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Patellofemoral Disorders Classification Confusion over classification of patellofemoral disorders exists in the literature. Wilk and associates (1998) noted that a comprehensive patellofemoral classification scheme should (1) clearly define diagnostic categories, (2) aid in the selection of appropriate treatment, and (3) allow the comparison of treatment approaches for a specific diagnosis. Evaluation of the Patellofemoral Joint Signs and Symptoms Physical Examination Both lower extremities should be examined with the patient in shorts only and without shoes. The patient should be examined and observed standing, walking, sitting, and lying supine. The ipsilateral knee, hip, foot, and ankle should be examined and compared with the opposite limb for symmetry, comparison of thigh muscular girths, Q-angles, and other factors. Physical examination also should include evaluation of: Clinical Tests for Patellofemoral Disorders Q-angle The Q-angle is the angle formed by the intersection of lines drawn from the anterior superior iliac spine to the center of the patella and from the center of the patella to the tibial tubercle (see Fig. 4–1). In essence, these lines represent the lines of action of the quadriceps musculature and patellar tendons, respectively, on the patella. It should be measured with the knee slightly flexed, to center the patella in the trochlear groove. Foot pronation (pes planus or flat feet) and limb internal rotation both increase the Q-angle. The range of normal for the Q-angle varies in the literature, and there is controversy whether the wider pelvic anatomy in women contributes to a greater Q-angle. The reported values of normal quoted are 10 degrees for men and 15 degrees for women. It is well accepted that patellar alignment is somewhat affected by the degree of valgus at the knee; however, the degree of valgus present is not a dependable pathologic marker for severity of symptoms. Soft Tissue Stabilizers of the Patella In addition to the bony stabilizers, there are medial and lateral soft tissue restraints to the patella. The medial restraints consist of the medial retinaculum, the medial patellofemoral ligament, and the VMO. The VMO is the most important dynamic stabilizer of the patella to resist lateral displacement. Its fibers are oriented at about a 50 to 55 degree angle to the long axis of the femur (Fig. 4–46). It inserts normally into the superomedial aspect of the patella along about one third to one half its length. However, in some cases of instability, the muscle may be absent or hypoplastic or may insert proximal to the patella. The lateral restraints consist of the lateral retinaculum, the vastus lateralis, and the iliotibial band. Contracture in any of these structures may exert a tethering effect on the patella (e.g., ELPS), and they must be appropriately assessed during evaluation of the patellofemoral region. Standing Alignment of the Extensor Mechanism Inspection of the entire lower extremity should be performed not only to assess the alignment of the extensor mechanism but also to look for pes planus, tibial torsion, genu varum or valgum, genu recurvatum, femoral anteversion, or limb-length discrepancy, all of which can contribute to patellofemoral dysfunction. It is important to evaluate the patient in a standing position. The weight-bearing position may unmask otherwise hidden deformities such as excessive forefoot pronation (which increases the relative standing Q-angle) or limb-length discrepancies. Observation of the gait pattern may reveal abnormalities in mechanics, such as foot hyperpronation, or avoidance patterns during stair descent. Muscular atrophy can be visualized qualitatively or measured quantitatively (circumferentially from a fixed point) with a tape measure. The presence of erythema or ecchymosis in a particular area may offer an additional clue to the underlying pathology. Local Palpation Palpation also reveals any tenderness that may be present in the soft tissues around the knee. Tenderness along the medial retinacular structures may be the result of injury occurring with patellar dislocation. As the patella dislocates laterally, the medial retinaculum has to tear to allow the lateral displacement of the knee cap. Lateral pain may be secondary to inflammation in lateral restraints, including the iliotibial band. Joint line tenderness typically indicates an underlying meniscal tear. Tenderness due to tendinitis or apophysitis in the quadriceps or patellar tendon will typically present with distinctly localized point tenderness at the area of involvement. Snapping or painful plicae may be felt, typically along the medial patellar border. Range of Motion (Hip, Knee, Ankle) ROM testing should include not only the knee but also the hip, ankle, and subtalar