Radiographic and navigation measurements of TKA limb alignment do not correlate

The limits of precision in conventionally instrumented computer-navigated total knee arthroplasty

PURPOSE

Computer-navigated total knee arthroplasty (TKA) improves the accuracy of component implantation. However, the final implant alignment may not match planned alignment. The hypothesis of this study is that although computer navigation improves alignment, imprecision may not be completely eliminated. The aim of the study was to establish the incidence and sources of imprecision during TKA using computer navigation to measure deviations from planned alignment.

METHODS

Computer navigation was used to quantify changes in planned alignment at four steps during 136 TKA's: application of cutting blocks, addition of definitive pin fixation, bone cuts and after prosthesis application. Mean changes in alignment deviation at each step in each plane were measured and the number of significant outliers (>3° from the planned resection plane) were assessed in each plane.

RESULTS

Overall changes in planned alignment were small and non-cumulative between steps but the incidence of outliers (cuts measured as >3° from planned alignment at each step) increased through the steps, with 21.3 % (n = 29) of final implants outlying in the tibial sagittal plane, which was the least precise plane. The highest number of outliers occurred after bone resection and the addition of pins to cutting blocks was also identified as a source of imprecision.

CONCLUSION

Despite improved accuracy of bone resection with computer-navigated TKA, the precision of bone cuts may be affected at several steps of the procedure. Cutting block application, bone resection and prosthesis application may all affect accuracy. Bone cuts should be made with meticulous care, whether navigated or not, and navigated cuts should be checked and corrected, particularly in the tibial sagittal plane.

LEVEL OF EVIDENCE

IV.

A comparison of radiological and computer navigation measurements of lower limb coronal alignment before and after total knee replacement

We compared lower limb coronal alignment measurements obtained pre- and post-operatively with long-leg radiographs and computer navigation in patients undergoing primary total knee replacement (TKR). A series of 185 patients had their pre- and post-implant radiological and computer-navigation system measurements of coronal alignment compared using the Bland-Altman method. The study included 81 men and 104 women with a mean age of 68.5 years (32 to 87) and a mean body mass index of 31.7 kg/m(2) (19 to 49). Pre-implant Bland-Altman limits of agreement were -9.4° to 8.6° with a repeatability coefficient of 9.0°. The Bland-Altman plot showed a tendency for the radiological measurement to indicate a higher level of pre-operative deformity than the corresponding navigation measurement. Post-implant limits of agreement were -5.0° to 5.4° with a repeatability coefficient of 5.2°. The tendency for valgus knees to have greater deformity on the radiograph was still seen, but was weaker for varus knees. The alignment seen or measured intra-operatively during TKR is not necessarily the same as the deformity seen on a standing long-leg radiograph either pre- or post-operatively. Further investigation into the effect of weight-bearing and surgical exposure of the joint on the mechanical femorotibial angle is required to enable the most appropriate intra-operative alignment to be selected.

Cutting and implanting errors in minimally invasive total knee arthroplasty using a navigation system

PURPOSE

The purpose of this study was to evaluate the accuracy of bone cutting and implantation in minimally invasive total knee arthroplasty with image-free navigation.

METHODS

The alignment of the tibial and femoral bone resection was measured in 40 knees during surgery. The alignment measurement was repeated after cementing the tibial and femoral components. We evaluated the cutting error and the implanting error.

RESULTS

The mean tibial cutting errors were 0.5 and 0.7° in the frontal and sagittal planes, respectively. The mean femoral cutting errors were 0.5 and 0.9° in the frontal and sagittal planes, respectively. The mean tibial implanting errors were 1.0 and 0.9° in the frontal and sagittal planes, respectively. The mean femoral implanting error was 0.7° in the frontal plane.

CONCLUSIONS

Computer-assisted navigation was useful in checking the alignment of both bone cut and cementation.

