PE Wear Research Articles

Insight on the in vivo wear characteristics of goat artificial cervical disc implanted for 6 months

Since the prosthesis may suffer overload or extreme motion during the daily activities, some special failure modes may be found in service. In order to give an insight on the in vivo stability of artificial cervical disc, the wear characteristics of goat prosthesis were studied after implanted in goat animal for 6 months. The prosthesis was designed with a ball-on-socket structure under the material combination of PE-on-TC4. The X-ray examination was performed to monitor the in vivo wear process. The worn morphology and wear debris were analyzed in detail by EDX and SEM. The result indicated that goat prosthesis revealed good safety and effectiveness during 6-month in vivo wear test. The wear damage occurred only on nucleus pulposus component with the dominant failure mode of surface fatigue and deformation. The damage distribution and wear severity was seriously uneven with a trend that the closer to the edge, the more severe the wear. For example, slippage phenomenon caused a wide and curved severe ploughing damage on the edge. Three kinds of debris were found including bone debris, carbon-oxygen compound debris and PE wear debris. Both bone debris and carbon-oxygen compound debris came from superior endplate while PE wear debris came from nucleus pulposus. The debris proportion for endplate was 82% for bone debris, 15% for carbon-oxygen compound debris and 3% for PE debris while for nucleus pulposus it was 8% for carbon-oxygen compound debris and 92% for PE debris. The size range of PE debris for nucleus pulposus was 0.1–100 μm, with an average size of 9.58 ± 16.34 μm. For the bone debris of endplate components, the size range was 0.1–600 μm, with an average size of 49.18 ± 94.54 μm. After wear test, the equivalent elastic modulus of nucleus pulposus increased from 28.55 MPa to 38.25 MPa. The results of FT-IR spectrum showed that the functional groups on the surface of polyethylene have not changed significantly after wear test. The results indicated that there were some differences in wear characteristics of wear morphology and wear debris between in vivo wear and in vitro wear.

Five-year polyethylene cup migration and PE wear of the Anatomic Dual Mobility acetabular construct.

Dual mobility implants have been successful in reducing postoperative hip dislocation but mid-term results of cup migration and polyethylene wear are missing in the literature. Therefore, we measured migration and wear at 5-year follow-up using radiostereometric analysis (RSA). A cohort of 44 patients (mean age 73, 36 female) with heterogeneous indications for hip arthroplasty but all with a high risk of hip dislocation received total hip replacement (THA) with The Anatomic Dual Mobility X3 monoblock acetabular construct and a highly crosslinked polyethylene liner. RSA images and Oxford Hip Scores were obtained perioperatively and 1, 2, and 5years postoperatively. Cup migration and polyethylene wear were calculated using RSA. Mean 2-year proximal cup translation was 0.26mm (95% CI 0.17; 0.36). Proximal cup translation was stable from 1- to 5-year follow-up. Mean 2-year cup inclination (z-rotation) was 0.23° (95% CI - 0.22; 0.68) and was greater in patients with osteoporosis compared to patients without osteoporosis (p = 0.04). Using 1-year follow-up as baseline, the 3D polyethylene wear rate was 0.07mm/year (0.05; 0.10). Oxford hip scores improved 19 (95% CI 14; 24) points from mean 21 (range 4; 39) at baseline, to 40 (9; 48) 2years postoperatively. There were no progressive radiolucent lines > 1mm. There was 1 revision for offset correction. Anatomic Dual Mobility monoblock cups were well-fixed, the polyethylene wear rate was low, and the clinical outcomes were good until 5-year follow-up suggesting good implant survival in patients of different age groups and with heterogeneous indications for THA.

Sensor-based measurement for advanced monitoring and early detection of PE wear in total knee arthroplasties

Abstract Polyethylene (PE) inlays of knee endoprostheses are exposed to constant mechanical stress causing particle abrasion and volumetric wear. With the current inlay surveillance strategy, significant change often can be only detected when the implant has already failed. To reduce medical complications arising from implant malposition or failure, early and accurate assessment of the implant condition is of great value. We present a novel concept to monitor PE inlays based on an implanted sensor. Requirements of sensor integration into endoprostheses were discussed and specified for an inlay monitoring concept. A planar eddy current sensor for measuring the gradual descent of the femoral component was proposed where inductive and capacitive sensor elements form a resonant circuit. The potential sensitivity of the proposed measuring method was tested in an experimental setup using an RFID tag as a sensor substitute. A measurement concept, including the sensor and an extracorporal readout coil, was described and the validity was verified using finite element method (FEM) simulation of a simplified knee model. The experiments showed that a significant resonant frequency shift occurs in the sensor with decreasing distance to the femoral component. FEM simulation demonstrated that the sensor could be powered and readout extracorporeally through inductive coupling with an external readout coil. The proposed concept is a promising solution for feasible and accurate reading of the implant status designed to meet medical requirements. It can enable autonomous and routine monitoring as well as early detection of critical inlay deformation with a home-use device.

