Acute knee Injury: What is the role of an MRI scan?


Introduction:

Acute traumatic knee injury most commonly results from sports injury, the commonest mechanism being a twisting force on the knee with a planted foot resulting from a cutting movement. While most often these are soft tissue injuries such as sprains of the external ligaments (medial or lateral collateral ligaments) that settle down with conservative measures, some are more serious injuries.


Presentation:

Immediate swelling in the knee (rather than after 24-48 hours) is one of the symptoms that may suggest a more serious injury such as an anterior cruciate ligament tear or a fracture. The other symptoms of a serious injury are locking, and feeling of instability although these are not usually apparent until the acute symptoms settle down. The treating Orthopaedician should be able to pick these injuries up by doing special tests on clinical examination.


The immediate treatment for an acute knee injury is always conservative (with a few exceptions) which includes a brace, pain killers, Ice and early physiotherapy.


What are these Exceptions?

Early knee X-ray is indicated in all patients with severe immediate swelling in the knee, as this can pick up bony injuries such as subtle tibial plateau fractures or a tibial spine fracture as illustrated in the x-ray. The management of these is slightly different and depends on the severity of fracture and displacement.



Indication for an MRI scan:

If symptoms do not settle down by 3-4 weeks, then an MRI scan of the knee is indicated. MRI is a very useful tool for picking up injuries in the knee that will not be seen on plain X-rays. It is very sensitive at picking up injuries to Cruciate ligaments or meniscal tears (See images). This protocol varies from center to center and even from country to country depending on access and affordability.





Does MRI have any side effects?

MRI is essentially a large magnet that aligns certain molecules in water in the body to itself and thereby producing an image. It has no radiation associated with it.

It has no known side effects to the human body.

There are however contra-indications to doing an MRI such as presence of pacemaker, presence of certain metal implants in the body, pregnancy etc.


Conclusion

MRI remains the gold standard of investigation for knee injuries.

Early MRI helps early diagnosis and treatment and prevents potential further injuries due to lack of treatment.


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