PERI-OPERATIVE PATELLAR FRACTURES: NO EASY OUT

Patella fracture after total knee arthroplasty has a variety of etiologies and has been reported to occur with an incidence ranging from 3% to 21%. Heavy patients with full flexion are at greatest risk for sustaining patella fracture. Overstuffing the patellofemoral joint with an oversized femoral component, an anteriorised femoral component or a femoral component placed in excessive extension can also overload the underlying patella. A similar phenomenon may be seen with underrsection of the patella or use of a thick button. Excessive patellar resection can predispose to patellar fracture as well. It has been demonstrated that a residual patella thickness of less than 15 mm can substantially increase anterior patellar strain. Asymmetric patellar resection can also critically alter the mechanical strength of the patella making it vulnerable to failure. Elevation of the tibiofemoral joint line, from excessive femoral resection and hastened by posterior cruciate ligament release, will result in a relative patella baja. This can cause early patellofemoral articulation, which may result in patellar impingement on the tibial insert in late flexion and ultimately predispose the patella to fracture. Surgical approach and soft tissue dissection should be as atraumatic to the patellar blood supply as possible to preserve the superolateral geniculate artery when performing a lateral retinacular release. The classification used by Goldberg, et al is helpful for planning appropriate intervention: Type I fractures: Avulsion type fractures generally involving the periphery of the patella without involving the implant. Type II fractures: Disrupt the cement-prosthesis interfaces of the quadriceps mechanism. Type IIIA fractures: Involve the pole of the patella with disruption of the patella ligament. Type IV fractures: Fracture dislocations of the patella. Non-operative treatment is preferred when fractures are non-displaced.