Conventional Polyethylene Inserts Research Articles

Improvement of rotational arc during deep flexion range of a novel designed polyethylene insert for posterior-stabilised total knee arthroplasty

BackgroundOne of the remaining issues in total knee arthroplasty (TKA) is achieving sufficient rotational arc during deep flexion range of the knee for specific postures such as the ‘seiza’ or cross-legged sitting. This study aimed to evaluate whether there was a change in the actual in vivo rotational arc during deep flexion range before and after a design change of polyethylene (PE) inserts. MethodsIn 50 posterior-stabilised TKA cases, knee kinematics, including rotational movement, were measured intraoperatively using an image-free navigation system to compare a newly designed PE insert with reduced the posterior lip with a conventional PE insert. Femoral–tibial rotational angles at 30°, 45°, 60°, 90°, 120°, and 130° knee flexion were evaluated. Varus/valgus instability, knee range of motion, and femoral rollback were also measured. Obtained parameters were compared between new and conventional PE inserts. The independent factors associated with rotational arc during deep flexion range (120° and 130° knee flexion) were analysed using multivariate analysis. ResultsThe newly designed PE insert demonstrated a significant increase in the rotational arc at 120° (22.9 ± 8.7° vs. 30.1 ± 11.9°, P < 0.001) and 130° (24.3 ± 9.5° vs. 32.5 ± 12.4°, P < 0.001) knee flexion compared with that with the conventionally designed posterior-stabilised insert. Multivariate analysis demonstrated that using the newly designed PE insert was an independent predictor of improved rotational arc during deep flexion range: regression coefficient was 11.2 (95% confidence interval 7.1–15.3, P < 0.001). ConclusionThe design change, which reduced the posterior lip of the PE insert, contributed to improved rotational arc in 120° and 130° deep flexion ranges.

No higher tibial post fracture rate with highly cross-linked polyethylene inserts in total knee arthroplasty at a minimum 10-year follow-up.

The purpose of this study was to assess tibial post fracture between highly cross-linked polyethylene (HXPE) and conventional polyethylene inserts in consecutive posterior-stabilized (PS) total knee arthroplasty (TKA) over a minimum 10-years follow-up period. Between July 2008 and December 2011, a consecutive series of 3264 primary TKAs was performed in 2098 patients using a PS total knee prosthesis at a single institution. The final cohort was classified into the HXPE group (792 cases) and the conventional group (2113 cases) according to insert material used during the procedure. The mean follow-up period was 11.4years in the HXPE group and 11.8years in the conventional group. Both cases of tibial post fracture occurred in the HXPE group, a complication rate of 0.25%. These two cases required replacement with a thicker tibial insert with retention of the femoral and tibial components. There were no cases of tibial post fracture in the conventional group. There was no difference in tibial post fracture rate between the HXPE group and the conventional group in PS TKA on long-term follow-up. IV.

High rate of tibial post-fracture in highly cross-linked polyethylene compared to conventional polyethylene in posterior-stabilized total knee arthroplasty at a minimum 12-year follow-up.

The purpose of this study was to assess tibial post-fracture between highly cross-linked polyethylene (HXPE) and conventional polyethylene inserts in consecutive posterior-stabilized (PS) total knee arthroplasty (TKA) over a minimum 12-year follow-up period. Between January 2007 and June 2008, a consecutive series of 2446 primary TKAs was performed in 1478 patients at a single institution. The final cohort was classified into two groups (1559 in the HXPE group and 887 in the conventional group) based on the insert material used during the procedure. The mean follow-up period was 13.1years in the HXPE group and 13.4years in the conventional group. All 16 cases of tibial post-fracture occurred in the HXPE group. This complication rate was 1.03%. The mean elapsed time from primary TKA to the diagnosis of post-fracture was 3.9years (range 0.5-10.0years). Ten cases required replacement with a thicker polyethylene insert, and six cases underwent tibial revision surgery. There were no cases of tibial post-fracture in the conventional group. Tibial post-fracture is not a rare complication in PS TKA with HXPE. Therefore, the possibility of a tibial post-fracture should be considered if newly developed pain, acute subluxation, effusion, patellar clunking, or instability occurs in patients treated with PS Scorpio knee system TKA using an HXPE insert. IV.

Highly cross-linked versus conventional polyethylene inserts in total hip arthroplasty, a five-year Roentgen stereophotogrammetric analysis randomised controlled trial.

