Introduction:. Dual mobility total hip arthroplasty (DM-THA) allows for very large femoral head size, which may be beneficial for hip range of motion (ROM). No clinical study has objectively compared ROM in patients with DM-THA and large (36-mm head) total hip arthroplasty (36-THA). The aim of this prospective case-control study is to test the hypotheses that DM-THA provides superior hip ROM compared to 36-THA by dynamic radiography, and that surgical approach (posterolateral [PL] versus modified anterolateral [AL]) has effect on post-operative hip ROM. Materials and Methods:. Sixteen patients (11 males, 5 females) who had undergone DM-THA with a minimum follow up of one year were age, sex and body mass index (BMI) matched to twenty patients (12 males, 8 females) with 36-THA, all operated upon by the senior author. Maximum hip-trunk flexion, extension and total hip-trunk ROM was calculated on standing lateral digital radiographs of the lower lumbar spine, pelvis and hip, using commercially available software (TraumaCad®, BrainLab, Munich, Germany) from three upright positions; standing neutral, standing with maximum hip flexion and standing with maximum hip extension. Contributions to motion from lumbo-sacral spine (LSS) and pelvic tilt were calculated and subtracted from hip-trunk measurements to quantify true hip flexion, extension and total true hip ROM. Statistical analysis (SPSS software, Chicago, IL) was performed on all radiographic measurements to detect difference in ROM between DM-THA and 36-THA, and to detect difference in ROM between THAs performed through posterolateral (THA-PL) and anterolateral (THA-AL) approaches. Results:. There was no significant difference in age, sex and BMI between groups (p > 0.05). In DM-THA versus 36-THA, hip-trunk flexion (118° +15.3° vs. 112.75° +16.44°), hip-trunk extension (20.88° +6.72° vs. 21.00° +6.00°) and total hip-trunk ROM (139.50° +17.86° vs. 133.75° +16.29°) revealed no statistically significant difference between groups (p > 0.05). Similarly, true hip flexion (100.63° +14.77° vs. 99.85° + 13.55°), extension (12.75 + 6.01° vs. 12.20 + 3.71°) and total true hip ROM (113.38° +19.28° vs. 112.05° +14.84°) did not show statistically significant difference between groups (p > 0.05). No significant difference in true hip flexion or extension existed between THA-PL and THA-AL (p > 0.05). There was no significant difference in total hip-trunk and total true hip ROM between males and females (p > 0.05). Patients with degenerative/stiff LSS (LSS ROM <15°) exhibited significant reduction in hip-trunk total ROM (130.62° +15.97°) compared to patients with flexible (ROM >15°) LSS (144.27° +15.56°) (p = 0.015), without any significant reduction in true total hip ROM (112.81° +16.59° vs. 112.40° +17.46, respectively) (p = 0.943). Conclusion:. DM-THA does not provide superior ROM compared to 36-THA as evidenced by dynamic radiography. PL/AL surgical approach, with presumptive violation of hip extensors/flexors, does not affect post-operative hip extension/flexion, respectively. THA patients with flexible LSS may exhibit apparent increased hip ROM due to compensatory movement at the LSS, rather than an actual increase in true hip ROM

INTRODUCTION

Component impingement in total hip arthroplasty (THA) can cause implant damage or dislocation. Dual mobility (DM) implants are thought to reduce dislocation risk, but impingement on metal acetabular bearings may cause femoral component notching. We studied the prevalence of (and risk factors for) femoral notching with DM across two institutions.

Introduction

The causes for revision of primary total hip arthroplasty (THA) are various and quite well known. The developing use of dual-mobility THA (DM-THA) seems a relevant option to decrease the risk of instability. Due to lack of long-term follow-up, this innovative retentive concept is suspected to increase the risk of polyethylene (PE) wear. The aim of the study was to analyse the causes for DM-THA revision and assess whether or not its occurrence is different from that of fixed-standard (FS) THA, particularly for aseptic loosening or wear and/or osteolysis.

Background. Instability and dislocation are some of the most important postoperative complications and potential causes of failure that dual mobility total hip arthroplasty (THA) systems continue to address. Studies have shown that increasing the relative head size provides patients implanted with smaller and larger cups increased stability, greater ROM and a lesser incidence of impingement, without compromising clinical results. The purpose of the current study was to review clinical outcomes in three groups of primary THA patients receiving a dual mobility acetabular shell. Methods. In two US based, post-market, multicenter studies, 450 patients received a primary cementless dual mobility THA. Patients were split into three groups based on cup size: ≤ 50mm, 52mm–56mm, and ≥ 58mm. Harris Hip Scores (HHS), Short Form 12 Physical Components (SF12 PCS), Lower Extremity Activity Scores (LEAS), and Euroqol 5D Score (EQ-5Ds) were collected preoperatively and through 2 years postoperative. Results. The current study displays gender differences among the three groups, with 90% female patients in the ≤ 50mm group, 66% male patients in the 52mm–56mm group and 100% males in the largest cup size group. A posterior/posterolateral approach was used in 94% of cases. The mean age range among the 3 groups was 60.5–61.7 and the two most common concurrent medical conditions were cardiovascular and musculoskeletal. There were no differences observed in clinical outcomes among any of the groups, all of which displayed significant increasing trends through 2 years postoperative (Figure 1). The HHS increased significantly from an average preoperative score of 54.5 to 92.9 and 93.7 at 1 and 2 years. Clinically significant improvements were seen at 2 years in SF12 PCS (+16.5) and the LEAS (+2.4) (Figures 1 and 3). The EQ-5D TTO increased from 0.62 preoperative to 0.91 at 2 years postoperative (Figure 2). There have been no failures due to dislocation reported in the current study population. Conclusion. Positive clinical outcomes for primary THA patients receiving a dual mobility system were seen in the current study, supporting their effectiveness. Regardless of the relative head size, all patients showed significant improvements postoperative with continued stability. As the primary risk factors for instability can include gender, age and increased comorbidities, the contemporary dual mobility system used in this study can address each patient's anatomic differences, improving quality of life and reducing the risk for dislocation, as well as the significant cost implications

