Electromagnetic bone segment tracking to control femoral derotation osteotomy-A saw bone study

Abstract

Correction of rotational gait abnormalities is common practice in pediatric orthopaedics such as in children with cerebral palsy. Femoral derotation osteotomy is established as a standard treatment, however, different authors reported substantial variability in outcomes following surgery with patients showing over- or under-correction. Only 60% of the applied correction is observed postoperatively, which strongly suggests intraoperative measurement error or loss of correction during surgery. This study was conducted to verify the impact of error sources in the derotation procedure and assess the utility of a newly developed, instrumented measurement system based on electromagnetic tracking aiming to improve the accuracy of rotational correction. A supracondylar derotation osteotomy was performed in 21 artificial femur sawbones and the amount of derotation was quantified during the procedure by the tracking system and by nine raters using a conventional goniometer. Accuracy of both measurement devices was determined by repeated computer tomography scans. Average derotation measured by the tracking system differed by 0.1° ± 1.6° from the defined reference measurement . In contrast, a high inter-rater variability was found in goniometric measurements (range: 10.8° ± 6.9°, mean interquartile distance: 6.6°). During fixation of the osteosynthesis, the tracking system reliably detected unintentional manipulation of the correction angle with a mean absolute change of 4.0° ± 3.2°. Our findings show that conventional control of femoral derotation is subject to relevant observer bias whereas instrumental tracking yields accuracy better than ±2°. The tracking system is a step towards more reliable and safe implementation of femoral correction, promising substantial improvements of patient safety in the future. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1106-1112, 2017.

Electromagnetic tracking for femoral derotation osteotomy—an in vivo study

“…In a previous saw bone study we introduced the system and presented results of the system in an in vitro setting. 21 The data of this trial suggested In the present study, the mean deviation of the EMT system to the CT reference measurement was 2.6˚and therefore, almost within the tolerance of the CT measurement error. This indicates that EMT tracking can deliver a precise dimension of the derotation performed in surgery.…”

“…Overall 10 derotations in nine patients were used for the evaluation of the EMT system. Mean age at the point of surgery was 23 years (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). Because of the design of the study and the requirements of the ethics committee only adult patients were included.…”

“…The objective of the present study was the clinical evaluation of an electromagnetic tracking system designed to improve accuracy of intraoperative derotation control. In a previous saw bone study we introduced the system and presented results of the system in an in vitro setting . The data of this trial suggested an improvement in the accuracy of derotation measurement with EM‐Tracking.…”

“…The intra‐operative measurement of the derotation angle and the effect of plate fixation during surgery have not been subject to profound investigation so far, but may contribute to the discrepancies seen between the desired and actual outcome of FDO as well . A recently published study from our facility showed that the traditional measurement of derotation with K‐wires and a standard goniometer is prone to large error due to high intra‐ and inter‐rater variability . This could be a partial explanation for both the problem of over‐ and under‐correction as well as the discrepancies between desired and actual outcome of the FDO as published by Kay et al and Dreher et al In the paper mentioned above, we introduced an electromagnetic tracking system for derotation osteotomies.…”

“…20 A recently published study from our facility showed that the traditional measurement of derotation with K-wires and a standard goniometer is prone to large error due to high intra-and inter-rater variability. 21 Ethical review committee statement: The local ethics committee approved the study. Correspondence to: Thomas Dreher (T: 0049-6221-56-0; F: 0049-6221-5626348; E-mail: thomas.dreher@med.uni-heidelberg.de) This could be a partial explanation for both the problem of over-and under-correction as well as the discrepancies between desired and actual outcome of the FDO as published by Kay et al 13 and Dreher et al 11 In the paper mentioned above, we introduced an electromagnetic tracking system for derotation osteotomies.…”