Introduction. Acetabular revision surgery is challenging due to severe bone defects. Burch-Schneider anti-protrusion cages (BS cage: Zimmer-Biomet) is one of the options for acetabular revision, however higher dislocation rate was reported. A computed tomography (CT)-based navigation system indicates us the planned direction for implantation of a cemented acetabular cup during surgery. A large diameter femoral head is also expected to reduce the dislocation rate. The purpose of this study is to investigate short-term results of BS cage in acetabular revision surgery combined with the CT-based navigation system and the use of large diameter femoral head. Methods. Sixteen hips of fifteen patients who underwent revision THA using allografts and BS cage between September 2013 and December 2017 were included in this study with the follow-up of 2.7 (0.1–5.0) years. There were 12 women and three men with a mean age of 78.6 years (range, 59–61 years). The cause of acetabular revision was aseptic loosening in all hips. The failed acetabular cup was carefully removed, and acetabular bone defect was graded using the Paprosky classification. Structural allografts were morselized and packed for all medial or contained defects. In some cases, solid allograft was implanted for segmental defects. BS cage was molded to optimize stability and congruity to the acetabulum and fixed with 6.5 mm titanium screws to the iliac bone. The inferior flange was slotted into the ischium. The upside-down trial cup was attached to a straight handle cup positioner with instrumental tracker (Figure 1) and placed on the rim of the BS cage to confirm the direction of the target angle for cement cup implantation under the CT-based navigation system (Stryker). After removing the cement spacer around the X3 RimFit cup (Stryker) onto the BS cage for available maximum large femoral head, the cement cup was implanted with confirming the direction of targeting angle. Japanese Orthopedic Association score (JOA score) of the hip was used for clinical assessment. Implant position, loosening, and consolidation of allograft were assessed using anterior and lateral radiographies of the pelvis. Results. Fifteen hips had a Paprosky IIIB defect, and one hip had a pelvic discontinuity. JOA score significantly improved postoperatively. No radiolucent lines and no displacement of BS cage could be found in 9 of 15 hips. Consolidation of allografts above the protrusion cage was observed in these patients. Displacement of BS cage (>5mm) was observed in 6 hips and displacement was stopped with allograft consolidation in 5 of 6 hips. The other patient showed lateral displacement of BS cage and underwent revision surgery. Average cup inclination and anteversion angles were 37.7±5.0 degree and 24.6±7.2 degree, respectively. 12 of 16 patients were included in Lewinnek's safe zone. One patient with 32 mm diameter of the femoral head had dislocation at 17 days postoperatively. All patients who received ≥36mm diameter of femoral head showed no dislocation. Conclusions. CT-based navigation system and the use of large femoral head may influence the prevention of dislocation in the acetabular revision surgery with BS cage for severe acetabular bone defects

Introduction:. Large diameter femoral heads have been used successfully to prevent dislocation after Total Hip Arthroplasty (THA). However, recent studies show that the peripheral region of contemporary femoral heads can directly impinge against the native soft-tissues, particularly the iliopsoas, leading to activity limiting anterior hip pain. This is because the spherical articular surface of contemporary prosthesis overhangs beyond that of the native anatomy (Fig. 1). The goal of this research was to develop an anatomically shaped, soft-tissue friendly large diameter femoral head that retains the benefits of contemporary implants. Methods:. Various Anatomically Contoured femoral Head (ACH) designs were constructed, wherein the articular surface extending from the pole to a theta (θ) angle, matched that of contemporary implants (Fig. 2). However, the articular surface in the peripheral region was moved inward towards the femoral head center, thereby reducing material that could impinge on the soft-tissues (Fig. 1 and Fig. 2). Finite element analysis was used to determine the femoroacetabular contact area under peak in vivo loads during different activities. Dynamic simulations were used to determine jump distance prior to posterior dislocation under different dislocation modes. Published data was used to compare the implant articular geometry to native anatomy (Fig. 3). These analyses were used to optimize the soft-tissue relief, while retaining the load bearing contact area, and the dislocation resistance of conventional implants. Results:. The resulting ACH prosthesis retained the large diameter profile of contemporary implants over an approximately hemispherical portion (Fig. 2). Beyond this, the peripheral articular surface was composed of smaller convex radii. With this design, the jump distance under posterior and anterior dislocation modes, and the femoroacetabular contact area under loads corresponding to walking, deep knee bend and chair sit, remained identical to that of contemporary implants. Additionally, while contemporary prosthesis extended beyond the native articular surface in the distal-medial and proximal-lateral regions (shaded grey), the ACH implant remained within the margins of the native anatomy (Fig. 3). Conclusion:. A novel large diameter anatomically contoured femoral head prosthesis was developed, to mitigate the soft-tissue impingement with contemporary prosthesis. The ACH retained the large diameter profile of contemporary implants over a hemispherical portion. However, in the peripheral region, the ACH had a smaller profile to reduce soft-tissue impingement

