Differences in measurement of lower limb alignment among different registration methods of navigation and radiographs in TKA using the OrthoPilot system

What Is the Correlation between Coronal Plane Alignment Measured on Pre- and Postoperative Weight-bearing Radiographs and Intraoperative Navigation When Stress Is Applied to the Knee?

This study examines the correlation between the weight-bearing (WB) long leg radiograph (LLR)-derived hip-knee-ankle angle (HKAA) and intraoperative supine computer-assisted surgery (CAS)-derived HKAA measurements at the beginning and end of total knee arthroplasty (TKA). The primary aim of the study was to determine if WB alignment could be mimicked or inferred based on intraoperative alignment findings. We conducted a prospective analysis from a cohort of 129 TKAs undergoing a CAS TKA at a single center by a single surgeon. The HKAA was recorded using the CAS navigation system immediately postregistration of navigation data and after implantation of the prosthesis. The intraoperative HKAA was recorded in both the supine "resting" position of the knee and also while the knee was manipulated in an effort to replicate the patient's WB alignment. These measurements were compared with the HKAA recorded on pre- and postoperative WB LLRs. There was a strong correlation between the preoperative WB LLR HKAA and the intraoperative preimplant CAS-derived stressed HKAA (R = 0.946). However, there was no correlation between the postoperative WB LLR HKAA and the postimplant insertion HKAA as measured intraoperatively via CAS for either a "resting" or "stressed" position of the operated knee (R = 0.165 and R = 0.041, respectively). Thus, the interpretation of intraoperative alignment data is potentially problematic. Despite technological advances in the development and utilization of computer navigation and robotics in arthroplasty to help obtain the optimal alignment, it would seem apparent from our study that this alignment does not correlate to upright stance postoperatively. Surgeons should apply caution to the strength of assumptions they place on intraoperative coronal plane alignment findings.

Mechanical Alignment in Knee Replacement Homogenizes Postoperative Coronal Hip-Knee-Ankle Angle in Varus Knees: A Navigation-Based Study

After knee replacement, postoperative lower limb alignment is influenced by the geometry of the prosthesis position and surrounding soft tissue that contributes to the hip-knee-ankle (HKA) angle. The purpose of this study is to determine the dynamic coronal HKA angle after mechanical alignment in total knee replacement using computer navigation. We conducted a pre-post design study of 71 patients with varus osteoarthritic knees on which total knee arthroplasty was performed. The HKA was measured before and at the end of the surgical procedure with the patient in the supine position using a navigation system at 30, 60, and 90 degrees of knee flexion. Postoperative implant position and flexion and extension gaps were assessed. HKA was clustered in three preoperative dynamic patterns (PDPs; Varus-Neutral, Varus-Valgus, and Varus-Varus). There were statistically significant differences in the dynamic coronal HKA between the preoperative and postoperative statuses after mechanically aligned knee replacement (with p < 0.0001) Before the surgical procedure, statistically significant differences were found between patterns at any angle of flexion confirming a well-differentiated preoperative dynamic behavior between the three groups. Postoperatively, 98.6% (71 out of 72) of the knees were within ± 3 degrees of the HKA at full extension. Fifty-eight knees (80.6%) were assessed to a "within-range" postoperative dynamic alignment at any grade of flexion considered. There are differences between the preoperative and postoperative status of the dynamic coronal HKA angle after mechanically aligned knee replacement. We proposed that an excellent dynamic HKA alignment is achieved not only at full extension within the range of 0 ± 3 degrees but also when this alignment is maintained at 30, 60, and 90 degrees.

Accuracy of computer navigation in total knee arthroplasty: A prospective computed tomography-based study

INTRODUCTION

Evidence now exists advocating the use of computer navigation in total knee arthroplasty (TKA). Despite the introduction of new navigation systems into clinical practice no evidence currently exists showing independent verification of their accuracy. The aim of this study was to validate the in vivo accuracy of the Exactech Guided Personalised Surgery (GPS) computer navigation system using a validated computed tomography (CT) measurement of alignment.

