What is a Complex Primary Knee Replacement?
Complex primary knee replacement is a joint replacement surgery performed on a severely damaged or deformed natural knee joint.
Causes for Complex Primary Knee Replacement
The various knee conditions that could result in complex primary knee replacement include:
- Previous incisions on the knee
- Severe coronal deformities of the knee
- Extra-articular knee deformities
- Previous knee osteotomies
Preoperative Preparation for Complex Primary Knee Replacement
A thorough evaluation of the unique characteristics of the patient’s knee with the help of advanced diagnostic imaging studies and detailed preoperative planning is performed to ensure positive surgical outcomes.
For previous incisions on the knee: The skin at the site of the previous knee incisions are examined. Depending on the condition of the skin, a new incision, or the same incision, or a part of the same incision may be used to access the knee joint. A prophylactic skin flap may also be necessary for soft tissue cover and better wound healing.
For severe coronal deformity: This can be a bowlegged or knock-knee deformity with an angle of greater than 20 degrees. Such deformities may be caused due to stress fractures, cartilage loss, and bone loss. Study of the gait pattern is an essential part of pre-operative planning as this provides useful information of the deforming forces acting on the knee and how the knee joint can be correctly aligned.
For extra-articular deformity: Preoperative radiographs are taken for assessment of the location of the axis and degree of deformity. The right surgical technique to correct the malignment and balance the extra-articular forces acting on the joint is planned and the appropriate prosthesis is chosen.
For previous knee osteotomies: When planning knee joint replacement after a distal femoral or high tibial osteotomy, variation from the normal knee anatomy is taken into consideration. Bone grafts or prosthesis stem extensions may be used to augment or bypass areas of weakness in the bone. Bone resections may also be required to ensure the joint is aligned correctly.
Complex Primary Knee Replacement Procedure
The goal of surgery is to relieve pain and restore the alignment and function of your knee.
- The surgery is performed under spinal or general anaesthesia. Based on the customised preoperative plan, your surgeon will make an incision in the skin over the affected knee to expose the knee joint. Then, the damaged portions of the femur bone are cut at appropriate angles using specialised jigs. The femoral component is attached to the end of the femur with or without bone cement.
- Your surgeon then cuts or shaves the damaged area of the tibia (shinbone) and the cartilage. This removes the deformed part of the bone and any bony growths, as well as creates a smooth surface on which the implants can be attached. Next, the tibial component is secured to the end of the bone with bone cement or screws.
- Your surgeon will place a plastic piece called an articular surface between the implants to provide a smooth gliding surface for movement. This plastic insert will support the body’s weight and allow the femur to move over the tibia like the original meniscus cartilage.
- The femur and the tibia with the new components are then put together to form the new knee joint.
- To make sure the patella (kneecap) glides smoothly over the new artificial knee, its rear surface is also prepared to receive a plastic component.
- With all the new components in place, the knee joint is tested through its range of motion. The entire joint is then irrigated and cleaned with a sterile solution. The incision is carefully closed; drains are inserted and a sterile dressing is placed over the incision.
Complex Primary Knee Replacement Postoperative Care
Rehabilitation begins immediately following the surgery. A physical therapist will teach you specific exercises to strengthen your leg and restore knee movement. Knee immobilisers are used to stabilise the knee. You will be able to walk with crutches or a walker. A continuous passive motion (CPM) machine may be used to move the knee joint. The continuous passive motion machine is a device attached to the treated leg that constantly moves the joint through a controlled range of motion, while you are at rest. Your physical therapist will also provide you with a home exercise program to strengthen your thigh and calf muscles.
Risks and Complications of Complex Primary Knee Replacement
As with any major surgery, the possible risks and complications associated with primary knee replacement surgery include:
- Knee stiffness
- Blood clots (deep vein thrombosis)
- Nerve and blood vessel damage
- Ligament injuries
- Patella (kneecap) dislocation
- Plastic liner wearing out
- Loosening of the implant