C.K. Kwoh

Individual magnetic resonance imaging and radiographic features of knee osteoarthritis in subjects with unilateral knee pain: The health, aging, and body composition study

OBJECTIVE Strong associations between radiographic features of knee osteoarthritis (OA) and pain have been demonstrated in persons with unilateral knee symptoms. This study was undertaken to compare radiographic and magnetic resonance imaging (MRI) features of knee OA and assess their ability to discriminate between painful and nonpainful knees in persons with unilateral symptoms. METHODS The study population included 283 individuals ages 70-79 years with unilateral knee pain who were enrolled in the Health, Aging, and Body Composition Study, a study of weight-related diseases and mobility. Radiographs of both knees were read for Kellgren/Lawrence (K/L) grade and individual radiographic features, and 1.5T MRIs were assessed using the Whole-Organ Magnetic Resonance Imaging Score. The association between structural features and pain was assessed using a within-person case-control design and conditional logistic regression. Receiver operating characteristic (ROC) analysis was then used to test the discriminatory performance of structural features. RESULTS In conditional logistic analyses, knee pain was significantly associated with both radiographic features (any joint space narrowing grade ≥ 1) (odds ratio 3.20 [95% confidence interval 1.79-5.71]) and MRI features (any cartilage defect scored ≥ 2) (odds ratio 3.67 [95% confidence interval 1.49-9.04]). However, in most subjects, MRI revealed osteophytes and cartilage and bone marrow lesions in both knees, and using ROC analysis, no individual structural feature discriminated well between painful and nonpainful knees. The best-performing MRI feature (synovitis/effusion) was not significantly more informative than K/L grade ≥ 2 (P = 0.42). CONCLUSION In persons with unilateral knee pain, MRI and radiographic features were associated with knee pain, confirming that structural abnormalities in the knee have an important role in the etiology of pain. However, no single MRI or radiographic finding performed well in discriminating between painful and nonpainful knees. Further work is needed to examine how structural and nonstructural factors influence knee pain.

Intra- and inter-observer reproducibility of volume measurement of knee cartilage segmented from the OAI MR image set using a novel semi-automated segmentation method

OBJECTIVE We developed a semi-automated method based on a graph-cuts algorithm for segmentation and volumetric measurements of the cartilage from high-resolution knee magnetic resonance (MR) images from the Osteoarthritis Initiative (OAI) database and assessed the intra- and inter-observer reproducibility of measurements obtained via this method. DESIGN MR image sets from 20 subjects of varying Kellgren-Lawrence (KL) grades (from 0 to IV) on fixed flexion knee radiographs were selected from the baseline double-echo and steady-state (DESS) knee MR images in the OAI database (0.B.1 Imaging Data set). Two trained radiologists independently performed the segmentation of knee cartilage twice using the semi-automated method. The volumes of segmented cartilage were computed and compared. The intra- and inter-observer reproducibility were determined by means of the coefficient of variation (CV%) of repeated cartilage segmented volume measurements. The subjects were also divided into the low- (0, I or II) and high-KL (III or IV) groups. The differences in cartilage volume measurements and CV% within and between the observers were tested with t tests. RESULTS The mean (+/-SD) intra-observer CV% for the 20 cases was 1.29 (+/-1.05)% for observer 1 and 1.67 (+/-1.14)% for observer 2, while the mean (+/-SD) inter-observer CV% was 1.31 (+/-1.26)% for session 1 and 1.79 (+/-1.72)% for session 2. There was no significant difference between the two intra-observer CV%s (P=0.272) and between the two inter-observer CV%s (P=0.353). The mean intra-observer CV% of the low-KL group was significantly smaller than that for the high-KL group for observer 1 (0.83 vs 1.86%: P=0.025). The segmentation processing times used by the two observers were significantly different (observer 1 vs 2): (mean 49+/-12 vs 33+/-6min) for session 1 and (49+/-8 vs 32+/-8min) for session 2. CONCLUSION The semi-automated graph-cuts method allowed us to segment and measure cartilage from high-resolution 3T MR images of the knee with high intra- and inter-observer reproducibility in subjects with varying severity of OA.

Susceptibility artifacts detected on 3T MRI of the knee: frequency, change over time and associations with radiographic findings: data from the joints on glucosamine study.

OBJECTIVE To determine the prevalence of intraarticular susceptibility artifacts and to detect longitudinal changes in the artifacts, on 3T magnetic resonance imaging (MRI) of the knee in a cohort of patients with knee pain, and to assess the association of susceptibility artifacts with radiographic intraarticular calcifications. DESIGN Three hundred and forty-six knees of 177 subjects aged 35-65 were included. 3T MRI was performed at baseline and at 6 months. Baseline radiographs were assessed for presence/absence of linear/punctate calcifications within the tibiofemoral joint (TFJ) space. Corresponding MRIs were assessed for susceptibility artifacts (i.e., linear/punctate hypointensities) in the TFJ space on coronal dual-echo steady-state (DESS) sequences. Kappa statistics were applied to determine agreement between findings on baseline DESS and radiography. Changes in artifacts over time were recorded. RESULTS In the medial compartment, 13 (4%) of the knees showed susceptibility artifacts at baseline. Six knees had persistent artifacts and six knees had incident artifacts at follow-up. Agreement between DESS and radiography was κ = 0.18 (-0.15, 0.51) in the medial compartment. Frequency of artifacts in the lateral compartment was low (2%). CONCLUSION Susceptibility artifacts detected on knee MRI are not frequent, and likely correspond to vacuum phenomena as they commonly change over time and are not associated with intraarticular calcifications. Radiologists should be aware of these artifacts as they can interfere with cartilage segmentation.

OP0153 Subchondral Bone Marrow Lesions Predict Incident Radiographic Osteoarthritis

Background Radiography is only able to depict structural joint damage at advanced stages of knee osteoarthritis. Pre-radiographic structural damage is likely to increase the risk of incident radiographic OA (ROA). Subchondral bone marrow lesions (BMLs) expose the joint to increased risk of cartilage loss locally but it is unknown if BMLs increase risk for incident ROA. Objectives The aim of the study was to assess if presence and severity of subchondral BMLs one year prior to the occurrence of incident ROA (time point “P-1”) and at study enrollment (“baseline”) increase the risk for incident ROA in a nested, matched case-control study in the Osteoarthritis Initiative (OAI) cohort. Methods Participants were drawn from the OAI including 4796 participants with, or at risk of knee osteoarthritis. We studied 110 knees that developed incident ROA before the 48 month visit based on the following definition: either KL 0 in both knees or KL 0 in one knee and KL 1 in the contralateral knee at baseline. They were each matched with a control knee that did not develop incident ROA, with the same KL grade in both knees at baseline. Matching was further done by gender and age within 5 years. MR images were acquired at four OAI clinical centers using Siemens Trio 3 T scanners. MRIs were read for subchondral BMLs in 14 articular subregions using the semiquantitative MOAKS system. Only BML size, which is scored from 0-3, was considered in the analyses. Analyses were performed on a knee level only considering all 14 articular subregions. Conditional logistic regression was applied to assess the risk of incident ROA in regard to maximum BML size per knee at P-1 and baseline. In addition, the number of subregions per knee exhibiting BMLs and the summed BML score per knee was analyzed in regard to risk for ROA for the time point P-1 and for baseline. Results Subjects were on average 58.6 years old (SD ± 8.5), predominantly female (62.8%) and overweight (mean BMI 28.0 SD ± 4.7). At P-1 risk of incident ROA was marginally increased for knees exhibiting BMLs with a maximum grade of 1 (odds ratio (OR) 1.83 95% confidence intervals [0.94,3.52]) and was significantly increased for BMLs with a maximum grade of ≥2 (OR 3.38 [1.64, 6.98]). Only knees with a maximum grade of ≥2 at baseline showed an increased risk of subsequent ROA (OR 2.18 [1.09,4.38]). Knees with ≥1 subregions affected by BMLs at P-1 had an increased risk of ROA (for 1 subregion OR 2.83 [1.43, 5.59], for ≥2 subregions OR 2.06 [1.05, 4.02]), while this was not the case for the baseline visit. A summed BML score of ≥4 increased risk of ROA at P-1 (OR 3.80 [1.37, 10.51] and baseline OR 2.86 [1.01, 8.08]). Conclusions Presence of any BMLs predicted incident ROA one year later compared with knees without BMLs. Risk for ROA was further increased for knees exhibiting large BMLs and a sum score of 4 or more. The subchodnral bone seems to play an importnant role in OA incidence. Of note at baseline, only knees with a maximum score of ≥2 exhibited an increased risk of ROA. BMLs seem to be an important predictor of ROA both at baseline and at one year prior to the development of ROA. Disclosure of Interest F. Roemer Shareholder of: Boston Imaging Core Lab, LLC, Consultant for: Merck Serono, NIH, C. K. Kwoh Consultant for: Novartis, M. Hannon: None Declared, R. Boudreau: None Declared, D. Hunter Grant/research support from: Australia Research Council Future Fellowship, Consultant for: DonJoy, NIH, Stryker, F. Eckstein Shareholder of: Chondrometrics, Z. Wang: None Declared, J. Grago: None Declared, A. Guermazi Shareholder of: Boston Imaging Core Lab, LLC, Consultant for: Astra Zeneca, Genzyme, Novartis, Stryker, Merck Serono

