Comparison of Femoral Angulation Measurement Between Radiographs and Anatomic Specimens Across a Broad Range of Varus Conformations

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.

Three-dimensional volume rendering planning, surgical treatment, and clinical outcomes for femoral and tibial detorsional osteotomies in dogs

OBJECTIVES

To describe a computed tomographic (CT) methodology for planning the correction of femoral and tibial torsion and report the clinical outcomes after femoral (FDO) and tibial (TDO) detorsional osteotomy in dogs affected by torsion malalignment and patellar luxation (PL).

STUDY DESIGN

Multicenter retrospective study.

ANIMALS

Eighteen client-owned dogs.

METHODS

Dogs underwent CT to measure femoral (FTA) and tibial torsion angle (TTA). Abnormal femoral external torsion was defined when FTA <20°, abnormal femoral internal torsion if FTA >35°; abnormal tibial external torsion was defined when TTA < -10°, and abnormal tibial internal torsion when TTA >2°. The cortical arch length (CAL) was measured with CT and used intraoperatively to determine the magnitude of correction. The medical records and radiographs were reviewed and used to report clinical and radiographic outcomes. Radiographs were reviewed to evaluate postoperative limb alignment, patellar position, and bone healing.

RESULTS

Twenty-two detorsional osteotomies were performed. Mean preoperative FTA was 14° for medial-PL and 45.2° for lateral-PL. Mean preoperative TTA was 11° for medial-PL. Physiological patellar tracking was restored in 22/22 of cases. CAL measurement allowed for correction of abnormal torsion in 19/22 of cases. Seventeen out 18 dogs had full or acceptable functional outcome. The median radiographic follow-up was 3 months. Major complications occurred in 2/22 cases, which suffered an iatrogenic abnormal femoral internal torsion and a persistent hindlimb lameness.

CONCLUSIONS

CAL can be measured with CT and used intraoperatively to guide the correction of abnormal torsion in dogs.

CLINICAL RELEVANCE

Abnormal femoral and tibial torsion are predisposing factors for PL. A higher complication rate is expected when FDO and TDO are performed in the same hindlimb.

Post-operative radiographic measures of pelvic limb alignment in dogs with medial patellar luxation after trochlear wedge recession versus trochlear block recession surgery

Background and Aim:

Anatomical and mechanical femoral angles are quite different among dog breeds. Most published data are about large dog breeds, however, medial luxation of patella is more common in small breeds. Measures of pelvic limb alignment are important for outcome of patellar luxation surgery. Therefore, the aim of the present study was to compare the values of anatomical and mechanical femoral and tibial angles in dogs before, immediately after, and 1 month after surgery for correction of medial patellar luxation (MPL).

Materials and Methods:

The study was conducted with 54 dogs (67 stifle joints) from four small breeds that underwent surgery by either trochlear block recession (36 stifle joints) or trochlear wedge recession (31 stifle joints) techniques.

Results:

In both trochleoplasty techniques, statistically significant differences in the values of the anatomical medial proximal femoral angle (aMPFA), anatomical lateral distal femoral angle (aLDFA), and femoral varus angle (in MPL Grade II) and of aMPFA and Q-angle (in MPL Grade III) were found out.

Conclusion:

After block recession surgery, more angles were positively influenced and this effect was more pronounced in patients with MPL Grade II.

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.