Factors affecting femoral rotational angle based on the posterior condylar axis in gap-based navigation-assisted total knee arthroplasty for valgus knee

<div><p>Background</p><p>Achieving proper rotational alignment of the femoral component in total knee arthroplasty (TKA) for valgus knee is challenging because of lateral condylar hypoplasia and lateral cartilage erosion. Gap-based navigation-assisted TKA enables surgeons to determine the angle of femoral component rotation (FCR) based on the posterior condylar axis. This study evaluated the possible factors that affect the rotational alignment of the femoral component based on the posterior condylar axis.</p><p>Materials and methods</p><p>Between 2008 and 2016, 28 knees were enrolled. The dependent variable for this study was FCR based on the posterior condylar axis, which was obtained from the navigation system archives. Multiple regression analysis was conducted to identify factors that might predict FCR, including body mass index (BMI), Kellgren-Lawrence grade (K-L grade), lateral distal femoral angles obtained from the navigation system and radiographs (NaviLDFA, XrayLDFA), hip-knee-ankle (HKA) axis, lateral gap under varus stress (LGVS), medial gap under valgus stress (MGVS), and side-to-side difference (STSD, MGVS − LGVS).</p><p>Results</p><p>The mean FCR was 6.1° ± 2.0°. Of all the potentially predictive factors evaluated in this study, only NaviLDFA (<i>β</i> = −0.668) and XrayLDFA (<i>β</i> = −0.714) predicted significantly FCR.</p><p>Conclusions</p><p>The LDFAs, as determined using radiographs and the navigation system, were both predictive of the rotational alignment of the femoral component based on the posterior condylar axis in gap-based TKA for valgus knee. A 1° increment with NaviLDFA led to a 0.668° decrement in FCR, and a 1° increment with XrayLDFA led to a 0.714° decrement. This suggests that symmetrical lateral condylar hypoplasia of the posterior and distal side occurs in lateral compartment end-stage osteoarthritis with valgus deformity.</p></div

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Comparison of preoperative and postoperative patellar tilt angles and the HKA axis.

<p>Comparison of preoperative and postoperative patellar tilt angles and the HKA axis.</p

Adjustment of femoral component rotational alignment.

<p>(A) To obtain a rectangular gap in the navigation femoral planning step, the femoral component rotation based on the posterior condylar axis and the varus-valgus angle were adjusted. A difference of <2 mm between the lateral extension/flexion gap and the medial extension/flexion gap was considered acceptable. (B) After distal femoral resection, the AP femoral cutting jig is located using the determined value during the planning step. The rotational position of the AP femoral cutting jig is displayed in real time. The <i>arrow line</i> indicates the actual femoral component rotation.</p

Obtaining NaviLDFA.

<p>(A) The angle between the true mechanical axis of the femur obtained using hip and knee kinematic analysis and distal femoral joint surfaces from the exact 4-point contact with a check plate. (B) The navigation system displays the quantified angle. This angle (<i>arrow line</i>) represents the lateral distal femoral angle from the navigation system (NaviLDFA).</p

Patellar tilt angle.

<p>(A) The preoperative patellar tilt angle is defined as the angle between the equatorial line of the patella and the line connecting the anterior limits of the femoral condyles in the Merchant view. (B) The postoperative patellar tilt angle is measured using the same method but with a line connecting the anterior limits of the femoral component instead of the femoral condyles.</p

Independent and dependent variables.

<p>Independent and dependent variables.</p

Measurement of HKA Axis, XrayLDFA, LGVS, and MGVS.

<p>The HKA axis and XrayLDFA were measured using a preoperative whole-leg standing radiograph (A). The HKA axis was measured using intersecting lines from the femoral and tibial mechanical axes. The XrayLDFA was a superolateral angle measured by intersecting the femoral mechanical axis line and distal femoral joint line. LGVS and MGVS were measured from varus (B) and valgus (C) stress radiographs, applying 130 N. The <i>dashed line</i> is the bisector of the angle between the distal femoral and proximal tibial joint lines (<i>black solid lines</i>). LGVS was measured from the lowest point of the lateral femoral condyle to its corresponding point on the tibial joint line (<i>red solid line</i>, drawn perpendicular to the <i>dashed line</i>). MGVS was measured using a similar method.</p

Correlations between FCR and all potential predictors.

<p>Correlations between FCR and all potential predictors.</p

Crystal structure of hyperthermophilic esterase EstE1 and the relationship between its dimerization and thermostability properties-5

<p><b>Copyright information:</b></p><p>Taken from "Crystal structure of hyperthermophilic esterase EstE1 and the relationship between its dimerization and thermostability properties"</p><p>http://www.biomedcentral.com/1472-6807/7/47</p><p>BMC Structural Biology 2007;7():47-47.</p><p>Published online 12 Jul 2007</p><p>PMCID:PMC1936996.</p><p></p> and EstE1(▯), in 20 mM potassium phosphate buffer (pH 7.0) were incubated at 80°C for the indicated times. Residual activities were then determined by measuring the amount of -nitrophenol released by esterase-catalyzed hydrolysis. The activity of a non-incubated sample was defined as 100