ABSTRACT
Utilizing the mechanical axis can decrease load on the joint and be beneficial when
analyzing bony deformities and planning surgical correction with osteotomies. The
aim of this study was to identify the normal mechanical axes of the first and second
metatarsals and use them to obtain the first/second mechanical intermetatarsal angle
(mIMA). The mechanical axis of the first metatarsal was used to obtain the mechanical
tibial sesamoid position (mTSP), which provides a mechanical relationship with the
sesamoid apparatus. The angular difference between the anatomic and mechanical axis
lines (anatomic-mechanical angle [AMA]) was determined for the first metatarsal and
for the second metatarsal. The commonly used first/second anatomic intermetatarsal
angle (aIMA) and anatomic tibial sesamoid position (aTSP) were also obtained and compared
with the first/second mIMA and mTSP. In this retrospective analysis, radiographs of
50 normal feet (40 patients) were assessed. Pearson's correlation coefficients were
used to measure reliability between obtained measurements. Mean first/second aIMA
was 8.6 ± 3.0 degrees, and first/second mIMA was 8.6 ± 2.6 degrees. First metatarsal
AMA was 1.1 ± 1.0 degrees; second metatarsal AMA was 2.0 ± 1.6 degrees. The mTSP was
2.8 ± 1.1, and aTSP was 2.9 ± 1.0. The TSP median was 3 (range, 1-5). Using the mechanical
axis method to obtain the first/second mIMA and the mTSP is reproducible and not affected
by anatomic changes to the shape of the metatarsal. Unlike the anatomical axis, the
mechanical axis does not change, therefore we recommend using the mechanical axis
during surgical planning and when obtaining preoperative and postoperative measurements
for the long bones of the foot, particularly for forefoot conditions such as hallux
valgus.
Level of Clinical Evidence
Keywords
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Article info
Publication history
Published online: April 04, 2022
Footnotes
Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflicts of Interest: NAS is a paid consultant for Arthrex. The following organizations supported the institution of NAS: DePuy Synthes, Integra LifeSciences, NuVasive Specialized Orthopedics, Orthofix, OrthoPediatrics, Paragon 28, Pega Medical, Smith & Nephew, Stryker, Treace Medical Concepts, and WishBone Medical Inc. JNF, PS, AD, and GAL do not have any conflicts to declare.
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