Aims

To investigate if preoperative CT improves detection of unstable trochanteric hip fractures.

Literature surrounding artificial intelligence (AI)-related applications for hip and knee arthroplasty has proliferated. However, meaningful advances that fundamentally transform the practice and delivery of joint arthroplasty are yet to be realized, despite the broad range of applications as we continue to search for meaningful and appropriate use of AI. AI literature in hip and knee arthroplasty between 2018 and 2021 regarding image-based analyses, value-based care, remote patient monitoring, and augmented reality was reviewed. Concerns surrounding meaningful use and appropriate methodological approaches of AI in joint arthroplasty research are summarized. Of the 233 AI-related orthopaedics articles published, 178 (76%) constituted original research, while the rest consisted of editorials or reviews. A total of 52% of original AI-related research concerns hip and knee arthroplasty (n = 92), and a narrative review is described. Three studies were externally validated. Pitfalls surrounding present-day research include conflating vernacular (“AI/machine learning”), repackaging limited registry data, prematurely releasing internally validated prediction models, appraising model architecture instead of inputted data, withholding code, and evaluating studies using antiquated regression-based guidelines. While AI has been applied to a variety of hip and knee arthroplasty applications with limited clinical impact, the future remains promising if the question is meaningful, the methodology is rigorous and transparent, the data are rich, and the model is externally validated. Simple checkpoints for meaningful AI adoption include ensuring applications focus on: administrative support over clinical evaluation and management; necessity of the advanced model; and the novelty of the question being answered.

Cite this article: Bone Joint J 2022;104-B(12):1292–1303.

Problem. Total hip replacement (THA) is among the most common and highest total spend elective operations in the United States. However, up to 7% of patients have 90-day complications after surgery, most frequently joint dislocation that is related to poor acetabular component positioning. These complications lead to patient morbidity and mortality, as well as significant cost to the health system. As such, surgeons and hospitals value navigation technology, but existing solutions including robotics and optical navigation are costly, time-consuming, and complex to learn, resulting in limited uptake globally. Solution. Augmented reality represents a navigation solution that is rapid, accurate, intuitive, easy to learn, and does not require large and costly equipment in the operating room. In addition to providing cutting edge technology to specialty orthopedic centers, augmented reality is a very attractive solution for lower volume and smaller operative settings such as ambulatory surgery centers that cannot justify purchases of large capital equipment navigation systems. Product. HipInsight™ is an augmented reality solution for navigation of the acetabular component in THA. HipInsight is a navigation solution that includes preoperative, cloud based surgical planning based on patient imaging and surgeon preference of implants as well as intraoperative guidance for placement of the acetabular component. Once the patient specific surgical plan is generated on the cloud-based planning system, holograms showing the optimal planned position of the acetabular component are exported in holographic format to a Microsoft HoloLens 2™, which the surgeon wears during placement of the acetabular component in total hip arthroplasty. The pelvis is registered using the HipXpert™ mechanical registration device, which takes 2–3 minutes to dock in the operating room. The surgeon then is able to view the patient's anatomy and optimal placement of the acetabular component under the skin in augmented reality. The surgeon then aligns the real cup impactor with the augmented reality projection of the cup impactor resulting in precise placement of the cup. Timescales. HipInsight was FDA cleared on January 28, 2021 for intraoperative use for placement of the acetabular component in total hip arthroplasty. The first case was performed in February 2021, and the product was launched to a select group of orthopedic surgeons in March 2021. Funding. HipInsight has been self-funded to date, and is beginning to engage in discussions to raise capital for a rapidly scaling commercial launch

