Q&A Discussion on Patellar Instability

Q1: What is patellar instability, and how is it diagnosed?

**A1:** Patellar instability refers to episodes where the patella (kneecap) either partially or fully dislocates from its normal position. It typically results from injury, ligament laxity, or an increased Q angle in the knee. Diagnosis varies depending on the timing of the condition. In acute cases, patellar dislocation is associated with a traumatic knee effusion. In chronic cases, it’s identified by passive patellar translation and a positive "J sign" during examination.

Q2: What demographic is most affected by patellar instability?

**A2:** Patellar instability most commonly affects individuals in their 2nd or 3rd decade of life. Women are more prone to chronic patellar subluxation due to associated malalignment.

Q3: What are the risk factors for patellar instability?

**A3:** Risk factors include ligamentous laxity (such as in Ehlers-Danlos syndrome), a history of prior patellar dislocation, and a condition called “miserable malalignment syndrome,” characterized by femoral anteversion, genu valgum, and external tibial torsion. Anatomical abnormalities like patella alta and trochlear dysplasia also contribute to instability.

Q4: Can you describe the common causes or mechanisms leading to patellar instability?

**A4:** Patellar instability usually occurs from a non-contact twisting injury where the knee is extended, and the foot is externally rotated. As a result, patients often reflexively contract their quadriceps, which can cause the patella to reduce itself. Direct trauma, such as a knee collision during sports, can also result in dislocation, though it is less common.

Q5: What structures provide stability to the patella?

**A5:** The patella is stabilized by both passive and dynamic structures. Passive stability is mainly provided by the medial patellofemoral ligament (MPFL), especially in the first 20-30 degrees of knee flexion. Bony structures, including the trochlear groove and patellar height, contribute to deeper knee flexion stability. Dynamic stability is ensured by the vastus medialis muscle, which attaches to the MPFL.

Q6: Howe is patellar instability classified?

**A6:** Patellar instability can be classified into three categories:

- **Acute traumatic instability:** Often results from direct trauma and affects both genders equally.

- **Chronic patholaxity:** Characterized by recurrent subluxation episodes, it’s more common in women and linked with malalignment.

- **Habitual instability:** Typically painless and associated with each flexion movement, it is often due to tight iliotibial bands or vastus lateralis muscle overpull.

Q7: What symptoms and physical examination findings are typical in patellar instability?

**A7:** Patients typically report feelings of instability and anterior knee pain. In acute cases, there may be a large hemarthrosis (swelling due to blood in the joint). Medial tenderness, increased passive patellar translation, and apprehension during lateral translation are also key findings. Chronic cases often show an increased Q angle and the presence of the "J sign."

Q8: What imaging studies are used to evaluate patellar instability?

**A8:** Radiographs are essential to rule out fractures or loose bodies. Specific signs on radiographs like the crossing sign, double contour sign, and sulcus angle help assess trochlear dysplasia. CT scans measure the TT-TG distance, which, if greater than 20mm, indicates abnormality. MRI is helpful in identifying osteochondral lesions, bone bruising, and MPFL tears.

Q9: What are the non-operative treatment options for patellar instability?

**A9:** Non-operative treatment is the first line of management for a first-time dislocation, focusing on NSAIDs, activity modification, physical therapy, and short-term immobilization. Strengthening exercises for the quadriceps, core, and hips, along with the use of patellar stabilizing braces, are also recommended.

Q10: When is surgical intervention indicated for patellar instability?

**A10:** Surgery is considered in cases of recurrent instability or when there is evidence of intraarticular damage like loose bodies. Procedures include arthroscopic debridement, MPFL reconstruction, and tibial tubercle osteotomy, depending on the patient’s condition and anatomical factors.

Q11: What complications can arise from patellar instability?

**A11:** The most common complication is recurrent dislocation, especially in younger patients. Other potential issues include medial patellar dislocation or patellofemoral arthritis, often as a result of previous surgical interventions aimed at stabilizing the patella.

Reference 

https://www.orthobullets.com/knee-and-sports/3020/patellar-instability