[Trends in navigation-handheld systems]. / Trends in der Navigation ­ Handheld-Systeme.

Navigation-assisted surgical procedures in orthopedics and trauma surgery have become increasingly widespread over the last 20 years. In addition to applications in spinal surgery, they are primarily available for knee and hip endoprosthetics. On the one hand, computer-assisted procedures have been increasingly expanded with robotic assistance systems in recent years, and on the other hand, so-called handheld navigation systems have been developed, which enable specialized use directly in the operating field at lower acquisition costs. The aim of this overview is to describe current handheld systems and to present the respective technical principles and the available scientific results. Three handheld systems for TKA use, two for THA use and one system to support pedicle screw placement on the spine are presented.

[Epiphysiolysis of the medial clavicle with posterior dislocation : Video article]. / Epiphysiolyse der medialen Klavikula mit posteriorer Luxation : Videobeitrag.

OBJECTIVE OF SURGERY: The goal of surgery is the anatomical reduction and stable internal fixation of an epiphysiolysis of the medial clavicle with posterior luxation in a child without harming intrathoracic structures. INDICATIONS: This case describes an acute epiphysiolysis of the medial clavicle Aitken type 0 with posterior dislocation. CONTRAINDICATIONS: Soft tissue infections within the region of the surgical access. Allergies against any materials used in the procedure. Successful closed reduction. Additional fracture of the clavicular shaft. SURGICAL TECHNIQUE: A detailed overview of the surgical technique is available through the video, which is accessible online as well as the graphic overview in this article. Longitudinal incision over the medial clavicle up to the sternoclavicular joint and preparation onto the bony structures. Display of the epiphysiolysis. Reduction of the medial clavicle. Introduction of two Kirscher wires along the longitudinal axis in the direction of the epiphysis and introduction of two sutures. Puncture of the cartilaginous epiphysis with the two sutures. Anatomical reduction of the medial clavicle and fixation by knots. With the continuous use of the sutures, fixation to the anterior periosteum and closure of the periosteum. Wound closure. FOLLOW-UP: For 6 weeks postoperative limitation of anteversion and abduction to 90°, afterwards unlimited functionality. No routine X­ray control. RESULT: After 6 months postoperative the patient is free of pain and has full range of motion. The Constant score is 97/100.

[Future implications of navigation in total knee arthroplasty]. / Gibt es noch Gründe für die Navigation in der Knieendoprothetik?

BACKGROUND: After more than two decades of experience with computer-assisted knee arthroplasty, extensive experience and study data are available, allowing a profound evaluation. Undoubtedly, computer-assisted knee arthroplasty has been proven to achieve excellent results for implant positioning and long-leg axis reconstruction. Thus, computer-assisted knee arthroplasty represents the current gold standard to avoid unintended malpositioning of total knee components for neutrally aligned implants and individualized implant alignment (kinematic alignment, adjusted mechanical alignment, and others). Previous studies could not show significant differences in functional outcomes and patient satisfaction. However, recent meta-analyses showed relevant advantages of computer-assisted knee arthroplasty. These results could be based on further developments in software-assisted soft tissue balancing and more sensitive evaluation methods of follow-up examinations. LONG-TERM OUTCOME: Further, international registries show advantages of computer-assisted knee arthroplasty regarding long-term outcomes. In particular, the Australian arthroplasty registry describes a significantly lower revision rate due to aseptic loosening/osteolysis in the computer-assisted knee arthroplasty group, analyzing a period of up to 17 years. These positive effects can already be proven six months following surgery. FUTURE PROSPECTS: However, despite demonstrated benefits, computer-assisted knee arthroplasty has not yet become established in daily routine, and wide regional variations in its use are observed. Newer developments such as robotic-assisted knee arthroplasty, primarily based on navigation techniques, are currently being heavily promoted. However, this new technology must justify its enormous additional costs and prove its advantages compared to computer-assisted knee arthroplasty. In the backdrop of the development of computer-assisted knee arthroplasty, this might be a difficult task.

Femoral flexion position is a highly variable factor in total knee arthroplasty: an analysis of 593 conventionally aligned total knee replacements.

