Development of a reinforced PMMA-based hip spacer adapted to patients' needs

A new mathematical model of compressive stress-strain behaviour of low viscosity and high viscosity bone cement with different strain rates

A new mathematical model of compressive stress-strain behaviour of low viscosity (LV) and high viscosity (HV) bone cement has been proposed to capture large uniaxial deformation under constant applied strain rate by incorporating three-term power law. The modeling capacity of the proposed model has been validated using uniaxial compressive test under eight different low strain rates ranging from 1.39 × 10^-4 s^-1 to 3.53 × 10^-2 s^-1 for low viscosity and high viscosity bone cement. The well agreement between the model and experimental response suggests that the proposed model can successfully predict rate dependent deformation behavior for Poly(methyl methacrylate) (PMMA) bone cement. Additionally, the proposed model was compared with the generalized Maxwell viscoelastic model and found to be in good agreement. The comparison of compressive responses over low strain rates for LV and HV bone cement reveals their rate-dependent compressive yield stress behaviour along with a higher value of compressive yield stress of LV bone cement compared to HV bone cement. For example, at the strain rate of 1.39 × 10^-4 s^-1 the mean value of compressive yield stress of LV bone cement was found to be 64.46 MPa, whereas for HV bone cement it was 54.00 MPa. Moreover, the modeling of experimental compressive yield stress with the Ree-Eyring molecular theory suggests that the variation of yield stress of PMMA bone cement can be predicted using two processes Ree-Eyring theory. The proposed constitutive model might be useful to characterize large deformation behaviour with high accuracy for PMMA bone cement. Finally, both variants of PMMA bone cement also exhibit ductile-like compressive behaviour below the strain rate of 2.1 × 10^-2 s^-1, whereas above this threshold strain rate, brittle-like compressive failure behavior is observed.

Finite element analysis of the mechanical strength of a new hip Spacer

BACKGROUND AND OBJECTIVE

At present, the influence of the internal metallic endoskeleton of Spacer on the biomechanical strength of Spacer remains unclear. The aim of this study was to analyze the mechanical stability of a novel Spacer applying a annular skeleton that mimics the structure of trabecular bone using finite element methods.

METHEDS

The femur models of three healthy individuals and skeletonless Spacer, K-Spacer, and AD-Spacer were assembled to create 15 3D models. Finite element analysis was performed in an Ansys Bench2022R1. Biomechanical parameters such as stress and strain of the Spacer, internal skeleton and femur were evaluated under three loads, which were applied with the maximum force borne by the hip joint (2100 N), standing on one leg (700 N), and standing on two legs (350 N). The mechanical properties of the new hip Spacer were evaluated.

RESULT

The stresses on the medial and lateral surfaces of the AD-Spacer and K-Spacer were smaller than the stresses in the state without skeletal support. The maximum stresses on the medial and lateral surfaces of the AD-Spacer were smaller than those of the inserted K-Spacer, and the difference gradually increased with the increase of force intensity. When the skeleton diameter was increased from 3 to 4 mm, the stresses in the medial and lateral sides of the AD-Spacer and K-Spacer necks decreased. The stress of both skeletons was concentrated at the neck, but the stress of the annular skeleton was evenly distributed on the medial and lateral sides of the skeleton. The mean stress in the proximal femur was higher in femurs with K-Spacer than in femurs with AD-Spacer.

CONCLUSIONS

AD-Spacer has lower stress and higher load-bearing capacity than K-Spacer, and the advantages of AD-Spacer are more obvious under the maximum load state of hip joint.

Retained Functional Antibiotic Hip Spacers Have High Rates of Stem Loosening, Subsidence, and Reoperation

BACKGROUND

Functional antibiotic hip spacers for treatment of periprosthetic joint infection may be retained in patients deemed too sick for reimplantation, or who elect to forego additional surgery. Our aim was to characterize reoperations, modes of failure, and function outcomes in patients who have retained hip spacers.

METHODS

We performed a retrospective review of 43 hips (42 patients) who underwent placement of an articulating hip spacer between January 1, 2014 and November 30, 2021 at a single orthopaedic surgical hospital. There were 27 patients (28 hips) who completed 2-stage exchange (TS group) and were reimplanted at mean 4 months (range, 2 to 10). The 15 patients (15 hips) underwent planned spacer retention (RS group). Mean follow-up was 2.9 years (range, 1 to 6.1 years). The RS group was older (74 vs 66 years, P=0.005) and had a higher age-adjusted Charlson Comorbidity Index (4.4 vs 3.3, P=0.04) compared with the TS group.

