**3.1 Clinical presentation**

A thorough history should be obtained, focusing on the mechanism of injury, the onset and duration of symptoms, any previous history of patellar symptoms, and prior nonoperative or operative treatment. Patients should be asked whether the previous treatment modalities relieved their symptoms. Patients with patellofemoral instability usually present with a history of peripatellar pain, recurrent swelling, crepitus, giving-way or instability, and weakness in the affected extremity. The knee pain may get worse while going down the stair or up the stairs, and during squatting and kneeling. In few cases, the patient may complain of mechanical catching or locking in the knee, and this indicates presence of a loose body (chondral or osteochondral fragment) in the joint. The patient may report that "my kneecap slides, slips, shifts, pops or jumps out of place" or "my kneecap pops or jumps back into place" with certain positions of the knee. Symptoms may occasionally be preceded by a history of traumatic episode but more commonly, the clinical symptoms are insidious in onset.

#### **3.2 Physical examination**

A meticulous comprehensive physical examination of the affected extremity as well as the opposite extremity should be performed. The patient should be examined in standing, sitting, and supine positions, while barefoot and dressed in shorts [30]. Gait pattern, obesity, posture and body habitus should be documented [30]. Patients with significant knee pain may demonstrate antalgic gait. A quadriceps avoidance gait (typically seen in patients with anterior cruciate deficiency) with reduced knee flexion in stance phase may be observed in some patients with patellofemoral instability. A Trendelenburg gait with a drop in the contralateral pelvis during stance phase indicates gluteus medius weakness. This change in pelvic obliquity tightens the ipsilateral iliotibial band, causing pain over the lateral aspect of the knee [30].

The skin of the involved extremity should be examined for presence of traumatic scars or surgical incision(s), or evidence of vasomotor dysfunction (such as, alterations in sweating, skin color, and temperature) and trophic changes in the skin, hair, or nails. Any muscle asymmetry of the thigh or calf should be recorded using a measuring tape, by taking circumferential measurements at a standard distance proximal and distal to the knee.

#### *Patellofemoral Instability DOI: http://dx.doi.org/10.5772/intechopen.99562*

The patient should be evaluated for any physical signs that may serve as prognosticators of patellar instability (**Table 1**). Generalized ligamentous hyperlaxity should be noted by examining finger metacarpophalangeal joint hyperextension, thumb-to-forearm apposition, knee hyperextension, and elbow hyperextension. Abnormalities in femoral anteversion should be measured by observing maximal prone internal and external hip rotation as well as rotation of the leg at the position of maximal prominence of the greater trochanter [52]. Similarly, transmalleolar axis and thigh-foot angle should be used to confirm excessive tibial torsion.

The range of motion and strength in the hip joint should be assessed as some patients with hip disorders may present with a referred knee pain. Examination of the foot should be performed. Some patients with lateral patellar dislocation may have pronation of the foot and hindfoot valgus. A complete neurovascular examination of the limb should be performed.

#### *3.2.1 Sitting examination*

The patient should next be examined in the sitting position, with the knees flexed at 90 degrees over the edge of the examination table. The position of the tibial tuberosity should be observed in relation to the center of the patella. Patella alta or baja can be easily observed from the side. The Q-angle (the angle between the quadriceps tendon and the patellar tendon) should be measured with the knee in flexion. Measurements of the Q-angle in full extension may be falsely low in patients with patellar subluxation. The angle is recorded by drawing one line from the anterior superior iliac spine to the center of the patella and another line from the center of the patella to the center of the tibial tuberosity. The mean Q-angle is about 10 degrees in men and 15 degrees in women [50].

Patellofemoral tracking is assessed as the patient sits on the edge of the examination table. The patient is asked to take the knee from flexion into full extension. The term *J sign* refers to an abnormal tracking pattern in which the patella sits lateral to the femoral sulcus in full extension; the movement of the patella appears in the shape of an upside-down *J* as the knee goes from flexion into full extension [30]. Conversely, the patella starts laterally with the knee in extension and makes an abrupt shift medially as it enters the femoral trochlea at about 20 to 30 degrees of knee flexion. The exact cause of the *J sign* is not known; however, factors such as VMO deficiency, underlying osseous morphology and soft tissue imbalance are postulated as causative factors for the occurrence of *J sign.*
