Patellar subluxation syndrome

Overview

Patellar subluxation syndrome, also referred to as patellar instability or recurrent patellar dislocation, is a condition in which the kneecap (patella) partially dislocates or slips out of its normal alignment in the trochlear groove of the femur. Unlike a complete dislocation, a subluxation means the patella moves out of place but returns either spontaneously or with minimal manipulation. This condition is commonly seen in adolescents and young adults, especially those involved in sports or activities that place stress on the knee joint. Over time, repeated episodes can damage the cartilage, increase instability, and lead to chronic knee pain and dysfunction.

Causes

Patellar subluxation syndrome occurs when the stabilizing structures around the knee are not able to keep the patella securely within the femoral groove. Several factors contribute to this condition, including:

• Congenital or anatomical factors: A shallow trochlear groove, high-riding patella (patella alta), or abnormal alignment of the lower limbs can predispose individuals to subluxation.

• Ligamentous laxity: Looseness in the ligaments, especially the medial patellofemoral ligament (MPFL), can allow the patella to move laterally more easily.

• Muscle imbalances: Weakness or imbalance in the quadriceps muscles, particularly the vastus medialis obliquus (VMO), can impair patellar tracking.

• Trauma: A direct blow or twisting injury can damage the soft tissue structures and lead to instability.

• Repetitive stress: High-impact or twisting movements, such as those in soccer, gymnastics, or basketball, can increase the risk over time.

Symptoms

The hallmark symptom of patellar subluxation syndrome is a feeling of the kneecap "slipping" or "giving way." Other associated symptoms include:

• Knee pain, especially along the front or inner side

• A popping or catching sensation during movement

• Swelling after activity or injury

• Visible or palpable movement of the patella out of place

• Weakness in the leg or difficulty with weight-bearing

• Fear or anxiety of the knee dislocating during sports or stairs

Repeated subluxation events can cause progressive damage to the joint surfaces, potentially leading to early-onset osteoarthritis.

Diagnosis

Diagnosis of patellar subluxation syndrome is based on clinical evaluation and imaging studies. The process typically includes:

• Medical history: A review of previous injuries, frequency of subluxation episodes, and activity level

• Physical examination: Assessment of patellar mobility, muscle strength, alignment, and ligament stability

• Patellar apprehension test: Gently pushing the kneecap laterally while watching for discomfort or muscle guarding, indicating instability

• X-rays: To assess bone structure, alignment, and trochlear groove shape

• MRI: Provides detailed images of the ligaments, cartilage, and other soft tissues to detect damage

• CT scan: May be used for detailed assessment of patellar tracking and rotational alignment

Treatment

Treatment for patellar subluxation syndrome can be either non-surgical or surgical, depending on the severity, frequency of dislocations, and the patient’s activity level.

Non-Surgical Management:

• Physical therapy: Strengthening the quadriceps, especially the VMO, and improving hip and core stability

• Bracing or taping: To support patellar alignment during activity

• Activity modification: Avoiding high-impact sports or movements that trigger subluxation

• Anti-inflammatory medications: To reduce pain and swelling

Surgical Management:

• MPFL reconstruction: Rebuilding the damaged medial ligament to stabilize the patella

• Tibial tubercle transfer (TTT): Repositioning the patellar tendon attachment to improve tracking

• Lateral release: Cutting tight lateral structures to reduce patellar pull

• Trochleoplasty: Deepening the trochlear groove in severe dysplasia cases

Surgery is typically considered for recurrent instability, structural deformities, or failure of conservative therapy.

Prognosis

The prognosis for individuals with patellar subluxation syndrome varies based on the underlying cause and the success of treatment. Many individuals respond well to non-surgical approaches, especially when the condition is caught early. With proper physical therapy and strengthening, it is often possible to return to sports and daily activities without recurrent instability. However, repeated subluxations can lead to long-term cartilage damage and arthritis, particularly if left untreated. Surgical outcomes are generally favorable, especially with modern techniques, although recovery may take several months. Long-term follow-up and adherence to rehabilitation protocols are essential for maintaining knee stability and preventing recurrence.