Introduction. Pitting damage on implants has been reported and attributed to use of electrocautery. This study aimed to distinguish how different TKA bearing surfaces are susceptible to this type of damage and whether surgeons were aware that this damage can occur. Methods. A survey was sent to Hip and Knee Society members to determine what percentage of adult reconstructive surgeons use electrocautery after implantation of components. Three bearing surfaces for primary TKA were selected: CoCr, Oxinium, and zirconium nitride (ZrN) to be damaged by electrocautery with a monopolar (MP, Bovie) and bipolar (BP, Aquamantys) electrocautery with three different energy settings. A comparison of surface damage and backscatter elemental analysis using SEM was performed. Average roughness (Ra), maximal peak-to-valley height (Rz,), kurtosis (Rk), and skewness (Rsk) measurements were collected using a profilometer (DektakXT, Bruker, Tucson, AZ) with a 2.5µm radius stylus to assess an area of 3.8mm by 3.2mm in the central portion of the area for each MP and BP energy setting used to impart damage to the bearing surfaces. A similar undamaged area for each bearing surface was also measured for roughness parameter comparison. Results. Median Rz and Ra measurements were larger for BP damaged areas compared to MP for all bearing surfaces.(Table 1) The Oxinium surface had the greatest increase in roughness parameters of all three bearing surfaces tested. Survey results indicate that a significant percentage of adult reconstructive surgeons use the electrocautery after implants are in place and are not aware of this type of damage. Backscatter SEM analysis found significant changes for BP damage compared to MP. Conclusion. Our in vitro study determined surface damage caused by electrocautery can have significant effects on the bearing surfaces of implants. Our survey determined many arthroplasty experts are unaware that this damage can occur. For any figures or tables, please contact the authors directly

