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Stress Radiography Used to Measure Results of New Surgical Technique for Knee Injury
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Posted on: 11/30/1999
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The authors of this study have developed a new way to treat injuries of the posterolateral corner (PLC). They are busy testing the results to see if this reconstruction technique might work better than others currently in use. What is the posterolateral corner (PLC) and where is it located in the body?
The PLC is in the knee where two ligaments and one tendon meet. Posterior refers to the back side of the knee joint. Lateral tells us the affected area is to the side. So we are talking about the posterolateral (side of the knee toward the back) area where the lateral collateral ligament, popliteofibular ligament (PFL), and the tendon of the popliteus muscle all meet.
These soft tissue structures at the posterolateral corner help keep the tibia (shin bone) from sliding backwards under the femur (thigh bone). When the posterolateral corner is injured, knee instability can develop. Injuries in this area occur most often as a result of a car accident, during sports play, or from a work injury.
A person with a weak posterolateral corner will experience hyperextension of the knee when walking or going up and down stairs. Hyperextension means the knee goes back past a straight (extended) position because the mechanism that holds it in neutral is torn or damaged in some way. Every time they take a step, the knee pushes back farther than it should. The natural response to this awkward problem is to walk with the knee slightly bent and avoid full extension.
Walking with the knee bent is a functional solution (it works), but it's not a very good long-term solution. Surgery to fix the problem hasn't been very successful. More than one-third of the patients treated for this problem end up with a poor result. What can be done?
Orthopedic surgeons from the University of Connecticut Health Center developed a way to reconstruct the damaged corner. They say they used dual femoral tunnels, a transfibular tunnel, and a free graft. Twenty-four patients were treated with this technique. They all had one or both of the cruciate ligaments (ligaments that criss-cross inside the knee) damaged, too. These were repaired at the same time as the posterolateral reconstruction procedure.
They describe the technique step-by-step but basically, they used donor graft from the hamstrings or one of several other tendons in the lower leg. By making tunnel holes in the bone, they could thread the graft through the bone, hold it in place with screws and restore the natural stability of the knee joint. By creating just the right amount of tension with the screws, they were able to closely mimic the natural, anatomic positioning of the three key features that normally make up the posterolateral corner.
To see how well this new technique worked, they tested the stability of the knee using a special device called the Telos. The patient was placed with the knee bent at a 90-degree angle. A special arm of the Telos pressed a force of 15 kg (2.2 pounds) against the upper part of the shin bone (just below the knee cap). The amount of posterior (backward) movement of the tibia is called posterior displacement.
There's a small amount of posterior tibial movement expected (and necessary) for normal knee function. Too much displacement is called posterior laxity. Laxity is another word for looseness. Using this type of stress radiography (X-ray), they could measure how much laxity was present after surgery. The images taken by the X-ray were placed on a computer, magnified, and then angles calculated to come up with the measurements.
The results showed a good-to-excellent result for all but two patients. Everyone was able to go back to work at their preinjury level. Those who participated in recreational or competitive sports were also able to return to those activities. Range-of-motion and stability were restored to the knees. There were a few complications as a result of the surgery. One patient had nerve palsy and another was unable to regain normal knee motion without additional surgery. Telos measurements indicated normal posterior translation without side-to-side joint laxity.
The authors suggest that the surgical management used in this study may help improve results after injuries to the posterolateral corner of the knee. The unique features of this surgical technique provide a more natural (anatomical) correction. All indications so far are that this technique is equal to other reconstruction methods with good outcomes. More studies are needed to evaluate patient satisfaction (not just surgeon satisfaction) with the results.
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References:
Clifford G. Rios, MD, et al. Posterolateral Corner Reconstruction of the Knee. In The American Journal of Sports Medicine. August 2010. Vol. 38. No. 8. Pp. 1564-1574.
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