Selected publications

1. Chir Organi Mov. 2003 Jul-Sep;88(3):273-80.
   Computer-assisted tridimensional preoperative planning in hip revision surgery
   Toni A, Traina F, Viceconti M
   It is often difficult to obtain excellent clinical results in complex cases of hip replacement surgery. Over recent years, in order to improve the success rate of this type of surgery, prosthetic implants that are more ductile and more reliable have been developed. At the same time, important progress has been made in improving the accuracy of surgical method. A great deal of effort has been made to improve methods of preoperative planning. The world over, computerized systems that aid the surgeon in his or her clinical practice (CAOS systems) have been developed. The authors present Hip-op, a new CAOS type system, for preoperative planning. In particular, the use of Hip-op in some very complex cases of hip revision surgery is reported. Based on clinical experience, it is believed that Hip-op is a useful system, one that is easy to use, and that it is capable of improving the accuracy of surgery.
   PMID: 15146944 [PubMed - indexed for MEDLINE]
2. Langenbecks Arch Surg. 2004 Oct;389(5):400-4. Epub 2004 Jan 15.
   New aspects and approaches in pre-operative planning of hip reconstruction: a computer simulation.
   Viceconti M, Chiarini A, Testi D, Taddei F, Bordini B, Traina F, Toni A
   BACKGROUND: All computer-aided surgery technologies assume that the surgeon knows the best position for the implant components. However, there is indirect evidence that simple anatomical information may not be sufficient for the surgeon to decide size and position of the implant in a repeatable manner. METHOD: In the present study we estimated the variability in choosing the size and position of the components of a cementless total hip replacement (THR), using template-on-radiograph as well as computed tomography (CT)-based computer-aided planning. In addition, using a computer model, we assessed the sensitivity to such variability of implant fitting, location of the joint centre, skeletal range of motion, and resting length of major hip muscles. Using templates, surgeons selected the size with variability up to 2.5 mm for the stem and up to 4 mm for the socket. A similar variability was also observed when the CT-based planning program was used. RESULTS: No major differences were found between surgeons. The standard deviation over repeated planning sessions of the selected position for each component, using the CT-based planning software, was found to be 3.9 mm and 8.9 degrees . CONCLUSION: On the basis of the computer simulation, this variability did not affect the selected biomechanical parameters in a drastic way, although some differences were observed, especially in the lever arm of the hip muscles.
   PMID: 14727119 [PubMed - indexed for MEDLINE]
3. Med Inform Internet Med. 2003 Mar;28(1):59-71.
   Accuracy and repeatability of cementless total hip replacement surgery in patients with deformed anatomies
   Lattanzi R, Grazi E, Testi D, Viceconti M, Cappello A, Toni A
   The present study is aimed to assess the repeatability of orthopaedic surgeons in planning total hip replacement surgery, and the Planned-vs.-Achieved accuracy obtainable with a conventional unassisted surgical procedure. A CT-based surgical planning system called Hip-Op was used for pre-operative planning the pose of the cementless components. The study group included only patients affected by severe deformities of the hip joint. In the repeatability study three surgeons were asked to repetitively plan the same three cases in a blind way. There was agreement among surgeons and also consistency for each surgeon in planning the implant position, while the most expert surgeon was more repeatable in planning the implant orientation. For all patients of the study group, the Planned-vs.-Achieved accuracy was computed as the difference between the spatial position of both prosthetic components derived from the post-operative CT scans and that achieved by the surgeon in the pre-operative planning. The average differences for the stem were lower than 5 mm for the position, and lower than 5 degrees for the orientation. For the socket the average differences increased to 8 mm and 10 degrees. The study shows the need for a more informative planning environment and for intra-operative supports, especially when deformed anatomies are involved.
   Publication Types: Clinical Trial Validation Studies
   PMID: 12851057 [PubMed - indexed for MEDLINE]
4. Med Eng Phys. 2003 Jun;25(5):371-7.
   CT-based surgical planning software improves the accuracy of total hip replacement preoperative planning.
