Medial knee injuries (those to the inside of the knee) are the most common type of knee injury. The medial ligament complex of the knee consists of: superficial medial collateral ligament (sMCL), also called the medial collateral ligament (MCL) or tibial collateral ligament deep medial collateral ligament (dMCL), or mid-third medial capsular ligament posterior oblique ligament (POL), or oblique fibers of the sMCL This complex is the major stabilizer of the medial knee. Injuries to the medial side of the knee are most commonly isolated to these ligaments. A thorough understanding of the anatomy and function of the medial knee structures, along with a detailed history and physical exam, are imperative to diagnosing and treating these injuries.
Symptoms Patients often complain of pain and swelling over the medial aspect of the knee joint. They may also report instability with side-to-side movement and during athletic performance that involves cutting or pivoting.
Complications Jacobson previously described the common problems to medial knee surgery. It was stressed that adequate diagnosis is imperative and all possible injuries should be evaluated and addressed intraoperatively. Damage to the saphenous nerve and its infrapatellar branch is possible during medial knee surgery, potentially causing numbness or pain over the medial knee and leg. As with all surgeries, there is a risk of bleeding, wound problems, deep vein thrombosis, and infection that can complicate the outcome and rehabilitation process. The long term complication of arthrofibrosis and heterotopic ossification (Pellegrini-Stieda syndrome) are problems that are best addressed with early range of motion and following defined rehabilitation protocols. Failure of graft due to intrinsic mechanical forces should be prevented with preoperative alignment assessment (osteotomy treatment) and proper rehabilitation.
Causes Medial knee injury is usually caused by a valgus knee force, a tibial external rotation force, or a combination thereof. This mechanism is often seen in sports that involve aggressive knee flexion like ice hockey, skiing, and football.
Anatomy and function
Structures on the medial side of the knee include the tibia, femur, vastus medialis obliquus muscle, semitendinosus tendon, gracilis tendon, sartorius tendon, adductor magnus tendon, medial head of the gastrocnemius muscle, semimembranosus tendon, medial meniscus, medial patellofemoral ligament (MPFL), sMCL, dMCL, and POL. It has been found that the most important structures for stabilization in this area of the knee are ligaments: sMCL, dMCL, and POL.
Bones The bones of the knee are the femur, patella, tibia, and fibula. The fibula is on the lateral side of the knee and the patella has little effect on the medial side of the knee. The bony congruity of the medial knee consists of the opposing surfaces of the medial femoral condyle and the medial tibial plateau. On the medial femoral condyle there are three bony landmarks that are important: the medial epicondyle, adductor tubercle, and gastrocnemius tubercle. The medial epicondyle is the most distal and anterior prominence. The adductor tubercle is just proximal and posterior to the medial epicondyle. The gastrocnemius tubercle is just distal and posterior to the adductor tubercle.
Ligaments and biomechanical function
The sMCL connects the femur to the tibia. It originates just proximal and posterior to the medial epicondyle (not directly on the epicondyle) and splits into two distinct sections. One tibial section attaches to soft tissue, 1 cm distal to the joint line. The other tibial section attaches directly to the tibia, anterior to the posteromedial tibial crest, 6 cm distal to the joint line. This distal attachment is the stronger of the two and makes up the floor of the pes anserine bursa. The proximal tibial attachment of the sMCL is the primary stabilizer to valgus force on the knee, whereas the distal tibial attachment is the primary stabilizer of external rotation at 30° of knee flexion.
The dMCL is a thickening of the medial aspect of the capsule surrounding the knee. It originates on the femur 1 cm distal to the sMCL origin and inserts 3–4 mm distal to the joint line. It runs parallel to and underneath the sMCL. The dMCL connects directly to the medial meniscus and therefore can be divided into meniscofemoral and meniscotibial ligament components.
The meniscofemoral ligament is longer than the meniscotibial ligament, which is shorter and thicker in nature. The meniscofemoral ligament is a primary internal rotation stabilizer and a secondary external rotation stabilizer, activated when the sMCL fails. The meniscotibial ligament acts to secondarily stabilize internal rotation.
The POL (called by older texts: oblique portion of the sMCL) is a fascial expansion with three main components: superficial, central (tibial), and capsular. The central arm is the strongest and thickest. It arises from the semimembranosus tendon and connects anterior and distal to the gastrocnemius tubercle via the posterior joint capsule. The POL, therefore, is not a stand-alone structure, but a thickening of the posteromedial joint capsule. It stabilizes internal rotation of the knee through all degrees of flexion but bears the most load when internally rotated in full extension. It also acts as a secondary external rotation stabilizer.
