Is radiographic measurement of distal femoral torsion reliable?

Concordance in Radiological Parameters of Different Knee Views After Total Knee Arthroplasty

Background Total knee arthroplasty (TKA) is a cost-effective treatment for the end-stage of knee osteoarthritis. Despite the improvements in this surgery, a significant percentage of patients still report dissatisfaction after knee arthroplasty. Radiological results have been used to predict clinical outcomes and satisfaction after knee replacement. This study aims to evaluate the concordance of a set of radiographic views to assess alignment on total knee arthroplasty. Methods A concordance study was designed with 105 patients (130 TKA) that underwent conventional total knee arthroplasty cruciate-retaining design recruited for the study and scheduled for their annual radiograph control. Measurements were performed on the following radiograph after total knee replacement: full-length standing anteroposterior and lateral radiograph, anteroposterior standing, lateral and axial knee view, and the knee "seated view". A musculoskeletal radiologist and a knee surgeon were recruited to perform the radiological measurement and then estimate the interobserver agreement.  Results There was an excellent correlation between Limb Length (LL), Hip-knee-ankle angle (HKA), Sagittal mechanical tibial component alignment (smTA), extension lateral and medial joint space (eLJS and eMJS), 90º flexion lateral and medial joint space (fLJS and fMJS) and Sagittal anatomic lateral view tibial component alignment (saLTA); the good correlation between Mechanical lateral femoral component alignment (mLFA), Sagittal anatomic tibial component alignment (saTA), Sagittal anatomic lateral view femoral component alignment 2 (saLFA2), Patella Height (PH); and moderate to poor correlation for the rest of measurements. Conclusion Excellent and good concordance can be achieved for radiographic measurements in different knee views to assess results after TKA. These findings must encourage future studies to address functional and survival outcomes using all knee views and not just one plane.

A Protocol to Systematic Radiographic Assessment of Primary Total Knee Arthroplasty

Although total knee arthroplasty (TKA) is considered one of the most successful procedures, however, a subset of patients are unsatisfied with the results, even with the introduction of new technologies and implant designs. Radiological assessment of TKA is still considered the most prevalent imaging modality for evaluating the knee joint pre-and postoperatively. Assessment of various angles and indices which could be measured in different radiographic views of the knee provides valuable information about the alignment of the entire limb and the individual prosthetic components, more so in the light of recent nuanced concepts of technique, alignment, and balance. This review article aims to present a comprehensive yet systematic approach to the most useful radiographic parameters for assessing the knee preoperatively and post-TKA by explaining the tools and techniques used for measuring various angles, indices and ratios in the coronal, sagittal and axial planes for diagnosis, preoperative planning, postoperative assessment, and routine follow-up. The protocol we followed in this review entailed first reporting the possible applications and software which could help in measuring these variables, then we mentioned the required series of knee radiographs. For the desired variables, we divided the assessment according to each plane, and in each, we reported the optimum position of the desired radiographic view followed by determining the axis and lines which will later form the desired angles to be measured; finally, we collected all the measurements in a table with the native knee values and the most accepted values after TKA.

Intra- and postoperative assessment of femoral component rotation in total knee arthroplasty: an EKA knee expert group clinical review

PURPOSE

Malrotation of the femoral component after primary total knee arthroplasty (TKA) is one of the most important problems leading to painful TKA requiring revision surgery.

METHODS

A comprehensive systematic review of the literature was performed to present current evidence on how to optimally place the femoral component in TKA. Several landmarks and techniques for intraoperative determination of femoral component placement and examination of their reliability were analyzed.

RESULTS

2806 articles were identified and 21 met the inclusion criteria. As there is no unquestioned gold standard, numerous approaches are possible which come along with specific advantages and disadvantages. In addition, imaging modalities and measurements regarding postoperative femoral component rotation were also investigated. Femoral component rotation measurements on three-dimensional (3D) reconstructed computerised tomography (CT) images displayed intraclass correlation coefficients (ICC) above 0.85, significantly better than those performed in radiographics or two-dimensional (2D) CT images. Thus, 3D CT images to accurately evaluate the femoral prosthetic component rotation are recommended, especially in unsatisfied patients after TKA.

CONCLUSION

The EKA Femoral Rotation Focus Group has not identified a single best reference method to determine femoral component rotation, but surgeons mostly prefer the measured resection technique using at least two landmarks for cross-checking the rotation.

LEVEL OF EVIDENCE

III.

Evaluating distal femoral torsion and posterior condylar line reliability for adjusting femoral component rotation in TKA, Egyptian population radiographic study

BACKGROUND

Femoral component rotational alignment is critical for successful TKA. The primary study objective is to measure the preoperative distal femoral torsion (DFT) of an Egyptian patient's cohort using a seated posteroanterior (PA) knee radiograph. The secondary objectives are to check the intraoperative reliability of using the posterior condylar line (PCL) as a reference for rotation and to measure postoperative component rotation using the same radiographic technique.

