CAOS 2023:Papers with Abstracts

Abstract. Morpho-functional analysis is a major aspect of preoperative planning for THA. This study aims to investigate whether pain or movement restrictions correlate with the morphofunctional parameters pelvic tilt, pelvic bend and pelvic rotation. Pre- and postoperative CT and EOS images, as well as score values of 201 Japanese patients were analyzed. No statistical relevant correlation between the score values and the parameters could be found (|rmax| = 0,38). However, the statistical power was found to be low for our data ((1-β ~ 0.10). Further research with larger data sets is desirable.

Abstract. Psoas syndrome after THA has received much attention in recent years. In some cases, the cause of pain cannot be found in a critical overhang of the implant cup, but is mainly unknown. We developed an approximation of modeling the medial part of the tendon of m. iliacus in 201 THA patients. We found length changes of the tendon of 7,73 mm ± 8,55 mm (range: -26,37 mm to 30,30 mm) and angular changes at the PSIS of 2,58 ° ± 1,72 ° (range: 0 to 7,91 °) and at the lesser trochanter of 10,53 ° ± 7,70 ° (range: 0,27 ° to 41,19 °). Furthermore, we identified 19 cases in whom the tendon wrapped over different bony structures than the acetabular region.
Hence, we think that the m. iliacus tendon should be considered for analysis of risk factors in the preoperative planning process for THA.

Abstract. In this study, we present and evaluate a suite of deep learning algorithms to assist orthopedic surgeons in the analysis of pre- and post-operative lower limb X-ray images. Deep learning algorithms obtained similar results as surgeons on the measurement of 10 different angles used for the assessment of the lower limb alignment.

Abstract. Robotic-assisted total hip arthroplasty (raTHA) was introduced in recent decades, offering proven advantages in improving the acetabular cup placement. However, the use of raTHA requires specific equipment and additional cost of $1,788 per case, raising the question of its cost-effectiveness. We believe that the use of raTHA may be substantially advantageous in complicated cases such as developmental dysplasia of the hip (DDH) with deformed anatomy, where proper prosthesis alignment is hard to achieve. Therefore, we conducted a systematic review and meta-analysis in accordance with the 2020 PRISMA to evaluate the benefits of raTHA over conventional total hip arthroplasty in DDH patients. From 80 studies that we found, only three were eligible. We primarily focused on the radiological outcomes and complications. However, functional outcomes were not compared and analyzed due to differences in reporting formats among the original studies. The analyses proved that raTHA was associated with a significantly increased rate of cup placement within Lewinnek's and Callanan’s safe zone. All studies had no report of any complications and revisions during the short term follow-up. Although statistical precision may have been affected by a limited number of studies, our review offers the first and most recent evidence-based analysis of the use of raTHA in secondary osteoarthritis caused by DDH. This meta-analysis revealed the potential benefits of the raTHA in improving radiological outcomes, which may outweigh the total costs in such well-selected cases.

Abstract. This study investigated the variability of the manual localization of anatomical landmarks of the distal femur using 3 different methods: CT, Mesh, and 3D printed models. From a CT database of 50 knees, 3D meshes were automatically generated and 3D printed. The main author performed twice, for each case, a registration of 11 distal femoral landmarks.
We investigated for each landmark and modality the:
• mean distance per modality
• averages distance between each modality
• deviation of each modality from the barycentre
• position of the new planes and axes relative to their starting position
Finally, the study was carried out on 41 knees, 9 of which had to be excluded because of 3D printing issues. 2706 manual annotations were performed.
Regarding the Intra-operator reproducibility, the average distances for each point and modality were between 1.49mm and 6.34mm. As for the analysis considering the barycenter no differences were found between the three modalities. However, some points showed more variability. But their impact on the 3 axes and the planes studied were found negligible. Mean angular variations for either axes or planes are all less than 0.5°.
In summary, no differences were found between the three modalities but some points showed more variability.

