The creep and wear of highly cross-linked polyethylene: a three-year randomised, controlled trial using radiostereometric analysis

The creep and wear behaviour of highly cross-linked polyethylene and standard polyethylene liners were examined in a prospective, double-blind randomised, controlled trial using radiostereometric analysis. We randomised 54 patients to receive hip replacements with either highly cross-linked polyethylene or standard liners and determined the three-dimensional penetration of the liners over three years. After three years the mean total penetration was 0.35 mm (SD 0.14) for the highly cross-linked polyethylene group and 0.45 mm (SD 0.19) for the standard group. The difference was statistically significant (p = 0.0184). From the pattern of penetration it was possible to discriminate creep from wear. Most (95%) of the creep occurred within six months of implantation and nearly all within the first year. There was no difference in the mean degree of creep between the two types of polyethylene (highly cross-linked polyethylene 0.26 mm, SD 0.17; standard 0.27 mm, SD 0.2; p = 0.83). There was, however, a significant difference (p = 0.012) in the mean wear rate (highly cross-linked polyethylene 0.03 mm/yr, SD 0.06; standard 0.07 mm/yr, SD 0.05). Creep and wear occurred in significantly different directions (p = 0.01); creep was predominantly proximal whereas wear was anterior, proximal and medial. We conclude that penetration in the first six months is creep-dominated, but after one year virtually all penetration is due to wear. Highly cross-linked polyethylene has a 60% lower rate of wear than standard polyethylene and therefore will probably perform better in the long term.     

The 6-year migration characteristics of a hydroxyapatite-coated femoral stem: a radiostereometric analysis study

A prospective cohort of 30 patients undergoing primary total hip arthroplasty for treatment of osteoarthritis was enrolled in a study to characterize the migration behavior of a clinically successful cementless stem. At 6 years, the mean subsidence of the stem was 0.63 mm (range, -0.33 to 3.68 mm); the mean rotation into retroversion was 1.41° (range, -1.33° to 7.48°). No stems had additional subsidence of more than 0.25 mm between 6 months and 6 years. The resultant mean subsidence between 2 and 6 years was 0.03 mm, which is below the limit measurable by radiostereometric analysis. The data demonstrate that subsidence of this cementless stem occurs within the first 6 months, after which there is persistent stabilization.     

The effect of adding tobramycin to Simplex P cement on femoral stem micromotion as measured by radiostereometric analysis: a 2-year randomized controlled trial

Background

Previous in vitro research on addition of antibiotics to bone cement has found no statistically significant deterioration in mechanical properties. However, no clinical studies have compared the performance of tobramycin-laden bone cement with that of standard bone cement (Simplex P).

Patients and Methods

23 patients (25 hips) were randomized to receive an Exeter (Stryker Orthopaedics) femoral stem cemented with either Simplex P (standard) or Simplex T (tobramycin-laden) cement. There were 2 years of follow-up, with scheduled radiostereometric (RSA) examinations.

Results

All stems migrated distally and showed some degree of retroversion. No clinically significant differences in stem subsidence or retroversion were found between the Simplex T and Simplex P cement groups after 2 years. Overall subsidence was less than in previous studies, probably due to a postponed initial post-surgical examination. Rates of subsidence in both cement groups were consistent with those from previous studies of Exeter stems.

