Dislocation and dissociation of bipolar hip hemiarthroplasty

Be aware of the "O" sign in the bipolar cup dissociation during closed reduction of bipolar dislocation: A case report

RATIONALE

Bipolar cup dissociation following hip hemiarthroplasty is a rare complication of which only a few cases have been reported, and it usually requires revision surgery because of difficulties in closed reduction.

PATIENT CONCERNS

We report the case of a 57-year-old man who underwent bipolar hemiarthroplasty 2 months ago caused by a left femoral neck fracture. Postoperatively, bipolar dislocation occurred thrice, and the patient showed bipolar cup dissociation during closed reduction maneuver at the recent visit. At the time of this event, no consideration was given to the shape of the prosthesis on the radiograph.

DIAGNOSES

The patient was diagnosed with early bipolar cup dissociation.

INTERVENTIONS

The patient underwent revision surgery to replace and reassemble the femoral head component.

OUTCOMES

No further dislocation occurred following the surgery.

LESSONS

To avoid dissociation of the components during closed reduction, it would be helpful to have knowledge of the "O" sign, a concentric circle shape of the prosthesis on the radiograph.

LEVEL OF EVIDENCE

Level V, case report.

Preprosthesis fracture of femoral and loosening of the femoral prosthesis during closed reduction of hip dislocation: A case report

INTRODUCTION

Dislocation after bipolar hip hemiarthroplasty is an uncommon complication. Although closed manoeuvre reduction under general anaesthesia is a common and effective method for dislocation of the hemiarthroplasty. However, closed reduction leads to preprosthesis fracture of femoral and loosening of femoral prosthesis is a rare situation, which requires incision reduction and a revision hemiarthroplasty.

PRESENTATION OF CASE

A 80-year-old female had cementless bipolar hip hemiarthroplasty due to a right femoral neck fracture. At the 11 days of postoperation, the patient had a dislocation of the hemiarthroplasty when squatting. The patient had preprosthesis fracture and loosening of the prosthesis during closed reduction. Eventually, the patient had an open reduction and femoral stem revision. There was no re-dislocation and no re-fracture at one-year follow-up.

DISCUSSION

Closed manoeuvre reduction is a common and effective method for dislocation of the hemiarthroplasty. But if not done properly, it may lead to preprosthesis fracture of femoral and loosening of the femoral prosthesis. Preprosthesis fracture of femoral and loosening of femoral prosthesis is a complex complication. This condition requires operative treatment. A personalized surgical plan and proper techniques should be done before the operation.

CONCLUSION

Closed reduction should be performed gently to avoid preprosthesis fracture and loosening of the prosthesis. If this happens, a high-resolution CT examination should be performed immediately to evaluate the fracture and the rotation of the prosthesis. In the case of dislocation after bipolar hip hemiarthroplasty in patients with Alzheimer's disease, we hypothesize that early wearing braces to limit squat might help prevent this condition.

Hip stress distribution - Predictor of dislocation in hip arthroplasties. A retrospective study of 149 arthroplasties

Dislocation after hip arthroplasty is still a major concern. Recent study of the volumetric wear of the cup has suggested that stresses studied in a one-legged stance model could predispose arthroplasty dislocation. The aim of this work was to study whether biomechanical parameters of contact stress distribution in total hip arthroplasty during a neutral hip position can predict a higher possibility of the arthroplasty dislocating. Biomechanical parameters were determined using 3-dimensional mathematical models of the one-legged stance within the HIPSTRESS method. Geometrical parameters were measured from standard anteroposterior X-ray images of the pelvis and proximal femora. Fifty-five patients subjected to total hip arthroplasty that later suffered dislocation of the head and, for comparison, ninety-four total hip arthroplasties that were functional at least 10 years after the implantation, were included in the study. Arthroplasties that suffered dislocation had on average a 6% higher resultant hip force than the control group (p = 0.004), 11% higher peak stress on the load-bearing area (p = 0.001) and a 50% more laterally positioned stress pole (p = 0.026), all parameters being less favorable in the group of unstable arthroplasties. There was no statistically significant difference in the gradient index or in the functional angle of the weight bearing. Our study showed that arthroplasties that show a tendency to push the head out of the cup in the representative body position—the one-legged stance—are prone to dislocation. An unfavorable resultant hip force, peak stress on the load bearing and laterally positioned stress pole are predictors of arthroplasty dislocation.

What Is the Frequency of Early Dissociation of Bipolar Cups and What Factors Are Associated With Dissociation?

BACKGROUND

Dissociation between a prosthetic cup and femoral head is a rare complication of bipolar hemiarthroplasty that usually occurs during closed reduction of a dislocated bipolar cup. The dissociation usually results in reoperation because closed reduction is challenging. To our knowledge, no study has reported on the frequency of bipolar cup-femoral head dissociation, and risk factors for dissociation are unknown.

QUESTIONS/PURPOSES

The purposes of this study were (1) to evaluate the frequency of dissociation of prosthetic femoral heads from bipolar cups during manual reduction of a dislocated bipolar hemiarthroplasty; and (2) to explore in a preliminary fashion any prosthesis or patient factors that may be associated with dissociation.

