Osteoarthritis is the commonest cause of chronic knee pain. It is best managed through a rehabilitative approach with focus on exercise, losing weight and improving the over all fitness. Some patients will need invasive treatments including joint replacement surgery if they fail to improve with conservative management. Newer techniques targeting the genicular nerves can be considered in patients who either wish to avoid sugery or are unfit for major surgery. Cooled radiofrequency ablation of the genicular nerve may provide long-term pain relief in these patients.
About 6% of adults age ≥ 30 have frequent knee pain and radiographic osteoarthritis. Marked osteoarthritic damage must be present, however, to detect characteristic changes with plain radiographs, and they are therefore not sensitive diagnostic tests.
Osteoarthritis is the clinical and pathological outcome of a range of disorders that results in structural and functional failure of synovial joints. Traditionally, it has been considered a disease of articular cartilage. The current concept holds that osteoarthritis involves the entire joint organ, including the subchondral bone, menisci, ligaments, periarticular muscle, capsule and synovium.
Osteoarthritis is caused by aberrant local mechanical factors acting within the context of systemic susceptibility. Systemic factors that increase the vulnerability of the joint to osteoarthritis include increasing age, female sex, and possibly nutritional deficiencies. While epidemiological studies have shown a major genetic component to risk that is probably polygenic, the genes responsible have not yet been identified.
Typically osteoarthritis presents as joint pain. The joint pain of osteoarthritis is typically described as exacerbated by activity and relieved by rest. In more advanced disease it is painful at rest and at night. Of the local events in the joint, loss of cartilage probably does not contribute directly to pain as it is aneural. In contrast, the subchondral bone, periosteum, synovium and joint capsule are all richly innervated and could be the source of nociceptive stimuli in osteoarthritis.
The diagnosis of osteoarthritis is usually made clinically and then confirmed by radiography. The clinical features that suggest the diagnosis include pain, stiffness, reduced movement, swelling, crepitus, and increased age (unusual before age 40) in the absence of systemic features (such as fever).
Magnetic resonance imaging may be used to facilitate the diagnosis of other causes of knee pain that can be confused with knee osteoarthritis (such as osteochondritis dissecans and avascular necrosis). Nearly all people with knee osteoarthritis have meniscal tears, and these are not necessarily a cause of increased symptoms. The menisci should not be removed unless there are symptoms of locking or extension blockade.
Because osteoarthritis is a non-inflammatory arthritis, laboratory findings are expected to be normal.
Aspirating a joint effusion should be considered if a diagnosis other than osteoarthritis (such as septic arthritis, gout, pseudogout) is suspected. Synovial fluid from affected joints is non-inflammatory (leucocyte count < 2000/mm3, clear, viscous).
The aims of management are:
Education: Encourage patients to participate in self management programmes and provide resources for social support and instruction on coping skills.
Weight loss: Encourage overweight patients with osteoarthritis of the hip and knee to lose weight through a combination of diet and exercise.
Exercise: Exercise increases aerobic capacity, muscle strength and endurance and facilitates weight loss. Patients should be encouraged to take part in a low impact aerobic exercise programme (walking, cycling, or swimming or other aquatic exercises). Exercises to strengthen the quadriceps lead to reductions in pain and improvements in function.
Knee braces and orthotics: For those with instability of the knee and varus misalignment, valgus bracing and orthotics shift the load away from the medial compartment and, in doing so, may provide relief of pain and improvement in function.
These include oral analgesics like paracetamol, NSAIDs, Cox II inhibitors and topical agents like capsaicin.
Glucosamine and chondroitin seem to have the same benefit as placebo and there is controversy over whether they also have structure modifying benefits.
Intra-articular steroids: When not otherwise contraindicated, intra-articular corticosteroids are of short term benefit for pain and function.
Intra-articular hyaluronic acid (viscosupplementation): Though the meta-analyses reviewing the efficacy of intra-articular hyaluronan are not in complete agreement, mainly because of variation in study methods, most suggest that the effect size is relatively small and the placebo response is significant.
Cooled radiofrequency treatment of Knee (COOLIEF): Radiofrequency (RF) neurotomy, when applied to articular branches of the knee, provides a therapeutic alternative for management of chronic pain associated with osteoarthritis of the knee. This technique may be a useful treatment for severe osteoarthritic pain refractory to other conservative treatments or patients who are not suitable for surgery.
Surgery is indicated when conservative management has failed and there is a significant functional disability because of pain.