Posterior Cortical Line Research Articles

Poster 246: Radiographic Landmarks for Femoral Tunnel Positioning During MPFC Reconstruction Vary With Trochlear Dysplasia

Objectives: Accurate femoral tunnel positioning during medial patellofemoral complex (MPFC) reconstruction has been shown to be critical in optimizing outcomes and avoiding complications. Multiple anatomic and radiographic studies have described methods to accurately identify the appropriate femoral attachment of the MPFC, commonly referencing the adductor tubercle and medial epicondyle as landmarks. However, these studies have been performed in normal knees, and the relevance to knees with patellar instability and anatomic risk factors has not been described. Therefore, the purpose of this study was to compare the radiographic positions of commonly utilized landmarks between symptomatic and normal knees. Methods: Three-dimensional (3D) models were created from computed tomography scans of knees with patellar instability and compared to age- and sex-matched control knees. On the 3D models, the locations of the adductor tubercle (AT), medial epicondyle (ME) and gastrocnemius tubercle (GT) were marked. A 2-dimensional perfect lateral view was then created from these models to simulate radiographs, and the radiographic location of each landmark was described with respect to the following: 1) anteroposterior relation to the posterior cortical line and 2) proximal-distal relationship to the posterior condylar line. The position of each landmark was compared between symptomatic and control groups, and linear regression analysis was performed to assess variations in position with severity of anatomic risk factors including trochlear dysplasia, tuberosity lateralization and patella alta. Results: Forty knees were included in this study, including 20 symptomatic and 20 control knees (8 men and 12 women in each group, age 21.5+/-6.9 years old vs 21.3+/-7.0 years old). On the 2D (radiographic) views, the ME landmarks in the symptomatic group were found to be significantly more posterior (6.9+/-3.7mm vs 9.5+/-4.2 mm, p = 0.031) and significantly more distal (9.2+/-4.4 vs 12.1+/-5.6, p = 0.047) than in the control group. For the AT, no significant differences were noted in the anteroposterior (0.7+/-2.4 vs 1.3+/-2.6 mm anterior to the posterior cortex, p = 0.238) or proximal-distal (4.9+/-2.8 vs 5.4+/-2.3mm proximal to the posterior condylar line, p = 0.259) positions. Similarly, no differences for the GT were found (4.4+/-3.4 vs 2.8+/-3.7 mm posterior to the posterior cortex, p = 0.100; and 5.1+/-4.6 vs 4.0+/-3.2 mm distal to the posterior condylar line, p = 0.175). An association between severity of trochlear dysplasia and posterior position of the AT was identified (R = 0.43, R2 = 0.18, p = 0.058). Conclusions: Although intraoperative fluoroscopy is commonly utilized to identify femoral tunnel positioning during MPFC reconstruction, this study demonstrates that commonly utilized anatomic reference points such as the medial epicondyle in symptomatic knees are more posterior and more distal on perfect lateral radiographs when compared to normal knees. Furthermore, the severity of trochlear dysplasia appears to influence radiographic AT position. These findings should be taken into consideration when utilizing fluoroscopy during MPFC reconstruction. Further studies are needed to identify optimal femoral tunnel positioning for knees with anatomic risk factors when performing surgical treatment for patellar instability.

Radiographic Landmark Measurements for the Femoral Footprint of the Medial Patellofemoral Complex May Be Affected by Visible Femoral Shaft Length on Lateral Knee Radiographs

