Background: Patellar complications following endoprosthetic reconstruction can occur as a result of anatomic, physiologic, and surgical reasons. Patellar impingement on tibial polyethylene is a complication of distal femoral replacement, and it is frequently related to inaccurate restoration of the joint line and to soft-tissue contracture. The purpose of our study was to determine the prevalence and type of patellar complications following distal femoral replacements after excisions of bone tumors.
Methods: The results of reconstruction with use of a rotating-hinge endoprosthesis following excision of a distal femoral tumor in forty-three patients were retrospectively reviewed. Patients were followed clinically and radiographically for a minimum of forty-eight months or until death. Pain status, functional scores, and the range of motion were determined from a prospectively maintained database. The ratio of the patellar tendon length to the height of the patellar tendon insertion, as described by Insall and Salvati, was calculated. In addition, we attempted to determine whether the position of the patella was associated with anterior knee pain or with the functional scores derived with use of the International Society of Limb Salvage (ISOLS) scoring system.
Results: Thirty-five patellar complications, including eleven cases of impingement, occurred in twenty-seven patients (63%). We found no difference, on the basis of our sample size, with regard to the presence of patellar pain, the range of motion, or the Insall-Salvati ratio between the patients with and those without impingement. The ratio of the patellar tendon length to the height of the patellar tendon insertion averaged 0.9 in the group with impingement and 1.4 in the group without impingement (p = 0.07). The ISOLS score averaged 21.2 points in the group with impingement compared with 24.2 points in the group without impingement (p = 0.01). Patella baja occurred in nine patients. The average ISOLS score (and standard deviation) was 20.1 +/- 4.4 points for the patients with patella baja compared with 24.8 +/- 3.9 points in the group with a normal patellar position (p = 0.004). Patellar fracture occurred in two patients, and osteonecrosis occurred in two patients. These patients were treated nonoperatively.
Conclusions: Patellar complications are common after distal femoral resection and endoprosthetic reconstruction. Patellar impingement on the polyethylene tibial bearing surface is a more common and important complication of distal femoral replacement than has been reported to date. Patella baja is also a relatively common complication, which has a negative impact on knee function.