History
Obtaining a thorough history of the patient's symptoms is important when establishing a diagnosis of patellar injury or dislocation.
A common symptom of patellar injury and dislocation is acute pain after direct contact or sudden change of direction (ie, a cutting maneuver). With sudden changes in direction, the femur medially rotates over the ground-stabilized tibia. Under these conditions, athletes commonly feel the knee giving way, which is the result of quadriceps inhibition from pain, a physiologic protective mechanism. Rapid swelling, intense knee pain, and difficulty with any knee flexion usually occur. Other dysfunctions with similar presentations and mechanism of injury are meniscal and ligamentous injuries, particularly injuries of the anterior cruciate ligament.
Symptoms may also manifest as a slowly progressive sensation of anterior knee pain with increased physical activity. Intense physical activity increases JRFs across the knee. Such activities include inclined ambulation, squatting, prolonged sitting, and going up and down stairs. [18] Anterior knee pain aggravated by activity is typical of chondral pathology. Knee pain that improves during physical activity but returns after activity suggests tendinitis.
A common symptom in nontraumatic patellofemoral problems is crepitus of the patellofemoral joint.
Physical Examination
The physical examination in cases of suspected patellar injury and dislocation begins with inspection.
In general, patellofemoral pathology does not cause any significant knee effusion. Acute patellar dislocation is an exception because knee joint effusion is common with this condition.
Other observations common in patellofemoral dysfunction include abnormal femoral anteversion, patella alta, tibial torsion, genu recurvatum, genu valgum, genu varum, pes planus, and ligamentous laxity. These factors often contribute to patellar injury and dislocation.
Following inspection, the examiner must palpate the knee and surrounding structures. Evaluate the patella by applying pressure to the superior pole, inferior pole, and medial and lateral aspects of the patella. Feel for changes in the quality of movement. Applying pressure to the superior pole (delivering the patella) allows the examiner to palpate for tenderness along the inferior, medial, and lateral aspects of the patella.
An evaluation of patients with patellofemoral pain must include an assessment of medial and lateral patellar glide. As noted previously, relative weakness of the VMO and tightness of the lateral soft-tissue structures may result in lateral patellar tilt; this tightness may manifest as decreased medial patellar glide.
In patients with an acute dislocation, significant tenderness medially near the medial retinaculum suggests a torn structure, often the MPFL. Individuals with patellofemoral pathology often experience pain with medial palpation. Tenderness noted superolaterally suggests chondral injury after dislocation. In the event of traumatic dislocation, soft-tissue lesions of the knee are commonly associated with intra-articular fractures and chondral injuries. These concomitant injuries contribute to the patient’s acute pain.
The examiner may also palpate the medial and lateral tissues of the distal quadriceps during initiation of terminal knee extension to appreciate a crude timing difference between the vastus lateralis (VL) and VMO. Some authors suggest that a delay in the contraction of the VMO plays a role in patellar maltracking.
Formal examination of vertical patellar positioning requires a radiographic evaluation. However, the examiner may make a gross estimate of the patella position, which may suggest either a superiorly positioned patella, patella alta, or an inferiorly positioned patella (ie, patella baja).
Chondromalacia may be evident by the presence of crepitus, which is a palpable grinding that occurs with knee flexion and extension and occurs secondary to chondral injuries of the patella undersurface and/or the distal femur. In persons with this condition, a patellar grind test and palpation of the medial and lateral patellar facets elicit pain.
Plicae can be palpated in many patients with patellar injury. Plicae are often tender.
Additionally, assess for tightness of the hamstrings (popliteal angle), quadriceps (Ely tests), and iliotibial band (Ober test). Muscular tightness affects patellar motion and function.
The apprehension test can be used to evaluate a patient for possible previous dislocation or subluxation and is performed as follows (see the image below):
Apprehension sign. The knee is placed at 30° flexion, and lateral pressure is applied. Medial instability results in apprehension by the patient.
This test involves applying a laterally directed force to the medial patella with the knee flexed 30°.
