When to order an investigation for a suspected ACL injury?

Hi all,

I have a patient whom I suspect has a partial ACL tear. The patient is a 35 year old female who 2 months ago was on a 4 hour hike where she fell 3-4 times during the hike, each time landing on her right knee. She was able to finish the hike and reported only a small effusion following the hike. At present, she is able to complete a 1 hour gym session of exercise bike, walking and other cardio based exercises, but reports mild pain in her knee towards the end of a session. She also reports difficulty with seated knee extension with an ankle weight.
Her main problem is the sensation of her knee 'giving way' at times, rather than pain. Her main reason for presenting was to get strengthening exercises for her knee.
On objective testing, medial and lateral ligaments were intact. She had greater laxity and a different end feel on anterior drawer test and lachmans test on the right knee.

I suspect she has a partial tear of her ACL. Does this history warrant a referral for an MRI?

Also, is there a set of criteria for referral for an MRI or other investigation when an ACL injury is suspected?

Not sure about criteria suffice to say only if you suspect a total rupture would you both. As there was no large effusion then this is unlikely. As you suggest it may be lax on that side but why did she fall? Unstable ankles? Slippery ground.

Any impact on the knee directly may have caused some articular bruising and or meniscal irritation. Be careful not to cause to much loading with any exercise in the initial phases as this might aggravate the underlying tissue that is trying to heal. Weakness post injury is not actually real 'weakness' and so strengthening need not always be the desired course of action. i.e. was it weak before?

Just some ideas but hope it helps.

just a note, i myself had a complete acl tear, this was confirmed through arthroscopy and repaired, without having a large haemarthrosis/effusion. i never had more than a minor effusion.... until I had the surgery! That was a different story! an mri showed just "acl disruption". haemarthrosis is present in the vast majority of complete tears but not in 100% of same.

If a client of mine were reporting repeated instances of instability and objectively there was laxity on lachmans/anterior drawer I would be looking to see if an MRI was possible. especially if the client was very active etc.

Thanks for that post. Fair point. I think in many cases the ACL undergoes repeated injury. Only perhaps a good first time injury would give the significant effusion. But who knows.

I suppose it's interesting that the MRI in your case might not have provided any more assistance than the clinical observation. Thoughts? Perhaps only refer for MRI if you have the direct intention of a surgical intervention at that time. If you initial intention is conservative management then wait until that either fails or succeeds? What do you think?

Where conservative management is possible I always try it, definitely. It's really all down to the client's wishes. If someone is happy to rehab the knee and probably avoid sports with rotatory forces on the knee etc I'm not going to be pushing for an MRI or surgical option. Obviously then if this fails further investigation is warranted.

On the other hand if someone presents to me with an objectively deficient ACL +/- episodes of instability and wants to get back so a higher level of for example, football, but is unwilling to have surgery I'l just go through the facts with them, the possibility of further injury etc and let them make in informed decision.

From talking to a number of specialised knee orthopods it seems to me that the importance placed on MRI's varies quite a lot. What does seem clear enough is that it is quite difficult to ascertain the actual level of damage to the ACL from an MRI. 20% 30% 50% tear etc. Even more difficult is equating the level damage to, say, the level of instability. It's possible for someone to have a 50% tear with a fairly stable knee but for someone else to be having recurrent episodes of instability. This may be to do with the exact area of damage and the different orientation of fibres in the ACL and their different roles in knee stability or may be to do with extrinsic controls eg quads strength/control etc. MRI can be used to confirm whether the ACL has been damaged further information is limited. In my case, my Ortho surgeon did not look at my knee scans and indeed did not even read the report. He checked my lachmans and anterior drawer. Attempted a pivot shift (that i was too apprehensive for him to go ahead with!) Asked what my problem was ( a number of times when i felt unstable and a number of actual episodes of instability with turns when running) and we agreed that a scope plus more than likely a repair was necessary.

So in short, yes, the MRI gave very little insight into my knee injury other than to confirm that the ACL was involved in some way. It was my subjective reports, the objective ACL tests and my wish to return to sports where twisting/turning is commonplace that were taken into account.

It would be interesting to know of other peoples experiences regarding this. Are surgeons interested in MRI results or are they proceeding with the surgical option on mainly clinical findings?

Excellent response, many thanks :)