Aims. This study aimed to investigate whether the use of CT-based navigation enhances: 1) the accuracy of cup placement; and 2) the achievement rate of required range of motion (ROM). Additionally, we investigated the impact of using a large femoral head and dual-mobility liner on the achievement rates. Methods. This retrospective study analyzed 60 manual and 51 CT-based navigated primary total hip arthroplasties performed at a single facility. Postoperative CT scans and CT-based simulation software were employed to measure the cup orientation and to simulate the ROM. We compared the absolute errors for radiological inclination (RI) and radiological anteversion (RA) between the two groups. We also examined whether the simulated ROM met the required ROM criteria, defined as flexion > 110°, internal rotation > 30°, extension > 30°, and external rotation > 30°. Furthermore, we performed simulations with 36 mm femoral head and dual-mobility liner. Results. The absolute errors of RI and RA from the preoperative plan were significantly smaller in the CT-based navigation group (3.7° (SD 3.5°) vs 5.1° (SD 3.5°); p = 0.022, and 3.9° (SD 3.5°) vs 6.8° (SD 5.0°); p = 0.001, respectively). The proportion of cases achieving the required ROM in all directions was significantly higher in the CT-based navigation group (42% vs 63%; p = 0.036). The achievement rates of the required ROM were significantly higher with the use of a 36 mm ball or dual-mobility liner compared to the use of a 32 mm ball (65% vs 51%; p = 0.040 and 77% vs 51%; p ≤ 0.001, respectively). Conclusion. CT-based navigation enhanced required ROM achievement rates by > 20%, regardless of the ball diameter. The improved accuracy of cup placement through CT-based navigation likely contributed to the enhancement. Furthermore, the use of large femoral heads and dual-mobility liners also improved the required ROM achievement rates. In cases with a high risk of dislocation, use of these devices is preferred. Cite this article: Bone Jt Open 2025;6(2):155–163

Aims. Excellent outcomes have been reported following CT-based robotic arm-assisted total hip arthroplasty (rTHA) compared with manual THA; however, its superiority over CT-based navigation THA (nTHA) remains unclear. This study aimed to determine whether a CT-based robotic arm-assisted system helps surgeons perform accurate cup placement, minimizes leg length, and offsets discrepancies more than a CT-based navigation system. Methods. We studied 60 hips from 54 patients who underwent rTHA between April 2021 and August 2023, and 45 hips from 44 patients who underwent nTHA between January 2020 and March 2021 with the same target cup orientation at the Department of Orthopedic Surgery at Ozu Memorial Hospital, Japan. After propensity score matching, each group had 37 hips. Postoperative acetabular component position and orientation were measured using the planning module of the CT-based navigation system. Postoperative leg length and offset discrepancies were evaluated using postoperative CT in patients who have unilateral hip osteoarthritis. Results. The absolute differences in radiological inclination (RI) and radiological anteversion (RA) from the target were significantly smaller in rTHA (RI 1.2° (SD 1.2°), RA 1.4° (SD 1.2°)) than in nTHA (RI 2.7° (SD 1.9°), RA 3.0° (SD 2.6°)) (p = 0.005 for RI, p = 0.002 for RA). The absolute distance of the target’s postoperative centre of rotation was significantly smaller in the mediolateral (ML) and superoinferior (SI) directions in rTHA (ML 1.1 mm (SD 0.8), SI 1.3 mm (SD 0.5)) than in nTHA (ML 1.9 mm (SD 0.9), SI 1.6 mm (SD 0.9)) (p = 0.002 for ML, p = 0.042 for SI). Absolute leg length and absolute discrepancies in the acetabular, femoral, and global offsets were significantly lower in the rTHA group than in the nTHA group (p = 0.042, p = 0.004, p = 0.003, and p = 0.010, respectively). In addition, the percentage of hips significantly differed with an absolute global offset discrepancy of ≤ 5 mm (p < 0.001). Conclusion. rTHA is more accurate in cup orientation and position than nTHA, effectively reducing postoperative leg length and offset discrepancy. Cite this article: Bone Jt Open 2024;6(1):3–11

