Choice of knee cartilage thickness change metric for different treatment goals in efficacy studies.

INTRODUCTION: In knee osteoarthritis, local increase and decrease in cartilage thickness has been observed over short time intervals. Hence, averaging cartilage change across large regions may not capture the complexity of structural alterations in disease progression. This study aims to examine the relative performance of different metrics of cartilage thickness change for different clinical studies scenarios. MATERIALS AND METHODS: Metrics for assessing cartilage thickness change were characterized by conventional measures of change versus absolute values (the magnitude) of change, and by different methods of summarizing change over (sub-) regions. Sample sizes for these metrics were derived for 6-24-month observation periods, and for different treatment efficacies. Treatment effects were derived from an observational trial with 6-, 12-, and 24-month follow-up, ranging from slowing cartilage loss to stimulating cartilage growth. RESULTS: Projected sample sizes ranged from 10 to >10,000 patients/arm (median = 164), depending on metric choice, treatment efficacy, and observation period. The smallest sample sizes for metrics using magnitude of change typically were half the size of those using conventional measures of change. Extreme values, e.g., minimum change or average of last four-ordered values of absolute change, required smaller sample sizes than metrics averaging over one or more regions. CONCLUSIONS: Metrics using extreme magnitudes of change were most efficient in detecting differences between treatment and placebo, i.e., involved the smallest sample sizes across different DMOAD study lengths and treatment efficacies. Ancillary metrics can be used to clarify whether differences between treatment and placebo indicate structural benefit when needed.

Plain radiography or magnetic resonance imaging (MRI): Which is better in assessing outcome in clinical trials of disease-modifying osteoarthritis drugs? Summary of a debate held at the World Congress of Osteoarthritis 2014.

Osteoarthritis (OA) is the most common disease of synovial joints and currently lacks treatment options that modify structural pathology. Imaging is ideally suited for directly evaluating efficacy of disease-modifying OA drugs (DMOADs) in clinical trials, with plain radiography and MRI being most often applied. The current article is based on a debate held on April 26, 2014, at the World Congress of Osteoarthritis: The authors were invited to contrast strengths and limitations of both methods, highlighting scientific evidence on reliability, construct-validity, and correlations with clinical outcome, and comparing their sensitivity to change in knee OA and sensitivity to DMOAD treatment. The authors concluded that MRI provides more comprehensive information on articular tissues pathology, and that implementation of radiography in clinical trials remains a challenge. However, neither technique has thus far been demonstrated to be strongly superior over the other; for the time being it therefore appears advisable to use both in parallel in clinical trials, to provide more evidence on their relative performance. Radiographic JSW strongly depends on adequate positioning; it is not specific to cartilage loss but also to the meniscus. MRI provides somewhat superior sensitivity to change compared with the commonly used non-fluoroscopic radiographic acquisition protocols, and has recently provided non-location-dependent measures of cartilage thickness loss and gain, which are potentially more sensitive in detecting DMOAD effects than radiographic JSW or region-specific MRI. Non-location-dependent measures of cartilage thickness change should thus be explored further in context of anabolic and anti-catabolic DMOADs.

The relationship between prevalent medial meniscal intrasubstance signal changes and incident medial meniscal tears in women over a 1-year period assessed with 3.0 T MRI.

OBJECTIVE: Intrasubstance meniscal signal changes not reaching the articular surface on fast spin echo (FSE) sequences are considered to represent mucoid degeneration on MRI. The aim of this study was to evaluate the association of prevalent intrasubstance signal changes with incident tears of the medial meniscus detected on 3.0 T MRI over a 1-year period. MATERIALS AND METHODS: A total of 161 women aged ≥ 40 years participated in a longitudinal 1-year observational study of knee osteoarthritis. MRI (3.0 T) was performed at baseline and 12-month follow-up. The anterior horn, body, and posterior horn of the medial meniscus were scored by two experienced musculoskeletal radiologists using the Boston-Leeds Osteoarthritis Knee Score (BLOKS) system. Four grades were used to describe the meniscal morphology: grade 0 (normal), grade 1 (intrasubstance signal changes not reaching the articular surface), grade 2 (single tears), and grade 3 (complex tears and maceration). Fisher's exact test and the Cochran-Armitage trend test were performed to evaluate whether baseline intrasubstance signal changes (grade 1) predict incident meniscal tears/maceration (grades 2 and/or 3) in the same subregion of the medial meniscus, when compared to subregions without pathology as the reference group (grade 0). RESULTS: Medial meniscal intrasubstance signal changes at baseline did not predict tears at follow-up when evaluating the anterior and posterior horns (left-sided p-values 0.06 and 0.59, respectively). No incident tears were detected in the body. CONCLUSION: We could not demonstrate an association between prevalent medial meniscal intrasubstance signal changes with incident tears over a 1-year period.