Abstract. Implant overhang in total knee arthroplasty is associated with adverse effects with regard to postoperative pain and function, whereas implant underhang or bone undercoverage has been linked to increased risk of bleeding and osteolysis. To determine the suitability of different standard implant systems for a certain population, an automated analysis of overhang, underhang and coverage would be favorable. Therefore, we developed an automated framework for femoral implant interface fit evaluation. To evaluate this framework, we used surface models of 433 cadaver knees and of one specific femoral implant size. An analysis of the bone-implant interface fit was performed for all knees for which the available implant size was selected on the basis of the knee’s size. The analysis involved the orientation of bone and implant via reference points, the virtual resection of the bone, and the derivation and comparison of bone-implant interface contours. Implant over-/underhang was evaluated for the entire contour and in specific zones (defined in the literature). Bone coverage was calculated for the entire interface. A good agreement with the literature with regard to mean values and ranges of over-/underhang was found. Limitations include the restriction to one specific implant system and size. Future analyses should focus on different implant sizes and systems as well as on the assessment of the tibial component.

Abstract. Estimation of glenoid bone loss following shoulder dislocation in a CT scan is often required to determine the appropriate surgery needed to restore shoulder stability [1]. Currently, the best method for measuring glenoid bone loss has not been universally defined, so various methods have been proposed [2,3]. They can be grouped into linear-based (most methods) and area-based measurement methods, without (standalone) or with a comparison with the healthy contralateral glenoid, which is not always included in the CT scan. In all cases, the measurements are performed manually, which is time-consuming, requires expertise, and is subject to observer variability.
This paper presents a novel automatic standalone linear-based method for glenoid bone loss quantification in shoulder CT scans.

Abstract. A common goal in total knee arthroplasty (TKA) is to obtain collateral ligament balance in both flexion and extension while maintaining neutral overall coronal alignment. Femoral component rotation is a key variable in achieving this goal. There are two prominent techniques used in TKA to determine implant orientation, measured resection and gap balancing, but there is some controversy over which technique is superior. At our institution, we regularly use both techniques over a wide range of patients with varying degrees of preoperative coronal deformity. We therefore asked, using intraoperative measurements from a surgical navigation system, can we detect significant differences in external rotation of the femoral component between measured resection and gap balancing techniques, and do any such differences occur more frequently or at higher levels at particular values of preoperative coronal deformity?
We analysed 3922 navigated TKA cases undertaken at our institution which had complete measurements of preoperative overall coronal alignment and external rotation of the femoral component relative to the dorsal condyles line. We then compared cases using measured resection to those using the gap balancing technique, stratifying patients by degree of preoperative coronal deformity and applying a two-sample t-test.
A total of 1969 cases that used measured resection and 1953 cases that used the gap balancing techniques were identified. We found no significant differences between the two techniques across most of the preoperative coronal deformity groupings, though small differences were detected in two specific subgroups: the femoral component was slightly more externally rotated in the measured resection cohort when the preoperative coronal deformity was between neutral and 50 valgus (mean ± standard deviation - measured resection: 3.60 ± 1.10, gap balancing: 3.00 ± 1.10, p < 0.00625) and between 50 valgus and 100 valgus (measured resection: 4.30 ± 1.40, gap balancing: 3.70 ± 1.30, p < 0.00625).
This study has shown that there were essentially no substantial differences between the external rotation of the femoral component between the gap balancing and measured resection techniques regardless of the degree of preoperative coronal deformity. Overall, we feel that surgical decisions regarding which technique to use should be based more on any correlations with other patient outcome measures that may be better elucidated in future studies.

