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. 2018 Jul 11;19(1):215.
doi: 10.1186/s12891-018-2140-5.

Single cut distal femoral osteotomy for correction of femoral torsion and valgus malformity in patellofemoral malalignment - proof of application of new trigonometrical calculations and 3D-printed cutting guides

Affiliations

Single cut distal femoral osteotomy for correction of femoral torsion and valgus malformity in patellofemoral malalignment - proof of application of new trigonometrical calculations and 3D-printed cutting guides

Florian B Imhoff et al. BMC Musculoskelet Disord. .

Abstract

Background: The purpose of this study was to perform a derotational osteotomy at the distal femur, as is done in cases of patellofemoral instability, and demonstrate the predictability of three-dimensional (3D) changes on axes in a cadaveric model by the use of a new mathematical approach.

Methods: Ten human cadaveric femurs, with increased antetorsion, underwent a visually observed derotational osteotomy at the distal femur by 20°, as is commonly done in clinics. For surgery, a single cut osteotomy with a defined cutting angle was calculated and given using a simple 3D-printed cutting guide per specimen, based on a newly-created trigonometrical model. To simulate post-operative straight frontal alignment in a normal range, a goal for the mechanical lateral distal femur angle (mLDFA) was set to 87.0° for five specimens (87-goal group) and 90.0° for five specimens (90-goal group). Specimens underwent pre- and post-operative radiographic analysis with CT scan for torsion and frontal plane x-ray for alignment measurements of mLDFA and anatomical mechanical angle (AMA).

Results: Performed derotation showed a mean of 19.69° ±1.08°SD (95% CI: 18.91° to 20.47°). Regarding frontal alignment, a mean mLDFA of 86.9° ±0.66°SD (87-goal-group) and 90.42° ±0.25° SD (90-goal group), was observed (p = 0.008). Overall, the mean difference between intended mLDFA-goal and post-operatively achieved mLDFA was 0.14° ±0.56° SD (95% CI: -0.26° to 0.54°).

Conclusion: A preoperative calculated angle for single cut derotational osteotomy at the distal femur leads to a clinically precise post-operative result on torsion and frontal alignment when using this approach.

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Conflict of interest statement

Authors’ information

Florian B. Imhoff, MD; Specialist Orthopaedic and Trauma Surgery; German Board Certified Currently: Postdoctoral Research Fellow at Uconn Health, Department of Orthopaedic Surgery 263 Farmington Avenue, Farmington, CT 06030, USA.

Ethics approval and consent to participate

The study was reported to the institutional review board (IRB) of the Uconn Health, University of Connecticut, and it was documented that no IRB approval was required (de-identified specimen do not constitute human subjects research). Specimen had been obtained from MedCure (MedCure, Inc., Cumberland, RI, USA). According to the distributors information, consent was obtained from the patient before death.

Consent for publication

Not applicable.

Competing interests

Authors IFB, SJ, MA, DT, SB declare that they have no conflict of interest and nothing to disclose.

Author BS is a consultant for Arthrex.

Author IAB is a consultant for Arthrosurface, Arthrex, and mediBayreuth.

Author ARA received an educational and institutional grant from Arthrex and is a consultant for Biorez.

Author BK is a consultant for Arthrex.

No-one of the above-mentioned authors has received personal financial support related to this study.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Planning of correction of frontal alignment (x-ray-grit is vanished for better visualization): a preoperative measurements and reference; b drawing of intended mechanical axis/center of femoral head; c measuring corrective angle at assumed cutting plane; d postoperative result
Fig. 2
Fig. 2
Calculation for clinical practice: Processing radiographically observed corrective angle and change of AMA to the remaining corrective angle, which leads to a defined oblique cutting angle
Fig. 3
Fig. 3
Elementary mathematical approach: a Increased antetorsion, decreased mLDFA; b If cutting plane is perpendicular, derotation leads to normal antetorsion and slight increased mLDFA; c If the cutting plane is oblique from a sagittal view, derotation leads to normal antetorsion and significant increased mLDFA
Fig. 4
Fig. 4
Surgery of specimens: a Cutting guide aligned parallel to the virtual shaft axis (distal: middle of the shaft; proximal: middle of the shaft at height of the greater trochanter), b Single cut osteotomy through the cutting guide, c Derotation by 20°, d plate fixation, resulting in slight varus change on the coronal axis
Fig. 5
Fig. 5
Illustration and Equation for change of AMA at cutting point
Fig. 6
Fig. 6
Mathematical equation, Denavit-Hartenberg Transformation: Development of equation for change of axis due to rotation and an oblique cutting angle
Fig. 7
Fig. 7
Illustration of schematic XYZ-coordinate for calculations of three dimensional effects; reverse equation for angle of coronal change (XZ-plane)

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