Assessing whether preoperative templates and planning can replace intraoperative computer-assisted surgery measurements in total knee arthroplasty

It is incumbent on the orthopedic community to assess current technologies available to predict the size of implants used for total knee arthroplasty (TKA) and whether they can accurately represent what will be visualized by surgeons intraoperatively. This study highlights the traditional practice of TKA by applying digitization software to streamline existing knowledge preoperatively in an effort to more accurately dimension the implants. The primary goal of the study was to assess the predictive value of a digitized templating system for TKA. The secondary goal was to ascertain whether varus, valgus, and flexion deformities were accurately predicted to intraoperative measures using computer-assisted surgery. Forty-three patients were prospectively assessed using standard-of-care 36-inch anteroposterior evaluations for determining mechanical angle and flexion contractures. Simultaneously, traditional radiographs were used as a sizing tool for the digitized software program. Statistical evaluation was completed by 2-tailed t test with incorporation of a varied window of acceptance (± 3° and ± 2° in mechanical angle and flexion contracture measurements, respectively). This study showed a poor correlation between the predictive value of the digitization software; just one-third of the cases were accurately predicted.

Femur positioning in navigated total knee arthroplasty

Navigated total knee arthroplasty (TKA) results in better restoration of neutral mechanical axis than does the conventional technique. Nevertheless, coronal malalignment has not been eliminated. It is yet unknown whether errors in implant positioning occur more on the femoral side, more on the tibial side, or equally on both sides. The hypothesis of this study was that a predominance of coronal component malalignment exists on the tibial side in navigated tibia-first TKA.Fifty-seven consecutive navigated (OrthoPilot; B. Braun Aesculap, Tuttlingen, Germany) TKAs were included in this retrospective study. Pre- and postoperative digital whole-leg standing radiographs were analyzed. Coronal alignment was measured for the whole leg pre- and postoperatively. Lateral distal femur angle and medial proximal tibia angle were analyzed on the preoperative radiographs. On the postoperative radiographs, coronal alignment of the femoral and tibial components were measured separately in reference to the tibial and femoral mechanical axis. The coronal alignment improved from 8.2° ± 3.7° preoperatively to 1.1° ± 1.2° postoperatively, with 5 (8%) outliers outside the 3° window. The femoral component was malaligned (0.6° ± 0.6°), whereas the tibial component showed a significantly higher deviation from the mechanical axis of 1.0° ± 1.1° (P=.009). The femoral component was positioned more precisely than the tibial component. The latter influences gap management in the tibia-first technique and may thereby have a relevant effect on joint stability. Accuracy of the surgical technique and differences in the mathematical algorithm for the determination of landmarks are possible reasons for the difference in precision between the femoral and tibial component positioning.

Computer guided restoration of joint line and femoral offset in cruciate substituting total knee arthroplasty

PURPOSE

This prospective study aimed to evaluate radiographically, change in joint line and femoral condylar offset with the optimized gap balancing technique in computer-assisted, primary, cruciate-substituting total knee arthroplasties (TKAs).

METHODS

One hundred and twenty-nine consecutive computer-assisted TKAs were evaluated radiographically using pre- and postoperative full-length standing hip-to-ankle, antero-posterior and lateral radiographs to assess change in knee deformity, joint line height and posterior condylar offset.

RESULTS

In 49% of knees, there was a net decrease (mean 2.2mm, range 0.2-8.4mm) in joint line height postoperatively whereas 46.5% of knees had a net increase in joint line height (mean 2.5mm, range 0.2-11.2mm). In 93% of the knees, joint line was restored to within ± 5 mm of preoperative values. In 53% of knees, there was a net increase (mean 2.9 mm, range 0.2-12 mm) in posterior offset postoperatively whereas 40% of knees had a net decrease in posterior offset (mean 4.2mm, range 0.6-20mm). In 82% of knees, the posterior offset was restored within ± 5 mm of preoperative values.

CONCLUSIONS

Based on radiographic evaluation in extension and at 30° flexion, the current study clearly demonstrates that joint line and posterior femoral condylar offset can be restored in the majority of computer-assisted, cruciate-substituting TKAs to within 5mm of their preoperative value. The optimized gap balancing feature of the computer software allows the surgeon to simulate the effect of simultaneously adjusting femoral component size, position and distal femoral resection level on joint line and posterior femoral offset.

Does computer-assisted surgery improve postoperative leg alignment and implant positioning following total knee arthroplasty? A meta-analysis of randomized controlled trials?

PURPOSE

Computer-assisted surgery has been proposed as a technique to improve implant alignment during total knee arthroplasty (TKA). However, there is still a debate over the accuracy of placing the femoral and tibial components using computer-assisted systems in TKA. The aim of this study is to establish whether computer-assisted surgery leads to superior mechanical leg axis and implant positioning than conventional technique in patients with primary TKA.

