Surgical Epicondylar Axis Research Articles

Combining the Sulcus Line and Posterior Condylar Axis Reduces Femoral Malrotation in Total Knee Arthroplasty

Objectives:Femoral component malrotation is a common cause of patient dissatisfaction after total knee arthroplasty. The Sulcus Line (SL) is formed from multiple points along the floor of the trochlear groove, and has been shown to be more accurate than Whiteside Line. A trochlear alignment guide (TAG) is required to maintain the accuracy of the SL and allow intraoperative comparison of the SL and the posterior condylar axis (PCA). The hypothesis is that averaging these two landmarks will lead to less femoral malrotation.Methods:Surgery was performed in 50 patients using the TAG. The component was inserted at a position between the SL and PCA. An intraoperative photograph was taken of the distal cut surface of the femur showing the pin-holes representing the SL, the PCA and the final component position. These were compared to the component position achieved relative to the surgical epicondylar axis (SEA) on a postoperative CT scan. Comparison was made between the final component position and the position which would have been achieved using either the SL or PCA individually. The theoretical position which could be achieved by averaging the SL and PCA was also calculated.Results:The SEA was identified on CT scan in 46 cases. The component position was 0.7° (SD 1.5°), SL was -0.8° (SD 2.1°), PCA was 1.1° (SD 2.1°), the calculated average position between SL and PCA was 0.1° (SD 1.5°). There was a significant decrease in variance between both the component position and the calculated average when each was compared to the SL and PCA individually. The number of outliers greater than 3° from the SEA was also significantly less (p<0.05) for both the component position (3/46, 6%) and the calculated average position(1/46, 2%) when each was compared to the SL (10/46, 22%) and PCA (11/46, 24%) individually. The rotational alignment of the trochlear and posterior condyles diverged from each other more than 4° in 11/46 (24%).Conclusion:Averaging the SL and the PCA intraoperatively leads to decreased femoral component malrotation compared to the use of either landmark individually.

Inaccurate rotational component position in image-free navigated unicompartmental knee arthroplasty

Background/ObjectiveThe success of unicompartmental knee arthroplasty (UKA) is highly dependent on the accuracy of component and leg alignment. Computer-assisted surgery is gaining popularity in total knee arthroplasty with numerous studies reporting improved accuracy and decreased variability in implant position and postoperative limb alignment compared with conventional techniques. However, literature evaluating the accuracy of computer-navigated UKA is limited. Therefore, this study aimed to investigate the accuracy of component positions in navigated UKA using a three-dimensional (3D) image-matching system. To the best of our knowledge, this study is the first to evaluate the accuracy of implant-placement position in UKA using 3D image-matching systems. MethodsTwenty-three knees in 22 patients (9 men, 13 women) underwent computer-assisted UKA performed by a senior surgeon from 2011 to 2013. All surgeries were performed with measured resection techniques using an image-free-navigation system. We recorded the coronal, sagittal, and rotational bone-resection angles towards the mechanical axis in the distal femur and proximal tibia using image-free navigation intraoperatively. The coronal, sagittal, and rotational alignments of the femoral and tibial components were also measured using the 3D image-matching system, and the accuracy of the navigated UKA was evaluated. The rotational alignment of the femur and tibia was defined as surgical epicondylar axis and Akagi's line, and a deviation over 3° from the AA was defined as an outlier. ResultsWe observed coronal outliers for the femoral component in four of the 23 patients, and for the tibial component in three of the 23 patients. We also observed sagittal outliers for the femoral component in five of 23 patients, and for the tibial component in three of the 23 patients. Twenty-two tibial components were placed in external rotation relative to the rotational reference line. ConclusionIn both coronal and sagittal alignments, there were a definite proportion of outliers. The ratio of outliers in rotational alignment was especially higher than that in coronal and sagittal alignments. In UKA, the identification of bony landmarks is difficult because of the small operation field. Therefore, careful surface mapping of particular bony landmarks is necessary, and it is not enough to use image-free navigation system in UKA.

Is the Surgical Epicondylar Axis the Center of Rotation in the Osteoarthritic Knee?

