Interobserver and intraobserver error in distal femur transepicondylar axis measurement with computed tomography

Preoperative planning of total knee arthroplasty: reliability of axial alignment using a three-dimensional planning approach

BACKGROUND

Preoperative templating of total knee arthroplasty (TKA) can nowadays be performed three-dimensionally with software solutions using computed tomography (CT) datasets. Currently there is no consensus concerning the axial orientation of TKA components in three-dimensional (3D) planning.

PURPOSE

To assess intra-/inter-observer reliability of detection of different bony landmarks in planning axial component alignment using axial CT images and 3D reconstructions.

MATERIAL AND METHODS

Intra- and inter-observer reliability of determination of four predefined axial femoral and tibial axes was calculated using data from CT scans. Axes determination was performed on the axial slices and on the 3D reconstruction using preoperative planning software. In summary, 61 datasets were analyzed by one medical student (intra-observer reliability) and 15 datasets were analyzed by four different observers independently (inter-observer reliability).

RESULTS

For the femur, clinical epicondylar axis and posterior condylar axis showed the best reliability with an inter-observer variability of 0.7° and 0.5°, respectively. For the tibia, posterior condylar axis provided best reliability (inter-observer variability: 1.7°). Overall variability was greater for tibial than for femoral axes. Reliability of axis determination was more accurate using axial CT slices rather than 3D reconstructions.

CONCLUSION

The femoral clinical epicondylar axis is highly reliable. Landmarks for the tibia are not as easily identifiable as for the femur. The tibial posterior condylar axis presents the axis with highest reliability. Based on these results, clinical epicondylar axis for orientation of the femoral TKA component and posterior condylar axis for the tibial implant, both defined on axial slices can be recommended.

Gender-Based Quantitative Analysis of the Grand Piano Sign in Mechanically Aligned Total Knee Arthroplasty in Asians

In mechanically aligned (MA) total knee arthroplasty (TKA), the grand piano sign helps surgeons to further ensure the proper external rotation of the femoral component. The goal of this study was to determine the sex-related differences in the shape of the anterior resection surface using 3D magnetic resonance imaging (MRI) models. MRI scans were performed on 267 consecutive patients (202 women and 65 men) with osteoarthritis who underwent TKA in order to reconstruct a 3D model. Virtual anterior condylar resection was performed based on the surgical transepicondylar axis (sTEA), Whiteside's line (WSL), and flexion-extension axis (FEA). On the anterior resection surface, both lateral length (LatL) and medial length (MedL) were measured, and the ratio between the two (MedL/LatL) was calculated. The mediolateral width of the distal femur (ML) and anterior resection surface (M'L') were measured, and the ratio between the M'L' and ML (M'L'/ML) was calculated. Both the lateral deviation (LD) and the ratio between LD and ML (LD/ML) were also determined. Morphological classification of the anterior resection surface was conducted based on the presence of a definite medial peak. When based on the sTEA or WSL, the MedL/LatL of female subjects was significantly greater than that of male subjects (p < 0.001 and p < 0.05, respectively). The MedL/LatL of the FEA was consistently larger than that obtained using the sTEA or WSL. Among female subjects, the MedL/LatL of the sTEA was significantly greater than that of the WSL, although this was not the case in either the total study population or the male subjects alone. When based on the sTEA, the M'L'/ML was statistically greater in the female subjects (p < 0.01). The LD was greater in the male subjects (p < 0.01), but there was no difference between the male and female subjects when comparing the LD/ML (p = 0.93). The proportion of double- and single-peak types was not significantly different between the sexes (p = 0.196). Surgeons should be aware that the shape of the anterior resection surface may differ depending on the sex of the patient. The results of this study provide more consistent surgical outcomes as well as fundamental anatomical data for designing suitable prostheses applicable to the Korean population.

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.

Gender differences exist in rotational anatomy of the distal femur in osteoarthritic knees using MRI

PURPOSE

Optimal rotational alignment of the femoral component is essential for total knee arthroplasty (TKA). The femoral transepicondylar axis (TEA), Whiteside's line (WSL), and posterior condylar axis (PCA) are various intra-operative references that can be used to determine femoral rotation, and each has advantages and disadvantages. This study aimed to define the rotational anatomy of the distal femur and investigate its relationship with gender in osteoarthritic knees.

