3D Slicer open-source software plug-in for vector-based angle calculation of canine hind limb alignment in computed tomographic images

BACKGROUND

Severe and complex angular limb deformities in dogs require accurate morphological assessment using diagnostic imaging to achieve successful orthopedic surgery. Computed tomography (CT) is commonly used to overcome projection errors in two-dimensional angular measurements of dog hindlimb alignment. Three-dimensional volume rendering (VR) techniques permit virtual positioning and variable projection, but the final CT-image that defines the projection plane for angular measurements remains two-dimensional.

OBJECTIVE

We wanted to develop a true three-dimensional open-source technique to measure the alignments of the hind limbs of dogs in CT scanners.

METHODS

We developed an open-source 3D Slicer plug-in, to perform angular measurements using vector calculations in three-dimensional space. In 113 CT-scans of canine pelvic limbs, femoral torsion, femoral varus, femorotibial rotation, tibial torsion, tibial varus and tibiotalar rotation angles were calculated and compared to an already validated technique using VoXim®.

RESULTS

Reference points were identified and measurements were possible in the 113 acquisitions. The greatest difference between the two techniques was 1.4° at only one tibial torsion angle. Mean values for all Bland-Altman plots did not show significant differences and were less than 0.07° for all comparisons.

DISCUSSION

Based on these results we considered angular measurements of canine hind limb alignment in CT scans using the 3D Slicer extension program sufficiently accurate for clinical orthopedic and surgical purposes in veterinary medicine.

CONCLUSION

With our open-source 3D Slicer extension software, we provide a free accessible tool for veterinary orthopedic surgeons and thus we hope to improve angular measurements in CT-scans of canine hind limb deformities through true three-dimensionality.

Comparison of CT-measured angles of pelvic limbs without patellar luxation of six canine breeds

Introduction

Dogs with medial patellar luxation can be affected by pelvic limb deformities whose corrective osteotomies and associated biomechanical rebalancing might provide higher success rates than standard surgical procedures limited to the stifle joint. In bilaterally affected canine patients, comparison with the contralateral normal limb is impossible. Reference values are useful for orthopedic decision-making. Inconsistency of published reference values might depend on methodology or canine breed. We hypothesized that canine pelvic limb alignment is breed-specific.

Methods

CT scans of 42 pelvic limbs of dog breeds predisposed for medial patellar luxation, with an orthotopic patellar position and stability were studied. Several angleswere measured with an open-source 3D Slicer plugin using vector calculations. The breeds were compared with a general linear model with a Bonferonni adjustment using SPSS.

Results

Chihuahuas, Pomeranians, Jack Russel Terriers, Pugs, French Bulldogs, Maltese were examined. In the order of the listed breeds, the angles were as follows: 28.3°±10.7°, 20.1°±2.9°, 35.4°±6.9°, 32.8°±3.0°, 19.0°±7.1°, 26.6°±5.3° for the antetorsion, 5.3°±1.8°, 2.8°±2.8°, 8°±4.4°, 3.8 °±3.1°, 4.7°±3.3°, 2.3°±3.3° for the femoral varus, of -5.5°±6.2°, 1.1°±4.1°, -5.2°±9.5°, 6.1°±8.0°, -0.1°±5.9°, -9.2°±4.7° for the tibial torsion, 2.0°±2.9°, 2.1°±2.7°, 6.4°±6.8°, 0.0°±5.7°, 3.0°±5.8°, 8.8°±8.6° for the tibial valgus, 1.2°±10.4°, 1.8°±3.4°, -1.7°±4.9°, -1.7°±9.4°, 5.1°±8.8°, -0.2°±8.6° for the femorotibial rotation and -3.4°±2.2°, 1.1°±4.1°, -2.8°±3.4°, -5.2°±4.0°, -2.1°±4.4°, -5.4°±3.7° for the tibiotalar rotation. There were significant differences between breeds in femoral torsion, femoral varus, and tibial torsion angles, but no significant differences in tibial valgus, femorotibial, and tibiotalar rotation angles.