Introduction. Infection remains as one of the major challenges of total joint surgery. One-stage irrigation, debridement and reimplantation, or two-stage revision surgery with a temporary implantation of antibiotic eluting bone cement spacer followed by reimplantation are two methods often used to treat infected patients with mixed outcomes. Like bone cement, ultra-high molecular weight polyethylene (UHMWPE) can also be used as a carrier for antibiotics. Recently, we demonstrated that vancomycin and rifampin can be delivered from UHMWPE implants at therapeutic levels to eradicate Staphylococcus aureus biofilm in a lupine animal model. There are regulatory challenges in translating these types of combination devices to clinical use. Last year, at this meeting, we presented the preliminary pre-clinical testing for a temporary UHMWPE spacer containing gentamicin sulfate as a first step towards clinical use. Since then, we carried out a survey among the Knee Society membership about their preference for spacer use in two-stage revision surgery and found that 43% prefer to use a CoCr femoral component on an all-poly cemented tibial insert, 22% prefer bone cement spacers molded in the OR, 20% prefer static bone cement spacers, and 14% prefer pre-formed bone cement spacers. We modified our implant design based on the majority's preference for a total knee system, rather than bone cement spacers, in the temporary two-stage approach. In this study, we explored the effect of gentamicin sulfate (GS) elution from UHMWPE/GS tibial inserts on bacterial colonization on CoCr surfaces. Methods. We characterized the gentamicin sulfate (GS) particles with scanning electron microscopy (SEM). We molded UHMWPE/GS powder blends and characterized the morphology using SEM and Energy Dispersive X-Ray Spectroscopy (EDS). We submerged samples of molded UHMWPE/GS in buffered phosphate solution (PBS) at 37°C and quantified the extent of GS elution into PBS with a method described by Gubernator et al. using o-phthaladehyde (OPA) [1]. Under basic conditions, OPA reacts with primary amino groups to form fluorescent complexes. Since gentamicin is the only source of such amino acids in our elution samples, the number of fluorescent complexes formed is directly proportional to the amount of gentamicin in the sample. Using this method, we could quantify gentamicin elution by measuring sample fluorescence post OPA-reaction. We used a plate reader to excite the fluorescent complexes formed in the OPA reaction and measured the resulting emission at wavelengths of 340 nm and 455 nm, respectively. We also quantified the effect of the standard cleaning protocol (heated sonication in alkaline water and alcohol) used to clean UHMWPE implants on subsequent GS elution from UHMWPE/GS samples using the OPA method. We used agar diffusion tests to characterize antibacterial properties of UHMWPE/GS samples after cleaning. For these tests, we collected eluents collected from UHMWPE/GS and gentamicin-impregnated bone cement (BC/GS) following 1, 2, 3, and 4 weeks of elution, and tested against S. aureus (ATCC 12600). We used the “daughter cells” method developed by Bechert et al. to assess anticolonizing properties of UHMWPE/GS [2,3]. We also characterized the colonization of bacteria on CoCr surfaces in the presence of GS eluting from UHMWPE/GS test samples. For this we modified a Pin-on-Disc (PoD) wear tester: An UHMWPE/GS pin and UHMWPE pin (control) articulated against an implant-finish CoCr disc with Tryptic Soy Broth containing S. Aureus as the lubricant. After 18 hrs, we rinsed the articular surfaces of the pin and disc and stamped them onto Agar gel to transfer any adherent bacteria. We incubated the Agar plate overnight such that adherent bacteria proliferated and became visible. Results. SEM characterized the GS particles as hollow spheres (Fig 1a). These formed small groups of agglomerated domains at the virgin resin boundaries of UHMWPE after molding (Fig 1b). Sulfur signature from the EDS analysis identified the agglomerated domains as GS particles (Fig 2). Elution of GS started with an initial burst and was followed by steady elution up to 12 weeks (Fig 3). Cleaning reduced the initial burst GS elution; and the elution remained unchanged after 2 days (Fig 4). The agar diffusion test showed simmilar inhibition zones for the eluents collected from UHMWPE/GS and BC/GS, suggesting that these samples yield similar antibacterial activity against S. aureus (Fig 5). UHMWPE/GS demonstrated pronounced anticolonizing properties, effectively mitigating the proliferation of S. aureus “daughter” cells. Anticolonizing activity of Palacos R+G was not significantly different when compared with UHMWPE/GS. The PoD test showed little-to-no colonization of CoCr surfaces in the presence of UHMWPE/GS pins, indicative of excellent antibacterial properties of UHMWPE/GS against S. aureus. Conclusion. SEM and EDS has allowed us to visualize domains of gentamicin sulfate particles in UHMWPE. Our OPA method has greater precision than traditional agar-well diffusion methods of measuring gentamicin concentration and showed that gentamicin sulfate-loaded UHMWPE elutes at the same rate as Palacos R+G. Pin-on-disc experiments and the daughter cell method both confirmed that these two materials have similar anticolonization abilities. We also found that using the standard cleaning protocol for UHMWPE orthopedic implants decreased the burst of gentamicin eluting from UHMWPE, but after 2 days, it had no effect compared to uncleaned UHMWPE/GS. Finally, we found that UHMWPE/GS can reduce the colonization of bacteria on CoCr. UHMWPE/GS continues to be a promising material for treating PJI. For figures, tables, or references, please contact authors directly

Introduction. The association between CoCr joint replacements and adverse tissue reactions has led to increased interest in alternative materials that are both biocompatible and wear-resistant. One approach is to manufacture components from titanium alloys with a hardened articulating surface to increase resistance to scratching and surface damage caused by third-body particles. In this study we investigate methods for characterizing the performance of retrieved TiAlV components with nitrogen-hardened bearing surfaces. Methods. Surface-hardened titanium knee implants (TiNidium) were retrieved from 18 patients (7.7 ±6.8 years) at revision surgery. After processing, the bearing surface of each component was characterized by stereomicroscopy, SEM, optical profilometry, and incremental nano-indentation hardness testing. A case-matched set of 18 CoCr components (6.7 ±5.6 years) were characterized for comparison. Results. Each bearing surface was graded for microscopic damage classified as pitting, abrasion, scratching, and burnishing using an Injury Severity Score. The components were divided into slight, average, and severe damage groups based on the resulting ISS scores. Representative specimens from each group were then subjected to SEM imaging, 12 roughness measurements, and 3 incremental nano-indentation hardness tests. Conclusion. There was no difference between the severity of surface damage of the hardened and CoCr components ((p=0.67); Table 1). The rate of surface damage was greatest in the first 2 years then decreased exponentially (Figure 1). Surface roughness (Ra) values were similar for both groups (TiAlV: 0.771um; CoCr: 0.884um) but decreased with the severity of visual damage in the TiNidium implants due to secondary burnishing of scratches. The hardness of the TiNidium implants varied with depth below the bearing surface in contrast to the CoCr controls in which hardness did not vary with depth (Figure 2). Our findings show that multiple complementary methods of are needed to adequately characterize the performance of surface hardened implants. For figures, tables, or references, please contact authors directly

Aims

This study aimed to investigate the relationship between changes in patellar height and clinical outcomes at a mean follow-up of 7.7 years (5 to 10) after fixed-bearing posterior-stabilized total knee arthroplasty (PS-TKA).