Long-Term Results of the Modular Physiological Wrist Prosthesis (MPW®) in Patients with Inflammatory Diseases.

The wrist is among the predilection sites of over 90% of cases of rheumatoid arthritis (RA). In advanced cases, total wrist arthroplasty (TWA) is an alternative to arthrodesis. The aim of this study is to present the long-term results of the modular physiological wrist prosthesis (MPW®) and to match them in context with the results of a standard population survey. In a retrospective study with follow-up, patients with an MPW® endoprosthesis were evaluated concerning the clinical and radiological outcome, complications were reviewed (incidence and type), and conversion to wrist fusion was assessed. Patient function measurements included the Mayo wrist score, the patient-specific wrist test, and therefore the DASH score (arm, shoulder, and hand). Thirty-four MPW® wrist prostheses were implanted in 32 patients, including thirty primary implantations and four changes of the type of the endoprosthesis. Sixteen patients (18 prostheses) underwent clinical and radiological follow-up. The average follow-up time was 8.5 years (1 to 16). Poor results of the MPW prosthesis are caused by the issues of balancing with luxation and increased PE wear. Salvage procedures included revision of the TWA or fusion. In successful cases, the flexion and extension movement averaged 40 degrees. The grip force was around 2.5 kg. The common DASH score was 79 points, with limited and problematic joints of the upper extremity. The MPW wrist prosthesis offered good pain relief and functional movement in over 80% of cases. The issues of dislocation and increased PE wear prevent better long-term results, as do the joints affected. A follow-up study with fittings under a contemporary anti-rheumatic therapy with biologicals suggests increasing score results. Type of study/level of evidence: Case series, IV.

Reduced wear in vitamin E-infused highly cross-linked polyethylene cups: 5-year results of a randomized controlled trial

Background and purpose — Vitamin E-infused polyethylene is a relatively new material in joint arthroplasty; there are no long-term reports, and only few mid-term results. Using radiostereometric analysis (RSA), we primarily determined whether vitamin E-infused highly cross-linked polyethylene (HXLPE/VitE) acetabular cups show less wear than ultra-high molecular weight polyethylene (UHMWPE) acetabular cups at 5 years after total hip arthroplasty (THA). We also assessed whether wear rates correlate with increasing cup inclination angles or cup sizes. Patients and methods — This is a 5-year follow-up of our previously reported randomized controlled trial of 62 patients with 3 years’ follow-up, who received THA with either an HXLPE/VitE or a UHMWPE acetabular cup. At 5 years, 40 patients were analyzed (22 in the HXLPE/VitE and 18 in the UHMWPE group). Results — HXLPE/VitE cups continued to show less cumulative femoral head penetration than UHMWPE cups (HXLPE/VitE: 0.24 mm, UHMWPE: 0.45 mm; p < 0.001). Distribution of wear was also more even with HXLPE/VitE cups than with UHMWPE cups (p = 0.002). Moreover, the difference in PE wear between 1 and 5 years in both groups showed no statistically significant correlation with increasing cup inclination angles or cup sizes. Finally, no osteolysis and implant loosening occurred, and no revision surgeries were required. Interpretation — Wear rates continue to be lower in HXLPE/VitE cups than in UHMWPE cups at 5 years of follow-up without correlation with increasing cup inclination angles or cup sizes. Finally, HXLPE/VitE cups may have the potential to prevent osteolysis and implant loosening.