Abstract. One of the goals of total knee arthroplasty (TKA) is to restore of extend the range of motion of the knee joint. A small proportion of patients who are candidates for TKA exhibit fixed flexion contracture (FFC), a condition which prevents the knee from reaching full extension and can be associated with preoperative coronal deformity. In treating FFC, surgeons have two options, either through extensive soft tissue releases or through additional resections of bone on the proximal tibia and distal femur to increase the extension gap. Usually, FFC can be corrected with just soft tissue release, however, sometimes needs to be combined with additional bone resections, especially in cases with varus or valgus coronal deformity. However, additional bone resections beyond 11mm on the femoral side can be associated with knee instability. We therefore asked, is there a relationship between preoperative coronal deformity and intraoperative bone resections required to treat patients with extreme FFC?
We analysed 3922 navigated TKA cases undertaken at our institution between March 2007 and October 2022. From this set, we identified 127 patients with extreme fixed flexion contracture (FFC) of greater than 150 and with post-operative FFC less than 50, indicating that the FFC had been resolved. Using simple linear regression and calculating the Pearson correlation coefficients, we related the preoperative coronal deformity to the maximum femoral and tibial resection depths between the medial and lateral sides. We then calculated the statistical significance and coefficient of determination.
For the 127 cases, the coefficients of determination were calculated to be 0.19 for the proximal tibia and 0.22 for the distal femur (p < 0.025). The correlation coefficients for the relationship between coronal deformity and femoral or tibial resection depths were 0.47 (p< 0.025) and -0.43 (p< 0.025), respectively.
In this study, we determined there was a moderate correlation (indicated as |0.40 – 0.59|) between the tibial and femoral bone resections required to treat extreme FFC in patients with varying degrees of preoperative coronal deformity. In planning to treat extreme FFC, surgeons should pay attention to the preoperative coronal deformity of patients as this will likely be an important factor in determining the required steps in successfully treating the FCC.

Abstract. Total knee arthroplasty (TKA) is a common approach to treating end-stage osteoarthritis of the knee while relieving pain and restoring joint function. However, the procedure has produced variations in postoperative outcomes, with up to 20% of patients left dissatisfied. Therefore, it is important to understand the preoperative and intraoperative factors that drive knee function post-TKA. Using intraoperative data acquired from a surgical navigation system and matched with patient pre- and postoperative data, this study aimed to identify preoperative and intraoperative predictors of PROMs measured using the Oxford Knee Score (OKS) at 1-year follow-up.
We analysed 363 cases of navigated TKA at our institution and matched them to preoperative and postoperative patient clinical records including age at index surgery, BMI, sex, presence of co-morbidities, EQ5D anxiety/depression score, and preoperative and postoperative OKS. Starting with a base model of 26 predictor variables, a linear regression model with backward elimination was used to identify predictors of postoperative OKS on a training set of 290 patients. 73 patients (20%) were randomly set aside to use as validation. We then used the remaining predictor variables to train two additional regression models: a Support Vector Machine (SVM) and a Boosted Decision Tree then calculated the coefficient of determination (R2) and percent of patients that where the postoperative OKS was correctly identified within the minimally important clinical difference of 4.9 when the models were applied to the validation set.
Of the 26 predictor variables, 10 predictors remained in the final model following backwards elimination, including four that were directly under the control of the surgeon. The R2 of the linear regression, SVM, and XGBoost models were 0.37, 0.30, and 0.29 respectively within the validation set. Percentages of patients with correctly predicted OKS within the MICD ranged from 52% to 57% (linear regression to SVM).
In this study, we identified sets of preoperative and intraoperative factors which are partially predictive of postoperative OKS at 1-year follow-up. Post-operative prediction models such as the models presented here will help to guide continued research into which intraoperative variables, including bony resection depths, implant alignment, and whether to do ligament releases in surgery, most affect implant function post-TKA and to inform patients and clinicians of possible clinical outcomes.

