Will buttons and a tightrope replace screws?

Syndesmotic injuries to the ankle occur in approximately 10 percent of all patients with ankle fractures, but they can also occur with soft-tissue injuries in the absence of fracture. They usually result from severe external rotation of the ankle, and treatment remains controversial.

Historically, treatment has involved tibiofibular transfixation using a syndesmotic screw. Surgery to reduce and fix the diastasis is recommended to prevent lateral talar shift. But recently, tightrope fixation—a new implant technology involving a fiberwire suture and two buttons—has been introduced. Gregory C. Berlet, MD, co-director of the AAOS “Current techniques in reconstructive foot and ankle surgery” course, reviewed the different methods during the 2-day program held Feb. 8-9, 2008, at the Orthopaedic Learning Center in Rosemont, Ill.

Screw fixation
Among the controversies in screw fixation are the size of the screw, the number of cortices engaged, and the placement (distance from the joint) of the screw. Complications associated with this conventional treatment include screw breakage and hardware pain, the need for a second surgery to remove the internal hardware, and the risk of subsequent diastasis if the screws are compromised before the ligament heals.

Screws constructed of bioabsorbable materials such as polylactic acid may reduce the need for a second surgical procedure. At least one study comparing fibular plate fixation with either bioabsorbable or metal screws showed similar results in both groups of patients, no loss of reduction in either group, and no signs of osteolysis or sterile effusion in the bioabsorbable group.

According to Dr. Berlet, screws should be inserted parallel to the level of the tibiotalar joint, 2 cm proximal to the joint, and in a 25-degree oblique anterior direction. Reduction of the syndesmosis should be maintained with forceps while the screw is being inserted; the foot should be held in mild dorsiflexion. Performing the insertion under fluoroscopy enables the surgeon to perform an external rotation test and ensure that the joint doesn’t open.

Weight bearing, which would normally begin at 6 weeks postoperative, can be delayed if screw breakage is a concern. Serial radiographs can be used to ensure that the position is held and the syndesmosis does not widen. Screws may be removed at 16 weeks postoperative.

Tightrope fixation
Tightrope fixation was developed as an alternative to avoid common screw complications. One or two fixation devices can be used, depending on the degree of stability required. The device consists of a fiberwire suture and two buttons—one oblong to enable it to pass through the bone and the other round to serve as a restraint on the lateral side.

“The buttons are very similar to the endobutton used in the knee,” explains Dr. Berlet. “It is an adaptation that has proven to be perhaps an even better application than the knee.”

Although no prospective comparison between tightrope and screw fixation has been performed, tightrope fixation has the following potential advantages: allowing physiologic motion at the syndesmosis; lowering the risk of hardware pain; eliminating screw breakage (no screw involved); and permitting an earlier return to motion and activity.

A large reduction clamp can be used to secure reduction of the syndesmosis during surgery. Plating is required for fractures in the lower third of the fibula to ensure appropriate length and rotation, but fractures at a higher level will not need to be plated. The tightrope fixation device can be used if plating is required, explains Dr. Berlet, because the round button on the fibular side of the device fits into the plate screw hole, typically through the third or fourth hole.

After drilling through all four cortices in the transmalleolar axis, the surgeon pulls the needle, with its tightrope and oblong button, from the lateral to the medial side. Once the oblong button emerges, the surgeon flips it parallel to the bone surface and exerts lateral tension to hold it flush. On the lateral side, the surgeon draws the round button tight against the fibula and tightens the sutures.

Dr. Berlet recommends leaving at least 1 cm of extra suture so that the knot can be turned down to minimize irritation.

A patient with an isolated syndesmosis who is treated with tightrope fixation may resume 50 percent weight bearing after 2 weeks and move to full weight bearing at 6 weeks, with the beginning of physical therapy.

A published study comparing screw and tightrope fixation found that patients who received tightrope fixation had higher functional scores both at 3 months and at 12 months with no loss of reduction on computed tomography examination.

Dr. Berlet emphasized the tightrope technique as one option for syndesmotic fixation. “The technique is easily adapted from previous experience with syndesmotic screws,” he said. “In our experience, the tightrope has been beneficial in allowing us to be proactive in the rehabilitation of our patients.”

Disclosure information for Dr. Berlet can be found online at www.aaos.org/disclosure

Mary Ann Porucznik is managing editor of AAOS Now. She can be reached at porucznik@aaos.org