Aims

Around the world, the emergence of robotic technology has improved surgical precision and accuracy in total knee arthroplasty (TKA). This territory-wide study compares the results of various robotic TKA (R-TKA) systems with those of conventional TKA (C-TKA) and computer-navigated TKA (N-TKA).

Aim

We aim to compare post-operative length of stay and cardiopulmonary morbidity in patients randomised to either navigated or conventional total knee arthroplasty (TKA).

We aim to compare post-operative length of stay and cardiopulmonary morbidity in patients randomised to either navigated or conventional total knee arthroplasty (TKA).

Patients undergoing primary TKA for osteoarthritis were prospectively assigned randomly to either navigation-guided or control groups and blinded to this.

All patients received a PFC implant (DePuy, Warsaw, IN). In the control group the standard femoral intramedullary and tibial extramedullary alignment rod was used. In the navigation group, the BrainLab (Munich, Germany) navigation system was used. All operations were carried out by one of two consultant orthopaedic knee surgeons.

Length of post operative hospital stay and the development of cardiopulmonary complication were recorded and groups compared.

100 patients were recruited (55 control vs 45 navigated). Patient demographics were similar in both groups.

Mean length of stay was 7 days in the control group (range 3-101), 5 days in the navigation group (range 3-10). The mode was 4 days in both groups.

7 patients (13%) stayed for >7 days in the control group, 3 patients (7%) stayed >7 days in the navigation group(p=0.339).

4 patients(7%) required >10 days inpatient stay in the control group, 0 patients required to stay in hospital for longer than 10 days in the navigation group(p=0.069).

The causes for the length of stay exceeding 10 days were pulmonary embolus in 3 patients, and chest infection in 1 patient.

Patients undergoing navigation-guided TKA required shorter post-operative inpatient stays than those undergoing arthroplasty using conventional techniques. Fewer patients in the navigation group required stays longer than 7 or 10 days. The difference in post-operative stay was associated with fewer respiratory complications in the navigated group.

Abstract. A number of postoperative complications of navigated total knee arthroplasty have been discussed in the literature, including tracker pin site infection and fracture. In this paper we discuss the low postoperative complication rate in a series of 3100 navigated total knee arthroplasties and the overall complication rate in a systematic analysis of the literature. Methods. 3100 consecutive patients with navigated total knee arthroplasties from 2001 to 2016 were retrospectively evaluated for complications specific to navigation. We discuss the two cases of postoperative fracture through tracker pin sites that we experienced and compare this systematically to the literature. Results. Postoperatively, our 3100 patient cohort experienced a total of two fractures through pin sites for an incidence of 0.065%. One was a distal femoral fracture which was treated surgically, and the other was a proximal tibial fracture treated nonoperatively. Due to our incorporation of the tracker sites within our operative incision, there were no identifiable pin site infections which others have noted. Our 0.065% fracture rate compares favorably with the 0.16% rate of fracture published in the literature. We had no separate pin site infections in comparison to the 0.47% incidence of separate pin site infection reported by those who use seperate percutaneous incisions for tracker placement. Conclusion. There is an extremely low risk of perioperative complications due to the instrumentation used in navigated total knee arthroplasty when utilizing the Stryker Navigation System and 4.0 mm anchoring pins placed within the surgical incision. Our experience has demonstrated that careful placement of the bicortical anchoring pin is important

To analyse the intra-operative variation in mechanical axes of the lower limb at various stages during navigated total knee replacement. A prospective study was performed to analyse the intra-operative variation in the mechanical axes of the lower limb during navigated total knee replacement. All consecutive patients who underwent navigated total knee replacement were included and patients with inadequate data were excluded from the study. The intra-operative initial, trial and the final mechanical hip-knee-ankle axes were recorded from the navigation system. The differences between these axes were calculated and analysed. There were forty patients, of which 24 were females and 16 males with the age ranging from 37-89 (average 68.4) years. The right knee was replaced in 27 and the left knee in 13 patients. The average initial mechanical axes alignment was 0.03° valgus (3° varus to 3° valgus), trial alignment 0.64° varus (3° varus to 1.5° valgus) and final alignment 0.25° varus (4° varus to 4° valgus). Average deviation from initial to trial axes was 0.97°, trial to final axes was 0.74° and initial to final axes was 1.08°. The correlation co-efficient between the initial and the trial axes was 0.25, trial and final axes was 0.43 & initial and final axes was 0.09. This study highlights a significant variation in mechanical axes between the different stages of navigated total knee replacement. The potential sources of intra-operative errors causing these changes could be soft tissue imbalance, variations in implant placement and possible tracker micro motion. Execution of bony cuts in near normal neutral alignment does not guarantee achievement of near normal final alignment. We advocate surgeons to be vigilant to avoid potential malalignment during navigated total knee replacement

