IntroductionOver the past decades many innovations were introduced in total knee arthroplasty (TKA) focusing on implant longevity and higher procedural precision; however, there are still a high number of dissatisfied patients. It was reported that better anatomical alignment may result in improved patient outcome; however, current technologies have limitations to achieve this. The aim of this video article is to describe the technique of individualized alignment in TKA with the use of image-based robotic assistance.MethodsThe technology is based on an individual patient knee model computed from segmented computed tomography (CT) scans. A preoperative planning of prosthesis position is conducted following the principle of kinematic alignment. Intraoperatively the soft tissue envelope is recorded and the computer predicts the gap balance based on the virtual planning. The prosthesis position is then adapted to achieve balanced gaps and to avoid soft tissue release. This technique is shown in a cadaver operation and clinical examples of two patients are described.ResultsWith the combination of anatomically oriented prosthesis positioning and minor adaptations with respect to the soft tissue, an individualized alignment is achieved with reduced need of soft tissue release. The robotic-assisted surgery guarantees a precise implementation of the planning. The initial experience showed a promising outcome in short-term follow-up.Video onlineThe online version of this article (10.1007/s00132-018-3637-1) contains a video on patient individualized alignment in total knee arthroplasty. The article and video are available in the electronic full text archive at SpringerMedizin.de under http://www.springermedizin.de/der-orthopaede. The video can be found at the end of the article as supplementary material.

Introduction Robotic-assisted surgery techniques are increasing in total knee arthroplasty (TKA). One crucial point is the prolonged time of surgery. The primary objective of this study was to determine the learning curve necessary to minimize the time of surgery. The secondary objective was to evaluate the accuracy of the implant alignment when using an imageless robotic system for TKA. Materials and methods In a case–control study, the first 70 consecutive robotic-assisted TKA procedures performed by a single senior surgeon were analyzed with regard to surgery time and implant alignment by comparing the intraoperative plan with the postoperative alignment. The evaluation of the learning curve with respect to surgery time was conducted using cumulative summation (CUSUM) analysis. The joint line height was measured with a new technique. Surgery time and joint line reconstruction were compared to 70 consecutive conventional TKA procedures. Results The learning curve for robotic TKA was completed after 11 cases. The learning curve did not influence the accuracy of joint line obliquity, joint line height, or limb alignment. The intraoperative plan designed for the robotic system was precisely implemented. The mean skin-to-skin time in the robotic group after the learning curve was completed did not differ from that in the manual group. A significant positive correlation was observed between the preoperative hip–knee–ankle angle and the postoperative distalization of the joint line in the robotic-assisted TKA group. Conclusion After completing the initial learning curve of 11 cases, the surgery time required to perform imageless robotic handpiece-assisted TKA was similar to that for the conventional technique. However, no learning curve was observed for the implant positioning when using the imageless robotic system. The implementation of the intraoperative plan was accurate up to < 2°. The precision of the system allows the implementation of different joint balancing approaches between valgus and varus morphotypes.

Aims and Objectives: In the past years, further development in knee replacement still continues. Computer-assisted surgery techniques in total knee arthroplasty (TKA) are on the rise. One point of criticism is the prolonged time of surgery and associated cost as known from old techniques like navigation. The primary objective of this study was to determine the learning curve for the time of surgery and accuracy in implant positioning for an imageless robotic system for TKA. Materials and Methods: In this prospective study, the first 30 robotic-assisted TKA from a single senior surgeon were analyzed with regard to time of surgery and accuracy of implant position on the basis of the intraoperative plan and the postoperative x-rays. This data was compared to the last 30 manual TKAs of the same surgeon with the same prosthesis. Evaluation of the learning curve was performed with CUSUM analysis. The time of surgery after finishing the learning curve in the robotic group was compared to the manual group. Results: The learning curve in the robotic group for surgery time was finished after 11 cases. The robotic experience did not affect the accuracy of implant positioning, such as limb alignment and restoration of the joint line. The mean absolute deviation of the postoperative limb alignment to the intraoperative plan was 2° (+/- 1,1). The mean absolute deviation of the medial proximal tibial (mPTA) and distal lateral femoral angle (dLFA) was 1° (+/- 0,9) for both. The mean surgery time in the robotic group after finishing the learning curve was 66 minutes (+/- 4,2) and in the total manual group 67 minutes (+/- 3,5) (n.s.). Conclusion: After finishing the initial learning curve of 11 cases for robotic-assisted TKA the time of surgery is equal to the manual conventional technique. However, there is no learning curve for implant positioning with the imageless robotic system. The implementation of the intraoperative plan is accurate to 1° with the robotic system.

