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Research Review By Dr. Shawn Thistle©


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Date Posted:

June 2011

Review Title:

Hip & Knee Osteoarthrtitis: Updates on Etiology, Imaging & Exercise

Studies Included:

  1. Molloy MG & Molloy CB. Contact sports and osteoarthritis. British Journal of Sports Medicine 2011; 45: 275–277.
  2. Caine DJ & Golightly YM. Osteoarthritis as an outcome of paediatric sport: an epidemiological perspective. British Journal of Sports Medicine 2011; 45: 298–303.
  3. Felson DT. Imaging abnormalities that correlate with joint pain. British Journal of Sports Medicine 2011; 45: 289–291.
  4. Bennell KL & Hinman RS. A review of the clinical evidence for exercise in osteoarthritis of the hip and knee. Journal of Science and Medicine in Sport 2011; 14: 4–9.

Background Information:

Osteoarthritis (OA) is a multifactorial, complex condition that involves progressive pathological changes to periosteal and subchondral bone, cartilage, synovium, intra-articular structures and peri-articular tissues. OA as a clinical syndrome results from a generally progressive loss of articular cartilage that is accompanied by attempted and eventually failed repair of cartilage, remodelling and sclerosis of the subchondral bone and in many instances the formation of subchondral bone cysts and/or marginal osteophytes (or bone spurs). OA is the most common joint disease in the world and the single greatest cause of disability for people over 18 years of age. To give you an idea of its prevalence, it affects more than twice as many people as does cardiac disease, and increases consistently in incidence and prevalence with age. Osteoarthritis can cause pain, stiffness, swelling, joint instability and muscle weakness, all of which can lead to severe impairment of physical function and reduced quality of life. It is also the direct cause of numerous surgical procedures ranging from arthroscopic debridement to complete joint replacement.

The March 2011 issue of the British Journal of Sports Medicine contained a number of articles on OA, 3 of which are discussed here in addition to another paper from the Journal of Science & Medicine in Sport. I thought this collection of papers could be reviewed together in this format to update our knowledge on some key concepts surrounding the risk factors for OA, the relationship of OA with exercise and sports participation as well as advanced imaging findings that correlate with joint pain.


Risk Factors for Hip & Knee OA:

The following are generally accepted as risk factors for developing OA:
  • Age
  • Female gender (particularly for knee OA)
  • Obesity
  • Previous joint injury (particularly ACL rupture in the knee)
  • Developmental or congenital deformity (ex. pediatric hip pathology such at Legg-Calves-Perthes or Slipped Capital Femoral Epiphysis)
  • Genetics (generally accepted but still requires clarification)
  • Muscle weakness
Imaging & Osteoarthritis of the Knee & Hip:

It is well established that common radiographic (plain film X-ray) findings such as joint space narrowing, osteophyte formation, subchondral sclerosis, cyst formation, and bone contour abnormalities correlate poorly with clinical symptomatology. Some patients have horrible looking joints on x-ray with no pain and others are in severe pain with no observed changes on x-ray. The main reason proposed to explain this discordance is that most pain-generating tissues cannot be adequately viewed on conventional x-rays. Specifically, anatomical studies have indicated that ligaments (especially their insertion sites), subchondral and periosteal bone, the outer rim of menisci, synovium and soft tissues can cause pain. MRI, of course, provides much higher levels of detail and as this imaging modality becomes more readily available, manual medicine providers will see more and more of them.

Felson & colleagues conducted a series of studies (1-3 in Additional References below) on patients with only radiographic evidence of knee OA. Some of these patients had pain, some did not. The investigators took MRI scans of the entire group to try and determine which MRI findings might be associated with pain in knee OA. Pertinent findings from their studies include:
  • Patients with radiographic OA who DID have pain were likely to have bone marrow lesions (35% of those with pain had bone marrow lesions vs only 2% of those without pain).
  • They were also more likely to have synovial thickening/synovitis on their MRI scans and effusions, especially large effusions that presumably stretched the articular capsule (which contains numerous nociceptive fibers that are sensitive to distension).
  • Periarticular lesions such as anserine bursitis were also more prevalent in those in pain, but they were uncommon lesions on MRI.
  • Bone marrow lesions visible on MRI also seem to correlate highly with knee malalignment (this is important because about 85% of knees with OA have a tibial varus or valgus alignment of at least 2°).
  • Although synovitis does seem to be related to pain in knee OA (present in about 50% of OA patients) – the ideal imaging modality for this condition is contrast MRI with gadolinium, which allows us to distinguish between synovial thickening and fluid.
  • It is important to remember that MRI may reveal numerous findings, and at this point we cannot be certain that only one of these findings is THE cause of pain in knee OA. In fact, some longitudinal evidence suggests that these MRI findings may vary over time. The exact relation between these variations and pain is still under investigation, but there is some suggestion that bone marrow changes and synovial changes may correlate with clinical pain levels.
  • The relationship between cartilage loss and pain is complicated. Although cartilage itself contains no pain fibers, its breakdown can release debris into a joint which may promote inflammation or synovitis (which is related to pain). Further, when bone becomes exposed due to excessive cartilage deterioration, pain may results due to bone’s inherent pain generating capacity.
  • Findings NOT association with pain: meniscus tears and Baker’s cysts are associated with knee OA but not pain; ACL tears are also associated with OA, but may not lead to pain.
Youth Sports Participation and OA:

It has long been suggested that high level sports participation or sports injuries sustained during youth can impact future incidence of major joint OA. In recent years some trends in youth sports participation have emerged, including: increased numbers of participants, particularly girls, increased duration and intensity of training, earlier specialisation and year-round training, and increased difficulty of skills practised. It goes without saying that physical activity has important and wide-ranging health benefits, but engaging sports and recreational activities at a young age also involves risk of injury. In their paper, Caine & Golightly evaluated the long-term musculoskeletal outcomes of youth sports injuries and participation. Pertinent findings of their study include:
  • Existing literature suggests that the ankle and knee are the most commonly injured joints in youth sports (roughly 20% and 15% of all sports injuries, respectively). The knee however, sustains injuries considered severe at the highest rate.
  • It has been well established that ACL tears and meniscus injuries correlate with early onset knee OA.
  • Based on existing evidence, a link between youth sports injuries, particularly acute injury of the knee or ankle and OA, is probable. A relationship may also exist between early OA development and intense participation in high-impact sports, but follow-up of elite young athletes into their early adult years is needed to examine this relationship.
  • Epiphyseal growth plate injuries: Growth plate cartilage is less resistant to stress than adult articular cartilage, and is also less resistant than adjacent bone to shear and tension forces. In addition, the growth plate may be 2-5 times weaker than surrounding fibrous tissue. For these reasons, forces experienced during injury that may result in a complete ligament tear or joint dislocation in an adult or older adolescent may produce a separation of the growth plate in a child. The relationship between epiphysis injuries and early-onset OA is understudied so no firm conclusions can be made at this time.
Sport & Recreational Activity & OA:

Exercise is good for the general health of joints. Regular exercise does not appear to increase the risk or progression of OA. However, excessive joint loading, be it through sports participation or occupation, is related to OA. The combination of optimal muscular strength, proprioception and reduced body mass index, all of which are associated with an active lifestyle, are joint protective. These factors promote normal physiological joint loading, a balance that may be lost in elite athletes, particularly those in contact sports. Awareness and prevention are paramount, and It is important to consider the following factors when evaluating risk of OA from sport and activity:
  • Non-modifiable factors: inheritance, epiphysial, congenital, hypermobility, malalignment, leg length inequality
  • Modifiable risk factors: musculoskeletal/biomechanical assessment findings (ex. landing mechanics, spinal stability etc.), selection based on weight vs. age, methods of skill development, training techniques – volume, periodization, appropriate rest etc.
A Brief Note on Exercise for Knee & Hip OA:

It is well accepted, based on existing literature and clinical practice guidelines, that exercise is a frontline intervention for patients with non-surgical knee and hip OA. In their narrative review, Bennell & Hinman summarize the literature on this important topic, emphasizing the following points:
  • Most exercise research has focused on knee OA (a paucity of literature exists for hip OA – meaning that the inclusion of exercise in CPGs is based largely on expert opinion)
  • Aerobic, strengthening, aquatic and Tai chi exercise are beneficial for improving pain and function in people with OA with benefits observed across the range of disease severities. There is no evidence at this time to suggest that one form of exercise is superior to others, although land-based exercise may be more advantageous than aquatic programs.
  • A combination of general aerobic and specific strengthening exercise is recommended.
  • There are very few contraindications to exercise in OA patients.
  • The optimal exercise dosage is yet to be determined and an individualized approach to exercise prescription is required based on an individual assessment of impairments, patient preference, co-morbidities and accessibility.
  • To be effective, exercise programs should be accompanied by advice and lifestyle modification.
  • Maximising adherence is key in the success of exercise therapy. This can be enhanced by the use of supervised exercise sessions (possibly in a supervised class format) in the initial exercise period followed by home exercises. Further, asking patients to return for intermittent consultations with the exercise practitioner, or attendance at “refresher” group exercise classes may also assist long-term adherence.
  • Few studies have evaluated the effects of exercise on structural disease progression and there is currently no evidence to show that exercise can be disease modifying.
  • The effectiveness of exercise is not dependant on radiographic severity of OA.

Clinical Application & Conclusions:

In the coming years, OA of the knee and hip will increase in prevalence as the population ages. As musculoskeletal medicine providers, it is our duty to stay abreast of all types of research on this condition so we can better assist our patients, whether or not the OA is the primary reason for a patient to visit us. Prudent use and interpretation of imaging findings is key to directing appropriate treatment, and as with many conditions, consistent and sustainable exercise is at the forefront of active management.

Additional References:

  1. Felson DT, Chaisson CE, Hill CL, et al. The association of bone marrow lesions with pain in knee osteoarthritis. Ann Intern Med 2001; 134:541–9.
  2. Hill CL, Gale DG, Chaisson CE, et al. Knee effusions, popliteal cysts, and synovial thickening: association with knee pain in osteoarthritis. J Rheumatol 2001; 28:1330–7.
  3. Hill CL, Gale DR, Chaisson CE, et al. Periarticular lesions detected on magnetic resonance imaging: prevalence in knees with and without symptoms. Arthritis Rheum 2003; 48:2836–44.

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