Abstract. The Coronal Plane Alignment of the Knee (CPAK) classification has been used to describe healthy and arthritic knee alignment as well as to predict phenotypes which could benefit from kinematic alignment using soft tissue balancing during TKA. At our institution, we have access to a large database of navigated TKA procedures including intra and postoperative mechanical hip-knee-ankle angle (mHKA) measurements, which are defined differently than the aHKA. It has been previously recognized that these alternative, but related, measures of coronal alignment may have different distributions. The primary aim of this study was therefore to determine if the CPAK classification frequencies described in the original publication by MacDessi et al. for the aHKA are similar to frequencies acquired using the mHKA. A secondary aim was to categorise postoperative TKA alignment at our institution utilising the mHKA-based CPAK classification.
We analysed data from 3947 total knee arthroplasty procedures undertaken using surgical navigation at our institution between March 2007 and October 2022. The mHKA was measured directly during the registration process while JLO was calculated using the mHKA and LDFA (JLO = HKA + 2xLDFA). This was completed twice for each case using the pre and postoperative mHKA and LDFA. Each case was then categorized as one of the nine CPAK phenotypes.
The pre-operative mean mHKA was 2.00 varus using surgical navigation (compared to 0.80 varus reported by Macdessi et al. using the aHKA). The pre-operative mean JLO was 1750 (versus 1740). Using the mHKA as opposed to the aHKA resulted in more knees being categorized as Class I (34.0% vs 19.4% ) or Class IV (17.5% vs 19.8%) and fewer in Class II (19.0% vs 32.2%) and Class V (6.3% vs 14.6%). All other differences in class frequencies were within 4%. For postoperative CPAK classification, a large majority of knees (72.7%) were categorized as Class V.
Our study using mHKA determined during navigated TKA showed that the majority of preoperative arthritic knees were Class I, II, and IV in contrast to the original CPAK publication where most preoperative knees were Class I, II, and III. For TKAs at our institution, the goal was to mechanically align knees to neutral mHKA and JLO. This reflects in our postoperative results in that 73% of all postoperative TKAs were categorized as Class V.

Abstract. Most CAOS for THA is used only for cup placement. Only Stryker Navigation provides real time
navigation for stem insertion, however, few surgeons use this system during stem insertion because its accuracy is believed to be low. We analyzed whether the additional reference points on distal femur improve the accuracy of stem placement. Sixty-three hips of 57 cases (13 males, 44 females, average age: 65.9 y.o.) were analyzed in the study. Proximal registration group (36 hips) were registered with 30 arbitrary points on proximal femur and distal registration group (27 hips) were registered with additional 4-8 points on the distal femoral condyle in addition to 30 arbitrary points on proximal femur. The differences (average ± standard deviation of absolute values) between the pre- and post-operative angles of stem anteversion were 3.7 ± 3.5°in the only proximal registration group, and 3.8 ± 3.1° in the distal addition group. The differences (average ± standard deviation of absolute values) between the pre- and intra-operative angles of stem anteversion were 3.6 ± 2.2° in the proximal registration group and 1.6 ± 1.7° in the distal registration group. Registration with additional distal reference points on femur did not improve accuracy and precision for stem placement. However, addition distal reference points provided intraoperative replication of preoperative planning. Future modifications are needed to improve accurately for stem insertion.

Abstract. Few surgeons use computer assisted surgery for stem placement in THA because its accuracy is not
sufficient rather than that for acetabular cup placement. Recently, cemented stem can be available in CT- based navigation, however, accuracy and precision of cemented stem alignment has not been reported. We compared accuracy and precision between cementless and cemented stems using the same CT-based navigation (Stryker hip navigation). We analyzed 43 cases (10 men, 33 women; average age 69.3 years) using cementless and cemented stem (Accolade II stem and Exeter stem [Stryker]) after CT-based navigation assisted THA. The differences (average ± standard deviation of absolute values) between the pre- and post-operative angles of stem anteversion were 3.8 ± 3.0° in the cementless group, and 2.4±1.8° in cemented group, respectively. There was a significant difference in precision in stem anteversion between the two groups. The accuracy and the precision of stem anteversion using the taper-wedge stem in this study was comparable to the previous reports using CT-based navigation. However, the precision of stem alignment with cemented stems was more accurate. When we used cemented stem, stem alignment consisted of 4 factors (stem flexion, varus, anteversion, and depth) could be completely controlled by checking the numbers on the navigation screens until bone cement hardened. Therefore, precision of cemented stem alignment using CT-based navigation are more accurate than that of cementless stems.

