First knee replacement implants were designed in the late 1950s in order to change damaged cartilage and bone of the knee. The knee replacement surgery quickly became one of the greatest examples of innovative surgery and has resulted in significant increase in the quality of life for people with damaged knees. As a result, the number of replacements has been growing dramatically every year.
The increasing need to upgrade the results of surgical outcomes has led to improvements in knowledge and understanding of knee function, more advanced surgical techniques and implant designs. Over the past years the number of implants available for the patients has significantly increased. Geometrical, anatomical, structural and functional solutions of latest knee implants impressively simulate natural knee joint allowing the knee implant to accomplish function of healthy knee joint such as flexing and rotating during the activities of daily life. There are multiple types of knee implants that doctors and patients can discuss before choosing the best option. Some of implants are mechanical which work as a simple joint and some of them are even computerized which have microprocessors and integrated fluid systems.
Total knee replacement and partial knee replacement are the main types of knees replacement surgery. Both surgeries show highly successful results. The difference is whether the entire knee joint needs replacement or only a part.
In a total replacement knee joint ant other biological materials that have been damaged by disease or etiological factors are replaced with foreign synthetic or organic materials.
Indications for partial knee replacement surgery are the same as for total knee replacement: to relieve pain and eliminate dysfunction of the knee, but for partial surgery disease should be isolated, ligaments need not to be damaged, and any deformity or lesion should be correctable.
In total knee replacement, the implants are used to resurface the ends of the femur and tibia. If only one side of the knee joint is damaged, partial knee replacement is applicable and smaller implants can be used to resurface only the damaged side.
Currently mostly used types of implants are fixed bearing and mobile bearing implants. It is known that both prostheses designs show very good survival rates around 95% in 10 years. Fixed bearing prostheses are most popular and accessible implants. A fixed bearing prosthesis includes a femoral detail having a medial and lateral condyle superficies and different tibial pallets allowing for maximum flexion of 110 degree at the knee joint. Usually it is made of strong materials such as titanium or cobalt chrome alloy. This design is the best choice for patients who do not have extra weight and who are not very active in sport or for elder people.
Mobile bearing implants are more suitable to younger and more active patients. Mobile implant provides patients with more impressive flexibility on the medial and lateral sides of the knee. Also because of the reduced wear of polyethylene and bone-prosthesis interface and more normal kinematics loosening after surgery is minimal.
Another type of implants retain or substitute posterior cruciate ligament. They are mostly recommended for patients with extremely damaged knees or elusive ligaments of the knee. Cruciate-retaining knee prosthetics are designed to support the knee joint by remaining the posterior cruciate ligament. Posterior-stabilized implants intend to change the posterior cruciate ligament by a polyethylene patch and femoral cam. Both implants prevent anterior rotation of the femur on the tibia and create stability. Potential advantages of these designs in comparison with fixed and mobile bearing models include less technically complicated procedure and more stable component interface and increased flexibility.
Success of surgery depends on correct selection of patients and proper implants for joint replacement. The choice of prosthesis depends on individual patient properties including age, weight, level of activity, health, cost of prosthesis, surgeon choice and experience of the surgeon. The most important components of knee implants are femoral component, tibial component and patellar component. All components of implant must be strong, flexible and resistant and should be designed of durable materials such as steel, cobalt, titanium, cement, ceramic or synthetic materials such as polyethylene which have to promote smooth movement and minimal future deterioration.
After knee replacement surgery positive achievements in pain and function management are quickly observed as well as quality of life and increased mobility. It may decrease social isolation and have other benefits, such as improved sport activity. Unfortunately, sometimes choosing wrong implant for wrong patient can lead to failure of knee replacement. Better understanding of the kinematics of the knee and changes in design can lead to better outcomes for patients.