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| Jon Giles, M.D. and Clifton Bingham, M.D.
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Abstract 526: Are Patients from Vulnerable Populations More Likely to Have TKR in Centers with Worse Outcomes? Postoperative complications after joint replacement surgery are increased in centers in which small numbers of procedures are performed. Here, Losina et al examine the racial, ethnic, and socioeconomic factors associated with patients' choosing to have total knee replacement (TKR) in low-volume surgical centers. Methods: All Medicare beneficiaries receiving TKR in the year 2000 were identified from claims. Geographic distances between patient home addresses and hospital addresses were calculated. Neighborhood information on demographic characteristics (ethnicity, wealth, education, etc) was obtained by linking patient zip codes to census data. Outcomes were the proportion of patients utilizing low-volume centers for TKR (defined as <26 procedures performed per year), and the proportion of patients bypassing high-volume centers to utilize low-volume centers. Multivariate analysis was used to determine the factors associated with utilization trends for low-volume centers. Results: In 2000, 121,432 patients in 3,196 hospitals filed Medicare claims for TKR. Approximately 113,000 of these patients had data available for analysis. 13,120 patients (12%) had TKR in a low-volume center. Factors associated with utilizing low-volume centers for TKR:
Nine percent of patients bypassed a higher volume center in favor of TKR in a low-volume center. Factors associated with bypassing a high-volume center for TKR in a low-volume center:
Among the urban sub-population, neighborhood factors associated with bypassing a high-volume center in favor of TKR in a low-volume center:
Conclusions: Rural populations and urban disadvantaged minorities are more likely to utilize low-volume centers for TKR, or bypass geographically closer high-volume centers in favor of TKR in low-volume centers. Editorial Comments: This study highlights disparities in health care utilization that are likely to have important effects on outcomes. Unfortunately, the study design does not permit exploration of the individual factors involved in the decision making to have TKR in a particular center (e.g., advertising, community utilization practices, beliefs about service eligibility, etc) that are at the heart of the differences outlined here. In addition, the geographic measurements used here reflect linear distance to hospitals and not necessarily driving distances. Nonetheless, these data identify an important need for education programs for patients and health care providers in rural and urban disadvantaged areas regarding the importance of utilizing high-volume centers for elective surgical procedures. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Abstract 560: Increased Tibial Bone Mineral Density Associated with Bone Marrow Lesions This group of investigators have continued their assessment of MRI imaging of in knee OA in patients from the Framingham cohort. The relationship between bone marrow lesions (BML) seen on MRI in patients with OA have been correlated with both pain and progression. However the pathobiological correlate to these lesions is unknown. The relationships between subchondral bone density and bone lesions has not been well investigated. It is unknown whether these BMLs occur in areas of localized increased or decreased bone mineral density. In this report the investigators evaluated the relationships between the presence of BML (also referred to as bone marrow edema) and femoral bone mineral density (BMD). Methods: Participants in the study were from the Framingham osteoarthritis cohort. All subjects had 1.5T MRI, medial and lateral femoral BMD using dual XRay absorbimetry, and weight bearing knee radiographs. Medial:lateral femoral BMD ratios (M:L BMD) were calculated. Bone marrow lesions (BML) in the medial and lateral compartments were assessed by a blinded observer with T2 fat-saturated imaging. Logistic regression was performed using BML as the outcome, with quartiles of M:L BMD ratios as predictors, and covariates of age, sex, BMI, and femoral neck BMD. Results: 271 subjects and 512 knees were assessed. 31% of the X Rays had K/L scores >= 2. 63% of knees in patients with OA had no BMLs, 17% had medial lesions, 11% had lateral, and 9% had both. Highest quartile ratios of M:L BMD (indicating increased medial compartment bone density) were significantly associated with medial BMLs, with an adjusted prevalence ratio of 3.1. Similarly lowest quartile ratios (indicating increased lateral bone density) were significantly associated with lateral BMLs on MRI with an adjusted prevalence ratio of 7.1. Based on these results the authors hypothesize that the higher ratios of M:L bone mineral density may indicate a local response to loading in the medial compartment (as would be seen with varus alignment). This localized increase in bone density is associated with the presence of BML in the concordant compartment of the knee. Editorial Comment: The authors present interesting data concerning MRI BMLs and localized bone density. Previous studies have shown that markers of bone turnover are increased in OA and further increased in progressive OA suggesting the participation of subchondral bone in the disease process. BMLs have also been correlated with pain and progression. The results of this study would suggest BMLs may represent a response to an increase in localized bone density in the compartment contiguous with BMLs. The limitations of this study are the low grade of osteoarthritis present in the patients (with only 31% having definite osteophytes defined by KL >2). Furthermore in this population only 37% of patients had detectable BMLs. These findings will be important to further evaluate in patients with a wider spectrum of OA severity. Results using additional modalities to assess the subchondral bone will be important in evaluating its participation in the OA process. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Abstract 1758: Bone marrow edema on magnetic resonance imaging is associated with type II collagen degradation in knee osteoarthritis : a 3 month longitudinal study Subchondral bone marrow edema (BME) detected by MRI is correlated with pain and progression in OA. Markers of cartilage degradation, notably CTXII, have also been shown to predict progression. The rate of change in these variables is not known nor have relationships between these two variables been well studied. Methods: 370 subjects with painful knee OA had MRI scans performed at baseline and 3 months. BME was scored from T2 weighted, fat suppressed images. Fasting levels of urinary type II collagen C terminal telopeptide (CTXII) reflecting cartilage degradation was also measured. Results: Subjects were obese with mean BMI 30.3 with significant levels of pain at baseline. 83% of subjects had BME lesions at baseline. Urinary CTXII levels were increased 2.4 fold compared to non-OA controls. Baseline BME total scores correlated with CTXII levels. 71% of subjects had no change in BME over 3 months, however, 20% had an increase in score, while 10% had a decrease in score. Baseline levels of CTX II were associated with worsening BME with patients in the highest tertile having a relative risk of 2.38 of BME worsening. In subjects in whom BME improved over the 3 months, there was an associated decrease in CTXII levels. Editorial Comment: These results show that both CTX II and BME lesions are not static but can change within a period of 3 months. The imaging and biomarkers track together suggesting a link between these two measurements. The longer term sequelae of short term changes in these markers and imaging techniques remains to be studied. Whether these markers can be used as surrogate measurements to evaluate the effectiveness of a structure modifying therapy will be important to determine. Questions remain regarding the utility of these measurements in clinical practice for OA to determine patients at risk for progression as interventions to slow disease progression are lacking. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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While radiographic joint space loss is felt to reflect a loss of cartilage, this has never been rigorously evaluated. Furthermore it is unknown if cartilage loss occurs in the absence of radiographic progression. This study (563) was a 30 month prospective study to evaluate relationships between MRI changes and X Ray changes in subjects with knee osteoarthritis. A related poster (232) evaluated the relationships between cartilage loss seen on MRI and OA pain and disability. Methods: This was a study of 219 subjects with symptomatic knee OA defined by pain and a definite osteophyte who had baseline and follow up imaging at 30 months. 1.5 T MRIs were performed with standardized assessments of cartilage in five different compartments of the knee by a reader blinded to the radiographic results. Cartilage loss was defined as an increase in score at any of the sites studied. Plain radiographs were semiflexed fluoroscopically positioned views which were graded by KL scales. Joint space loss was defined as an increase in joint space narrowing score (0-3 scale) by one grade. Relationships between cartilage loss and joint space loss measured with XRay were examined using Sperman rank correlation and a GEE proportional odds logistic regression adjusting for age, sex, and BMI. In the related poster, WOMAC pain, disability, and pain measured by VAS were also evaluated in a regression analysis to determine if cartilage loss was correlated with increased pain or disability. Results: Subjects had a range of baseline KL scores with 28% KL grade 1, 26% KL grade 2, and 43% KL grade 3. Medial joint space loss was detected in 16% of subjects over 30 months whereas cartilage loss was detectable in 45% of subjects over this period of time. In subjects with no progression by X Ray, 45% had detectable cartilage loss by MRI. Cartilage loss occurred in the central femur and tibial plates. Lateral joint space loss was seen in 8% of subjects by X Ray with cartilage loss by MRI in 22% of subjects. Cartilage loss by MRI was seen in 20% of subjects who did not have demonstrable JS progression on plain X Ray. While cartilage loss occurred more in the central femur and tibial plates, loss was also seen more diffusely.In the separate poster, no association was found between cartilage loss on MRI and WOMAC pain, WOMAC disability, or pain measured by VAS. Editorial Comments: This is the first large scale study to demonstrate that cartilage loss detected by MRI correlates with joint space loss on X Ray. The results suggest that MRI may be more