Tibial tunnel placement key in single-bundle ACL reconstruction

Customizing the tunnel prevents roof impingement.

Issue: February 2006

Good tibial tunnel placement is crucial to successful anterior cruciate ligament replacement, a leading orthopedic surgeon told colleagues during a recent course. Graft size, coronal angle and notch width are critical in preventing impingement and preserving function, he said.

Stephen M. Howell, MD, showed a single-bundle technique designed to improve rotation, flexion and extension at Orthopedics Today NY 2005 — A comprehensive CME course.

“Proper tunnel placement is key to your ACL success or failure,” Howell said. “If you put one tunnel in the wrong place in the coronal or sagittal plane, it cannot be overcome by the best graft material, the best fixation and best rehab.” Incorrect tibial tunnel placement may cause posterior cruciate ligament (PCL) and roof impingement, Howell said.

PCL impingement

PCL impingement decreases flexion and rotation control, and may cause laxity to some degree, Howell said.

“If you get the tibial tunnel wrong in the coronal and sagittal planes, your femoral tunnels will be wrong as well,” Howell said. “So, the key tunnel is the tibial tunnel.”

PCL impingement occurs during knee flexion, when the femoral tunnel is at the apex of the notch or when the tibial tunnel is drilled vertically, Howell said.

“If you put the tibial tunnel at 80° or 75° or 90°, your femoral tunnel is going to be high at the notch and your graft will wrap on the PCL as you flex the knee,” he said. He showed an arthroscopic image in which a high notch caused the graft to stretch, reducing rotation control. Also, with the knee at 30° flexion in the pivot shift position, the graft was slack because it was wrapped around the PCL, not stretched due to slippage at the fixation sites, he said.

To prevent PCL impingement, Howell advised surgeons to notice that the graft is going to be larger and more round than the intact ACL. He showed a graft of 8 mm or 9 mm. “I rarely go bigger than 9 mm,” he said. “But it has to be squished down if you’re going to put it in the notch without doing a wallplasty. And what does it do? It deforms the PCL and that gives you the impingement.”

To maintain a round graft, Howell suggested doing a wallplasty, removing a small amount of bone from the lateral femoral condyle, typically more from the superior than the inferior half. There, the graft may sit laterally, away from the PCL, preventing PCL impingement, he said.

The surgeon should ensure that the lateral edge of the tibial tunnel goes through the apex of the lateral tibial spine. “That moves a graft laterally and moves a femoral tunnel laterally, away from the PCL,” Howell said. “You don't want to place it medial to the tibial spine because your femoral tunnel moves back towards the PCL and that causes the problem with flexion.”

Customizing the tibial tunnel

Roof impingement, the opposite of PCL impingement, takes place during knee extension, not flexion, when the tibial tunnel is anterior to the intercondylar roof. Complications include extension loss. Some laxity may result from the graft stretching over time, Howell said.

To avoid roof impingement, Howell advised surgeons to place the tibial tunnel about 4 mm or 5 mm posterior to the roof with the knee in full extension and place the graft without doing a roofplasty.

Howell, in his presentation, showed how he “customizes” the tibial tunnel to prevent roof impingement. Customizing helps the surgeon handle patients’ roof angles varying from 23° to 60° and hyperextension ranging from 5° to 15°. The technique also lets the surgeon avoid increasing the graft and doing a roofplasty, which increases graft tension and laxity, he said.

In customizing the tibial tunnel, Howell made an incision for the medial portal directly against the medial edge of the tendon to place a guide into the notch. He advised surgeons to identify the margins of the lateral half of the notch, to remove the remnant of the ACL and be able to see the lateral edge of the PCL and lateral femoral condylar wall.

Since the notch is very narrow at the apex and the graft is 8 mm or 9 mm, he advised making 8 mm or 9 mm of space between the PCL and lateral femoral condyle. He suggested doing a minor wallplasty without removing too much bone inferiorally.

In his presentation, Howell showed how he widened the apex of the notch and avoided doing a roofplasty, noting that he widens the notch enough to bring the 9.5-mm wide tip of the guide back in, creating a good fit. That way, “There’s no impingement on the PCL. We’re not forcing the PCL medial with the tip of the guide, so ... we have our notch wide enough for our graft.”

Howell also showed how he inserts the guide with the knee in full hyperextension and drills with the knee in full extension to account for varied knee extension involving the roof angle. He places an alignment rod into the guide handle to get a 60° to 65° angle in the coronal plane. He orients the rod parallel to the joint line and perpendicular to the tibia, and drills through the guide’s lateral hole, moving the tunnel away from the medial spine and closer to the lateral spine. Aligning the wire over the PCL between the lateral femoral condyle and the PCL may cause PCL impingement, he said.

“Now, after we’ve drilled the tibial tunnel, we can check for roof impingement by bringing the knee in full extension and taking the metal rod the same diameter of your graft,” Howell said. “If it easily goes into the knee, you don’t have any roof impingement. If it’s not going on top of the PCL and it’s lateral to it and your femoral tunnel is now going to be down the sidewall, you don’t have PCL impingement.”

For more information:
Howell S. Why and where to place tunnels and grafts for single-bundle ACL. Presented at Orthopedics Today NY 2005 — A comprehensive CME course. Nov. 19-20, 2005. New York.