Abstract. Introduction. Component mal-positioning in total hip replacement (THR) and total knee replacement (TKR) can increase the risk of revision for various reasons. Compared to conventional surgery, relatively improved accuracy of implant positioning can be achieved using computer assisted technologies including navigation, patient-specific jigs, and robotic systems. However, it is not known whether application of these technologies has improved prosthesis survival in the real-world. This study aimed to compare risk of revision for all-causes following primary THR and TKR, and revision for dislocation following primary THR performed using computer assisted technologies compared to conventional technique. Methods. We performed an observational study using National Joint Registry data. All adult patients undergoing primary THR and TKR for osteoarthritis between 01/04/2003 to 31/12/2020 were eligible. Patients who received metal-on-metal bearing THR were excluded. We generated propensity score weights, using Sturmer weight trimming, based on: age, gender, ASA grade, side, operation funding, year of surgery, approach, and fixation. Specific additional variables included position and bearing for THR and patellar resurfacing for TKR. For THR, effective sample sizes and duration of follow up for conventional versus computer-guided and robotic-assisted analyses were 9,379 and 10,600 procedures, and approximately 18 and 4 years, respectively. For TKR, effective sample sizes and durations of follow up for conventional versus computer-guided, patient-specific jigs, and robotic-assisted groups were 92,579 procedures over 18 years, 11,665 procedures over 8 years, and 644 procedures over 3 years, respectively. Outcomes were assessed using Kaplan-Meier analysis and expressed using hazard ratios (HR) and 95% confidence intervals (CI). Results. For THR, analysis comparing computer-guided versus conventional technique demonstrated HR of 0.771 (95%CI 0.573–1.036) p=0.085, and 0.594 (95%CI 0.297–1.190) p=0.142, for revision for all-causes and dislocation, respectively. When comparing robotic-assisted versus conventional technique, HR for revision for all-causes was 0.480 (95%CI 0.067 –3.452) p=0.466. For TKR, compared to conventional surgery, HR for all-cause revision for procedures performed using computer guidance and patient-specific jigs were 0.967 (95% CI 0.888–1.052) p=0.430, and 0.937 (95% CI 0.708–1.241) p=0.65, respectively. HR for analysis comparing robotic-assisted versus conventional technique was 2.0940 (0.2423, 18.0995) p = 0.50. Conclusions. This is the largest study investigating this topic utilising propensity score analysis methods. We did not find a statistically significant difference in revision for all-causes and dislocation although these analyses are underpowered to detect smaller differences in effect size between groups. Additional comparison for revision for dislocation between robotic-assisted versus conventionally performed THR was not performed as this is a subset of revision for all-causes and wide confidence intervals were already observed for that analysis. It is also important to mention this NJR analysis study is of an observational study design which has inherent limitations. Nonetheless, this is the most feasible study design to answer this research question requiring use of a large data set due to revision being a rare outcome. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Summary. Computer assisted surgery (CAS) during total knee arthroplasty (TKA) is known to improve prosthetic alignment in coronal and sagittal plane. In this systematic review, no evidence is found that CAS also improves axial component orientation when used during TKA. Introduction. Primary total knee arthroplasty (TKA) is a safe and cost-effective treatment for end-stage knee osteoarthritis. Correct prosthesis alignment is essential, since malpositioning of the prosthesis leads to worse functional outcome and increased wear, which compromises survival of the prosthesis. Computer assisted surgery (CAS) has been developed to enhance prosthesis alignment during TKA. CAS significantly improves postoperative coronal and sagittal alignment compared to conventional TKA. However, the influence of CAS on rotational alignment is a matter of debate. Therefore purpose of this review is to assess published evidence on the influence of CAS during TKA on postoperative rotational alignment. Patients and Methods. This review was performed according to the PRISMA Statement. An electronic literature search was performed in Pubmed, Medline and Embase on studies published between 1991 and April 2013. Studies were included when rotational alignment following imageless CAS-TKA was compared to rotational alignment following conventional TKA. At least one of the following outcome measures had to be assessed: 1) rotational alignment of the femoral component, 2) rotational alignment of the tibial component, 3) tibiofemoral mismatch, 4) the amount of rotational outliers of the femoral component, 5) the amount of rotational outliers of the tibial component. Study selection was performed in two stages and data extraction and methodological quality assessment was conducted independently by two reviewers. Standardized mean difference (SMD) with 95% confidence interval (95% CI) was calculated for continuous variables. The SMDs were interpreted according to Cohen: an SMD of 0.2–0.4 was considered a small effect; 0.5–0.7 was considered moderate; and ≥ 0.8 was considered a large effect. For the comparison