Nerve entry points of the first layer of plantar intrinsics

Laura Tungate, R Claire Aland, Peter G. Noakes, Mark Midwinter

The School of Biomedical Sciences, The University of Queensland, Brisbane, Australia

Objectives: Nerve entry points (NEPs) are where nerve branches enter epimysium surrounding a muscle belly to innervate muscle. Many limb muscles have multiple NEPs. Whilst these are often well known for larger muscles, information is limited or nonexistent for foot intrinsic muscles. This study describes the number, location and distribution of NEPs in the first layer of plantar intrinsic muscles.
Methods: Sixteen adult human lower limbs (pairs from 8 donors) were dissected. Origin, location and number of NEPs were recorded for abductor hallucis (AH), flexor digitorum brevis (FDB) and abductor digiti minimi (ADM).
Results: Nerves innervating the first layer of plantar intrinsic muscles all originated from the medial plantar nerve. AH had a mode of 2 NEPs (range 2–3), FDB had a mode of 3 (range 1–4), and AbDM had a mode of 2 (range 1–4). NEPs entered muscles only via the deep surface in 14/16 AH, 15/16 FDB 15/16 ADM. Fewer muscles had NEPs on both superficial and deep surfaces (1/16 for AH, FDB and ADM), and 2/16 AH had only superficially entering NEPs. No FDB and ADM had only superficial NEPs. There was no apparent preference for medial or lateral entry. AH and ADM NEPs consistently penetrated the proximal two-thirds of the muscle belly, while NEPS mostly entered the distal two-thirds of the FDB muscle belly.
Conclusions: This is the first report of NEPs for FDB, and extends limited reports for AH and ADM. These results suggest locations for nerve blocks for spasticity and electromyography.

Keywords: nerve entry points; plantar intrinsic muscles

Ethical statement: This study was approved by the UQ Ethics committee (2022/HE001372), and Anatomy Teaching and Research Management Committee (RA2 – 2022-013) and was conducted in accordance with the Declaration of Helsinki Principles.

Funding statement: This work was supported by internal UQ funds to School of Biomedical Science – student support funds. PGN is supported by NMHRC Ideas Grant (2029824) and Motor Neuron Disease Australia (IG 2326). MM is supported by NHMRC ideas grant 2021074.