Interpretation

Subsidence of the femoral stem after 2 years was similar in the Simplex T (tobramycin-laden) and Simplex P (standard) groups.When antibiotic-laden bone cement (ABLC) was introduced in 1970, there were concerns that the addition of antibiotic powder to bone cement could compromise the mechanical properties of the cement, and therefore increase the risk of aseptic loosening of arthoplasty components (Murray 1984, Lundberg and Hedlund 2007). Since then, numerous in vitro studies have shown that the addition of less than 2 g of antibiotic to 40 g cement powder has a negligible effect on the mechanical strength and fixation properties of bone cements (Davies and Harris 1991, Klekamp et al. 1999, Bourne 2004). However, there is some debate about the appropriateness of laboratory testing of cement properties (Nottrott et al. 2008) since regulatory standards require that bone cement be tested after 24 h of ageing under dry conditions at 23°C (an environment very unlike that of the human body), and not over an extended time (Nottrott et al. 2008). Furthermore, success in the laboratory does not guarantee long-term clinical success, as seen with the disastrous outcomes with Boneloc cement (Gebuhr et al. 2000). This underscores the need for rigorous clinical testing and in vivo measurements of new products prior to adopting them for routine use (Thanner et al. 1995, Hallan et al. 2006).Large cohort studies have shown that the prophylactic use of ABLC is associated with a lower risk of infection-based revision (Havelin et al. 1995, Engesæter et al. 2003). Unfortunately, such studies may have underestimated the true aseptic loosening-based failure rates, as some patients with loose implants may never undergo revision (Soderman et al. 2001). Radiostereometric analysis (RSA) has also been used to investigate the performance of new antibiotic-laden cements (Adalberth et al. 2002, Hallan et al. 2006). Hallan et al. (2006) compared the extent and patterns of migration between Charnley total hips randomly cemented with either Refobacin-loaded Palamed G or gentamicin-loaded Palacos R, and found similar migration patterns. Such studies are useful for comparing different ABLCs, but studies that directly examine the effect of adding antibiotic to a specific cement on the risk aseptic loosening are needed. Thus, we determined whether the addition of tobramycin to Simplex P cement increases the risk of long-term aseptic loosening as predicted by implant micromotion detected by RSA. We selected tobramycin-laden Simplex cement (Simplex T), as it was a relatively new ABLC introduced into North America at the start of this study in 2003.     

Limited femorotomy: Removing a well-fixed,cementless femoral stem

We present a technique of a longitudinal posterior femorotomy that does not extend to the greater trochanter leaving the abductors intact. This technique allows safe, effective removal of well-fixed proximally coated cementless femoral stems with minimal bone loss and allows revision to metaphyseal fitting stems. We present results of this technique in 18 patients with a minimum 6-year follow-up. Harris hip scores increased from 68.2 to 92.4, all stems had evidence of good bony ingrowth, no evidence of migration, all femorotomies healed and there is no evidence of stress shielding or osteolysis. None required re-revision of femoral prosthesis.     

Removal of a well-fixed cementless femoral stem using a microsagittal saw

Well-fixed cementless femoral components are troublesome to extract. This article describes a technique to extract a well-fixed cementless stem in which the stem is extracted with a bent microsagittal saw blade after a longitudinal cortical window is made.     

Migration of the femoral stem after impaction bone grafting. First results of an ongoing,randomised study of the exeter and elite plus femoral stems using radiostereometric analysis

We report the initial results of an ongoing randomised, prospective study on migration of the Exeter and Elite Plus femoral stems after impaction allografting, as measured by radiostereometry. Clinically, the impaction technique gave good results for both stems. The mean subsidence in the first year was 1.30 mm and 0.20 mm for the Exeter and the Elite Plus stems, respectively. In the second year, the Exeter stem continued to subside further by a mean of 0.42 mm, while the Elite Plus stem did not do so. Subsidence of the Exeter stem correlated with deficiency of bone stock as graded on the Gustilo and Pasternak scale. This correlation was not found for the Elite Plus stem. None of the other parameters which were studied predisposed to subsidence. There was no significant association between the amount of subsidence and the radiological appearance of the graft for either stem. Our findings do not support the theory that radial compression, due to subsidence of the Exeter stem, is the essential stimulus for remodelling in impaction allografting.     

First-time revision using impacted morsellised allograft bone with a cemented Exeter stem: radiostereometric analysis of stem migration over nine years