Rates of change and sensitivity to change in cartilage morphology in healthy knees and in knees with mild, moderate, and end-stage radiographic osteoarthritis: results from 831 participants from the Osteoarthritis Initiative.

OBJECTIVE: To study the longitudinal rate of (and sensitivity to) change of knee cartilage thickness across defined stages of radiographic osteoarthritis (OA), specifically healthy knees and knees with end-stage radiographic OA. METHODS: One knee of 831 Osteoarthritis Initiative participants was examined: 112 healthy knees, without radiographic OA or risk factors for knee OA, and 719 radiographic OA knees (310 calculated Kellgren/Lawrence [K/L] grade 2, 300 calculated K/L grade 3, and 109 calculated K/L grade 4). Subregional change in thickness was assessed after segmentation of weight-bearing femorotibial cartilage at baseline and 1 year from coronal magnetic resonance imaging (MRI). Regional and ordered values (OVs) of change were compared by baseline radiographic OA status. RESULTS: Healthy knees displayed small changes in plates and subregions (±0.7%; standardized response mean [SRM] ±0.15), with OVs being symmetrically distributed close to zero. In calculated K/L grade 2 knees, changes in cartilage thickness were small (<1%; minimal SRM -0.22) and not significantly different from healthy knees. Knees with calculated K/L grade 3 showed substantial loss of cartilage thickness (up to -2.5%; minimal SRM -0.35), with OV1 changes being significantly (P < 0.05) greater than those in healthy knees. Calculated K/L grade 4 knees displayed the largest rate of loss across radiographic OA grades (up to -3.9%; minimal SRM -0.51), with OV1 changes also significantly (P < 0.05) greater than in healthy knees. CONCLUSION: MRI-based cartilage thickness showed high rates of loss in knees with moderate and end-stage radiographic OA, and small rates (indistinguishable from healthy knees) in mild radiographic OA. From the perspective of sensitivity to change, end-stage radiographic OA knees need not be excluded from longitudinal studies using MRI cartilage morphology as an end point.

Comparison of radiographic joint space width with magnetic resonance imaging cartilage morphometry: analysis of longitudinal data from the Osteoarthritis Initiative.

OBJECTIVE: Magnetic resonance imaging (MRI) and radiography are established imaging modalities for the assessment of knee osteoarthritis (OA). The objective of our study was to compare the responsiveness of radiographic joint space width (JSW) with MRI-derived measures of cartilage morphometry for OA progression in participants from the Osteoarthritis Initiative (OAI). METHODS: This study examined the baseline and 12-month visits of a subset of 150 subjects from the OAI. Measurement of radiographic JSW was facilitated by the use of automated software that delineated the femoral and tibial margins of the joint. Measures of medial compartment minimum JSW and JSW at fixed locations were compared with cartilage morphometry measures derived from MRI. The results were stratified by Kellgren/Lawrence (K/L) scale grade and by tibiofemoral anatomic axis angle. In order to examine the relative responsiveness of various techniques, we calculated the standardized response mean (SRM) between the 2 visits. RESULTS: The SRM for radiographic JSW measured at the optimal location was -0.32 compared with -0.39 for the most responsive MRI measure. For the subgroup with a K/L scale grade of 2 or 3, the most responsive SRM values were -0.34 for radiographic JSW and -0.42 for MRI. CONCLUSION: Our study demonstrates that new measures using a software analysis of digital knee radiographic images are comparable with MRI in detecting OA progression, and potentially superior when considering the cost-effectiveness of the 2 imaging modalities.

A three-dimensional quantitative method to measure meniscus shape, position, and signal intensity using MR images: a pilot study and preliminary results in knee osteoarthritis.