Axial Rotational Alignment of Mobile-Bearing Total Ankle Arthroplasty

Category:Ankle ArthritisIntroduction/Purpose:In total ankle arthroplasty (TAA), component malpositioning is a major cause of implant failure, possibly due to the altered force patterns caused by the malpositioning which are then transmitted to the bone-implant interface or neighboring joints during physiological loading. Mobile-bearing TAA with their second interface, may allow the talus to adapt its position based upon the individual anatomy. However, no data exist on the change in component positioning after implantation. It is unclear whether it is the result of initial positioning during implantation or secondary adjustments such as possible soft tissue adaptions. We aimed to determine the relative axial rotation between the talar and tibial components at the end of surgery and after a minimum of 3 years follow-up.Methods:The relative rotation between the tibial and talar components was measured in two groups. First, intraoperatively before wound closure, in a consecutive series of 58 patients (60 ankles; age 61.8 [31 to 86] years; females 25, males, 35) who underwent TAA between February and November 2018. A K-wire inserted along the medial border of the tibial component and a rectangular marker positioned at the anterior surface of PE insert were used to determine the angle of rotation. Second, in 48 patients (48 ankles; age 60.2 [31 - 82] years; females, 24; males, 24) out of 1411 patients who underwent TAA between January 2003 and December 2015, and in whom a weight-bearing CT scan was taken for evaluation at 6.3 (range, 3.0 -16.3) years. The medial border of the tibial component and a perpendicular line to the anterior surface of the PE insert were used to determine the angle of rotation.Results:The angle of rotation, thus the relative position of the talar component compared to the tibial component, did not differ between the two groups (p = 0.2). While the talus was internally rotated by 1.7 (range, -14.0 - 14.0) degrees at the end of surgery, it was internally rotated by 1.5 (range, -13.0 – 19.5) degrees after a minimum follow-up of 3 years (Figure 1).Conclusion:Although there was no significant difference in average axial position measured intraoperatively compared to a 3- years follow-up, there was a wide range of rotational measurements. The possibility of the talar component to find its position as given by individual anatomy may be crucial in TAA to avoid non-physiological joint loads and shear forces which may otherwise result in increased PE wear. Due to the wide range of measurements, our data suggests that axial talar rotation cannot be predicted preoperatively or intraoperatively by surgical techniques that reference the transtibial axis, tibial tuberosity and transmalleolar axis as guidance for tibial component positioning.

Evaluation of in vivo wear of vitamin E-diffused highly crosslinked polyethylene at five years: a multicentre radiostereometric analysis study.

The primary aim of this study was to compare the wear properties of vitamin E-diffused, highly crosslinked polyethylene (VEPE) and one formulation of moderately crosslinked and mechanically annealed ultra-high molecular weight polyethylene (ModXLPE) in patients five years after primary total hip arthroplasty (THA). The secondary aim was to assess the clinical results of patients treated with VEPE by evaluating patient-reported outcome measures (PROMs), radiological evidence of fixation, and the incidence of mechanical failure. A total of 208 patients (221 THAs) from four international centres were recruited into a prospective study involving radiostereometric analysis (RSA) and the assessment of clinical outcomes. A total of 193 hips (87%) were reviewed at the five-year follow-up. Of these, 136 (70%) received VEPE (vs ModXLPE) liners and 68 (35%) received ceramic (vs metal) femoral heads. PROMs and radiographs were collected preoperatively and at one, two, and five years postoperatively. In addition, RSA images were collected to measure PE wear postoperatively and at one, two, and five years after surgery. We observed similar bedding in one year postoperatively and wear two years postoperatively between the two types of liner. However, there was significantly more penetration of the femoral head in the ModXLPE cohort compared with the VEPE cohort five years postoperatively (p < 0.001). The only variables independently predictive of increased wear were ModXLPE (vs VEPE) liner type (β = 0.22, p = 0.010) and metal (vs ceramic) femoral head (β = 0.21, p = 0.013). There was no association between increased wear and the development of radiolucency (p = 0.866) or PROMs. No patient had evidence of osteolysis. Five years postoperatively, patients with VEPE (vs ModXLPE) and ceramic (vs metal) femoral heads had decreased wear. The rates of wear for both liners were very low and have not led to any osteolysis or implant failure due to aseptic loosening.

Progress in Wear Resistant Materials for Total Hip Arthroplasty

Current trends in total hip arthroplasty (THA) are to develop novel artificial hip joints with high wear resistance and mechanical reliability with a potential to last for at least 25–30 years for both young and old active patients. Currently used artificial hip joints are mainly composed of femoral head of monolithic alumina or alumina-zirconia composites articulating against cross-linked polyethylene liner of acetabular cup or Co-Cr alloy in a self-mated configuration. However, the possibility of fracture of ceramics or its composites, PE wear debris-induced osteolysis, and hypersensitivity issue due to metal ion release cannot be eliminated. In some cases, thin ultra-hard diamond-based, TiN coatings on Ti-6A-4V or thin zirconia layer on the Zr-Nb alloy have been fabricated to develop high wear resistant bearing surfaces. However, these coatings showed poor adhesion in tribological testing. To provide high wear resistance and mechanical reliability to femoral head, a new kind of ceramic/metal artificial hip joint hybrid was recently proposed in which 10–15 μm thick dense layer of pure α-alumina was formed onto Ti-6Al-4V alloy by deposition of Al metal layer by cold spraying or cold metal transfer methods with 1–2 μm thick Al3Ti reaction layer formed at their interface to improve adhesion. An optimal micro-arc oxidation treatment transformed Al to dense α-alumina layer, which showed high Vickers hardness 1900 HV and good adhesion to the substrate. Further tribological and cytotoxicity analyses of these hybrids will determine their efficacy for potential use in THA.