BACKGROUNDPolyethylene (PE) particles produced by wear of the acetabular insert are thought to cause osteolysis and thereby aseptic loosening of the implant in total hip arthroplasty (THA). As highly cross-linked polyethylene (HXLPE) is presumed to give lower wear rates, in vivo studies are needed to confirm this.AIMTo compare the wear of REXPOL, a HXPLE, with conventional PE within the first five years after implantation using Roentgen stereophotogrammetric analysis (RSA).METHODSPatients were randomised to receive either a HXLPE (REXPOL) or a conventional PE insert during primary THA. RSA images were obtained directly postoperative and after 6 wk, 12 wk, 6 mo, 12 mo, 24 mo and five years. Functional outcomes were assessed using the Hip Injury and Osteoarthritis Outcome Score and Harris Hip Score at baseline and five years after surgery.RESULTSThe HXLPE (REXPOL) showed less wear in the latero-medial direction. Significant wear rates of conventional PE were seen in the latero-medial and center-proximal direction and in volume and corrected volume, whereas the REXPOL did not show these outcomes over time. Improvement from baseline in functional outcome did not significantly differ.CONCLUSIONTotal 3D wear is less in THAs inserted with a REXPOL inlay than a conventional PE inlay after five years. This study confirms, for the first, that the REXPOL HXLPE inlay is preferred to standard PE.

CORR Insights®: How do knee implants perform past the second decade? Nineteen- to 25-year followup of the Press-fit Condylar design TKA.

Where Are We Now? In the last three decades, TKA has established its position as the gold standard surgical treatment for severe, symptomatic knee osteoarthritis (OA). Although TKA is common procedure, published studies with long-term clinical and radiological followup are few [2, 6]. In register studies, there has been a constant reduction in risk of revision over time [8]. For example, a patient who had an operation in 2000 has a lower risk for revision than the patient who had a similar operation in 1990 with a similar followup time. Challenges with TKA — perhaps even more than THA — are more related to function and patient satisfaction [10]. The number of of TKAs are increasing in developed countries, especially among young patients with primary knee OA [5, 7]. Therefore, there is a clear need for publications with long-term clinical and radiological followup. Where Do We Need To Go? In the current study, Papil el al. report the results of the Press-fit Condylar TKA system (DePuy Orthopaedics, Warsaw, IN, USA) in 160 TKAs performed between 1986 and 1989. The authors noted an 87% survivorship for revision for any reason (95% CI, 80%-92%), and a 98% Kaplan-Meier survivorship for revision for aseptic loosening (95% CI, 93%-99%) at the mean 20-year followup (range, 19-25 years). The Knee Society Score did not seem to provide useful information regarding long-term outcome in older patients, since, as expected, the score decreased over time as occurs with normal aging. Also, there was substantial loss to radiographic followup in this report, and more detailed radiological analysis would have provided useful information on polyethylene wear and subsequent osteolysis. In their study, Papil el al. found aseptic loosening to be uncommon, justifying the continued use of cemented TKAs. Additionally, the number of revisions from polyethylene wear was also low. Currently, use of new designs such as uncemented TKA implants and crosslinked polyethylene inserts is increasing [1, 8]. However, polyethylene wear and aseptic loosening seem to be uncommon. On the other hand, there is a need to improve functional outcome after TKA. Moving forward, we must provide more scientific data to support the use of new TKA innovations. How Do We Get There? Further prospective, randomized clinical studies are needed to compare uncemented and cemented TKA implants with similar polyethylene characteristics. In addition, there is a need for prospective randomized clinical studies comparing conventional polyethylene inserts with crosslinked polyethylene liners used in same implant in order to avoid bias caused differences in the implant geometry. Long-term studies providing data on patient reported outcome measures such as the WOMAC [4], Oxford Knee Score [3], and Short Form-12 (SF-12) [9] would also be useful. In the future, we should focus on maximizing knee function and patient satisfaction by improving the function of TKA implants.

Wear, delamination, and fatigue resistance of melt‐annealed highly crosslinked UHMWPE cruciate‐retaining knee inserts under activities of daily living

The wear, delamination, and fatigue resistance of artificially aged gamma irradiation-sterilized conventional polyethylene (CPE) and gas-plasma-sterilized melt-annealed highly crosslinked polyethylene tibial inserts (HXPE) were compared. Six CPE and 12 HXPE (six irradiated at 58 kGy and six at 72 kGy) left knee inserts were wear tested for 5.5 million cycles (Mc) under loads and motions that mimic activities of daily living, such as walking, chair rise, stair ascent, and deep squatting. Another six HXPE (72 kGy) and six CPE inserts were also tested under conditions that could produce severe delamination for 8 Mc. Ten other knees (five 72 kGy HXPE and five CPE) were subjected to posterior edge loading fatigue testing for 5 Mc. The HXPE inserts had an average wear rate reduction of about 80% relative to their CPE counterparts during all activities. All of the CPE inserts delaminated and fractured during high cycle deep squat (152 degrees flexion) motions, while all the HXPE remained intact. None of the HXPE inserts delaminated after 8 Mc, while all of the CPE inserts developed delamination damage within 1.5-5.8 Mc of delamination testing. All CPE inserts developed subsurface cracks and delamination within 2.8 Mc during posterior edge loading fatigue studies, while none of the HXPE inserts showed cracking or delamination after 5 Mc. These results show that aged HXPE has higher wear and fatigue resistance than aged CPE, and offers potential long-term advantages for young active patients with sustained activities of daily living.

