Anatomical Axis Of Femur Research Articles

Is a "sulcus cut" technique effective for determining the level of distal femoral resection in total knee arthroplasty?

Determining the level of distal femoral resection is crucial when performing total knee arthroplasty (TKA). However, variations in distal femoral resection are encountered unexpectedly. A "sulcus cut" technique is sometimes used to determine the level of distal femoral resection, but its effectiveness has not been evaluated. The aim of this study was to examine the reliability of the sulcus cut technique using computer simulation for preoperative planning. This study group comprised 40 knees in 34 patients (22 women, 12 men) scheduled for TKA. The preoperative planning software of a computed tomography (CT)-based navigation system was used. We determined the resected level of the femur so that the bone-implant interface of the femoral component was adjusted to the deepest subchondral bone of the trochlear groove in coronal CT images. We then measured each perpendicular distance from the resected surface of the proximal femur to the most distal point of the lateral and medial femoral condyles. The mean distances of the distal-lateral and distal-medial condylar resections from the femoral sulcus were 7mm (±1mm) and 8mm (±1mm), respectively. The resection level did not differ significantly between men and women or between different component sizes. There was a slightly positive correlation between the femoral mechanical and anatomical axis angle and the distance of the distal-lateral condylar resection from the femoral sulcus. The sulcus cut technique can be used to determine the desirable level of the distal femoral resection in TKA. Case series, Level IV.

Three-dimensional reconstruction method for measuring the knee valgus angle of the femur in northern Chinese adults.

The purpose of this study was to establish a method for measuring the knee valgus angle from the anatomical and mechanical axes on three-dimensional reconstruction imaging models, and to use this method for estimating an average knee valgus angle value for northern Chinese adults. Computed tomographic angiography data in DICOM format for 128 normal femurs from 64 adult subjects were chosen for analysis. After the femur images were subjected to three-dimensional reconstruction, the deepest point in the intercondylar notch (point A), the midpoint of the medullary cavity 20 cm above the knee-joint line (point B), and the landmark of the femoral head rotation center (point C) were identified on each three-dimensional model. The knee valgus angle was defined as the angle enclosed by the distal femoral anatomical axis (line AB) and the femoral mechanical axis (line AC). The average (mean±SD) of knee valgus angle for the 128 femurs was 6.20°±1.20° (range, 3.05° to 10.64°). Significant positive correlations were found between the knee valgus angles of the right and left sides and between the knee valgus angle and age. During total knee arthroplasty, choosing a valgus cut angle of approximately 6° may achieve a good result in reestablishing the natural mechanical alignment of the lower extremity for patients of northern Chinese ethnicity. Larger valgus cut angles should be chosen for older patients.

The normal radiological anteroposterior alignment of the lower limb in children.

The development of reconstructive surgery of the lower limbs aimed at multilevel correction demands a precise knowledge of the physiological variations in general radiological parameters of the lower limbs in children of various age groups. It is crucial in systemic skeletal diseases, when deformities affect limbs and the surgeon does not have an intact limb as a reference. The aim of this retrospective study was to establish the normal radiological values of lower limb parameters used in the surgical correction of deformities in children of various age groups. Teleradiographs of the lower limbs taken in children with unilateral congenital or posttraumatic deformity were retrospectively reviewed. Weight-bearing full-length anteroposterior radiographs of the entire lower extremities were taken in a standing position. The study involved 215 extremities of 208 children (93 girls and 115 boys); the ages ranged from 2 years 1 month to 15 years 11 months old. Key variables included the anatomic medial proximal femoral angle (aMPFA), anatomic lateral distal femoral angle (aLDFA), anatomic medial proximal tibial angle (aMPTA), anatomic lateral distal tibial angle (aLDTA), mechanical axis deviation (MAD), the angle formed by the femoral anatomical axis and the mechanical axis of the lower limb. The means and dynamics of variations, standard deviations (SD) and 95% confidence intervals of each parameter were calculated for each age and gender group. Simple regression analysis was performed to determine the relationship between the patient's age and the magnitude of aMPFA, aLDFA, aMPTA and aLDTA. Simple regression analysis showed a significant inverse correlation between patient age and the magnitude of aMPFA: the correlation coefficient was -0.77. A statistically significant inverse correlation between the MAD and the angle between the anatomic femoral axis and mechanical limb axis was found: the correlation coefficient was -0.53. In general, the received values were concordant to results of other studies. It concerned the MAD, aLDFA, aMPTA and angle between the mechanical limb axis and anatomic femoral axis. This is the first chronological evaluation of aMPFA and aLDTA from a relavively large series of patients. These normative data should be taken into consideration when evaluating lower limb alignment in children or applied in practice for planning and evaluation of the quality of surgical correction of complex deformities.

