Patellar Instability Clint R Beicker MD June 5, 2015 Please note change from program

Objectives Review the anatomy and biomechanics of the MPFL and structures that provide patellofemoral stability Discuss the management of the first-time patellar dislocation Review surgical treatment of recurrent patellar instability and expected rehabilitation and return to activity

Incidence of primary patellar dislocation is 5.8 cases / 100,000 population 43 cases / 100,000 population in children Peak incidence at age 15 Highest risk of acute dislocation (and recurrence) is females age Acute patellofemoral dislocation is most common acute knee disorder in children and adolescents 2 nd most common cause of hemarthrosis in adolescent knee Redislocation rates range from % A common problem

Osseous component Trochlear morphology Bony Alignment Dynamic component Extensor Mechanism function Static/Ligamentous component MPFL Medial Patellofemoral Ligament Patellar stability

MPFL Anatomy Runs in layer 2 on the medial aspect of knee Origin: 1.9 mm anterior / 3.8 mm distal to adductor tubercle Insertion: superior 2/3rds of patella – Broad insertion over 28 mm over superior patella Average length 59.8 mm

Primary restraint to patellofemoral instability at 0-30 degrees of flexion Provides over 50% of medial restraint to patella Tensile strength = 208 N Tear occurs at femur (66%), patella (13%) and midsubstance (21%) Once patella is engaged in the trochlear groove, lateral patellar facet provides primary resistance force Medial patellofemoral ligament (MPFL )

Exam Assess overall limb alignment Assess generalized ligamentous laxity Tenderness patella, along MPFL, at femur Crepitance Effusion Patellar Glide test Patellar apprehension sign Patella tilt J sign Evaluation

J Sign

Evaluation Radiographs AP, lateral, Merchant views Fractures Trochlear dysplasia Crossing sign Dejour classification Patellar height Caton-Deschamps Blackburne-Peel Insall-Salvati Patellar tilt Patellar position/subluxation

Evaluation Radiographs AP, lateral, Merchant views Fractures

Evaluation Radiographs: AP, lateral, Merchant views Trochlear dysplasia Crossing sign

Evaluation Trochlear dysplasia

Evaluation Radiographs: AP, lateral, Merchant views

CT/MRI TT-TG (anterior tibial tubercle – trochlear groove) distance Originally via CT Can do via MRI underestimates TT-TG by 3-4 mm) Value >20 mm is strong predictor of instability

Advanced Imaging Evaluation When to get an MRI Large knee effusion Recurrent dislocation Fracture on xray Clinical concern -*Up to 95% incidence of cartilage lesions on MRI *Nomura et al – Arthroscopy – 2003

All Patellar Dislocations are not the same because the underlying anatomy is not the same

Management of the 1 st time dislocator

Nonoperative treatment for first time dislocation (222 pts) 62 % successs rate overall (38% redislocation) The worst combination: 31 % success if open physis and trochlear dysplasia 51% of patients with recurrence required surgery Can We Predict Recurrence?

Have we improved our outcomes? Hawkins et al – 1986 – AJSM 27 patients with acute dislocations treated either operatively with MPFL +LR (7 pts) or non-operatively (20 pts) “Although the incidence of recurrence among those individuals can be decreased [with surgery], at least 30% to 50% of all patients having sustained a primary patellar dislocation will continue to have symptoms of instability and/or anterior knee pain.”

2,000 patients in meta-analysis Conclusion: Operative treatment after 1 st patellar dislocation results in lower recurrence (29% vs 34%) but does not affect functional outcome score

Not all patellar dislocations are the same

Non-operative management Immobilization Closed chain exercises – -quad (VMO) strengthening -gluteal strengthening -core strengthening Patellar taping

Patellar stabilization surgery Nearly 30 different surgical procedure exist…

Post-operative Rehab

Thank You