Total hip arthroplasty (THA) and intramedullary (IM) nailing fixation have become the most successful surgical interventions among the orthopedic community [
Some narrow canals are barely able to safely accept intramedullary hardware. The intramedullary femoral guide rod can be jammed into the femoral isthmus during the process of total hip arthroplasty, and this jamming can be avoided with precise preoperative measurements regarding the diameter and location of the canal isthmus [
With the development of medical image processing and medical engineering techniques, computer-aided design (CAD) software has been used to accurately define and quantify the 3D geometry of the femoral canal with morphologic parameters. Kim et al. published the first paper measuring the femoral canal using CAD software in order to design new femoral stems that ideally distribute the stress to the bone. Since then, many related studies have been performed on this topic [
This study established an automated and objective method of measuring the parameters and orientation of the canal isthmus in 3D space using CAD software. Ideally, this method could optimize the choice and design of femoral implants and identify difficulties that may be encountered during femoral canal-related surgeries.
This medical imaging investigation was approved by the Ethics Committee of the Chinese PLA General Hospital. Requirements for informed consent were waived due to the retrospective study design. Furthermore, the patients’ data were made anonymous.
In total, 204 patients with normal femoral morphologies who underwent lower-extremity CT angiography between December 2009 and December 2012 were included in this study. Some patients were included in our previous study [
Based on the CT data in Digital Imaging and Communication in Medicine (DICOM) format, 3D models of the whole femur and femoral canal were reconstructed using the Mimics software according to the steps described below.
After the whole femur mask was created, the cortical bone mask was created based on the threshold (ranging from 226 HU to 3071 HU) according to guidelines of the Mimics software [
Using Mimics software, a 3D model of the femoral medullary canal was created between the lesser trochanter and the flare of the condyles. An arc centerline was fitted to the canal model using the centerline fit function. The diameters of all the inscribed circles along the arc centerlines were created with 1 mm intervals and exported to determine the isthmus location. In this case, the isthmus diameter was 10.50 mm.
Because of the inconsistent positioning of the patients’ bodies during the CT scans, an idealized coordinate system was reconstructed based on the femur-specific anatomy and geometry to normalize the femur orientation.
The 3D femur models were imported into 3DS Max software (Autodesk, San Rafael, CA, USA). Two planes representing the global Cartesian
In the femur-customized coordinate system, the anatomical parameters of the femur and its isthmus tube were determined, including the femoral length (F-length), isthmus height (I-height), distance between the isthmus and LT in the
The femur-customized anatomical coordinate system was constructed according to the
In the femur-customized coordinate system, an arc centerline was fitted to the 3D model of the femoral medullary canal using the centerline fit function of Mimics software [
After an arc centerline was fitted to the 3D model of the femoral medullary canal, the radius of the arc was calculated and considered to represent the femur radius.
The diameters of all the inscribed circles along the arc centerline were exported to identify the three smallest continuous inscribed circles. Among these three circles, the smallest diameter was considered to be the isthmus diameter, and the corresponding center was considered to be the femoral canal isthmus. The distance between the femoral canal isthmus and the center of the LT in the
The 3D model of the femoral medullary canal isthmus was constructed and created after including all the previously mentioned inscribed circles close to the canal isthmus with the diameters within 1 mm plus the isthmus diameter, which was termed the isthmus tube. The centers of the inscribed circles at the two ends of the isthmus tube were termed points P1 and P2, respectively. The midpoint between points P1 and P2 was determined and considered to be the midpoint of the isthmus tube (Figure
The locations of the canal isthmus and isthmus tube in the femur were expressed as the distances from the center of the isthmus to the horizontal plane and the distance from the midpoint of the isthmus tube to the horizontal plane, respectively. The length of the isthmus tube was considered to be the distance between points P1 and P2. The length of the isthmus tube in the
In the femur-customized coordinate system, the intersection of the angles between the axis of the isthmus tube and the horizontal plane in the sagittal plane was termed the lateral angle of the isthmus tube (L-angle).
