Patella Alta - High Riding Patella

What is Patella Alta?

This is the condition where a person is born with a kneecap (patella) positioned higher in the front of the knee than the average.  They are very often good athletes and seem to do well in high jump, triple jump and basket ball. The problem with patella alta is that the knee cap is very mobile from side to side and is predisposed to dislocation during sporting activities. Once the patella has dislocated several times it is called recurrent dislocation and can be a major nuisance to the sporting individual causing them to give up all sporting activities. It has been the end of many basket-ball and football players' careers, in whom the condition is common.  In some people the dislocation is incomplete and then it is called subluxation of the patella. 

In extreme cases the patient may be able to dislocate the patella at will and they sometimes do it as a party trick. This is called habitual dislocation.  As its name suggests it can become a habit.  It is not clever because it still creates minor damage and will result in osteoarthritis in the longer term. 

Both dislocation and subluxation are extremely painful and both result in damage to the hyaline cartilage under the patella and to the groove in which the patella runs (the trochlear groove of the femur) which after a time causes osteoarthritis of the patellofemoral joint with severe pain and weakness of the muscles.

How is Patella alta diagnosed?

Clinically the high riding patella is often noticed as a 'nobbly knee'. With the patient lying down and the knee bent to 90 degrees the patella tends to be on the top of the knee and slightly on one side. The pain is often felt at the tip of the patella.

Typical picture of 'Nobbly' Knees with pain at the tip of the patella.

What do the X-rays look like?

This is a measurement of the amount of overlap between the joint surfaces of the patella and the trochlear groove. In this case there is no overlap at all. The joint surface of the patella is far above the joint surface of the trochlear groove. This patella is very unstable and can dislocate at any time (habitual dislocation). There are other measurements to gauge the severity of the high riding patella and actually make an estimate of where the patella should be.

What does the MRI scan look like?

See the picture below. In the 'sagittal' (side view) images of the knee joint the patella is not only high riding, but also there is damage to the undersurface of the patella. Also you will notice that the patella tendon is lax indicating that if the quadriceps muscles were working properly the tendon would be tightened and the patella would move upwards a bit.

Notice also the irregularity on of the undersurface of the patella. It should be covered with hyaline cartilage and this should be smooth and regular in appearance on MRI. In this case the cartilage covering is beginning to degenerate and fragment. This condition is called "chondromalacia" which means softening of the cartilage. It is painful and is the first sign of damage to the joint surface. If the process continues it will result in bone articulating on bone with serious osteoarthritis which may require joint replacement. 

 

What can be done to correct the high riding patella?

First of all the patella and the patellofemoral joint should be inspected by arthroscopy. 

The damage to the hyaline cartilage of the patella is clearly seen at arthroscopy.

 Under the same anaesthetic a three inch incision is made on the outer side of the patellar tendon with the tibial tubercle about halfway down the incision

The following is a set of diagrams to show an operation which I pioneered in 1993 and which has become increasingly popular with patients who have patellar instability.

1. A drill-hole is made into the tibial tubercle.

2. A piece of bone is removed from the tibia - exactly the  length of the planned transfer.

3. The remaining tibial tubercle is moved into the space and held in the new position by a single screw.

4. A drill hole is made through the tibia to take a wire which holds the screw head and bone fragment firmly in place.

5. Finally the wire is tightened and secured.

 This is a post-operative Xray of a patient's knee 3 months after the procedure.

Post-op recovery and rehab

Patients are kept in hospital overnight after the surgery, and are normally ready for discharge home the morning after the operation.

You will be given crutches to use and a knee brace to wear. The hinge mechanism of the strap on knee brace is specifically to prevent you from bending your knee too much whilst the bone from the tibial tuberosity osteotomy is healing up. Initially, the brace is usually locked at 0 to 20 degrees flexion, but the range of flexion is often increased as the knee starts to heal. Most people are ready to get rid of the knee brace and the crutches by 6 weeks post-op.

From 6 weeks post-op onwards, you will need to start regular intensive physiotherapy treatments (ideally 2 or 3 sessions a week to start with), to help you regain the movement, strength and then reflexes in your knee. By 3 months post-op most patients' knees are sufficiently healed for them to be able to start impact-type exercise, starting with lunges then building up to gentle jogging, and then slowly getting back to full exercise/sport whenever your physiotherapist feels that your neuromuscular control and strength is good enough. It can, however, take people anything up to 6 months to fully get over this kind of surgery.


Article written by
Mr Angus Strover
Consultant Knee Surgeon , London
Last updated 6/05/12 by Mr Ian McDermott


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