Cannulated screw fixation is currently the treatment of choice for slipped capital femoral epiphyses (SCFE). A SCFE module of the Bonedoc simulator was created in order to test the ability of advanced trainees to place the screw in the correct position, and the practicality of using the simulator within the orthopaedic surgery training curriculum.

Bonedoc (University of Auckland) is a virtual reality simulator of image guided orthopaedic operations1. This simulator runs in Internet Explorer (Microsoft, USA) using the Octaga (Octaga, Norway) plugin. The total download is around 4 MB. The SCFE module was created from a CT scan of a Grade 2 acute on chronic SCFE. DICOM images were imported into 3DView (www.rmrsystems.co.uk) and a mesh created. The generic femur from the DHS module was morphed within the CAD package Blender (Blender.org) to conform to this reconstructed SCFE mesh.

Forty two advanced trainees operated on the same virtual SCFE during a training weekend. The trainees had 25 minutes to become familiar with the simulator and complete the operative case. The trainees performed all tasks relevant to the operation. At the operation’s conclusion the trainees self-assessed their performance. Subsequently the simulator provided surgically relevant objective feedback on aspects such as exact position of the screw, misplaced attempts and the number of x-rays. The results were analysed using SAS (SAS Institute, USA) in subgroups based on year on the scheme, as well as correlated within each operation.

There was no difference in the accuracy with which the virtual slipped capital femoral epiphysis was pinned by trainees in different years in the training programme. However, 26 of the 39 of the virtual screws were placed in the superior direction. There was no correlation between number of X-ray images taken and final accuracy of screw placement. The number of misplaced drill holes was correlated both with number of X-ray images taken (p< 0.01) and operative time (p< 0.01) but not with final accuracy of the screw. An increase in misplaced attempts was correlated with angulation errors in the anterior plane (p< 0.01). There was no correlation between the trainees’ self assessment and any of the measured variables.

The Bonedoc simulator provides a means to test trainees on technical aspects of a surgical procedure. It provides objective results, which can mimic real world outcomes. In addition, the ability to test all trainees on the same virtual operative case allows standardisation of assessment. All trainees completed the task to a similar level of accuracy, which may reflect the overall skill level in advanced trainees within the New Zealand. However, many trainees placed the screw in the superior portion of the femoral head, which is thought to increase the risk of avascular necrosis2. Further work is required to evaluate how accurately performance on the simulator predicts performance in the operating theatre

Background: Computer Assisted Orthopaedic Surgery continues to evolve. Electromagnetic Computer Navigation has recently emerged as a new modality of CAOS that promises increased accuracy, as well as increased portability and practicality. However, there are very few studies examining this new technique and comparing it to conventional TKJR.

Methods: We carried out a prospective randomised study comparing the conventional jig-based technique of TKJR versus EM navigation (Medtronic). We examined parameters such as surgical time, blood loss, days in hospital post operatively, and complication rate. Further, we assessed the accuracy of the two techniques with the CT Scan “Perth Protocol”. Parameters measured included femoral component flexion, extension, alignment and rotation, tibial alignment, posterior slope and femorotibial mismatch.

Results: Mean Oxford Knee Score was 47.5; the mean age was 70 (67–74). 43% were female and 57% male. Half were navigated and half conventional. The mean Hb change in 48 hours, as a reflection of blood loss was 14.5% for the conventional group and 14.25% for the navigated group. Mean Surgical Time for the conventional group was 90 minutes and the navigated was 120 minutes. The average stay in hospital for both groups was 5 days after the operation. The measurements according to the Perth Protocol suggested increased accuracy in femoral alignment, posterior slope, and reduced femorotibial mismatch. Femoral rotation was not significantly different and femoral flexion extension was not significantly different. The only major complication occurred in the navigated group with a dislocated knee in a patient afflicted with multiple sclerosis.

Summary: These preliminary results suggest that EM navigation is a safe and accurate technique. It has the additional advantage of portability and increased user friendliness compared to other navigation methods. When compared to conventional jig-based techniques, it is more accurate, increases surgical time by an average 30 minutes, there is no significant difference in blood loss at 48 hours, patient’s stay in hospital is not prolonged and the rate of complications does not exceed that of conventional surgery.

Electromagnetic Navigation is in its infancy, and the authors feel that surgical time and accuracy will improve with more frequent use and the development of increasingly more sophisticated software packages. Our study continues.