Navigation improves accuracy of rotational alignment in total knee arthroplasty

Three-dimensional analysis of image-free navigation system for total knee arthroplasty

Malalignment causes abnormal forces that may lead to loosening after knee replacement. Whether a computer-assisted technique can improve the precision of implant positioning guaranteeing good long-term results in total knee arthroplasty, this is a matter of discussion. The authors evaluate the alignment accuracy of 20 primary total knee arthroplasties, performed using an image-free computer navigation systems, with standardized CT protocol and three-dimensional digital model reconstruction. The results of this study demonstrate that the image-free navigation system is able to improve accuracy in axial limb alignment and positioning of the components in the majority of cases; moreover, the difference between the mean mechanical axis value of the navigation system (179.7° ± 1.7°) and the median mean value obtained during the post-operative evaluation (180.3° ± 1.9°) is not statistically significant (P = 0.28).

Optimized functional femoral rotation in navigated total knee arthroplasty considering ligament tension

Femoral malrotation in total knee arthroplasty is correlated to an increased number of revisions. Anatomic landmarks such as Whiteside line, posterior condyle axis and transepicondylar axis are used for determining femoral component rotation. The femoral rotation achieved with the anatomical landmarks is compared to the femoral rotation achieved by a navigated ligament tension-based tibia-first technique. Ninety-three consecutive patients with gonarthritis were prospectively enrolled. Intraoperatively the anatomical landmarks for femoral rotation and the achieved femoral rotation using a navigated tension-based tibia-first technique were determined and stored for further comparison. A pre- and postoperative functional diagram displaying the extension and flexion and varus or valgus positions was also part of the evaluation. Using anatomical landmarks the rotational errors ranged from 12.2° of internal rotation to 15.5° of external rotation from parallel to the tibial resection surface at 90° flexion. A statistical significant improved femoral rotation was achieved using the ligament tension-based method with a rotational error ranged from 3.0° of internal rotation to 2.4° of external rotation. The functional analyses demonstrated statistical significant lower varus/valgus deviations within the flexion range and an improved maximum varus deviation at 90° flexion using the ligament tension-based method. Compared to the anatomical landmarks a balanced, almost parallel flexion gap was achieved using a navigation technique taking the ligament tension of the knee joint into account. As a result the improved femoral rotation was demonstrated by the functional evaluation. Unilateral overloading of the polyethylene inlay and unilateral instability can thus be avoided.

Imageless navigation system does not improve component rotational alignment in total knee arthroplasty

BACKGROUND

The aim of computer-assisted surgery is to improve accuracy and limit the range of surgical variability. However, a worldwide debate exists regarding the importance and usefulness of computer-assisted navigation for total knee arthroplasty (TKA). The main purpose of this study is to summarize and compare the radiographic outcomes of TKA performed using imageless computer-assisted navigation compared with conventional techniques.

MATERIALS AND METHODS

An electronic search of PubMed, EMBASE, Web of Science, and Cochrane library databases was made, in addition to manual search of major orthopedic journals. A meta-analysis of 29 quasi-randomized/randomized controlled trials (quasi-RCTs/RCTs) and 11 prospective comparative studies was conducted through a random effects model. Additional a priori sources of clinical heterogeneity were evaluated by subgroup analysis with regard to radiographic methods.

RESULTS

When the outlier cut-off value of lower limb axis was defined as ±2° or ±3° from the neutral, the postoperative full-length radiographs demonstrated that the risk ratio was 0.54 or 0.39, respectively, which were in favor of the navigated group. When the cut-off value used for the alignment in the coronal and sagittal plane was 2° or 3°, imageless navigation significantly reduced the outlier rate of the femoral and tibial components compared with the conventional group. Notably, computed tomography scans demonstrated no statistically significant differences between the two groups regarding the outliers in the rotational alignment of the femoral and tibial components; however, there was strong statistical heterogeneity.

CONCLUSIONS

Our results indicated that imageless computer-assisted navigation systems improve lower limb axis and component orientation in the coronal and sagittal planes, but not the rotational alignment in TKA. Further multiple-center clinical trials with long-term follow-up are needed to determine differences in the clinical and functional outcomes of knee arthroplasties performed using computer-assisted techniques.

Computer-assisted high tibial osteotomy: preliminary results

Open-wedge high tibial osteotomy (HTO) is an established technique for the treatment of symptomatic varus malaligned knees. In this study, we prospectively followed up 13 patients (14 knees) who underwent navigation system-supported HTO for varus knee deformity. Preoperatively all patients underwent a physical examination, and anteroposterior and laterolateral lower limb weight-bearing digital radiographs were obtained. The following parameters were examined: (1) Insall-Salvati index; (2) posterior tibial slope angle; (3) mechanical femorotibial angle; (4) inferior limb length. At a mean follow-up of 12.6 months, clinical examination showed satisfactory results in all patients. The mean Modified Cincinnati Rating System Questionnaire rating increased significantly from 46.5 ± 7.2 to 84.6 ± 8, while the mean Knee Society Score increased significantly from 51.4 ± 9.9 to 85.1 ± 7.3. The mean Insall-Salvati index changed from 1.11 preoperatively to 1.10 postoperatively (P=.742). According to the navigation system data, the femorotibial mechanical axis was corrected from a varus of 6.3° ± 1.9° to a valgus of 2.1° ± 1.6°. These data matched postoperative radiographic lower limb weight-bearing data. In the group of patients in whom we evaluated the posterior tibial slope with the navigation system, we detected an increase of 0.3° ± 0.4° compared with the preoperative radiographic examination evaluations; the comparison between the postoperative and the preoperative radiograhic examination results showed an increase of 0.5° ± 0.7° (P=.87). The results of our study seem to show greater accuracy of mechanical axis correction and smaller increase in tibial slope when a navigation system is used in open-wedge HTO.

