Patellar Fracture Type and Prognosis in Condylar Total Knee Arthroplasty

Abstract

Fractures of the patella occurred following implantation of 36 condylar total knee arthroplasties in 35 patients. The end results were evaluated in relation to fracture type after an average 4.5-year follow-up period. The follow-up observations included a physical examination, quantitative knee score, and roentgenographic evaluations of extremity alignment and implant position. Twenty-two of the 36 knees had a good or excellent knee score and 14 had a fair or worse score at the time of the latest follow-up evaluation. The satisfactory knees had an average arc of motion of 100°, while the unsatisfactory knees had an average arc of motion of 80°. Fourteen fractures through the mid-body or superior pole of the patella not involving the implant, cement, or quadriceps mechanism (Type I) and two nondisplaced fractures through the inferior pole of the patella (Type IIIB) were managed nonoperatively, with all knees rating either a good or excellent score. Fractures of the patella disrupting the quadriceps mechanism or implant/bone/cement composite (Type II) were managed operatively in the six knees. Fractures of the inferior pole of the patella with disruption of the patellar ligament (Type IIIA) were managed operatively in seven of eight knees (one patient refused surgery). Lateral fracture-dislocations were managed operatively in all six knees. Six of the knees operated upon had a good or better score, and nine knees were rated as poor or failed. Those fractures in which major deviations from neutral extremity alignment and implant position were seen had the more severe patellar fracturqs and the poorest outcomes. The degree of patellar resection, patellar coverage by the resection, patellar coverage by the patellar component, or component thickness had no statistically significant bearing on the fracture site or type. The overall results indicate that fractures not associated with dislocation of the patella, implant loosening, or complete extensor mechanism disruption usually recover function with non-surgical management. Knees with implant loosening, patellar dislocation, or complete quadriceps disruption require operative intervention. The end results may be improved by returning the knee to neutral alignment and position.