METHODS

From May 2003 to August 2016, 60 bipolar hemiarthroplasties were treated at three institutions as a result of early (within 3 years) dislocation after arthroplasty; of these, 55 could be identified and categorized in terms of the type of locking mechanism used, and these were the patients evaluated in this retrospective study. Because the index hemiarthroplasties were not performed exclusively at the three participating centers, we cannot comment on the indications for prosthesis selection in these patients (such as why some patients may have received components with single rather than double locking mechanisms). Manual reduction was attempted in all patients. Although 34 dislocations were manually reduced, 21 hips underwent surgical intervention because they could not be closed reduced (14 hips) or because of bipolar cup-femoral head dissociation (seven hips). We compared patients' demographics and prosthetic factors between the dissociation group (n = 7) and the nondissociation group (n = 48).

RESULTS

Bipolar cup-femoral head dissociation occurred in seven of 55 patients with dislocations (13%). Among the seven dissociated cups, six had a single polyethylene locking ring, whereas 20 of 48 nondissociation cups (42%) had the single locking ring (p = 0.044). We found no other patient or prosthesis factors associated with dissociation.

CONCLUSIONS

Bipolar cups with a single locking mechanism (rather than a double locking mechanism) may be associated with an increased risk of bipolar cup-femoral head dissociation. However, because we could not evaluate prosthesis indications in this study, and because our sample size was too small to control for potential confounding variables, future studies are needed to confirm this finding. All the same, because good alternatives are available, we do not recommend the use of this type of locking mechanism in bipolar hemiarthroplasty.

LEVEL OF EVIDENCE

Level III, therapeutic study.

What Are the Risk Factors for Dislocation of Hip Bipolar Hemiarthroplasty Through the Anterolateral Approach? A Nested Case-control Study

BACKGROUND

Hip dislocation after treatment of a femoral neck fracture with a hemiarthroplasty remains an important problem in the treatment of hip fractures, but the associations between patient factors and surgical factors, and how these factors contribute to dislocation in patients who have undergone bipolar hemiarthroplasty through an anterolateral approach for femoral neck fracture currently are only poorly characterized.

QUESTIONS/PURPOSES

We evaluated patients with bipolar hemiarthroplasty dislocation after surgery for femoral neck fracture treated through an anterolateral approach and asked: (1) What are the frequency, characteristics, and risk factors of bipolar hemiarthroplasty dislocations? (2) What are the frequency, characteristics, and risk factors of bipolar hemiarthroplasty dissociations?

METHODS

A review of hospital records for patients who underwent bipolar hip hemiarthroplasty for femoral neck fracture at one hospital between July 2004 and August 2014 was conducted. During that time, 1428 patients were admitted with a diagnosis of femoral neck fracture; 508 of these patients underwent bipolar hip hemiarthroplasty, of whom 61 died and 23 were lost to followup during the first year, leaving 424 (83%) available for analysis. The remainder of the patients during that time were treated with internal fixation (512), unipoloar hip arthroplasty (17), or THA (391). For each patient with dislocation, we selected five control patients from the cohort according to sex, age (± 3 years), and year of entry in the study to eliminate some confounding factors. We recorded patient characteristics regarding demographics, medical comorbidities, Katz score, American Society of Anesthesiologists score, Mini-Mental State Examination (MMSE) score, and anesthesia type. Medical comorbidities included diabetes, chronic pulmonary disease, heart disease, neuromuscular diseases, and dementia. Univariate analyses were used to search for possible risk factors. Conditional logistic regression analyses on dislocation or dissociation were performed to estimate hazard rates (HRs) and corresponding 95% CIs with covariates of a probability less than 0.1 in univariate analysis.

RESULTS

In this cohort, there were 26 dislocations including four that were also dissociations. The proportion of patients experiencing a dislocation was 6% (26 of 424). The mean interval from surgery to dislocation was 56 weeks (range, 0-433 weeks), and 18 dislocations (69%) occurred within 3 months after surgery. Three variables were independently associated with an increased risk of hip dislocation: dementia (HR, 3.51; 95% CI, 1.19-10.38; p = 0.02), discrepancy of offset (HR, 1.72; 95% CI, 1.15-2.58; p = 0.008), and lower MMSE score (HR, 0.93; 95% CI, 0.88-0.98; p = 0.007). The proportion of patients experiencing a dissociation was 0.9% (four of 424). The result of conditional logistic regression for dissociation showed that cup size smaller than 43 mm was the risk factor (HR = 513.05). However, there was no statistical difference with the probability equaling 0.47.

CONCLUSIONS

After the anterolateral approach for treatment of femoral neck fracture using bipolar hemiarthroplasty, 6% of hips dislocated and 0.9% experienced dissociation. Cognitive dysfunction and discrepancy of offset were independent risk factors associated with an increased risk of prosthetic dislocation. The small cup without a safety ring may be the risk factor of dissociation. Discrepancy of offset should be avoided during the operation by performing an accurate femoral osteotomy and choosing an adequate femoral stem neck length. For patients with cognitive dysfunction and a small cup, suturing the joint capsule during the operation and reinforcing protective measures after surgery might reduce the occurrence of dislocation and dissociation, however a study addressing this is necessary to confirm this.

LEVEL OF EVIDENCE

Level III, therapeutic study.