Aims: Aim of this study is to review the role of biomechanical modelling in computer aided orthopaedic surgery (CAOS), and to identify the issues that prevent a wider adoption of biomechanical modelling in the clinical practice.

Methods: we reviewed the experience we cumulated over the years in the use of biomechanical models to answer clinically relevant questions in the domains of joint prosthetics design and of skeletal strength under pathological conditions. also summarised the studies done in the past few years on the use of computer aided systems in the pre-operative planning, with particular reference to the Hip-OpA9 surgical planner for total hip replacement. Last, we analyse the improvements that the introduction of new technologies such as the Multimod Application Framework is likely to allow in a near future. All this information was combined in order to establish two possible scenarios for the next generation of computer aided orthopaedic surgery solutions: the use of biomechanics models as pre-operative and intra-operative decision-support instruments, and the role of multisensorial interfaces in CAOS applications.

Results: With this review we found that various technology limitation still limit a wider introduction of biomechanics modelling in CAOS. Specific research activities must be focused on the generation of patient-specific models of the musculo-skeletal apparatus that are not only anatomically but also functionally correct and accurate.

Conclusions: While multimodal imaging (CT+MRI+ SPECT) may provide the best results, solutions are being developed which are compatible with the logistics of the clinical practice.

Computer-aided surgery (CAS) aims not to replace the surgeon but to assist him in difficult areas. The cost of the system means it has to produce markedly improved clinical results. CAS gained acceptance in neurosurgery. In knee surgery, CAS has improved the accuracy of tibiofemoral alignment and bone cuts. It has also helped deal with problems such as soft tissue balancing. This report of our experiences looks at intra-articular and extra-articular forces around the knee, the use of spacer blocks, surgical techniques and results

To determine the current practice of scoliosis surgery in the UK. A 10 point questionnaire was constructed to identify the philosophy of surgeons on various aspects of scoliosis surgery such as choice of implant, bone graft, autologous blood transfusion (ABT), cord monitoring and computer assisted surgery. Results are compared with the current best evidence. Consultants and Fellows attending the 2009 British Scoliosis Society meeting. 50 questionnaires were completed: 45 Consultants and 5 Fellows. All pedicle screw construct favored by 25/50, hybrid 24/50 (one undecided). Posterior construct of less than 10 levels, 20/50 would not cross-link, 11/50 used one and 19/20 used two or more. More than ten levels 17/50 considered cross-links unnecessary, 4/50 used one and 29/50 used two or more. 88% preferred titanium alloy implants, while a mixture of stainless steel and cobalt chrome was used by others. For bone graft, substitutes (24), iliac crest (14), allograft (12) and demineralised bone matrix (9) in addition to local bone. 10/50 would use recombinant bone morphogenetic protein (3 for revision cases only). 39/50 routinely used intra-operative cell salvage or ABT drains and 4/50 never used autologous blood. All used cord monitoring, Sensory (19/50), Motor (2/50) and combined (29/50). None used computer-aided surgery. 26 operated alone 12 operated in pairs and 12 varied depending on type of case. This survey has brought to light interesting variations in scoliosis surgery in UK. It may reflect the conflicting evidence in the literature

There are many reports in the literature about the benefits of computer-aided surgery with regards to improved limb alignment, reduced blood loss and embolic events but surgeons remain sceptical about its routine use because of availability, cost and time implications. To maximise these benefits and overcome the distractions, a modified navigation technique has been developed after evaluation of the standard measurements. The true varus/valgus angle of the distal femoral cut achieved with navigation is unknown but represents presumed accurate alignment with regards to the mechanical axis through the femoral head. With placement of the femoral tracker in the medial supracondylar region clear of the intramedullary canal, the navigated cut was correlated with the cut placement determined with the standard intramedullary jig in 10 patients undergoing knee replacement. In addition, jigged femoral rotation was checked with the tracker placement. Tibial slope, varus/valgus angle and rotation were determined using surgeon placement of an external alignment jig and confirmed with tracker placement. The navigated distal femoral cut ranged from +3 degrees to −2 degrees when measured against the distal cutting block stabilised over an intramedullary rod. The femoral rotation was within 1 degree of the trans-epicondylar line as outlined by navigation when a 3 degree externally rotated jig was used. All of the tibial measurements were within 0.5 degrees of the navigated planned positions. The femoral cuts are presumed to be accurately determined with navigation as judged from long-leg alignment x-rays but this study highlights the potential error if a fixed valgus cut angle with alignment jigs is used. Tibial preparation, however, was accurately predicted by the surgeon using a traditional external alignment jig. Bone preparation time was reduced to 4 minutes (modified technique) compared to 12 minutes (full navigation, p< 0.05). With this information, computer-aided navigation is now routinely used to determine the distal femoral cut only and an external alignment jig is used for tibial preparation without navigation. The reduction in blood loss and embolic events and improved limb alignment is now achieved with a reduction in preparation time over full navigated techniques. Use of the pinless surface mounted femoral jig alone highlights these advantages further

