Introduction
This chapter describes the clinical background for medial knee instability and the indications for surgical treatment of medial collateral ligament (MCL) and posteromedial corner injuries. Historically, treatment of acute medial collateral ligament injuries has focused on nonoperative therapies with early controlled motion with relatively good reported patient outcomes. However, more severe acute and symptomatic chronic medial knee injuries may require operative management. Injuries that involve all medial and posteromedial structures, the superficial MCL, the deep MCL, the posterior oblique ligament and the posterior capsule are characterised as a grade 3 injury and have a greater risk of developing chronic medial and rotatory instability requiring surgical treatment. In this chapter the anatomical and biomechanical background for medial knee laxity is presented and related to clinical evaluation. Treatment decision strategies are detailed based on clinical and imaging findings. Finally the key techniques for anatomical reconstruction of the MCL are described, including their clinical outcomes.
Anatomy
The primary structures involved in medial knee stabilisation are the superficial medial collateral ligament (sMCL), posterior oblique ligament (POL) and deep MCL ( Fig. 8.1 ). The sMCL, also named the tibial collateral ligament, is the largest structure of the medial aspect of the knee. This structure has one femoral and two tibial attachments. The femoral attachment is oval and is located just posterior to the medial epicondyle. Distally, the sMCL has two tibial attachments. The proximal tibial attachment of is a soft tissue attachment over the termination of the anterior arm of the semimembranosus tendon located 10 to 12 mm distal to the tibial joint line. The distal tibial attachment has a broad attachment directly to bone at an average of 60 mm distal to the tibial joint line and is located just anterior to the posteromedial crest of the tibia. The POL is a fibrous extension of the distal aspect of the semimembranosus, which blends with and reinforces the posteromedial joint capsule (see Fig. 8.1 ).
It consists of three facial attachments, the superficial, the central and capsular arms extending from the semimembranosus tendon immediately posterior to the sMCL. The superficial arm of the consist of a thin fascial expansion that follows the posterior border of the superficial MCL. The central arm is considered to be the main component of the POL, arising from the main semimembranosus tendon, reinforcing the deep MCL (dMCL) directly attaching to the posterior joint capsule and posterior meniscus and continuing proximally with the capsule to the POL femoral insertion just posterior to the medial epicondyle. The capsular arm comes off the distal aspect of the semimembranosus tendon, attaching to the meniscofemoral portion of the joint capsule and in its proximal course connecting to the medial head of the gastrocnemius and the adductor magnus tendon. The dMCL is composed of the thickened medial joint capsule, which is deep to the sMCL. It is divided into meniscofemoral and meniscotibial components. The meniscofemoral ligament portion has an attachment 12 mm distal and deep to the sMCL’s femoral attachment.
Biomechanical Properties of the Medial Knee Structures
The primary valgus stabilising structure of the knee is the sMCL, which is an almost isometric structure with a strength of 550 N. The POL is tight in extension and becomes lax in flexion and contributes to external rotatory stability. POL tears can result in anteromedial instability, where the tibial plateau subluxates anteromedially during an external rotation load.
The biomechanical properties of combined anatomical reconstruction of the MCL and POL on valgus and rotatory stability have been investigated in a cadaveric study. The anatomical reconstruction technique involved a two-strand reconstruction of both the superficial MCL and POL with hamstring grafts and interference screw fixation at their anatomical femoral and tibial insertion sites. The reconstruction also used anchor fixation at the proximal tibial insertion of the superficial MCL graft. This study found a significant increase in valgus angulation and external rotation after sectioning the medial knee structures. This was recovered after an anatomical medial knee reconstruction. The study concluded that an anatomical medial knee reconstruction could restore preinjury stability to a knee with a complete sMCL and POL injury, while avoiding overconstraining the reconstructed ligament grafts. Another study by Petersen et al. tested the importance of the POL in PCL-deficient knees. In their study sectioning of the sMCL and deep MCL did not increase posterior instability, whereas sectioning of the POL resulted in significant increased posterior instability.
Diagnosis
Injury classifications
The most widely used medial knee injury grading scale is the American Medical Association Standard Nomenclature of Athletic Injuries in which medial collateral injuries are graded from I to III ( Table 8.1 ). Grade I, or a first-degree tear, presents with localised tenderness along the ligament with no valgus laxity. Grade II, or second-degree tears, present with broadened tenderness and an increased joint gapping but with an endpoint. This is consistent with a complete torn superficial MCL and incomplete posterior oblique fibre tearing. Grade III, or third-degree tears, have a clear valgus laxity without any resistance to an applied valgus stress. A grade III injury represents a complete disruption of all medial structures, including the superficial MCL, the deep MCL and the POL. Isolated medial knee injuries have also been classified in accordance to the amount of laxity observed at 30 degrees of knee flexion with a valgus applied moment. These are grade 1+, 2+ and 3+, which have been reported to correspond to 3 to 5 mm, 6 to 10 mm and greater than 10 mm of subjective medial joint line gapping laxity, respectively, compared with the noninjured contralateral side.
