Transepicondylar axes for femoral component rotation might produce flexion asymmetry during total knee arthroplasty in knees with proximal tibia vara

Changes in the femoral varus and rotational profiles are correlated in women with varus osteoarthritic lower limbs

INTRODUCTION

Previous studies have reported the relationship between coronal alignment of the lower limbs and the rotational profile of the femur and tibia. However, the relationship between coronal alignment of the femur and tibia and their rotational profiles in patients with varus osteoarthritic knees is unclear.

METHODS

One hundred women with varus osteoarthritic knees (varus OA group) and 50 women with neutrally aligned lower limbs without osteoarthritis (non-OA group) were evaluated retrospectively. The coronal alignment and rotational profile of the femur and tibia were evaluated, and the correlation between coronal alignment and rotational profile was analyzed, respectively.

RESULTS

The femoral anteversion, posterior condylar angle of the distal femur, and tibial torsion were significantly smaller in the varus OA group than in the non-OA group. In the varus OA group, the femoral anteversion and rotational profile of the distal femur had significantly negative correlations with the degree of femoral varus, while tibial torsion was not related to the degree of tibial varus. In the non-OA group, there was no relationship between coronal alignment and rotational profiles of the femur and tibia in both the varus OA and non-OA groups.

CONCLUSION

Femoral anteversion and the rotational profile of the distal femur were negatively correlated with the degree of femoral varus in Asian women with varus osteoarthritic knees. This study enhanced the understanding of the relationship between changes in coronal alignment of the femur and tibia and their rotational profiles in patients with varus osteoarthritic lower limbs, although this study was limited by the small sample sizes and methodological quality.

Investigation of femoral condyle height changes during flexion of the knee: implication to gap balance in TKA surgery

BACKGROUND

Gap balance of the knee at 0° and 90° of flexion has been pursued in total knee arthroplasty (TKA) with the trans-epicondyle axis (TEA) as a reference. This study investigated the height changes of the tibiofemoral articulation and compared the data with the femoral condyle height changes measured using different flexion axes.

MATERIALS AND METHODS

Twenty healthy knees were investigated during an in vivo weightbearing flexion using a technique combining MRI and a dual fluoroscopic imaging system (DFIS). The tibiofemoral contact points and the femoral condyle heights [measured using: TEA, geometric center axis (GCA), and iso-height axis (IHA)] were determined at each flexion angle. The height changes of the articular contact points and the femoral condyles were compared along the flexion path.

RESULTS

The changes of the medial and lateral contact point heights were within 2.5 mm along the flexion path. The changes of the medial and lateral condyle heights were within 8.9 mm for TEA, within 4.2 mm for GCA and within 3.0 mm for IHA. The height changes measured by the contact points and IHA are similar (p > 0.05), and both are significantly smaller than those measured using the TEA and GCA (p < 0.05).

CONCLUSIONS

The TEA and GCA measured varying femoral condyle heights, but the IHA resulted in minimal condyle height changes and could better represent the articulation characteristics of the knee. The data suggested that the IHA could be used as an alternative reference to guide surgical preparation of gap balance along the knee flexion path during TKA surgeries.

There are isoheight points that measure constant femoral condyle heights along the knee flexion path

PURPOSE

It is a challenge to evaluate the maintenance of medial and lateral soft tissue balance in total knee arthroplasty (TKA). This study aimed to determine the "isoheight" points and the "isoheight" axis (IHA) that can measure constant medial/lateral condyle heights during flexion of the knee, and compare the IHA with two major anatomical axes, the transepicondylar axis (TEA) and the geometric center axis (GCA).

METHODS

Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging system while performing a single-legged lunge (0°-120°). The isoheight points of the medial and lateral femoral condyles were defined as the locations with the least amount of changes in heights during the knee flexion; an IHA is the line connecting the medial and lateral isoheight points. The measured changes of the condyle heights using the IHA were compared with those measured using the TEA and GCA.

RESULTS

Overall, the IHA was posterior and distal to the TEA, and anterior to the GCA. The isoheight points measured condyle height changes within 1.2 ± 2.3 mm at the medial and 0.7 ± 3.3 mm at the lateral sides during the knee flexion. Between 0° and 45°, the condyle height changes measured using the GCA (medial: 3.0 ± 1.8 mm, lateral: 2.3 ± 2.0 mm) were significantly larger than those of the IHA and the TEA (p < 0.05). Between 90° and 120°, the changes of the condyle heights measured using the TEA (medial: 5.3 ± 1.8 mm, lateral: 3.3 ± 1.8 mm) were significantly larger than those of the IHA and GCA (p < 0.05).