Computer modeling to predict effects of implant malpositioning during TKA

Computer-assisted surgery has focused on alignment of implants and soft tissue balancing but the end results during surgery as they pertain to long-term function of the implants are not yet realized. One parameter that continues to be variable despite the use of computer navigation is the placement of the implants in the transverse plane. The objective of this study was to determine whether implant and anatomic registrations could be used in a computer model (LifeMOD/KneeSIM, LifeModeler, Inc., San Clemente, California) to show differences in the resulting contact patterns of the medial and lateral condyles of the polyethylene insert. The simulations included tibiofemoral and patellofemoral contact, passive soft tissue (medial and lateral collateral, and posterior cruciate ligaments, as well as the capsular tissues), and active muscle elements (quadriceps and hamstrings). Components of a fixed-bearing cruciate-retaining total knee (Columbus knee system; B. Braun Aesculap, Tuttlingen, Germany) were imported into the model. The systems were subjected to one 60-second cycle of a lunge. Both the femoral and the tibial components were positioned in 5° of internal or external rotation in varying combinations and the resulting kinematics analyzed. The resulting kinematics showed variations in anteroposterior translation of the lateral and medial femoral condyles that resembled several of those reported in the literature for individual patients with a cruciate-retaining knee implant system.

Computer-assisted total knee arthroplasty: Does the tibial component remain at malposition risk?

OBJECTIVES

The development of computer-assisted surgery in total knee arthroplasty continues its search for better accuracy in the spatial positioning of prosthetic components and in achieving the best ideal ligament balance. Many studies have underscored the value of computer-assisted navigation in obtaining precise bone cuts in terms of both orientation and location, which would optimize bone resection and thereby fulfill ligament balancing requirements. Yet improving bone cut accuracy can be undermined by positioning errors of the component at the final stage of implantation. The objective of this prospective study was to assess this possible loss of accuracy and to suggest possible solutions to minimize this risk.

MATERIAL AND METHODS

A consecutive series of 50 total knee arthroplasties was studied using an imageless computer navigation system. This study compared the spatial orientation of the prosthesis components determined using software (frontal positioning for the femoral component, frontal and sagittal positioning for the tibial component) with the recorded orientation of the corresponding bone cuts, which allowed us to quantify the loss of accuracy of these predefined positions after cutting. Trial and final implant orientation was taken into account. Moreover, the mechanical axes of the lower limb, the trial and then the final prosthesis in place were compared. Two procedures were abandoned in the study and two patient files were incomplete, which left a series of 46 cases (29 females and 17 males; mean age at surgery, 67 years; mean BMI, 31.27).

RESULTS

Bone cut orientation was consistently found to be satisfactory. Frontal orientation of the final femoral component (0.2° valgus) did not differ statistically significantly from the distal femoral cut (0.3° valgus) and from the orientation of the trial femoral component, as was true of the slope of the tibial component (4.8°) versus the tibial cut (6.3°) and the mechanical axis of the lower limb with the trial prosthesis and the final implant. The frontal plane orientation of the tibial component (0.6° varus) differed statistically significantly from the bone cut (0.1° valgus).

DISCUSSION

Several studies have demonstrated the value of computer-assisted surgery, notably in the accuracy of the bone cuts, confirming the work reported herein. The loss of accuracy observed between the bone cut and the final implantation can only be explained by soft tissues between the prosthesis and the bone cut, unequal cement thickness, an orientation error in the impaction handle when placing the final implant, or a conflict between the prosthetic keel and cortical bone. Better exposure of the tibial plateaus, discontinuation of cement use, and navigated impaction ancillary tools could reduce these errors.

LEVEL OF EVIDENCE

Level IV. Prospective study.

A computed tomography based study on rotational alignment accuracy of the femoral component in total knee arthroplasty using computer-assisted orthopaedic surgery

Rotation of the femoral component in total knee arthroplasty (TKA) is of high importance in respect of the balancing of the knee and the patellofemoral joint. Though it is shown that computer assisted surgery (CAOS) improves the anteroposterior (AP) alignment in TKA, it is still unknown whether navigation helps in finding the accurate rotation or even improving rotation. Therefore the aim of our study was to evaluate the postoperative femoral component rotation on computed tomography (CT) with the intraoperative data of the navigation system. In 20 navigated TKAs the difference between the intraoperative stored rotation data of the femoral component and the postoperative rotation on CT was measured using the condylar twist angle (CTA). This is the angle between the epicondylar axis and the posterior condylar axis. Statistical analysis consisted of the intraclass correlation coefficient (ICC) and Bland-Altman plot. The mean intraoperative rotation CTA based on CAOS was 3.5° (range 2.4–8.6°). The postoperative CT scan showed a mean CTA of 4.0° (1.7–7.2). The ICC between the two observers was 0.81, and within observers this was 0.84 and 0.82, respectively. However, the ICC of the CAOS CTA versus the postoperative CT CTA was only 0.38. Though CAOS is being used for optimising the position of a TKA, this study shows that the (virtual) individual rotational position of the femoral component using a CAOS system is significantly different from the position on a postoperative CT scan.

Radiographic assessment of alignment following TKA: outline of a standardized protocol and assessment of a newly devised trigonometric method of analysis

BACKGROUND

An important determinant of long-term outcomes following total knee arthroplasty (TKA) is post-operative alignment as measured on radiographs. Thus far, radiographs have been measured using the goniometer method (GM) and no standard protocol has been followed. The aim of this prospective study was to: (i) outline a protocol for radiographic measurement following TKA; and (ii) compare the accuracy of the traditional GM with a new trigonometric method (TM) of radiographic analysis.

METHODS

A protocol for the measurement of alignment on radiographs following TKA was outlined in detail with step-by-step instructions. A new TM of angle measurement was also delineated. Alignment was measured on 51 post-operative TKA radiographs. A single angle was chosen and measured by two observers using both the GM and TM.

RESULTS

The TM had a precision of 1.06 degrees compared with 1.5 degrees using the GM. The standard deviation of the TM was significantly smaller than the GM (P= 0.033). The intra-class correlation coefficient of the TM was 0.94 versus 0.90 for the GM.

CONCLUSION

The study detailed a protocol for the measurement of axial alignment of the limbs and components following TKA, and provided evidence that a newer TM of angle measurement was superior in terms of precision and intra-rater reliability in comparison with the traditional method.

