When are patients with osteoarthritis referred for surgery?

Current treatment strategies in hip and knee osteoarthritis (OA) involve a combined approach that includes not only modification of risk factors and conservative treatment but also joint-preserving surgical therapy in the early stages, or joint replacement in late OA. With the recent development of new etiological concepts (i.e. hip dysplasia and femoroacetabular impingement as major risk factors for hip OA), treatment alternatives for joint preservation could be extended significantly. Satisfactory results of osteotomies and other reconstructive procedures around hip and knee joints can only be expected in early OA (Kellgren/Lawrence grade 0-II). If patients with advanced radiographic OA grades III-IV do not respond to conservative treatment over at least 3 months and express a relevant burden of disease, joint replacement might be considered. Prior to surgery, potential contraindications must be excluded, patient expectations need to be discussed, and modifiable risk factors, which may negatively influence the outcome, should be optimized.

[Partial or full component exchange in hip revision? : The relevance of off-label use and mix & match]. / Partieller oder vollständiger Wechsel in der Hüftrevisionsendoprothetik? : Bedeutung von Off-Label-Anwendung und Mix & Match.

Off-label use is frequently practiced in hip revision arthroplasty, as there may be indications for the application of implants for purposes outside the one the manufacturers intended (i.e. large bone and soft tissue defects, obesity). Patients may also benefit from selective application of mix & match in hip revision, when the exchange of one component only is necessary and the invasiveness of surgery can be reduced. Currently, there are no formal guidelines for these situations. Therefore, within a recent EFORT initiative, evidence- and consensus-based recommendations have been developed for the safe application of off-label use and mix & match in revision hip and knee arthroplasty.

[Management of complications following tumor endoprosthetic replacement]. / Komplikationsmanagement nach Tumorendoprothesen.

BACKGROUND: Tumor endoprostheses are available as modular systems with which bone defects can be partially reconstructed, usually close to the joints, or as a total replacement of long tubular bones. As a result of continuously improved survival times, they are used with bone tumors, skeletal metastases and, increasingly, in revision arthroplasty. OBJECTIVES: Presentation of the most common complications of tumor endoprostheses and a description of their management, including treatment recommendations. MATERIALS AND METHODS: The current knowledge and our own experience of complication management with the use of megaprostheses are presented. RESULTS: The number of tumor endoprostheses procedures is limited, so that a limited number of studies and classifications are available. Periprosthetic infections involving the soft tissues represent the most serious failure after perioperative dying and local recurrence of the tumor. Two-stage revision remains the gold standard in periprosthetic infection, even if one-stage revision is justifiable in selective indications. Periprosthetic infection and local recurrence is associated with the risk of secondary amputations. Mechanical failure can be treated more easily. Specific socket systems for proximal femoral replacement and attachment tubing allow for adequate soft tissue reconstruction, restoration of joint function, and minimize the risk of dislocation. CONCLUSIONS: In comparison to primary arthroplasty, the risk of failure following tumor endoprosthetic replacement is increased but is basically controllable by revision surgery.

[The S2k guideline: Indications for knee endoprosthesis : Evidence and consent-based indications for total knee arthroplasty]. / S2k-Leitlinie: Indikation Knieendoprothese : Evidenz- und konsensbasierte Indikationsstellung in der Knie-Endoprothetik (EKIT-Knie).

Total knee arthroplasty (TKA) is one of the most frequent surgical procedures in orthopaedic surgery. Until now there have not been any standardized indication criteria, which might contribute to the large geographical differences in the frequency of TKA. This guideline aims to consent minimal requirements (main criteria), additional important aspects (minor criteria), as well as relative and absolute contraindications for TKA. The following main criteria have been consented: knee pain, radiological confirmation of osteoarthritis or osteonecrosis, inadequate response to conservative treatment, adverse impact of knee disease on the patient's quality of life and the burden of suffering due to the knee disease. Relative contraindications have been consented as severe general disease with reduced life expectancy and a BMI ≥40; absolute contraindications are an active infection and if the patient is not able to undergo major surgery.

[Personality and comorbidity: are there "difficult patients" in hip arthroplasty?]. / Persönlichkeitsprofil und Komorbidität: Gibt es den "schwierigen Patienten" in der primären Hüftendoprothetik?