METHODS

Major electronic databases were systematically searched to identify relevant studies without language restriction. A meta-analysis of 41 randomized controlled trials (RCTs) or quasi-RCTs was performed in a random effects model. A subgroup analysis was conducted by type of navigation system to explore the clinical heterogeneity between these trials. The following radiographic parameters were used to compare computer-assisted surgery with conventional technique: (1) mechanical leg axis, (2) femoral component coronal alignment, (3) tibial component coronal alignment, (4) femoral component sagittal alignment, and (5) tibial component sagittal alignment.

RESULTS

For the mechanical leg axis and coronal positioning of femoral and tibial components, there are statistically significant reductions in the number of patients with malalignment in the CAS group if the outlier cutoff value is ±3 or 2° in the coronal and sagittal planes, respectively. Subgroup analysis demonstrates that CT-free navigation systems provide better alignment than conventional techniques in the coronal and sagittal alignment of femoral components within ±3 and 2°. If the outlier cutoff value for the tibial sagittal alignment is ±2°, the outlier percentages are higher in the CT-free navigation group than in the conventional group. However, there was no significant difference in the tibial sagittal alignment at ±3°.

CONCLUSION

Computer-assisted surgery does improve mechanical leg axis and component orientation in TKAs. However, high-quality RCTs are necessary to determine whether surgeons could use computer-assisted techniques to achieve a targeted tibial slope in TKA.

LEVEL OF EVIDENCE

Therapeutic study (Systematic review of Level I/II studies), Level II.

Precision of Ci-navigated extension and flexion gap balancing in total knee arthroplasty and analysis of potential predictive variables

INTRODUCTION

The aim of this study was to evaluate the accuracy of final limb alignment and flexion-extension and medial-lateral gap balancing in computer navigated total knee arthroplasty and to analyze various possible predictive variables that may affect the gaps in computer navigated knee arthroplasty.

MATERIALS AND METHODS

The DePuy Ci system, a nonimage-based passive optical computer navigation system, was used in 225 patients with knee osteoarthritis to assist for the total knee arthroplasty. From the raw data the Ci-verified pre- and postoperative leg axis in extension, angle of tibia and femur resection, the flexion and extension angle, the medial and lateral extension and flexion gaps were extracted; and differences in gaps were calculated and subjected to statistical analysis. Leg alignment and implant position were determined only by the navigation system. Preoperative variables were evaluated for their impact on the final flexion/extension and medial/lateral gaps achieved.

RESULTS

Though the preoperative femoro-tibial coronal alignment had a large variance, postoperatively 98.22% of the knee was found to be between -3° and +3° in the coronal limb alignment axis. The Ci-verified femoral and tibial cuts in the coronal plane showed a good accuracy. The sagittal alignment of the femoral cut ranged from 8.20° flexion to 3.20° of extension. Rectangular extension and flexion gaps were achieved with ≤3 mm of difference in gaps on medial and lateral sides in 98 and 93% of knees, respectively. Difference between extension and flexion gaps on the medial side was ≤3 mm in 83% and on the lateral side in 84% of the knees. Of all the possible predictive variables analyzed, Pearson correlation and multiple regression analysis showed significant correlation only between the medial-lateral gap difference in extension and the Ci-verified femoral cut, tibial cut and limb axis, all in the coronal plane.

CONCLUSION

Computer-assisted navigated total knee replacement allows for accurate gap balancing that is not dependent on the various pre- and intraoperative factors mentioned, including age, sex, Range of motion preoperative deformity and grade of osteoarthritis. The Ci-calculated and verified tibial, and femoral cuts are the only possible factors affecting the extension gap.

Residual varus alignment does not compromise results of TKAs in patients with preoperative varus

BACKGROUND

Postoperative varus alignment has been associated with lower IKS scores and increased failure rates. Appropriate positioning of TKA components therefore is a key concern of surgeons. However, obtaining neutral alignment can be challenging in patients with substantial preoperative varus deformity and it is unclear whether residual deformity influences revision rates.

QUESTIONS/PURPOSES

We asked: (1) in patients with preoperative varus deformities, does residual postoperative varus limb alignment lead to increased revision rates or lower IKS scores compared with correction to neutral alignment, (2) does placing the tibial component in varus alignment lead to increased revision rates and lower IKS scores, (3) does femoral component alignment affect revision rates and IKS scores, and (4) do these findings change in patients with at least 10° varus alignment preoperatively?

