Technique

: Fig. 1 – Lateral position

As the surgery is performed with the patient placed in a lateral position, it is crucial to provide stable support on the back and front of the pelvis. As shown in Fig. 1, the dorsal (back) foot end of the operating table is removed so that the leg can be positioned dorsally in a hyper-extended position in order to expose the femur. The incision is started at the middle of the greater trochanter, on its ventral (front) border, and extended about 5 to 7 cm towards the anterior superior iliac spine.

: Incision

Subcutaneous tissue is separated up to the fasciae until the tract with the fascia is exposed. Next, the tract is incised approximately 4 mm medial to the border of the underlying fascia, and the incision is extended distally and proximally in the direction of the fibres. The ventral part of the tract is then lifted with forceps in order to perform initially sharp dissection of the tensor fascia lata muscle, followed by blunt dissection to separate the muscle from the intermuscular septum to the neck of the femur. A straight Hohmann retractor is placed at the base of the greater trochanter and another on the femoral calcar to retract the muscles. This results in exposure of the capsule. A T-shaped capsular excision is then made.

: Opening the joint capsule

After placing Hohmann retractors below the capsule, osteotomy is performed at the base of the neck of the femur, at the position determined during preoperative planning. A chisel inserted in the osteotomy site is used to tilt the neck of the femur forward in order to insert a corkscrew along the axis of the femoral neck. By twisting the corkscrew several times, the femoral head is freed and subsequently extracted. To expose the acetabulum, we use two Hohmann retractors, one positioned medially and the other laterally, and a third double-bent retractor positioned distally. The acetabulum is then reamed using MI instruments in the usual manner before insertion of the acetabular cup (usually a Pinnacle cup). Although straight standard instruments can be used in slender patients, we recommend that angled MI instruments be used so that surgeons can gain experience using these instruments in these relatively easy cases and not just in obese patients, who are more difficult to perform surgery on in the beginning. It is crucial to avoid excessive anteversion of the cup during insertion. The insertion instrument should be positioned approximately parallel to the axis of the operating table at a 45-degree angle of inclination. The fibres of the transverse ligament can be used as a landmark for orientation.
A Hohmann retractor is placed dorsolateral to the trochanter to expose the femur, which is then rotated outwardly and placed in a hyperextended position.

: Leg position for exposure of the femur

The lower leg is placed in a bag or a second stocking to ensure sterility. It is important that the lower leg be positioned perpendicular to the floor during assessment of femoral antetorsion. Subsequently, another Hohmann elevator is positioned along the calcar. The entire femoral entry plane must now be displayed carefully for correct determination of the point of entry. We generally use a sharp spoon to open the femur before inserting medullary reamers.

The prosthesis is inserted while closely checking the degree of femoral antetorsion. After repositioning, the joint capsule is closed with single interrupted sutures, and the fascia with a single continuous suture. The surgery is generally completed in about 45 minutes, and it is performed in an internervous plane without detaching muscles and tendons and without resecting the capsule. To date, we have performed several hundred MicroHip surgeries and have not observed any nerve lesions or fractures of the greater trochanter so far. Our greatest initial challenge was proper alignment of the acetabulum. However, this too can be accomplished safely and reliably provided the above-mentioned guidelines are followed carefully. Calcar fissures are generally no problem if they occur. However, they can be avoided altogether by exposing the femur properly so that the correct entry point can be determined.