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

The effect of weight-bearing positions on coronal lower limb alignment: A systematic review

BACKGROUND

The coronal alignment of the lower limb is generally accepted as a major determinant of surgical outcome in total knee arthroplasty (TKA). To achieve the ideal post-operative alignment, surgeons need to be aware of the influence that weight-bearing positions have on the final knee alignment. Therefore, this review aims to define the effect of varying weight-bearing positions on the coronal alignment of the lower limb. We hypothesized that a coronal alignment deformity increases with loading.

METHODS

The PubMed, Medline and google scholar databases were searched systematically in June 2022. Only studies which compared coronal alignment with a standardized radiographic protocol in the single leg, double leg and supine positions were included. To obtain pooled estimates of the effect of different weight-bearing positions, random-effect analysis were fitted using SAS.

RESULTS

Compared to the supine position, double leg weight-bearing positions were found to be associated with a more pronounced varus deformity (mean difference in HKA is 1,76° (95% CI 1,32: 2,21), p < 0.0001)). The mean difference in HKA between double leg and single leg weight-bearing conditions was 1.43° (95% CI (-0,042;2,90), p = 0.0528).

CONCLUSION

The overall knee alignment was found to be influenced by the weight-bearing position. An average difference of 1.76° in HKA-angle was found between a double leg-stance and supine position, tending to increased varus in the former weight-bearing position. It is therefore possible that the deformity could increase by 1.76° if knee surgeons only follow a pre-op planning based on double-leg stance full length radiographs.

Comparison of weight-bearing full-length radiography and three-dimensional computed tomography scan-based models to assess knee joint coronal alignment following total knee arthroplasty

BACKGROUND

The validity of standing long-leg radiography (LLR) - the standard method for evaluating coronal alignment after total knee arthroplasty (TKA) - remains controversial. We evaluated the measurement reliability and validity of LLR following TKA by comparing postoperative radiographs with three-dimensional computed tomography (3DCT) scans of the lower extremities.

METHODS

We retrospectively collected the data of 55 knees from 44 patients who underwent postoperative 3DCT and 5-day and 6-month LLR for coronal alignment evaluation following TKA. The coronal femoral component angle (CFA) and coronal tibial component angle (CTA) were measured using 3DCT and LLR images. Correlations between the hip-knee-ankle angle (HKAA), CFA and CTA were analysed using Pearson's correlation coefficient (PCC); Bland-Altman plots were constructed to assess agreement between 5-day and 6-month radiographic and 3DCT scan measurements.

RESULTS

The mean difference in HKAA between 3DCT, and 5-day and 6-month LLR was 1.3 ± 1° and 1.1 ± 0.7°, respectively. Differences of >1° in HKAA between 3DCT, and 5-day and 6-month LLR were observed in 31 (56.4%) and 28 (50.9%) knees, respectively; differences of >2° in these parameters were observed in 15 (27.3%) and nine (16.4%) knees, respectively. The 3DCT scan and radiograph measurements of HKAA, CFA and CTA were strongly correlated (PCC, 0.81-0.92; P < 0.001). Bland-Altman plot validity was within acceptable limits.

CONCLUSION

LLR shows good reliability and validity for measuring coronal alignment. When comparing 3DCT scans and radiographs, a high number of HKAA values differed by more than 1° and 2°; this indicates that rigorous alignment evaluation requires 3DCT measurements.

False malalignment after computer-navigated total knee arthroplasty

BACKGROUND

Although computer navigation has improved component alignment in total knee arthroplasty (TKA), radiographic outliers are reported with a wide range in literature even using this technique. We hypothesized that the postoperative malalignment after computer-navigated TKA was partially derived from the inherent problems with two-dimensional (2D) measurement such as inaccuracies in measurement due to the knee position during the radiographic examination and the direction of the X-ray beam. We therefore conducted this study to determine how often knees with malalignment on 2D imaging were truly mal-aligned on three-dimensional (3D) reconstructed imaging.

METHODS

Sixty-two computer-navigated primary TKAs performed in 47 patients were included in this study. In all cases, a weight-bearing long-leg radiograph was obtained after TKA. 3D measurements were performed for outliers 2° or more in coronal alignment of the femoral or tibial component.

RESULTS

For the 18 femoral mal-aligned components on 2D imaging, eight (44.4%) were not truly mal-aligned on 3D imaging (P = 0.0014). For the eight tibial mal-aligned components on 2D imaging, all knees (100%) were not truly mal-aligned on 3D imaging (P < 0.0001).

CONCLUSIONS

A considerable number of the false malalignments were included on 2D measurement. Postoperative component alignment in the computer-navigated TKA might be much better than previously reported.

Gradual change in knee extension following total knee arthroplasty using ultracongruent inserts

BACKGROUND

Total knee arthroplasty (TKA) using an ultracongruent (UC) insert is widely performed. Lack of the posterior cruciate ligament or post-cam mechanism is a concern in terms of range of motion. The flexion angle of UC TKA had been well investigated; however, natural history and correlation factors of the postoperative extension angle have not been well documented. This study aimed to investigate time-dependent changes in extension after TKA using UC inserts, and to evaluate factors that correlated with the postoperative extension angle.

METHODS

This study reviewed 388 gap-balanced UC TKAs (331 patients) without hyperextension at navigation and performed between November 2010 and December 2014. The extension angle (a positive number indicates hyperextension) was measured on full-extension lateral radiographs. The extension angles from five days post-operation to final follow-up were investigated. Factors correlated with the postoperative extension angle were evaluated using multiple regression analysis.

RESULTS

Mean follow-up duration was 46.2 months. Until two years, the extension angle gradually increased; mean angles at five days/six months/one year/two years/and final follow-up were: -9.2°/-2.6°/0.6°/1.0°/1.0°, respectively. Female sex (β = -0.15, P = 0.002) and pre-operative hyperextension (β = 0.31, P < 0.001) were associated with postoperative hyperextension deformity.

CONCLUSIONS

Following UC TKA, knees became gradually more extended until two years post-operation. Sex and pre-operative extension angle were predictive factors for the postoperative extension angle following UC TKA.

LEVEL OF EVIDENCE

Level 4, Case series.

Reliability and Validity of the Femorotibial Mechanical Axis Angle in Primary Total Knee Arthroplasty: Navigation versus Weight Bearing or Supine Whole Leg Radiographs

Purpose

To evaluate the reliability and validity of the femorotibial mechanical axis angle from radiographs in the weight bearing (WB) and supine positions compared with navigation-measured values.

Materials and Methods

Sixty-eight cases of navigation-assisted total knee arthroplasty (TKA) were included. The pre- and postoperative whole leg radiographs (WLRs) in WB and supine positions were compared with the initial and final navigation values.

Results

The mean mechanical axis angle from the preoperative WBWLR and navigation were not statistically different (p=0.079) and were correlated strongly with each other (intraclass correlation [ICC], 0.818). However, on postoperative measurements, although the WBWLR and navigation values were not different (p=0.098), they were not correlated with each other (ICC, 0.093). The standard error of measurement was 1.8°±3.6° for the preoperative WBWLR and 2.5°±4.8° for the postoperative WBWLR. The validity that was determined by the Bland-Altman plot was not acceptable for both pre- and postoperative measurements.

Conclusions

The preoperative WBWLR could provide accurate but not precise measurement value of the femorotibial mechanical axis angle for navigation-assisted TKA, and postoperative measurements in navigation were not comparable with radiographic measurements. The lack of agreement was found between the radiographic and navigation measurements of the coronal alignment regardless of pre- or postoperative evaluation although the accuracy was found acceptable.

Level of Evidence

Level 4.

Frontal alignment in total knee arthroplasty. Comparative study between radiographic measurement and surgical navigation

OBJECTIVE

To establish the concordance between angulation of the femoro-tibial mechanical axis measured with x-rays and surgical navigation in both the pre and postoperative period after a total knee arthroplasty (TKA) was implanted.

MATERIAL AND METHOD

Pre and postoperative measurements were analyzed in 88 TKA of the same model and all performed with the same surgical navigation system. The mechanical frontal angle (MFA) and femoro-tibial anatomic angle were measured before and after the TKA. The angulation was digitally measured with a teleradiography. In the navigation, the femoro-tibial angle at rest, forced varus and valgus were registered and the average of these three measurements was calculated.