PATIENTS AND METHODS

From a prospective database, we identified 553 patients undergoing TKAs for varus osteoarthritis. Patients were divided into those with residual postoperative varus and those with neutral postoperative alignment. Revision rates and International Knee Society (IKS) scores were compared between the two groups and assessed based on postoperative component alignment. Survival analysis was conducted with revision as the endpoint. The analysis was repeated in a subgroup of patients with at least 10° preoperative varus. Minimum followup was 2 years (median, 4.7 years; range, 2-19.8 years).

RESULTS

The two groups had similar survival rates to 10 years and similar IKS scores. Varus tibial component alignment and valgus femoral component alignment were associated with lower mean scores. Revision rates and scores were similar in a subgroup of patients with substantial preoperative varus.

CONCLUSIONS

Our data suggest residual postoperative varus deformity after TKA does not increase survival rates at medium-term in patients with preoperative varus deformities, providing tibial component varus is avoided. Tibial component varus negatively influences IKS score.

LEVEL OF EVIDENCE

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

Quantification of the difference between 3D CT and plain radiograph for measurement of the position of medial unicompartmental knee replacements

The aim of this study was to quantify the differences in measurements obtained from 3D Computed Tomography and plain radiograph, for the positioning of the tibial component of the Oxford unicompartmental knee replacement. Post-operative 3D Computed Tomography data and plain radiographs (long antero-posterior (AP) and short lateral) were obtained for 28 knees of patients who had undergone medial unicompartmental knee replacement. Parameters of the orientation/positioning of the tibial component: Varus/valgus, posterior tibial slope and rotation were measured with both modalities. Bland-Altman plots were used to calculate the 1.96 standard deviation limits of agreement (LOA) between imaging modalities. Intra class correlation was used to assess inter-method and inter-rater reliability (>0.81 = very good reliability). Radiographs were less reliable in all parameters, when compared with 3D CT (intra class correlation coefficients: tibial rotation 0.94 vs 0.96, varus/valgus 0.76 vs 0.94, and posterior tibial slope 0.82 vs 0.92). The LOA were -4.9° to 3.4° for varus/valgus (bias -0.7°, one third >3° different); -4.9° to 0.1° for posterior tibial slope (bias -2.4°, one third >3° different); and -20.6° to 16.1° for rotation (bias -2.2°, one third >10° different). There was some disagreement between measurement by 3D Computed Tomography and plain radiograph for all three parameters of tibial component orientation, especially tibial rotation. This will be particularly relevant to research into the relationship between the accuracy of implant positioning/orientation and patient satisfaction/implant survival rates. This method offers a more reliable standard for the reporting of knee arthroplasty.

Plain radiograph fails to reflect the alignment and advantages of navigation in total knee arthroplasty

The study purposed to determine if a navigation in total knee arthroplasty (TKA) leads to accurate limb alignment and component position than the conventional technique as measured by full length standing radiographs and to evaluate the correlation between navigation and radiographic measurements. A total of 160 knees underwent navigation (n = 80) or conventional (n = 80) TKAs. The frontal femoral alignment was more accurate in navigation TKAs, whereas mechanical axis and frontal tibial alignment were similar in both techniques. Although the intraoperative navigation alignment showed no outliers, postoperative radiographic measure resulted as much as 20% of outliers, and there was no correlation between the two measurements. This lack of correlation and inherent limitations in measuring TKA alignment may bring to question if plain radiograph are useful to determine if alignment achieved by navigation is accurate.

Do residents perform TKAs using computer navigation as accurately as consultants?

The implantation of a total knee arthroplasty (TKA) is a milestone in a resident's surgical training. Studies demonstrate higher loosening rates after TKA by inexperienced surgeons. Alignment outliers should be avoided to achieve a long implant survival. Therefore, our study questioned whether residents implant knee prostheses using computer navigation as accurately as experienced consultants. The data for 662 consecutive TKAs were analyzed retrospectively. The operations were performed by 4 consultants (n=555) and 5 residents under supervision by a consultant (n=107). Cutting errors were recorded from the navigation data. The postoperative mechanical axis and operation time were recorded. Operation time was significantly prolonged if residents performed the operation vs consultants (139 vs 122 minutes, respectively). The analysis of cutting errors within each surgeon's first 20 navigated operations resulted in no significant difference between residents and consultants. During the subsequent operations, a trend toward a more accurate placement of the prosthesis was detected for consultants. The rate of outliers with a mechanical axis deviation >2° was low and did not significantly differ between residents and consultants (3.7% vs 2.3%, respectively). Our study shows that residents implant their first TKA using computer navigation as accurately as experienced consultants. However, the residents' operations take longer and therefore incur additional costs for the teaching clinic.

