Computer-assisted cup placement techniques in total hip arthroplasty improve accuracy of placement.

Malposition of the acetabular component during hip arthroplasty increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer-assisted orthopaedic systems have been described, but their accuracy is not well established. The purpose of this study was to determine the reproducibility and accuracy of conventional versus computer-assisted techniques for positioning the acetabular component in total hip arthroplasty. Using a lateral approach, 150 cups were placed by 10 surgeons in 10 identical plastic pelvis models (freehand, with a mechanical guide, using computer assistance). Conditions for cup implantations were made to mimic the operating room situation. Preoperative planning was done from a computed tomography scan. The accuracy of cup abduction and anteversion was assessed with an electromagnetic system. Freehand placement revealed a mean accuracy of cup anteversion and abduction of 10 degrees and 3.5 degrees, respectively (maximum error, 35 degrees). With the cup positioner, these angles measured 8 degrees and 4 degrees (maximum error, 29.8 degrees), respectively, and using computer assistance, 1.5 degrees and 2.5 degrees degrees (maximum error, 8 degrees), respectively. Computer-assisted cup placement was an accurate and reproducible technique for total hip arthroplasty. It was more accurate than traditional methods of cup positioning.

Delayed referral and gram-negative organisms increase the conversion thoracotomy rate in patients undergoing video-assisted thoracoscopic surgery for empyema

BACKGROUND: The role of video-assisted thoracoscopic surgery in the treatment of pleural empyema was assessed in a consecutive series of 328 patients between 1992 and 2002. An analysis of the predicting factors for conversion thoracotomy in presumed stage II empyema was performed. METHODS: Empyema stage III with pleural thickening and signs of restriction on computer tomography imaging was treated by open decortication, whereas a thoracoscopic debridement was attempted in presumed stage II disease. Conversion thoracotomy was liberally used during thoracoscopy if stage III disease was found at surgery. Predictive factors for conversion thoracotomy were calculated in a multivariate analysis among several variables such as age, sex, time interval between onset of symptoms and surgery, involved microorganisms, and underlying cause of empyema. RESULTS: Of the 328 patients surgically treated for stage II and III empyema, 150 underwent primary open decortication for presumed stage III disease. One hundred seventy-eight patients with presumed stage II empyema underwent a video-assisted thoracoscopic approach. Of these 178 patients, thoracoscopic debridement was successful in 99 of 178 patients (56%), and conversion thoracotomy and open decortication was judged necessary in 79 of 178 patients (44%). The conversion thoracotomy rate was higher in parapneumonic empyema (55%) as compared with posttraumatic (32%) or postoperative (29%) empyema; however, delayed referral (p < 0.0001) and gram-negative microorganisms (p < 0.01) were the only significant predictors for conversion thoracotomy in a multivariate analysis. CONCLUSIONS: Video-assisted thoracoscopic debridement offers an elegant, minimally invasive approach in a number of patients with presumed stage II empyema. However, to achieve a high success rate with the video-assisted thoracoscopic approach, early referral of the patients to surgery is required. Conversion thoracotomy should be liberally used in case of chronicity, especially after delayed referral (> 2 weeks) and in the presence of gram-negative organisms.

Computer-assisted design and manufacture of implants in the late reconstruction of extensive orbital fractures

To evaluate the use of computer-assisted designed and manufactured (CAD/CAM) orbital wall and floor implants for late reconstruction of extensive orbital fractures.

Computer-assisted arthroplasty using bioengineered autografts

Recent advances in tissue-engineered cartilage open the door to new clinical treatments of joint lesions. Common to all therapies with in-vitro-engineered autografts is the need for optimal fit of the construct to allow screwless implantation and optimal integration into the live joint. Computer-assisted surgery (CAS) techniques are prime candidates to ensure the required accuracy, while at the same time simplifying the procedure. A pilot study has been conducted aiming at assembling a new set of methods to support ankle joint arthroplasty using bioengineered autografts. Computer assistance allows planning of the implant shape on a computed tomography (CT) image, manufacturing the construct according to the plan, and interoperatively navigating the surgical tools for implantation. A rotational symmetric model of the joint surface was used to avoid segmentation of the CT image; new software was developed to determine the joint axis and make the implant shape parameterizable. A complete cycle of treatment from planning to operation was conducted on a human cadaveric foot, thus proving the feasibility of computer-assisted arthroplasty using bioengineered autografts

