Biomechanical study of a low-cost external fixator for diaphyseal fractures of long bones.

BACKGROUND: External fixation improves open fracture management in emerging countries. However, sophisticated models are often expensive and unavailable. We assessed the biomechanical properties of a low-cost external fixation system in comparison with the Hoffmann® 3 system, as a reference. METHODS: Transversal, oblique, and comminuted fractures were created in the diaphysis of tibia sawbones. Six external fixators were tested in three modes of loading-axial compression, medio-lateral (ML) bending, and torsion-in order to determine construction stiffness. The fixator construct implies two uniplanar (UUEF1, UUEF2) depending the pin-rods fixation system and two biplanar (UBEF1, UBEF2) designs based on different bar to bar connections. The designed low-cost fixators were compared to a Hoffmann® 3 fixator single rod (H3-SR) and double rod (H3-DR). Twenty-seven constructs were stabilized with UUEF1, UUEF2, and H3-SR (nine constructs each). Nine constructs were stabilized with UBEF1, UBEF2, and H3-DR (three constructs each). RESULTS: UUEF2 was significantly stiffer than H3-SR (p < 0.001) in axial compression for oblique fractures and UUEF1 was significantly stiffer than H3-SR (p = 0.009) in ML bending for transversal fractures. Both UUEFs were significantly stiffer than H3-SR in axial compression and torsion (p < 0.05), and inferior to H3-SR in ML bending, for comminuted fractures. In the same fracture pattern, UBEFs were significantly stiffer than H3-DR (p = 0.001) in axial compression and torsion, while only UBEF1 was significantly stiffer than H3-DR in ML bending (p = 0.013). CONCLUSIONS: The results demonstrated that the stiffness of the UUEF and UBEF device compares to the reference fixator and may be helpful in maintaining fracture reduction. Fatigue testing and clinical assessment must be conducted to ensure that the objective of bone healing is achievable with such low-cost devices.

Gait in patients with adolescent idiopathic scoliosis. Effect of surgery at 10 years of follow-up.

PURPOSE: To assess radiological and gait biomechanical changes before, at one and 10 years after surgery in AIS patients. METHODS: This clinical prospective study included fifteen adult women (mean[SD] age: 26 [1] years) diagnosed with thoraco-lumbar/lumbar AIS and operated 10 years ago. Clinical, radiological and gait variables, including kinematics, electromyography (EMG), mechanics and energetics were compared between presurgery (S0), 1 year (S1) and 10 years (S2) postsurgery period using a one way repeated measure ANOVA. RESULTS: The Cobb angle of the scoliosis curve was reduced by 55% at 1 year postsugery but only by 37% at 10 years postsurgery suggesting a loss of 32% over time. Frontal plumb line C7-S1 distance was significantly improved by surgery (-44%) and remained stable at 10 years postsurgery. Lower limb kinematics was not affected by the surgery at long term. Excessive bilateral activation of lombo-pelvic muscles, observed before surgery, decreased significantly at S1 and S2 period. Mechanical energy increased significantly between S0, S1 and S2 session, without any change for the energetic variables. CONCLUSIONS: Between 1 and 10 years post-surgery, thoraco-lumbar/lumbar AIS women showed a few decompensation of the curve without any change of the improved frontal body balance. Lower limbs and pelvic motion, during gait, was not affected by the surgery. But presurgical excessive EMG activity of the lumbo-pelvic muscle and reduced mechanical energy produced to walk get similar to normal patterns. Only the oxygen consumption remained excessive probably due to physical deconditioning or postural instability.

Pedicle screw insertion accuracy in terms of breach and reposition using a new intraoperative cone beam computed tomography imaging technique and evaluation of the factors associated with these parameters of accuracy: a series of 695 screws.

PURPOSE: The goals of this study were to assess the accuracy of pedicle screw insertion using an intraoperative cone beam computed tomography (CBCT) system, and to analyze the factors potentially influencing this accuracy. METHODS: Six hundred and ninety-five pedicle screws were inserted in 118 patients between October 2013 and March 2016. Screw insertion was performed using 2D-fluoroscopy or CBCT-based navigation. Accuracy was assessed in terms of breach and reposition. All the intraoperative CBCT scans, done after screw insertion, were reviewed to assess the accuracy of screw placement using two established classification systems: Gertzbein and Heary. Generalized linear mixed models were used to model the odds (95% CI) for a screw to lead to a breach according to the independent variables. RESULTS: The breach rate was 11.7% using the Gertzbein classification and 15.4% using the Heary classification. Seventeen screws (2.4%) were repositioned intraoperatively. The only factor affecting statistically the odds to have a breach was the indication of surgery. The patients with non-degenerative disease had a significantly higher risk of breach than those with degenerative disease. CONCLUSION: Use of intraoperative CBCT as 2D-fluoroscopy or coupled with a navigation system for pedicle screw insertion is accurate in terms of breach occurrence and reposition. However, these rates depend on the classification or grading system used. Use of a navigation system does not decrease the risk of breach significantly. And the risk of breach is higher in non-degenerative conditions (trauma, scoliosis, infection, and malignancy disease) than in degenerative diseases.

