Chronic Subluxation of Patella
With the use of axial patellofemoral radiographs (Merchant views),20 the clinician can determine if the “patella is well centered in the trochlear sulcus and stable” (an important part of the definition of LPCS). If the patient has no symptoms of recurrent instability or patellar dislocation, and these radiographs show a laterally subluxed patella (one not well centered in the trochlea), the diagnosis is most likely CSP, a moderate form of patellofemoral dysplasia (section II of the Table). In addition to the 4 abnormalities used in the diagnosis of LPCS (mentioned earlier), trochlear dysplasia also comes into play in the diagnosis of CSP. Just as the other abnormalities can vary from mild to severe, trochlear dysplasia can vary from mild (slightly shallow sulcus angle) to severe (flat or even convex sulcus angle). As the sulcus becomes shallower, the patella slides more laterally, increasing the likelihood of patellar dislocation.
As the patient with CSP gives no history of episodic patellar instability, treatment for CSP is almost identical to that for LPCS, with the primary focus on isometric quadriceps strengthening (DeHaven isometric exercises)27 and hip abductor muscle strengthening. In the presence of CSP radiographically, it is important to use McConnell taping and/or patellar bracing during muscular strengthening. A patient who achieves 20-lb isometric quadriceps strength, demonstrates a normal step-down test, and is assumed to be asymptomatic can be allowed to return to sports activities with use of a patellar brace. The patient should be counseled that there is an increased risk for patellar dislocation because of this chronic subluxation and the shallower sulcus.
As in LPCS, CSP symptoms that persist after dynamic strength is regained may require surgical intervention. The severity of identified abnormal factors (tight LR, increased Q angle, trochlear dysplasia) guides the surgeon in selecting appropriate corrective technique(s).
Recurrent Dislocation of Patella
Admittedly, given the number and subtlety of abnormal factors, the diagnosis of LPCS as a cause of patellofemoral pain can be challenging. However, RDP is at the opposite end of the spectrum. A history of prior patellar dislocation(s) almost always makes the diagnosis of RDP easier. The patient occasionally complains of a recurrent symptom, the knee “going out” or “giving way,” indicating that the diagnosis might be RDP. By carefully asking what the patient was doing and what happened when the knee “went out”, the clinician may be able to determine if the injury stemmed from sudden patellar pain causing reflex inhibition of the quadriceps or was a true dislocation. Both may be described as “going out” or “giving way”.
Assessment for the same 7 abnormalities helps establish the diagnosis, a logical treatment plan, and a guide for indicated surgery. The diagnostic focus is MPFL laxity and trochlear dysplasia. Prior lateral dislocation of the patella almost always requires rupture of the normal MPFL. The infrequent exception is a patient with hyper-elasticity of the skin and multiple joints (Ehlers-Danlos syndrome). Trochlear dysplasia is a significant risk factor for patellar dislocation. If the trochlea is normal and there is no MPFL laxity, the diagnosis of RDP should be questioned.
If surgery is indicated, the surgeon uses a list of the patient’s abnormalities and their severity as a guide in selecting reconstructive techniques. The more abnormalities found and the greater the severity of each, the more techniques are needed to achieve success. Preoperative exercises help speed postoperative recovery by addressing quadriceps and hip abductor weakness. In addition, an active exercise program gives the surgeon insight into the patient’s desire for and commitment to recovery. Other physical abnormalities to be considered in preoperative planning include MPFL laxity, LR tightness, increased Q angle, patella alta, and trochlear dysplasia.
Surgical tips: 1. When releasing the LR, never cut the vastus lateralis tendon, as this has a high likelihood of causing iatrogenic medial patellar subluxation.29 2. When medializing the TT, consider compensating for a shallow trochlea by “over-correcting” the Q angle to 5° to 10° measured with a surgical goniometer intraoperatively.
Summary
Basing clinical classification of disorders on etiology is a simple and effective way to diagnose common patellofemoral conditions. Identifying and rating the severity of patellofemoral dysplasia, using 7 commonly found physical abnormalities, guide the physician to a proper diagnosis and down logical treatment pathways. These principles should be incorporated into the routine evaluation of patellofemoral disorders to optimize diagnosis, formulate a treatment plan, and improve patient outcomes. After all, this is what our patients are asking us to do: Try to find what’s wrong, and then try to fix it!
Am J Orthop. 2017;46(2):68-75. Copyright Frontline Medical Communications Inc. 2017. All rights reserved.