Loss of anterior cruciate ligament integrity and the development of radiographic knee osteoarthritis: a sub-study of the osteoarthritis initiative

INTRODUCTION The aim of this study was to determine whether loss of ACL integrity in an older cohort precedes the onset of radiographic OA (ROA). METHODS Participants in this nested case-control study were selected from the Osteoarthritis Initiative (OAI) study who had risk factors for OA development but did not have ROA (Kellgren-Lawrence grading (KLG) of 0 or 1) in both knees at baseline. The MRIs were assessed for the presence of ACL tears. Case knees were defined by the development of ROA on knee radiographs between the 12 and 48 month visits. Their radiographs were assessed at P0 (time of onset of radiographic knee OA), 1 year prior to P0 (P-1) and at baseline. Controls were selected from amongst those who did not develop incident ROA and were matched to cases. RESULTS 355 persons who developed ROA were matched to 355 controls. No relationship between loss of ACL integrity and incident ROA was found at any assessment time point. Odds ratios (OR) for baseline, 1 year prior to incident ROA (P1) and at point of occurrence of incident ROA (P0) were 2.00 (0.66-6.06), 2.5 (0.76-8.24) and 2.75 (0.85-8.88) respectively. A significant risk of incident ROA was found in participants who had a history of knee injury with an OR of 1.51 (1.05-2.16). CONCLUSION Loss of ACL integrity does not confer a significantly increased risk of incident ROA in an older adult cohort. In contrast, a history of knee injury was associated with an increased risk of incident ROA.

SAT0322 Presence of large bone marrow lesions (BMLS) and worsening of BMLS in the medial TIBIO-femoral joint increase risk for knee replacement – data from the osteoarthritis initiative

Background Total knee joint replacement (TKR) is a cost-effective procedure with good long-term outcomes. However, there is no clear consensus on indications for TKR. Subchondral bone marrow lesions (BMLs), have been identifiied as important disease features relevant for not only clinical disease manifestations such as pain but also for structural progression. Thus, BMLs are promising biomarkers for structural progression to important clinical outcomes such as TKR. Objectives The aims of this study were therefore to test whether presence and size of BMLs were associated with increased odds of TKR, and if worsening of BMLs over time is also associated with TKR. Methods We studied 121 knees from OAI participants (age 45-78 years) that underwent TKR before the 48 month visit for the time point prior to TKR, i.e. “T0” (i.e. for a TKR reported at the 48 month (M) visit, T0 =36M and T-1 =24M) and 121 control knees that did not undergo TKR that were matched for radiographic disease stage, gender, and age and were assessed at the same T0 and T-1 follow-up visit. Images were acquired at four OAI clinical centers using dedicated 3 T scanners. MRIs were read for subchondral BMLs in 14 articular subregions using the semiquantitative MOAKS system. Only BML size, which is scored from 0-3, was considered in the analyses. Analyses were performed on a plate (medial tibia, medial femur, lateral tibia, lateral femur, trochlea, patella) and compartmental level (medial tibio-femoral joint [TFJ], lateral TFJ and patello-femoral joint – [PFJ]). Conditional logistic regression was applied to assess the risk of TKR in regard to maximum BML size per plate at T0. In addition, the number of subregions per compartment showing BML worsening from the time point prior T0 (=T-1) to T0 was analyzed in regard to risk for TKR following T0. Results Subjects were on average 65.3 years old (SD ± 8.6), predominantly female (58.1%) and overweight (mean BMI 29.6 SD ± 4.9). The odds for TKR were significantly increased for the group exhibiting large (i.e. grade 3) BMLs in the medial compartment when compared to the knees without BMLs at T0 as the reference (unadjusted OR 2.62, 95% confidence interval [CI] 1.16-5.91 for medial tibia, and 2.35, 95% CI 1.10-5.00 for medial femur, respectively). Further, the odds for TKR were significantly increased for knees with ≥3 subregions exhibiting increase in BML size in the medial TF compartment from T-1 to T0 compared to knees with no subregions showing worsening (OR 3.35, 95%CI 1.14-9.82). No significant associations were found for the lateral TFJ and PFJ and respective plates cross-sectionally or longitudinally. Conclusions On a plate-level analysis, presence of large BMLs in the medial femur and/or tibia at the time point prior to TKR suggests increased risk of TKR, while presence of large BMLs in the lateral TFJ or in the PFJ does not. Worsening of BML size in ≥3 subregions in the medial TF compartment from T-1 to T0 also indicates increased risk for TKR when compared to knees without worsening in any subregion in the same compartment. Disclosure of Interest F. Roemer Shareholder of: Boston Imaging Core Lab (BICL),LLC., Consultant for: Merck Serono, NIH, C. Kwoh Consultant for: Novartis, D. Hunter Grant/Research support from: Australia Research Council Future Fellowship, Consultant for: DonJoy, NIH, Stryker, R. Boudreau: None Declared, M. Hannon: None Declared, F. Eckstein Shareholder of: Chondrometrics, Z. Wang: None Declared, M. John Employee of: Novartis, A. Guermazi Shareholder of: Boston Imaging Core Lab (BICL),LLC., Consultant for: Astra Zeneca, Genzyme, Novartis, Stryker,Merck Serono

