Patellar InstabilityClint 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 10-17• Acute patellofemoral dislocation is

most common acute knee disorder in children and adolescents

• 2nd most common cause of hemarthrosis in adolescent knee

• Redislocation rates range from 20-55 %

A common problem

• Osseous component• Trochlear morphology• Bony Alignment

• Dynamic component• Extensor Mechanism function

• Static/Ligamentous component

• MPFL Medial Patellofemoral Ligament

Patellar stability

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

EvaluationRadiographs• 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

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 1st 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 1st 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