PURPOSE: In contrast to coronal alignment, only few is known about sagittal alignment in total knee arthroplasty (TKA). The aim of this study was to identify the flexion position of the femoral component in a routine surgical setting of conventional TKA and to evaluate potential predictors for the degree of femoral flexion. METHODS: A retrospective study was performed on 593 primary TKA using the conventional intramedullary alignment technique for distal femur. Femoral flexion was measured by the verification mode of a pinless navigation system. Correlations between femoral flexion and patient-specific data, surgery-related factors and measurements of a preoperative anterior-posterior long-leg X-ray were analysed. RESULTS: The distal femoral resection showed a mean flexion of 5.5° ± 2.5° to the mechanical axis with high variation between 2.5° extension and 14° flexion. In a multivariate regression model, body height (p = 0.023), body weight (p = 0.046) and body mass index (p = 0.026) showed significant positive correlation to femoral flexion. There was no correlation to any preoperative alignment data from the anterior-posterior long-leg film. The sagittal position was also independent from surgery-related factors such as different knee systems or surgeons. CONCLUSIONS: Femoral flexion is a highly variable characteristic in conventionally aligned TKA. Increasing body height, body weight and body mass index were identified as predictors for a high degree of femoral flexion. LEVEL OF EVIDENCE: III.

Effective Graft Preservation by Following a Standard Protocol for the Treatment of Knee Joint Infection after Anterior Cruciate Ligament Reconstruction.

Knee joint infections constitute a rare but devastating complication after anterior cruciate ligament (ACL) reconstruction. We hypothesized that effective infection therapy and graft preservation is possible following a standard treatment protocol. We retrospectively analyzed all patients admitted to our center with suspected infection of the knee after ACL reconstruction between 2010 and 2012. Following a standardized protocol, blood samples were drawn and synovial fluid was analyzed. Furthermore, the protocol consisted of arthroscopic lavages and debridements of the anterior and posterior joint compartments over three incisions, and targeted antibiotic therapy over a period of 6 weeks. Surgeries were repeated every 2 days until clinical signs of infections resolved, but at least two times. Mean observation period was 10 months. Forty-one patients aged 31 ( ± 9.9) years and admitted 14 ( ± 7.5) days after ACL reconstruction were included. Pathogens were found in 34 patients and coagulase-negative staphylococci were isolated most commonly (31 isolates in 28 patients). Quinolones were the most commonly used antibiotic agents. Mean number of operations was 3.8 ( ± 1.4). Following the standard protocol, primary successful infection treatment with graft preservation was possible in 37 of the included 41 patients. Graft preservation was achieved in 100% of the included patients with Gaechter stage 1 and 2 infections. Knee joint infection after ACL reconstruction was successfully treated following a standardized protocol, and graft preservation was reliably achieved especially in cases with infections at an early stage.

Reliable Alignment in Total Knee Arthroplasty by the Use of an iPod-Based Navigation System.

Axial alignment is one of the main objectives in total knee arthroplasty (TKA). Computer-assisted surgery (CAS) is more accurate regarding limb alignment reconstruction compared to the conventional technique. The aim of this study was to analyse the precision of the innovative navigation system DASH® by Brainlab and to evaluate the reliability of intraoperatively acquired data. A retrospective analysis of 40 patients was performed, who underwent CAS TKA using the iPod-based navigation system DASH. Pre- and postoperative axial alignment were measured on standardized radiographs by two independent observers. These data were compared with the navigation data. Furthermore, interobserver reliability was measured. The duration of surgery was monitored. The mean difference between the preoperative mechanical axis by X-ray and the first intraoperatively measured limb axis by the navigation system was 2.4°. The postoperative X-rays showed a mean difference of 1.3° compared to the final navigation measurement. According to radiographic measurements, 88% of arthroplasties had a postoperative limb axis within ±3°. The mean additional time needed for navigation was 5 minutes. We could prove very good precision for the DASH system, which is comparable to established navigation devices with only negligible expenditure of time compared to conventional TKA.

Bacterial contamination of open fractures - pathogens, antibiotic resistances and therapeutic regimes in four hospitals of the trauma network Cologne, Germany.

