Histological maturation of an Achilles tendon allograft six years after revision anterior cruciate ligament reconstruction: a case report.

Revision anterior cruciate ligament (ACL) reconstruction (ACLR) increasingly relies on allografts to avoid additional donor-site morbidity and to address complex instability patterns. However, long-term intra-articular histological data on allograft remodeling remain scarce. We report an uncommon opportunity to evaluate the substance of a fresh-frozen Achilles tendon allograft six years after revision ACLR. A 41-year-old male had undergone revision ACLR using an over-the-top technique combined with lateral extra-articular tenodesis after failure of a hamstring autograft. Six years later, arthroscopy for a bucket-handle medial meniscus tear confirmed a clinically stable graft and allowed collection of multiple intra-articular graft biopsies. Specimens were formalin-fixed, paraffin-embedded, sectioned at 5 μm, and stained with Azan-Mallory stain for histological evaluation. Histology demonstrated a largely organized extracellular matrix with parallel collagen bundles populated by spindle-shaped tenoblasts, together with focal areas of intersecting fibers, heterogeneous nuclear morphology, and persistent microvascularity. The histological findings were organized in a structured descriptive assessment to improve transparency while recognizing that no universally accepted histological score exists for ACL graft maturation. The findings were interpreted as compatible with advanced but incomplete ligamentization. Clinically, the graft remained stable, supporting the possibility of a dissociation between biological maturation and functional outcome. LEVEL OF EVIDENCE: IV, case report.