RESULTS

The mean preoperative MFA measured on the radiograph was 4.55°. The mean of the same angle measured on the postoperative radiograph was 1.72°, (p=0.05). The mean of the MFA measured with navigation before TKA was 3.12° and after the implant with navigation was 0.53 (P=.013). The concordance coefficient between the MFA in teleradiography and in navigation was 0.869 (P<.001) preoperatively and 0.709 postoperatively (P=.017).

CONCLUSIONS

We found a strong concordance between radiographic and surgical navigation measurements of the MFA. This may imply that teleradiography is not necessary when using surgical navigation in TKA.

Do CAS measurements correlate with EOS 3D alignment measurements in primary TKA?

PURPOSE

Objective of this study was to compare intraoperative computer-assisted surgery (CAS) alignment measurements during total knee arthroplasty (TKA) with pre- and postoperative coronal alignment measurements using EOS 3D reconstructions.

METHODS

In a prospective study, 56 TKAs using imageless CAS were performed and coronal alignment measurements were recorded twice: before bone cuts were made and after implantation of the prosthesis. Pre- and postoperative coronal alignment measurements were performed using EOS 3D reconstructions. Thanks to the EOS radiostereography system, measurement errors due to malpositioning and deformity during acquisition are eliminated. CAS measurements were compared with EOS 3D reconstructions. Varus/valgus angle (VV), mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA) were measured.

RESULTS

Significantly different VV angles were measured pre- and postoperatively with CAS compared to EOS. For preoperative measurements, mLDFA did not differ significantly, but a significantly larger mMPTA in valgus was measured with CAS.

CONCLUSION

Results of this study indicate that differences in alignment measurements between CAS measurements and pre- and postoperative EOS 3D are due mainly to the difference between weight-bearing and non-weight-bearing position and potential errors in validity and reliability of the CAS system. EOS 3D measurements overestimate VV angle in lower limbs with substantial mechanical axis deviation. For lower limbs with minor mechanical axis deviation as well as for mMPTA measurements, CAS measures more valgus than EOS. Eventually the results of this study are of clinical relevance, since it raises concerns regarding the validity and reliability of CAS systems in TKA.

LEVEL OF EVIDENCE

IIb.

Measurement of lower limb alignment: there are within-person differences between weight-bearing and non-weight-bearing measurement modalities

PURPOSE

Previous studies have compared weight-bearing mechanical leg axis (MLA) measurements to non-weight-bearing measurement modalities. Most of these studies compared mean or median values and did not analyse within-person differences between measurements. This study evaluates the within-person agreement of MLA measurements between weight-bearing full-length radiographs (FLR) and non-weight-bearing measurement modalities (computer-assisted surgery (CAS) navigation or MRI).

MATERIALS AND METHODS

Two independent observers measured the MLA on pre- and postoperative weight-bearing FLR in 168 patients. These measurements were compared to non-weight-bearing measurements obtained by CAS navigation or MRI. Absolute differences in individual subjects were calculated to determine the agreement between measurement modalities. Linear regression was used to evaluate the possibility that other independent variables impact the differences in measurements.

RESULTS

A difference was found in preoperative measurements between FLR and CAS navigation (mean of 2.5° with limit of agreement (1.96 SD) of 6.4°), as well as between FLR and MRI measurements (mean of 2.4° with limit of agreement (1.96 SD) of 6.9°). Postoperatively, the mean difference between MLA measured on FLR compared to CAS navigation was 1.5° (limit of agreement (1.96 SD) of 4.6°). Linear regression analysis showed that weight-bearing MLA measurements vary significantly from non-weight-bearing MLA measurements. Differences were more severe in patients with mediolateral instability (p = 0.010), age (p = 0.049) and ≥3° varus or valgus alignment (p = 0.008).

CONCLUSION

The clinical importance of this study lies in the finding that there are within-person differences between weight-bearing and non-weight-bearing measurement modalities. This has implications for preoperative planning, performing total knee arthroplasty (TKA), and clinical follow-up after TKA surgery using CAS navigation or patient-specific instrumentation.

LEVEL OF EVIDENCE

III.

[The Berlin diagnostic algorithm for painful knee TKA]

BACKGROUND

Approximately 20% of patients are unsatisfied with their postoperative results after total knee arthroplasty (TKA). Main causes for revision surgery are periprosthetic infection, aseptic loosing, instability and malalignment. In rare cases secondary progression of osteoarthritis of the patella, periprosthetic fractures, extensor mechanism insufficiency, polyethylene wear and arthrofibrosis can cause the necessity for a reintervention. Identifying the reason for a painful knee arthroplasty can be very difficult, but is a prerequisite for a successful therapy.

