Patella bone density is lower in knee osteoarthritis patients experiencing moderate-to-severe pain at rest.

OBJECTIVE: To determine differences in patellar subchondral bone mineral density (BMD) between knee osteoarthritis (OA) patients with differing levels of pain at rest. METHODS: The preoperative knee of 41 total knee replacement (TKR) patients was scanned using QCT and scored for pain using Western Ontario McMasters Osteoarthritis Index (WOMAC). 'Pain at rest' was defined as average pain while lying//sitting and nocturnal pain. Participants were divided into groups: 'mild-to-no pain at rest' and 'moderate-to-severe pain at rest'. We used a depth-specific CT-based mapping technique to measure patellar subchondral BMD at depths of 0-2.5 mm, 2.5-5 mm, and 5-7.5 mm from the subchondral surface. Mean lateral and medial facet BMD were compared between groups using MANCOVA. RESULTS: Mean adjusted BMD was lower in participants with 'moderate-to-severe pain at rest' over the total lateral facet at depths of 0-2.5 mm (10% lower, p=0.041), 2.5-5 mm (20% lower, p=0.017), and 5-7.5 mm (25% lower, p=0.004), and over the total medial facet at 2.5-5 mm (22% lower, p=0.033) and 5-7.5 mm (28% lower, p=0.016). CONCLUSIONS: In OA patients with 'moderate-to-severe pain at rest', depth-specific density measures demonstrated up to 28% lower lateral and medial subchondral BMD. Patients with high levels of pain at rest may have reduced amounts of native bone prior to TKR.

Knee osteoarthritis patients with severe nocturnal pain have altered proximal tibial subchondral bone mineral density.

OBJECTIVE: Our objective was to investigate relationships between proximal tibial subchondral bone mineral density (BMD) and nocturnal pain in patients with knee osteoarthritis (OA). METHODS: The preoperative knee of 42 patients booked for knee arthroplasty was scanned using quantitative computed tomography (QCT). Pain was measured using the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and participants were categorized into three groups: 'no pain', 'moderate pain', and 'severe pain' while lying down at night. We used depth-specific image processing to assess tibial subchondral BMD at normalized depths of 0-2.5 mm, 2.5-5.0 mm and 5-10 mm relative to the subchondral surface. Regional analyses of each medial and lateral plateau included total BMD and maximum BMD within a 10 mm diameter core or 'focal spot'. The association between WOMAC pain scores and BMD measurements was assessed using Spearman's rank correlation. Regional BMD was compared pairwise between pain and no pain groups using multivariate analysis of covariance using age, sex, and BMI as covariates and Bonferroni adjustment for multiple comparisons. RESULTS: Lateral focal BMD at the 2.5-5 mm depth was related to nocturnal pain (ρ = 0.388, P = 0.011). The lateral focal BMD was 33% higher in participants with 'severe pain' than participants with 'no pain' at 2.5-5 mm depth (P = 0.028) and 32% higher at 5-10 mm depth (P = 0.049). There were no BMD differences at 0-2.5 mm from the subchondral surface. CONCLUSION: This study suggests that local subchondral bone density may have a role in elucidating OA-related pain pathogenesis.

The relationship of tibial bone perfusion to pain in knee osteoarthritis.

OBJECTIVE: To confirm altered perfusion within tibial bone marrow lesions (BMLs) and improve our understanding on the relationship between BMLs and pain in knee osteoarthritis (OA). METHODS: Participants with moderate to severe knee OA were recruited and pain was assessed using the pain subscale of the Western Ontario and McMaster Universities Arthritis Index (WOMAC). Subchondral tibial BMLs were identified and graded on magnetic resonance imaging (MRI) proton density-weighted (PDW) fat suppressed images. A pharmacokinetic model was used to analyze perfusion parameters on dynamic contrast enhanced (DCE) MRI which represent transfer rates in and out of the BMLs. The relation between perfusion and pain was evaluated using multivariable linear regression after adjustment for BML grade, age, gender and body mass index (BMI). RESULTS: There were 37 participants (mean age 64.9 years, range 46-86) with radiographic Kellgren and Lawrence grades of 3 and 4 in the study knee; 75.6% had BMLs that were classified grades 1 and 2. The mean WOMAC pain score was 10.3 (0-20 scale). There was a significant correlation between BML K(el) (rate of contrast elimination) and BML grade (P = 0.001 univariate, P = 0.002 multivariate analyses), although we did not demonstrate any significant multivariate association between BML perfusion and pain. We also found an inverse relationship between pain at sleep and BML grade (P < 0.05). CONCLUSIONS: The absence of any significant association between bone perfusion and pain implies that the relationship of tibial BMLs to pain in OA is still incompletely understood. BMLs are just one component of the whole knee joint and are formed from various causes, all of which interact and collectively contribute to the genesis of pain in OA.