Use of a monoblock dual-mobility acetabular component in primary total hip arthroplasty in patients at high risk of dislocation

INTRODUCTION

Dislocation is amongst the most common complications following total hip arthroplasty (THA). Dual-mobility bearings have been suggested as one way to reduce the risk of dislocation, particularly among patients at increased risk. The purpose of this study was to determine the outcomes of a monoblock dual-mobility shell for patients at high risk for dislocation following primary THA.

METHODS

A total of 155 primary THAs with a monoblock, cementless dual-mobility acetabular component were performed in patients at high risk for dislocation. Two patients died prior to their two-year follow-up. The remaining 153 THAs were followed for a mean of 5.1 years (range: 2.1 to 9.3).

RESULTS

There were no dislocations; however, four patients underwent revision surgery: one for an early periprosthetic acetabular fracture, one for an early periprosthetic femoral fracture, one for a late periprosthetic femoral fracture, and one for leg-length discrepancy. Intraoperative complications included one periprosthetic acetabular fracture treated with protected weight-bearing and one intraoperative proximal femoral fracture treated with cerclage wiring. Harris Hip Scores improved from a mean of 42.4 points preoperatively to a mean of 82.4 points postoperatively (p < 0.001). No cups were radiographically loose. At a mean follow-up of 5.1 years, survivorship of the acetabular component was 99.3% (95% CI, 98.1-100%) and survivorship without any reoperation was 97.4% (95% CI, 95.9-100%).

DISCUSSION

Although there were no dislocations in this high-risk population, periprosthetic fractures of the femur and acetabulum were common with the implants utilised.

Dual-mobility bearings in complex revision hip arthroplasty

BACKGROUND

Revision total hip arthroplasty (rTHA) is associated with an increased dislocation risk. Dual-mobility (DM) bearings have been used to address this issue. Such constructs offer increased range of motion and enhanced stability whilst avoiding some issues associated with fully-constrained devices. DM bearings have been used in our unit since 2013.

METHODS

All rTHA cases since 2013 were reviewed using the following criteria: (1) use of a DM bearing; (2) extensive soft tissue or bone loss resulting from ARMD, infection or multiple revisions, or requiring custom or megaprosthetic reconstruction; (3) minimum 2-month follow-up.

RESULTS

52 cases were identified with a median of 2 previous operations (range 1-6) and mean follow-up of 14 (2-41) months. The Novae-Stick component was used in 50 cases, the Avantage in 2 and the Trident MDM in 1 case. 19 required acetabular reconstruction using trabecular metal and four required custom acetabular components. 19 required femoral reconstruction with a proximal or total femoral replacement.Postoperatively, 8 patients (15.4%) sustained a dislocation at a mean of 1.6 (range 1-3) months. 3 (5.8%) requiring re-revision. 1 required excision arthroplasty and 2 a constrained liner, 1 of which went on to have further instability. There were no intraprosthetic dislocations.

CONCLUSIONS

Dual-mobility components are a viable option in the complex rTHA setting. Early dislocations can occur but the rate of instability is acceptable in this high-risk group.

Early unexpected failure of a vitamin E-infused highly cross-linked polyethylene liner: A case report

RATIONALE

Total hip arthroplasty (THA) with a polyethylene (PE) liner is 1 of the most effective and successful treatment strategies for end-stage hip disorders. Vitamin E-infused highly cross-linked polyethylene is theoretically known to prevent failure due to oxidative degradation in the body, and is resistant to wear; therefore, successful long-term survival of THA is expected.

PATIENT CONCERNS

In June 2019, approximately 1.5 years after THA, the patient sat down and stood up without any specific issue; however, an unusual bullet sound occurred around the left hip joint. Since then, his discomfort persisted, and he was admitted to the emergency department.

DIAGNOSIS

Plain radiography and metal artifact reduction computed tomography performed in the emergency department revealed eccentric elevation of the prosthetic femoral head and suspected PE liner failure.

INTERVENTION

Revision surgery was performed for modular component exchange. To reduce the dislocation risk without performing cup exchange, conversion to dual-mobility articulation was performed.

OUTCOMES

During the regular follow-up post-surgery, the patient could perform daily life activities without any discomfort, and dislocation was not observed. At 2 years postoperatively, no significant changes were observed in the radiographic images.

LESSONS

This case report presents an unexpected failure of THA due to superior rim fracture and excessive wear at the locking mechanism of the vitamin E-infused highly cross-linked polyethylene liner. This is an interesting case, as early PE liner failure occurred without strong labor intensity or trauma. A modular component exchange was performed with a dual-mobility bearing, and no issues were observed approximately 2 years after the reoperation. Therefore, third-generation highly cross-linked polyethylene liners can also cause early failure without a clear cause, and this case report highlights the necessity of considering several strategies for reoperation.

STUDY DESIGN

Case report.

Dual mobility bearings withstand loading from steeper cup-inclinations without substantial wear

Steep cup abduction angles with adverse joint loading may increase traditional polyethylene bearing wear in total hip arthroplasties. However, there have been few reports evaluating the effect of cup inclination on the wear of dual-mobility devices. In a hip joint simulation, we compared the short-term wear of two-sizes of modular highly cross-linked dual-mobility bearings (28 mm femoral head diameter/42 mm polyethylene insert outer diameter/54 mm acetabular shell diameter; 22.2 mm femoral head diameter/36 mm polyethylene insert outer diameter/48 mm acetabular shell diameter) at 50 and 65° of cup inclination with modular 28 mm femoral head on 54 mm cup diameter metal-on-highly cross-linked polyethylene bearings. Increasing inclination from 50-65° had no changes in volumetric wear of 28/42/54 mm (mean, 1.7 vs. 1.2 mm3 /million cycles, respectively; p = 0.50) and 22.2/36/48 mm (mean, 1.7 vs. 1.2 mm3/million cycles, respectively; p = 0.48) dual mobility bearings. At 65°, 22.2/36/48 mm dual-mobility bearings had lower volumetric loss (mean, 2.2 vs. 6.3 mm(3) ; p = 0.03) and wear rates (mean, 1.2 vs. 2.7 mm3/million cycles; p = 0.02) compared to metal-on-highly cross-linked polyethylene bearings. Modern-generation dual-mobility designs with highly cross-linked polyethylenes may potentially withstand edge-loading from steeper cup-inclinations without substantial decreases in wear.