The knee is composed of three compartments, the (1) medial compartment, (2)lateral compartment, and (3) patellofemoral compartment.
Osteoarthritis is a degenerative condition affecting articular cartilage, when is limited to a single compartment of the knee, known as unicompartmental arthritis.
Anatomy and Function
Unicompartmental arthritis is an example of osteoarthritis affecting either the medial or lateral compartment of the knee. While osteoarthritis most commonly affects both compartments, certain factors may predispose to the uneven development of osteoarthritis. These factors include:
- Malalignment: Patients with malaligned knees are commonly known as being “bowlegged” (varus malformation) or “knock-kneed” (valgus malformation).
- Articular cartilage injury
- Untreated Meniscusinjury.
Diagnosis of arthritis is made through a combination of history and physical exam as well as imaging.
A history of pain isolated to the medial or lateral portions of the knee associated with joint swelling and stiffness is suggestive of arthritis.
On physical exam, orthopedic surgeons and sports medicine specialists will evaluate the alignment of the knee to assess for joint malalignment indicative of uneven load distribution.
X-rays of the knee will be taken and may demonstrate signs of osteoarthritis limited to one compartment of the knee. These signs include joint space narrowing, bone spur formation, and increased density of the bone adjacent to the overloaded compartment.
Treatment choice depends on many factors considered by the orthopedic surgeon or sports medicine specialist like age, activity level, degree of symptoms, and the underlying cause of arthritis.
- Weight loss and physiotherapy
- Injection -Multiple injections are available to help relieve the pain of unicompartmental osteoarthritis
- Corticosteroid injectionsare commonly used to decrease the inflammation of an osteoarthritic knee and relieve associated pain. Pain relief typically last from 4-6 months.
- Viscosupplementation – Hyaluron is a natural component of joint fluid that helps to lubricate and absorb shock. Hyaluron injections are thought to help restore the shock-absorbing functions of an osteoarthritic knee and protect damaged cartilage.
The decision for which injection to be used depends on the staging of arthritis and can be discussed with the orthopaedic surgeon.
- Bracing-If the underlying problem of osteoarthritis is malalignment of the knee, a special brace, called anoffloader brace, may be worn by the patient.
- Articular Cartilage Restoration Procedures–
These options are typically most appropriate for smaller cartilage defects in younger patients and include:
- Osteochondral allograft transplantation
- Autologous chondrocyte implantation
In this procedure, a wedge of bone is cut out from either the tibia (a high tibial osteotomy) or the femur (a distal femoral osteotomy).
The goal of this procedure is to relieve the uneven distribution of weight across the knee and prevent progression of osteoarthritis.
Patients are typically not allowed to bear weight on the leg for 6 weeks and aren’t able to return to full activity until 6 months.
- Advantages: retain native knee joint, allow for continued normal activity level.
The optimal candidate for osteotomy is a highly active, highly motivated patient willing to deal with the long and painful recovery process. Additionally, there must be clear demonstration of knee malalignment as well as truly isolated unicompartmental osteoarthritis.
In certain situations, the best treatment for unicompartmental osteoarthritis may be replacing the damaged portion of the joint.
- Advantages: quicker recovery than total knee replacement, less pain than total knee replacement, may be a more “natural” feel than total knee replacement
An ideal candidate is a young patient with true unicompartmental osteoarthritis and mild deformity with minimal fixed deformities.
- Advantages: removal of all osteoarthritic cartilage, more predictable pain relief.