Abstract. Atrophy of thigh muscles significantly affects patients with hip diseases, thus quantifying the muscle volume can play an important role. Thigh circumference measurement has been used to predict thigh muscle volumes and atrophy. However, the validity of the measurement level, impact of error, and the relationship between each thigh muscle volumes at each measurement level remain not fully evaluated. In this study, we aimed to clarify the relationship between thigh circumference and the cross-sectional area (CSA) of each muscles using the deep learning model for automatic segmentation of the skin and muscles from CT images.
Using 3D models, the thigh circumference and the CSAs of each muscle were measured at 0 cm to 20 cm above the superior aspect of the patella with 1 cm increment. evaluate the correlation between thigh circumference and CSAs.
Thigh circumference tends to increase from distal to proximal, and for muscle’s CSA to increase as well. A strong correlation between muscle CSA and thigh circumference was observed above 5-10 cm, with a maximum correlation observed with the entire thigh muscle at 12 cm. Similar correlations were also observed around the level of maximum correlation. The correlation coefficients suggest that the measurement level should be adjusted for individual muscles. The correlation coefficients near the level of maximum correlation were almost equal, indicating that the influence of measurement level error is likely minimal.

Abstract. This study aims at comparing the nnU-Net, an open-source deep learning framework, with a previous customized U-Net model that we developed for the automatic segmentation of tibial and femoral bones from CT scans. The main purpose of our work is to develop a segmentation module that could be integrated into a surgical planning software for the design of customized Total Knee Prosthesis. The nnU-Net framework was chosen for its user-friendly design and features developed for medical imaging.
The same dataset of 112 CT scans of lower limbs from 63 patients was used to train and test both our customized U-Net model and the nnU-Net model. All these data were manually annotated. The evaluation was done by computing the Average Symetric Surface Distance, the Dice Coefficient, the Hausdorff Distance, the precision, the recall and the Jaccard Index. Both models yielded similar results on these metrics, but the nnU-Net model is easier to setup.
The performances of both models are also consistent with the literature, however, further tests on pathological data will be needed.

Abstract. Fractures of the sacroiliac joint often require treatment through internal fixation. This procedure is typically guided by the use of intraoperative fluoroscopy, using an untracked C-arm device. However, this involves ionizing radiation exposure and the possibility of screw malplacement. We introduce the Navigated Orthopaedic Fixation using Ultrasound System (NOFUSS): an ultrasound (US) based end-to-end system for providing real-time navigation for iliosacral screw (ISS) insertions. Our system consists of an US imaging device and an optical tracking camera, together with computational algorithms for automatic processing of intraoperative data. In a cadaver trial of 6 specimens, we found that the ISS insertions performed using NOFUSS demonstrated accuracy comparable to conventional fluoroscopy guidance in the three specimens for which we could obtain good ultrasound images, reduced insertion time, and required no ionizing radiation.

Abstract. Total Knee Arthroplasty is a frequently performed surgery. Patient specific planning and implants may improve surgical outcome. For this purpose, 3D models of the bones are required, which are typically generated by using computed tomography. A radiation free and cheaper alternative could be ultrasound. However, bone segmentation and a competitive method of creating a complete bone model are a challenge.
In this work a fully-automatic bone reconstruction pipeline using ultrasound, which includes machine learning based image segmentation and an interpolation algorithm for missing areas using statistical shape models, is presented and evaluation results with free hand probe guidance are outlined. A mean surface distance error of 0.96 mm for femur bone reconstruction is achieved. Furthermore, a robotic scanning approach is presented to automate the entire process. Autonomous scanning of the anterior distal femur was successful for 4 out of 5 probands. On average, 54 % of the accessed bone surface could be reconstructed.

Abstract. Up to 35% of total knee arthroplasty (TKA) patients experience short term anterior knee pain (AKP) and up to 20% of non-revised knees experience anterior knee pain in the long term. Patellofemoral pain is the primary cause of AKP and accounts for over 8% of revision TKA procedures in Australia. This study introduces a geometric patello- femoral ligament analysis model which was used to differentiate between patients with and without post-operative anterior knee pain.
All patients received pre- and post-operative CT scans and lateral flexed radiograph. The CT scans were segmented and landmarked before being registered to the flexed radiographs. The antero-posterior (AP) of the medial and lateral patellar edge relative to the medial and lateral femoral epicondyles were measured pre- operatively, post-operatively as well as the difference between the two states. These measurements were analysed for their impacts on patient outcome using the Kujala score.
Both medial and lateral antero-posterior patellofemoral offsets had statistically significant, moderate inverse correlations with the overall Kujala score. However, no statistically significant relationship was observed between the post- operative Kujala score and the pre-operative AP offsets or the change in AP offset between the pre- and post-operative states.
The results suggest that a higher medial or lateral post-operative patellofemoral AP offset, potentially due to the overstuffing of the patellofemoral joint, may result in inferior patient outcomes and residual AKP. Overall, it is imperative to consider the possible causes of post-operative AKP and models should be developed to inform surgeons in a clinical setting.

