Some knee dislocations are rare, obvious and extremely serious. Others are far less serious but far more common.
Dislocation of the kneecap
The commonest knee dislocation involves your kneecap (patella). The kneecap sits in a groove and, as the knee bends, the patella travels along this groove. But an injury – often a sporting one – can cause the kneecap to pop out of the groove. This form of dislocation is very easy to confuse with another sports knee injury: an ACL rupture.
The confusion is easy to explain. Both tend to be caused by a force to the knee that pushes it inwards, with internal rotation of the femur and external rotation of the tibia. Both will result in immediate swelling and pain. Within a day or two even a clinical examination, although valuable, can struggle to tell the two injuries apart.
A first-time kneecap dislocation will often settle down after a few weeks and can be remedied completely with a six week to six month course of physiotherapy. Yet it’s important to have the injury properly assessed in the acute knee clinic, where an MRI scan can help resolve the question of patella dislocation or ACL tear.
Some dislocated patellae will require arthroscopic (keyhole) surgery and that’s particularly likely in those patients where an initial dislocation leads to recurring instability, when the kneecap develops a habit of popping out of its groove. These patients may require a patella stabilisation operation known as an MPFL. That’s particularly likely if you’re young and female. Youth brings with it an increased risk of hypermobility or hyperlaxity (being ‘double jointed’). Being female makes you more likely to be ‘knock-kneed’ (males tend towards being bowlegged), increasing the risk of a dislocated kneecap.
A patellar dislocation can sometimes occur with a fracture of either the femur or the patella. This fracture dislocation is more serious and you’ll need urgent surgery within two weeks. Again, the key to a faster and more successful recovery is to seek a swift diagnosis after injury.
There is another type of knee dislocation. This one won’t leave you wondering whether to seek medical help or whether you should leave it to ‘see how things settle’. This will be an immediate ambulance trip to A&E.
A tibiofemoral dislocation, as the name suggests is a dislocation of the tibia and femur. It’s a rare, high energy injury – most commonly seen in road traffic accidents but we do see it in rugby players too – and it is limb-threateningly serious.
This injury can damage the blood supply and nerves supplying the lower leg. You’ll need an immediate MRI scan and, once the knee is returned to its correct position, you’ll require multi-ligament reconstruction. Because of the risk to the blood supply, you’ll also need a vascular assessment and an angiogram will be needed to ensure the artery at the back of the leg hasn’t been injured. Because of the risk to the nerves, you may also need the attention of a plastic surgeon to carry out nerve repairs.
With so many different surgeons potentially required – orthopaedic, vascular and plastic – this type of dislocation will usually be dealt with by major trauma centres.
So if you think your knee is dislocated but you’re not sure, the chances are it’s either a kneecap dislocation or an ACL tear. Because if your knee really was dislocated, you’d definitely know it.
Knee Cap Problems
Patella problems can lead to pain or a feeling of instability, & there are several potential causes & treatments. Find out more about them all.
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