In patients with a previous dislocation or subluxation, this is very distressing. Patients often resist this test and become very apprehensive. Many times, the patient grabs the examiner's hand to prevent further pain and relieve apprehension.
With no previous patellar dislocation, the apprehension test is tolerated well.
Assessing lateral patellar tracking with knee motion is an important part of the examination for patellofemoral dysfunction.
A positive J sign indicates lateral patellar tracking. A positive J sign is observed as the patella tracking laterally when the patient brings the knee from flexion to extension (ie, the patella moves notably laterally at terminal knee extension). This can be visualized well if the examiner places a digit on both the medial and lateral aspects of the superior patella.
A healthy patella moves mostly superiorly and slightly laterally at terminal knee extension.
The Q-angle should be assessed in persons with patellar injury or dislocation.
The Q-angle is the intersection between 2 anatomic lines on the anterior thigh. The first line is drawn from the anterior superior iliac spine to the center of the patella. The second line is drawn from the center of the tibial tubercle to the center of the patella.
Foot position needs to be standardized in the evaluation of the Q-angle because tibial torsion and foot pronation/supination change the Q-angle. The Q-angle is also impacted by femoral anteversion.
Supine and standing measurements also yield different values. Therefore, the Q-angle must be measured in a consistent fashion. The knee must be exposed to all physiologic forces to improve accurate measurement.
Measuring a clinically significant Q-angle requires the patella to be centered in the trochlear groove. Some authors recommend measurement of the Q-angle at 30° of knee flexion to move the patella into the proximal portion of the trochlea. Patients with patellofemoral malalignment may have a laterally positioned patella in full knee extension; this position falsely decreases the measured Q-angle.
Authors disagree on the reference range values, with values from 10º to 20° being a commonly accepted range.
Traditional teaching holds that females have a larger Q-angle than males, secondary to a wider pelvic structure. A study by Grelsamer et al found the mean difference in Q-angles between men and women to be only 2.3°. [19] The authors found that, on average, taller people had smaller Q-angles than shorter people, regardless of sex, and surmised that the differences between males and females was related to the longer femur in males.
Clinically, an increased Q-angle may alert the treating physician to a potential cause for a patient's knee pain. However, the clinical usefulness of the Q-angle is debated. In a review article, Post et al reported that data correlating Q-angle measurements with patients’ clinical symptoms do not exist. [12] The authors noted that studies have shown that up to 60% of patients with patellofemoral symptoms have normal Q-angles. Post et al surmised that the Q-angle as a measurement of valgus force vectors across the anterior knee is not without value; rather, they suggest that its value as an isolated clinical tool is questionable. [12] Interpretation of a patient’s Q-angle should be part of a multifactorial evaluation.
Other authors have noted that rehabilitation programs for individuals with Q-angles greater than 15° are as successful as those for individuals with Q-angles less than 15°.
The senior author of this article doubts the importance of measuring Q-angles because more pertinent information can be obtained by other physical examination assessments of flexibility, patellar positioning, and mobility. In addition, a Q-angle measurement is a static assessment of a dynamic problem and, therefore, is limited in providing information pertinent to developing a treatment plan.
The bipartite patella is not a rare patellar variant. Typically asymptomatic, the bipartite patella is difficult to identify during a physical examination. Suspicion should arise when anterior knee pain and swelling are present. A symptomatic bipartite patella is easily revealed through radiologic films and commonly manifests with displacement of a fragment.
When assessing individuals in the pediatric population, patellofemoral pain may indicate growth center abnormalities affecting the tibial tubercle (eg, Osgood-Schlatter disease) or affecting the distal pole of the patella (eg, Sinding-Larsen-Johansson syndrome).
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Apprehension sign. The knee is placed at 30° flexion, and lateral pressure is applied. Medial instability results in apprehension by the patient.
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Anatomic morphology of patellar insertion into the intercondylar notch.
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Muscles influencing patellar biomechanics.
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The Q angle can be measured while the patient is standing or while the knee is at 20° of flexion (ie, at neutral), with maximum internal or external rotation of the tibia.
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Ligament constraints of the patella.