Recent innovations in total ankle replacement (TAR) have led to improvements in implant survivorship, accuracy of component positioning and sizing, and patient outcomes. CT-generated pre-operative plans and cutting guides show promising results in terms of placement enhancement and reproducibility in clinical studies. The purpose of this study was to determine the accuracy of 1) implant sizes used and 2) alignment corrections obtained intraoperatively using the cutting guides provided, compared to what was predicted in the CT generated pre-operative plans. This is a retrospective study looking at 36 patients who underwent total ankle arthroplasty using a CT generated pre-operative planning system between July 2015 and December 2017. Personalized pre-operative planning data was obtained from the implant company. Two evaluators took measurements of the angle corrected using pre- and post-operative weight bearing ankle AP X-rays. All patients had a minimum three-month follow-up with weightbearing postoperative radiographs. The actual correction calculated from the radiographic assessment was compared with the predicted angles obtained from pre-operative plans. The predicted and predicted alternative component sizes and actual sizes used were also compared. If either a predicted or predicted alternative size was implanted, we considered it to be accurate. Average age for all patients was 64 years (range 40–83), with a body mass index of 28.2 ± 5.6. All surgeries were performed by two foot and ankle surgeons. The average total surgical time was 110 ± 23 minutes. Pre-operative alignment ranged from 36.7 degrees valgus to 20 degrees varus. Average predicted coronal alignment correction was 0.8 degrees varus ± 9.3 degrees (range, 18.2 degrees valgus to 29 degrees varus) and average correction obtained was 2.1 degrees valgus ± 11.1 degrees. Average post-op alignment was consistently within 5 degrees of neutral. There were no significant differences between the predicted alignments and the postoperative weightbearing alignments. The predicted tibia implant size was accurate in all cases. The predicted sizes were less accurate for talar implants and predicted the actual talar implant size used in 66% of cases. In all cases of predicted talar size mismatch, surgical plans predicted 1 implant size larger than used. Preliminary analyses of our data is comparable to previous studies looking at similar outcomes. However, our study had higher pre-operative deformities. Despite that, post-op alignments were consistently within 5 degress of neutral with no significant difference between the predicted and actual corrections. Tibial implant sizes are highly accurate while talar implant sizes had a trend of being one size smaller than predicted. Moreover, this effect seems to be more pronounced in the earlier cases likely reflective of increasing surgeon comfort with the implant with each subsequent case. These results confirm that pre-operative cutting guides are indeed helpful in intra-operative implant selection and positioning, however, there is still some room for innovation

Introduction. The achieved anteversion of uncemented stems is to a large extent limited by the internal anatomy of the bone. A better understanding of this has recently become an unmet need because of the increased use of uncemented stems. We aimed to assess plan compliance in six degrees of freedom to evaluate the accuracy of PSI and guides for stem positioning in primary THAs. Materials and Methods. We prospectively collected 3D plans generated from preoperative CTs of 30 consecutive THAs (17 left and 13 right hips), in 29 patients with OA, consisting of 16 males and 13 females (median age 68 years, range 46–83 years). A single CT-based planning system and cementless type of implant were used. Post operatively, all patients had a CT scan which was reconstructed using state-of-the-art software solution: the plan and CT reconstruction models were. Outcome measures: 1) discrepancy between planned and achieved stem orientation angles Fig.2&3; 2) clinical outcome. Results. 1) The mean (±SD) discrepancy was low for: Varus-valgus −1.1 ± 1.4 deg (IQR −2.2 – 0.3 deg); Anterior-posterior 0.1 ± 1.6 deg (IQR −0.7 – 1.3 deg). The discrepancy was higher for femoral version −1.4 ± 8.2 deg (IQR −8.3 – 7.2 deg). 3D-CT planning correctly predicted sizes in 93% of the femoral components. 2) There was no intra-operative fracture, no case showed evidence of early periprosthetic osseous injury. Discussion. Surgeons and engineers should be cautious with their expectation of achieving the planned femoral stem version of an uncemented femoral stem from the pre-operative 3D-CT plan. Conclusion. This is the first study to 3D-mensionally evaluate 3D-printed patient-specific instrumentation and guides for achieved femoral stem component orientation vis-à-vis to the plan. The tools allow accurate implant orientation, however there is still potential for improvement. For any figures or tables, please contact the authors directly

Aims

This study aims to determine the proportion of patients with end-stage knee osteoarthritis (OA) possibly suitable for partial (PKA) or combined partial knee arthroplasty (CPKA) according to patterns of full-thickness cartilage loss and anterior cruciate ligament (ACL) status.

Objectives

The use of the haptically bounded saw blades in robotic-assisted total knee arthroplasty (RTKA) can potentially help to limit surrounding soft-tissue injuries. However, there are limited data characterizing these injuries for cruciate-retaining (CR) TKA with the use of this technique. The objective of this cadaver study was to compare the extent of soft-tissue damage sustained through a robotic-assisted, haptically guided TKA (RATKA) versus a manual TKA (MTKA) approach.

