Retropatellar Arthrosis: Causes, Symptoms and Treatment

What is Retropatellar Arthrosis?

Retropatellar arthrosis (also known as patellofemoral osteoarthritis) is a degenerative joint disease affecting the cartilage on the back surface of the kneecap (patella) and the opposing surface of the thighbone (femur). Unlike general knee osteoarthritis, this condition specifically targets the patellofemoral joint – the joint formed between the kneecap and the femur. As the protective cartilage gradually wears away, patients experience pain, swelling, and reduced mobility in the knee.

Causes

The development of retropatellar arthrosis is typically multifactorial, involving a combination of mechanical and biological influences:

• Overuse and improper loading: Long-term high-impact sports, repeated kneeling, squatting, or occupational knee strain can lead to progressive cartilage damage.
• Excess body weight: Increased body mass significantly raises the pressure exerted on the patellofemoral joint during everyday activities.
• Malalignment: Conditions such as a laterally displaced kneecap (patella lateralis), a high-riding kneecap (patella alta), or knock-knee deformity lead to uneven cartilage wear.
• Previous injuries: Past kneecap dislocations, fractures, or cartilage lesions can initiate the degenerative process.
• Genetic predisposition: A family history of osteoarthritis increases personal risk.
• Age-related changes: With advancing age, cartilage loses its elasticity and capacity for self-repair.

Symptoms

The symptoms of retropatellar arthrosis are characteristic and can often be distinguished from other knee conditions:

• Pain behind or around the kneecap, particularly during stair climbing, walking downhill, deep squatting, or prolonged sitting with bent knees (known as the cinema sign or theatre sign).
• Start-up pain: Discomfort at the beginning of movement that tends to ease after a few steps.
• Swelling and a sensation of warmth around the kneecap.
• Grinding or crunching sensations (crepitus) during knee movement.
• Feeling of instability or knee giving way under load.
• Morning stiffness or stiffness after prolonged rest.

Diagnosis

Diagnosis is typically made by an orthopaedic specialist or sports medicine physician and includes the following steps:

• Medical history: Assessment of symptoms, previous injuries, occupation, and physical activity.
• Physical examination: Evaluation of kneecap mobility, palpation for tenderness, gait analysis, and assessment of alignment.
• X-ray imaging: Reveals joint space narrowing and bony changes such as osteophytes. An axial (sunrise) view of the patella is particularly informative.
• MRI (Magnetic Resonance Imaging): Provides detailed assessment of cartilage thickness, ligament integrity, and soft tissue changes.
• Ultrasound: Helpful for detecting joint effusions and soft tissue abnormalities.

Treatment

Treatment of retropatellar arthrosis depends on the severity of the condition and aims to relieve pain, maintain function, and slow disease progression.

Conservative Treatment

• Physiotherapy: Targeted strengthening of the vastus medialis obliquus (VMO) muscle to improve kneecap tracking and joint stability.
• Weight management: Reducing excess body weight to decrease joint load.
• Orthotic supports: Knee braces or patellar taping to stabilize kneecap alignment.
• Pain relief medication: Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or diclofenac for short-term pain control.
• Injection therapy: Corticosteroid or hyaluronic acid injections into the joint to reduce inflammation and pain.
• Cold and heat therapy: Supportive measures for symptom relief.
• Activity modification: Avoiding high-load squats and kneecap-stressing sports; switching to low-impact activities such as swimming or cycling.

Surgical Treatment

When conservative measures are insufficient and arthrosis is severe, surgical options may be considered:

• Arthroscopy: Minimally invasive joint lavage and smoothing of damaged cartilage surfaces.
• Corrective osteotomy: Surgical realignment of bone in cases of underlying malalignment.
• Cartilage repair procedures: Such as microfracture or autologous chondrocyte implantation for localised cartilage defects.
• Partial joint replacement: In end-stage disease, replacement of the patellofemoral joint with a partial prosthesis (patellofemoral arthroplasty).

Prognosis and Course

Retropatellar arthrosis is a chronic, progressive condition that tends to worsen over time. However, with early and consistent treatment, disease progression can be significantly slowed and quality of life substantially improved. Regular medical follow-up and a joint-friendly lifestyle play a key role in long-term outcomes.

References

1. Crossley KM, Stefanik JJ, Selfe J, et al. 2016 Patellofemoral pain consensus statement from the 4th International Patellofemoral Pain Research Retreat. British Journal of Sports Medicine. 2016;50(14):839-843.
2. Hinman RS, Crossley KM. Patellofemoral joint osteoarthritis: an important subgroup of knee osteoarthritis. Rheumatology. 2007;46(7):1057-1062.
3. World Health Organization (WHO): Musculoskeletal conditions. Fact Sheet. Geneva: WHO, 2021. Available at: https://www.who.int/news-room/fact-sheets/detail/musculoskeletal-conditions