Total knee replacement surgery is a surgery usually performed for arthritis of the knee that is causing severe and persistent symptoms and limiting a person's function. This type of arthritis occurs as the articular cartilage is worn away or becomes increasingly damaged in the knee. Knee replacement is usually reserved for patients who no longer respond to conservative means of treatment -- and preferably individuals who are over 60 years of age. Unfortunately, workers often have significant arthritis in their knees and are completely unaware of it until they sustain an injury and develop pain. Even minor injuries can cause the onset of pain in a previously asymptomatic, arthritic knee. If the pain does not respond to conservative treatment, it often leads the worker to believe that their arthritis developed as a result of their occupational injury.
Patients with more mild "degenerative changes" (early arthritis) in their knees often sustain injuries at work that result in meniscal tears. Although the MRI scan will often state that there are degenerative findings, the sudden onset of pain associated with the injury indicates that the meniscal tear was likely more acute in nature. These patients were usually minimally symptomatic or asymptomatic prior to their injuries. In this situation, a simple arthroscopy will often relieve the pain and allow the worker to return to his prior level of activity -- including work. Findings at the time of arthroscopy will help to determine the extent (or lack) of pre-existing arthritis if the arthroscopy is performed in a timely fashion.
Work-related injuries do not commonly lead to severe arthritis, and worker's compensation carriers are often reluctant to accept claims of arthritis as compensable due to the fact that arthritis most commonly occurs over a long period of time as part of a degenerative process. In addition, when the injured worker develops arthritis that no longer responds to conservative treatment and requires knee replacement, the surgery is costly and requires life-long follow-up. This further contributes to the reluctance of carriers to accept claims that arthritis is related to an occupational injury. X-rays of the knee taken prior to or soon after an injury are often very helpful in distinguishing between pre-existing arthritis and post-traumatic degenerative arthritis. Post-traumatic arthritis can occur fairly rapidly after an injury in which there is an intra-articular fracture or other trauma to the cartilage. The onset is usually much slower if the arthritis develops as a result of partial meniscectomy for a meniscal tear. The meniscus acts as a shock absorber to protect the articular cartilage in the knee, so more meniscal resection is likely to lead to earlier onset of arthritis. However, this gradual onset of arthritis typically takes several years to develop.
When a knee replacement becomes necessary, it is usually a very successful operation and will allow the worker to return to relatively normal function once he is fully recovered. The procedure involves admission to the hospital and the patient is typically given a general anesthetic, but other types of anesthesia such as spinal or epidural anesthesia are also options. Nerve blocks to control the pain during and after the surgery are often used, as well.
The operation typically lasts 1 1/2 -2 1/2 hours but occasionally may take longer. An incision is made in the front of the knee, and the interior of the knee exposed. Approximately one-quarter to one-half inch of bone is removed from each of the surfaces of the knee. A new metal and plastic surface is placed on the cut surfaces of the bone to replace the worn surfaces of the joint. There are many types of prostheses, and the type chosen will depend on several factors, including: age, weight, activity level, ligament stability, and the quality of bone at the time of surgery. Typically, people undergoing total knee replacement will be in the hospital for three or four days learning a physical therapy program and regaining their ability to walk, move their knee, and perform activities of daily living.
When a person is medically stable and functioning fairly well, they will usually go home. About 10 percent of people go to a rehab facility to continue physical therapy there for one-to-two weeks or more. Physical therapy continues at home with a home therapist for two-to-four weeks followed by a period of outpatient physical therapy -- usually for an additional one-to-two months. The initial period after the surgery concentrates on regaining range of motion in the knee. It is important to work on regaining range of motion as quickly as possible, with the goal of regaining 90-to-100 degrees of motion in the knee within the first few weeks. Typically, it is necessary to use a walker for two-to-four weeks and then transition to a cane. Full recovery from knee replacement surgery requires three-to-six months and sometimes as long as a year. Fortunately, workers can usually return to more sedentary occupations after only six-to-eight weeks.
Typically, the artificial knee prosthesis does wear with time. It is sometimes necessary to have the prosthesis replaced either because of wear of the prosthesis or progressive damage in the bone or ligaments around the artificial knee. There is about a one percent per year need for additional surgery on the knee to revise or replace the original artificial knee. The risk of receiving a second operation is therefore about five-to-10 percent at 10 years and 10-to-15 percent at 15 years post surgery. Revision operations are typically more complex than the original operation and often do not result in a knee that functions as well as the original operation.
Total knee replacements typically are very successful procedures providing long-term improved function and decreased pain in 90-to-95 percent of individuals undergoing these procedures.
Mark A. Petty, MD, specializes in sports medicine, arthroscopic surgery, and joint reconstructive surgery at The Orthopaedic Institute in Florida. He may be reached at 888-860-7050, www.toi-health.com.