The relationship between the surgical epicondylar axis (SEA) and the rotational axis of the distal femur remains unclear. We investigated the relationship between the SEA and the distal femur and whether the SEA can be used as the rotational axis of the knee. Angular and linear measurements of 70 femora at 0°, 30°, 60°, 90°, and 120° of flexion were recorded. Results showed that the SEA was a logical and appropriate parameter as a principal axis for knee flexion at least between 0° and 60° of flexion. The study has important implications for the design and positioning of femoral components in total knee arthroplasty.

Clinical faceoff: Neutrally versus kinematically aligned TKA.

While the number of primary TKAs completed in the United States is expected to increase dramatically in the years to come, approximately 20% of patients undergoing primary TKA are dissatisfied with the procedure [5, 11]. As such, substantial healthcare resources have been devoted to the development and use of patient-specific instrumentation (PSI), computer navigation, robotics, and other tools that help achieve a neutrally aligned TKA in the coronal plane [1, 2, 14]. On the other hand, some investigators support a different approach: The concept of a kinematically aligned TKA [6, 8–10]. In general terms, a neutrally aligned TKA cuts the distal femur and proximal tibia 90° to the respective mechanical axes, while a kinematically aligned TKA incorporates 3° of varus into the tibia and an additional 3° of valgus into the femur. However, there remains considerable controversy in this area, in large measure because of a relative paucity of research comparing the approaches. As such, I have invited two internationally known experts to discuss these two approaches to obtaining a well-aligned TKA – the neutrally aligned and kinematically aligned techniques.

Preoperative morphometric differences in the distal femur are based on skeletal size in Japanese patients undergoing total knee arthroplasty.

The objectives of this study were to measure the morphometric parameters of preoperative distal femurs to determine the differences by diagnosis and gender after accounting for skeletal size. One-hundred and seventy-nine Japanese patients who underwent total knee arthroplasty (TKA) (25 males and 154 females) were assessed. The anteroposterior length (AP), mediolateral width (ML), aspect ratio (AR), surgical epicondylar axis (SEA) to posterior condylar axis (PCA) angle, and Whiteside to SEA angle were measured on preoperative computed tomography scans. The AP/ML, AR/ML, SEA/PCA, and Whiteside/PCA relationships were evaluated and compared by patient diagnosis and gender. The results were also compared with the sizes of 10 currently available TKA implants in Japan. The mean AP, ML, AR, SEA/PCA angle, and Whiteside/PCA angle were 58.8mm, 64.7mm, 0.91, external rotation (ER) 3.5°, and ER 1.6°, respectively. AP and AR each were significantly correlated with ML (p<0.001). AP, ML, and AR were not significantly different between patients diagnosed with osteoarthritis and rheumatoid arthritis. AP/ML and AR/ML were significantly correlated within each diagnosis (p<0.001), but the analysis of covariance showed no significant differences between the diagnoses. AP and ML were significantly longer (p<0.001) in males (63.6, 72.7mm) than in females (58.1, 63.4mm), while AR was smaller in males (0.88 vs. 0.92), with significant correlations for AP/ML (male: p<0.010, female: p<0.001) and AR/ML (male: p=0.002, female: p<0.001) in each gender. However, the analysis of covariance showed no significant differences between gender in the AP/ML and AR/MR correlations. The AP/ML ratio of our data was similar to the size variations of the 10 TKA implants, but the AR/ML ratio was quite different from almost all the implants. No differences in preoperative femur morphometry were found between patients with different diagnoses, but the gender difference in AR was related to the difference in skeletal size between males and females. Case series with no comparison groups, Level IV.

Relationship Between Mechanical Axis-Derived and Anatomic Landmark-Derived Femoral Rotation in TKA: A Three-Dimensional CT Study

We sought to determine the relationship between the mechanical axis-derived and the anatomic landmark-derived femoral rotational axes using three dimensional computed tomographic images of 20 lower extremities. The mechanical axis-derived femoral rotational axis was created on the distal articular surface of the femur using coronal mechanical limb axis and the reconstructed images of the femur. Then, we measured the angular difference between mechanical axis-derived and anatomic landmark-derived femoral rotational axes. The mechanical axis-derived femoral rotational axis was externally rotated with a mean of 2.2° (range, 0 to 4.7°; SD, 1.0) compared with the surgical epicondylar axis. Our findings should be considered to obtain a proper femoral rotational axis in total knee arthroplasty.