Aims

Many patients undergoing total knee arthroplasty (TKA) have severe osteoarthritis (OA) in both knees and may consider either simultaneous or staged bilateral TKA. The implications of simultaneous versus staged bilateral TKA for return to work are not well understood. We hypothesized that employed patients who underwent simultaneous bilateral TKA would have significantly fewer days missed from work compared with the sum of days missed from each operation for patients who underwent staged bilateral TKA.

Aims

The mobile bearing Oxford unicompartmental knee arthroplasty (OUKA) is recommended to be performed with the leg in the hanging leg (HL) position, and the thigh placed in a stirrup. This comparative cadaveric study assesses implant positioning and intraoperative kinematics of OUKA implanted either in the HL position or in the supine leg (SL) position.

Aims

Stiffness is a common complication after total knee arthroplasty (TKA). Pathogenesis is not understood, treatment options are limited, and diagnosis is challenging. The aim of this study was to investigate if MRI can be used to visualize intra-articular scarring in patients with stiff, painful knee arthroplasties.

Aims

Vitamin E-infused highly cross-linked polyethylene (E1) has recently been introduced in total knee arthroplasty (TKA). An in vitro wear simulator study showed that E1 reduced polyethylene wear. However there is no published information regarding in vivo wear. Previous reports suggest that newly introduced materials which reduce in vitro polyethylene wear do not necessarily reduce in vivo polyethylene wear. To assist in the evaluation of the newly introduced material before widespread use, we established an in vivo polyethylene wear particle analysis for TKA. The aim of this study was to compare in vivo polyethylene wear particle generation between E1 and conventional polyethylene (ArCom) in TKA.

Aims

This study compares the PFC total knee arthroplasty (TKA) system in a prospective randomized control trial (RCT) of the mobile-bearing rotating-platform (RP) TKA against the fixed-bearing (FB) TKA. This is the largest RCT with the longest follow-up where cruciate-retaining PFC total knee arthroplasties are compared in a non-bilateral TKA study.

Aims

We conducted a randomised controlled trial to assess the accuracy of positioning and alignment of the components in total knee arthroplasty (TKA), comparing those undertaken using standard intramedullary cutting jigs and those with patient-specific instruments (PSI).

Aims

Knee joint distraction (KJD) is a relatively new, knee-joint preserving procedure with the goal of delaying total knee arthroplasty (TKA) in young and middle-aged patients. We present a randomised controlled trial comparing the two.

We examined whether enamel matrix derivative (EMD) could improve healing of the tendon–bone interface following reconstruction of the anterior cruciate ligament (ACL) using a hamstring tendon in a rat model. ACL reconstruction was performed in both knees of 30 Sprague-Dawley rats using the flexor digitorum tendon. The effect of commercially available EMD (EMDOGAIN), a preparation of matrix proteins from developing porcine teeth, was evaluated. In the left knee joint the space around the tendon–bone interface was filled with 40 µl of EMD mixed with propylene glycol alginate (PGA). In the right knee joint PGA alone was used. The ligament reconstructions were evaluated histologically and biomechanically at four, eight and 12 weeks (n = 5 at each time point). At eight weeks, EMD had induced a significant increase in collagen fibres connecting to bone at the tendon–bone interface (p = 0.047), whereas the control group had few fibres and the tendon–bone interface was composed of cellular and vascular fibrous tissues. At both eight and 12 weeks, the mean load to failure in the treated specimens was higher than in the controls (p = 0.009). EMD improved histological tendon–bone healing at eight weeks and biomechanical healing at both eight and 12 weeks. EMD might therefore have a human application to enhance tendon–bone repair in ACL reconstruction.

