Thin Polyethylene Liners Research Articles

In THA, Large Metal Heads in Thin Polyethylene Liners Versus Standard Metal Heads Did Not Differ for Liner Wear or Most PROs at 5 Years

In THA, Large Metal Heads in Thin Polyethylene Liners Versus Standard Metal Heads Did Not Differ for Liner Wear or Most PROs at 5 Years

Safety of using a large femoral head on thin polyethylene for total hip arthroplasty based on different types of polyethylene

The use of a large femoral head in total hip arthroplasty (THA) to stabilize and reduce the incidence of dislocation is on the increase, but concerns arise when combining them with small acetabular components due to potential mechanical failures in thin polyethylene (PE) liners. A single-institution, retrospective cohort study was conducted on 116 patients with minimum 2-year follow-up who received 36-mm femoral heads and acetabular components ≤ 52 mm, using either remelted highly cross-linked polyethylene (remelted HXLPE) or vitamin E-infused HXLPE (VEPE). Osteolysis and implant loosening were not observed in either group. Although a fracture of the PE liner was observed in each group (1.7%), the clinical outcomes were excellent, as the mean modified Harris Hip Score (mHHS) at the last follow-up was 93.5. Moreover, the mean linear wear rates measured by digital imaging software in both groups were low, with 0.035 mm/y in remelted HXLPE and 0.030 mm/y in VEPE. In conclusion, The use of a large femoral head on a thin PE liner can be a viable treatment option in patients who need to prioritize stability; however, careful attention should be paid to mechanical fractures of the PE liner.

Primary THA Using Thin Polyethylene Liners and Large Femoral Heads: A Minimum 5-Year Follow-Up.

Large femoral head sizes are commonly used in total hip arthroplasty (THA) to minimize the risk of instability. With small acetabular cup-size, large femoral head diameter often results in the use of thin polyethylene liners. The purpose of this study was to evaluate clinical and radiographic results of large femoral heads against thin polyethylene liners with minimum 5-year follow-up. This was a retrospective review identifying 58 primary THAs utilizing thin polyethylene inserts from one manufacturer (X3 polyethylene, Stryker, Mahwah, NJ) and large femoral heads (36 mm or greater) with minimum 5-year follow-up. A total of 3 patients were deceased and 11 lost to follow-up, leaving 44 patients for review. All patients were female with mean age 65.7 (range 26-85) and mean body mass index (BMI) 29.9 (range 19.6-45.4). Average length of follow-up was 8.5 years (range 5.1-11.3). Outcome measures included survivorship, complications, PROMs and radiographic analysis. There were four revisions: two aseptic loosening, one prosthetic joint infection, and one recurrent dislocation. Average HOOS-Jr, FJS-12, and patient satisfaction using Likert score was 94.3/100, 92.9/100, and 4.69/5.00, respectively, with 94% of patients reporting being satisfied or very satisfied. Radiographic analysis at average of 8.5 years demonstrated well-fixed implants without evidence of progressive radiolucent lines, osteolysis, or failure of the polyethylene liner. Survivorship using failure of the thin polyethylene liner as the endpoint was 100% at an average of 8.5 years. Thin polyethylene liners used with large femoral head sizes in small acetabular cups demonstrated excellent results at average 8.5-year follow-up with no cases of liner fracture or osteolysis.

Is the use of thin, highly cross-linked polyethylene liners safe in total hip arthroplasty?

Due to the high number of total hip arthroplasties (THA) revised due to instability, the use of large femoral heads to reduce instability is justifiable. It is critical to determine whether or not large femoral heads used in conjunction with thin polyethylene liners lead to increased wear rates, which can lead to osteolysis. Therefore, by using validated wear-analysis software, we evaluated linear wear rates in a consecutive cohort of patients who underwent primary THA with thin polyethylene liners. All patients were selected from a consecutive, prospectively collected database of 241 THAs performed at a single institution by two fellowship-trained joint-reconstruction surgeons between July 2007 and June 2011. These patients were 1:1 matched to a cohort of patients who had conventional-thickness polyethylene liners. No significant differences were observed between linear wear rates of thin or conventional-thickness liners. The Kaplan-Meier survivorship for both cohorts was 100 %, and no cases of polyethylene fracture were observed in either cohort. Our results suggest that according to a mean follow-up of 4 years, the use of thin liners in THA is promising. Longer follow-up is required to assess whether these outcomes are observed later.