Fabrication and properties of UHMWPE grafted with acrylamide polymer brushes

Osteolysis which is triggered by inflammatory responses to PE wear particles in the artificial hip joints is a serious issue. In order to prolonging the service life of artificial joints and endow the low tribological properties of the bearing surface of ultra-high molecular weight polyethylene (UHMWPE), hydrophilic acrylamide (AM) was grafted onto the surface of UHMWPE powders with the method of ultraviolet irradiation (UV) and then the modified UHMWPE powders were hot pressed as the bulk materials. The tribological properties of modified UHMWPE were investigated under distilled water, saline, calf serum by sliding against stainless steel ball. The measurement of Fourier-transform infrared (FT-IR) spectroscopy, Energy different spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS) indicate that AM was successfully grafted onto the surface of UHMWPE powders by UV irradiation. The contact angle of UHMWPE is 95° which is higher than that of modified UHMWPE and the wettability of UHMWPE-g-AM is effectively improved. The tensile strength of modified sample decreases. The friction coefficient of modified sample is lower than that of untreated UHMWPE in aqueous lubricants during a long-term friction. The modified UHMWPE with the diameter of 58–75 μm has the lowest friction coefficient in calf serum which is about 0.075. The wear tests of knee joint moving simulator show that the pure UHMWPE has the highest wear rate, about 8 × 10−7 mm3(N · m)−1 and the wear rate of grafted UHMWPE decreases gradually water with the decrease of powder diameter. The sample with the 58–75 μm powder diameter has the lowest wear rate which is about 4.8 × 10−7mm3(N · m)−1 . The tribological properties of UHMWPE grafted with AM has been improved and the grafting hydrophilic PAM polymer brushes are helpful to form a lubricating film of water, which leads to the improvement of the lubricity.

Changes in surface topography at the TKA backside articulation following in vivo service: a retrieval analysis.

With the advent of modular total knee arthroplasty (TKA) systems, backside wear at the articulation between the ultra-high-molecular-weight-polyethylene (UHMWPE) component undersurface and the tibial baseplate has received increasing attention as a source of clinically significant polyethylene wear debris. The aim of this study was to investigate the reciprocating interface at the TKA undersurface articulation using profilometry after in vivo service. Our null hypothesis was that there would be no discernible pattern or relationship between the metal tibial baseplate and UHMWPE surface profile. A nanoscale analysis of thirty retrieved fixed-bearing TKA explants was performed. Surface roughness (Sa) and skewness (Ssk) were measured on both the UHMWPE component undersurface and the tibial baseplate of explants using a non-contacting profilometer (1 nm resolution). Four pristine unimplanted components of two different designs (Stryker Kinemax and DePuy PFC) were examined for control purposes. Mean explant baseplate surface roughness was 1.24 μm (0.04-3.01 μm). Mean explant UHMWPE undersurface roughness was 1.16 μm (0.23-2.44 μm). Each explant had an individual roughness pattern with unique baseplate and undersurface UHMWPE surface roughness that was different from, but closely related to, surface topography observed in control implants of the same manufacturer and design. Following in vivo service, UHMWPE undersurface showed changes towards a negative skewness, demonstrating that wear is occurring at the backside interface. In vivo loading of the TKA prosthesis leads to measurable changes in surface profile at the backside articulation, which appear to be dependent on several factors including implant design and in vivo duration. These findings are consistent with wear occurring at this surface. Findings of this study would support the use of a polished tibial tray over an unpolished design in total knee arthroplasty with the goal of reducing PE wear by means of providing a smoother backside countersurface for the UHMWPE component.