METHOD

Consecutive patients who underwent TKA using the GPS Navigation System at our institution were prospectively recruited. Intraoperative parameters of 3D alignment as measured by the GPS navigation system were recorded and compared against the postoperative measurements of alignment measured using the Perth CT Protocol to assess the accuracy of the GPS navigation system.

RESULTS

29 consecutive patients (13 male, 16 female) who underwent TKA were prospectively recruited. Overall, for all measures of 3D alignment the mean difference between intraoperatively recorded and postoperative CT-measured alignment was 1.55° ± 0.22° (95% confidence interval). Individual measurement differences in the femoral prosthesis were: coronal alignment 1.64° ± 0.52°; flexion 2.07° ± 0.55°; rotation 1.38° ± 0.33° Differences in the tibial prosthesis were: coronal alignment 2.03° ± 0.53°; slope 1.14° ± 0.39° The whole limb coronal alignment difference was 2.34° ± 0.83° CONCLUSION: The Exactech GPS Navigation system is very accurate with a high concordance between intraoperative and postoperative measures of alignment and prosthesis positioning. We therefore confidently validate the system and support its continued use in clinical practice. Other navigation systems should undergo a similar validation process.

A whole leg radiograph is not necessary for postoperative determination of the mechanical leg axis after total knee arthroplasty

BACKGROUND

Anteroposterior (AP) whole leg radiographs (WLR) in the standing position for assessment of the mechanical leg axis are generally performed preoperatively for the planning of total knee replacement (TKR) and postoperatively to assess the leg axis. The objective of the present study was to investigate whether, if preoperative WLR are available, postoperative AP standard knee radiographs in the standing position are sufficient for calculating the mechanical leg axis.

METHODS

In the present prospective study, the mechanical and the anatomical leg axes were determined on the basis of WLR from 104 patients prior to implantation of a TKR and the difference was calculated. Twelve weeks postoperatively, standing long AP radiographs and WLR were prepared. In addition, the mechanical axis was calculated by adding the preoperative difference between the anatomical and mechanical axis to the anatomical axis from the postoperative AP radiographs. Accuracy, bias and level of agreement for calculated relative to measured mechanical alignment were determined.

RESULTS

Mean accuracy of calculated mechanical alignment was 0.5° ± 0.4°, and mean bias was 0.0° ± 0.6° (p = 1.00). Bland-Altman analysis revealed a 95% upper and lower level of agreement of - 1.3° and 1.3°, respectively.

CONCLUSION

A preoperative WLR and a postoperative long AP knee standard radiograph are sufficient to determine the mechanical leg axis after TKR. If these are available, it is possible to do without WLR after TKR, particularly since they involve higher radiation exposure, are time-consuming, and are also prone to errors in the first postoperative weeks.

LEVEL OF EVIDENCE

II diagnostic study.

Difference between Mechanical Alignment in Navigation and Scanogram during Total Knee Arthroplasty

Introduction

Malpositioning of the implant results in polyethylene wear and loosing of implant after total knee arthroplasty. Scanogram is often used for measurement of limb alignment. Computer navigation provides real time measurements and thus, the aim is to see any association pre- and postoperatively between coronal alignments measured on scanogram to computer navigation during total knee arthroplasty.

Material and Methods

We prospectively gathered data of 200 patients with advanced degenerative symptomatic arthritis, who were consecutively selected for primary total knee arthroplasty with computer navigation. Every patient's pre- and postoperative scanogram were compared to the intraoperative computer navigation findings.

Results

The results show that the preoperative mean mechanical axis on navigation was 10.65° (SD ± 6.95) and on scanogram it was 10.38° (SD ± 6.89). On the other hand, the mean postoperative mechanical axis on navigation was 0.69° (SD ± 0.87) and on scanogram it was 2.73° (SD ± 2.10). Preoperatively, there was no significant difference (p value = 0.46) between the two. However, the postoperative outcomes suggest that there was a noteworthy difference, with no correlation between the mean Hip-Knee Ankle Axis (HKA) and intraoperative mechanical axis (p value <0.0001).