Introduction. Kinematics post-TKA are complex; component alignment, component geometry and the patient specific musculoskeletal environment contribute towards the kinematic and kinetic outcomes of TKA. Tibial rotation in particular is largely uncontrolled during TKA and affects both tibiofemoral and patellofemoral kinematics. Given the complex nature of post- TKA kinematics, this study sought to characterize the contribution of tibial tray rotation to kinematic outcome variability across three separate knee geometries in a simulated framework. Method. Five 50. th. percentile knees were selected from a database of planned TKAs produced as part of a pre-operative dynamic planning system. Virtual surgery was performed using Stryker (Kalamazoo, MI) Triathlon CR and PS and MatOrtho (Leatherhead, UK) SAIPH knee medially stabilised (MS) components. All components were initially planned in mechanical alignment, with the femoral component neutral to the surgical TEA. Each knee was simulated through a deep knee bend, and the kinematics extracted. The tibial tray rotational alignment was then rotated internally and externally by 5° & 10°. The computational model simulates a patient specific deep knee bend and has been validated against a cadaveric Oxford Knee Rig. Preoperative CT imaging was obtained, landmarking to identify all patient specific axes and ligament attachment sites was performed by pairs of trained biomedical engineers. Ethics for this study is covered by Bellberry Human Research Ethics Committee application number 2012-03-710. Results and Discussion. From the 360 Knee Systems database, 1847 knees were analysed, giving an average coronal alignment of 4.25°±5.66° varus. Five knees were selected with alignments between 4.1° and 4.3° varus. Kinematic outcomes were averaged over the 5 knees. The component geometries resulted in characteristically distinct kinematics, in which femoral rollback was most constrained by the PS components, whereas tibiofemoral axial rotation was most constrained in MS components. Patella lateral shift was comparable amongst all components in extension, medialising in flexion. Patella shift remained more lateral in MS components compared to PS and CR. Average patella lateral shift, medial and lateral facet rollback separated by tibial tray rotation are shown for all component systems in Figure 1. Medial and lateral facet rollback in the PS and CR components are symmetrical and opposite, indicating that with tibial tray rotation, the tibiofemoral articulation point balances between component rotation and neutral alignment, reflecting the restoring force exerted by the simulated collateral ligaments. As such, with higher internal tibial rotation and subsequent lateralisation of the tubercle, patella lateral shift increases. MS medial and lateral facet rollback however are not symmetrical nor opposite, reflecting the chirality of the tibiofemoral articulation. With internal tibial tray rotation, relatively high lateral facet rollback is observed, lateralising the femoral component centre, giving the patella component a relatively more medial position. Conclusions. Component geometry was found here to produce characteristically distinct tibiofemoral and patellofemoral kinematics. Medial stabilised components reported asymmetric kinematic changes, compared to either CR or PS components, in which a higher rate of change was observed for internal tray rotation, indicating that neutral or external rotation of medial stabilised components will result in more predictable kinematic outcomes

Introduction. Accurate acetabular cup orientation could lead to successful surgical results in total hip arthroplasty (THA). We introduce a novel CT-based three-dimensional (3D) planning system, HipCOMPASS (Fig.1) and TARGET (Fig.2), which enable to design suitable alignment not only cup also surgical devices calculatingly, according to each pelvic inclination. Patients and Methods. We performed THA in 45 hips in 43 patients (female 37 and 6 men) between April 2014 and October 2015. Average age were 68 years old. THA operation was based on each parameter of the cup and device, providing a preoperative planning by ZedView system. HipCOMPASS and TARGET is linked with ZedView software, which is simultaneously calibrated adjustable parameters on this devices. Cup alignment was assessed by ZedView as well. Results. The differences of component alignment from the preoperative planning were shown in Tables. Conclusion. HipCOMPASS and TARGET might be more accurate than conventional method and more accessible system than navigation system in THA

