Introduction. Re-revision due to instability and dislocation can occur in up to 1 in 4 cases following revision total hip arthroplasty (THA). Optimal placement of components during revision surgery is thus critical in avoiding re-revision. Computer-assisted navigation has been shown to improve the accuracy and precision of component placement in primary THA; however, its role in revision surgery is less well documented. The purpose of our study was to evaluate the effect of computer-assisted navigation on component placement in revision total hip arthroplasty, as compared with conventional surgery. Methods. To examine the effect of navigation on acetabular component placement in revision THA, we retrospectively reviewed data from a multi-centre cohort of 128 patients having undergone revision THA between March 2017 and January 2019. An imageless computer navigation device (Intellijoint HIP®, Intellijoint Surgical, Kitchener, ON, Canada) was utilized in 69 surgeries and conventional methods were used in 59 surgeries. Acetabular component placement (anteversion, inclination) and the proportion of acetabular components placed in a functional safe zone (40° inclination/20° anteversion) were compared between navigation assisted and conventional THA groups. Results. Mean inclination decreased post-operatively versus baseline in both the navigation (44.9°±12.1° vs. 43.0°±6.8°, p=0.65) and control (45.8°±19.4° vs. 42.8°±7.1°, p=0.08) groups. Mean anteversion increased in both study groups, with a significant increase noted in the navigation group (18.6°±8.5° vs. 21.6°±7.8°, p=0.04) but not in the control group (19.4°±9.6° vs. 21.2°±9.8°, p=0.33). Post-operatively, a greater proportion of acetabular components were within ±10° of a functional target (40° inclination, 20° anteversion) in the navigation group (inclination: 59/67 (88%), anteversion: 56/67 (84%)) than in the control group (49/59 (83%) and 41/59, (69%), respectively). Acetabular component precision in both study groups improved post-operatively versus baseline. Variance in inclination improved significantly in both control (50.6° vs. 112.4°, p=0.002) and navigation (46.2° vs. 141.1°, p<0.001) groups. Anteversion variance worsened in the control group (96.3° vs. 87.6°, p=0.36) but the navigation group showed improvement (61.2° vs. 72.7°, p=0.25). Post-operative variance amongst cup orientations in the navigation group (IN: 46.2°; AV: 61.2°) indicated significantly better precision than that observed in the control group (IN: 50.6°, p=0.36; AV: 96.3°, p=0.04). Discussion. Re-revision is required in up to 25% of revision THA cases, of which 36% are caused by instability. This places a significant burden on the health care system and highlights the importance of accurate component placement. Our data indicate that the use of imageless navigation in revision THA – by minimizing the likelihood of outliers – may contribute to lower rates of re-revision by improving component orientation in revision THA. Conclusion. Utilizing imageless navigation in revision THAs results in more consistent placement of the acetabular component as compared to non-navigated revision surgeries