Introduction:. High failure rates with large diameter, metal on metal hip replacements have highlighted a potential issue with the head/stem taper junction as one of the significant sources of metal ion release. Postulated reasons as to why this may be such a problem with large head metal on metal hip replacements is due to the increased torque achieved by the larger head size. This may be responsible for applying greater micromotion between the head and stem taper and consequently greater amounts of fretting corrosion. The aim of this study was to perform short term in vitro electrochemical tests to assess the effect of increasing head diameter and torque on the fretting corrosion susceptibility of the head/stem taper interface and to investigate its effect on different material combinations. Methods:. 36 mm Cobalt Chrome (CoCr) femoral heads were coupled with either a CoCr or Titanium (Ti) stem with 12/14 tapers, all with a smooth surface finish. Increasing perpendicular horizontal offsets in the sagittal plane created incremental increases in torque. Offset increments of 0 mm, 5.4 mm and 7.5 mm were selected (Figure 1) to simulate the torque force equivalent to 9 Nm, 12 Nm and 17 Nm. An inverted hip replacement setup was used (ASTM F1875-98) (Figure 2). Components were statically loaded at 0 kN and 2.3 kN prior to sinusoidal cyclic loading and electrochemical testing. Mean & fretting currents were calculated every 50 cycles up to a maximum of 1000 cycles of sinusoidal cyclic loading at 3 Hz along with the Overall Mean Current (OMC), Overall Mean Fretting Current (OMFC) and Overall Current change (OCC). Results:. There was a significant increase in the mean current (R = 0.992, p = 0.008) and fretting current (R = 0.929, p = 0.071) for CoCr-CoCr and in the mean current (R = 0.780, p = 0.005) and fretting current (R = 0.810, p = 0.006) for CoCr-Ti material combinations, with increasing femoral offsets. The highest currents (mean and fretting) were produced at 7.5 mm and the lowest at 0 mm offsets. The proportional relationship between torque and corrosion was observed for both CoCr-CoCr and CoCr-Ti material combinations. With low torques we saw higher OMC and OMFC with the Co-Ti material combination however with higher torques we saw higher OMC and OMFC with the CoCr-CoCr combination (Figure 3). Conclusion:. Increasing torque leads to increased susceptibility to fretting corrosion at the modular head/stem taper interface of total hip replacements for both head stem material combinations. This study highlights the risk of high frictional torque, independent of material combination, on the head/ stem with the use of large heads. This is particularly relevant with the increasing use of larger diameter femoral heads across all bearing material combinations, in current hip arthroplasty practice

The Accolade®TMZF is a taper-wedge cementless metaphyseal coated femoral stem widely utilized from 2002-2012. In recent years, there have been reports of early catastrophic failure of this implant. Establishing a deeper understanding of the rate and causes of revision in patients who developed aseptic failure in stems with documented concerns about high failure rates is critical. Understanding any potential patient or implant factors which are risk factors for failure is important to inform both clinicians and patients. We propose a study to establish the long-term survival of this stem and analyze patients who underwent aseptic revision to understand the causes and risk factors for failure. A retrospective review was undertaken of all patients who received a primary total hip arthroplasty with an Accolade® TMZF stem at a high-volume arthroplasty center. The causes and timing of revision surgery were documented and cross referenced with the Canadian Institute of Health Information Discharge Abstract Database to minimize loss to follow-up. Survivorship analysis was performed with use of the Kaplan-Meier curves to determine the overall and aseptic survival rates at final follow-up. Patient and implant factors commonly associated with aseptic failure were extracted and Cox proportional hazards model was used. A consecutive series of 2609 unilateral primary THA patients implanted with an Accolade®TMZF femoral hip stem were included. Mean time from primary surgery was 12.4 years (range 22 days to 19.5 years). Cumulative survival was 96.1% ± 0.2 at final follow-up. One hundred and seven patients underwent revision surgery with aseptic loosening of the femoral component was the most common cause of aseptic failure in this cohort (33/2609, 1.3%). Younger age and larger femoral head offset were independent risk factors for aseptic failure. To our knowledge, this is the largest series representing the longest follow-up of this taper-wedge cementless femoral implant. Despite early concerns, the Accolade® TMZF stem has excellent survivorship in this cohort. Trunnionosis as a recognized cause for revision surgery was rare. Younger age and larger femoral head offset were independent risk factors for aseptic failure