Large diameter femoral heads: is bigger always better?

Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip replacements (THR). Hence, there is great interest in maximising stability to prevent this complication. Head size has been recognised to have a strong influence on the risk of dislocation post-operatively. As femoral head size increases, stability is augmented, secondary to an increase in impingement-free range of movement. Larger head sizes also greatly increase the 'jump distance' required for the head to dislocate in an appropriately positioned cup. Level-one studies support the use of larger diameter heads as they decrease the risk of dislocation following primary and revision THR. Highly cross-linked polyethylene has allowed us to increase femoral head size, without a marked increase in wear. However, the thin polyethylene liners necessary to accommodate larger heads may increase the risk of liner fracture and larger heads have also been implicated in causing soft-tissue impingement resulting in groin pain. Larger diameter heads also impart larger forces on the femoral trunnion, which may contribute to corrosion, metal release, and adverse local tissue reactions. Alternative large bearings including large ceramic heads and dual mobility bearings may mitigate some of these risks, and several of these devices have been used with clinical success.

Effect of Microseparation and Third-Body Particles on Dual-Mobility Crosslinked Hip Liner Wear

Large heads have been recommended to reduce the risk of dislocation after total hip arthroplasty. One of the issues with larger heads is the risk of increased wear and damage in thin polyethylene liners. Dual-mobility liners have been proposed as an alternative to large heads. We tested the wear performance of highly crosslinked dual-mobility liners under adverse conditions simulating microseparation and third-body wear. No measurable increase in polyethylene wear rate was found in the presence of third-body particles. Microseparation induced a small increase in wear rate (2.9mm3/million cycles). A finite element model simulating microseparation in dual-mobility liners was validated using these experimental results. The results of our study indicate that highly crosslinked dual-mobility liners have high tolerance for third-body particles and microseparation.

Papers Presented at the Annual Meetings of The Hip Society 2012: Editorial Comment

This symposium is composed of selected papers delivered at the Fall 2011 Closed Meeting of The Hip Society in New Albany, OH, USA, and the Open Scientific Meeting of The Hip Society on Specialty Day at the 2012 Annual Meeting of the American Academy of Orthopaedic Surgeons in San Francisco, CA, USA. These meetings focused on current basic and clinical research related to novel biomaterials and alternative bearing surfaces, outcome studies on different surgical techniques and prosthesis designs for primary and revision hip arthroplasty, patient characteristics that may influence clinical outcome, and hip-preserving procedures. Metal-on-metal (MOM) hip articulations continue to undergo close scrutiny. Indeed, a recent FDA panel meeting was held to discuss pertinent scientific and clinical aspects related to this articulation. The present Hip Society symposium highlights several important studies that address topics such as the interpretation of metal ion levels after MOM hip arthroplasty and outcome studies on MOM total and resurfacing hip arthroplasty. Whereas some MOM bearings appear to be functioning quite well, others have been withdrawn from the market. Ongoing clinical surveillance, including periodic analysis of metal ion levels and imaging studies using advanced metal suppression techniques, will shed more light on the future of this bearing couple. Acetabular components containing crosslinked polyethylene (XLPE) continue to perform well in the intermediate term. Coupled with a metal or ceramic femoral head, XLPE now is the material of choice for the acetabular side. Larger femoral heads are being used with XLPE to obtain a more stable articulation, decreasing the dislocation rate substantially. Furthermore, patient activity appears to decrease with age, thus giving the possibility of increased longevity of currently implanted XLPE liners. However, overly thin polyethylene liners and suboptimal cup position are still discouraged because of the possibility of fracture of the plastic. Which patient characteristics increase the complication rate after THA? Recent evidence implicates smoking and excessive alcohol use as potential risk factors for early failure. Dislocation is also increased in patients with neurologic disorders and in complex revision cases. So-called minimally invasive surgical approaches have also garnered much recent attention. However, it appears no one surgical approach leads to a better outcome in experienced hands. Revision surgery on the femoral side often presents great challenges due to deficient bone stock and soft tissue compromise. Recent intermediate-term studies have shown modular tapered stems can have a satisfactory outcome in these difficult situations. Longer-term studies are needed to compare clinical outcomes with monoblock revision stems. This symposium highlights some of the important basic and clinical research reported by members of The Hip Society and serves an educational purpose for surgeons undertaking surgical procedures of the hip. The studies reported in this symposium have all undergone rigorous peer review. The Hip Society is pleased to present this information to help improve patient outcomes and stimulate ongoing research in this area. Fig. 1 Stuart B. Goodman MD, PhD is shown.