In this study, only the selection of the medullary canal between the LT and flare of the condyles and the location of the center of the LT were manipulated manually. These results could influence the radius of the femur and the distance between the LT and isthmus. Thus, a reliability study was performed to evaluate the intra- and interobserver reliability of this method for calculating the femur radius and distance between the LT and isthmus.
Based on Walter et al.’s method [
After validity of the established measurement method was confirmed, the anatomical parameters of the femurs were extracted by Xiu-yun Su and Zhe Zhao, and the anatomical parameters of the canals were measured by Chen Li and Jian-feng Zhou. The abbreviations of the anatomical parameters were listed in Table
The abbreviations of the anatomical parameters of the femurs and canals.
Items | Abbreviations |
---|---|
Femoral length | F-length |
Femoral radius | F-radius |
Isthmus diameter | I-diameter |
Height of the isthmus | I-height |
Ratio of the height of the isthmus versus the femoral length | I-index |
Distance between the isthmus and the LT in the |
LI-distance |
Length of the isthmus tube in the |
|
Ratio of the height of the midpoint of the isthmus tube versus the femoral length | T-index |
Length of the isthmus tube | T-length |
AP-angle of the isthmus tube | AP-angle |
Lateral angle of the isthmus tube | L-angle |
After verifying the normal distribution of the data by the Kolmogorov-Smimov test, the data with or without normal distribution were tested using Student’s
The population characteristics and the anatomical parameters of the femur and isthmus are summarized in Table
The main characteristics of the population and the anatomical parameters of the femur and the isthmus.
Items | Male ( |
Female ( |
Student’s |
Total ( |
||||
---|---|---|---|---|---|---|---|---|
Mean ± SD | Range | Mean ± SD | Range |
|
|
Mean ± SD | Range | |
Age (y) | 64.84 ± 12.95 | 15–85 | 69.67 ± 8.5 | 50–85 | — | 0.002 |
66.33 ± 12 | 15–85 |
Height (m) | 1.69 ± 0.059 | 1.48–1.84 | 1.59 ± 0.061 | 1.40–1.77 | 16.929 | <0.001 | 1.66 ± 0.078 | 1.40–1.84 |
Weight (kg) | 68.59 ± 9.9 | 43–97 | 62.35 ± 9.9 | 37–86 | 5.884 | <0.001 | 66.66 ± 10.3 | 37–97 |
F-length (mm) | 437.75 ± 19.81 | 386–485 | 406.70 ± 22.04 | 352–487 | 14.121 | <0.001 | 428.16 ± 25.03 | 352–487 |
F-radius (mm) | 1007.30 ± 205.7 | 616–2029 | 880.52 ± 171.32 | 511–1375 | 6.044 | <0.001 | 968.15 ± 204.12 | 511–2029 |
I-diameter (mm) | 10.68 ± 1.39 | 6.60–16.20 | 10.05 ± 1.71 | 6.00–14.00 | 3.93 | <0.001 | 10.49 ± 1.52 | 6.00–16.20 |
I-height (mm) | 242.6 ± 23 | 166.22–317.6 | 221.66 ± 25.46 | 137.15–284.8 | 8.21 | <0.001 | 236.13 ± 25.66 | 137.15–317.6 |
I-index | 0.55 ± 0.046 | 0.37–0.75 | 0.54 ± 0.052 | 0.35–0.68 | 1.95 | 0.052 | 0.55 ± 0.048 | 0.35–0.75 |
LI-distance (mm) | 117.06 ± 21.69 | 34.16–197.47 | 114.66 ± 20.87 | 63.98–186.25 | 1.04 | 0.3 | 116.31 ± 21.45 | 34.16–197.47 |
|
57.63 ± 22.2 | 7.21–136.83 | 61.29 ± 22.33 | 10.71–122.19 | −1.54 | 0.12 | 58.76 ± 22.28 | 7.21–136.83 |
T-index | 0.55 ± 0.04 | 0.42–0.69 | 0.55 ± 0.044 | 0.37–0.66 | 0.765 | 0.45 | 0.55 ± 0.04 | 0.37–0.69 |
T-length (mm) | 60.87 ± 37.11 | 7.39–545.45 | 62.44 ± 22.7 | 11.28–123.97 | −0.440 | 0.66 | 61.36 ± 33.32 | 7.39–545.45 |
AP-angle (degrees) | 80.57 ± 4.55 | 16.27–89.23 | 81.21 ± 2.79 | 71.39–89.17 | −1.459 | 0.15 | 80.77 ± 4.1 | 16.27–89.23 |
L-angle (degrees) | 84.69 ± 1.96 | 69.16–90.33 | 83.89 ± 1.39 | 79.94–89.38 | 4.183 | <0.001 | 84.44 ± 1.84 | 69.16–90.33 |
Table
Reliability study results.
