Radiographic findings including joint space narrowing and MRI detected bone marrow lesions, synovitis and effusion are significantly associated with the long term risk of total knee arthroplasty (TKA)  in knee osteoarthritis patients.

Osteoarthritis (OA) is the most chronic joint disorder with an estimated prevalence of 15% worldwide, mainly affecting population aged between 56 to 84. Previous studies reported that aging and obesity were strongly associated with OA.

Obesity is known to be an essential risk factor for knee OA. A recent systematic review showed that 25% cases of knee pain were associated with overweight and obesity and only 5% were caused due to any previous knee injury. At the end stage of OA, total knee arthroplasty (TKA) is the only effective treatment. A recent study conducted by Weinstein et al determined that 52% of patients with knee OA are likely to undergo TKA. For imaging of knee OA, the conventional radiography is the most commonly used method. But the results of this method are not well correlated with symptoms. Magnetic resonance imaging (MRI) offers the ability to visualize all structures in and around the knee, including cartilage, subchondral bone and soft tissue. Specific pathologic findings on MRI, including bone marrow lesions (BMLs) and synovitis, are moderately correlated with pain and are associated with risk of TKA in studies with short-term follow-up as well as with progression of Joint space narrowing (JSN).

Therefore, this study was conducted to analyze whether clinical, radiographic and MRI findings, including Bone marrow lesion (BML) and synovitis, correlate with the incidence of TKA during a mean follow-up period of 15 years.

Rationale behind the research:

None of the studies till now analyze the finding of radiographic, MRI with the incidence of TKA. Therefore, in this study  the impact of these finding on the TKA were analysed.

Objective:

To evaluate the link between clinical, radiographic or MRI findings and long-term risk for TKA in persons with knee osteoarthritis.

Study outcome measures:

Clinical, radiographic and MRI findings were analyzed for associations with subsequent TKA.

Study Outcomes:

• Incidence of TKA in relation to different degrees of JSN, BML, synovitis and effusion: Significant associations between TKA and JSN (adjusted OR 5.0 (95% CI 2.6 – 9.9)), radiological sum score (adjusted OR 1.7 (95% CI 1.3 – 2.1)), BML (adjusted OR 2.3 (95% CI 1.3 – 4.0)), synovitis (adjusted OR 2.8 (95% CI 1.5 – 5.2)) and effusion (adjusted OR 1.9 (95% CI 1.2 – 3.1)) was observed. (Figure 1)

Figure 1: Kaplan-Meier plot showing the cumulative incidence of TKA in relation to different degrees of JSN, BML, synovitis and effusion

• Cox proportional hazard ratios:

Cox proportional hazard ratio showed a statistically significant hazard ratio for JSN, radiological sum score, BML, synovitis and effusion with the risk for TKA.

• Baseline characteristics and predictors of unilateral versus bilateral knee replacement, univariate and multivariate analyses:

The 66 participants with TKA at follow-up were compared in relation to unilateral versus bilateral TKA; only BMI was associated with the risk of bilateral vs. unilateral TKA (OR 2.3 (95% CI 1.2 – 4.3)) 

The results of this study revealed that after the 15 years of follow-up study the radiographic findings, precisely the degree of JSN, and MRI detected BML, synovitis, and effusion were highly associated with TKA.

According to the Danish national guidelines, the indications for TKA are based on symptoms and objective findings. It is, however, without the radiographic images of OA, especially JSN, the surgeon would not operate on a knee. Thus, a relative contra-indication for TKA is absence of or minimal radiologic changes. Previous studies showed that JSN has also be associated with the progression of knee OA. Two studies conducted by Oak et al and Raynauld et al also showed the significant relation of JSN with worsening of knee OA.

The number of previous studies showed the significant association of BML, synovitis, and effusion with the risk of TKA. However, these studies had a relatively short follow-up time. The results of this study also showed similar results as of previous studies with long-term risk of TKA. This study showed that long-term risk of TKA was dependent on the number of structural changes on radiographs and signs of synovial inflammation or BMLs on MR images.

No significant association was found between baseline BMI and TKA. Thus, the results suggest that a higher BMI does not increase the risk of TKA in knees with symptomatic OA. However, it seems that an increased BMI predisposes to the development of OA in the opposite knee. Other studies have similarly reported that an elevated BMI influences the incident but not the progression of knee OA.

In conclusion, radiographic changes associated with knee OA as well as MRI detected BMLs, synovitis, and effusion were significantly related to the risk of TKA in patients with knee OA. However, an increased BMI was seen in participants with knee OA requiring TKA in the opposite knee during follow-up.