Take-Home Points
- Patellofemoral disorders should be classified and diagnosed according to specific diagnostic categories (eg, lateral patellar compression syndrome) based on etiology rather than nondescriptive terminology (eg, internal derangement, patellofemoral pain syndrome).
- Patellofemoral dysplasia defines a spectrum of abnormalities ranging from the mild lateral patellar compression syndrome to the severe recurrent patellar dislocation.
- There is an inverse relationship between patient activity level and underlying patellofemoral dysplasia. This relationship determines threshold levels for each patient becoming symptomatic.
- Patients should be examined for 7 physical abnormalities, and if present, in what severity. These 7 are: vastus medialis obliquus deficiency, medial patellofemoral ligament laxity, lateral retinaculum tightness, increased quadriceps angle, hip abductor weakness, patella alta, and trochlear dysplasia.
- Advanced imaging is rarely, if ever, needed to make a diagnosis or to formulate an initial treatment plan for these common patellofemoral disorders.
To diagnose any disease or disorder implies an understanding of the condition’s cause(s), which should then lead to a logical treatment plan. For all too long, however, the diagnosis and treatment of patellofemoral disorders have been hampered by diagnoses that lack specific definitions based on etiology. A few of these are: internal derangement, chondromalacia patellae, patellar maltracking, and patellofemoral pain syndrome.
To simplify the diagnosis of patellofemoral disorders, we use a clinical classification based on etiology. This system’s defined diagnostic categories are useful in identifying probable cause(s), which can be appropriately evaluated and treated (Table).1 In simple terms, the philosophy of this approach is to try to find out what’s wrong, and try to fix it!
This clinical classification provides a framework for common patellofemoral conditions that are more easily diagnosed, yet is intentionally incomplete omitting rare conditions (eg, tumors, metabolic bone disease, neurologic conditions).
Patellofemoral Dysplasia
Patellofemoral dysplasia (or extensor mechanism malfunction) is a cluster of physical abnormalities relating to the patellofemoral joint that vary from mild to severe and affect the normal function of that joint. As such, patellofemoral dysplasia itself should be considered on a continuum of mild to severe. To simplify the diagnosis, the clinician should systematically identify these factors and their severity. Armed with this information, the clinician can make the diagnosis and formulate a logical treatment plan for each individual patient.
This article focuses on 7 physical abnormalities that are most likely developmental and that can be identified through physical and radiologic examination. When and how each patient with patellofemoral dysplasia becomes symptomatic are determined by 2 key factors: patellofemoral dysplasia severity and activity level (sedentary to strenuous), in an inverse relationship (Figure 1).2
Seven Key Patellofemoral Physical Abnormalities
Of the 7 commonly identified physical abnormalities that affect the normal functioning of the patellofemoral joint, 5 are discovered by physical examination and 2 by radiography; CT and MRI are seldom needed in the initial evaluation. The most accurate and objective method should be used to assess the presence and severity of each abnormality.
The 7 abnormalities are vastus medialis obliquus (VMO) deficiency, medial patellofemoral ligament (MPFL) laxity, lateral retinaculum (LR) tightness, increased quadriceps (Q) angle, hip abductor weakness, patella alta, and trochlear dysplasia. We list these not in order of importance but in the order in which they are usually encountered during initial evaluation. We advocate for examining both knees including axial patellofemoral radiographs because patellofemoral disorders are frequently bilateral. It is helpful to use an abnormality checklist so none are forgotten. Also useful is a simple shorthand for findings: 0 = normal (no abnormality), 1 = mild abnormality, 2 = moderate abnormality, 3 = severe abnormality, with the right knee always recorded first (R/L). For example, severe left MPFL laxity is recorded as 0/3. Numerical values (eg, Q angles) can be directly recorded in this manner: 14°/23°.