Trochleoplasty: Indications, Diagnosis, and Patient Selection

What are the indications for trochleoplasty?

Trochleoplasty is a specialized surgical procedure primarily indicated for individuals experiencing recurrent patellar instability due, in large part, to significant trochlear dysplasia, a malformation of the femoral trochlear groove.

Introduction to Trochleoplasty and Patellar Instability

The knee joint, specifically the patellofemoral articulation, relies on precise alignment and stability for efficient movement. The patella (kneecap) tracks within a groove on the distal femur called the trochlear groove. This groove, along with surrounding ligaments and muscles, guides the patella during knee flexion and extension, preventing it from displacing.

Patellar instability occurs when the kneecap repeatedly dislocates or subluxes (partially dislocates) from this groove. While various factors can contribute to instability, including ligamentous laxity, muscle imbalance, or an increased Q-angle, a significant anatomical contributor is often trochlear dysplasia. When conservative treatments fail, and anatomical abnormalities are severe, surgical intervention becomes necessary. Trochleoplasty is one such advanced surgical option.

Understanding Trochlear Dysplasia

Trochlear dysplasia refers to an abnormal shape or shallowness of the femoral trochlear groove. Instead of a well-defined, concave groove that cradles the patella, the trochlea may be flat, convex, or have a prominent anterior spur. This structural anomaly significantly reduces the bony constraint on the patella, making it prone to lateral displacement, especially during activities that load the knee.

The severity of trochlear dysplasia is often classified using the Dejour classification system (Type A, B, C, D), based on specific features identified on imaging (primarily lateral knee X-rays and MRI scans). Higher grades of dysplasia (e.g., Types B, C, D) are strongly correlated with recurrent patellar dislocations and are key indicators for trochleoplasty.

Primary Indications for Trochleoplasty

Trochleoplasty is not a first-line treatment for all cases of patellar instability. It is a technically demanding procedure with specific indications, generally reserved for patients with severe underlying anatomical deficiencies. The primary indications include:

• Recurrent Patellar Dislocations or Subluxations: This is the most common and critical indication. Patients must have a history of multiple symptomatic episodes where the patella has either completely dislocated or partially shifted out of its groove, causing pain, giving way, or functional limitation.
• High-Grade Trochlear Dysplasia: As assessed by imaging (MRI and CT scans), significant morphological abnormalities of the trochlea are a prerequisite. This typically corresponds to Dejour Type B, C, or D dysplasia, where the groove is either flat, convex, or has a prominent spur that actively pushes the patella laterally.
• Failure of Conservative Treatment: Prior to considering surgery, patients should have undergone a supervised course of conservative management, including physical therapy focusing on quadriceps strengthening (especially vastus medialis obliquus), core stability, and proprioceptive training, often coupled with bracing. Trochleoplasty is considered when these measures fail to stabilize the patella and alleviate symptoms.
• Persistent Symptoms Despite Other Surgical Interventions: In some cases, patients may have undergone isolated soft tissue procedures, such as medial patellofemoral ligament (MPFL) reconstruction, but continue to experience instability due to an unaddressed severe bony trochlear deformity. In these scenarios, trochleoplasty may be indicated as a revision procedure or as a primary procedure combined with MPFL reconstruction.
• Significant Apprehension and Functional Limitation: Beyond objective instability, patients who experience severe apprehension (fear of dislocation) during daily activities, exercise, or sports, leading to significant functional limitations and impact on quality of life, may be candidates, provided the underlying anatomical conditions are met.
• Specific Anatomical Considerations:
  • Elevated Tibial Tubercle-Trochlear Groove (TT-TG) Distance: While a high TT-TG distance (indicating lateralization of the patellar tendon insertion) often warrants a tibial tubercle osteotomy, severe trochlear dysplasia can exacerbate this maltracking, making trochleoplasty a necessary complementary procedure.
  • Patella Alta with Dysplasia: An abnormally high-riding patella combined with trochlear dysplasia further reduces bony engagement, increasing instability risk. Trochleoplasty can improve patellar engagement in such cases.

Diagnostic Considerations

A thorough diagnostic workup is crucial to determine candidacy for trochleoplasty:

• Clinical Examination: Assessment of patellar tracking, apprehension, range of motion, and identification of any generalized ligamentous laxity.
• Imaging Studies:
  • X-rays: Standing AP, lateral, and Merchant (patellar skyline) views to assess patellar position, joint space, and initial signs of trochlear morphology.
  • MRI (Magnetic Resonance Imaging): The gold standard for evaluating trochlear morphology, cartilage status, and soft tissue structures like the MPFL. It provides detailed visualization of the trochlear groove's depth and shape.
  • CT Scan (Computed Tomography): Often used to precisely measure bony anatomy, including the TT-TG distance and rotational deformities, which may influence surgical planning.

Surgical Considerations and Patient Selection

The decision to perform trochleoplasty is complex and multifaceted. It involves careful consideration of the patient's age, activity level, overall knee health (e.g., presence of arthritis), and the specific type and severity of trochlear dysplasia. The goal is to create a more stable, functional patellofemoral joint while minimizing the risk of complications, such as patellofemoral arthritis, which can occur if the trochlear groove is over-deepened.

Conclusion

Trochleoplasty is a powerful tool in the surgical management of severe patellar instability, particularly when caused by significant trochlear dysplasia. It aims to restore the anatomical constraint of the trochlear groove, thereby preventing recurrent dislocations and improving the quality of life for affected individuals. However, due to its complexity and potential risks, it is reserved for carefully selected patients who meet stringent diagnostic and clinical criteria after conservative measures have proven ineffective.