In patients with developmental dysplasia of the hip (DDH) chronic joint dislocation induces remodeling of the soft tissue with contractures, muscle atrophy, especially of the hip abductors muscles, leading to severe motor dysfunction, pain and disability (1). The aim pf the present work is to explore if a correct positioning of the prosthetic implants through 3D skeletal modeling surgical planning technologies and an adequate customized rehabilitation can be beneficial for patients with DDH in improving functional performance. The project included two branches: a methodology branch of software development for the muscular efficiency calculation, which was inserted in the Hip-Op surgical planning system (2), developed at IOR to allow surgical planning for patients with complex hip joint impairment; and a clinical branch which involved the use of the developed software as part of a clinical multicentric randomized trial. 50 patients with DDH were randomized in two groups: a simple surgical planning group and an advanced surgical planning with muscular study group. The latter followed a customized rehabilitation program for the strenghtening of hip abductor muscles. All patients were assessed before surgery (T0) and at 3 (T1) and 6 months (T2) postoperatively using clinical outcome (WOMAC, HHS, ROM, MMT, SF12, 10mt WT) and instrumental measures (Dynamometric MT). Pre- and post-operative musculoskeletal parameters obtained by the software (i.e., leg length discrepancy, hip abductor muscle lengths and lever arms) using Hip-Op during the surgical planning were considered. One Way ANOVA for ROM measurement showed a significant improvement at T2 in patients included in experimental group, as well as WOMAC, HHS and SF12 score. The Dynamometric MT score showed significant differences between at T2 (p<0.009). Spearman's rank correlation coefficients showed a significant correlation between both pre- and post-operative abductors lever arm (mm) and hip abductor muscle strength at T2 (ρ = −0.55 pre-op and ρ = −0.51 post-op, p p<0.012 and p<0.02 respectively) and between the operated pre-postoperative leg length variation (mm) and the hip abductor muscle strength (ρ = −0.55, p p<0.013). Results so far obtained showed an improvement of functional outcomes in patients undergoing hip replacement surgery who followed therapeutic diagnostic pathway sincluding a preoperative planning including the assessment of the abductiors lever arm and a dedicated rehabilitation program for the strenghtening of abductios. Particularly interesting is the inverse relationship between the strength of the hip abductor muscles and the variation of the postoperative abductor lever arm

Aims

Patient-specific glenoid guides (PSGs) claim an improvement in accuracy and reproducibility of the positioning of components in total shoulder arthroplasty (TSA). The results have not yet been confirmed in a prospective clinical trial. Our aim was to assess whether the use of PSGs in patients with osteoarthritis of the shoulder would allow accurate and reliable implantation of the glenoid component.

Introduction. Accurate acetabular cup orientation could lead to successful surgical results in total hip arthroplasty (THA). We introduce a novel CT-based three-dimensional (3D) planning system, HipCOMPASS (Fg.1) and TARGET (Fig.2), which enable to design suitable alignment not only cup also surgical devices calculatingly, according to each pelvic inclination. Patients and methods. We performed THA in 13 patients (10 female and 3 men) between September 2014 and April 2014. Average age were 67 years old. THA operation was based on each parameter of the cup and device, providing a preoperative planning by ZedView system. HipCOMPASS and TARGET is linked with ZedView software, which is simultaneously calibrated adjustable parameters on this devices. Cup alignment was assessed by ZedView as well. Result. The differences of component alignment from the preoperative planning were shown in table. Conclusion. HipCOMPASS and TARGET might be more accurate than conventional method and more accessible system than navigation system in THA