To assess the effect of visible femoral shaft length on the accuracy of radiographic landmarks of the medial patellofemoral complex (MPFC). In 9 cadaveric knees, the MPFC footprint was exposed on the medial femur, and its proximal and distal boundaries were marked. Lateral fluoroscopic images of the knee were assessed in 1-cm length increments, beginning 1 cm proximal to the medial condyle and continuing proximally to 8 cm. The MPFC midpoint was described on each image relative to the posterior cortical line of the femur and a line perpendicular to this line through the proximal margin of the medial condyle. In addition, the MPFC midpoint was assessed relative to a line from the proximal posterior cortex to the midpoint of Blumensaat line. Using the posterior cortical line as a reference, the MPFC radiographic landmark moved anteriorly with decreasing visible femoral shaft on radiographs, particularly at 4 cm and less. However, no proximal-distal change was noted. Linear regression analysis demonstrated a relationship between visible femoral shaft and MPFC position on radiographs (R= 0.461, R2= 0.212, B= -0.636, P < .001). For every centimeter decrease in the visible femoral shaft, the radiographic MPFC footprint moved anteriorly by 0.636 mm. Receiver operating characteristic curve analysis revealed that a minimum of 4 cm of femoral shaft on lateral radiographs is required for accurate MPFC footprint localization (area under the curve= 0.80; sensitivity= 76.7%; specificity= 69.0%; P < .001). In contrast, no anterior-posterior change was seen when referencing a line from the proximal posterior cortex to the midpoint of Blumensaat line. When using the posterior cortical line to identify the midpoint of the MPFC, at least 4 cm of femoral shaft should be visible for accurate assessment. If less than 4 cm of shaft is visible, a line through the midpoint of Blumensaat line and the proximal posterior cortex can be used as an alternative method to estimate the position of the femoral footprint. As fluoroscopy is frequently used intraoperatively for MPFC reconstruction, our findings may serve as a guide when assessing femoral tunnel placement on fluoroscopy.

Poster 132: Femoral length on lateral knee radiographs influences accuracy of radiographic landmarks for MPFC reconstruction

Objectives: Accuracy of femoral tunnel positioning is critical during medial patellofemoral complex (MPFC) reconstruction, as even 5mm of malpositioning has been associated with altered patellofemoral contact pressures. To help identify the appropriate position for femoral tunnel placement, Schottle and others have described radiographic landmarks to identify the MPFC footprint on lateral knee radiographs. These measurements are based on an extension of the posterior cortical line, which can vary based on the length of the femur visible on the radiograph. Because the scope of view can vary between intraoperative imaging modalities, the aim of this study was to assess the effect of femoral length on the accuracy of radiographic landmarks of the MPFC. Methods: In 9 unpaired cadaveric knees, the MPFC footprint was exposed on the medial femur, and the proximal and distal boundaries of the footprint were marked. Lateral fluoroscopic images of the knee were obtained and assessed in 1 cm length increments, beginning 1cm proximal to the posterior condyle and continuing proximally to a femoral length of 8 cms. The MPFC midpoint was described on each image relative to the posterior cortical line of the femur and a line perpendicular to this line, relative to the proximal margin of the posterior condyle. Linear regression analysis was used to assess the effect of femoral length on the radiographic position of the MPFC. ROC curve analysis and Delong test were used, and the minimum amount of femoral length required on radiographs to accurately identify an anatomic femoral tunnel was determined using Youden’s J statistic. Results: Using the posterior cortical line as a reference, the radiographic description of the MPFC footprint moved anteriorly with decreasing femoral length on the radiographs, particularly at 4cm and less. However, no proximal-distal change was seen in relation to the line through the proximal margin of the posterior condyle with changing femoral lengths. Linear regression analysis showed a significant relationship between the femoral length and anterior radiographic position of the MPFC on radiographs (R = 0.461, R2 = 0.212, B= -0.636, p &lt; 0.001). The slope coefficient was -0.636 mm, indicating that for every cm decrease in femoral length, the actual anatomic footprint of the MPFC moves anteriorly by 0.636 mm in relation to the posterior cortical line. Furthermore, ROC curve analysis revealed that a minimum of 4 cm of femoral length on lateral radiographs is required to accurately localize the footprint of the MPFC (AUC 0.80; sensitivity 76.7 %; specificity 69 %; p &lt; 0.001). Conclusions: The radiographic landmarks for the MPFC femoral footprint can change depending on the length of the distal femur visible on radiographs. We found that at least 4cm of the femoral shaft should be visible for the radiographic landmarks to be accurate. As fluoroscopy is frequently used intraoperatively for MPFC reconstruction, our findings may serve as a guide for accurate femoral tunnel placement.

