The foundations of computer assisted surgery

Using navigation systems in general orthopaedic surgery and, in particular, knee replacement is becoming more and more accepted. This paper describes the basic technological concepts of modern computer assisted surgical systems. It explains the variation in currently available systems and outlines research activities that will potentially influence future products. In general, each navigation system is defined by three components: (1) the therapeutic object is the anatomical structure that is operated on using the navigation system, (2) the virtual object represents an image of the therapeutic object, with radiological images or computer generated models potentially being used, and (3) last but not least, the navigator acquires the spatial position and orientation of instruments and anatomy thus providing the necessary data to replay surgical action in real-time on the navigation system's screen.

CT radiation dose for computer-assisted endoscopic sinus surgery: dose survey and determination of dose-reduction limits

BACKGROUND AND PURPOSE: Computer-assisted navigation is increasingly used in functional endoscopic sinus surgery (FESS) to prevent injury to vital structures, necessitating preparative CT and, thus, radiation exposure. The purpose of our study was to investigate currently used radiation doses for CT in computer-assisted navigation in sinus surgery (CAS-CT) and to assess minimal doses required. MATERIALS AND METHODS: A questionnaire inquiring about dose parameters used for CAS-CT was sent to 30 radiologic institutions. The feasibility of low-dose registration was tested with a phantom. The influence of CAS-CT dose on technical accuracy and on the practical performance of 5 ear, nose, and throat (ENT) surgeons was evaluated with cadaver heads. RESULTS: The questionnaire response rate was 63%. Variation between minimal and maximal dose used for CAS-CT was 18-fold. Phantom registration was possible with doses as low as 1.1 mGy. No dose dependence on technical accuracy was found. ENT surgeons were able to identify anatomic landmarks on scans with a dose as low as 3.1 mGy. CONCLUSIONS: The vast dose difference between institutions mirrors different attitudes toward image quality and radiation-protection issues rather than being technically founded, and many patients undergo CAS-CT at higher doses than necessary. The only limit for dose reduction in CT for computer-assisted endoscopic sinus surgery is the ENT surgeon's ability to cope with impaired image quality, whereas there is no technically justified lower dose limit. We recommend, generally, doses used for the typical diagnostic low-dose sinus CT (120 kV/20-50 mAs). When no diagnostic image quality is needed, even a reduction down to a third is possible.

Vascular adaptation of the internal thoracic artery graft early and late after bypass surgery

OBJECTIVE: Flow mismatch between the supplying artery and the myocardial perfusion region has been observed in patients with internal thoracic artery grafts. Thus coronary flow changes of arterial (internal thoracic artery grafts) and saphenous (saphenous vein grafts) bypass grafts were studied early and late after coronary artery bypass grafting. METHODS: Thirty patients undergoing elective bypass surgery (internal thoracic artery and saphenous vein grafts) were studied intraoperatively and (17 patients) 3 to 10 months postoperatively. Coronary flow was measured intraoperatively with the transit-time Doppler scanning technique. Postoperatively, flow velocity and coronary flow reserve were determined with the Doppler flow wire technique. Quantitative angiographic analysis was used to determine vessel size for calculation of absolute flow. RESULTS: Intraoperatively, internal thoracic artery graft flow was significantly lower than saphenous vein graft flow (31 +/- 8 vs 58 +/- 29 mL/min, P < .01). Postoperatively, internal thoracic artery graft flow increased significantly to 42 +/- 24 mL/min at 3 months and to 56 +/- 30 mL/min (P < .02 vs intraoperative value) at 10 months, respectively. However, saphenous vein graft flow remained unchanged over time (58 +/- 29 to 50 +/- 27 mL/min at 3 months and 46 +/- 27 mL/min at 10 months). Coronary flow reserve was abnormally low intraoperatively in the internal thoracic artery (1.3 +/- 0.3) and saphenous vein (1.6 +/- 0.5) grafts but increased significantly to normal values in both types of graft at follow-up. CONCLUSIONS: Bypass flow of the internal thoracic artery graft is significantly reduced intraoperatively when compared with that of the saphenous vein graft. However, 3 and 10 months after the operation, flow of the internal thoracic artery graft increases significantly and is similar to saphenous vein graft flow. This finding can be explained by an early flow mismatch of the native internal thoracic artery in the presence of a large perfusion territory. During follow-up, there is vascular remodeling of the internal thoracic artery, probably because of endothelium-mediated mechanisms.

