Introduction
Patellofemoral arthritis is the most common reason for knee joint pain caused due to degenerative changes to the articular cartilage, which may further precipitate osteoarthritis. Patellofemoral arthritis may be present in just one compartment or in conjunction with femorotibial arthritis in either the medial or lateral compartments or both.
Who Is Susceptible to Patellofemoral Arthritis?
An estimation suggests the prevalence of 14 million osteoarthritic knee patients in the US, half of which are below the age of 65. According to a symptomatic study, around 50 percent of the patients complaining of knee pain have patellofemoral involvement. A cadaver study of 65 years and above showed patellofemoral osteoarthritis in 79 percent of the cases. And around 50 percent of the patients undergoing meniscectomy have chondromalacia (deterioration of the cartilage present on the underside of the patella).
What Causes Patellofemoral Arthritis?
Patellofemoral arthritis is the deterioration of the knee joint in combination with chondromalacia. This frequently precipitates the development of osteoarthritis. Patellofemoral arthritis is considered a separate condition from the medial and lateral compartment femorotibial arthritis.
Patients with a history of instability, dislocation, subluxation, laxity, or malalignment resulting in lateralization, muscle imbalance, or high riding palette (patella alta) often end up with patellofemoral arthritis. ACL or anterior cruciate ligament reconstruction with the help of a hamstring or patellar tendon graft has proven to be a risk factor for patellofemoral arthritis.
Other risk factors for patellofemoral arthritis are colon age, obesity, intra-articular or patellar fracture history, history of dislocation or subluxation, overuse of the joint through high-intensity sports like running or weight training, and history of arthritis of other joints. Some systemic disorders also precipitate patellofemoral arthritis, like rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis (inflammatory arthritis causing bone fusion), juvenile idiopathic arthritis (arthritis in kids), and SLE (systemic lupus erythematosus).
What Is the Pathophysiology of Patellofemoral Arthritis?
Patellofemoral arthritis combines the degeneration of articular cartilage, also known as chondromalacia, and an abnormal biomechanical tracking of the patella within the groove, most often in the lateral patellar facet. Out of all the facets, the lateral facet is the one that is mostly overloaded; this is due to the lateral misalignment of the patella within the groove in the arthritic state and the direction of the force vector of the quadriceps muscle and knee extensors. The development and progression of the condition are also accelerated by valgus knee alignment, dysplasia of the patella or the groove, and malrotation of the tibia.
Other factors contributing to the degeneration of the joint developing secondary to abnormal stress on the patella, secondary myofascial mechanical disruption, atrophied vastus medialis obliquus, loss of function of the lateral retinaculum, and deficiency of the medial patellofemoral ligament. Apart from intra-articular fractures of the patella and trochlea caused by any kind of trauma, patella instability, osteo- or inflammatory arthritis, obesity, and quality of the cartilage also pose risk factors for the development of patellofemoral arthritis. A tear of the medial patellofemoral ligament, with or without subluxation or dislocation, can subsequently lead to patellofemoral instability and arthritis.
What Is the Histopathology of Patellofemoral Arthritis?
On microscopic analysis of the affected patellofemoral joint, it reveals the presence of chondrocytes, collagen fibers, proteoglycans, and water.
What Are the Signs and Symptoms of Patellofemoral Arthritis?
The most common symptom of the condition is anterior knee pain which typically worsens by standing up or sitting down, walking up and down the stairs while kneeling, and doing lunges, and squats. Essentially any motion that increases knee flexion, which in turn increases the load on the joint, causes the associated pain. Patients have also reported symptoms of popping, cracking, and grinding stiffness, pseudo-locking, and a sensation of instability or giving way.
A gate examination reveals increased anterior and lateral pelvic tilt on the contralateral side, increased reduction of the hip, and lower hip extension during stance. And effusion, quadricep, or hamstring atrophy may also be observed. The patella may be tilted inwards or outwards.
During physical palpation, the joint may reveal crepitus tenderness and a positive Clarke test. Clarke’s test, also known as the patellar grind test, is performed with the patient in a supine position and knees in full extension when the examiner places their hands on the proximal patella and the patient slowly contracts their quadriceps muscle while preventing the proximal moment of the knee cap. A positive test is painful to the patient. If the examiner moves the patella in a superior-inferior or medial hyphen lateral direction while applying posteriorly-directed pressure and the patient gives a painful response, then the patient shows a positive patellar apprehension test. This test looks for the laxity or mobility of the patella and can suggest the development of patellofemoral arthritis.