Purpose. The purpose of this study was to evaluate the postoperative maximal flexion of Robotic assisted TKA which does not increase the posterior condylar offset after surgery and compare CT and conventional radiography in measuring the posterior condylar offset changes. Materials and method. 50 knees of 37 patients who underwent Robotic TKA and underwent follow-up minimal one year were evaluated. CT based preoperative surgical planning system was designed not to increase posterior condylar offset (PCO) after surgery. Maximal flexion angle of the knee was evaluated at 1 year after surgery. The change in PCO and joint line on x-ray and CT were evaluated. Results. The mean preoperative knee flexion was 121° (sd: 9.21; range: 80–135), and it was improved to 125.3° (sd: 4.85; range: 115–140) postoperatively. On radiographic evaluation, the mean preoperative PCO was 26.4 mm (sd: 0.5; range: 14.8 mm to 36.3 mm) and the mean postoperative PCO was 23.0 mm (sd: 0.37; range: 16.0 mm to 34.3 mm). On CT evaluation, the mean medial PCO was 28.7± 2.4 mm preoperatively and 24.9± 2.2 mm postoperatively. The mean lateral PCO was 26.3± 2.4 mm preoperatively and 24.9± 2.2 mm postoperatively. There were no significant correlations between x-ray and CT measurement in PCO and joint line. There were no significant correlations between the changes in the posterior condylar offsets and the postoperative knee flexion. Conclusion. After Robotic assisted TKA which is planned not to increase the medial and lateral posterior condylar offset, satisfactory maximal flexion angle of the knee was gained in all patients. Changes in medial and lateral posterior condylar offsets were not correlated with the postoperative knee flexion angle. And changes in PCO and joint line measured by x-ray did not reflect those of the medial and lateral condyle, and joint line on CT

Background. The Robotic Spinal Surgery System (RSSS) is a robot system designed for pedicle screw insertion containing image based navigation system, trajectory planning system and force state recognition system. The special force state recognition system can guarantee the safety during the operation. The RSSS is helpful in pedicle screw insertion surgery and it will be applied in clinic in the near future. In this study, we evaluated the accuracy and safety of RSSS in an animal experiment. Methods. Computer tomography (CT) scan data for two anesthetised experimental sheep was acquired using the C-arm and transferred to RSSS for pre-surgery screw trajectory planning. With the assist of RSSS, we inserted 8 and 4 screws into two sheep respectively. Operation time and blood loss during the surgery were recorded, and CT scan was repeated after surgery. Real screw position and trajectory acquired by the post-surgery CT scan and ideal trajectory planned by RSSS were compared to evaluate the accuracy and safety of RSSS. The result is shown as mean±SD. Results. We planted totally 12 screws into two sheep. The operation time for each sheep is 140min and 110min, and the blood loss is 100ml and 80 ml respectively. Compared with planned trajectory, the average deviation of the entry points in lateral and axial view are 1.07±0.56mm and 1.25±0.42mm and the mean screw deviation angles in later and axial view are 1.78±0.98°and 2.52±1.03°respectively. The RSSS successfully recognised the force stages and guaranteed the safety during the drilling process. There is no penetration in all 12 pedicles, and all the screws fell into group A according to the Gertzbein-Robbins classification. Conclusion. This animal study demonstrated the accuracy and safety of the RSSS, which also supported the potential application in clinic

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

Background. The distal part of the radius is the most common localisation of fractures of the human body. Dislocated intraarticular fractures of the distal radius (FDR) are frequently treated by open reduction and internal fixation with a volar locking plate (VLP) under fluoroscopic guidance. Typically the locking screws are placed subchondral near the joint line to achieve maximum stability of the osteosynthesis. To avoid intraarticular screw placement an intraoperative virtual implant planning system (VIPS) as an application for mobile C-arms was established. The aim of the study was the validation of the implemented VIPS comparing the intraoperative planning with the actual placement of the screws. The study was conducted as a single-centre randomised controlled trial in a primary care institution. The hypothesis of the study was that there is conformity between the virtual implant position and the real implant placement. Patients/Material and Methods. 30 patients with FDR type A3, C1 and C2 according to the AO-classification were randomised in two treatment groups and allocated either in the conventional or in the VIPS group in which the patients underwent an intraoperative planning before screw placement. The randomisation was performed on the basis of a computer-generated code. After fracture reduction an initial diaphyseal fixation of the plate was done. Then the matching of the three-dimensional virtual plate with the image of the real plate in the fluoroscopy shots in two planes was performed automatically. The implant placement was planned intraoperatively in terms of orientation, angulation and length of the screws. After the placement of four or five locking screws the implant position was verified with an intraoperative three-dimensional mobile C-arm scan. The locking screws near the joint line were examined and compared in relation to the actual and the planned inclination angle, the azimuth angle which is determined analogue to a compass rose and the screw-tip distance. The planned and actual parameters of the locking screws were then statistically analysed applying the Shapiro-Wilk - and the Students t-test. Results. 15 patients with FDR were treated in the VIPS arm. In the VIPS group six fractures type A3 one type C1 and eight type C2 were included. The control group showed a similar fracture distribution with six type A3 and nine type C2 fractures. The discrepancy between the actual and the planned screw-tip distance was 2,24 ± 0,97 mm and did not differ significantly (p>0,05). The angle of the planned and actual screw placement also did not vary significantly (p>0,05). The difference of the actual to the planned azimut angle accounted for 18,69°± 29,84. The planned and real inclination of the screws differed by 1,66° ± 4,46. Conclusion. The analysis shows that the screws were almost placed as planned. Differences between actual and planned placement of the screws were observed but were not statistically significant. Therefore the hypothesis of the study can be accepted. We assume, that the precise planning of the screw placement in FDR with VIPS can be transported into the surgical treatment