sensitive in detecting progression than plain radiographs given that almost 40% of patients with cartilage loss detectable with MRI did not show loss on plain radiography as evaluated in this study. The lack of association between cartilage loss on MRI and symptoms and disability suggest that pain may be related to other knee structures rather than cartilage. While these results are important in advancing our understanding of cartilage lesions and joint space narrowing, an important caveat should be considered. The definition of joint space loss was defined in this study using a semiquantitative grading scale rather than a precise measurement of mm of joint space as traditionally employed to assess joint space in OA clinical trials to date. The correlation between these measurements was not reported. The findings in this study will be important in defining progression in the future for clinical studies of OA drugs and point to the possible dissociation between pain and structure in OA. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
Abstract 840: Two Year Evaluation of Disease Progression by Quantitative Magnetic Resonance Imaging in a Large Primary Osteoarthritis Patient Population Various MRI techniques have been advocated for following OA of the knee. These have included assessments of individual cartilage defects, bone marrow lesions, cartilage thickness, and cartilage volume. This study evaluated the change in cartilage volume measurements in knee OA over 2 years. Methods: 110 patients who were participating in a large osteoarthritis clinical trial had serial knee X Ray and MRI performed. Patients were enrolled in the study based on qualifying knee X Ray with medial compartment > lateral compartment narrowing. Total cartilage volume and medial and lateral compartment cartilage volume were measured. Mean loss of cartilage volume as a percent change from baseline was calculated. Results: Most patients demonstrated some loss of cartilage volume over 2 years. In the total study population, mean changes in total cartilage volume were shown to decrease 3.7% at 1 year and 5.6% at 2 years. Medial volume decreased greater than lateral volume as would be expected in patients with prevalent medial compartment joint space loss at baseline. The investigators described three populations of patients based on their rates of progression. A group of rapid progressors represented 10% of the total study population in which average cartilage volume loss was 13.2% of total cartilage volume. Similar numbers of subjects (44% each) were described as intermediate progressors with loss of 7.2% and slow progressors with loss of 2.3%. Editorial Comment: This study is showed that MRI detects changes in total cartilage volume as rapidly as 1 year, the first time point of assessment in this study. A group of patients with knee OA appear to have the most rapid cartilage volume loss. Further evaluation of clinical features and biochemical markers to more fully describe this subset of patients will be extremely important moving forward as these may be the most appropriate group for targeted therapeutic interventions. Investigations into the association of cartilage volume loss with other MRI features such as bone marrow lesions, osteophytes, and cartilage thickness will be useful to follow in longitudinal studies for rates of change and interrelationships between these features as well as with signs and symptoms of disease. Whether any one or combination of these variables predicts ultimate joint failure has not been demonstrated. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
Abstract 823: Comparison of Knee Alignment by X Ray and Goniometer McDaniel, Vail, and Kraus Varus and valgus alignment at the knee have been shown to be associated with progressive osteoarthritis. Determining the angle of alignment has traditionally been performed with whole leg radiographs, a technique that is neither clinically practical nor possible in large scale clinical trials. These investigators assessed the utility of a simple clinical goniometric measurement of angulation at the knee compared to traditional whole leg X Rays as well as PA semiflexed XRays. Methods: 104 knees from 52 participants were evaluated with whole leg X Rays, PA semiflexed knee X Rays, and goniometric clinical assessments using the center at the patella and the arms along the tibial and femoral shafts. Results: A strong correlation was found between the measurement of the mechanical axis using the whole limb X Rays and the goniometric measurements (r=0.72, p< 0.0001). A strong association was also found between the anatomic axis of the PA knee film and the whole leg films (r=0.74, p< 0.0001). A weaker but still significant association was found between measurements of the PA semiflexed view angle and goniometric measurement (r=0.57, p< 0.0001). Editorial Comment: These results would indicate that a simple goniometric measurement performs quite well in assessing varus and valgus alignment at the knee such that whole leg measurements may not be necessary. Similarly a simple PA semiflexed view also provides significant information as to alignment. Adding a goniometric assessment to patients enrolled in prospective studies may provide additional information to assess the possible effects of alignment on progression. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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