Introduction. Roentgen stereophotogrammetric analysis (RSA) is currently the gold standard to measure early prosthetic migration which can predict aseptic loosening. However, RSA has some limitations such as the need for perioperative placed markers and exposure to X-radiation during follow up. Therefore, this study evaluates if low field MRI could be an alternative for RSA. Low field MRI was chosen because it is less hampered by metal artifacts of the prosthesis than high field MRI. Methods. 3D models of both the tibial component of a total knee prosthesis (Genesis II, Smith and Nephew) and the porcine tibia were made. The tibial component was implanted in the tibial bone. Consequently, 17 acquisitions with the low field MRI scanner (Esaote G-scan 0.25T) in transverse direction with a 2D PD weighted metal artifact reducing sequence PD-XMAR (TE/TR 10/1020ms, slice thickness 3mm, FOV 180×180×120 mm³, matrix size 224×224) were made. The first five acquisitions were made without repositioning the cadaver, the second twelve after slightly repositioning the cadaver within limits that are expected to be encountered in a clinical setting. Hence, in these 17 acquisitions no prosthetic-bone motions were induced. The scans were segmented and registered with Mimics. Virtual translation and rotation of the prosthesis with respect to the bone between two scans were calculated using a Procrustes algorithm. The first five scans without repositioning were used to calculate the measurement error, the following twelve to calculate the precision of low field MRI to measure prosthetic migration. Results were expressed as the maximum total point motion, mean error and 95% CI and expressed in boxplots. Results. The error of the method to measure the prosthetic position without repositioning has a mean translation between 0.09 and 0.22mm with a 95%CI between 0.30 and 0.46mm. The mean rotation was between 0.02° and 0.11° with a 95%CI between 0.18° and 0.32° with a MTPM of 0.45mm. The precision of low field MRI to measure migration with repositioning has a mean translation between 0.02 and 0.12mm with a 95%CI between 1.16mm and 1.86mm. The mean rotation was between 0.01° and 0.15° with a 95%CI between 1.78° and 3.26° with a MTPM of 2.35mm. The overall registration error was largest in the distal-proximal direction. Discussion. At the moment the low field MRI technique is not as accurate as this gold standard RSA. The accuracy of RSA varies between 0.05 and 0.5 mm for translation and 0.15 ° to 1.15 ° for rotation (95% confidence intervals). However, results are comparable with markerless RSA studies. The largest measurement error was found in the distal-proximal direction, which can be explained by the through-plane resolution of 3 mm, which is larger than the in-plane resolution of 0.8×0.8 mm². Future research should focus on improving resolution in the distal-proximal direction which would improve the precision. Moreover, an actual migration study should be performed to proof the true value of this low field MRI base markerless and X-radiation free alternative to measure prosthetic migration

Introduction. Restoration of normal hip biomechanics is vital for success of total hip arthroplasty (THA). This requires accurate placement of implants and restoration of limb length and offset. The purpose of this study was to assess the precision and accuracy of computer navigation system in predicting cup placement and restoring limb length and offset. Material and Methods. An analysis of 259 consecutive patients who had THA performed with imageless computer navigation system was carried out. All surgeries were done by single surgeon (KD) using similar technique. Acetabular cup abduction and anteversion, medialisation or lateralisation of offset and limb length change were compared between navigation measurements and follow-up radiographs. Precision, accuracy, sensitivity and specificity were calculated to assess navigation for cup orientation and student t-test used for evaluation of offset and limb length change. A p value of <0.05 was considered significant for evaluation. Results. Mean cup abduction and anteversion was 40.35° (SD, 5.81) and 18.46° (SD, 6.79) in postop radiographs compared to 41° (SD, 5.03) and 14.76° (SD, 6.11) for navigation measurements. Intraoperative navigation measurements had high precision and specificity for determining cup abduction and anteversion (precision >95%, specificity >90%). Accuracy for determining cup abduction was 96.13% compared to 72.2% for cup anteversion. Change in limb length and offset was mean 6.46mm (SD, 5.68) and −1.07mm (SD, 5.75) on radiograph evaluation and 5.41mm (SD, 5.11) and −2.24mm (SD, 5.87) from navigation measurements respectively, the difference being not significant in both (p value > 0.2). Radiograph and navigation had a mean difference of 1.01mm (SD, 2.83) for offset measurements and a mean difference of 1.05mm (SD, 4.37) for postop limb length assessment. Discussion. To the best of our knowledge this is the largest single surgeon study of navigated THA. We found that computer navigation assessment of acetabular cup abduction and anteversion and limb length and offset restoration has high probability of predicting correct placement of implants. To conclude, navigation can serve as an excellent tool for appropriate placement of implants and restoring limb length and offset in THA