METHODS

Magnetic resonance imaging (MRI) was obtained from 1522 patients (1298 females and 224 males) with end-stage knee osteoarthritis prior to TKA. MRI was constructed into three-dimensional models. The angles between the TEA and WSL, WSL and PCA, and TEA and PCA were calculated for each patient. In addition, gender differences in femoral rotation were evaluated.

RESULTS

The PCA was 2.2° ± 1.0° internally rotated relative to the TEA. WSL was 1.2° ± 2.8° externally rotated relative to the TEA. The WSL to TEA relationship exhibited greater variability than the PCA to TEA relationship. PCA was more internally rotated and WSL was more externally rotated relative to TEA in female group than male group. Based on the standard reference rules of 3° external rotation from the PCA that has been conventionally used, 15.7% of patients showed external rotation lower 1° or greater than 5° external rotation from the PCA. In the mean external rotation of the TEA from the PCA (2.2°) from this population; however, the percentage of patients showing ± 2° from their TEA dropped to 5.1% of patients.

CONCLUSION

Gender difference and variability exist in distal femoral rotational anatomy. These data can be useful in consideration of femoral anatomy variability and gender difference. The same cutting angle may lead to malrotation of the femoral component.

LEVEL OF EVIDENCE

Consecutive patients, level III.

Femoral Component Axial Rotation in the Gap-Balancing Approach to Total Knee Arthroplasty: Measurement by Computed Tomography

BACKGROUND

Rotational malalignment of total knee arthroplasty (TKA) is a potential cause for revision surgery; therefore, it is important to have valid criteria for evaluation of normal component rotational alignment. Because computed tomography (CT) is considered the most accurate method to assess the rotational alignment of prosthetic components, the objectives in this study were define the femoral component (FC) rotation by measuring the posterior condylar angle (PCA) and the condylar twist angle (CTA) in a patient population that underwent gap-balancing TKA; determine the reliability of the FC rotation by using these measurements; evaluate the inter-relationship between the PCA and CTA; and finally evaluate the frequency and agreement in identification of the medial epicondyle sulcus (MES).

METHODS AND RESULTS

In this retrospective study, 2 radiologists examined 50 CT scans. Mean PCA values of -2.26° and -2.56° (internal rotation) and CTA values of -5.54° and -6.28° (internal rotation) were attained by 2 observers with a higher interobserver concordance for the PCA. Both measurements were considered to be reliable. There was moderate interobserver agreement for MES identification, with the MES present in 64% and 78% of patients, as identified by 2 observers.

CONCLUSION

Mean FC rotation values as evaluated by PCA were -2.26° and -2.56° and as evaluated by CTA were -5.54° and -6.28°. PCA and CTA measurement by CT is reliable; however, the use of PCA is preferable because of the higher observer concordance. PCA can be inferred by subtracting 3° or 4° from the CTA. MES was identified in 64% and 78% of patients, with only moderate interobserver agreement.

Combined Rotational Alignment Change after Total Knee Arthroplasty in Different Tibial Component Designs: Implications for Optimal Tibial Component Rotational Alignment

Purpose

The rotational alignment of the femoral and tibial components is closely related to the results after total knee arthroplasty (TKA). In this study, we measured the combined rotational alignment change (ΔCR) after TKA and compared the different influence of symmetric and asymmetric tibial component designs on the combined rotational alignment.

Materials and Methods

Eighty-four patients (mean age, 67.9 years) were included. A symmetric tibial component was used in 51 knees (group I), whereas an asymmetric tibial component was used in 50 knees (group II). We measured the angles of four anatomical landmarks by using preoperative and postoperative computed tomography images. The combined rotational alignment and the amount of change were calculated. The correlation between the isolated tibial component rotation (ITR) and ΔCR was analyzed by using the Spearman correlation coefficient.

