Arthroscopy of the Knee

Introduction

Arthroscopy of the knee is an operation in which a small camera, and possibly surgical instruments, are inserted into the knee through two or three small puncture wounds.  Understanding what the basic procedure entails is straightforward if we look at the etymology of the word.

  •  arthro- :  relating to joints
  •  scopy: viewing, observation or examination

Arthroscopic procedures have equivalents in other branches of surgery.  Examples include laparoscopy (laparo-: of the abdominal wall) in general surgery and cystoscopy (cysto-: relating to the urinary bladder) in urology.

In the most basic of arthroscopic procedures, the structures within the knee are viewed and assessed using a camera called an arthroscope, with a view to diagnosis.   The structures examined include the meniscus, the synovium, the articular cartilage and the cruciate ligaments.

Depending on findings, additional therapeutic procedures can be carried out via the insertion of surgical instruments.  Such procedures include:

Arthroscopic procedures

  • Debridement: Particularly in patients with mechanical symptoms such as locking, debridement can be helpful by removing a torn piece of meniscus – in which case the procedure is called an arthroscopic meniscectomy – or other tissue.  Rough, damaged articular cartilage can also be treated in this way.
  • Mensical repair: In certain cases, repair of a torn meniscus can yield better results than mensisectomy.
  • Loose Body Removal: Some injuries can cause fragments of bone, cartilage or other soft tissues to break off within the knee.  These can be found and removed arthroscopically.

A first guide to interpreting arthroscopic images

Many patients seen on the ward and in clinics will have arthroscopy reports and associated images in their notes.  For medical students, junior doctors and the patients themselves, these images can sometimes be disorientating, as it is necessary to imagine you are inside the knee to work out what the different structures are.  Here, a few simple rules for orienting oneself to the images are presented.

  • Rule 1: Ensure you determine which knee you are supposed to be looking at.  This simple step is key to understanding which side of the image is lateral and is which is medial.
  •  Rule 2: Most of the images are taken looking antero-posteriorly – i.e. from the front of the knee towards the back.  The exception to this rule is those images taken looking upwards at the patella-femoral joint.
  • Rule 3: The surgeon handling the arthroscope will keep the tibial plateaus horizontal and towards the bottom of the image whenever they can be seen.
  • Rule 4: The surgeon will have manipulated the knee to open up the joint space in the area where each image is being taken.  This can give a false impression of the spatial relationship between the articular surfaces and the soft tissues.

The images below, of a left knee joint, are annotated with reference to the rules above, to clarify which part of the joint they show.

This is the inside of a left knee, viewed from the front.  Any structures on the left of the page are therefore on the medial side of the knee, and those on the right are lateral.

left medial

The tibial plateaus are kept horizontal at the bottom of the image.

The medial meniscus is shown ‘floating’ between the two articular surfaces.  Under normal load, the meniscus would be compressed between the two.

This is the inside of a left knee, viewed from the front.  Any structures on the left of the page are therefore on the medial side of the knee, and those on the right are lateral.

The tibia plateaus are kept horizontal at  the bottom of the image.

In this case, we can see a defect in the articular cartilage of the lateral tibial plateau, as indicated by the probe.

left medial

Again, this is the inside of a left knee, this time viewed looking upwards at the patella-femoral joint.  Lateral and medial are the same as the images above.

The key to understanding the orientation of this image is to recognise the wedge-shaped posterior surface of the patella and the trochea groove of the femoral condyles.

In this case, the articular surfaces to the bottom of the image are the femoral condyles.