This study aimed to examine the changing trends in the reasons for total hip replacement (THR) revision surgery, in one country over a twenty-one year period, in order to assess whether changes in arthroplasty practices have impacted revision patterns and whether an awareness of these changes can be used to guide clinical practice and reduce future revision rates. The reason for revision THR performed between January 1999 and December 2019 was extracted from the New Zealand Joint Registry (NZJR). The results were then grouped into seven 3-year periods to allow for clearer visualization of trends. The reasons were compared across the seven time periods and trends in prosthesis use, patient age, gender, BMI and ASA grade were also reviewed. We compared the reasons for early revision, within one year, with the overall revision rates. There were 20,740 revision THR registered of which 7665 were revisions of hips with the index procedure registered during the 21 year period. There has been a statistically significant increase in both femoral fracture (4.1 – 14.9%, p<0.001) and pain (8.1 – 14.9%, p<0.001) as a reason for hip revision. While dislocation has significantly decreased from 57.6% to 17.1% (p<0.001). Deep infection decreased over the first 15 years but has subsequently seen further increases over the last 6 years. Conversely both femoral and acetabular loosening increased over the first 12 years but have subsequently decreased over the last 9 years. The rate of early revisions rose from 0.86% to 1.30% of all revision procedures, with a significant rise in revision for deep infection (13-33% of all causes, p<0.001) and femoral fracture (4-18%, p<0.001), whereas revision for dislocation decreased (59-30%, p<0.001). Adjusting for age and gender femoral fracture and deep infection rates remained significant for both (p<0.05). Adjusting for age, gender and ASA was only significant for infection. The most troubling finding was the increased rate of deep infection in revision THR, with no obvious linked pattern, whereas, the reduction in revision for dislocation, aseptic femoral and acetabular loosening can be linked to the changing patterns of the use of larger femoral heads and improved bearing surfaces

With the introduction of highly crosslinked polyethylene (HXLPE) in total hip arthroplasty (THA), orthopaedic surgeons have moved towards using larger femoral heads at the cost of thinner liners to decrease the risk of instability. Several short and mid-term studies have shown minimal liner wear with the use HXLPE liners, but the safety of using thinner HXPLE liners to maximize femoral head size remains uncertain and concerns that this may lead to premature failure exist. Our objective was to analyze the outcomes for primary THA done with HXLPE liners in patients who have a 36-mm head or larger and a cup of 52-mm or smaller, with a minimum of 10-year follow-up. Additionally, linear and volumetric wear rates of the HXLPE were evaluated in those with a minimum of seven-year follow-up. We hypothesized that there would be minimal wear and good clinical outcome. Between 2000 and 2010, we retrospectively identified 55 patients that underwent a primary THA performed in a high-volume single tertiary referral center using HXLPE liners with 36-mm or larger heads in cups with an outer diameter of or 52-mm or smaller. Patient characteristics, implant details including liner thickness, death, complications, and all cause revisions were recorded. Patients that had a minimum radiographic follow-up of seven years were assessed radiographically for linear and volumetric wear. Wear was calculated using ROMAN, a validated open-source software by two independent researchers on anteroposterior X-rays of the pelvis. A total of 55 patients were identified and included, with a mean age of 74.8 (range 38.67 - 95.9) years and a mean BMI of 28.98 (range 18.87 - 63-68). Fifty-one (94.4%) of patients were female. Twenty-six (47.7%) patients died during the follow-up period. Three patients were revised, none for liner wear, fracture or dissociation. Twenty-two patients had a radiographic follow-up of minimum seven years (mean 9.9 years, min-max 7.5 –13.7) and were included in the long-term radiographic analysis. Liner thickness was 5.5 mm at 45 degrees in all cases but one, who had a liner thickness of 4.7mm, and all patients had a cobalt-chrome head. Cup sizes were 52mm (n=15, 68%) and 50mm (n=7, 32%). Mean linear liner wear was 0.0470 mm/year (range 0 - 0.2628 mm) and mean volumetric wear was 127.69 mm3/year (range 0 - 721.23 mm3/year). Using HXLPE liners with 36-mm heads or bigger in 52-mm cups or smaller is safe, with low rates of linear and volumetric wear in the mid to long-term follow-up. Patients did not require revision surgery for liner complications, including liner fracture, dissociation, or wear. Our results suggest that the advantages of using larger heads should outweigh the potential risks of using thin HXLPE liners

Increased femoral head size reduces the rate of dislocation after total hip arthroplasty (THA). With the introduction of highly crosslinked polyethylene (HXLPE) liners in THA there has been a trend towards using larger size femoral heads in relatively smaller cup sizes, theoretically increasing the risk of liner fracture, wear, or aseptic loosening. Short to medium follow-up studies have not demonstrated a negative effect of using thinner HXLPE liners. However, there is concern that these thinner liners may prematurely fail in the long-term, especially in those with thinner liners. The aim of this study was to evaluate the long-term survival and revision rates of HXLPE liners in primary THA, as well as the effect of liner thickness on these outcomes. We hypothesized that there would be no significant differences between the different liner thicknesses. We performed a retrospective database analysis from a single center of all primary total hip replacements using HXLPE liners from 2010 and earlier, including all femoral head sizes. All procedures were performed by fellowship trained arthroplasty surgeons. Patient characteristics, implant details including liner thickness, death, and revisions (all causes) were recorded. Patients were grouped for analysis for each millimeter of PE thickness (e.g. 4.0-4.9mm, 5.0-5.9mm). Kaplan-Meier survival estimates were estimated with all-cause and aseptic revisions as the endpoints. A total of 2354 patients (2584 hips) were included (mean age 64.3 years, min-max 19-96). Mean BMI was 29.0 and 47.6% was female. Mean follow-up was 13.2 years (range 11.0-18.8). Liner thickness varied from 4.9 to 12.7 mm. Seven patients had a liner thickness <5.0mm and 859 had a liner thickness of <6.0mm. Head sizes were 28mm (n=85, 3.3%), 32mm (n=1214, 47.0%), 36mm (n=1176, 45.5%), and 40mm (n=109, 4.2%), and 98.4% were metal heads. There were 101 revisions, and in 78 of these cases the liner was revised. Reason for revision was instability/dislocation (n=34), pseudotumor/aseptic lymphocyte-dominant vasculitis associated lesion (n=18), fracture (n=17), early loosening (n=11), infection (n=7), aseptic loosening (n=4), and other (n=10). When grouped by liner thickness, there were no significant differences between the groups when looking at all-cause revision (p=0.112) or aseptic revision (p=0.116). In our cohort, there were no significant differences in all-cause or aseptic revisions between any of the liner thickness groups at long-term follow-up. Our results indicate that using thinner HXPE liners to maximize femoral head size in THA does not lead to increased complications or liner failures at medium to long term follow-up. As such, orthopedic surgeons can consider the use of larger heads at the cost of liner thickness a safe practice to reduce the risk of dislocation after THA when using HXLPE liners