Deviations between intra-operative navigation data and post-operative weight-bearing X-rays

Several studies have shown that computer-navigated TKA reduces the rate of outliers. Thirty-one consecutive patients were operated on by the same surgeon using a computer assisted navigation system. Data collected by the system included the final mechanical axis of the extremity (HKA angle) and the coronal angle of the tibial and femoral implants. These same values were measured using CAD software on full weight-bearing long X-rays taken 6 weeks post-surgery. Deviations were observed when X-ray measurements were compared to intra-operative data collected from the navigation system. A statistically significant difference was found in the tibial cut (1.29 degrees +/- 1.35 degrees; p < 0.0001) and in the HKA (1.59 degrees +/- 2.36 degrees; p = 0.0007). Outliers of more than 3 degrees were observed in the coronal plane of the tibial implant in 9.6% of patients, in the coronal plane of the femoral implant in 6.4% of patients, and in the HKA angle of 29% of patients. Our results indicate that the use of navigation alone is insufficient to prevent outliers beyond an acceptable range of 3 degrees .

Tibial stress fracture after computer-navigated total knee arthroplasty

A correct alignment of the tibial and femoral component is one of the most important factors determining favourable long-term results of a total knee arthroplasty (TKA). The accuracy provided by the use of the computer navigation systems has been widely described in the literature so that their use has become increasingly popular in recent years; however, unpredictable complications, such as displaced or stress femoral or tibial fractures, have been reported to occur a few weeks after the operation. We present a case of a stress tibial fracture that occurred after a TKA performed with the use of a computer navigation system. The stress fracture, which eventually healed without further complications, occurred at one of the pinhole sites used for the placement of the tibial trackers.

Lower-limb alignment and posterior tibial slope in Pakistanis: a radiographic study

PURPOSE

To assess the lower-limb alignment and posterior tibial slope in Pakistanis.

METHODS

40 male and 19 female healthy Pakistanis aged 20 to 45 years were recruited. A full weight-bearing anteroposterior radiograph of the entire lower limb of each subject was obtained. The axial alignment was measured based on the centres of the femoral head, knee, and ankle. The tibiofemoral (TF) angle, knee joint line obliquity angle (angle J), and posterior tibial slope were determined.

RESULTS

The mean TF angle was more varus in men than women (178.4 degrees vs. 180.0 degrees, p<0.001). The mean angle J was more medially inclined in men than women (93.4 degrees vs. 91.4 degrees, p=0.007). The mean medial tibial slope was greater in women than men (16.0 degrees vs. 12.5 degrees, p<0.001). The posterior tibial slope was greater in women than men (14.1 degrees vs. 12.5 degrees, p=0.02), and was greater than the 5 degrees to 10 degrees commonly reported.

CONCLUSIONS

Knee alignment and geometry vary in different population subsets. With regard to total knee arthroplasty, the more medially inclined angle J in Pakistani men suggests that an anteroposterior cut of the distal femur should be in increased external rotation, compared with Pakistani women. Whereas the greater posterior tibial slope in Pakistanis suggests that a proximal tibial cut with a greater posterior tibial slope may reduce the chance of tibial loosening and increase postoperative knee range of motion, especially when using posterior cruciate ligament-retaining designs.

Computer assisted pelvic tumor resection and reconstruction with a custom-made prosthesis using an innovative adaptation and its validation

Computer aided musculoskeletal tumor surgery is a novel concept. Ideally, computer navigation enables the integration of preoperative information concerning tumor extent and regional anatomy to facilitate execution of a surgical resection. Accurate resection helps oncological clearance and facilitates precise fitting of a custom prosthesis. We adapted a commercially available computer navigation platform for spine, and used it to plan and execute pelvic bone resection and custom pelvic prosthetic reconstruction in a patient with a metastatic tumor affecting the acetabulum. The surgery was simulated and validated using a plaster bone model based on the patient's preoperative CT data, before performing the procedure on the patient.

Computer-assisted revision of total knee arthroplasty

Revision total knee prosthesis still remains a difficult procedure. Particularly, challenging is the restoration of the joint line to a normal position and the attainment of correct lower limb alignment and healthy bone support for the implants. Computer assistance improves accuracy during the implantation of primary total knees. The goal of this study was to evaluate the usefulness of computer assisted surgery (CAS) in total knee prosthesis revision. We revised 15 NKII total knee arthroplasties with the Navitrack system and compared the mechanical alignment and the joint line level on pre- and postoperative radiographs. After revision, the joint line position was restored. The knee with the revision prosthesis was aligned in the frontal plan with implants fixed perpendicularly to the mechanical axis. It is possible to correctly revise knee prosthesis with computer assistance only and without having to use a conventional ancillary. We had a permanent control of the joint line position and have performed the revision surgery following the same steps as in a primary implantation.

Three-dimensional analysis of computed tomography-based navigation system for total knee arthroplasty: the accuracy of computed tomography-based navigation system

We evaluated the postoperative alignment of 37 primary total knee arthroplasties performed using a computed tomography-based navigation system (Vector Vision Knee 1.5; Brain Lab, Germany) with a new 3-dimensional analysis. The mean coronal femoral angle was 89.0 degrees +/- 1.4 degrees (85.5 degrees -92.8 degrees ), and the coronal tibial component was 89.2 degrees +/- 1.0 degrees (87.4 degrees -91.6 degrees ). The hip-knee-ankle angle was observed to be 178.2 degrees +/- 1.5 degrees (173.9 degrees -181.8 degrees ). The external rotational alignment of the femoral component relative to the surgical epicondylar axis was -0.5 degrees +/- 1.7 degrees (-3.2 degrees to 3.4 degrees ). The results demonstrated that a computed tomography-based navigation system provided a reasonably satisfactory component alignment. The discrepancy between the 2-dimensional and 3-dimensional evaluations was 1.0 degrees +/- 0.9 degrees (0.1 degrees -3.4 degrees ). Three-dimensional analysis is necessary to evaluate the accuracy of the navigation system.

Minimally invasive computer-navigated total knee arthroplasty

Modern computerized knee navigation systems aid surgeons both in the conventional and in the minimally invasive approach to optimize mechanical and rotational alignments of the components in all three planes to avoid any malrotation and/or any errors in coronal, sagittal, and axial alignments. The advantages of minimally invasive total knee arthroplasty can be achieved without loss of accuracy. There is increasing evidence of a positive correlation between accurate mechanical alignment after total knee arthroplasty and functional as well as quality-of-life patient outcomes.

Navigational predictors in determining the necessity for collateral ligament release in total knee replacement

The requirement for release of collateral ligaments to achieve a stable, balanced total knee replacement has been reported to arise in about 50% to 100% of procedures. This wide range reflects a lack of standardised quantitative indicators to determine the necessity for a release. Using recent advances in computerised navigation, we describe two navigational predictors which provide quantitative measures that can be used to identify the need for release. The first was the ability to restore the mechanical axis before any bone resection was performed and the second was the discrepancy in the measured medial and lateral joint spaces after the tibial osteotomy, but before any femoral resection.