Results

The mean ΔCR was −0.1°±6.3° in group I and −4.8°±5.7° in group II after TKA. Excluding the intercomponent rotation, the change was −1.0°±7.3° and −6.7°±6.7° in group I and group II, respectively. A correlation analysis between the ITR and tibial component rotation relative to the tibial tuberosity showed a statistically significant correlation.

Conclusions

The combined lower limb rotational alignment was internally rotated in both symmetric and asymmetric tibial component designs after TKA. The asymmetric tibial component was better than the symmetric tibial component in achieving internally rotated combined lower limb rotational alignment. The internal rotation of the symmetric tibial component relative to the tibial tuberosity tip should fall within 20° to correct the externally deformed lower limb.

Alignment in knee flexion position during navigation-assisted total knee arthroplasty

PURPOSE

The aim of this study was to demonstrate the lower limb alignment in knee flexion position after navigation-assisted total knee arthroplasty using the gap technique and to identify the correlative factors.

METHODS

One hundred and twenty consecutive osteoarthritic knees (120 patients) were prospectively enrolled for intraoperative data collection. All TKA surgeries were performed using the navigation system (OrthoPilot™, version 4.0; B. Braun Aesculap, Tuttlingen, Germany). Before and after final prosthesis implantation, the lower limb navigation alignment in both knee extension (0°) and knee flexion (90°) position was recorded. The knee flexion alignment was divided into three groups: varus, neutral and valgus alignment. To determine the factors of the alignment in knee flexion position, preoperative demographics, radiologic and intraoperative data were obtained. Pearson's correlation (r) analysis was performed to find the correlation. The Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index were compared between groups.

RESULTS

Although all postoperative extension alignment was within neutral position (between -2° and +2°), postoperative knee flexion alignment was divided into three groups: varus (≤-3°), 24 cases (20 %); neutral (between -2° and +2°), 85 cases (70.8 %) and valgus (≥+3°) alignment, 11 cases (9.2 %). There were a good correlation of alignment in knee flexion position with the rotation of femoral component relative to posterior condylar axis (r = -0.502, p = 0.000) and weak correlations with posterior femoral cut thickness (lateral condyle) (r = 0.207, p = 0.026), medial flexion (90°) gap after femoral component rotation adjustment (r = 0.276, p = 0.003). Other variables did not show correlations. There were no statistical clinical differences between varus, neutral and valgus knee flexion alignment groups.

CONCLUSION

About 30 % of the cases showed malalignment of more than 3° in knee flexion position although with neutral alignment in extension position. The knee flexion alignment had a good correlation with the rotation of femoral component relative to posterior condylar axis. Neutral alignment in knee flexion position may be adjusted by femoral component rotation especially by the use of navigation system.

LEVEL OF EVIDENCE

IV.

Reproducibility of digital measurements of lower-limb deformity on plain radiographs and agreement with CT measurements

INTRODUCTION

Five angles (HKA, HKS, alpha, beta, tibial slope) are used for goniometry in total knee arthroplasty. The reproducibility of the measurement of these angles has been assessed on plain and digitized x-rays, but to our knowledge, this has not been confirmed on x-rays taken on the PACS system and they have not been compared to computed tomography (CT) measurements, the reference for angle measurement. This prospective study aimed to: (1) evaluate the inter- and intrarater reliability of the measurement of these angles on digital x-rays taken on a PACS; (2) determine the agreement of these measurements with those obtained using a CT protocol.

HYPOTHESIS

The measurements of these five angles on digitized radiographs are reproducible and in agreement with CT values.

MATERIAL AND METHODS

Forty-two patients suffering from knee osteoarthritis and scheduled for total knee arthroplasty were included in the study. Each patient had a PACS digitized x-ray and a CT intended to produce patient-specific instrumentation (Symbios, Yverdon, Switzerland) including measurements of the angles evaluated. Four senior orthopaedic surgeon-raters measured all the angles twice. Inter- and intrarater reliability was then calculated as well as the agreement between the second measurement of each rater and the CT measurement using interclass correlation and kappa coefficients (data provided as means and 95% confidence intervals).