Discussion

Our hypothesis is therefore partially correct. Our results are limited to small dogs prone to medial patellar luxation and might not be generalized. To establish robust reference values larger case numbers and more breeds should be evaluated. In conclusion, canine pelvic limb alignment reference values for small dogs with a predisposition for medial patellar luxation should be considered breed-specific.

Accuracy of Caudocranial Canine Femoral Radiographs Compared to Computed Tomography Multiplanar Reconstructions for Measurement of Anatomic Lateral Distal Femoral Angle

OBJECTIVE

 This study aimed to compare the accuracy of sternal recumbency caudocranially obtained radiographs of canine femora to computed tomographic (CT) frontal plane reconstructions of the same femora for assessing anatomic distal lateral femoral angles (aLDFA).

STUDY DESIGN

 Multicentre, retrospective study utilizing 81 matched radiographic and CT studies of clinical patients undergoing assessment for various issues were reviewed. Anatomic lateral distal femoral angles were measured, and accuracy assessed with descriptive statistics and Bland-Altman plot analysis, with CT considered the reference standard. Sensitivity and specificity of a cut-off for measured aLDFA (102 degrees) were determined to assess radiography as a screening tool for significant deformity.

RESULTS

 Radiographs on average overestimated aLDFA by 1.8 degrees compared to CT. Bland-Altman analysis identified a 15.4 degrees 95% limit of agreement range and a tendency for greater overestimation at higher average measured value. Radiographic measurement of aLDFA of 102 degrees or less had a 90% sensitivity, 71.83% specificity, and 98.08% negative predictive value for the CT measurement being less than 102 degrees.

CONCLUSION

 Accuracy of aLDFA measurement by caudocranial radiographs does not demonstrate sufficient accuracy when compared to CT frontal plane reconstructions with unpredictable differences. Radiographic assessment is a useful screening tool to exclude animals with a true aLDFA of greater than 102 degrees with a high degree of certainty.

Computed tomographic angular measurements using a bone-centered three-dimensional coordinate system are accurate in a femoral torsional deformity model and precise in clinical canine patients

Introduction

In small animal orthopedics, angular measurements in the canine femur are often applied in clinical patients with bone deformities and especially in complex and severe cases. Computed tomography (CT) has been shown to be more precise and accurate than two-dimensional radiography, and several methods are described. Measurement techniques evaluated in normal bones must prove accuracy in deformed bones in clinical settings.

Objectives

The goals of our study were to evaluate the accuracy of canine femoral torsion angle measurements in a femoral torsional deformity model and to test repeatability and reproducibility of canine femoral neck inclination, torsion, and varus angle measurements in CT datasets of dogs applying a CT-based technique using a three-dimensional (3D) bone-centered coordinate system.

Materials and methods

For precision testing, femoral torsion, femoral neck inclination, and femoral varus angles were measured in CT data of 68 canine hind limbs by two operators, and their results were compared. For accuracy testing, a femoral torsional deformity model was preset from 0° to +/-90° with a goniometer and scanned. Torsion angles were measured in the CT data and compared to the preset value.

Results

In the femoral torsion model, the Bland-Altman plots demonstrated a mean difference of 2.11°, and the Passing-Bablok analysis demonstrated a correlation between goniometer and CT-based measurements. In the clinical CT scans, intra- and interobserver agreement resulted in coefficients of variation for repeated measurements (%) between 1.99 and 8.26 for the femoral torsion, between 0.59 and 4.47 for the femoral neck inclination, and between 1.06 and 5.15 for the femoral varus angles.

Discussion

Evaluation of femoral malformations with torsional deformities is the target area of this technique. Further studies are required to assess its value in different types, degrees, and combinations of osseous deformities and to establish normal reference values and guidelines for corrective osteotomies.

Conclusion

Based on the results of this study, the accuracy of the torsion angle measurements and the precision of inclination, torsion, and the varus angle measurements were considered acceptable for clinical application.