Accuracy of a new intraoperative cone beam CT imaging technique (Artis zeego II) compared to postoperative CT scan for assessment of pedicle screws placement and breaches detection.

PURPOSE: The goal of this study was to compare the accuracy of a novel intraoperative cone beam computed tomography (CBCT) imaging technique with that of conventional computed tomography (CT) scans for assessment of pedicle screw placement and breach detection. METHODS: Three hundred and forty-eight pedicle screws were inserted in 58 patients between October 2013 and March 2016. All patients had an intraoperative CBCT scan and a conventional CT scan to verify the placement of the screws. The CBCT and CT images were reviewed by two surgeons to assess the accuracy of screw placement and detect pedicle breaches using two established classification systems. Agreement on screw placement between intraoperative CBCT and postoperative CT was assessed using Kappa and Gwet's coefficients. Using CT scanning as the gold standard, the sensitivity, specificity, positive predictive value, and negative predictive value were calculated to determine the ability of CBCT imaging to accurately evaluate screw placement. RESULTS: The Kappa coefficient was 0.78 using the Gertzbein classification and 0.80 using the Heary classification, indicating a substantial agreement between the intraoperative CBCT and postoperative CT images. Gwet's coefficient was 0.94 for both classifications, indicating almost perfect agreement. The sensitivity, specificity, positive predictive value and negative predictive value of the CBCT images were 77, 98, 86, and 96%, respectively, for the Gertzbein classification and 79, 98, 88, and 96%, respectively, for the Heary classification. CONCLUSIONS: Intraoperative CBCT provides accurate assessment of pedicle screw placement and enables intraoperative repositioning of misplaced screws. This technique may make postoperative CT imaging unnecessary.

Accuracy of Computer-Aided Techniques in Orthopaedic Surgery: How Can It Be Defined, Measured Experimentally, and Analyzed from a Clinical Perspective?

Surgical accuracy is multifactorial. Therefore, it is crucial to consider all influencing factors when investigating the accuracy of a surgical procedure, such as the surgeon's experience, the assistive technologies that may be used by the surgeon, and the patient factors associated with the specific anatomical site. For in vitro preclinical investigations, accuracy should be linked to the concepts of trueness (e.g., distance from the surgical target) and precision (e.g., variability in relation to the surgical target) to gather preclinical, quantitative, objective data on the accuracy of completed surgical procedures that have been performed with assistive technologies. The clinical relevance of improvements in accuracy that have been observed experimentally may be evaluated by analyzing the impact on the risk of failure and by taking into account the level of tolerance in relation to the surgical target (e.g., the extent of the safety zone). The International Organization for Standardization (ISO) methodology enables preclinical testing of new assistive technologies to quantify improvements in accuracy and assess the benefits in terms of reducing the risk of failure and achieving surgical targets with tighter tolerances before the testing of clinical outcomes.

Delta method and bootstrap in linear mixed models to estimate a proportion when no event is observed: application to intralesional resection in bone tumor surgery.

Resecting bone tumors requires good cutting accuracy to reduce the occurrence of local recurrence. This issue is considerably reduced with a navigated technology. The estimation of extreme proportions is challenging especially with small or moderate sample sizes. When no success is observed, the commonly used binomial proportion confidence interval is not suitable while the rule of three provides a simple solution. Unfortunately, these approaches are unable to differentiate between different unobserved events. Different delta methods and bootstrap procedures are compared in univariate and linear mixed models with simulations and real data by assuming the normality. The delta method on the z-score and parametric bootstrap provide similar results but the delta method requires the estimation of the covariance matrix of the estimates. In mixed models, the observed Fisher information matrix with unbounded variance components should be preferred. The parametric bootstrap, easier to apply, outperforms the delta method for larger sample sizes but it may be time costly. Copyright © 2016 John Wiley & Sons, Ltd.

