How should chronic bilateral patellar dislocation be evaluated and managed?

Chronic Bilateral Patellar Dislocation: Evaluation and Management

For chronic bilateral patellar dislocation, begin with standing AP and lateral knee radiographs plus axial patellofemoral views to assess patellar tilt, subluxation, and component alignment, followed by CT to evaluate tibial tuberosity-trochlear groove (TT-TG) distance and trochlear dysplasia severity, then proceed with medial patellofemoral ligament (MPFL) reconstruction as the primary surgical intervention when conservative management fails.

Initial Imaging Evaluation

Radiographic assessment forms the foundation of evaluation:

• Obtain standing anteroposterior (AP) and lateral knee radiographs plus tangential axial views of the patellofemoral joint bilaterally 1
• Axial radiographs specifically demonstrate the degree of patellar tilt or subluxation 1
• Weight-bearing axial radiographs better assess patellofemoral kinematics in chronic cases 1
• Standing long-leg (hip-to-ankle) views provide optimal assessment of lower limb mechanical axis alignment when malalignment is suspected 1

Advanced imaging is essential for surgical planning:

• CT is the primary modality for measuring TT-TG distance (surgical threshold >20 mm) and assessing trochlear dysplasia severity 2, 3
• MRI identifies MPFL tears and associated osteochondral injuries 3
• Combined CT and MRI provide superior diagnostic accuracy compared to either modality alone—in first-time dislocations, combined imaging identified surgical indications in 21 of 26 patients versus 13 with MRI alone 3
• CT with metal artifact reduction techniques can detect patellar complications when prior arthroplasty is present 1

Anatomic Risk Factor Assessment

Identify specific predisposing factors that guide surgical decision-making:

• Trochlear dysplasia: Dejour classification D represents severe dysplasia requiring trochleoplasty consideration 4, 2
• TT-TG distance: Measure on CT; >20 mm indicates need for tibial tubercle osteotomy 4, 2
• Patella alta: Increases instability risk and may require tibial tubercle distalization 4
• Femoral and tibial component malrotation: Excessive combined internal rotation directly correlates with patellofemoral complications severity 1
• Familial predisposition: Bilateral recurrent dislocation in multiple family members suggests genetic inheritance of trochlear dysplasia 5

Management Algorithm

Conservative Management (Initial Approach for Non-Surgical Candidates)

Physical therapy should target both hip and knee strengthening:

• Initiate knee-targeted exercise therapy as the primary intervention 1
• Add hip-and-knee targeted exercise therapy for patients with poor tolerance to loaded knee flexion 1
• Modify task/load/intensity/frequency based on tissue irritability 1
• Education must underpin all interventions to challenge inaccurate beliefs, manage load, and reduce fear 1

Prefabricated foot orthoses provide short-term benefit:

• Prescribe for patients who respond favorably to treatment direction tests 1
• Customize for comfort by modifying density and geometry 1

Surgical Management (Primary Treatment for Recurrent Dislocation)

MPFL reconstruction is the primary surgical intervention:

• Isolated MPFL reconstruction is effective for patients without anatomic high-risk factors (TT-TG ≤20 mm, no severe trochlear dysplasia) 4, 2
• At 3-year follow-up, MPFL reconstruction reduced persistent instability to 16.7% versus 53.6% with rehabilitation alone (OR 5.8,95% CI 1.7-19.4) 2
• Use allograft tissue for reconstruction in chronic cases with severe osteoarthritis requiring concurrent total knee arthroplasty 6

Tibial tubercle osteotomy addresses bony malalignment:

• Indicated when TT-TG distance >20 mm or patella alta is present 4
• Realigns the extensor mechanism to prevent recurrent dislocation 4
• Can be combined with MPFL reconstruction for comprehensive correction 4

Trochleoplasty for severe trochlear dysplasia:

• Consider for patients with Dejour type D trochlear dysplasia 4
• Alternative to tibial tubercle osteotomy in dysplasia cases 4

Extensive lateral release with MPFL reconstruction for chronic fixed dislocation:

• Required for long-standing cases (>20 years) with fixed lateral displacement 7
• Combines soft tissue balancing with ligamentous reconstruction 7

Special Considerations

Post-total knee arthroplasty patellar dislocation:

• Patellofemoral instability occurs in 1% to 12% of TKA cases, most commonly from internal malrotation of femoral/tibial components 1
• CT is the primary modality for measuring component rotation and planning revision 1
• Novel techniques include vastus lateralis anchor repositioning to convert lateral force into medial stabilization 8
• Combined MPFL reconstruction with patellar resurfacing addresses both instability and arthritis 6

Bilateral simultaneous treatment:

• Limited evidence supports simultaneous bilateral procedures in patients <70 years with ASA status 1-2 1
• Consider staged procedures for older patients or those with multiple comorbidities 1

Critical Pitfalls to Avoid

• Do not rely on radiographs alone—CT and MRI provide essential information for surgical planning that radiographs cannot detect 3
• Do not perform isolated MPFL reconstruction when TT-TG >20 mm—this requires concurrent tibial tubercle osteotomy 4, 2
• Do not overlook component malrotation in post-TKA cases—the amount of excessive combined internal rotation directly correlates with complication severity 1
• Do not assume symmetry—bilateral cases may have different anatomic risk factors requiring individualized surgical approaches for each knee 5