To analyse the intra-operative variation in mechanical axes of the lower limb at various stages during navigated total knee replacement. A prospective study was performed to analyse the intra-operative variation in the mechanical axes of the lower limb during navigated total knee replacement. All consecutive patients who underwent navigated total knee replacement were included and patients with inadequate data were excluded from the study. The intra-operative initial, trial and the final mechanical hip-knee-ankle axes were recorded from the navigation system. The differences between these axes were calculated and analysed. There were forty patients, of which 24 were females and 16 males with the age ranging from 37–89 (average 68.4) years. The right knee was replaced in 27 and the left knee in 13 patients. The average initial mechanical axes alignment was 0.03° valgus (3° varus to 3° valgus), trial alignment 0.64° varus (3° varus to 1.5° valgus) and final alignment 0.25° varus (4° varus to 4° valgus). Average deviation from initial to trial axes was 0.97°, trial to final axes was 0.74° and initial to final axes was 1.08°. The cor-relation co-efficient between the initial and the trial axes was 0.25, trial and final axes was 0.43 & initial and final axes was 0.09. This study highlights a significant variation in mechanical axes between the different stages of navigated total knee replacement. The potential sources of intra-operative errors causing these changes could be soft tissue imbalance, variations in implant placement and possible tracker micro motion. Execution of bony cuts in near normal neutral alignment does not guarantee achievement of near normal final alignment. We advocate surgeons to be vigilant to avoid potential malalignment during navigated total knee replacement

Purpose. The purpose of this study was to compare joint line changes between posterior-stabilized (PS) and cruciate-retaining (CR) computer navigated total knee arthroplasties (TKA) and to evaluate the impact on functional outcome. Background. Restoration of the native joint line has been a common goal in all TKA designs. Computer-navigated TKA in increasingly being favoured by many surgeons, due to increased precision and lesser complications. Few studies have reported the effect of computer navigated TKA on joint line restoration. It remains to be seen if the greater precision offered by computer-navigated TKA in restoration of joint line translates to improvement in functional outcome. Methods. This study assessed joint line changes following computer-assisted navigated total knee arthroplasty (TKA). A total of 195 patients were followed up for a period of 2 years following primary surgery. The change in the joint line was calculated based on the verified bony resections and the final thickness of the insert. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t-test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups at 6 months and 2 years of follow-up. Results. A total of 112 CR knees and 83 PS knees were analyzed. PS knees had a significantly greater joint line change as compared to CR knees with a p-value of 0.04 (Figure 1). Although the knee, function and oxford knee questionnaire scores were significantly better in the CR group at the 6-month follow-up, this did not translate into any significant difference in functional scores at the 2-year follow-up. It was also found that the PS group had significantly better final range of motion. Conclusion. CR knees are associated with significantly less joint line changes than PS knees in computer navigated TKA. PS knees have a greater range of motion at 2 years of follow-up. No significant difference in outcome was noted at 2 years follow-up

