The “Gastrocnemius–Achilles Tendon–Calcaneus Complex”: Different Responses after Percutaneous versus Vulpius Achilles Tendon Lengthening in New Zealand White Rabbits

BACKGROUND: This study aimed to describe the clinical, radiological, biomechanical, electromyographic, and histoenzymologic modifications in the “Gastrocnemius–Achilles Tendon–Calcaneus complex” caused by percutaneous Achilles tendon lengthening (PATL) versus Vulpius Achilles tendon lengthening (VATL) in New Zealand White (NZW) rabbits. MATERIALS AND METHODS: Eight female NZW rabbits were used at 7 months of age. Two rabbits were euthanized before surgery for anatomical dissection, three underwent PATL (two bilateral and one unilateral), and the three others underwent VATL (two bilateral and one unilateral). Clinical examination, biomechanics, electromyography, standard radiographs and magnetic resonance imaging (MRI), and histology and histoenzymology were assessed after surgery. RESULTS: At the end of the experiment, the subjects showed good clinical status but different functional outcomes of surgery: rabbits submitted to PATL developed permanent limp and lost their capacity to jump compared to rabbits submitted to VATL which remained able to ambulate and jump normally. Standard radiographs and MRI showed that PATL led to significantly greater increase in dorsal or anterior flexion of the tibiotarsal angle (TT angle) compared to VATL, whereas electromyographic and histoenzymologic observations of muscle unit showed little or no variation between the two groups of operated rabbits. CONCLUSIONS: Although PATL leads to greater improvement in dorsal or anterior flexion (TT angle) of the rabbit ankle compared to VATL, it has negative effects on functional outcome as it reduces the contractile capacity of the rabbit muscle unit, ultimately impairing the ability to ambulate and jump.