Computer-Assisted Planning and Patient-Specific Instruments for Bone Tumor Resection within the Pelvis: A Series of 11 Patients.

Pelvic bone tumor resection is challenging due to complex geometry, limited visibility, and restricted workspace. Accurate resection including a safe margin is required to decrease the risk of local recurrence. This clinical study reports 11 cases of pelvic bone tumor resected by using patient-specific instruments. Magnetic resonance imaging was used to delineate the tumor and computerized tomography to localize it in 3D. Resection planning consisted in desired cutting planes around the tumor including a safe margin. The instruments were designed to fit into unique position on the bony structure and to indicate the desired resection planes. Intraoperatively, instruments were positioned freehand by the surgeon and bone cutting was performed with an oscillating saw. Histopathological analysis of resected specimens showed tumor-free bone resection margins for all cases. Available postoperative computed tomography was registered to preoperative computed tomography to measure location accuracy (minimal distance between an achieved and desired cut planes) and errors on safe margin (minimal distance between the achieved cut planes and the tumor boundary). The location accuracy averaged 2.5 mm. Errors in safe margin averaged -0.8 mm. Instruments described in this study may improve bone tumor surgery within the pelvis by providing good cutting accuracy and clinically acceptable margins.

MRI evaluation of resection margins in bone tumour surgery.

In 12 patients operated on for bone sarcoma resection, a postoperative magnetic resonance imaging of the resection specimens was obtained in order to assess the surgical margins. Margins were classified according to MRI in R0, R1, and R2 by three independent observers: a radiologist and two orthopaedic surgeons. Final margin evaluation (R0, R1, and R2) was assessed by a confirmed pathologist. Agreement for margin evaluation between the pathologist and the radiologist was perfect (κ = 1). Agreement between the pathologist and an experienced orthopaedic surgeon was very good while it was fair between the pathologist and a junior orthopaedic surgeon. MRI should be considered as a tool to give quick information about the adequacy of margins and to help the pathologist to focus on doubtful areas and to spare time in specimen analysis. But it may not replace the pathological evaluation that gives additional information about tumor necrosis. This study shows that MRI extemporaneous analysis of a resection specimen may be efficient in bone tumor oncologic surgery, if made by an experienced radiologist with perfect agreement with the pathologist.

MRI-Based Assessment of Safe Margins in Tumor Surgery.

Introduction. In surgical oncology, histological analysis of excised tumor specimen is the conventional method to assess the safety of the resection margins. We tested the feasibility of using MRI to assess the resection margins of freshly explanted tumor specimens in rats. Materials and Methods. Fourteen specimen of sarcoma were resected in rats and analysed both with MRI and histologically. Slicing of the specimen was identical for the two methods and corresponding slices were paired. 498 margins were measured in length and classified using the UICC classification (R0, R1, and R2). Results. The mean difference between the 498 margins measured both with histology and MRI was 0.3 mm (SD 1.0 mm). The agreement interval of the two measurement methods was [-1.7 mm; 2.2 mm]. In terms of the UICC classification, a strict correlation was observed between MRI- and histology-based classifications (κ = 0.84, P < 0.05). Discussion. This experimental study showed the feasibility to use MRI images of excised tumor specimen to assess the resection margins with the same degree of accuracy as the conventional histopathological analysis. When completed, MRI acquisition of resected tumors may alert the surgeon in case of inadequate margin and help advantageously the histopathological analysis.

Improved accuracy with 3D planning and patient-specific instruments during simulated pelvic bone tumor surgery.

