Revision Hip Arthroplasty Case Title: The Use of Acetabular Augments for Revision Total Hip Arthroplasty

Case Title: The Use

of Acetabular Augments for Revision Total Hip Arthroplasty

 

 

Demographics

 

Age: 71 years old

Sex: Male

BMI: 37

 

1. Relevant Past Medical History

    

   Principal pathologies: Osteolysis and mechanical failure of total hip prosthesis.

   Previous surgical procedures: Left total hip arthroplasty, left tibia open reduction internal fixation and skin grafting, right ankle open reduction internal fixation.

   Medication: Multivitamins, Aleve.

   Other: Obesity, former smoker (quit at the age of 61 years).

   History of presenting complaint: Patient presented to the clinic with activity-related left hip pain for approximately one year. The patient also complained of night pain. The patient did not complain of instability.

    

2. Clinical Examination

    

   Symptoms: Activity-related left hip/proximal thigh pain, limb length discrepancy

   Range of motion: Flexion 90°, internal rotation 0°, external rotation 30°

   Specific tests: Antalgic gait, left limb shorter than right limb by 2 inches

   Main disability: Activity-related pain

   Scoring: Lower extremity functional scale—29/80

   Neurovascular evaluation: Intact distal pulses, sensory-motor exam normal in all nerve distributions

3. Preoperative Radiological Assessment/Imaging

   (Figs. 19.17, 19.18, and 19.19)

    

    

    

   Fig. 19.17 Anteroposterior pelvis radiograph depicting a cemented total hip arthroplasty with eccentricity of the femoral head in the polyethylene liner

    

    

    

    

    

    

    

   Fig. 19.18 Anteroposterior radiograph of the left hip showing osteolytic defects in the medial proximal femoral cortex

   Fig. 19.19 Lateral radiograph of the left hip showing osteolytic defects in the posterior proximal femoral cortex Other: Interventional radiology-guided aspiration of the left hip joint fluid showed no organisms on gram stain and gram-negative cultures

    

4. Preoperative Planning

    

   Diagnosis: Left total hip arthroplasty wear and aseptic loosening (Figs. 19.17, 19.18 and 19.19)

   Possible treatment options: Acetabular com-ponent—hemispherical porous-coated shell, jumbo shell, oblong shell, impaction bone grafting, structural allograft, porous tantalum cups and augments, porous tantalum cup-cage

    

   construct. Femoral component—proximally coated femoral implants, fully coated stems, revision monolithic/modular stems

   Chosen treatment method: Acetabulum— porous tantalum cup with an augment. Femur— revision fully coated modular stem

   Selection of implants if applicable and rational: Acetabulum—Zimmer highly porous cup with acetabular augment to account for the acetabular bony defect. Femur—Stryker Restoration Modular stem with cobalt-chrome head to account for the femoral bony defect

   Expected difficulties: Sciatic nerve entrapment in scar tissue. Gaining adequate exposure to components, fixation of implants, managing acetabular and femoral bone loss

   Strategies to overcome difficulties: Extensile posterior approach, appropriate implant extraction instruments, performing an extended trochanteric osteotomy (ETO) to aid in removal of implants, access to revision implants, augments, bone graft, plates, cables

   Templating: Acetate prints

    

5. Surgical Note

    

   Patient’s position: Lateral decubitus

   Type of anesthesia: General endotracheal anesthesia

   Surgical approach: Posterior

   Main steps:

    

    

   Reconstruction techniques: Acetabulum— augment buttress, morcellized bone grafting, porous tantalum shell. Femur—modular revision stem, trochanteric plate, cerclage cables (Figs. 19.20 and 19.21).

    

   1. Identified and protected sciatic nerve.

   2. Obtain adequate exposure to femoral and acetabular components.

   3. Obtain tissue for frozen sample and intraoperative tissue culture for microbiological analysis.

   4. Remove acetabular component and cement mantle.

   5. Ream acetabulum.

   6. Augment placed to buttress acetabular roof defect.

   7. Bone graft impacted into native acetabulum floor.

   8. Acetabular cup placed along with dome screws.

   9. Cement at the cup-augment interface.

   10. Perform extended trochanteric osteotomy to gain access to cement mantle and femoral component.

   11. Extract femoral component.

   12. Guide wire placed in the femur for sequential reaming.

   13. Proximal reaming performed.

   14. Trial components placed and intraoperative range of motion and stability assessed.

   15. Final components placed.

   16. Trochanteric osteotomy repaired using a plate, cerclage cables, and allograft strut.

   17. Vancomycin powder and betadine irrigation.

   18. Sequential layered complex closure.

   19. Intraoperative X-rays.

6. Intraoperative Challenges

    

   Challenges and solutions: Access to the compo-nents—extensile posterior approach and extended trochanteric osteotomy. Filling acetabular defect—impaction bone grafting, trabecular metal augment, and trabecular metal shell. Filling femoral defect—modular conical diaphyseal fitting stem

   Unanticipated problems and solution: Excessive scar tissue around neurological struc-tures—intraoperative neurological monitoring. Acetabular cement mantle—Moreland instruments. Femoral cement mantle and component extraction—extended trochanteric osteotomy

    

   Thorough description of decision-making, including the reason for the final decision:

    

   1. Positioning and approach—since the patient had undergone the index surgery with a posterior approach to the hip, the same approach was utilized and extended as necessary to obtain adequate exposure. The sciatic nerve was identified, and we did not note significant scar tissue around the nerve. We were also able to use the piriformis and external rotators to protect the nerve intraoperatively. We did not feel the need to have intraoperative neurological monitoring for the sciatic nerve.