During total knee replacement (TKR), surgical navigation systems (SNS) allow accurate prosthesis component implantation by tracking the tibio-femoral joint (TFJ) kinematics in the original articulation at the beginning of the operation, after relevant trial components implantation, and, ultimately, after final component implantation and cementation. It is known that TKR also alters normal patello-femoral joint (PFJ) kinematics resulting frequently in PFJ disorders and TKR failure. More importantly, patellar tracking in case of resurfacing is further affected by patellar bone preparation and relevant component positioning. The traditional technique used to perform patellar resurfacing, even in navigated TKR, is based only on visual inspection of the patellar articular aspect for clamping patellar cutting jig and on a simple calliper to check for patellar thickness before and after bone cut, and, thus, without any computer assistance. Even though the inclusion in in-vivo navigated TKR of a procedure for supporting also patellar resurfacing based on patient-specific bone morphology seems fundamental, this have been completely disregarded till now, whose efficacy being assessed only in-vitro. This procedure has been developed, together with relevant software and surgical instrumentation, as an extension of current SNS, i.e. TKR is navigated, at the same time measuring the effects of every surgical action on PFJ kinematics. The aim of this study was to report on the first in-vivo experiences during TKR with patellar resurfacing. Four patients affected by primary gonarthrosis were implanted with a fixed bearing posterior-stabilised prosthesis (NRG, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. All TKR were performed by means of two SNS (Stryker®-Leibinger, Freiburg, Germany) with the standard femoral/tibial trackers, the pointer, and a specially-designed patellar tracker. The novel procedure for patellar tracking was approved by the local ethical committee; the patients gave informed consent prior the surgery. This procedure implies the use of a second system, i.e. the patellar SNS (PSNS), with dedicated software for supporting patellar resurfacing and relative data processing/storing, in addition to the traditional knee SNS (KSNS). TFJ anatomical survey and kinematics data are shared between the two. Before surgery, both systems were initialised and the patellar tracker was assembled with a sterile procedure by shaping a metal grid mounted with three markers to be tracked by PSNS only. The additional patellar-resection-plane and patellar-cut-verification probes were instrumented with a standard tracker and a relevant reference frame was defined on these by digitisation with PSNS. Afterwards, the procedures for standard navigation were performed to calculate preoperative joint deformities and TFJ kinematics. The anatomical survey was performed also with PSNS, with relevant patellar anatomical reference frame definition and PFJ kinematics assessment according to a recent proposal. Standard procedures for femoral and tibial component implantation, and TFJ kinematics assessment were then performed by using relevant trial components. Afterwards, the procedure for patellar resection begun. Once the surgeon had arranged and fixed the patellar cutting jig at the desired position, the patellar-resection-plane probe was inserted into the slot for the saw blade. With this in place, the PSNS captured tracker data to calculate the planned level of patellar bone cut and the patellar cut orientation. Then the cut was executed, and the accuracy of this actual bone cut was assessed by means of the patellar-cut-verification probe. The trial patellar component was positioned, and, with all three trial components in place, TFJ and PFJ kinematics were assessed. Possible adjustments in component positioning could still be performed, until both kinematics were satisfactory. Finally, final components were implanted and cemented, and final TFJ and PFJ kinematics were acquired. A sterile calliper and pre- and post-implantation lower limb X-rays were used to check for the patellar thickness and final lower limb alignment. The novel surgical technique was performed successfully in all four cases without complication, resulting in 30 min longer TKR. The final lower limb alignment was within 0.5°, the resurfaced patella was 0.4±1.3 mm thinner than in the native, the patellar cut was 1.5°±3.0° laterally tilted. PFJ kinematics was taken within the reference normality. The patella implantation parameters were confirmed also by X-ray inspection; discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. At the present experimental phase, a second separate PSNS was utilised not to affect the standard navigated TKR. The results reported support relevance, feasibility and efficacy of patellar tracking and PFJ kinematics assessment in in-vivo navigated TKR. The encouraging in-vivo results may lay ground for the design of a future clinical patella navigation system the surgeon could use to perform a more comprehensive assessment of the original whole knee anatomy and kinematics, i.e. including also PFJ. Patellar bone preparation would be supported for suitable patellar component positioning in case of resurfacing but, conceptually, also in not resurfacing if patellar anatomy and tracking assessment by SNS reveals no abnormality. After suitable adjustment and further tests, in the future if this procedure will be routinely applied during navigated TKR, abnormalities at both TFJ and PFJ can be corrected intra-operatively by more cautious bone cut preparation on the femur, tibia and also patella, in case of resurfacing, and by correct prosthetic component positioning

INTRODUCTION. Total knee arthroplasty (TKA) is considered a highly successful procedure. Survival rates of more than 90% after 10 years are generally reported. However, complications and revisions may still occur for many reasons, and some of them may be related to the operative technique. Computer assistance has been suggested to improve the accuracy of implantation of a TKA (Jenny 2005). Short term results are still controversial (Roberts 2015). However, few long term results have been documented (Song 2016). The present study was designed to evaluate the long-term (more than 10 years) results of a TKA which was routinely implanted with help of a non-image based navigation system. The 5- to 8-year of this specific TKA has already been documented (Jenny 2013). The hypothesis of this study will be that the 10 year survival rate of this TKA will be improved in comparison to historical papers when analyzing survival rates and knee function as evaluated by the Knee Society Score (KSS). MATERIAL AND METHODS. All patients operated on between 2001 and 2004 for implantation of a navigated TKA were eligible for this study. Usual demographic and peri-operative items have been record. All patients were prospectively followed with clinical and radiological examination. All patients were contacted after the 10 year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Patients who did not return were interviewed by phone call. For patients lost of follow-up, family or general practitioner was contacted to obtain relevant information about prosthesis survival. Survival curve was plotted according to Kaplan-Meier. RESULTS. 247 TKAs were implanted during the study time-frame. 225 cases had an optimal lower limb axis (HKA angle between 177° and 183°) after TKA (91%). Final follow-up (including death or revision) was obtained for 200 cases (81%). Clinical status after 10 years was obtained for 146 cases (59%) (KSS, 102 cases – Oxford questionnaire, 146 cases – radiologic evaluation, 94 cases). 4 prosthetic revisions were performed for mechanical reasons during the follow-up time (1%). The 10 year survival rate was 98%. The mean KSS was 188 points. The mean Oxford score was 55 points. No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. DISCUSSION. This study confirms our initial hypothesis, namely quite satisfactory results of navigated implanted TKA after more than 10 years. Navigation, whose precision is no longer to be demonstrated, probably contributed to the quality of the results. A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the TKA. Other authors did observe similar results (Baumbach 2016). However, superiority of navigated TKA in comparison to conventional implanted TKA is difficult to prove because of the subtle differences expected in mostly underpowered studies. Longer term follow-up may be required

