SuPeRior IN situ Thp: Surgical Technique

The patient is positioned in the lateral decubitus, as anterior on the OR-table as possible with dual anterior support on the ipsi- and contralateral SIAS and a long posterior sacral support to stabilize the pelvis. The leg is positioned in 45 to 60° of flexion, slight adduction and 20° of internal rotation. A mayo table with soft cushion supports the foot and ankle. This position is maintained throughout the procedure.

The skin is incised in line with the femur, starting at the tip of the greater trochanter, for a length of 8 to 15 cm. Subcutis and the gluteus maximus is split along its fibers, avoiding violation of the fascia and bursa of the greater trochanter. A Charnley retractor spreads the fibers of the gluteus maximus. The interval between gluteus minimus, piriformis and internal obturator tendon is exposed. An anterior retractor is placed under the gluteus medius but over the piriformis and gluteus minimus. The piriformis is freed from its capsular attachment and an incision is made in the capsule, immediately posterior to the piriformis, effectively releasing the capsule and femoral insertion of the internal obturator tendon. A stay suture is placed through capsule and internal obturator tendon. At this point, the capsule can be mobilized at the acetabular rim for increased exposure. A second neck retractor is placed inside the capsule along the posterior neck. The anterior retractor is repositioned inside the capsule along the anterior neck. This exposes the fossa piriformis.

The lateral and superior part of the femoral neck is exposed at the base of the greater trochanter. Bleeding branches of the ascending branch of the medial femoral artery are coagulated. A sharp femoral canal reamer is advanced from the fossa piriformis in the direction of femoral shaft. A second femoral reamer is used to broaden the entry point.
At this point the anteversion is checked, and internal rotation of the leg is adjusted by altering the height of the mayo stand. A small rectangular box chisel is used to open femoral neck and head as to mark the desired anteversion. At this point the neck can be cut with or without a guidance device. In order to facilitate the neck cut, a small size broach with a flat cutting surface can be inserted to the desired depth. The reference point from which insertion depth is measured, is the anterior and horizontal part of the femoral neck, which is visible both on the preoperative template and during surgery. The femoral neck is cut along the plane of this guidance broach and the femoral head is removed with a cork screw.
At this point one can opt for either acetabular preparation or femur first preparation.

An anterior acetabular retractor is placed over the anterior border of acetabulum (10L /2R o’clock position). This moves the femur away in an antero-inferior direction. The superior acetabulum is exposed with a sharp pin at the 12 o’clock position. At this point, if desired, both anterior and posterior capsule can be released from the acetabulum border. A second Charnley pin is placed at the 3L / 9R o’clock position. The inferior retractor is positioned postero-inferior at the level of the posterior horn of the acetabulum. It is essential not to place the retractor underneath the transvers ligament. A superior but circumferential view of the acetabulum is created. Adequate view of transverse ligament and acetabular rim should be achieved. Excessive osteophytes that can block reamer entry are removed at this stage (fig 4.).
Reamers with a curved reamer handle and a curved acetabular impactor are essential. The acetabulum is prepared with sequential reaming, first exposing the floor of the acetabulum and then creating peripheral press fit. The trial cup is used to check cup anteversion and inclination. The transvers acetabular ligament is used as a guide for anteversion. Inclination is checked with the impactor guide and comparing templated and intra-operative position of the cup with the acetabular rim at the 12° clock position.

The assistant pushes the leg in a posterior direction, with the knee in adduction and the leg in 20-30° of internal rotation. This brings the neck at the posterior-superior edge of the acetabulum. A gluteus medius retractor and a femoral elevator are used to expose the entry of the femoral canal. Excessive internal rotation should be avoided as this will bring the external obturator tendon under tension and this can block the entrance of the femoral canal. Standard femoral broaching is now possible. After assembly of a trial prosthesis, the hip can be reduced by lifting the femur with a bone hook and an axial push/pull, whilst avoiding excessive internal rotation. At this point a fluoroscopic control can be done. The hip is dislocated by femoral traction and lifting the head out of the acetabulum, not with internal rotation. Definitive implants are placed and final reduction performed.