Effect of calibration error on bone tracking accuracy with fluoroscopy.

Model-based 3D-fluoroscopy can quantify joint kinematics with 1 mm and 1 deg accuracy level. A calibration based on the acquisition of devices of known geometry is usually applied to size the system. This study aimed at quantifying the sensitivity of the fluoroscopic pose estimation accuracy specifically to errors in the calibration process, excluding other sources of error. X-ray focus calibration error was quantified for different calibration setups, and its propagation to the pose estimation was characterized in-silico. Focus reference position influenced the calibration error dispersion, while calibration cage pose affected its bias. In the worst-case scenario, the estimation error of the principal point and of the focus distance was lower than 1 mm and 2 mm, respectively. The consequent estimation of joint angles was scarcely influenced by calibration errors. A linear trend was highlighted for joint translations, with a sensitivity proportional to the distance between the model and the image plane, resulting in a submillimeter error for realistic calibration errors. The biased component of the error is compensated when computing relative joint kinematics between two segments.

In vitro quantification of the performance of model-based mono-planar and bi-planar fluoroscopy for 3D joint kinematics estimation.

Model-based mono-planar and bi-planar 3D fluoroscopy methods can quantify intact joints kinematics with performance/cost trade-off. The aim of this study was to compare the performances of mono- and bi-planar setups to a marker-based gold-standard, during dynamic phantom knee acquisitions. Absolute pose errors for in-plane parameters were lower than 0.6 mm or 0.6° for both mono- and bi-planar setups. Mono-planar setups resulted critical in quantifying the out-of-plane translation (error < 6.5 mm), and bi-planar in quantifying the rotation along bone longitudinal axis (error < 1.3°). These errors propagated to joint angles and translations differently depending on the alignment of the anatomical axes and the fluoroscopic reference frames. Internal-external rotation was the least accurate angle both with mono- (error < 4.4°) and bi-planar (error < 1.7°) setups, due to bone longitudinal symmetries. Results highlighted that accuracy for mono-planar in-plane pose parameters is comparable to bi-planar, but with halved computational costs, halved segmentation time and halved ionizing radiation dose. Bi-planar analysis better compensated for the out-of-plane uncertainty that is differently propagated to relative kinematics depending on the setup. To take its full benefits, the motion task to be investigated should be designed to maintain the joint inside the visible volume introducing constraints with respect to mono-planar analysis.

Prosthetic component segmentation with blur compensation: a fast method for 3D fluoroscopy.

A new method for prosthetic component segmentation from fluoroscopic images is presented. The hybrid approach we propose combines diffusion filtering, region growing and level-set techniques without exploiting any a priori knowledge of the analyzed geometry. The method was evaluated on a synthetic dataset including 270 images of knee and hip prosthesis merged to real fluoroscopic data simulating different conditions of blurring and illumination gradient. The performance of the method was assessed by comparing estimated contours to references using different metrics. Results showed that the segmentation procedure is fast, accurate, independent on the operator as well as on the specific geometrical characteristics of the prosthetic component, and able to compensate for amount of blurring and illumination gradient. Importantly, the method allows a strong reduction of required user interaction time when compared to traditional segmentation techniques. Its effectiveness and robustness in different image conditions, together with simplicity and fast implementation, make this prosthetic component segmentation procedure promising and suitable for multiple clinical applications including assessment of in vivo joint kinematics in a variety of cases.

Re-use of explanted osteosynthesis devices: a reliable and inexpensive reprocessing protocol.

INTRODUCTION: Orthopaedic surgical treatments emphasizing immobilization using open reduction and internal fixation with osteosynthesis devices are widely accepted for their efficacy in treating complex fractures and reducing permanent musculoskeletal deformity. However, such treatments are profoundly underutilized in low- and middle-income countries (LMIC), partially due to inadequate availability of the costly osteosynthesis devices. Orthopaedic surgeons in some LMIC regularly re-use osteosynthesis devices in an effort to meet treatment demands, even though such devices typically are regulated for single-use only. The purpose of this study is to report a reprocessing protocol applied to explanted osteosynthesis devices obtained at a leading trauma care hospital. METHODS: Explanted osteosynthesis devices were identified through a Register of Explanted Orthopaedic Prostheses. Guidelines to handle ethical issues were approved by the local Ethical Committee and informed patient consent was obtained at the time of explant surgery. Primary acceptance criteria were established and applied to osteosynthesis devices explanted between 2005 and 2008. A rigorous protocol for conducting decontamination and visual inspection based on specific screening criteria was implemented using simple equipment that is readily available in LMIC. RESULTS: A total of 2050 osteosynthesis devices, including a large variety of plates, screws and staples, were reprocessed using the decontamination and inspection protocols. The acceptance rate was 66%. Estimated labour time and implementation time of the protocol to reprocess a typical osteosynthesis unit (1 plate and 5 screws) was 25 min, with an estimated fixed cost (in Italy) of €10 per unit for implementing the protocol, plus an additional €5 for final sterilization at the end-user hospital site. DISCUSSION: This study was motivated by the treatment demands encountered by orthopaedic surgeons providing medical treatment in several different LMIC and their need for access to basic osteosynthesis devices. The rigorous decontamination protocol and generalized inspection criteria proved useful for efficiently screening a large volume of devices. Given that re-used osteosynthesis devices can yield satisfactory results, this study addresses potential complications of re-used devices and valid concerns that relate to patient safety. Implementing this defined reprocessing protocol into existing re-use practises in LMIC helps to limit the risks of inadequate sterilization and structural failure without adding additional risks to patients receiving re-used devices.

Functional reaching discloses perceptive impairment in diplegic children with cerebral palsy.

The currently accepted definition classifies Cerebral Palsy (CP) as a mere posture and movement disorder. Conversely, some authors have recently associated the presence of several motor dysfunctions exhibited by diplegic children with CP to an impairment in the perceptive system. The aim of the present study was to investigate the influence of the Perceptive Impairment (PI) on motor control and to appraise if the PI can be revealed by a reaching task. A functional reach and touch experiment was accomplished from sitting posture considering different directions and distances. Typically developing and diplegic children with CP were enrolled and, the latter, a priori divided in two subgroups considering a positive or negative diagnosis of PI. The reaching trials were quantified by means of centre of pressure analysis in terms of the overall quality of the task, and accuracy and effectiveness of postural adjustments and Anticipatory Postural Adjustments (APAs). The three groups showed statistically significant differences in terms of percentage of touched target, and of time spent and maximum distance covered to reach the target. In particular, PI caused a major difficulty in accomplishing the reaching tasks, thus a lower autonomy level in action. Overall, the PI strongly affected the anticipatory control system. Children with PI, rarely recruited APAs, each of which was characterized by small amplitude and inaccuracy in direction. The lack of effective APAs indicated how PI strongly influenced the motor control strategy. The present study demonstrates that the PI is a primary syndrome responsible for the long-term prognosis beside the motor and the postural disorders in CP.