BACKGROUND: Concomitant disorders at the time of surgery in addition to psychological and socioeconomic patient characteristics may influence treatment outcomes in hip arthroplasty. OBJECTIVES: To describe the impact of these factors on perioperative complications and postoperative results in terms of function, quality of life, and patient satisfaction. MATERIALS AND METHODS: Review of relevant clinical studies, meta-analyses, and presentation of our own results. RESULTS: Comorbidities in general, especially in combination, increase the perioperative risk profile. Socioeconomic factors (education, professional qualifications, social deprivation) in addition to psychological variables (depression, distressed personality) can have a major impact on postoperative functional outcomes and patient satisfaction. CONCLUSIONS: It is of crucial importance to avoid inequalities in the provision of joint replacement for patients with hip osteoarthritis and co-existing risk factors. Preventive strategies should be implemented to reduce the negative impact of comorbidities on treatment outcome. Personalized communication and education may be helpful in avoiding unrealistic patient expectations before hip replacement.

[Ipsilateral THA after stemmed TKA: Risk of interprosthetic fracture?]. / Ipsilaterale Hüftendoprothese nach stielgeführter Knieendoprothese: Risiko einer interprothetischen Fraktur?

BACKGROUND: There is an increasing number of patients who have undergone stemmed total knee arthroplasty and total hip arthroplasty in the same leg. These patients may be at increased risk of periprosthetic and interprostethic fracture. Etiology and the potential therapy strategies are not well represented in the current literature. OBJECTIVES: Determination of the risk factors for interprosthetic fractures and possible prevention. MATERIALS AND METHODS: We performed a review of the literature and additionally a survey among experts (members of the German Association for Arthroplasty [AE]) to investigate the risk and the necessity for a preventive internal fixation. RESULTS: There are only a few biomechanical studies. The interprosthetic distance seems to have little influence on the fracture risk, but the thickness of the cortex and the cortical area at the diaphysis seems to be important. The value of a bridging osteosynthesis remains uncertain. Ninety experts took part in the survey. The risk of fracture risk was estimated to be only slight to medium. Opinions regarding the necessity of preventive internal fixation were heterogeneous. CONCLUSIONS: The indication for preventive internal fixation could be derived neither from the literature nor from the survey of experts. The thickness of the cortex and co-morbidities (osteoporosis, tendency to fall, and medication) seem to be more important than the interprosthetic distance.

[Objectifying results in total knee arthroplasty: Is "patient satisfaction" adequate]. / Ergebnisobjektivierung bei Knietotalendoprothesen : Reicht die "Patientenzufriedenheit"?

BACKGROUND: Arthroplasty is an effective treatment for end-stage osteoarthritis of the knee and is one of Germany's most frequently performed orthopedic procedures. DISCUSSION: However, a considerable number of patient are not satisfied with the results after knee arthroplasty. The patient's perspective is particularly important for shared decision making. "Patient satisfaction" with the surgery is an expression of the patient's perspective, but might not be sufficient as the only outcome measure. There is no international consensus which outcome measures should be used after knee arthroplasty. CONCLUSION: Therefore, different measurement tools are used for the acquisition of a variety of outcome measures in order to quantify the results of knee arthroplasty. These tools should be used according to their reliability, validity, and responsiveness. This article provides an overview about available measurement tools.

[The German Cartilage Registry (KnorpelRegister DGOU) for evaluation of surgical treatment for cartilage defects: experience after six months including first demographic data]. / Das KnorpelRegister DGOU zur Erfassung von Behandlungsergebnissen nach Knorpeloperationen: Erfahrungen nach 6 Monaten und erste epidemiologische Daten.