These predictors showed a significant association with the need for collateral ligament release (p < 0.001). The first predictor using the knee stress test in extension showed a sensitivity of 100% and a specificity of 98% and the second, the difference between medial and lateral gaps in millimetres, a sensitivity of 83% and a specificity of 95%. The use of the two navigational predictors meant that only ten of the 93 patients required collateral ligament release to achieve a stable, neutral knee.

Comparison of computer-assisted navigation and conventional instrumentation for bilateral total knee arthroplasty

This prospective study analyzed computer-assisted surgery (CAS) navigation and conventional instrumentation in bilateral total knee arthroplasty. Sixty patients underwent CAS navigation in 1 knee and conventional instrumentation in the contralateral knee randomly. The target zone resided in the reconstructed mechanical axis within a range of 3 degrees varus or valgus. The reconstructed mechanical axes in the CAS navigation group were significantly closer to planned axes than those in the conventional group. Average blood loss in the CAS navigation group was lower, whereas mean tourniquet time was longer than in the conventional group. No surgery-related complications existed in either group. The results indicate that, despite longer operative time, CAS navigation total knee arthroplasty is a safe procedure and outperforms conventional technique in accuracy of leg axes.

Does accurate anatomical alignment result in better function and quality of life? Comparing conventional and computer-assisted total knee arthroplasty

This is a randomized prospective controlled trial comparing the alignment, function, and patient quality-of-life outcomes between patients undergoing conventional (CONV) and computer-assisted (CAS) knee arthroplasty. One hundred and fifteen patients (60 CAS, 55 CONV) underwent cemented total knee arthroplasty. Three patients were lost to follow-up. Eighty-eight percent (CAS) vs 61% (CONV) of knees achieved a mechanical axis within 3 degrees of neutral (P = .003). Aligning femoral rotation with the epicondylar axis was accurately achieved in CAS and CONV with no significant difference. Patients with coronal alignment within 3 degrees of neutral had superior International Knee Society and Short-Form 12 physical scores at 6 weeks, 3 months, 6 months, and 12 months after surgery. Computer-assisted total knee arthroplasty achieves greater accuracy in implant alignment and this correlates with better knee function and improved quality of life.

Arthroscopy-assisted computer navigation in high tibial osteotomy for varus knee deformity

PURPOSE

To assess the accuracy of knee alignment after high tibial osteotomy (HTO) for varus knee deformity using arthroscopy-assisted computer navigation.

METHODS

Six men and 4 women aged 47 to 53 (mean, 49) years underwent medial open wedge HTO for varus knee deformity and medial unicompartmental osteoarthritis using arthroscopy-assisted computer navigation with fluoroscopy. Patients were followed up for a mean of 23 (range, 11-32) months. Intra- and post-operative leg alignments were compared.

RESULTS

The mean postoperative coronal plane alignment was 2.7 (range,1-4) degree valgus; the mean deviation from intra-operative computer images was one (range, 0.1-1.9) degree; 5 knees had less valgus in the postoperative radiographs than the intra-operative computer images.

CONCLUSION

Despite being more technically demanding, time consuming, and costly, arthroscopy-assisted computer navigation is safe, accurate, and reliable for HTO.

Mechanical accuracy of navigated minimally invasive total knee arthroplasty (MIS TKA)

This study was designed to provide evidence that computer-navigated minimally invasive total knee arthroplasty (MIS CN-TKA) enables identical mechanical accuracy as conventional computer navigated total knee arthroplasty (CN-TKA) while reducing rehabilitation time and hospital stay of the patients. Two groups of 20 patients requiring total knee arthroplasty due to degenerative or posttraumatic knee osteoarthritis were included. Twenty consecutive patients received conventional CN-TKA and 20 consecutive patients received minimally invasive CN-TKA. Mechanical and rotational alignments were measured preoperatively and 6 months postoperatively on long-standing radiographs, on conventional coronal and sagittal views and on CT-scans of the knee. Length of skin incision, operating time, blood loss, length of hospital stay, postoperative ROM and HSS as well as KSS scores were determined. Postoperative mechanical axis improved significantly in both groups. Coronal and sagittal component positioning were accurate in both groups without significant differences. Rotational alignment showed the desired reproducible values without significant differences between the two groups. The posterior slope of the tibial component was significantly reconstructed to match the preoperative condition in both groups. The coronal alignment of the femoral and tibial components showed accurate reproducible results for implantation of both components in both groups. Length of skin incision was significantly shorter in the MIS CN-TKA. Duration of hospital stay was significantly reduced in the MIS CN-TKA group. Operating time and blood loss were similar in both groups. Postoperative ROM after the first 3 months was significantly higher in MIS CN-TKA, but after 6 months differences were minimal. Clinical outcome scores were identical for both groups 6 months after surgery. The advantages of CN-TKA are well known. Performing computer navigated TKA in combination with a minimally invasive approach in this study lead to a reduction of hospital stay and an initially increased ROM without differences in operating time and blood loss. Computer navigation in TKA preserves accurate coronal, sagittal and rotational components alignment even with a minimally invasive approach.

Computer-assisted surgical navigation does not improve the alignment and orientation of the components in total knee arthroplasty

BACKGROUND

Whether total knee arthroplasty with use of computer-assisted surgical navigation can improve the limb and component alignment is a matter of debate. We hypothesized that total knee arthroplasty with use of computer-assisted surgical navigation is superior to conventional total knee arthroplasty with regard to the precision of implant positioning.

METHODS

Sequential simultaneous bilateral total knee arthroplasties were carried out in 160 patients (320 knees). One knee was replaced with use of a computer-assisted surgical navigation system, and the other was replaced conventionally without use of computer-assisted surgical navigation. The two methods were compared for accuracy of orientation and alignment of the components as determined by radiographs and computed tomography scans. The mean duration of follow-up was 3.4 years.