Key Points:. Historically, 22.25, 26, 28, or 32 mm metal femoral heads were used in primary total hip arthroplasty, but innovations in materials now permit head sizes 36 mm or larger. Stability and wear of primary total hip arthroplasty are related to the diameter and material of the femoral head. Larger diameter femoral heads are associated with increased joint stability through increases in arc range of motion and excursion distance prior to dislocation. Fixation of the acetabular component may be related to the size of the femoral head, with increased frictional torque associated with large diameter heads and certain polyethylene. Linear wear of highly crosslinked polyethylenes seems unrelated to femoral head diameter, but larger heads have been reported to have higher volumetric wear. Mechanically assisted crevice corrosion at the connection between the modular femoral head and neck may be associated with the femoral head size and material. Cobalt chromium alloy, alumina ceramic composite, or oxidised zirconium femoral heads on highly crosslinked polyethylene are the most commonly used bearing surfaces, but each may have unique risks and benefits. Conclusions. At present, there is a wave of enthusiasm for the routine use of “large” (32, 36 mm, or larger) femoral heads with highly crosslinked polyethylene for the vast majority of patients having a primary THA. It may be reasonable to consider the “graduated femoral head-outer acetabular diameter system”, using 28 mm femoral heads with “smaller” acetabular components (<50 mm), 32 mm femoral heads with acetabular components 50 – 56 mm outer diameter, and 36 mm or larger femoral heads with acetabular components 58 mm or larger in diameter, to minimise both the risk of dislocation and the frictional torque. Although the linear wear of highly crosslinked polyethylene appears to be independent of head size, the reported increase in volumetric wear with large femoral heads and highly crosslinked polyethylene requires further study, and should temper the use of femoral heads 36 mm or larger in younger and more active patients. With its long and successful history, it is difficult to recommend the complete abandonment of the cobalt chromium alloy femoral head in all patients having a primary THA. Alumina ceramic or oxidised zirconium heads may be considered for younger, heavier, and more active patients, who seem to have the highest risk of trunnion corrosion. Surgeons and patients should be aware of the unique possible complications of these two newer femoral head materials

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip arthroplasties in the United States. Hence, there is great interest in maximising stability to prevent this complication. Highly cross-linked polyethylene has allowed us to increase femoral head size, without a clinically important increase in wear. Head size has long been recognised to have a strong influence on the risk of dislocation postoperatively. As femoral head size increases, stability is augmented, secondary to a decrease in component-to-component impingement, which is theoretically eliminated at head sizes greater than 36mm in diameter (however osseous impingement can still occur). Larger head sizes also greatly increase the “jump distance” required for the head to dislocate (in an appropriately positioned cup) and eliminate the need for skirts. Level one studies support the use of larger diameter heads as decreasing the risk of dislocation following primary and revision THA. Larger diameter heads do, however, have negatives with the most recent concern being larger forces imparted upon the trunnion, which may contribute to adverse local tissue reactions (ALTR) which have recently been reported in patients with a metal on polyethylene bearing. However, in the series by Cooper et al, 32mm was the most common head size identified with no head sizes >36mm in this series. This suggests that the cause of ALTR is probably multifactorial and while femoral head size may be a contributor, the trunnion itself may be more important including its diameter, length and modulus of elasticity as well as the specific finish of the taper. Finally, when larger femoral head sizes are used in smaller acetabular components, the result is a thinner polyethylene liner, which may increase the risk of liner breakage. Larger diameter bearings may also increase the risk of squeaking in ceramic on ceramic bearing couples. Hence, the decision on femoral head size probably should include a balance between patient risk factors for instability and the risks of increased head size. Hence for revision procedures, and in primary cases where the risk of dislocation is known to be high, the risk of a larger femoral head is probably outweighed by the benefits of enhanced stability if a larger femoral head is utilised

