Subchondral Bone Attrition is a Reflection of Compartment-Specific Mechanical Load: The MOST Study

Title:

Subchondral Bone Attrition is a Reflection of Compartment-Specific Mechanical Load: The MOST Study

Author(s):

T. Neogi¹, M. Nevitt², J. Niu¹, L. Sharma³, CE Lewis⁴, J. Torner⁵, K. Javaid², D. Felson¹. ¹BUSM, Boston, MA; ²UCSF, SF, CA; ³Northwestern U, Chicago, IL; ⁴UAB, Birmingham, AL; ⁵UIowa, Iowa City, IA

Purpose: While subchondral bone is thought to have an important role in OA progression, subchondral bone attrition (SBA) as detected by x-rays was traditionally thought to be a late finding in OA. However, SBA can be seen on MRI even in early OA, and may be related to mechanical and systemic factors which can contribute to altered properties of subchondral bone and OA progression. For example, focal loading related to malalignment, or presence of low bone density may predispose to SBA. We evaluated the effects of malalignment and bone density on the presence and incidence of SBA.

Methods: The Multicenter Osteoarthritis (MOST) Study is a NIH-funded longitudinal observational study of individuals who have or are at high risk for knee OA. Alignment was measured on baseline PA long-limb films at the knee and categorized as neutral (179-181^o), varus (<179^o) and valgus (>181^o). BMD of the right femoral neck (g/cm2) was assessed (Hologic 4500A) at baseline and categorized into age- and sex-specific tertiles. At baseline and 30-month follow-up, participants had knee MRIs performed (1.0 T; axial and sagittal proton density fat suppressed and coronal STIR sequences). MRIs were graded using WORMS in 5 subregions within each of the medial and lateral tibiofemoral (TF) compartments (central, posterior femur; anterior, central, posterior tibia) for SBA (0-3). A knee was eligible for the incident SBA analysis if SBA score=0 in all subregions within a compartment at baseline. We evaluated the association of alignment and BMD with baseline presence of SBA (score≥1) and incident SBA (any score increase from 0 at baseline) using logistic regression for the medial and lateral TF compartments separately. GEE was used to account for correlations between knees within a subject. All analyses were adjusted for age, sex, and BMI, and analyses including BMD were additionally adjusted for bone-modulating medication use.

Results: There were 999 participants (1063 knees) with measures available for analyses (mean age 63, mean BMI 30.2, 63% female). 36% had baseline SBA and 50% had knee OA. Results in the Table demonstrate an association between presence of and incident SBA with varus alignment in the medial compartment, and with valgus alignment in the lateral compartment. Low BMD was not associated with SBA.

Conclusions: Presence and incidence of SBA are associated with malalignment, but not lower bone density. SBA is thus likely a marker of increased load experienced by overlying cartilage, and may in turn contribute to increased forces transmitted to the cartilage due to altered properties of subchondral bone related to SBA.

Disclosures:

T. Neogi, None; M. Nevitt, None; J. Niu, None; L. Sharma, None; C. Lewis, None; J. Torner, None; K. Javaid, None; D. Felson, None.