This pilot study presents a technique for three-dimensional and quantitative analysis of meniscus shape, position, and signal intensity and compares results in knees with (n = 20) and without (n = 11) radiographic osteoarthritis. 3-T MR images with 2mm section thickness were acquired using a proton density-weighted, fat-suppressed, coronal, fast spin-echo sequence. Segmentation of the tibial, femoral, and external surface of the medial meniscus and the tibial joint surface was performed. Three-dimensional parameters were computed to describe the shape, position, and signal intensity of the entire meniscus and three subregions (body, anterior, and posterior horn). Key results included a greater size (i.e., volume, surface areas, and thickness), increased medial extrusion (i.e., greater extrusion distance, greater meniscal area uncovered by tibial surface), and elevated signal intensity of the medial meniscus in osteoarthritis than in nonosteoarthritis knees, particularly in the meniscus body. These results need to be confirmed in larger cohorts, preferably under weight-bearing conditions.

An efficient subset of morphological measures for articular cartilage in the healthy and diseased human knee.

The relationship between three-dimensional, MRI-based morphologic measurements commonly taken of knee cartilage was examined to determine whether a subset of variables fully reflects differences observed in cartilage in cross-sectional and longitudinal studies. The benefits of a subset of measures include increased statistical power due to reduced multiple comparisons, improved understanding of relationships between the morphologic measures of articular knee cartilage, and greater efficiency in reporting results. One hundred fifty-two women (77 healthy and 75 with knee osteoarthritis) had coronal 3-T MR images of the knee acquired at baseline and at 24 months. Measures of femorotibial cartilage morphology (surface area, thickness, volume, etc.) were determined in the medial and lateral tibia and femur. Cartilage thickness (mean cartilage thickness over the total area of the [subchondral] bone), total subchondral bone area, and percentage of denuded area of the subchondral bone were found to explain over 90% of the cross-sectional and longitudinal variation observed in other measures of cartilage morphology commonly reported in knee osteoarthritis. Hence, these three measures of cartilage morphology explain nearly all variation in a larger set of common cartilage morphology measures both cross-sectionally and longitudinally, both in healthy and in osteoarthritic knees. These variables hence define an efficient subset for describing structural status and change in osteoarthritic cartilage.

The Relationship between Meniscal Tears and Meniscal Position.

OBJECTIVE: To investigate how different types of meniscal tears predispose to different patterns of meniscal position in subjects with and without symptomatic knee osteoarthritis (OA). METHODS: A cross-sectional analysis of 161 women participating in an observational study to evaluate knee OA progression was performed using baseline MRI data. Meniscal morphologic features were scored in three separate locations. Meniscal position measures were determined for extrusion and proportion of coverage. Analysis was performed using multiple linear regression models treating each tear type as an individual variable with a binary response. RESULTS: Complex tears, cysts and maceration of the medial meniscus were associated with more medial (p=0.0004, p=0.004, p <0.0001, respectively) and anterior extrusion (p =0.03, p=0.03, p<0.0001, respectively) than normal menisci. Horizontal tears of the lateral meniscus had more lateral (p=0.005) and anterior extrusion (p<0.0001) than normal menisci. Anterior and body tears of the medial meniscus were associated with more anterior extrusion (p=0.0006, p=0.01, respectively), whereas meniscal body tears alone had more medial extrusion than normal menisci (p= 0.0002). Meniscal body tears of the lateral meniscus had more lateral extrusion than normal menisci (p=0.01). CONCLUSION: Anterior horn and meniscal body tears and the more severe macerated and complex tear types predisposed to more medial meniscal extrusion. Laterally, only meniscal body and horizontal tears significantly affected extrusion, potentially reflecting a lower overall prevalence of lateral meniscal tears. These results may have important implications in identifying tear types associated with more meniscal dysfunction, with the ultimate goal of identifying those at greatest risk for knee OA progression.

Does the use of ordered values of subregional change in cartilage thickness improve the detection of disease progression in longitudinal studies of osteoarthritis?