Previously, radiostereometric analysis following hip revision performed using impacted morsellised allograft bone and a cemented Exeter stem has shown continuous subsidence of the stem for up to five years. It is not known whether the subsidence continues thereafter. In our study, 17 of 25 consecutive osteo-arthritic patients with aseptically loose stems who underwent first-time revision using impacted morsellised allograft bone and a cemented Exeter stem were followed by yearly radiostereometric examinations for nine years. The mean subsidence at six weeks was 1.1 mm (0.1 to 2.3), from six weeks to one year 1.3 mm (0 to 2.6), from one to five years 0.7 mm (0 to 2.0), and from five to nine years 0.7 mm (0.1 to 3.1). That from six weeks to nine years was 2.7 mm (0 to 6.4) (95% confidence interval 2.0 to 3.5). The Charnley pain score significantly improved after revision, and was maintained at nine years, but walking ability deteriorated slightly as follow-up extended. Of the eight patients who were not followed for nine years, two had early subsidence exceeding 11 mm. Our findings show that in osteo-arthritic patients who undergo revision for aseptic loosening of the stem using impacted morsellised allograft bone and a cemented Exeter stem, migration of the stem continues over nine years at a slower rate after the first year, but without clinical deterioration or radiological loosening.     

A randomised,controlled trial of cemented versus cementless press-fit condylar total knee replacement. Ten-year survival analysis

We have carried out a long-term survival analysis of a prospective, randomised trial comparing cemented with cementless fixation of press-fit condylar primary total knee replacements. A consecutive series of 501 replacements received either cemented (219 patients, 277 implants) or cementless (177 patients, 224 implants) fixation. The patients were contacted at a mean follow-up of 7.4 years (2.7 to 13.0) to establish the rate of survival of the implant. The ten-year survival was compared using life-table and Cox's proportional hazard analysis. No patient was lost to follow-up. The survival at ten years was 95.3% (95% CI 90.3 to 97.8) and 95.6% (95% CI 89.5 to 98.2) in the cemented and cementless groups, respectively. The hazard ratio for failure in cemented compared with cementless prostheses was 0.97 (95% CI 0.36 to 2.6). A comparison of the clinical outcome at ten years in 80 knees showed no difference between the two groups. The survival of the press-fit condylar total knee replacement at ten years is good irrespective of the method of fixation and brings into question the use of more expensive cementless implants.     

A randomised controlled trial of cemented versus cementless press-fit condylar total knee replacement: 15-year survival analysis

We report the long-term survival of a prospective randomised consecutive series of 501 primary knee replacements using the press-fit condylar posterior cruciate ligament-retaining prosthesis. Patients received either cemented (219 patients, 277 implants) or cementless (177 patients, 224 implants) fixation. Altogether, 44 of 501 knees (8.8%) underwent revision surgery (24 cemented vs 20 cementless). For cemented knees the 15-year survival rate was 80.7% (95% confidence interval (CI) 71.5 to 87.4) and for cementless knees it was 75.3% (95% CI 63.5 to 84.3). There was no significant difference between the two groups (cemented vs cementless; hazard ratio (HR) 0.83, 95% CI 0.45 to 1.52, p = 0.55). When comparing the covariates there was no significant difference in the rates of survival between the side of operation (HR 0.58, p = 0.07), age (HR 0.97, p = 0.10) and diagnosis (HR 1.25 p = 0.72). However, there was a significant gender difference, with males having a higher failure rate with cemented fixation (HR 2.48, p = 0.004). Females had a similar failure rate in both groups. This single-surgeon series, with no loss to follow-up, provides reliable data of the revision rates of one of the most commonly-used total knee replacements. The survival of the press-fit condylar total knee replacement remained good at 15 years, irrespective of the method of fixation.     

A study of the Elite Plus femoral component using radiostereometric analysis

We performed a three-year radiostereometric analysis (RSA) study of the Elite Plus femoral component on 25 patients undergoing primary total hip replacement. Additional assessments and measurements from standard radiographs were also made. Subsidence of the stem occurred at the cement-stem interface. At 36 months the subsidence of the stem centroid was a mean of 0.30 mm (0.02 to 1.28), and was continuing at a slow rate. At the same time point, internal rotation and posterior migration of the femoral head had ceased. One stem migrated excessively and additional assessments suggested that this was probably due to high patient demand. The failure rate of 4% in our study is consistent with data from arthroplasty registers but contrasts with poor results from another RSA study, and from some clinical studies. We believe that the surgical technique, particularly the use of high-viscosity cement, may have been an important factor contributing to our results.     

