Knee Pain

Osteoarthritis is the most prevalent form of arthritis, with an associated risk of mobility disability (defined as needing help with walking or climbing stairs) for those with affected knees being greater than that due to any other medical condition in people aged ≥ 65. Osteoarthritis of the knee causes pain, limits activity, and impairs quality of life. The societal burden (both in terms of personal suffering and use of health resources) is expected to increase with the increasing prevalence of obesity and the ageing of the community.

Osteoarthritis is a multifactorial process in which mechanical factors have a central role and is characterized by changes in structure and function of the whole joint. There is no cure, and current therapeutic strategies are primarily aimed at reducing pain and improving joint function.

EPIDEMIOLOGY OF KNEE OSTEOARTHRITIS

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.

Pathophysiology of osteoarthritis

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.

CLINICAL FEATURES OF KNEE OSTEOARTHRITIS

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.

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Diagnosis and investigations

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).

Management of knee osteoarthritis

The aims of management are:

  • Education patients about the disease and its management
  • Controlling pain
  • Improving function
  • Altering the disease process and its consequences

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Non-pharmacological treatments

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.

PHARMACOLOGICAL TREATMENTS

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.

Interventional treatments in patients with knee osteoarthritis

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

Surgery is indicated when conservative management has failed and there is a significant functional disability because of pain.

Summary

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.

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