The German Cartilage Registry (KnorpelRegister DGOU) has been introduced in October 2013 and aims on the evaluation of patients who underwent cartilage repair for symptomatic cartilage defects. It represents a nation-wide cohort study which has been introduced by the working group "Tissue Regeneration" of the Germany Society of Orthopaedic Surgery and Traumatology and is technically based upon a web-based remote data entry (RDE) system. The present article describes first experiences with the registry including patient and treatment characteristics. Between October 2013 and April 2014, a total of 230 patients who had undergone surgical cartilage repair for symptomatic full-thickness cartilage defects of the knee has been included in the German Cartilage Registry from 23 cartilage repair centres. Mean age was 37.11 years (SD 13.61) and mean defect size was 3.68 cm(2) (SD 0.23). Since the introduction of the KnorpelRegister DGOU the total number of registered patients has increased steadily up to the most recent figure of 72 patients within one month. Patients were treated mainly according to the recommended therapies. The highest percentage in therapy is represented by the bone marrow stimulation techniques (55.02 %) as well as by the autologous chondrocyte transplantation (34.92 %). Unlike the patient collective in the majority of prospective randomised controlled trials, the patient population within the registry shows a high proportion of patients with accompanying pathologies, with an age of more than 50 years at the time of treatment and with unfavourably assessed accompanying pathologies such as an affection of the opposite cartilage surface or a previously resected meniscus. In summary, the technical platform and forms of documentation of the KnorpelRegister DGOU have proved to be very promising within the first six months. Unlike data from other clinical trials, the previous analysis of the patients' data and therapies reflects successfully the actual medical care situation of patients with cartilage defects of the knee joint. This analysis also provides new information on subgroups of patients that have not yet been recorded in the scientific literature. This will be part of the first analysis of clinical treatment data. An expansion of the KnorpelRegister DGOU to patients with cartilage defects of the ankle and hip joints is already decided upon and initialised.

[Complications of metal-on-metal tribological pairing]. / Komplikationen bei Metall-Metall-Gleitpaarungen.

BACKGROUND: Metal-on-metal (MoM) tribological pairing results in less volumetric abrasion than pairing with the conventionally used polyethylene and is associated with a lower risk of material failure compared to other hard-hard pairings. An increased frequency of problem cases in recent years has led to a great increase in uncertainty. Against this background in this article the current aspects of epidemiology, etiology, diagnostics and treatment of complications in MoM hip joint endoprostheses will be discussed. EPIDEMIOLOGY AND ETIOLOGY: Based on the results from national endoprosthesis registers and selected clinical studies an evaluation of the rate of local complications from MoM tribological pairings was undertaken. A differentiation was made between MoM pairings in pedicled small head prostheses (≤ 32 mm), large head (> 32 mm) and surface replacement (OFE) endoprostheses. Each year MoM endoprostheses release on average 10(12)-10(14) cobalt (Co) and chromium (Cr) nanoparticles per patient. This release of metal ions and particles can lead to a variety of tissue reactions. DIAGNOSTICS: A differentiation must be made between regular routine diagnostics within the framework of implant follow-up screening and specific investigations due to the occurrence of complaints. The diagnostics for patients treated with MoM hip endoprostheses consists of a standardized step-wise approach considering possible differential diagnoses and the utilization of modern laboratory chemical and radiological methods. When problems occur, a differentiation should preferentially be made between complaints not caused by metal and mechanical problems (e.g. prosthesis loosening and impingement) and symptoms due to periprosthetic infections. THERAPY OF COMPLICATIONS: The normal standards for hip endoprosthetics are also valid for periprosthetic infections, fractures and other general complications. Specific measures are, however, necessary for complications due to metal-specific risks.

[Minimally invasive surgery for knee total arthroplasty - evidence-based advantages?]. / Minimalinvasive Zugänge am Kniegelenk - evidenzbasierter Vorteil in der Knieendoprothetik?

The impact of minimally invasive surgical techniques for implantation of a total knee arthroplasty is evaluated according to evidence-based medicine criteria. The patient-relevant clinical question can be formulated as: Is the rehabilitation of osteoarthritis patients with minimally invasive implantation of total knee arthroplasty faster compared to those with the conventional approach. The available literature is sorted and critically appraised with regard to methodological quality and risk of bias. Following the results of the meta-analyses the clinical question can be positively answered. Following the aspect of a structured evolution for surgical techniques, the meaning of a minimally invasive technique for total knee arthroplasty cannot be answered finally. Under the impression of more frequent surgical complications, the rating of the procedure is conservative. A general advantage is not apparent. Further studies investigating surgical learning curves, proper patient selection and the selection of the patient for such techniques are required, before the final judgement on the use of this technique can be formed.

[Update on metal-on-metal hip joints]. / Update Metall-Metall-Gleitpaarungen.

Increasing data are available describing risk factors for the development of local and systemic adverse events following operations using metal-on-metal (MoM) hip implants. The prevalence and clinical relevance of metal-associated problems are, however, still under debate. They can be influenced by type and position of implant as well as patient-specific factors. Patients with small MoM heads (maximum diameter 32 mm) and subgroups of resurfacing arthroplasty can achieve good long-term survival. The use of large head MoM implants (diameters greater than 36 mm), however, is currently not advised due to the unsatisfactory results.

