Intramedullary Axis Research Articles

The Traditional Intramedullary Axis Underestimates the Medial Tibial Slope Compared to Transmalleolar Sagittal Axis in Image-based Robotic-Assisted Unicompartimental Knee Arthroplasty.

The medial unicompartmental knee arthroplasty (mUKA) has been recognized as an excellent treatment for medial knee osteoarthritis. The posterior tibial slope (PTS) is measured radiographically with the intramedullary axis (IMA) to the tibial baseplate on the sagittal plane radiograph. However, in most computer-navigated or robotic mUKAs, the PTS is set from a transmalleolar axis (TMA).The PTS difference was evaluatedbetween the sagittal TMA and the sagittal IMA of patients undergoing a CT-based primary robotic-assisted mUKA.We retrospectively reviewed the preoperative computed tomography (CT) scans taken according to the MAKO system protocol (Stryker) of 67 patients undergoing mUKAs. We measured the angular difference between the IMA and the TMA in the sagittal plane.Using the TMA to set the PTS the estimation of the slope of the medial tibial plateau would increase by an average of 1.9 ± 3.2 degreescompared to the IMA. Furthermore, in nineknees, PTS was decreased.Tibial components implanted with the help of a CT scan-based preoperative planning MAKO will show an average of 1.9 degrees more than those measured on sagittal radiographs potentially of concern for knee kinematics. A universal language is needed to standardize the slope calculation and the respective reference axis used.

Discrepancies in Sagittal Alignment of the Lower Extremity Among Different Brands of Robotic Total Knee Arthroplasty Systems

BackgroundThere is an increasing number of different brands of robotic total knee arthroplasty (TKA) systems. Most robotic TKA systems share the same coronal alignment, while the definitions of sagittal alignment vary. The purpose of this study was to investigate whether these discrepancies impact the sagittal alignment of the lower extremity. MethodsA total of 72 lower extremity computed tomography scans were included in our study, and 3-dimensional models were obtained using software. A total of 7 brands of robotic TKA systems were included in the study. The lower extremity axes were defined based on the surgical guide for each implant. We also set the intramedullary axis as a reference to evaluate the discrepancies in sagittal alignment of each brand of robotic system. ResultsOn the femoral side, the axis definition was the same for all 7 robotic TKA systems. The robotic TKA axes showed a 2.41° (1.58°, 3.38°) deviation from the intramedullary axis. On the tibial side, the 7 robots had different axis definitions. The tibial mechanical axis of 6 of the TKA systems was more flexed than that of the intramedullary axis, which means the posterior tibial slope was decreased while the tibial mechanical axis of the remaining system was more extended. ConclusionsThe sagittal alignment of the lower extremity for 7 different brands of robotic TKA systems differed from each other and all deviated from the intramedullary axis. Surgeons should be aware of this discrepancy when using different brands of robotic TKA systems to avoid unexpected sagittal alignment and corresponding adverse clinical outcomes. Level of EvidenceLevel IV, Therapeutic Study.

Referencing the center of the femoral head during robotic or computer-navigated primary total knee arthroplasty results in less femoral component flexion than the traditional intramedullary axis

BackgroundDuring robotic and computer-navigated primary total knee arthroplasty (TKA), the center of the femoral head is utilized as the proximal reference point for femoral component position rather than the intramedullary axis. We sought to analyze the effect on femoral component flexion–extension position between these two reference points. MethodsWe obtained CT 3D-reconstructions of 50 cadaveric intact femurs. We defined the navigation axis as the line from center of the femoral head to center of the knee (lowest point of the trochlear groove) and the intramedullary axis as the line from center of the knee to center of the canal at the isthmus. Differences between these axes in the sagittal plane were measured. Degree of femoral bow and femoral neck anteversion were correlated with the differences between the two femoral axes. ResultsOn average, the navigated axis was 1.4° (range, −1.4° to 4.1°) posterior to the intramedullary axis. As such, the femoral component would have on average 1.4° less flexion compared with techniques referencing the intramedullary canal. A more anterior intramedullary compared with navigated axis (i.e., less femoral flexion) was associated with more femoral bow (R2 = 0.7, P < 0.001) and less femoral neck anteversion (R2 = 0.5, P < 0.05). ConclusionComputer-navigated or robotic TKA in which the center of the femoral head is utilized as a reference point, results in 1.4° less femoral component flexion than would be achieved by referencing the intramedullary canal. Surgeons should be aware of these differences as they may ultimately influence knee kinematics.

