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How I use… The Image Intensifier for Minimally invasive Periacetabular Osteotomy Marcus J K Bankes and Vasanth Eswaramoorthy
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btaining and interpreting images is essential for success in PAO and much time can be saved if a specific routine can be established. Whilst a radiographer familiar with the procedure is helpful, it is by no means essential using the method we outline.
Marcus Bankes leads the Young Adult Hip Unit at Guy’s and St Thomas’ Foundation NHS Trust and was appointed Consultant Orthopaedic Surgeon in 2002. His particular interests include the surgical treatment of hip dysplasia and he pioneered the use of minimally invasive PAO in the UK. He was also one of the first surgeons to submit data to the Non-Arthroplasty Hip Registry and was the first Chair of its Steering Group.
Vasanth Eswaramoorthy is currently a post CCT Arthroplasty fellow at St. George’s Hospital, London. He completed his orthopaedic training in the South East London training programme. His special interest is in young adult hip surgery and has previously completed the young adult hip fellowship at Guy’s Hospital.
It is also extremely advantageous for the surgeon to take a few moments prior to getting scrubbed to demonstrate to the radiographer the manoeuvres needed to achieve adequate intra operative images, particularly the threestep false profile view, whilst the patient is being draped. These extra minutes more than pay dividends in time saved from efficient imaging during the procedure. After performing the pubic osteotomy the draped C-arm should be positioned contralateral to the operating side at the level of the patient’s pelvis. An AP hip image is obtained with the C-arm in a position of maximal horizontal movement away from the base (chassis). The base is then locked (brakes on the wheels). This has two advantages: the base is as far as possible from the operative field and the symphysis can be imaged by just retracting the C-arm horizontally.
The false profile (FP) view is obtained by a three-step manoeuvre of the C-arm: lowering the C-arm as close to the floor as possible, whilst simultaneously rotating the arm to 55 degrees (orbital rotation) and then withdrawing the C-arm horizontally until the X-ray source touches the table (Pictured below). The height of the beam can be conveniently adjusted by horizontal movement of the C-arm and/or the operating table. The beam should not be adjusted by raising the vertical height of the C-arm as this introduces another unnecessary dimension. It is during the external ischial cut that efficient radiography pays dividends as the II is switched often between the AP and FP views. The external surface of the ischium is not flat and often the lateral part of the cut is started with only the medial tine in contact with the bone. The ischium is usually cut from lateral to medial, usually with three passes of the osteotome. As the osteotome moves more medially, there is a normal artefactual appearance of the osteotome seeming to get further away from the joint. The II is left in the FP position to make the internal ischial and posterior column cuts. Prior to the iliac osteotomy a pre-correction AP view of the hip is obtained with the hip in extension, corrected for rotation by viewing the symphysis, which is easily visualised by withdrawing the C-arm 8-10cm on the horizontal lock. The II can also be used to produce a simulated weight bearing view of the hip with appropriate tilting of the tube either cephalad or caudad so that the outline of the obturator foramen on the pre-operative weight bearing pelvic radiograph is replicated on the image intensifier. The iliac osteotomy usually starts just below the ASIS but may need to be higher than this in cases of more severe dysplasia. The level of the iliac osteotomy is checked on the AP view to ensure a safe distance from the acetabulum and the II returned to the FP position to allow access to make the iliac cut and mobilise the fragment. The position is checked with both AP and FP views, then fixed with three 4.5mm self-tapping cortical screws mostly using the FP view. n
JTO | Volume 07 | Issue 01 | March 2019 | boa.ac.uk | 35