Reliability of computer-assisted surgery as an intraoperative ruler in navigated high tibial osteotomy

BACKGROUND

Computer-assisted surgery (CAS) can act as an intraoperative ruler in high tibial osteotomy (HTO) to visualize continuously the leg during surgery.

QUESTIONS

The aim of the study is to evaluate the accuracy of CAS with respect to preoperative planning and postoperative deviation from the planned leg axis in HTO. In addition, the influence of surgeon experience as well as operation time and perioperative complications are analyzed.

METHODS

A prospective multicenter study case series with follow-up at 6 weeks was performed in six centers. Medial open-wedge HTO with Tomofix(®) was done using computer assisted navigation technique with the Brainlab VV Osteotomy 1.0 module.

RESULTS

Fifty-one patients with medial gonarthritis were treated with navigated HTO. The follow-up rate was 98%. The majority of HTO-CAS patients fell within the tolerated limit of ±3° for leg axis deviation, however, seven patients were reported with deviations outside of this range: three patients had deviations of >3°-4.5° and four patients >4.5°, respectively. Eight intraoperative complications were documented, partially resulting from technical problems associated with the navigation system. During the 6-week follow-up period, three postoperative complications were experienced, all not associated with navigation technology.

CONCLUSIONS

In about 85% of cases, a perfect result in terms of deviation of the planned mechanical leg axis could be achieved. Computer assistance in HTO proved to be a helpful tool regarding intraoperative control of leg axis.

LEVEL OF EVIDENCE

Level I, High quality prospective study (all patients were enrolled at the same preoperative planning point with ≥80% follow-up of enrolled patients).

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.

Functional outcome after computer-assisted versus conventional total knee arthroplasty: a randomized controlled study

Despite the frequent use of computer-assisted total knee arthroplasty (TKA) and better radiological results for coronal alignment reported in many studies, there is still no evidence of improved clinical outcomes when compared to conventional TKA. We compared alignment after navigated TKA and conventional TKA in 80 randomized patients. Seventy three patients were available for physical and radiological examination at 20 month after surgery. Both groups showed similar Knee Society Score results, with medians of 89 points (navigated 49-95 points, conventional 48-95 points, n.s.) in the Knee Score and 70 points (navigated 45-100 points, conventional 40-100 points, n.s.) in the Function Score. The median improvement in the Knee Society Knee Score was 45 points (-3 to 88 points) in the navigated group and 35 points (-13 to 62 points) in the conventional group (P = 0.03), and the Knee Society Function Score improvement was 15 points (-10 to 50 points) in the navigated group versus 10 points (-10 to 50 points) in the conventional group (n.s.). The current health state at follow-up using the EuroQuol questionnaire was similar in both groups, with medians of 67 points in the navigated group and 65 points in the conventional group. This investigation did show slightly greater functional improvement at short-term follow-up in the navigated TKA group. Longer follow-up will be required to assess the possible benefit of computer-assisted navigation.

Novel approach to reducing discrepancies in radiographic and navigational limb alignments in computer-assisted TKA

This study was conducted (1) to document discrepancies between preoperative and postoperative radiographic measurements and postregistration and postimplantation intraoperative navigational measurements of coronal limb alignments, and (2) to identify predictors of discrepancies between radiographic and navigational measures. In addition, we propose the use of a novel radiographic measuring method, and we demonstrate that this method reduces discrepancies. For 107 total knee arthroplasties performed using a navigation system, coronal alignment were assessed using preoperative and postoperative whole limb radiographs using the standard and novel radiographic methods. During surgery, coronal limb alignment was measured using the navigation system postregistration and postprosthesis implantation. Strengths of correlations and discrepancies between radiographic and navigational assessments were compared between the standard and novel methods. Multivariate regression was performed to identify predictors of discrepancies. Differences between radiographic and navigational measurements were observed for both preoperative and postoperative assessments, but discrepancies were greater for preoperative assessments, despite their stronger correlations. Extent of preoperative varus deformity was identified as the strongest predictor of discrepancy in preoperative radiographic and navigational measurements, and varus malalignment was identified as the strongest predictor of discrepancy in postoperative measurements. Strengths of correlations between radiographic and navigational measurements were similar for the standard and novel radiographic methods, but discrepancies between the 2 were significantly smaller for the novel method for both preoperative and postoperative assessments. The authors propose the use of the described novel radiographic method that reduces discrepancies between radiographic and navigational measurements.