of the amount of outliers for femoral and tibial component rotation, the Odds ratio (OR) and 95% CI was calculated. The OR represents the odds of outliers occurring in the CAS group compared with the conventional group. An OR of < 1 favors the CAS group. The OR is considered statistically significant when the 95% CI does not include the value of 1. Results. Seventeen studies met the inclusion criteria. One study was considered of high, 15 studies of medium and one study of low methodological quality. SMD for rotation of the femoral component was −0.07 (−0.19–0.04). For rotation of the tibial component, the SMD was 0.11 (−0.01–0.24). Regarding tibiofemoral mismatch, the SMD was −0.27 (−0.57–0.02). For femoral outliers, the OR was 1.05 (0.78–1.43) and for tibial outliers the OR was 1.12 (0.86–1.47). Discussion / Conclusion. Results of this review show no evidence that CAS-TKA leads to better rotational alignment of the femoral or tibial component or tibiofemoral mismatch. Also no evidence was found that CAS results in a decrease of the amount of outliers regarding femoral or tibial component orientation. However, these conclusions have to be interpreted with caution. The number of included studies was low and strong heterogeneity existed between the studies. Of the 17 included studies, only one study was considered of high methodological quality. Moreover, different methods for assessing tibial component rotation have been used in the studies included

Background. In certain clinical situations, complex local anatomy and limitations of surgical exposure can make adequate and bone tumor ablation, resection and reconstruction very challenging. We wished to review our clinical experience and accuracy achieved with entirely virtually planned single stage tumor ablation/resection and reconstructions. Methods. We report 6 cases of bone tumors in which tumor removal (by radio-frequency (RF) ablation and/or resection) and subsequent reconstruction were based entirely on pre-operative virtual analysis and planning. All interventions were accomplished with specifically designed and pre-operatively manufactured 3D-printed drill & resection guides. Immediate subsequent defect reconstruction was either performed with a precisely matching allograft (n=1) or composite metal implant (n=5) consisting of a defect specific titanium scaffold and multiple integrated fixation features to provide optimal immediate stability as well as subsequent opportunity for osseointegration. We reviewed the sequence of all procedural steps as well as the accuracy of each saw blade or drill trajectory by direct intra-operative measurement, post-operative margin status and virtual comparison of pre- and post-operative CT scans. Results. Intra-operative application/assembly of the resection guides could be accomplished with relative ease in all cases, permitting quick and efficient reproduction of the planned osteotomies as well as RF-probe trajectories with a high degree of accuracy. Histologically all resection margins were negative as planned except in one case where one pelvic resection was extended due to intraoperative concern of possible local tumor progression. All implants could be placed as planned, with post-operative imaging demonstrating satisfactory implant position. Virtual analysis of post-operative CT scans confirmeded minimal deviation of final implant position from the pre-operative plan. Conclusion. Reliable, accurate placement of tumor biopsy/ablation tracts and resection planes and their optimal alignment with respect to critical structures, tumor extent and desired preservation of unaffected bone is the most challenging and time consuming step during the analysis and planning phase. However it is also the crucial step with regard to subsequent design and production of clinically and oncologically meaningful case-specific drill/resection guides and implants. If these prerequisites are met, computer assisted virtual planning along with 3Dprinting-technology can afford high intraoperative accuracy, contribute to increased intra-operative surgeon confidence and decreased operative time

The surgical management of musculoskeletal tumours is a challenging problem, particularly in pelvic and diaphyseal tumour resection where accurate determination of bony transection points is extremely important to optimise oncologic, functional and reconstructive options. The use of computer assisted navigation in these cases could improve surgical precision and achieve pre-planned oncological margins with improved accuracy. We resected musculoskeletal tumours in ten patients using commercially available computer navigation software (Orthomap 3D, Stryker UK Ltd). Of the five pelvic tumours, two underwent biological reconstruction with extra corporeal irradiation, two endoprosthetic replacement (EPR) and one did not require bony reconstruction. Three tibial diaphyseal tumours had biological reconstruction. One patient with proximal femoral sarcoma underwent extra-articular resection and EPR. One soft tissue sarcoma of the adductor compartment involving the femur was resected with EPR. Histological examination of the resected specimens revealed tumour free margins in all cases. Post-operative radiographs and CT show resection and reconstruction as planned in all cases. Several learning points were identified related to juvenile bony anatomy and intra-operative registration. The use of computer navigation in musculoskeletal oncology allows integration of local anatomy and tumour extent to identify resection margins accurately. Furthermore, it can aid in reconstruction following tumour resection. Our experience thus far has been encouraging. Further clinical trials are required to evaluate its long-term impact on functional & oncological outcomes

