BLOG: Patellofemoral pain syndrome — A diagnosis that does not exist
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by Akbar Y. Maniya, MD; Diana C. Patterson, MD; and Ronald P. Grelsamer, MD
The generic term “patellofemoral pain syndrome” is frequently cited as a specific diagnosis, but it has never been specifically defined. In fact, it is not a diagnosis per se. To facilitate the arrival at a specific diagnosis, we categorize anterior knee pain into conditions pertaining to the patella proper, conditions pertaining to the peripatellar soft tissues and conditions altogether unrelated directly to the extensor mechanism.
Due to its persistently ubiquitous use, the so-called patellofemoral syndrome warrants renewed discussion. The term “patellofemoral pain syndrome” is not so much a diagnosis as an amalgam of disparate pathologies with similar presenting symptoms.
While the generic term “patellofemoral pain syndrome” (PFPS) is frequently cited in the literature as a specific diagnosis, it has never been defined and, may in fact, defy definition. Having recognized that little correlation exists between knee pain and patellar cartilage lesions, the orthopedic community has gradually abandoned the term "chondromalacia patellae.” Alas, there has been a gradual shift to PFPS, a term that is equally imprecise and misleading. The use of either chondromalacia patellae or PFPS incorrectly leads the clinician (and the patient) to believe that a distinct diagnosis has been made and that a clear, definitive treatment can be initiated. A syndrome, by definition, encompasses a specific, validated set of symptoms and findings. No such specific criteria have ever been established for a “patellofemoral pain syndrome.” Thus, PFPS is not even a true syndrome. There appear to be as many definitions as there are authors purporting to study it. Nevertheless, due to its persistently ubiquitous use (and in the United States, the existence of ICD-10 diagnosis codes), it warrants renewed discussion.
“Patellofemoral pain syndrome” is in fact an umbrella term encompassing disparate conditions, making it fruitless to offer generic “treatment options for PFPS.” It falls on the orthopedist to make as specific a diagnosis as possible.
We have found it useful to classify “anterior knee pain” into several categories: 1) conditions not involving the extensor mechanism including tightness of the iliotibial band (ITB), neuromas, torsional deformities, inflammatory conditions, gait disorders, referred pain or overuse; 2) intrinsic pathologies of the patella proper, including arthritis, osteochondral lesions, stress fractures and, though quite rare, infections and tumors; and 3) disorders of the extensor mechanism outside the patella proper, such as lateral retinacular tightness, patellar tendonitis, patella alta/baja and patellofemoral instability. Instability, which has been extensively covered in the literature and is now rarely misdiagnosed, is included in this list for completeness but will not be discussed further in this review.
Conditions unrelated to the extensor mechanism of the knee
Iliotibial band tightness can lead to its inflammation as it passes over the lateral femoral condyle and the underlying bursa. The tenderness is typically at the anterolateral aspect of the knee, but the pain can be referred to the anterior knee. The hallmark of a tight ITB is a positive Ober test. Iliotibial band tightness is stereotypically described in cross country runners training on hills (“runner’s knee”). Excess hip adduction and internal rotation of the knee during running has been found in patients with ITB syndrome. There is generally no role for imaging in this diagnosis, except to rule out other pathologies. Treatment consists of rest and NSAIDs acutely, stretching and massage subacutely, and physical therapy and/or injection in the longer term along with modifications of exercise techniques when feasible.
The infrapatellar branch of the saphenous nerve innervating the skin of the anterior knee can become irritated and can occasionally feature a frank neuroma. Inflammation of this nerve must be considered in anyone with a history of blunt trauma to the front of the knee, such as a fall onto the front of the knee or an impact against a dashboard. The diagnosis is made by eliciting signs of nerve irritation such as a positive Tinel sign, pain with light percussion, gentle squeezing and/or light scratching of the skin. An MRI can detect a large neuroma but will not detect mild nerve irritation. An MRI can, however, detect an irrelevant torn meniscus and lead to unnecessary arthroscopies. When a neuroma is present, its excision is curative.
An inflamed plica can present as anterior knee pain and, very rarely, can progress to erosion of the underlying cartilage. The pain may be worse with loading of the knee, prolonged sitting and may be accompanied by clicking and locking. Exam findings may include tenderness to palpation, along with a hard, palpable cord over the medial femoral condyle. This diagnosis became prevalent with the popularization of knee arthroscopy in the 1980s, and for a time was fruitlessly blamed for many cases of unexplained anterior knee pain. In the senior author’s experience, dividing a plica rarely relieves a patient’s knee pain.
Torsional issues such as excessive femoral anteversion, tibial torsion or metatarsus adductus place abnormal forces across the patellofemoral joint. While the resulting pain may be localized to the front of the knee, the patella is but an innocent bystander.
Referred pain from an L4 radiculopathy or hip pathology may present as anterior knee pain. A lack of awareness can lead to a delay in diagnosis, a particularly problematic situation when dealing with time -sensitive conditions such as a slipped capital femoral epiphysis (SCFE). Indeed, a SCFE that presents as knee pain has been shown to result in a significant delay in diagnosis.
Reflex sympathetic dystrophy/complex regional pain syndrome (CRPS) should be considered in situations where the knee pain is out of proportion to the examination, particularly if hyperalgesia, autonomic changes, trophic changes, edema and/or erythema are present. Patellar osteopenia can be a radiographic sign of CRPS, but this is neither a sensitive nor specific finding. A sympathetic blockade can be both diagnostic and therapeutic, though this remains a controversial area.
