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Knee News

New Y-Graft Technique for Dislocating Kneecap

The patella or kneecap is a marvelous and complex structure. Held over the knee joint by soft tissue structures, it moves or "tracks" up and down with knee motion. Anatomists are still exploring and learning how the patellar tracking mechanism really works. Understanding normal patellar anatomy and kinematics (movement) will help surgeons repair and restore this part of the knee when injury leads to chronic, painful patellar dislocations.

In fact, it is estimated that a second recurrent (repeated) patellar dislocations occur in almost half of all cases where a first or primary dislocation has occurred. There are many possible reasons for this scenario.

Sometimes the torn medial patellofemoral ligament (MPFL) fails to heal. Or the MPFL heals in the wrong position (stretched or torn fibers are now too long). This soft tissue structure provides passive restraint (holds the patella in place) as the kneecap moves during the first 30 degrees of knee flexion.

Other factors may be at work as well such as the resting position of the patella over the knee joint (pulled up too high or pushed down too low can cause problems). Weakness of the vastus medialis oblique (portion of the quadriceps muscle along the front inside of the thigh/knee) may be an important feature of patellar instability.

Studies have now shown that this soft tissue structure blends with a portion of the medial patellofemoral ligament (MPFL). The two structures work together to keep the patella in the center of the knee as it starts tracking during knee flexion. To help restore the knee to as close to normal anatomy after recurrent dislocations, a new surgical technique has been developed.

In this study, surgeons in China report on the results of this new approach they call the Y-graft technique. They compare the outcomes of the Y-graft with the more commonly used C-graft technique. They describe each method and provide drawings to assist surgeons in understanding the differences between these two surgical approaches.

The basic difference is in the shape of the graft tissue and the fixation sequence. Fixation sequence refers to how and when the two ends of each graft are attached. For example, the C-graft procedure attaches both ends to the femur (lower leg bone) at the same time. Tension on the two ends of the graft is set at the same time.

The Y-graft technique allows the surgeon to apply tension to the separate ends one at a time with the knee in zero degrees of flexion (i.e., straight) and then at 30 degrees of flexion. This separate graft tensioning helps mimic the more normal anatomy (alignment) and kinematics (movement). A special table summarizing the differences between these two fixation methods is also provided to help surgeons understand how the two techniques compare.

Results comparing two patient groups with chronic, painful patellar dislocations (one group had the Y-graft, the second group had the C-graft) were measured using clinical tests and CT scans. Knee function, patellar stability, and patellar angles were the main outcome measures. With regular follow-up for two years, they found that the Y-graft did provide better knee function compared with the C-graft. And the Y-graft (double-bundle technique) restored normal patellar tracking much better than the C-graft (single-bundle technique).

But the clinical results were not significantly better in the Y-graft group as might be expected. For example, patellar angles quickly returned to normal for both groups. Knee range-of-motion was also fully restored for all patients in both groups. No one in either group had any more patellar dislocations during the first two years of follow-up.

Right now, there is no agreement or consensus on the best way to reconstruct a torn medial patellofemoral ligament (MPFL) in order to restore patellar stability. This study showed that the new Y-graft technique has the strength needed to hold the kneecap in place during movement requiring patellar tracking up and down over the knee. The Y-graft outperformed the more commonly used C-graft technique. Further follow-up is needed now because recurrent patellar dislocations tend to develop more as time goes by.


Huijun Kang, MD, et al. Comparison of 2 Different Techniques for Anatomic Reconstruction of the Medial Patellofemoral Ligament. In The American Journal of Sports Medicine. May 2013. Vol. 41. No. 5. Pp. 1013-1021.

06/20/2013

*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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