Dynamic RSA for the evaluation of inducible micromotion of Oxford UKA during step-up and step-down motion

Background and purpose — Implant inducible micromotions have been suggested to reflect the quality of the fixation interface. We investigated the usability of dynamic RSA for evaluation of inducible micromotions of the Oxford Unicompartmental Knee Arthroplasty (UKA) tibial component, and evaluated factors that have been suggested to compromise the fixation, such as fixation method, component alignment, and radiolucent lines (RLLs). Patients and methods — 15 patients (12 men) with a mean age of 69 (55–86) years, with an Oxford UKA (7 cemented), were studied after a mean time in situ of 4.4 (3.6–5.1) years. 4 had tibial RLLs. Each patient was recorded with dynamic RSA (10 frames/second) during a step-up/step-down motion. Inducible micromotions were calculated for the tibial component with respect to the tibia bone. Postoperative component alignment was measured with model-based RSA and RLLs were measured on screened radiographs. Results — All tibial components showed inducible micromotions as a function of the step-cycle motion with a mean subsidence of up to −0.06 mm (95% CI: −0.10 to −0.03). Tibial component inducible micromotions were similar for cemented fixation and cementless fixation. Patients with tibial RLLs had 0.5° (95% CI: 0.18–0.81) greater inducible medio-lateral tilt of the tibial component. There was a correlation between postoperative posterior slope of the tibial plateau and inducible anterior-posterior tilt. Interpretation — All patients had inducible micromotions of the tibial component during step-cycle motion. RLLs and a high posterior slope increased the magnitude of inducible micromotions. This suggests that dynamic RSA is a valuable clinical tool for the evaluation of functional implant fixation

Automated measurement of diagnostic angles for hip dysplasia

A fully automatic method for measuring diagnostic angles of hip dysplasia is presented. The method consists of the automatic segmentation of CT images and detection of anatomical landmarks on the femur and acetabulum. The standard angles used in the diagnosis of hip dysplasia are subsequently automatically calculated. Previous work in automating the measuring of angles required the manual segmentation or delineation of the articular joint surface. In the current work automatic segmentation is established using graph-cuts with a cost function based on a sheetness score to detect the sheet-like structure of the bone. Anatomical landmarks are subsequently detected using heuristics based on ray-tracing and the distance to the approximated acetabulur joint surface. Standard diagnositic angles are finally calculated and presented for interpretation. Experiments using 26 patients, showed a good agreement with gold standard manual measurements by an expert radiologist as performed in daily practice. The mean difference for the five angles was between-1:1 and 2:0 degrees with a concordance correlation coefficient between 0:87 and 0:93. The standard deviation varied between 2:3 and 4:1 degrees. These values correspond to values found in evaluating interobserver and intraobserver variation for manual measurements. The method can be used in clinical practice to replace the current manual measurements performed by radiologists. In the future, the method will be integrated into an intraoperative surgical guidance system

Reliable Angle Assessment During Periacetabular Osteotomy with a Novel Device

We developed and assessed a measuring device for intraoperative assessment of the acetabular index and center edge angle during acetabular reorientation in periacetabular osteotomy. We asked whether reliable assessment of angles could be made using the device; to be reliable we presumed the variability of angle measurements should not exceed that of inherent variability when assessing angles on radiographs (± 5°). The device was mounted bilaterally on the pelvis, and using fluoroscopy, angle measurements were obtained with adjustable measuring discs. We conducted a cadaver study to assess intraobserver and interobserver variability of the device and to assess if pelvic positioning influenced variation of measurements. Intraoperative measurements of 35 consecutive patients were compared with measurements on postoperative radiographs. Intraoperatively obtained angle measurements differed less than ± 5° from measurements on postoperative radiographs and the intraobserver and interobserver variability of the device were confined within ± 5°. Positioning did not influence the variation of angle measurements beyond intraobserver variability of the device when applying arcs of tilt and rotation of ± 12.5°. We believe the device is a potentially helpful tool in the periacetabular osteotomy. It is simple to use and facilitates repeated reliable angle measurements during acetabular reorientation, making intraoperative radiographs unnecessary