Trochlear Dysplasia: Causes, Symptoms & Treatment
Trochlear dysplasia is a congenital malformation of the trochlear groove of the femur, leading to patellar instability, knee pain, and an increased risk of kneecap dislocation.
Things worth knowing about "Trochlear dysplasia"
Trochlear dysplasia is a congenital malformation of the trochlear groove of the femur, leading to patellar instability, knee pain, and an increased risk of kneecap dislocation.
What is Trochlear Dysplasia?
Trochlear dysplasia is a congenital or developmental abnormality of the femoral trochlea – the groove at the lower end of the thighbone (femur) in which the kneecap (patella) glides during flexion and extension of the knee. In trochlear dysplasia, this groove is abnormally shallow, flat, asymmetric, or even convex (bulging outward), preventing the patella from tracking properly. It is recognized as one of the most common anatomical causes of patellofemoral instability.
Causes and Development
The exact cause of trochlear dysplasia is not fully understood. Both genetic predisposition and biomechanical influences during skeletal growth are believed to contribute. Reduced mechanical loading of the trochlea during childhood – for example due to an altered patellar pull direction – may result in inadequate formation of the trochlear groove.
Dejour Classification
The most widely used classification system was developed by French orthopaedic surgeon Henri Dejour and describes four grades of severity:
- Type A: Shallow trochlea with a preserved sulcus; mild dysplasia
- Type B: Flat or convex trochlea with a supratrochlear spur
- Type C: Asymmetric trochlea with a hypoplastic medial facet
- Type D: Severely asymmetric trochlea with a vertical cliff between the facets (cliff sign)
Types A and B are considered low-grade dysplasia, while Types C and D represent high-grade dysplasia.
Symptoms
Patients with trochlear dysplasia commonly experience:
- Pain at the front of the knee (anterior knee pain syndrome), particularly when climbing stairs, squatting, or sitting for extended periods
- A feeling of instability or the knee "giving way"
- Patellar dislocation: the kneecap fully slips out of the groove
- Patellar subluxation: partial displacement of the kneecap
- Swelling of the knee joint following dislocation episodes
Diagnosis
Diagnosis is based on a combination of clinical examination and imaging studies.
Clinical Examination
The physician assesses knee range of motion, patellar stability (e.g., using the apprehension test), lower limb alignment, and muscle strength.
Imaging
- X-ray in strict lateral view: Identification of the crossing sign, supratrochlear spur, or double contour sign
- MRI (Magnetic Resonance Imaging): Detailed assessment of cartilage structures and the degree of dysplasia
- CT (Computed Tomography): Measurement of the TT-TG distance (tibial tuberosity to trochlear groove), which quantifies the lateral displacement of the patella
Treatment
Conservative Treatment
For milder forms of trochlear dysplasia or first-time dislocations, conservative management is usually recommended:
- Physiotherapy to strengthen the knee-stabilizing muscles, especially the vastus medialis obliquus
- Patellar taping or bracing to improve kneecap tracking
- Pain management with anti-inflammatory medications (e.g., NSAIDs)
Surgical Treatment
Surgery is considered for high-grade dysplasia, recurrent dislocations, or failure of conservative treatment:
- Trochleoplasty: Surgical deepening and reshaping of the trochlear groove; addresses the underlying anatomical cause directly
- MPFL reconstruction (medial patellofemoral ligament): Reconstruction of the medial restraint of the patella
- Tibial tubercle osteotomy (e.g., medialization or anteromedial transfer): Repositioning of the patellar tendon attachment to improve patellar tracking
- Combined procedures when multiple risk factors are present
Prognosis
The prognosis depends on the severity of the dysplasia and the chosen treatment. With appropriate management and surgical correction where necessary, most patients can achieve significant symptom relief and stable knee function. If left untreated, trochlear dysplasia may lead to progressive cartilage damage and early-onset patellofemoral osteoarthritis.
References
- Dejour H, Walch G, Nove-Josserand L, Guier C. - Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26.
- Lustig S, Servien E, Neyret P. - Trochlear dysplasia and patellar instability. In: Scott WN (ed.) Insall & Scott Surgery of the Knee. 5th ed. Churchill Livingstone, 2012.
- Nelitz M. - Trochleoplasty in trochlear dysplasia. Der Orthopäde. 2018;47(1):36-43.
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