Items | Intraobserver | Interobserver | ||
---|---|---|---|---|
ICC | 95% CI | ICC | 95% CI | |
F-radius | 0.998 | 0.995–0.999 | 0.997 | 0.994–0.998 |
LI-distance | 0.995 | 0.993–0.997 | 0.994 | 0.991–0.996 |
Paired samples
Items | Left side (mean ± SD) | Right side (mean ± SD) | Difference (mean ± SD) |
|
|
---|---|---|---|---|---|
F-length (mm) | 428.48 ± 24.92 | 427.84 ± 25.18 | 0.63 ± 3.69 | 2.446 | 0.015 |
F-radius (mm) | 997.14 ± 217.56 | 939.16 ± 185.78 | 57.98 ± 95.79 | 8.645 | <0.001 |
I-diameter (mm) | 10.59 ± 1.51 | 10.39 ± 1.53 | 0.2 ± 0.61 | 4.697 | <0.001 |
I-height (mm) | 236.95 ± 26.43 | 235.31 ± 24.89 | 1.64 ± 21.59 | 1.085 | 0.279 |
I-index | 0.55 ± 0.051 | 0.55 ± 0.045 | 0.0033 ± 0.051 | 0.917 | 0.36 |
LI-distance (mm) | 115.15 ± 22.26 | 117.48 ± 20.59 | −2.33 ± 21.66 | −1.539 | 0.125 |
|
58.51 ± 22.24 | 59.01 ± 22.38 | −0.49 ± 23.66 | −0.298 | 0.766 |
T-index | 0.55 ± 0.04 | 0.55 ± 0.044 | 0.0037 ± 0.031 | 1.692 | 0.092 |
T-length (mm) | 62.06 ± 40.8 | 60.65 ± 23.66 | 1.41 ± 42.42 | 0.475 | 0.635 |
AP-angle (degrees) | 80.99 ± 2.83 | 80.54 ± 5.05 | 0.46 ± 5.2 | 1.254 | 0.211 |
L-angle (degrees) | 84.58 ± 2 | 84.31 ± 1.65 | 0.28 ± 1.54 | 2.565 | 0.011 |
Pearson’s correlation analyses were performed to detect correlations among the general characteristics of the included population and the anatomical parameters of the femur and canal isthmus (Table
The correlation analysis between the main characteristics of the population and the anatomical parameters of the femur and the isthmus.