Introduction of a bone-centered three-dimensional coordinate system enables computed tomographic canine femoral angle measurements independent of positioning

Introduction

Measurement of torsional deformities and varus alignment in the canine femur is clinically and surgically important but difficult. Computed tomography (CT) generates true three-dimensional (3D) information and is used to overcome the limitations of radiography. The 3D CT images can be rotated freely, but the final view for angle measurements remains a subjective variable decision, especially in severe and complex angular and torsional deformities. The aim of this study was the development of a technique to measure femoral angles in a truly three-dimensional way, independent of femoral positioning.

Methods

To be able to set reference points in any image and at arbitrary positions of the CT series, the 3D coordinates of the reference points were used for mathematical calculation of the angle measurements using the 3D medical imaging Software VoXim^®. Anatomical reference points were described in multiplanar reconstructions and volume rendering CT. A 3D bone-centered coordinate system was introduced and aligned with the anatomical planes of the femur. For torsion angle measurements, the transverse projection plane was mathematically defined by orthogonality to the longitudinal diaphyseal axis. For varus angle measurements, the dorsal plane was defined by a femoral retrocondylar axis. Independence positioning was tested by comparison of angle measurement results in repeated scans of 13 femur bones in different parallel and two double oblique (15/45°) positions in the gantry. Femoralvarus (or valgus), neck version (torsion), and inclination angles were measured, each in two variations.

Results

Resulting mean differences ranged between -0.9° and 1.3° for all six determined types of angles and in a difference of <1° for 17 out of 18 comparisons by subtraction of the mean angles between different positions, with one outlier of 1.3°. Intra- and inter-observer agreements determined by repeated measurements resulted in coefficients of variation for repeated measurements between 0.2 and 13.5%.

Discussion

The introduction of a bone-centered 3D coordinate system and mathematical definition of projection planes enabled 3D CT measurements of canine femoral varus and neck version and inclination angles. Agreement between angular measurements results of bones scanned in different positions on the CT table demonstrated that the technique is independent of femoral positioning.

Quantifying the variability between multiple multiplanar reconstructions of computed tomography scans

Background

Multiplanar reconstructions of computed tomography (CT) scans can alleviate issues with bone or joint positioning during scan acquisition. The repeatability of these reconstructions is dependent on human operators applying reconstruction criteria, and therefore is subject to error, which could affect measurement reliability for angular or spatial measurements made for orthopaedic surgery.

We describe a method for quantifying inter-reconstruction variability numerically and graphically using metadata from the CT header to find vectors describing reconstruction axis alignment. The approach is demonstrated using 3 sets of computed tomographic reconstructions of 24 vulpine femorotibial joints.

Results

Vectors describing axis alignments permitted identification and subsequent analysis of deviations from optimal alignment between reconstruction sets. For the worked example, alignment deviations equivalent to femoral abduction/adduction were nearly twice those for extension/flexion, and simulation of the effects of these deviations on measurements closely matched published data.

Conclusions

The method presented here is straightforward and permits numerical and graphical analysis of reconstruction variability. Reconstruction alignment variability should be considered before adopting new reconstruction criteria for clinical use, and evaluated whenever there is suspicion that reconstruction variability could unduly influence subsequent measurements. These evaluations may help drive improvements in reconstruction criteria. The methods described here could also be employed for comparing patient positioning between scans and between different scan modalities.

A three-dimensional computed tomographic volume rendering methodology to measure the tibial torsion angle in dogs

OBJECTIVE

To describe a three-dimensional (3D) computed tomographic (CT) methodology to measure the tibial torsion angle (TTa) and to evaluate intrarater and interrater agreements and accuracy through comparison with anatomic measurements.

STUDY DESIGN

Ex vivo cadaveric study.

SAMPLE POPULATION

Thirty-six tibiae from 18 dogs.

