IMPLEMENTING RADIOSTEREOMETRIC ANALYSIS IN A LOW DOSE BIPLANAR SLOT SCANNER

Abstract

Slipped Capital Femoral Epiphysis (SCFE) is a condition affecting young adolescents in which the proximal femoral metaphysis 'slips' in relation to the capital epiphysis. If left untreated, children are at an increased risk of developing avascular necrosis and secondary osteoarthritis. In-situ fixation remains central in the standard of care. Conventional radiography does not afford accurate post-surgical assessment of physeal fusion; leading to avascular necrosis in cases of persistent physeal non-union. Therefore, a clinical need exists to accurately quantify post-surgical physeal micromotion as an indicator of surgical success. RadioStereometric Analysis (RSA) offer better accuracy than conventional radiography, but requires serial X-ray exams increasing cumulative radiation exposure, concerning in paediatric populations. In the pursuit of the As Low As Reasonably Achievable (ALARA) principle and predominantly in the paediatric realm, there is a need to reduce radiation dose; the EOS imager offers to redefine ALARA. The EOS imager is a biplanar imaging system with three-dimensional capabilities and has demonstrated radiation reduction of 6 to 9 times depending on anatomical location. The purpose of this thesis was to uniquely demonstrate the RSA technique in the EOS imager. A phantom study was conducted to compare RSA accuracy and precision in the digital flat-panel and the EOS imaging modalities. The accuracy and precision of RSA in the EOS imager and in the standard technique was better than 0.05mm±0.06mm and 0.37°±0.36° and 0.07mm±0.05mm and 0.18°±0.32°, respectively. The phantom study demonstrated RSA accuracy and precision deemed acceptable for successful post-surgical physeal micromotion assessment in the EOS modality. Next, a human study was conducted to demonstrate the feasibility of the RSA technique in the EOS imager in human subjects, and to provide an indication of the precision of the system. Three subjects were recruited from an on-going Total Knee Arthroplasty (TKA) research study at the local hospital. Employing a zero displacement double exam protocol, subjects were imaged in the EOS imager. The precision of EOS RSA was better than ±0.84mm and ±0.91°, near the limit of accepted RSA precision and was confounded by patient motion during EOS scans. This thesis is the first demonstration of the EOS RSA technique and the results of the thesis suggest acceptable accuracy in quantifying post-surgical SCFE micromotion. Improvements in precision can be explored with patient restraints. This technique can then be used to quantify post-surgical longitudinal micromotion or instantaneous micromotion with an inducible displacement protocol. Metrics stemming from the increasing employment of this assessment technique can be used to indicate post-surgical stability and outcomes in the SCFE population.