RESULTS

The mean preoperative Knee Society score was 26 points, with an improvement to 92 points postoperatively, in the computer-assisted total knee arthroplasty group and 25 points, with an improvement to 93 points postoperatively, in the conventional total knee arthroplasty group. Preoperative and postoperative ranges of motion of the knees were similar in both groups. The operating and tourniquet times were significantly longer in the computer-assisted total knee arthroplasty group than in the conventional total knee arthroplasty group (p < 0.001). The groups were not significantly different with regard to the accuracy of component positioning and the number of outliers for the various radiographic parameters (p > 0.05).

CONCLUSIONS

Our data demonstrate that total knee arthroplasty with use of computer-assisted surgical navigation did not result in more accurate implant positioning than that achieved in conventional total knee arthroplasty, as determined by both radiographs and computed tomography scans.

Radiographic and navigation measurements of TKA limb alignment do not correlate

Precise pre- and postoperative anatomic measurements are necessary to plan, perform, and evaluate total knee arthroplasty (TKA). We evaluated the relationship between radiographic and navigation alignment measurements, identified sources of error in radiographic and navigated alignment assessment, and determined the differences between desired and clinically accepted alignment. Fifty-eight computer-assisted TKAs were performed and limb alignment measurements were recorded both pre- and postoperatively with standard radiographs and with an intraoperative navigation system. Intraoperative navigation produced consistent navigation-generated alignment results that were within 1 degrees of the desired alignment. The difference between preoperative radiographic and navigation measurements varied by as much as 12 degrees and the difference between postoperative radiographic and navigation measurements varied by as much as 8 degrees. This discrepancy depended on the degree of limb deformity. Postoperative radiographic measurements have inherent limitations. Navigation can generate precise, accurate, and reproducible alignment measurements. This technology can function as an effective tool for assessing pre- and postoperative limb alignment and relating intraoperative alignment measurements to clinical and functional outcomes.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Determining femoral component position using CAS and measured resection

To evaluate the ability of computer-assisted surgery (CAS) to accurately size and determine rotational alignment of the femoral component in TKA, the author reviewed femoral component position after 50 consecutive primary TKAs using a femur-first, measured resection workflow. The computer software used allowed femoral rotation to be selected based on epicondylar axis, posterior condylar axis, or anteroposterior axis. The final femoral component size and position was determined by the surgeon to avoid anterior notching, match the posterior-medial condyle resection, and flexed to match the plane of the anterior femoral cortex. Femoral sizing was confirmed intraoperatively with a standard sizing guide. The femoral component was downsized in 52% of patients from the size recommended by the computer software. The posterior condylar axis matched the implanted rotational position of the femoral component to within 1 degrees in 64% of patients in contrast to the epicondylar axis (32%) and anteroposterior axis (26%). CAS provides information to make surgical decisions but does not replace clinical judgment. Landmark referencing may be compromised by limited surgical exposures leading to variation in implant positioning by computer software. A clear understanding of the principles of TKA is critical when using CAS to optimize implant sizing and position.

Computer navigation-assisted versus minimally invasive TKA: benefits and drawbacks

Computer-navigated and minimally invasive TKAs are emerging technologies that have distinct strengths and weaknesses. We compared duration of surgery, length of hospitalization, Knee Society scores, radiographic alignments, and complications in two unselected groups of 81 consecutive knees that underwent TKA using either a minimally invasive approach or computer navigation. The two groups were operated on by two different surgeons over differing timeframes. The mean surgical time was longer in the navigated group by 63 minutes. The Knee Society scores and lengths of hospitalization of the two groups were similar. The postoperative component alignments of the two groups were similar; the mean femoral valgus and tibial varus angles of the navigation group changed from 96 degrees and 88 degrees preoperatively to 95 degrees and 89 degrees postoperatively, respectively, and in the minimally invasive group, the mean femoral valgus angles and tibial varus angles changed from 97 degrees and 88 degrees preoperatively to 95 degrees and 89 degrees postoperatively, respectively. There were 11 major and three minor complications in the navigation group, including one revision, two femoral shaft fractures, four reoperations for knee stiffness, and four instances of bleeding from tracker sites. We believe the higher incidence of complications in addition to the longer operative time in the navigated group may outweigh any potential radiographic benefits.

LEVEL OF EVIDENCE

Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

The evaluation of post-operative alignment in total knee replacement using a CT-based navigation system

We compared the alignment of 39 total knee replacements implanted using the conventional alignment guide system with 37 implanted using a CT-based navigation system, performed by a single surgeon. The knees were evaluated using full-length weight-bearing anteroposterior radiographs, lateral radiographs and CT scans. The mean hip-knee-ankle angle, coronal femoral component angle and coronal tibial component angle were 181.8 degrees (174.2 degrees to 188.3 degrees), 88.5 degrees (84.0 degrees to 91.8 degrees) and 89.7 degrees (86.3 degrees to 95.1 degrees), respectively for the conventional group and 180.8 degrees (178.2 degrees to 185.1 degrees), 89.3 degrees (85.8 degrees to 92.0 degrees) and 89.9 degrees (88.0 degrees to 93.0 degrees), respectively for the navigated group. The mean sagittal femoral component angle was 85.5 degrees (80.6 degrees to 92.8 degrees) for the conventional group and 89.6 degrees (85.5 degrees to 94.0 degrees) for the navigated group. The mean rotational femoral and tibial component angles were -0.7 degrees (-8.8 degrees to 9.8 degrees) and -3.3 degrees (-16.8 degrees to 5.8 degrees) for the conventional group and -0.6 degrees (-3.5 degrees to 3.0 degrees) and 0.3 degrees (-5.3 degrees to 7.7 degrees) for the navigated group. The ideal angles of all alignments in the navigated group were obtained at significantly higher rates than in the conventional group. Our results demonstrated significant improvements in component positioning with a CT-based navigation system, especially with respect to rotational alignment.

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.

Averaging different alignment axes improves femoral rotational alignment in computer-navigated total knee arthroplasty

BACKGROUND

Computer navigation systems generally establish the rotational alignment axis of the femoral component on the basis of user-defined anatomic landmarks. However, navigation systems can also record knee kinematics and average alignment axes established with multiple techniques. We hypothesized that establishing femoral rotational alignment with the use of kinematic techniques is more accurate and precise (repeatable) than the use of anatomic techniques and that establishing femoral rotational alignment by averaging the results of different alignment techniques is more accurate and precise than the use of a single technique.