CONCLUSION

There are isoheight points in the medial and lateral femoral condyles that can measure constant heights along the full range of knee flexion and could be used to formulate an "isoheight" axis (IHA) of the femur. The condyle height changes measured by the TEA and GCA were greater than the IHA measurements along the flexion path. These data could be used as a valuable reference to evaluate the condyle height changes after TKA surgeries and help achieve soft tissue balance and optimal knee kinematics along the flexion path.

LEVEL OF EVIDENCE

IV.

Bone resection for mechanically aligned total knee arthroplasty creates frequent gap modifications and imbalances

PURPOSE

The objective of this study was to calculate bone resection thicknesses and resulting gap sizes, simulating a measured resection mechanical alignment (MA) technique for total knee arthroplasty (TKA).

METHODS

MA bone resections were simulated on 1000 consecutive lower limb CT scans from patients undergoing TKA. Femoral rotation was aligned with either the surgical trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Imbalances in the extension space, flexion space, medial compartment and lateral compartment were calculated.

RESULTS

Extension space imbalances (≥ 3 mm) occurred in 25% of varus and 54% of valgus knees and severe imbalances (≥ 5 mm) were present in up to 8% of varus and 19% of valgus knees. Higher flexion space imbalance rates were created with TEA versus PC (p < 0.001). Using TEA, only 49% of varus and 18% of valgus knees had < 3 mm of imbalance throughout the extension and flexion spaces, and medial and lateral compartments.

CONCLUSION

A systematic use of the simulated measured resection MA technique for TKA leads to many cases with imbalance. Some imbalances may not be correctable surgically and may result in TKA instability. Modified versions of the MA technique or other alignment methods that better reproduce knee anatomies should be explored.

LEVEL OF EVIDENCE

2.

Femoral Component Rotation in Total Knee Arthroplasty: A Comparison Between Transepicondylar Axis and Posterior Condylar Line Referencing

BACKGROUND

Proper rotational alignment of the femoral component is critical for a successful total knee arthroplasty (TKA). Controversy remains regarding the optimal intraoperative reference to determine femoral component rotation.

METHODS

Thirty-one patients who underwent magnetic resonance imaging of a TKA between April 2008 and November 2015 were retrospectively reviewed. A single surgeon performed the TKA using a posterior condylar angle of 3° (PCA group) or surgical transepicondylar axis (TEA group) to determine femoral component rotation. The hip-knee-ankle angle and the tibial plateau-tibial shaft angle (TPTSA) were measured on full-length x-rays, and the rotation of the femoral component was measured as compared to the TEA on magnetic resonance imaging (negative values indicate internal rotation).

RESULTS

The median measured rotational deviation of the femoral component from the TEA was significantly higher in the PCA group than in the TEA group (-3.8 ± 2.9° and -1.4 ± 1.9°, respectively) (P = .02). When knees with preoperative varus and neutral alignment were evaluated, the median measured rotational deviation of the femoral component was significantly higher in the fixed PCL group than in the TEA group (-3.4 ± 3.3° and -0.61 ± 1.3°, respectively) (P = .04). Linear regression used to evaluate the relationship between the TPTSA and femoral component rotational deviation from the TEA revealed similar near zero slopes (P = .90); however, the Y intercepts in the TEA group were significantly higher than the PCA group (-2.8 ± 0.7 and -5.5 ± 1.1, respectively) (P = .007).

CONCLUSION

The use of the surgical TEA as an intraoperative rotational reference is more reliable than the PCA in valgus, varus, and neutrally aligned knees independent from the magnitude of the TPTSA.

The plane of the distal femur anterior cortex is a useful index for femoral component rotation in total knee arthroplasty

OBJECTIVE

To investigate the reference role of the plane of the distal femur anterior cortex in determining the lateral rotation angle of femoral component in total knee arthroplasty (TKA).

METHODS

Computed tomography (CT) scan was performed for full length of both lower limbs in 27 patients, and a total of 53 legs were examined by radiological department of the First Affiliated Hospital of Sun Yat-sen University. Case inclusion criteria were as follows: no obvious congenital bone deformity on the lower limbs, no knee purulent infection, and no severe knee deformity after surgery. 3D reconstruction was performed by Mimics 16.0 software for the scan images to calculate the angle between the plane of the distal femur anterior cortex and the Posterior Condylar Line (PCL) (defined as FPA), and the angle between the plane of the distal femur anterior cortex and the Clinical Epicondylar Axis (CEA) (defined as ACA), as well as the angle between the CEA and PCL, known as the condylar twist angle (CTA). Finally, Kolmogorov-Smirnov test and Student's t test were used to analyze the measured value.

