Contents
Introduction
Anterior cruciate ligament (ACL) ruptures are common sporting injuries. If untreated, they can result in chronic knee instability, and resultant degenerative changes – such as arthritis, and chondral damage.
Early diagnosis and treatment can prevent this long-term damage.
Treatment typically involves ligament reconstruction. Colloquially “knee reconstruction” surgery typically refers to ACL repair.
There is a high success rate of return to sport at all levels of competition after surgery.
Epidemiology and Aetiology
- ACL rupture accounts for half of all knee injuries
- Incidence of about 1 in 3000 per year
- More common in females (4:1)
- Thought to be due to altered landing biomechanics (quad dominance)
- Particularly risky sports include basketball, skiing and football (soccer)
- May be associated with meniscal tear and medial collateral ligament injury.
- Triad of ACL, medial meniscus and medial collateral ligament is common
Pathophysiology
- The anterior cruciate ligament is made up of two bundles of fibres, anteromedial and posterolateral bundles
- Made up of 90% type I collagen and 10% type III collagen
- Blood supply is via the middle geniculate artery
- Innervated by the poster articular France of the tibial nerve
- Function – prevents anterior translation of the tibia relative to the femur
Mechanisms of injury
- Internal tibial rotation on a flexed knee (pivoting injury) – typically when landing from a jump, or quickly pivoting
- Strong valgus force / force applied to lateral aspect of the knee – e.g. a rugby tackle or football tackle on a fixed foot
Presentation
- Acute onset of pain during sport
- “Felt a pop”
- Pain deep inside the knee
- Acute onset swelling (70% of cases) – typically <30 minutes since injury
- Difficulty weight bearing
- Sensation of knee instability
Examination
On knee examination:
- Large knee effusion
- Positive drawer test (either direction, but classically anterior drawer test)
- Lachman test – lacks and endpoint
- Movement >5mm is abnormal
- Compare with the other side
- A Lachman test is a modified drawer test with he knee flexed only to 15-20 degrees
Investigation
X-ray
- AP, lateral, skyline view
- Often normal
- A Segond fracture – avulsion of the proximal tibia – is diagnostic for ACL injury
MRI
- Can confirm ACL rupture
Management
Conservative management
- May be appropriate in some cases
- Be aware of the increased risk of long-term meniscal and other injury
- Suitable for sedentary patients, or those in recreational level sport without any pivoting activities
- Typically involves a period of rest for 6-8 weeks followed by 3 months of graduated return to activity under supervision of physiotherapist
Operative management
- ACL reconstruction
- Younger, active patients
- Can restore full ROM to the knee
- Typically a graft is used
- Autografts(from another site within the patient) are typically from the patellar tendon (most common) hamstring or quadriceps tendon
- Allografts (from another patient)
- There is not clear evidence as to which techniques is best – both have pros and cons. One major difference is the requirement to harvest the autograft, which can result in secondary issues – such as patellar tendon rupture (typically occurs during rehab phase), or long-term hamstring weakness. Allografts also have a higher risk of re-ruptre compare to autografts when used in younger patients, and there is a small chance of disease transmission (such as HIV) – but risk is extremely low (<1:1million)
- Complications
- Septic arthritis (<1%)
- Failure of graft
- Reduced ROM following procedure (can be minimised with effective rehab)
- Patella tendon rupture (if used for graft)
- ACL repair
- High failure rates
- Not widely practised
Concurrent meniscal and collateral ligament injuries should be treated at the same time and when treated, improve the overall outcome.
Post-op rehabilitation
- Immediate
- Ice
- Immediate weight bearing (reducing long-term patellofemoral pain)
- Early full passive extension
- Early
- Avoid exercises that stress the graft
- Eccentric strengthening at 3 weeks
- Core and gluteal strengthening
- Squats and leg press are suitable exercsies
- Return to play
- Typically no sooner than 9 months post surgery (poor evidence for this recommendation)
- Earlier return associated with higher re-rupture rates
- Only return once has passed sport specific exercise tests – such as hopping on one leg
- Typically no sooner than 9 months post surgery (poor evidence for this recommendation)
- Prevention of re-rupture
- Land from jumping with more knee flexion
- Hamstring strengthening to reduce quad dominance
- “Fall” training – especially for skiers!