Automated extraction of the femoral anatomical axis for determining the intramedullary rod parameters in total knee arthroplasty.

The automated extraction of anatomical reference parameters may improve speed, precision and accuracy of surgical procedures. In this study, an automated method for extracting the femoral anatomical axis (FAA) from a 3D surface mesh, based on geometrical entity fitting, is presented. This was applied to conventional total knee arthroplasty, which uses an intramedullary rod (FIR) to orient the femoral prosthesis with respect to the FAA. The orientation and entry point of a FIR with a length of 200 mm are automatically determined from the FAA, as it has been shown that errors in these parameters may lead to malalignment of the mechanical axis. Moreover, the effect of partially scanning the leg was investigated by creating reduced femur models and comparing the results with the full models. Precise measurements are obtained for 50 models by using a central and two outer parts, with lengths of 20 and 120 mm, which correspond to 58% of the mean femoral length. The deviations were less than 2 mm for the FAA, 2.8 mm for the FAA endpoints and 0.7° and 1.3 mm for the FIR orientation and entry point. The computer-based techniques might eventually be used for preoperative planning of total knee arthroplasty.

Patellofemoral joint kinematics: The circular path of the patella around the trochlear axis

Differing descriptions of patellar motion relative to the femur have resulted from previous studies. We hypothesized that patellar kinematics would correlate to the trochlear geometry and that differing descriptions could be reconciled by accounting for differing alignments of measurement axes. Seven normal fresh-frozen knees were CT scanned, and their kinematics with quadriceps loading was measured by an optical tracker system. Kinematics was calculated in relation to the femoral epicondylar, anatomic, and mechanical axes. A novel trochlear axis was defined, between the centers of spheres best fitted to the medial and lateral trochlear articular surfaces. The path of the center of the patella was circular and uniplanar (root-mean-square error 0.3 mm) above 16+/-3 degrees (mean+/-SD) knee flexion. In the coronal plane, this circle was aligned 6+/-2 degrees from the femoral anatomical axis, close to the mechanical axis alignment. It was 91+/-3 degrees from the epicondylar axis, and 88+/-3 degrees from the trochlear axis. In the transverse plane it was 91+/-3 degrees and 88+/-3 degrees from the epicondylar and trochlear axes, respectively. Manipulation of the data to different axis alignments showed that differing previously published data could be reconciled. The circular path of patellar motion around the trochlea, aligned with the mechanical axis of the leg, is easily visualized and understood.

Design of patient-specific hip implants based on the 3D geometry of the human femur

Total hip replacement (THR) is a surgical procedure that replaces a diseased hip joint with implants. Due to the various size and shapes of human hip joint of every individual, a chosen commercial hip implant sometimes may not be the best-fit to a patient, or even it cannot be applied because of its discrepancy. To solve the problem of a possible geometric mismatch between a selected implant and the hip joint, we develop a software system that designs a patient-specific hip implant by investigating the anatomical geometry of the patient's hip joints. The major technical challenge of the proposed system is to extract some typical 3D geometry parameters with respect to the patient's 3D bone anatomy and then creates a custom-made hip implant based upon the extracted parameters. This paper describes the overall procedure of creating a patient-specific hip implant based upon the geometry of the patient's femur. The parameters include femoral shaft isthmus, anatomical femoral axis, femoral head center/radius, head offset length, femoral neck, neck shaft angle, anteversion, and canal flare index (CFI). Some of them are semi-automatically recognized and extracted, but others must be determined with the surgeon's intervention. All the parameters are sufficient to construct a primitive 3D geometry model of the specified femur, so that a patient-specific hip implant for individual patients can then be determined from the information of those extracted geometry parameters. The stability of patient-specific implants has been increased by maximizing contact area with the bone. Currently the proposed system is exclusive for the design of a hip implant; however, the concepts are general enough to be applied to any other human joints such as the shoulder, the knee, or the spine. The feasibility and reliability of the method has been tested on some examples.