Polyethylene in total hip arthroplasty: half a century in the limelight

Polyethylene in total hip arthroplasty: half a century in the limelight

Differences in Highly Cross-Linked Polyethylene Wear Between Zirconia and Cobalt-Chromium Femoral Heads in Japanese Patients: A prospective, randomized study

The purpose of this study was to compare highly cross-linked polyethylene wear between the zirconia head and the cobalt-chromium head in Japanese patients. A prospective, randomized study was performed to evaluate the outcomes in 32 hips that had zirconia heads and in 30 hips that had cobalt-chromium heads. The mean follow-up periods of both groups were same (5 years). There were no significant differences between the zirconia head and the cobalt-chromium head in the mean polyethylene linear wear per year and the mean volumetric polyethylene wear per year in the steady phase. This study indicates that zirconia head offers no benefits over metal head in terms of wear reduction at 5 years in Japanese patients who have lightweight and thin polyethylene liners.

The Effect of Polyethylene Thickness on the Wear of Highly Cross-Linked Acetabular Liners in a “Near-Impingement” Hip Simulator Model

Concern for stability and increased range of motion in THA has increased popularity of large femoral heads, while thin polyethylene liners have allowed acetabular component thickness to remain constant. Highly cross-linked polyethylene improves wear, but is accompanied by reduced toughness. Decreasing thickness may increase wear or cause gross fracture, especially at extremes of motion when contact between head and acetabulum nears the liner edge. We determined the effect of liner thickness on wear with large diameter heads in a near impingement model.

Catastrophic Failure of Ceramic-Polyethylene Bearing Total Hip Arthroplasty

Complications of ceramic-polyethylene bearing total hip arthroplasty (THA) include osteolysis, loosening, dislocation, and component failure. Catastrophic acetabular component failure involves severe damage to both the polyethylene liner and metal shell. This case study presents the first reported complete wear-through of the acetabular portion of a ceramic-polyethylene arthroplasty presenting as a dislocation and a review of the literature. In this study, a patient's alumina ceramic femoral head penetrated the polyethylene liner and titanium shell and presented as a dislocated THA. The contributing factors for this catastrophic failure include young patient age, high activity level, thin polyethylene liner, backside wear, component positioning, polyethylene sterilization with γ irradiation in air, and lack of appropriate follow-up. Revision THA was performed without complications.

Analysis and Results of Dissociation of the Polyethylene Liner in the Harris-Galante I Acetabular Component

The Harris-Galante I modular acetabular components (Zimmer, Warsaw, Ind) were most widely used in the 1980s in primary and revision total hip arthroplasty. We assessed 76 primary total hip arthroplasties performed using Harris-Galante I modular acetabular components. Dissociation of the polyethylene liner occurred in 5 patients and required revision surgery. None of the 76 hips had fractures of the metal locking tines on the metal shell. Liner dissociation was attributed to fatigue fracture of the polyethylene, a result of a gap between the liner and the metal shell. The thin polyethylene liner rim aggravated failure. The revision technique was to cement the polyethylene liner into the well-fixed Harris-Galante metal shell. The average follow-up observation period after revision surgery was 6.4 years; and there was no recurrence of dissociation, which supports the use of our revision technique.

Total Hip Arthroplasty Requiring Subtrochanteric Osteotomy for Developmental Hip Dysplasia: 5- to 14-Year Results

This study evaluated total hip arthroplasty in patients with developmental hip dysplasia requiring femoral subtrochanteric shortening derotational osteotomy (SDO). Twenty-three total hip arthroplasties that required SDO were evaluated at an average follow-up of 8 years (range, 5-14 years). Clinical and radiographic data were retrospectively reviewed. Four hips (17%) failed requiring revision. Time to revision averaged 4 years (range, 1-8 years) with polyethylene wear and osteolysis etiologic in 3 of 4 failures. Survivorship was 75% at 14 years. Subtrochanteric SDO provided reliable correction of dysplastic femoral deformity, facilitated hip reduction at the anatomic center, and demonstrated predictable union in all cases. Wear-induced osteolysis was the major reason for revision, probably due to the relatively thin polyethylene liners required for the small acetabular components used in young, active patients.

