Page created on October 25, 2021. Last updated on March 21, 2023 at 10:22

Summary

• Ligament injuries are common injuries. In case of ligament injury the patient may report hearing or feeling a “pop”, “cracking” or “crunch”, and experiencing instability of the knee when walking. Swelling of the knee develops immediately. The ACL is the most commonly injured knee ligament, occuring due to external rotation of the knee. ACL injury is often treated surgically, with arthoscopic reconstruction of the ACL with a tendon graft.
• Many examination manoueuvres are useful for examination of ligament injuries, including Lachman (for ACL), drawer test (for ACL, PCL), patella dip test, valgus stress test (for MCL) and varus stress test (for LCL). MRI is the best image modality.
• Meniscal injuries are also common injuries. They occur due to sudden twisting of the knee with the lower leg in a fixed position. Symptoms include pain, swelling, and joint lock-up. Swelling of the knee develops slowly. The patient might have felt something “slipping” or “tearing”. Treatment is surgical and may be suture or resection.
• Many examination manoueuvres are useful for examination of meniscal injuries, including Apley test, McMurray test, and Thessaly test. MRI is the best image modality.
• The “unhappy triad” refers to simulatenous injury of the ACL, MCL, and medial meniscus. It requires surgical treatment.
• Patellar fractures are rare and often due to direct trauma. It’s important to evaluate whether the extensor function is intact, as disrupted extensor mechanism is an indication for surgery.

Ligament injuries of the knee

Definition and epidemiology

Knee injuries in general, including ligament and meniscal injuries and patellar fractures, are common injuries.

The anterior cruciate ligament (ACL) prevents anterior translation of the tibia, tibial rotation, and valgus/varus displacement. The ACL is the most commonly injured knee ligament, accounting for approximately half of all knee injuries. It’s more common among females.

The posterior cruciate ligament (PCL) is the largest and strongest intra-articular ligament of the knee. It prevents posterior translation of the tibia. The medial collateral ligament (MCL) prevents valgus stress and tibial rotation. The lateral collateral ligament (LCL) prevents varus stress and tibial rotation.

The “unhappy triad” refers to simultaneous injury of the ACL, MCL, and medial meniscus.

Etiology

ACL injury occurs mostly due to external rotation of the knee during sports. It may also occur due to high energy trauma due to forced hyperextension of the knee.

PCL injury occurs due to forced hyperflexion with plantarflexed foot, often occurring during sports. It may also occur due to high energy trauma due to blow to a flexed knee.

Clinical features

Symptoms include knee instability when walking, pain, and swelling (may be due to haemarthrosis). Swelling occurs immediately in ACL injuries. The patient reporting hearing a “pop”, “cracking” or “crunching” sound is suspicious for a ligament injury.

Diagnosis and evaluation

Many physical examination manoeuvres are used in the evaluation of knee ligament injuries.

The valgus stress test involves applying valgus stress to the knee (by pushing medially) while the knee is in extension and 20 – 30° flexion. Widening of the joint space, felt as medial laxity, indicates MCL, ACL, or posteromedial capsule injury.

The varus stress test involves applying varus stress to the knee (by pushing lateral) while the knee is in extension and 20 – 30° flexion. Widening of the joint space, felt as lateral laxity, indicates LCL, ACL, or posterolateral capsule injury.

Lachman test involves having the patient’s knee in light flexion (15 – 20°), gripping the upper part of the tibia with one hand and the lower part of the femur with the other, and attempting to “pull” the tibia anteriorly. If the tibia can be pulled 3 – 4 mm anteriorly (anterior tibial translation, compare with the other side), the test is positive and indicates ACL injury. Lachman test is superior to the drawer test for diagnosing ACL injuries.

Anterior-posterior drawer test is similar to Lachman test. The patient’s knee is in 90° flexion, and the examiner fixes the patient’s foot on the table and attempts to pull the proximal tibia anteriorly and push it posteriorly. Anterior laxity (translation) indicates ACL injury, while posterior laxity indicates PCL injury.

The patella dip test may be used to demonstrate intraarticular fluid (not only in ligament injuries), including haemarthrosis. The suprapatellar recess is compressed with one hand and try to push the patella into the knee with the other hand. In case intraarticular fluid is present, pushing the patella feels like it’s floating on fluid and you can “dip” it into the fluid.

MRI is the best modality to diagnose soft tissue injuries like ligament and meniscal injuries. Ultrasound may also be used.