Results at a minimum of 10 years of follow-up for AMS and PerFix HA-coated cementless total hip arthroplasty: impact of cross-linked polyethylene on implant longevity

PurposeThe purpose of this study was to report results at a minimum of 10years for hydroxyapatite (HA) coating on the titanium arc-sprayed cementless total hip arthroplasty (THA) and to evaluate the impact of cross-linked polyethylene (XLPE) on implant longevity. MethodsA total of 131 consecutive primary THAs in 123 patients using an AMS acetabular cup and a PerFix HA stem were retrospectively reviewed. Conventional PE was used for 62 hips (CPE group) and cross-linked PE for 69 hips (XLPE group), with mean follow-up periods of 13 and 11.5years, respectively. These patients were reviewed using the Japanese Orthopaedic Association (JOA) Hip Score and evaluated in terms of PE wear, osteolysis, and implant survival. ResultsThe JOA score improved from 42.6 to 83.9 points at the final follow-up. The mean wear rate of 0.12mm/year in the CPE group was significantly greater than that of XLPE at 0.007mm/year. In the CPE group, ten (16.1%) and two (3.2%) hips, respectively, underwent PE exchange due to severe wear and acetabular revision due to loosening associated with osteolysis. Three patients had revision in the XLPE group: one cup for aseptic loosening, one PE for recurrent dislocation, and one stem for neck fracture. No evident osteolysis was seen in the XLPE group. Kaplan–Meier survivorship with any revision as the end point shows that the 12-year survival rate was 97.7% for cups, 93.8% for PE liners, and 99.2% for stems. Multivariate analysis revealed that the use of XLPE significantly reduced the risk of revision, with the odds ratio (OR) of 4.3. ConclusionsAMS and PerFix HA components in this series show excellent implant fixation; however, high rates of PE wear and subsequent osteolysis were limiting factors in long-term success. Low wear rates with XLPE suggest improved implant longevity.

Antimicrobial agents and low-molecular weight polypeptides affect polyethylene wear in knee simulator testing

A series of eight wear tests with six different calf serum lubricants were performed on a displacement-controlled knee simulator. The calf serum lubricants varied in constituent fractions, dilutive media, and antimicrobial agent. The difference in low-molecular weight polypeptide concentration was determined in all calf serum lubricants and this allowed exploration of its role in the PE wear process. Sodium azide was not an effective antimicrobial agent. The subsequently used antibiotic–antimycotic mixture was initially effective in eliminating bacterial growth but its efficacy became exhausted as the testing period progressed. In the present pilot study, a predator bacterium Bdellovibrio bacteriovorus was shown to prey on the antibiotic resistant bacterium, suggesting its potential use in knee simulator wear testing.

Aseptic glenoid loosening or failure in total shoulder arthroplasty: revision with glenoid reimplantation

Reimplantation of a new glenoid component for symptomatic glenoid failure after total shoulder arthroplasty (TSA) is a well-established surgical strategy. In case of aseptic glenoid loosening or failure, revision of TSA by reimplantation of a cemented glenoid implant would be a reliable therapeutic option. This retrospective multicenter study included 42 TSAs with symptomatic failed glenoids revised by reimplantation of an all-polyethylene (PE), cemented glenoid component. All patients were reviewed clinically and radiologically, with a mean follow-up of 74 months. The failed initial glenoid component was metal backed in 32 cases and PE cemented in 10. The main cause of glenoid failure was component loosening in 19 cases (46%) and PE wear or dissociation in 23 (54%). Associated complications were very frequent, including rotator cuff tears, subscapularis insufficiency, and prosthesis instability. At last follow-up, 7 patients (17%) had already been re-revised because of symptomatic recurrent glenoid loosening. The overall rate of recurrent glenoid loosening (re-revision plus radiologic loosening) was 67%. Soft-tissue problems and prosthetic instability were significantly associated with recurrent loosening. Of the 10 associated bone grafts performed during the revision procedure, all were partially or totally lysed. At follow-up, the mean Constant score was 57 points (gain of 16 points) and the mean active anterior elevation was 125° (gain of 19°). This study suggests that revision of a TSA with reimplantation of an all-PE cemented glenoid component does not solve the problem of glenoid loosening. Soft-tissue failure and prosthetic instability are underestimated preoperatively and may explain, in part, the high rate of recurrent glenoid loosening.

Semi-quantitative assessment methods for backside polyethylene damage in modular total knee replacements

Two semi-quantitative grading methods (referred to as the Hood/Wasielewski-method and the Modified-method) were described and then applied to 52 retrieved tibial polyethylene inserts from modular total knee replacements. Their ability to assess backside surface damage was compared. The damage score correlation with the implantation period greater than 24 months was better using the Modified-method (R=0.524, p=0.006) than using the Hood/Wasielewski-method (R=0.328, p=0.102). Also, the Modified-method gave significantly higher damage scores for males with gamma-in-air irradiated polyethylene inserts whereas the Hood/Wasielewski-method did not. Thus, the damage score obtained using the Modified-method seemed to provide a better representation of clinical surface damage and possibly PE wear.

