Description of the condition
The medial knee ligaments are found on the inwards facing side of the knee joint. These connect the femur (thigh bone) to the tibia (shinbone) and, together with the lateral (outwards facing) ligaments found on the other side of the knee, help control the sideways motion of the knee joint. The medial ligaments comprise three main ligaments: the superficial medial collateral ligament (MCL), the deep MCL and the posterior oblique ligament (POL), which is part of the posteromedial complex (PMC) of the knee. The superficial MCL is the main restraint against valgus knee instability (gaping open of the inner aspect of the knee joint), whereas the POL and deep MCL provide secondary restraints against valgus loads (forces directed towards the inner (or midline) aspect of the knee) and are also important restraints to internal and external rotational forces (forces that move the leg position so that the foot is turned inwards or outwards, respectively) (Coobs 2010). The PMC stabilises the knee in extension, and contributes one-third of the restraint of the knee to valgus loads with the knee in extension. The medial knee ligaments are among the most commonly injured ligaments of the knee (Phisitkul 2006). Injuries to the medial knee ligaments are most common in young people during sporting activities, have an annual incidence of 0.24 per 1000 and occur more often in males (2:1 male to female ratio) (Daniel 2003; Wijdicks 2010). These injuries also occur frequently in skeletally immature persons.
Medial ligament injuries usually occur after direct impact to the lateral, or outer, aspect of the knee, thigh or leg while the foot is planted on the ground. This results in a direct valgus stress (in relative terms, the foot moves away from the midline, while the knee joint is forced towards the midline) to the knee joint and is the most common mechanism of this injury amongst contact athletes. The medial knee ligaments can also be injured without direct trauma if a valgus knee stress (forcing the knee inwards) occurs together with tibial external rotation, that is, the position of the leg is rotated so that the foot is pointing outwards (Marchant 2011). This pattern of injury is more frequent during pivoting activities in sports such as skiing, basketball and football. If either mechanism of injury occurs with high energy, a more complex ligamentous knee injury can occur that may also involve either the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL), or both (Harner 2004). These two cruciate ligaments, which are arranged as a cross in the centre of the knee joint, provide stability while permitting a large range of movement.
The most established clinical classification for medial knee ligament injuries is the American Medical Association Standard Nomenclature of Athletic Injuries system (American Medical Association 1966) that utilises valgus stress-testing to define the severity of injury. This classification system has since been modified to include also an assessment of laxity (Hughston 1994). Grade I injuries demonstrate localised tenderness with no instability and result from microscopic tears to the superficial MCL or deep MCL; grade II injuries show more generalised tenderness but still no instability and represent incomplete but gross tears of the superficial MCL or deep MCL; and grade III injuries exhibit instability on valgus stress-testing representing complete disruption of medial knee ligaments. Grade III injuries can be sub-classified by their degree of laxity on applying a valgus stress (performed with the knee at 30° of flexion) with 1+, 2+ and 3+ subtypes assigned to 3 to 5 mm, 6 to 10 mm and > 10 mm medial joint opening, respectively, compared with the knee joint of the uninjured, opposite lower limb.
This grading system can help determine injury severity and treatment decisions and inform long-term prognosis. Grade I and II medial knee ligament injuries may lead to reduced knee function and preliminary osteoarthritic joint changes at long-term follow-up (Lundberg 1996), and patients with isolated grade III injuries often progress to develop chronic joint laxity and early osteoarthritis (Kannus 1988; Reider 1994). Most people sustaining grade I injuries experience minimal symptoms and do not seek medical consultation, whereas grade II and III injuries each comprise 48% of those patients who do present for medical assessment (Grant 2012). Further ligamentous injuries are identified in 78% of grade III injuries; ACL disruption is the most frequent concurrent ligamentous injury (Fetto 1978). Patients with combined MCL and ACL injuries also commonly have POL ruptures, with 35% having ruptured the entire PMC (Halinen 2006).
A second commonly used classification system for injuries to the medial ligaments of the knee was described by Fetto and Marshall (Fetto 1978). In this classification system, grade I injuries are those with no valgus instability at both 0 and 30 degrees of knee flexion; grade II injuries are those stable at 0 degrees of knee flexion, but with valgus instability at 30 degrees of knee flexion; and grade III injuries are those with valgus instability at both 0 and 30 degrees of knee flexion. This classification system is simple to apply during clinical examination and it can identify the instability from disruption of all medial structures of the knee, which may inform the treatment strategy. Magnetic resonance imaging can also assist treatment decisions by determining the anatomic location of the injuries to the medial knee ligaments.