METHODS

Tibial torsion angle of each tibia was measured by using two CT techniques (axial and 3D volume rendering) by three raters who blindly measured TTa in duplicate. A semitransparent bone filter was used to enhance the visibility of the target anatomical landmarks for the 3D volume rendering CT technique. Tibial torsion angle was also quantitated in tibial specimens. Intrarater and interrater agreements were analyzed by using intraclass coefficients (ICC). Accuracy was evaluated by using adjusted R² coefficients (R²  > 80% was considered acceptable).

RESULTS

The 3D volume rendering CT technique had excellent intrarater and interrater agreements (ICC > 0.94) and an R² value of 97%. The axial CT technique had good to excellent intrarater and interrater agreements (0.8 < ICC < 0.95) and an R² of 86%. No difference was found between axial and 3D CT techniques. A mean internal TT angle of approximately -6° was found with CT and anatomic measurements.

CONCLUSION

The 3D volume rendering and axial CT techniques were precise and accurate for measuring TTa in dogs unaffected by patellar luxation.

CLINICAL RELEVANCE

Combining 3D bone manipulation with application of a semitransparent filter allows simultaneous visualization of anatomic landmarks, which may facilitate the evaluation of complex bone deformations. Internal tibial torsion may be present in nonchondrodystrophic dogs without patella luxation.

A computed tomographic graphical approach to guide correction of femoral torsion

OBJECTIVE

To report geometric methods to assess femoral transverse bone morphology and develop a virtual method to guide the surgical correction of femoral torsional deformities.

STUDY DESIGN

Observational study.

SAMPLE POPULATION

Sixteen client-owned dogs comprising 14 normal femurs and 14 femurs with angulation-rotation bone deformities.

METHODS

Femoral torsion angle was measured with computed tomographic (CT) three-dimensional (3D) multiplanar reconstruction. Distal femoral transverse morphology was estimated with geometric methods and compared to direct measurements to span a target 20° angle on 3D reconstructions. A virtual correction of 20° was performed, and 3D-printed bone models were created. Femoral torsion of corrected bone models was compared to precorrection.

RESULTS

Geometric estimates with an arc and chord of the metaphyseal area and chord of a best fit circle did not differ from direct measurement of femoral cortical length along the cranial cortex. Femoral torsion differed between normal femurs (25.8° ± 6°) and those with deformity (36.9° ± 8.4°, P < .001). Torsion that was measured on corrected 3D bone models did not differ from the expected torsion (preoperative +20°).

CONCLUSION

Geometric methods provided an accurate estimate of distal femoral transverse bone morphology. Rotation of the distal femur based on geometric methods resulted in an accurate correction of torsion.

CLINICAL SIGNIFICANCE

Femoral bone diameter can be measured on a CT cross-section, and rotation distance can be calculated to achieve a desired correction of torsion. This approach provides a simple and accurate method to guide the correction of femoral torsion.

Computed tomographic localization of the deepest portion of the femoral trochlear groove in healthy dogs

OBJECTIVE

To validate a computed tomographic (CT) method to measure the femoral trochlear groove depth (FTGD).

STUDY DESIGN

Cadaveric study.

SAMPLE POPULATION

Fifteen dogs, 26 femoral trochleae.

METHODS

Five points were identified from proximal to distal (proximal point [PP], P25, P50, P75, and distal point [DP]) along the trochlea via three-dimensional volume-rendering function on the sagittal plane and measured on multiplanar reconstruction images. Each rater repeated measurements in duplicate, unaware of the identity of the joint. The FTGD was quantitated on the anatomical specimens and statistically compared with CT measurements. Intrarater and interrater agreements were analyzed by using intraclass coefficients. Accuracy was evaluated by using either adjusted R² coefficients (R²  > 80% was considered acceptable) or Student's t test. The ratio of the patellar and the trochlear width and the ratio of the patellar craniocaudal thickness inside the trochlear groove were calculated at three different patellar locations.

