Description of the condition
The anterior cruciate ligament (ACL) of the knee joint plays an essential role in both static (standing or squatting) and dynamic (walking or running) knee stability. Primarily, the ACL prevents anterior translation (forward movement) of the tibia relative to the femur in the sagittal (antero-posterior) plane, aiding stabilisation of the joint from a flexed (bent) to a near full extension (straight) position of the knee.
Rupture of the ACL is a common injury, mainly affecting young, physically active individuals; with an estimated 200,000 ACL ruptures per year in the United States (Spindler 2008). It is often injured during sporting activities such as football, skiing and basketball (Bahr 2003). In over 70% of cases, the injury is caused by a non-contact mechanism such as sudden deceleration combined with changing direction or pivoting or landing with the knee in nearly full extension after a jump (Hernandez 2006). Contact (traumatic) mechanisms of injury usually involve a translational force applied to the anterior aspect of a fixed lower leg (Hewett 2006). The acute injury is frequently characterised by knee pain and an audible ‘popping’ sound at the time of injury. The injured person presents with knee pain, swelling, haemarthrosis (bleeding into the joint space), instability with further activity and painful range of motion.
In approximately 10% of cases, the ACL injury occurs in isolation; however, in the majority of cases it is combined with other injuries, typically to the collateral ligaments, subchondral bone and meniscii (Miyasaka 1991; Bowers 2005; Hernandez 2006).
Diagnostic imaging, including magnetic resonance imaging (MRI), is used for confirmation of the diagnosis of ACL injury or rupture, and evaluation of associated pathology such as articular cartilage injury and meniscal and associated ligamentous tears; all of which play a role in maintaining stability of the knee (Crawford 2007).
Chronic ACL injury can have a profound effect on the knee kinematics (movements) of those affected. Common problems include recurrent knee instability (giving way) and symptoms of associated meniscal or articular cartilage damage such as intermittent swelling or a locking sensation (Hernandez 2006). Furthermore, the injury can lead to poor reported quality of life (Spindler 2008) and decreased activity levels (Thorstensson 2009). It is also associated with increased risk of secondary osteoarthritis of the knee irrespective of treatment (Øiestad 2009; Rout 2013). These related morbidities have been shown to be associated with high healthcare expenditure (Frobell 2010).
Description of the intervention
Surgical treatment for ACL rupture has evolved from simple repair using suturing or suturing with some sort of augmentation to ACL reconstruction, which involves reconstruction of the ligament using a substitute graft of tendon or ligament fixed into position in pre-prepared drill holes. ACL reconstruction is increasingly performed as an arthroscopic procedure. Of those who undergo surgical reconstruction, 94% are performed within one year of the initial injury (Collins 2013). ACL reconstruction is the predominant method of surgery in current practice and hundreds of thousands of these operations are carried out each year.
Three types of grafts are commonly used: those from the patient's body (autograft), cadaveric human donors (allograft) or a synthetic ligament substitute. Commonly, the hamstring tendons of semitendinosus and gracilis are harvested from the limb of the ruptured ACL and this graft is removed during the reconstruction operation. Alternatively, a bone-patella tendon-bone (BPTB) construct uses a section of the middle of the patella (kneecap) tendon with bone at either end. The relative merits of hamstring and BPTB grafts have been reviewed (Mohtadi 2011).
Conservative (non-operative) treatment for people with an ACL rupture can include the use of cryotherapy (ice), continuous passive motion (movement of the joint by a machine), restrictive bracing, electrotherapy (muscle stimulation) and exercises aimed at strengthening and balance. The use of plaster casts for initial immobilisation of the knee is very uncommon nowadays (Linko 2009).
Rehabilitation regimens used for both treatment options commonly use a three-stage progressive programme: acute, recovery and functional phases (Micheo 2010). The acute stage following injury, or immediately after surgery, aims to restore range of motion and resolve inflammation. The recovery phase is from approximately three to six weeks, with the aim of improving lower limb muscle strength and functional stability. Finally, the functional stage of rehabilitation (from six weeks onwards) concentrates on returning to previous levels of activity and decreasing the risk of re-injury (Kvist 2004). There is little consensus over the most effective rehabilitation protocol for achieving these aims (Negus 2012).
Whilst surgical interventions have become commonplace for athletic individuals, initial non-operative (conservative) treatments based around physiotherapy are used more commonly in the general population (Linko 2009).
How the intervention might work
All treatments aim to reduce knee pain and instability and restore function. However, the optimal management strategy following rupture of the ACL remains controversial. In the short term, reconstructive surgery may improve knee function for those experiencing severe instability in activity or repeated episodes of ‘giving way’, or both. However, all surgery involves an increased risk of complications such as infection. In particular, for reconstruction using autograft, significant donor site morbidity can occur, including anterior knee pain with BPTB grafts and pain and weakness of knee flexors with hamstring grafts (Spindler 2004; Mohtadi 2011).
Although studies of conservative treatment have demonstrated satisfactory results with patients returning to pre-injury activity level (Kostogiannis 2007; Linko 2009; Frobell 2013), the long-term results, in particular relating to the development of early onset osteoarthritis, are still debatable. Radiographically-diagnosed osteoarthritis has been reported in 20% to 50% of ACL-deficient knees at 10 years post injury compared with 5% in uninjured knees (Lohmander 2007; Øiestad 2009; Ajuied 2013). However, surgery has not been shown to offer protection against long-term degenerative change (Øiestad 2009; Rout 2013). Moreover, recent studies have suggested structured neuromuscular rehabilitation might provide effective recovery following ACL rupture without increasing the risks of long-term degenerative change (Delincé 2012).
Why it is important to do this review
The management of ACL injuries includes both reconstructive surgery and conservative treatments. It is unclear whether stabilising the knee surgically produces any benefit for the knee in comparison with conservative interventions. The previous Cochrane review in this area (Linko 2009) found that there was insufficient evidence to determine whether surgery or conservative management was superior for the treatment of ACL rupture and highlighted the need for good quality randomised controlled trials (RCTs) of current practice, particularly ACL reconstruction. Current surgical practice has also changed in terms of the population, with an increasing number of ACL reconstructions being performed on a young athletic (adolescent) cohort (Ramski 2013). These point to the need for a systematic review of the evidence from randomised trials comparing the effects of the current surgical versus conservative treatment methods for ACL rupture.