Knee Osteoarthritis | Diagnosis & Treatment for Physiotherapists

Introduction

A classical feature of knee osteoarthritis are histological changes of the quality and thickness of joint cartilage. A decrease in joint cartilage leads to hypertrophy of the subchondral bone and osteophyte formation at the edges of the joint surfaces. Another consequence is chronic inflammation of the synovial tissue. All of these changes lead to irregular joint surfaces, bony enlargement, possible thickening of the joint capsule and eventually hydrops. The resulting decrease in joint space is visible on radiographic imagery, which is why we also speak of “radiological osteoarthritis”.

The most commonly used classification system for radiological osteoarthritis is the Kellgren & Lawrence scale (Kohn et al. 2016):

• Grade 0: no radiographic features of OA are present
• Grade 1: doubtful joint space narrowing and possible osteophytic lipping
• Grade 2: definite osteophytes and possible joint space narrowing on an anteroposterior weight-bearing radiograph
• Grade 3: multiple osteophytes, definite joint space narrowing, sclerosis, possible bony deformity
• Grade 4: large osteophytes, marked joint space narrowing, severe sclerosis, and definite bony deformity

Pain is the most evident limiting factor in osteoarthritis. As previously mentioned, the pathophysiology describes a loss of cartilage but nociceptors are missing in joint cartilage. We know that a decrease in joint cartilage occurs also in those without clinical symptoms (radiological osteoarthritis). Nociceptors are present in tissues surrounding the knee joint such as the joint capsule, ligaments, the synovium, and the outer edges of the menisci. These nociceptors get triggered by the inflammation that occurs.
Knee osteoarthritis can occur post-traumatically, as a process of aging, and in other inflammatory conditions affecting the quality of joint cartilage.

Epidemiology

Knee (and hip) osteoarthritis is the most common musculoskeletal pathology with knee osteoarthritis being more prevalent than hip osteoarthritis. The point prevalence of osteoarthritis in the Netherlands in 2007 was 24,5/1000 in males and 42,7/1000 in females. Around the world, the prevalence is reported at 3,8%. (Cross et al. 2014)

The incidence of osteoarthritis in the Netherlands in 2007 was 2,8/1000 with an expected increase of 40% between 2000 and 2020. If we take the dramatic increase in obesity into account (BMI >30), this number may be even higher.

Clinical Picture

A cardinal symptom of knee osteoarthritis is knee pain. Patients mostly experience pain when starting to move or after prolonged loading. The pain usually increases over the course of the day. They may also report hearing or feeling crepitations.

Patients typically report morning stiffness of up to 30 minutes but conversely may also tell you that they feel instability due to an increased valgus/varus position of the knee caused by the joint irregularities.

Physical Examination

While there may be radiological evidence of osteoarthritis as graded by the Kellgren & Lawrence scale, this does not correspond with clinical symptoms. For example, the Framingham study showed that only about 21% of hips with radiological evidence of osteoarthritis were frequently painful, and vice-versa in those who had frequently painful hips only about 16% had evidence of osteoarthritis upon x-ray examination (Kim et al. 2015)  Today we know that degenerative changes are normal in pretty much any part of the body. The reason why some people develop symptoms (ie. pain) while others don’t are multifaceted, which is why the psychosocial and environmental factors are especially important when considering the diagnosis of osteoarthritis.

For this reason, Décary et al. (2018) derived a diagnostic cluster for symptomatic OA compared to the radiological OA cluster of Altman we mentioned above:

Other orthopedic tests for knee osteoarthritis are:

• Passive Range of Motion of the knee joint
• Active Range of Motion of the knee joint

Treatment

The following video summarizes recommendations for managing lower limb osteoarthritis based on a guideline review by Walsh et al. (2017):

While fitting a prosthetic joint is common in osteoarthritis, this should be reserved for the most severe cases. Exercise therapy is a promising and well-researched measure to increase the quality of life of those with symptomatic OA. However, Zou et al. (2016) showed that 75% of the overall treatment effect of interventions such as exercise was attributable to contextual effects rather than to the specific effect of the treatment. Think of it this way: Patients who were highly limited in their physical abilities due to OA got to explore movement in a gradual and supervised way, and received education, which allowed them to do more, desensitize their system, and thus lower pain. While they probably also got stronger, this effect was minor compared to these non-specific effects.

You can check a video on the details of exercise therapy in knee OA in this video:

Would you like to learn more about osteoarthritis? Then check out the following resources:

• Leg Extensions – Dangerous for Your Knees or Great Rehab Exercise?
• Updates on Exercise for Knee Osteoarthritis
• Podcast Episode 014: Knee Osteoarthritis with Anthony Teoli

References

Cross, M., Smith, E., Hoy, D., Nolte, S., Ackerman, I., Fransen, M., … & March, L. (2014). The global burden of hip and knee osteoarthritis: estimates from the global burden of disease 2010 study. Annals of the rheumatic diseases, 73(7), 1323-1330.

Altman, R., Asch, E., Bloch, D., Bole, G., Borenstein, D., Brandt, K., … & Wolfe, F. (1986). Development of criteria for the classification and reporting of osteoarthritis: classification of osteoarthritis of the knee. Arthritis & Rheumatism: Official Journal of the American College of Rheumatology, 29(8), 1039-1049.

Cross, M., Smith, E., Hoy, D., Nolte, S., Ackerman, I., Fransen, M., … & March, L. (2014). The global burden of hip and knee osteoarthritis: estimates from the global burden of disease 2010 study. Annals of the rheumatic diseases, 73(7), 1323-1330.

Fransen, M., McConnell, S., Harmer, A. R., Van der Esch, M., Simic, M., & Bennell, K. L. (2015). Exercise for osteoarthritis of the knee. Cochrane database of systematic reviews, (1).

Walsh, N. E., Pearson, J., & Healey, E. L. (2017). Physiotherapy management of lower limb osteoarthritis. British medical bulletin, 122(1), 151-161.

Zou, K., Wong, J., Abdullah, N., Chen, X., Smith, T., Doherty, M., & Zhang, W. (2016). Examination of overall treatment effect and the proportion attributable to contextual effect in osteoarthritis: meta-analysis of randomised controlled trials. Annals of the rheumatic diseases, 75(11), 1964-1970.