joints. Pathology in the hip may present as referred knee pain, and abnormal mechanics in the foot and ankle can lead to increased stresses in the soft tissue structures of the knee that may present as pain. While ranging the knee, the presence of crepitation and patellar tracking should be assessed. Palpable crepitus may or may not be painful and may or may not indicate significant underlying pathology, although it should raise the suspicion of articular cartilage injury or soft tissue impingement. The patella grind or compression test (Fig. 4–47) will help to elucidate the etiology. To perform this test, one applies a compressive force to the patella as the knee is brought through a ROM. The reproduction of pain with or without accompanying crepitus is indicative of articular cartilage damage. More experienced examiners may be able to further localize the pain to specific regions of the patella or trochlea with subtle changes in the site of compression. Flexibility of the Lower Extremity Flexibility of the lower extremity must be evaluated. Quadriceps, hamstring, or iliotibial band tightness may all contribute to patellofemoral symptoms. Quadriceps flexibility may be tested with the patient in a prone or lateral position. The hip is extended and the knee progressively flexed. Limitation of knee flexion or compensatory hip flexion is indicative of quadriceps tightness. Hamstring flexibility can be tested (Fig. 4–48). The Ober test (Fig. 4–49) is used to assess iliotibial band flexibility. The test is done with the patient in a side-lying position with the leg being measured up above the other. The lower hip is flexed to flatten lumbar lordosis and stabilize the pelvis. The examiner, positioned behind the patient, gently grasps the leg proximally just below the knee, flexes the knee to apply a mild stretch on the quadriceps, and flexes the hip to 90 degrees to flatten the lumbar lordosis. The hip is then extended to neutral, and any flexion contracture is noted. With the opposite hand at the iliac crest to stabilize the pelvis and prevent the patient from rolling backward, the examiner maximally abducts and extends the hip. The abducted and extended hip is then allowed to adduct by gravity while the knee is kept flexed, the pelvis stabilized, and the femur in neutral rotation. Generally, the thigh should adduct to a position at least parallel to the examining table. Palpation proximal to the lateral femoral condyle with the iliotibial band on stretch is frequently painful to patients with iliotibial band and lateral retinacular tightness. When this is found, iliotibial band stretches become a valuable part of the treatment plan. Again, bilateral comparison is important. Ober’s position is useful in the treatment (stretching) as well as in the diagnosis of iliotibial band tightness. J-sign Evaluation of patellar tracking begins with the knee in full extension. In this position, the patella typically rests just lateral to the midline. As the knee moves into flexion, at around 10 to 30 degrees, the patella centers into the trochlear groove and proceeds to track in a relatively straight path with progressive knee flexion. This normal path should progress smoothly. A sharp jump of the patella into the trochlear groove sometimes referred to as the J-sign, or late centering of the patella, should raise the suspicion of patellar instability. Examination for knee instability should include a full evaluation of the cruciate and collateral ligaments to assess for any rotatory component, as well as to examine the patellar restraints. Patients with posterolateral corner knee instability may develop secondary patellar instability owing to a dynamic increase in the Q-angle. Similarly, patients with chronic MCL laxity may also develop secondary patellar instability. Apprehension on medial or lateral displacement testing of the patella should raise the suspicion of underlying instability in the patellar restraints. Superior and inferior patellar mobility should also be assessed; they may be decreased in situations of global contracture. Patellar Glide Test The patellar glide test is useful to assess the medial and lateral patellar restraints. In extension, the patella lies above the trochlear groove and should be freely mobile both medially and laterally. As the knee is flexed to 20 degrees, the patella should center in the trochlear groove, providing both bony and soft tissue stability. Lateral Glide Test The lateral glide test evaluates the integrity of the medial restraints. Lateral translation is measured as a percentage of patellar width (Fig. 4–50). Translations of 25% of patellar width are considered normal; translations greater than 50% indicate laxity within the medial restraints. The medial patellofemoral ligament has been noted to provide 53% of the stabilizing force to resist lateral