A relatively young person with knee arthritis, which is almost exclusively on one side of the knee, with severe pain and limited ambulatory tolerance, is a candidate for uni-condylar knee replacement. When knee pain from osteoarthritis, interferes with daily activity, walking tolerance, and independence, it is time to consider this alternative. Patients may choose a uni-condylar knee replacement when they have exhausted conservative measures and they cannot maintain normal activities of daily living.
The end of the femur and tibia form the knee joint. They are covered with a thin, smooth layer of cartilage. In the knee hyaline (surface) and meniscal cartilage cushion the joint and absorb shock. Normally this cartilage is lubricated by a few drops of synovial fluid. The lining of the joint which produces this fluid is synovium. With cartilage debris from wear, the synovium proliferates and produces excess fluid. Cartilage has poor healing capabilities; as it wears away, the bone becomes exposed. The bone surfaces rubbing against each other cause pain, while cartilage has no sensation. There are no predictable or satisfactory methods for reversing the damage of arthritis when this includes a large weight-bearing area of the involved joint. When nonsurgical alternatives cannot bring a suitable level of relief, uni-condylar joint replacement is a realistic alternative. Unicondylar Knee Replacement is generally considered in a patient in their 50's unlike Total Knee Replacement, which is indicated in patients generally 60 or greater in age. This is because Total Knee Replacement at a young age is likely to fail over time, requiring revision surgery which is more complicated and may be less successful. Revision of a Unicondylar Knee Replacement is easier and generally can be accomplished using a Primary Knee Replacement which would normally be used in an older patient initially.
A Uni-condylar Knee replacement or arthroplasty consists of three pieces. The bearing surface is made of rugged polyethylene (high-density plastic) supported by alloy metals. These components resurface the femoral and tibial surfaces on the worn side only. This has the advantage of sparing the Anterior Cruciate Ligament and Posterior Cruciate Ligament, leading to improved knee function, and usually a more normal range of motion. The femoral component (the end of the thigh bone) is made of stainless steel. The tibial component (the top of the shin bone) is a Titanium tray with the plastic insert locked in. This mates with the femoral component. There is no patellar component (kneecap) and severe patellar arthritis may be a relative contraindication to Uni-condylar Knee Replacement. Knee alignment is corrected during Unicondylar Knee Replacement to normalize loading on both sides of the knee.
The components of a knee replacement are held to the bone with "cement". The cement is a plastic polymer that serves as an adhesive grout.
Replacement joints come in many different sizes and are precision engineered to feel and move as much like a real joint as possible. Most people with an artificial knee joint are not aware of a difference between the feel of the implant and their original knee. A Unicondylar Knee replacement allows for nearly normal motion of the knee. In the knee suitable for replacement, the range of motion is often improved following surgery. Design changes continue in existing prostheses in an effort to yield better function and longevity. A well-implanted prosthesis, in a compliant patient, usually lasts for many years. Since many prostheses now used are improved designs, we can only guess at their longevity. Trauma, wear or loosening may make it necessary to replace a uni-condylar prosthesis. Revision to a Total Knee Replacement may be necessary if the opposite side of the knee wears out. Every effort must be made to prolong the life of the Uni-condylar Knee Replacement which is implanted first. A working life of 10-15 years is reasonable, and more may be possible. Physical activity level, body weight, and patient age are strongly related to the longevity of knee replacement. The main object of a Uni-condylar Knee Replacement is relief of pain. Other goals include the correction of deformity and restoration of stability. Prosthetic design constraints limit the range of motion to approximately 0-110º. It should be emphasized that total knee replacements are not done to allow patients to return to unlimited activities and high-level sports. Fitness may be maintained by swimming, bicycling, and walking. Golfing and even skiing in some individuals may be considered, but impact loading such as running or jumping should be minimized.
The ideal patient is 50 to 60 years of age. Younger patients tend to be more active leading to premature loosening of the replacement. Young age is a relative contraindication to total knee replacement. Extreme osteoporosis (softening of the bone) or ligament instability are also relative contraindications to Unicondylar Knee replacement. In patients with a significant history of past infection of the knee, knee replacement is contraindicated because of the risk of reactivating the infection.
A patient with recurrent urinary tract infection secondary to chronic kidney stones, urethral stricture, or other genitourinary problems should have urologic evaluation prior to total knee replacement.
Special precautions against infection are taken before, during and after surgery. Antibiotics are used routinely peri-operatively. A special surgical room and techniques for a sterile environment are used during surgery. I always use antibiotics incorporated into the cement to lower the risk of infection. Although the risk is very low, the occurrence of late infection can be catastrophic and may require the removal of the prosthesis. To minimize the risk of infection, prophylactic antibiotics are given any time dental manipulation, urinary tract surgery or instrumentation or significant bowel procedures are performed. Any skin infection should also be treated with antibiotics as well, since late prosthetic implant infection may be related to a skin infection. There is also a risk of deep vein thrombosis (clot) after total knee replacement, and patients are generally treated with coumadin from the day before surgery until two or three weeks following surgery. This substantially reduces the risk of deep venous clot.
