Talk: Bone Mineral Density Is Associated with Dynamic Joint Loads in Osteoarthritis Predisposed Knees (2009 ACR/ARHP Annual Scientific Meeting)

Sunday, October 18, 2009: 5:30 PM

108 B (Pennsylvania Convention Center)

Anisha Dua¹, Laura E. Thorp¹, Joel A. Block¹ and Najia Shakoor², ¹Rush-University Med Ctr, Chicago, IL, ²Rush University Medical Center, Chicago, IL

Presentation Number: 633

Purpose: We have previously shown that subjects with endstage unilateral hip osteoarthritis (OA) more commonly develop endstage OA of the contralateral knee rather than the ipsilateral knee, and that these subjects have higher dynamic joint loads at the contralateral knee than the ipsilateral knee. Local bone mineral density (BMD) reflects the loading history of that bone; hence, BMD may be a marker of excessive loading of the knee joint as well as of early asymptomatic OA. Here, we evaluated subjects who had unilateral hip OA but who were asymptomatic at their knees, to test the hypothesis that asymmetric loading of the knees induced by unilateral hip OA results in elevated BMD at the medial tibial plateau of the contralateral knee compared with the ipsilateral knee, and that these BMD asymmetries correlate with dynamic joint loading at the knees.

Method: Fifty subjects with symptomatic unilateral hip OA and asymptomatic knees were evaluated. Subjects had moderate to severe radiographic unilateral hip OA using the Kellgren Lawrence (KL) grading system. Subjects were asymptomatic at the knees (WOMAC pain during walking <20 mm out of 100 mm). Subjects underwent DXA scanning of bilateral knees and these scans were evaluated in a blinded manner by a trained investigator using a previously validated method. The BMD of the medial and lateral regions of the tibial plateau and the distal tibial shaft were measured in each knee. Subjects also underwent gait analyses using an optoelectronic camera system and multicomponent force plate. Inverse dynamics were used to calculate dynamic joint loads and the peak external knee adduction moment, a validated marker of medial compartment knee loading, was used as the primary load parameter. Paired t-tests were used to evaluate differences in BMD and loading between the knees and Spearman correlations were used to evaluate correlations between BMD and loading. p<0.05 was considered significant.

Results: Bone mineral density was significantly increased at the contralateral medial tibial plateau compared with the ipsilateral medial tibial plateau (0.912g/cm²±0.208 vs 0.869g/cm²±0.196 p=0.040). Furthermore, a direct correlation was found between the medial knee load (peak external knee adduction moment) and BMD at the contralateral medial knee (rho=0.381, p=0.008). No significant differences were noted for BMD at the lateral compartments of the two knees.

Conclusions: This study demonstrates that unilateral hip OA is associated with increased BMD at the contralateral medial knee when compared with the ipsilateral medial knee, that BMD alterations are directly correlated with loading alterations at the OA-predisposed knee (contralateral knee), and that these events occur even in asymptomatic, clinically uninvolved knees. These findings suggest that BMD alterations may be a surrogate marker for joint loading and OA progression, even in asymptomatic subjects. Although further investigation is necessary to delineate causal relationships, BMD may be a useful tool to follow structural progression in longitudinal OA studies.

Keywords: bone density and osteoarthritis

Disclosure: A. Dua, None; L. E. Thorp, None; J. A. Block, None; N. Shakoor, None.

633 - Bone Mineral Density Is Associated with Dynamic Joint Loads in Osteoarthritis Predisposed Knees