| Isolated Superficial MCL Lesion | Combined Superficial MCL and Posteromedial Injury | |
|---|---|---|
| Manual valgus testing 0 degrees | No gapping | Increased gapping |
| Manual valgus testing 20–30 degrees | Increased gapping without endpoint | Increased gapping without endpoint |
| Positive anterior drawer test | No | Yes |
| Positive dial test | No | Yes |
| Stress radiography 0 degrees | >1.7 mm | >6.5 mm |
| Stress radiography 20–30 degrees | > 3.2 mm | >9.8 mm |
Clinical evaluation of valgus instability
Examination of the superficial MCL is performed by valgus stress tests, which should be performed at both 0 and 20 to 30 degrees of flexion. The American Medical Association Standard Nomenclature of Athletic Injuries with grades I to III is the primary classification system for the clinical evaluation of MCL injuries. In a grade I injury there is no valgus gapping but tenderness along the MCL fibres. In a grade II injury, there is clearly increased medial joint gapping but with a clear endpoint including pain along the MCL with potential medial sided swelling. In a grade III injury there is clear laxity without any endpoint to an applied valgus stress, often with considerable swelling and pain along the medial ligament structures. Isolated medial knee injuries have also been classified in accordance with the amount of laxity observed at 30 degrees of knee flexion with a valgus applied moment. These are grade 1+, 2+ and 3+, which have been reported to correspond to 3 to 5 mm, 6 to 10 mm and greater than 10 mm of subjective medial joint line gapping laxity, respectively, compared with the noninjured contralateral side.
A finding of valgus laxity at 0 degrees indicates either a concomitant cruciate ligament injury or an injury and laxity of the posteromedial structures, including the POL.
Anteromedial instability and posteromedial injury assessment
Anteromedial instability is characterised by a combined tear of the superficial MCL, POL and posteromedial capsule. The anteromedial drawer test and the dial test can evaluate this combined lesion (see Table 8.1 ).
The anteromedial drawer test is performed by flexing the knee to approximately 90 degrees while externally rotating the foot 10 to 15 degrees and applying an anteromedial rotational force to the knee. Anteromedial tibial plateau subluxation is present with a positive test and is indicative of a POL and posteromedial capsule injury or a severe distal sMCL tear.
Also, a complete injury to the medial structures will cause increased external rotation at both 30 and 90 degrees of knee flexion resulting in a positive dial test. However, it is important to palpate the tibial plateau in relation to the femoral condyle while performing the dial test. If the tibial plateau shifts anteromedially, it is indicative of anteromedial instability, whereas a posterolateral subluxation is a sign of posterolateral instability.
Imaging Evaluation of Medial Injuries
Stress radiography
Valgus stress radiographs can be useful for quantitative grading of medial knee instability and to identify the insufficient structures that result in the medial compartment gapping. One study reported that compared with the intact knee, medial joint gapping increases of 1.7 mm and 3.2 mm were produced at 0 degrees and 20 degrees flexion, respectively, by a clinician-applied load when isolated complete superficial MCL injury was present. A complete medial knee injury involving sectioning of the superficial and deep MCL and POL resulted in gapping increases of 6.5 mm and 9.8 mm at 0 degrees and 20 degrees, respectively. These stress radiographic data suggest that a finding of stress radiographic laxity increase of more than 3 mm is a good indication of support for the decision of surgical treatment with MCL reconstruction ( Fig. 8.2 ).
Magnetic resonance imaging
Magnetic resonance imaging (MRI) is used to determine the location of the tear and the severity of the injury. MCL injuries are graded into three groups on MRI, much in the same way as many other ligaments: Grade 1 (minor sprain): High signal is seen medial (superficial) to the ligament, which looks normal, representing oedema in part of the ligament fibres. Grade 2 (severe sprain or partial tear): High signal is seen medial to the ligament, with high signal or partial disruption of the ligament ( Fig. 8.3A ). Grade 3: There is complete disruption of the ligament ( Fig. 8.3B ). The location of MCL injury is most often at the proximal aspect of the MCL fibre close to the femoral insertion.
Ultrasonography
Ultrasonography may have a role as an initial imaging modality in patients with suspected medial MCL tears because it is highly sensitive and can also be used as a dynamic tool by performing stress examination in chronic MCL lesions when other imaging methods are not available.
Treatment Algorithm
Treatment strategies in acute medial sided injuries optimally can be decided after the history is obtained concerning the injury mechanism, objective clinical evaluation, stress radiographs and MRI evaluation, which will enable classification of the MCL complex injury (see Table 8.1 ). For chronic lesions the same principles are valid, with optimal treatment decision possible after history of injury mechanism, objective clinical evaluation and MRI scanning and stress radiographic evaluation which will enable both classification of the MCL complex injury and the degree of biomechanical compromise from the injury. An algorithm for treatment can be seen in Table 8.2 .
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