Patellar Stabilization: Causes, Therapy & Surgery

What is Patellar Stabilization?

Patellar stabilization encompasses all medical interventions aimed at keeping the kneecap (patella) in its correct anatomical position and ensuring smooth, stable movement within the knee joint. Under normal circumstances, the patella glides along a cartilage-lined groove on the thighbone (femur) called the trochlea. When instability occurs, the kneecap may slip out of this groove or become chronically malaligned, leading to pain, cartilage damage, and functional impairment.

Causes of Patellar Instability

Patellar instability can result from a variety of causes:

• Traumatic dislocation: A sudden injury or movement causes the kneecap to dislocate from its groove (patellar luxation).
• Anatomical variants: A shallow trochlear groove (trochlear dysplasia), a high-riding kneecap (patella alta), or increased patellar tilt predispose individuals to instability.
• Joint laxity: General hypermobility of the joints can contribute to patellar instability.
• Muscular imbalances: Weakness of the inner thigh muscle (vastus medialis obliquus) combined with overactive lateral structures can pull the patella outward.
• Medial patellofemoral ligament (MPFL) injury: The MPFL is the primary restraint against lateral patellar displacement and is almost always torn during a first-time dislocation.

Symptoms

Patients with patellar instability commonly report the following symptoms:

• Pain at the front of the knee, especially when climbing stairs or squatting
• A feeling of instability or the kneecap slipping out of place
• Swelling of the knee joint following a dislocation episode
• Visible malalignment of the kneecap
• Limited range of motion and muscle atrophy in chronic cases

Diagnosis

The diagnosis of patellar instability is based on a combination of clinical examination and imaging studies:

• Clinical examination: The physician assesses mobility, stability, and pain points around the knee. Specific tests such as the apprehension test may be performed.
• X-ray: Used to evaluate bone structure and the position of the kneecap.
• MRI (magnetic resonance imaging): Provides detailed visualization of ligament injuries (especially the MPFL), cartilage damage, and anatomical abnormalities.
• CT (computed tomography): Used to measure the TT-TG distance (tibial tuberosity to trochlear groove distance), which is essential for surgical planning.

Treatment

Conservative Therapy

Following a first-time dislocation without significant associated injuries, a conservative approach is often attempted first:

• Physiotherapy: Targeted strengthening of the vastus medialis obliquus (VMO) and the entire quadriceps muscle group to improve dynamic patellar tracking.
• Orthoses and braces: Specialized knee braces or patellar tracking supports can help maintain kneecap alignment during daily activities.
• Taping: The McConnell taping technique can temporarily correct patellar position and reduce pain.
• Anti-inflammatory medications: Used for pain relief during acute inflammation.

Surgical Treatment

Surgery is indicated in cases of recurrent dislocations, significant anatomical abnormalities, or failure of conservative management. The following procedures may be used:

• MPFL reconstruction: The torn medial patellofemoral ligament is reconstructed using a tendon graft (most commonly the gracilis tendon). This is the most frequently performed procedure for recurrent patellar instability.
• Tibial tubercle osteotomy (TTO / TT-TG correction): The attachment point of the patellar tendon on the shinbone is surgically repositioned to optimize the pull direction of the patella.
• Trochleoplasty: In cases of severe trochlear dysplasia, the groove is surgically deepened to provide better guidance for the kneecap.
• Lateral release: Division of excessively tight lateral retinacular structures; however, this is rarely performed in isolation today.

Aftercare and Rehabilitation

After surgical patellar stabilization, a structured rehabilitation program is essential for a successful outcome. Typical aftercare includes:

• Partial weight-bearing with crutches during the first weeks
• A guided physiotherapy program to restore muscle strength, range of motion, and coordination
• Gradual return to sports activity, typically after 4 to 6 months
• Regular follow-up appointments with the treating physician

Prognosis

The prognosis following patellar stabilization is generally good when the correct procedure is selected and performed appropriately. MPFL reconstruction shows success rates exceeding 90% in clinical studies. The long-term outcome depends heavily on the choice of procedure and adherence to rehabilitation. Untreated or repeatedly dislocating patellae can lead to permanent cartilage damage and early-onset osteoarthritis of the knee joint.

References

1. Dejour, D. et al. - Patellofemoral Instability: Diagnosis and Treatment. EFORT Open Reviews, 2021.
2. Petersen, W. et al. - Guideline on Patellar Dislocation. German Society for Orthopaedics and Orthopaedic Surgery (DGOOC), 2016.
3. Amboss GmbH - Patellar Dislocation and Patellar Instability. AMBOSS Medical Knowledge, 2023.