Correlation of radiographic and navigated measurements of TKA limb alignment: a matter of time?

Valid and reproducible measurements of limb alignment are prerequisites for planning, performing and evaluating TKAs. Although navigation systems have been shown to be reproducible tool for intraoperative TKA alignment measurements, particular doubt has been raised on the correlation with postoperative radiographic measurements. The aim of the present study was to evaluate whether the association of postoperative radiographic and navigation measurements of limb alignment was dependent on the time of acquisition. For this purpose, we retrospectively compared two groups of patients who underwent computer-assisted cemented TKA for osteoarthritis of the knee. Intraoperative navigation measurements (OrthoPilot™, Aesculap, Tuttlingen, Germany) were recorded before any cuts were made and again after implants had been placed. Long leg standing radiographs were acquired preoperatively in both the groups and either 2 weeks or 3 months postoperatively and AP limb alignment measurements were correlated with those of the respective navigation assessments. Preoperative deformity was similar in both the groups and correlation between radiographic and navigation measurements was excellent in both groups (ρ = 0.845 and 0.945, respectively). However, both mean and maximum discrepancies between radiographic and navigation measurements of leg alignment were significantly larger when radiographs were obtained 2 weeks (2.6° ± 2.1°, max. 10°) when compared with 3 months (1.8° ± 1.4°, max. 5°) postoperatively (P = 0.026). Accordingly, correlation between radiographic and navigation measurements was poor when radiographs were obtained 2 weeks postoperatively (ρ = 0.26, n.s.) but in the range of preoperative assessments when obtained 3 months postoperatively (ρ = 0.841, P < 0.001). Radiographic and navigation measurements of TKA limb alignment correlate well preoperatively. Equally good correlations can only be achieved when postoperative radiographic measurements are delayed to a time when more patients achieve full or near-full extension and are able to bear full weight leading to more valid radiographs.

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

High tibial osteotomy (HTO) is an established treatment option for isolated medial osteoarthritis in young and active patients. One important factor for success of this procedure is the degree of correction of the weight-bearing line. Computer-assisted navigation systems are believed to improve the precision of axis correction through intraoperative real-time monitoring. This study investigates the precision of correction of the weight-bearing line in open-wedge HTO with and without a navigation system.

Nineteen legs of well-preserved human cadaver were randomly assigned to navigated (n = 10) or conventional (n = 9) HTO. In order to achieve a sufficient amount of correction in all legs the weight-bearing line was aimed at 80 percent of the width of the tibial plateau.

The mean deviation of the weight-bearing line from the desired 80 percent was 1 percent in the navigated and 8.6 percent in the conventional operated legs (p = 0.002). The weight-bearing line of all navigated but only 5 of the 9 conventional operated legs was within a ± 5 percent tolerance level (p = 0.33).

Navigated open-wedge HTO achieved better correction of the weight-bearing line than the conventional method in human cadaver legs. Future studies have to prove this advantage in a clinical setting and it's effect on patient outcome.

Navigation-assisted minimal invasive total knee arthroplasty in patients with extra-articular femoral deformity

In the presence of extra-articular femoral deformity, total knee arthroplasty (TKA) is difficult to perform because of altered anatomical axis and distorted landmarks. Although minimal invasive surgery (MIS) has known advantage of earlier rehabilitation, MIS with this deformity may have higher incidence of component malposition due to inadequate exposure. Navigation has been shown to increase the accuracy of alignment and may compensate possible complication of MIS. We report 4 cases with extra-articular femoral deformity that underwent MIS-TKA using an image-free navigation system in which preoperatively planned mechanical alignment was surgically achieved with proper positioning of the implants as well as soft tissue balance. Navigation-assisted MIS-TKA may become a valuable mean especially for a patient with a deformed femur in which conventional instruments are difficult to use correctly.

