Recurrent Instability of the Patella (RIP) Score

RIP Score Calculator

Age at First Dislocation

Bilateral Patellar Instability

Trochlear Dysplasia

TT-TG Distance >20 mm

Patellar Height Ratio >1.2

RIP Score: –

Score: 0

Default scoring assumes 0 for un-set fields.

Predicts risk of recurrent instability after primary patellar dislocation.

Why Use

Can be used to educate patients and parents on the risk of future patellar dislocations after the first episode. Aid in discussion during informed consent for operative and nonoperative management of first-time patellar dislocators. Can be an objective factor in deciding between operative and nonoperative management of a first-time patellar dislocation.

When to Use

Patients with a first-time patellar dislocation (adults and adolescents).

Formula

Addition of the selected points: Variable Points Age <25 years 2 Skeletal immaturity (open distal femoral and proximal tibial physes on plain radiographs) 1 Dejour A-D dysplasia (on plain radiographs and T2-weighted MRI) 1 TT-TG/PL ≥0.5 (on T2-weighted MRI) 1

Pearls / Pitfalls

Does not take into account uncommon risk factors such as excessive femoral internal rotation, excessive valgus limb alignment, or generalized patholaxity (e.g. as in Ehlers-Danlos syndrome). Not applicable for obligate flexion dislocation. Chondral or osteochondral fractures are managed differently. Relevant to most presentations of first-time patellar dislocations. Includes physeal status (physeal closure may be imminent). Does not take into account the site of the medial patellar restraint tear (femoral tears have a higher rate of recurrent patellar instability).

Management

Physical examination and imaging findings should be included to allow a rational final course of action.

Critical Actions

Assess for other factors that can influence the decision between operative and nonoperative management.

Advice

Exam: in addition to standard knee examination plus patellar tracking, “J” and evidence of obligatory dislocation (flexion dislocators are appropriate for RIP scoring), assess internal rotation of the hip/femur in prone position. If >45 degrees, obtain rotational imaging study; assess laxity with Beighton scoring, and if elevated obtain a specific diagnosis, e.g. Ehlers-Danlos type. Radiographs: in addition to assigning Dejour trochlear type, Caton Deschamps patellar height ratio, and tilt, assess mechanical axis for evidence of excessive limb valgus. MRI: Assess TT-PCL in addition to TT-TG and patellar height; assess for chondral and osteochondral fracture and loose bodies (medial patella and lateral aspect lateral femoral condyle).

More Information

Interpretation: RIP Score Risk group Risk of recurrent instability At 1 year At 2 years At 5 years At 10 years 0-1 Low 0% 0% 0% 0% 2-3 Intermediate 16.7% 27.8% 30.6% 30.6% 4-5 High 15.6% 37.5% 65.6% 79.2% Note: recurrent instability paradoxically decreases slightly at one year for high vs intermediate risk. This is a limitation of the data from Hevesi 2019 .