Sagittal Alignment in Total Knee Arthroplasty: Are There Any Discrepancies Between Robotic-Assisted and Manual Axis Orientation?

Sagittal alignment determines the extension and flexion of knee prostheses in total knee arthroplasty (TKA). The definition of the sagittal axes may be different between the Mako TKA system (Stryker) and the conventional manual intramedullary approach. Whether there is any discrepancy between the 2 approaches has not been well studied. We retrospectively analyzed 60 full-length computed tomographic (CT) scans of the lower extremities of 54 patients. The femur and tibia were modeled by using Mimics (Materialise). The Mako mechanical axes were determined according to the Mako TKA Surgical Guide. The manual intramedullary axes were determined according to the central axis of the tibial proximal and femoral distal medullary cavities. The femoral, tibial, and combined angular discrepancies were measured in the sagittal plane. On the femoral side, the Mako mechanical axis was more likely to be located in an extended position relative to the manual intramedullary axis (56 of 60 knees). The median angular discrepancy was 2.46° (interquartile range [IQR], 1.56° to 3.43° [range, -1.06° to 5.24°]). On the tibial side, the Mako mechanical axis was likely to be located in a flexed position relative to the manual intramedullary axis (57 of 60 knees). The median angular discrepancy was 2.40° (IQR, 1.87° to 2.84° [range, -0.79° to 4.20°]). The angular discrepancy of the femoral-tibial sagittal angle was 4.63° (IQR, 3.71° to 5.64° [range, 1.20° to 9.02°]). Compared with manual TKA, the Mako system is more likely to result in a decreased posterior tibial slope and extension of the femoral prosthesis. It may also influence the evaluation of lower-extremity extension and flexion. When using the Mako system, special attention should be given to these discrepancies. Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Posterior Tibial Slope in Computer-Navigated Total Knee Arthroplasty: The Transmalleolar Sagittal Axis Underestimates Slope Compared to Traditional Intramedullary Axis.

Tibial slope in total knee arthroplasty (TKA) impacts knee flexion, balance, and ligament strain. Implants were initially designed with tibial slope recommendations based on the intramedullary axis. However, technology-assisted TKA, such as robotics or navigation, determines slope from the ankle-knee axis connecting the center of the transmalleolar line to the proximal exit point of the tibial shaft axis. We sought to quantify the difference in tibial slope between the traditional intramedullary and transmalleolar sagittal tibial axes. We retrospectively identified 40 TKAs with preoperative computed tomography scans. We reconstructed the 3-dimensional geometry of the tibia and fibula and determined the intramedullary axis as the best fit cylinder to the tibial shaft. We defined the transmalleolar axis according to accepted industry standards. We measured the angular difference between both axes in the sagittal plane. The transmalleolar axis was radiographically posterior to the intramedullary axis in 39 knees. Utilizing the transmalleolar axis to set posterior tibial slope would reduce the posterior tibial slope by a mean of 1.9° ± 1.3° compared to the intramedullary axis. Furthermore, the posterior slope would be reduced between 0° and 2° in 24 knees (60%), between 2° and 4° in 10 knees (25%), and more than 4° in 5 knees (13%). Tibial components implanted with technology assistance referencing the transmalleolar axis to set posterior slope will show an average of 1.9° less posterior slope when measured in sagittal plain radiographs, potentially concerning for knee kinematics.

Use of Fulcrum Positioning as a Balancing Tool During Total Knee Arthroplasty on a Robotic Platform.

Total knee arthroplasty is a common procedure performed to improve pain and dysfunction attributed to arthritis, yet postoperative patient dissatisfaction rates remain relatively high. Patient satisfaction and outcomes have been linked to successful joint gap balancing in the coronal and sagittal planes intraoperatively. In previously described balancing techniques, the fulcrum used for alignment changes is customarily centered on the intramedullary axis generating symmetric changes in medial and lateral gaps. We propose a novel technique in the literature that, with the use of robotic-arm assisted technology or similar systems, allows manipulation of the fulcrum center of rotation during pre-resection planning and intraoperative gap establishment before bony cuts to asymmetrically influence medial and lateral, flexion and extension gaps to aid in balancing during total knee arthroplasty.