Introduction. There is great interest in technologies to improve the accuracy and precision in placing implants for total hip arthroplasty (THA). Malik et al. (J Arthroplasty, 2010) showed that an imageless navigation system could be used to produce accurate measures of acetabular cup alignment compared to a CT-based alignment method using an imaging phantom. In this study we sought to compare the precision of an image-based navigation system with post-operative CT scans in a clinical patient cohort who received navigation-assisted THA. Methods. Eighteen patients with 20 hips consented to this IRB-approved analysis of intra- and post-operative THA cup alignment. All patients received THA with image-assisted alignment (MAKO Surgical, Fort Lauderdale). Nominal cup placement, subject to intraoperative surgeon adjustment and approval, was 40° radiographic inclination (RI) and 20° radiographic anteversion (RA) according to the definitions of Murray (JBJS-Br, 1993). Intraoperative cup alignment was measured by collecting five points on the cup rim with an optically tracked stylus. Postoperative cup alignment was measured by registering pre- and post-operative pelvic models generated from CT scans, and determining the postoperative cup orientation relative to the pre-operative pelvis coordinate system (Figure 1). Repeated measures testing of the CT-based measurements on 10 patient scans showed precision and bias of 0.7° and 0° for radiographic inclination, and 0.6° and 0.1° for radiographic anteversion. Results. Mean cup alignment with navigation and CT was within 1° of the nominal target values (Figure 2). There was not a significant difference in the cup inclination measure between intraoperative and CT-based measures, while the intraoperative measure of anteversion showed a 2° bias compared to the CT-based measures. Using a 5° difference between the intraoperative and postoperative measures as the definition for cup placement outliers, 2 cups (10%) were outliers for inclination and 3 cups (15%) were outliers for anteversion (Figure 3). No cup in this series was an outlier for both inclination and anteversion. Discussion. Optical navigation to confirm cup placement appears to result in relatively few alignment outliers, with no outliers for both angles and no single difference greater than 10°. Although differences between intraoperative and CT-based measures were small, it appears acquisition of a larger number of points on the cup rim could further enhance the precision of the navigation-based surgeon feedback. Consistent with previous studies, cup alignment using optical navigation is more precise than cup alignment using traditional manual methods

Obesity is a risk factor for acetabular malposition when total hip arthroplasty (THA) is performed with manual orientation techniques. However, conflicting evidence exists regarding the usefulness of computer-assisted surgery for performing THA in obese patients. The purpose of this study was to compare the precision and accuracy of imageless navigation for acetabular component placement in obese versus non-obese patients. After institutional review board approval, 459 THA performed for primary hip osteoarthritis were reviewed retrospectively. The same imageless navigation system was used for acetabular component placement in all THA. During surgery the supine anterior pelvic plane was referenced superficially. THA was performed via posterolateral approach in the lateral position. A hemispherical acetabular component was used, with target inclination of 40° and target anteversion of 25°. Computer software was used to determine acetabular orientation on postoperative anteroposterior pelvic radiographs. Obese patients (BMI ≥ 30 kg/m2) were compared to non-obese patients. A 5° difference in mean orientation angles was considered clinically significant. Orientation error (accuracy) was defined as the absolute difference between the target orientation and the measured orientation. Student's t test was used to compare means. Hartley's test compared variances of the mean differences (precision). Fisher exact tests examined the relationship between obesity and component placement in the target zone (target ± 10°) for inclination and version. All statistical tests were two-sided with a significance level of 0.05. Differences in mean inclination and anteversion between obese and non-obese groups were 1.1° (p=0.02 and p=0.08, respectively), and not clinically significant. Inclination accuracy trended toward improvement for non-obese patients (p=0.06). Inclination precision was better for non-obese patients (p=0.006). Accuracy and precision for anteversion were equal between the two groups (p=0.19 and p=0.95, respectively). There was no relationship between obesity and placement of the acetabulum outside of the target ranges for inclination (p=0.13), anteversion (p=0.39) or both (p=0.99), with a trend toward more inclination outliers in obese patients versus non-obese patients (7.3% versus 3.9%). The observed differences in mean acetabular orientation angles were not clinically significant (< 5°), although inclination orientation was less accurate and precise for obese patients. In contrast to existing literature, we found no difference in the accuracy and precision with regard to anteversion in obese and non-obese patients. We propose that accurate superficial registration of landmarks in obese patients is achievable, and the use of imageless navigation likely improves acetabular positioning in obese and non-obese patients

