TKA – Approach To Patellar Fracture

TKA – Approach to Patellar Fracture

Factors Associated with Patellar Fractures
1. Trauma (intuitive) 5. Vascular Compromise
2. Patellar Instability 6. Increased Flexion
3. Component Design 7. Improper Patellar Resection
4. Component Malposition 8. Revision TKA

Patellar Instability
– eccentricity and magnitude of patellofemoral loads increase with patellar subluxation, thus enhancing risk of fracture.
– instability is probably a HUGE factor

Improper Patellar Resection
– too much resection, too little resection, or asymmetric resection can all increase the change of fracture
– leaving less than 15 mm of patella after the resection significantly increases the strain in it
– taking too little also overstuffs the patellofemoral joint
– asymmetric resection basically refers to the mistake of taking too much off the lateral facet – remember, it is not a symmetric wafer that you are cutting off the patella – it should be very thin on the lateral side

Vascular Compromise
– the lateral release may sacrifice the superior lateral geniculate artery supply; the medial supply is cut when you do the medial parapatellar incision, so this lateral supply is more important
– the intraosseous supply comes from a midpatellar vessel in the middle one third, then a polar supply from the fat pad distally, and a proximal supply from the quadriceps tendon
– the clinical significance of AVN is unknown – if you see it, just leave it
Component Malposition
– elevation of the joint line causes patella baja and can increase stress on the component
– lower extremity alignment, or coverage of the patella by the prosthesis
(this may all relate to patellar instability)

Increased Flexion
– patients that can flex > 95 generate high patellofemoral compressive forces

Management

– depends on fracture pattern, location, remaining bone stock, integrity of bone-cement-component interface, and competence of extensor mechanism

If non or minimally displaced and extensor mechanism is intact – treat in a cast in extension, 6 weeks
If displaced or extensor mechanism is not intact – need to do something. Is the component stable?
– consider whether the fracture is such that you can fix it if the component is stable. Cerclage wiring or screws
– if unfixable, consider partial or complete patellectomy – may be more predictable than ORIF
– alternatively, if unfixable, consider removing the patellar component and letting the bone heal, anticipating that you might reconstruct it at a later date.