Surgery for Patellar Instability in AthletesPatients with chronically dislocating or otherwise unstable kneecaps have a condition called patellar instability. This condition poses a treatment challenge because of the unique and complex anatomy and biomechanics of the patellofemoral joint (where the kneecap articulates or moves against the leg bones). And this problem is fairly common, especially among the young, athletic population.
That's why the American Academy of Orthopaedic Surgeons (AAOS) has put together this instructional course lecture for orthopedic surgeons. The authors present current recommendations for treatment with intraoperative and arthroscopic color photos of surgical techniques provided. The goal of surgery is to restore the normal anatomy of the patellofemoral joint. But there are many ways to approach this. The authors propose a three-step procedure to treat patellar instability when surgery is called for.
Before any attempt is made to surgically repair or reconstruct the patellofemoral joint, an understanding is needed of the basic mechanics and functional anatomy of this joint and just what it is that causes patellar instability. The patella slides and glides up and down over the front of the leg through a track called the trochlear groove. The quadriceps muscle along the front of the thigh and the medial patellofemoral ligament are two important soft tissue structures that help hold the patella in place, thus providing patellar stability.
Other important anatomical features contributing to patellar stability/instability include the surrounding fascia (connective tissue), shape of the patella, depth of the trochlear groove, and other ligaments (e.g., meniscofemoral ligament, posterior oblique ligament). Most of these soft tissue structures provide restraint, a force known to hold the patella in place where it belongs. Change in any one of these factors can result in rotation or translation of the patella away from the trochlear groove. When that happens the patella can sublux (partial dislocation) or fully dislocate.
Sometimes athletes experience a traumatic patellar dislocation that is reduced (relocated) spontaneously (on its own) and that's the end of the episode. But for those athletes who have an anatomical predisposition to patellar dislocation, the condition can become chronic. If the structure of the patella is flat instead of curved to cup the femur or if the muscles or ligaments are unbalanced in some way, the patella may slip off the groove with or without spontaneous reduction.
The patient with patellar instability may feel like the knee is going to give out from underneath him or her. Sometimes, the leg just collapses out from underneath them without any warning. Painful symptoms may develop over time. More than one patellar dislocation is considered a major patellar instability. It's at this point that most athletes seek professional help.
A sports medicine physician or orthopedic surgeon examines the patient, performing necessary tests to document patellar instability. Knee range-of-motion and quality of patellar motion are observed and measured. The various ligaments can be palpated and/or tested for integrity or deficiency. The strength and quality of muscular contraction are assessed for the quadriceps muscle. The Q-angle, which is the angle of pull of the quadriceps muscle on the patella is measured. An increased Q-angle results in pulling the patella laterally (toward the outside of the joint away from the other knee). With enough pull and not enough restraint, the patella can be pulled so far over that it pops out of the groove and dislocates.
Sometimes imaging studies can be helpful. X-rays have the least value in this area. Unless the patella is fractured or there are bone spurs, X-rays don't really show any problems that would confirm a diagnosis of chronic patellar instability or offer information as to why the problem is occurring. CT scans can show an abnormal tilt of the patella and give some information about the bony prominence (the tibial tubercle) that inserts into the trochlear groove. MRIs can show ligament damage and even bone bruises from a recent patellar dislocation.
Although the first-line of treatment is nonoperative with activity modification, taping, bracing, and exercises, the major focus of this review article was on the operative management of patellar instability. Surgery is indicated when conservative (nonoperative) care fails to improve symptoms and/or the patella continues to dislocate.
There isn't one specific surgical procedure that can be done on everyone with patellar instability. The surgeon takes into consideration the age of the patient, activity level (and specific sports involvement), anatomical factors, and the overall condition of the patellofemoral joint. If there is generalized joint laxity or congenital changes (present at birth) in the shape of the patella, further reconstruction may be necessary before patellar stability is fully restored.
The authors describe the three-step procedure advised for this condition. First, patellar tracking up and down the trochlear groove must be restored. Then everything necessary to keep the patella tracking normally must be done. This step usually involves restoring the soft tissue restraints needed to prevent a lateral pull on the patella. It may be necessary to perform a tendon graft or shave off some of the bone that is preventing normal trochlear tracking. And finally, the Q-angle must be corrected. Exactly how the Q-angle is corrected depends on the underlying pathologic (abnormal) anatomy and altered biomechanics.
The authors offer a detailed description of repair and realignment procedures. They start with the surgeon's decision whether to repair or to reconstruct the joint. Again, this is an individual decision made on a case-by-case basis. Repairing the medial patellofemoral ligament requires the surgeon to find where it has torn away from the patella and reattach it. Different types of incisions and sutures are used depending on the location of the rupture. After making the repair, the surgeon checks knee motion to make sure the patella is tracking properly. Getting just the right amount of tension is important to avoid tightening the structures too much.
Reconstruction procedures are used more often when there is chronic instability, not from a traumatic injury, but from malalignment, laxity, and poor restraint mechanisms. Tendon grafts from the hamstrings are often used when the patient's own ligament is deficient. Soft-tissue grafting techniques are described including where to drill holes for pins and buttons used to hold the graft in place.
Fluoroscopy, a special real-time X-ray allows the surgeon to make sure placement of the graft and hardware is accurate. The authors note that there are many ways to reconstruct the patellofemoral ligament. Both graft choices and fixation methods vary depending on what alignment problems are present and how much tension is needed. Less commonly used procedures described in this article include medial imbrication and vastus medialis obliquus advancement, lateral retinacular release, the Fulkerson procedure (tibial tubercle transfer), and trocheoplasty.
Following any of these surgical procedures, patients wear a protective (hinged) brace for a period of time and enter into a rehab program. The brace limits both the amount of weight that can be put on the knee and the motion. Motion is gradually increased every two weeks for six weeks. Quadriceps strengthening is the main focus of rehab but the physical therapist will also make sure the patient's posture, joint proprioception (joint sense of its own position), and kinesthetic awareness (leg sense of movement) are fully restored as well. Sports specific exercises enable the athlete to return to sports approximately 12 weeks after surgery.
The authors conclude that more studies are needed to compare the results of the various repair and reconstructive procedures that are done for patellar instability. Currently, success rates for the different methods range from 71 to 93 per cent. Long-term results at the 10-, 15-, and 20-year mark are also needed. For now, having review articles like this one give surgeons an idea of what other surgeons are doing, the rationale for selecting one procedure over another, and individual patient factors to consider when making the decision to treat surgically.
Daniel E. Redziniak, MD, et al. Patellar Instability. In The Journal of Bone & Joint Surgery. September 2009. Vol. 91-A. No. 9. Pp. 2264-2275.
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