PATELLOFEMORAL PAIN SYNDROME (ANTERIOR KNEE PAIN)
Patellofemoral pain syndrome, commonly known as anterior knee pain, is a concise description of the discomfort originating from the patellofemoral joint. However, it is important to note that the pain can also arise from the surrounding soft tissues and pathologies affecting the knee region. The diagnosis and treatment of this condition, which presents as knee pain during daily activities and hinders participation in sports, pose significant challenges. In the late 1960s, patellar chondromalacia was associated with anterior knee pain, and it was considered an idiopathic condition. However, contemporary understanding suggests that the syndrome frequently develops due to excessive stretching of the peripatellar retinaculum.
Anatomy:
Anatomically speaking, the patellofemoral joint serves as a protective and supportive component of the knee joint’s anterior region. It provides mechanical support to the quadriceps muscle and contributes to the extensor mechanism of the knee. The diagnosis and treatment of patellofemoral pain, which manifests as knee pain during daily activities and hinders participation in sports activities, can be challenging. In the past, patellofemoral pain was primarily attributed to patellar chondromalacia (softening of the articular surface of the patella) and considered idiopathic. However, it is now commonly believed that it often develops due to excessive tension in the peripatellar retinaculum.
The quadriceps muscles, including vastus lateralis, vastus intermedius, vastus medialis, and rectus femoris, extend to the patella through the strong and tendon-like structure called the quadriceps tendon. Apart from these muscles, the vastus medialis obliquus provides medial support to the patella, while the vastus lateralis obliquus offers lateral support. The patellar tendon continues distally from the patella and attaches to the tibial tuberosity. This alignment determines the course of the quadriceps tendon as it tracks over the trochlear groove of the femur. In the context of anterior knee issues, the iliotibial band is another important structure to consider. Originating as an extension of the tensor fasciae latae muscle on the lateral thigh, it extends laterally, contributes to dynamic and static stability, and attaches to the Gerdy tubercle on the lateral aspect of the tibia. It can cause irritation of the lateral epicondyle with repetitive knee flexion-extension movements.
The alignment of the patellofemoral joint is determined by the Q angle of the quadriceps. This angle is formed by the lines connecting the anterior-superior iliac spine, the midpoint of the patella, and the tibial tuberosity. Normal values for the Q angle range from 8º to 14º in males and 11º to 20º in females, with values above 20º considered abnormal.
Plicae are normal anatomical structures found in the patellofemoral region. However, repetitive trauma or friction with anatomical prominences can lead to their thickening and the development of issues.
The bony anatomy of the patellofemoral joint consists of the patella and the trochlea of the femur, along with its medial, lateral, and non-articular distal facets. The patella may have a dominant medial or lateral facet, with the lateral facet being concave and the medial facet convex. Additionally, during the later stages of knee flexion, an additional facet comes into play in the medial region. The classification of patellar morphology into different types, such as those proposed by Wiberg and Baumgartl, is useful in determining the localization of cartilage pathologies based on the specific parts of the patella that come into contact with the trochlea during varying degrees of knee flexion.
Classification:
Various classifications have been utilized in the categorization of patellofemoral joint diseases. Initially, these conditions were grouped under the umbrella term “patellar chondromalacia.” However, it has since been acknowledged that patellar chondromalacia specifically refers to the lesion of the patellar articular cartilage, which can arise from factors such as excessive loading on the patellofemoral joint, malalignment of the patellofemoral axis, and infrequently, direct trauma.
Insall devised a classification system based on the extent of articular cartilage deterioration in patellofemoral diseases.
Merchant, on the other hand, formulated a more practical and advantageous classification for patellofemoral diseases. This classification, comprising five primary sections as depicted in Table II, encompasses post-traumatic issues, patellofemoral dysplasia, idiopathic chondromalacia, osteochondritis dissecans, and synovial plica.
Clinical Findings:
Symptoms: Pain: Anterior knee pain can present as a throbbing, dull, or pulsating sensation. It is particularly noticeable during activities like climbing stairs or when the knee is flexed at a 90-degree angle, such as during long journeys or while sitting in a movie theater.
Crepitation: Often originating from patellofemoral arthritis, crepitation refers to a friction sound that can be either audibly heard or sensed by the patient. However, it is not a characteristic indicator of anterior knee pain.
