The Transition to an Anterior-Based Muscle Sparing Approach Improves Early Postoperative Function but is Associated with a Learning Curve

This protocol demonstrates and highlights the technique and intricacies of the anterior-based muscle sparing approach, abbreviated ABMS, for total hip arthroplasty. The ABMS approach allows the surgeon to efficiently perform total hip arthroplasties in the lateral decubitus position, combining the advantages of the posterior approach and the direct anterior approach. Surgeons transitioning to the EBMS approach should make themselves familiar with the extent of capsular release during capsulotomy, as this step dictates the exposure of the acetabulum and the femur.

Before the surgery, meet the patient in the pre-operative holding area and mark the correct hip side with a skin marker. Palpate and mark the proximal border of greater trochanter, or GT, the anterior border of the proximal femur, and the anterior border of the gluteus medius, or GM, fascia, which is tighter than the fascia overlying the tensor fasciae latae muscle. After positioning the patient in a lateral decubitus position with the operated hip facing up, perform sterile prepping and draping, and cover the exposed skin with iodine-impregnated adhesive.

Wrap a sterile elastic bandage around the waist of the assistant 1 to create a belt, which will serve to hold a sterile Mayo stand cover attached to the belt with the two non-penetrating clamps, like a kangaroo bag. Position the surgeon in front of the patient, and assistant 1 and assistant 2 behind the patient. Instruct assistant 1 to abduct the hip.

Incise the skin sharply with a number 10 blade, following the skin mark, cut down to the fascia with a knife, and use a clean lab sponge to expose the fascia. Identify the perforating vessels as they pierce through the fascia, locating the interval between the GM and tensor fasciae latae, or TFL. Distally open the fascia parallel to the orientation of the fascial fibers, and curve anteriorly at the mid portion of the incision, staying posterior to the perforating vessels.

To dissect the muscle plane between the TFL anteriorly and the gluteus muscles posteriorly, run a finger along the GM toward the GT and let the finger drop anteriorly into the space between the GM and TFL. Once the finger is in the space, palpate the femoral neck and posterior portion of the femoral neck by elevating the gluteus medius and minimus posteriorly. While assistant 1 is holding the hip abducted, place a curved Hohmann retractor over the posterior neck outside the capsule to retract the gluteae muscles, Then place a straight Hohmann retractor over the anterior neck outside the capsule, under the TFL and the reflected head of the rectus femoris tendon.

Instruct assistant 1 to rotate the hip slightly externally and make an H-shaped capsulotomy using electrocautery with the bar of the H longitudinally along the femoral neck. Ensure that the distal line of the H is far lateral connecting the tip of the GT and the medial around the neck to release the capsule and clean out the trochanteric fossa and intertrochanteric ridge. Using electrocautery, go through the entire capsule proximally toward the head and acetabular rim, which is felt as a step with an electrocautery tip.

At the acetabular rim, turn the electrocautery by 90 degrees and release the capsule along the acetabular rim medially and laterally. Reposition the retractors underneath the capsule with the assistant holding the leg in abduction. With assistant 1 increasing the external rotation and extension, make a subcapital femoral neck cut oblique from proximal to distal to facilitate the lift of the distal femur.

Hold the anterior number 7 retractor. With a key elevator positioned at the osteotomy site, level the femoral neck into the surgical field while assistant 1 hyperextends the hip to dislodge the osteotomy. Instruct assistant 1 to place the leg in the kangaroo bag and externally rotate the hip so that the patella is pointing upward and the tibia is perpendicular to the floor.

Reposition the number 17 retractor over the GT and clean up the trochanteric fossa from the soft tissue using electrocautery. Instruct assistant 1 to adduct the hip so that the femoral neck is elevated more out of the wound. To perform the femoral neck cut, at the plant level distal to the trochanteric fossa, use an oscillating saw to cut the medial neck, proceeding to the lateral neck, paying attention not to violate the GT.Remove the free bone piece of the femoral neck with an osteotome and grasper.

Remove the Hohmann retractors and instruct assistant 1 to place the leg out of the bag in a neutral position on the Mayo stand to allow hip abduction and slight flexion. Place number 15 or number 17 retractors over the posterior acetabulum and the number 7 retractor over the anterior acetabulum. Push through the capsule with the spike.

To remove the femoral head, push on the inferior part of the head to dislodge it superiorly, then use a grasper to remove the head. Remove the labrum using a long knife and incise the inferior capsule if it is in the hemisphere of the acetabulum. Ream the acetabulum to appropriate size, starting 1 millimeter smaller than the planned cup diameter Then insert the final acetabular component in 40 degrees abduction and 10 to 15 degrees anteversion.

Insert the final polyethylene liner by manually placing it within the acetabular component and then impacting the liner in the acetabular component to engage the locking mechanism. While assistant 1 places the leg in the kangaroo bag and rotates the hip externally to 90 degrees, place a 2-pronged retractor under the posteromedial aspect of the femoral neck, and the number 17 retractor over the GT.Then instruct assistant 1 to extend and adduct the hip. Perform release along the anterior portion of the GT to deliver the femur out of the wound.

Then open the proximal femur with a box cutter and canal finder. Broach to an appropriate size and length, and place the final stem with templated offset To perform a trial reduction, instruct assistant 1 to apply slight traction and internally rotate the hip while the surgeon uses a head pusher to guide the ball into the socket. To check the hip for anterior and posterior stability, place the number 17 retractor over the posterior acetabulum to visualize the hip.

Perform a shuck test in longitudinal and lateral traction. To dislocate the hip, place a bone hook around the neck and instruct assistant 1 to apply traction and external rotation. Remove the trial head, irrigate the cup, insert the final head, and reduce the hip.

Replace the number 17 retractor outside the capsule. Reapproximate the capsule with a non-absorbable suture. Repair the gluteal fascia with a synthetic braided absorbable suture while the leg is in slight abduction and external rotation.

Close the subcutaneous tissue with a 2-0 braided absorbable suture in skin, with sterile skin staples. Six weeks after the total hip arthroplasty, the mean Oxford hip score was 35 points after the anterior-based muscle sparing, or ABMS approach, and 29 after the posterior approach, or PA.The hip disability and osteoarthritis outcome score and forgotten joint score did not differ significantly after six weeks between the two approaches. At six months after total hip arthroplasty no differences in outcome scores were observed.

The difference in the mean surgical time across the three patient groups showed that the surgery time significantly reduced from a mean of 113 minutes for the first 10 patients to a mean of 67 minutes for the surgery's 21 to 30, indicating a learning curve regarding surgical efficiency. At six weeks the postoperative x-rays of the presented patient demonstrated restored leg length and femoral offset. Incising the fascia at the border of the gluteus medius and the tensor fasciae latae will avoid unnecessary muscle damage, and the correct capsular release during capsulotomy will allow for adequate exposure of the acetabulum and the femur.

Once comfortable with the ABMS approach for primary total hip arthroplasties, the approach can be utilized without restriction on patient selection, and can be extended to revision total hip arthroplasties.