Comparison of high-flex and conventional implants for bilateral total knee arthroplasty

Clinical and radiographical outcomes of conventional versus high-flex implants were compared in a prospective study in twenty patients one year after bilateral total knee replacement. First, a conventional posterior stabilized total knee arthroplasty (TKA) was implanted in one limb. Six to eight months later, the contralateral knee of each patient was replaced with a high-flexion design TKA. Clinical and radiological parameters including Knee Society objective and functional Scores (KSS), range of motion, tibial slope, position of the femoral component, angles between the components and the anatomical axis of femur and tibia and final varus or valgus alignment were evaluated one year after the operation.One year after surgery, for PS implants mean knee score and mean functional score were 79 points (range 72 to 93 points) and 81 points (range 70 to 100 points), whereas for RPF knees they were 86 points (range 76 to 93 points) and 91 points (range 75 to 100 points) respectively. Mean maximal flexion 97o in the PS group and 118o in the RPF knees. These results were significantly better for the High flex implants. No differences were found in the radiological results.We conclude that the high flexion TKA is associated with a higher range of motion of the knee resulting in better functional outcomes.

The Accuracy of Lower Extremity Alignment in a Total Knee Arthroplasty Using Computer-Assisted Navigation System

Purpose: This study assessed the accuracy of the alignment of the lower extremity and the position of the components in a total knee arthroplasty (TKA), which was performed using a computer-assisted navigation system. Materials and Methods: This study reviewed 40 TKA using a manual alignment system (group A) and 36 TKA using the Orthopilot ® 4.0 navigation system (group B). The radiographs taken 2 months after surgery were used to measure the femoro-tibial angle, the mechanical axis deviation, and the inclination of the femoral and tibial component. A value within the optimum±3° was defined as an ‘acceptable’ and a value over the optimum±3° was befined as an ‘outlier’. Results: The coronal inclination of the femoral component to the anatomical femoral axis showed outliers in 13 knees in group A and 1 knee in group B. The coronal inclination of the femoral component to the mechanical axis revealed 17 and 2 outliers in each group, respectively. The coronal inclination of the tibial component and sagittal inclination of femoral component showed no significant differences between two groups, but the sagittal inclination of tibial component showed 16 and no outlier in each group, respectively. Concerning the femoro-tibial angle, there were 9 outliers in group A and 2 outliers in group B. The mechanical axis deviation showed 9 and 2 outliers in groups A and B, respectively. Conclusion: The navigation system helped to produce more ‘acceptable’ and less ‘outlier’ results than the manual alignment system. The alignment of the lower extremity after a TKA can be achieved more accurately using the navigation system.

The cartilaginous and osseous geometry of the femoral trochlear groove

Photography was used to study the geometry of the cartilaginous and osseous contours of the distal femur and the orientation of the trochlear groove in 9 fresh-frozen and 24 embalmed knees. The sulcus angle (146.1 degrees +/-5.5 degrees ) decreased from 0 degrees to 50 degrees of femoral flexion then increased afterwards. The maximum slope of the lateral femoral condyle (20.2 degrees +/-5.2 degrees ) also decreased with flexion. Both the sulcus angle ( p=0.0007) and maximum slope ( p=0.0001) were larger at 0 degrees than they were for 60 degrees cartilaginous surfaces. The lateral femoral condylar height decreased, whilst the medial femoral condylar height increased as the flexion increased. The femoral groove was midway between the two femoral epicondyles (49.5+/-3.9%), but deviated laterally as the flexion angle increased. The groove axis deviated distally and laterally from the femoral anatomical axis for both cartilaginous and bony surfaces, and the angle between the groove and anatomical axes was similar for both cartilaginous (19.1 degrees ) and osseous (16.8 degrees ) surfaces. Articular cartilage is not well represented on radiography yet it had a significant effect on the distal femoral geometry, and should be taken into account when evaluating the patellofemoral joint.

