The Role of Varus and Valgus Alignment in the Initial Development of Cartilage Damage at the Knee: The MOST Study.

Leena Sharma, MD¹,Orit Almagor²,Joan S. Chmiel²,David T. Felson, MD, MPH³,Ali Guermazi⁴,Frank Roemer⁴,James Torner⁵,Cora E. Lewis⁶,Neil Segal⁵,John A. Lynch⁷,Derek Cooke⁸,Jean Hietpas⁷,Michael C. Nevitt, PhD⁹. ¹Northwestern University, Chicago, IL,²Northwestern University,³Boston University, Boston, MA,⁴Boston University,⁵University of Iowa,⁶UAB,⁷UCSF,⁸Queens University,⁹UCSF, San Francisco, CA

Purpose: Varus and valgus alignment are each associated with subsequent progression of knee OA but their role in incident disease is less certain. Radiographic measures of incident OA cannot capture cartilage tissue change directly or reveal the compartment of initial disease. We identified knees with normal cartilage morphology by MRI in all tibial and femoral subregions at baseline to test the hypothesis: varus alignment is associated with incident medial cartilage damage and valgus alignment is associated with incident lateral cartilage damage.

Methods: MOST includes persons at risk for or with knee OA. In all participants, full-limb x-rays were acquired at baseline, and MRI (1.0T extremity system) at baseline and 30 months later. Varus malalignment was defined as ≤ 178° (hip-knee-ankle angle) and valgus as ≥ 182°. Cartilage and menisci were assessed using WORMS. In knees with normal baseline cartilage morphology (WORMS score 0 in all subregions), we used logistic regression with GEE to examine the association between baseline alignment and incident cartilage damage (WORMS score ≥ 2 at 30 months in ≥ 1 subregion) adjusting for age, gender, BMI, laxity, and meniscal tear and extrusion.

Results: Of 1881 knees, 293 knees (110 varus, 55 valgus, 128 neutral) from 256 persons (mean age 60 years, BMI 28.6, 67% women) had normal cartilage morphology in all subregions at baseline. At 30 months, 34 had incident medial and 15 had incident lateral cartilage damage. As shown in Table 1, varus alignment was associated with a significantly increased risk of new medial cartilage damage vs. either reference group (non-varus or neutral) and when analyzed as a continuous variable. This relationship held even when knees with medial meniscal tear or extrusion were excluded (adjusted OR 1.37/1° varus, 95% CI 1.11, 1.68). Significant relationships were not detected for valgus and incident lateral disease (Table 2), possibly due in part to the low frequency of this outcome. In addition, varus was protective against incident lateral damage [adjusted OR 0.75/1°, 95% CI 0.59, 0.95] and valgus against incident medial damage [adjusted OR 0.72/1°, 95% CI 0.63, 0.83].

Conclusion: In knees with normal cartilage morphology, varus alignment was associated with the initial development of cartilage damage in the more loaded compartment, and both varus and valgus were associated with a reduced risk of incident damage in the less loaded compartment. These results suggest that varus alignment is a risk factor for incident cartilage damage in knees without OA and provide further evidence that varus alignment increases the risk of incident knee OA.

Keywords: osteoarthritis, malalignment, magnetic resonance imaging (MRI), risk factors, knee osteoarthritis

Disclosure:

• Leena Sharma: Nothing to disclose.
• Orit Almagor: Nothing to disclose.
• Joan Chmiel: Nothing to disclose.
• David Felson: Nothing to disclose.
• Ali Guermazi: Nothing to disclose.
• Frank Roemer:Nothing to disclose.
• James Torner: Nothing to disclose.
• Cora Lewis: Nothing to disclose.
• Neil Segal: Nothing to disclose.
• John Lynch: Nothing to disclose.
• Derek Cooke:  Nothing to disclose.
• Jean Hietpas: Nothing to disclose.
• Michael Nevitt:  Nothing to disclose