Periprosthetic joint infection (PJI) remains one of the most common causes of revision knee arthroplasty. Controversy continues to surround the proper operative technique of PJI in knee arthroplasty with single- or two-stage replacement. Significant variations are seen in the eradication rates of PJI and in implant survival rates. This detailed retrospective analysis of a single tertiary center is intended to provide further data and insight comparing single- and two-stage revision surgery. A retrospective analysis of all revision total knee arthroplasty (TKA) surgeries from 2013 to 2019 was performed and screened with respect to single- or two-stage TKA revisions. Single- and two-stage revisions were analyzed with regard to implant survival, revision rate, microbiological spectrum, and other typical demographic characteristics. A total of 63 patients were included, with 15 patients undergoing single-stage revision and 48 patients undergoing two-stage revision. The mean follow-up time was 40.7 to 43.7 months. Statistically, no difference was found between both groups in overall survival (54.4% vs. 70.1%, p = 0.68) and implant survival with respect to reinfection (71.4% vs. 82.4%, p = 0.48). Further, high reinfection rates were found for patients with difficult-to-treat organisms and low- to semi-constrained implant types, in comparison to constrained implant types. A statistically comparable revision rate for recurrence of infection could be shown for both groups, although a tendency to higher reinfection rate for single-stage change was evident. The revision rate in this single-center study was comparably high, which could be caused by the high comorbidity and high proportion of difficult-to-treat bacteria in patients at a tertiary center. In this patient population, the expectation of implant survival should be critically discussed with patients.

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Purpose The purpose of this study was to examine the predictive value concerning clinical outcome and implant survival, as well as the accuracy of individual tests of a recently published radiographic decision aid for unicondylar knee arthroplasty indication findings. Methods In the retrospective part of the study, 98 consecutive patients who had undergone unicondylar knee arthroplasty (Phase 3 Oxford medial UKA) were included, using revision questionnaires, as well as the Forgotten Joint Score‐12 (FJS‐12) and Knee Osteoarthritis Outcome Score (KOOS) and analysed for suitability of the radiographic decision aid. Inappropriate and appropriate indications were then compared concerning the clinical outcome and implant survival. The prospective part of the study assessed the accuracy of the decision aid's radiographic tests (varus and valgus stress views, true lateral view and skyline view), and included 90 patients. Definition as appropriate for UKA procedure included medial bone‐on‐bone situation in varus stress views, full‐thickness lateral cartilage and functional medial collateral ligament in valgus stress views, functional anterior cruciate ligament (ACL) in true lateral views and absence of lateral facet osteoarthritis with bone loss in skyline views. Pre‐operative radiographic assessment with respect to the decision aid was then compared with intraoperative articular conditions. The clinical outcome was analysed using non‐parametric tests (Mann–Whitney U), and revision rates were compared using the Fisher's exact test. Accuracy assessment included calculations of the sensitivity, specificity, negative predictive value and positive predictive value. A p value < 0.05 was considered statistically significant. Results Appropriate unicondylar knee arthroplasty with respect to the decision aid showed a significantly lower revision rate compared to inappropriate unicondylar knee arthroplasty (7.3% vs. 50.0%, p < 0.0001), as well as higher clinical outcome scores (FJS‐12: 53.13 vs. 31.25, p = 0.041 and KOOS‐QDL: 68.75 vs. 50.0, p = 0.036). The overall sensitivity (70.1%) and specificity (76.2%) for the radiographic decision aid was comparably low, which was essentially based on false negative cases (22.7%) regarding medial bone‐to‐bone conditions. Conclusion The radiographic decision aid is a helpful tool to predict clinical outcome and implant survival of mobile‐bearing unicondylar knee arthroplasty. Strict use of the radiographic decision aid may lead to increased exclusion of appropriate patients with unicondylar knee arthroplasty implantation.

