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Different References for Valgus Cut Angle in Total Knee Arthroplasty
Hamidreza Yazdi1,2,3,4,5,6, Ara Nazarian1,2,3,4,5,6, Jim S Wu1,2,3,4,5,6
1Department of knee Surgery, Firoozgar Hospital, Neuromusculoskeletal Research Center, Iran University of Medical Sciences, Tehran, Iran.
The Archives of Bone and Joint Surgery
|September 4, 2018
Summary
The definition of the femur's anatomical axis impacts valgus cut angle (VCA) measurements in total knee arthroplasty (TKA). Using the full femur axis versus the distal half yields significantly different VCA results in both normal and varus aligned femurs.
Area of Science:
- Orthopedic Surgery
- Biomedical Engineering
- Radiology
Background:
- Preoperative measurement of the valgus cut angle (VCA) in total knee arthroplasty (TKA) relies on three-joint alignment radiographs.
- The anatomical axis of the femur can be defined using its full length or its distal half, potentially leading to variations in VCA measurements.
- Intramedullary femoral guides used in TKA may align with either the distal half or near full anatomical axis.
Purpose of the Study:
- To compare the VCA measurements obtained using the full-length femur anatomical axis versus the distal half femur anatomical axis.
- To assess these differences in both normally aligned and varus-aligned femurs.
- To determine if the definition of the anatomical axis significantly impacts VCA in TKA planning.
Main Methods:
- Full-length weight-bearing radiographs were utilized to assess three-joint alignment in normal (LDFA = 87º ± 2º) and varus (LDFA >89º) aligned femurs.
- Two orthopedic surgeons independently measured the full-length anatomical axis-mechanical axis angle (angle 1) and the distal half anatomical axis-mechanical axis angle (angle 2) using DICOM viewer software.
- Statistical comparison of angles 1 and 2 was performed for both normal and varus aligned femurs.
Main Results:
- The study included 97 normally aligned and 97 varus aligned femurs.
- In normally aligned femurs, angle 1 (mean 5.05° ± 0.76°) and angle 2 (mean 3.62° ± 1.19°) were statistically different (P=0.0001).
- In varus aligned femurs, angle 1 (mean 5.42° ± 0.85°) and angle 2 (mean 4.23° ± 1.27°) also showed statistically significant differences (P=0.0047).
Conclusions:
- The method used to define the femur's anatomical axis significantly influences VCA measurements.
- These differences were observed in both normal and varus aligned femurs.
- Surgeons should consider the definition of the anatomical axis and the length of the intramedullary guide when determining the preoperative VCA in TKA.
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