INTRODUCTION: The bacterial contamination of soft tissues and bone in open fractures leads to an infection rate of up to 50%. Pathogens and their resistance against therapeutic agents change with time and vary in different regions. In this work, our aims were to characterize the bacterial spectrum present in open fractures, analyze the bacterial resistance to antibiotic agents and question the EAST guideline recommendations for antibiotic prophylaxis after open fractures in a German Trauma Network. MATERIALS AND METHODS: We conducted a retrospective cohort study and included all patients with open fractures from 1(st) of January 2011 until the 31(st) of December 2014 in four hospitals of the trauma network cologne. Soft tissue damage was classified according to the Gustilo Anderson classification. RESULTS: We included 123 patients. Forty-five injuries (37%) were classified I°, 45 (37%) as II° and 33 (27%) as III°. Lower leg (34%) was the most commonly injured location. An antibiotic prophylaxis was administered to 109 patients (89%). In 107 of them (98%) a cephalosporin or cephalosporin combination was given. In 35 of the patients (28%), microbiological samples were taken of the fracture site. Wound cultures were positive in 21 patients (60%). Fifty percent of the bacterial detections occurred in III° fractures. Coagulase negative Staphylococci (COST) were the most frequent pathogens. In II° open fractures one gram-negative strain was isolated. Fewest resistances were seen against quinolones and co-trimoxazole. DISCUSSION: The recommended EAST guideline prophylaxis would have covered all but one bacterium (97% of positive cultures). One Escherichia coli was found in a II° open fracture and would have been missed. One of the isolated Staphylococci epidermidis and an Enterococcus faecium were resistant against gentamycin and first- and second-generation-cephalosporin's which were used as prophylaxis frequently. However, a regional adaption of the EAST guidelines seems not justified due to the rather low number of cases in our study. CONCLUSION: The EAST guideline seems to be adequate in a high percentage of cases (97%) in the setting of the trauma network cologne. Further research should be guided at identification of initial open fracture pathogens to improve the efficiency of antibiotic prophylaxis.

Current state of treatment of acute acromioclavicular joint injuries in Germany: is there a difference between specialists and non-specialists? A survey of German trauma and orthopaedic departments.

PURPOSE: The purpose of this study was to evaluate currently preferred treatment strategies as well as the acceptance of new arthroscopic techniques among German orthopaedic surgeons. We assumed that surgeons specialized in shoulder surgery and arthroscopy would treat acute acromioclavicular joint dislocations different to non-specialized surgeons. METHODS: Seven hundred and ninety-six orthopaedic and/or trauma departments were found through the German hospital directory of 2012. Corresponding websites were searched for the email address of the chair of shoulder surgery (if applicable) or the department. Seven hundred forty-six emails with the request for study participation including a link to an online survey of 36 questions were sent. In 60 emails, the recipient was unknown. RESULTS: Two hundred and three (30 %) surgeons participated in the survey. one hundred and one were members of the AGA (German-speaking Society for Arthroscopy and Joint-Surgery) and/or of the DVSE (German Association of Shoulder and Elbow Surgery) and regarded as specialists, while 102 were non-members and regarded as non-specialists. According to the treatment of Rockwood I/II and IV-VI injuries, no significant differences were found. Seventy-four % of non-specialists and 67 % of specialists preferred surgical treatment for Rockwood III injuries (P = 0.046). Non-specialists would use the hook plate in 56 % followed by the TightRope in 16 %; specialists would use the TightRope in 38 % followed by the hook plate in 32 % (P = 0.004). CONCLUSIONS: The majority of German orthopaedic and trauma surgeons advise surgical treatment for Rockwood III injuries. Specialists recommend surgery less often. Non-specialists prefer the hook plate, whereas specialists prefer the arthroscopic TightRope technique. LEVEL OF EVIDENCE: Observational survey, Level IV.

How do we face patients' expectations in joint arthroplasty?

INTRODUCTION: Patients' expectations have become increasingly important over the last decade, as the fulfilment of preoperative expectations has been shown to be associated with postoperative satisfaction. Understanding the pattern of patients' expectations is necessary to provide a better basis for recommendations to patients opting for arthroplasty. The aim of this study was to show patients' expectations of joint replacement surgery in Germany and to elucidate factors, which might have an influence. MATERIALS AND METHODS: A retrospective analysis of anonymously collected data was performed on people participating in a patient information event for joint replacement surgery. They were asked to complete a survey, which consisted of five questions requesting demographic data and three questions regarding preoperative expectations. The latter were taken from the New Knee Society Score. An expectation score (0-12 points) was generated by adding the single point values of the three questions. RESULTS: 180 attendees were included in this study. The distribution of patients' expectations was remarkably skewed towards high expectations, the mean expectation score was 10.17. 87.2 % of participants had high and very high expectations and only 12.8 % had low and moderate expectations. Patients' expectations were independent of age and previous participation in a patient information event. Female gender and a history of arthroplasty led to a slightly higher expectation score. Patients with isolated knee pain had significantly lower expectations than patients suffering from isolated hip pain. CONCLUSIONS: This study shows that the majority of patients have high expectations regarding joint replacement surgery. To improve postoperative patients' satisfaction a straightforward physician-patient communication is necessary to prevent patients from potentially unrealistic expectations and therefore dissatisfaction with surgery.