RESULTS

Overall survivorship free of reinfection was 91% at 1 year and 86% at 5 years. There were 6 RS hips that underwent reimplantation for spacer failure at a mean of 23 months (range, 6 to 71) months and 8 had radiographic stem loosening / subsidence. Patients who had a retained spacer at final follow-up were more likely to require a walker (P=0.005) or wheelchair (P=0.049) compared with patients who underwent reimplantation.

CONCLUSIONS

Retained hip spacers can decrease overall surgical burden, but are associated with high rates of stem loosening, subsidence, and unplanned reoperation. Planned spacer retention should be undertaken with caution in patients healthy enough to undergo reimplantation.

Developing PMMA/Coffee Husk Green Composites to Meet the Individual Requirements of People with Disabilities: Hip Spacer Case Study

When replacing a damaged artificial hip joint, treatment involves using antibiotic-laced bone cement as a spacer. One of the most popular materials used for spacers is PMMA; however, it has limitations in terms of mechanical and tribological properties. To overcome such limitations, the current paper proposes utilizing a natural filler, coffee husk, as a reinforcement for PMMA. The coffee husk filler was first prepared using the ball-milling technique. PMMA composites with varying weight fractions of coffee husk (0, 2, 4, 6, and 8 wt.%) were prepared. The hardness was measured to estimate the mechanical properties of the produced composites, and the compression test was utilized to estimate the Young modulus and compressive yield strength. Furthermore, the tribological properties of the composites were evaluated by measuring the friction coefficient and wear by rubbing the composite samples against stainless steel and cow bone counterparts under different normal loads. The wear mechanisms were identified via scanning electron microscopy. Finally, a finite element model for the hip joint was built to investigate the load-carrying capacity of the composites under human loading conditions. The results show that incorporating coffee husk particles can enhance both the mechanical and tribological properties of the PMMA composites. The finite element results are consistent with the experimental findings, indicating the potential of the coffee husk as a promising filler material for enhancing the performance of PMMA-based biomaterials.

A Three-Parameter Weibull Distribution Method to Determine the Fracture Property of PMMA Bone Cement

Poly (methyl methacrylate) (PMMA) bone cement is an excellent biological material for anchoring joint replacements. Tensile strength ft and fracture toughness KIC have a considerable impact on its application and service life. Considering the variability of PMMA bone cement, a three-parameter Weibull distribution method is suggested in the current study to evaluate its tensile strength and fracture toughness distribution. The coefficients of variation for tensile strength and fracture toughness were the minimum when the characteristic crack of PMMA bone cement was αch∗=8dav. Using the simple equation αch∗=8dav and fictitious crack length Δαfic=1.0dav, the mean value μ (= 43.23 MPa), minimum value ftmin (= 26.29 MPa), standard deviation σ (= 6.42 MPa) of tensile strength, and these values of fracture toughness (μ = 1.77 MPa⋅m1/2, KICmin = 1.02 MPa⋅m1/2, σ = 0.2644 MPa⋅m1/2) were determined simultaneously through experimental data from a wedge splitting test. Based on the statistical analysis, the prediction line between peak load Pmax and equivalent area Ae1Ae2 was obtained with 95% reliability. Nearly all experimental data are located within the scope of a 95% confidence interval. Furthermore, relationships were established between tensile strength, fracture toughness, and peak load Pmax. Consequently, it was revealed that peak load might be used to easily obtain PMMA bone cement fracture characteristics. Finally, the critical geometric dimension value of the PMMA bone cement sample with a linear elastic fracture was estimated.

High Rates of Spacer Fracture in the Setting of Extended Trochanteric Osteotomy With a Specific Thin-Core Articulating Antibiotic Hip Spacer

BACKGROUND

Two-stage revision remains the standard of care for prosthetic joint infection after total hip arthroplasty. However, there are substantial complications associated with articulating antibiotic hip spacers. Handmade and molded spacers have been shown to have higher rates of spacer fracture than antibiotic-coated prostheses (ACPs). The aim of this study is to review outcomes with an implant that is often categorized as an ACP spacer, the Zimmer-Biomet StageOne Select Femoral Spacer (ZBSO).

