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.
Level of Evidence: Prognostic Level IV. See Instructions
to Authors for a complete description of levels of evidence.