Updated January 01, 2014.
Osteoarthritis affects the knee joint more than any other joint. To fully understand your treatment options for knee osteoarthritis, you should first learn about the basic anatomy of the knee.
Three Knee Compartments
There are three compartments of the knee. Each compartment is named after the two bones that join together in that compartment of the knee joint. The three compartments are:
-medial (inside) femoro-tibial compartment
-lateral (outside) femoro-tibial compartment
-patellofemoral compartment (formed by the kneecap and femur)
Osteoarthritis can affect one, two, or three compartments of the knee. When all three are affected, it's called tricompartmental osteoarthritis. There are several conservative treatments to help relieve knee osteoarthritis. When conservative treatments fail to be effective, you may be a candidate for knee replacement surgery.
Determining the Affected Knee Compartment
A physical examination may provide the first indication of what compartment is affected. Your doctor will ask you to stand and to walk. While standing, your doctor will observe you for any postural deformity, such as valgus (knock-kneed) or varus (bow-legged) deformity. There may also be obvious or subtle differences in leg length. When you are asked to walk, your doctor will observe gait abnormalities, such as limping to one side.
X-rays will be needed to confirm cartilage loss and joint damage associated with the abnormalities observed during your physical examination. On x-ray imaging, cartilage loss shows up as narrowing of the space between the ends of the bones forming the joint.
This is referred to as (i.e., joint space narrowing). Often, the narrowing of the joint space appears on one side. Medial narrowing is observed in 75% of knee osteoarthritis patients and can cause a bow-legged stance and gait. Lateral narrowing, which is less common and observed in about 26% of knee osteoarthritis patients, is associated with a knock-kneed stance and gait. Close to half of knee osteoarthritis patients have evidence of patello-femoral damage on x-rays.
Surgical Replacement of Affected Compartments
When only one knee compartment is involved, your doctor and orthopedic surgeon may recommend a partial knee replacement or unicompartmental knee replacement, rather than a total knee replacement. Although the decision to have a partial knee replacement seems straightforward, there are factors to consider. It may be just a matter of time before the other compartments wear out and more surgery is needed. Would it be better to have a total knee replacement rather than a partial knee replacement and not have any concerns about the need for future surgeries? Your doctor will assess the severity of your condition and offer advice.
Besides a unicompartmental knee replacement or a total knee replacement, there is also a bicompartmental knee replacement. The bicompartmental knee replacement is an option for patients with knee osteoarthritis of the medial and patellofemoral compartments.
Compared to total knee replacement, the unicompartmental and bicompartmental knee replacements preserve normal bone and the two cruciate ligaments.
The Bottom Line
Most knee osteoarthritis patients have unequal involvement of the three knee compartments. Treatment options, especially surgical options, depend on whether you have unicompartmental, bicompartmental, or tricompartmental knee osteoarthritis.
Sources:
All About Osteoarthritis. The Lower Body. Pages 102-105. Nancy E. Lane and Daniel J. Wallace. Oxford University Press. 2002.
Bicompartmental Knee Arthroplasty: A Bone-sparing, Ligament-sparing, and Minimally Invasive Alternative for Active Patients. Rolston L. MD et al. OrthoSuperSite. August 1, 2007.
Frontera: Essentials of Physical Medicine and Rehabilitation, 2nd ed. p. 345 Copyright © 2008 Saunders, An Imprint of Elsevier.