Pediatrics: pulley system controls paths of human muscles

March 1, 2009

Surgeons should review the new discoveries in orbital anatomy and consider expanding their surgical armamentarium to include surgery of the pulley system says one ophthalmologist.

Key Points

Atlanta-The concept that connective tissue pulleys control the paths of all the extraocular muscles was presented by Joseph Demer, MD, PhD, in the keynote address of pediatric subspecialty day at the American Academy of Ophthalmology annual meeting. He asked surgeons to consider surgery of the pulley system as a surgical option. His concept was developed from nearly two decades of support from the National Eye Institute, Bethesda, MD.

Two fundamental, new principles were emphasized by Dr. Demer, the Leonard Apt Professor of Ophthalmology, David Geffen Medical School, University of California, Los Angeles. They are:

"This is crucial to ocular motility because shifts in the location of the pulleys change the location of the functional origins of the muscles and thus change their pulling directions and the relative proportions of the horizontal, vertical, and torsional actions of the extraocular muscles," Dr. Demer said. "These systematic changes are necessary for normal neuroregulation of binocular alignment."

"Surgeons can manipulate the pulleys directly, and thus we have more ability to influence ocular motility than we had previously believed," Dr. Demer said.

Strabismus can result from several pathologies of the rectus muscle pulleys, he said.

For instance, incomitant strabismus can result from heterotopy of the rectus pulleys, from instability of the rectus pulleys, and from hindrance to normal anteroposterior pulley shifts. Degeneration of ligaments around the pulleys is a common cause of horizontal and vertical strabismus in older adults, Dr. Demer added.

Pulley surgeries

Imaging the orbit is vital to establishing correct diagnoses, Dr. Demer said. Imaging the coronal plane is usually the best approach, he added.

Efficacious pulley surgeries are emerging, according to Dr. Demer. These surgeries include pulley posterior fixation (the Clark operation), which he claimed is an easier and safer "fadenoperation;" repair of the abnormal pulley position; and augmented rectus transposition.

In pulley posterior fixation, Dr. Demer said, key points to remember are that adding tension to the pulley suspension can create a desirable mechanical restriction in the field of action of a muscle, the pulley tissues should be dissected conservatively, and permanent sutures can be placed from the pulley to the adjacent muscle without suturing to the sclera.

The conventional surgical approaches to correct strabismus expose the anterior portions of the pulleys. Dr. Demer suggested that conservative handling of the pulleys is important.

"Surgeons usually can cut less connective tissue at every surgical step," he said. "Surgeons should think about and document what they do to the connective tissues."

Dr. Demer advised using nonabsorbable sutures during repair of an abnormal inferiorly displaced lateral rectus pulley. The following should be performed, he said:

For paralytic strabismus, Dr. Demer said, rectus transposition augmented with posterior scleral sutures is more effective than full tendon-width rectus transposition alone. The procedure results in large shifts in pulley position toward the direction of the paralyzed muscle, he said.