Optimal Flexion for the Femoral Component in TKR: A Study of Angle Between Mechanical Axis and Distal Anatomic Intramedullary Axis Using 3D Reconstructed CT Scans in 407 Osteoarthritic Knees Studied in India.

The femoral component is generally aligned perpendicularly to the distal femoral intramedullary axis with conventional instruments. Various aids like computer navigation, patient-specific instrumentation and robotic surgery use the mechanical axis as the reference for the femoral component alignment. We studied the flexion of the distal femoral intramedullary axis compared to the mechanical axis using an interactive 3D tool in 407 Indian osteoarthritic knees undergoing total knee replacement to better understand optimal flexion alignment. 407 knees (301-Female, 106-Male) in Indian patients undergoing total knee replacement underwent CT scans. A 3D interactive knee system was used for 3D reconstruction and planning. Distal femoral flexion angle (DFFA) was calculated between the anatomic distal femoral (intramedullary) axis and the mechanical axis. Statistical analysis was performed using ANOVA test and Chi-square test using a data analysis tool pack (Analysis ToolPak by Excel Easy) additionally installed in Microsoft Excel 2010. The mean DFFA was found to be 2.54 with a standard deviation of 1.38. The maximum and minimum values noted were 7.5 and 0.5 respectively. There was no correlation found between sex, age, height or weight (p > 0.05). While taking the distal femur cut with systems other than an intramedullary rod, in Indian osteoarthritic knees, it would be safer to take the distal femoral cut between 2 and 3 degrees of flexion to mechanical axis, as it would ensure that the cut is within 3 degrees from the anatomic axis for 98% patients. Most surgeons routinely using navigation or similar aids take the cut at 0 degrees of flexion to the mechanical axis. This will lead to more than 3 degrees of extension with reference to the intramedullary axis in more than 39% patients. This would result in either an increase in femoral component sizing or an increased risk of notching.

Femur bowing could be a risk factor for implant flexion in conventional total knee arthroplasty and notching in navigated total knee arthroplasty.

This study aimed to investigate the relationship between preoperative femoral axes and femoral implant position and to determine how femoral sagittal axes, including femoral anterior bowing, influence the femoral component position in total knee arthroplasty (TKA). The relationship between femoral axes (femoral anterior bowing, mechanical axis and the anterior cortical line, intramedullary axis) and implant position was compared in 50 conventional and 50 navigated TKAs. Outliers with more than a 3° margin of error in placement of the femoral component compared with the mechanical axis in the sagittal plane were calculated. The femoral component flexion angle was 3.1° in the conventional group and 1.6° in the navigation group (p<0.001). Anterior femoral bowing correlated positively with the angle between the mechanical axis and implant (r=0.360, p=0.010) in the conventional group and negatively with the angle between the anterior cortical line and flange of the femoral component (r=-0.355, p=0.010) in navigated TKAs. Incidence of outliers was 48% (24 patients) in the conventional group compared with 10% (five patients) in the navigated group (p=0.008). Femoral anterior bowing was an influential factor for implant position and could be a risk factor for both femoral implant flexion in conventional TKAs and notching in navigated TKAs. The results of this study should be considered by surgeons when assessing the risk factors for femoral geometry before performing TKAs, as these results may help them to avoid an overly flexed or extended position of the femoral component, which would affect clinical long-term survival. Retrospective comparative study, Level III.

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.

Transhumeral Portal for Arthroscopic Glenohumeral Resurfacing Procedures: A Cadaveric Study of the Safety and Accuracy

To evaluate the safety and accuracy of a transhumeral portal to arthroscopically access and prepare the glenohumeral articular surface without subscapularis transection or glenohumeral dislocation. In 10 fresh-frozen cadaveric shoulders, we used a transhumeral portal and an anterior mini-open rotator interval exposure to arthroscopically prepare the humeral and glenoid articular surfaces. To evaluate our technique, we measured the distance from the portal to the branches of the axillary nerve and the biceps groove on the humeral extra-articular surface, the angle of trajectory of the portal through the humerus, and the accuracy of targeting the center-center of the humeral and glenoid surfaces. The transhumeral portal allows perpendicular access to the humeral and glenoid articular surfaces without damage to the subscapularis, supraspinatus, or axillary nerve. The transhumeral portal courses an average of 20.7 ± 15.0 mm from the closest terminal branch of the anterior branch of the axillary nerve, enters the humerus 8.8 ± 2.7 mm lateral to the biceps groove, and traverses the humerus at an angle of 46.0° ± 4.3° relative to the humeral intramedullary axis. Arthroscopic guidance resulted in an average distance of 8.1 ± 5.6 mm from the humeral center and 3.9 ± 1.0 mm from the glenoid center. Creating an arthroscopic transhumeral portal allows perpendicular access to the humeral and glenoid articular surfaces without injury to the axillary nerve, subscapularis transection, or dislocation of the glenohumeral joint. However, this transhumeral portal did traverse within 5 mm of a terminal branch of the anterior branch of the axillary nerve in 20% of our specimens. These findings describe an arthroscopic transhumeral portal that achieves perpendicular access to the glenohumeral joint surfaces without transection of the subscapularis or dislocation of the glenohumeral joint. This transhumeral portal may assist in articular cartilage repair and resurfacing of the glenohumeral joint.

Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle

The purpose of this study was to define the relationship between the humeral neck-shaft angle (NSA) and variations in the ideal entry portal aligned with the long axis of the intramedullary canal of the proximal humerus. Three-dimensional images of 36 cadaveric humeri with various NSAs were reconstructed by a computerized surgical simulation program. The anteroposterior, mediolateral, and linear distances between a line from the center of the proximal medullary canal to the bicipital groove were measured. Differences among humeri with various NSAs were analyzed. The intramedullary axis line was located a mean of 9±2mm posteriorly and 11±3mm medially from the bicipital groove. The axis line was 9±2mm posterior and 11±2mm medial with a standard NSA. The axis line in humeri with a varus NSA was 8±2mm posteriorly and 9±2mm medially, whereas the axis line was 10±3mm posteriorly and 14±3mm medially with a valgus NSA. The differences in the mediolateral distances between the groups were significant (P<.00009). Care should be taken in choosing the entry portal position in humeri with various NSAs as the entry portal position differs according to the NSA. It is recommended that the location of the entry portal be moved toward the center of the humeral head to align with the centerline of the intramedullary canal in humeri with a valgus NSA in particular.

Lesser tuberosity is more reliable than bicipital groove when determining orientation of humeral head in primary shoulder arthroplasty

The objective of the study was to provide statistical evaluation of position of bone landmarks of proximal humerus in relation to transepicondylar line and find out which one is the most suitable for setup of the head retroversion in case of humeral head destruction. We measured 185 dry humeral preparations (92 left, 93 right). Structures of interest on the proximal humerus were marked with pointers of custom made steel frame. Angular relationships between the humeral head axis and medial margin of the greater tuberosity, lateral margin of the lesser tuberosity, bicipital groove, and crest of the greater tuberosity were evaluated with respect to intramedullary axis of the proximal humeral shaft. The angle between the humeral head axis and medial margin of greater tuberosity was 11.5 +/- 9.0 degrees , the angle between the lateral margin of the lesser tuberosity and the axis was 47.5 +/- 7.4 degrees , the angle between the bicipital groove and the axis was 31.6 +/- 8.8 degrees at the level of the humeral head. The angle between the crest of the greater tuberosity and the axis was 26.6 +/- 9.6 degrees in plane of the surgical neck. We statistically proved that the lateral margin of lesser tuberosity is more reliable than the bicipital groove; medial margin of the greater and transepicondylar line for reconstruction of humeral head retroversion. We suggest that the lesser tuberosity should be used to determine the retroversion, especially in cases when the margin of humeral head was destructed.

Reconstructing Proximal Humeral Fractures Using the Bicipital Groove as a Landmark

Controversy persists in the literature regarding the use of the bicipital groove as an anatomic landmark to restore humeral head retroversion when treating complex proximal humeral fractures with arthroplasty. We quantified the three-dimensional geometry of the bicipital groove in 49 dried humeri relative to the intramedullary axis, quantified the reliability of using the bicipital groove as an anatomic landmark, and compared this reliability with that of the conventional technique that uses a fixed, average angle relative to the epicondylar axis to establish humeral head retroversion. The data show the anterior offset of the bicipital groove is nearly constant from proximal (7.3 mm +/- 2.8 mm) to distal (7.2 mm +/- 1.5 mm) relative to the intramedullary axis. Given the consistency, the distal bicipital groove (at the level of the surgical neck) is a reasonable landmark to establish humeral head retroversion after complex proximal humeral fractures having reliability (angular error of 7.9 degrees +/- 5.8 degrees) as good as or better than the conventional fixed-angle technique.