The December 2024 Spine Roundup³⁶⁰ looks at: Rostral facet joint violations in robotic- and navigation-assisted pedicle screw placement; The inhibitory effect of non-steroidal anti-inflammatory drugs and opioids on spinal fusion: an animal model;L5-S1 transforaminal lumbar interbody fusion is associated with increased revisions compared to L4-L5 TLIF at two years; Immediate versus gradual brace weaning protocols in adolescent idiopathic scoliosis: a randomized clinical trial; Effectiveness and cost-effectiveness of an individualized, progressive walking, and education intervention for the prevention of low back pain recurrence in Australia (WalkBack): a randomized controlled trial; Usefulness and limitations of intraoperative pathological diagnosis using frozen sections for spinal cord tumours; Effect of preoperative HbA1c and blood glucose level on the surgical site infection after lumbar instrumentation surgery; How good are surgeons at achieving their alignment goals?

Advanced 3D imaging and CT-based navigation have emerged as valuable tools to use in total knee arthroplasty (TKA), for both preoperative planning and the intraoperative execution of different philosophies of alignment. Preoperative planning using CT-based 3D imaging enables more accurate prediction of the size of components, enhancing surgical workflow and optimizing the precision of the positioning of components. Surgeons can assess alignment, osteophytes, and arthritic changes better. These scans provide improved insights into the patellofemoral joint and facilitate tibial sizing and the evaluation of implant-bone contact area in cementless TKA. Preoperative CT imaging is also required for the development of patient-specific instrumentation cutting guides, aiming to reduce intraoperative blood loss and improve the surgical technique in complex cases. Intraoperative CT-based navigation and haptic guidance facilitates precise execution of the preoperative plan, aiming for optimal positioning of the components and accurate alignment, as determined by the surgeon’s philosophy. It also helps reduce iatrogenic injury to the periarticular soft-tissue structures with subsequent reduction in the local and systemic inflammatory response, enhancing early outcomes. Despite the increased costs and radiation exposure associated with CT-based navigation, these many benefits have facilitated the adoption of imaged based robotic surgery into routine practice. Further research on ultra-low-dose CT scans and exploration of the possible translation of the use of 3D imaging into improved clinical outcomes are required to justify its broader implementation. Cite this article: Bone Joint J 2024;106-B(9):892–897

Aims

Precise implant positioning, tailored to individual spinopelvic biomechanics and phenotype, is paramount for stability in total hip arthroplasty (THA). Despite a few studies on instability prediction, there is a notable gap in research utilizing artificial intelligence (AI). The objective of our pilot study was to evaluate the feasibility of developing an AI algorithm tailored to individual spinopelvic mechanics and patient phenotype for predicting impingement.

Aims

Femoral component anteversion is an important factor in the success of total hip arthroplasty (THA). This retrospective study aimed to investigate the accuracy of femoral component anteversion with the Mako THA system and software using the Exeter cemented femoral component, compared to the Accolade II cementless femoral component.

Aims

This study aimed to develop and validate a fully automated system that quantifies proximal femoral bone mineral density (BMD) from CT images.

Rotational acetabular osteotomy (RAO), one of periacetabular osteotomies, is an effective joint-preserving surgical treatment for developmental dysplasia of the hip. Since 2013, we have been using a CT-based navigation for RAO to perform safe and accurate osteotomy. CT-based navigation allows precise osteotomy during surgery but cannot track the bony fragment after osteotomy. Thus, it is an issue to achieve successful reorientation in accordance with preoperative planning. In this presentation, we introduce a new method to achieve reorientation and evaluate its accuracy. Thirty joints in which CT-based navigated RAO was performed were included in this study. For the first 20 joints, reorientation was confirmed by tracing the lateral aspect of rotated fragment with navigation and checked if it matched with the preoperative planning. For the latter 10 joints, a new method was adopted. Four fiducial points were made on lateral side of the acetabulum in the preoperative 3-dimensional model and intraoperatively, rotation of the osteotomized bone was performed so that the 4 fiducial points match the preoperative plan. To assess the accuracy of position of rotated fragment in each group, preoperative planning and postoperative CT were compared. A total of 24 radial reformat images of postoperative CT were obtained at a half-hour interval following the clockface system around the acetabulum. In every radial image, femoral head coverage of actual postop- and planned were measured to evaluate the accuracy of acetabular fragment repositioning. The 4-fiducial method significantly reduced the reorientation error. Especially in the 12:00 to 1:00 position of the acetabulum, there were significantly fewer errors (p<0.01) and fewer cases with under-correction of the lateral acetabular coverage. With the new method with 4 reference fiducials, reorientation of the acetabulum could be obtained as planned with lesser errors

Accurate cup placement in total hip arthroplasty (THA) for the patients with developmental dysplasia of the hip (DDH) is one of the challenges due to distinctive bone deformity. Robotic-arm assisted system have been developed to improve the accuracy of implant placement. This study aimed to compare the accuracy of robotic-arm assisted (Robo-THA), CT-based navigated (Navi-THA), and manual (M-THA) cup position and orientation in THA for DDH. A total of 285 patients (335 hips) including 202 M-THAs, 45 Navi-THAs, and 88 Robo-THA were analyzed. The choice of procedure followed the patient's preferences. Horizontal and vertical center of rotation (HCOR and VCOR) were measured for cup position, and radiographic inclination (RI) and anteversion (RA) were measured for cup orientation. The propensity score-matching was performed among three groups to compare the absolute error from the preoperative target position and angle. Navi-THA showed significantly smaller absolute errors than M-THA in RI (3.6° and 5.4°) and RA (3.8° and 6.0°), however, there were no significant differences between them in HCOR (2.5 mm and 3.0 mm) or VCOR (2.2 mm and 2.6 mm). In contrast, Robo-THA showed significantly smaller absolute errors of cup position than both M-THA and Navi-THA (HCOR: 1.7 mm and 2.9 mm, vs. M-THA, 1.6 mm and 2.5 mm vs. Navi-THA, VCOR:1.7 mm and 2.4 mm, vs. M-THA, 1.4 mm and 2.2 mm vs. Navi-THA). Robo-THA also showed significantly smaller absolute errors of cup orientation than both M-THA and Navi-THA (RI: 1.4° and 5.7°, vs. M-THA, 1.5° and 3.6°, vs. Navi-THA, RA: 1.9° and 5.8° vs. M-THA, 2.1° and 3.8° vs. Navi-THA). Robotic-arm assisted system showed more accurate cup position and orientation compared to manual and CT-based navigation in THA for DDH. CT-based navigation increased the accuracy of cup orientation compared to manual procedures, but not cup position

Accurate evaluation of lower limb coronal alignment is essential for effective pre-operative planning of knee arthroplasty. Weightbearing hip-knee-ankle (HKA) radiographs are considered the gold standard. Mako SmartRobotics uses CT-based navigation to provide intra-operative data on lower limb coronal alignment during robotic assisted knee arthroplasty. This study aimed to compare the correlation between the two methods in assessing coronal plane alignment. Patients undergoing Mako partial (PKA) or total knee arthroplasty (TKA) were identified from our hospital database. The hospital PACS system was used to measure pre-operative coronal plane alignment on HKA radiographs. This data was correlated to the intraoperative deformity assessment during Mako PKA and TKA surgery. 443 consecutive Mako knee arthroplasties were performed between November 2019 and December 2021. Weightbearing HKA radiographs were done in 56% of cases. Data for intraoperative coronal plane alignment was available for 414 patients. 378 knees were aligned in varus, and 36 in valgus. Mean varus deformity was 7.46° (SD 3.89) on HKA vs 7.13° (SD 3.56) on Mako intraoperative assessment, with a moderate correlation (R= 0.50, p<0.0001). Intraoperative varus deformity of 0-4° correlated to HKA measured varus (within 3°) in 60% of cases, compared to 28% for 5-9°, 17% for 10-14°, and in no cases with >15° deformity. Mean valgus deformity was 6.44° (SD 4.68) on HKA vs 4.75° (SD 3.79) for Mako, with poor correlation (R=0.18, p=0.38). In this series, the correlation between weightbearing HKA radiographs and intraoperative alignment assessment using Mako SmartRobotics appears to be poor, with greater deformities having poorer correlation