Paper 06: Femoral length on lateral knee radiographs influences accuracy of radiographic landmarks for MPFC reconstruction

Objectives: Accuracy of femoral tunnel positioning is critical during medial patellofemoral complex (MPFC) reconstruction, as even 5mm of malpositioning has been associated with altered patellofemoral contact pressures. To help identify the appropriate position for femoral tunnel placement, Schottle and others have described radiographic landmarks to identify the MPFC footprint on lateral knee radiographs. These measurements are based on an extension of the posterior cortical line, which can vary based on the length of the femur visible on the radiograph. Because the scope of view can vary between intraoperative imaging modalities, the aim of this study was to assess the effect of femoral length on the accuracy of radiographic landmarks of the MPFC. Methods: In 9 unpaired cadaveric knees, the MPFC footprint was exposed on the medial femur, and the proximal and distal boundaries of the footprint were marked. Lateral fluoroscopic images of the knee were obtained and assessed in 1 cm length increments, beginning 1cm proximal to the posterior condyle and continuing proximally to a femoral length of 8 cms. The MPFC midpoint was described on each image relative to the posterior cortical line of the femur and a line perpendicular to this line, relative to the proximal margin of the posterior condyle. Linear regression analysis was used to assess the effect of femoral length on the radiographic position of the MPFC. ROC curve analysis and Delong test were used to determine ROC curve analysis and Delong test were used, and the minimum amount of femoral length required on radiographs to accurately identify an anatomic femoral tunnel was determined using Youden’s J statistic. Results: Using the posterior cortical line as a reference, the radiographic description of the MPFC footprint moved anteriorly with decreasing femoral length on the radiographs, particularly at 4cm and less. However, no proximal-distal change was seen in relation to the line through the proximal margin of the posterior condyle with changing femoral lengths. Linear regression analysis showed a significant relationship between the femoral length and anterior position of the MPFC on radiographs (R = 0.461, R2 = 0.212, B= -0.636, p &lt; 0.001). The slope coefficient was -0.636 mm, indicating that for every cm decrease in femoral length, the actual anatomic footprint of the MPFC moves anteriorly by 0.636 mm in relation to the posterior cortical line. Furthermore, ROC curve analysis revealed that a minimum of 4 cm of femoral length on lateral radiographs is required to accurately localize the footprint of the MPFC (AUC 0.79; sensitivity 76.7 %; specificity 69 %; p &lt; 0.001). Conclusions: The radiographic landmarks for the MPFC femoral footprint can change depending on the length of the distal femur visible on radiographs. We found that at least 4cm of the femoral shaft should be visible for the radiographic landmarks to be accurate. As fluoroscopy is frequently used intraoperatively for MPFC reconstruction, our findings may serve as a guide for accurate femoral tunnel placement.

Radiographic Landmarks for the Femoral Attachment of the Medial Patellofemoral Complex: A Cadaveric Study

To report the radiographic landmarks for the medial patellofemoral complex (MPFC) footprint on the medial femur and describe the difference between the radiographic positions corresponding to the medial quadriceps tendon femoral ligament (MQTFL) and medial patellofemoral ligament (MPFL) fibers. In 8 unpaired cadaveric knees, the MPFC footprint was exposed on the medial femur, and the proximal and distal boundaries of the footprint were marked. Lateral fluoroscopic images of the knee were obtained and analyzed using Image J. The proximal boundary corresponding to the MQTFL, the MPFC midpoint, and distal boundary corresponding to the MPFL were described radiographically and compared for differences in position. The proximal MQTFL footprint was 0.8 ± 0.6 mm anterior (P= .013) and 5.2 ± 1.8 mm proximal to the MPFC midpoint (P <.001), whereas the distal MPFL footprint was 0.8 ± 0.7 mm posterior (P= .012) and 5.9 ± 1.1 mm distal to the radiographic MPFC midpoint (P <.001). The radiographic point corresponding to the distal MPFL footprint was 0.8 ± 0.9 mm posterior (P= .011) and 11.1 ± 2.3 mm distal to the radiographic point of the proximal MQTFL footprint (P <.001). When using the point of intersection of the posterior cortical line and the proximal posterior condyle as a reference, 91.6% of all points correlating to the MQTFL, MPFC midpoint and MPFL, were within 10 mm in any direction from this radiographic landmark. On fluoroscopic imaging, the proximal MQTFL and distal MPFL fibers had significantly different radiographic positions from the MPFC midpoint on the femur. These findings should be considered when reconstructing specific components of the MPFC. As fluoroscopy is often used intraoperatively to guide graft placement, our findings may serve as a reference when differentiating the locations of the MPFL vs MQTFL on the femur for anatomic reconstruction.

