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Computer-aided navigation in secondary reconstruction of post-traumatic deformities of the zygoma
Journalof Cranio-MaxillofaeialSurgery(1998)26, 68-69 © 1998EuropeanAssociationfor Cranio-MaxillofacialSurgery
Letter to the Editor Table - Test record 2 on the Polhemus tracking system in the presence of an operating table (distance 50 cm) a Langenbeck retractor (distance 10 cm) and a drill handle (distance 10 cm)
Computer-aided navigation in secondary reconstruction of post-traumatic deformities of the zygoma E Watzinger, F. Wanschitz, A. Wagner, G. Enislidis, W Millesi, A. Baumann, R. Ewers Journal of Cranio-MaxillofacialSurgery25 (1997) 198-202
Polhemus deviation [ram] 0.6 0.7 0.8 1.2 1.6 1.8 2.4 2.7 2.9 3 3.4 3.6 3.7 4.2 4.3 4.8 4.9 5 6 6.1 6.2 6.6 7.2 7.3 7.8 7.9 8.4 8.6 9.6 10.2 12 12.6 13.2 15.6 16.8 19.2 21.6 22.8 24.3
Sir We hold the opinion that the electromagnetic tracking system described (Polhemus) is definitely not suitable for computer assisted surgery. Recent investigations with the method, which have been described by Marmulla et al (1997) show how the accuracy of the Polhemus electromagnetic system ranges between 0.6mm and 24.3mm, delivering serious spherical deviations in the presence of metal, rotating instruments and Circuits (Table). In an unfavourable environment even deviations of up to 38 mm can be registered. Besides static deviations of electromagnetic fields, caused by the operating table or other metallic objects in the environment of an operating room, there are severe dynamic distortions caused by the use of surgical instruments (for example, a Langenbeck retractor or a drill handle). The dynamic deviation caused by these tools ranges up to 20 mm and depends on the distance between surgical tool and the electromagnetic sensor. Investigations on the accuracy of the Polhemus electromagnetic tracking device mentioned of the Vienna Department of Biomedical Engineering and Physics (Birkfelner et al., 1997) confirm these results. A system with an inherent 95% percentile deviation of 1.5 cm or more cannot be a helpful device for surgeons, nor can it be used as a navigation system. Furthermore, the intraoperative inaccuracy increases while two sensors are used, one for the positioning of the patient's head and one for the navigation of a tool. It is not understood how the authors can find satisfactory operation results in the secondary reconstruction of post-traumatic deformities of the zygoma while they use an electromagnetic tracking system in the environment of an operating room.
Frequency 5 6 4 4 4 3 2 6 3 6 4 7 4 3 3 4 3 3 3 2 2 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1
Mean inherent precision: 4.9 ram, standard deviation 4.7 ram; 95% percentile on 15.6 ram.
References Birkfelner W.., F. Watzinger, F. Wanschitz, G Enislidis, D. Rafolt, R. Nowotony, R. Ewers, H. Bergmann: Evaluation of magnetic position digitizers for computer assisted surgery. Computer assisted surgery (1997), Abstracts from CIS 97, S17-098 Marmulla R., M. Hilbert, N. Niederdellmann: Inherent precision of mechanical, infrared and laser-guided navigation systems for computer-assisted surgery. J. Cranio-Maxillofac. Surg 25
Dr Dr R. Marmulla Department of Oral and Maxillofacial Surgery University Hospital Regensburg Germany
(1997) 198-202.
Prof Dr Dr H. Niederdellmann Department of Oral and Maxillofacial Surgery University Hospital Regensburg Germany 68
Letter to the Editor Table - Test record 2 on the Polhemus tracking system in the presence of an operating table (distance 50 cm) a Langenbeck retractor (distance 10 cm) and a drill handle (distance 10 cm)
Computer-aided navigation in secondary reconstruction of post-traumatic deformities of the zygoma E Watzinger, F. Wanschitz, A. Wagner, G. Enislidis, W Millesi, A. Baumann, R. Ewers Journal of Cranio-MaxillofacialSurgery25 (1997) 198-202
Polhemus deviation [ram] 0.6 0.7 0.8 1.2 1.6 1.8 2.4 2.7 2.9 3 3.4 3.6 3.7 4.2 4.3 4.8 4.9 5 6 6.1 6.2 6.6 7.2 7.3 7.8 7.9 8.4 8.6 9.6 10.2 12 12.6 13.2 15.6 16.8 19.2 21.6 22.8 24.3
Sir We hold the opinion that the electromagnetic tracking system described (Polhemus) is definitely not suitable for computer assisted surgery. Recent investigations with the method, which have been described by Marmulla et al (1997) show how the accuracy of the Polhemus electromagnetic system ranges between 0.6mm and 24.3mm, delivering serious spherical deviations in the presence of metal, rotating instruments and Circuits (Table). In an unfavourable environment even deviations of up to 38 mm can be registered. Besides static deviations of electromagnetic fields, caused by the operating table or other metallic objects in the environment of an operating room, there are severe dynamic distortions caused by the use of surgical instruments (for example, a Langenbeck retractor or a drill handle). The dynamic deviation caused by these tools ranges up to 20 mm and depends on the distance between surgical tool and the electromagnetic sensor. Investigations on the accuracy of the Polhemus electromagnetic tracking device mentioned of the Vienna Department of Biomedical Engineering and Physics (Birkfelner et al., 1997) confirm these results. A system with an inherent 95% percentile deviation of 1.5 cm or more cannot be a helpful device for surgeons, nor can it be used as a navigation system. Furthermore, the intraoperative inaccuracy increases while two sensors are used, one for the positioning of the patient's head and one for the navigation of a tool. It is not understood how the authors can find satisfactory operation results in the secondary reconstruction of post-traumatic deformities of the zygoma while they use an electromagnetic tracking system in the environment of an operating room.
Frequency 5 6 4 4 4 3 2 6 3 6 4 7 4 3 3 4 3 3 3 2 2 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1
Mean inherent precision: 4.9 ram, standard deviation 4.7 ram; 95% percentile on 15.6 ram.
References Birkfelner W.., F. Watzinger, F. Wanschitz, G Enislidis, D. Rafolt, R. Nowotony, R. Ewers, H. Bergmann: Evaluation of magnetic position digitizers for computer assisted surgery. Computer assisted surgery (1997), Abstracts from CIS 97, S17-098 Marmulla R., M. Hilbert, N. Niederdellmann: Inherent precision of mechanical, infrared and laser-guided navigation systems for computer-assisted surgery. J. Cranio-Maxillofac. Surg 25
Dr Dr R. Marmulla Department of Oral and Maxillofacial Surgery University Hospital Regensburg Germany
(1997) 198-202.
Prof Dr Dr H. Niederdellmann Department of Oral and Maxillofacial Surgery University Hospital Regensburg Germany 68