Imaging of the Knee

Introduction

Imaging of the knee is a commonly requested examination. Some examinations are more appropriate/accurate for specific clinical indications. We have been asked by the local orthopaedic surgeons to clarify to other referring doctors/health professionals the most appropriate investigations for specific clinical questions. Some of these clinical questions are best clarified with MRI. Unfortunately for political/financial reasons there are barriers to MRI access. All recognised specialists including orthopaedic surgeons, sports medicine, musculoskeletal medicine, rheumatologists, and occupational health specialists are able to order these studies either via ACC or private insurance. Emergency department specialists are also able to order MRI examinations through ACC and these doctors now have clinics at the 24 Hour Surgery.

Not all patients require imaging. The following list assumes some form of imaging is required and does not imply that imaging is necessary for all the listed conditions.

X-Rays

All patients require these.

Ultrasound

Indicated for:

    Patella/quadriceps tendon abnormalities.

    ? DVT.

    Muscle tears e.g. hamstrings, rectus femoris.

    Confirmation of Baker's cyst.

    U/S guided procedures eg, autologous blood injection patella tendon.

Can be used for:

    Initial characterisation of periarticular mass lesions (only able to prove presence of true mass and differentiate cystic from solid).

    Collateral ligament abnormalities e.g. ITB friction syndrome BUT is less reliable than MRI for these indications.

Should NOT be used for:

    Evaluation of meniscal tearing.

    Evaluation of acute intra-articular derangement eg ? ACL tear.

MRI

Investigation of choice for all internal derangements of knee (if required clinically):

    Cruciate/collateral ligament evaluation (in conjunction with clinical examination)

    Meniscal tears.

    Chondral injuries (acute osteochondral injuries/OCD)

    Occult fractures, microtrabecular injury/bone bruising,insufficiency fracture/SONK.

    Assessment of cartilage loss in Osteoarthritis (i.e. unicompartmental vs total knee replacement)

    Patella dislocation and associated chondral/ligamentous abnormalities and intra-articular bodies.

Investigation of choice;

    Mass lesions around the knee.

    Further characterisation of tendon abnormalities and other equivocal ultrasound findings.