Purpose This study aimed to validate a new joint line measurement technique in total knee arthroplasty for separated assessment of the medial and lateral femoral joint line alteration with 3D-surface scan technology. Separate assessment of the medial and lateral joint line alteration may improve TKA alignment assessment regarding to joint line restoration in kinematic alignment and use of robotic-assisted TKA surgery. Methods The medial and lateral joint line difference after TKA implantation on an artificial bone model was analyzed and compared with a 3D-scan and full femoral radiographs pre- and postoperatively. Radiographic analysis included the perpendicular distance between the most distal point of the medial and lateral condyle and the reproduced preoperative lateral distal femoral angle (LDFA). For evaluation of validity and reliability, radiographs were captured initially with true anteroposterior view and subsequently with combined flexion and rotation malpositioning. Reliability of the introduced measurement technique in between three observers was tested with intraclass correlation coefficient (ICC). Results Radiographic measurement showed a mean difference of 0.9 mm on the medial side and 0.6 mm on the lateral side when compared to the 3D-surface scan measurement. The reliability of measurement accuracy was ≤ 1 mm in x-rays with < 10° flexion error regardless to malrotation in these images. The ICC test showed very good reliability for the medial joint line evaluation and good reliability for lateral joint line evaluation (ICC 0.92, ICC 0.86 respectively). Conclusion The new introduced joint line measurement method showed a sufficient reliability, accuracy and precision. It provides separated information about medial and lateral joint line alteration in TKA surgery in absolute values. Level of evidence V - Experimental Study

Aims and Objectives: The use of robotic-arm assisted total knee arthroplasty promises more precision in TKA implant technique. Precise implantation is elemental in improving functional and radiological outcome after TKA. The posterior condylar offset ratio (PCOR) is one important radiological parameter in total knee arthroplasty (TKA). The PCOR correlates with the maximum range-of-motion of the knee. A decrease of PCOR in TKA could lead to early impingement of the tibial insert with a consecutive decreased flexion range of the knee. The primary objective of this study was to determine differences in PCOR reconstruction after TKA between manual and robotic arm-assisted TKA surgery. Materials and Methods: A total of 80 patients undergoing primary TKA performed by one single senior surgeon were included in this prospective study. Two groups (Robotic arm-assisted TKA group, manual TKA group, n=40 patients each) were compared on the basis of hip-knee-ankle angle (HKA), medial proximal tibial angle (mPTA), distal lateral femoral angle (dLFA) and PCOR. Weight-bearing full-leg a.p. radiographs, as well as lateral knee radiographs, were performed pre- and postoperatively. All surgeries were performed with one single posterior stabilized TKA prosthesis type. Statistics consisted of parametric t-testing with a level of significance of p<0.05. Results: Preoperative limb alignment, mPTA and dLFA did not differ in between groups (each p>0.05). Postoperative mean PCOR was larger in the robotic arm-assisted TKA group (0.51 ± 0.05 vs. manual TKA group 0.47 ± 0.05, p=0.006). The absolute mean difference of pre- and postoperative PCOR was higher in the manual TKA group when compared to the robotic arm-assisted TKA group (-0.059 vs. -0.017, p=0.001). Manual TKA group showed a mean relative deviation of 12,03% (± 9,1%) in pre- to postoperative PCOR, whereas a mean relative deviation of 3.9 % (± 4.5%) was found in the robotic arm-assisted TKA group. Conclusion: Robotic arm-assisted TKA showed higher precision regarding postoperative PCOR with lower absolute mean differences and less relative deviation in pre- and postoperative PCOR when compared to manual TKA. A precise reconstruction of PCOR correlates with a better functional outcome as shown in previous studies before.