How To Diagnose Patellofemoral Arthritis?
- Physical Examination: The condition is diagnosed first with a detailed history of any arthritic or joint-related issues or surgeries, along with physical examinations, including the Clarke test and patellar apprehension test.
- Radiographic Evaluation: Standard radiographs of the joint with AP, lateral and axial views can be ordered, which might show space narrowing, subchondral sclerosis, osteophytes, articular degeneration, and patellar misalignment. The lateral view evaluates the alignment of the patella, and femoral condyle dysplasia, while the axial view evaluates the patellar malalignment and the groove depth. Both views can be evaluated together to assess the degree of degradation of the joint.
- Other Imaging Studies: Additionally, a computed tomography scan (CT) can be performed for better analysis of the joint. CT, although unnecessary, can help to determine lateral patellar subluxation or femoral trochlear dysplasia. In case of traumatic injury where patellar osteochondritis dissecans or ligamentous injury is expected, magnetic resonance imaging (MRI) has to be performed. In the absence of a radiograph, ultrasound may be used but with limited diagnostic ability. Arthroscopy is a great method of diagnosis and therapeutic treatment. Other systemic causes of patellofemoral arthritis should also be considered by ordering serological tests for Lyme disease, rheumatoid arthritis, and gonococcal arthritis.
What Is the Staging of Patellofemoral Arthritis?
Radiographic studies define patellofemoral arthritis into four stages:
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Mild - Involving greater than three millimeters of the joint space.
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Moderate - Involving less than three millimeters of the joint space without any bony contact.
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Severe-bony Surfaces - In contact over less than 25 percent of the joint surface.
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Very Severe - Bony contact involving 100 percent of the joint surface.
How to Treat Patellofemoral Arthritis?
General Management:
Patello femoral arthritis can be managed by weight loss, activity modification, decreasing the frequency of squats, lunges, jumps, and other activities involving prolonged flexion, and increasing activities that give less stress to the anterior knee.
Pharmacological Therapy:
Pharmacological options include prescriptions of analgesics, Glucosamine, and Chondroitin sulfate. Intraarticular corticosteroid injections are the first-line therapy. In some patients, viscosupplementation can also be used. Regenerative medicine modalities like the use of platelet-rich plasma have been considered in treating patellofemoral osteoarthritis with mixed success.
Joint Support Modalities:
Other management modalities include Kinesio-taping of the patella, using a knee sleeve with compressions, patella stabilizing braces, and hinged braces.
Surgical Treatment:
Surgical management modalities include arthroscopy with debridement of the patellar cartilage, which may also include relieving the lateral patellar retinaculum, reattachment or reconstruction of the medial patellofemoral ligament, or re-advancement of the vastus medialis obliquus. Other surgical treatment options include tibial tubercle osteotomy, autologous chondrocyte implantation, patelloplasty, and total knee arthroplasty.
What Is the Differential Diagnosis of Patellofemoral Arthritis?
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Primary or secondary osteoarthritis.
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Iliotibial band syndrome.
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Disc herniation.
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Tendonitis.
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Neuroma.
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Gout.
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Pseudogout.
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Lyme disease.
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Septic arthritis.
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Gonococcal arthritis.
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Rheumatoid arthritis.
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Psoriatic arthritis.
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Seronegative arthritis.
What Is the Prognosis of Patellofemoral Arthritis?
The prognosis is quite variable in this condition as it is a progressive degenerative disease that requires aggressive management relative to the progressing stage. In younger individuals, conservative treatment can help them regain normal routine while in stages that involve femorotibial joint, obesity, or other chronic medical conditions; they require bolder approaches.
What Are the Complications of Patellofemoral Arthritis?
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Infection.
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Quadriceps weakness.
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Loss of normal function.
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Femorotibial osteoarthritis (type of knee arthritis).
Conclusion
Prevention is the first line of treatment that targets maintaining and increasing quadricep muscle, hip, and core strength. Modifying the activity pattern and technique in patients developing patellofemoral pain can stall the advancement of arthritis. Keeping a watch on the body weight and weight-loss interventions can also reduce the undue load on the patellofemoral joint. Fracture boots are available to prevent the dislocation of the area.