Trauma surgeries in the pelvic area are often difficult and prolonged processes that require comprehensive preoperative planning based on a CT scan. Preoperative planning is essential for the appreciation and spatial visualisation of the bone fragments, for planning the reduction strategy, and for determining the optimal type, size, and location of the fixation hardware. We have developed a novel haptic-based patient specific preoperative planning system for pelvic bone fractures surgery planning. The system provides a virtual environment in which 3D bone fragments and fixation hardware models are interactively manipulated with full spatial depth and tactile perception. It supports the choice of the surgical approach and the planning of the two mains steps of bone fracture surgery: reduction and fixation. The purpose of the tool is to provide an intuitive haptic spatial interface for the manipulation of bone fracture 3D models extracted from CT images, to support the selection of bone fragments, the annotation of the fracture surface, the selection and placement of fixation screws, and the creation and placement of fixation plates with an anatomically fit shape. The system incorporates ligament models that constrain the bone fragments motions and provides a realistic interactive fracture reduction support feeling to the surgeon. It allows the surgeon to view the fracture from various directions, thereby allowing fast and accurate fracture reduction planning. Two haptic devices, one for each hand, provide tactile feedback when objects touch without interpenetrating. To facilitate the reduction, the system provides an interactive, haptic fracture surface annotation tool and a fracture reduction algorithm that automatically minimises the pairwise distance between the fracture surfaces. For fracture fixation, the system provides a screw creation and placement capability as well as custom anatomical-fit fixation plate creation and placement. The screw placement is facilitated by the transparent viewing mode that allows the surgeon to navigate the screws inside the bone fragments while constraining them to remain within the bone fragments with haptic forces. Our experimental results with five surgeons show that the method allows highly accurate reduction planning to within 1 mm or less. To evaluate the alignment in terms of quantity, we created a model of an artificial fracture in a healthy pelvis bone. The created model is placed in its anatomic location thus allowing us to measure the error in relation to its initial position. We calculate the anatomic alignment error by measuring the Hausdorff distance in mm between the fragment positioned in the desired location and the fragment placed by the surgeon. The new haptic-based system also supports patient-specific training of pelvic fracture surgeries

