Medial knee injuries
Medial knee injuries | |
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Knee diagram (normal) |
Medial knee injuries (those to the inside of the knee) are the most common type of knee injury.[1] The medial ligament complex of the knee consists of:[2]
- 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.[1][3] 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.[4][5]
Complications
Jacobson previously described the common problems to medial knee surgery.
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.[3][4][5]
Anatomy and function
Structures on the medial side of the knee include the
Bones
The bones of the knee are the
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.
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.[2][9] 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 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.
The MPFL arises from the fibers of the vastus medialis obliquus muscle and attaches distally to the superior medial aspect of the patella.[2] This ligament acts to keep the patella within the trochlear groove during flexion and extension.[2] 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.
Diagnosis
The majority of medial knee injuries are isolated ligamentous injuries. Most patients will relate a history of a
Physical exam
The physical exam should always begin with a visual inspection of the joint for any outward signs of trauma.
- 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.[4][5]
- 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
- Dial Test (anteromedial rotation test)- This test should be executed with the patient lying both supine and 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.[4][5][13]
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.[5][6][14] 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.[15] 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.[15] 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.[4][5]
Radiographs
Anterior-posterior (AP) radiographs are useful for reliably assessing normal anatomical landmarks. Bilateral valgus stress AP images can show a difference in medial joint space gapping. It has been reported that an isolated grade III sMCL tear will show an increase in medial compartment gapping of 1.7 mm at 0° of knee flexion and 3.2 mm at 20° of knee flexion, compared to the contralateral knee. Additionally, a complete medial ligamentous disruption (sMCL, dMCL, and POL) will show increased gapping by 6.5 mm at 0° and 9.8 mm at 20° during valgus stress testing.[15] Pellegrini-Stieda syndrome can also be seen on AP radiographs. This finding is due to calcification of the sMCL (heterotopic ossification) caused by the chronic tear of the ligament.[5][16]
MRI
Knee MRIs should be avoided for knee pain without mechanical symptoms or effusion, and upon non-successful results from a functional rehabilitation program.[20]
Treatment
Treatment of medial knee injuries varies depending on location and classification of the injuries.[6][21] The consensus of many studies is that isolated grade I, II, and III injuries are usually well suited to non-operative treatment protocols. Acute grade III injuries with concomitant multiligament injuries or knee dislocation involving medial side injury should undergo surgical treatment. Chronic grade III injuries should also undergo surgical treatment if the patient is experiencing rotational instability or side-to-side instability.[4][5]
Nonoperative treatment
Conservative treatment of isolated medial knee injuries (grades I-III) begins with controlling swelling and protecting the knee. Swelling is managed well with rest, ice, elevation, and compression wraps.
Operative treatment
It has been reported that severe acute and chronic grade III medial knee injuries often involve the sMCL in combination with the POL.[10][24] Direct surgical repair or reconstruction, therefore, should be performed for both of these ligaments because they both play an important role in static medial knee stability.[25] The biomechanically validated approach is to reconstruct both the POL and both divisions of the sMCL.[26][27]
Severe acute tears
Surgery involving direct repair (with or without augmentation from a
Chronic instability
Underlying causes of chronic medial knee instability must be identified before surgical reconstruction is performed. More specifically, patients with genu valgum (knock-kneed) alignment must be evaluated and treated with an osteotomy(s) to establish balanced forces on knee ligaments, preventing premature failure of concurrent cruciate ligament reconstruction. These patients should be rehabilitated after the osteotomy heals before it can be verified that they do not still have functional limitations. Once proper alignment is achieved, reconstruction can be performed.[4]
Anatomic medial knee reconstruction
This technique, described in detail by LaPrade et al., uses two grafts in four separate tunnels. An incision is made over the medial knee 4 cm medial to the patella, and extended distally 7 to 8 cm past the joint line, directly over the pes anserinus tendons.[27]
Within the
Moving to the femoral attachments of the ligaments, the first step is identifying the adductor magnus muscle tendon, and its corresponding attachment site, near the adductor tubercle. Just distal and slightly anterior to this tubercle is the bony prominence of the medial epicondyle. The attachment site of the sMCL can be identified slightly proximal and posterior to the epicondyle. An eyelet pin can now be passed transversely through the femur at this site. The tunnel at this location, however, should be drilled after identifying the POL attachment site.[27]
The next step of identifying the POL femoral attachment is done by locating the
The next aspect of the surgery is preparation and placement of the reconstruction grafts. The preparation can be done while the other steps are being completed by another surgeon or physician's assistant. The semitendinosus tendon can be harvested using a hamstring stripper for use as the reconstruction autograft.
Securing the POL graft is done in full knee extension. The graft is pulled tight and fixed using a bioabsorbable screw. The knee is then flexed to 20°. Making sure the tibia remains in neutral rotation, a varus force is used to ensure there is no medial compartment gapping of the knee. The sMCL graft is then tightened and fixed with a bioabsorbable screw.[27]
The final step of reconstruction ligament fixation is the proximal tibial attachment of the sMCL. This
Rehabilitation
- Nonoperative Rehabilitation As mentioned in the Nonoperative Treatment section, the principles of rehabilitation are to control
- Postoperative Rehabilitation Postoperative rehabilitation protocols for reconstructed or repaired medial knee injuries focus on protecting the ligaments/grafts, managing swelling, reactivating the quadriceps, and establishing range of motion. A safe range of motion ("safe zone") should be measured by the surgeon intraoperatively and relayed to the rehabilitation specialist to prevent overstressing the ligaments during rehabilitation. The ideal passive range of motion is 0 to 90° of flexion on postoperative day one after surgery and should be followed for 2 weeks, as tolerated, with a goal of 130° of flexion at the end of the 6th week. To protect the newly reconstructed ligaments, a hinged knee brace should be used.plyometric and agility exercises are started at 16 weeks. Brisk walking for 1 to 2 miles should be well tolerated before the patient starts a jogging program. Return to sports may be assessed at this point, providing no functional or stability deficits are present. Rehabilitation should be supervised by a professional specialist working along with the surgeon. Protocols may be adjusted in the presence of concomitant ligament reconstructions or osteotomies.[4][5][8] Valgus stress AP radiographs (mentioned above) are an excellent and cost-effective way to monitor postoperative results and follow-up.[15]
Future research
Future research with regard to medial knee injuries should evaluate clinical outcomes between different reconstruction techniques.[8] Determining the advantages and disadvantages of these techniques would also be beneficial for optimizing treatment.
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