Radiographic changes of the femoral neck after total hip resurfacing

Significant femoral neck narrowing following hip resurfacing arthroplasty has been observed. Several factors contributing to the physiopathology of femoral neck narrowing have been suggested. The aim of this study was to evaluate the femoral neck radiographic changes observed after hip resurfacing at a minimum follow-up period of 5 years and to determine their causes. We conducted a prospective study of 57 hip resurfacing arthroplasties performed in 53 patients (30 men, 23 women) of mean age 49.2 years (32-65) at surgery. These patients were clinically reviewed (inguinal pain during walking, WOMAC and UCLA scores) at 2 years and radiographically examined at 1, 2 and 5 postoperative years. The accuracy of our computer-aided measurement method was 1mm. Measurement of femoral neck to implant ratio was performed to assess the amount of neck thinning at the femoral neck-implant junction (N/H) and midway between the implant and the inter-trochanteric line (N(1/2)H) on an AP radiograph. Neck-thinning greater than 10% was considered as significant. Any other radiographic morphologic change in the femoral neck was investigated. Metallic ion concentration in blood was measured. A uni- and multivariate analysis was performed to determine the correlation with radiographic changes. In one third of the patients, femoral neck narrowing was greater than 1mm at 2 and 5 postoperative years. Such result corresponds to a mean decrease in neck to implant ratio (N/H) of 5.9% (range, 2.3 to 9.4) at 2 years and 8.3% (range, 2.5 to 23.8) at 5 years. At 5 postoperative years, an overall neck thinning greater than 10% was reported in 3 patients (with a 10- to 17-% increase in femoral neck narrowing between the 2nd and the 5th postoperative year). In one case, neck thinning was associated with fracture of the femoral stem managed with revision surgery during which femoral neck necrosis was confirmed. Neck thinning was, in these cases, circumferential to the neck-implant junction. There was no significant negative impact on clinical scores and no relationship could be established between neck thinning and factors such as BMI or patient activity. Moreover, neck thinning greater than 10% was reported in two cases after 2 postoperative years through the appearance of a localized femoral neck notching which was absent in the postoperative period, secondary to a femoroacetabular impingement. Femoral neck narrowing used to be a common phenomenon after HR when polyethylene acetabular bearings were implanted thus inducing osteolysis secondary to PE wear debris. The incidence of such phenomenon has decreased but still occurs after HR when using a metal-on-metal bearing surface. It has an early occurence but stabilizes after 2 postoperative years. Changes in mechanical stress distribution in the neck region after hip resurfacing have been hypothesized to be a cause of neck thinning. Other aetiologies may be suggested. An overall evolutive femoral neck narrowing after 2 postoperative years should raise the suspicion of necrosis leading to a risk of loosening, fracture or implant failure. Therefore, radiographic monitoring should be conducted. The presence of femoral neck notching secondary to femoroacetabular impingement represents a differential diagnosis which conservative treatment is advocated in the absence of any associated symptoms.

17-year follow-up of the rough-blasted threaded Weill cup in uncemented total hip arthroplasty

For uncemented hip arthroplasty, various cup designs are available. The threaded Weill acetabular component (Weill cup; Zimmer, Winterthur, Switzerland) has been used for more than 20 years, with poor results of the smooth threaded design. Our study was intended to assess the 17-year outcome of the rough-blasted option of the threaded Weill cup. Between 1987 and 1988, a series of 86 rough-blasted threaded Weill cups were implanted in combination with the CLS Spotorno stem (Zimmer Ltd, Germany) The patients' mean age at the time of surgery was 50 years (range 19-67 years). 67 out of 86 hips (78%) were available for a follow-up at a mean of 17 years (range 16-18 years). Radiographs were available from 55 out of 63 unrevised hips (87%) and analyzed for radiolucency and PE wear. Two out of 86 cups (3%) were revised due to aseptic loosening and another two cups (3%) were awaiting revision for the same reason. Ten patients (10 cups, 12%) were lost to follow-up, and nine patients with nine cups (11%) had deceased without radiographic signs of cup failure. Cup survival with "revision or awaiting revision" as endpoint was 86% (95% CI 75-92%). No deep infections occurred, and no polyethylene insert was exchanged. The Harris hip score was excellent in 37 out of 67 clinically examined hips (55%), good in 18 hips (26%), satisfactory in 5 hips (8%) and moderate or poor in 5 hips (8%) and 2 hips (3%), respectively. The rough-blasted threaded Weill cup provides a good long-term performance in cementless total hip arthroplasty. The results compare favourably to the smooth threaded cup design.