Effect of the Osteotomy Length on the Change of the Posterior Tibial Slope With a Simple Distraction of the Posterior Gap in the Uni- and Biplanar Open-Wedge High Tibial Osteotomy

To (1) determine the length of the osteotomy at the anterior and posterior cortex, (2) compare between uni- and biplanar osteotomy, and (3) evaluate the relationship between the extent of the osteotomy and change of the posterior tibial slope. A prospective comparative study of 24 uniplanar and 30 biplanar osteotomies was performed. To evaluate the length of osteotomy, osteotomy lines of the anterior and posterior cortex were analyzed in the 3-dimensional surface models. For slope measurement, the intramedullary axis of the proximal tibia (slope P), posterior cortical line of the proximal tibia (slope C), and anterior cortical line of the proximal fibula (slope F) were used. An analysis of the changes in the posterior tibial slope was performed independently using a pre- and postoperative lateral plane radiograph. In the uniplanar osteotomy, ratios of the osteotomized length to the total cortical length aligned with the osteotomized plane were larger in the anterior cortex (0.91 in uniplanar v 0.46 in biplanar; P = 0) and posterior cortex (0.97 in uniplanar v 0.79 ratio in biplanar; P = 0). Furthermore, the posterior tibial slope was maintained in both groups and the ratios between the anterior and posterior gap in both groups were 0.57 and 0.63, respectively. The maintenance of the slope was not related to any specific variables. Additionally, these phenomena did not differ between those patients who underwent uni- and those who underwent biplanar osteotomy. Increase in the posterior tibial slope was prevented with appropriate uni- or biplanar osteotomy with a simple distraction at the most posterior gap. However, in the uniplanar osteotomy, the ratio of the osteotomized length to the total cortical length was larger in both the anterior and posterior cortex.

Posterior tibial slope accuracy with patient-specific cutting guides during total knee arthroplasty: A preliminary study of 50 cases

BackgroundPatient-specific cutting guides were recently introduced to facilitate total knee arthroplasty (TKA). Their accuracy in achieving optimal implant alignment remains controversial. The objective of this study was to evaluate postoperative radiographic outcomes of 50 TKA procedures with special attention to posterior tibial slope (PTS), which is difficult to control intraoperatively. We hypothesized that patient-specific cutting guides failed to consistently produce the planned PTS. Material and methodsThe Signature™ patient-specific cutting guides (Biomet) developed from magnetic resonance imaging data were used in a prospective case-series of 50 TKAs. The target PTS was 2°. Standardised digitised radiographs were obtained postoperatively and evaluated by an independent reader. Reproducibility of the radiographic measurements was assessed on 20 cases. The posterior cortical line of the proximal tibia was chosen as the reference for PTS measurement. Inaccuracy was defined as an at least 2° difference in either direction compared to the target. ResultsThe implant PTS was within 2° of the target in 72% of knees. In the remaining 28%, PTS was either excessive (n=10; maximum, 9°) or reversed (n=4; maximum, –6°). The postoperative hip-knee-ankle angle was 0°±3° in 88% of knees, and the greatest deviation was 9° of varus. ConclusionThese findings support our hypothesis that patient-specific instrumentation decreases PTS accuracy. They are consistent with recently published data. In contrast, patient-specific instrumentation provided accurate alignment in the coronal plane. Level of evidenceIV, cohort study.