RESULTS

The inter- and intrarater reliability values were excellent for the HKA, alpha, and beta angles (with, respectively, a coefficient of 0.99 [0.97-0.99], 0.84 [0.76-0.9], and 0.94 [0.86-0.96] interrater reliability and 0.98 [0.96-0.99], 0.86 [0.75-0.92], and 0.65 [0.44-0.8] intrarater reliability). Interrater reliability was low for HKS and tibial slope angles (coefficients all<0.4 for interrater reliability and <0.7 for intrarater reliability). The x-ray/CT agreement was very good for the HKA, alpha, and beta angles (0.81 [0.67-0.99], 0.74 [0.56-0.91], and 0.74 [0.45-0.92], respectively) and low for the HKS and tibial slope angles (all<0.45).

DISCUSSION/CONCLUSION

The HKA, alpha, and beta angles were reproducible for digital radiographs and showed good agreement with CT measurements. HKS and tibial slope angles should be used with greater caution, and other navigation methods or patient-specific instrumentation should be explored.

LEVEL OF EVIDENCE

Level III, prospective, comparative diagnostic case-control study.

Two-dimensional planning can result in internal rotation of the femoral component in total knee arthroplasty

PURPOSE

The first purpose of this study was to compare the reproducibility of two-dimensional (2D) and three-dimensional (3D) measurements for preoperative planning of the femoral side in total knee arthroplasty (TKA). The second purpose was to evaluate the factors affecting the differences between the 2D and 3D measurements.

METHODS

Two-dimensional and 3D measurements for preoperative planning of the femoral side in TKA were evaluated in 75 varus knees with osteoarthritis. The femoral valgus angle, defined as the angle between the mechanical and anatomical axes of the femur, and the clinical rotation angle and surgical rotation angle, defined by the angles between the posterior condylar line and the clinical or surgical transepicondylar axes, respectively, were analysed using 2D (radiographs and axial CT slices) and 3D (3D bone models reconstructed from CT images) measurements.

RESULTS

For all variables, 3D measurements were more reliable and reproducible than 2D measurements. The medians and ranges of the clinical rotation angle and surgical rotation angle were 6.6° (-1.7° to 12.1°) and 2.3° (-2.5° to 8.6°) in 2D, and 7.1° (2.7° to 11.4°) and 3.0° (-2.0° to 7.5°) in 3D. Varus/valgus alteration of the CT scanning direction relative to the mechanical axis affected the difference in clinical rotation angles between 2D and 3D measurements.

CONCLUSION

Significantly, smaller values of the clinical rotation angle and surgical rotation angle were obtained by 2D compared to 3D measurements, which could result in internal rotation of the femoral component even if the surgeon performs the bone cutting precisely. Regarding clinical relevance, first, this study confirmed the reliability of 3D measurements. Second, it underscored the risk of internal rotation of the femoral component when using 2D measurement, even with precise bone cutting technique. These results will help surgeons avoid malpositioning of the femoral component if 2D measurements are used for preoperative planning in TKA.

LEVEL OF EVIDENCE

Prospective comparative study, Level Ш.

Poor reproducibility of the MRI measurement of distal femoral torsion

Recent publications on patient-specific instrumentation for total knee arthroplasty have reported considerable variability in the axial positioning of the cutting guides for the femoral component. These personalized cutting guides are manufactured based on bone shape data, generated from magnetic resonance imaging (MRI) or computed tomography (CT). The goal of this study was to compare the reproducibility and accuracy of distal femoral torsion (DFT) values measured using these two imaging modalities. We hypothesized that MRI does not reproducibly and consistently measure DFT and is not as accurate as CT scan.

METHODS

Anonymized radiology records from 54 patients that included MRI and CT scans of the knee were read in random order by two observers, on two separate occasions. These records were from patients being considered for a meniscal or osteochondral graft and who had their knee explored, but who had not undergone femoral or tibial surgery and were free of osteoarthritis. The DFT was estimated using the posterior condylar angle (PCA), using both its anatomical and surgical definitions. The intra- and inter-observer reproducibility of the MRI and the differences relative to CT scan measurements were analysed.