Introduction. RSA is widely accepted as a precise method to asses wear and migration early in the postoperative period. In traditional RSA, one segment defines both the acetabular shell and the polyethylene liner. However, inserting beads into the liner permits employment of the shell and liner as two separate segments, thus enabling distinct analysis of the precision of three measurement methods in determining wear and acetabular shell migration. The purpose of this in vivo follow-up study was to determine if assigning the shell and liner as one combined, or two individual segments affected the precision of RSA measurements of wear and shell stability. Methods. The UmRSA program was used to analyze the double examinations of 51 hips to determine if there was a difference in precision among 3 measurement methods: the shell only, the liner only, and the shell + liner combined segment. Tantalum beads were inserted into the liner and pelvic bone surrounding the shell intraoperatively for the purpose of RSA. Polyethylene wear was measured using point motion of the center of the head with respect to 3 different segments: 1) liner only, 2) the shell only and, 3) shell + liner segment. Cup stability was measured by segment motion comparing the stable pelvic segment to 1) the liner segment, 2) the shell only segment, and 3) the shell + liner segment. The Wilcoxon paired signed-ranks test was used to determine differences in condition number and bead counts among the 3 measurement methods (p ≤0.05). Results. The 95% confidence interval, calculated from double examinations, established the precision of each method. The shell + liner and liner only methods had a precision of 0.03mm when measuring both wear and shell migration. The shell only method precision was 0.07mm when measuring wear and 0.08mm when measuring shell migration, making it the least desirable method. In both the wear and migration analyses, the shell + liner condition number was significantly lower and the bead count was significantly higher than those of the shell only and liner only methods, indicating a superior RSA analysis on all counts compared to the shell only and liner only methods. Discussion. Insertion of beads in the polyethylene improves the precision of wear and shell migration measurements. A greater dispersion and number of beads when combining the liner with the shell generated more reliable results in both analyses by engaging a larger portion of the radiograph. The liner beads also allow measurement of cup rotation of the shell + liner segment, which is not possible when using the shell segment alone, due to the 2D nature of the program's algorithm to detect the edge of the cup. As the prediction of implant survivorship in the early postoperative period relies heavily upon RSA, it is crucial to use the most precise system to monitor these implants and the shell+ liner method meets that standard

This study presents the use of precision surface machining on artificial joint bearing surfaces in order to inhibit macrophage activation. Ultra-high molecular weight polyethylene (UHMWPE) is widely used as a bearing material in polymer-on-hard joint prostheses. However, UHMWPE wear particles are considered to be a major factor in long-term osteolysis and implant loosening. Several studies report that wear particle size is a critical factor in macrophage activation, with particles in the size range of 0.1 – 1.0 μm being the most biological active. The surface for a conventional Co-Cr-Mo alloy joint implant generally has a 10.0 – 20.0 nm roughness. After precision machining, the Co-Cr-Mo alloy surface had a 1.0 – 2.0 nm roughness with scattered concave shapes up to 50 nm in depth. This precision surface machining method used a typical lapping method, but the relationship between the slurry and the machining surface was strictly controlled in order to emphasize the micro-erosion mechanism. A pin-on-disc wear tester capable of multidirectional motion was used to verify that the new surface was the most appropriate for joints. Tests were carried out in 25% (v/v) fetal calf serum with sodium azide to retard bacterial growth. UHMWPE pins, 12.0 mm in diameter with a mean molecular weight of 6.0 million, were placed on the Co-Cr-Mo alloy disc at a contact pressure of 6.0 MPa. A sliding speed of 12.1 mm/s, and a total sliding distance of 15.0 km were applied. The new surface reduced the amount of UHMWPE wear, which would ensure the long-term durability of joints. The new surface also enlarged the size of UHMWPE particles, but did not change their morphological aspect. Primary human peripheral blood mononuclear phagocytes were cultured with the particles. The wear particles generated on the new surface inhibited the production of IL-6, which indicates a reduction of induced tissue reaction and joint loosening

