Robotic-Assisted Total Hip Arthroplasty Through the Posterior Approach.

Abstract

Background: Robotic-assisted total hip arthroplasty (THA) through the posterior approach is indicated in cases of symptomatic hip arthritis. The goal of the procedure is to relieve pain and restore function while minimizing postoperative complications such as dislocation. Dislocation often occurs despite traditionally well placed components^1,2. The hip-spine relationship can be a causative factor in postoperative instability, particularly in patients with altered spinopelvic kinematics as a result of spinal fusions or degenerative spine disease, in whom component placement based on anatomic landmarks may lead to functional malpositioning^3,4. Therefore, we present our technique for robotic-assisted THA through the posterior approach, which incorporates patient-specific spinopelvic kinematic data to maximize impingement-free range of motion and minimize the risk of dislocation.

Description: Preoperative computed tomography (CT) scans are obtained in order to generate a 3D model of the patient's unique hip anatomy. Lateral lumbar radiographs with the patient in the sitting and standing positions are also obtained preoperatively. The sacral slope is measured in each position, imported into the robotic software, and utilized to aid in positioning the components for optimal leg length, offset, and stability of the hip replacement based on the patient's unique spino-kinematic profile. The procedure begins with 3 partially threaded pins being driven into the ipsilateral iliac crest about 2 cm posterior to the anterior superior iliac spine. The robotic pelvic array is fastened to the pins. A standard posterior approach to the hip is utilized. Skin and subcutaneous tissues are dissected down to the iliotibial band and gluteus maximus fascia. The fascia is longitudinally incised, and a small metallic pin is malleted into the distal aspect of the greater trochanter. Initial leg length and offset values are captured. The short external rotators and posterior hip capsule are elevated. The hip is dislocated, and a neck resection is made at a level determined preoperatively with use of the robotic software. The acetabulum is exposed, and osseous registration is carried out to establish a relationship between the 3D model built with use of the robotic software and the patient's anatomy in vivo. The acetabulum is single-reamed, and the final cup is impacted in the desired position. The proximal femur is broached with increasingly sized broaches until rotational and axial stability has been achieved. A trial femoral neck and head are attached to the final broach, and the hip is reduced. Posterior and anterior hip stability are assessed, and leg length and offset are rechecked via the robotic system. Once the surgeon is satisfied, the hip is dislocated, the broach is removed, and the final femoral stem and head are manually implanted. The hip is then reduced for the final time. Closure is performed according to surgeon preference.

Alternatives: Surgical alternatives include THA with use of manual instrumentation or navigation through other approaches to the hip, including the direct anterior, anterolateral, and direct lateral approaches^5-7. Nonoperative alternatives include physical therapy, the use of nonsteroidal anti-inflammatory pain medication, and intra-articular corticosteroid injections⁸.

Rationale: Robotic-assisted THA is particularly advantageous in patients with abnormal spinopelvic kinematics who require precise and specific component positioning to optimize hip stability^9-11. In these patients, manually placing components relative to anatomic landmarks may lead to functional malpositioning and ultimately dislocation. Additionally, cases in which there is an anticipated difficulty in acetabular exposure or preparation because of a large body habitus or large pannus, retained acetabular hardware, or severe acetabular wear or dysplasia may benefit from the use of this technique⁹.

Expected outcomes: Patients who undergo robotic-assisted THA through the posterior approach should expect excellent clinical outcomes in addition to low rates of complication and revision¹². Robotic-assisted THA has been shown to lower the risk of dislocation compared with manual techniques^10,11. In a study by Bendich et al., a robotic-assisted THA cohort had a 0.3 odds ratio of reoperation for dislocation compared with a manual THA cohort¹⁰.

Important tips: Stable array pins are critical in order to obtain accurate leg length and offset measurements intraoperatively.When registering the acetabulum via the robotic software, aim for maximum spread of captured points to ensure accuracy of cup placement.In large-statured patients or patients with a particularly stiff hip, in whom anterior femoral retraction is difficult, disconnect the reamer from the robotic arm and place it into the acetabulum by hand before reconnecting it to the robotic arm. Remove the anterior acetabular retractor and set the reaming orientation to 50° of inclination and 10° of anteversion. Final cup position is kept in the desired orientation.Remember that the robotic-assistance device is just a surgical tool, and the quality of its output relies on the quality of its input. If there is concern for an error in component placement, intraoperative radiographs should be obtained.

Acronyms and abbreviations: THA = total hip arthroplastyCT = computed tomographyDVT = deep vein thrombosisIT = iliotibial.