Anatomical analysis of the femoral condyle in normal and osteoarthritic knees

It is important to understand anatomical feature of the distal femoral condyle for treatment of osteoarthritic knees. Detailed measurement of the femoral condyle geometry, however, has not been available in osteoarthritic knees including valgus deformity. This study evaluated femoral condyle geometry in 30 normal knees, 30 osteoarthritic knees with varus deformity, and 30 osteoarthritic knees with valgus deformity using radiographs and magnetic resonance imaging (MRI). In radiographic analysis in the coronal plane, the femoral joint angle (lateral angle between the femoral anatomic axis and a tangent to femoral condyles) was 83.3° in the normal knees, 83.8° in the varus knees, and 80.7° in the valgus knees. In MRI analysis in the axial plane, the posterior condylar tangent showed 6.4° of internal rotation relative to the transepicondylar axis in the normal knees, 6.1° in the varus knees, and 11.5° in the valgus knees. These results suggested that there was no hypoplasia of the medial condyle in the varus knees, but the lateral condyle in the valgus knees was severely distorted. Surgeons should take this deformity of the lateral femoral condyle into account when total knee arthroplasty is performed for a valgus knee.

Reliability of the transepicondylar line as a parameter of femoral axial alignment

The purpose of this research was to determine the significance of the transepicondylar line as a parameter of femoral axial alignment. Standing full-length X-ray films of 124 knees of 91 patients (63 women, 28 men) with osteoarthritis, rheumatoid arthritis, or osteonecrosis were used in this study, in which the lateral angles formed by the femoral anatomical axis intersecting with the transepicondylar line (angle a′), horizontal line (angle b′), and femoral condylar line (angle r′) were measured. The mean value of angle b′ in knees with neutral alignment was significantly smaller than that in knees with varus alignment, and significantly larger than that in knees with valgus alignment; no significant difference was found in angle a′. Also, there was no significant difference in angle a′ among the patients with osteoarthritis, rheumatoid arthritis, and osteonecrosis. These findings suggest that the transepicondylar line, which is a stable reference of femoral rotation, is also a very reliable parameter of axial alignment of the femur. In the future design of extramedullary guiding for total knee arthroplasty, the transepicondylar line may play an important role as a parameter for proper and accurate implant setting.

Accuracy of intramedullary femoral alignment in total knee replacement: intraoperative assessment of alignment rod position

Current knee replacement techniques favour intramedullary (IM) alignment instrumentation for the guidance of distal femoral resection. Accurate femoral resection depends on the IM alignment guide lying along the line of the anatomical femoral axis, any discrepancy will affect the placement of the femoral cutting jig causing an inaccuracy of the femoral component position in the coronal plane. This study recorded the intra-operative alignment rod position prior to femoral resection. A variation of 5.3° (1.6° varus to 3.7° valgus) was found in relation to the true femoral anatomical axis. This study reveals that IM femoral alignment techniques often place the femoral resection jig in 1–2° more valgus than anticipated which reflects distal femoral anatomy.

The accuracy of femoral intramedullary guides in total knee arthroplasty

Of the technical factors important in achieving a successful total knee arthroplasty, limb alignment has been demonstrated to be most influential in determining implant survival. Intramedullary femoral guide systems rely on placement of the intramedullary rod along the anatomic axis of the femur. In this article, the accuracy of the femoral intramedullary guide is investigated using radiographs and a mathematical model. The femoral anatomic axis was drawn on 40 consecutive, preoperative, 3-ft standing radiographs. Using a mathematical model, the potential angular error in the distal femoral cut from aberrant placement of the intramedullary rod was estimated. Calculated values correlated with measured values from plain radiographs and an intramedullary guide template. The anatomic axis was found to exit the distal femur at an average of 6.6 mm medial to the center of the femoral notch. Substantial malalignment error resulted from minor malposition of the intramedullary rod. Most books and diagrams demonstrating the use of intramedullary guides indicate that the entry point is at the center of the femoral notch. These results show that the true entry point is medial to the center of the notch, and rod placement error results in excessive valgus alignment. Preoperative drawing of the anatomic axis on a 3-ft or 18-inch anteroposterior radiograph is recommended. The results both demonstrate the importance of correct use of the guide and heighten cognizance among surgeons performing total knee arthroplasty as to the limitations of the intramedullary guides.

