Anatomy
For many orthopaedic surgeons, gross anatomy of the hip joint is not a problem. It is something they live with most days. Arthroscopic anatomy is different, structures being seen from a few millimetres away, and magnified ten times or more. Little has been written on the in-vivo arthroscopic anatomy of the hip (Arthroscopy 1994;10(4):392-399). In my early days I had to largely make it up as I went along. However, it is imperative to know the normal in order to understand the abnormal. The stellate crease, for example, was a finding that I was sure was pathological when I first commenced hip arthroscopy, only subsequently to discover that it was found in almost everyone!
Once inside a hip it is important to adhere to a preplanned 'tour' of the joint. Using a lateral (supratrochanteric) approach, and assuming the joint is reasonably distractible, you can see at least the top 50% of the femoral head, and certainly down as far as the fovea. Sweep from anterior to posterior, concentrating on rotating the arthroscope to improve the view rather than leverage. That is why a 70 degree arthroscope is best for hip arthroscopy - it has a wider field of view than the 30 degree version.
Once you have reached the posterior aspect of the joint inspect the posterior gutter, down the back of the femoral neck, identify the zona orbicularis, and then pick up the labrum. Look for the perilabral sulcus, and the labral groove, starting from the most inferior part of the posterior limb of the lunate surface of the acetabulum. Then follow the labrum up and around. I refer to labral lesions like the hours on a clock face. Using a lateral approach you may lose sight of the labrum between 1100 and 1300, though if you carefully withdraw the arthroscope you can usually pick up most of the structure. Then continue your sweep around the clock face, picking up the labral groove and perilabral sulcus anteriorly. Note how the labrum is more ribbon-like superiorly and cord-like inferiorly. Look at the anterior gutter, extending down the front of the femoral neck and the anterior part of the zona orbicularis. Then sweep further inferiorly to the lowermost part of the anterior aspect of the acetabular lunate surface and identify the transverse ligament arising there. Sometimes the transverse ligament is in continuity with the labrum, sometimes it is an independent entity.
Labral groove seen posteroinferiorly.
Perilabral sulcus
Transverse ligament
Just beyond the transverse ligament you can see the upper part of the inferior recess. It is most unlikely you will gain access to the inferior recess form a lateral approach. You will need to create an anterior portal to do so. I normally miss out the inferior recess for most routine hip arthroscopies. Once you have identified the transverse ligament, return to the fovea of the femoral head and follow the ligamentum teres as far as you can. Because you have distracted the femoral head inferiorly the ligamentum will be buckled and compressed. In order to test its integrity ask an assistant to rotate the femur internally and externally. This will allow you to see if the ligamentum is intact or otherwise. Rotation (if your distracter allows it) is also a good way of seeing the lowermost parts of the anterior and posterior aspects of the acetabular lunate surfaces
Ligamentum teres
Fovea
Anterior gutter
You will now find yourself in the cotyloid fossa of the acetabulum. This contains synovium and fat, as well as the ligamentum. The soft tissue lies like a flap in the fossa, so frequently lifts up with the pressure of fluid irrigation revealing the bare area of bone beneath. Do not mistake this for a labral tear. Some do, misjudging the margins of the cotyloid fossa as the margins of the true acetabulum. At the anterosuperior (1000 hours) and posterosuperior (1400 hours) aspects of the cotyloid fossa you will often find a structure looking like a candle flame. This is the stellate crease and possibly represents the point of fusion of the triradiate cartilage. Occasionally a deep groove can be seen running across the front (and occasionally back) of the socket. This is the iliopubic groove (ischiopubic when posterior) and can easily be mistaken for a fracture. It is frequently seen in dysplastic hips.
Cotyloid fossa contents. Note how fluid pressure has lifted up the
soft tissue flap, exposing bare bone beneath
Soft tissue contents of cotyloid fossa
- femoral head above, acetabulum below
Stellate crease
Once the 'tour' is complete you should then insert a cannula and probe in order to feel the consistency of the articular cartilage, and further inspect any suspicious areas. Probing points below the fovea is difficult, due to the curve of the femoral head. Try to be sure to pass the cannula over, rather than through, the acetabular labrum You can do this under direct vision, the cannula normally appearing anteriorly. The socket is slightly shallower there, allowing better access for instruments. Once you have identified your pathology, if there is anything to be done, please