Abstract
Background
Radiographic measurements to study sagittal alignment in the setting of knee are frequently
difficult to evaluate due the presence of a prosthesis or implant that obscures traditional
radiographic landmarks. In this paper we present a novel method of determining sagittal
femoral alignment in the presence of obscuring implants.
Methods
98 full-length femoral radiographs were reviewed and divided into two groups. In Group
1, the Distal Mechanical Point (DMP) was used to calculate the Distal Mechanical Ratio
(DMR), defined as the ratio of the linear distance from the DMP to the anterior cortical
axis divided by the distance from the anterior cortical axis to posterior condylar
cortex. In group 2, the sagittal mechanical axis was measured using the true DMP (tDMP)
and then separately measured using the DMR to find the calculated DMP (cDMP), and
the angular variance between the calculated (cSMA) and true (tSMA) sagittal mechanical
axis was calculated, as well as the linear distance between the tDMP and cDMP. Twenty
additional patients with knee replacements were then selected and two observers used
a cSMA to determine a femoral prosthesis flexion angle (FPFA), with intraobserver
correlation calculated.
Results
The mean DMR was found to be 0.24, with high intraobserver correlation and normal
distribution. Validation of the model demonstrated angular variance between tSMA and
cSMA less than 1 degree and linear distance between tDMP and cDMP less than 1 mm.
Calculation of cCMA in the presence of total knee arthroplasty revealed very strong
intraobserver correlation of 0.89.
Conclusion
The Distal Mechanical Ratio reliably predicted the true Sagittal Mechanical Axis within
1 degree and true Distal Mechanical Point within 1 mm, indicating that it may be a
valuable tool for evaluating sagittal femoral alignment in cases where anatomic landmarks
may be absent or obscured.
Keywords
Abbreviations:
DMP (Distal mechanical point), DMR (Distal medcahnical ratio), SMA (Sagittal mechanical axis), FPFA (Femoral prosthesis flexion angle)To read this article in full you will need to make a payment
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Article info
Publication history
Published online: December 07, 2022
Accepted:
November 15,
2022
Received in revised form:
November 12,
2022
Received:
October 20,
2021
Footnotes
☆This project supported by an unrestricted research grant from the Glen E. and Rita K. Roney Fund at the Department of Orthopaedic Surgery, Baylor Scott and White Medical Center – Temple.
Identification
Copyright
© 2022 Elsevier B.V. All rights reserved.
