Article
Distal femoral rotational osteotomy to correct femoral antetorsion leads to an increased peak pressure on the medial aspect of the patella
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Published: | November 6, 2018 |
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Objectives: Patellofemoral instability (PFI) is multifactorial and therefore a detailed knowledge of the various, interrelated risk factors and the pathomechanisms is required. Femoral antetorsion, through the medialization of the trochlea, is an important risk factor of PFI. It affects all corresponding static and dynamic factors of PFI as it is essential for alignment and muscular strain. The purpose of this study was to investigate the retropatellar pressure distribution during distal femoral rotational osteotomy. We hypothesized that torsion significantly influences the medial and lateral aspect of retropatellar peak pressure distribution.
Methods: Nine fresh frozen human knee specimen were used for this study. Each specimen was embedded in custom-made 3D-printed casts. Retropatellar pressure was measured by means of a pressure sensitive film. The tibia was connected to the tip of the robotic test system, which consisted of an arm robot and a multidimensional force torque sensor. The femur and the rotatable loading mechanism were attached to the robot's base frame. The vastus medialis, the vastus medialis obliqus, the rectus femoris, the vastus lateralis and the tractus iliotibialis were fixed to cable wires and statically loaded (12.5, 12.5, 50, 50 and 50 N).
Each of the five different muscle strings were positioned individually regarding the anatomic characteristics.
The analysis concentrated on the investigation of the peak pressure on the medial and lateral aspect of the patella during the adjustment-osteotomy of the femur. To mimic the intervention the loading frame was designed to rotate manually in 5 ° steps around the anatomical femoralaxis simulating a torsion from -5 to 15°. The peak pressure was each measured in 0°, 15°, 30°, 45°, 60° and 90° flexion. A two-factorial variance analysis with repeated measurements has been performed.
Results: Mean age of specimens was 66.1 +- 11.5 (range 43-77) years with a mean Caton-Deschamps index of 0.95 +- 0.09 (range 0.79-1.06) indicating a physiological patella height. The medial and lateral aspect of the patella were analyzed separately. The medial aspect of the patella showed a significant influence of femoral derotation (external) with constantly lower peak pressures in all flexion angles (p<0.05) and a decrease of peak pressure with progressive derotation form 15° external rotation to 5° internal rotation (p< 0.05). On the contrary, the rotation had no significant influence on the peak pressure of the lateral patella aspect through the different flexion angles (p >0.05), but a consistent increase of peak pressure from 0° to 90° flexion could be shown (p<0.05).
Conclusion: Distal femoral rotational osteotomy to correct a pathological femoral antetorsion leads to an increased peak pressure on the medial aspect of the patella, but does not result in an increased peak pressure on the lateral patella.