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Introduction
In 1958, McKeever introduced patellar
resurfacing implants [1-4], and in 1979, Blazina
[5] and Lubinus [6] developed patellofemoral
arthroplasty (PFA) as a less invasive alternative
to total knee arthroplasty (TKA) for the
treatment of isolated patellofemoral arthritis.
Early PFA models produced poor clinical
outcomes, due to improper patient selection,
imprecise surgical technique, and flawed
“trochlear resurfacing” designs that replaced
the degenerative cartilage without correcting
the underlying osseous deformities [7-11].
Later PFA models produced improved clinical
outcomes, attributed to better patient selection,
accurate surgical instrumentation, and enhanced
‘trochlear cutting’ designs that replaced the
subchondral bone and corrected the depth and
orientation of the trochlear groove [8-10, 12,
13, 11].
Both TKA and PFA are used to treat late
isolated patellofemoral arthritis, and there
remains considerable controversy as to which
option is most suitable [8]. Failures of PFA
implants are associated with two types of post-
operative complications: (
i
) late complications
due to the spread of arthritis to the tibiofemoral
joint [11, 12, 8, 10, 14, 15], and (
ii
) early
complications due to patellar mal-tracking,
including painful instability, subluxation or
dislocation [12, 8, 10, 14, 15]. Beyond the
contributions of surgical technique, mal-
tracking complications could also be related to
implant design parameters. In particular, the
authors question whether trochlear components
of contemporary PFA implants exhibit
geometric characteristics that would be
consistent with the radiographic definition of
dysplasia of the anatomic trochlea.
The standard method to assess the trochlea in
patients is to measure the sulcus angle in
“skyline” radiographs: with the knees in 45º of
flexion as described by Merchant [18, 19] or
with the knees in 30º of flexion as described by
Brattström [20]. In healthy knees the mean
sulcus angle is 138º in the “Merchant view”
[18, 19, 21] or 142º in the ‘Brattström view’
[20], whereas in knees with trochlear dysplasia
the sulcus angle exceeds 144º in the “Merchant
view” [22] or 143º in the “Brattström view”
[23]. Furthermore, the height of the lateral
trochlear facet in healthy knees was reported in
the radiographic study of Brattström [20] to be
between 4.2 and 6.5mm (at 30º of flexion) and
in the cadaver study of Shih
et al.
[24] to be 6.6
± 1.8mm (at 0º of flexion). A recent study by
Dejour
et al.
[25] revealed that some TKA
designs exhibit characteristics of trochlear
dysplasia and that in many models the sulcus
angle exceeded those radiographic indicators
of dysplasia by over 10º. Since many PFA
Evidence of Trochlear
Dysplasia in Patellofemoral
Arthroplasty Designs
M. Saffarini, P.G. Ntagiopoulos,
G. Demey, B. Le Negaret, D. Dejour