Development of a Rabbit Chronic-Like Rotator Cuff Injury Model for Study of Fibrosis and Muscular Fatty Degeneration
March 31st, 2023
This study details procedures for establishing a chronic-like rabbit rotator cuff (RC) injury. Specifically, the injury is created in the subscapularis (SSC) muscle-tendon/myotendinous unit to mimic human RC anatomy and pathophysiology, including severe muscle fatty degeneration (FD). This protocol can be applied to study RC injuries and assess regenerative therapies.
This protocol demonstrates a complex surgical technique for inducing a chronic-like rotator cuff injury in rabbits, and is useful in studying rotator cuff pathogenesis and developing regenerative therapies. Rabbits are mid to large animal models that are easy to house logistically, manipulate surgically, and show high levels of rotator cuff muscle fatty degeneration when injured, similar to humans. The subscapularis injury model shown here is anatomically analogous to the supraspinatus bone tendon muscle complex, one of the most frequently injured rotator cuff units.
To begin, prepare the surgical window by shaving the intended incision site of an anesthetized rabbit. Using cotton swabs, clean the area with three alternating applications of Betadine and 70%alcohol in circular motions. Administer 20 milligrams per kilogram of cephalexin intramuscularly as a prophylactic anti-infective agent.
Make a three to four centimeter skin incision inferior to the clavicle, split the deltopectoral interval using a scissor, and retract to gain access to the shoulder. To locate the subscapularis muscle tendon unit, first identify the coracobrachialis muscle. Then identify the subscapularis tendon and insert a right angle clamp to expose the entire tendon at its insertion on the lesser tuberosity of the humerus.
Isolate the subscapularis muscle tendon. After administering pre-surgery analgesic locally near the transection site, wrap the subscapularis muscle tendon unit in silicone-based penrose tubing to prevent undesired attachment to the surrounding tissues and aid subsequent tissue retrieval. To induce injury, create a full thickness transection at the muscle tendon junction using a surgical number 11 scalpel.
Where necessary, stop bleeding by applying pressure with a piece of gauze and use saline to irrigate the wound as needed. To close the wound, use a 4-0 polyglycolic acid suture to reapproximate the deltoid muscle tissue and a 4-0 nylon or silk suture to close the skin wound, followed by wound cleaning. Administer 0.03 milligrams per kilogram of buprenorphine subcutaneously as an analgesic once immediately after surgery, and twice daily for the next 48 hours.
The histological analysis of the chronic-like rotator cuff injury model at four weeks is shown in this figure. The H&E staining confirmed the loss of muscle cellularity and organization, which was replaced with large numbers of adipocytes in injured subscapularis muscles relative to the control group. The quantification of the injured muscle fat accumulation percentage is presented in this figure.
Masson's trichrome staining also confirmed muscle atrophy and disorganized collagen fiber arrangements in injured subscapularis muscles relative to the control group. The quantification of the proportion of muscle and fibrotic tissue are shown in this figure. The assessment showed a reduction in muscle cellularity for injured subscapularis muscles relative to the control group.
A high degree of fibrosis was also observed in injured subscapularis muscles. Identifying the subscapularis tendon and wrapping the subscapularis muscle tendon unit in penrose tubing are the most important steps of this procedure. Following this procedure, a therapeutic intervention may be applied.
In this case, the analyses described here, along with additional myography or gait analysis, may be used to assess intervention outcome. This technique is crucial for aiding researchers in the study of rotator cuff pathophysiology, as well as facilitating the development of novel therapeutics for muscle tendon repair and regeneration.
Overview
This study presents a complex surgical technique for inducing a chronic-like rotator cuff injury in rabbits, providing a relevant model for studying rotator cuff pathogenesis and developing regenerative therapies. The subscapularis muscle-tendon unit is targeted to replicate human rotator cuff injuries, which include marked muscle fatty degeneration.
Key Study Components
Research Area
- Rotator cuff injury modeling
- Muscle degeneration and repair mechanisms
- Veterinary surgical techniques
Background
- Rabbits serve as a mid to large animal model with anatomical similarities to human rotator cuffs.
- The study focuses on replicating severe muscle fatty degeneration seen in human injuries.
- Subscapularis injuries are comparable to the frequently injured supraspinatus tendon.
Methods Used
- Surgical induction of rotator cuff injury via full thickness transection
- Use of rabbit as the biological model
- Histological analysis and quantification of fat accumulation and fibrosis
Main Results
- Confirmed loss of muscle cellularity replaced by adipocytes in the injured group.
- Histological staining revealed muscle atrophy and abnormal collagen arrangements.
- Quantitative assessments demonstrated significant differences between injured and control groups.
Conclusions
- The procedure establishes a viable model for further research into rotator cuff pathophysiology.
- The findings are significant for developing novel therapeutic strategies for muscle tendon repair and regeneration.
Frequently Asked Questions
Executive Industry Relevance
Establishing a chronic-like rabbit rotator cuff injury model enables translational investigation of muscle fibrosis and fatty degeneration, key barriers in musculoskeletal regenerative medicine. This model provides a controlled platform for interrogating disease mechanisms and evaluating therapeutic interventions relevant to human rotator cuff pathology. Its anatomical and pathophysiological fidelity supports predictive confidence in early-stage target validation and preclinical research.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables mechanistic de-risking of fibrosis and fatty degeneration pathways in musculoskeletal disease.
- Supports functional target validation by recapitulating clinically relevant muscle-tendon degeneration.
- Facilitates hypothesis-driven interrogation of regenerative and anti-fibrotic strategies.
Screening & Assay Development
- Provides a validated in vivo system for quantitative histological and functional readouts.
- Enables reproducible assessment of intervention efficacy using standardized injury and analysis protocols.
- Supports assay development for quantifying muscle atrophy, fat accumulation, and fibrosis.
Translational & Preclinical Research
- Aligns with disease-relevant endpoints observed in human rotator cuff pathology.
- Enables continuity from discovery through preclinical validation of regenerative candidates.
- Supports risk-adjusted advancement of therapies targeting muscle-tendon repair.
Pipeline & Workflow Integration
This rabbit model integrates into the discovery-to-preclinical continuum for musculoskeletal and regenerative medicine programs.
- Discovery Biology: Facilitates hypothesis testing on fibrosis and fatty degeneration mechanisms in a controlled in vivo context.
- Screening: Provides standardized, reproducible injury and histological quantification for intervention assessment.
- Analytics: Enables quantitative measurement of muscle fat content and fibrosis for comparative analysis.
- Translational Research: Bridges early discovery findings with preclinical validation in a disease-relevant system.
- Enterprise Reuse: Serves as a reusable platform for iterative evaluation of diverse therapeutic modalities.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence in target validation and mechanistic de-risking for muscle-tendon pathology.
- Operational Value: Standardizes in vivo modeling and histological analysis for reproducibility and scalability.
- Strategic Value: Informs go/no-go decisions for regenerative and anti-fibrotic candidates, reducing late-stage biological risk.
- Portfolio Impact: Enables risk-adjusted prioritization of therapeutic programs targeting chronic muscle-tendon degeneration.
Implementation Considerations
- Requires surgical expertise in animal models and post-operative care protocols.
- Necessitates access to histological staining and quantitative image analysis infrastructure.
- Demands cross-team standardization of injury induction and outcome measurement.
- Adaptation to other species or injury sites may require protocol optimization.
- Model limitations include species-specific responses and the need for longitudinal validation.