Background. Stress fractures at tracker after computer navigated total knee replacement are rare. Periprosthetic fracture after Minimally Invasive Plate Osteosynthesis (MIPO) of stress fracture through femoral tracker is unique in orthopaedic literature. We are reporting this unique presentation of periprosthetic fractures after MIPO for stress fracture involving femoral pin site track in computer assisted total knee arthroplasty, treated by reconstruction nail (PFNA). Methods. A 75-year old female, who had computer navigated right total knee replacement, was admitted 6 weeks later with increasing pain over distal thigh for 3 weeks without trauma. Prior to onset of pain, she achieved a range of movements of 0–105 degrees. Perioperative radiographs did not suggest obvious osteoporosis, pre-existent benign or malignant lesion, or fracture. Radiographs demonstrated transverse fracture of distal third of femur through pin site track. We fixed the fracture with 11-hole combihole locking plate by MIPO technique. Eight weeks later, she was readmitted with periprosthetic fracture through screw hole at the tip of MIPO Plate and treated by Reconstruction Nail (PFNA), removal of locking screws and refixation of intermediate segment with unicortical locking screws. Then she was protected with plaster cylinder for 4 weeks and hinged brace for 2 months. Results. Retrograde nail for navigation pin site stress fracture entails intraarticular approach with attendant risks including scatches to prosthesis and joint infection. So we opted to fix by MIPO technique. Periprosthetic fracture at the top of MIPO merits fixation with antegrade nail in conjunction with conversion of screws in the proximal part of the plate to unicortical locking screws. Overlap of at least 3cms offers biomechanical superiority. She made an uneventful recovery and was started on osteoporosis treatment, pending DEXA scan. Conclusion. Reconstruction Nail (PFNA), refixation of intermediate segment with unicortical locking screws constitutes a logical management option for the unique periprosthetic fracture after MIPO of stress fracture involving femoral pin site track in computer assisted total knee replacement

Summary Statement. Navigated total knee arthroplasty (TKA) is becoming increasingly popular in the United States. Compared to traditional unnavigated TKA, the use of navigation is associated with decreased blood transfusions and shorter hospital stays. Introduction. Navigated total knee arthroplasty (TKA) is a recent modification to standard TKA with many purported benefits in regards to component positioning. Controversy currently exists though regarding its clinical benefits. The purpose of this study was to assess recent national trends in navigated and unnavigated total knee arthroplasty and to evaluate perioperative outcomes for each group. Methods. International Classification of Disease - 9th Revision (ICD-9) procedure codes were used to search the National Hospital Discharge Survey (NHDS) for all patients admitted to US hospitals after navigated and unnavigated TKA for each year between 2005 and 2010. Data regarding patient demographics, hospitalization length, discharge disposition, blood transfusions, deep vein thrombosis, pulmonary embolism, mortality, and hospital location were gathered from the NHDS. Trends were evaluated by linear regression with Pearson's correlation coefficient (r) and statistical comparisons were made using Student's t-test, z-test for proportions, and chi-square analysis with a significance level of 0.05. Results. 22,443 patients admitted for TKA were identified. 578 (2.6%) of these patients had a TKA utilizing navigation. After adjusting for fluctuations in annual TKA performed, the use of navigation in TKA demonstrated a strong positive correlation with time (r=0.71), significantly increasing from an average utilization rate of 2.2% between 2005–2007 to 3.2% between 2008–2010 (p<0.01). The location of the hospital was found to significantly impact the utilization of navigation, with the lowest rate seen in the Midwest region (2.0%) of the US and the highest rate seen in the South region (3.0%). The mean age of navigated patients was 66.0 years. This group included 211 men and 367 women. The unnavigated group had a mean patient age that was insignificantly higher at 66.4 years (p=0.37) and included 7,815 men and 14,047 women. Gender was also not significantly different (p=0.71) between those with navigated TKA and those with unnavigated TKA. The number of medical co-morbidities was significantly higher in those with navigation (mean 5.4 diagnoses) than those without navigation (mean 5.1 diagnoses, p=0.01). Average hospitalization length also varied based on navigation status, with significantly shorter stays for those with navigation (3.3 days, range 1–11) compared to those without (3.6 days, range 1–73, p<0.01). The rate of blood transfusion was significantly lower in the navigated group (13.0%) versus the unnavigated group (17.4%, p<0.01). There was no difference in the rate of deep vein thrombosis (0.69% vs 0.53%, p=0.64) or pulmonary embolism (0.17% vs 0.47%, p=0.10). Mortality was also not significantly different for navigated TKA (0.17%) when compared to unnavigated TKA (0.08%, p=0.61). Discharge disposition did not significantly vary based on navigation status either, with 65.5% of navigated patients and 67.0% of unnavigated patients able to go directly home (p=0.55) after their inpatient stay. Discussion/Conclusion. This study demonstrates that the use of navigated TKA in the US is rising. Additionally, despite having more medical co-mobidities, the navigated population required less blood transfusions and shorter lengths of stay. Interestingly, navigation utilization demonstrated variability based on hospital region. The reasons for this are not immediately clear, but may be related to differences in regional training