Introduction. Radiostereometric Analysis (RSA) is an imaging method that is increasingly being utilized for monitoring fixation of orthopaedic implants in randomized clinical trials. Extensive RSA research has been conducted over the last 35+ years using standard clinical x-ray acquisition modalities that irradiate screen/film media or Computed Radiography (CR) plates. The precision of RSA can depend on a number of factors including modality image quality. Objective. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw. Methods. A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0 mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovine tibia segment. Six additional 1.0 mm tantalum beads were inserted into the bone segment superiorly, distally and adjacent to the pedicle screw. The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSA carbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plates were placed below the calibration cage and irradiated 8 times at 100, 125 kV at 2.5 mAs. For DR additional test were performed at 150 kV, and again at 100 kV at 0.5 mAs. At the time of abstract submission CR results at these settings were not available. To determine precision, the standard deviation of 3D vector distances between beads was determined using RSA for each of the different imaging parameters. Results. Standard deviations of the inter-bead distances measured in the pedicle screw were 44.4 and 32.1 μm (N=8) respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system, compared to 109.0, 55.8 μm for CR [Fig. 1]. The distances between the bone implanted beads provided standard deviations of 24.4 and 22.7 μm respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system, compared to 33.1 and 33.0 μm with the CR system. Further increasing the photon energy to 150 kV with the DR system reduces the precision error to 22.4 μm in the pedicle screw and remains approximately the same at 21.0 μm in bone. Lowering the mAs while maintaining 100 kV increases the precision error in the pedicle screw (64 μm) and showed no significant difference in bone (24.4 μm). Conclusion. The current phantom design is basic in nature and does not account for any soft tissue scatter. However, initial results indicate a considerable reduction in precision error when using DR compared to CR imaging equipment for RSA analysis. Increasing the kV did not significantly influence the precision in measuring bead locations in bone. For embedded tantalum beads within a titanium pedicle screw, imaging at higher kV values with the described DR imaging system did allow more precise localization. This approach may be useful in assessing the in vivo position of spine or other titanium implants

Purpose. Radiostereometric Analysis (RSA) is a well developed imaging technique used to estimate implant fixation of orthopaedic implants in randomized clinical trials. The precision of RSA depends on a number of factors including image quality related to the individual modality properties. This study assesses the precision of RSA with a novel Digital Radiography (DR) system compared to a CR imaging system using different imaging techniques. Additionally, the study assesses the precision of locating beads embedded in a modified spine pedicle screw. Method. A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0 mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovine tibia segment. Six additional 1.0 mm tantalum beads were inserted into the bone segment – superiorly, distally and adjacent to the pedicle screw. The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSA carbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plates were placed below the calibration cage and irradiated 15 times at 100, 125 kV at 2.5 mAs. To determine precision, the standard deviation of 3D vector distances between beads was determined using RSA for each of the different imaging parameters. Results. The precision error (PE), defined as the standard deviation of the 3D Bone Marker marker locations for CR is 35.5 m for 100kV at 0.5 mAs setting and 42.2, 39.4, and 26.7 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. However, for DR, the PE is 27.5 m for 100kV at 0.5 mAs setting and 25.7, 25.1, and 20.1 m for the 2.5 mAs at 100, 125, and 150 kV settings. The PE for Screw Marker 3D locations, for CR is 38.2 m for the 100kV at 0.5 mAs setting and 55.2, 47.3, and 37.1 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. However for DR, the PE is 40.3 m for 100kV at 0.5 mAs setting and 33.2, 24.9, and 17.0 m for the 2.5 mAs at 100, 125, and 150 kV settings respectively. The PE for all Bone Marker and Screw Marker 3D locations were significantly lower (P<0.05) for the DR technology than the CR technology except at the 100kV at 0.5 mAs exposure of the Screw Marker, P = 0.589. Conclusion. The PE decreases for increasing kV, especially in the case of screw markers where the error goes from 33 micron (100kV) to 17 micron (150 kV). Increasing the mAs reduces the error for the DR, but increases the error for CR. Increasing the kV did not significantly influence the precision in measuring bead locations in bone. For embedded tantalum beads within a titanium pedicle screw, imaging at higher kV values with the described DR imaging system did allow more precise localization. The current phantom design is basic in nature and does not account for any soft tissue scatter. However, initial results indicate a gain in precision when using DR compared to CR imaging equipment for RSA analysis