RESULTS

The average intra-observer difference for the MRI evaluation of the anatomical PCA was 0.8±1.2°; it was 0.4±0.9° for the surgical PCA. More than 1° difference from the average was found in 8 cases (14%) using the anatomical PCA measurement and 4 cases (7.4%) when using the surgical PCA (P=0.4). The intraclass correlation coefficients (ICCs) were 0.67 (95% CI: 0.33-0.85) and 0.74 (95% CI: 0.47-0.89) for the anatomical and surgical PCA, respectively. The average inter-observer difference for the MRI evaluation of the anatomical PCA was 1.6±1.4°; it was 1.5±1.0° for the surgical PCA. More than 1° difference from the average was found in 27 cases (50%) using the anatomical PCA measurement and 22 cases (40%) when using the surgical PCA (P=0.4). The ICCs were 0.31 (95% CI: 0.14-0.65) and 0.48 (95% CI: 0.06-0.75) for the anatomical and surgical PCA, respectively. The average differences between the CT and MRI measurements were 1.4±1.1° (0.2-5°) and 1.1±0.8° (0-3.6°) for the anatomical and surgical PCA, respectively. Greater than 1° difference between CT and MRI was found in 29 records (54%) for the anatomical PCA and in 18 records (33%) for the surgical PCA (P=0.03).

CONCLUSION

DFT measurement on MRI is more reproducible and consistent when using the surgical PCA. MRI measurements differed by more than 1° relative to CT measurements in more than one-third of cases.

CASE CONTROL STUDY

Level III.

Can rotational alignment of total knee arthroplasty be measured on MRI?

BACKGROUND AND PURPOSE

The aim of this study was to investigate the potential of MRI to determine rotational alignment after TKA in comparison to the gold standard, CT.

METHODS

Rotational alignment was measured in the transverse plane on CT and MR-images in 14 patients prior to TKA revision. Differences between CT and MRI measurements were analysed.

RESULTS

There was a strong correlation between CT and MRI measurements for both the tibial (r = 0.929) and femoral (r = 0.942) components with a mean difference of 0.47 ± 1.3 and 0.13 ± 3.2 degrees, respectively.

INTERPRETATION

Despite artefact formation, it can be concluded that the rotational alignment of metallic TKA components can be measured by MRI as accurately as by CT.

Effect of rotational alignment on outcome of total knee arthroplasty

BACKGROUND AND PURPOSE

Poor outcomes have been linked to errors in rotational alignment of total knee arthroplasty components. The aims of this study were to determine the correlation between rotational alignment and outcome, to review the success of revision for malrotated total knee arthroplasty, and to determine whether evidence-based guidelines for malrotated total knee arthroplasty can be proposed.

PATIENTS AND METHODS

We conducted a systematic review including all studies reporting on both rotational alignment and functional outcome. Comparable studies were used in a correlation analysis and results of revision were analyzed separately.

RESULTS

846 studies were identified, 25 of which met the inclusion criteria. From this selection, 11 studies could be included in the correlation analysis. A medium positive correlation (ρ = 0.44, 95% CI: 0.27-0.59) and a large positive correlation (ρ = 0.68, 95% CI: 0.64-0.73) were found between external rotation of the tibial component and the femoral component, respectively, and the Knee Society score. Revision for malrotation gave positive results in all 6 studies in this field.

INTERPRETATION

Medium and large positive correlations were found between tibial and femoral component rotational alignment on the one hand and better functional outcome on the other. Revision of malrotated total knee arthroplasty may be successful. However, a clear cutoff point for revision for malrotated total knee arthroplasty components could not be identified.

Femoral component rotation in total knee arthroplasty: an MRI-based evaluation of our options

Proper femoral component rotation is crucial in successful total knee arthroplasty. Rotation using anatomic landmarks has traditionally referenced the transepicondylar axis (TEA), Whiteside's Line (WSL), or posterior condylar axis (PCA). TEA is thought to best approximate the flexion-axis of the knee, however WSL or PCA are common surrogates in the operating room. This study evaluated 560 knees using MRI-based planning software to assess the relationship of WSL and PCA to the TEA and determine if the relationships were influenced by pre-operative coronal deformity. Results showed the WSL-TEA relationship has more variability than PCA-TEA and that the PCA is more internally rotated in females and valgus knees. Axis options and historical assumptions about axis relationships may need to be reassessed as imaging technology advances.