Giving Way: This is a significant manifestation of patellofemoral joint involvement. It occurs when the knee flexes and extends under weight-bearing conditions (e.g., descending stairs or walking downhill). Weakness in the quadriceps muscle can also contribute to this symptom. Differential diagnosis is necessary to distinguish it from knee instability and meniscal tears.
Locking: During weight-bearing knee extension, locking can occur due to issues within the trochlear and patellar regions. It is usually a temporary condition and should not be mistaken for meniscal tears.
Swelling: Swelling, although uncommonly encountered during physical examinations, can be a transient occurrence. It may be observed in cases of severe patellofemoral malalignment, chondral pathologies where loose proteoglycan-cartilage fragments are present in the joint, synovial diseases, bleeding, and traumatic injuries.
Physiotherapy:
Before commencing the examination of a patient experiencing patellofemoral pain, it is crucial to allocate sufficient time for gathering the patient’s history. Understanding the nature of the pain, its onset, duration, presence of any traumatic events, and specific associated symptoms can provide valuable insights. In cases where the pain originates from a blunt trauma to the knee during flexion, it can lead to chondral and subchondral injuries. On the other hand, if the pain has developed without any traumatic event, it is important to consider potential malalignment issues. The characterization of the pain can offer valuable clues in elucidating the underlying problem. For instance, the presence of crepitus along with the pain might indicate the presence of a flap lesion in the loose articular cartilage. Additionally, a sharp, electric-like pain can be attributed to post-surgical infrapatellar nerve injury and entrapment. Diffuse and non-localizable pains may be associated with reflex sympathetic dystrophy (RSD) or systemic diseases. It is crucial to carefully differentiate between knee pain caused by blunt trauma and that arising from hip pathologies. Obtaining an accurate localization of the pain from the patient is paramount, as it can often correlate with retinacular pain. Occasionally, patients may report the origin of the pain to be behind the kneecap. Therefore, it is essential to make a clear distinction, as such pain could be indicative of patellar tendinitis, impingement of the fat pad, plica syndrome, or other intra-articular problems. It is worth noting that Baker’s cyst can also contribute to anterior knee pain. Crepitus is typically associated with cartilage lesions in the patella or trochlea, although postoperative scar tissue, synovitis, osteophytes, and plica can also generate crepitus. The presence of fluid accumulation in the knee, resulting from cartilage damage and debris-induced synovitis, signifies an inflammatory process. Consequently, when gathering the patient’s history, it is important to assess the possibility of patellar instability and the associated pain it may cause. Patellar subluxation or dislocation during movements, stemming from malalignment, should be considered, as it holds significance for treatment planning. Moreover, investigating the presence of concurrent comorbidities is crucial in order to obtain a comprehensive history. Conditions such as psoriasis, Lyme disease, connective tissue disorders, and ulcerative colitis can manifest as arthritis, leading to knee pain.
The patient presenting with anterior knee pain should undergo a comprehensive examination in different positions, including standing, sitting, supine, and prone. During the standing position, careful attention is paid to assess the alignment of the knee in terms of varus-valgus, hip anteversion or retroversion, pronation of the feet, and overall postural characteristics. In the sitting position, the patient is instructed to actively perform knee extension and flexion, allowing the observation of patellar movement and its interaction with the trochlea. It is typically expected that the patella will adapt to the trochlea within the initial 10º-15º of flexion. Subsequently, while in the supine position, passive flexion and extension of the knee are employed to evaluate the path followed by the patella. In full knee extension, the patella is compressed to assess for the presence of pain. Additionally, crepitus and any associated discomfort are investigated during passive knee movements. Palpation of the peripatellar retinacular structures, quadriceps, and patellar tendon attachments is conducted with the patient in the supine position. Moreover, the patient is placed in the prone position to evaluate excessive quadriceps tightness and pain at different degrees of flexion. Any signs of abnormal hair growth and swelling in the area are noted, as they may be indicative of reflex sympathetic dystrophy (RSD).
During the examination, it is expected that the patella can be medially shifted by approximately 1/4 of its width when the knee is flexed at 20º-30º, while a lateral lift of approximately 15º from the lateral side is possible when the knee is fully extended. In cases where these movements cannot be achieved, the presence of lateral peripatellar tightness should be considered. Lastly, the patient’s gait should be observed during ambulation to identify any antalgic or abnormal patterns. If feasible, a re-evaluation after a 10-15 minute walk may provide additional insights.