Conclusion

Postoperative mechanical alignment values after total knee arthroplasty are lower on navigation than measured on standing full length hip to ankle scanogram.

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.

Intra- and post-operative accuracy assessments of two different patient-specific instrumentation systems for total knee replacement

PURPOSE

The aim of this study is to assess and compare the accuracy of two different patient-specific instrumentation (PSI) systems for total knee replacement, both intra-operatively for bone preparation and post-operatively for final component alignment.

METHODS

Twenty-five patients were treated according to a computer tomography (CT)-based PSI system (group A) and 25 to a magnetic resonance imaging (MRI)/X-ray-based system (group B). Alignments on the three anatomical planes and resection thickness at the cutting blocks and at the resulting bone cuts were recorded intra-operatively by a standard surgical navigation system. Alignments of the prosthetic components and mechanical axis were also measured post-operatively on radiographs. These measurements at both the femur and tibia were compared with those of the corresponding pre-operative planning, considering discrepancies larger than 3° as outliers.

RESULTS

In both groups, the mean absolute differences between pre-operatively planned alignments and corresponding intra- and post-operative measurements ranged from a minimum of 1.2° to a maximum of 2.9° in all three anatomical planes. In both groups and in both femur and tibia, the plane with the smallest percentage of outliers was the coronal, maximum 17%. The comparison between two groups was statistically significant (p = 0.02) in the femoral sagittal plane, where group B showed smaller alignment discrepancies at the cutting blocks.

CONCLUSIONS

Both PSI systems showed good alignments in the coronal plane in all stages. For a few measurements, a better performance was observed in the MRI/X-ray-based system than in the CT-based system.

LEVEL OF EVIDENCE

I.

Effect of foot rotation on the mechanical axis and correlation between knee and whole leg radiographs

PURPOSE

The purposes of this study were (1) to evaluate the foot rotational effects on local and whole leg alignment and (2) to confirm the correlation between local and whole leg alignment. The hypotheses of this study were that (1) the alignment would become varus if the rotation of the foot changes from internal to external rotation, and (2) there would be some correlation between local and whole leg radiographs, and local knee radiographs could then be used indirectly for the assessment of whole leg alignment in patients with bilateral medial compartment knee osteoarthritis.

METHODS

A total of 80 lower limbs with genu varum of patients who complained of medial knee pain were examined. The standing anterior-posterior view of whole leg radiographs was taken in the four foot positions, and a custom-made foot plate was used for the attainment of accurate radiographs: feet straight ahead with foot contact at the medial side (R: routine), feet straight ahead at shoulder width (N: neutral), 30° external rotated (ER) and 15° internal rotated (IR) position. In order to obtain a local radiograph of the knee, we took only whole leg radiographs and selected the area of interest on the whole leg radiograph. We evaluated the total width of the tibia plateau (Total), the length of the weight-bearing line, the ratio of weight-bearing line/Total and femorotibial angle (FTA).

RESULTS

The absolute value of weight-bearing line was shifted laterally in the 30° ER position and shifted medially in the 15° IR position compared to the neutral position (1.8 mm lateral and 0.2 mm medial in the WLR; 3.5 mm lateral and 3 mm medial in the local radiograph). Significant statistical differences were observed in the local knee weight-bearing line; however, no significant statistical differences were observed in the weight-bearing line of the whole leg radiograph (n.s.). Results of the % (weight-bearing line/Total) were similar to those of weight-bearing line. The FTA of the local radiograph showed statistical differences, and it showed more valgus in the 30° ER position. In the correlation analysis between whole leg radiograph and local knee radiograph, moderate correlation (correlation coefficient = 0.67) was observed; however, significant statistical differences were observed in the comparison of weight-bearing line and % weight-bearing line/Total (p < 0.01 and < 0.01, respectively) between local knee and whole leg radiograph.

CONCLUSIONS

Foot position of ER could show less varus alignment and the reverse could occur in the IR position, compared to the neutral foot position. The severity of varus alignment could be underestimated in the local radiograph, compared with that of whole leg radiograph.