The sulcus line of the trochlear groove is more accurate than Whiteside's Line in determining femoral component rotation.

Purpose The sulcus line (SL) is a three-dimensional curve produced from multiple points along the trochlear groove. Whiteside’s Line, also known as the anteroposterior axis (APA), is derived from single anterior and posterior points. The purposes of the two studies presented in this paper are to (1) assess the results from the clinical use of the SL in a large clinical series, (2) measure the SL and the APA on three-dimensional CT reconstructions, (3) demonstrate the effect of parallax error on the use of the APA and (4) determine the accuracy of an axis derived by combining the SL and the posterior condylar axis (PCA).MethodsIn the first study, we assessed the SL using a large, single surgeon series of consecutive patients undergoing primary total knee arthroplasties. The post-operative CT scans of patients (n = 200) were examined to determine the final rotational alignment of the femoral component. In the second study, measurements were taken in a series of 3DCT reconstructions of osteoarthritic knees (n = 44).Results The mean position of the femoral component in the clinical series was 0.6° externally rotated to the surgical epicondylar axis, with a standard deviation of 2.9° (ranges from −7.2° to 6.7°). On the 3DCT reconstructions, the APA (88.2° ± 4.2°) had significantly higher variance than the SL (90.3° ± 2.7°) (F = 5.82 and p = 0.017). An axis derived by averaging the SL and the PCA+3° produced a significant decrease in both the number of outliers (p = 0.03 vs. PCA and p = 0.007 vs. SL) and the variance (F = 6.15 and p = 0.015 vs. SL). The coronal alignment of the SL varied widely relative to the mechanical axis (0.4° ± 3.8°) and the distal condylar surface (2.6° ± 4.3°).ConclusionsThe multiple points used to determine the SL confer anatomical and geometrical advantages, and therefore, it should be considered a separate rotational landmark to the APA. These findings may explain the high degree of variability in the measurement of the APA which is documented in the literature. Combining a geometrically correct SL and the PCA is likely to further improve accuracy.

Rotational alignment of the distal femur: anthropometric measurements with CT-based patient-specific instruments planning show high variability of the posterior condylar angle.

Finding the anatomical landmarks used for correct femoral axial alignment can be difficult. The posterior condylar line (PCL) is probably the easiest to find during surgery. The aim of this study was to analyse whether a predetermined fixed angle referencing of the PCL could help find the surgical epicondylar axis (SEA) and this based on a large CT database with enough Caucasian diversity to be representable. A total of 2,637 CT scans and 3D reconstructions from patients on four continents, executed for preoperative planning and creation of patient-specific instrumentation, were used to perform anthropometric measurements and to measure the posterior condylar angle (PCA) between the surgical epicondylar angle and the PCL. The mean (SD) PCA was 4° (1.4°) of external rotation. A significant correlation was found between more external rotation of the SEA and more proximal varus of the tibia or more distal valgus of the femur. For 59% of the study population, 4° external rotation from the PCL would be the right amount of axial rotation to align the femoral component in line with the SEA. Nine per cent needs less, and 32% needs more than 4° of axial rotation. On 105 (4%) CT-based 3D models, external rotation between 7° and 11° was measured and 77 (73%) of those cases were in varus or neutral alignment. In 132 patients, bilateral measurements were available and 94 (71%) had rotation within 1° of the opposite side. This last finding underlines that there is even an intra-individual difference in distal femoral anatomy that can range from 1° to 5°. This study was performed on a very large anthropometric CT and 3D models database and showed that there is a 41% risk of malalignment if a fixed PCA referenced of the PCL is used in total knee arthroplasty. The clinical importance of this study is the observation that femoral axial anatomy is individual and also that it is determined by the tibial anatomy. A group of patients needs more than the average external rotation because they have more distal femoral valgus with dysplastic condyles or more proximal tibial varus with a bigger medial condyle. III.

