Sunday, 29 January 2012

Lateral Knees - How to fix them when it all goes badly

For some reason, no one seems to like lateral knees, especially students. I remember hating them, though I can't quite remember why, I suspect it had something to do with the fact that it was so obvious when you got them wrong. That doesn't mean they are easy to get right however. I have a system for doing lateral knees that still only probably works 8 times out 10. You can think you have everything absolutely perfect and it will still look wrong.  I don't know whether I just wasn't paying attention one day at uni, but I can never remember being taught how to figure out how to fix your lateral knee. I don't think it was just me however because a lot of students I work with now don't seem to know either (or they are just humouring me and secretly thinking I'm stupid - all valid options)
In any case, here are a few tips I have picked up (or had forced upon me!) that will hopefully make lateral knees a little easier.

Standard Lateral Knee (patient rolled onto side)

  • Ask the patient to roll right up onto their side/hip - not merely roll their leg out
  • Keep the other leg behind the one you are x-raying - I find rolling it over the top will more often than not make you over rotated HOWEVER
  • If the patient is struggling to roll onto their side (often the case with large patients) have the bring their other leg over the top
  • Try and feel for the epicondyles to see if they feel superimposed (not always possible to determine)
  • 2 finger  rule - I never really got this but people swear by it. I believe your 2nd and 3rd fingers should sit between the patella and the table when correctly positioned - can be difficult with large knees however
  • Feel for the tibial spine, this should be running parallel to the table. If not, place a small sponge under the ankle to raise the lower leg and open the joint space.
  • Angle up 5 degrees (again, seems to work most of the time but not fool proof)
  • Slight bend in knee - should never be 45 degrees!
Assessing Rotation
  • The best tip I have learned is to look at the fibula
  • If you can see too much fibula - the knee is over rotated - try lifting the knee up off the cassette slightly or rolling the patients hips back towards the table slightly
  • If most of the fibula is behind the tibia, you are under rotated - this is when rolling the other leg over the top may be useful  or simply rolling the patient slightly more onto their hip
  • It is usually only a very small movement required to fix the rotation

Trauma or Horizontal Beam Lateral
  • Should always be performed after trauma (regardless of whether the patient can roll for a lateral) to assess for fluid 
  • Have a slight bend in the knee if tolerable to open the joint space
  • Can feel for the epicondyles to assess rotation but again can be difficult with large knees or swelling
  • Use ankle as an indicator however remember that some people's feet turn out/in so that may be misleading
  • Again, I find feeling for the tibial spine to be most accurate. Run your hand down the spine to ensure it is running parallel to the table
  • As the beam is now going lateral to medial (as opposed to medial to lateral in a standard AP) angle down 5 degrees 
Assessing Rotation
  • If you see too much fibula, the leg is under rotated. Turn the whole leg slightly inwards
  • If you don't seen enough fibular, the leg is over rotated. Turn the whole leg slightly outwards.



Again, these are general rules, however I find them to be successful most of the time. You will always find that one shonky knee which you just can't seem to get right. Don't be afraid to concede defeat after a few attempts. For some reason, a new set of eyes and hands will annoying get it right when you continue to fail. 

Remember to feel for landmarks to see if you are in the right position. These include the tibial spine, epicondyles and patella. For trauma or post surgical knees, try feeling the unaffected knee to get an idea of normal anatomy (patients also appreciate not poking their sore knee). This will also help get an idea of correct centring position as often swollen knees and be misleading. 

Finally, if you image a lot of knee replacements, remember that the joint is artificially made and therefore a lot easier to show perfect superimposition of condyles and a large joint space. With knees suffering from bad OA, the joint space is often tiny and the condyles may be uneven to start with, making superimposition very difficult. Don't necessarily expect a normal knee to look like a TKR replacement knee.

Please let us know if you have come across any other tips for lateral knees!


13 comments:

  1. Hi any tips on rolled lateral hips especially on larger patients it is my nemesis at the moment

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  2. thanks very helpful

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  3. Thankyou for posting your blog. I've been a tech for six years and it seems lately I've needed a refresher on lateral knees.

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  4. I've just discovered your blog. . . I like what I've seen so far. Particularly the 10 bad reasons for a portable xray.

    My tip for lateral knee positioning is to put either a large boomerang (we still have ours from our film days) or a k-basin under the ankle. It puts almost everyone's tibia parallel to the table. Then I just need to worry about rotation. . . not just your nemesis but pretty much anyone who doesn't work in an ortho center

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  5. I work in an orthopedic facility and all spine, knee and feet are done standing. for some reason Im inconsistent with the standing lateral knee. Sometimes its perfect and other times its got significant rotation. I do the same thing everytime. I know that everyone has different anatomy but I cant figure it out. On the table I got it down, but standing is bothering me, any tips?

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  6. TRY BENDING THE KNEE SLIGHLY, LESS THAN 45 DEGREES WHEN DOING A LATERAL WHEN STANDING. HAVE THE PT STAND SIDEWAYS WITH LEGS APART AS IF IN A WALKING PATTERN...THAT SEEM STO HELP, I TOO WORK IN A ORTHO FACILITY. I AM AN ROT AND XRAY TECH.,

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  8. Does anyone have any hints on how to reposition the tube angle on lateral knees when the condyles are lined up anterior/posterior but not superior/inferior?

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    1. As you may know, the medial condyle is located lower than the lateral condyle of the femur; to compensate for this "superior/inferior" difference, you may angulate the beam 3-5 degrees cephalad. And always remember: in order to tell the difference between which condyle is not aligned correctly, the one that seems LARGER is the medial condyle.

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    2. **It appears larger on the image because it is further away from the IR causing magnification (in comparison to the lateral condyle which would be closest to the bucky).

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