In orthopaedic surgery, resection of pelvic bone tumors can be inaccurate due to complex geometry, limited visibility and restricted working space of the pelvis. The present study investigated accuracy of patient-specific instrumentation (PSI) for bone-cutting during simulated tumor surgery within the pelvis. A synthetic pelvic bone model was imaged using a CT-scanner. The set of images was reconstructed in 3D and resection of a simulated periacetabular tumor was defined with four target planes (ischium, pubis, anterior ilium, and posterior ilium) with a 10-mm desired safe margin. Patient-specific instruments for bone-cutting were designed and manufactured using rapid-prototyping technology. Twenty-four surgeons (10 senior and 14 junior) were asked to perform tumor resection. After cutting, ISO1101 location and flatness parameters, achieved surgical margins and the time were measured. With PSI, the location accuracy of the cut planes with respect to the target planes averaged 1 and 1.2 mm in the anterior and posterior ilium, 2 mm in the pubis and 3.7 mm in the ischium (p < 0.0001). Results in terms of the location of the cut planes and the achieved surgical margins did not reveal any significant difference between senior and junior surgeons (p = 0.2214 and 0.8449, respectively). The maximum differences between the achieved margins and the 10-mm desired safe margin were found in the pubis (3.1 and 5.1 mm for senior and junior surgeons respectively). Of the 24 simulated resection, there was no intralesional tumor cutting. This study demonstrates that using PSI technology during simulated bone cuts of the pelvis can provide good cutting accuracy. Compared to a previous report on computer assistance for pelvic bone cutting, PSI technology clearly demonstrates an equivalent value-added for bone cutting accuracy than navigation technology. When in vivo validated, PSI technology may improve pelvic bone tumor surgery by providing clinically acceptable margins.

Computer-assisted planning and navigation improves cutting accuracy during simulated bone tumor surgery of the pelvis.

BACKGROUND: Resection of bone tumors within the pelvis requires good cutting accuracy to achieve satisfactory safe margins. Manually controlled bone cutting can result in serious errors, especially due to the complex three-dimensional geometry, limited visibility, and restricted working space of the pelvic bone. This experimental study investigated cutting accuracy during navigated and non-navigated simulated bone tumor cutting in the pelvis. METHODS: A periacetabular tumor resection was simulated using a pelvic bone model. Twenty-three operators (10 senior and 13 junior surgeons) were asked to perform the tumor cutting, initially according to a freehand procedure and later with the aid of a navigation system. Before cutting, each operator used preoperative planning software to define four target planes around the tumor with a 10-mm desired safe margin. After cutting, the location and flatness of the cut planes were measured, as well as the achieved surgical margins and the time required for each cutting procedure. RESULTS: The location of the cut planes with respect to the target planes was significantly improved by using the navigated cutting procedure, averaging 2.8 mm as compared to 11.2 mm for the freehand cutting procedure (p < 0.001). There was no intralesional tumor cutting when using the navigation system. The maximum difference between the achieved margins and the 10-mm desired safe margin was 6.5 mm with the navigated cutting process (compared to 13 mm with the freehand cutting process). CONCLUSIONS: Cutting accuracy during simulated bone cuts of the pelvis can be significantly improved by using a freehand process assisted by a navigation system. When fully validated with complementary in vivo studies, the planning and navigation-guided technologies that have been developed for the present study may improve bone cutting accuracy during pelvic tumor resection by providing clinically acceptable margins.

Toward the next generation of simulator for intraoperative navigation of scoliotic spine surgeries.

Surgical navigation systems are useful for planning pedicle screw positioning and guiding drilling trajectories. However, it is not yet possible to intraoperatively predict the correction of the scoliotic spine resulting from specific screw and rod configuration and instrumentation maneuvers. In this context, the objective of this study is to develop a novel intraoperative simulator for navigated scoliotic spine surgeries. An instrumentation strategy (pedicle screw insertion, rod attachment and rotation, set screw tightening) was computationally simulated on a synthetic model of a scoliotic spine using the preoperative radiographs in the standing position and various parameters recreating the preoperative conditions. The intraoperative decubitus position was then simulated. The resulting geometry was identified using a navigation system and transferred to the simulator, which enabled the updating of the preoperative planning, computing of clinical indices (Cobb angles, etc.) and simulation of instrumentation maneuvers. The Cobb angle decreased from 34° to 24° between the simulated pre- and intraoperative spine (before the instrumentation). Difference in pedicle screw positioning between the preoperative planning and the intraoperative situation was less than 0.5 mm. The intraoperative simulation of the rod attachment and rotation maneuvers resulted in a 12° Cobb angle. In conclusion, this preliminary study is a first step toward developing an integrated simulator for preoperative planning and intraoperative navigation of scoliotic spine surgeries. Once completed, the new intraoperative simulator will enable the surgeon to obtain real-time biomechanical feedback during the navigated surgery of a scoliotic spine, and may contribute to improve the resulting correction and instrumentation parameters (instrumented levels, surgical maneuvers, generated forces, etc.).

Computer-Navigated Bone Cutting in the Resection of a Pelvic Bone Tumor and Reconstruction with a Massive Bone Allograft.

INTRODUCTION: We present here a surgical technique using a navigation system and an oscillating saw for the resection of a pelvic bone tumor combined with an allograft reconstruction. STEP 1 PREOPERATIVE PLANNING: The surgeon and radiologist together delineate the tumor on each magnetic resonance imaging (MRI) slice; then the surgeon defines target planes for tumor resection and transfers them to the allograft. STEP 2 PATIENT POSITIONING AND SURGICAL EXPOSURE: With the patient in the lateral decubitus position, combine ilioinguinal with iliocrural and obturator surgical approaches to expose the ilium. STEP 3 NAVIGATED TUMOR RESECTION: Perform the osteotomies using the navigation system to guide the saw blade, following predefined target planes; perform a biopsy. STEP 4 NAVIGATED ALLOGRAFT CUTTING: Perform the osteotomies using the navigating saw, following the same target planes as used for the tumor resection. STEP 5 PELVIC RECONSTRUCTION: Fix the graft and cement a femoral stem in place; then reinsert all detached tendons and elevated muscles. RESULTS & PREOP/POSTOP IMAGES: Editor's note: This technique is based on preliminary work that has not been presented in a peer-reviewed case series publication. WHAT TO WATCH FOR: IndicationsContraindicationsPitfalls & Challenges.

Computer-assisted resection and reconstruction of pelvic tumor sarcoma.

Pelvic sarcoma is associated with a relatively poor prognosis, due to the difficulty in obtaining an adequate surgical margin given the complex pelvic anatomy. Magnetic resonance imaging and computerized tomography allow valuable surgical resection planning, but intraoperative localization remains hazardous. Surgical navigation systems could be of great benefit in surgical oncology, especially in difficult tumor location; however, no commercial surgical oncology software is currently available. A customized navigation software was developed and used to perform a synovial sarcoma resection and allograft reconstruction. The software permitted preoperative planning with defined target planes and intraoperative navigation with a free-hand saw blade. The allograft was cut according to the same planes. Histological examination revealed tumor-free resection margins. Allograft fitting to the pelvis of the patient was excellent and allowed stable osteosynthesis. We believe this to be the first case of combined computer-assisted tumor resection and reconstruction with an allograft.

Computer-assisted and robot-assisted technologies to improve bone-cutting accuracy when integrated with a freehand process using an oscillating saw.

BACKGROUND: In orthopaedic surgery, many interventions involve freehand bone cutting with an oscillating saw. Such freehand procedures can produce large cutting errors due to the complex hand-controlled positioning of the surgical tool. This study was performed to investigate the potential improvements in cutting accuracy when computer-assisted and robot-assisted technologies are applied to a freehand bone-cutting process when no jigs are available. METHODS: We designed an experiment based on a geometrical model of the cutting process with use of a simulated bone of rectangular geometry. The target planes were defined by three variables: a cut height (t) and two orientation angles (beta and gamma). A series of 156 cuts were performed by six operators employing three technologically different procedures: freehand, navigated freehand, and robot-assisted cutting. After cutting, we measured the error in the height t, the absolute error in the angles beta and gamma, the flatness, and the location of the cut plane with respect to the target plane. RESULTS: The location of the cut plane averaged 2.8 mm after use of the navigated freehand process compared with 5.2 mm after use of the freehand process (p < 0.0001). Further improvements were obtained with use of the robot-assisted process, which provided an average location of 1.7 mm (p < 0.0001). CONCLUSIONS: Significant improvements in cutting accuracy can be achieved when a navigation system or an industrial robot is integrated into a freehand bone-cutting process when no jigs are available. The procedure for navigated hand-controlled positioning of the oscillating saw appears to be easy to learn and use.

Formalin fixation could interfere with the clinical assessment of the tumor-free margin in tumor surgery: magnetic resonance imaging-based study.

OBJECTIVES: The tumor-free margin in bone and soft-tissue cancer is a key factor for subsequent treatment. While flattening and shrinkage of specimens after formalin fixation have been described in breast cancer, there are no data for bone and soft tissue sarcoma. Fixation could interfere with the accuracy of the assessment of the tumor-free margin. METHODS: The influence of formalin fixation was assessed on forelimb specimens in a preclinical porcine model. The specimens were subjected to magnetic resonance imaging before and after formalin fixation. Weight, width and height of the specimen were measured and different consecutive volumes (total, muscles, bones and fatty tissue) were obtained by segmentation. RESULTS: After formalin fixation, the weight increased, total volume and muscle volume slightly increased while bone did not change and fatty tissue decreased. The width of the specimens increased while their height decreased. CONCLUSIONS: Formalin fixation caused slight muscle expansion, fatty tissue shrinkage and flattening of the specimen. These changes could interfere with the assessment of the tumor-free margin in clinical practice.