AIM

The aim of this article is to provide an efficient analysis of the painful TKA by using a reproducible algorithm.

DISCUSSION

Basic building blocks are the medical history with the core issues of pain character and the time curve of pain concerning surgery. This is followed by the basic diagnostics, including clinical, radiological, and infectiological investigations. Unique failures like periprosthetic infection or aseptic loosening can thereby be diagnosed in the majority of cases. If the cause of pain is not clearly attributable using the basic diagnostics tool, further infectiological investigation or diagnostic imaging are necessary. If the findings are inconsistent, uncommon causes of symptoms, such as extra-articular pathologies, causalgia or arthrofibrosis, have to be considered. In cases of ongoing unexplained pain, a revision is not indicated. These patients should be re-evaluated after a period of time.

Inter-observer reliability of measurements performed on digital long-leg standing radiographs and assessment of validity compared to 3D CT-scan

BACKGROUND

Long-leg radiographs (LLR) are often used in orthopaedics to assess limb alignment in patients undergoing total knee arthroplasty (TKA). However, there are still concerns about the adequacy of measurements performed on LLR. We assessed the reliability and validity of measurements on LLR using three-dimensional computed tomography (3D CT)-scan as a gold standard.

METHODS

Six different surgeons measured the mechanical axis and position of the femoral and tibial components individually on 24 LLR. Intraclass correlation coefficients (ICC) were calculated to obtain reliability and Bland-Altman plots were constructed to assess agreement between measurements on LLR and measurements on 3D CT-scan.

RESULTS

ICC agreement for the six observer measurements on LLR was 0.70 for the femoral component and 0.80 for the tibial component. The mean difference between measurements performed on LLR and 3D CT-scan was 0.3° for the femoral component and -1.1° for the tibial component. Variation of the difference between LLR and 3D CT-scan for the femoral component was 1.1° and 0.9° for the tibial component. 95% of the differences between measurements performed on LLR and 3D CT-scan were between -1.9 and 2.4° (femoral component) and between -2.9 and 0.7 (tibial component).

CONCLUSION

Measurements on LLR show moderate to good reliability and, when compared to 3D CT-scan, show good validity.

CLINICAL TRIAL REGISTRATION NUMBER

institutional review board Atrium-Orbis-Zuyd, number: 11-T-15.

LEVEL OF EVIDENCE

Prospective cohort study, Level II.

Intra-operative deviation in limb alignment occurring at implantation in total knee arthroplasty

BACKGROUND

Long-term survival of knee replacement depends on accurate alignment. Despite improvements in cut accuracy mal-alignment of 3° or more is still seen. All methods share common implantation techniques. This study examines the effect of implantation on overall limb alignment relating it to cut alignment and trial alignment.

METHODS

A retrospective review of navigated primary knee replacements was undertaken (n=113). Overall coronal limb alignments for the aggregated cuts, trial and final implanted components were examined.

RESULTS

All 113 knees had coronal aggregated cut alignment within 2° of neutral (range: 2° varus to 2° valgus). With trial components 99 knees (88%) had an overall coronal limb alignment within 2° of neutral (range: 3° varus to 4° valgus). After final implantation 106 knees (94%) were within 2° of neutral (range: 4° varus to 4° valgus). Forty eight knees (42%) showed no alignment deviation occurring between trial and the final implanted prostheses and 16 knees (14%) shoed a deviation of 2° or more. There was a correlation of both aggregated cut (r=0.284, p=0.002) and trial (r=0.794, p<0.001) with final alignment. There was no significant difference between the final alignment and the aggregated cut alignment(mean difference=-0.15°, p=0.254) or trial alignment (mean difference -0.13°, p=0.155).

CONCLUSIONS

Even when the aggregated alignment produced by the bone cuts is accurate, inaccuracy in final alignment can result from the implantation process. It may be productive for surgeons to concentrate on the implantation process to improve alignment and reduce outliers.

Agreement between radiological and computer navigation measurement of lower limb alignment

PURPOSE

Accurate and reproducible measurements of limb alignment are necessary for planning, performing and evaluation of reconstructive knee surgery. Aim of this study was the comparison of the alignment measured on long-leg standing radiographs with the intraoperative data from a navigation system.