Analgesic efficacy and tolerability of intravenous morphine versus combined intravenous morphine and oxycodone in a 2-center, randomized, double-blind, pilot trial of patients with moderate to severe pain after total hip replacement.

BACKGROUND: Results from studies with a combination of oral morphine and oxycodone in postsurgical patients demonstrate significant analgesia and a tolerability profile comparable to other pain medications at morphine-equivalent doses. However, an intravenous (IV) combination has not previously been studied. OBJECTIVE: This study evaluated the efficacy and tolerability of IV morphine versus a combination of IV morphine and IV oxycodone in a 1:1 ratio. METHODS: This was a 2-center, randomized, double-blind, active-controlled pilot trial of 40 patients who had undergone total hip replacement. After surgery, when pain levels reached ≥4 (on the 11-point Numerical Pain Rating Scale), patients were randomized to 1 of 2 treatment groups. In part 1 of the study, patients were dosed every 5 minutes for the first 65 minutes (up to 13 doses) with study drug, provided that vital signs criteria were met. After an initial loading dose of either morphine 1.5 mg coadministered with oxycodone 1.5 mg or morphine 3 mg alone, patients received IV morphine 1.5 mg or IV morphine 0.75 mg/IV oxycodone 0.75 mg every 5 minutes. If patients achieved a pain score of 2 or experienced intolerable adverse events to drug when stable, they were permitted to enter part 2. In part 2, patients received blinded study medication (IV morphine plus IV oxycodone [0.5 mg/0.5 mg] or 1 mg IV morphine alone) via patient-controlled analgesia (PCA) for 47 hours. RESULTS: At baseline, treatment groups were comparable except for a higher proportion of females in the IV morphine group. Baseline pain intensity averaged 7 on the Numerical Pain Rating Scale of 0 to 10. One patient in the morphine group and 2 patients in the morphine/oxycodone group discontinued the study. The sum of the pain intensity differences from baseline to 65 minutes during the dose-titration phase was 1.8 for morphine alone versus 2.7 for morphine/oxycodone (P = 0.12); these values occurred at the same median number of doses (12) for each group. In part 2 (PCA dosing) of the study, similar levels of analgesia were achieved. During the study, 24% of the IV morphine/oxycodone group and 37% of the IV morphine group experienced nausea, and 10% of the IV morphine/oxycodone group and 16% of the IV morphine group had emesis. Two patients in the IV morphine/oxycodone group and 4 in the IV morphine alone group experienced oxygen desaturation. CONCLUSIONS: The combination of IV morphine and oxycodone provided pain relief with an acceptable tolerability profile in these patients experiencing moderate to severe postoperative pain. However, as an explorative pilot study, the power was not adequate to demonstrate statistical significance for differences between IV morphine/oxycodone and IV morphine alone. European Clinical Trials Data Base registration code: EudraCT-No. 2008-008527-14.

Sports activity after total hip resurfacing.

BACKGROUND: Little is known about sports activity after total hip resurfacing. HYPOTHESIS: Patients undergoing total hip resurfacing can have a high level of sports activity. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: The authors evaluated the level of sports activities with a standardized questionnaire in 138 consecutive patients (152 hips) 2 years after total hip resurfacing. Range of motion, Harris hip score, and Oxford score were assessed, and radiological analysis was performed. RESULTS: Preoperatively, 98% of all patients participated in sports activities. Two years postoperatively, 98% of the patients participated in at least 1 sports activity. The level of sports activity decreased after surgery. The number of sports activities per patient decreased from 3.6 preoperatively to 3.2 postoperatively. Intermediate- and high-impact sports, especially tennis, soccer, jogging, squash, and volleyball, showed a significant decrease while the low-impact sports (stationary cycling, Nordic walking, and fitness/weight training) showed a significant increase. Physical activity level at the time of follow-up as measured by the Grimby scale was significantly higher than in the year before surgery. Duration of sports participation per week increased significantly after surgery. Men had a significantly higher sport level than women before and after surgery. Eighty-two percent felt no restriction while performing sports. One-third missed certain sports activities such as jogging, soccer, tennis, and downhill skiing. The Harris hip and Oxford scores showed a significant increase postoperatively. CONCLUSION: The results of this short-term follow-up study show that sports activity after total hip resurfacing surgery is still possible. Physical activity level increased with a shift toward low-impact sports. Duration of sports participation increased. High-impact sports activities decreased. These findings can be important for the decision-making process for hip surgery and should be communicated to the patient.