PCL balancing, an example of the need to couple detailed biomechanical parameters with clinical functional outcome

Although the results of a total knee replacement (TKR) are described as being good, many patients are not satisfied after the operation with certain limitations such as the inability to perform sports or other vigorous activities [10, 15]. This motivates engineers and surgeons in their search for superior implant materials and designs, leading to innovations such as surgical navigation and patient-specific cutting blocks, as well as high flex and anatomically formed knee designs. There is even a revival of interest for the bi-cruciate retaining knee implant. Besides these technical topics, the discussion about some more fundamental issues still continues. Still no consensus whether the posterior cruciate ligament (PCL) should be retained or substituted in TKR has been reached. Advocates for both PCL substitution and PCL retention can point to excellent clinical and radiographic results in the literature. Furthermore, findings in the area of biomechanics, histology, and gait analysis do not show convincing evidence for one technique above the other [11]. However, PCL balancing seems to be a factor of major importance. To function properly, the PCL must be accurately tensioned during TKR. This may seem evident, but clinical papers reporting on cruciate-retaining TKRs scarcely report on the functional status of the PCL or the contact point in the operated patients, even though several authors did discuss their finding that PCL insufficiency might be an explanation for some inferior results found for PCL-retaining implants [4, 14]. Thus far, little scientific data have been published regarding balancing issues related to the PCL, a topic generally considered to be complex. It seems crucial that the PCL is placed under appropriate tension such that the kinetic benefits of its retention can be enhanced while the adverse effects of either an excessively tight or lax PCL can be avoided. It is essential that a balanced situation is (re)created during TKR since a too tight PCL may result in decreased ROM, potentially affect PE wear, and implant fixation due to posterior loading [12, 13], whereas a too slack PCL may lead to AP instability, which could result in pain, effusion, impaired function, and higher contact stresses [1, 13]. But what actually happens during PCL balancing? In two cohort studies, we investigated the relation between flexion gap height and translation of the tibia when the knee was distracted by a tensor. By measuring distances, forces and by performing statistical analyses, we found that balancing the flexion gap is an extremely delicate technique. With a mono-block tensor, the ratio between gap height increase and anterior tibial translation was 1:1.25 [3]. For a bi-compartmental tensor, a higher ratio was found, being 1:1.9. To make it more complex, this ratio was the highest for knees with a steep PCL and with those in which the collateral ligaments had been released during the procedure. In short, the effects of gap distraction were highly variable between patients [7]. Hence, only a 2-mm change in tibia bone cut height, a change of 2–3 degrees in slope of the tibia cut, a change of 2–3 mm in the bone cut on the posterior condyles of the femur or in PE-insert thickness all can make a difference between a perfectly balanced PCL and one that has been too tightly or too loosely balanced. Without computer navigation, these slight variations are easily made. When the tibia moves forward during distraction of the flexion gap (whether from the implant, a spacer or a P. J. C. Heesterbeek (&) Research, Development & Education, Sint Maartenskliniek, Nijmegen, The Netherlands e-mail: p.heesterbeek@maartenskliniek.nl

Mittelfristige Ergebnisse nach Implantation des anatomisch geformten Geradschafts IMAGE im Rahmen der primären Hüftendoprothetik – eine prospektive Studie

The IMAGE prosthesis was developed with the objective of proximal load induction to avoid stress shielding and proximal bone resorption. In this study patients were followed clinically and radiologically with a special emphasis on osteointegration of the shaft in the proximal and distal regions. In addition, the reconstruction of the bony geometry of the proximal humerus was investigated. 95 consecutive patients (mean age: 61.1 years) with an IMAGE shaft were followed up prospectively over five years after primary hip arthroplasty. Radiologically, the osteointegration was appraised on the basis of the parameters cortical bone hypertrophy, radiolucent lines, shaft sintering and the position of the rotational centre. The clinical parameters assessed were the Harris hip score (HSS) and the WOMAC score. In Dorr C configuration no distal cortical bone hypertrophy was visible, in contrast to 19% in types A and B. By means of this criterion in 81% of the cases, a metaphyseal anchoring can be assumed. In 20% of the cases proximal and in 11.1% distal radiolucent lines were found. In only 3.3 % of the patients were the radiolucent lines due to unwanted distal osteointegration. In most cases the reasons were PE wear and metallosis. In 18.8% a distal anchoring was visible. Sintering (in total 18 prostheses) was greatest in Dorr C configuration and high-grade osteoporosis. The difference in offset reconstruction was 4.23 mm on average. In reconstruction of the rotational centre the variability was between 2.0 and 6.9 mm. 94.13 points were attained in the HHS and 10.13 points in the WOMAC score. Specific complications related to the implantation were not observed. Proximal stress transmission can be supported and the danger of stress shielding can be reduced by means of an appropriate design of a prosthetic stem. Distal corticoid hypertrophy was found in only 19% of the patients with the prosthesis model investigated as compared to 60% having prostheses with distal femoral anchoring. The medium-term clinical results are excellent, so that the shaft appears suitable for primary as well as secondary osteoarthritis of the hip joint.

