Summary: The ARRS Annual Meeting presentation underscores a notable prevalence of accessory infraglenoid muscle (AIGM) in patients with teres minor fatty infiltration (TMFI), underscoring its significance in TMFI diagnosis and its potential to influence surgical outcomes, while also suggesting its potential role in reducing the need for additional imaging in TMFI evaluation.

Key Takeaways:

  1. A high prevalence of accessory infraglenoid muscle (AIGM) was found in patients with teres minor fatty infiltration (TMFI), emphasizing its significance in TMFI cases.
  2. Detecting accessory infraglenoid muscle (AIGM) in teres minor fatty infiltration (TMFI) cases is crucial, given its potential to affect surgical outcomes and its ability to minimize the necessity for additional imaging.
  3. AIGM was frequently observed to adjoin the axillary nerve in TMFI patients, suggesting a potential association with concurrent axillary neuropathy.—————————————————————————————————————————————————————————

The Magna Cum Laude Award-Winning Online Poster presented at the 124th ARRS Annual Meeting revealed a substantial prevalence (89%) of accessory infraglenoid muscle (AIGM) in patients with teres minor fatty infiltration (TMFI), in contrast to those without (30%). Furthermore, within the TMFI group, numerous AIGMs were observed to adjoin the axillary nerve, leading to concurrent axillary neuropathy.

Importance of AIGM Detection in TMFI Cases

“These results stress the importance of looking for AIGM in the setting of TMFI, as TMFI on preoperative MRI has been associated with poor postsurgical outcomes,” says Jennifer Padwal, MD, a radiology resident at Stanford University Medical Center in California. “And the presence of AIGM on shoulder MRI could negate the need for additional imaging to evaluate the cause of TMFI.” 

Padwal and her colleagues conducted an institutional review of all shoulder MRIs, analyzing 100 patients with documented TMFI (76 men, 24 women; mean age, 58.6 years). A corresponding sample of 100 shoulder MRIs in patients without TMFI (53 men, 47 women; mean age, 56.4 years) was also assessed for comparison. Two radiologists (one musculoskeletal attending with 25 years of experience and a 4th-year radiology resident) reviewed all scans to identify AIGM with diagnostic confidence, recording muscle origin and insertion. Additionally, in TMFI cases, the distance between the AIGM and axillary nerve was measured, documenting any abnormal axillary nerve signal. TMFI severity was graded using Goutallier classification, and the presence of atrophy and/or edema was noted.

AIGM Origin and Axillary Nerve Contact in TMFI

At the ARRS Annual Meeting, TMFI was observed to be grade 1 in 33%, grade 2 in 32%, grade 3 in 13%, and grade 4 in 14% of cases, with intramuscular edema noted in 33 patients and atrophy in 21 patients. AIGM was detected in 89 out of 100 patients with TMFI and in 30 out of 100 patients without TMFI. Across all cases, AIGM originated from the inferior glenoid neck and inserted onto the humeral neck/proximal humeral diaphysis. In patients with TMFI, the inferior margin of AIGM contacted the axillary nerve in 39 cases (46%), resulting in abnormal signal in 23 cases (27%).

Featured image: Coronal MR images show definite small AIGM (blue arrows), corresponding to diagnostic confidence of 4. In addition, there is high-grade glenohumeral osteoarthrosis, as well as small joint effusion (purple arrow).