Analysis of knee functional flexion axis in navigated TKA: identification and repeatability before and after implant positioning

PURPOSE

Providing correct rotational alignment of femoral component in total knee arthroplasty (TKA) is mandatory to achieve correct kinematics, good ligament balance and patellar tracking. The purpose of this study was to evaluate potential clinical applications of functional flexion axis (FFA) by analysing the differences between pre- and post-implant placement. This evaluation was supported by the analysis of repeatability, assessing the robustness of the proposed method.

METHODS

Anatomical acquisitions and passive kinematics were acquired on 87 patients undergoing TKA using a commercial navigation system. Knee FFA was estimated, before and after implant positioning, from three flexion-extension movements between 0 and 120°. The angle between FFA and transepicondylar axis was analysed in frontal and axial planes. Repeatability coefficient and intraclass correlation coefficient (ICC) were used to analyse the reliability and the agreement in identifying the axis.

RESULTS

The analysed angle presented differences between pre- and post-operative conditions only in the frontal plane (from -8.3 ± 5.5° to -2.8 ± 5.3°) (p < 0.0001). There was good intraobserver reliability and agreement. Repeatability coefficient ranged between 4.4° (3.7-4.9°) and 3.4° (2.9-3.8°), the ICC between 0.87 (0.83-0.91) and 0.93 (0.90-0.95) and the standard deviation ranged between 1.3 and 1.0°.

CONCLUSIONS

The present study demonstrated that TKA affected the estimation of FFA only in the frontal plane. This method reported good repeatability, demonstrating its usefulness for clinical purposes particularly to evaluate rotational positioning of the femoral component in the axial plane.

LEVEL OF EVIDENCE

Case series, Level IV.

Is radiographic measurement of distal femoral torsion reliable?

BACKGROUND

Distal femur torsion (DFT) is a crucial parameter in knee replacement surgery. The reference standard for measuring DFT is posterior condylar angle (PCA) measurement using computed tomography (CT). The objective of this study was to assess the feasibility and reliability of a radiographic PCA measurement method.

MATERIALS AND METHODS

We studied 125 osteoarthritic knees in 79 patients (42 women and 37 men) with a mean age of 71.6 ± 8.8 years (range 47 to 86 years); 32 knees were aligned, 85 in varus, and eight in valgus. DFT was measured on an antero-posterior (AP) radiograph of the knee in 90° of flexion (known as the seated AP view). The PCA was defined as the angle subtended by the tangent to the posterior condyles and the transepicondylar axis (anatomic PCA [aPCA]) or the line connecting the lateral epicondyle to the medial sulcus (surgical PCA [sPCA]). The PCA was conventionally recorded as positive in the event of external torsion and negative in the event of internal torsion. PCA measurements were performed three times by each of five observers to allow assessments of inter-observer and test-retest reliabilities.

RESULTS

aPCA was consistently negative (mean, -6.1 ± 1.6°) (range, 0 to -10°); inter-observer and test-retest reliability were satisfactory (0.54<rw 0.80). sPCA was positive in 41 knees and negative in 84 knees) (mean, -0.3 ± 1.4°) (range, -5° to +2°); inter-observer and test-retest reliabilities were poor (0.28<r<0.69). A weak but significant correlation was found between aPCA and coronal alignment, with a trend towards greater internal torsion in the group of valgus knees.

CONCLUSION

Radiographic measurement of DFT is simple and non-invasive. Measurement reproducibility was satisfactory for aPCA but not for sPCA. aPCA showed marked inter-individual variability and tended to increase when the knee was in valgus. Mean aPCA values were comparable to those reported using CT. In contrast to CT, radiographic DFT measurement can easily be incorporated into the pre- and postoperative work-ups for knee replacement surgery, provided the patient can achieve 90° of knee flexion.

LEVEL OF EVIDENCE

Level IV, prospective cohort study.