Purpose. Dislocation after revision total hip is a common complication. The purpose of this study was to assess whether a large femoral head (36/40mm) would result in a decreased dislocation rate compared to a standard head (32mm). Method. A randomized clinical trial was undertaken to assess the effect of large femoral heads on dislocation after revision total hip. Patients undergoing revision hip arthroplasty at seven centers were randomized to 32mm head or 36/40mm head. Patients were stratified according to surgeon. Primary endpoint was dislocation. Rates were compared with Fishers exact test. Secondary outcome measures were quality of life: WOMAC, SF-36 and satisfaction. One hundred eighty four patients were randomized: 92 in the 32mm head group and 92 in the large head group. Baseline demographics were similar in the two groups. Patients were followed from two to five years postoperatively. Results. In the large head group dislocation rate was 1.1% (1/92) versus 8.7% (8/92) for the 32mm head (p=0.035). In this study there was no difference in quality of life between the two groups. Conclusion. This randomized clinical trial demonstrates that a large femoral head (36/40mm) can significantly reduce dislocation rate in patients undergoing revision total hip. As a result of this study the authors now routinely use large heads in all revision hip arthroplasty

INTRODUCTION:. Recent trends in total hip arthroplasty (THA) have resulted in the use of larger acetabular components to achieve larger femoral head sizes to reduce dislocation, and improve range of motion and stability. Such practices can result in significant acetabular bone loss at the time of index THA, increasing risk of anterior/posterior wall compromise, reducing component coverage, component fixation, ingrowth surface and bone stock for future revision surgery. We report here on the effects of increasing acetabular reaming on component coverage and bone loss in a radiographic CT scan based computer model system. METHODS:. A total of 74 normal cadaveric pelves with nonarthritic hip joints underwent thin slice CT scan followed by upload of these scans into the FDA approved radiographic analysis software. Utilizing this software package, baseline three-dimensional calculations of femoral head size and acetabular size were obtained. The software was used to produce a CT scan based model that would simulate reaming and placement of acetabular components in these pelves that were 125, 133 and 150% the size of the native femoral head. Calculations were made of cross sectional area bone loss from anterior/posterior columns, and loss of component coverage with increasing size. RESULTS:. Use of acetabular components that were 125, 133 and 150% the size of the native femoral head led to a average loss of 23, 27% and 33% loss of cross-sectional acetabular bone and an average 7, 16 and 27% loss of acetabular component coverage. CONCLUSION:. The CT scan/computer based model described here demonstrates that acetabular preparation and use of large components simply to gain larger femoral head size can result in significant bone loss and reduced component coverage. Operating hip surgeons attempting to utilize such large components must take great caution when attempting to maximize acetabular component size

Metal on metal total hip arthroplasty provides the potential improvement in articular wear and the use of large-diameter femoral heads following the prospect for reduction in the risk of dislocation. The purpose of this study was to compare the clinical and radiographic outcomes as well as serum metal ion level between the two different component designs with small and large femoral heads in metal on metal total hip arthroplasty. We studied 39 patients with large head (Magnum®, Biomet; cup size minus 6 mm) and 37 patients with small head (M2a taper®, Biomet; 28 or 32 mm head) of metal on metal total hip arthroplasty between December 2009 to October 2011 with follow-up of 2.1 years (1.0–3.3 years) after surgery. Harris Hip Score, UCLA activity score, EQ-5D, radiographic assessment, and serum cobalt and chromium ion levels were evaluated. Harris Hip Score, UCLA activity score, and EQ-5D were improved after surgery in small and large head groups, however, no significant differences were observed between both groups. Cup inclination was below 50 degree in all prosthesis. No loosening and no osteolysis were observed. Cobalt and chromium ion was not detected before surgery; however, metal ion levels of both groups were increased after surgery in time dependent manner. There was no significant difference between two groups at one year after surgery. One patient in each group showed the increase of cobalt ion level over 7 ppb (15.4 ppb, 12.9 ppb) without any clinical symptom including pain. Cup inclination was 29 degree in both patients and cup anteversion was 38 and 41 degree, respectively. There was no significant difference of ion levels between both groups. No dislocation was observed in large head group while one dislocation occurred in small head group. No patients required the revision surgery. This metal on metal component, especially with large femoral heads, showed the good clinical results at the maximum follow up of 3.3 year after surgery. However, the ion level of two patients increased over 7 ppb and longer follow-up will be needed

