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

Abstract

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.

Figure 1

Methodological sequence for CT-TOMASD analyses in the patella consists of converting CT grayscale intensity to BMD using a QCT reference phantom (a), followed by semi-automatic patellar segmentation in the transverse plane (b). Peripheral and interior boundary points are manually selected (c) to define medial and lateral facets; with the patella reoriented relative to ‘best fit’ planes passing through facet boundary points (d). A surface projection image-processing algorithm is performed to map 3D subchondral density in relation to depth (measured from the subchondral surface) directly at the patellar surface (e). CT-TOMASD analyses of the average BMD of each facet are performed (f).

Figure 2

Representative topographical color maps of average patellar BMD at depths of 0-2.5 mm, 2.5-5 mm and 5-7.5 mm in one participant reporting ‘mild-to-no pain at rest’ (top row) and one reporting ‘moderate-to-severe pain at rest’ (bottom row).

Figure 3

Adjusted mean difference and 95% confidence intervals in BMD between ‘mild-to-no pain at rest’ and ‘moderate-to-severe pain at rest’ groups at the medial and lateral facets at depths of 0-2.5 mm, 2.5-5 mm and 5-7.5 mm from the subchondral surface.