Histological evaluation of medial collateral ligament bursa injection, a new conservative treatment, in a rabbit model of medial meniscus horizontal tear.

Background: The ultrasound-guided medial collateral ligament bursa injection technique is safe, reproducible, and effective in treating symptomatic degenerative medial meniscal tears. However, the mechanisms of action and optimal drug combinations remain unclear. This study aimed to evaluate and compare the histological changes caused by injections of corticosteroids and hyaluronic acid into the medial collateral ligament bursa in a rabbit model of medial meniscus horizontal tears. Furthermore, we compared neovascularization and neurogenesis between different treatments.

Methods: The medial meniscus horizontal tear rabbit model was created. Medial collateral ligament bursa injection with triamcinolone acetonide, purified sodium hyaluronate, saline, or needle alone was performed after model creation. The area of the medial collateral ligament bursa was measured. Immunostaining validation (cluster of differentiation31, smooth muscle alpha-actin, calcitonin gene-related peptide, and 4',6-diamidino-2-phenylindole) of the medial collateral ligament bursa injections was performed 2 and 4 weeks after injection.

Results: The group injected with triamcinolone acetonide had a smaller area of the medial collateral ligament bursa than did the other groups. The groups injected with triamcinolone acetonide and purified sodium hyaluronate had lower neovascularization levels than did the other groups. The calcitonin gene-related peptide count was lower in the group injected with triamcinolone acetonide than in the other groups. Corticosteroid and hyaluronic acid injections into the medial collateral ligament bursa suppressed neovascularization and calcitonin gene-related peptide expression, while steroid injections caused adipose tissue and synovial tissue atrophy.

Conclusions: The present study revealed that ultrasound-guided triamcinolone or hyaluronic injections into the medial collateral ligament bursa inhibited neovascularization within it and concomitantly reduced calcitonin gene-related peptide release from neurogenesis. Hence, medial collateral ligament bursa injection should be considered a new treatment option for symptomatic horizontal meniscal tears.