   Viceconti M, Lattanzi R, Antonietti B, Paderni S, Olmi R, Sudanese A, Toni A
   The present study is aimed to compare accuracy and the repeatability in planning total hip replacements with the conventional templates on radiographs to that attainable on the same clinical cases when using CT-based planning software. The sizes of the cementless components planned with new computer aided preoperative planning system called Hip-Op and with standard templates were compared to those effectively implanted. The study group intentionally included only difficult clinical cases. The most common aetiology was congenital dysplasia of hip (65.6%). The Hip-Op planning system allowed the surgeons to obtain a preoperative planning more accurate than with templates, especially for the socket. Assuming correct a size planned one calliper above or below that implanted the accuracy increased from 83% for the stem and 69% for the socket when using templates to 86% for the stem and 93% for the socket when using the Hip-Op system. The repeatability of the Hip-Op system was found comparable to that of the template procedure, which is much more familiar to the surgeons. Furthermore, the repeatability of the preoperative planning with the Hip-Op system was consistent between surgeons, independently from their major or minor experience. The study clearly shows the advantages of a three-dimensional computer-based preoperative planning over the traditional template planning, especially when deformed anatomies are involved. The surgical planning performed with the Hip-Op system is accurate and repeatable, especially for the socket and for less experienced surgeons.
   Publication Types: Clinical Trial Validation Studies
   PMID: 12711234 [PubMed - indexed for MEDLINE]
5. Med Inform Internet Med. 2002 Jun;27(2):71-83.
   Hip-Op: an innovative software to plan total hip replacement surgery
   Lattanzi R, Viceconti M, Zannoni C, Quadrani P, Toni A
   This paper describes an innovative surgical simulation software environment for the pre-operative planning of total hip replacement surgery. The software is a CT-based three-dimensional planning environment, with a user-friendly graphic user interface based on the multimodal display visualization paradigm. Although it relies on a fully three dimensional internal representation, this approach represents the relevant anatomical objects by means of multiple views, each simulating a different medical imaging modality familiar to the medical professional. In the Hip-Op program the multimodal display interface integrates four different display modalities: orthogonal radiographs, Blended slices, CT slices, and arbitrary slices. A conventional surface rendering view is also available. The user 'navigates' the prosthetic components, which are dynamically selected from a library of available parts, within the CT volume while the implant and the patient anatomy are simultaneously rendered in each specialized view. Beside a consideration of anatomical compatibility, the surgeon may evaluate the planned implant type, size and position, also on the basis of two analysis modules that compute the achieved level of implant fitting and filling. After being evaluated in an internal clinical trial, the software is currently made available as freeware at http:// www.ior.it/hipop/.
   PMID: 12507267 [PubMed - indexed for MEDLINE]
6. Comput Methods Programs Biomed. 2004 May;74(2):143-50.
   Validation of two algorithms to evaluate the interface between bone and orthopaedic implants
   Testi D, Simeoni M, Zannoni C, Viceconti M
   The level of fit and fill of the prosthetic stem in the femoral canal is an important parameter when planning a cementless total hip arthroplasty. However, the standard templates used in combination with radiographs are not always effective in the pre-operative evaluation of the level of fitting. For this reason, two algorithms were developed able to provide clinically relevant three-dimensional indicators of the implant fit and fill in the host femur, based on the CT data of each specific patient as collected in vivo. In this study the computational methods were described and validated using digital phantom datasets. Then the algorithms were applied for in vivo datasets and the sensitivity of each indicator was evaluated. The validation showed that the two algorithms are accurate from a computational point of view. Moreover, the in vivo testing demonstrated that the developed methods provide reasonable quantitative indicators of the stem positioning in the femoral CT dataset.
   Publication Types: Evaluation Studies Validation Studies
   PMID: 15013595 [PubMed - indexed for MEDLINE]
7. Med Eng Phys. 2004 Apr;26(3):237-45.
   Specialised CT scan protocols for 3-D pre-operative planning of total hip replacement.
   Lattanzi R, Baruffaldi F, Zannoni C, Viceconti M
   X-ray computer tomography (CT) provides an accurate source of information in orthopaedics. Many computer aided orthopaedic surgery systems are based on CT images; thus, obtaining high resolution images is important. However, this may result in an excessive radiation dose for the patient. This study is aimed at developing a special CT scanning protocol for the hip region that can be adopted in clinical practise for 3-D pre-operative planning of total hip replacement surgery. Optimisation of CT acquisition parameters is investigated for both axial and spiral CT and the two resulting protocols are compared in terms of effective radiation dose to the patient. Results show that spiral CT with D=3 and P=1.5 in regions with higher morphological and density gradients and D=5 and P=1.5 in regions where the morphology is more regular degrades the image quality slightly but allows acquisition of a higher number of images at comparable costs, increasing the longitudinal resolution of the acquired data set. The effective dose is comparable to that of a standard pelvic CT exam. Adjusting the axial CT scan parameters the effective dose can be reduced, however lowering the accuracy of 3-D bone geometry reconstruction.