Computer-assisted total knee arthroplasty versus the conventional technique: how precise is navigation in clinical routine?

Restoration of the mechanical leg axis and component positioning are crucial factors affecting long-term results in total knee arthroplasty (TKA). In a prospective study, 1,000 patients were operated on either using a CT-free navigation system or the conventional jig-based technique. Leg alignment and component orientation were determined on postoperative X-rays. The mechanical leg axis was significantly better in the computer-assisted group (95%, within +/-3 degrees varus/valgus) compared to the conventional group (74%, within +/-3 degrees varus/valgus) (P < 0.001). On average, the operating time was increased by 8 min in the computer-assisted group. No significant differences were seen between senior and younger surgeons regarding postoperative leg alignment and operating time. Computer-assisted TKA leads to a more accurate restoration of leg alignment and component orientation compared to the conventional jig-based technique. Potential benefits in long-term outcome and functional improvement require further investigation.

The effect of femoral component rotation on patellar tracking in total knee arthroplasty.

Rotational adjustment of the femoral component in total knee arthroplasty influences patellar tracking. Sixty patients underwent TKA; the femoral component was placed parallel to the epicondylar axis in 30 patients and the femoral component was placed in 3 degrees external rotation to the posterior condylar axis in 30 patients. The epicondylar axis was identified using an image-guided navigation system. Mean patellar shift was 2.65 degrees for the computer assisted group and 3.50 degrees for the control group. Mean patellar tilt was 4.88 degrees for the computer assisted group and 6.68 degrees for the control group. Aligning the femoral component parallel to the epicondylar axis leads to significantly better patellar tracking.

The effectiveness of sequential medial soft tissue release on coronal alignment in total knee arthroplasty: using a computer navigation model.

Soft tissue management is a major step in total knee arthroplasty. We aimed to analyze the relationship between sequential medial soft tissue release and the resulting change in the anteroposterior limb axis and the tibiofemoral gaps. Measurements were obtained using a CT-free navigation system (Ci navigation system, DePuy I-Orthopaedics, Munich, Germany). Concerning leg axis, each release step led to significant (P < .001) effects. The highest effect was seen for the 6-cm release in extension and the release of medial collateral ligament in 90 degrees flexion. The medial gap difference was significant for each release step except the 4-cm release in extension. The highest increase resulted when sacrificing the entire posterior cruciate ligament in extension and in 90 degrees flexion. Implementation of computer-assisted surgery allows this first navigation-controlled study, elucidating the effect of soft tissue release in total knee arthroplasty.

Gap configuration and anteroposterior leg axis after sequential medial ligament release in rotating-platform total knee arthroplasty.

BACKGROUND: Soft tissue management is a major issue in total knee replacement. There have been very few papers dealing with its effect on leg axis and tibiofemoral gap. METHODS: In a cadaver specimen study, we analyzed this effect by performing a sequential medial soft tissue release after a mobile-bearing total knee arthroplasty. Measurements were obtained using a CT-free navigation system (Ci navigation system). RESULTS: We found the highest increase in leg axis and medial gap when releasing the anteromedial tibial sleeve of the capsule 6 cm below the joint line, in extension, and after dividing the medial collateral ligament, in flexion, when releasing the medial half of the posterior cruciate ligament. There were differences in amount of change between extension and flexion, especially when releasing the medial half of the posterior cruciate ligament. In extension, the lateral gap remained the same as in flexion. INTERPRETATION: Implementation of computer-assisted surgery has allowed this first navigation-controlled study investigating the effect of soft tissue release in TKR with rotating platform. Each sequential release step has the desired effect on a.p. leg axis and tibiofemoral gaps. It is important that the differences between the effects in extension and flexion be noted.

Computer-assisted cannulated screw fixation for slipped capital femoral epiphysis.

