Characterizing Osteophyte Formation in Knee Osteoarthritis: Application of Machine Learning Quantification of a Computerized Tomography Cohort: Implications for Treatment.

BACKGROUND: Osteophytes are commonly used to diagnose and guide knee osteoarthritis (OA) treatment, but their causes are unclear. Although they are not typically the focus of knee arthroplasty surgeons, they can predict case difficulty and length. Furthermore, their extent and location may yield much information about the knee joint status. The aims of this computed tomography-based study in patients awaiting total or partial knee arthroplasty were to: (1) measure osteophyte volume in anatomical subregions and relative change as total volume increases; (2) determine whether medial and/or lateral OA affects osteophyte distribution; and (3) explore relationships between osteophytes and OA severity. METHODS: Data were obtained from 4,928 computed tomography scans. Machine-learning-based imaging analyses enabled osteophyte segmentation and quantification, divided into anatomical regions. Mean three-dimensional joint space narrowing was assessed in medial and lateral compartments. A Bayesian model assessed the uniformity of osteophyte distribution. We correlated femoral osteophyte volumes with B-scores, a validated OA status measure. RESULTS: Total tibial (25%) and femoral osteophyte volumes (75%) within each knee correlated strongly (R2 = 0.85). Medial osteophytes (65.3%) were larger than lateral osteophytes (34.6%), with similar proportions in both the femur and tibia. Osteophyte growth was found in all compartments, and as total osteophyte volume increased, the relative distribution of osteophytes between compartments did not markedly change. No evidence of variation was found in the regional distribution of osteophyte volume between knees with medial, lateral, both, or no three-dimensional joint space narrowing in the femur or tibia. There was a direct relationship between osteophyte volume and OA severity. CONCLUSIONS: Osteophyte volume increased in both medial and lateral compartments proportionally with total osteophyte volume, regardless of OA location. The peripheral position of femoral osteophytes does not appear to contribute to load-bearing. This suggests that osteophytic growth represents a 'whole-knee'/global response. This work may have broad applications for knee OA, both surgically and nonoperatively.

Machine-learning, MRI bone shape and important clinical outcomes in osteoarthritis: data from the Osteoarthritis Initiative.

OBJECTIVES: Osteoarthritis (OA) structural status is imperfectly classified using radiographic assessment. Statistical shape modelling (SSM), a form of machine-learning, provides precise quantification of a characteristic 3D OA bone shape. We aimed to determine the benefits of this novel measure of OA status for assessing risks of clinically important outcomes. METHODS: The study used 4796 individuals from the Osteoarthritis Initiative cohort. SSM-derived femur bone shape (B-score) was measured from all 9433 baseline knee MRIs. We examined the relationship between B-score, radiographic Kellgren-Lawrence grade (KLG) and current and future pain and function as well as total knee replacement (TKR) up to 8 years. RESULTS: B-score repeatability supported 40 discrete grades. KLG and B-score were both associated with risk of current and future pain, functional limitation and TKR; logistic regression curves were similar. However, each KLG included a wide range of B-scores. For example, for KLG3, risk of pain was 34.4 (95% CI 31.7 to 37.0)%, but B-scores within KLG3 knees ranged from 0 to 6; for B-score 0, risk was 17.0 (16.1 to 17.9)% while for B-score 6, it was 52.1 (48.8 to 55.4)%. For TKR, KLG3 risk was 15.3 (13.3 to 17.3)%; while B-score 0 had negligible risk, B-score 6 risk was 35.6 (31.8 to 39.6)%. Age, sex and body mass index had negligible effects on association between B-score and symptoms. CONCLUSIONS: B-score provides reader-independent quantification using a single time-point, providing unambiguous OA status with defined clinical risks across the whole range of disease including pre-radiographic OA. B-score heralds a step-change in OA stratification for interventions and improved personalised assessment, analogous to the T-score in osteoporosis.

Opportunistic Quantitative CT Bone Mineral Density Measurement at the Proximal Femur Using Routine Contrast-Enhanced Scans: Direct Comparison With DXA in 355 Adults.

