patella-instability copy

Patellar Instability Overview

  • Definition: Patellar instability refers to conditions involving patellar dislocation, subluxation, and general symptomatic instability.

  • Prevalence: Affects between 7 to 49 individuals per 100,000, accounting for 11% of musculoskeletal issues and 16-25% of injuries in runners, with a higher incidence in females.

Anatomy and Biomechanics

  • Functional Anatomy: Understanding the structure and mechanics of the patellofemoral joint is essential.

  • Patellar Engagement: In full extension, the patella does not engage the trochlear groove. Pivots centrally in flexion, engaging at about 90 degrees.

  • Stabilization Mechanisms: The quadriceps acts as a dynamic stabilizer, while the medial patellofemoral ligament (MPFL) provides static support against lateral translation.

  • Contact Dynamics: As flexion increases, the patella contacts the trochlea differently, allowing deeper engagement and articulation with femoral condyles.

Classification of Patellar Instability

  • Types of Instability:

    • Congenital

    • Traumatic

    • Habitual

    • Obligatory

    • Subluxation and dislocation

  • Functional Classification: Developed by Dejour et al., assessing symptoms and joint alignment.

Etiology of Patellar Instability

  • Contributing Factors:

    • Structural and functional imbalances

    • Patella alta and trochlear dysplasia reducing patella containment.

    • Improper alignment leads to lateral dislocation or subluxation during flexion.

Clinical Presentation

  • Symptoms: Patients report anterior knee pain, episodes of knee giving way, and discomfort during activities.

  • History Assessment: Determine onset relating to trauma and prior treatments.

Physical Examination

  • Examination Techniques:

    • Assess patellar engagement with knee flexed.

    • Ligamentous examination to rule out ACL or MCL injuries.

  • Stability Assessment: Lateral movement of the patella can indicate instability. Use of specific tests like the patellar grind test.

  • Q Angle Measurement: Evaluates knee alignment contributing to instability, with normative values differing between sexes (8-10º males; 15-20º females).

Imaging Techniques

  • Radiographs: Limited utility; useful for assessing patellar height and osteochondral damage.

  • CT Scans: Measures patellar tilt and tibial tubercle-trochlear groove distance, crucial for assessing lateral patellar instability.

  • MRI: Identifies ruptures and associated injuries; can visualize bone bruises from dislocation events.

Management Approaches

Nonoperative Management

  • Rehabilitation Goals: Effective management includes strengthening and stretching without inducing pain.

  • Interventions:

    • Quadriceps strengthening, core stability exercises, patient education on activity modifications.

    • Use of braces, taping, orthotics for exaggerated foot movement, and analgesics.

Operative Management

Indications for Surgery

  • When to Operate: Recommended when nonoperative treatment fails, based on clinical evaluation and patient history.

Surgical Techniques

  • Proximal Realignment: Adjusts tension by repairing or reconstructing the MPFL.

    • Considerations include assessing ligament damage and potential lateral release.

  • Distal Realignment: Tibial tubercle transfer to correct knee mechanics involved in tracking.

  • Postoperative Care: Use of hinged braces and progressive rehabilitation typically sees patients back to activity within three months.

Specific Procedures

  • Medial Patellofemoral Ligament (MPFL) Repair: Techniques involve repairing torn ligaments using sutures or grafts based on the level of damage.

  • Tibial Tubercle Transfer: Adjusts patellar tracking by transferring tuberosity.

  • Trochleoplasty: Rarely used, as long-term outcomes are uncertain; aims to rectify trochlear dysplasia effects.

Conclusion

  • Effective treatment of patellar instability utilizes a combination of surgical and non-surgical techniques tailored to the patient's symptoms, anatomical findings, and functional needs. Future research should evaluate the long-term efficacy of various surgical interventions for patellar stability.