The Efficacy of Intramedullary Femoral Alignment in Total Knee Replacement

The angle formed between the femoral anatomic axis and the femoral prosthesis was measured on radiographs of 201 total knee arthroplasties. The radiographs were taken on a 51 inch x 14 inch cassette and had to have satisfactory centering and minimal rotation to be included. All total knee arthroplasties had intramedullary femoral alignment. The mean femoral component angle (relative to the femoral anatomic axis) was 6.1 degrees valgus, with a standard deviation of 2 degrees and a range from 2 degrees to 12 degrees valgus. Seventeen knees (8.5%) had a femoral component angle that was < or = 2 degrees valgus or > or = 10 degrees valgus. In 4 knees, medial femoral bowing of the distal third of the femoral shaft caused an excessive valgus cut. In 7 knees, a capacious femoral canal was present that potentially allowed for divergence of the relatively undersized guide rod in the canal. Overall, 8.5% of cuts were believed to be less than ideal. Preoperative radiographs of the entire femur should identify patients in whom errors are more likely and allow for templating the amount of distal femoral bone to be resected. Extra caution is needed in bowed femora and in capacious femoral canals.

Femoral intramedullary instrumentation in total knee arthroplasty: the role of pre-operative X-ray analysis

Intramedullary instrumentation is currently considered as the standard technique for making the distal femoral cut in total knee arthroplasty. The purpose of this investigation was to determine the variance in the angle between the femoral mechanical axis (FMA) and the femoral anatomical axis (FAA). This angle was measured in 73 arthritic patients. The mean angle for varus knees was 7.7° (range 4°–12°). The mean angle for valgus knees was 5.8° (range 4°–7°). The difference between both groups was statistically significant. It is concluded that the FMA-FAA angle should be measured using X-rays and used on instrumentation jigs to avoid femoral malalignment in the coronal plane.

Radiological analysis of normal axial alignment of femur and tibia in view of total knee arthroplasty

Alignment of the anatomical and mechanical axes of the lower extremities was analyzed using standardized radiographs in two series of 66 femur and 44 tibia specimens. A new anatomical axis, the distal femoral anatomical axis, was introduced. This axis corresponds to the overall femoral anatomical axis and encloses a valgus angle of 6 o with the mechanical axis of the femur. It allows for design of shorter intramedullary guiding instruments that will still be in congruency with true femur geometry. Comparison with computerized calculations of angles on computed tomography scans on a series of 38 bones shows a high precision of measurement on standard radiographs in neutral rotation.

Normal Axial Alignment of the Lower Extremity and Load-Bearing Distribution at the Knee

Based on a series of 120 normal subjects of different gender and age, the geometry of the knee joint was analyzed using a full-length weight-bearing roentgenogram of the lower extremity. A special computer program based on the theory of a rigid body spring model was applied to calculate the important anatomic and biomechanical factors of the knee joint. The tibiofemoral mechanical angle was 1.2 degrees varus. Hence, it is difficult to rationalize the 3 degree varus placement of the tibial component in total knee arthroplasty suggested by some authors. The distal femoral anatomic valgus (measured from the lower one-half of the femur) was 4.2 degrees in reference to its mechanical axis. This angle became 4.9 degrees when the full-length femoral anatomic axis was used. When simulating a one-legged weight-bearing stance by shifting the upper-body gravity closer to the knee joint, 75% of the knee joint load passed through the medial tibial plateau. The knee joint-line obliquity was more varus in male subjects. The female subjects had a higher peak joint pressure and a greater patello-tibial Q angle. Age had little effect on the factors relating to axial alignment of the lower extremity and load transmission through the knee joint.