The surgical epicondylar axis is a consistent reference of the distal femur in the coronal and axial planes

Various rotational landmarks including the surgical epicondylar axis (SEA) are used for preoperative planning and intra-operative reference of total knee arthroplasty (TKA) in the axial plane. The aim of the study was to elucidate the relationships between the SEA and other femoral anatomical landmarks, including the mechanical axis, distal and posterior knee joints, the trochlear groove, and the anterior femoral condyle, in both the coronal and axial planes. Angular and linear measurements were taken of sixty femora using Orthomap3D, which has a tool to analyse computed tomography image data that makes it possible to measure three-dimensional distances and angles precisely. The inter- and intra-observer reliabilities of these measurements were evaluated. Comparisons were made according to height, weight, body mass index, and gender. The angle between the mechanical axis and the SEA was 90.2° (95% CI 90.0°-90.4°). There was a significant correlation for each linear measurement between the SEA and the distal/posterior knee joint line and for each linear measurement between the SEA and the anterior medial/lateral femoral condyle. A significant difference was observed between genders in the linear measurements. Significant correlations were found between height and weight and linear parameters. Knowledge of the relationships between the SEA and other femoral anatomical landmarks is useful in preoperative planning, intra-operative landmark, and postoperative assessment of TKA. The SEA is a consistent parameter of femoral alignment in the coronal plane and a stable reference for femoral rotation in the axial plane. III.

The combined Whiteside’s and posterior condylar line as a reliable reference to describe axial distal femoral anatomy in patient-specific instrument planning

Aligning the femoral component in the axial plane parallel to the surgical epicondylar axis (SEA) has been generally recommended. In this retrospective study on the axial anatomy of the distal femur, as determined by the patient-specific instruments (PSI) planning tool based on MRI and 3D reconstructions, the different rotational axes were compared. The purpose of this study was to compare the impact of posterior axial anatomy on anterior anatomy and to compare the different angles of rotation obtained by a PSI-planning engineer. The preoperative planning of 77 PSI patients with a mean (SD) age of 65.6 (9.6)years undergoing primary total knee replacement for osteoarthritis was analysed for rotational anatomy of the distal femur. The angles between the posterior condylar line (PCL) and the SEA called posterior condylar angle (PCA), between Whiteside's line and the SEA and finally between Whiteside's line and the PCL, were retrieved from the PSI axial rotation planning screen. The mean (SD) PCA was 3.2° (1.4°). The mean (SD) angle between Whiteside's line and the SEA was 91.4° (2.2°), and the mean (SD) angle between Whiteside's line and the PCL was 94.5° (2.3°). No significant difference for this last rotational parameter was found in between varus and valgus knees. Patient-specific instrument's preoperative planning found consistent angles to describe the distal femoral anatomy as previously published in the literature. The angle between Whiteside's line and the PCL as measured on PSI planning is a mean angle of 94.5° (2.3°) for both varus and valgus knees. Setting a fixed PCA of 5° of external rotation referenced of the PCL makes this planning repeatable during conventional surgery. Therapeutic study, Level III.

Internal Rotation of Femoral Component Affects Functional Activities After TKA—Survey With The 2011 Knee Society Score

The 2011 Knee Society Knee Scoring System (KSS) was developed as a new patient-derived outcome measure to better characterize satisfaction, expectations, and physical activities after total knee arthroplasty. The rotational alignment of the femoral and tibial components was assessed with computed tomography in 75 patients (92 knees), and its effect on the scores of the KSS was evaluated. Internal rotation of the femoral component relative to the surgical epicondylar axis significantly decreased the score of functional activities and slightly decreased the score of satisfaction. Femoral component malrotation did not affect the scores of symptoms and expectations. Tibial component malrotation did not affect any of the scores of the 2011 KSS. Surgeons should avoid internal rotation of the femoral component to preserve functional activities.

