Cemented monoblock dual mobility implant with fully porous cup promising for revision THA
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Hip instability and mechanical loosening after total hip arthroplasty are some of the most common complications that can require revision surgery.
With the growing rates of revision THAs expected in the next few decades, it is increasingly important to understand the diagnosis and appropriate treatment strategies for these complications. Certain factors, such as component malpositioning, soft tissue tensioning, component loosening and implant wear, can lead to a need for revision THA. Acetabular bone loss can present a significant challenge to surgeons when attempting to revise a failed THA. Bone loss can make adequate acetabular fixation of revision components more difficult and lead to suboptimal positioning of the acetabular component.
Source: Akram Habibi, MD, and Ran Schwarzkopf, MD, MSc
Prior techniques for overcoming these challenges have included the use of acetabular augments, fully porous shells and custom implants based on the patient’s unique anatomy. Appropriate component placement and implant costs have been a concern for these revision acetabular implants. A cemented monoblock dual mobility implant into a fully porous cup allows for improved osseous fixation in the setting of acetabular bone loss and reduced the risk of hip instability. Moreover, cementation of the dual mobility implant allows for improved control of anteversion and inclination of the dual mobility implant and decoupling of the outer acetabular shell from the inner dual mobility cup, providing more control of implant positioning and improved hip stability. This acetabular revision construct offers excellent midterm outcomes for patients requiring complex acetabular reconstruction while decreasing the risk of hip instability.
Preoperative history
Our patient is a 74-year-old woman, who is otherwise healthy, presenting with increased right hip pain during the past few months. She had a past surgical history of a right THA 14 years ago that was revised for instability at an outside institution 1 year prior to presentation. Her past medical history is significant for L4/5 spinal fusion. Preoperative radiographs and CT scans of the pelvis demonstrated loosening of the acetabular component and bone loss of the anterior and posterior walls and columns, with the acetabular component breaching the quadrilateral plate (Figure 1).
Due to evidence of loosening on imaging and continued right hip pain, she was indicated for a revision THA. Preoperatively, an infection workup was completed and was negative. The plan for the revision was for an isolated acetabular revision using a fully porous acetabular shell and a cemented dual mobility monoblock acetabular cup.
Surgical technique
The patient was placed in a lateral decubitus position and the prior incision was utilized. A modified Kocher-Langenbeck approach was used for the exposure. Once the joint was exposed and prior to dislocation, the computer navigation pins were placed to allow for comparison of the new acetabular position and the removed acetabular cup, as well as length and offset changes after completing the revision THA. The hip was dislocated and a subgluteal pocket was made to mobilize the femoral stem trunnion to aid in acetabular exposure. Once the acetabular component was adequately exposed, the acetabular liner and acetabular screws were removed. A contoured osteotome was used to disrupt any remaining bone-implant interface around the circumference of the implant and the acetabular component was removed. No pelvic discontinuity was found after removal of the acetabular components. Any remaining scar tissue was excised to allow for improved visualization and ensure adequate contact of the acetabular shell and bone interface.
The acetabulum was line-to-line reamed until bleeding bone was encountered, being careful to avoid over medialization and disruption of the medial acetabular wall. A trial was placed within the acetabulum to evaluate if there was adequate fixation and if any acetabular augments would be necessary. A revision fully porous acetabular shell with circumferential locking screw holes (Figure 2) was used to allow for screw fixation circumferentially, including posterior-inferior and anterior toward the ischium and pubis. After securing the porous acetabular shell, the implant was thoroughly irrigated and dried prior to cementation.
Cement was applied to the inner part of the acetabular shell and the outer surface of the monoblock dual mobility acetabular cup (Figure 3) to ensure adequate fixation. The dual mobility implant was pressurized into the cement mantle (Figure 4). Excess cement was removed while the cement was drying under direct visualization and the position of the dual mobility cup was adjusted to approximately 25° anteversion and 40° inclination. Orientation of both the fully porous acetabular shell and the dual mobility cup were confirmed with computer navigation. Stability of the implant was assessed after the cement cured. The hip was found to be stable throughout range of motion. The acetabulum was thoroughly irrigated, and the remaining capsule was closed with a braided, nonabsorbable suture, followed by closure of the remaining soft tissue in a layered fashion. Intraoperative radiographs were performed to assess implant position.
Postoperative protocol
The patient was made weight-bearing as tolerated with posterior hip precautions postoperatively. Hip precautions were implemented for 3 months and included avoidance of hip flexion greater than 90°, crossing legs and hip internal rotation. The patient was able to progress with physical therapy while admitted and was discharged on postoperative day 2.
At her follow-up appointment, her incision was well healed, and she had increased ambulation with a walker. She had range of motion of 0° to 90° of flexion, 20° external rotation and 20° abduction and she was pain free. Radiographic imaging at that time demonstrated a well-fixed acetabular shell without evidence of loosening and a well-positioned cemented monoblock dual mobility cup (Figure 5).
- References:
- Bozic KJ, et al. J Bone Joint Surg Am. 2009;doi:10.2106/JBJS.H.00155.
- Mancino F, et al. Orthop Rev (Pavia). 2020;doi:10.4081/or.2020.8655.
- Muthusamy N, et al. J Hip Surg. 2022;doi:10.1055/s-0042-1756277.
- Shichman I, et al. Arthroplast Today. 2023;doi:10.1016/j.artd.2023.101152.
- For more information:
- Akram Habibi, MD, and Ran Schwarzkopf, MD, MSc, can be reached at the department of orthopedic surgery at NYU Langone Health in New York. Schwarzkopf’s email: ran.schwarzkopf@nyulangone.org.
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