Effect of cleft palate repair on the susceptibility to contraction-induced injury of single permeabilized muscle fibers from congenitally-clefted goat palates.

OBJECTIVE: Despite cleft palate repair, velopharyngeal competence is not achieved in approximately 15% of patients, often necessitating secondary surgical correction. Velopharyngeal competence postrepair may require the conversion of levator veli palatini muscle fibers from injury-susceptible type 2 fibers to injury-resistant type 1 fibers. As an initial step to determining the validity of this theory, we tested the hypothesis that, in most cases, repair induces the transformation to type 1 fibers, thus diminishing susceptibility to injury.
INTERVENTIONS: Single permeabilized levator veli palatini muscle fibers were obtained from normal palates and nonrepaired congenitally-clefted palates of young (2 months old) and adult (14 to 15 months old) goats and from repaired palates of adult goats (8 months old). Repair was done at 2 months of age using a modified von Langenbeck technique. MAIN OUTCOME MEASURES: Fiber type was determined by contractile properties and susceptibility to injury was assessed by force deficit, the decrease in maximum force following a lengthening contraction protocol expressed as a percentage of initial force.
RESULTS: For normal palates and cleft palates of young goats, the majority of the fibers were type 2 with force deficits of approximately 40%. Following repair, 80% of the fibers were type 1 with force deficits of 20% +/- 2%; these deficits were 45% of those for nonrepaired cleft palates of adult goats (p < .0001).
CONCLUSION: The decrease in the percentage of type 2 fibers and susceptibility to injury may be important for the development of a functional levator veli palatini muscle postrepair.