Intrinsic patellar pathology
Though more common on the lateral aspect of the medial femoral condyle, osteochondritis dissecans (OCD) can occur in the patella and is more difficult to treat in that location. Osteochondritis dissecans is a disorder of the subchondral bone; the overlying cartilage is intact.
A “dorsal defect” of the patella may be discovered incidentally on radiographs as a hole in the bone and/or presents as anterior knee pain. Contrary to OCD, the cartilage of a dorsal defect exhibits signs of degeneration. Though dorsal defects are benign, usually with self-limited symptoms, these have on rare occasion been reported to be a nidus for fracture. One way to address painful patellar lesions, especially those laterally located, is to unload them via the Fulkerson osteotomy.
Stress fractures of the patella are rare, but suspicion should remain high in cases of atraumatic knee pain in patients involved in repetitive, high patellofemoral stress activities like sprinting, jumping, kicking and martial arts. These fractures can be apparent on radiographs but may require MRI for detection.
A bipartite patella can be mistaken for an acute fracture; accordingly, a certain index of suspicion should be maintained for vertical fractures involving the lateral portion of the patella. A symmetrical finding on the opposite patella (not always present) seals the diagnosis.
Patellar tumors are rare. Most are benign and include giant cell tumors (GCT) and chondroblastomas, which account for 33% and 16% of all primary patellar tumors, respectively. The most common malignant patellar tumor is osteosarcoma, comprising 6% of all primary patellar tumors. These present with chronic knee pain that may fluctuate during a period of months and are often accompanied by a large soft tissue mass on exam that is tender to palpation.
Like instability, patellofemoral arthritis is not often labeled as PFPS due to its straightforward diagnosis. Patellofemoral arthritis may be due to direct trauma, malalignment, dislocation(s) and/or dysplasia. In one radiographic study, trochlear dysplasia was found in 96% of patients presenting with isolated patellofemoral arthritis and a history of documented dislocation and in just 3% of CT scans of asymptomatic controls with no history of patellar dislocation. A frequently associated demographic risk factor is obesity. Indeed, the patellofemoral compartment experiences five times a person’s body weight when a person rises from a chair; thus, excessive weight is greatly magnified across the patellofemoral joint and predisposes it to arthritis. Nonsurgical approaches include standard knee arthritis treatments, though physical therapy must be modified to minimize patellofemoral stresses. Surgical options include marrow stimulation or cartilage restoration for discrete chondral lesions, tibial tuberosity transfers, patellofemoral replacements and total knee arthroplasty. Marrow stimulation procedures, such as microfracture or subchondral drilling, can transiently improve symptoms, but are generally limited to lesions less than 2 cm in diameter, require an open procedure to achieve a perpendicular approach and may not provide lasting relief. Cartilage restoration utilizing a range of grafts has shown acceptable results for greater than 2 years. However, these outcomes are most reliable in “young” patients with discrete full-thickness lesions with distinct boundaries and are not suitable for diffuse cartilage loss or widespread eburnated, exposed bone. Tibial tuberosity transfers (also known as AMZ or Fulkerson procedure) work best in the setting of distolateral patellar lesions without a “kissing” lesion on the trochlea. Patellofemoral arthroplasty is now an accepted option with successful results, especially in patients at limited risk of femorotibial degeneration; these would be patients whose arthritis has a clear patellofemoral origin such as dysplasia or trauma. At the other extreme would be patients with inflammatory arthritis whose first manifestation is in the patellofemoral compartment.
Disorders of the extensor mechanism
These conditions are common. Patellar tendonitis/tendinopathy (“jumper’s knee”) presents with pain over the lower portion of the patella and upper shin; the pathognomonic finding is tenderness at the junction of the inferior pole and the patellar tendon. The differential diagnosis must include inflammation of the underlying fat pad, hence the need for thoughtful palpation. Corticosteroid injections into the tendon are not recommended. In recalcitrant cases, arthroscopic or open tenotomy for a well-defined lesion can be considered.
Tightness of the lateral patellar retinaculum with ensuing patellar tilt is a form of extensor malalignment (also known as misalignment). Occurring on its own or within a constellation of other findings including an abnormally positioned vastus medialis oblique, a laterally positioned tibial tuberosity (resulting in an increased Q angle) and a dysplastic trochlea. Tension of the lateral retinaculum and resulting lateral patellar tilt lead to increased contact pressures on the lateral aspect of the patella, a condition known as excessive lateral pressure syndrome. This can be associated with abnormal neuromatous tissue in the lateral retinaculum. On the physical examination, palpation of the retinaculum and/or pressure under the lateral facet elicits pain. Appropriate imaging includes axial views with just 30° of flexion when possible because patellar position typically improves with deeper flexion. A tight lateral retinaculum is usually well addressed by a knowledgeable physical therapist and only rarely requires surgery.
A history of sudden increased activity should tip off the clinician to this diagnosis. The main differential diagnosis is a stress fracture.
The term “patellofemoral pain syndrome” is an amalgam of disparate pathologies with similar presenting symptoms. This generic term should be avoided in favor of a specific diagnoses.
We encourage physicians to not perfunctorily use an umbrella term to simplify a visit, as important, treatable and even critical diagnoses may be missed. Palpation of the peripatellar soft tissues remains a critical part of the evaluation. Finally, in the absence of any clear knee pathology, it behooves the orthopedist to evaluate the lower extremity in its entirety.
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Akbar Y. Maniya, MD, Diana C. Patterson, MD; and Ronald P. Grelsamer, MD, are from the department of orthopedic surgery at The Icahn School of Medicine at the Mount Sinai Medical Center in New York.
Disclosures: Maniya, Patterson and Grelsamer report no relevant financial disclosures.
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