Knee extensor mechanism injury around the knee are severe injuries, which require early treatment in order to prevent shortening of the extensor mechanism which will necessitate reconstructive procedures with less predictable results. Although the clinical diagnosis is fairly straightforward when looked for, it is surprising how often these injuries are initially missed. The reason for this may be that many of these conditions only have subtle abnormalities on standard x-rays, which may be missed during non-orthopaedic or non-radiological review.
Patella tendon avulsion injurys usually occur in teenage boys. The “pulled-off” fragment of bone requires reduction in order to allow it to heal back onto the tibia. While treatment in an extension brace is sometimes possible, significant displacement of the fracture fragment or extension of the fracture line into the knee joint may require open reduction and internal fixation. Implant removal may be necessary in children with a significant amount of growth remaining.
Patella tendon disruptions or in-substance tears usually occur in older patients and are due to a checked extension of the knee, which places an excessive isometric or eccentric strain on the tendon, leading to failure. Often tendon disruption is preceded by a period of tendonitis. Treatment of these injuries is inevitably surgical and requires open reduction and suture fixation of the patella tendon, often with augmentation of the repair. While most joint injuries are managed surgically with a view to early range motion of the joint in order to prevent stiffness, this cannot be allowed with patellar tendon reconstructions. The patient remains in an extension brace for between 6 to 8 weeks before range of motion exercises are begun.
Patella fractures do not always lead to extensor mechanism disruption, the direct trauma type fracture where the patient falls onto the bent knee may result in a stellate fracture, with significant damage of the patellofemoral joint cartilage associated, however, the extensor mechanism may remain in continuity. Displaced, transverse fractures, however, do constitute an extensor mechanism disruption and are often associated with retinacular injuries. These fractures require accurate open reduction and internal fixation, both with a view to recreate extensor mechanism function and preventing early onset patellofemoral joint osteoarthritis, which may occur if there is an articular surface mismatch remaining. With good implant fixation, these patients may undergo relatively early range of motion exercises of the knee.
Quadriceps tendon disruptions often occur in elderly patients with common with medical conditions. The mechanism of injury is similar to that of the patella tendon disruption. Again, these injuries are frequently preceded by a period of tendonitis. Surgical repair and extension brace immobilisation is required.
