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Does patellofemoral osteoarthritis may be idiopathic?
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Obesity (BMI greater than 30) has been found
to predispose a person to patellofemoral
arthritis [3, 11].
Diagnosis of isolated
Patello Femoral
osteoarthritis
Pain is the primary symtom but can be
particularlychallengingtolinktopatellofemoral
joint because a large number of conditions can
refer pain to the anterior aspect of the knee, and
can even be referred from elsewhere in the
knee [7] or from distant sites such as hip or
spine [9, 13].
A patient with isolated patellofemoral arthritis
typically describes anterior knee pain when
rising from a seated position and/or going
dowstairs or upstairs, standing on one leg with
the knee semi-flexed, running with short steps,
squatting down [5, 9]. Sometimes, there may
be pseudolocking due to “kissing” lesions, or
even true locking from osteophytes [5].
Clinical presentation is somewhat non specific:
crepitus on grinding the patella or during knee
movement and effusion are common [8, 12].
Akey sign of symptomatic patellofemoral arthri
tis on the physical examination is tenderness of
the lateral (or occasionally medial) facet of the
patella [9].
Abnormal patellar tracking and patella tilt can
be signs of instability. Abnormal torsional signs
of the lower limb can explain malalignment.
A complete examination is mandatory,
including hip and spine.
A routine series of radiographs is necessary,
including standing anteroposterior, 45° postero
anterior flexion weightbearing, lateral and
skyline view (Merchant view) radiographs [2].
Narrowing of the patellofemoral joint space on
the 45° skyline view is the most informative
radiograph to classify the site and stage of
arthritis, and to identify possible osteophytes,
cysts or erosions (saw tooth arthritis [1]).
When maltracking is suspected, a CT scan can
be usefull.
MRI doesn’t bring specific informations for
patellofemoral arthritis.
Discussion
The first step in diagnosing patellofemoral
arthritis is to affirm that anterior knee pain is
related to patellofemoral joint. Neither
symptoms nore clinical examination findings
are specific, and, on the other hand, quite
specific signs are sometimes painless (eg
crepitation). Although, pain arising from the
medial compartment may be confused with
patellofemoral arthritis [7].
The second step, relating pain to patellofemoral
joint damage, is not that easy because pain
sometimes exists without any cartilage lesions,
probably due to dysfunctions of the extensor
mechanism, mostly treated by physiotherapy
[4, 13].
Nevertheless, limited lesions of the articular
cartilage are difficult to diagnose and injected
CT scan can be usefull. But direct relation
between cartilage lesion and pain is not so
clear: arthroscopic findings show often patellar
or trochlear chondral lesions without any
patellofemoral complaint [4].
When painfull patellofemoral osteoarthritis is
clinically diagnosed, radiographic findings are
necessary to stage the degree of arthritis, its
site, and also to eliminate arthritis of another
compartment. Routine radiographs are mostly
sufficiant, especially lateral [2] view and 45°
skyline view.
Once the isolated character of patellofemoral
arthritis is done, its etiology must be under
standable, because it can help its prevention, or
the type of treatment.