OBJECTIVE: To propose a novel strategy for more efficiently measuring changes in cartilage thickness in osteoarthritis (OA) using magnetic resonance imaging, and to hypothesize that determining the magnitude of thickness change independent of the anatomic location provides improved discrimination between healthy subjects and OA participants longitudinally. METHODS: A total of 148 women were imaged; 90 were Kellgren/Lawrence (K/L) grade 0, 30 were K/L grade 2, and 28 were K/L grade 3. Magnetic resonance images (3T) were acquired at baseline and at 24 months. Changes in femorotibial cartilage thickness were determined in 5 tibial and 3 femoral medial and lateral subregions, respectively (conventional approach). The new strategy provided ordered values of subregional change in each compartment, ranked according to the direction and magnitude of change. RESULTS: Using the new ordered values approach, the minimal P value for the differences in 2-year change in medial cartilage thickness of K/L grade 3 and K/L grade 0 participants was 0.001 (Wilcoxon test), with 4 ordered medial subregions differing significantly between both groups. With the conventional approach, only 1 medial subregion differed significantly between K/L grade 3 and K/L grade 0 (P = 0.037). Cartilage thickening was significantly greater in K/L grade 2 versus K/L grade 0 participants in 1 medial subregion using the conventional approach (P = 0.016), and in 2 medial subregions (minimal P = 0.007) using the ordered values approach. CONCLUSION: The novel ordered values approach is more sensitive in detecting cartilage thinning in K/L grade 3 and cartilage thickening in K/L grade 2 versus K/L grade 0 participants. The new method may be particularly useful in the context of other comparisons, e.g., a group treated with a disease-modifying OA drug versus one treated with a placebo.

Longitudinal quantitative MR imaging of cartilage morphology in the presence of gadopentetate dimeglumine (Gd-DTPA).

MRI-based cartilage morphometry can monitor cartilage loss in osteoarthritis. Intravenous Gd-DTPA injection is needed for compositional (proteoglycan) cartilage imaging with delayed gadolinium enhanced MRI (dGEMRIC). However, longitudinal changes of cartilage morphology have not been compared in the presence and absence of Gd-DTPA. Baseline and 2-year follow-up images were acquired in 41 female participants with definite medial radiographic osteoarthritis, both before and 2 h after Gd-DTPA injection, and cartilage thickness was measured. In the absence of Gd-DTPA, a 2.6% reduction in cartilage thickness was observed between baseline and follow-up in the central subregion of the medial femorotibial compartment (standardized response mean [SRM]= -0.33; P<0.05), but only a 0.7% reduction (SRM= -0.10; P=0.51) in the presence of Gd-DTPA. The findings suggest that morphometric cartilage measurement in the presence of Gd-DTPA needs to undergo further validation, before one can recommend longitudinal dGEMRIC and morphological cartilage imaging to be performed in a single session.

Do MRI features at baseline predict radiographic joint space narrowing in the medial compartment of the osteoarthritic knee 2 years later?

PURPOSE: The purpose of the study was to relate magnetic resonance imaging (MRI) features at baseline with radiographically determined joint space narrowing (JSN) in the medial compartment of the knee after 2 years in a group of patients with symptomatic osteoarthritis at multiple joint sites. MATERIALS AND METHODS: MRI of the knee and standardized radiographs were obtained at baseline and after 2 years in 186 patients (81% female; aged 43-76 years; mean 60 years). MRI was analyzed for bone marrow lesions, cysts, osteophytes, hyaline cartilage defects, joint effusion, and meniscal pathology in the medial compartment. Radiographs were scored semiquantitatively for JSN in the medial tibiofemoral joint using the Osteoarthritis Research Society International (OARSI) atlas. Radiological progression was defined as > or =1 grade increase. Associations between baseline magnetic resonance (MR) parameters and subsequent radiographic JSN changes were assessed using logistic regression. Relative risk (RR) was then calculated. RESULTS: Radiographic progression of JSN was observed in 17 (9.1%) of 186 patients. Eleven patients had a Kellgren and Lawrence (KL) score of > or =2. A significant association was observed between all patients and meniscal tears (RR 3.57; confidence interval (CI) 1.08-10.0) and meniscal subluxation (RR 2.73; CI 1.20-5.41), between KL < 2 and meniscal subluxation (RR 11.3; CI 2.49-29.49) and KL > or = 2 and meniscus tears (RR 8.91; CI 1.13-22.84) and radiographic JSN 2 years later. Follow-up MR in 15 of 17 patients with progressive JSN showed only new meniscal abnormalities and no progression of cartilage loss. CONCLUSION: Meniscal pathology (tears and/or meniscal subluxation) was the only MRI parameter to be associated with subsequent radiographic progression of JSN in the medial tibiofemoral compartment on a radiograph 2 years later, as assessed by the OARSI score.