For patients undergoing routine contrast-enhanced CT examinations, an opportunity exists for concurrent osteoporosis screening without additional radiation exposure or patient time using proximal femur CT X-ray absorptiometry (CTXA). We investigated the effect of i.v. contrast enhancement on femoral neck CTXA T-score measurement compared with DXA. This cohort included 355 adults (277 female; mean age, 59.7 ± 13.3 years; range, 21 to 90 years) who underwent standard contrast-enhanced CT assessment at 120 kVp over an 8-year interval, as well as DXA BMD assessment within 100 days of the CT study (mean 46 ± 30 days). Linear regression and a Bland-Altman plot were performed to compare DXA and CTXA results. CTXA diagnostic sensitivity and specificity was evaluated with DXA as the reference standard. There was good correlation between DXA and CTXA (r2 = 0.824 for both areal BMD and T-scores) and the SD of the distribution of residuals was 0.063 g/cm2 or 0.45 T-score units. There was no trend in differences between the two measurements and a small bias was noted with DXA T-score +0.18 units higher than CTXA. CTXA had a sensitivity for discriminating normal from low bone mineral density of 94.9% (95% CI, 90.6% to 97.4%). For opportunistic osteoporosis screening at routine post-contrast abdominopelvic CT scans, CTXA produces T-scores similar to DXA. Because femoral neck CTXA BMD measurement is now included in the WHO Fracture Risk Assessment Tool (FRAX) tool, this opportunistic method could help to increase osteoporosis screening because it can be applied regardless of the clinical indication for CT scanning. © 2016 American Society for Bone and Mineral Research.

Direct Comparison of Unenhanced and Contrast-Enhanced CT for Opportunistic Proximal Femur Bone Mineral Density Measurement: Implications for Osteoporosis Screening.

OBJECTIVE: For patients undergoing contrast-enhanced CT examinations that include the proximal femur, an opportunity exists for concurrent screening bone mineral density (BMD) measurement. We investigated the effect of IV contrast enhancement on CT-derived x-ray absorptiometry areal BMD measurement. MATERIALS AND METHODS: Our cohort included 410 adults (mean age, 65.3 ± 10.0 years; range, 49-95 years) who underwent split-bolus CT urography at 120 kVp. Areal femoral neck BMD in g/cm(2) was measured on both unenhanced and contrast-enhanced CT series with asynchronous phantom calibration. Constant offset and multiplicative factor corrections for the contrast-enhanced series were derived from the Bland-Altman plot linear regression slopes. RESULTS: Mean unenhanced and contrast-enhanced areal femoral neck BMD values were 0.681 ± 0.118 and 0.713 ± 0.123 g/cm(2), respectively. The SD of the distribution of residuals for the constant offset and multiplicative model corrections were 0.0232 and 0.0231, respectively. The constant offset correction associated with contrast enhancement was 0.032 ± 0.023 g/cm(2), which corresponds to 0.29 ± 0.21 T-score units using the CT-derived x-ray absorptiometry young normal areal femoral neck BMD reference SD of 0.111 g/cm(2). CONCLUSION: For the purposes of opportunistic osteoporosis screening, contrast-enhanced abdominopelvic CT studies are equivalent to unenhanced CT and can therefore be used for femoral neck BMD assessment. This measure could greatly enhance osteoporosis screening.

Quantitative computed tomography and opportunistic bone density screening by dual use of computed tomography scans.

Central dual-energy X-ray absorptiometry (DXA) of the lumbar spine and proximal femur is the preferred method for bone mineral density (BMD) testing. Despite the fracture risk statistics, osteoporosis testing with DXA remains underused. However, BMD can also be assessed with quantitative computed tomography (QCT) that may be available when access to DXA is restricted. For patients undergoing a primary CT study of the abdomen or pelvis, a potential opportunity exists for concurrent BMD screening by QCT without the need for any additional imaging, radiation exposure, or patient time.

CTXA hip--an extension of classical DXA measurements using quantitative CT.

Bone mineral density (BMD) estimates for the proximal femur using Dual Energy X-ray Absorptiometry (DXA) are currently considered the standard for making a diagnosis of osteoporosis in an individual patient using BMD alone. We have compared BMD results from a commercial Quantitative CT (QCT) BMD analysis system, "CTXA Hip", which provides clinical data for the proximal femur, to results from DXA. We have also used CTXA Hip to determine cortical and trabecular contributions to total BMD. Sixty-nine patients were scanned using 3D QCT and DXA. CTXA Hip BMD measurements for Total Hip and Femoral Neck were compared to DXA results. Twenty-two women were scanned at 0, 1, 2 years and CTXA Hip and DXA results analyzed for long-term reproducibility. Long-term reproducibility calculated as root-mean-square averages of SDs in vivo was 0.012 g/cm2 (CV = 1.8%) for CTXA Total Hip and 0.011 g/cm2 (CV = 2.0%) for CTXA Femoral Neck compared to 0.014 g/cm2 (CV = 2.0%) and 0.016 g/cm2 (CV = 2.7%), respectively, for DXA. The correlation of Total Hip BMD CTXA vs. DXA was R = 0.97 and for Femoral Neck was R = 0.95 (SEE 0.044 g/cm2 in both cases). Cortical bone comprised 62±5% (mean ± SD) of total hipbone mass in osteoporotic women. CTXA Hip provides substantially the same clinical information as conventional DXA and in addition provides estimates of BMD in separate cortical and trabecular bone compartments, which may be useful in evaluation of bone strength.