METHODS

Twelve orthopaedic surgeons used three anatomic and two kinematic alignment techniques to establish femoral rotational alignment axes in a series of nine cadaver knees. The axes derived with the individual anatomic and kinematic techniques as well as the axes derived with six combination techniques--i.e., those involving averaging of the alignments established with two of the individual techniques--were compared against a reference axis established with computed tomography images of each femur.

RESULTS

The kinematic methods were not more accurate (did not have smaller mean errors) or more precise (repeatable) than the anatomic techniques. The combination techniques were accurate (five of the six had a mean error of <5 degrees ) and significantly more precise than all but one of the single methods. The percentage of measurements with <5 degrees of error as compared with the reference epicondylar axis was 37% for the individual anatomic techniques, 30% for the individual kinematic techniques, and 58% for the combination techniques.

CONCLUSIONS

Averaging the results of kinematic and anatomic techniques, which is possible with computer navigation systems, appears to improve the accuracy of rotational alignment of the femoral component. The number of rotational alignment outliers was reduced when combination techniques were used; however, they are still a problem and continued improvement in methods to accurately establish rotation of the femoral component in total knee arthroplasty is needed.

Results of an initial experience with custom-fit positioning total knee arthroplasty in a series of 48 patients

The custom-fit approach to total knee arthroplasty in conjunction with removal of osteophytes and preservation of ligaments rapidly returned function; restored motion, stability, and postoperative mechanical axis alignment; effected high patient satisfaction; and had an acceptable clinical outcome.

Current state and future of joint replacements in the hip and knee

Joint replacements of the hip and knee are among the most clinically successful operations. According to figures compiled by the American Academy of Orthopaedic Surgeons, the number of primary total hip replacements performed in the USA was 220,000 in 2003. This was 38% more than in 1996 and this number is expected to rise to 572,000 (plus another 97,000 revisions) by 2030. The number of primary total knee replacements performed in 2003 was approximately 418,000 and is expected to rise exponentially with the increasing numbers of baby boomers and the aging population. Current research focuses not only on extending implant longevity, but also on improving function to meet the increased demands of today's patients, who are likely to be younger and more active than their predecessors two decades ago. Potential advancements in arthroplasty surgery include new, more wear-resistant bearing surfaces, porous metals to enhance osseointegration and replace lost bone stock, a clearer understanding of the biological processes associated with periprosthetic osteolysis, minimally invasive surgery and computer assisted surgery. Long-term studies are needed to establish the efficacy of these new technologies.

Navigated unicompartmental knee replacement

Computer-aided systems have been developed recently to improve the precision of implantation of unicompartmental knee replacement (UKR) or total knee replacement. Minimal invasive techniques have been developed to decrease the surgical trauma related to the prosthesis implantation. However, there might be a concern about the potential of minimal invasive techniques for a loss of accuracy. Navigation systems might address this issue. We are currently using routinely a nonimage-based navigation for total knee replacement. We developed a modified system for UKR, suitable for either a conventional or a mini-invasive approach. Navigated implantation of a UKR allowed improving the accuracy of the radiologic implantation. Mini-invasive implantation was effective, but the accuracy may not reach that of the conventional navigated technique and should be still improved. Minimal invasive techniques have to be validated because a loss of accuracy will negatively influence long-term outcomes.

The accuracy of bone resections made during computer navigated total knee replacement. Do we resect what the computer plans we resect?

Many studies have shown that computer navigation in total knee arthroplasty aids the surgeon to place the prosthesis in a more accurate overall alignment. Bony resection creates the flexion and extension gaps; important in balancing the knee and implant selection in TKR. The computer plans the bone cuts but has variables that it cannot control: the surgeon, the saw blade thickness and oscillation, the accuracy of the jigs, movement of the pins, and the quality of initial mapping data inputted by the surgeon. The accuracy of computer navigated bone resections are validated on cadavers, but this is the first study to compare the predicted bone cuts to that physically resected during TKR. For 89 patients undergoing primary TKR, the bone cut from the distal femur and proximal tibia was measured using Vernier callipers and compared to the computer calculation of the same. Results show that computer measurement of the physical space left by the resected bone is accurate.

Evaluation of anatomic references for tibial sagittal alignment in total knee arthroplasty

The authors aimed to demonstrate the relationship between the sagittal mechanical axis of the tibia and other reference axes of the tibia and fibula in patients with advanced osteoarthritis of the knee joints, and then to identify a reliable landmark in order to minimize posterior tibial slope measurement errors. We evaluated 133 osteoarthritic knees with neutral or varus deformity in 64 female and 8 male patients. Axial computed tomographic images of whole tibiae including knee and ankle joints were obtained and reconstructed using 3-dimensional imaging software. Angles between the mechanical axis (MA), the tibial anatomical axis (TAA), the anterior tibial cortex (ATC) and the fibular shaft axis (FSA) were measured, and then medial and lateral tibial slope angles were measured using all axes. Mean angles between MA and the other anatomical reference lines (TAA, ATC and FSA) were 0.9, 2.2 and -2.1 degrees, respectively. The mean values of lateral tibial slopes with respect to MA, TAA, ATC and FSA were 8.7, 10, 12 and 7.3, respectively, and their intra- and inter-observer reliabilities were higher than those of medial tibial slopes. Although posterior tibial slope change markedly according to the reference axis used, the axes used in conventional TKA showed significant correlations with each other, and thus, may be used safely if differences with the mechanical axis are considered. Moreover, the lateral tibial slope might have advantages over the medial tibial slope in terms of restoration of the natural tibial slope.

Computer navigation did not improve alignment in a lower-volume total knee practice

Postoperative alignment of the implanted prosthesis in computer-navigated TKA has been reported to be superior to that using the conventional technique. There is an assumption that use of computer navigation techniques can make an inexperienced or occasional TKA surgeon perform more like an expert TKA surgeon. To assess improved accuracy in recreation of mechanical alignment in TKA performed using computer navigation, a retrospective review of the experience of one of the authors (WPY) before and after using computer navigation was performed. We reviewed the radiographic results of 104 TKAs (52 computer navigation, 52 conventional technique) and found the accuracy of postoperative radiographic alignment of the implanted prosthesis was not improved by using computer navigation as judged by (1) overall limb alignment (case: varus 1.3 degrees ; control: varus 0.3 degrees ); (2) femoral component alignment (case: 90.3 degrees ; control: 90.3 degrees ); and (3) tibial component alignment (case: 89 degrees ; control: 90 degrees ). Significant factors that affected postoperative overall mechanical alignment in the current navigation series included severity of the preoperative deformity, amount of error in making bone cuts, and experience of the surgeon in using the computer navigation system.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Alignment deviation between bone resection and final implant positioning in computer-navigated total knee arthroplasty

BACKGROUND

Computer-navigated total knee arthroplasty is aimed at improving accuracy in the positioning of prosthetic components and realigning the lower limb. The optimal position and orientation of the bone resection planes are targeted by the navigation system, but, after these are obtained, additional manual surgical actions, which may considerably affect final component alignment, are necessary for implantation. The aim of this study was to measure the alignment deviation caused by standard impaction of the tibial and femoral components following bone resections with use of navigation control.