A Virtual Joystick as a Novel Interaction Modality for Surgeon-Computer Interaction During Computer-Assisted Surgical Procedures

Interacting with a computer system in the operating room (OR) can be a frustrating experience for a surgeon, who currently has to verbally delegate to an assistant every computer interaction task. This indirect mode of interaction is time consuming, error prone and can lead to poor usability of OR computer systems. This thesis describes the design and evaluation of a joystick-like device that allows direct surgeon control of the computer in the OR. The device was tested extensively in comparison to a mouse and delegated dictation with seven surgeons, eleven residents, and five graduate students. The device contains no electronic parts, is easy to use, is unobtrusive, has no physical connection to the computer and makes use of an existing tool in the OR. We performed a user study to determine its effectiveness in allowing a user to perform all the tasks they would be expected to perform on an OR computer system during a computer-assisted surgery. Dictation was found to be superior to the joystick in qualitative measures, but the joystick was preferred over dictation in user satisfaction responses. The mouse outperformed both joystick and dictation, but it is not a readily accepted modality in the OR.

A Virtual Joystick as a Novel Interaction Modality for Surgeon-Computer Interaction During Computer-Assisted Surgical Procedures

Interacting with a computer system in the operating room (OR) can be a frustrating experience for a surgeon, who currently has to verbally delegate to an assistant every computer interaction task. This indirect mode of interaction is time consuming, error prone and can lead to poor usability of OR computer systems. This thesis describes the design and evaluation of a joystick-like device that allows direct surgeon control of the computer in the OR. The device was tested extensively in comparison to a mouse and delegated dictation with seven surgeons, eleven residents, and five graduate students. The device contains no electronic parts, is easy to use, is unobtrusive, has no physical connection to the computer and makes use of an existing tool in the OR. We performed a user study to determine its effectiveness in allowing a user to perform all the tasks they would be expected to perform on an OR computer system during a computer-assisted surgery. Dictation was found to be superior to the joystick in qualitative measures, but the joystick was preferred over dictation in user satisfaction responses. The mouse outperformed both joystick and dictation, but it is not a readily accepted modality in the OR.

Computer-Assisted Numerical Analysis for Oxygen and Carbon Dioxide Mass Transfer in Blood Oxygenators

A two-dimensional numeric simulator is developed to predict the nonlinear, convective-reactive, oxygen mass exchange in a cross-flow hollow fiber blood oxygenator. The numeric simulator also calculates the carbon dioxide mass exchange, as hemoglobin affinity to oxygen is affected by the local pH value, which depends mostly on the local carbon dioxide content in blood. Blood pH calculation inside the oxygenator is made by the simultaneous solution of an equation that takes into account the blood buffering capacity and the classical Henderson-Hasselbach equation. The modeling of the mass transfer conductance in the blood comprises a global factor, which is a function of the Reynolds number, and a local factor, which takes into account the amount of oxygen reacted to hemoglobin. The simulator is calibrated against experimental data for an in-line fiber bundle. The results are: (i) the calibration process allows the precise determination of the mass transfer conductance for both oxygen and carbon dioxide; (ii) very alkaline pH values occur in the blood path at the gas inlet side of the fiber bundle; (iii) the parametric analysis of the effect of the blood base excess (BE) shows that V(CO2) is similar in the case of blood metabolic alkalosis, metabolic acidosis, or normal BE, for a similar blood inlet P(CO2), although the condition of metabolic alkalosis is the worst case, as the pH in the vicinity of the gas inlet is the most alkaline; (iv) the parametric analysis of the effect of the gas flow to blood flow ratio (Q(G)/Q(B)) shows that V(CO2) variation with the gas flow is almost linear up to Q(G)/Q(B) = 2.0. V(O2) is not affected by the gas flow as it was observed that by increasing the gas flow up to eight times, the V(O2) grows only 1%. The mass exchange of carbon dioxide uses the full length of the hollow-fiber only if Q(G)/Q(B) > 2.0, as it was observed that only in this condition does the local variation of pH and blood P(CO2) comprise the whole fiber bundle.