Fractures and dislocations of the knee joint
The knee consists of two separate joints:
- Femoral tibial (between femoral condyles and articular surface of the Tibia)
- Femoropatellar (between the patella and the femur)
The knee is a biconcave pivot-hinge joint with the following range of motion:
- Extension-flexion 5-0-140
- Lateral rotation-medial rotation 30-0-10
The main ligaments that hold the joint together are:
- Anteriorly
- Patella ligament with quadriceps femoris tendon
- Lateral/medial
- Lateral and medial retinaculum patellae
- Lateral and medial collateral ligaments
- Posterior
- Oblique popliteal ligament
- Popliteal arcuate ligament
- Inside the joint
- Anterior and posterior cruciate ligament
- Meniscofemoral ligament
Vasculature of the joint comes from branches of the popliteal artery, these are:
- Inferior medial and lateral knee artery
- Medial genus artery
In this question we shall consider two main types of fracture, patella fractures and fractures of the Tibial plateau, as well as dislocations of the knee.
Patellar fractures
Such fractures are commonly the result of direct heavy trauma to the knee, such as a fall. As the patella is constantly under tension from the quadriceps tendon these fractures are usually displaced. Patients will often present with “Dome” effusion, tenderness and possibly a palpable defect, with inability to extend the knee.
We can classify patellar fractures as follows:
- Nondisplaced
- Transverse
- Vertical
- Stellate
- inferior/superior pole
- Comminuted
Treatment for nondisplaced fractures can be treated with a simple brace for 6-8 weeks. If displacement is greater than 2-3mm then ORIF (e.g. tension bands) are indicated to restore the articular surface. Finally in cases where there is severe comminution a full or partial patellectomy may be required.
The main risks following the fracture are osteoarthritis with decreased motion, osteonecrosis and refracture!
It is also worth noting that the patella can be dislocated by a sharpt rotation, often occurs where there is an underlying patella deformity such as as hypermobility.
Tibial plateau fractures
Caused by axial load and varus/valgus stress. Such fractures are commonly associated with meniscal and ligament tears and should also be considered in the treatment. The significant axial load may also cause metaphyseal injury, as bone will compress and lead to functional bone loss, a bone graft may be needed.
The fracture presents as expected, history of trauma, pain, swelling, inability to bear weight, effusion and tenderness. We classify tibial plateau fractures into six different types:
- I - Lateral plateau split fracture
- II - Lateral split/depression fracture
- III - Lateral plateau depression
- IV - Medial plateau split fracture
- V - Bicondylar plateau fracture