Future directions in knee replacement

The use of artificial joints for the treatment of osteoarthritis is expected to expand considerably over the next decade. While newer technologies can offer yet further improvements in total knee systems, implementation will be strongly affected by the need to satisfy apparently competing requirements. Patients expect quicker rehabilitation, improved performance, and lifelong durability; on the other hand, economic constraints require a reduction in cost for each procedure, as well as early intervention and preventative measures, while there is increased pressure from health care systems to use evidence-based medicine as the standard of choice for implants and techniques. The success of a knee replacement depends on the design itself, the surgical technique, the rehabilitation, and, not least, the patient. The major goal of the implant design can be redefined as a restoration of normal knee mechanics, whether by maximum preservation of tissues, or by guiding surfaces that replace their function. Surgical technique needs to be less invasive but achieve optimal patient-specific alignment and soft tissue balancing. Rehabilitation procedures must achieve the expectations of realistic patients. Testing and evaluation methods need to be upgraded for enhanced predictability. This paper discusses current trends and future possibilities to address this expansive scope of design criteria.

Computer assistance increases precision of component placement in total knee arthroplasty with articular deformity

BACKGROUND

The accuracy of computer navigation applied to total knee arthroplasty (TKA) in knees with severe deformity has not been studied.

QUESTIONS/PURPOSES

The purpose of this study was to compare the radiographic alignment achieved in total knee replacements performed with and without navigation and to search for differences in the final alignment of two groups of patients (with and without previous joint deformities) using the same system of surgical navigation.

METHODS

The first series comprised 40 arthroplasties with minimal preoperative deformity. In 20 of them, surgical navigation was used, whereas the other 20 were performed with conventional jig-based technique. We compared the femoral angle, tibial angle, and femorotibial angle (FTA) by performing a post-TKA CT of the entire limb. In the second series, 40 additional TKAs were studied; in this case, however, they presented preoperative deformities greater than 10 masculine in the frontal plane.

RESULTS

The positioning of the femoral and tibial component was more accurate in the group treated with surgical navigation and FTA improvement was statistically significant. When comparing the results of both series, FTA precision was always higher when using computer-assisted surgery. As for optimal FTA, data showed the use of surgical navigation improved the results both in the group with preoperative deformity greater than 10 degrees in the frontal plane and in the group with minimal preoperative knee deformity.

CONCLUSIONS

Surgical navigation obtains better radiographic results in the positioning of the femoral and tibial components and in the final axis of the limb in arthroplasties performed on both deformed and more normally aligned knees.

LEVEL OF EVIDENCE

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

What should be considered in using standard knee radiographs to estimate mechanical alignment of the knee?

OBJECTIVE

Anatomical tibiofemoral angle (anatomical TFA) of the knee measured on standard knee radiographs is still widely used as proxy for mechanical tibiofemoral angle (mechanical TFA), because of the practical and economic limitations in using full-limb radiographs. However, reported differences between anatomical and mechanical TFAs show wide variations. The first aim of this study was to determine whether gender, the presence of advanced osteoarthritis (OA), and history of total knee arthroplasty (TKA) influence the differences between anatomical and mechanical TFAs. The second aim was to identify anatomical features that cause divergences between anatomical and mechanical TFAs, and the final aim was to determine whether anatomical TFA measured using reference points more distant from the knee provides more accurate estimates of mechanical TFA.

DESIGN

In 102 knees with advanced OA before and after TKAs and 99 control knees with no/minimal OA, we assessed the differences between two anatomical TFAs, namely, anatomical TFA1 and anatomical TFA2, which were based on conventional or more distant proximal and distal reference points on standard knee radiographs, respectively, and the mechanical TFA measured on full-limb radiographs. These differences were investigated for women vs men, no/minimal OA vs advanced OA, and for knees before vs after TKA. Regression analyses were performed to determine associations between femoral and tibial anatomical characteristics and the differences between mechanical and anatomical TFAs.

RESULTS

The OA group showed significantly greater differences between mechanical and anatomical TFAs than the control group for both genders. In OA and TKA group, women were more likely to have greater mean differences between mechanical and anatomical TFAs than men. However, TKA did not significantly affect these differences. Femoral and tibial bowing angles, particularly of the femur, were found to be the major contributors to divergences between mechanical and two anatomical TFAs. Furthermore, anatomical TFA2 was found to provide more accurate estimates of mechanical TFA.