A cementless, elastic press-fit socket with and without screws: A 2-year randomized controlled radiostereometric analysis of 37 hips

Background

The acetabular component has remained the weakest link in hip arthroplasty regarding achievement of long-term survival. Primary fixation is a prerequisite for long-term performance. For this reason, we investigated the stability of a unique cementless titanium-coated elastic monoblock socket and the influence of supplementary screw fixation.

Patient and methods

During 2006–2008, we performed a randomized controlled trial on 37 patients (mean age 63 years (SD 7), 22 females) in whom we implanted a cementless press-fit socket. The socket was implanted with additional screw fixation (group A, n = 19) and without additional screw fixation (group B, n = 18). Using radiostereometric analysis with a 2-year follow-up, we determined the stability of the socket. Clinically relevant migration was defined as > 1 mm translation and > 2º rotation. Clinical scores were determined.

Results

The sockets without screw fixation showed a statistically significantly higher proximal translation compared to the socket with additional screw fixation. However, this higher migration was below the clinically relevant threshold. The numbers of migratory sockets were not significantly different between groups. After the 2-year follow-up, there were no clinically relevant differences between groups A and B regarding the clinical scores. 1 patient dropped out of the study. In the others, no sockets were revised.

Interpretation

We found that additional screw fixation is not necessary to achieve stability of the cementless press-fit elastic RM socket. We saw no postoperative benefit or clinical effect of additional screw fixation.During the last 5 years, several long-term reports on different methods to achieve primary stability in cementless sockets have shown excellent survival using aseptic loosening as the endpoint (Kim 2005, Kim et al. 2005, Firestone et al. 2007, Suckel et al. 2009, Pakvis et al. 2011).During the last 2 decades, we have used the cementless RM classic socket with good to excellent long-term results (Diks et al. 2005, Pakvis et al. 2011). Ihle et al. (2008) also reported good long-term results for this cementless, titanium particle-coated socket. This socket is based on the philosophy that an elastic polyethylene RM socket (approx 1,000 N/mm²), in contrast to a titanium-calcium phosphate rigid metal shell (approx 105,000 N/mm²), provides the elastic properties of acetabular bone (approx 500–6,000 N/mm²). The resulting physiological distribution of articular forces protects the acetabular bone and provides optimal conditions for ingrowth, with subsequent long-term component fixation. Due to stress shielding, rigid sockets may reduce the acetabular bone quality (Wright et al. 2001, Huo and Osier 2008). In comparison to femoral stress shielding, acetabular stress shielding results in osteolysis and component migration requiring revision surgery.The primary stability of the RM classic socket is achieved by 2 pegs and additional screw fixation; secondary stability is achieved from biological ingrowth into the titanium-particle coating. At our specialized orthopedic training hospital, we have encountered implantation difficulties, leading to a learning curve for optimal positioning of the pegs. In a primary series, this resulted in malpositioning of the socket and a high rate of early to short-term revisions (Diks et al. 2005). The new design of the peg-less, titanium particle-coated RM press-fit cup is expected to make it easier to implant (Figure 1).Open in a separate windowFigure 1.The cementless, titanium particle-coated RM press-fit socket.The effect of adding screws to a press-fit socket to optimize primary stability has been unclear. Some authors have seen no additional effect (Onsten et al. 1996, Thanner et al. 2000, Rohrl et al. 2006, Roth et al. 2006, Iorio et al. 2010), while other authors have described an extra stabilizing effect of the screws on the primary stability of press-fit sockets (Hadjari et al. 1994, Thanner et al. 1996). When additional screw fixation is used, some potentially negative effects on long-term survival must be accepted. The development of osteolytic lesions is believed to be the result of the transmission of articular pressure and of wear particles to the acetabular bone via the screw channels (Schmalzried et al. 1997).To our knowledge, only Thanner et al. (2000) have performed a radiostereometric analysis-based (RSA) randomized controlled trial (RCT); they found no effect of the additional screw fixation in a rigid metal-backed modular titanium-mesh HA- (hydroxyapatite-) coated socket.We performed an RCT to evaluate the stability of the cementless, RM press-fit socket with and without additional screw fixation. We used RSA to determine the stability in each group. We hypothesized that there would be a difference in stability between the cementless RM press-fit sockets with additional screw fixation and those without: that due to the elastic modulus of the RM press-fit socket without additional screw fixation, there would be a larger degree of migration shortly after surgery but that it would stabilize during the two-year follow-up.     