Introduction. Precision Freehand Sculpting(PFS), is a hand-held semi-active robotic technology for bone shaping that works within the surgical navigation framework. PFS can alternate between two control modes – one based on control of exposure of the cutting bur (“Exposure Control”) and another based on the control of the speed of the cutting bur (“Speed Control”). In this study we evaluate the performance of PFS in preparing the femoral bone surface for unicondylar knee replacement (UKR). Methods. The experiment is designed to prepare a synthetic bone for unicondylar knee replacement (UKR). The implant plan is mapped to individual specimen using a jig that fit in a unique and repeatable way to all specimens. During bone preparation, the PFS handpiece and the specimen are both tracked with the Polaris Spectra (Northern Digital Inc.) using passive reflective markers. The cutting plan is specified so that the specimens can receive a specially designed implant after the cut is finished. The implant is a modified commercial design with three planar back faces and two pegs. In addition there are 10 conical divots on the implant surface that can be used to register the implant after it is placed on the prepared bone surface. The distal and distal-anterior facets were cut with a 5 mm cylindrical bur using Extension Control. The posterior facet and the post holes were cut using 6 mm spherical bur using Speed Control. Three subjects cut 5 specimens each. One subject was an experienced PFS user. The second user was somewhat less experienced, and the third user was completely inexperienced with the use of PFS. The performance was evaluated in terms of the implant fit and the performance time. The final implant fit was characterized using a MicroScribe MX desktop coordinate measuring arm. Results. The average cut times for the first two cuts combined were 4:45 min, and for the posterior cut 3:26 min. The average distances/st.dev. from the planned implant position were 0.54 /0.23 mm and the angular differences were average/st.dev. of 1.08/ 0.53 degrees. Conclusions. All specimens were cut accurately, and with clinically acceptable surface finish. No implants were significantly malpositioned, nor were any unable to be positioned due to poor fit or planar malalignment. For both experienced users, the procedure times were short, averaging below 8 min, whereas the inexperienced user demonstrated rapid improvement in performance time

Background. In our pursuit of surgical accuracy and precision we often neglect to evaluate our results objectively. With the use of Computerised Tomography (CT) in pre-operative planning we can use the same technology in order to evaluate surgical accuracy. Hypothesis. The use of Patient Specific Instrumentation (CT based) produces an accurate intra operative guide for precision cutting in knee arthroplasty. Method. A prospective study using Patient Specific Instrumentation (customized cutting blocks) was performed on 35 patients. The small cohort value is due to the high costs of post-operative CT. A CT based software was used to evaluate the pre-operative knee alignment. Surgery was planned and verified on a web based programme with the use of 3D models. Cutting blocks were custom made and used as intra operative guide to make the relevant cuts. Pre and post-operative CT scans were compared for AP and lateral alignment, femoral external rotation and flexion and tibial slope. Knee Society scores were also used to evaluate the clinical outcome. Results. The values for AP and lateral limb alignment, femoral external rotation and flexion were the same as the pre-operative values with no significant deviation (maximum 2 degree difference). The posterior tibial slope was the only value that showed significant deviation from the pre-planned values. Conclusion. There was a significant difference for the posterior tibial slope but otherwise we found no difference in pre and post-operative limb alignment measurements. Pre-operative planning with the use of CT based customised cutting blocks is a reliable and accurate option to obtain optimal alignment and prosthetic orientation in total knee arthroplasty. NO DISCLOSURES

Robotic surgical systems reduce the cognitive workload of the surgeon by assisting in guidance and operational tasks. As a result, higher precision and a decreased surgery time are achieved, while human errors are minimised. However, most of robotic systems are expensive, bulky and limited to specific applications. In this paper a novel semi-automatic robotic system is evaluated, that offers the high accuracies of robotic surgery while remaining small, universally applicable and easy to use. The system is composed of a universally applicable handheld device, called Smart Screwdriver (SSD) and an application specific kinematic chain serving as a tool guide. The guide mechanism is equipped with motion screws. By inserting the SSD into a screw head, the screw is identified automatically and the required number of revolutions is executed to achieve the desired pose of the tool guide. The usability of the system was evaluated according to IEC 60601-1-6 using pedicle screw implementation as an example. The achieved positioning accuracies of the drill sleeve were comparable to those of fully automatic robotic systems with −0.54 ± 0.93 mm (max: − 2.08 mm) in medial/lateral-direction and 0.17 ± 0.51 mm (max: 1.39 mm) in cranial/caudal- direction in the pedicle isthmus. Additionally, the system is cost-effective, safe, easy to integrate in the surgical workflow and universally applicable to applications in which a static position in one or more DOF is to be adjusted

