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Evidence of Trochlear Dysplasia in Patellofemoral Arthroplasty Designs
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implant by design rather than by “generation”:
(
i
) “trochlear cutting” PFA, which require
complete removal of the native trochlea, and
(
ii
) “trochlear resurfacing” PFA, where the
implant replaces the worn cartilage without
altering the shape of the native trochlea.
Trochlear cutting implants permit the surgeon
to alter the position of the trochlear groove and
thereby correct the TT-TG alignment. Trochlear
resurfacing implants do not permit such
realignment unless the operative technique
involves distal realignment like a TTosteotomy.
Dejour and Allain [27] demonstrated that
implant survival was higher for trochlear
cutting imlplants and trochlear resurfacing
implants combined with distal realignment,
compared to trochlear resurfacing implants
without distal realignment.
The strengths of this study were that it featured
five designs that are in clinical use, and that the
measurement techniques were consistent and
reproducible. In addition, the “scale factor”
was minimized by studying specimens from
the middle of the size range and by referring to
a non-dimensional variable of sulcus angle.
The main weaknesses of the study were the
consideration of the trochlear component and
not the patellar component, and the focus on
static design features rather than dynamic
implant performance.
Conclusion
The current study presented a quantitative
comparison of crucial design parameters of
contemporary PFA implants and revealed that
some
trochlear
components
exhibit
characteristics of dysplasia. Such components
suppress essential anatomic for normal
patellofemoral tracking. We therefore advise
surgeons to use implants with a deep trochlear
sulcus (“trochlear-cutting”) particularly in
patients with history of patellofemoral
disorders, and to adapt their surgical techniques
and extensor mechanism if the selected implant
has a shallow trochlear sulcus (“trochlear-
resurfacing”).
Abstract
Purpose:
The design of the trochlear compartment is
crucial in patellofemoral arthroplasty (PFA), because
78% of patients with isolated patellofemoral arthritis
present concomitant trochlear dysplasia with patellar
mal-tracking, and therefore remain predisposed to
post-operative patellar subluxation and dislocation.
The study investigated whether current PFA implants
are designed with anatomic trochlear parameters
such as the sulcus angle, lateral facet height and
groove orientation.
Methods:
Fivetrochlearcomponentsofcommercially
available PFA implants were scanned and the
generated 3D surfaces were measured using
engineering design software. The mediolateral
trochlear profiles were plotted at various flexion
angles (0°, 15°, 30° and 45°) to deduce the following
variables: sulcus angle, height of lateral facet and
trochlear groove orientation.
Results:
Four specimens had sulcus angle greater
than 144° in the 45° of flexion, and all five specimens
had sulcus angle greater than 143° in 30° of flexion.
Three specimens had a facet less than 5mm high
through the entire range of early flexion (0° to 30°),
and two specimens had a facet less than 5mm high
beyond early flexion (30° to 45°). The trochlear
groove was oriented laterally in all specimens (range
1.6º to 13.5º).
Conclusions:
Current PFA trochlear components are
not always designed with anatomic parameters and
some models exhibit characteristics of trochlear
dysplasia. Surgeons are therefore advised to implant
components with a deep sulcus, particularly in
patients with history of patellofemoral disorders, and
to adapt the surgical technique and extensor
mechanism if the component implanted has a shallow
sulcus, to ensure normal patellar tracking.