Selection of massive bone allografts using shape-matching 3-dimensional registration.

BACKGROUND AND PURPOSE: Massive bone allografts are used when surgery causes large segmental defects. Shape-matching is the primary criterion for selection of an allograft. The current selection method, based on 2-dimensional template comparison, is inefficient for 3-dimensional complex bones. We have analyzed a 3-dimensional (3-D) registration method to match the anatomy of the allograft with that of the recipient. METHODS: 3-D CT-based registration was performed to match the shapes of both bones. We used the registration to align the allograft volume onto the recipient's bone. Hemipelvic allograft selection was tested in 10 virtual recipients with a panel of 10 potential allografts, including one from the recipient himself (trap graft). 4 observers were asked to visually inspect the superposition of allograft over the recipient, to classify the allografts into 4 categories according to the matching of anatomic zones, and to select the 3 best matching allografts. The results obtained using the registration method were compared with those from a previous study on the template method. RESULTS: Using the registration method, the observers systematically detected the trap graft. Selections of the 3 best matching allografts performed using registration and template methods were different. Selection of the 3 best matching allografts was improved by the registration method. Finally, reproducibility of the selection was improved when using the registration method. INTERPRETATION: 3-D CT registration provides more useful information than the template method but the final decision lies with the surgeon, who should select the optimal allograft according to his or her own preferences and the needs of the recipient.

Ergonomic evaluation of 3D plane positioning using a mouse and a haptic device.

BACKGROUND: Preoperative planning and intraoperative assistance are needed to improve accuracy in tumour surgery. To be accepted, these processes must be efficient. An experiment was conducted to compare a mouse and a haptic device, with and without force feedback, to perform plan positioning in a 3D space. Ergonomics and performance factors were investigated during the experiment. Positioning strategies were observed. METHODS: The task completion time, number of 3D orientations and failure rate were analysed. A questionnaire on ergonomics was filled out by each participant. RESULTS: The haptic device showed a significantly lower failure rate and was quicker and more ergonomic than the mouse. The force feedback was not beneficial to the accomplishment of the task. CONCLUSIONS: The haptic device is intuitive, ergonomic and more efficient than the mouse for positioning a 3D plane into a 3D space. Useful observations regarding positioning strategies will improve the integration of haptic devices into medical applications.

Measurement of bone cyst fluid volume using k-means clustering.

We designed a semiautomatic segmentation method to easily measure the volume of a bone cyst (simple or aneurysmal) from magnetic resonance imaging (MRI). This method only considers the fluid part of the cyst, even when there are several fluid intensities (fluid-fluid levels) or the cyst is multi-loculated. The nonhomogeneity phenomenon inherent in MRI was handled by a k-means clustering algorithm that classified all of the voxels corresponding to the cyst fluid as the same voxel intensity. Level-set segmentation was expanded into the whole cyst volume and the resulting segmented volume provided the measured cyst volume. The semiautomatic method was compared with the usual manual method (manual contour tracing) in terms of its ability to measure a known volume of water (gold standard) as well as the volume of 29 bone cysts. Both methods were equivalent with regards to the gold standard, but the semiautomatic method was more accurate. In terms of the experimental measurements, the semiautomatic method was more repeatable and reproducible, and less time-consuming and fastidious than the manual method. Our semiautomatic method uses only freeware and can be used routinely whenever measurement of a bone cyst volume is needed.

Accuracy in planar cutting of bones: an ISO-based evaluation.

BACKGROUND: Computer- and robot-assisted technologies are capable of improving the accuracy of planar cutting in orthopaedic surgery. This study is a first step toward formulating and validating a new evaluation methodology for planar bone cutting, based on the standards from the International Organization for Standardization. METHODS: Our experimental test bed consisted of a purely geometrical model of the cutting process around a simulated bone. Cuts were performed at three levels of surgical assistance: unassisted, computer-assisted and robot-assisted. We measured three parameters of the standard ISO1101:2004: flatness, parallelism and location of the cut plane. RESULTS: The location was the most relevant parameter for assessing cutting errors. The three levels of assistance were easily distinguished using the location parameter. CONCLUSIONS: Our ISO methodology employs the location to obtain all information about translational and rotational cutting errors. Location may be used on any osseous structure to compare the performance of existing assistance technologies.