As further improvements in surgical accuracy are made possible by computer-aided surgery, there is a demand for new pre- and post- surgical assessment and more accurate intra-operative registration techniques. Ultrasonic palpation is being used in navigated hip surgery but as yet little work had been published on the identification of anatomical landmarks used in knee surgery with this technique. The aim of this study was to investigate the accuracy of the identification of the femoral condyles with ultrasound in both saline and in tissue mimicking material (TMM). The system comprised of an image free navigation system (OrthoPilot, B Braun Aesculap) synchronized with a standard B-mode ultrasound system (Echoblaster 128, TELEMED) used with passive trackers. Bony anatomy was represented by two sawbone phantoms; one involving an isolated femur and one simulated knee joint. Both phantoms had fiducial markers in the form of steel pins inserted into the condylar eminences of the femur, providing sharply defined structural interfaces for determination of inter-condylar distance (ICD). Initial testing was completed in a waterbath filled with saline (NaCl 4500ppm) maintained at 22°C. Further testing used both sawbone phantoms encased in TMM. To gain accurate dimensions of the ICD, 3D models of both sawbone phantoms were created using a high-resolution non-contact 3D digitiser (Konica Minolta Sensing Inc.) and measurements taken using Geomagic software. Measurements for all test set-ups were repeated and mean (SD) values calculated. The mean ICD measurement (SD) of the isolated femur from the high resolution 3D model was 53.6mm (1.2mm) (n=4). The ICD for the isolated femur in the saline water bath was 48.8mm (0.7mm) (n=5). For the isolated femur encased in TMM the mean ICD was 54.6mm (0.7mm) (n=4) with the probe positioned parallel to the shaft of the femur and 52.2mm (0.4mm) (n=5) with the probe held perpendicular to the femur. For the second phantom, which consisted of an articulated knee joint, the mean ICD measured from the high-resolution 3D model was 43.5mm (1.0mm) (n=5). When encased in TMM, the mean ICD derived from the navigation system was 42.6mm (1.4mm) (n=5). Average ICD measurements for phantoms encased in TMM were within 1mm of that determined by high resolution, non-contact 3D digitization. However, results in the saline waterbath were less accurate, with an average difference of 4.8mm in ICD measurement. We believe these differences largely reflect the digitisation error associated with manual registration of the fiducial markers and highlights the difficulty in using this method and taking measurements within one scanned plane. Hence we are now developing a new method of automatic registration that uses multiple scans and will hopefully provide a more accurate outcome

Improving the accuracy of measuring 6 degree of freedom tibiofemoral kinematics is a crucial step in gait analysis, but skin-marker estimated kinematics are subject to soft tissue artefacts. Fluoroscopic systems have been reported to achieve high accurate kinematics, but their induced irradiation, limited field of view, and high cost hampers routine usage on large patient cohorts. The aim of this study is to assess the feasibility of measuring tibiofemoral kinematics using multi-channel A-mode ultrasound system in cadaver experiment and to assess its achievable accuracy. A full cadaver was placed with its back on a surgery table while its legs were overhanging the edge of the table. Upper body was fixated and right leg was moved by means of pulling a rope. Two bone pins with optical markers were mounted to the femur and tibia separately to measure the ground truth of motion. Six custom holders containing 30 A-mode ultrasound transducers and 18 optical markers were mounted to six anatomical regions. By measuring the bone to ultrasound transducer distance and using the spatial information of the optical markers on the holders, 30 bone surface points were determined. The corresponding bones (femur and tibia) were registered to these acquired points after which the tibiofemoral kinematics were determined. This study presents a multi-channel A-mode ultrasound system and the first results have shown its feasibility of reconstructing tibiofemoral kinematics in cadaver experiment. Although the reconstructed tibiofemoral kinematics is less accurate than a fluoroscopic system, it outperforms a skin-mounted markers system. Thus, this A-mode Ultrasound approach could provide a non-invasive and non-radiative method for measuring tibiofemoral kinematics, which may be used in clinic gait analysis or even computer-aided orthopaedic surgery

Introduction. Recently, computer-aided orthopaedic surgery has enabled three dimensional (3D) preoperative planning, navigation systems and patient matched instrument, and they provide good clinical results in total knee arthroplasty. However, the preoperative planning methods and the criteria in total elbow arthroplasty (TEA) still have not sufficiently established due to the uncertainty of 3D anatomical geometry of the elbow joints. In order to clarify the 3D anatomical geometry, this study measured 3D bone models of the normal elbow joints. Additionally this study attempted to apply the 3D preoperative planning to ordinary surgery. Then the postoperative position of implant has evaluated as compared with the position in 3D preoperative planning. Methods. Three dimensional bone measurements on 4 normal cases were performed. Three dimensional bone models were constructed with CT image using Bone Viewer®(ORTHREE Co., Ltd.). TEA was performed with FINE® Total Elbow System (Nakashima Medical Co., Ltd.) for 3 rheumatoid arthritis (RA) cases (Fig. 1). Three dimensional preoperative planning was based on this bone measurement, and postoperative position of implant were evaluated. The postoperative assessments were evaluated by superimposing preoperative planning image on postoperative CT image using Bone Simulator® (ORTHREE Co., Ltd.). This study only covers humeral part. Results. The results of 3D bone measurements on 4 normal cases shows the average internal rotation angle between the flexion-extension axis and the epicondyles axis in the distal humerus was 2.2 degrees. The average valgus tilt of the distal humerus was 3.7 degrees. Postoperative position of humeral component for 3 RA cases was installed at proximal and valgus position compared to the preoperative planning. Discussion. This study indicates that ordinary two dimensional criteria and 3D anatomical one in the elbow joint may be different in several bony landmarks such as rotation, varus and valgus. Additionally these results show the differences between postoperative position of implant and preoperative position in 3D planning. More studies need to be conducted to validate postoperative evaluation and preoperative planning