Survivorship of uncemented PE/metal acetabular components in young patients. Prospective study with an 8-13 year follow-up

Introduction Although young patients with total hip prostheses are known to have a greater functional demand, there are few prospective studies on uncemented cups with a metal/polyethylene (PE) bearing surface. Purpose To assess the outcome and the survivorship of acetabular components in young patients with a minimum 8-year follow-up, as well as the factors leading to cup mechanical failure. Materials and methods Prospective study of 42 primary uncemented total hip arthroplasties with a metal/PE bearing surface, in 34 patients with a mean age of 52.5 years (range: 28-60), and initial diagnosis of primary osteoarthritis in 61% of cases. The Harris score was used for the functional assessment. Digitalized radiographs and computer image analysis were used to study the positioning and the incorporation of the components, as well as PE wear rates. Results Mean postoperative follow-up was 11 years (range: 8-13). Functionally, 36 cases (85.7%) had a satisfactory outcome. Radiologically there was one case of stem instability and 4 cases of acetabular instability, which had to be revised; there was also one case of a deep infection. Thirty-one cases (73.8%) showed some degree of PE wear, with a mean annual linear loss of 0.20 ± 0.09 mm. Aggregate PE survivorship at 11 years was 25% (95% CI: 37.1-64.5). The wear was more intense in the younger patients (p=0.05), in the more obese ones (p = 0.04) and in verticalized cups (p=0.01); no statistically significant relationship was found (p>0.05) with gender, previous diagnosis, neck length or use of acetabular screws. The cases with the greatest wear showed a higher incidence of periacetabular osteolysis (p=0.001). Conclusions Although the percentage of satisfactory results has been acceptable, the high incidence of survivorship-shortening PE wear would seem to preclude the use o fan uncemented metal/PE acetabular component in patients younger than 60 years of age, especially if they are obese.

Supervivencia del componente acetabular no cementado con par polietileno-metal en pacientes jóvenes: estudio prospectivo con seguimiento de 8 a 13 años

Introduction Although young patients with total hip prostheses are known to have a greater functional demand, there are few prospective studies on uncemented cups with a metal/polyethylene (PE) bearing surface. Purpose To assess the outcome and the survivorship of acetabular components in young patients with a minimum 8-year follow-up, as well as the factors leading to cup mechanical failure. Material and method Prospective study of 42 primary uncemented total hip arthroplasties with a metal/PE bearing surface, in 34 patients with a mean age of 52.5 (range, 28–60) years, and initial diagnosis of primary osteoarthritis in 61% of cases. The Harris score was used for the functional assessment. Digitalized radiographs and computer image analysis were used to study the positioning and the incorporation of the components, as well as PE wear rates. Results Mean postoperative follow-up was 11 (range, 8–13) years. Functionally, 36 (85.7%) cases had a satisfactory outcome. Radiologically there was one case of stem instability and 4 cases of acetabular instability, which had to be revised; there was also one case of a deep infection. Thirty-one cases (73.8%) showed some degree of PE wear, with a mean annual linear loss of 0.2±0.09 mm. Aggregate PE survivorship at 11 years was 25% (95% CI, 37.1–64.5). The wear was more intense in the younger patients (p=0.05), in the more obese ones (p=0.04) and in verticalized cups (p=0.01); no statistically significant relationship was found (p>0,05) with gender, previous diagnosis, neck length or use of acetabular screws. The cases with the greatest wear showed a higher incidence of periacetabular osteolysis (p=0.001). Conclusions Although the percentage of satisfactory results has been acceptable, the high incidence of survivorship-shortening PE wear would seem to preclude the use o fan uncemented metal/PE acetabular component in patients younger than 60 years of age, especially if they are obese.