RESULTS

Good to excellent intrarater and interrater agreements were observed in four of five trochlear points (P25, P50, P75, and DP), and accuracy was acceptable for these points (R²  > 80%). Computed tomographic measurements differed from the mean anatomical measurements at three of five points (PP, P50, and P75; P < .01), overestimating the FTGD by an overall mean of 0.18 mm (range, 0.02-0.3). P25 and P50 were the deepest points measured.

CONCLUSION

Computed tomography allowed precise measurements of trochlear groove depth except for the most proximal point. The deepest trochlear points were P25 and P50. P25 was the most precise and accurate point measured, while PP was the least consistent.

CLINICAL SIGNIFICANCE

The deepest portion of the trochlea groove may be located between P25 and P50. Evaluation of this CT method in dogs with patellar luxation is recommended.

Accuracy of an automated three-dimensional technique for the computation of femoral angles in dogs

AIMS

The purpose of the study was to evaluate the accuracy of a three-dimensional (3D) automated technique (computer-aided design (aCAD)) for the measurement of three canine femoral angles: anatomical lateral distal femoral angle (aLDFA), femoral neck angle (FNA) and femoral torsion angle.

METHODS

Twenty-eight femurs equally divided intotwo groups (normal and abnormal) were obtained from 14 dogs of different conformations (dolicomorphic and chondrodystrophicCT scans and 3D scanner acquisitions were used to create stereolithographic (STL) files , which were run in a CAD platform. Two blinded observers separately performed the measurements using the STL obtained from CT scans (CT aCAD) and 3D scanner (3D aCAD), which was considered the gold standard method. C orrelation coefficients were used to investigate the strength of the relationship between the two measurements.

RESULTS

A ccuracy of the aCAD computation was good, being always above the threshold of R² of greater than 80 per cent for all three angles assessed in both groups. a LDFA and FNA were the most accurate angles (accuracy >90 per cent).

CONCLUSIONS

The proposed 3D aCAD protocol can be considered a reliable technique to assess femoral angle measurements in canine femur. The developed algorithm automatically calculates the femoral angles in 3D, thus considering the subjective intrinsic femur morphology. The main benefit relies on a fast user-independent computation, which avoids user-related measurement variability. The accuracy of 3D details may be helpful for patellar luxation and femoral bone deformity correction, as well as for the design of patient- specific, custom-made hip prosthesis implants.

Accuracy of patient-specific three-dimensional-printed osteotomy and reduction guides for distal femoral osteotomy in dogs with medial patella luxation

OBJECTIVE

To compare precorrectional and postcorrectional femoral alignment following distal femoral osteotomy using patient-specific 3-dimensional (3D)-printed osteotomy and reduction guides in vivo and ex vivo.

STUDY DESIGN

Prospective study.

SAMPLE POPULATION

Ten client-owned dogs and matching 3D-printed plastic bone models.

METHODS

Distal femoral osteotomy was performed via a standard approach using osteotomy and reduction guides developed with computer-aided design software prior to 3D-printing. Femoral osteotomy and reduction was also performed on 3D-printed models of each femur with identical reprinted guides. Femoral varus angle (FVA) and femoral torsion angle (FTA) were measured on postoperative computed tomographic images by 3 observers.

RESULTS

In vivo, the mean difference between target and achieved postoperative was 2.29° (±2.29°, P = .0076) for the FVA, and 1.67° (±2.08°, P = .300) for the FTA. Ex vivo, the mean difference between target and achieved postoperative was 0.29° (±1.50°, P = .813) for the FVA, and -2.33° (±3.21°, P = .336) for the FTA. Intraobserver intraclass correlation coefficients (ICC; 0.736-0.998) and interobserver ICC (0.829 to 0.996) were consistent with an excellent agreement.

CONCLUSION

Use of 3D-printed osteotomy and reduction guides allowed accurate correction of FTA in vivo and both FVA and FTA ex vivo.

CLINICAL SIGNIFICANCE

Use of 3D-printed osteotomy and reduction guides may improve the accuracy of correction of femoral alignment but warrant further evaluation of surgical time, perioperative complications, and patient outcomes compared with conventional techniques.