METHODS

Ninety-one primary total knee arthroplasties were performed with an image-free knee navigation system. The alignment of the tibial and femoral bone resections was measured in three planes during surgery by the instrumented probe of the system. The alignment measure was repeated after final tibial and femoral component implantation with cement. The alignment deviations between the two measures were considered the positioning error associated with the final manual implantation of the components.

RESULTS

The alignment deviations between the bone resections and the subsequent implant placement were >1 degrees in the frontal plane of the femur and in the frontal and sagittal planes of the tibia in 20%, 11%, and 33% of the patients, respectively. The deviations were >2 degrees in 4%, 3%, and 9% of the patients, respectively. Deviations as large as 3 degrees were found at the tibia in the sagittal plane (the posterior slope).

CONCLUSIONS

Positioning of the femoral and tibial components in total knee arthroplasty, which mainly involves cementation and impaction of the final components, can introduce a considerable error in alignment, regardless of how accurately the resection planes are made. After computer-navigated total knee arthroplasty, it would be useful therefore to check the alignment of the prosthetic component carefully before the cement hardens.

[Computer-assisted total-knee arthroplasty. Comparison of two successive systems. Learning curve]

PURPOSE OF THE STUDY

The increasing popularity of total-knee arthroplasty has led to many technical improvements both in the field of prosthesis design and implanted material and instrumentation. The recent advent of computer-assisted techniques is the fruit of a search for more precision for the bone cuts and better ligament balance. The purpose of the present study was to demonstrate how easy it is to use navigation systems by examining the difficulties encountered by one operator with navigation experience when the material was changed.

MATERIAL AND METHODS

The first 30 total-knee arthroplasties implanted with a new navigation system were investigated. Elements specifically related to navigation difficulties were studied. The series was composed of 16 women and 14 men, mean age 65.9 years at the time of surgery (range, 43 to 84). Mean BMI was 30.66 (range, 23.05 to 39.54). All patients were reviewed by the operator using a standard X-ray protocol. Mean follow-up was six months. The 30 arthroplasties were consecutive, with no exclusions excepting revision procedures. Primary or post-traumatic degeneration was the main reason for surgery. This series was compared with two prior series of 30 prostheses each, implanted with a different navigation system. The first 30 and last 30 implantations using the previous navigation system were thus compared in terms of operative time and precision (comparison of postoperative alignment and implant position). The study focused on difficulties encountered when using the new system, on intra- and postoperative complications and on assessment of implant position.

RESULTS

All procedures were totally performed with the navigation system, no interruptions. Operative time was lengthened by an average of 18 min (range, 0 to 45 min). There were no complications specifically related to the navigation system. The position of the implants was assessed in the frontal and sagittal plane on the plain X-rays and with a goniometer. Computed tomography was used to assess femoral component rotation. The overall alignment of the lower limb was within the "ideal" range of +/-3 degrees in 97% (average 0.1 degrees varus). The position of the femoral implant and the tibial plate was correct in the frontal and sagittal planes and no internal rotation of the femoral piece was noted on the 27 ct scan studies (mean 1.9 degrees external rotation). Implant accuracy was equivalent to that observed in the series of the last 30 implants using the prior navigation system. The learning curve was shorter.

DISCUSSION

This small series demonstrated the absence of major problems with the new navigation system. The length of the learning curve was acceptable. This study demonstrated that prior experience with navigation is beneficial because the learning curve with the new system was shorter and the accuracy of implantation was equivalent to that achieved with the prior system. Widespread use of computer-assisted surgery should enable continued improvement in ancillary systems in the upcoming years, particularly concerning rotatory position of the femoral implants, which is still a problem. Cost containment will also be a necessary goal.

Intraoperative assessment of femoral component rotational alignment in total knee arthroplasty

Poor clinical results following total knee arthroplasty like flexion gap instability or anterior knee pain may be related to femoral component rotational malalignment. The transepicondylar axis has been recommended as a landmark to consistently recreate a balanced flexion gap. However, the reproducibility to identify the transepicondylar axis intraoperatively is low. In this feasibility study we wanted to find out whether fluoroscopy-based CT scans obtained by a motorized mobile C-arm (Iso C 3D) may be useful to asses the transepicondylar axis intraoperatively. Following the femoral resections the Iso C 3D was used intraoperatively in ten knees with mild to severe deformities. On multiplanar reconstructions of the distal femur the clinical epicondylar axis as well as the angle to the posterior cut (condylar twist angle) could be easily measured. The scanning time was 40 s and the extra time needed for the whole setup about five to ten minutes. The Iso C 3D was helpful to intraoperatively identify the transepicondylar axis and the condylar twist angle, especially in cases with severe deformity or dysplasia when standard landmarks are difficult to determine.

Scientific evidence supporting computer-assisted surgery and minimally invasive surgery for total knee arthroplasty

This review provides an overview of the field of minimally invasive surgery and computer-assisted surgery for total knee arthroplasty. The authors have examined the complete body of literature for scientific evidence supporting the use of these new technologies and how the literature specifically supports commonly asked questions. There is controversy concerning the benefits of minimally invasive surgery and computer-assisted surgery for total knee arthroplasty. However, in most studies the results are similar for minimally invasive surgery compared to standard approaches. Computer-assisted navigation has been found in some studies to improve radiographic alignment of total knee arthroplasty. The authors believe that there is evidence for both technologies to be at least equivalent in terms of results, as well as expectations of increased success with the techniques. Both technologies have led manufacturers to invest more effort into newer prosthetic instrumentations and designs to facilitate these techniques.