Pearson |
Age | Height | Weight | F-length | F-radius | I-diameter | I-height | LI-distance |
|
T-length | AP-angle | L-angle | I-index | T-index |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Age | 1 | −0.345 |
−0.371 |
−0.290 |
−0.072 | −0.006 | −0.272 |
0.059 | 0.05 | 0.042 | 0.059 | −0.079 | −0.141 |
−0.078 |
Height |
|
1 | 0.537 |
0.841 |
0.327 |
0.220 |
0.512 |
0.176 |
−0.132 |
−0.038 | −0.110 |
0.175 |
0.074 | 0.052 |
Weight |
|
|
1 | 0.423 |
0.110 |
0.112 |
0.323 |
0.007 | 0.019 | 0.011 | −0.074 | 0.061 | 0.120 |
0.054 |
F-length |
|
|
|
1 | 0.357 |
0.240 |
0.600 |
0.221 |
−0.059 | 0.037 | −0.102 |
0.221 |
0.083 | 0.025 |
F-radius |
|
|
|
|
1 | −0.016 | 0.239 |
0.05 | −0.122 |
0.059 | −0.036 | 0.309 |
0.06 | 0.054 |
I-diameter |
|
|
|
|
|
1 | 0.071 | 0.118 |
0.129 |
0.074 | −0.109 |
0.113 |
−0.07 | −0.118 |
I-height |
|
|
|
|
|
|
1 | −0.622 |
0.076 | 0.093 | 0.001 | −0.246 |
0.844 |
0.619 |
LI-distance |
|
|
|
|
|
|
|
1 | −0.122 |
−0.074 | −0.068 | 0.477 |
−0.916 |
−0.679 |
|
|
|
|
|
|
|
|
|
1 | 0.644 |
0.078 | −0.05 | 0.148 |
0.189 |
T-length |
|
|
|
|
|
|
|
|
|
1 | −0.004 | 0.06 | 0.100 |
0.155 |
AP-angle |
|
|
|
|
|
|
|
|
|
|
1 | 0.104 |
0.067 | 0.101 |
L-angle |
|
|
|
|
|
|
|
|
|
|
|
1 | −0.443 |
−0.588 |
I-index |
|
|
|
|
|
|
|
|
|
|
|
|
1 | 0.760 |
T-index |
|
|
|
|
|
|
|
|
|
|
|
|
|
1 |
Stepwise linear regression analyses were applied with the I-diameter,
Previous studies regarding the morphology of the femur and its canal were performed primarily by anthropologists and anatomists [
The radiograph is the most common tool for determining the dimensions and location of the femoral canal [
Summary of the measurement methods and results of the femoral canal isthmus reported in previous studies.
Author | Year | Number | Subject | Origin | I-diameter (mean ± SD, mm) | LI-distance (mean ± SD, mm) | Methods |
---|---|---|---|---|---|---|---|
Onoue et al. [ |
1979 | 160 | Patients | Japanese | 10.9 ± 1.9 | NA | AP radiograph |
11.2 ± 2.3 (ML); 14.2 ± 2.9 (AP) | NA | CT scan | |||||
Noble et al. [ |
1988 | 200 | Cadavers | Caucasian | 12.3 ± 2.3 (ML); 16.9 ± 3.5 (AP) | 113.4 ± 16.4 | Radiograph |
Rubin et al. [ |
1992 | 32 | Cadavers | Swiss | 13.1 ± 2.1 | 105.7 ± 17.9 | AP radiograph |
Noble et al. [ |
1995 | 80 | Cadavers | Caucasian | 12.1 ± 2 (ML); 15.7 ± 2.9 (AP) | 119.4 ± 16.2 | Radiograph |
Husmann et al. [ |
1997 | 310 | Patients | Caucasian | 11.6 ± 2.7 | NA | AP radiograph |
Bo et al. [ |
1997 | 100 | Patients | Japanese | 11.90 ± 2.60 (ML); 10.40 ± 2.60 (AP) | 73.00 ± 18.90 | 3D reconstruction |
Laine et al. [ |
2000 | 50 | Cadavers | Finnish | 11.06 ± 1.88 (ML); 14.09 ± 2.81 (AP) | 110 ± 15 | 3D reconstruction |
Massin et al. [ |
2000 | 200 | Patients | French | 12.40 ± 2.30 | NA | AP radiograph |
Mahaisavariya et al. [ |
2002 | 108 | Cadavers | Thai | 10.05 ± 1.81 | 112.93 ± 17.96 | 3D reconstruction |
Khang et al. [ |
2003 | 200 | Volunteers | Korean | 11.0 ± 2.0 (ML); 12.6 ± 2.3 (AP) | 117.0 ± 4.5 | 3D reconstruction |
Noble et al. [ |
2003 | 53 | Volunteers | Caucasian | 12.7 ± 2.4 (ML); 13.9 ± 3.2 (AP) | 109.3 ± 15.8 | 3D reconstruction |
Atilla et al. [ |
2007 | 114 | Cadavers | Turkish | 10.7 ± 1.84 | 104.0 ± 27.9 | AP radiograph |
Wang et al. [ |
2009 | 18 | Cadavers | Chinese | 12.02 ± 1.13 (ML); 14.67 ± 1.52 (AP) | NA | Canal cast mold |
Uzel et al. [ |
2011 | 106 | Patients | Mixed | 13.6 ± 0.90 (Afro-Caribbean); 15.3 ± 1.96 (French) | NA | AP radiograph |
Rawal et al. [ |
2012 | 98 | Patients | Indian | 9.02 ± 1.92 (ML); 11.47 ± 2.11 (AP) | 107.8 ± 9.73 | 3D reconstruction |
Milligan et al. [ |
2013 | 1685 | Patients | Caucasian | 12.69 ± 2.44 (F); 13.27 ± 2.21 (M) | NA | AP radiograph |