Aims

This study aimed to evaluate the accuracy of implant placement with robotic-arm assisted total hip arthroplasty (THA) in patients with developmental dysplasia of the hip (DDH).

Introduction. Reverse shoulder Arthroplasty is a successful treatment for gleno-humeral osteoarthritis. However, components loosening and painful prostheses, related to components wrong positioning, are still a problem for those patients who underwent this kind of surgery. Several new technology has been developed the improve the implant positioning. CT-based intraoperative navigation system is a suitable technology that allow the surgeon to prepare the implant site exactly as planned with preoperative software. Method. Thirty reverse shoulder prostheses were performed at Modena Polyclinic using GPS CT-based intraoperative navigation system (Exactech, Gainsville, Florida). Walch classification was used to assess glenoid type. Planned version and inclination of the glenoid component, planned seating, final version and inclination of the reamer were recorded. Intraoperative and perioperative complication were recorded. Planned positioning was conducted aiming to the maximum seating, avoiding retroversion >10° and superior inclination. Results. Eight patients were male, 22 were female. Mean age was 75 years old (range 58–87). 4 glenoid were type B3, four were B2, 10 cases were B1, 12 case were A1/A2. Posterior or superior augment was used in 15 cases. Mean planned seating was 93%. Mean preoperative version was -7.5±6.9°; Mean planned version was -2±2.8°; Mean intraoperative measured version was -1.9±2.8°; no statistical difference was found between planned and intraoperative version (p=0.16). Mean preoperative inclination was 1.8±6.°; Mean planned inclination was -2.2±2.4°; Mean intraoperative measured inclination was -2.1.9±2.3°; no statistical difference was found between planned and intraoperative version or inclination (respectively p=0.16 and p=0.32). Mean surgical time was 71 minute (range 51–82). Three cases of coracoid ruptures were reported, 1 failure of the system occurred. Discussion. GPS navigation system allows the surgeon to prepare the implant site as planned on Preoperative software in Reverse shoulder arthroplasty, with no statistical difference between planned orientation and intraoperative measured orientation. That means that even in the most difficult cases the surgeon is able to find a good positioning (93% seating)and to replicate it in the operative room. Only one failure of the system occurred, because too much time was passed between CT scan and surgery (9 months). Three coracoid fractures occurred in the first 10 cases: these could be addressed to a lack of confidence with the double lateralization of this prosthesis which increase tensioning on the coracoid and a lack of confidence in tracker positioning, which should be made as proximal as it is possible. Finally, the system needs several improvements to be considered a breakthrough technology, such as humeral component positioning and final control of the implant, but by now is a useful way to improve our surgery, especially in difficult cases

Aims

Appropriate acetabular component placement has been proposed for prevention of postoperative dislocation in total hip arthroplasty (THA). Manual placements often cause outliers in spite of attempts to insert the component within the intended safe zone; therefore, some surgeons routinely evaluate intraoperative pelvic radiographs to exclude excessive acetabular component malposition. However, their evaluation is often ambiguous in case of the tilted or rotated pelvic position. The purpose of this study was to develop the computational analysis to digitalize the acetabular component orientation regardless of the pelvic tilt or rotation.

