Introduction 1 3 4 1 5 6 1 7 Materials and methods Patient population This retrospective study included 200 individuals who were referred for MRI of the hindfoot due to the presence of foot pain. These were individuals seen in a subspecialty teleradiology group practice with participant referrals from 40 states. The study was conducted with data from August 2006 to January 2007 and included patients of all ages. The study group was composed of 100 consecutive individuals with abductor digiti minimi atrophy and 100 consecutive individuals without abductor digiti minimi atrophy. No eligible participants were excluded. The subspecialty teleradiology group practice does not have an Institutional Review Board (IRB), and the study was conducted in compliance with the Declaration of Helsinki principles and the Health Insurance Portability and Accountability Act. Owing to the retrospective nature of the study, informed consent was not obtained. Participants’ ages ranged from 10–92 years [mean = 49.0 years, standard deviation (SD) = 16.9 years] and included 139 women and 61 men. MRI technique Patients were scanned in magnets ranging from 0.2 T to 1.5 T. Long- and short-axis fat and fluid sensitive sequences were obtained without the administration of gadolinium. The technical parameters for all magnet strengths were as follows: sagittal T1-weighted, sagittal short-tau inversion recovery (STIR), oblique axial STIR, coronal T1-weighted, coronal STIR, plantar flexed axial proton density, axial T2-weighted, and axial T2-weighted with fat saturation or STIR. Data acquisition 1 2 Fig. 1 ADM  Fig. 2 ADM  Statistical analysis Age and gender distribution, as well as the frequency of plantar fasciitis, calcaneal spur formation, calcaneal edema, PTTD, and Achilles tendon dysfunction, were compared in patients with and without ADMA. Age was compared with analysis of variance (ANOVA). For the categorical variables we used, as appropriate, Pearson chi-square analyses or Fisher’s exact test to compare the proportion of those with atrophy to those without. We used logistic regression to determine odds ratios and 95% confidence intervals for each of the variables to atrophy. First, we included each variable in a univariate model to determine its relationship to atrophy. We then simultaneously included all the variables in a multivariate analysis to determine the relationship of the variable to atrophy, while simultaneously adjusting for all the other variables. Alpha level was at 0.05, and all tests were two-sided. SPSS version 15.0 (2006) (SPSS, Chicago, USA) was used for the analyses. Results n 1 P Table 1 Comparisons of demographic and clinical variables for those with and without atrophy of the abductor digiti minimi muscle Variable n n P a   <0.001 [Mean (SD)] 40.8 (15.8) 57.2 (13.7)  Gender   0.28 Women 66.0% (66) 73.0% (73)  Men 34.0% (34) 27.0% (27)  Achilles tendinosis   <0.001 No 97.0% (97) 78.0% (78)  Yes 3.0% (3) 22.0% (22)  Calcaneal edema   0.005 No 97.0% (97) 85.0% (85)  Yes 3.0% (3) 15.0% (15)  Calcaneal spur   <0.001 No 93.0% (93) 52.0% (52)  Yes 7.0% (7) 48.0% (48)  Other tendon abnormality   0.60 No 81.0% (81) 78.0% (78)  Yes 19.0% (19) 22.0% (22)  b   <0.001 No 89.0% (89) 47.5% (47)  Yes 11.0% (11) 52.5% (52)  PTTD    No 89.0% (89) 68.0% (68)  Yes 11.0% (11) 32.0% (32) <0.001 a b Patients with atrophy compared to those without atrophy had significantly greater proportions of Achilles tendinosis, calcaneal edema, calcaneal spur, plantar fasciitis, and PTT dysfunction. 2 P P n P Table 2 OR CI Variable Univariate OR (95% CI) P Multivariate OR (95% CI)  P Age (years) 1.08 (1.05, 1.11) < 0.001 1.06 (1.03, 1.09) < 0.001 Gender  0.28  0.51  Women 1.00  1.00   Men 0.72 (0.39, 1.32)  0.75 (0.33, 1.73)  Achilles tendinosis  < 0.001  0.09  No 1.00  1.00   Yes 9.12 (2.63, 31.60)  3.69 (0.81, 16.88)  Calcaneal edema  0.007  0.47  No 1.00  1.00   Yes 5.71 (1.60, 20.39)  1.89 (0.35, 10.19)  Calcaneal spur  < 0.001  0.02  No 1.00  1.00   Yes 12.26 (5.18, 29.10)  3.60 (1.28, 10.17)  Other tendon abnormality  0.60  0.71  No 1.00  1.00   Yes 1.20 (0.60, 2.39)  1.19 (0.48, 2.97)  Plantar fasciitis  < 0.001  0.01  No 1.00  1.00   Yes 8.95 (4.27, 18.77)  3.35 (1.31, 8.56)  PTTD  0.001  0.31  No 1.00  1.00   Yes 3.81 (1.79, 8.10)  1.72 (0.60, 4.88)  Of the 200 patients in the study, the consensus reviewers (U.C. and A.L) disagreed with findings in the initial report of eight , three with ADMA and five without ADMA. In two of the cases of ADMA, the presence of a calcaneal spur was not mentioned in the initial report. In the third case of ADMA, the presence of posterior tibial tendinosis was not mentioned in the initial report. For three of the five patients without ADMA, the presence of a calcaneal spur was not mentioned in the initial report. For one of the patients without ADMA, the presence of Achilles tendinosis was not mentioned in the initial report. For one patient without ADMA, the presence of plantar fasciitis was not mentioned. Discussion Patients with ADMA had a significantly greater frequency of Achilles tendinosis, calcaneal edema, calcaneal spur, plantar fasciitis, and posterior tibialis tendon dysfunction than those without ADMA. After logistic regression analysis, only increased age, calcaneal spur, and plantar fasciitis remained significantly associated with ADMA. 1 8 3 4 7 9 11 3 12 7 8 13 Fig. 3 PTN ICN LPN MPN  Fig. 4 ADM FDB AH  5 7 14 15 7 14 5 16 17 Limitations of the study include retrospective data collection, which may lead to selection bias; however, we attempted to minimize selection bias by including 100 consecutive patients in each study group. In addition, the inclusion of 15 pediatric patients might have affected the results, as younger patients are less likely to have degenerative conditions of the foot or ankle and could potentially have falsely decreased the frequency of findings in the group of patients without abductor digiti minimi atrophy. However, a repeat statistical analysis, from which the pediatric patients had been excluded, demonstrated no significant difference in results. In summary, our study showed a significant association between atrophy of the abductor digit minimi muscle, an MRI manifestation of Baxter’s neuropathy, with age, plantar calcaneal spur formation, and plantar fasciitis. These findings support the notion of an etiologic role for compression of the inferior calcaneal nerve as it passes anterior to the medial calcaneal tuberosity in the development of Baxter’s neuropathy.