NavioPFS™ is a hand-held robotic technology for bone shaping that employs computer control of a high-speed bone drill. There are two control modes – one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. The unicondylar knee replacement (UKR) application uses the image-free approach in which a mix of direct and kinematic referencing is used to define all parameters relevant for planning. After the bone cutting plan is generated, the user freely moves the NavioPFS handpiece over the bone surface, and carves out the parts of the bone targeted for removal. The real-time control loop controls the depth or speed of cut, thus resulting in the planned bone preparation. This experiment evaluates the accuracy of bone preparation and implant placement on cadaveric knees in a simulated clinical setting. Three operators performed medial UKR on two cadaver specimens (4 knees) using a proprietary implant design that takes advantage of the NavioPFS approach. In order to measure the placement of components, each component included a set of 8 conical divots in predetermined locations. To establish a shared reference frame, a set of four fiducial screws is inserted in each bone. All bones were cut using a 5 mm spherical bur. Exposure Control was the primary mode of operation for both condylar cuts – although the users utilised Speed Control to perform some of the more posterior burring activities and to prepare the peg holes. Postoperatively, positions of conical divots on the femoral and tibial implants and on the respective four fiducial screws were measured using a Microscribe digitising arm in order to compare the final and the planned implant position. All implants were placed within 1.5 mm of target position in any particular direction. Maximum translation error was 1.31 mm. Maximum rotational error was 1.90 degrees on a femoral and 3.26 degrees on a tibial component. RMS error over all components was 0.69mm/1.23 degrees. This is the first report of the performance of the NavioPFS system under clinical conditions. Although preliminary, the results are overall in accordance with previous sawbones studies and with the reports from comparable semi-active robotic systems that use real time control loop to control the cutting performance. The use of NavioPFS in UKR eliminates the need for conventional instrumentation and allows access to the bone through a reduced incision. By leveraging the surgeon's skill in manipulating soft tissues and actively optimising the tool's access to the bone, combined with the precision and reproducibility of the robotic control of bone cutting, we expect to make UKR surgery available to a wider patient population with isolated medial osteoarthritis that might otherwise receive a total knee replacement. In addition to accurate bone shaping with a handheld robotically controlled tool, NavioPFS system for UKR incorporates a CT-free planning system. This approach combines the practical advantages of not requiring pre-operative medical images, while still accurately gathering all key information, both geometric and kinematic, necessary for UKR planning

In the last years custom-fit cutting guides using magnetic resonance imaging (MRI) were introduced by orthopedic surgeons for total knee arthroplasty (TKA). One of the advantages of these shape-fitting jigs is the possibility to transfer the preoperative planning of the TKA directly to the individual patient's bone. However, one has to be aware, that the jigs are designed for single-use and have to be custom made by an external manufacturer. This increases the cost of implantation and unlinks the surgeon from this process. In addition a potentially necessary adjustment of the preoperatively planned implant size and position in a surgical situation is not possible. The purpose of our development was to combine the advantages of custom-fit cutting guides as a 3-D-computer-assisted planning tool with the option to adjust and improve the preoperative planning and the jig in the actual surgical situation. In addition no outside jig manufacturing would occur in this concept. This leaves the surgeon in control of the entire process. The purpose of this study was to examine the reliability of this screw-based shape – fitting system. In order to do this we assessed the inter- and intra-observer reliability of the recurrent placement of the plate on a set of bone samples with preset screws. We developed a plate with the dimension of 66 × 76 × 10 mm, containing 443 threaded holes. A connector for further instrumentation is mounted on the proximal part of the plate,. As the plate and the screws are made of aluminum and steel, sterilization is possible. After computer tomography (CT) scans were taken from three human femoral bones, eight to nine variably positioned screws (50.45 mm length, 2.75 mm diameter), reversibly fixed by locknuts, formed an imprint of a bone's surface. For calculating precise screw positions, a computer-based planning software was developed resulting in a three-dimensional reconstruction of the bony surfaces. The plate was integrated in the 3-D reconstruction software. With a defined distance to the distal part of the femurs, allowed the proper length and position of the screws to be calculated. These calculations were transferred to the screws on the real plate. In the next step the plate was positioned on the bony surface and after reaching the planned position the plate's connector was rigidly fixed to the bone. The plate was removed to give place to link saw jigs to the connector. Planning and setting of the plate and the screws were conducted on three femoral bones. Examinations were performed by five investigators with ten repetitions on each bone with three distinct plates. Intra- and inter-observer variability was assessed by measuring the variation in plate position between the trials. The jigs were placed in a mean frontal tilting (medial to lateral) of 0.83°. The mean axial tilting (proximal to distal) was 1.66° and the mean shift on the axis from proximal to distal 8.48 mm. The shift and the tilting were significantly bone dependent but not user dependent. Compared with previous studies the deviation from the mechanical axis were comparable with conventional TKA (2.6° and 0.4°), computer assisted TKA (1.4° and 1.9°) and Custom-fit TKA (1.2°). We developed a preoperative planning system for TKA that allows a transfer of the planning and the calculated imprint of the bones surface on a grid-plate during surgery by the surgeons themselves. Neither external manufacturers to create a fixed device nor a navigation system is necessary. Results showed the functioning of the screw – based shape fitting technique within the accuracy mentioned above. These findings are encouraging to do further research to examine the ideal number of screws to offer a perfect fitting