Medial sixth of the patellar tendon at the tibial attachment is useful for the anterior reference in rotational alignment of the tibial component

The anteroposterior (AP) axis connecting the middle of the posterior cruciate ligament to the medial border of the patellar tendon at its attachment has been introduced as a reproducible and reliable reference perpendicular to the surgical epicondylar axis in healthy knees. A recent literature has reported that the AP axis of the tibia is, on average, almost perpendicular to the surgical epicondylar axis also in varus and valgus knees and can be used as a tibial rotational reference to minimize the risk for rotational mismatch between the femoral and tibial components in total knee arthroplasty (TKA). However, it is difficult to identify the AP axis after tibial resection. The purpose of the current study was to determine a modified AP axis that runs parallel to the AP axis and passes through the centre of the cut surface in osteoarthritic knees. Preoperative computed tomography scans on 30 varus and 30 valgus knees undergoing TKA were studied using a three-dimensional software. The modified AP axis that runs parallel to the AP axis and passes through the centre of the cut surface was drawn. We investigated where the modified AP axis crossed the patellar tendon at its tibial attachment. The modified AP axis passed through the medial 1/6 of the patellar tendon (4mm from medial edge) at its attachment in both varus and valgus knees. The AP axis of the tibia is useful as a tibial rotational reference in cutting the proximal tibia, but it is difficult to identify the AP axis after tibial resection. The clinical relevance of this study is that medial 1/6 of the patellar tendon at its attachment would be a useful landmark in aligning the tibial component. IV.

Paper 105: Changes in Patellar Alignment After Total Knee Arthroplasty

Although the results of total knee arthroplasty continue to improve, problems related to the patellofemoral joint remain significant. This study examined the factors affecting patellar alignment after total knee arthroplasty and subsequent changes during a postoperative period of 5.3 years. Fifty-five knees in 39 patients were retrospectively evaluated by radiography for postoperative patellar alignment. This study included four men and 35 women with a mean follow-up time of 5.3 years (range: 2.5 to 8.4). All procedures utilized identical surgical technique; through a midline skin incision and medial parapatellar arthrotomy, the patella was fully everted. We adjusted the rotation of the femoral component until it was parallel to the surgical epicondylar axis. Using the posterior femoral condyles as references, we inserted the femoral components with 3° to 5° of external rotation to the posterior condylar axis according to preoperative CT scans. Tibial components were set using the medial third of the tibial tuberosity as a reference. All patellae were resurfaced with three-peg offset-dome all-polyethylene patellar component. Patellar alignment was assessed by measuring the lateral tilt and lateral displacement in skyline views taken with the knees at approximately 60° of flexion. Patellar alignment was evaluated one month after surgery, and at final follow-up. Changes in patellar lateral tilt angle and lateral displacement in the postoperative period were calculated using data obtained one month after surgery and at final follow-up. We did not observe severe malalignment of the femorotibial joint, patellar bone fracture, prosthesis failure, or any other clinical complications after TKA in any cases. The mean patellar lateral tilt angle was -0.7° (range: −13.7 to 7.0°) one month after surgery and −0.4° (range: −11.4 to 11.6°) at final follow-up. The mean patellar lateral displacement was 1.1mm (−2.7 to 6.6mm) one month after surgery and 0.9mm (−3.7 to 5.8mm) at final follow-up. We observed a negative correlation between the patellar resection angle and lateral tilt one month after surgery (p<0.0001) and between the patellar resection angle and patellar lateral displacement one month after surgery (p=0.0003). Lateral retinacular release was required for thirteen knees. In these cases, the resection angle was significantly smaller than that seen in knees without lateral retinacular release (p=0.0012). These results demonstrate that a smaller resection angle correlated with an increased frequency of lateral retinacular release. The change in patellar lateral tilt angle after 5.3 years was 0.3° (range: −7.2 to 7.0°), while the change in patellar lateral displacement was −0.3 mm (range: −5.2 to 3.7 mm). These changes did not significantly correlate with patellar alignment at any time point, resection angle, resection thickness, lateral retinacular release, or clinical results. The postoperative femorotibial alignment, however, exhibited a statistically significant correlation with the changes in lateral tilt angle (p=0.020). A more varus postoperative alignment correlated with increased lateral tilt of the patella in the postoperative period. We observed a satisfactory patellar alignment after a postoperative period of 5.3 years. The patellar resection angle had a significant effect on postoperative patellar alignment. Our findings suggest that leaving a thicker patellar remnant on the medial side can decrease postoperative lateral tilt and the resulting need for lateral retinacular release. Postoperative changes in patellar alignment were very small; none of the knees demonstrated complications of the patellofemoral joints. In this study, we observed the tendency that a postoperative varus alignment leads to patellar lateral tilt. Surgeons should pay scrupulous attention to femorotibial alignment during total knee arthroplasty to decrease patellofemoral complications and femorotibial problems.