Urinary TIINE concentrations in a randomized controlled trial of doxycycline in knee osteoarthritis: implications of the lack of association between TIINE levels and joint space narrowing.

OBJECTIVE: To use the collagenase cleavage site neoepitope, TIINE, a marker of type II collagen breakdown in cartilage, to analyze the mechanism underlying the slowing of joint space narrowing (JSN) in patients with knee osteoarthritis treated with doxycycline. METHODS: The creatinine-adjusted urinary TIINE concentration was determined at baseline and every 6 months thereafter in a subset of patients who completed a 30-month randomized, placebo-controlled study of the effect of doxycycline on radiographic progression of JSN. The subset was selected a priori to permit comparison of 60 radiographic progressors with 60 radiographic nonprogressors. JSN was determined in highly standardized, semiflexed anteroposterior images. RESULTS: The coefficient of variation of TIINE concentrations over the 5 study visits was 30%. At the 5 semiannual followup visits, the mean TIINE concentration for doxycycline-treated patients was higher than that for the placebo group. In both treatment groups, the correlation between TIINE levels and JSN in the index knee was weak (for doxycycline, r(2) = 0.06, P = 0.08; for placebo, r(2) = 0.06, P = 0.05). CONCLUSION: High variability from visit to visit limits the sensitivity of the TIINE assay for detecting changes in individual patients and restricts its utility to group comparisons. The increase in TIINE concentration with treatment indicates that inhibition of collagenase-mediated breakdown of type II collagen in articular cartilage is unlikely to have accounted for the observed reduction of JSN in the index knees of patients in the doxycycline treatment group.

Bone marrow edema-like lesions change in volume in the majority of patients with osteoarthritis; associations with clinical features.

It has been suggested that bone marrow edema-like (BME) lesions in the knee are associated with progression of osteoarthritis (OA). The purpose of our study in patients with OA was to evaluate prospectively changes of BME lesions over 2 years and their relationship with clinical features. Magnetic resonance (MR) images of the knee were obtained from 182 patients (20% male; aged 43-76 years; mean age 59 years) who had been diagnosed with familial symptomatic OA at multiple joint sites. MR images were made at baseline and at 2 years follow-up. BME lesions in 2 years were associated with clinical features assessed by Western Ontario and McMaster Universities Osteoarthritis (WOMAC) scores. A total of 327 BME lesions were recorded. Total size of BME lesions changed in 90 patients (66%). Size of individual lesions changed in 147 foci (45%): new lesions appeared in 69 (21%), existing lesions disappeared in 32 (10%), increased in size in 26 (8%) and decreased in size in 20 (6%) lesions. Increase or decrease of BME lesions, over a 2-year time period, was not associated with severity of WOMAC scores. BME lesions fluctuated in the majority of patients with OA over a 2-year time period. These changes were not associated with severity of WOMAC scores at the study end point.

Quantitative imaging of cartilage morphology at 3.0 Tesla in the presence of gadopentate dimeglumine (Gd-DTPA).

MRI-based cartilage morphometry was previously validated in the absence of gadopentate dimeglumine (Gd-DTPA). However, Gd-DTPA is required for compositional (proteoglycan) imaging using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC). Therefore, the effect of Gd-DTPA on cartilage morphometry was studied. A total of 165 female participants (67 with and 98 without osteoarthritis [OA]) were imaged at 3.0 Tesla before and 2 hr after intravenous Gd-DTPA injection. Flip angles in post-Gd-DTPA scans varied between 12 degrees and 35 degrees . Cartilage volume and thickness of post- vs. pre-Gd-DTPA scans showed intraclass correlation coefficients (ICCs) of 0.85 > or = r > or = 0.95, mean differences between -2.1% and +1.1%, and standard deviations (SDs) of differences between 4.7% and 9.2%. Mixed-effect models found no consistent impact of flip angle and OA status on post- vs. pre-Gd-DTPA differences. Accurate morphological measurements of cartilage can be obtained after Gd-DTPA injection, allowing compositional and morphological imaging to be combined into one session.

Measurement of radiographic joint space width in the tibiofemoral compartment of the osteoarthritic knee: comparison of standing anteroposterior and Lyon schuss views.

