Anatomic medial knee reconstruction recovers knee stability, load distribution

Investigation finds that two tunnels may be needed to reconstruct both of the medial knee structures.

Using an anatomic medial knee reconstruction technique may restore the native ligamentous load distribution and knee stability in patients with superficial medial collateral and posterior oblique ligament injuries, while helping surgeons avoid the complication of overconstraint.

“An anatomic medial knee reconstruction technique can restore native stability to the knee that has a severe acute chronic medial knee injury,” Benjamin R. Coobs, MD, said during his presentation at the American Orthopaedic Society for Sports Medicine 2009 Annual Meeting. “This reconstruction technique does provide a viable option for patients that may require surgery.”

The research was conducted by investigators at the University of Minneapolis and the University of Oslo and received the society’s Excellence in Research Award.

Three knee states

The investigators tested 10 non-paired cadaveric knees in the following states:

• with the medial knee structures intact;
• with the superficial medial collateral (SMCL) and posterior oblique ligament (POL) sectioned; and
• with the medial knee anatomically reconstructed.

They tested the knees at 0°, 20°, 30°, 60° and 90° of knee flexion with a 10 Nm valgus load, 5 Nm external and internal rotational torques and 88 Nm anterior and posterior drawer loads. The investigators used a six-degree of freedom electromagnetic motion tracking system to measure the position of the tibia in relation to the femur and used modified buckle transducers to measure the load on the intact and reconstructed ligaments.

Shown here (left to right): Ray Larson; Betty Larson (Coob’s grandparents); Steinar Johansen, MD; Lindsay Coobs; Benjamin Coobs MD; Robert LaPrade MD, PhD; Chad Griffith MD and Lars Engebretsen MD, PhD.  Coobs is displaying the AOSSM’s Excellence in Research Award that the investigators won for their study. Images: Coobs BR

For the anatomic medial knee reconstruction, surgeons harvested the semitendinosus and split the tendon into two grafts, a 16-cm length for the SMCL reconstruction and a 12 cm length for the POL reconstruction. They drilled four tunnels at the anatomic attachment sites of the SMCL and POL and sutured the SMCL graft just below the joint line and into the soft tissues at its proximal tibial attachment.

“The SMCL was tensioned in neutral rotation at 30· of knee flexion,” Coobs said. “The POL was tensioned in neutral rotation at 0° of knee flexion.”

Recovered stability

The investigators found significant increases in valgus angulation, external rotation and internal rotation at all of the tested degrees of knee flexion after sectioning the SMCL and POL.

“This instability was recovered to near-normal stability following our anatomic reconstruction technique,” Coobs said.

This intraoperative image shows the SMCL and POL grafts after femoral fixation and before surgeons attached the grafts to the tibia.

After passing below the capsule, the SMCL and POL grafts are shown prior to final fixation of the SMCL into the tibia at 6 cm distal to the joint line.

An alternative view of the grafts before final fixation of the SMCL. The investigators found that this technique restored native knee stability.

The investigators also found no significant difference between the amount of tensile loading observed between the intact native medial knee structures and reconstructed ligaments.

“This confirms that no overconstraint occurred with our reconstruction,” Coobs said.

In addition, he noted that using one femoral tunnel to reconstruct both the SMCL and POL during pilot testing failed in all cases regardless of the applied fixation method.

“This suggests to us that two femoral tunnels are probably required,” Coobs said. “The clinical implication is that two tunnels may be necessary when reconstructing both the SMCL and POL in order for the reconstruction to tolerate early range of motion.”

He also noted that both research centers are performing prospective outcome studies evaluating the reconstruction technique in vivo.

For more information:

Benjamin R. Coobs, MD, can be reached at the University of Minneapolis, Orthopaedic Surgery Office, 2450 Riverside Ave. R-200, Minneapolis, MN 55454; 612-273-9400; e-mail: coob0001@umn.edu. He has no direct financial interest in any products or companies mentioned in this article.

Reference:

Coobs BR, Wijdicks CA, Armitage BM, et al. An in vitro analysis of an anatomic medial knee reconstruction. Presented at the American Orthopaedic Society for Sports Medicine 2009 Annual Meeting. June 9-12, 2009. Keystone, Colo.