Relationship between the tibial anteroposterior axis and the surgical epicondylar axis in varus and valgus knees

Proper rotational alignment in total knee arthroplasty (TKA) is essential for successful outcomes. The surgical epicondylar axis (SEA) has been frequently used to determine the femoral rotational alignment, and the anteroposterior (AP) axis of the tibia described in previous study has been introduced as a line perpendicular to the SEA in healthy knees. However, the rotational relationship between the distal femur and the proximal tibia would vary between normal and osteoarthritic knees, and a question remains whether the rotational relationship between the SEA and the AP axis of the tibia would be the same between normal and osteoarthritic knees. This study aims to determine whether the AP axis of the tibia is actually perpendicular to the SEA and useful for the tibial rotational alignment also in osteoarthritic knees. Preoperative computed tomography scans on 25 varus and 25 valgus knees undergoing TKA were studied. The SEA and the AP axis of the tibia were identified using a three-dimensional software, and the angle between the line perpendicular to the projected SEA and the AP axis was measured. The AP axis of the tibia was 1.7° ± 4.3° and 2.0° ± 4.0° internally rotated relative to the line perpendicular to the SEA in the varus and valgus groups, respectively. The AP axis of the tibia was, on average, perpendicular to the SEA in both varus and valgus knees. The AP axis would be useful for setting the tibial component with minimal rotational mismatch. IV.

Influence of the Position of the Fibular Head After Implantation of a Total Knee Prosthesis on Femorotibial Rotation

A gold standard for the correct rotation of the tibial component has not been established in total knee arthroplasty (TKA). The target parameter of correct rotation is the facilitation of femorotibial rotation over the entire range of motion with no implant overhang. Although the origin of the lateral collateral ligament is a recognized landmark for determining the rotation of the femoral component (epicondylar axis), the attachment of the lateral collateral ligament has not been taken into consideration for adjusting tibial rotation until now. The objective of the current investigation was to examine whether the position of the fibular head, as the attachment of the lateral collateral ligament, influences femorotibial rotation. Seventy patients who underwent TKA were enrolled in this retrospective study. Computed tomography (CT) of the operated knee was performed 6 months postoperatively in all cases and the position of the lateral facet of the fibular head and the tibial tuberosity, and the geometric center of the tibia and the femoral epicondyles were determined. The angle between the lateral facet of the fibular head, the geometric center of the tibia, and the tibial tuberosity was 45.7°±6.9°. The angle between the surgical epicondylar axis and the line from tibial tuberosity to tibial center was 69°±8.3°. This close correlation (R=.73; P<.001) shows that the position of the fibular head determines femorotibial rotation. The fibular head may become a helpful landmark for establishing the rotation of the tibial component; it could be useful in interpretation of postoperative CT scans in knees suspected of tibial malrotation.

Kinematic analysis of the flexion axis for correct femoral component placement

This study evaluates a new method for intraoperative determination of femoral component rotation by a navigation system (flexion axis, FA) driven by joint stability over the range of motion. Seventy-five patients were treated with a navigated total knee replacement. Intraoperatively, the posterior condylar axis (PCA), the Whiteside's line (WL), and the surgical epicondylar axis (EA) were palpated, the flexion gap (FG) was determined, and the FA was calculated. The anatomical landmarks, lines, and angles were determined based on a postoperative computed tomography in all knees. The femoral rotation was intraoperatively determined by the surgeon based on the knowledge of the EA, the PCA, and the FG but not the FA. The deviation of the palpated EA was 3.5° [0°-13.8°], of the PCA externally rotated by 3° was 2.2° [0°-9.6°], of the WL was 3.8° [0.1°-10.0°], of the FG was 2.5° [0.2°-8.8°], and of the FA was 2.5° [0°-10.0°]. The FA is a new functionally acquired axis for the determination of optimal femoral component alignment. Whether the FA leads to clinically superior results must be clarified by subsequent studies.