subluxation, and normally presents with a solid endpoint when the lateral glide test is performed. Reproduction of the patient’s symptoms with passive lateral translation of the patella pulling on the medial structures is referred to as a positive lateral apprehension sign. This signals lateral patellar instability. Medial Glide Test The medial glide test is performed with the knee in full extension. The patella is centered on the trochlear groove and medial translation from this “zero” point is measured in millimeters. Greater than 10 mm of translation is abnormal. The lateral retinacular laxity may be due to a hypermobile patella or, less commonly, medial instability. Medial patellar instability is rare and usually presents as an iatrogenic complication following patellar realignment surgery, typically from an overaggressive lateral release. Six to 10 mm of translation is considered normal. Translation less than 6 mm medially indicates a tight lateral restraint and may be associated with ELPS. Patellar Tilt A tight lateral restraint may contribute to patellar tilt. Patellar tilt is evaluated as the knee is brought to full extension and an attempt is made to elevate the lateral border of the patella (Fig. 4–51). Normally, the lateral border should be able to be elevated 0 to 20 degrees above the medial border. Less than 0 degrees indicates tethering by a tight lateral retinaculum, vastus lateralis, or iliotibial band. Presence of clinical and radiographic lateral patellar tilt is indicative of tight lateral structures. This may be responsible for ELPS. If extensive rehabilitation fails, the presence of a lateral patellar tilt correlates with a successful outcome after lateral release. Bassett Sign Tenderness over the medial epicondyle of the femur may represent an injury to the medial patellofemoral ligament in the patient with an acute or recurrent patellar dislocation. Lateral Pull Test This test is performed by contraction of the quadriceps with the knee in full extension. It is a positive (abnormal) test if lateral displacement of the patellar is observed. This test demonstrates excessive dynamic lateral forces. Radiographic Evaluation Three views of the patella, an AP, a lateral in 30 degrees of knee flexion, and an axial image, should be obtained. The AP view can assess for the presence of any fractures, which should be distinguished from a bipartate patella, a normal variant. The overall size, shape, and gross alignment of the patella can also be ascertained. The lateral view is used to evaluate the patellofemoral joint space and to look for patella alta (see Fig. 4–1) or baja. In addition, the presence of fragmentation of the tibial tubercle or inferior patellar pole can be seen. Both the AP and the lateral views can also be used to confirm the presence and location of any loose bodies or osteochondral defects that may exist. An axial image, typically a Merchant (knee flexed 45 degrees and x-ray beam angled 30 degrees to axis of the femur) or skyline view, may be the most important. It is used to assess patellar tilt and patellar subluxation. The anatomy of the trochlear groove is also well visualized and the depth and presence of any condylar dysplasia can be determined. One important point deserves mention. The radiographs visualize only the subchondral bone of the patella and trochlea and do not show the articular cartilage. The articular surfaces are not necessarily of uniform thickness in these regions. Therefore, any measurements made from plain radiographs are only an indirect indication of the actual anatomic structure. Assessment begins with the measurement of the sulcus angle (Fig. 4–52). A line is drawn along the medial and lateral walls of the trochlea. The angle formed between them is the sulcus angle. Greater than 150 degree is abnormal and indicates a shallow or dysplastic groove that may have a predisposition for patellar instability. Patellofemoral subluxation is evaluated by measurement of the congruence angle (see Fig. 4–52). The angle is formed by a line drawn from the apex of the trochlear groove bisecting the sulcus angle and a line drawn from the apex of the groove to the apex of the patella. A lateral position of the patella apex relative to the apex of the trochlea is considered positive. A normal congruence angle has been described as –6 degrees ±6 degrees. Patellar tilt is evaluated by the patellofemoral angle (Fig. 4–53). This angle is formed by the lines drawn along the articular surfaces of the lateral patella facet and the lateral wall of the trochlear groove. The lines should be roughly parallel. Divergence is measured as a positive angle and is considered normal, whereas convergence of the lines is measured as a negative angle and indicates the presence of abnormal patellar tilt. |
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