Distal femur rotation relates to joint obliquity in ACL-deficient Chinese

BACKGROUND

The lower limb osteometry of Chinese differs from that of whites. The joint line of the knee in the coronal plane in Chinese is more medially inclined and the posterior condylar angle of the distal femur in the axial plane is larger. However, it is unclear whether there is any direct association between the coronal plane and axial plane osteometry.

QUESTIONS/PURPOSES

We asked whether the joint line obliquity of the knee is related to the posterior condylar angle of the distal femur in young Chinese subjects.

METHODS

Ninety-nine young Chinese patients with anterior cruciate ligament injuries were recruited. The lower limb alignment and joint line obliquity were measured using standing long radiographs of the whole lower limb. The rotational alignment of the distal femur was assessed in the axial cuts of the MRI.

RESULTS

The distal femur rotational alignment was associated with the obliquity of the knee in Chinese. The posterior condylar angle was 5° ± 2°. The knee was 5° ± 3° medially inclined.

CONCLUSIONS

The joint line of the knee in a group of young Chinese patients was more medially inclined than that of whites. The posterior condylar angle of the distal femur was larger. The presence of an association between distal femur rotational alignment and joint line obliquity in this group of young Chinese patients suggests a possible developmental cause explaining the difference in osteometry between races.

The gap technique does not rotate the femur parallel to the epicondylar axis

INTRODUCTION

In the analysis of painful total knee replacements, the surgical epicondylar axis (SEA) has become established as a standard in the diagnosis of femoral component rotation. It remains unclear whether the gap technique widely used to determine femoral rotation, when applied correctly, results in a rotation parallel to the SEA.

METHOD

In this prospective study, 69 patients (69 joints) were included who received a navigated bicondylar surface replacement due to primary arthritis of the knee joint.

RESULTS

In 67 cases in which a perfect soft-tissue balancing of the extension gap (<1° asymmetry) was achieved, the flexion gap and the rotation of the femoral component necessary for its symmetry was determined and documented. The femoral component was implanted additionally taking into account the posterior condylar axis and the Whiteside's line. Postoperatively, the rotation of the femoral component to the SEA was determined and this was used to calculate the angle between a femur implanted according to the gap technique and the SEA. If the gap technique had been used consistently, it would have resulted in a deviation of the femoral components by -0.6° ± 2.9° (-7.4°-5.9°) from the SEA. The absolute deviation would have been 2.4° ± 1.8°, with a range between 0.2° and 7.4°.

CONCLUSION

Even if the extension gap is perfectly balanced, the gap technique does not lead to a parallel alignment of the femoral component to the SEA. Since the clinical results of this technique are equivalent to those of the femur first technique in the literature, an evaluation of this deviation as a malalignment must be considered critically.

How precise can bony landmarks be determined on a CT scan of the knee?

The purpose of this study was to describe the intra- and inter-observer variability of the registration of bony landmarks and alignment axes on a Computed Axial Tomography (CT) scan. Six cadaver specimens were scanned. Three-dimensional surface models of the knee were created. Three observers marked anatomic surface landmarks and alignment landmarks. The intra- and inter-observer variability of the point and axis registration was performed. Mean intra-observer precision ranks around 1 mm for all landmarks. The intra-class correlation coefficient (ICC) for inter-observer variability ranked higher than 0.98 for all landmarks. The highest recorded intra- and inter-observer variability was 1.3 mm and 3.5 mm respectively and was observed for the lateral femoral epicondyle. The lowest variability in the determination of axes was found for the femoral mechanical axis (intra-observer 0.12 degrees and inter-observer 0.19 degrees) and for the tibial mechanical axis (respectively 0.15 degrees and 0.28 degrees). In the horizontal plane the lowest variability was observed for the posterior condylar line of the femur (intra-observer 0.17 degrees and inter-observer 0.78 degrees) and for the transverse axis (respectively 1.89 degrees and 2.03) on the tibia. This study demonstrates low intra- and inter-observer variability in the CT registration of landmarks that define the coordinate system of the femur and the tibia. In the femur, the horizontal plane projections of the posterior condylar line and the surgical and anatomical transepicondylar axis can be determined precisely on a CT scan, using the described methodology. In the tibia, the best result is obtained for the tibial transverse axis.