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.