Effects of cartilage remnants of the posterior femoral condyles on femoral component rotation in varus knee osteoarthritis

Preoperative planning of total knee arthroplasty (TKA) based on computerized tomography (CT) data can produce a femoral rotational error due to lack of information on the femoral cartilage thickness. The research question of this study is how much femoral rotational error is expected due to the cartilage remnants when using the posterior condylar angles (PCA, angle between the posterior condylar line and the surgical epicondylar axis (SEA)) on CT data. CT arthrography was performed for 35 consecutive varus osteoarthritic knees in 31 patients who underwent TKA, on which the cartilage thicknesses of the posterior femoral condyles were measured. The PCAs when including or excluding the cartilage remnants were also measured. The cartilage thicknesses of the medial and lateral posterior condyles averaged 0.39mm (SD=0.53) and 1.55mm (SD=0.26), respectively (p<0.0001). When the cartilage was included or excluded, the PCA averaged 2.2° (SD=1.5) and 3.3° (SD=1.5), respectively (p=0.002). The cartilage remnants in the posterior femoral condyles produced an average of 1.1° and a maximum of 2.1° of additional femoral external rotation when using CT data for the preoperative planning. CT scan measurements of femoral rotation are subject to error. Although this is said to be small and within the safety margin for setting the femoral component parallel to the trans-epicondylar axis, this difference should be considered by surgeons who use the posterior condylar axis, in order to avoid excessive external rotation of the femoral component.

Anatomical Study of the Radius and Center of Curvature of the Distal Femoral Condyle

In this anatomical study, the anteroposterior curvature of the surface of 16 cadaveric distal femurs was examined in terms of radii and center point. Those two parameters attract high interest due to their significance for total knee arthroplasty. Basically, two different conclusions have been drawn in foregoing studies: (1) The curvature shows a constant radius and (2) the curvature shows a variable radius. The investigations were based on a new method combining three-dimensional laser-scanning and planar geometrical analyses. This method is aimed at providing high accuracy and high local resolution. The high-precision laser scanning enables the exact reproduction of the distal femurs-including their cartilage tissue-as a three-dimensional computer model. The surface curvature was investigated on intersection planes that were oriented perpendicularly to the surgical epicondylar line. Three planes were placed at the central part of each condyle. The intersection of either plane with the femur model was approximated with the help of a b-spline, yielding three b-splines on each condyle. The radii and center points of the circles, approximating the local curvature of the b-splines, were then evaluated. The results from all three b-splines were averaged in order to increase the reliability of the method. The results show the variation in the surface curvatures of the investigated samples of condyles. These variations are expressed in the pattern of the center points and the radii of the curvatures. The standard deviations of the radii for a 90 deg arc on the posterior condyle range from 0.6 mm up to 5.1 mm, with an average of 2.4 mm laterally and 2.2 mm medially. No correlation was found between the curvature of the lateral and medial condyles. Within the range of the investigated 16 samples, the conclusion can be drawn that the condyle surface curvature is not constant and different for all specimens when viewed along the surgical epicondylar axis. For the portion of the condylar surface that articulates with the tibia during knee flexion-extension, the determined center points approximate the location of the centers of rotation. The results suggest that the concept of a fixed flexion-extension axis is not applicable for every specimen.

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

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. 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. 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°. 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.

Rotation of the femoral component in total knee arthroplasty—a refresher

Malrotation of the femoral component is a common cause of therapy-resistant pain after total knee arthroplasty. There is no consensus about the best technique to intraoperatively determine the correct femoral component rotation. Established landmarks are the posterior condylar axis, surgical epicondylar axis, Whiteside’s line, and flexion gap symmetry. In contrast to this, only the epicondylar axis and the flexion gap stability can be controlled postoperatively. The article gives an overview about what is, based on the actual literature nowadays, defined to be a correct femoral rotation.