Purpose. Femoral shaft fractures are routinely treated using antegrade intramedullary nailing under fluoroscopic guidance. Malreduction is common and can be due to multiple factors. Correct entry point identification can help minimize malreduction and the risk of iatrogenic fracture. This study aims to compare landmark identification used to guide nail entry, the piriformis fossa (PF) and the trochanteric tip (T), via computer navigation and conventional fluoroscopy. Method. The location of the PF and T were digitized under direct visualization with a three-dimensional scribe on ten, fresh-frozen cadaveric right femora (two male, eight female) by three fellowship trained orthopaedic surgeons. To estimate inter- and intraobserver reliability of the direct measurements, an intraclass correlation coefficient was calculated with a minimum of two weeks between measurements. Under navigation, each specimen was draped and antero-posterior (AP) and lateral radiographs of the proximal femur were taken with a c-arm and image intensifier. The c-arm was positioned in a neutral position (0 for AP, 90 for lateral) and rotated in 5 increments, yielding a range of acceptable images. Images, in increments of 5, within the AP range (with a neutral lateral) were loaded into a navigation system (Stryker, MI). A single surgeon digitized the T and PF directly based on conventional fluoroscopy, and again directed by navigation, yielding two measurements per entry point per specimen. This was repeated for the lateral range. Hierarchical linear modelling and a Wilcox rank test were used to determine differences in accuracy and precision, respectively, in the identification of PF and T using computer navigation vs. conventional fluoroscopy. Results. The average range of suitable images for both the AP and lateral images was 29 (range of 25 to 30). The location of the PF and T was found to be reliable for a single observer (0.98 and 0.99) and between observers (0.96 and 0.93). Similar accuracy was found in identifying PF under navigation and fluoroscopy (0.05 to 1.4 cm and 0.1 to 1.5 cm respectively, p = 0.26), whereas improved accuracy was found for T using fluoroscopy (0.07 to 2.5 cm) as compared to navigation (0.2 to 2.2 cm, p < 0.001). For both the PF and T, the navigation-based points had greater precision than those selected by fluoroscopy alone (p = 0.001 and p = 0.024). Conclusion. The ideal entry point, under direct visualization, was highly repeatable, indicating that the surgeons could identify their targeted point of entry for both the PF and T. However, there is an arc of approximately 30, through which acceptable AP and lateral images can be obtained. Throughout this range, the location of the PF and T can vary up to 1.5 and 2 cm, respectively. Navigation was less accurate than fluoroscopy in the T selection, yet had greater precision for both points. Thus, while navigation may decrease accuracy in selection of the T, it is more repeatable overall and equally accurate in selecting the PF

Objective. Several researchers have reported that imageless navigation is a reliable technique and results in more precise cup placement compared to conventional freehand techniques, however, few studies have been reported about the accuracy of the femoral stem placement. The primary aim of this study was to evaluate the precision of an imageless navigation system in measuring the limb length change. The secondary aim was to evaluate LLD following imageless navigation THA with modified registration technique in semilateral decubitus position. Methods. The authors reviewed 66 cases receiving cementless THA with imageless navigation from September 2013 to December 2014. The radiographic limb length change measured from pre-operative and post-operative digital x-ray was compared with the intraoperative calculation by the navigation system. Postoperative LLD in unilateral cases and second operation of staged bilateral cases were also recorded. Results. The mean radiographic limb length change measured on digital x-ray was 17.4 mm (5 to 29.3, SD 5.7). The mean limb length change calculated by navigation system was 16.8 mm (3 to 28, SD 5.9). The mean paired difference was 2.27 mm (−6 to 8, SD 0.9). This difference was significant (p=0.01). There was significant correlation between LL change measured on digital x-ray and which were calculated by navigation system (r=0.95, p<0.001). The navigation system had an accuracy of within 1 mm of the radiographic measurement in 7.6% of cases, within 2 mm in 39.4% of cases and within 5 mm in 93.9% of cases. The mean postoperative LLD was 2 mm (0 to 7, SD 1.9), 92% were within 5 mm. Conclusion. This study showed that the imageless navigation THA with modified registration technique in semilateral decubitus position offered a precise limb length measurement and the results were very encouraging for clinical use to minimize LLD in THA

Background

Manually instrumented knee arthroplasty is associated with variability in implant and limb alignment and ligament balance. When malalignment, patellar maltracking, soft tissue impingement or ligament instability result, this can lead to decreased patient satisfaction and early failure. Robotic technology was introduced to improve surgical planning and execution. Haptic robotic-arm assisted total knee arthroplasty (TKA) leverages three-dimensional planning, optical navigation, dynamic intraoperative assessment of soft tissue laxity, and guided bone preparation utilizing a power saw constrained within haptic boundaries by the robotic arm. This technology became clinically available for TKA in 2016. We report our early experience with adoption of this technique.

