Patellofemoral osteoarthritis

What is Patellofemoral Osteoarthritis?

Patellofemoral osteoarthritis (PFA) is a wear and tear of the cartilage behind the kneecap and on the anterior joint of the thigh. It can occur in isolation or be part of generalized knee osteoarthritis. Stress-related pain in the front of the knee is characteristic, often accompanied by rubbing noises (crepitations) and temporary swelling.

In contrast to “classic” gonarthrosis of the inner or outer compartment, PFA is particularly evident during activities with high flexion and pressure on the kneecap - such as walking down stairs, downhill, while squatting or getting up from a sitting position.

Anatomy and biomechanics of the patellar joint

The patella sits in a guide (trochlea femoris) of the femur. When it bends, it slides in this plain bearing. The quadriceps and patellar tendons transmit forces that, depending on the flexion angle, can lead to high contact pressures - especially between 60° and 90° of knee flexion.

• Patella: Sesamoid bone, increases the lever arm of the quadriceps
• Trochlea: bony guide rail with medial and lateral facets
• Soft tissues: retinacula, MPFL (medial patellofemoral ligament), capsule
• Muscles: Quadriceps (especially vastus medialis), hip abductors/external rotators

Disturbances in guidance (maltracking) - for example due to shape variations (trochlear dysplasia, patella alta), muscular imbalances or axial deviations - increase local pressure peaks and promote cartilage wear.

Typical symptoms

• Anterior knee pain, load-dependent
• Increased pain when walking down stairs, downhill, while squatting
• Start-up pain after sitting (“cinema sign”)
• Rubbing noise or feeling behind the kneecap
• Occasional swelling/effusion with a feeling of tension
• Feeling of “folding away” without real instability
• Rare: feeling of blockage with accompanying problems (e.g. loose joint bodies)

The intensity fluctuates: phases of less pain often alternate with states of irritation. Cold temperatures, sitting for long periods of time with a bent knee and deep bending angles can cause discomfort.

Causes and risk factors

• Maltracking/malalignment: increased lateral pressure load, increased Q angle
• Shape variants: trochlear dysplasia, patella alta, lateral patellar tilt
• Muscular imbalance: weak vastus medialis, weak hip abductors/external rotators
• Previous injuries: patellar luxation, fractures, ligament injuries
• Overload: frequent kneeling/squatting, jumping sports, rapid increase in load
• Obesity: increased stress on joints
• Biological factors: female gender, connective tissue laxity
• Accompanying factors: foot pronation, knock knees (valgus), rotation tendencies of the leg axis

Often several factors come together. For therapy, it is crucial to record and specifically address mechanical influencing factors (guidance, axis, muscles).

Differentiation from other causes of anterior knee pain

• Chondropathia patellae (softer cartilage, often younger, stress-dependent pain)
• Plica mediopatellaris syndrome (incarceration of a fold of mucous membrane)
• Synovitis/irritable effusion after overload
• Osteochondrosis dissecans (circumscribed bony-cartilaginous lesion, usually younger)
• Hoffa fat body impingement
• Patella tendinopathy/quadriceps tendon irritation (insertion problems)
• Meniscal pathology and gonarthrosis of other compartments

A precise clinical examination with imaging diagnostics helps to classify the cause and identify overlaps.

Diagnostics: clinical and imaging

At the beginning there is anamnesis and functional examination: pressure pain behind/around the patella, crepitus, tracking assessment, patellar sliding test, apprehension test, J-Sign, inspection of the leg and foot axis, muscle function and coordination.

• X-ray: a. p., lateral and tangential patellar images (e.g. Merchant/Skyline) to assess the patellofemoral joint space, osteophytes, patellar height and tilt
• MRI: assessment of cartilage, subchondral bone (bone marrow lesions), retinacula, MPFL, accompanying pathologies
• Sonography: Assessment of effusions and tendon structures (supplementary)

Radiologically, patellofemoral arthrosis is often classified according to Ivano (stages I–IV). The findings are always compared with your symptoms and functional status - the extent in the image does not alone explain the severity of the pain.

Conservative therapy – the central building block

Most patients benefit from structured, multi-stage conservative treatment. The aim is to reduce pain and irritation, improve joint guidance and control stress in everyday life and sports.

Important: Exercise is more effective than rest. The pain threshold serves as a control: slight discomfort (e.g. up to 3/10) during/24 hours after the exercise is tolerable, persistent pain peaks are a signal for adaptation.

Movement and exercises – what helps the kneecap joint?

• Straight leg extension isometric with slight flexion (20–30°)
• Mini squats, wall slides or sit-to-stands with a narrow stance
• Flat step-ups/step-downs, focus on axis control (no valgus)
• Hip abduction with mini band, clamshells, side forearm support
• Bicycle ergometer: low to moderate intensity, high saddle, smooth cadence

Deep lunges, jumps and bends over 90° should be avoided or carefully dosed during stimulation phases. Technique correction (knee over foot, pelvic stability) is central.

When does an operation make sense?

Surgical options are only considered if structured conservative therapy has been exhausted over several months and a relevant functional limitation still exists - and the cause can be clearly assigned.

• Arthroscopic measures: diagnostics, targeted debridement for mechanical irritations; with generalized wear and tear, the benefit is limited.
• Cartilage reconstruction (e.g. microfracture, AMIC, ACI): only for circumscribed retropatellar defects and intact framework conditions; often in combination with correction of the patellar guidance.
• Soft tissue and realignment procedures: lateral release/retinaculum detachment in cases of proven lateral overload; Anteromedialization of the tibial tuberosity (Fulkerson tibialization) to relieve pressure on the lateral facet cartilage.
• Patellofemoral partial prosthesis: option for advanced isolated PFA without significant osteoarthritis of the remaining compartments; Careful indication, later conversion to total endoprosthesis possible.
• Total knee endoprosthesis (TEP): for multi-compartment osteoarthritis.

Rehabilitation and results depend heavily on the method chosen, accompanying factors (axis/guidance problems) and consistent follow-up treatment. There can be no guaranteed result; The aim is a noticeable improvement in functionality with realistic expectations.

Your treatment in Hamburg-Winterhude

In our orthopedic practice at Dorotheenstrasse 48, 22301 Hamburg, we rely on clear diagnostics, understandable information and a conservative therapy concept as standard. We take your sporting and professional requirements into account and work closely with physiotherapy partners.

• Structured findings including functional and axial analysis
• Imaging as required (X-ray, MRI request)
• Individual exercise and activity program with monitoring
• Bandage/tape advice, shoe and insoles recommendations
• Injection procedure with clear indication and information
• Surgical advice if conservative measures are not sufficient

Everyday tips and prevention

• Stairs: shorter steps, use handrails, do not “fall” into a deep squat
• Workplace: pad kneeling activities and plan breaks
• Sport: Cycling, walking, aqua jogging are usually well tolerated; Dose jumping and contact sports
• Saddle high, cadence 80-90/min, light to moderate load
• Keep an eye on your weight and strengthen your hips and thighs regularly
• Warm up before exercise, increasing in small steps

Course and prognosis

The process is individual. Many people achieve significant relief from symptoms and better resilience with consistent conservative therapy. Recurring states of irritation are possible and can usually be easily controlled with adjustments to training and everyday life. Early, cause-oriented treatment improves the chances of stabilization.

When should you seek medical advice?

• Severe, persistent pain or significant swelling/warmth
• Feeling of blocking, repeated buckling with risk of falling
• Fever, redness, general feeling of illness
• After recent trauma with inability to bear weight
• Complaints > 6 weeks despite protection and personal measures