Many middle aged men and women develop osteoarthritis of the knee. In Caucasians, Osteoarthritis of the knee affects the inner half or medial compartment to start with and then proceeds to affect the outer half or lateral compartment. The erect posture of man and a few other animals contributes to 60% of weight transmission through the inner side of the joint which contributes to wear. Localized attrition occurs in the beginning as a so called “lesion”. Later it gradually affects the front and inner portion of the inner half of the lower end of the thigh and leg bones (anter- medial wear). This is obvious on standing x rays as a pit or depression. Clinically these individuals may be bow legged since childhood.
The standard permanent surgical treatment for osteoarthritis knee has been a total knee replacement. However the ideal candidate for a TKR is a person beyond 65 years, when he can live out the life of an artificial joint which is about 15 years. Clearly someone in their fifties is not suited for a TKR as his/her life span would exceed that of the joint and he would need a revision knee replacement later on. Surgical alternatives include an osteotomy and a Uni condylar knee replacement. In an osteotomy, the thigh or leg bone is divided and re aligned so that the abnormal weight bearing axis is normalized. Pain relief is provided for a period of up to 10 years but is not total. An osteotomy is the logical operation for patients with bow legs and knock knees in the working class whose work demands would wear out an artificial joint. It is not the right procedure when there is no deformity.
A unicondylar or partial knee replacement substitutes the worn half of the joint with prosthesis. The bony resection is restricted to the affected half alone sparing the outer half and the patella unlike a total knee replacement. The operation can be done by a minimally invasive technique sparing the quadriceps muscle. The pre requisites are that the one half alone must be worn as seen on x- rays and the anterior cruciate ligament should be intact. The technique of insertion is demanding but the rewards to the patient are numerous. Shorter hospital stay, quicker recovery, small incisions, no blood transfusion, less pain, less cost (vs. TKR) and better function (squatting, kneeling, climbing stairs) are the much acclaimed benefits. The knee feels more natural as sensations carried by the ligaments are intact.
A partial knee replacement will survive for 10 – 15 years in averagely built patients, thus buying them time before arthritis affects the other compartment and a total knee replacement becomes necessary.
The Oxford unicompartmental knee is a representative type and is a mobile bearing uni knee. The wear rates are low. Survivorship analysis is 98% at 15 years.
Recently implants have been introduced which replace only two compartments. This is the Journey Deuce prosthesis which replaces the patello-femoral and medial compartments alone, leaving the lateral compartment untouched.
In the US uni-compartmental knee replacements are making resurgence after a revival in the 1990’s.
In summary partial knee replacements serve to buy time in middle aged patients. Patients can extend their prosthetic life to 25 years by having a partial knee replacement and then a total knee.
The author is a knee surgeon in Chennai at the knee surgery centre. He is affiliated to the Chettinad health city and Kamakshi memorial hospitals.
For a knee surgery appointment, you can mail him at akvenkat15@hotmail.com
Visit www.kneeindia.com
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