METHODS

The records of 135 consecutive patients who received computer-assisted TKA were examined. Technical quality of the long-leg radiographs (LLRs) was classified good, acceptable or poor according to the rotation of the leg. The difference between radiographic and navigation measurements of leg alignment was assessed.

RESULTS

Preoperative LLRs were rated as good 56.3% (71.1% postoperatively), acceptable in 37.0% (20.0% postoperatively) and poor in 6.7% (8.9% postoperatively). The median difference between radiographic and navigation measurements increased with reduced quality of the LLR [good 1.5° (range 0.0°-9.9°), acceptable 2.5° (range 0.0°-15.0°), poor 4.5° (range 0.2°-9.5°)], but not with greater deformity. Median difference between both measurements in good radiographs was 1.7° (range 0.0°-9.9°) preoperatively and 1.2° (range 0.0°-7.0°) postoperatively.

CONCLUSION

Difference between radiographic and navigation measurements of lower limb alignment is low if the LLR are obtained in neutral rotation. Larger differences between both measurements can occur even under these ideal conditions, and it is still unclear which measurement is closer to reality. Therefore, even if a navigation system is used during surgery, long-leg standing radiographs should currently not be abandoned.

LEVEL OF EVIDENCE

III.

Intramedullary control of distal femoral resection results in precise coronal alignment in TKA

INTRODUCTION

There is still a relevant rate of outliers in coronal alignment >3° when the conventional technique is used, potentially accompanied by a poorer long-term clinical outcome and a reduced longevity of the implant. Intraoperative implementation of preoperative planning and above all checking of the bone resections carried out are decisive for reinstating a straight leg axis. Intramedullary control of femoral resection has not been described to date. The objective of this study was to present a new technique for the intramedullary control of femoral resection and the results obtained using this method.

METHODS

All patients who underwent primary total knee arthroplasty with the new intramedullary control of femoral resection were included in this retrospective study. The frequency of the need for correction of the saw cuts was documented. The radiological assessment included pre- and postoperative whole-leg standing radiographs. In the process, the whole-leg axis, AMA, entry point, LDFA and MPTA were evaluated preoperatively. On the postoperative radiographs, the whole-leg axis and the alignment of the femoral and tibial components were evaluated.

RESULTS

One hundred and sixty-two total knee arthroplasties (TKAs) were included in the study. The average age was 68.7 years. The preoperative malalignment was on the average 8.2° ± 4.7° (23.8° varus to 17.3° valgus). The postoperative whole-leg axis was on the average 1.3° ± 1.1° (5.5° varus to 4.3° valgus). The femoral component showed a deviation from the mechanical axis of 0.1° ± 1.2° (4.3° varus to 3.7° valgus) and the tibial component a deviation from the mechanical tibial axis of 0.3° ± 1.2° (4.2° varus to 2.5° valgus).

CONCLUSIONS

The new technique of intramedullary control of distal femoral resection, together with preoperative planning, leads to a precise alignment of the femoral component in the coronal plane. Thus, for the first time, a simple and effective tool for checking distal femoral resection is available for standardized use.

The influence of leg length difference on clinical outcome after revision TKA

BACKGROUND

The purpose of this paper was to document the incidence of leg length changes after revision total knee arthroplasty (TKA) and its effect on clinical outcome.

METHODS

Leg length difference (LLD) was prospectively measured in 85 patients using digital standing full leg radiography before and after revision TKA. Additionally the patient's subjective perception of LLD was assessed postoperatively. Linear regression models were used to study the correlation between each of these parameters and the clinical outcome after 1 year. Clinical outcome was evaluated by means of the Knee Society Score (KSS).

RESULTS

Revision TKA resulted on average in an increased leg length of 5.3 mm. Sixty-five legs (76%) were lengthened with the procedure, 17 (20%) were shortened and three (4%) remained of identical length. Increased leg length after revision was positively correlated with clinical outcome at 3 months (Spearman r=0.22, p=0.044) and 1 year (Spearman r=0.26, p=0.027). The evidence for this correlation remained after correction for age, gender and diagnosis (p=0.012). The most important contributors to improved clinical outcome scores were improved pain score (Spearman r=0.19, p=0.09) and increased stability (Spearman r=0.13, p=0.24), rather than range of motion (Spearman r=-0.02, p=0.85).