With the identification of literature shortfalls on the techniques employed in intraoperative navigated (ION) spinal surgery, we outline a number of measures which have been synthesised into a coherent operative technique. These include positioning, dissection, management of the reference frame, the grip, the angle of attack, the drill, the template, the pedicle screw, the wire, and navigated intrathecal analgesia. Optimizing techniques to improve accuracy allow an overall reduction of the repetition of the surgical steps with its associated productivity benefits including time, cost, radiation, and safety.

Cite this article: Bone Joint J 2020;102-B(3):371–375.

Introduction. Acetabular revision surgery is challenging due to severe bone defects. Burch-Schneider anti-protrusion cages (BS cage: Zimmer-Biomet) is one of the options for acetabular revision, however higher dislocation rate was reported. A computed tomography (CT)-based navigation system indicates us the planned direction for implantation of a cemented acetabular cup during surgery. A large diameter femoral head is also expected to reduce the dislocation rate. The purpose of this study is to investigate short-term results of BS cage in acetabular revision surgery combined with the CT-based navigation system and the use of large diameter femoral head. Methods. Sixteen hips of fifteen patients who underwent revision THA using allografts and BS cage between September 2013 and December 2017 were included in this study with the follow-up of 2.7 (0.1–5.0) years. There were 12 women and three men with a mean age of 78.6 years (range, 59–61 years). The cause of acetabular revision was aseptic loosening in all hips. The failed acetabular cup was carefully removed, and acetabular bone defect was graded using the Paprosky classification. Structural allografts were morselized and packed for all medial or contained defects. In some cases, solid allograft was implanted for segmental defects. BS cage was molded to optimize stability and congruity to the acetabulum and fixed with 6.5 mm titanium screws to the iliac bone. The inferior flange was slotted into the ischium. The upside-down trial cup was attached to a straight handle cup positioner with instrumental tracker (Figure 1) and placed on the rim of the BS cage to confirm the direction of the target angle for cement cup implantation under the CT-based navigation system (Stryker). After removing the cement spacer around the X3 RimFit cup (Stryker) onto the BS cage for available maximum large femoral head, the cement cup was implanted with confirming the direction of targeting angle. Japanese Orthopedic Association score (JOA score) of the hip was used for clinical assessment. Implant position, loosening, and consolidation of allograft were assessed using anterior and lateral radiographies of the pelvis. Results. Fifteen hips had a Paprosky IIIB defect, and one hip had a pelvic discontinuity. JOA score significantly improved postoperatively. No radiolucent lines and no displacement of BS cage could be found in 9 of 15 hips. Consolidation of allografts above the protrusion cage was observed in these patients. Displacement of BS cage (>5mm) was observed in 6 hips and displacement was stopped with allograft consolidation in 5 of 6 hips. The other patient showed lateral displacement of BS cage and underwent revision surgery. Average cup inclination and anteversion angles were 37.7±5.0 degree and 24.6±7.2 degree, respectively. 12 of 16 patients were included in Lewinnek's safe zone. One patient with 32 mm diameter of the femoral head had dislocation at 17 days postoperatively. All patients who received ≥36mm diameter of femoral head showed no dislocation. Conclusions. CT-based navigation system and the use of large femoral head may influence the prevention of dislocation in the acetabular revision surgery with BS cage for severe acetabular bone defects