Catastrophic Failure of a Modular Revision Total Hip Polyethylene Insert

Early catastrophic failure of a modular polyethylene component is a potential problem after revision total hip arthroplasty. We describe an unusual case of polyethylene failure that occurred within 18 months of implantation in which no obvious technical error or mechanical failure was identified. The acetabular polyethylene insert was prepared with gas plasma sterilization, and the shelf life was 4 months. Radiographic evaluation used generalized Hough transforms to assess the cup articulation. We identified cup penetration of 2.8 mm before revision and catastrophic destruction of the polyethylene liner at the time of revision. Possible factors implicated for failure included a thin polyethylene liner, increased hip separation, femoral head mismatch, and the high activity level of a younger patient. We believe that this case report highlights the need for future investigations of these subtle factors.

Developmental hip dysplasia treated with total hip arthroplasty with a straight stem and a threaded cup.

Operative strategies to overcome the anatomical anomalies in patients with osteoarthritis secondary to developmental dysplasia of the hip remain controversial. The objective of this study was to determine the outcomes of total hip replacement with a grit-blasted cementless threaded cup and a cementless straight stem in patients with developmental dysplasia. Ninety-three patients with developmental hip dysplasia who had been treated with a total of 121 cementless total hip arthroplasties were clinically assessed at a mean of 9.3 years. The acetabular reconstruction was done with a cementless threaded cup, which was medialized to ensure that at least one thread was anchored in the bone in order to achieve good primary stability. All radiographs were analyzed retrospectively. Kaplan-Meier survivorship analysis, with radiographic evidence of aseptic loosening as the end point, predicted a survival rate of 97.5% for the acetabular component and 100% for the femoral stem at 9.3 years. The average Harris hip score for the unrevised hips improved from 34.0 points preoperatively to 84.1 points at the latest follow-up evaluation. The average total volume of polyethylene wear at the time of final follow-up was 73.6 mm(3). These wear and loosening rates demonstrate that very good results were achieved in this relatively young patient population when the hip joint center had been properly restored, even when a small cup with a thin polyethylene liner had been used.

Arthopor 2 acetabular component with screw fixation in primary hip arthroplasty: A 7- to 9-year follow-up study

The first 100 consecutive primary hip arthroplasties with the Arthopor 2 acetabular component (Joint Medical Products, Stamford, CT) with supplemental screw fixation performed by the senior author were prospectively studied. The mean patient age was 57 years. Seventy-seven cemented and 23 cementless stems were placed, with 32-mm femoral heads used in most of the patients. Eighty-six hips were reviewed at 7–8.8 years (mean, 7.8 years). The mean Harris hip score at final follow-up evaluation was 94 points. No cups have been revised, although 2 cups in patients with radiation osteonecrosis were loose radiographically. One patient underwent revision of a severely worn liner. Despite a relatively high mean linear wear rate of 0.27 mm/y (range, 0.13–0.57 mm/y), no radiographic evidence of pelvic osteolysis was seen. The Arthopor 2 cup performed well with respect to pelvic osteolysis, despite the presence of substantial polyethylene debris. The relatively high polyethylene wear rate is attributed in part to the younger patient population and the use of 32-mm femoral heads paired with thin polyethylene liners.

Hydroxyapatite Coated Implants

Two high risk groups for total hip arthroplasty, 136 patients (155 hips) younger than 50 years of age (average age, 38 years) and 44 patients (53 hips) with the diagnosis of avascular necrosis, have a minimum followup of 5 years and a mean followup of 6.8 years. The average Harris Hip Score at last followup totaled 93 and 90, respectively, and thigh pain was reported in 1.3% and 3.8%, respectively. All patients in both groups received the same hydroxyapatite coated femoral stem and the mechanical failure was 0%. No stem was revised for aseptic loosening, 100% of stems were bony stable by radiographic criteria, new bone formation was progressive about the femoral stem, and 0% endosteal lysis was found. The acetabular components had a mechanical failure rate of 10% and 7.5%, respectively, without osteolysis, and an additional 7% and 7.5% failure as a direct result of progressive osteolysis. The results with the porous press fit and hydroxyapatite threaded sockets were far superior to that of the smooth hydroxyapatite press fit sockets and socket failure was associated with thin polyethylene liners and the use of 32-mm head diameters. These findings show a high success rate with a nonporous hydroxyapatite coated titanium femoral stem. However, hydroxyapatite on a smooth acetabular component yielded less predictable results indicating that for long term fixation of the acetabulum an interlock of bone is preferred.