CONCLUSIONS

The results from our work indicate that revision TKA tends to lengthen the leg by approximately 5mm. Contrary to what might be expected, leg lengthening after revision TKA is correlated with improved clinical outcome.

LEVEL OF EVIDENCE

Level 2b.

Does the severity of preoperative varus deformity influence postoperative alignment in both conventional and computer-assisted total knee arthroplasty?

PURPOSE

The postoperative alignment was compared according to the severity of preoperative varus deformity in computer-assisted and conventional total knee arthroplasty (CAS-TKA).

METHODS

The study reviewed 127 consecutive CAS-TKA and 236 conventional TKA, retrospectively. In CAS-TKA, 77 knees with a varus deformity ≤15.0° were classified in group CAS-A and 50 knees with a varus deformity >15.0° were classified in group CAS-B. In conventional groups, 204 knees with a varus deformity ≤15.0 were classified in group Conventional-A and 32 knees with a varus deformity >15.0° were classified in group Conventional-B. The postoperative mechanical axis (MA) was compared among groups CAS-A, CAS-B, Conventional-A and Conventional-B.

RESULTS

The average postoperative MA was 0.7° varus in group CAS-A, 2.8° varus in group CAS-B, 1.1° varus in group Conventional-A and 3.2° varus in group Conventional-B (p < 0.001). The postoperative MA was within 3° in 81.8, 62.0, 58.8 and 37.5 % of group CAS-A, CAS-B, Conventional-A and Conventional-B, respectively.

CONCLUSIONS

The severity of preoperative varus deformity influences postoperative alignment despite using CAS. More careful correction of the alignment is required, especially in TKA performed on patients with a greater varus deformity.

LEVEL OF EVIDENCE

III.

The long leg radiograph is a reliable method of assessing alignment when compared to computer-assisted navigation and computer tomography

BACKGROUND

The mechanical alignment of the knee is an important factor in planning for, and subsequently assessing the success of a knee replacement. It is most commonly measured using a long-leg anteroposterior radiograph (LLR) encompassing the hip, knee and ankle. Other modalities of measuring alignment include computer tomography (CT) and intra-operative computer navigation (Cas). Recent studies comparing LLRs to Cas in measuring alignment have shown significant differences between the two and have hypothesized that Cas is a more accurate modality. This study aims to investigate the accuracy of the above mentioned modalities.

METHODOLOGY

A prospective study was undertaken comparing alignment as measured by long-leg radiographs and computer tomography to intra-operative navigation measurements in 40 patients undergoing a primary total knee replacement to test this hypothesis. Alignment was measured three times by three observers. Intra- and inter-observer correlation was sought between modalities.

RESULTS

Intra-observer correlation was excellent in all cases (>0.98) with a coefficient of repeatability <1.1°. Inter-observer correlation was also excellent measuring >0.960 using LLRs and >0.970 using CT with coefficient of repeatability <2.8°. Inter-modality correlation proved to be higher when comparing LLRs and CT (>0.893), than when comparing either of these modalities with Cas (>0.643 and >0.671 respectively). Pre-operative values had the greatest variability.

CONCLUSION

Given its availability and reduced radiation dose when compared to CT, LLRs should remain the mainstay of measuring the mechanical alignment of the lower limb, especially post-operatively.

LEVEL OF EVIDENCE

II.

Influence of navigation system updates on total knee arthroplasty

BACKGROUND

The purpose of this study was to evaluate the influence of image-free computer-assisted navigation system update on outcome in total knee arthroplasty.

METHODS

Thirty-three knees were replaced using the Stryker 3.1 image-free navigation system and 49 knees were replaced using the Stryker 4.0 system. One surgeon took part in all procedures as chief surgeon or first assistant. All patients received the Stryker Scopio NRG CR total knee prosthesis. We compared the accuracy of component positioning measured using radiographs and CT scans, operating time and clinical outcome 1 year after surgery.