Background. Accurate acetabular cup positioning is considered to be essential to prevent postoperative dislocation and improve the long-term outcome of total hip arthroplasty (THA). Recently various devices such as navigation systems and patient-specific guides have been used to ensure the accuracy of acetabular cup positioning. Objectives. The present study evaluated the usefulness of CT-based three-dimensional THA preoperative planning for acetabular cup positioning. Methods. This study included 120 hips aged mean 68.3 years, who underwent primary THA using CT-based THA preoperative planning software ZedHip® (LEXI, Tokyo Japan) and postoperative CT imaging (Fig.1). The surgical approach adopted the modified Watson-Jones approach in the lateral decubitus position and Trident HA acetabular cups were used for all cases. Preoperatively the optimum cup size and position in the acetabular were decided using the ZedHip® software, taking into consideration femoral anteversion and to achieve the maximum range of motion in dynamic motion simulation. Radiographic inclination (RI) was selected in the range between 40°∼45° and radiographic anteversion (RA) in the range between 5°∼25°. Three-dimensional planning images of the cup positioning were obtained from the ZedHip® software, and the distances between the edge of the implant and anatomical landmarks such as the edge of the anterior or superior acetabular wall were measured on the three-dimensional images and recorded (Fig.2). Intraoperatively, the RI and RA were confirmed by reference to these distances and the acetabular cup was inserted. Relative positional information of the implant was extracted from postoperative CT imaging using the ZedHip® software and used to reproduce the position of the implant on preoperative CT imaging with the software image matching function. The difference between the preoperative planning and the actual implant position was measured to assess the accuracy of acetabular cup positioning using the ZedHip® software. Results. Actual cup size corresponded with that of preoperative planning in 95% of cases (114 hips). Postoperative mean RI was 42.3° ± 4.2° (95% confidence interval (CI), 41.5° ∼ 43.0°) and mean RA was 16.1° ± 5.9° (95%CI, 15.0° ∼ 17.1°). Deviation from the target RI was 4.2° ± 3.7° (95%CI, 3.5° ∼ 4.9°) and deviation from the target RA was 4.0° ± 3.6° (95%CI, 3.4° ∼ 4.7°). Overall 116 hips (96.7%) were within the RI safe zone (30° ∼ 50°) and 108 hips (90.0%) were within the RA safe zone (5° ∼ 25°), and 105 hips (87.5%) were within both the RI and RA safe zones (Fig.3). Mean cup shift from preoperative planning was 0.0mm ± 3.0mm to the cranial side in the cranio-caudal direction, 2.1mm ± 3.0mm to the anterior side in the antero-posterior direction, and 1.7mm ± 2.1mm to the lateral side in the medio-lateral direction. Conclusion. The accuracy of acetabular cup positioning using our method of CT-based three-dimensional THA preoperative planning was slightly inferior to reported values for CT-based navigation, but obviously superior to those without navigation and similar to those with portable navigation. CT-based three-dimensional THA preoperative planning is effective for acetabular cup positioning, and has better cost performance than expensive CT-based navigation. For any figures or tables, please contact the authors directly

Introduction. Total shoulder replacement is a successful treatment for gleno-humeral osteoarthritis. However, components loosening and painful prostheses, related to components wrong positioning, are still a problem for those patients who underwent this kind of surgery. CT-based intraoperative navigation system is a suitable option to improve accuracy and precision of the implants as previously described in literature for others district. Method. Eleven reverse shoulder prostheses were performed at Modena Polyclinic from October 2018 to April 2019 using GPS CT-based intraoperative navigation system (Exactech, Gainsville, Florida). In the preoperative planning, Walch classification was used to assess glenoid type. The choice of inclination of the glenoid component, the screw length, as well as the inclination of the reamer was study and recorded using specific software using the CT scan of shoulder of each patient (Fig.1, Fig.2). Intraoperative and perioperative complications were recorded. Three patients were male, eight were female. Mean age was 72 years old (range 58=84). Three glenoid were type B2, six cases were B1, two case were type C1. Results. In all cases treated by reverse shoulder prostheses we had obtain good functional results at preliminary follow up. Eight degree posterior augment was used in seven case. Planned version was 0° in eight case, an anti-version of 3° was planned in the other three cases. Final reaming was as preoperatively planned in all cases except one. Mean surgical time was 71 minutes (range 51–82). One case of coracoid rupture has been reported. In all cases the system worked in proper manner without failures, no case of infection was reported. Discussion. It is well known as the more accurate placement of the glenoid led to enhanced long-term survivorship of the implant and decrease complication rates in RSTA. Our first experience with GPS navigation system has been satisfied. Good components’ positioning has been reached in all cases, without deviation from the preoperative planning. Pre-operative preparation using software has been always respected except in one case in which we decided to ream 1mm less to avoid excessive bone loss. In 3 case we decide to increase glenoid anti-version to allow a good cage containment in the scapula. No failure of the system has been recorded, with a little increase in the surgical time respect to traditional surgeries performed in our institute. The first case performed reported coracoid fracture, probably due to lack of experience in coracoid tracker positioning. It is very important to set the surgical theatre and the position of the patient in order to make the coracoid tracker visible for the computer. Screw positioning and length is decisively improved with GPS system compared with traditional implant. The most important advantage is to avoid the malposition of the glenoid component, solving problems like loosening or restriction in shoulder range of motion. We believe that a final cross check between preoperative planning and final control of the prostheses implanted, should be used in the future, but by now the GPS navigation system is a useful way to improve our surgery, especially in difficult cases. For any figures or tables, please contact the authors directly

