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CURRENT CONCEPTS
Treating Patellofemoral Cartilage Lesions
Aaron J. Krych, MD
Associate Professor, Mayo Clinic Rochester, MN, USA
Additional Authors:
Bruce A. Levy, MD
Professor, Mayo Clinic, Rochester, MN, USA
Norimasa Nakamura, MD, PhD, FRCS
Professor, Institute for Medical Science in Sports, Osaka, JAPAN
Patellofemoral articular cartilage lesions are common in the young, active patient, and can be a challenging problem. Fortunately, recent advances have helped our understanding and ability to treat these patellofemoral lesions by addressing concomitant background factors associated with cartilage lesions. As well, new cartilage restoration techniques are now available with encouraging short term results.
In our opinion, the most fundamental aspect of approaching the patient with patellofemoral cartilage lesions is in recognition and understanding of the pathology leading to or associated with the defect. Is this simply an acute lateral patellar dislocation causing a medial patellar facet lesion, or is this a chronic lesion from trochlear dysplasia and abnormal contact pressures? As we have learned, patellofemoral instability may represent a complex spectrum of pathology and include genu valgus, increased femoral anteversion, increased tibial tubercle – trochlear groove (TT-TG) distance, patella alta, trochlear dysplasia, and medial patellofemoral ligament (MPFL) tear / insufficiency. The most commonly associated factors encountered with cartilage lesions include MPFL insufficiency addressed with MPFL reconstruction, trochlear dysplasia with trochleoplasty, distal malalignment with TTO, and tight lateral retinaculum with lateral retinacular lengthening. It’s therefore essential to recognize that any successful cartilage restoration procedure requires concomitant pathology correction.
MFPL insufficiency can be suspected on clinical history from a history of lateral subluxation or dislocation or a sensation of instability and confirmed on examination with a positive lateral patellar apprehension test. The MRI is very helpful in determining the location of tear (femoral, patellar, or both) in the acute setting, and evaluating the quality of the remaining ligament in the chronic setting. However, as with the cruciate and collateral ligaments in the knee, we feel the exam is the most important for determining the function of the ligament. There are many techniques to reconstruct the MPFL as anatomically as possible.
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In the setting of cartilage restoration surgery, it is vital to ensure the graft is not overtensioned to create increased medial patellofemoral contact pressure leading to pain and possible cartilage wear.
Trochlear dysplasia is best characterized by the Dejour classification. We find it helpful to evaluate both radiographs and the MRI for trochlear morphology. The lateral radiograph is helpful to look for a cross-over sign on the anterior cortex, but the Merchant view can be helpful as well. The MRI includes not only the bone structure on the axial images, but also includes the articular cartilage. Typically in dysplasia there is a convexity of the trochlea that causes both abnormal tracking of the patella and also increased contact pressure with a convex on convex articulation, rather than the normal convex on concave articulation to evenly disperse contact forces over the patellofemoral joint. There are many emerging techniques for trochleoplasty. We find the grooveplasty described by Lars Peterson to be an efficient and straightforward method of eliminating the convex trochlea and creating a good proximal entry point for guiding the alignment of the patellar with knee flexion.
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