Anatomy of the Knee
The knee is the largest joint in the body. Due to the anatomy of our bodies our hips and knees bear 4 times our body weight! The knee is a hinge joint between the femur and tibia. The knee joint is made of 3 parts: the medial, lateral and patellofemoral compartments.
Between the femur and tibia are menisci which function as cushions between the bones and provide lubrication to the joint. Surrounding the knee are several bursa that protect the joint and can sometimes become inflamed causing localized pain and swelling (bursitis).
The anterior cruciate retaining ligament (ACL), posterior cruciate ligament (PCL), the medial and lateral collateral ligaments (MCL/LCL) all connect the tibia to the femur and are responsible for joint stability. Tears to the ligaments can be treated conservatively or with arthroscopy.
ACL: prevents the tibia from moving forward and away from the femur. Damaged by trauma and results in “instability or giving out” of knee.
PCL: prevents the tibia from slipping to far back. “Dash board” injury.
LCL: prevents excessive lateral movement or medial rotation of the knee. Often becomes tight when patient is “knock kneed” (genu valgus). Often damaged by lateral blunt force trauma.
Normal Knee Arthritic Knee
Roughly 10 million Americans suffer from OA. OA is a chronic, irreversible condition that can affect one or multiple joints; it is sometimes referred to as wear and tear arthritis. Arthritis is an inflammation within the joint caused by break down of the cartilage at the end of the bones. As the cartilage is worn down and not replaced there is more friction and inflammation leading to worsening symptoms. Bone spurs may eventually form creating increasing stiffness and crunching/grinding noises with movement. Weight bearing joints are more symptomatic than non-weight bearing joints due to increased force.
It is unclear why OA affects some and not others but researchers suspect a multifactoral etiology. Data from the National Institute of Health (NIH) has shown that by the age of 65 more than ½ of all people will have evidence of OA on x-ray. Before the age of 45 more men than woman are affected but after age 45, woman develop more OA than their male counterparts.
Osteoarthritis is most common in the medial compartment, hence knock kneed varus deformity is more common than a valgus (bow legged deformity).
Symptoms of OA:
5. tenderness to touch
Diagnosis of OA:
2. crepitus (grinding)
3. tenderness/joint pain
Plain x-rays show OA, MRI/CT scan is not required unless ligamentous/meniscul tear is suspected. Infection is ruled out.
Treatment of Knee OA
Conservative treatment with NSAIDs, ice, unloading braces (put in picture of unloading brace), physical therapy (maybe list local PT groups, good exercises, pool therapy) and cortisone injections (link to injections) are first line therapy. Once these treatments fail/are no longer effective AND your radiographs show moderate to advanced DJD it is time to talk to your surgeon about knee replacement.
Typically if you are of normal weight (BMI) AND your symptoms/ disease are isolated to 1 compartment an unilateral knee replacement may be best suited for you. If your symptoms include more than one area or you have extensive degenerative changes in more than one area a total knee replacement is indicated.
Whether a total knee or partial knee replacement is indicated the surgeon will remove the diseased (arthritic) bone and replace the surface of your femur and tibia with a combination of cobalt-chrome and titanium. The knee cap is then resurfaced with a polyethylene button to make sure it “tracks” properly and does not go on to develop OA. Between the metal pieces and in the joint space a hard plastic is inserted and acts as cartilage.