CONCLUSIONS

We found that the differences between mechanical and anatomical TFAs depend on gender and the presence of advanced OA, but not on a history of TKA. These findings indicate that prediction of mechanical TFA based on anatomical TFA is dependent on study population characteristics. This study also shows that the presence of lateral bowing of the femur is a major cause of mechanical TFA to anatomical TFA variations associated with gender and advanced OA. To reduce the adverse effects of anatomical variations on estimations of mechanical TFA based on an anatomical TFA method, more distant proximal and distal reference points are recommended to determine anatomical TFA value on standard knee radiographs.

Execution accuracy of bone resection and implant fixation in computer assisted minimally invasive total knee arthroplasty

While computer assisted total knee arthroplasty (TKA) has been documented to increase the surgical accuracy in the planning process, there is little information about the accuracy in execution processes. We aimed to determine the accuracy of execution processes for bone resections and implant fixation in TKAs performed with the techniques of computer assisted navigation and minimally invasive surgery. Execution deviations, defined as the differences between planned targets and executed results, were evaluated for bone resections and implant fixation in 107 TKAs. In tibia resection, the mean resection thickness, coronal alignment, and sagittal alignment were 0.2mm smaller, 0.3 degrees more valgus, 0.3 degrees less posterior slope than the planned, respectively. In femur resection, the mean resection thicknesses in the medial and lateral femoral condyles, coronal alignment, and sagittal alignment were 0.6mm smaller, 0.8mm smaller, 0.1 degrees more varus, and 0.7 degrees less posterior slope than the planned, respectively. In implant fixation, the mean coronal alignment and degree of extension was 0.7 degrees more valgus and 1.6 degrees decrease than the planned, respectively. Only the occurrence of unacceptable executions in implant fixation had significant effects on the final coronal alignment. The density of a bone and the quality of saw blade had significant effect on the accuracy of bone resections. Execution deviations from planned alignment commonly occur in computer-assisted minimally invasive TKA, resulting typically from the techniques of bone resections and implant fixation, and this information should be considered to improve the surgical accuracy of navigated TKAs.

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

Objective

High tibial osteotomy (HTO) is one treatment option for young and active patients with unicompartmental osteoarthritis. The success of this procedure substantially depends on the degree of correction of the mechanical axis. Computer-assisted navigation systems are believed to improve the precision of axis correction through intraoperative real-time monitoring. This study investigates the accuracy of limb alignment measurements with a navigation system on a cadaver specimen.

Materials and methods

The measurements were performed on a well-preserved cadaver specimen with a mechanical leg axis of 4° varus. Data was collected during the HTO workflow. Repeated serial measurements were undertaken by four different surgeons. After these measurements, different landmarks were deliberately set at the wrong place to examine the influence of mistakes during registration.

Results

There was a high intra-and interobserver reliability with a mean mechanical leg axis of 3.9° ± 0.7° and a mean error of 0.6°. The grossly incorrect placement of landmarks for knee and ankle center resulted in an incorrect mechanical leg axis of 1° valgus up to 10° varus.

Conclusion

The computer-assisted navigation system provided precise information about the mechanical leg axis, irrespective of the observer's experience.

Reliability of leg alignment using the OrthoPilot system depends on knee position: a cadaveric study

Despite the increase in clinical use of navigation systems in total knee arthroplasty, few studies have focused on the reproducibility of these systems. The aim of the present study was to assess the influence of knee position and observer experience on intra- and inter-observer agreement in limb alignment assessment with the OrthoPilot system. Limb alignment in the coronal plane and extension range of the knee were assessed in four embalmed cadaveric specimens by five independent observers and measurements were repeated four times to determine intra- and inter-observer agreement, expressed as intraclass correlation coefficients (ICCs). Additionally, navigation results were compared against figures from conventional measurement of leg alignment (ground truth). Intra- and inter-observer agreements were excellent for assessing the extension range (ICC, 0.97 and 0.95) and the coronal femuro-tibial axis in knee extension (ICC, 0.92 and 0.88) but were generally worse in knee flexion (ICC, 0.62 and 0.55). There was an increased tendency of intraobserver errors in observers with less clinical experience. Mean correlation with conventional measurements was fair (Spearman's rho 0.61). The OrthoPilot system showed excellent reproducibility for assessment of extension range and coronal limb alignment. However, assessments of coronal limb alignment in flexion were prone to error and caution should be taken when relying on these measurements.