Introduction: Computer-assisted minimal invasive total knee arthroplasty (MIS-TKA) provides the patient with the advantages of computer navigated total knee arthroplasty (CN-TKA) and early mobilization and progressive rehabilitation because of minor soft tissue injury. Since conventional landmarks are not visible for the surgeon throughout the operation, he must rely on the data displayed by the computer navigation system. This study was designed to assure that MIS-TKA reveals identical mechanical accuracy as conventional computer navigated TKA while reducing rehabilitation time. Materials and methods: The Stryker knee navigation system was used intraoperatively. There were forty patients included in this study: 20 consecutive patients received computer navigated TKA (Scorpio) and 20 consecutive patients received MIS-TKA (Stryker-MIS Scorpio). Preoperatively and 6 months after the operation all patients received orthoradiograms and a CT-scan of the knee to determine mechanical and rotational alignment. Intraoperatively data shown by the navigation system was recorded. The HSS knee score was recorded preoperatively and 6 months postoperatively. Length of skin incision, length of hospital stay and postoperative range of motion were also determined. Results: Analysis showed that the mechanical axis improved in both groups to less than 1° of varus. Rotational alignment of the femoral component showed reproducible values of less than 2° of rotation without significant differences between the two groups. Also, ligament laxity was almost identical preoperatively and postoperatively in 0°, 45° and 90° of knee flexion. Length of skin incision was significantly shorter in MIS-TKA. HSS knee score improved from a mean of 76 points (range 57–96) preoperatively to a mean of 92 points (range 64–100) 6 months postoperatively for both groups. Patients from the MIS-TKA group revealed a quicker recovery time than patients from the CN-TKA group. ROM improved sooner after the operation in the MIS-TKA group, however after 6 months both systems reached the same ROM. The length of hospital stay was significantly reduced by the MIS-TKA group. Discussion: The Stryker knee navigation system aids the surgeon to precisely optimize mechanical and rotational alignment and to avoid malrotation and axial malalignment not only in CN-TKA but also in MIS-TKA. We have found no significant differences in preoperative and postoperative ligament laxity between the two groups. The advantages of minimal soft tissue damage in MIS-TKA can be achieved without loss of accuracy and with a great benefit for the patient

Introduction: There is an ongoing discussion about potential risks and benefits of minimally invasive approaches (MIS) in total joint replacement. The aim of this study was to evaluate, whether a higher incidence of malalignments could be observed after minimally invasive navigated TKA and wether the results in the early postoperative period were better compared to standard approaches. Methods: A total of 50 patients were treated with a navigated (OrthoPilot 4.2) Columbus knee prosthesis (BBraun Aesculap, Germany). In 25 patients either a standard or a minimally invasive (mini-mid-vastus) approach was carried out. In both groups the same exclusion criteria for MIS were adopted. Initially during surgery (Nav1a) and finally after implantation of the original components (Nav1b) the mechanical leg axis, passive range of motion and stability were measured by navigation according to the common workflow of the system. After restarting the software the same parameters were evaluated once more in a second procedure (Nav2) by reacquisition of joint centers both kinematically and by anatomical landmark palpation with the original prosthesis already implanted. Nav2 was conducted independantly from the initial surgical procedure. To validate the intraoperative measurements additional pre- and postoperative long-leg-standing radiographs were made. During the the first 10 days postoperatively daily range of motion (ROM) and pain (VAS) were measured. Perioperative blood loss and complications were documented. Results were analyzed by student’s t-test. Results: Both groups were comparable with regard to preoperative demografic, radiologic and intraoperative data (Nav1a). There were no significant differences between the groups concerning intraoperative measurements of mechanical leg axis, passive range of motion and stability by Nav1b and Nav2. Additionally no differences were found for the alignment in the postoperative radiographs. The length of the skin incisions were significantly shorter in the minimally invasive group. Postoperative ROM was significantly higher and pain was significantly less intensive in the MIS group. Blood loss and complication rates were comparable. Discussion: If the exclusion criteria for MIS were accepted no differences regarding the quality of alignment, passive range of motion and ligament stability could be demonstrated between conventional and MIS navigated TKA. Patients with MIS navigated TKA performed superior in terms of early p.o. function and pain. From the authors point of view the technically demanding minimally invasive implantation of knee prostheses should be exclusively performed with support of navigation