METHODS

100 arthritic knees, 22 males, 78 females, 95 Varus and five valgus. A long anteroposterior radiograph [Hip to knee to ankle (HKA)] for coronal alignment assessment, and the anatomical posterior condylar angle (aPCA) between the anatomical transepicondylar axis (aTEA) and the PCL was measured in the seated PA knee radiographs for evaluating the DFT and component rotation. Intraoperative rotation was adjusted to 3° external rotation to the PCL.

RESULTS

HKA improved from a preoperative mean 170.4° ± 6.2 to a postoperative mean 178.3° ± 1.5 (p < 0.005). DFT was internal in all knees; the mean aPCA was -4.5 ± 2.4 (0° to -9°), femoral component rotation significantly changed to a mean aPCA of -3.6 ± 2.3 (0° to -7°) (p = 0.005). Acceptable intraoperative patellar tracking in 94%, and patellar subluxation needed a lateral retinacular release in 2% (two valgus knees). The preoperative DFT was not affected by sex or direction of coronal deformity; more external DFT noticed in severe varus deformity.

CONCLUSIONS

All keens had an internal DFT not affected by sex, or coronal deformity direction. Using PCL as a guide to adjust femoral component rotation is a valid technique in our population.

Is distal femoral torsion the same in both of a patient's legs? Morphometric CT study

INTRODUCTION

The rotational position of the femoral component is a primary driver of success in total knee arthroplasty. However, distal femoral torsion (DFT) varies greatly between individuals. Measuring DFT preoperatively by CT in combination with computer-assisted surgery can significantly improve the rotational positioning of the femoral component. However, a preoperative CT scan is costly and exposes the patient to radiation. These are doubled when the patient is undergoing bilateral arthroplasty. The aim of this study was to determine the DFT in both knees of a patient undergoing bilateral arthroplasty. We hypothesized that DFT was symmetric between a patient's two knees and was independent of frontal alignment.

MATERIAL AND METHODS

In this retrospective study of TKA cases performed between December 2008 and March 2015, 82 patients (mean age 73years) who underwent two-stage bilateral TKA (164 knees) were included. A preoperative CT scan of each knee was performed to measure the DFT using the surgical posterior condylar angle (PCA) described by Yoshioka. Two observers performed the measurements twice each, to allow calculation of the intraclass and interclass correlation coefficients.

RESULTS

The mean PCA was 5.4° (±1.48) in the right knee and 5.4° (±1.45) in the left knee, with a left/right difference ranging from 0 to 2.2° (p=0.8). In the entire cohort, 84.6% of patients had a left/right difference of less than 1°. We found no significant differences in DFT in knees with large or small frontal deformity (deformity<10°, p=0.7; deformity>10°, p=0.5) or the presence of varus or valgus (p=0.9). The intraclass correlation coefficient was excellent (94%) and the interclass correlation coefficient was moderate to good (60% for left knees, 53% for right knees).

DISCUSSION

Based on CT scan measurements, the DFT in both knees of an arthritic patient is comparable and this measurement is reproducible. This means that a single, unilateral preoperative CT scan is sufficient for planning purposes.

LEVEL OF EVIDENCE

IV (retrospective cohort study).

Partially loaded plain radiographic measurement to evaluate rotational alignment in total knee arthroplasty

PURPOSE

Rotational alignment of prosthetic components after total knee arthroplasty (TKA) is predominantly monitored with computer tomography (CT), for example by relating the anatomical transepicondylar axis (a-TEA) of the native femur to the posterior bicondylar axis of the prosthetic component (PBCA). The purpose of the present study was to portray a reliable, novel plain radiographic method that likewise enables the evaluation of rotational positioning of prosthetic components in TKA. Furthermore, it was intended to evaluate the prosthetic femoro-tibial functional behavior under loaded conditions.

METHODS

Modified plain axial radiographs under partial weight bearing (20 kg) were performed in 63 patients (63 knees) after TKA. On the obtained radiographs, all established, relevant anatomic, and prosthetic axis and angles reflecting the rotational position of the femoral (i.e., a-TEA/PBCA angle) and tibial component were detected twice by two independent examiners with an interval of one month. Additionally, in 14 cases with anterior knee pain after surgery, radiographic results were compared to obtained computer tomography images; intraclass coefficients (ICC's) for intra- and inter-rater reliability were calculated.

RESULTS

All pre-assigned axis and angles could be identified doubtlessly by both examiners in all investigated knees. For all measurements, ICC's for intra-rater and inter-rater reliability ranged from 0.75 to 0.96. The comparison of the radiographic measurements with corresponding CT results (n = 14) revealed no significant differences (p > 0.05). Rotational alignment of the tibial tray in relation to the native tibial bone was not measurable due to display overlaying. Femoro-tibial behaviour of the prosthetic components under partial loading showed a high variability.

