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Bony approach to patellar instability corrects patella alta, trochlear dysplasia
French expert compares the European ‘bony’ and North American soft tissue treatment approaches.
Orthopaedic surgeons may be able to successfully resolve patellar instability by surgically correcting bony abnormalities in patients with any of four specific instability factors, particularly if those factors exceed certain statistical thresholds.
So says David DeJour, MD, of Lyon, France, who is from the “Lyon school” of patellar instability treatment, which advocates using mostly a “bony” approach to treatment. The alternate school of thought, associated with North America, favors a soft tissue approach, usually by reconstructing the medial patellofemoral ligament (MPFL).
“The main difference between the American point of view and our point of view is we take care of the bony abnormalities, which are the patella alta and trochlear dysplasia,” DeJour told Orthopaedics Today International.
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In a combined lecture with Elizabeth A. Arendt, MD, of Minneapolis, U.S.A., who is a proponent of the soft tissue approach, DeJour presented his bony approach at the 2007 International Society of Arthroscopy, Knee Surgery and Orthopaedic Sport Medicine Congress.
Instability factors
Investigators from Lyon who conducted a landmark 1987 study identified four instability factors critical for diagnosing and treating patellar instability: trochlear dysplasia, patella alta, patellar tilt and tibial tubercle (TT) to trochlear groove (TG) distance, or TT-TG >20 mm on a computed tomography (CT) scan.
According to DeJour, that 337-patient study also identified statistical thresholds associated with some of those instability factors. “When we find some abnormalities, we will correct them, and we will correct them one by one,” he said.
DeJour said his presentation’s main take-home message emphasized the importance of initially making the right diagnosis before considering any kind of patellar instability treatment. But doing so is not always easy since patients with these knee disorders typically present with a mix of pain and instability, he noted.
Bony treatments
Before operating, surgeons should clearly distinguish between pain and instability.
“[For patients] with pain alone, we never do surgery. However, for instability, we sometimes do some surgery,” DeJour said. “If you don’t really understand why a patient has pain and you do surgery, he or she could be made worse, and after that it’s absolutely finished because the patient will have pain all the time.”
DeJour performs a trochleoplasty to treat patellofemoral instability when trochlear dysplasia is the main factor. He told Orthopaedics Today International it is so common, everyone should consider it first as a possible cause of instability.
Dysplasia and dislocation
In the 1987 study, “Henri DeJour found trochlear dysplasia in 96% of the population with true patellar dislocation, but he found trochlear dysplasia only in 3% of the normal population. So, the trochlear dysplasia is the highest instability factor,” he said. “Probably the second biggest factor is patella alta.”
For patella alta, DeJour performs distalization of the distal TT.
“We do a TT osteotomy and pull it down and usually combine that with an MPFL-plasty to repair the medial side and the medial retinaculum. It’s a combination procedure,” he said.
MPFL-plasty certainly helps correct patellar tilt, but should rarely be done as an isolated procedure, he said.
“We are nearly sure that when your patella dislocates, it’s not due to the MPFL rupture. The MPFL rupture is a dislocation consequence, but is not the initial instability factor,” DeJour said.
Imaging aids
Information from a “true profile” radiograph — a true lateral view of the knee — and a CT scan helps determine if patients have multiple instability risk factors and the extent of their bony abnormalities. Such radiographs help DeJour better visualize the trochlear anatomy.
“This true profile X-ray for us is absolutely fundamental because you can see … the trochlear dysplasia, so we can grade it … and measure the patella alta,” he said.
DeJour may request CT scans just before surgery using the Lyon protocol, which involves measuring both patellar tilt and TT-TG distance.
“The diagnosis and surgical indication is based on the clinical exam, clinical history [and] X-rays,” he said. However, CT scans are invaluable for patients suspected of needing surgery because they help surgeons decide exactly which procedure to perform.
Sharing opinions
DeJour and other European knee surgeons believe they have learned much from collaborating with Americans via the International Patellofemoral Study Group (IPSG) and, as a result, possess a greater appreciation for when MPFL reconstruction is indicated.
Consequently, Americans have started to understand and accept the bony abnormalities, like trochlear dysplasia, DeJour said. “It has become well established as a very high instability factor.”
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Images: DeJour D |
For more information:References:
- David DeJour, MD, can be reached at Corolyon Sauvegarde, 8 Avenue Ben Gourion, 69009 Lyon, France; +33-472-20-28-20; e-mail: corolyon@wanadoo.fr. He has no financial conflicts to disclose.
- DeJour D. Lecture: How I treat patellar instability in a patient with patella alta, femoral dysplasia and knee pain. Presented at the 2007 International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine Congress. May 27-31, 2007. Florence, Italy.
- DeJour H, Walch G, Neyret P, Adeleine P. Dysplasia of the femoral trochlea. Rev Chir Orthop Reparatrice Appar Mot. 1990; 76(1):45-54.