Introduction. Robotic-assisted hip arthroplasty helps acetabular preparation and implantation with the assistance of a robotic arm. A computed tomography (CT)-based navigation system is also helpful for acetabular preparation and implantation, however, there is no report to compare these methods. The purpose of this study is to compare the acetabular cup position between the assistance of the robotic arm and the CT-based navigation system in total hip arthroplasty for patients with osteoarthritis secondary to developmental dysplasia of the hip. Methods. We studied 31 hips of 28 patients who underwent the robotic-assisted hip arthroplasty (MAKO group) between August 2018 and March 2019 and 119 hips of 112 patients who received THA under CT-based navigation (CT-navi group) between September 2015 and November 2018. The preoperative diagnosis of all patients was osteoarthritis secondary to developmental dysplasia of the hip. They received the same cementless cup (Trident, Stryker). Robotic-assisted hip arthroplasty were performed by four surgeons while THA under CT-based navigation were performed by single senior surgeon. Target angle was 40 degree of radiological cup inclination (RI) and 15 degree of radiological cup anteversion (RA) in all patients. Propensity score matching was used to match the patients by gender, age, weight, height, BMI, and surgical approach in the two groups and 30 patients in each group were included in this study. Postoperative cup position was assessed using postoperative anterior-posterior pelvic radiograph by the Lewinnek's methods. The differences between target and postoperative cup position were investigated. Results. The acetabular cup position of all cases in both Mako and CT-navi group within Lewinnek's safe zone (RI: 40±10 degree; RA: 15±10 degree) in group were within this zone. Three was no significant difference of RI between Mako and CT-navi group (40.0 ± 2.1 degree vs 39.7± 3.6 degree). RA was 15.0 ± 1.2 degree and 17.0 ± 1.9 degree in MAKO group and in CT-navi group, respectively, with significant difference (p<0.001). The differences of RA between target and postoperative angle were smaller in MAKO group than CT-navi group (0.60± 1.05 degree vs 2.34± 1.40 degree, p<0.001). The difference or RI in MAKO group was smaller than in CT-navi, however, there was no significance between them (1.67± 1.27 degree vs 2.39± 2.68 degree, p=0.197). Conclusions. Both the assistance of the robotic arm and the CT-based navigation system were helpful to achieve the acetabular cup implantation, however, MAKO system achieved more accurate acetabular cup implantation than CT-based navigation system in total hip arthroplasty for the patients with OA secondary to DDH. Longer follow-up is necessary to investigate the clinical outcome

Aims

We analyzed the acetabular morphology of Crowe type IV hips using CT data to identify a landmark for the ideal placement of the centre of the acetabular component, as assessed by morphometric geometrical analysis, and its reliability.