   PMID: 14984845 [PubMed - indexed for MEDLINE]
8. Comput Methods Programs Biomed. 2003 Jun;71(2):117-27.
   A new method to compare planned and achieved position of an orthopaedic implant.
   Popescu F, Viceconti M, Grazi E, Cappello A
   The present study describes an automatic method to evaluate the efficacy of a computer aided orthopaedic surgery system by comparing the position of the joint implant, as derived from post-operative computed tomography (CT) scans, to that planned by the surgeon before the operation. The method relies on two spatial registrations, one to align the post-operative femur with the pre-operative femur, the second to compute the planned versus achieved (PVA) accuracy as the roto-translation that registers the pre-operative implant position with the post-operative position. Two surface registration algorithms (a generic average distance minimisation and the specialised iterative closest point (ICP) method) were comparatively evaluated first on a set of test cases to measure the absolute accuracy and robustness with respect to peculiar situations such as a distant starting point. The average distance method failed the registration of one test case and showed peak errors of 0.97 degrees on the rotations and 3.09 mm on the translations. The ICP method was found much more efficient and was able to register all test cases. The peak error was 0.44 degrees on the rotations and 0.67 mm on the translations. The ICP method was then used to compute the PVA accuracy on six clinical cases treated with a CT-based planning system in combination with conventional surgical procedures. The method successfully processed all cases demonstrating the efficacy of the proposed procedure in the specific application.
   PMID: 12758133 [PubMed - indexed for MEDLINE]
9. Med Inform Internet Med. 2002 Mar;27(1):21-32.
   Effect of display modality on spatial accuracy of orthopaedic surgery pre-operative planning applications.
   Viceconti M, Lattanzi R, Zannoni C, Cappello A
   Graphical representation of a patient's anatomy is fairly similar in the majority of orthopaedic surgery planning programs. The position of implantable devices is usually established using a three-pane window showing 2D cross sections of the CT data set taken on three user-selectable orthogonal planes. In some cases this orthogonal-plane representation is replaced or extended by interactive 3D visualization, obtained using surface rendering techniques. These ways to represent the CT data come naturally and easily to the programmer. However, the efficacy of these display strategies is questionable. The present study aims to assess if the display modality used to visualize CT data affects the inherent spatial accuracy achievable in a surgical planning application. A group of users was asked to perform repeatedly a specific planning task using various display interfaces to the same underlying software application. The planning task was designed to allow an assessment of the accuracy with which each user was able to position the prosthetic component. A specialized interface, called multimodal display, presented a peak error of 0.45 mm and 0.95 deg, significantly lower than the 2.4 mm and 4 deg for the othogonal slices interface, and the 3.8 mm and 16.7 deg for the 3D-rendering interface. The results of this study indicate an important effect of the type of visualization modality used to represent CT data on final accuracy of the planning operation.
   PMID: 12509120 [PubMed - indexed for MEDLINE]
10. Comput Methods Programs Biomed. 2003 Feb;70(2):121-7.
    An automated method to position prosthetic components within multiple anatomical spaces.
    Viceconti M, Testi D, Simeoni M, Zannoni C
    The level of fit and fill of a stem in the host femur is the most critical factor for the mechanical stability and success of the prosthesis. It would be useful to have a simulation tool able to investigate the anatomical compatibility of a new implant in a large library of femoral anatomies in the early phases of the design process. In order to realise this tool, it is necessary to develop an automatic method for the positioning of the stem in a database of anatomies. The aim of this study was to develop and evaluate a method for the automatic positioning of the stem geometry in the anatomical CT dataset. Two different strategies were considered: a completely automatic registration technique and a semi-automatic method based on an anatomical referencing. The two procedures were compared to the manual positioning obtained by an expert surgeon in a set of nine CT datasets. For both methods in each femur the positioning and the orientation of the stem were good. The results showed a better level of fitting for the automatic method, while the shift of the hip joint centre was lower for the anatomical referencing technique. However, the anatomical referencing method requires a higher computational effort without being significantly better than the automatic method. For this reason, the automatic method should be chosen to develop the automatic positioning of a stem in a database of anatomies.
    PMID: 12507788 [PubMed - indexed for MEDLINE]