RESULTS

The average value of FPA was -4.70 ± 3.77°, that of CTA, +5.04 ± 2.36°, and that of ACA, -9.17 ± 5.78°. Each angle measured above has no significant differences in the gender (P > 0.05).

CONCLUSION

ACA was measured to be 9.17 ± 5.78° on the direction of medial femoral rotation, proving that the plane of distal femur anterior cortex plays a relatively accurate reference role in determining the lateral rotation angle of the femoral component in TKA.

Normal Femorotibial Rotational Alignment and Implications for Total Knee Arthroplasty: an MRI Analysis

BACKGROUND

Rotational alignment of prosthetic components in total knee arthroplasty (TKA) is important to successful outcomes. Component malrotation is a known cause of revision and understanding normal rotational alignment may help recreate normal joint kinematics. To date, no large MRI study assessing femorotibial rotational alignment in nonarthritic knees has been undertaken.

QUESTIONS/PURPOSES

Is Insall's tibial axis a reliable rotational landmark against common femoral rotational axes in the nonarthritic patient population?

METHODS

We reviewed 544 knee MRI scans performed for suspected soft tissue pathology and identified Insall's tibial rotational axis as well as the femoral clinical trans-epicondylar axis (TEAc), femoral surgical trans-epicondylar axis (TEAs), posterior condylar articular axis (PCA), and a modified Eckhoff's cylindrical axis. The perpendiculars of these axes were superimposed on Insall's tibial axis, and the angular differences were measured.

RESULTS

Insall's axis was internally rotated to the TEAc by 1.4°, externally rotated to Eckhoff's cylindrical axis by 1.8°, externally rotated to the TEAs by 2.7°, and externally rotated to the PCA by 3.5°. The mean deviation from 0° (optimal alignment for each femoral axis) was significantly greater for the PCA relative to all other femoral axis.

CONCLUSION

Insall's axis is a reliable landmark for rotational positioning of the tibial component and may optimize femorotibial kinematics in fixed-bearing TKA.

Is end-stage lateral osteoarthritic knee always valgus? Mechanical alignment analysis and radiographic severity assessment

Background

We hypothesized that not all persons with end-stage lateral osteoarthritis (OA) have valgus malalignment and that full extension radiographs may underreport radiographic disease severity. The purpose of this study was to examine the demographic and radiographic features of end-stage lateral compartment knee OA.

Materials and methods

We retrospectively studied 133 knees in 113 patients who had undergone total knee arthroplasty between June 2008 and August 2010. All patients had predominantly lateral idiopathic compartment OA according to the compartment-specific Kellgren–Lawrence grade (KLG). The mechanical axis angle (MAA), compartment-specific KLG and joint space narrowing (JSN) of the tibiofemoral joint at extension and 30° of knee flexion, tibia vara angle, tibial slope angle, body mass index, age, and sex were surveyed.

Results

End-stage lateral compartment knee OA has varus (37.6 %), neutral (22.6 %), and valgus (39.8 %) MAA on both-leg standing hip-knee-ankle radiographs. KLGs at 30° of knee flexion (fKLG) were grades 3 and 4 in all patients. However, for KLGs at full extension (eKLG), 54 % of all patients had grades 3 and 4. The others (46 %) showed grades 1 and 2. We observed significant differences in lateral compartment eKLG/eJSN (2.3/2.3 mm in varus, 2.5/1.9 mm in neutral, 2.9/1.6 mm in valgus, p = 0.01 and 0.03, respectively), tibia vara angle (4.9° in varus, 4.1° in neutral, 3.0° in valgus, p < 0.01), and medial compartment eKLG/eJSN (2.1/3.1 mm in varus, 2.0/3.4 mm in neutral, 1.8/4.3 mm in valgus, p < 0.01 and 0.01, respectively) between MAA groups, except for the tibial slope angle (9.7° in varus, 10.1° in neutral, 9.8° in valgus, p = 0.31).

Conclusion

Varus alignment was paradoxically shown in approximately one-third of those with end-stage lateral knee OA on both-leg standing hip-knee-ankle radiographs. Films taken in full extension underreported the degree of OA radiographic severity.

Level of evidence

Level IV, observational study.