CONCLUSION

We were able to establish a new reliable radiographic technique that is able to show the most established and relevant anatomic landmarks and prosthetic axis after TKA to assess the rotational alignment of the prosthetic components in TKA in relation to the distal femur. The evaluation of the femoro-tibal behaviour instead shows a high variability and so far does not allow valid explanatory conclusions.

Pre-operative radiological measurement of femoral rotation for prosthetic positioning in total knee arthroplasty

PURPOSE

This study outlines the benefits of the seated view radiograph of the knee in evaluation of the pre-operative individual distal femoral torsion (DFT) and for the follow-up of the post-operative rotational positioning of the femoral component in total knee arthroplasty.

METHODS

Study on 20 patients who underwent total knee arthroplasty and the correlation between the DFT measured before surgery with this radiology view, the intra-operative external rotation (ER) necessary for the parallel positioning of the femoral component with the transepicondylar axis (TEA) and the post-operative femoral rotational alignment of the prosthesis on the same view.

RESULTS

In 90 % of cases the values of internal DFT were between -1(0) and -8(0), while the mean value of the internal rotation (IR) was -4.45(0). The mean value of the ER applied to the posterior bone resection was 4.25(0) (0(0)-7(0)), showing a statistically significant correlation between the pre-operative measurement and the intra-operative one of the posterior condylar angle (PCA) (r = 0.890, p = 0.000). Residual internal femoral malrotation has been identified in four cases, its mean value being 0.4(0). In three patients the pre-operative value of the PCA was higher than the intra-operative one and an internal malrotation of the post-operative femoral component was observed.

CONCLUSIONS

The results are encouraging for the further use of this pre-operative view with the premises of increasing the accuracy of prosthetic positioning and reducing the mechanical complications.

Cup Implant Planning Based on 2-D/3-D Radiographic Pelvis Reconstruction-First Clinical Results

GOAL

In the following, we will present a newly developed X-ray calibration phantom and its integration for 2-D/3-D pelvis reconstruction and subsequent automatic cup planning. Two different planning strategies were applied and evaluated with clinical data.

METHODS

Two different cup planning methods were investigated: The first planning strategy is based on a combined pelvis and cup statistical atlas. Thereby, the pelvis part of the combined atlas is matched to the reconstructed pelvis model, resulting in an optimized cup planning. The second planning strategy analyzes the morphology of the reconstructed pelvis model to determine the best fitting cup implant.

RESULTS

The first planning strategy was compared to 3-D CT-based planning. Digitally reconstructed radiographs of THA patients with differently severe pathologies were used to evaluate the accuracy of predicting the cup size and position. Within a discrepancy of one cup size, the size was correctly identified in 100% of the cases for Crowe type I datasets and in 77.8% of the cases for Crowe type II, III, and IV datasets. The second planning strategy was analyzed with respect to the eventually implanted cup size. In seven patients, the estimated cup diameter was correct within one cup size, while the estimation for the remaining five patients differed by two cup sizes.

CONCLUSION

While both planning strategies showed the same prediction rate with a discrepancy of one cup size (87.5%), the prediction of the exact cup size was increased for the statistical atlas-based strategy (56%) in contrast to the anatomically driven approach (37.5%).

SIGNIFICANCE

The proposed approach demonstrated the clinical validity of using 2-D/3-D reconstruction technique for cup planning.

Reproducibility of condylar twist angle measurement using computed tomography and axial radiography of the distal femur

INTRODUCTION

It is essential to understand rotational alignment of the distal femur when performing total knee arthroplasty (TKA). Several rotational landmarks including condylar twist angle (CTA) are used for preoperative planning and during TKA. Axial radiography of the distal femur is used for measuring the CTA, and assessing rotational alignment in TKA. The aim of this study was to investigate the reliability and the reproducibility of the CTA using two different methods and evaluate if CTA differed between varus and valgus knees and between normal and osteoarthritic knees.

MATERIALS AND METHODS

CTA were obtained from 144 knees (77 patients) having total knee or hip arthroplasty using computed tomography (CT) and axial radiography. Subjects were divided into five groups based on femorotibial angle (FTA) and into four groups based on the severity of knee osteoarthritis. The intra-observer and inter-observer reliabilities of these methods and inter-method differences were evaluated.

RESULTS

The mean CTA was 7.02° with axial radiography, and 6.87° with CT images. There were no significant differences among the five FTA groups and among the four osteoarthritis groups. In total, intra-/inter-observer, and inter-method intraclass correlation coefficients were substantial or almost perfect in the scoring system of Landis et al. However, discrepancies ≥ 2° between the two methods were observed in more than 20% of knees.

CONCLUSION

The CTA should be reassessed by more than two observers or two methods for precise preoperative TKA planning in cases where it is difficult to identify the bony landmarks for CTA measurements.

LEVEL OF EVIDENCE

Level III.