Description of the intervention
Several treatment options exist for injuries to the medial ligaments of the knee. Less severe injuries are generally treated conservatively (non-surgically), and more severe injuries are considered for surgical intervention. Initial conservative therapy generally involves rest, ice, compression and elevation. Use of a controlled motion knee brace for approximately six weeks (to permit protected knee motion) and a functional rehabilitation programme is typical non-surgical treatment for isolated incomplete tears and select complete tears of the medial knee ligaments (Holden 1983; Petermann 1993).
Surgical treatment of medial ligament injuries may involve acute repair of selected isolated complete tears, or delayed repair of acute injuries if further concurrent ligament injuries are best managed by being allowed to heal first (Phisitkul 2006). Surgical repair may involve direct repair of injured or ruptured ligaments or reconstruction with autograft (harvest of tissue (often a tendon) from the patient) or allograft (harvest of tissue from a donor patient) material, or synthetic grafts. Post-operative physiotherapy is usually tailored to the extent of the injury and surgical repair, but generally involves controlled motion bracing and a period of restricted weight-bearing.
How the intervention might work
The choice of intervention used to treat injuries to the medial ligaments of the knee will depend on the severity of the injury, the magnitude of joint laxity, and whether or not there are combined ligamentous injuries. Healing of the injured medial ligament complex progresses through the classic stages of haemorrhage, inflammation, repair and remodelling, and the capacity of these ligaments to heal is influenced by the location and extent of the injury (Frank 1995). For microscopic and incomplete injuries to the medial knee ligaments, conservative management may involve staged progression of both mobilisation and weight-bearing by the affected knee joint, and use of supportive braces during the direct healing process. Though bracing and protected weight-bearing are traditionally recommended for isolated medial collateral ligament injuries, they may also be a hindrance to patients and restrict functional rehabilitation.
The decision whether to use surgical or non-surgical intervention will depend upon the anatomical proximity of the torn ligament ends, and an assessment of their capacity to directly heal or not. Failure of non-surgical management may also indicate conversion to surgical management, should chronic pain or knee joint laxity develop. In the context of associated ligament injuries to the ACL or PCL, the anatomical proximity of the torn medial collateral ligaments is again assessed and the knee joint assessed for medial instability. Injuries to the PMC may not heal with non-surgical management when they occur as part of a multi-ligament injury, and therefore need to be identified to inform appropriate treatment decisions. The anticipated benefits of surgery must be balanced against the risk of complications, such as post-operative infection, and failure of the repair or graft.
The surgical options of direct repair or reconstruction of injured medial knee structures aim to restore normal load-sharing properties of these structures (Wijdicks 2010). In adults, surgical techniques to achieve this may include direct repair of the superficial MCL and POL, advancement of the superficial MCL insertion to the tibia or femur, pes anserinus transfer and a variety of reconstruction strategies. Surgical treatment for combined injuries may involve any combination of reconstruction for all ligaments, ACL reconstruction and MCL repair, ACL reconstruction and non-surgical management of the MCL, or MCL repair and non-surgical management for the ACL (Grant 2012). Early post-operative rehabilitation may require a gradual increase of knee motion and weight-bearing to allow for ligament healing, graft integration and patient comfort.
The surgical options for treating isolated or combined injuries to the medial ligaments of the knee sustained by skeletally immature persons may differ from adults due to the risk of damage to an open physis (bony growth plate) and subsequent growth disturbance. Surgical options may therefore depend upon the skeletal bone age assessed by skeletal plain radiographs and pubertal development using the Tanner scale (Marshall 1969; Marshall 1970), which reflect the extent of remaining growth. Surgical options used in skeletally immature patients can include extraphyseal reconstruction, partial transphyseal reconstruction, or complete transphyseal reconstruction. Post-operative rehabilitation in skeletally immature patients may require extended follow-up to monitor for potential growth disturbance.
Why it is important to do this review
In some populations, injuries to the medial knee ligaments are the most common knee injury (Swenson 2013). More severe injuries, including when in combination with other knee ligament injuries, may lead to chronic joint dysfunction and early degenerative joint changes. The optimal management of MCL injuries remains controversial, in particular, the surgical management of grade III injuries and complex ligamentous injuries that also involve other knee ligaments (Wijdicks 2010). This review will examine and summarise current evidence regarding the management of these injuries in order to help guide their clinical management and future areas of research.