Yonsei Med J.  2013 Nov;54(6):1505-1510. 10.3349/ymj.2013.54.6.1505.

Easy Identification of Mechanical Axis during Total Knee Arthroplasty

• Seo JG
• Moon YW
• Kim SM
• Jo BC
• Park SH

• KMID: 1798150
• DOI: http://doi.org/10.3349/ymj.2013.54.6.1505

Abstract

PURPOSE
We devised an intraoperatively identifiable mechanical axis (IIMA) as a reference of alignment in total knee arthroplasty (TKA).
MATERIALS AND METHODS
Between February 2010 and January 2011, primary TKAs were consecutively performed on 672 patients (1007 knees) using an IIMA as a reference in the coronal plane.
RESULTS
The alignment of the lower extremity improved from a mean of 11.4+/-6.7degrees (-10.3-34.4degrees) of varus preop. to 0.7+/-3.5degrees (-5.2-8.6degrees) immediately after surgery. Mean alignment of the femoral component in the coronal plane was 89.3+/-2.3degrees (83.4-97.2degrees) postop. and mean alignment of the tibial component was 90.4+/-2.2degrees (85.1-94.2degrees) postop.
CONCLUSION
This study showed that IIMA could be of considerable value as a new guider of alignment that is easily accessible and highly effective during total knee arthroplasty.

Keyword

Lower limb neutral mechanical axis; inter-femoral head center distance; extramedullary reference; total knee arthroplasty

MeSH Terms

Arthroplasty, Replacement, Knee/*methods
Femur/surgery
Humans
Tibia/surgery

Figure

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  Fig. 1 Proximal and distal coronal mechanical axis markers are located above the femoral head and the ankle center. Mechanical axis can be identified by the line which connects the two mechanical axis markers.

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  Fig. 2 Instruments for IIMA system is composed of two parts. Proximal part has ruler and frame with markers and distal part ruler has the same structure to that of proximal ruler. IIMA, intraoperatively identifiable mechanical axis.

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  Fig. 3 (A) Distance between femoral head centers (H-line) is measured on radiographs. H-line is bisected perpendicularly by the body center line. (B) H-line can be replicated on a ruler with two markers.

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  Fig. 4 The center of the ruler was located on the body center line which connects the xiphoid process and the symphysis pubis. Inter-femoral head center distance is bisected perpendicularly by the body center line.

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  Fig. 5 Replicated H-line with two markers are shown proximal to the hip center and distal to the ankle center. Conjoined marker with visible line constitute mechanical axis that is parallel to the body center line. (A) IIMA and pre-op. limb alignment is illustrated. (B) Correct limb alignment can be confirmed when the hip, knee and ankle ccenters are located on the IIMA. (C) After cementing of total knee components, whole limb alignment can be compared to the visualized mechanical axis (Bovie line). IIMA, intraoperatively identifiable mechanical axis.

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