Lower Limb: Knee & Patellar dislocations

Question 1

describe how knee dislocations can occur

Answer 1

with high energy injuries or with severe hyperextension and/or rotational forces with a sporting injury
(uncommon)

Question 2

why is a knee dislocation considered a medical emergency

Answer 2

due to high incidence of vascular injury, nerve injury and compartment syndrome

Question 3

describe how obvious knee dislocations should be treated

Answer 3

urgently with thorough neurovascular assessment and vascular surgery referral with further investigation and revascularisation as required

Question 4

what further investigations may be needed for knee dislocations

Answer 4

doppler, duplex scan, or angiogram

Question 5

why is multi-ligament reconstruction often required for knee dislocations

Answer 5

because in order for the knee to dislocate multiple ligaments are torn

Question 6

what should you be suspicious of in knee injuries with grossinstability

Answer 6

be aware it could have been a momentary true knee dislocation with spontaneous reduction, so check neurovascular status

Question 7

describe the mechanisms that leads to virtually all lateral patellar dislocations

Answer 7

either a direct blow (eg clash of knees), or contraction of the quadriceps with a rotational force when patella not engaged in trochlea

Question 8

describe the reduction of the patella after dislocation

Answer 8

may remain dislocated requiring manipulation to reduce, but more commonly spontaneously reduce when knee is straightened

Question 9

what groups of people are patellar dislocations more common in

Answer 9

adolescents, particularly females

Question 10

what are patellar dislocations predisposed by

Answer 10

generalised ligamentous laxity, valgus alignment of the knee, rotational malalignment, a shallow trochlear groove

Question 11

what clinical features are seen with a patellar dislocation

Answer 11

tenderness of medial retinaculum(medial patellofemoral ligament torn) and may have haemarthrosis

Question 12

what type of fracture can occur in association with a patellar dislocation

Answer 12

osteochondral fracture with sheared off/detached fragments

Question 13

describe the recurrence rate of patellar dislocations

Answer 13

around 10% first time patients will experience a 2nd patellar dislocation, and 50% of those will have multiple recurrent dislocations

Question 14

what treatment is the mainstay for recurrent patellar dislocation

Answer 14

temporary splintage followed by physiotherapy, and many adolescents stabilise with age