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Introduction
Isolated patellofemoral arthritis can be
successfully treated with patellofemoral arthro
plasty (PFA). The outcome is determined by
the prosthesis design, surgical technique and
patient selection.
Historically, poor patient selection was thought
to be the main cause of unsatisfactory outcomes
following PFA. Whilst this most certainly was
partly to blame, prosthetic design and failure to
restore or correct patellofemoral biomechanics
may have played a more significant role in the
high revision rates. Biomechanical analysis of
the older inlay designs and an appreciation for
the causes and effects of malpositioning and
misalignment have aided the development of
contemporary second and third generation
PFAs. These newer onlay designs, coupled
with improved surgical instrumentation, have
shown better clinical outcomes, with the
majority of failures relating to the progression
of tibiofemoral arthritis rather than surgical
complications. Greater understanding of the
variations in pattern of progression of the
underlying pathologies, such as trochlear dys
plasia and idiopathic patellofemoral arthritis,
has resulted in surgeons adoptingmore stringent
selection criteria. This, coupled with apprecia
tion of biomechanical abnormalities requiring
surgical correction, has also contributed to
lower failure rates.
The aim of this article is to highlight the design
issues of previous patellofemoral arthroplasties
and how the problems encountered with these
implants have influenced the development of
newer second and third generation prostheses.
The ideal design features that are required to
provide improved clinical outcomes based on
biomechanical and material theory as well as
patient selection will also be discussed.
Past Patellofemoral
Prosthesis Design Issues
In the past, the most frequent complaints
following patellofemoral arthroplasty were of
patellar instability manifesting as snapping,
clunking or subluxation and anterior knee pain
[1-4]. These symptoms, most commonly asso
ciated with the older first-generation patello
femoral arthroplasties, were almost certainly
related to the flawed designs of their trochlear
components.
The critical features of trochlear component
geometry are the degree of constraint, the
dimensions of both medial-lateral width and
proximal extension of the anterior flange, and
the sagittal radius of curvature.
The Richards (or Blazina) I and II (Smith &
Nephew Richards Inc., Memphis, Tennessee)
The Principles of an Ideal
Patellofemoral
Arthroplasty
M. Odumenya, S.J. Krikler, A.A. Amis