Proximal and distal alignment of normal canine femurs: A morphometric analysis

Many researchers are interested in femoral conformation because most orthopaedic problems of the long bones occur in the femur and its joints. The neck-shaft (NSA) and the anteversion (AVA) angles are good predictors for understanding the orientation of the proximal end of the femur. The varus (aLDFA) and procurvatum (CDFA) angles have also been used to understand the orientation of the distal end of the femur. The purposes of this study were to investigate the relationship between the proximal and distal angles of the femur and to compare the distal femoral angles in male and female dogs in order to investigate the sexual dimorphism. The measurements of normal CDFAs, which have not been previously reported, may also provide a database of canine distal femoral morphology. A total of 75 cleaned healthy femora from different breeds or mixed breed of dogs were used. The three-dimensional images were reconstructed from computed tomographic images. The AVA, NSA, aLDFA and CDFA were measured on the 3D images. The correlation coefficients were calculated among the measured angles. The distal femoral angles were also compared between male and female femora. The 95% confidence intervals of the AVA and the NSA were calculated to be 24.22°-29.50° and 144.97°-147.50°, respectively. The 95% confidence intervals of the aLDFA and the CDFA for all studied dogs were 92.62°-94.08° and 89.09°-91.94°, respectively. The NSA showed no correlation with either the aLDFA or CDFA. There was a weak inverse correlation between the AVA and CDFA and a weak positive correlation between the AVA and aLDFA. The differences in the aLDFA and CDFA measurements between male and female dog were not significant. In conclusion, femoral version, regardless of the plane, might have little influence on distal femoral morphology in normal dogs. Besides this, there is no evidence of a sexual dimorphism in the varus and procurvatum angles of the dog distal femur. The data from this study may be used in both orthopaedic studies and for clinical applications related to the distal femur of dogs.

A comparison of anatomical lateral distal femoral angles obtained with four femoral axis methods in canine femora

Objectives: To report the repeatability and reproducibility of four different anatomical proximal femoral axis (a-PFA) methods for measuring anatomical lateral distal femoral angle (a-LDFA), and to compare a-LDFA values produced by each method at three different femoral elevation angles.

Methods: Digital radiographs were obtained of seven dry canine femora at 0°, 12.5° and 25° elevations. Using image analysis software, landmarks defining four different a-PFA and the condylar axis were identified by two independent observers on two separate occasions. Corresponding a-LDFA were calculated for each femur, elevation and a-PFA. Repeatability and reproducibility parameters were calculated and compared statistically, along with the effect of technique and elevation on a-LDFA value.

Results: Interobserver repeatability coefficients were subjectively better for three of the a-PFA methods at 2° compared to the fourth at 3.1°. Median a-LDFA increased significantly (p 0.002) with increasing femoral elevation for all a-PFA methods, with a median increase of 3.3°. The median difference in a-LDFA between a-PFA methods yielding the highest and lowest measurements was 2.6° over all three elevations.

Clinical significance: The combined effects of a-PFA choice, femoral elevation and measurement reproducibility may produce typical errors of ± 2.6°, which could have implications for the selection of candidates for corrective osteotomies. Clinicians need to be aware that values obtained with one method and femoral elevation may not be equivalent to values obtained with other methods or elevations.

Femoral rotation unpredictably affects radiographic anatomical lateral distal femoral angle measurements

Objective: To describe the effects of internal and external femoral rotation on radiographic measurements of the anatomical lateral distal femoral angle (a-LDFA) using two methods for defining the anatomical proximal femoral axis (a-PFA).

Methods: Digital radiographs were obtained of 14 right femora at five degree intervals from 10° external rotation to 10° internal rotation. Using freely available software, a-LDFA measurements were made using two different a-PFA by a single observer on one occasion.

