chapter 3: History and Physical Examination
Onset of the Problem
The onset of patellofemoral symptoms provides important clues to the diagnosis. Acute high‑energy injuries disrupt normal soft‑tissue restraints, musculotendinous units or cause bony injury. Acute injuries generally fall into two categories: those involving indirect trauma and those involving blunt trauma. High‑energy indirect forces can cause acute patellar dislocation/subluxation in athletes during valgus/external rotation injuries. A typical example of high‑energy blunt trauma is an automobile accident in which the anterior knee strikes the dashboard. The pathoanatomy of each of these conditions is different. By understanding the differences, the examiner can focus his/her examination appropriately.
The high incidence of osteochondral injury in cases of significant patellar subluxation or dislocation should make the examiner suspicious of loose bodies or articular incongruity on physical and radiographic examinations. Compressive and shearing forces typically cause osteochondral injuries on the distal medial patella or the lateral femoral condyle. Acute lateral instability strains or tears the medial patellofemoral ligaments and medial retinaculum. Often, this tear occurs at the femoral insertion of the medial patellofemoral ligaments, producing tenderness near the medial epicondyle that can lead to misdiagnosis as medial collateral ligament (MCL) sprain if the clinician does not carefully differentiate these structures on examination (5).
Blunt traumatic injuries often result in chondral injury and bone contusion when the force applied is less than that necessary to produce macroscopic fracture. The knee is usually flexed during such injuries and therefore the lesions are usually on the proximal patella. Because most knees of the general population do not have pre‑existing malalignment, most knees that sustain blunt trauma are not malaligned at the time of injury. However, if the injury occurred months or years ago and pain continues, loss of normal flexibility and strength must be considered in designing a treatment plan. In recent or old blunt anterior knee trauma, one must be aware of potential posterior cruciate ligament injury. Chronic posterior cruciate ligament (PCL) deficiency can cause chronic anterior knee pain as a result of relative "posteriorization" of the tibial tubercle that increases patellofemoral joint reaction force.
just as pathologic fractures occur through weakened and susceptible bone, relatively low‑energy "injuries" that cause subluxation or dislocation should suggest the possibility of underlying static or dynamic malalignment. Complaints of a truly insidious nature should raise suspicion of underlying strength/flexibility deficits and/or potential bony malalignment. Patients with insidious onset of symptoms or low‑energy injuries should be considered especially likely to have underlying patellar malalignment and the examination should focus on bony and soft‑tissue malalignment factors.
Inside Chapter 3: