Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement
The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.
Patella Alta Is Associated with Patellofemoral Malalignment: The MOST Study
Stefanik1, J.J., Zhu1, Y., Zumwalt1, A.C., Gross2, K.D., Clancy1, M., Lynch3, J.A., Law4, L.A. Frey
BUSM, Boston, MA
MGH Inst Health Prof, Boston, MA
UCSF, San Francisco, CA
UIowa, Iowa City, IA
UAB, Birmingham, AL
Boston University School of Medicine, Boston, MA
USC, Los Angeles, CA
Purpose:
Research on risk factors for patellofemoral joint (PFJ) osteoarthritis (OA) has focused on patellar malalignment (patellar tilt angle and lateral displacement or bisect offset) and trochlear morphology (sulcus angle). 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. Patella alta is measured on a lateral knee radiograph by the Insall-Salvati ratio (ISR), a ratio between the length of the patellar tendon and length of the patella. Subjects with higher ISRs are hypothesized to have increased patellar malalignment due to the lack of osseous stability when the patella articulates superior to the femoral trochlea. The purpose of this study was to determine the association between the ISR and measures of PFJ malalignment, specifically patellar tilt angle (PTA) and bisect offset (BO).
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 weight bearing and flexed lateral knee radiographs and PTA and BO on baseline knee MRIs in 486 knees, one knee per subject. PTA was defined as the angle between a line connecting the posterior femoral condyles and a line defining the maximal patellar width. BO is a measure of the percent of the patellar lateral to the midline of the trochlea. ANOVA was used to determine the association between quartiles of the ISR and BO and PTA in two separate analyses.
Results:
The mean ISR was 1.10, mean BO 59.79%, and mean PTA 8.81 degrees. The mean age of the sample was 62, mean BMI 30, and 60% of subjects were female. The means for BO and PTA were 9.82 and 3.56 greater in the highest ISR quartile compared to those in the lowest ISR quartile (see table). Similar results were seen when adjusting for isokinetic knee extensor strength, age, sex, and BMI.
Conclusion:
Our results support the hypothesis that high ISRs, indicative of patella alta, are associated with increased PFJ malalignment. Since the ISR is unlikely to change over time, patella alta may be an important risk factor for PFJ OA, as it may cause patellofemoral malalignment.Longitudinal studies are needed to determine if higher ISRs increase the risk for PFJ malaignment.
| Insall-Salvati Ratio (ISR) | |||||
|---|---|---|---|---|---|
| Quartile 1 | Quartile 2 | 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) | ||||
| Bisect Offset | |||||
| Mean (%) | 55.98 | 58.76 | 58.60 | 65.80 | <0.0001 |
| Patellar Tilt Angle | |||||
| Mean (degrees) | 7.54 | 8.17 | 8.34 | 11.13 | <0.0001 |
To cite this abstract, please use the following information:
Stefanik, J.J., Zhu, Y., Zumwalt, A.C., Gross, K.D., Clancy, M., Lynch, J.A., et al; Patella Alta Is Associated with Patellofemoral Malalignment: The MOST Study [abstract]. Arthritis Rheum 2009;60 Suppl 10 :218
DOI: 10.1002/art.25301