Introduction

Total Knee Arthroplasty (TKA) is highly successful in treatment of end-stage degenerative arthritis of the knee. CT-based Patient-Specific Instrumentation (PSI) utilizes a CT scan of the lower extremity to create a three-dimensional model of the patient's anatomy, plan the surgery, and provide unique patient-specific resection blocks for the surgery.

There are few published studies utilizing CT-PSI. The present study prospectively evaluates clinical, operative, and radiographic outcomes from 100 CT-based TKAs using this technology (MyKnee®, Medacta International S.A., Castel San Pietro, Switzerland).

Background

Surgeons are waiting for a hassle free, time saving, precise and accurate guide for hip arthroplasty. Industry are waiting for instruments to reduce manufacturing costs associated with washing, assembling, sterilization and transportation. Patient specific / custom made surgical guides may deliver these goals but current systems have had limited assessments.

We comprehensively assessed a new guiding system for the acetabular component of hip replacement, “Bullseye”.

Purpose:

Imageless navigation has improved the accuracy of acetabular cup placement but relies on manual identification of pelvic anatomy. Thick soft tissues in obese patients could obscure these landmarks and result in large variances of cup placement. The purpose of this study was to investigate the relationship between BMI, soft tissue thickness, navigated cup and final post-operative cup position.

Awareness that minimising tip apex distance (TAD) when inserting a sliding hip screw reduces the risk of screw cut out is important for orthopaedic trainees. The advent of the Picture Archive and Communication System (PACS) has made the accurate measurement of TAD from x-rays and image intensifier films much easier. This study was to determine whether TAD would be reduced if a surgeon knew that his performance was being continually monitored.

31 consecutive cases of sliding hip screw insertion by a single group of surgeons were identified and the TAD measured. The mean TAD was 16.11mm (8.87mm-25.47mm). The same surgeons were then re-educated as to the importance of the TAD and informed that their results would be monitored and discussed. The next 34 consecutive cases were collected prospectively. The mean TAD in these cases was 13.83mm (6.72mm-21.51mm). There was a significant difference between the TAD for the two groups using the two-tailed t-test (p=0.034). There was one implant failure in the pre education group and none in the post education group.

These results suggest that awareness of surveillance improves surgical performance even if the importance of the variable being assessed is already known.

Introduction. Recent technological advancements have led to the introduction of robotic-assisted total knee arthroplasty to improve the accuracy and precision of bony resections and implant position. However, the in vivo accuracy is not widely reported. The primary objective of this study is to determine the accuracy and precision of a cut block positioning robotic arm. Method. Seventy-seven patients underwent total knee arthroplasty with various workflows and alignment targets by three arthroplasty-trained surgeons with previous experience using the ROSA® Knee System. Accuracy and precision were determined by measuring the difference between various workflow time points, including the final pre-operative plan, validated resection angle, and post-operative radiographs. The mean difference between the measurements determined accuracy, and the standard deviation represented precision. Results. The accuracy and precision for all angles comparing the final planned resection and validated resection angles was 0.90° ± 0.76°. The proportion within 3° ranged from 97.9% to 100%. The accuracy and precision for all angles comparing the final intra- operative plan and post-operative radiographs was 1.95 ± 1.48°. The proportion of patients within 3° was 93.2%, 95.3%, 96.6%, and 71.4% for the distal femur, proximal tibia, femoral flexion, and tibial slope angles when the final intra-operative plan was compared to post-operative radiographs. No patients had a postoperative complication requiring revision at the final follow-up. Conclusions. This study demonstrates that the ROSA Knee System has accurate and precise coronal plane resections with few outliers. However, the tibial slope demonstrated decreased accuracy and precision were measured on post-operative short-leg lateral radiographs with this platform