European multidisciplinary consensus statement on the use and monitoring of metal-on-metal bearings for total hip replacement and hip resurfacing.

INTRODUCTION: There is an ongoing debate about the optimal use of metal-on-metal (MoM) bearings in total hip replacement, since there are uncertainties about local and systemic adverse effects due to wear and corrosion of these bearings. Despite various national recommendations, efforts to achieve international harmonization of specific evidence-based recommendations for best practice are still lacking. HYPOTHESIS: An international consensus study group should be able to develop recommendations on the use and monitoring of MoM bearings, preferably at the European level, through a multidisciplinary approach, by integrating the perspectives of various stakeholders. MATERIALS AND METHODS: Twenty-one experts representing three stakeholder groups and eight countries participated in this European consensus study, which consisted of a consensus meeting, subsequent structured discussion, and consensus voting. RESULTS: The current statement defines first of all benefits, local and systemic risks, as well as uncertain issues related to MoM bearings. Safety assessment after implantation of MoM comprises all patients. A closer follow-up is recommended for large head MoM (≥36mm) and resurfacing. In these implants basic follow-up should consist of x-rays and metal ion measurement of cobalt in whole blood, performed with GF-AAS or ICP-MS. Clinical and/or radiographic abnormality as well as elevated ion levels needs additional imaging (ultrasound, CT-scan and/or MARS-MRI). Cobalt values less than 2 µg/L are probably devoid of clinical concern, the threshold value for clinical concern is expected to be within the range of 2-7 µg/L. DISCUSSION: This is the first multinational, interdisciplinary, and multiprofessional approach for developing a recommendation for the use and monitoring of MoM bearings in total hip replacement. The current recommendations are in partial agreement with previous statements regarding the extent of follow-up and imaging techniques. They however differ from previous communications regarding measurement of metal ions and especially the investigated medium, technique, and eventual threshold levels. LEVEL OF EVIDENCE: Level V, expert opinion/agreement conference.

Efficacy and safety of rivaroxaban or fondaparinux thromboprophylaxis in major orthopedic surgery: findings from the ORTHO-TEP registry.

BACKGROUND: Thromboprophylaxis with rivaroxaban (R) is superior to enoxaparin in patients undergoing major orthopedic surgery (MOS). However, rivaroxaban has never been directly compared with fondaparinux (F), which also shows superior efficacy over enoxaparin. The clinical impact of switching from fondaparinux to rivaroxaban thromboprophylaxis is unclear. OBJECTIVES: To evaluate the efficacy and safety of rivaroxaban or fondaparinux thromboprophylaxis in unselected patients undergoing MOS. PATIENTS/METHODS: This is a monocentric, retrospective cohort study in 5061 consecutive patients undergoing MOS at our centre, comparing rates of symptomatic VTE, bleeding and surgical complications, length of hospital stay and risk factors for VTE. RESULTS: Rates of symptomatic VTE were 5.6% (F) and 2.1% (R; P < 0.001), with rates for distal DVT being 3.9 vs. 1.1% (P < 0.001). Rates of major VTE were numerically higher with fondaparinux (1.8 vs. 1.1%), but not statistically significant. Rates of severe bleeding (bleeding leading to surgical revision or death, occurring in a critical site, or transfusion of at least two units of packed red blood cells) were statistically lower with rivaroxaban compared with fondaparinux (2.9 vs. 4.9%; P = 0.010). The mean length of hospital stay was significantly shorter in the rivaroxaban group (8.3 days, 95% CI 8.1-8.5 vs. 9.3 days, 9.1-9.5; P < 0.001). CONCLUSION: Based on an indirect comparison of two consecutive cohorts, our data suggest that thromboprophylaxis with rivaroxaban is associated with less VTE and bleeding events than fondaparinux in unselected patients undergoing MOS. Prospective comparisons are warranted to confirm our findings.

[Long-term results in total knee arthroplasty. A meta-analysis of revision rates and functional outcome]. / Langzeitergebnisse in der Knieendoprothetik : Metaanalyse zu Revisionsrate und funktionellem Ergebnis.