Pre-operative variables are increasingly being used to determine eligibility for total knee replacement (TKR). This study was undertaken to evaluate the relationships, interactions and predictive capacity of variables available pre- and post-operatively on patient satisfaction following TKR. Using nationally collected patient reported outcome measures and data from the National Joint Registry for England and Wales, we identified 22 798 patients who underwent TKR for osteoarthritis between August 2008 and September 2010. The ability of specific covariates to predict satisfaction was assessed using ordinal logistic regression and structural equational modelling. Only 4959 (22%) of 22 278 patients rated the results of their TKR as ‘excellent’, despite the majority (71%, n = 15 882) perceiving their knee symptoms to be much improved. The strongest predictors of satisfaction were post-operative variables. Satisfaction was significantly and positively related to the perception of symptom improvement (operative success) and the post-operative EuroQol-5D score. While also significant within the models pre-operative variables were less important and had a minimal influence upon post-operative satisfaction. The most robust predictions of satisfaction occurred only when both pre- and post-operative variables were considered together. These findings question the appropriateness of restricting access to care based on arbitrary pre-operative thresholds as these factors have little bearing on post-operative satisfaction.

Cite this article: Bone Joint J 2013;95-B:1359–65.

The role of modular tibial implants in total knee replacement is not fully defined. We performed a prospective randomised controlled clinical trial using radiostereophotogrammetric analysis to compare the performance of an all-polyethylene tibia with a metal-backed cruciate-retaining condylar design, PFC-∑ total knee replacement for up to 24 months. There were 51 patients who were randomised into two treatment groups. There were 10 subsequent withdrawals, leaving 21 all-polyethylene and 20 metal-backed tibial implants. No patient was lost to follow-up. There were no significant demographic differences between the groups. At two years one metal-backed implant showed migration > 1 mm, but no polyethylene implant reached this level. There was a significant increase in the SF-12 and Oxford knee scores after operation in both groups.

In an uncomplicated primary total knee replacement the all-polyethylene PFC-∑ tibial prosthesis showed no statistical difference in migration from that of the metal-backed counterpart. There was no difference in the clinical results as assessed by the SF-12, the Oxford knee score, alignment or range of movement at 24 months, although these assessment measures were not statistically powered in this study.

Clinical experience of impaction bone grafting for revision knee arthroplasty is limited, with initial stability of the tibial tray emerging as a major concern. The length of the stem and its diameter have been altered to improve stability. Our aim was to investigate the effect of the type of stem, support of the rim and graft impaction on early stability of the tray.

We developed a system for impaction grafting of trays which we used with morsellised bone in artificial tibiae. Trays with short, long thick or long thin stems were implanted, with or without support of the rim. They were cyclically loaded while measuring relative movement.

Long-stemmed trays migrated 4.5 times less than short-stemmed trays, regardless of diameter. Those with support migrated 2.8 times less than those without. The migration of short-stemmed trays correlated inversely with the density of the impacted groups. That of impaction-grafted tibial trays was in the range reported for uncemented primary trays. Movements of short-stemmed trays without cortical support were largest and sensitive to the degree of compaction of the graft. If support of the rim was sufficient or a long stem was used, impacted morsellised bone graft achieved adequate initial stability.

Despite many claims of good wear properties following total knee replacement (TKR) with an oxidised zirconium (OxZr) femoral component, there are conflicting clinical results. We hypothesised that there would be no difference in either the mid-term clinical and radiological outcomes or the characteristics of the polyethylene wear particles (weight, size and shape) in patients using an OxZr or cobalt-chrome (CoCr) femoral component. In all 331 patients underwent bilateral TKR, receiving an OxZr femoral component in one knee and a CoCr femoral component in the other. The mean follow-up was 7.5 years (6 to 8). Following aspiration, polyethylene wear particles were analysed using thermogravimetric methods and scanning electron microscopy. At the most recent follow-up, the mean Knee Society score, Western Ontario and McMaster Universities Osteoarthritis Index score, range of movement and satisfaction score were not significantly different in the two groups. The mean weight, size, aspect ratio and roundness of the aspirated wear particles were similar for each femoral component. Survivorship of the femoral, tibial and patellar components was 100% in both groups.

In the absence of evidence of an advantage in the medium term we cannot justify the additional expense of an OxZr femoral component.

