Implementation of a miniaturised navigation system in head and neck surgery for the detection and removal of foreign bodies

The removal of embedded blast-generated fragments from soft tissue is very difficult, especially in the head and neck regions. First, because many retained foreign materials are non-metallic and can, therefore, not be detected by fluoroscopy, and second, because a broad exploration of the soft tissue is not possible in the facial area for functional and cosmetic reasons. Intraoperative navigation computer-assisted surgery (CAS) may facilitate the retrieval of foreign bodies and reduce exploration trauma. In a blind trial, five test specimens of different materials (glass, metal, wood, plastic, and stone) were inserted on the left and right sides of the head and neck of ten body donors through an intraoral incision. A second physician then detected and removed the foreign bodies from one side of the body without and from the other side of the body with navigation. We measured the duration of surgery, the extent of tissue trauma caused during surgery, the time it took to remove the foreign bodies, and the subjective evaluation of the usefulness of navigation. With the aid of the navigation system, the various foreign bodies were detected after an average of 26.7 (±35.1) s (p < 0.0001) and removed after an average of 79.1 (±66.2) s (p = 0.0239), with an average incision length of 10.0 (±3.5) mm. Without the navigation system, the foreign bodies were located after an average of 86.5 (±77.7) s and removed after an average of 74.1 (±45.9) s, with an average incision length of 13.0 mm (±3.6) mm (=0.0007). Intraoperative navigation systems are a valuable tool for removing foreign bodies from the soft tissue of the face and neck. Both the duration of surgery and the incision length can be reduced using navigation systems. Depending on the material of the foreign bodies and the signal intensity in the CT/MRI scanner, however, the detection reliability varies. All in all, navigation is considered to be a useful tool.

The forces generated within the musculature of the left ventricular wall

OBJECTIVES

To test the hypothesis that two populations of myocardial fibres-fibres aligned parallel to the surfaces of the wall and an additional population of fibres that extend obliquely through the wall-when working in concert produce a dualistic, self stabilising arrangement.

METHODS

Assessment of tensile forces in the walls of seven porcine hearts by using needle probes. Ventricular diameter was measured with microsonometry and the intracavitary pressure through a fluid filled catheter. Positive inotropism was induced by dopamine, and negative inotropism by thiopental. The preload was raised by volume load and lowered by withdrawal of blood. Afterload was increased by inflation of a balloon in the aortic root. The anatomical orientation of the fibres was established subsequently in histological sections.

RESULTS

The forces in the fibres parallel to the surface decreased 20-35% during systolic shrinkage of the ventricle, during negative inotropism, and during ventricular unloading. They increased 10-30% on positive inotropic stimulation and with augmentation in preload and afterload. The forces in the oblique transmural fibres increased 8-65% during systole, on positive inotropic medication, with an increase in afterload and during ventricular shrinkage, and decreased 36% on negative inotropic medication. There was a delay of up to 147 ms in the drop in activity during relaxation in the oblique transmural fibres.

CONCLUSION

Although the two populations of myocardial fibres are densely interwoven, it is possible to distinguish their functions with force probes. The delayed drop in force during relaxation in obliquely oriented fibres indicates that they are hindered in their shortening to an extent that parallels any increase in mural thickness. The transmural fibres, therefore, contribute to stiffening of the ventricular wall and hence to confining ventricular compliance.