Baharuddin et al. [ |
2014 | 60 | Patients | Malay | 9.73 ± 1.80 (ML); 13.12 ± 2.46 (AP) | 112.83 ± 11.80 | 3D reconstruction |
Our study | 2015 | 408 | Patients | Chinese | 10.49 ± 1.52 | 116.31 ± 21.45 | 3D reconstruction |
ML: mediolateral width; AP: anteroposterior width; F: female; M: male.
Because AP or lateral radiographs can only provide a rough 2D approximation of the actual dimensions of the femoral canal, the limitations of traditional radiology are obvious regarding measurements of the morphologic parameters of the irregular femoral canal compared to 3D space. Considering the remarkable variability among individuals regarding endosteal morphology, a standardized measurement method based on 2D radiographs is not possible. The measurement methods based on the CT data might provide more precise descriptions [
Using a technique that was very similar to ours, Baharuddin et al. reported that the isthmus width and the distance between the isthmus and LT were 9.73 and 112.83 mm, respectively [
To determine the position and dimensions of the isthmus more precisely, CT scans at 1.2 mm intervals were obtained. We reconstructed 3D femur and canal models. We used Mimics software to fit the centerline of the 3D canal model into an arc. The smallest inscribing circles along the arc centerline of the canal were calculated at 1 mm intervals. Among these circles, the smallest one was considered to be the isthmus. Furthermore, to describe the anatomy of the femoral isthmus in 3D space, an isthmus tube was reconstructed, and the direction of the tube was expressed as the intersecting angles between its axis and the horizontal plane in the coronary and sagittal planes, respectively. These results indicate that it might be inappropriate to measure and determine the orientation of the isthmus or the canal from AP or lateral radiographs.
Based on previous studies, the remarkable variability of isthmus parameters is consistent with the observation that the geometry of the isthmus is determined by a large number of factors, including the general characteristics of the individual and femoral anatomical parameters. These factors create unique isthmus geometries, like the other characteristics of femoral anatomy. Although a paired sample
Onoue et al. suggested that older patients have larger isthmus diameters [
This study had some limitations. The included population primarily consisted of elderly Chinese individuals. These measurements may not be representative of other ages or populations in other countries. In addition, there might be other important influential factors of the femoral canal isthmus, from either the general characteristics or the femoral anatomy, rather than the factors included in the present study. Further studies are needed to be performed to find out more meaningful factors to evaluate the anatomy of the canal isthmus.
In conclusion, the current study developed a new measurement approach to evaluate the anatomical morphology of the femoral canal isthmus and determined the most influential factors on the location and dimension of the isthmus. Furthermore, this study was useful for establishing the methodological basis for preoperative assessments of the femur canal-related surgeries and developments of the femoral implants more suitable for the anatomy of old Chinese.
The authors declare that they have no conflict of interests.
Dr. Xiu-yun Su, Dr. Jing-xin Zhao, and Dr. Zhe Zhao have contributed equally to this work.
Thanks are due to Dr. Song Zhang, Dr. Lin Han, and Dr. Xiao-feng Yu, who participated in reconstructing the 3D femoral modal. This work was partially supported by China Postdoctoral Science Foundation (no. 2013M542448).