The influence of smoothing techniques on the accuracy of the reference finite helical axis when applied to 2D-3D registrations.

Highspeed Biplanar Videoradiography (HSBV) permits recording of 3D bone movements with sub-millimeter precision. 2D-3D registrations are performed to quantify bone movements, providing a series of affine transformation matrices (ATMs). These registrations may result in alignment errors that produce inaccurate kinematics. Smoothing techniques can be applied to the ATMs to reduce these inaccuracies. Which techniques are best for this application remain unknown. The purpose of this study was to investigate the performance of six smoothing techniques on ATMs obtained from HSBV. Performance was assessed by measuring the accuracy of three reference finite helical axis (rFHA) measures during a turntable rotation: orientation, dispersion, and rotation speed difference (RSD = rFHA RS-turntable RS). A 3D printed femur and tibia were mounted to the turntable and rotations recorded with HSBV. The rFHA was calculated for the bones using each smoothing technique and ranked using a Friedman test. The relative percent change to the unsmoothed data was reported. A spline filter with outlier removal (SPOUT) was ranked the best technique, producing the most accurate RSDs for the femur (-79.64%) and tibia (-70.59%). SPOUT was the top performing smoothing technique. Further investigations using SPOUT are required for in-vivo human movements.

Reproducibility and repeatability of a semi-automated pipeline to quantify trapeziometacarpal joint angles using dynamic computed tomography.

BACKGROUND: The trapeziometacarpal (TMC) joint is a mechanically complex joint and is commonly affected by musculoskeletal diseases such as osteoarthritis. Quantifying in vivo TMC joint biomechanics, such as joint angles, with traditional reflective marker-based methods can be difficult due to the joint's location in the hand. Dynamic computed tomography (CT) can facilitate the quantification of TMC joint motion by continuously capturing three-dimensional volumes over time. However, post-processing of dynamic CT datasets can be time intensive and automated methods are needed to reduce processing times to allow for application to larger clinical studies. The purpose of this work is to introduce a fast, semi-automated pipeline to quantify joint angles from dynamic CT scans of the TMC joint and evaluate the associated error in joint angle and translation computation by means of a reproducibility and repeatability study. METHODS: Ten cadaveric hands were scanned with dynamic CT using a passive motion device to move thumbs in a radial abduction-adduction motion. Static CT scans and high-resolution peripheral quantitative CT scans were also acquired to generate high-resolution bone meshes. Abduction-adduction, flexion-extension, and axial rotation angles were computed using a joint coordinate system. Reproducibility and repeatability were assessed using intraclass correlation coefficients, Bland-Altman analysis, and root mean square errors. Target registration errors were computed to evaluate errors associated with image registration. RESULTS: We found good repeatability for flexion-extension, abduction-adduction, and axial rotation angles. Reproducibility was moderate for all three angles. Joint translations exhibited greater repeatability than reproducibility. Specimens with greater joint degeneration had lower repeatability and reproducibility. We found that the difference in resulting joint angles and translations were likely due to differences in segment coordinate system definition between multiple raters, rather than due to registration errors. CONCLUSIONS: The proposed semi-automatic processing pipeline was fast, repeatable, and moderately reproducible when quantifying TMC joint angles and translations. This work provides a range of errors for TMC joint angles from dynamic CT scans using manually selected anatomical landmarks.

Bracing of pectus carinatum: A quantitative analysis.

BACKGROUND/PURPOSE: Primary treatment of pectus carinatum (PC) is performed with an external brace that compresses the protrusion. Patients are 'prescribed' a brace tightening force. However, no visual guides exist to display this force magnitude. The purpose of this study was to determine the repeatability of patients in applying their prescribed force over time and to determine whether the protrusion stiffness influences the patient-applied forces and the protrusion correction rate. METHODS: Twenty-one male participants (12-17years) with chondrogladiolar PC were recruited at the time of brace fitting. Participants were evaluated on three visits: fitting, one month postfitting, and two months postfitting. Differences between prescribed force and patient-applied force were evaluated. Relationships of patient-applied force and correction rate with protrusion stiffness were assessed. RESULTS: Majority of individuals followed for two months (75%) had a significantly different patient-applied force (p<0.05) from their prescribed force. Protrusion stiffness had a positive relationship with patient-applied force, but no relationship with correction rate. CONCLUSION: Patients did not follow their prescribed force. Magnitudes of these differences require further investigation to determine clinical significance. Patient-applied forces were influenced by protrusion stiffness, but correction rate was not. Other factors may influence these variables, such as patient compliance. LEVEL OF EVIDENCE: Treatment Study - Level IV.