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Introduction
The patellofemoral joint (PFJ) is a unique
articulation with a complex architecture. Its
motion differs from that of most other joints in
that it is mostly comprised of sliding rather
than rolling. This places unique challenges on
the articular cartilage. The most common
disorders of the PFJ are thought to occur as a
result of alterations in the mechanics of this
joint, leading to cartilage overload or gross
instability.
Diagnosis of patellofemoral instability can be
difficult because patellar instability, patello
femoral pain, meniscal and cruciate ligament
insufficiencies can produce a similar pre
sentation of nonspecific pain and knee instability.
Thus, careful evaluation including history,
examination and imaging are helpful in making
the correct diagnosis. This chapter focuses on
the physical examination. A general approach is
taken for completeness of the examination; but
itmust be emphasized that onlydirect assessment
of patellar motion limits can document MPFL
insufficiency, which is necessary for a correct
diagnosis of patellar instability.
Clinical Evaluation
Pertinent history
The knee extensor mechanism is a complicated
and delicate system, the treatment of which is
only further complicated by surgery if the
surgeon has not clearly defined the pathological
basis of the presenting complaint. The chief
complaint should guide the workup and the
discussion of treatment options; this will help
the physician to focus on the patient’s needs
and expectations. For example, the patient who
seeks help for relief of daily pain has a very
different problem than one complaining of
occasional sharp pain and giving-way.Although
pain itself can result in knee instability (a
symptom), it is important to differentiate
painful knee giving-way from episodic pain
due to excessive patellofemoral laxity. The
latter is due specifically to insufficient constraint
of mediolateral patellar motion. Pain and
catching in early flexion points to an articular
lesion at the inferior patella or proximal
trochlea; pain throughout the range indicates a
more diffuse, perhaps extra-articular process.
The Clinical Examination
in Patellar Instability
D.C. Fithian