Surgical steps of MIS-THA posterolateral single incision approach

Before placing the body position, first, adjust the operating table to a horizontal position. The inclination of the operating table front and rear or up and down will directly affect the correct installation of the acetabular anteversion and pitch angles. The body position adopts the conventional lateral position, usually, the front baffle is fixed to the pubic symphysis, the rear baffle is fixed to the sacroiliac joint, and the upper body needs to be perpendicular to the operating table surface, parallel to the operating table edge, and the two sacroiliac lines are perpendicular to the operating table. The pelvis must be firmly fixed (pictured below).

If the pelvis is tilted anteriorly, posteriorly, or up or down, it will affect the exposure of the acetabulum and femur, and hinder the correct judgment of the anteversion angle of the acetabulum and the length of the lower extremity.

After the surgical area has been disinfected and draped, use a sterile marker to mark the surgical incision. Mark the closest point of the greater trochanter. Make a slightly oblique incision centered 2.0cm below the apex of the greater trochanter, with a length of 7-8cm. As a whole, the incision can be moved slightly backward by 0.5cm, which is more conducive to exposure to the surgical field (upper side picture as below). Cut the skin and subcutaneous tissue (inferior side picture as below).

Find out the tip of the greater trochanter, and cut the open fascia from far to near after the mid-shaft of the femur (upper side picture as below), cut the gluteus maximus fascia along the direction of the gluteus maximus fiber, and bluntly separate the gluteus maximus, and pay attention to electrocoagulation. Small blood vessels between the fibers of the gluteus maximus (inferior side picture as below).

When incising the fascia, it can go beyond the skin incision and subtly separate the fascia by 1-2 cm, which can significantly expand the exposure range. Bend the knee, internally rotate and extend the hip joint, cut the external bursa of the greater trochanter, and separate it back to expose the external rotator muscles of the hip joint. At this time, carefully identify the acetabular branch of the inferior gluteal artery located at the lower edge of the piriformis muscle(upper side picture as below), and the branch of the medial circumflex femoral artery located on the upper edge of the quadratus femoris muscle (inferior side picture as below), which is coagulated or ligated.

The gap between the gluteus minimus and the joint capsule was separated with a periosteal peeler along the upper edge of the piriformis muscle, and a Hohmann retractor was inserted to pull the gluteus minimus upward. Cut off the piriformis, superior obturator, obturator internus, inferior obturator, and proximal ?-? quadratus femoris from the insertion point of the femur (as below) and pull it posteriorly using the abdominal retractor or large "S" retractor.

The Hohmann retractor was inserted into the joint capsule below the femoral neck and pulled downward. Fully expose the posterior joint capsule. When the joint capsule is removed, the acetabular rim side can be incised in an arc first, the joint capsule will be retracted to the femoral neck side, and then the joint capsule attached to the femoral neck can be incised so that the posterior hip joint can be easily and completely removed. Capsule, exposing the hip joint (as below). For patients with femoral neck fractures, the joint capsule can be cut in a "T" shape and retained, and the joint capsule can be sutured at the end of the operation.

Flexion, adduction, and internal rotation of the hip dislocates the hip posteriorly, removes the soft tissue behind the femoral neck and in the area of the piriform fossa, and exposes the intertrochanteric ridge and the junction between the greater trochanter and the femoral neck. A Hohmann retractor is placed on the upper and lower edges of the femoral neck, and the lesser trochanter is found with fingers. According to the preoperative preparation plan, a marking line is made on the predetermined osteotomy site with an electric knife. The angle between the marking line and the longitudinal axis of the femur needs to be determined according to different false The femoral neck osteotomy was performed with this marking line as the guide. For cases with difficult hip dislocation or femoral neck fracture, femoral neck osteotomy can be performed first, and then the femoral head can be removed using a head extractor (as below).

After removing the femoral head, pay attention to observe whether the acetabular anatomy is normal and whether there is an osteophyte that affects the correct judgment of the operator on the acetabular anteversion and pitch angles. The joint capsule in front of the acetabulum needs to be treated differently according to different situations, and the joint capsule in front of the fresh femoral neck fracture does not need to be removed. If the anterior joint capsule is removed, the soft tissue around the hip joint will be more relaxed, which may easily cause hip dislocation; or in order to stabilize the hip joint, the use of a longer neck will easily lead to the lengthening of the affected limb. For the joint capsule with limb shortening and contracture before hip osteoarthritis surgery, it will obviously limit the extension of the lower limb, so the anterior joint capsule usually needs to be removed together.

The affected hip can be internally rotated to 90° or more while the anterior joint capsule is removed. After removing the joint capsule, use a Hohmann retractor to place it at 4 or 8 o'clock in front of the acetabular rim (right or left hip), pull the greater trochanter forward, and then flex the affected hip and rotate it internally by about 30°, avoiding the acetabulum. The reamer collides with the calcar and the lesser trochanter as it enters the acetabulum. The posterior rim of the acetabulum can be exposed using deep or abdominal retractors. The labrum was removed and the bone surrounding the acetabulum was clearly exposed (as below).

Before using the acetabular reamer, the anatomical landmarks of the acetabulum should be identified first. The equine fossa and the fat tissue in the fossa represent the bottom of the acetabulum, and the transverse ligament represents the lower edge of the acetabulum. In the cases with obvious acetabular osteophyte, these important anatomical marks are often hidden, and attention should be paid to finding these anatomical marks during the operation, which is the guarantee for the correct installation of the acetabular cup. When reaming the acetabulum, an acetabular reamer with offset (as below) can be used,

First, use a small acetabular file to grind the bottom of the socket vertically, generally, smooth the horseshoe socket, and then increase the acetabular file one by one, paying attention to the angles of pitch and anteversion and the grinding depth. Use the acetabular cup try-out prosthesis to determine whether the prosthesis and the bone bed achieve a proper press fit to avoid acetabular fractures and undersized prostheses when the prosthesis is implanted.