Abstract. Excessive post-operative tibiofemoral rotational mismatch can result in inferior patient outcomes. This highlights the importance considering the femoral axial alignment during tibial axial alignment. This study investigates different tibial rotational references including Insall’s axis, Cobb’s axis, and the projection of the TEA on the proximal tibial plateau in the CT, weightbearing and extension distracted positions.
All patients obtained a pre-operative long-leg supine CT scan, weightbearing antero-posterior radiograph and an extension distracted radiograph. Each CT scan was segmented and landmarked, and the resulting 3D bone models were registered to the two radiographs. The position of Insall’s axis was determined relative to Cobb’s axis and the projection of the surgical TEA on the proximal tibia in the supine CT, weightbearing and extension distracted positions.
From the 325 joints analysed, the mean external rotation of Insall’s axis relative to Cobb’s axis and the projection of the TEA in the CT, weightbearing and extension distracted positions was 4.84°±3.37°, 9.67°±4.71°, 9.65°±6.59° and 8.31°±6.44°, respectively.
Although numerous tibial rotational reference axes exist, there is a lack of consensus amongst surgeons on which is most appropriate during TKA. Since tibial and femoral axial rotation mismatch is associated with post-operative knee pain, it is important to consider references for axial rotation which can be used to align both femoral and tibial components. A better understanding of the different tibial rotational reference axes including functional axes may assist the industry in reaching a consensus on a single or few reference axes for reporting purposes.

Abstract. The ability to detect and localise surgical tools using RGB cameras during robotic assisted surgery can allow for the development of various implementations, such as vision- based active constraints and refinements in robot path planning, which can ultimately lead in improved patient safety during operation. For this purpose, the proposed network, SimPS-Net capable of both detection and 3D pose estimation of standard surgical tools using a single RGB camera, is introduced. In addition to the network, a novel dataset generated for training and testing is presented. The proposed network achieved a mean DICE coefficient of 85.0%, while also exhibiting a low average error of 5.5mm and 3.3◦ for 3D position and orientation respectively, thus outperforming the competing networks.

Abstract. Introduction: Robotic assisted total knee arthroplasty (RATKA) was proven that improved component position, ligament balanced and decreased outlier leading to improved clinical results and implant survivorship. Aiming of this study is comparison of short-term clinical and radiologic outcomes between RATKA versus conventional TKA (CMTKA) in Thabo Crown Prince Hospital, Thailand.
Methods: Retrospective cohort study by single surgeon, from July 2020 to August 2022 compared 51 RATKA and 49 CMTKA. Baseline data and short-term clinical outcomes including knee society score (KSS), operative time, estimated blood loss (EBL), length of stay (LOS), complications and radiologic outcomes were collected at postoperatively 3 months follow up.
Results: There was no statistically significant difference in KSS, EBL, LOS and complications between RATKA and CMTKA (P < 0.05). Operative time was significant greater in RATKA (138 vs. 162 min, P < 0.05). Radiologic outcomes in CMTKA, posterior condylar Offset, posterior condylar deviation, tibial slope was significant higher (P < 0.05). In subgroup analysis, patients with post operative tibial slope ≥ 7° (poor clinical outcomes) in CMTKA significantly higher than in RATKA (P = 0.021).
Conclusions: Imageless - robotic assisted total knee arthroplasty demonstrated that more benefit in posterior condylar offset and posterior tibial slope restoration and seem to be better in short-term clinical outcomes.

