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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.

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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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