BACKGROUND: Total knee arthroplasty (TKA) is one of the most common procedures in orthopedic surgery and clinical success can be characterized by the revision rate and improvement of function. To quantify both characteristics two independent meta-analyses have been performed. MATERIALS AND METHODS: A search in Medline provided a total of 96 studies on revision rates and 63 studies with functional results with a minimum follow-up of 5 years. RESULTS: A total of 911 revisions among 20,873 TKAs were identified corresponding to a meta-revision rate of 4.4% after a mean follow-up of 10.7 years. Most common causes for revision were aseptic loosening (31%), infection (23%), polyethylene wear (16%) and patellar problems (14%). Revision rates were higher in younger patients (7.0% <60 years at time of operation, 5.0% between 60 to 70 years and 2.2% >70 years), after cementless TKA (8.3% cementless versus 3.6% cemented) and in studies with a higher rate of patients with rheumatoid arthritis. The second meta-analysis revealed a meta-improvement based on the Knee Society Knee Score of 51.3%, for the Knee Society Function Score of 30.6%, for the Hospital for Special Surgery Score of 36.1% and for the New Jersey Orthopedic Hospital Knee Evaluation System of 33.6%. CONCLUSION: TKA is a successful treatment for osteoarthritis of the knee with an expectable revision rate of less than 5% within 10 years and a long-lasting functional improvement of more than 30% in any assessment score.

[Clinical pathway for total knee arthroplasty (EGON). II. The impact of enhanced patient information]. / Klinischer Behandlungspfad zur Implantation einer Oberflächenknieendoprothese (EGON). II: Effekt einer intensivierten Patienteninformation.

PURPOSE: The effects of the introduction of a clinical pathway and enhanced patient information on patients' satisfaction were investigated in the current study. MATERIAL AND METHODS: In a prospective cohort study patients were systematically interviewed about the preparation and the clinical course during implantation of a total knee arthroplasty. The study included 132 patients before (cohort I) and 128 after (cohort II) introduction of a clinical pathway. All patients of cohort II were offered the opportunity to attend an enhanced patient information lecture. The collected data were analysed in a descriptive manner. Items with more than 10% negative answers constituted the need for improvement. RESULTS: Regarding preparation of the operation there was a need for improvement of 11 items in cohort I and 4 in cohort II. With respect to the clinical course there was a slight increase from 6 to 7 items that required improvement. The enhanced information about the treatment and the clinical course were assessed positively. Patients were unsatisfied with the individual explanation of the X-rays. Of 128 patients from cohort II, 58 decided to participate in the information session for patients. The patients who had attended were more interested in receiving additional information. The success of the operation (gain in WOMAC score of at least 20%) showed a substantial effect on patient satisfaction. CONCLUSION: With increased patient information the knowledge and patient satisfaction within clinical pathways can be improved.

[Clinical pathway for total knee arthroplasty. I: Pathway conception and effect on functional quality of results]. / Klinischer Behandlungspfad zur Implantation einer Oberflächenknieendoprothese (EGON). I: Pfadkonzeption und Effekt auf funktionelle Ergebnisqualität.

PURPOSE: The aim of the current study was to evaluate patient-centred and economic outcomes after introduction of a clinical pathway for total knee arthroplasty. METHODS: In a prospective trial two sequential cohorts of patients undergoing total knee arthroplasty were recruited. Baseline treatment was surveyed in cohort I and the clinical pathway was developed and evaluated in cohort II. Data from WOMAC, EQ-5D as well as partial cost data were collected. The study design was ratified by the local Independent Ethics Committee. RESULTS: There was an increase in WOMAC score of 39% for cohort I and 35% for cohort II in 3 months follow-up. Similar results were found for ED-5D with an increase of 30% for cohort I and 25% for cohort II. Partial cost rates could be lowered from 4303 EUR to 419 EUR. Despite this significant cost saving we were not able to improve the ratio of improvement in quality of life to costs. CONCLUSION: With the aid of a clinical pathway the process for implementation of a total knee arthroplasty was improved and treatment quality assured.

Precision of navigated and conventional open-wedge high tibial osteotomy in a cadaver study.

