243 / 460
K.F. Almqvist, A.A.M. Dhollander, P. Verdonk, J. Victor
242
is compromised by its function as a weight
bearing joint. With abnormal use or increasing
age, the involved joint will present the common
anatomical changes of osteoarthritis. In postural
primary osteoarthritis the joint is subjected to
increased loading due to static abnormalities
with degenerative changes as a result, e.g. in the
knee due to trochleodysplasia or patella alta.
In secondary osteoarthritis the joint tissues are
abnormal at the onset of the disease. This
condition can occur when the articular cartilage
has previously been affected by transient but
recurrent inflammation of the synovial mem
brane as seen in haemochromatosis, in chondro
calcinosis or in burned-out rheumatoid arthritis.
Inherited disorders of articular cartilage collagen
molecules and metabolic disorders such as
ochronosis, acromegaly and chondrocalcinosis
can also be the underlying cause of this subgroup
of osteoarthritis. Furthermore, secondary osteo
arthritis will be present in joints in which the
subchondral bone has previously been affected
e.g. after intra-articular fractures or chondral
trauma. Secondary osteoarthritis has a higher
incidence in patients who also present primary
osteoarthritis.
Trauma to a joint with articular incongruity and
recurrent instability will also generate
osteoarthritic changes. The development of
clinical and radiological osteoarthritis in these
weight bearing joints is more frequent in people
with generalized osteoarthritis than in those
without.
Genetic, metabolic and endocrine (primary)
factors will alter the physical properties of
articular cartilage determining who will be a
candidate for developing osteoarthritis, whereas
trauma or increased stress determine when and
where osteoarthritis will occur.
Since the progression of the disease is slow, the
symptoms occur at an advanced age, at variable
intervals after the initiating event. The
degenerative changes are more related to
impact loading than to frictional wear.
Defining and diagnosis of early knee
OA
[14]
Usually the diagnosis of knee OA can be made
by history and physical examination including
signs/symptoms of knee pain with joint
stiffness, joint crepitus and functional limita
tions of the knee, typically in a population
above 45-50 years old. Diagnosis is confirmed
by conventional radiographs demonstrating
changes such as joint space narrowing, osteo
phytes, subchondral bone sclerosis and cysts.
The radiograps are graded according to
Kellgren (II-IV) or in the patellofemoral joint
graded according to Iwano. Early OA of the
knee is somewhat more complicated as the
patient show limited and sporadic signs/
symptoms, only becoming manifest under
certain conditions such as after long term
loading (jogging or other sports activities…).
This early form of knee OA is thought to be a
process that displays a number of tissue related
phenomena leading to the loss of homeostasis
of the knee, and in most cases leading to
established OA. It is the clinical recurrence of
pain and discomfort of the knee, short periods
of stiffness, with in between long periods of
very little clinical manifestations eg. slight
swelling of the joint, probably due to sponta
neous adaption of the patient, that sets the
clinician to perform additional investigations
(radiographs, ultrasound, MR or arthroscopy).
In these cases the history and the clinical
examination often suggest a local problem of
mechanical nature. Classical radiographs in
general are quite disappointing in this sense
that, certainly if no earlier X-rays are available
as in most cases, very few specific signals are
seen. Some joint space narrowing in one
compartment, some hints for the formation of
what may probably become an osteophyte, and
thus typically at best qualified by a Kellgren I
or Iwano I, could be seen. It reveals very little
of potentially many more tissue processes in
the joint. In addition, the robustness of this last
scoring categories is however difficult, and
studies reveal the quite poor intra- and inter
reader reproducibility of this scoring system.