Introduction: There is an ongoing discussion about potential risks and benefits of minimally invasive approaches (MIS) in total joint replacement. The aim of this study was to evaluate, whether a higher incidence of misalignments could be observed after minimally invasive navigated TKA and whether the results in the early postoperative period were better compared to standard approaches. Methods: A total of 50 patients were treated with a navigated (OrthoPilot 4.2) Columbus knee prosthesis (BBraun Aesculap, Tuttlingen, Germany). In 25 patients either a standard or a minimally invasive (mini-mid-vastus) approach was carried out. In both groups the same exclusion criteria for MIS were adopted. Initially during surgery (Nav1a) and finally after implantation of the original components (Nav1b) the mechanical leg axis, passive range of motion and stability were measured by navigation according the common workflow of the system. After restarting the software the same parameters were evaluated once more in a second procedure (Nav2) by reacquisition of joint centres both kinematically and by anatomical landmark palpation with the original prosthesis already implanted. Nav2 was conducted independently from the initial surgical procedure. To validate the intraoperative measurements additional pre- and postoperative long-leg-standing radiographs were made. During the first 10 days postoperatively daily range of motion (ROM) and pain (VAS) were measured. Perioperative blood loss and complications were documented. Results were analyzed by student’s t-test. Results: Both groups were comparable with regards to preoperative demographic, radiological and intraoperative data (Nav1a). There were no significant differences between the groups concerning intraoperative measurements of mechanical leg axis, passive range of motion and stability by Nav1b and Nav2. Additionally no differences were found for the alignment in the postoperative radiographs. The length of the skin incision was significantly shorter in the minimally invasive group. Postoperative ROM was significantly higher and pain was significantly less intensive in the MIS group. Blood loss and complication rates were comparable. Discussion: If the exclusion criteria for MIS were accepted no differences regarding the quality of alignment, passive range of motion and ligament stability could be demonstrated between conventional and MIS navigated TKA. Patients with MIS navigated TKA performed superior in terms of early postoperative function and pain. From the authors point of view the technically demanding minimally invasive implantation of the knee prosthesis should be exclusively performed with support of navigation

Introduction: Computer navigation in total knee arthroplasty (TKA) may assist the surgeon with precise information about ligament tension and varus/valgus alignment throughout the complete range of motion, but there is only little information about how much ligament laxity is needed and how much laxity is too much. In the current study we measured the mechanical axis and opening of the joint at different time points, in different degrees of knee flexion and with varus and valgus stress during the procedure of computer navigated TKA. Methods: Forty-nine consecutive patients underwent a MIS computer navigated TKA. With the Stryker Knee Navigation System varus/valgus alignment and distraction/compression was measured in 0°, 45° and 90° of knee flexion immediate after digitalization of the knee and after fascial closure. Values were noted in a neutral position and with maximal varus and maximal valgus stress applied. Patients with posterior stabilized implants were compared to those with cruciate retaining implants. Patients with preoperative varus malalignment or valgus malalignment were compared to patients with straight preoperative mechanical axes. Results: At the beginning of the operative procedure the mean mechanical alignment was 1.9° varus at 0° knee flexion, 1.5° varus at 45° knee flexion and 1.5° varus at 90° knee flexion. Patients showed a mean mediolateral joint opening of 6.1° at 0° knee flexion, 5.9° at 45° knee flexion and 4.5° at 90° knee flexion. After implantation of the knee prosthesis and fascial closure mechanical alignment was 0.3° varus at 0° knee flexion, 0° varus at 45° knee flexion and 0.2° varus at 90° knee flexion. Mean joint laxity was 3.4° at 0° knee flexion, 3.1° at 45° knee flexion and 2.3° at 90° knee flexion. There was more lateral than medial joint opening postoperatively in 45° and 90° knee flexion regardless of the prosthesis type implanted. Preoperative varus and valgus malalignment could be reduced to values identical with those patients with straight preoperative mechanical axes. Discussion: Mean varus/valgus laxity after implantation of a MIS computer navigated TKA was lower than prior to prosthesis implantation. Varus/valgus laxity of an approximate total range of 1.5°–2° can be achieved at all measured degrees of knee flexion and seems to be the ideal laxity for TKA. Computer navigation in TKA can consistently reduce preoperative varus/valgus malalignment to a level comparable to patients with preoperatively normal mechanical axes. More lateral joint opening is found before as well as after implantation of the prosthesis in 45° and 90° of knee flexion. The type of prosthesis implanted seems not to effect postoperative joint laxity