Hip dislocation and recurrent instability continue to be a major cause of failure despite advances in materials to optimise offset and head size. The most common cause of revision after total hip arthroplasty (THA) remains recurrent dislocation (22.5%). Dislocation rates following revision THA are even higher than primary THA, and can be as high as 27%. Dual mobility acetabular components were introduced in 1974 by Bousquet to reduce dislocation risk and maintain the low friction concept introduced by Charnley. Dual mobility THA has gained wide acceptance in Europe, but there are still concerns regarding its long-term outcomes in the United States. However, even with noncrosslinked polyethylene and poor implant design, survivorship at 22 years has been shown to be 75%. Little has been published on modular dual mobility (MDM) THA in the revision setting. During revision THA, the benefits of enhanced stability may outweigh the risks of potential unforeseen complications. We present the early results of MDM revision THAs with a low complication rate. In our series, we had a 1.6% dislocation rate, which is significantly lower than what has been published in the literature. However, we urge caution with its use in off label cases, as one of the dislocations was intraprosthetic upon attempted reduction requiring revision to a constrained liner

Background:. Dual mobility components in total hip arthroplasty have been successfully in use in Europe for greater than 25 years. However, these implants have only recently obtained FDA approval and acceptance among North American arthroplasty surgeons. Both decreased dislocation rate and decreased wear rates have been proposed benefits of dual mobility components. These components have been used for primary total hip arthroplasty in patients at high risk for dislocation, total hip arthroplasty in the setting of femoral neck fracture, revision for hip instability, and revision for large metal-on-metal (MoM) hip articulation. The literature for the North American experience is lacking. Purpose:. We report indications, short term outcomes, and complications of a series of subjects who received dual mobility outcomes at one institution. Study Design:. Consecutive subjects who received dual mobility total hip arthroplasty components from February 2010 and April 2013 were identified. Charts were retrospectively reviewed for surgical indications, comorbidities, component sizes, and perioperative complications including infection, dislocation, mechanical failure, and reoperation. Results:. 86 hips in 83 subjects underwent total hip arthroplasty or revision total hip arthroplasty using dual mobility components. There were 56 primary total hips and 30 revision total hips. Indications included small acetabular components in the setting of AVN (13 hips), DDH (12 hips) or severe inflammatory arthritis (5 hips), femoral neck fracture (5 hips), intraoperative instability (6 hips), recurrent postoperative instability (5 hips), and revision of large MoM articulations in the setting of failed hip resurfacing (10 hips) or failed MoM total hip arthroplasty (6 hips). Mean follow up was 1 year (3 months to 3.3 years). There were no complications in the primary total hip group. In the revision total hip group, only one hip dislocated and this was in a patient with familial dysautonomia and insensitivity to pain. One subject underwent reoperation for acute prosthetic joint infection. No other complications were encountered. Overall dislocation rate was 1.1% and overall complication rate was 2.2%. Conclusions:. These results closely mirror that of the European literature. Dual mobility articulations in total hip arthroplasty have a low short term complication rate in this cohort and provide a simple solution to difficult cases. Indications for these implants include primary and revision total hip arthroplasty in patients at high risk for instability and revision of large MoM implants including hip resurfacing

Introduction:. Microseparation has resulted in more than ten-fold increase in ceramic-on-ceramic and metal-on-metal bearing wear, and even fracture in a zirconia head [1–4]. However, despite the greater microseparation reported clinically for metal-on-polyethylene wear, less is known about its potential detrimental effects for this bearing couple. This study was therefore designed to simulate the effects of micromotion using finite element analysis and to validate computational predictions with experimental wear testing. Methods:. Experimental wear rates for low and highly crosslinked polyethylene hip liners were obtained from a previously reported conventional hip wear simulator study [5]. A finite element model of the wear simulation for this design was constructed to replicate experimental conditions and to compute the wear coefficients that matched the experimental wear rates. We have previous described out this method of validation for knee wear simulation studies [6,7]. This wear coefficient was used to predict wear in a Dual-Mobility hip component (Fig 1). Dual mobility total hip arthroplasty components, Restoration ADM (Fig 1), with highly crosslinked acetabular liners were experimentally tested: the control group was subjected to wear testing using the ISO 14242-1 waveform on a hip wear simulator. The microseparation group was subjected to a nominal 0.8 mm lateral microseparation during the swing phase by engaging lateral force springs and reducing the swing phase vertical force. Results:. The wear coefficients that matched experimental wear rates for the low and highly crosslinked polyethylene liners were 4.57×10. −10. and 5.89×10. −11. mm. 3. N. −1. mm. −1. , respectively. Introducing microseparation in the conventional hip increased the wear rate by 15.59 mm. 3. /million cycles in the low crosslinked liner and by 1.12 mm. 3. /million cycles in the highly crosslinked liner (Fig 2). Discussion:. Microseparation did increase predicted wear rates for the low crosslinked polyethylene liner and supports the hypothesis that microseparation can adversely affect the wear of hip arthroplasty. However, the predicted and experimental increase for the dual mobility highly crosslinked liners due to microseparation was low (3.3 mm. 3. and 2.9 mm. 3. /million cycles, respectively) and below the threshold for clinical relevance. The small increase in wear rate in our study supports the high wear tolerance to wear of a dual-mobility sequentially crosslinked polyethylene liner