High tibial osteotomy (HTO) is an established treatment option for isolated medial osteoarthritis in young and active patients. One important factor for success of this procedure is the degree of correction of the weight-bearing line. Computer-assisted navigation systems are believed to improve the precision of axis correction through intraoperative real-time monitoring. This study investigates the precision of correction of the weight-bearing line in open-wedge HTO with and without a navigation system. Nineteen legs of well-preserved human cadaver were randomly assigned to navigated (n = 10) or conventional (n = 9) HTO. In order to achieve a sufficient amount of correction in all legs the weight-bearing line was aimed at 80 percent of the width of the tibial plateau. The mean deviation of the weight-bearing line from the desired 80 percent was 1 percent in the navigated and 8.6 percent in the conventional operated legs (p = 0.002). The weight-bearing line of all navigated but only 5 of the 9 conventional operated legs was within a +/- 5 percent tolerance level (p = 0.33). Navigated open-wedge HTO achieved better correction of the weight-bearing line than the conventional method in human cadaver legs. Future studies have to prove this advantage in a clinical setting and it's effect on patient outcome.

Reliability of limb alignment measurement for high tibial osteotomy with a navigation system.

OBJECTIVE: High tibial osteotomy (HTO) is one treatment option for young and active patients with unicompartmental osteoarthritis. The success of this procedure substantially depends on the degree of correction of the mechanical axis. Computer-assisted navigation systems are believed to improve the precision of axis correction through intraoperative real-time monitoring. This study investigates the accuracy of limb alignment measurements with a navigation system on a cadaver specimen. MATERIALS AND METHODS: The measurements were performed on a well-preserved cadaver specimen with a mechanical leg axis of 4 degrees varus. Data was collected during the HTO workflow. Repeated serial measurements were undertaken by four different surgeons. After these measurements, different landmarks were deliberately set at the wrong place to examine the influence of mistakes during registration. RESULTS: There was a high intra- and interobserver reliability with a mean mechanical leg axis of 3.9 degrees +/- 0.7 degrees and a mean error of 0.6 degrees. The grossly incorrect placement of landmarks for knee and ankle center resulted in an incorrect mechanical leg axis of 1 degrees valgus up to 10 degrees varus. CONCLUSION: The computer-assisted navigation system provided precise information about the mechanical leg axis, irrespective of the observer's experience.

[Cost analysis for navigation in knee endoprosthetics]. / Kostenanalyse zur Navigation in der Knieendoprothetik.

BACKGROUND: Total knee arthroplasty (TKA) is one of the most frequent procedures in orthopaedic surgery. The outcome depends on a range of factors including alignment of the leg and the positioning of the implant in addition to patient-associated factors. Computer-assisted navigation systems can improve the restoration of a neutral leg alignment. This procedure has been established especially in Europe and North America. The additional expenses are not reimbursed in the German DRG system (Diagnosis Related Groups). In the present study a cost analysis of computer-assisted TKA compared to the conventional technique was performed. METHODS: The acquisition expenses of various navigation systems (5 and 10 year depreciation), annual costs for maintenance and software updates as well as the accompanying costs per operation (consumables, additional operating time) were considered. The additional operating time was determined on the basis of a meta-analysis according to the current literature. Situations with 25, 50, 100, 200 and 500 computer-assisted TKAs per year were simulated. RESULTS: The amount of the incremental costs of the computer-assisted TKA depends mainly on the annual volume and the additional operating time. A relevant decrease of the incremental costs was detected between 50 and 100 procedures per year. In a model with 100 computer-assisted TKAs per year an additional operating time of 14 mins and a 10 year depreciation of the investment costs, the incremental expenses amount to 300-395 depending on the navigation system. CONCLUSIONS: Computer-assisted TKA is associated with additional costs. From an economical point of view an amount of more than 50 procedures per year appears to be favourable. The cost-effectiveness could be estimated if long-term results will show a reduction of revisions or a better clinical outcome.

Computer-assisted and conventional total knee replacement: a comparative, prospective, randomised study with radiological and CT evaluation.

After obtaining informed consent, 80 patients were randomised to undergo a navigated or conventional total knee replacement. All received a cemented, unconstrained, cruciate-retaining implant with a rotating platform. Full-length standing and lateral radiographs and CT scans of the hip, knee and ankle joint were carried out five to seven days after operation. No notable differences were found between computer-assisted navigation and conventional implantation techniques as regards the rotational alignment of the femoral or tibial components. Although the deviation from the transepicondylar axis was relatively low, there was a considerable range of deviation for the tibial rotational alignment. There was no statistically significant difference regarding the occurrence pattern of outliers in mechanical malalignment but the number of outliers was reduced in the navigated group.