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Recurrent patella dislocation has many underlying causes – a number are purely caused by an initial traumatic incident – but many have other factors. In particular – issues that change the direction of forces pulling on the patella such as knock-knees, tibial tubercle laterally positioned, and in-toeing gait are all factors.  Lax ligaments and a high sitting kneecap (patella alta) are other factors.

In-toe gait & femoral version
Some people naturally walk pigeon-toed, with the foot slight pointing inwards when it is flat on the ground. If they try to walk “normally” a variety of muscles are recruited to help – in doing so, the muscles that tend to pull the kneecap out of its groove work harder, and the muscles keeping it in the groove become wasted. So the scene is set for one day the kneecap to pop out.  Once it has started popping out – it keeps doing so.  The underlying problem starts with the femur being at the extreme of the normal range.  The rotation between the hip and the knee is usually 10 degrees “anteverted” – if instead the femur has 35 degrees of anteversion – 25 degrees more than usual, this person will have an in-toe gait, and also risk patella dislocation.

Femoral version & childhood
The shape of the femur changes through childhood – the majority start off with a high amount of anteversion, and it gradually reduces.  By skeletal maturity – approximately 12-14 years of age in girls and 14-16 in boys – the shape is set.
DJM. V1.0 14/8/2016

Subtrochanteric Osteotomy & Fixion Expandable Nail
To be able to rotate the bone – the operation needs to cut the bone about 8cm below the tip, and the bone then needs to be held in the derotated position.  It is possible to do this through an incision 2cm in the buttock, use a special saw within the bone, and then insert a rod through that site.  To ensure it won’t rotate back to the old position – it needs to be locked in position – either with screws drilled through the nail, or in this case – the Fixion nail can be inflated, expanding it so the ribbed surfaces get a grip on the bone.

Risks of this surgery

  • Additional surgery may be required at the knee to correct damage at that level.
  • The nail might need removal.
  • The bone could fail to heal and additional surgery would be required.
  • Infections can occur but the likelihood is less than 1%.

Mr David Mitchell