FRI0302 Worsening of HOFFA-synovitis and effusion-synovitis increase risk for total knee replacement

Background Total knee joint replacement (TKR) is a cost-effective procedure with good long-term outcomes. However, at present there is no clear consensus on indications for TKR. Imaging biomarkers capable of predicting TKR therefore are urgently needed and may be helpful in clinical studies and trials which utilize TKR as an outcome. Hoffa-synovitis and effusion-synovitis, which may be assessed on non-contrast enhanced MRI, have been identified as important disease features relevant for clinical disease manifestations such as pain but may also be relevant for structural progression. Furthermore, worsening or improvement in these inflammatory imaging markers is associated with worsening or improvement in pain. For these reasons Hoffa- and effusion-synovitis are promising candidate imaging biomarkers for TKR. Objectives Aim of the study was to assess if presence or worsening of Hoffa- and effusion-synovitis prior to TKR increases risk for TKR and if change in these two measures prior to TKR further affects the risk for TKR. Methods We studied 121 knees from OAI participants (age 45-78 years) that underwent TKR before the 48 month visit using the time point prior to TKR, (e.g. for a TKR reported at the 48 month (M) visit, T0 =36M and T-1 =24M) and 121 control knees that did not undergo TKR that were matched for radiographic disease stage, gender, and age and were assessed at the same T0 and T-1 follow-up visit. Images were acquired at four OAI clinical centers using dedicated 3 T scanners. MRIs were read for Hoffa- and effusion-synovitis using the semiquantitative MOAKS system, which scores both features from 0-3 with 0 being normal and 3 coding severe structural changes. Conditional logistic regression comparing matched knees was applied to assess the risk of TKR at T0. In addition change in Hoffa- and effusion-synovitis from the time point prior (T-1) to T0 was analyzed in regard to risk for TKR following T0. Results Subjects were on average 65.5 years old (SD ± 8.6), predominantly female (58.1%) and overweight (mean BMI 29.5 SD ± 4.88). In the comparison of the T0 time point, the odds for TKR were significantly increased for the group exhibiting any effusion-synovitis at T0 when compared to the knees without effusion-synovitis at T0 as the reference (OR 2.45 95% confidence interval [CI] 1.22-4.95). No significant associations were found for presence of Hoffa-synovitis at T0 (OR 1.11, 95% CI 0.58-2.15). Worsening of either Hoffa- and effusion-synovitis from T-1 to T0 was associated with increased odds for TKR (OR 7.0, 95% CI 1.59,30.80 and 2.27, 95% CI 1.11,4.62 respectively). Conclusions Presence of effusion-synovitis at the time point prior to TKR (T0) increases risk of TKR, while presence of Hoffa-synovitis does not. The latter finding is likely explained by the non-specific character of this imaging marker. Worsening of Hoffa- and effusion-synovitis from T-1 to T0 both increase risk for TKR. Presence and change of these imaging markers are important prognostic markers in regard to the structural progression of knee OA using TKR as the outcome measure. Disclosure of Interest A. Guermazi Shareholder of: Boston Imaging Core Lab (BICL),LLC., Consultant for: Facet Solutions, Genzyme, Novartis, Stryker,Merck Serono, F. Roemer Shareholder of: Boston Imaging Core Lab (BICL), LLC., Consultant for: Merck Serono, NIH, M. Hannon: None Declared, R. Boudreau: None Declared, D. Hunter Grant/Research support from: Australia Research Council Future Fellowship, Consultant for: DonJoy, NIH, Stryker, F. Eckstein Shareholder of: Chondrometrics, D. Hayashi: None Declared, Z. Wang: None Declared, C. K. Kwoh Consultant for: Novartis

