Association of Baxter's Neuropathy and Fatty Infiltration of the Abductor Digiti Minimi Muscle on Magnetic Resonance Imaging: A Systematic Review

Background Fatty infiltration—or fatty atrophy—of the abductor digiti minimi (ADM) muscle of the foot on magnetic resonance imaging (MRI) has been attributed to entrapment of the first branch of the lateral plantar nerve (i.e., Baxter's neuropathy), a condition associated with plantar heel pain (PHP). The aim of this study was to investigate the evidence relating to the association between fatty infiltration of ADM and Baxter's neuropathy. Methods This systematic review conducted searches in MEDLINE, CINAHL, SPORTDiscus, Embase and the Cochrane Library from 20 th June 2023 to 19 th of March 2024. Peer‐reviewed articles of retrospective, cross‐sectional observational, or cohort studies written in English that investigated the prevalence or frequency of fatty infiltration of ADM on MRI in adult participants were included. Study quality and risk of bias were assessed using the National Institutes of Health quality assessment tool for observational cohort and cross‐sectional studies. Results Four studies (1052 participants) were identified and included in the review. Two studies were retrospective studies and two studies were cross‐sectional observational studies. Only one study was rated ‘good’ on quality assessment. The reported prevalence of fatty infiltration of ADM on MRI was reported to be between 4% and 11% in the general population. Prevalence was also reported to be similar in people with and without generalised foot pain (approximately 8% and 6%, respectively). No studies reported prevalence in specific populations with PHP or with Baxter's neuropathy. Conclusion The association between fatty infiltration of ADM on MRI and entrapment of the first branch of the lateral plantar nerve as part of PHP still remains unknown due to the lack of robust evidence. Additional high‐quality studies investigating the association between PHP and fatty infiltration of ADM on MRI would be worthwhile to improve our understanding of the diagnostic value of MRI for this condition, which may aid decision‐making for the treatment of PHP, particularly surgical treatment of Baxter's neuropathy.