Disorders of the patello-femoral joint, that is the articulation between the undersurface of the patella and the front of the femur (the trochlea groove), are very common.
They can be broadly divided into two groups – patella instability and pain.
This is where the patella dislocates or subluxes (partially dislocates).
In everyone the pull of the quadriceps muscles tends to pull the patella laterally.
In some patients this tendency is greater than others due to their own individual body shape and bony anatomy.
These patients are pre-disposed to subluxation or dislocation and can dislocate their patella for the first time with less severe, and for some patients, even trivial trauma.
Some patients without such a pre-disposition can sustain a more severe injury that causes the patella to dislocate.
When a patella dislocates for the first time, it causes rupture or stretching of a ligament on the inside of the knee called the medial patello-femoral ligament (MPFL). This ligament normally is the primary restraint preventing lateral dislocation of the patella.
After a dislocation this ligament remains stretched and no longer restrains the patella resulting in an increased risk of further dislocations/subluxations.
The overall risk of having further episodes of patella instability is in the order of 50%, although the individual risk varies enormously depending on the pre-disposing factors present.
The diagnosis is often clear with a history of lateral dislocation of the patella followed by marked pain and swelling.On examination there is tenderness over the stretched MPFL.
After the pain and swelling of the acute injury has settled abnormal lateral movement of the patella is often apparent and patients are often very apprehensive when the patella is moved laterally (patella apprehension).
An MRI scan can occasionally be of use to confirm the diagnosis and to identify any other injuries in the acutely painful and swollen knee following a dislocation.
All patients need a period of rest and rehabilitation following the acute injury. This should include a program of physiotherapy to regain a full range of movement and improve muscle function around the knee.
Many patients are able to prevent further episodes of subluxation or dislocation by performing exercises taught though a physiotherapy programme aimed at improving the ability of the quadriceps, in particular, the function of the VMO (vastus medialis obliquitis) muscles to prevent patella dislocation.
Unfortunately some patients continue to experience patella instability symptoms despite a properly performed exercise programme and these patients can require surgery to prevent further episodes of dislocation.
Surgery is most commonly in the form of a medial patello-femoral ligament reconstruction but can also involve realignment of the patello-femoral joint with an osteotomy of tibial tuberosity to alter the angle of pull of the quadriceps tendon and sometimes more complex operations.
Anterior Knee pain
Anterior knee pain (pain at the front of the knee) is common and can be caused by a variety of conditions including:
In addition to the acute problems of dislocation, the tendency of the patella to be pulled laterally can lead to increased pressure on the lateral aspect of the patello-femoral joint, leading to pain, muscle weakness and the development of tight tissues on the lateral aspect of the knee lateral retinaculum.
Degenerative conditions (wear and tear arthritis)
The patello-femoral joint can also develop wear and tear arthritis
Patella tendonitis (jumper’s knee). This is a degenerative process affecting the patella tendon that typically occurs where the patella tendon attaches to the patella.
Most patello-femoral problems are diagnosed clinically on the basis of the history of symptoms and the findings on examination.
X-rays and MRI scans can help to confirm the diagnosis and the severity of the condition.
Fortunately, most patients with anterior knee pain from whatever cause benefit from physiotherapy that is tailored to their precise problem.
Surgery can be indicated for patients who do not respond sufficiently to physiotherapy and they can often benefit from arthroscopic intervention.
For patients with a tight lateral retinaculum, arthroscopic lateral release, where the tight tissues are divided to reduce pressure on the patella, can be of great benefit.
Patients who develop severe arthritis affecting the patello-femoral compartment of the knee only might eventually require a patello-femoral joint replacement.