Anterior knee pain (pain
at the front of the knee) is common and can be caused by a variety
of conditions.
The patello-femoral joint refers to the part of the knee joint at
the front of the knee between the patella [knee cap] and femur [thigh
bone]. The patella is connected to the quadriceps tendon at the
top of the patella. This tendon attaches the quadriceps muscles
which are attached to the femur and pelvis above. The patellar tendon
goes from the bottom of the patella to the front of the tibia and
attaches at a point called the ‘tibial tubercle’. When
the quadriceps muscle contracts , it pulls the patella which in
turns pulls on the tibial tubercle. This causes the knee to extend
[straighten]. As the knee moves, the patella glides across the front
of the knee joint in a shallow groove (trochlear groove).
There are several types of abnormalities that may occur. The patella
may:
- dislocate (slip out of place)
- sublux (partially slip out of place)
- fracture (break)
- develop degenerate arthritis (wear)
- develop a tracking problem
A tracking problem refers to when the patella stays in place in front
of the knee but no longer remains centred in the front part of the
femur known as the trochlear groove.
When tracking problems occur, the patella develops abnormal biomechanics
that can result in increased pressure on the underside of the patella.
The pain that results from this has been given a variety of different
names and can simply be referred to as anterior knee pain. The essential
abnormality affects the joint between the patella and the trochlear
groove of the femur. Normally, the patella sits centrally in the groove.
However, if it begins to move to one side of the groove, the amount
of pressure on the under-side of the knee cap changes and this results
in the development of pain initially and, if untreated, the end result
can be osteoarthritis of the patella.
The centering of the patella in the trochlear groove is related to
the strength of the vastus medialis obliqus [VMO] muscle, and the
ligaments which pull the patella inwards, and the vastus lateralis
muscle and ligaments which pull the knee cap towards the outside [lateral]
aspect of the knee. There needs to be a balance of these forces.
In addition, the size and shape of the bones themselves play an important
role.
If any imbalance occurs the patella begins to move laterally [towards
the outside] within the trochlear groove. As it flexes, the tension
increases on the tight lateral structures. In turn, this causes pain
with bent knee activities. This results in abnormally increased contact
between the femur and the patellar articular surface which may eventually
result in arthritis. If the imbalance is overwhelming, then the patella
may actually slip out of place [dislocate].
« A side view showing the patello-femoral
joint »
After taking a full history of the problem, an examination is made
of the knee looking at the tracking of the patella, the strength of
the muscles above the knee, the tightness of the tissues around the
knee cap and areas of tenderness. Specific tests may also be used
to assess the patello-femoral joint.
It is often necessary to take x-rays of the knee sometimes using multiple
views. Finally, more sophisticated imaging including MRI or CT scan
may sometimes be required.
Non-operative treatment: The majority of pain at
the front of the knee can be resolved with non-surgical treatment.
This treatment is directed at improving the balance of the patella
at the front of the knee and normally involves physiotherapy and a
home exercise programme.
Operative treatment: In some cases, arthroscopic
surgery may be indicated. Less commonly, a bigger operation to improve
the stability of the patello-femoral joint is required.
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