We investigated the role of ion release in the assessment of fixation of the implant after total knee replacement and hypothesised that ion monitoring could be a useful parameter in the diagnosis of prosthetic loosening. We enrolled 59 patients with unilateral procedures and measured their serum aluminium, titanium, chromium and cobalt ion levels, blinded to the clinical and radiological outcome which was considered to be the reference standard. The cut-off levels for detection of the ions were obtained by measuring the levels in 41 healthy blood donors who had no implants. Based on the clinical and radiological evaluation the patients were divided into two groups with either stable (n = 24) or loosened (n = 35) implants.

A significant increase in the mean level of Cr ions was seen in the group with failed implants (p = 0.001). The diagnostic accuracy was 71% providing strong evidence of failure when the level of Cr ions exceeded the cut-off value. The possibility of distinguishing loosening from other causes of failure was demonstrated by the higher diagnostic accuracy of 83%, when considering only patients with failure attributable to loosening.

Measurement of the serum level of Cr ions may be of value for detecting failure due to loosening when the diagnosis is in doubt. The other metal ions studies did not have any diagnostic value.

We have developed a new tensor for total knee replacements which is designed to assist with soft-tissue balancing throughout the full range of movement with a reduced patellofemoral joint. Using this tensor in 40 patients with osteoarthritis we compared the intra-operative joint gap in cruciate-retaining and posterior-stabilised total knee replacements at 0°, 10°, 45°, 90° and 135° of flexion, with the patella both everted and reduced.

While the measurement of the joint gap with a reduced patella in posterior-stabilised knees increased from extension to flexion, it remained constant for cruciate-retaining joints throughout a full range of movement. The joint gaps at deep knee flexion were significantly smaller for both types of prosthetic knee when the patellofemoral joint was reduced (p < 0.05).

We describe a cohort of patients with a high rate of mid-term failure following Kinemax Plus total knee replacement inserted between 1998 and 2001. This implant has been recorded as having a survival rate of 96% at ten years. However, in our series the survival rate was 75% at nine years. This was also significantly lower than that of subsequent consecutive series of PFC Sigma knee replacements performed by the same surgeon. No differences were found in the clinical and radiological parameters between the two groups. At revision the most striking finding was polyethylene wear. An independent analysis of the polyethylene components was therefore undertaken. Scanning electron microscopy revealed type 2 fusion defects in the ultra-high molecular weight polyethylene (UHMWPE), which indicated incomplete boundary fusion. Other abnormalities consistent with weak UHMWPE particle interface strength were present in both the explanted inserts and in unused inserts from the same period.

We consider that these type 2 fusion defects are the cause of the early failure of the Kinemax implants. This may represent a manufacturing defect resulting in a form of programmed polyethylene failure.

The Oxford mobile-bearing unicompartmental knee replacement (UKR) is an effective and safe treatment for osteoarthritis of the medial compartment. The results in the lateral compartment have been disappointing due to a high early rate of dislocation of the bearing. A series using a newly designed domed tibial component is reported.

The first 50 consecutive domed lateral Oxford UKRs in 50 patients with a mean follow-up of three years (2.0 to 4.3) were included. Clinical scores were obtained prospectively and Kaplan-Meier survival analysis was performed for different endpoints. Radiological variables related to the position and alignment of the components were measured.

One patient died and none was lost to follow-up. The cumulative incidence of dislocation was 6.2% (95% confidence interval (CI) 2.0 to 17.9) at three years. Survival using revision for any reason and aseptic revision was 94% (95% CI 82 to 98) and 96% (95% CI 85 to 99) at three years, respectively. Outcome scores, visual analogue scale for pain and maximum knee flexion showed a significant improvement (p < 0.001). The mean Oxford knee score was 43 (sd 5.3), the mean Objective American Knee Society score was 91 (sd 13.9) and the mean Functional American Knee Society score was 90 (sd 17.5). The mean maximum flexion was 127° (90° to 145°). Significant elevation of the lateral joint line as measured by the proximal tibial varus angle (p = 0.04) was evident in the dislocation group when compared with the non-dislocation group.

Clinical results are excellent and short-term survival has improved when compared with earlier series. The risk of dislocation remains higher using a mobile-bearing UKR in the lateral compartment when compared with the medial compartment. Patients should be informed about this complication. To avoid dislocations, care must be taken not to elevate the lateral joint line.