OBJECTIVE: To evaluate progression of joint space narrowing in radiographs of osteoarthritic (OA) knees imaged in both the standing anteroposterior (AP) and the Lyon schuss positions, using alternative methods to measure joint space width (JSW). METHODS: Standing AP (extended view) and Lyon schuss (posteroanterior [PA] view, with 20-30 degrees of flexion) radiographic images of 58 OA knees were obtained twice (at baseline and 2 years later). With both methods, fluoroscopy was used to align the anterior and posterior margins of the medial or lateral tibial plateau with the central x-ray beam. Minimum JSW, mean JSW, and joint space area (JSA) of the medial or lateral femorotibial joint space were measured using a new digital image analysis system. The effects of knee flexion versus extension and parallel versus nonparallel tibial plateau alignment were evaluated with respect to the reproducibility of JSW in repeated examinations (intraclass correlation coefficient [ICC]), the mean of within-knee standard deviations of repeated measurements (SD(m)), and the sensitivity to changes in JSW in serial radiographs (standardized response mean [SRM]). RESULTS: The performance of the new software, as assessed by the reproducibility of repeated measurements of minimum JSW on the same image, was excellent in both the standing AP (ICC = 0.98) and Lyon schuss radiographs (2 SD(m) = 0.5 mm, ICC = 0.98). The reproducibility in different radiographs of the same knee was not evaluated. However, over 2 years, the mean (+/- SD) decrease in the minimum JSW of OA knees was 0.17 +/- 0.75 mm in standing AP radiographs (P not significant) and 0.24 +/- 0.50 mm in Lyon schuss views (P = 0.007), with SRMs of 0.23 and 0.48, respectively. The quality of alignment of the tibial plateau was satisfactory (<1 mm between anterior and posterior margins of the medial tibial plateau) in 66% of the pairs of Lyon schuss radiographs and in 57% of the pairs of standing AP radiographs. In the Lyon schuss radiographs, SRM was highly dependent on tibial plateau alignment. Minimum JSW was more sensitive to change than was mean JSW or JSA, in paired Lyon schuss radiographs that exhibited satisfactory alignment. CONCLUSION: Compared with the standing AP radiograph, PA imaging of the knee in 20-30 degrees flexion (the schuss position) increases the reproducibility of radiographic JSW measurements in OA knees and the sensitivity to change in JSW in serial radiographs. Sensitivity to change in minimum JSW is notably increased by aligning the medial tibial plateau with the central x-ray beam in the Lyon schuss radiograph.

Assessment of specific mRNA levels in cartilage regions in a lapine model of osteoarthritis.

Osteoarthritis (OA) is the most common form of arthritis and patients with meniscal and ligament injuries of the knee are at high risk to develop the disease. The purpose of this study was to evaluate molecular and structural changes occurring in four articular cartilage (AC) regions from the knees of anterior cruciate ligament (ACL)-transected rabbits at 3 and 8 weeks post-surgery. Rabbit AC from the lateral and medial femoral condyles (LFC and MFC) as well as from the medial and lateral tibial plateau (MTP and LTP) were processed for histology and for semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for a subset of relevant molecules (collagen II, aggrecan. biglycan, decorin, fibromodulin, MMP-1, -3, -13, and TIMP-1). While the most severe histological changes were observed in the MTP starting as early as 3 weeks post-ACL transection based on Mankin scores, histological examination demonstrated a progression of osteoarthritic changes in the MFC from 3 to 8 weeks post-surgery. In contrast, very few changes were observed within both the LFC and LTP, and these changes did not worsen with increasing time after surgery. The water content increased significantly in the MFC at 8 weeks post-ACL transection and at both 3 and 8 weeks post-ACL transection in the MTP. Significant decreases in DNA content were observed for the MFC, LTP and MTP at 8 weeks post-ACL transection. Total RNA yields from the MFC and MTP were significantly elevated at 8 weeks post-ACL transection, while in the lateral compartment total RNA was unchanged following ACL transection. Analysis of mRNA levels for a subset of matrix molecules, proteinases and proteinase inhibitors, by RT-PCR demonstrated significant region-specific changes at the mRNA level following ACL transection. These results show that following ACL transection, complex molecular, as well as structural changes occur early in cartilage and that the observed changes are both region-specific and time-dependent.