title: Involvement of the muscle-tendon junction in skeletal muscle atrophy: an ultrastructural study.
abstract: BACKGROUND
  The muscle-tendon junction (MTJ) is a physiologically vital tissue interface and a highly specialized region in the muscle-tendon unit. It is the weakest point in the muscle-tendon unit, making it susceptible to strain injuries. Nonetheless, knowledge of the pathological changes affecting this region and of its response to the atrophy process is very limited. The aim of the study was to examine MTJ ultrastructural morphology in patients with different conditions that induce skeletal muscle atrophy and to attempt a grading of the atrophy process.
  
  
  METHODS
  Fifteen patients undergoing amputation in the distal or proximal third of the lower leg due to chronic or acute conditions were divided into two groups. Specimens of gastrocnemius muscle collected at the time of surgery were analyzed by histology and electron microscopy. The contact between muscle and tendon was measured using a dedicated software that calculated semi-automatically the base (B) and perimeter (P) of muscle cell finger-like processes at the MTJ.
  
  
  RESULTS
  Electron microscopy. The cells in the atrophic muscle of the chronic group were shallow and bulky. In the acute group, the myotendinous endings differed significantly in their structure from those of the chronic group. In atrophic muscle, the contact between muscle and tendon was reduced by quantitative and qualitative changes in the myotendinous endings. The B/P ratio allowed definition of three grades of myotendinous ending degeneration.
  
  
  CONCLUSIONS
  It is unclear whether degenerative changes induced by immobilization in muscle and, specifically, the MTJ are temporary and reversible or permanent.
  
  
  CONCLUSIONS
  This preliminary study suggested a classification of ultrastructural MTJ changes into grade 0, reflecting a quite normal MTJ; grade 1, an intermediate process that might lead to irreversible atrophy or to recovery, spontaneously or with drug therapy; and grade 2, irreversible process with complete structural alteration.
authors.affiliation: Cattedra di Ortopedia e Traumatologia, Università Politecnica delle Marche, Azienda Ospedaliero-Universitaria, Ospedali Riuniti di Ancona, Ancona, Italy. l.depalma@univpm.it
authors.forename: L
authors.initials: L
authors.lastname: de Palma
authors.forename: M
authors.initials: M
authors.lastname: Marinelli
authors.forename: M
authors.initials: M
authors.lastname: Pavan
authors.forename: C
authors.initials: C
authors.lastname: Bertoni-Freddari
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology* / Q000648:ultrastructure*; D009133:Muscular Atrophy / Q000473:pathology*; D010019:Osteomyelitis / Q000473:pathology; D013710:Tendons / Q000473:pathology* / Q000648:ultrastructure*