Adjustable sutures: experimental assessment of final muscle position.

The likelihood of forward "creep" of muscles recessed with the use of adjustable loops of suture in the correction of strabismus was investigated. Twelve orthotropic dogs underwent both regular and loop recessions of the lateral and medial rectus muscles; the data for two of the dogs were excluded because of loss of muscles. Three months later it was found that in the majority of cases the recessed muscles had minimally advanced from the position of surgical placement. Although the type of recession made little difference to the results, the mean forward creep was much greater for the medial rectus muscles (1.55 +/- 0.68 mm [p less than 0.01] and 2.00 +/- 2.44 mm [p = 0.09] for those undergoing regular and loop recessions respectively) than for the lateral rectus muscles (0.35 +/- 0.58 mm and 0.60 +/- 0.62 mm respectively). During the operations the amount of contraction of the medial rectus muscle had been noted to vary. It is likely that in some instances the tension on the suture loops was insufficient to hold them taut, and the muscles therefore adhered to the sclera at variable sites. Hence, adequate intrinsic muscle tone may be important for predictable clinical results of loop recession.