There has been a renewed interest in surface replacement arthroplasty over the last decade, with the hope and expectation that this procedure would provide an advantage over conventional total hip arthroplasty, especially in the young, active patient. More specifically, the promises of surface replacement arthroplasty have been: 1) preservation of bone stock so that future revisions would be easier, 2) potential to be minimally invasive in their approach, 3) better functional outcomes because of the stability associated with a larger femoral head with potential associated proprioceptive advantages, and 4) improved survivorship. Unfortunately, these promises have not been realised. Surface replacement arthroplasty does maintain more initial bone stock on the femur, but also tends to remove more bone initially on the acetabular side. Long term, it is the loss of acetabular bone stock that is more problematic from a reconstructive perspective. Further, the “simple” revision afforded in surface replacement arthroplasty has led to reports of inferior clinical outcomes, especially with respect to subjective complaints of pain. Surface replacement arthroplasty is more invasive than conventional total hip arthroplasty as the femoral head is maintained and the window to the acetabulum is subsequently partially blocked. This is exacerbated by the fact that many of these patients are young active males. There is no compelling evidence that surface replacement arthroplasty offers improved functional outcomes over conventional total hip arthroplasty, particularly when considering gait and proprioception. Some studies have in fact shown inferior outcomes. The concept of the larger femoral head in surface replacement arthroplasty providing increased range of motion and subsequent better function is flawed as it is the head-to-neck ratio that appears to be a more important determinant of outcome in this sense. Total hip arthroplasty generally has a more favorable ratio. Surface replacement arthroplasty has inferior survivorship to conventional total hip arthroplasty, even when accounting for the younger age of this patient cohort. This finding is consistent across multiple national joint replacement registries. The outcomes and survivorship are particularly poor in females, with many authors now advocating that the procedure be reserved for males. Surface replacement arthroplasty has introduced several new problems and mechanisms of failures, most concerning of which is the formation of pseudotumors in some patients. It is unclear as to who is at risk for this significant complication, and the ability to diagnose and treat this disorder is difficult and still in evolution. Likely associated is the significant elevation of metal ions in the serum and urine of some surface replacement arthroplasty patients. Neck fractures and loss of bone stock around the femoral implant have also been noted as problematic for these devices. Some of these problems have led to specific surface replacement arthroplasty systems being recalled. Finally, surface replacement arthroplasties are premium products with associated increased costs, which, frankly, are not justified

The need for a more durable, metal free, non-osteolytic particle generating material in Total Hip Replacement (THR) is urgently required to reduce revision surgeries. Current used materials; ceramic, metal and UHMWPE remain discrepant for long-term use. Polyimide (MP-1™) is a high performance biopolymer, originating from aerospace industry. MP-1™ is heat resistant, highly cross-linked and exhibits a self-lubrication property required for bearings and articulating joints. Being resistant to fatigue, creep and chemicals and serializable by autoclave or irradiation, MP-1™ is ideal for medical devices. Finalizing pre-clinical testing, two patients were implanted 13 years ago after informed consent. A PM (Post Mortem) retrieval at 6.5 years, showed no measureable wear, a bland synovium, and no osteoclastic or bone marrow reaction. The 13Y patients' hip, a revision from Polyethylene wear to MP-1™, has an unchanged radiograph and is fully active (Fig. 1). The Ethical Committee approved 100 patients with a single surgeon (PJB) post-marketing trial running Delta ceramic femoral ball against MP-1™ liner. Age range is from 81 to 33 years. The younger patients now being offered MP-1™, in view of the retrieval data. The MP-1™ acetabular liner is 4mm thick, as currently used in a LIMA PF shell, which replaces polyethylene, ceramic or dual mobility options. Out of the 78 enrolled patients, 52 patients have the implant for more than 5 years. The only “Complications” in a few patients was an initial squeak which spontaneously disappears by 10 days and never returns. This is likely due to reduced clearance between head and liner and likely easily correctable. There have been no dislocations or restrictions on activity level. Oxford and Harris Hip scores along with radiology, blood and clinical examination are collected during follow-up. MP-1™ liner on Delta ceramic head in THA, or in the future with MP-1 head, looks very promising with advantages of ease of sterilization, insignificant wear, no tissue reactivity and ability to have thin section and larger femoral heads if desired for larger range of motion. MP-1™ biomaterial is used for other medical devices as well such as dental implants and trauma nails, plates and screws. For any figures or tables, please contact the authors directly

INTRODUCTION. Femoral head diameter has a major influence on stability and dislocation resistance after Total Hip Arthroplasty (THA). Although routine use of large heads is common, several recent studies have shown that contemporary large head prostheses can directly impinge against native soft tissues, particularly the iliopsoas which wraps around the femoral head, leading to refractory anterior hip pain. To address this, we developed a novel Anatomically Contoured large diameter femoral Head (ACH). We hypothesized that anatomical contouring of the ACH implant for soft tissue relief would not compromise dislocation resistance, and the ACH implant would provide increased stability compared to small heads. METHODS. In this study the dislocation resistance of a 36 mm ACH was compared to that of 28 mm and 36 mm contemporary heads. The ACH implant was based on a 36 mm sphere with smaller radii used to contour the peripheral region below the equator of the head. MSC Adams was used for dynamic simulations based on two previously described dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal rotation of the hip and a posterosuperior directed joint force; (B) posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction and a posteromedial force direction (Fig. 1). Impingement-free motion (motion without neck impingement against the acetabular liner) and jump distance (head separation from acetabulum prior to dislocation) were measured to evaluate the dislocation risk of each implant. The acetabular cup was placed at 42.5° abduction and 19.7° anteversion, while the femoral component was anteverted by 9.75° based on published data. RESULTS. The results showed no differences between the novel anatomically contoured 36 mm head and a conventional 36 mm head for both dislocation modes. The 36 mm ACH and conventional head showed greater impingement-free motion compared to the 28 mm conventional head, with an increase of 7° for dislocation mode A, and 4° for mode B. Relative to the 28 mm head, the jump distance for the 36 mm ACH and the 36 mm conventional head increased by 1.5 mm for dislocation mode A, and 2 mm for mode B (Fig. 2 and Fig. 3). CONCLUSION. The novel Anatomically Contoured large diameter femoral Head (ACH) showed increased dislocation resistance compared to a conventional small diameter head and matched the stability of a conventional large head of the same size. This confirmed the hypothesis that large femoral heads can be anatomically shaped to alleviate the risk of soft-tissue impingement, as in the ACH implant, without jeopardizing the desired stability