Tension controlled ligament balanced total knee arthroplasty: 5-year results of a soft tissue orientated surgical technique

INTRODUCTION

Posterior cruciate ligament (PCL)-retaining prostheses give good outcomes and are commonly used. This retrospective study investigated outcomes from total knee arthroplasty (TKA) using the ligament balancing technique to implant a PCL-retaining knee prosthesis (balanSystrade mark knee system) with either a mobile or a fixed bearing polyethylene inlay.

MATERIALS AND METHODS

A retrospective study was performed on patients treated with TKA at one surgical centre between 1997 and 2001. In this period 182 surgeries were performed. Clinical assessments of the implant used the Knee Society Score (KSS). Subjective assessments used visual analogue scale (VAS) for pain and patient satisfaction. The Western Ontario and McMasters Universities Osteoarthritis Index (WOMAC) was used to assess pain, stiffness and function of the knee. Radiographic analysis was performed to determine frontal and sagittal alignment and loosening.

RESULTS

A total of 109 knee implants in 95 patients (26 men; 69 women) were followed up. Seventy-three cases were not available for follow-up due to bad health or death of the patient; 74% of 109 reviewed implants had fixed bearings and 26% had mobile bearings. The mean age at surgery was 72.9 +/- 7.35 years (range 54.7-92.4). The mean KSS was 160 +/- 28.3 points. The KSS was greater for men and was significantly reduced when another disease was present. The type of bearing, surgical approach, and pre-operative alignment for patients affected by varus or valgus gonarthrosis had no significant impact on KSS and ROM. According to VAS the mean scores for pain and satisfaction were 1.48 (0 = no pain) and 9.2 (10 = very satisfied), respectively. The WOMAC mean scores for pain (87.0), stiffness (82.3) and function (78.6) were high (best outcome score of 100). There were no revisions due to aseptic loosening or wear.

CONCLUSION

Total knee arthroplasty performed with a PCL-retaining prosthesis implanted by using a soft tissue oriented surgical technique is a safe procedure and was associated with good results. So far, there were few complications and no need for revision due to aseptic loosening. In addition, most of the patients reported little pain and were satisfied with the outcome. These good outcomes are comparable with other studies reporting on PCL-retaining prostheses.

Computer-assisted minimally invasive total knee arthroplasty compared with standard total knee arthroplasty. A prospective, randomized study

BACKGROUND

There is little information on the feasibility of computer navigation when using a minimally invasive approach for total knee arthroplasty, during which the anatomic landmarks for registration may be obscured. The purpose of the present study was to determine the radiographic accuracy of this technique and to compare the rate of functional recovery between patients who underwent computer-assisted minimally invasive arthroplasty and those who underwent conventional total knee arthroplasty.

METHODS

One hundred and eight consecutive patients were randomized to undergo computer-assisted minimally invasive total knee arthroplasty or conventional total knee arthroplasty. Perioperative pain management was standardized. The clinical parameters, long-leg radiographs, and functional assessment scores were evaluated for six months postoperatively.

RESULTS

Patients who underwent computer-assisted minimally invasive total knee arthroplasty had a significantly longer operative time (by a mean of twenty-four minutes) and a significantly shorter inpatient stay (3.3 compared with 4.5 days) in comparison with those who underwent conventional arthroplasty (p </= 0.001). Significantly more patients in the computer-assisted minimally invasive total knee arthroplasty group were able to walk independently for more than thirty minutes at one month (p = 0.04). The percentage of patients with a coronal tibiofemoral angle within +/-3 degrees of the ideal was 92% for the computer-assisted minimally invasive total knee arthroplasty group, compared with 68% for the conventional total knee arthroplasty group (p = 0.003).

CONCLUSIONS

Although specific clinical parameters reflect an early increased rate of functional recovery in association with computer-assisted minimally invasive total knee arthroplasty within the first postoperative month, the main advantage of this technique over conventional total knee arthroplasty is improved postoperative radiographic alignment without increased short-term complications.

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.

Interobserver and intra-observer errors in obtaining visually selected anatomical landmarks during registration process in non-image-based navigation-assisted total knee arthroplasty

This study investigated the errors of obtaining visually selected anatomic landmarks for use in the registration process in a passive optical non-image-based computer-assisted total knee arthroplasty system in 5 fresh frozen cadavers. The projected maximum errors in the femoral mechanical axis (due to registration errors of the center of the distal femur) were 0.7 degrees in the coronal and 1.4 degrees in the sagittal plane. The projected maximum errors in the tibial mechanical axis arising from registration errors of the center of the proximal tibia were 1.3 degrees in the coronal and 2 degrees in the sagittal plane. The projected maximum errors in the transepicondylar axis were 9.1 degrees (registration errors of the medial femoral epicondyle) and 7.2 degrees (registration errors of the lateral femoral epicondyle). It should be noted that the results may be partly related to the use of the particular system in this experiment.

Six sigma analysis of computer-assisted surgery tracking protocols in TKA

In computer-assisted surgery, efficacy relies on the overall precision of the method, of which the tracking technology is an integral feature. Does electromagnetic tracking perform clinically as well as standard optical tracking technologies? A pilot study using a computer-assisted surgery system and one lower extremity from an embalmed cadaver evaluated the mechanical axis, the transepicondylar axis, and the anteroposterior axis of Whiteside (anteroposterior axis). Using three-dimensional computed tomography and direct anatomic measurements, the baseline value for the mechanical axis was 4.9 degrees varus and the tibial shaft axis was 4.6 degrees varus. All tests were performed in a standard operating room using an imageless referencing protocol. Repeatability of one surgeon performing eight trials revealed optical mechanical axis mean of 5.8 degrees varus (standard deviation, 0.3 degree) and electromagnetic mechanical axis mean of 5.3 degrees varus (standard deviation, 0.9 degree); reproducibility of three surgeons performing eight trials each revealed optical mechanical axis mean of 6.3 degrees varus (standard deviation, 0.6 degree) and electromagnetic mechanical axis mean of 5.2 degrees varus (standard deviation, 0.8 degree). Precision was satisfactory for both optical and electromagnetic tracking for mechanical axis assessment, but outliers were identified with electromagnetic tracking causing concern for efficacy. Assessment of the transepicondylar or the anteroposterior axis measurements was not satisfactory with either the optical or electromagnetic system.