Patients are admitted on the day of surgery and hospitalized for one or two days. During the hospital stay, the emphasis is placed on regaining knee motion and strength, and activities of daily living. The faster patients are able to return home, the better they often do. It is unusual for Uni-condylar Knee Replacement patients to need rehabilitation before returning home. Therapy should continue at home with daily range of motion exercises, strengthening and gait training. This may be aided by the use of a home physical therapist, followed by outpatient therapy. In the highly motivated patient, therapy may be done entirely on a home program. Straight leg raising, bending over the seat of a chair, and maintaining full extension with a pillow beneath the ankle, are used with ambulation and functional exercise like an exercise bicycle to regain function.
Transfusion of blood is rarely necessary, especially in younger patients without a significant cardiac or pulmonary history. Blood work following surgery is monitored as a precaution.
The most serious complication after total joint replacement is an infection. This occurs in less than 0.5% of knee replacement, but the incidence is minimized with prophylactic antibiotics and antibiotic cement. If infection occurs, removal of the prosthesis at least temporarily is often necessary. Deep venous thrombosis (clot) may also occur. This is minimized by the use of anticoagulant medication, which is started in the preoperative period and is continued for two weeks after surgery. Safe control of anticoagulation requires weekly blood tests and necessary adjustment.
Sports Medicine and Orthopaedics takes care of most Orthopaedic, Sports Medicine, Total Joint and Fracture problems in East Providence, Rhode Island
A person with advanced knee arthritis and severe pain and limited ambulatory tolerance is a candidate for total knee replacement. When knee pain from osteoarthritis, interferes with daily activity, walking tolerance, and independence, it is time to consider this alternative. Many individuals choose a total knee replacement so they can maintain normal activities of daily living.
The anterior cruciate ligament is the most commonly disrupted knee ligament tear in the knee. Our understanding of its role in knee stability, diagnosis of injury and surgical reconstruction have all advanced in recent years. the anatomy of the human knee is shown in the drawing. The collateral ligaments provide stability in a side to side plane. The anterior and posterior cruciate ligaments provide stability in a front-to-back plane. Additionally, these ligaments which are within the joint, provide a linkage system which guides the complex rolling-gliding motion of the knee. The menisci (cartilage) on both the inside and outside of the knee increase the contact area between the joint surfaces. In this way, they decrease the load in any one area of surface cartilage. A tear of the anterior cruciate is often associated with a meniscal or a collateral ligament tear. These injuries occur most often in athletics, but accidents or work injuries may also disrupt the cruciate if the mechanism of injury is similar. The injury may simply occur with a sudden change in direction while running, or with hypertension of the knee. Often an audible "pop" is heard or a sensation of "tearing" within the knee is felt. Within a few hours or a day, the knee swells and weight bearing may become difficult. If left untreated, many knees with this injury become unstable and are referred to as a "trick" knee. They may buckle unexpectedly, especially with rapid changes in direction and result in falls or other injuries.
The most common knee injury is related to the semilunar (meniscus) cartilage tear. There are two of these in each knee. One is medial (on the inside) and the other is lateral (on the outside) of the knee. Each appears like a crescent moon and is attached on its outer edge to the knee capsule and at each end to the tibia by ligament attachments. The meniscus is responsible for a four-fold increase in surface contact between the bones of the knee (tibia and femur). The meniscus also aids in shock absorption between the joint surfaces and aids in knee stability and lubrication. Complete loss of the meniscus is known to cause eventual arthritis. Each meniscus is made of cartilage. The outside one third has a blood supply and the capacity to heal. The inner two-thirds of the meniscus has more limited capacity to heal. A tear of the meniscus may occur following major trauma or none at all. This depends on the age of the individual and prior injury and activities. Not all tears are symptomatic, and many older patients are unaware they have a tear. Symptomatic tears are those which cause knee pain, locking, knee catching, clicking, stiffness, or recurrent swelling. Untreated symptomatic tears may cause permanent damage (arthritis) because the torn meniscus rubs on the surface of the joint like "sand in a ball-bearing". These tears are best treated early.
The word "chondromalacia" means cartilage (chondro) softening (malacia). This may occur in any joint but is commonly used to describe surface changes of the knee cap (patella). Patellar chondromalacia truly describes cartilage changes seen microscopically but has been generalized to encompass the clinical condition. The patella, or kneecap, is an oblong bone which is embedded within the extensor tendon of the knee. The patella increases the leverage of the extensor muscles (quadriceps) and acts also as a pulley, around the femoral groove. Both the patella and the femoral groove which it contacts, have smooth cartilage surfaces lubricated by synovial fluid (joint oil). The cartilage also absorbs enormous loads during daily activities. Walking on level ground exerts a contact force of one-half body weight. Climbing stairs increases the force to four times body weight. Arising from a squat can generate patellar forces up to eight times body weight. Chondromalacia may occur as a result of a direct blow to the patella, fracture or patellar dislocation, or more commonly, over a period of years because of wear and tear, patellar arthritis develops because of patellar maltracking. This occurs because of overuse, coupled with anatomic malalignment and supporting soft tissue imbalance. The anatomic factors responsible for the alignment and patella tracking are tibiofemoral angle (knock-knee or bow-leg), tibiofemoral rotational alignment, patellar and femoral groove shape and congruity, and capsular and muscular balance. In general, "maltracking" from any cause exposes the cartilage of patella and femur to localized excessive load and accelerated wear. The condition is more common in women and is frequently seen during adolescence. It is often associated with activities which induce high patella femoral loads such as hill climbing, cross-country running, jumping, and squatting.