SAT0323 Marked bilateral symmetricity of cartilage damage, bone marrow lesions and meniscal damage in subjects with knee pain and with or without radiographic osteoarthritis: The jog study

Background Several risk factors for osteoarthritis (OA) have been described to be associated with an increased risk for incident radiographic OA, on a local (joint) or systemic (person) level 1. While radiography depicts articular changes only late in the disease process, magnetic resonance imaging (MRI) is capable of visualizing tissue pathology at a much earlier stage. Most MRI-based studies have used a one knee per person approach and thus data on bilaterality of OA features is sparse. One study described a symmetrical pattern for hand OA based on radiography but there are no studies assessing bilaterality of MRI based OA-features on the knee joint 2. Objectives Study aim was to describe symmetricity of MRI-detected OA features in a cohort with radiographic OA and knee pain. Methods 169 subjects aged 35-65 with chronic, frequent knee pain were included. 3T MRI of both knees was performed using the same pulse sequence protocol as in the Osteoarthritis Initiative (OAI). Knees were semiquantitatively assessed according to the WORMS system by one expert MSK radiologist. Cartilage damage and bone marrow lesions (BMLs) were read in five plates (medial/lateral femur, medial lateral tibia, patella, femoral trochlea) while meniscal damage was read in three medial and three lateral subregions. Chi2tests were used to compare the proportion of people with unilateral tissue pathology to the proportion what would be expected if the two knees were independent. For this analysis, all MRI features were divided into present (score≥1) and absent (score=0). We further used linear weighted (w) kappa statistics to describe agreement of cartilage damage and BMLs in the same articular plates using the full WORMS scores (0-4 for cartilage and 0-3 for BML). Results 51.2% of participants were men, mean age was 52.1 (±6.2) years old, mean BMI was 29.0 (± 4.1). The worst Kellgren/Lawrence (KL) grades in either knee were: K/L 0: 37 (21.9%) knees, K/L 1: 14 (8.3%) knees, K/L 2: 26 (15.4%) knees, K/L 3: 78 (46.2%) knees K/L 4: 14 (8.3). All plates showed a significant lower degree of unilaterality for any cartilage damage (ranging between 15.5% and 32.0%) than expected (ranging between 27.1% and 50.2%). For any BMLs the degree of unilaterality was lower for the patella, trochlea, medial tibia, and medial femur; for any meniscal damage the degree of unilaterality was lower for all medial meniscal subregions but not lateral. All plates showed higher overall % agreement (range 69-91%) than expected (range 50-87%) for cartilage damage and BMLs. Moderate agreement (w-kappa 0.4-0.6) was observed for patellar and trochlear cartilage damage (0.59 and 0.54) and patellar (0.41) BMLs. Conclusions A higher degree of symmetricity of articular tissue damage than expected by chance was observed in this cohort of subjects with knee pain. These findings support the hypothesis that OA is a multifactorial disease triggered by risk factors on an individual joint level but also by person-based risk factors that predispose joints not only to radiographic OA but also to articular tissue damage commonly associated with OA. References Felson DT, et al. Ann Intern Med 2000; 133:635-646. Niu J, et al. Rheumatology 2003;42:343–348. Disclosure of Interest F. Roemer Shareholder of: Boston Imaging Core Lab (BICL),LLC., Consultant for: Merck Serono, NIH, C. Kwoh Consultant for: Novartis, M. Hannon: None Declared, R. Boudreau: None Declared, S. Green: None Declared, J. Jakicic: None Declared, C. Moore: None Declared, A. Guermazi Shareholder of: Boston Imaging Core Lab (BICL),LLC., Consultant for: Astra Zeneca, Genzyme, Novartis, Stryker,Merck Serono

SAT0493 Medial Meniscal Damage and Extrusion Increase Risk of Incident Radiographic Osteoarthritis