Robotic and navigated TKA procedures have been introduced to improve component placement precision for the purpose of improving implant survivorship and other clinical outcomes. Although numerous studies have shown enhanced precision in placing components, adoption of technology-assistance (TA) for TKA has been relatively slow. One reason for this has been the difficulty in demonstrating the cost-effectiveness of implementing TA-TKA systems and assessing their impact on revision rates. In this study, we aimed to use a simulation approach to answer the following questions: (1) Can we determine the distribution of likely reductions in TKA revision rates attributable to TA-TKA in an average US patient population? And, (2) What reduction in TKA revision rates are required to achieve economic neutrality?. In a previous study, we developed a method for creating large sets of simulated TKA patient populations with distributions of patient-specific factors (age at index surgery, sex, BMI) and one surgeon-controlled factor (coronal alignment) drawn from registry data and published literature. Effect sizes of each factor on implant survival was modeled using large clinical studies. For 10,000 simulated TKA patients, we simulated 20,000 TKA surgeries, evenly split between groups representing coronal alignment precisions reported for manual (±3°) and TA-TKA (±1.0°), calculating the patient-specific survival curve for each group. Extending our previous study, we incorporated the probability of each patient's expected survival into our model using publicly available actuarial data. This allowed us to calculate a patient-specific estimate of the Reduction in Lifetime Risk of Revision (RLRR) for each simulated patient. Our analysis showed that 90% of patients will achieve an RLRRof 1.5% or less in an average US TKA population. We then conducted a simplified economic analysis with the goal of determining the net cost of using TA-TKA per case when factoring in future savings by TKA revision rates. We assumed an average cost of revision surgery to be $75,000 as reported by Delanois (2017) and an average added cost incurred by TA-TKA to be $6,000 per case as reported by Antonis (2019). We estimate the net cost per TA-TKA case (CNet) to be the added cost per TA-TKA intervention (CInt), less the cost of revision surgery (CRev) multiplied by the estimated RLRR: CNet = CInt - CRev∗RLRR. We find that, under these assumptions, use of TA-TKA increases expected costs for all patients with an RLRR of under 8%. Based on these results, it appears that it would not be cost-effective to use TA-TKA on more than a small fraction of the typical US TKA patient population if the goal is to reduce overall costs through reducing revision risks. However, we note that this simulation does not consider other possible reported benefits of TA-TKA surgery, such as improved functional and pain outcome scores which may justify its use on other grounds. Alternative costs incurred by TA-TKA will be evaluated in a future study. To reach economic neutrality, TA-TKA systems either must reduce the added cost per intervention or increase RLRR by better addressing the root causes of revision

Purpose:. To compare accuracy of transepicondylar axis as a reference for femoral component rotation in primary navigated versus non navigated total knee arthroplasty in severely deformed knees. Methods:. A prospective study done from dec 2009 to dec 2011 at tertiary centre. 180 knees were included (124 females and 56 males). All cases were randomly allocated into 2 groups: navigated and non navigated. All surgeries were carried out by two senior arthroplasty surgeons. All patients undergoing primary total knee replacement were included and all revision cases were excluded. Intraoperative assessment of TEA was done by palpating most prominent point on lateral epicondyle and sulcus on medial epicondyle and passing a k wire through it. Confirmation is done under image intensifier C arm with epicondylar view in Non navigated knees. Postoperative TEA was assessed by taking CT scan, measuring condylar twist angle and posterior condylar angle (PCA). Results:. The mean PCA was around 4° with TEA as reference in Navigated and 6° in Non navigated knees and only 7% patients required an additional lateral release of which 2% patient had preop patellar maltracking. No postoperative patellar maltracking was seen. Anterior knee pain was present in 10% patients. No postop infection is noted. Alignment ranging from 4° to 8° external rotation. Conclusion:. Navigation is most accurate measure for TEA as reference, as compared to non navigated TKA, which can lead to excessive external rotation especially in severely deformed knees

