We thank Dr. Grelsamer for his interest in our study and for the
opportunity to discuss the custom approach to patellofemoral arthroplasty in
more detail. Dr. Grelsamer correctly observes that our published series does
not include patients with a flat or convex femoral trochlea. While we agree
that the treatment of patients with isolated patellofemoral arthritis and
concomitant severe trochlear dysplasia can be a challenge, we believe that a
custom approach to patellofemoral arthroplasty is a reasonable treatment
option for this indication.
The posterior (bone-contact) surface of the custom patellofemoral implant
is designed to replicate the native surface and is defined by a preoperative
computed tomography scan. In contrast, the prosthetic femoral trochlea is
designed to conform to the articular radius of the mating patellar implant and
is thickened laterally and medially along its borders to compensate for any
lack of native medial-lateral stability. The thickness of the custom implant
along the patellar tracking arc is designed to reestablish the anterior
position of the femur.
Stability of the implant construct and extensor mechanism is fundamental to
the successful outcome of any patellofemoral arthroplasty, including the
custom approach. The presence of trochlear dysplasia, as Dr. Grelsamer points
out, further underscores the importance of achieving a stable and balanced
extensor mechanism intraoperatively. A convex trochlea may increase the
tendency to overstuff the patellofemoral joint, and this possibility must be
addressed during the design of the custom implant and during the implantation
procedure.
Finally, we agree with Dr. Grelsamer that patellofemoral arthroplasty is
indicated in elderly patients with isolated patellofemoral arthritis whose
medial-lateral compartments would not be expected to become symptomatic during
their lifetime. The purpose of our study, though, was to report on the use of
custom patellofemoral arthroplasty in a younger population.