Abstract. Distal Radius Fractures (DRFs) are the most common type of fracture with a high incidence rate, accounting for 17.5% of all adult fractures. The established clinical workflow for patients with a suspicion of DRF calls for the acquisition of two radiographic X-ray images (radiographs) of the wrist in anteroposterior (AP) and lateral (LAT) views [1]. Radiographic parameters (RPs), which are linear angle and distance measurements derived from the AP and LAT radiographs, have been shown to provide objective support for effective decision making in determining clinical treatment of distal radius fractures (DRFs) [2]. Recently, we showed that providing computed RPs to orthopedic surgeons may improve the consistency of the radiographic judgment and influence their clinical decision for the treatment of DRFs [3]. However, calculating the RPs manually from radiographs requires experience, is time consuming, and is subject to observer variability.
This paper presents a novel deep learning automatic method for computing the six anatomical RPs associated with DRFs in AP and LAT forearm radiographs.

Abstract. The development of 3D printing technology has had a significant impact on the medical field. This technology has made it possible to create custom-made implants that can be flexibly adapted to the bone defects of individual patients. In this study, total hip arthroplasty (THA) using the custom-made implant developed in Japan, was reviewed in patients with severe acetabular bone defects. The accuracy of each implant placement was examined.
We retrospectively studied 10 patients who underwent THA with T-REX® (Teijin Nakashima Medical) at our institution between 2020 and 2022. A 3D pelvic model of each patient was created based on preoperative computed tomography (CT) data. The 3D CAD system was used to preoperatively plan the construction of an augmentation and a flange, where necessary. A pelvic model and an implant copy made to the same shape as the custom-made implant were used as a patient-specific guide. Postoperative CT data confirmed implant placement and determined alignment errors.
The absolute errors of implant alignment were 3.92 degrees for inclination, 1.81 degrees for anteversion, and 5.48 degrees for rotation. Absolute errors of 1.87 mm in the internal/external direction, 1.55 mm in the anteroposterior direction, and 1.10 mm in the vertical direction were also observed.
In conclusion, T-REX® implants can be accurately placed during THA in cases with severe acetabular bone defects. These implants can be expected to provide firm initial fixation by taking advantage of the flexibility in their design, making them a useful treatment option for patients.

Abstract. Curved periacetabular osteotomy (CPO) is technically demanding procedure because we have to enter the osteotomy site from inside of pelvis without direct view of hip joint. To achieve this tricky procedure without troubles such as posterior column fracture or intraarticular osteotomy, we used CT-based navigation. To investigate accuracy of osteotomy in patients who underwent CT-based navigation assisted CPO, pre- and post-operative CT images were measured with three dimensional (3D) image analyzing software. The 3D image analysis demonstrated that our osteotomies were not so accurate because each standard deviation of measurement values were not small. Our clinical data showed that 73% patients developed cartilage degeneration after CPO in postoperative X-ray films. Painful hips were observed in 26.9% and one hip was converted to total hip arthroplasty within 3 years after CPO. The first reason of these inaccuracy and unsatisfaction of our CPO was lack of consensus for true target zone of rotated acetabulum in CPO. We determined each final acetabular position by checking with intraoperative fluoroscopic 2D images. The second reason was that the current CT- based navigation could only assist osteotomy of ilium and quadrilateral surface. In addition, our navigation could not assist acetabular rotation in real time. Further improvements are required to achieve more accurate and successful CPO with computer assisted surgery.

Abstract. In orthopaedic oncology, computer navigation and 3D-printed guides facilitate precise osteotomies only after surgical exposure[1,2]. Visualizing virtual 3D models on the 2D flat screen of the computer station lacks depth perception and parallax compared to physical 3D models. Before surgeries start, it is challenging to mentally process and superimpose the virtual data onto patients’ anatomy for surgical assessment. Mixed Reality is an immersive technology merging real and virtual worlds, and users can interact with digital objects[3]. Through Head-Mounted Displays (HMD), surgeons directly visualize holographic models that overlay tumor patients’ anatomies in their physical environment before surgeries start. Clinical case reports of MR application are limited to spine and shoulder arthroplasty, and no data in orthopaedic oncology.