Radiographic landmarks for tunnel placement in reconstruction of the medial patellofemoral ligament

To verify the findings of previous studies in confirming radiographic landmarks for the femoral attachment of the medial patellofemoral ligament (MPFL), but also to define radiographic landmarks for the patellar attachment. Assess the effect of limb rotation upon these radiographic landmarks. The medial patellofemoral ligament was identified in ten fresh-frozen human cadaveric knees. A headed pin was used to mark the centre of the femoral and patellar attachments. True lateral radiographs were performed followed by lateral radiographs in 10° and 20° of internal and external rotation. Posterior-anterior and proximal-distal position of the headed pin was evaluated. The femoral attachment averaged 3.8 ± 5.0 mm anterior to the posterior femoral cortical line and 0.9 ± 2.4 mm distal to the perpendicular line intersecting the posterior aspect of Blumensaat's line. The patellar attachment averaged 7.4 ± 3.5 mm anterior to the posterior patellar cortical line, 5.4 ± 2.6 mm distal to the perpendicular line intersecting the proximal margin of the patellar articular surface. There was a significant relationship between limb rotation and distance of femoral and patellar attachment from the posterior cortical line (P < 0.0001 and P < 0.0002 respectively). Radiographic landmarks for the femoral attachment of the MPFL identified in this study are comparable with other recent work. This study describes new radiographic landmarks for the patellar attachment of the MPFL and highlights that it is essential to acquire true lateral radiographs if these radiographic landmarks are to be interpreted accurately.

Anatomical References to Assess the Posterior Tibial Slope in Total Knee Arthroplasty: A Comparison of 5 Anatomical Axes

There has been no consensus on an ideal anatomical reference to determine the posterior slope of tibia plateau. Posterior slope of the medial tibia plateau was measured with reference to a proposed mechanical axis (MA) and 5clinically relevant anatomical references in 90 osteoarthritic knees of 66 female patients undergoing total knee arthroplasty. The MA was defined as the line connecting the midpoints of the medial tibia plateau and the tibial plafond, and 5anatomical references included the anterior cortical line of tibia, anatomical axis of proximal and central tibia, posterior cortical line of proximal tibia, and fibular shaft axis. The average posterior slope was 10.6° with reference to the MA, and the amount of posterior slope varied widely among the patients and depending on the anatomical reference used to measure. This study indicates that the anatomical reference used to measure the posterior slope should be identified in studies where posterior slope is used to evaluate the sagittal alignment of total knee arthroplasty.

A Radiologic Study of the Reference Line for Measuring Posterior Slope Angle on Lateral View of the Knee

Purpose: This study evaluated the radiological reference line of the posterior slope angle on the lateral view of a plain knee radiograph. Materials and Methods: The lateral view of the plain knee and whole tibia radiographs were analyzed from thirty seven patients (fifty-two cases) who had undergone total knee arthroplasty. The posterior slope angle was measured on the lateral view of the tibia. On the lateral view of the knee, the posterior slope angle was measured with reference to the proximal tibial anatomical axis, the proximal tibial anterior cortical line, the proximal tibial posterior cortical line and the proximal fibular anatomical axis. These values were compared with the posterior slope angle measured on the whole tibia lateral view. Results: The posterior slope angle, which was measured by the anterior cortical line as a reference line, was tilted slightly anteriorly to that measured by the whole tibial lateral anatomical axis (0.15 degree in average; anterior slope 3.95- posterior slope 5.57 degree). This difference was smallest among that of the measured angle by the other reference lines (p ＜ 0.001). Conclusion: The anterior cortical line of the proximal tibia appears to be the most reliable reference line for measuring the posterior slope angle on a knee lateral radiograph after TKA.

True Femoral Anteversion During Primary Total Hip Arthroplasty: Use of Postoperative Computed Tomography–Based Sections

This study investigated a reference line that is closer to the true femoral anteversion on only the cutting surface of the proximal femoral neck during a femoral stem insertion in a cementless total hip arthroplasty. A postoperative computed tomography of both hips from 33 consecutive patients after a unilateral primary cementless total hip arthroplasty with an avascular necrosis of the femoral head was taken to observe the positioning of the stem and its correlation with the true anteversion of the contralateral side. The average of the midcortical angle was 14.1° ± 6.8° on the lesion side and 0.1° ± 1.3° more than the true anteversion on the contralateral side. This study has shown that anteversion using a midcortical line between the anterior cortical line and the posterior cortical line is compatible with the true femoral anteversion. However, further investigation is required to confirm the true femoral anteversion.