4-12 weeks following the ACL reconstruction
    • Graft necrosis stimulates ingrowth of new blood vessels (revascularisation) and migration and multiplication of new cells
    • Mechanical properties of the graft are at their weakest point between 6-8 weeks postoperatively:
      • This is due to cellular death, revascularisation, loss of collagen orientation and density
    • Failure to appreciate this and continuing with aggressive rehabilitation during this phase can compromise the integrity of the ACL graft and stretch it out
  • Ligamentisation phase:
    • This proceeds from 12 weeks postoperatively
    • Cellularity of the graft normalises at around 3-6 months
    • Blood supply to the graft and collagen fibre organisation return to normal at around 12 months
    • Remodelling of the ACL reconstruction continues for two years postoperatively
    • Full biological and mechanical restoration of an ACL reconstruction takes at least one year and there is increasing evidence that it’s more likely two years
    • It is therefore of paramount importance to compensate for the graft weakness with optimal rehabilitation to improve strength in both lower limbs, core, neuromuscular control, and balance

What is the risk of ACL failure?
  • The quoted risk in the medical literature is 2-5% failure within 5 years
  • This risk goes up to 3-10% within 10 years
  •  The risk of ACL failure has been quoted at >40% in the hands of non-specialist orthopaedic surgeons
  • Interestingly the risk of ACL tear on the other knee within two years after the operation is similar to the failure of the knee that had the ACL reconstruction
  • However, studies that have at least 5 years follow up from ACL reconstruction, show that the other knee has a near double risk of ACL failure than the operated side
  • It is therefore imperative for patients to be aware of the increased risk of ACL failure to the non-operated knee, so that postoperative rehabilitation involves both knees
  • Medical literature has shown that the addition of a lateral extraarticular tenodesis to an ACL reconstruction, reduces the risk of ACL graft failure by 40% in patients at higher risk of ACL graft rupture

What is rehabilitation like following an ACL reconstruction?
  • Rehabilitation starts on the first day straight after the ACL reconstruction
  • The patient can walk full weight bearing from the first day
  • Crutches are used for the first few days for balance purposes
  • A knee brace is applied only if a meniscal repair is carried out at the same time:
    • The brace allows movement from full straight (0 degrees) to 90 degrees of knee flexion (bend)
    • Flexion (bending) the knee beyond 90 degrees puts additional stresses on the back part of the meniscus and can thus pull apart the meniscal repair
    • If meniscectomy is carried out no knee brace is required and there are no restrictions to knee movement
  • A top priority following an ACL reconstruction is to get rid of the knee swelling which has the benefit of:
    • Providing pain relief
    • Reducing knee stiffness
    • Earlier return of full range of motion
    • Expediting recovery 
    • Faster progression to higher intensity exercises
  • To get rid of the swelling regular cycles of the following is required throughout the day:
    • Rest:
      • This helps to reduce strain on the knee and subsequent swelling
    • Ice:
      • Frequent icing of the knee helps to reduce inflammation and swelling inside the knee
    • Compression with an elastic bandage:
      • Wrapping the knee up with an elastic bandage will help reduce knee swelling
    • Elevation:
      • Elevating the leg will help reduce knee swelling with the help of gravity
  • Another main priority following ACL reconstruction is getting the knee fully straight which is more important than bending the knee:
    • If knee straightening is not achieved straight away it can be easily lost and very hard to recover
    • Bending the knee is easier to achieve even at a later date
    • However exercises for both straightening and bending the knee are commenced from the first day

When can I return to sport following ACL reconstruction?
  • Timing of return to competitive sport is a widely discussed topic with increasing evidence showing later return to sport reduces risk of ACL re-rupture
  • There are a number of return-to-sports tests to help screen those that are ready to return to competitive play
  • One of the key requirements is that the operated leg needs to achieve at least 90% of the strength and hop assessments tests as the unaffected leg
  • Despite being the best screening tools available for return to play they are not 100% predictable
  • Numerous studies show that return to competitive sport prior to six months post operation carries a high failure rate and a 10% reduction of risk is noticed for each month between 6 and 9 months
  • Current medical literature shows that the risk of ACL failure reduces the most by 12 months but continues to reduce even further until 2 years following ACL reconstruction
  • However being absent for two years from competitive sports has other drawbacks
  • So the recommended time to return to  competitive sports stands at 9-12 months following an ACL reconstruction with ever increasing evidence pointing at 12 months being the best time
  • However the time to return to competitive sports also depends on the patient having passed all the milestones of a rigorous ACL rehabilitation programme and has been cleared by their orthopaedic surgeon
  • Key improvements required in the ACL rehabilitation is not only strengthening, but also in having the correct technique whilst running, changing direction, and landing after a jump 
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