Blunt traumatic thoracic aortic injuries: early or delayed repair-results of an American Association for the Surgery of Trauma prospective study

BACKGROUND: The traditional approach to stable blunt thoracic aortic injuries (TAI) is immediate repair, with delayed repair reserved for patients with major associated injuries. In recent years, there has been a trend toward delayed repair, even in low-risk patients. This study evaluates the current practices in the surgical community regarding the timing of aortic repair and its effects on outcomes. METHODS: This was a prospective, observational multicenter study sponsored by the American Association for the Surgery of Trauma. The study included patients with blunt TAI scheduled for aortic repair by open or endovascular procedure. Patients in extremis and those managed without aortic repair were excluded. The data collection included demographics, initial clinical presentation, Injury Severity Scores, type and site of aortic injury, type of aortic repair (open or endovascular repair), and time from injury to aortic repair. The study patients were divided into an early repair (< or = 24 hours) and delayed repair groups (> 24 hours). The outcome variables included survival, ventilator days, intensive care unit (ICU) and hospital lengths of stay, blood transfusions, and complications. The outcomes in the two groups were compared with multivariate analysis after adjusting for age, Glasgow Coma Scale, hypotension, major associated injuries, and type of aortic repair. A second multivariate analysis compared outcomes between early and delayed repair, in patients with and patients without major associated injuries. RESULTS: There were 178 patients with TAI eligible for inclusion and analysis, 109 (61.2%) of which underwent early repair and 69 (38.8%) delayed repair. The two groups had similar epidemiologic, injury severity, and type of repair characteristics. The adjusted mortality was significantly higher in the early repair group (adjusted OR [95% CI] 7.78 [1.69-35.70], adjusted p value = 0.008). The adjusted complication rate was similar in the two groups. However, delayed repair was associated with significantly longer ICU and hospital lengths of stay. Analysis of the 108 patients without major associated injuries, adjusting for age, Glasgow Coma Scale, hypotension, and type of aortic repair, showed that in early repair there was a trend toward higher mortality rate (adjusted OR 9.08 [0.88-93.78], adjusted p value = 0.064) but a significantly lower complication rate (adjusted OR 0.4 [0.18-0.96], adjusted p value 0.040) and shorter ICU stay (adjusted p value = 0.021) than the delayed repair group. A similar analysis of the 68 patients with major associated injuries, showed a strong trend toward higher mortality in the early repair group (adjusted OR 9.39 [0.93-95.18], adjusted p value = 0.058). The complication rate was similar in both groups (adjusted p value = 0.239). CONCLUSIONS: Delayed repair of stable blunt TAI is associated with improved survival, irrespective of the presence or not of major associated injuries. However, delayed repair is associated with a longer length of ICU stay and in the group of patients with no major associated injuries a significantly higher complication rate.

C-Port Flex-A-assisted automated anastomosis for high-flow extracranial-intracranial bypass surgery in patients with symptomatic carotid artery occlusion: a feasibility study. Clinical article

OBJECT: Preliminary experience with the C-Port Flex-A Anastomosis System (Cardica, Inc.) to enable rapid automated anastomosis has been reported in coronary artery bypass surgery. The goal of the current study was to define the feasibility and safety of this method for high-flow extracranial-intracranial (EC-IC) bypass surgery in a clinical series. METHODS: In a prospective study design, patients with symptomatic carotid artery (CA) occlusion were selected for C-Port-assisted high-flow EC-IC bypass surgery if they met the following criteria: 1) transient or moderate permanent symptoms of focal ischemia; 2) CA occlusion; 3) hemodynamic instability; and 4) had provided informed consent. Bypasses were done using a radial artery graft that was proximally anastomosed to the superficial temporal artery trunk, the cervical external, or common CA. All distal cerebral anastomoses were performed on M2 branches using the C-Port Flex-A system. RESULTS: Within 6 months, 10 patients were enrolled in the study. The distal automated anastomosis could be accomplished in all patients; the median temporary occlusion time was 16.6+/-3.4 minutes. Intraoperative digital subtraction angiography (DSA) confirmed good bypass function in 9 patients, and in 1 the anastomosis was classified as fair. There was 1 major perioperative complication that consisted of the creation of a pseudoaneurysm due to a hardware problem. In all but 1 case the bypass was shown to be patent on DSA after 7 days; furthermore, in 1 patient a late occlusion developed due to vasospasm after a sylvian hemorrhage. One-week follow-up DSA revealed transient asymptomatic extracranial spasm of the donor artery and the radial artery graft in 1 case. Two patients developed a limited zone of infarction on CT scanning during the follow-up course. CONCLUSIONS: In patients with symptomatic CA occlusion, C-Port Flex-A-assisted high-flow EC-IC bypass surgery is a technically feasible procedure. The system needs further modification to achieve a faster and safer anastomosis to enable a conclusive comparison with standard and laser-assisted methods for high-flow bypass surgery.