The aim of this project is to test the parameters of Patient Specific Instruments (PSIs) and measuring accuracy of surgical cuts using sawblades with different depths of PSI cutting guide slot. Clear operative oncological margins are the main target in malignant bone tumour resections. Novel techniques like patient specific instruments (PSIs) are becoming more popular in orthopaedic oncology surgeries and arthroplasty in general with studies suggesting improved accuracy and reduced operating time using PSIs compared to conventional techniques and computer assisted surgery. Improved accuracy would allow preservation of more natural bone of patients with smaller tumour margin. Novel low-cost technology improving accuracy of surgical cuts, would facilitate highly delicate surgeries such as Joint Preserving Surgery (JPS) that improves quality of life for patients by preserving the tibial plateau and muscle attachments around the knee whilst removing bone tumours with adequate tumour margins. There are no universal guidelines on PSI designs and there are no studies showing how specific design of PSIs would affect accuracy of the surgical cuts. We hypothesised if an increased depth of the cutting slot guide for sawblades on the PSI would improve accuracy of cuts. A pilot drybone experiment was set up, testing 3 different designs of a PSI with changing cutting slot depth, simulating removal of a tumour on the proximal tibia. A handheld 3D scanner (Artec Spider, Luxembourg) was used to scan tibia drybones and Computer Aided Design (CAD) software was used to simulate osteosarcoma position and plan intentioned cuts. PSI were designed accordingly to allow sufficient tumour. The only change for the 3 designs is the cutting slot depth (10mm, 15mm & 20mm). 7 orthopaedic surgeons were recruited to participate and perform JPS on the drybones using each design 2 times. Each fragment was then scanned with the 3D scanner and were then matched onto the reference tibia with customized software to calculate how each cut (inferior-superior-vertical) deviated from plan in millimetres and degrees. In order to tackle PSI placement error, a dedicated 3D-printed mould was used. Comparing actual cuts to planned cuts, changing the height of the cutting slot guide on the designed PSI did not deviate accuracy enough to interfere with a tumour resection margin set to maximum 10mm. We have obtained very accurate cuts with the mean deviations(error) for the 3 different designs were: [10mm slot: 0.76 ± 0.52mm, 2.37 ± 1.26°], [15 mm slot: 0.43 ± 0.40 mm, 1.89 ± 1.04°] and [20 mm: 0.74 ± 0.65 mm, 2.40 ± 1.78°] respectively, with no significant difference between mean error for each design overall, but the inferior cuts deviation in mm did show to be more precise with 15 mm cutting slot (p<0.05). Simulating a cut to resect an osteosarcoma, none of the proposed designs introduced error that would interfere with the tumour margin set. Though 15mm showed increased precision on only one parameter, we concluded that 10mm cutting slot would be sufficient for the accuracy needed for this specific surgical intervention. Future work would include comparing PSI slot depth with position of knee implants after arthroplasty, and how optimisation of other design parameters of PSIs can continue to improve accuracy of orthopaedic surgery and allow increase of bone and joint preservation

Total knee arthroplasty (TKA) is a common orthopaedic procedure. Traditionally the surgeon, based on experience, releases the medial structures in knees with varus deformity and lateral structures in knees with valgus deformity until subjectively they feel that they have achieved the intended alignment. The hypothesis for this study was that deformed knees do not routinely require releases to achieve an aligned lower limb in TKA. A single surgeon consecutive cohort of 74 patients undergoing computer navigated TKA was examined. The mechanical axes were taken as the references for distal femoral and proximal tibial cuts. The trans-epicondylar axis was taken as the reference for frontal femoral and posterior condylar cuts. A soft tissue release was undertaken after the bony cuts had been made if the mechanical femoro-tibial (MFT) angle in extension did not come to within 2° of neutral as shown by computer readings. The post-operative alignment was recorded on the navigation system and also analysed with hip-knee-ankle (HKA) radiographs. The range of pre-operative deformities on HKA radiographs was 15° varus to 27° valgus with a mean of 5° varus (SD 7.4°). Only two patients required a medial release. None of the patients required a lateral release. The post implant navigation value was within 2° of neutral in all cases. Post-operative HKA radiographs was available for 71 patients. The mean MFT angle from radiographs was 0.1° valgus (SD 2.1°). The range was from 6° varus to 7° valgus but only six patients (8.5%) were outside the ±3° range. The kinematic analysis also showed it to be within 2 degrees of neutral throughout the flexion making sure it is well balanced in 88% cases. This series has shown that over 90% of patients had limbs aligned appropriately without the need for routine soft tissue releases. The use of computer assisted bone cuts leads to a low level of collateral release in TKA