Redefining the Radiological Diagnosis:
The examination of the knee in cases of patellofemoral pain requires various imaging techniques, including standard anteroposterior, lateral, and axial views. These images help assess the alignment of the patella with the femoral trochlea, identify bone pathologies, and evaluate joint space narrowing. Lateral and anteroposterior views taken with the knee flexed at 30º provide a clear visualization of tibiofemoral joint space. Axial views, obtained at different degrees of flexion, offer valuable insights into the patellofemoral joint relationship.
To assess patellar alignment, the Merchant and Laurin methods are employed. The Merchant view, taken at 45º flexion with a 30º beam angle, allows for the observation of patellar tilt and subluxation. In a normal patellofemoral relationship, the patella should align centrally with the trochlear sulcus, and any lateral deviation indicates a malalignment. The Laurin method, on the other hand, measures the angle between lines drawn through the lateral facet of the patella and the femoral condyles to diagnose patellar tilt accurately.
In cases where further details are required, computed tomography (CT) scans can be performed. CT imaging allows for the assessment of patellar alignment and subluxation at different degrees of knee flexion. Additionally, dynamic CT can provide valuable information about patellofemoral alignment during knee motion. Magnetic resonance imaging (MRI) is less commonly used for patellofemoral joint evaluation but can offer insights into cartilage health.
Furthermore, bone scintigraphy may be employed to identify hidden fractures, assess patellar tendinitis, and diagnose reflex sympathetic dystrophy (RSD). These imaging techniques, along with clinical examination, aid in accurately diagnosing and understanding patellofemoral pain.
Conservative Approach:
The primary course of action for patients with patellofemoral issues should be conservative treatment. Nonsteroidal anti-inflammatory drugs (NSAIDs) can assist in reducing pain. It’s important to note that significant inflammation may not always be present in all cases, but applying ice can be beneficial if inflammation is detected. Establishing trust between patients and their doctors is fundamental to the treatment process.
Utilizing knee braces and employing simple bandaging techniques can help prevent patellar tilt and subluxation, thus decreasing anterior knee pain.
Patients are encouraged to follow simple exercise programs at home. Quadriceps stretching in the prone position and lateral retinaculum stretching exercises are recommended, particularly in cases where patellar tilt is observed. Quadriceps strengthening exercises using ankle weights are implemented. Both closed and open kinetic chain exercises yield similar results, while eccentric isokinetic exercises are specifically useful for treating patellar tendinitis.
Regardless of the selected exercise method for anterior knee pain, it is crucial to identify pain-free ranges of motion and administer treatment within those boundaries. Managing chronic anterior knee pain, especially in cases of reflex sympathetic dystrophy, can pose a challenge.
Surgical Treatment:
In instances where patients do not experience significant improvement with conservative measures over an extended period, surgical intervention may be necessary.
Arthroscopy and Lateral Retinacular Release (LRR): In cases where there is no patellar misalignment and no presence of reflex sympathetic dystrophy (RSD), arthroscopic debridement can potentially yield positive outcomes for cartilage lesions. However, it is important to note that many patients with cartilage lesions also exhibit misalignment. Therefore, in such cases, it is recommended to consider lateral retinacular release in addition to debridement. It is worth mentioning that better results are typically observed in patients with patellar tilt and minimal or no cartilage damage. It is crucial to avoid the misconception of performing LRR in all cases of anterior knee pain.
Tibial Tubercle Osteotomies: For patients experiencing recurrent patellar subluxation and dislocation, as well as those with misalignment and mature bone, the anteromedial transfer of the tibial tubercle is suggested as a potential solution. This procedure can be complemented with lateral release and medial plication (known as the Elmslie-Trillat procedure).
Patellectomy-Patellar Resurfacing: In cases of advanced patellar degeneration and significant functional impairment, patellectomy or the application of patellofemoral prostheses may be considered as a final option.
Other Soft Tissue Interventions: It is worth noting that some patients may experience anterior knee pain due to factors such as painful neuromas, scarring, or chronic patellar tendinitis resulting from previous surgical interventions. In such cases, scar and neuroma excisions can help alleviate the pain. In instances where chronic patellar tendinitis persists despite 6-9 months of conservative treatment, the recommended approach involves the removal of the degenerated tendon section. Furthermore, surgical interventions such as excision of intra-articular hemangiomas and pathological medial plica are also among the suggested treatment options for anterior knee pain suspected to be associated with these conditions.