Treatment

ACL may be treated conservatively or surgically. Conservative therapy is indicated for chronic injuries, patients with minimal activity, if there is no instability, and if there is no associated injury. It involves immobilisation, brace, and physiotherapy. In most cases, surgery is performed. Surgery is usually arthroscopic and involves reconstruction of the ACL with a tendon graft. Native (autograft), cadaver (allograft), or synthetic grafts may be used. Non-synthetic grafts are usually taken from patellar, hamstring, or quadriceps tendons. Treatment of other ligament injuries were not included in lecture.

Treatment of the unhappy triad requires surgical treatment with meniscal repair and ACL reconstruction.

Meniscal injuries of the knee

Definition and epidemiology

Meniscal injuries (tears) are also common sports injuries. Typically, these injuries cause “clicking” or “popping” and the sensation of the knee not moving properly during rotation of the knee joint. Injury of the medial meniscus is more common than the lateral, impairing external rotation.

The function of the menisci is to provide a deeper joint surface, reduce stress, and stabilise the joint. The blood supply of the menisci is best at the outer (lateral) edge (red zone) and poorest at the inner (medial) edge (white zone).

Etiology

Meniscal injuries occur due to sudden twisting of the knee with the lower leg in a fixed position.

Classification

Tears are classified according to their morphology:

• Localisation of tear
  • Medial meniscus
  • Lateral meniscus
• Dignity of tear
  • Simple
  • Complex (combination of multiple types)
• Type of tear
  • Vertical tear
  • Radial tear
  • Horizontal tear
  • Displaced tear
    • Bucket handle tear
    • Parrot beak tear

Clinical features

Symptoms include pain, swelling, and joint lock-up. Swelling may be due to hydrops or haemarthrosis due to a meniscal tear. Swelling develops over the subsequent 24 hours (and not immediately as in ligament injuries).

The sensation of something “slipping” or “tearing” is suspicious for meniscal injury. There may be pain upon palpation of the relevant joint space.

Diagnosis and evaluation

Many physical examination manoeuvres are used in the evaluation of meniscal injuries. The sensitivity of the McMurray and Apley tests are in the 50-60s percentages. The Thessaly test has much higher sensitivity (80-90%) but is not as widely used.

Apley test involves having the patient prone with the hip extended and knee flexed. Then, the patient’s upper leg is fixated (with the examiner’s leg), the knee is brought to 90° flexion. Then, the lower leg is internally and externally rotated both with and without applying downward pressure on the foot. External rotation tests the medial meniscus while internal rotation tests the lateral. Positive findings include increased pain during rotation when downward pressure is applied.

McMurray test involves having the patient supine with the hip and knee flexed. Then, varus stress and internal rotation is applied to the knee, after which the knee is extended. This tests the lateral meniscus, and positive findings include pain in the lateral joint space or “clicking” or “locking” in the knee. The test is then repeated while applying valgus stress and external rotation, which tests the medial meniscus.

Thessaly test involves having the patient and examiner facing each other (holding hands for support), and having the patient stand on one knee, flexing the knee to 20°, and rotating their body back and forth. Positive findings include pain or a locking or catching sensation.

MRI is the best modality to diagnose soft tissue injuries like ligament and meniscal injuries. Ultrasound may also be used.

Treatment

Treatment is almost always surgical and involves arthroscopy with suture, partial or total resection, or meniscus transplantation. Tears in the red zone of the meniscus have good prognosis due to good blood flow, while tears in the white zone rarely heal and instead require resection.

Patellar fractures

Definition and epidemiology

Patellar fractures are the result of blunt trauma to the patella or due to a contracting quadriceps. These fractures are rare, accounting for approximately 1% of all fractures.

Etiology

Fall onto flexed knee or the knee hitting the dashboard during motor vehicle accident are the most frequent causes of patellar fracture.

Classification

Patellar fractures are classified according to their morphology:

• Undisplaced
• Transverse
• Lower or upper pole
• Comminuted undisplaced
• Comminuted displaced
• Vertical
• Osteochondral

Clinical features

Symptoms include swollen knee and patellar pain and tenderness.

Diagnosis and evaluation

During physical examination it’s important to evaluate the extensor function, as disrupted extensor mechanism is an indication for surgery. Patient should be challenged to extend their knee fully against gravity. However, pain may prevent full extension, and it may be difficult to discern whether abnormal extension is due to pain or a disrupted mechanism. Physical examination will likely also reveal intraarticular fluid.

X-ray is usually sufficient for diagnosis. Ultrasound or CT/MRI may be used to exclude other injuries.

Treatment

For undisplaced, closed patella fractures with intact extensor mechanism, conservative treatment is sufficient.

For displaced or avulsed patella fractures, surgery is necessary. Surgery involves tension band wiring or partial patellectomy with anchoring the patella.