Knee Osteoarthritis Flashcards
What is osteoarthritis?
Osteoarthritis (OA) is a degenerative joint disease, characterised by the loss of articular cartilage. This is associated with periarticular bone response, the features of which can be seen on plain film radiographs.
What are the risk factors for knee OA?
Genetic factors: estimates suggest a genetic component for hand, knee and hip OA at around 40-60%, however the specific genes involved remain largely unknown.
Constitutional factors: factors including increasing age, female gender, obesity and low bone density (specifically in the progression of OA).
Local factors: previous joint injury, occupational or recreational stresses on the joint, reduced surrounding muscle strength or any joint laxity or malalignment.
What are the clincial features of knee OA?
The most common feature of knee OA is pain. Pain is typically felt around the knee, however can radiate to the thigh and hip. This pain is usually exacerbated by exercise and relieved by rest.
Patients will often have bilateral disease. There is associated joint stiffness, which can result in reduced function, and even joint swelling in severe cases.
On examination, there will be a reduced range of movement and often evidence of muscle wasting. Crepitus can be felt in severe cases.
What investigations should be ordered for knee OA?
Most cases of OA can be investigated with a plain film radiograph alone (lateral and antero-posterior (AP) views).
Further views, such as a skyline view of the knee, can be useful to further assess for any patellar involvement.
Additional investigations are only required when alternative differentials are suspected, such as blood tests for any infective cause or MRI imaging in ligamentous injury.
What are the 4 cardinal signs of OA?
The diagnostic features that can be seen are (mnemonic LOSS):
- Loss of joint space
- Osteophytes
- Subchondral sclerosis
- Subchondral cysts
What is shown on the image?
Left knee OA, demonstrating extensive osteophytes, narrowing of the joint space (arrow), and increased subchondral bone density.
Briefly describe The Kellgren and Lawrence system for classifying knee OA
The Kellgren and Lawrence system can be used to classify the severity of knee OA:
- Grade 0- no radiographic features of OA are present
- Grade 1- unclear joint space narrowing and possible osteophytic lipping
- Grade 2- definite osteophytes and possible joint space narrowing on AP weight-bearing views
- Grade 3- multiple osteophytes, definite joint space narrowing, evidence of sclerosis and possible bony deformity
- Grade 4- large osteophytes, marked joint space narrowing, severe sclerosis and definite bony deformity
Briefly describe the initial management of knee OA
Lifestyle modifications play an essential part of the management plan, including weight loss, regular exercise, and smoking cessation. Adequate pain control is important, using the WHO analgesic ladder, to ensure ongoing mobility and quality of life.
Physiotherapy is commonly used and should be provided for all individuals with OA, aiming to slow disease progression and improve joint mechanics.
If conservative management efforts do not work, surgical management is warranted, which is typically either total or partial knee replacement.
Briefly describe surgical management of knee OA
Total knee replacement (TKR) is the standard treatment for advanced osteoarthritis.
Around 10% of patients only require partial (unicondylar) knee replacement, which is mainly used for those with disease localised to either the medial or lateral compartment, meaning the affected compartment will be replaced and healthy compartment left intact. Partial knee replacements are more conservative, therefore have faster recovery times, but may need conversion to total knee replacement at a later date.
Briefly describe the use of Total Knee Replacements (TKR)
During this procedure, plastic and metal inserts are used to replace bone and cartilage in all sections of the knee.
The vast majority of total knee replacements will function for at least 10 years and the majority of patients experience a significant reduction in knee pain.
What is shown in the image?
Plain Film Radiograph following a Total Knee Replacement.
What differentials should be considered for knee OA?
The main differentials to consider is a patient presenting with joint pain and stiffness includes any meniscal or ligament injury, referred pain from another joint or the back, crystal arthropathies or patellofemoral arthritis.