The selection of an acetabular component for primary hip arthroplasty has narrowed significantly over the past 10 years. Although monoblock components demonstrated excellent long-term success the difficulty with insertion and failure to fully appreciate full coaptation of contact with the acetabular floor has led to almost complete elimination of its utilization. Modular acetabular components usually with titanium shells and highly crosslinked polyethylene are by far the most utilised today. This is particularly true with mid-term results demonstrating excellent wear rates and extremely low failure rates and the concern of possible mechanical failure of highly crosslinked polyethylene not being a clinical problem. Ceramic liners are also used but problems with squeaking articulations and liner chipping have made highly crosslinked polyethylene the preferred liner material. Metal-on-metal except in surface replacement arthroplasty is rarely used in primary hip arthroplasty. With instability in total hip replacement still being a significant and the leading cause of revision hip replacement the dual mobility articulation has emerged as an increasingly used acetabular component. This is composed of either a monoblock cobalt chrome socket articulating with a large polyethylene liner into which the femoral head is constrained. The polyethylene liner becomes essentially a larger femoral head articulation and hip stability is significantly improved. A modular dual mobility can also be utilised with a titanium shell and a cobalt chrome liner inserted into the shell and then a dual mobility articulation. In a recent series of 182 dual mobility cups, all monoblock ADM, in high risk patients undergoing primary total hip replacement there was 1 interprosthetic dislocation which occurred during reduction of a dislocation. Average follow up was 4.4 years with a range of 2–6.6 years

Purpose. Use of a large femoral head metal-on-metal bearing in total hip arthroplasty may offer an advantage in terms of dislocation rates and more natural joint kinematics. The acetabular component is more rigid however in these prostheses and if not placed accurately can lead to increased levels of metal ion release. A prospective randomized controlled trial was conducted to quantify bone mineral density on the acetabular side, as well as compare metal ion levels from a standard metal-on-polyethylene bearing to a large head metal-on-metal bearing in primary total hip arthroplasty. Method. Fifty patients were randomized to receive total hip arthroplasty with either the CONSERVE A-Class Total Hip with BFH femoral head or the Lineage acetabular component with polyethylene insert and cobalt chrome femoral head. There were 27 females (11 BFH) and 23 males (14 BFH), with a mean overall age of 61.6 (range 47.7–73.2). Serum levels of cobalt, chromium, and titanium were measured at regular intervals up to two years. Harris Hip Score, WOMAC, UCLA, and RAND-36 were completed at these same intervals. Standard radiographs as well as periprosthetic BMD were performed. Results. Bone mineral density in acetabular zones II, III, and IV was greater in the BFH group compared with the metal on poly group (p= 0.030, 0.046, and 0.019 respectively). Serum levels of cobalt (2.31 microg/mL vs 0.23 microg/mL, p=<0.001) and chromium (1.53 microg/mL vs 0.21 microg/mL, p=<0.001) were statistically higher in the BFH group compared with the metal-on-polyethylene group at one year post-op. There was no significant difference in serum titanium levels between groups. Conclusion. At short term follow up the load transfer to the acetabular bony bed differed between the two groups, with the more rigid shells demonstrating increased BMD in certain zones when compared with metal on poly. Serum levels of certain ions were 7–15 fold higher in the metal-on-metal large femoral head design compared with a standard metal-on-polyethylene. We await results on any clinical differences in performance and complications in this group of patients. Systemic implications of these ion levels are not known and further study is warranted

