Title: Transverse Periprosthetic Patellar Fracture following (Cementless) Total Knee Arthroplasty

Author(s): Andrew Metz, DO; Andrew Cramer, DO; Jack Gordon, MS

Email: AMetz1@mercy.com

Introduction: Although one of the more serious and rare complications following total knee arthroplasty (TKA), periprosthetic patella fractures are one of the least studied to provide sufficient guidelines on operative fixation for adequate patient outcomes. This case report explains a case following a cementless TKA where the patient sustained a transverse periprosthetic patella fracture and his subsequent surgical fixation plus post operative progression.

Case Report(s): A 70-year-old male, underwent a Mako robotic assisted right total knee arthroplasty for end stage degenerative joint disease. He is a truck driver and a smoker that had a history of multiple knee corticosteroid injections with no relief prior to surgery. He exercises on average 2 times a week. His pre-operative range of motion was flexion from 5-120 degrees. His patella tracked midline and his knee was stable on varus/valgus. Surgery involved a medial parapatellar approach and normal placement of cementless press fit femoral, tibial and patellar components.  Seven weeks post op the patient reported a loud pop and immediate pain in his knee during physical therapy while doing a deep squat. He presented to the clinic where he stated he had some pain and stiffness but was otherwise doing well. His incision was clean and intact with no signs of dehiscence or drainage. He could straight leg raise with about a 10 degree lag indicating the extensor mechanism was not intact. He was able to actively flex the knee to 95 degrees.  Repeat radiographs were then obtained (3) which are below, demonstrating a transverse mid patellar fracture with the patellar component still attached to the distal fragment and full distraction of both halves of the patella. This would classify this periprosthetic patellar fracture as a type II on the Ortiguera and Berry classification system. Following the clinical visit it was decided with the patient to perform Open Reduction Internal Fixation of this patellar fracture the next week. The same incision form the previous surgery was used. We contemplated removing the patellar component, but it was well fixed in the distal fragment of the fracture. We were able to provide near anatomical reduction of the patellar fracture. At that point two K wires were passed through the patella, proximal to distal, avoiding the patellar component pegs. Using fluoroscopy in the lateral position we were able to verify that the wires were in a good position. We then used a drill for our screw tunnels which was passed over the K wires. Two cannulated screws were then passed over the K wires. Fiber Wire tape suture was then passed through the cannulated screws and tied together in a figure 8 fashion providing good reduction and intraoperative support to this patellar fracture.  The small third fragment identified intraoperatively Was then sutured back into its native position using 0 vicryl suture through bone tunnels and attached back to the main patella.

Discussion: Following surgical intervention with the above-described technique the patient has followed up multiple times with imaging and evaluation occurring. Since surgery patient has maintained and intact extensor mechanism possible indicating successful repair technique. Although not described before the above technique may be studied in the future for successful periprosthetic patellar repair given the lack of literature on the subject with proven methods