Modern total knee replacements aim to reconstruct a physiological kinematic behaviour, and specifically femoral roll-back and automatic tibial rotation. A specific software derived from a clinically used navigation system was developed to allow in vivo registration of the knee kinematics before and after total knee replacement. The study was designed to test for the feasibility of the intra-operative registration of the knee kinematics during standard, navigated total knee replacement. The software measures the respective movement of the femur and the tibia, and specially antero-posterior translation and tibial rotation during passive knee flexion. Kinematic registration was performed twice during an usual procedure of navigated total knee replacement: 1) Before any bone resection or ligamentous balancing; 2) After fixation of the final implants. 200 cases of total knee replacement have been analysed. Post-operative kinematic was classified as following: 1) Occurrence of a normal femoral roll-back during knee flexion, no roll-back or paradoxical femoral roll-forward. 2) Occurrence of a normal tibial internal rotation during knee flexion, no tibial rotation or paradoxical tibial external rotation. All patients were followed up for a minimal period of 12 months, and reevaluated at the latest follow-up visit for clinical and functional results with completion of the Knee Society Scores. Recording the kinematic was possible in all cases. The results of both pre-operative and post-operative registrations were analysed on a qualitative manner. The results were close to those already published in both experimental and clinical studies. About femoral roll-back, 54% had a normal femoral roll-back during knee flexion after total knee replacement, 13% had no significant roll-back and 33% had a paradoxical femoral roll-forward. About tibia rotation, 65% had a normal tibia internal rotation during knee flexion, 16% had no significant tibia rotation and 19 had a paradoxical tibia external rotation. The mean Knee Score was 92/100 ± 10 points. There was a significant correlation between the post-operative kinematic behaviour and the Function Score, with better score for the patients having a physiological femoral roll-back and a physiological tibial internal rotation during knee flexion (p<0.01). Intra-operative analysis of the kinematic of the knee during total knee replacement may offer the chance to modify the kinematic behaviour of the implant and to choose the best fitted constraint to the patient's native knee in order to impact positively the functional result

Cognitive dysfunction has been well documented following total knee replacement. Possible causes that have been postulated include cerebral emboli, post-operative complications and pain. The aim of this study is to compare cognitive decline in patients undergoing conventional total knee replacement (TKR), navigated total knee replacement and total hip replacement (THR). We prospectively analysed 75 patients undergoing lower limb arthroplasty. Group 1 consisted of 25 conventional TKR’s, group 2 consisted of 25 navigated TKR’s and group 3 consisted of 25 THR’s. Cognitive function was assessed by 11 validated neuropsychological tests preoperatively, at 1 week post-operatively and at 6 months post-operatively. Testing was carried out by a clinical psychologist. At day 6 post-operatively 55% of group 1, 83% of group 2 and 61% of group 3 patients had a significant cognitive decline. Group 2 had a significantly greater cognitive decline at day 6 compared to the other 2 groups. At 6 months significant cognitive decline was found in all 3 groups to 21%, 16% and 34% respectively. Group 2 demonstrated the greatest improvement in cognition from day 6 to 6 months post-operatively. Significant cognitive decline occurs in two-thirds (66%) of all patients undergoing lower limb arthroplasty at day 6 and remains significant in a quarter (25%) of patients at 6 months. There was no significant difference in cognitive decline in patients undergoing hip and knee arthroplasty

The influence of BMI on outcomes from TKA remains unclear. The purpose of this study was to evaluate if navigation affected the outcomes of TKA in obese patients. Sixty-four (mean age 65 yrs±7) consecutive computer navigated TKA’s were compared with a matched group of 64 (65yrs±8) conventional TKA’s in patients with a BMI > 35. The groups were matched for age, gender, diagnosis and operative technique. Patients were reviewed pre-operatively and 6 weeks and 1 year post-operatively. All patients had clinical and radiological assessment and were scored using the Oxford knee score. There were significant improvements (p< 0.001) in all clinical outcomes at 6 weeks and 1 year post-operatively in both groups. No significant differences were found between groups 6 weeks post surgery. The computer navigated group performed significantly better in post operative knee flexion (Nav 99° ± 10, Conv 94° ±12, p< 0.05) and Oxford scores (Nav 20 ± 10, Conv 25±12, p< 0.01) at 1 year compared to the conventional group. There were significantly (p< 0.05) more flexion contractures one year post-operatively in the conventional group which correlated significantly (p< 0.001) with decreased maximal knee flexion at one year. This study suggests that navigated TKA produces better early clinical outcomes than conventional TKA in the obese patients possibly due to improved sagittal alignment as evidenced by the lack of flexion contractures 1 year post-operatively