Introduction. Large diameter femoral heads provide increased range-of-motion and reduced dislocation rates compared to smaller diameter femoral heads. However, several recent studies have reported that contemporary large head prostheses can directly impinge against the local soft tissues leading to anterior hip pain. To address this we developed a novel Anatomically Contoured large diameter femoral Head (ACH) that maintains the profile of a large diameter femoral head over a hemispherical portion and then contours inward the distal profile of the head for soft-tissue relief. We hypothesized that the distal contouring of the ACH articular surface would not affect contact area. The impact of component placement, femoral head to acetabular liner radial clearance, and joint loading during different activities was investigated. Methods. A finite element model was used to assess the femoroacetabular contact area of a 36 mm diameter conventional head and a 36 mm ACH (Fig. 1). It included a rigid acetabular shell, plastically deformable UHMWPE acetabular liner, rigid femoral head and rigid femoral stem. The femoral stem was placed at 0°, 10° and 20° of anteversion. The acetabular shell and liner were placed in 20°, 40° and 60° of abduction and 0°, 20° and 40° of anteversion. The femoral head to acetabular liner radial clearances modeled were 0.06 mm, 0.13 mm and 0.5 mm. Three loading cases corresponding to peak in vivo loads during walking, chair sit and deep-knee bend were analyzed (Fig. 2). This allowed a range of component positions and maximum joint loads to be studied. Results. Under all tested conditions there was no difference between the two implants (Fig. 3). The contact area for both prosthesis depended on the radial clearance between the head and liner. The conventional head contact area (standard deviation) in mm. 2. for 0.5 mm, 0.13 mm and 0.06 mm of radial clearance was 230.5 (70.2), 419.8 (48.7) and 575.4 (60.1) respectively. Similarly, for the ACH these were 230.5 (70.4), 420.1 (48.7) and 575.9 (59.4). The average data for a head and radial clearance combination included all component placements and load conditions completed. A student T-Test (p = 0.05) confirmed that the ACH had the same contact area as the conventional head for all radial clearances. Conclusion. This study showed that, as intended, an anatomically contoured large diameter femoral head designed to provide soft-tissue relief maintained the load bearing articular contact area of a conventional implant. The novel ACH prosthesis could mitigate the risk of soft-tissue impingement with contemporary large head implants while retaining their benefits of additional stability and range-of-motion

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip arthroplasties in the United States. We have advocated identifying the primary cause of instability to plan appropriate treatment (Wera, Della Valle, et al., JOA 2012). Once implant position, leg length, and offset have been optimised and sources of impingement have been removed, the surgeon can opt for a large femoral head, a dual mobility articulation or a constrained liner. Given the limitations of constrained liners, we have looked to dual mobility articulations as an alternative, including its use in patients with abductor deficiency. We retrospectively compared a consecutive series of revision THA that were at high risk for instability and treated with either a constrained liner or a dual mobility articulation. At a minimum of two years, there were ten dislocations in the constrained group (10/43 or 23.3%) compared to three in the dual-mobility group (3/36 or 8.3%; p = 0.06). With repeat revision for instability as an endpoint, the failure rate was 23% for the constrained group and 5.5% for the dual mobility group (p = 0.03). We have also performed a systematic review of the published literature on the use of dual mobility in revision THA. Of the 3,088 hips reviewed, the dislocation rate was 2.2%, the risk of intraprosthetic dislocation was 0.3% and overall survivorship was 96.6% at 5 years. Dual mobility articulations offer anatomic sized femoral heads that greatly increase jump distance, without many of the negatives of a constrained liner. While dual mobility is associated with its own concerns and problems (including intraprosthetic dislocation and wear) our initial results suggest that they are a viable alternative to a constrained liner, even in the most challenging situations

Background. Large head metal on metal total hip arthroplasty MOM THA have been consistently shown substantial improvement in wear performance compared with metal on polyethylene articulations. Large diameter femoral heads theoretically can reduce dislocation risk by increasing range of motion before impingement, increasing prosthetic jump distance. However, early failure associated with adverse local tissue reactions (ALTRs) to metal debris is an emerging problem after MOM THA. The purpose of this study was to evaluate mid-term results of MOM THA. Materials and Methods. Twenty-five patients, 28 hips were included in this study. The average age of the patients at the time of surgery was 66.9 years. Three patients were men and 22 were women. MOM THAs were performed using 28 PINNACLE Cup system (DepPuy) (C-STEM: 23, S-ROM: 5) with posterior approach and head size of 36mm. Twenty-five primary THAs due to osteoarthritis in 22 cases and rheumatoid arthritis (RA) in one, and two revisions due to recurrent dislocation THA patients, were performed. The average follow up was 56.7 months. Evaluation items are JOA score, cup anteversion /lateral opening angle, and complications. Indication of the system were applied for patients with high risk of dislocation such as recurrent dislocation in primary and/or THAs, posterior pelvic tilt, elderly, RA and mental disorders. Results. The average JOA score improved from 48.3 (range: 26–77) preoperatively to 88.3 (range: 55–100) postoperatively. The average cup anteversion was 21.7 degrees (range: 2–38) and average lateral opening was 45.5 degrees (range: 37–60). Three patients (12%) developed dislocation. Two patients (8%) required reoperations from the deep infection. One female patient (4%) remained hip pain and was suspected pseudotumor / ALTR, which was confirmed by computed tomography and magnetic resonance imaging. Conclusion. Large femoral head MOM THA was useful for patients with recurrent dislocation in revision THA. However, three patients developed dislocation in primary THAs (12% of primary cases), which suggested that the more accurate placement of the acetabular cup is important even in the large diameter cup. Although only one case (4%) revealed ALTR, however, continuous careful follow-up would be necessary in the MOM system