   2. Tissue samples—we decided to send tissue samples for frozen section and microbiological analysis especially to detect acute inflammation. Since the results were negative for acute inflammation, we decided to proceed with the revision surgery. Alternatively, we would have performed a two-stage revision with antibiotic spacer placement.

   3. Acetabulum—once the acetabular components were removed, the bony void was classified as a Paprosky type IIIB defect, and we found that an appropriately sized trabecular metal augment could be used to buttress the roof of the acetabulum. Also, a porous tantalum multi-hole shell with impaction bone grafting was selected to achieve stability of the acetabular component.

   4. Femur—since the patient had a long-stem cemented femoral component, we elected to perform an extended trochanteric osteotomy to gain access to the cement mantle and to aid in the extraction of the femoral component. We also elected to use a trochanteric plate with several cerclage cables and an allograft strut to augment stability for the revision femoral component. A modular femoral revision component that gave primary diaphyseal fixation was chosen due to severe proximal femoral bone loss secondary to osteolysis.

7. Postoperative Radiographs

   (Figs. 19.20 and 19.21)

    

    

    

   Fig. 19.20 Anteroposterior pelvic radiograph depicting a porous tantalum cup and augment with multiple screws and a uncemented modular revision femoral stem supported by an allograft strut and a trochanteric plate with cerclage cables

    

    

    

    

    

   Fig. 19.21 Lateral radiograph of the left hip demonstrating a fully coated uncemented modular revision stem, trochanteric plate, cerclage cables, and porous tantalum cup with an augment

    

8. Postoperative Management

    

   Chemoprophylaxis and anticoagulant treatment period: Aspirin 325 mg by mouth twice daily for four weeks postoperatively.

   Gait/limb loading until full loading: 25–50% partial weight bearing on the operative limb for six weeks postoperatively with subsequent progression to full weight bearing.

    

9. Follow-Up and Complications

    

   No complications were noted postoperatively.

    

10. Discussion

     

    Advantages of the applied method: Porous tantalum cups have a high volumetric porosity (75–85%) and high frictional characteristics that make them conducive to biological fixation with extensive bony ingrowth. They are safe and biocompatible and have a modulus of elasticity (3 MPa) similar to that of subchondral bone to allow better physiologic load transfer and a higher endurance limit, yield strength, and ultimate strength. In acetabular revisions, porous tantalum cups have shown encouraging early results, and porous tantalum augments may serve as a structural bone graft substitute. Another advantage is that modularity of components to match bony defects results in a minimal need to remodel the host bone.

    Disadvantages of the method: Porous tantalum cups and augments have limitations including notch sensitivity, brittleness, and the lack of host bone stock restoration. They are also expensive to use and may not be readily available universally to the arthroplasty surgeon.

    Alternative evidence-based techniques for the case: Contained acetabular defects—standard cemented/uncemented primary-type cup with morcellized bone graft or impaction grafting with mesh and a cemented cup. Global contained defects can be treated with morcellized bone graft protected by reconstruction cage contact and a cemented cup. Uncontained acetabular defects—high hip center arthroplasty, oblong or eccentric cups, jumbo cups, minor/major column structural allografts, reconstruction cages/

    custom-made triflange cups, and porous tantalum cup-cage constructs.

    Why is the chosen technique better for this case? Our patient had a Paprosky type IIIB acetabular defect which means that the columns are no longer supportive; there is a superomedial migration of the femoral head with teardrop lysis, and there is a rim defect from the 9 o’clock to 5 o’clock position. Also, based on the Saleh and Gross classification and based on the actual bone stock remaining at final reaming after implant/ cement/debris removal, our patient had a type III defect—uncontained segmental defect involving less than 50% of the acetabulum and one column. Treatment strategies for Paprosky type IIIB defects are focused on restoring the superior support for a hemispherical cup with minimal removal of host bone. Options include high hip center arthroplasty, oblong/eccentric cups, jumbo cups, minor structural allograft, or porous tantalum cups and augments. High hip center arthroplasty has several biomechanical disadvantages related to abductor function. Hip stability may also be compromised due to bony impingement and small femoral head dictated by a small cup. High-offset femoral components are often used which may increase the bending moment on the stem and lead to loosening. Oblong/eccentric cups are technically challenging to place, and special reamers are often required making component position difficult to obtain. Simultaneous restoration of an appropriate hip center of rotation, contact on host bone, and proper version and inclination can be difficult. Jumbo cups, on the other hand, include the sacrifice of a large amount of host bone and can lead to soft tissue impingement especially of the iliopsoas. Minor structural allografts, even though are a very good alternative for porous tantalum cups and augments, are not universally available and do have a potential for disease transmission and the possibility of late graft resorption and collapse. Porous tantalum cups and augments have shown very good early results for type III defects, 96.4–98% survivorship at 1–4 years. In case of our patient with limited bone stock and already compromised soft tissue function from injury-related complications leading to a THA, porous tantalum cups and cages seemed to be the best option for reconstruction [37–39].

     

    Indications and contraindications for your technique: Indications—Paprosky type IIIB acetabular defect, revision acetabular surgery. Contraindications—infection, pelvic discontinuity [37–39].

    Learning curve and how to manage complications: These cases are best managed by a fellowship-trained adult reconstruction surgery who is familiar with the use of various options to manage acetabular and femoral bone loss in cases of revision surgery.

    Level of evidence concerning the superiority of this method against others: IV.