RESULTS

The mean hip-knee-ankle, frontal femoral and tibial component angle were 179.8° (ideally implanted 85%), 89.8° (88%), 90.4° (88%) respectively for the 3.1 group and 179.5° (96%), 90.6° (92%), 90.2° (94%) for the 4.0 group. The mean sagittal tibial component angle was 85.5° (82%) for the 3.1 group and 85.6° (92%) for the 4.0 group. The mean rotational femoral and tibial component angle were -0.5° (81%), -0.7° (73%) for the 3.1 group and 0.0° (84%), 0.4° (72%) for the 4.0 group. There were no statistically significant findings with regard to component positioning. Operating time was significantly longer in the 3.1 group (3.1 group: 137 min, 4.1group: 125 min, P < 0.01). No significant difference was detected in postoperative clinical outcome.

CONCLUSION

The navigation system update from Stryker 3.1 to Stryker 4.0 reduced operating time by 12 min. However, there were no statistically significant findings with regard to component positioning and clinical outcome.

Computer-assisted navigation for the intraoperative assessment of lower limb alignment in high tibial osteotomy can avoid outliers compared with the conventional technique

PURPOSE

Longterm outcomes after valgization high tibial osteotomy (HTO) to treat varus osteoarthritis seem to depend mainly on correction precision. Intraoperative assessment of leg alignment based on radiological visualization of the mechanical axis is difficult and its precision is limited. A promising approach to improving precision is to make use of navigation systems. The case-control study reported here involved the evaluation of patients whose varus osteoarthritis had been treated by open-wedge high tibial ostoetomy, and an analysis of the effect of computer-guided navigation on postoperative leg alignment.

METHODS

Forty patients with medial varus osteoarthritis managed by open-wedge high tibial osteotomy using a surgical navigation system were included in the present study (Group 1). They were compared with a retrospective control group (Group 2) of 40 patients with respect to postoperative leg alignment, correlation of planned and definitive correction, and postoperative deviation from the Fujisawa point.

RESULTS

The mean values for planned and definitive correction showed no significant differences for identical demographic data. As a percentage of the width of the tibial plateau the postoperative weight-bearing radiographs showed a mechanical line that intersected with the knee base line at the desired value of 62% (Fujisawa point) in 58.8% (SD ± 6.1) in Group 1 and in 58.6% (SD ± 8.1) in Group 2. Despite similar mean values a significantly higher number of corrections were outside the reference area (n = 7) in the non-navigated group, whereby all corrections were within the desired range in the navigated group. There were no significant differences in operation time.

CONCLUSIONS

This study showed that the use of a navigation system can not increase the precision of the open-wedge HTO procedure in patients with varus osteoarthritis but it can eliminate the outliers of a well defined range.

LEVEL OF EVIDENCE

Case-control study, Retrospective comparative study, Level III.

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.

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.

Preliminary experience with the patient-specific templating total knee arthroplasty

BACKGROUND AND PURPOSE

Patient-specific templating total knee arthroplasty (TKA) is a new method for alignment of a total knee arthroplasty that uses disposable guides. We present the results of the first 40 consecutive patients who were operated on using this technique.

METHODS

In this case-control study, we compared blood loss, operation time, and alignment of 40 TKAs performed using a patient-specific templating alignment technique with values from a matched control group of patients who were operated on by conventional intramedullary alignment technique. Alignment of the mechanical axis of the leg and flexion/extension and varus/valgus of the individual prosthesis components were measured on standing, long-leg, and standard lateral digital radiographs. The fraction of outliers (> 3˚) was determined.

RESULTS

Mean mechanical axis of templating TKAs was 181° with a fraction of outliers of 0.3, and mean mechanical axis of conventional TKAs was 179˚ (outlier fraction 0.5). Fraction of outliers in the frontal plane for femoral components was 0.05 in the templating TKAs and 0.4 in the conventional TKAs, and for tibial components the corresponding values were 0.2 and 0.2. In the templating TKAs and conventional TKAs, fraction of outliers in the sagittal plane was 0.4 and 0.9, respectively, for femoral components and 0.4 and 0.6 for tibial components. Mean operation time was 10 min shorter and blood loss was 60 mL less for templating TKA than for intramedullary-aligned TKAs.

INTERPRETATION

Patient-specific templating TKA showed improved accuracy of alignment and a small reduction in blood loss and operating time compared to intramedullary-aligned TKA, but the fraction of outliers was relatively high. Larger RCTs are needed for further evaluation of the technique and to define the future role of patient-specific template alignment techniques for TKA.

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.

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.