Presentation: The Association Between Patella Alta and Structural Features of Patellofemoral Joint Osteoarthritis (OA) On MRI: The MOST Study (ACR/ARHP Annual Scientific Meeting)

Sunday, October 18, 2009: 5:45 PM

108 B (Pennsylvania Convention Center)

J.J. Stefanik¹, Y. Zhu¹, A.C. Zumwalt¹, K.D. Gross², M. Clancy¹, J. A. Lynch³, L.A. Frey Law⁴, C.E. Lewis⁵, F.W. Roemer¹, C.M. Powers⁶, A. Guermazi¹ and David T. Felson⁷, ¹BUSM, Boston, MA, ²MGH Inst Health Prof, Boston, MA, ³UCSF, San Francisco, CA, ⁴UIowa, Iowa City, IA, ⁵UAB, Birmingham, AL, ⁶University of Southern California, Los Angeles, CA, ⁷Boston University School of Medicine, Boston, MA

Presentation Number: 634

Purpose: Research on risk factors for patellofemoral joint (PFJ) osteoarthritis (OA) has focused on PFJ alignment and trochlear morphology. Patella alta (PA), a high riding patella, has received much less attention despite being a known risk factor for patellar subluxation and dislocation in young persons. PA is measured by the Insall-Salvati ratio (ISR), the ratio between the length of the patellar tendon and length of the patella. One possible mechanism for PFJ OA development is decreased contact area between opposing joint surfaces causing increased stress on cartilage and bone. Recently the ISR, but not patellofemoral alignment, has been shown to be associated with decreased contact area in the PFJ. The purpose of this study was to examine the relation of the ISR to prevalence of cartilage damage and measures of bone damage, specifically bone marrow lesions (BMLs) and subchondral bone attrition (SBA), in the lateral PFJ compartment.

Methods: The MOST study is an NIH funded cohort study of persons aged 50-79 years with or at risk for knee OA. We measured the ISR on the baseline flexed and weight bearing lateral radiographs in 486 knees, one knee per subject. Cartilage damage, BMLs, and SBA were graded at baseline on MRI using the WORMS scale (0-6, 0-3, and 0-3 respectively) on the patellar and trochlear facets. We divided the ISR into quartiles and dichotomized cartilage damage (≥2), BMLs (≥1), and SBA (≥1) into presence or absence of pathology. We examined the association between the ISR and cartilage damage, BMLs, and SBA in the lateral PFJ using logistic regression with GEE to account for the correlation between patellar and trochlear readings from the same knee. All analyses were adjusted for age, sex, and BMI.

Results: The mean age of the sample was 62, mean BMI 30, mean ISR 1.10, and 60% of subjects were female. Of the 486 knees studied, 35% had cartilage damage, 21% BMLs, and 14% SBA. Compared with subjects in the lowest ISR quartile, those in the highest quartile had 2.7 (95% CI 1.8, 4.4), 3.2 (1.9 5.4), and 6.0 (3.0, 12.4) times more likely to have lateral PFJ cartilage damage, BMLs, and SBA respectively.

Conclusion: Subjects with a high ISR, indicative of patella alta, are more likely to have cartilage damage, BMLs, and SBA in the lateral PFJ, supporting the hypothesis that subjects with an increased ISR have increased PFJ stress. Future research is needed to evaluate whether a high ISR increases the risk of PFJ OA and to investigate the association between the ISR, measures of PFJ alignment, PFJ OA, and pain.

Insall-Salvati Ratio (ISR)

Quartile 1

Quartile2

Quartile 3

Quartile 4

P for trend

0.64-0.99

1.00-1.08

1.09-1.20

1.21-1.58

(continuous ISR)

n=128 knees

n=106 knees

n=128 knees

n=124 knees

(low)

(high)

Cartilage Damage

% WORMS ≥2

25

36

32

46

Adjusted OR (95% CI)

1.0 (reference)

1.7 (1.0, 2.7)

1.5 (0.9, 2.3)

2.7 (1.8, 4.4)

<0.0001

Bone Marrow Lesions

% WORMS ≥1

14

19

18

32

Adjusted OR (95% CI)

1.0 (reference)

1.4 (0.8, 2.6)

1.3 (0.7, 2.3)

3.2 (1.9 5.4)

<0.0001

Subchondral Bone Attrition

% WORMS ≥1

6

17

10

25

Adjusted OR (95% CI)

1.0 (reference)

3.3 (1.6, 7.0)

1.7 (0.8, 3.7)

6.0 (3.0, 12.4)

<0.0001

Keywords: osteoarthritis

Disclosure: J. J. Stefanik, None; Y. Zhu, None; A. C. Zumwalt, None; K. D. Gross, None; M. Clancy, None; J. A. Lynch, None; L. A. Frey Law, None; C. E. Lewis, None; F. W. Roemer, None; C. M. Powers, None; A. Guermazi, BICL, LLC, 4, Synarc, Inc., 1, GE Healthcare, 2, MerckSerono, Facet Solutions, 5 ; D. T. Felson, None.

Insall-Salvati Ratio (ISR)
	Quartile 1	Quartile2	Quartile 3	Quartile 4	P for trend
	0.64-0.99	1.00-1.08	1.09-1.20	1.21-1.58	(continuous ISR)
	n=128 knees	n=106 knees	n=128 knees	n=124 knees
	(low)			(high)
Cartilage Damage
% WORMS ≥2	25	36	32	46
Adjusted OR (95% CI)	1.0 (reference)	1.7 (1.0, 2.7)	1.5 (0.9, 2.3)	2.7 (1.8, 4.4)	<0.0001
Bone Marrow Lesions
% WORMS ≥1	14	19	18	32
Adjusted OR (95% CI)	1.0 (reference)	1.4 (0.8, 2.6)	1.3 (0.7, 2.3)	3.2 (1.9 5.4)	<0.0001
Subchondral Bone Attrition
% WORMS ≥1	6	17	10	25
Adjusted OR (95% CI)	1.0 (reference)	3.3 (1.6, 7.0)	1.7 (0.8, 3.7)	6.0 (3.0, 12.4)	<0.0001

634 - The Association Between Patella Alta and Structural Features of Patellofemoral Joint Osteoarthritis (OA) On MRI: The MOST Study