Results: Mean a-LDFA was significantly greater at 10° external rotation than at any other rotation. The response of individual femora to rotation was unpredictable, although fairly stable within ±5° of zero rotation. Mean a-LDFA for the two a-PFA methods differed by 1.5°, but were otherwise similarly affected by femoral rotation.

Clinical significance: If zero femoral elevation can be achieved for radiography, a-LDFA measurements do not vary much with mild femoral rotation (±5°). Outside of this range, a-LDFA varies unpredictably with femoral rotation.

Impact of femoral varus on complications and outcome associated with corrective surgery for medial patellar luxation

OBJECTIVES

To evaluate the association of femoral varus with postoperative complications and outcome following standard corrective surgery for medial patellar luxation (MPL) without distal femoral osteotomy (DFO) in dogs.

METHODS

In a retrospective study spanning a 12 year period, 87 stifles with MPL that were treated by standard surgical techniques were included. Inclination angle (ICA), femoral varus angle (FVA), anatomical lateral distal femoral angle (aLDFA), and mechanical lateral distal femoral angle (mLDFA) were measured. Postoperative complications were noted and outcome evaluated. Associations between potential risk factors and both complication rate and outcome were assessed.

RESULTS

Postoperative complications occurred in 19 stifles, five of which were major. There was no evidence of an association between FVA (p = 0.41) or aLDFA (p = 0.38) and any complication. There was also no evidence of an association between FVA (p = 0.31) or aLDFA (p = 0.38) and any major complication. Dogs with a larger aLDFA had increased odds of a poorer outcome (p = 0.01) as did dogs that suffered a major complication (p = 0.0001).

CLINICAL SIGNIFICANCE

Based on radiographic measurements, there is no evidence of an association between FVA and the incidence of postoperative complications following standard MPL correction. Traditional surgical techniques appear to be appropriate for most cases of MPL and further work is required to better define selection criteria for including DFO in the treatment of these cases.

Computation of Femoral Canine Morphometric Parameters in Three-Dimensional Geometrical Models

OBJECTIVE

To define and validate a method for the measurement of 3-dimensional (3D) morphometric parameters in polygonal mesh models of canine femora.

STUDY DESIGN

Ex vivo/computerized model.

SAMPLE POPULATION

Sixteen femora from 8 medium to large-breed canine cadavers (mean body weight 28.3 kg, mean age 5.3 years).

METHODS

Femora were measured with a 3D scanner, obtaining 3D meshes. A computer-aided design-based (CAD) software tool was purposely developed, which allowed automatic calculation of morphometric parameters on a mesh model. Anatomic and mechanical lateral proximal femoral angles (aLPFA and mLPFA), anatomic and mechanical lateral distal femoral angles (aLDFA and mLDFA), femoral neck angle (FNA), femoral torsion angle (FTA), and femoral varus angle (FVA) were measured in 3D space. Angles were also measured onto projected planes and radiographic images.

RESULTS

Mean (SD) femoral angles (degrees) measured in 3D space were: aLPFA 115.2 (3.9), mLPFA 105.5 (4.2), aLDFA 88.6 (4.5), mLDFA 93.4 (3.9), FNA 129.6 (4.3), FTA 45 (4.5), and FVA -1.4 (4.5). Onto projection planes, aLPFA was 103.7 (5.9), mLPFA 98.4 (5.3), aLDFA 88.3 (5.5), mLDFA 93.6 (4.2), FNA 132.1 (3.5), FTA 19.1 (5.7), and FVA -1.7 (5.5). With radiographic imaging, aLPFA was 109.6 (5.9), mLPFA 105.3 (5.2), aLDFA 92.6 (3.8), mLDFA 96.9 (2.9), FNA 120.2 (8.0), FTA 30.2 (5.7), and FVA 2.6 (3.8).

CONCLUSION

The proposed method gives reliable and consistent information about 3D bone conformation. Results are obtained automatically and depend only on femur morphology, avoiding any operator-related bias. Angles in 3D space are different from those measured with standard radiographic methods, mainly due to the different definition of femoral axes.