Contrast-enhanced micro-computed tomography of articular cartilage morphology with ioversol and iomeprol.

Non-ionic, low-osmolar contrast agents (CAs) used for computed tomography, such as Optiray (ioversol) and Iomeron (iomeprol), are associated with the reduced risk of adverse reactions and toxicity in comparison with ionic CAs, such as Hexabrix. Hexabrix has previously been used for imaging articular cartilage but has been commercially discontinued. This study aimed to evaluate the efficacy of Optiray and Iomeron as alternatives for visualisation of articular cartilage in small animal joints using contrast-enhanced micro-computed tomography (CECT). For this purpose, mouse femora were immersed in different concentrations (20%-50%) of Optiray 350 or Iomeron 350 for periods of time starting at five minutes. The femoral condyles were scanned ex vivo using CECT, and regions of articular cartilage manually contoured to calculate mean attenuation at each time point and concentration. For both CAs, a 30% CA concentration produced a mean cartilage attenuation optimally distinct from both bone and background signal, whilst 5-min immersion times were sufficient for equilibration of CA absorption. Additionally, plugs of bovine articular cartilage were digested by chondroitinase ABC to produce a spectrum of glycosaminoglycan (GAG) content. These samples were immersed in CA and assessed for any correlation between mean attenuation and GAG content. No significant correlation was found between attenuation and cartilage GAG content for either CAs. In conclusion, Optiray and Iomeron enable high-resolution morphological assessment of articular cartilage in small animals using CECT; however, they are not indicative of GAG content.

Kinematic function of knee implant designs across a range of daily activities.

The aim of this randomized controlled trial was to measure and compare six-degree-of-freedom (6-DOF) knee joint motion of three total knee arthroplasty (TKA) implant designs across a range of daily activities. Seventy-five TKA patients were recruited to this study and randomly assigned a posterior-stabilized (PS), cruciate-retaining (CR), or medial-stabilized (MS) implant. Six months after surgery, patients performed five activities of daily living: level walking, step-up, step-down, sit-to-stand, and stand-to-sit. Mobile biplane X-ray imaging was used to measure 6-DOF knee kinematics and the center of rotation of the knee in the transverse plane for each activity. Mean 6-DOF knee kinematics were consistently similar for PS and CR, whereas MS was more externally rotated and abducted, and lateral shift was lower across all activities. Peak-to-peak anterior drawer for MS was also significantly lower during walking, step-up, and step-down (p < 0.017). The center of rotation of the knee in the transverse plane was located on the medial side for MS, whereas PS and CR rotated about the lateral compartment or close to the tibial origin. The kinematic function of MS was more similar to that of the healthy knee than PS and CR based on reduced paradoxical anterior translation at low flexion angles and a transverse center of rotation located in the medial compartment. Overall, 6-DOF knee joint motion for PS and CR were similar across all daily activities, whereas that measured for MS was appreciably different. The kinematic patterns observed for MS reflects a highly conforming medial articulation in the MS design.

A microCT imaging protocol for reproducible and efficient quantitative morphometric analysis (QMA) of joint structures of the in situ mouse tibio-femoral joint.

Micro-computed tomography (microCT) offers a three-dimensional (3D), high-resolution technique for the visualisation and analysis of bone microstructure. Using contrast-enhanced microCT, this capability has been expanded in recent studies to include cartilage morphometry and whole joint measures, known together as quantitative morphometric analysis (QMA). However, one of the main challenges in quantitative analysis of joint images is sensitivity to joint pose and alignment, which may influence measures related to both joint space and joint biomechanics. Thus, this study proposes a novel microCT imaging protocol for reproducible and efficient QMA of in situ mouse tibio-femoral joint. This work consists of two parts: an in situ diffusion kinetics study for a known cationic iodinated contrast agent (CA4+) for QMA of the cartilage, and a joint positioning and image processing workflow for whole joint QMA. In the diffusion kinetics study, 8 mice were injected at both of their tibio-femoral joints with distinct CA4+ concentrations and diffusion times. The mice were scanned at different time points after injection, and evaluated using attenuation and cartilage QMA measures. Results show that cartilage segmentation and QMA could be performed for CA4+ solution at a concentration of 48 mg/ml, and that reliable measurement and quantification of cartilage were achieved after 5 min of diffusion following contrast agent injection. We established the joint positioning and image processing workflow by developing a novel positioning device to control joint pose during scanning, and a spherical harmonics-based image processing workflow to ensure consistent alignment during image processing. Both legs of seven mice were scanned 10 times, 5 prior to receiving CA4+ and 5 after, and evaluated using whole joint QMA parameters. Joint QMA evaluation of the workflow showed excellent reproducibility; intraclass correlation coefficients ranged from 0.794 to 0.930, confirming that the imaging protocol enables reproducible and efficient QMA of joint structures in preclinical models, and that contrast agent injection did not cause significant alteration to the measured parameters.