1. J Shoulder Elbow Surg. 2020 Dec;29(12):e478-e490. doi: 
10.1016/j.jse.2020.03.038. Epub 2020 Jun 9.

In vivo testing of an injectable matrix gel for the treatment of shoulder cuff 
muscle fatty degeneration.

Huynh T(1), Kim JT(1), Dunlap G(1), Ahmadi S(2), Wolchok JC(3).

Author information:
(1)Department of Biomedical Engineering, University of Arkansas, Fayetteville, 
AR, USA.
(2)College of Medicine, Orthopedic Surgery, University of Arkansas for Medical 
Science, Little Rock, AR, USA.
(3)Department of Biomedical Engineering, University of Arkansas, Fayetteville, 
AR, USA; College of Medicine, Orthopedic Surgery, University of Arkansas for 
Medical Science, Little Rock, AR, USA. Electronic address: jwolchok@uark.edu.

INTRODUCTION: Extracellular matrix (ECM) gels have shown efficacy for the 
treatment of damaged tissues, most notably cardiac muscle. We hypothesized that 
the ECM gel prepared from skeletal muscle could be used as a treatment strategy 
for fatty shoulder cuff muscle degeneration.
METHODS: We conducted experiments to (1) evaluate host biocompatibility to ECM 
gel injection using a rat model and (2) examine the effect of ECM gel injection 
on muscle recovery after delayed repair of a released supraspinatus (SSP) tendon 
using a rabbit model.
RESULTS: The host biocompatibility to the ECM gel was characterized by a 
transient rise (first 2 weeks only) in several genes associated with macrophage 
infiltration, matrix deposition, and inflammatory cytokine production. By 8 
weeks all genes had returned to baseline levels and no evidence of fibrosis or 
chronic inflammation was observed from histology. When gel injection was 
combined with SSP tendon repair, we observed a significant reduction (7%) in SSP 
muscle atrophy (24 + 3% reduction from uninjured) when compared with treatment 
with tendon repair only (31 + 7% reduction). Although fatty degeneration was 
elevated in both treatment groups, fat content trended lower (2%) in response to 
combined tendon repair and intramuscular ECM injection (4.1 + 2.1%) when 
compared with tendon repair only (6.1 + 2.9%). Transcriptome analysis revealed 
adipogenesis and osteoarthritis pathway activation in the repair only group. 
These key pathways were abrogated in response to treatment using combined repair 
plus gel.
DISCUSSION: The findings suggest that ECM injection had a modest but positive 
effect on muscle mass, fatty degeneration, and key cellular signaling pathways.

Copyright © 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. 
Published by Elsevier Inc. All rights reserved.

DOI: 10.1016/j.jse.2020.03.038
PMCID: PMC7669596
PMID: 32713662 [Indexed for MEDLINE]