In slipped capital femoral epiphysis (SCFE), cannulated screw fixation is a standard procedure. The aim of this study was to investigate the feasibility of a fluoroscopy-supported navigation system for screw fixation in SCFE. Using a fluoroscopy-enhanced navigation system, a cannulated screw fixation was performed in seven hips of four patients. The navigation system showed a high feasibility in instrument visualization and implant placing. The mean x-ray time was 6.2 seconds. Initial experiences are very promising and show advantages of the fluoroscopy-supported navigation. Considerably reduced x-ray exposure for patients and surgeons is possible. In the future, further efforts will be necessary to develop navigation-specific instruments to enhance the precision of screw positioning.

Midvastus approach in total knee arthroplasty: a randomized, double-blinded study on early rehabilitation.

The medial parapatellar approach has become the standard technique in total knee arthroplasty (TKA). However, recent studies have reported superior results regarding functional recovery when using the midvastus approach. It was the aim of this study to evaluate the early functional outcome of both surgical techniques. In a prospective, double-blinded, randomized study, 50 patients for TKA were consecutively operated on either by the medial parapatellar or the midvastus approach. Exclusion criteria were defined as previous open knee surgery and leg deformity of more than 10 degrees varus or valgus. TKA was performed in all patients by one surgeon using the same type of implants in both groups. Pain scores (VAS) were documented and follow-up data including quadriceps strength and proprioception were obtained 3 weeks and 6 weeks postoperatively. Both groups were comparable in preoperative demographic data. Postoperatively, patients in the midvastus group demonstrated significantly lower pain in rest (VAS: mean 2.25 vs. 3.03) and under movement (VAS: mean 2.92 vs. 3.13). Further, they showed superior isometric quadriceps strength at 3 weeks (41.4 vs. 27.6 Nm) and 6 weeks (47.6 vs. 35.5 Nm). Moreover, this group showed a superior postoperative proprioception, while the range of motion was similar in both groups. The midvastus approach offers advantages over the standard parapatellar arthrotomy, in the early rehabilitation period. No adverse effects were observed associated with this approach. Therefore, the midvastus approach should be considered as a valuable alternative in TKA.

Revision total knee arthroplasty: a comparison of postoperative leg alignment after computer-assisted implantation versus the conventional technique.

Accurate reconstruction of leg alignment is one important factor for long-term survival in total knee arthroplasty (TKA). Recent developments in computer-assisted surgery focused on systems improving TKA. The aim of the study is to compare the results of computer-assisted revision TKA with the conventional technique. We hypothesize that a significantly better leg alignment and component orientation is achieved when using a navigation system for revision TKA. In a prospective study, two groups of 25 revision TKAs each were operated on using either a CT-free navigation system or the classical surgeon-controlled technique. The postoperative leg alignment was analysed on long-leg coronal and lateral X-rays. The mechanical limb axis was significantly better in the navigation-based group. Twenty-three patients (92%) in the computer-assisted group had a postoperative leg axis between 3 degrees varus/valgus deviation, while 19 patients (76%) in the conventional group had a comparable result (p<0.05). Further, significant differences were seen for the coronal orientation of the femoral component. Computer-assisted revision TKA leads to a superior restoration of leg alignment compared with the conventional technique. Particularly the real-time presentation of the actual leg axis and the flexion and extension gaps is useful in revision TKA. Potential benefits in long-term outcome and functional improvement require additional investigation.

Navigation in total-knee arthroplasty: CT-based implantation compared with the conventional technique.

Background Exact axial limb alignment in total-knee arthroplasty (TKA) is important for a successful outcome. We evaluated the efficiency of computer-assisted implantation in TKA and compared it with the classical surgeon-controlled technique. Patients and methods We implanted 100 TKA using either the computer-assisted technique (50) or the conventional approach (50). There were no significant differences between the groups regarding the preoperative leg deformity. Accuracy of implantation was determined in postoperative long-leg coronal and lateral radiographs. Results A postoperative leg axis between 3 degrees varus and 3 degrees valgus was achieved in 46 patients in the group with computer-assisted implantation and 36 patients in the control group (p=0.01). A significant difference was also seen for the femoral component alignment in frontal plane. No complications influencing the clinical outcome were observed. Interpretation A CT-based navigation system improves the accuracy of TKA, but higher costs and time-consuming planning will mean that its usage is limited to special cases. Additional tools such as ligament balancing, which are presently only available with the CT-free software module, require to be added to the CT-based system.