Background Radiography is only able to depict structural joint damage at advanced stages of knee osteoarthritis (OA). Pre-radiographic structural damage to the joint is likely to increase the risk of incident radiographic OA (ROA). The menisci are crucial for preservation of joint integrity and meniscal damage alters joint biomechanics, potentially leading to greater peak stress and a more rapid onset of ROA. Objectives The aim of the study was to assess if presence and severity of meniscal damage and extrusion one year prior to the occurrence of incident ROA (timepoint “P-1”) increases the risk for incident ROA in a nested, matched case-control study in the Osteoarthritis Initiative (OAI) cohort. Methods Participants were drawn from the OAI including 4796 participants with, or at risk of knee OA. We studied 105 knees that developed incident ROA before the 48 month visit. Knees were selected based on the following definition: either KL 0 in both knees or KL1 in both knees or KL 0 in one knee and KL 1 in the contralateral knee at baseline. They were matched with a control knee that did not develop incident ROA, with the same KL grade in both knees at baseline, and for gender and age within 5 years. MR images were acquired at four OAI clinical centers using Siemens Trio 3 T scanners. MRIs were read for medial (m) and lateral (l) meniscal morphology in the m/l anterior horn, m/l body, m/l posterior horn using the semiquantitative MOAKS system. In MOAKS, grade 0 depicts a normal meniscus and grade 1 intrameniscal signal changes, grades 2-5 code different types of meniscal tears while grades 6-8 code different grades of meniscal maceration. Extrusion was scored on coronal images from 0-3. Conditional logistic regression was used to assess the risk of incident ROA based on the extent of meniscal damage and extrusion one year prior to the case defining visit (i.e. at P-1). Results Subjects were on average 58.8 years old (SD ± 8.6), predominantly female (62.9%) and overweight (mean BMI 27.9 SD ± 4.6). Risk of incident ROA was significantly increased for knees exhibiting any pathology of the medial meniscal body at P-1 (OR=2.5 95% confidence interval [CI] [1.28, 4.88]) or anterior lateral horn (OR = 6.67 95% CI[1.98, 22.43]) when compared to the knees with normal meniscal morphology in that region as the reference. Knees with a maximum MOAKS grade of ≥2 in any of the 3 locations of the medial compartment had an increased risk for incident ROA (OR= 4.27, 95% CI [1.66, 10.98]). Knees with any medial extrusion had an increased risk of ROA incidence when compared to knees without medial extrusion (OR=2.77 95% CI [1.47, 5.22]. Conclusions Any pathology of the medial meniscal body or the lateral anterior horn predicted incident ROA one year later. A maximum grade of 2 or more medially predicted incident ROA compared to knees with a maximum grade of 0 or 1. In addition, any medial extrusion increased risk for ROA. Disclosure of Interest A. Guermazi Shareholder of: Boston Imaging Core Lab, LLC, Consultant for: Astra Zeneca, Genzyme, Novartis, Stryker, Merck Serono, C. K. Kwoh: None Declared, M. Hannon: None Declared, D. Hunter Grant/research support from: Australia Research Council Future Fellowship, Consultant for: DonJoy, NIH, Stryker, R. Boudreau: None Declared, F. Eckstein Shareholder of: Chondrometrics, J. Grago: None Declared, Z. Wang: None Declared, F. Roemer: None Declared

380 CARTILAGE THICKNESS, DENUDED AREAS, AND BONE SIZE IN KNEES PRIOR TO TOTAL KNEE REPLACEMENT (TKR) – DATA FROM THE OSTEOARTHRITIS INITIATIVE

380 CARTILAGE THICKNESS, DENUDED AREAS, AND BONE SIZE IN KNEES PRIOR TO TOTAL KNEE REPLACEMENT (TKR) – DATA FROM THE OSTEOARTHRITIS INITIATIVE F. Eckstein, C.K. Kwoh, R. Boudreau, Z. Wang, M.J. Hannon, S. Cotofana, M. Hudelmaier, W. Wirth, A. Guermazi, M. Nevitt, M.R. John, D.J. Hunter, for the OAI investigators. Paracelsus Med. Univ. & Chondrometrics GmbH, Salzburg, Austria; Div. of Rheumatology and Clinical Immunology, Univ. of Pittsburgh and Pittsburgh VAHS, Pittsburgh, PA, USA; Dept. of Epidemiology, Grad. Sch. of Publ. Hlth., Univ. of Pittsburgh, Pittsburgh, PA, USA; BICL Inc. & Boston Univ., Boston, MA, USA; OAI Coordinating Ctr., UCSF, San Francisco, CA, USA; Novartis Pharma AG, Basel, Switzerland; Royal North Shore Hosp. & Northern Clinical Sch., Univ. Sydney, Sydney, Australia