The MPFL arises from the fibers of the vastus medialis obliquus muscle and attaches distally to the superior medial aspect of the patella. This ligament acts to keep the patella within the trochlear groove during flexion and extension. It is rarely injured from a medial knee injury unless there is a concurrent lateral patellar subluxation or dislocation.
Tendons and muscles The adductor magnus tendon attaches to the distal medial femoral condyle just posterior and proximal to the adductor tubercle. It has a fascial expansion on the distal-medial aspect that attaches to the medial gastrocnemius tendon, capsular arm of the POL, and posteromedial joint capsule. The thick distal lateral aspect attaches to the medial supracondylar ridge. The adductor magnus tendon is an excellent, consistent landmark because it is rarely injured. The vastus medialis obliquus muscle courses over the anteromedial thigh, attaching along the adductor magnus anterior border and to the quadratus femoris tendon. The medial gastrocnemius tendon arises proximal and posterior to the gastrocnemius tubercle of the medial femoral condyle. This is another important landmark because it is rarely injured and attaches close to the capsular arm of the POL, thus helping the surgeon locate the femoral attachment of the POL.
Diagnosis The majority of medial knee injuries are isolated ligamentous injuries. Most patients will relate a history of a traumatic blow to the lateral aspect of the knee (causing a valgus force) or a non-contact valgus force. Acute injuries are much easier to diagnose clinically, while chronic injuries may be less apparent due to difficulty in differentiating from a lateral knee injury, possibly requiring valgus stress radiographs.
Physical exam The physical exam should always begin with a visual inspection of the joint for any outward signs of trauma. Palpation should follow paying close attention to effusion and subjective tenderness during the exam. The practitioner should also evaluate the contralateral (non-injured) knee to note any differences in gross appearance and landmarks. Palpation should focus specifically on the meniscofemoral and meniscotibial aspects of the sMCL. It has been reported that injury to one versus other has implications for healing, so localization of the site of injury is beneficial. Testing of the knee joint should be done using the following techniques and the findings compared to the contralateral, normal knee: Valgus stress at 0° and 20°- This test puts direct stress on the medial knee structures, reproducing the mechanism of injury. Valgus stress testing is done with the patient supine on the exam table. The lower extremity, supported by the examiner, is abducted. The examiner's fingers monitor the medial joint space for gapping while placing the opposite hand on the ankle. The knee is placed in 20° of flexion. The examiner then uses their own thigh as a fulcrum at the knee and applies a valgus force (pulling the foot and ankle away from the patient's body). The force is then used to establish the amount of gapping present within the joint. It has been reported that 20° of flexion is best for isolating the sMCL, allowing the practitioner to establish the degree of injury (see Classification). Additional testing is done at 0° to determine if a Grade III injury is present. Anteromedial drawer test- This test is performed with the patient supine with the knee flexed to 80-90°. The foot is externally rotated 10-15° and the examiner supplies an anterior and external rotational force. The joint can then be evaluated for tibial anteromedial rotation, taking care to recognize the possibility of posterolateral corner instability giving similar rotational test results. As always, compare the test in the opposite knee. Dial Test (anteromedial rotation test)- This test should be executed with the patient lying both supine and prone. When the patient is supine, the knees must be flexed 30° off the table. The thigh is then stabilized and the foot externally rotated. The examiner watches for the tibial tubercle of the affected knee to rotate as the foot rotates, comparing it to the contralateral knee. A positive test will show rotation of greater than 10-15° of rotation compared to the opposite knee. This is most easily assessed with a hand placed over the tibia while testing. When the patient is prone, the knee is flexed to 90° and both feet are externally rotated and compared, noting the difference from the non-injured joint. Similar to the anteromedial drawer test, a false positive test can result from a posterolateral corner injury. Testing at both 30° and 90° helps to distinguish between these injuries: one should monitor where the tibial rotation occurs (anteromedial or posterolateral) in the supine position and also assess for medial or lateral joint line gapping to differentiate between these two injuries.
Classification
Grading of medial knee injuries is dependent on the amount of medial joint space gapping found upon valgus stress testing with the knee in 20° of flexion. Grade I injuries have no instability clinically and are associated with tenderness only, representing a mild sprain. Grade II injuries have broad tenderness over the medial knee and have some gapping with a firm end-point during valgus testing; this represents a partial tear of the ligaments. Grade III injuries have a complete ligamentous tear. There will be no end-point to valgus stress testing. The historic quantified definition of grades I, II, and III represented 0–5 mm, 5–10 mm, and >10 mm of medial compartment gapping, respectively. LaPrade et al. reported, however, that a simulated grade III sMCL injury showed only 3.2 mm of increased medial compartment gapping compared to the intact state. Additionally, with the knee in full extension, if valgus stress testing reveals more than 1–2 mm of medial compartment gapping present, a concomitant anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) injury is suspected.
Radiographs