Derotational Osteotomy of the Distal Femur for the Treatment of Patellofemoral Instability Simultaneously Leads to the Correction of Frontal Alignment: A Laboratory Cadaveric Study

Abstract

Background:Derotational osteotomy of the distal femur allows the anatomic treatment of patellofemoral maltracking due to increased femoral antetorsion. However, such rotational osteotomy procedures have a high potential of intended/unintended changes of frontal alignment.Purpose/Hypothesis:The purpose of this study was to perform derotational osteotomy of the distal femur and to demonstrate the utility of a novel trigonometric approach to address 3-dimensional (3D) changes on 2-dimensional imaging (axial computed tomography [CT] and frontal-plane radiography). The hypothesis was that 1-step single-cut osteotomy can simultaneously correct torsion and frontal alignment based on preoperatively calculated cutting angles.Study Design:Controlled laboratory study.Methods:Eight human cadaveric whole legs (4 lower limb torsos) underwent derotational osteotomy of the distal femur of 20°. A straight leg axis, determined as a mechanical femorotibial angle (mFTA) of 0°, was chosen as a goal for postoperative frontal alignment. The inclination of the cutting angle from the lateral view was calculated individually for each cadaveric leg and was represented by a simple 3D-printed cutting guide for surgery. Specimens underwent CT for the measurement of torsion, while the frontal leg axis was determined on an upright radiograph preoperatively and postoperatively. Preoperative and postoperative angles were compared with the mathematical prediction model.Results:The preoperative mFTA ranged from –3.9° (valgus) to +3.4° (varus) (mean, –0.2° ± 2.6°). A postoperative mean mFTA of 0.37° ± 0.69° (95% CI, –0.22° to 0.95°) was achieved (P = .01). Derotation showed a mean of 19.1° ± 2.1° (95% CI, 17.3°-20.8°). The oblique cutting plane for the correction of valgus legs showed a mean of 5.9° ± 6.8° and, for the correction of varus legs, a mean of –10.0° ± 4.5° projected on the perpendicular plane to the virtual anatomic shaft axis from the sagittal view.Conclusion:Single-cut distal femoral osteotomy can be performed to simultaneously address rotational as well as frontal alignment using a preoperatively defined oblique cut, as determined by the presented reproducible calculation model.Clinical Relevance:This study adds important knowledge to the technique of derotational osteotomy. This approach provides an individual, oblique single cut for the correction of torsion and frontal axis within a clinically insignificant margin. Simplified tables for calculation and a surgical reference make this model reproducible and safe.

Coronal and Transverse Malalignment in Pediatric Patellofemoral Instability

“…Osteotomies can be placed about the intertrochanteric, subtrochanteric, diaphyseal, or distal metaphyseal regions and fixed with a plate, an intramedullary nail, external fixator, or a combination thereof [43,104,105]. The literature has described corrective osteotomy in patients with radiographic femoral anteversion >20 • to 25 • [106][107][108][109] The effect of transverse plane correction on other planes is an important consideration [110,111]. Using computer modeling from CT data of a femur, Nelitz et al demonstrated that proximal femoral osteotomies created varus alignment and distal osteotomies created valgus alignment [112].…”

Three dimensional CT analysis of the change in rotational alignment in double level osteotomy after double level osteotomy performed for varus osteoarthritic knees

“…As regards three-dimensional alignment change in a femoral osteotomy, a cadaveric study by Imhoff et al. showed coupled rotational and coronal plane (varus/valgus) alignment changes occurring in corrective femoral osteotomy 14 Several clinical studies have examined the postoperative change in rotational alignment after OWHTO; however, the reported results are somewhat discordant. An increased internal rotation of the distal bony fragment (decreased tibial torsion) was shown in some studies, 13 , 15 while no significant postoperative change was noted in another study.…”

“…Since the alignment is three-dimensional in nature, the postoperative changes induced by osteotomy should be assessed on a three-dimensional basis; however, the analyses conducted in the majority of the previous relevant studies were limited to alignment on coronal plane. 9 , 10 , 11 In regards to high tibial osteotomy and distal femoral osteotomy, there have been some studies investigating rotational changes induced by the osteotomy, 12 , 13 , 14 , 15 , 16 while no study has investigated the change in rotational alignment after DLO.…”

Retrograde Intramedullary Nail Fixation for Derotational Femoral Osteotomy for Recurrent Femoropatellar Instability

“…However, Imhoff et al demonstrated, in a cadaveric study, the importance of the orientation of the cut in the distal femur to avoid changes in the coronal orientation of the limb, when a distal femoral derotational osteotomy is performed [27]. More importantly, by a single cut in the distal femur, the coronal and the rotational problem of the patient can be addressed by choosing the patient-specific oblique cut [28]; these promising results must be validated in the operating room. In summary, the planning of the derotational osteotomy must consider the effects in the coronal and sagittal planes and the patient-specific segment of femur maltorsion.…”