Comparison between highly cross-linked and conventional polyethylene in total knee arthroplasty

The use of highly cross-linked polyethylene in total knee prostheses is still controversial. The aim of the present study was to compare radiographic and clinical results of using conventional and highly cross-linked polyethylene in cruciate retaining total knee prostheses of completely the same design. Two hundred and two consecutive total knee arthroplasties (NexGen CR, Zimmer) were performed using the same procedure. The first consecutive 113 knees had conventional polyethylene insert and following consecutive 89 knees had highly cross-linked polyethylene insert (Prolong, Zimmer). Differences in the age, gender, and diagnosis between two groups were not statistically significant. Preoperative range of motion (ROM) of the knee, and Knee Society Score (KSS) was better in highly cross-linked polyethylene group. Clinical and radiographic results were evaluated at two years after operation. The difference of ROM and KSS between groups was not statistically significant. There was no revision surgery. No knee exhibited osteolysis, aseptic loosening, or polyethylene failure. There was no early catastrophic clinical failure due to use of the new material.

Five-year Experience with Crossfire?? Highly Cross-linked Polyethylene

Our purpose was to compare the clinical wear performance of highly cross-linked (Crossfire) polyethylene with conventional (N2Vac) polyethylene total hip bearings. We implanted 56 hips (47 patients) with Crossfire acetabular bearing liners and compared their wear performance with 53 conventional polyethylene inserts. Wear and clinical data were collected retrospectively at a minimum 4-year and average 5-year followup. The linear femoral head penetration rate measured from plain radiographs was 0.055 mm/year +/- 0.022 mm/year for the Crossfire polyethylene and 0.138 mm/year +/- 0.073 mm/year for the control, a reduction of 60% for the Crossfire components. Calculated annual wear was 0.036 mm/year for the Crossfire components and 0.131 mm/year for the controls, a reduction of 72%. Radiographic review at most recent followup showed a reduction in erosive osteolytic lesions of the proximal femur for the Crossfire components compared with controls, also suggesting a reduction in debris release for the Crossfire components. Complications leading to revision were not seen in the Crossfire or control groups. These clinical findings suggest that this particular highly cross-linked polyethylene can provide wear reduction and an alternate bearing surface for active patient populations. Therapeutic study, Level III (retrospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

In vivo wear of bilateral total hip replacements: conventional versus crosslinked polyethylene

Crosslinked polyethylene (PE) was developed to reduce volumetric wear in prosthetic joints. Hip simulator studies have shown promising results but there is as yet limited clinical data. We identified three patients with bilateral total hip replacements who received a crosslinked PE liner (Marathon, DePuy, Warsaw, IN, USA) on one side and a conventional PE insert (Enduron, DePuy) on the contralateral side. As an assessment of in vivo PE wear, linear head penetration was measured on standardized radiographs using a validated computer-assisted technique. In all the three cases, a marked reduction of more than 70% in volumetric wear was found in association with Marathon crosslinked PE. These case reports support the efficacy of this type of crosslinked PE in a selected group that allows direct comparison of the two different materials without the influence of patient-related factors such as activity, gender, weight, or others.

Aggressive wear testing of a cross-linked polyethylene in total knee arthroplasty.

Recently, highly cross-linked polyethylenes with high wear and oxidation resistance have been developed. These materials may improve the in vivo performance of polyethylene components used in total knee arthroplasty. To date, the in vitro knee wear testing of these new polyethylenes has been done under conditions of normal gait. However, their critical assessment also must include aggressive in vitro fatigue and wear testing. In the current study, an aggressive in vitro knee wear and device fatigue model simulating a tight posterior cruciate ligament balance during stair climbing was developed and used to assess the performance of one type of highly cross-linked polyethylene tibial knee insert in comparison with conventional polyethylene. The highly cross-linked inserts and one group of conventional inserts were tested after sterilization. One additional group of conventional inserts was subjected to accelerated aging before testing. The articular surfaces of the inserts were inspected visually for surface delamination, cracking, and pitting at regular intervals during the test. The aged conventional polyethylene inserts showed extensive delamination and cracking as early as 50,000 cycles. In contrast, the unaged conventional and highly cross-linked polyethylene inserts did not show any subsurface cracking or delamination at 0.5 million cycles. The appearance and location of delamination that occurred in the aged conventional inserts tested with the current model previously have been observed in vivo with posterior cruciate-sparing design knee arthroplasties with a tight posterior cruciate ligament.