Insert the acetabular cup prosthesis into the prepared acetabular bed. For cases where the anatomical structure of the hip joint is basically normal and there is no obvious bone hyperplasia in the hip joint, the anatomical structure of the acetabular rim can be referred to for positioning to ensure that the cup rim and the acetabular rim are parallel after the acetabular cup is implanted. For cases with obvious bone hyperplasia, it is necessary to use anatomical markers and external positioning rods for positioning to ensure that the positioning rods are horizontal, and the lateral alignment sight is parallel to the body so that the acetabular prosthesis can achieve 45° abduction and 20° forward flexion (as below).

The use of the press-fit technique in the rigid acetabulum typically results in a prosthesis diameter of only 1 mm larger than the rasp and can be as much as 2 mm in the case of relatively loose bones. Briefly tap the acetabular component with a hammer several times to securely insert the acetabular component into the acetabulum and ensure that the component is in close contact with the acetabular floor. If the press fit is reliable, it can be fixed without screws. For cases where the fixation is not very reliable, the acetabular auxiliary fixation screw is used, and the acetabular screw is screwed into the upper posterior quadrant, which can reduce the risk of nerve and blood vessel injury.

Bend the knee joint, flex, adduct, and internally rotate the hip joint. The assistant puts one palm on the inside of the ankle joint, the other hand on the front and outside of the knee joint, and pushes the lower limb toward the proximal end, and the sole of the foot is facing the ceiling. Correctly estimate the anteversion angle of the femoral neck. Using a box osteotome, the surgeon drills into the medullary cavity of the proximal femur from the medial aspect of the greater trochanter and lateral aspect of the femoral neck to remove bone (as below).

Use a pointed medullary cavity drill to open the medullary cavity, paying attention to grinding away the medial part of the greater trochanter. Then use a smooth round-headed intramedullary drill for reaming. The depth of reaming should be determined according to the required installation depth of the femoral prosthesis (as below). Corresponding or appreciable resistance from the intramedullary cortex can be felt.

After the reaming is completed, the pulp cavity is started to be ripped with a rasp (upper side picture as below). It is recommended to use a dedicated intramedullary file connection handle with an offset to avoid damage to the skin proximal to the incision when filing the pulp. Install the 9mm intramedullary file on the connecting handle and start filing the intramedullary cavity. This small intramedullary rasp creates a prosthetic implant channel in the proximal femur. As a general guideline, after a 9mm rasp is used, a rasp at least 2 sizes smaller than the prosthesis size determined in the preoperative plan can be used. In the process of broaching, attention should be paid to controlling the anteversion of the intramedullary rasps. Generally, the rasps should be inserted along the long axis of the femoral neck osteotomy surface, so that a 15° anteversion of the femoral prosthesis can be obtained (inferior side picture as below). When filing the pulp, be sure to make the pulp chamber file enter with each hammering. If the pulp chamber file can enter 5mm below the predetermined osteotomy plane, replace the pulp chamber file with a larger size, and repeat this process until the pulp chamber file is in the predetermined osteotomy plane and no longer enters the medullary cavity with the hammer.

Insert the sample liner into the acetabular cup to determine the appropriate acetabular liner height. Insert the specimen femoral head and try to reduce the hip joint. Check the length of the affected limb and the femoral offset with reference to the limb length measured before the hip dislocation. Replace the femoral head of the specimen and adjust the neck length to obtain the desired result. When satisfactory lower extremity length, femoral offset, range of motion, and joint stability were obtained, the hip joint was dislocated again, and the acetabular and femoral side trial prostheses were removed.

Install the acetabular liner into the acetabular cup by hand with the proper rotation. Before inserting the acetabular liner, make sure that no soft tissue is involved, and hit the liner. For polyethylene linings with raised sides, the raised sides are generally placed at the top rear. However, if the hip joint is found to be dislocated in a certain direction during the stability test, the heightened side can be placed on the dislocation-prone side.

The femoral medullary cavity is exposed, the prosthesis is inserted into the femoral medullary cavity, and then the prosthesis is carefully driven with a hammer (upper side picture as below). A rotary lever can be inserted into the prosthesis extraction hole to ensure proper femoral anteversion. The prosthesis is fully seated when the proximal portion of most of the microporous coating surface of the prosthesis is flush with the osteotomy line. If the intramedullary file is perfectly matched to the corresponding prosthesis size, a better proximal press fit can be obtained. The most distal portion (medial side) of the coating surface is flush with the prosthesis, and then gradually increases proximally until the proximal part can be thickened by 0.5mm (each side). In this way, the prosthesis is 1 mm larger than the intramedullary file in both anteroposterior and inner and outer diameters. This relationship can be seen in the template. So, when the prosthesis is fully implanted, there is a 0.5mm press fit on each face. Note that metaphyseal compression provides greater anti-rotational stability to the prosthesis than the intramedullary rasp. After the prosthesis stem is installed, place the selected femoral head on the tapered neck, and ensure that the two are firmly combined by tightening and using a femoral head beater (inferior side picture as below).

The hip was repositioned, and limb length, joint stability, range of motion, and abductor tone were tested one final time. After the bleeding is completely stopped, the wound is rinsed and the external rotator muscle group is carefully repaired (upper side picture as below). Close the incision layer by layer (inferior side picture as below).

If there is not much bleeding on the wound surface, negative pressure suction can be omitted. The preoperative X-ray film of this right femoral neck fracture case (upper side picture as below) underwent posterolateral single-incision minimally invasive total hip arthroplasty. The limb length and offset were restored, and the prosthesis installation position was satisfactory (inferior side picture as below).