Aseptic stem loosening in primary THA: migration analysis of cemented and cementless fixation

Early migration has reportedly been predictive for later implant failure. Using four different migration patterns, this study aimed to analyse migration behaviour of the two types of implant fixation—cemented and cementless—throughout the process of loosening. Migrational behaviour of 69 revised stems (49 cemented, 20 uncemented) was analysed retrospectively with EBRA-FCA (Einzel-Bild-Röntgen-Analyse, Femoral Component Analysis). Uncemented stems failed after early and late onset migration alike, while late migration was the predominant pattern in cemented stems. Mean prosthetic failure after early migration occurred 5.8 (±4.4) years postoperatively due to insufficient primary stability. Initially stable stems with late onset migration were revised after 12.4 (±4.5) years. Measurement of early migration was found to be a valuable tool to screen short-term and mid-term failure. In the long run the method’s sensitivity decreased. Late onset migration, however, preceded long-term failure by a mean of three years.     

Haemoconcentration of residual cardiopulmonary bypass blood using Hemosep®: a randomised controlled trial

Cardiac surgery and cardiopulmonary bypass are associated with haemodilution, activation of haemostasis and blood transfusion. We undertook a randomised controlled trial that included 53 patients in order to compare autotransfusion of residual cardiopulmonary bypass blood with residual blood concentrated using the novel Hemosep^® device. There was no difference in patients' mean (SD) haemoglobin concentration after autotransfusion of unprocessed blood compared with Hemosep; 103.5 (10.2) g.l^?1 vs 106.2 (12.4) g.l^?1, respectively, p = 0.40. The mean (SD) change in haemoglobin concentration after autotransfusion was 5.9 (5.3) g.l^?1 in the control group compared with 4.9 (6.3) g.l^?1 in the Hemosep group, p = 0.545. Adjusted for baseline haemoglobin concentrations, the estimated mean (95% CI) difference in change in haemoglobin concentration (control vs Hemosep) was 0.57 (?2.65 to 3.79) g.l^?1, p = 0.72. This was despite Hemosep's reducing the weight of the blood from a mean (SD) of 778.7 (243.0) g to 607.3 (248.2) g, p < 0.001. The haemoglobin concentration in the processed blood increased from a mean (SD) of 87.0 (15.1) g.l^?1 to 103.7 (17.4) g.l^?1, p < 0.001. We conclude that Hemosep is capable of haemoconcentration when employed to process residual cardiopulmonary bypass blood, but that this is insufficient to increase patient haemoglobin.     

The effect of a collar and surface finish on cemented femoral stems: a prospective randomised trial of four stem designs

Purpose

The optimal design for a cemented femoral stem remains a matter of debate. Over time, the shape, surface finish and collar have all been modified in various ways. A clear consensus has not yet emerged regarding the relative merits of even the most basic design features of the stem. We undertook a prospective randomised trial comparing surface finish and the effect of a collar on cemented femoral component subsidence, survivorship and clinical function.

Methods

One hundred and sixty three primary total hip replacement patients were recruited prospectively and randomised to one of four groups to receive a cemented femoral stem with either a matt or polished finish, and with or without a collar.

Results

At two years, although there was a trend for increased subsidence in the matt collarless group, this was not statistically significant (p = 0.18). At a mean of 10.1 years follow-up, WOMAC scores for the surviving implants were good, (Range of means 89–93) without significant differences. Using revision or radiographic loosening as the endpoint, survivorship of the entire cohort was 93 % at 11 yrs, (CI 87–97 %). There were no significant differences in survivorship between the two groups with polished stems or the two groups with matt stems. A comparison of the two collarless stems demonstrated a statistically significant difference in survivorship between polished (100 %) and matt (88 %) finishes (p = 0.02).

Conclusions

In the presence of a collar, surface finish did not significantly affect survivorship or function. Between the two collarless groups a polished surface conferred an improved survivorship.