METHODS

A retrospective review was performed of 63 patients who underwent placement of a ZBSO. Patients were compared based on whether or not an extended trochanteric osteotomy (ETO) was performed using Fisher's exact and t-tests.

RESULTS

Five patients were excluded due to lack of follow-up or death shortly after stage 1 surgery, leaving 58 patients. Spacer fracture was noted in 5 of 58 patients (8.6%). Sixteen patients underwent ETO and 25.0% suffered a spacer fracture compared to 2.3% without ETO (odds ratio 13.7, P = .0248). There was no association between patient demographics or ETO length and spacer fracture. Two patients had periprosthetic fractures (3.4%) and 4 had dislocations (6.9%). Forty-nine patients (84.4%) went on to second-stage revision; of those 26.5% failed to clear the infection and required an average of 2.2 additional surgeries.

CONCLUSION

The ZBSO spacer has overall complication rates similar to previously reported spacer series. Although the ZBSO looks like an ACP spacer, in the setting of ETO, it behaves like a molded or handmade spacer with a high rate of spacer fracture (25%) due to the small diameter of the core. This implant should be used with caution in combination with an ETO.

Quasi-static analysis of hip cement spacers

The use of temporary hip prosthesis made of orthopedic cement (spacer) in conjunction with antibiotics became a widespread method used for treating prosthetic infections despite the fact that this method makes bone cement (PMMA) more fragile. The necessity to incorporate reinforcement is therefore crucial to strengthen the bone cement. In this study, a validated Finite Element Modelling (FEM) was used to analyze the behavior of spacers. This FEM model uses a non-linear dynamic explicit integration to simulate the mechanical behavior of the spacer under quasi-static loading. In addition to this FEM, Extended Finite Element Method (XFEM) was also used to investigate the fracture behavior of the spacers reinforced with titanium, ceramic and stainless-steel spacer stems. The effect of the material on the performance of the reinforced spacers was also analyzed. The results showed that numerical modelling based on explicit finite element using ABAQUS/Explicit is an effective method to predict the different spacers' mechanical behavior. The simulated crack initiation and propagation were in a good agreement with experimental observations. The FEM models developed in this study can help mechanical designers and engineers to improve the prostheses' quality and durability.

Influence of several biodegradable components added to pure and nanosilver-doped PMMA bone cements on its biological and mechanical properties

Acrylic bone cements (BC) are wildly used in medicine. Despite favorable mechanical properties, processability and inject capability, BC lack bioactivity. To overcome this, we investigated the effects of selected biodegradable additives to create a partially-degradable BC and also we evaluated its combination with nanosilver (AgNp). We hypothesized that using above strategies it would be possible to obtain bioactive BC. The Cemex was used as the base material, modified at 2.5, 5 or 10 wt% with either cellulose, chitosan, magnesium, polydioxanone or tricalcium-phosphate. The resulted modified BC was examined for surface morphology, wettability, porosity, mechanical and nanomechanical properties and cytocompatibility. The composite BC doped with AgNp was also examined for its release and antibacterial properties. The results showed that it is possible to create modified cement and all studied modifiers increased its porosity. Applying the additives slightly decreased BC wettability and mechanical properties, but the positive effect of the additives was observed in nanomechanical research. The relatively poor cytocompatibility of modified BC was attributed to the unreacted monomer release, except for polydioxanone modification which increased cells viability. Furthermore, all additives facilitated AgNp release and increased BC antibacterial effectiveness. Our present studies suggest the optimal content of biodegradable component for BC is 5 wt%. At this content, an improvement in BC porosity is achieved without significant deterioration of BC physical and mechanical properties. Polydioxanone and cellulose seem to be the most promising additives that improve porosity and antibacterial properties of antibiotic or nanosilver-loaded BC. Partially-degradable BC may be a good strategy to improve their antibacterial effectiveness, but some caution is still required regarding their cytocompatibility. STATEMENT OF SIGNIFICANCE: The lack of bone cement bioactivity is the main limitation of its effectiveness in medicine. To overcome this, we have created composite cements with partially-degradable properties. We also modified these cements with nanosilver to provide antibacterial properties. We examined five various additives at three different contents to modify a selected bone cement. Our results broaden the knowledge about potential modifiers and properties of composite cements. We selected the optimal content and the most promising additives, and showed that the combination of these additives with nanosilver would increase cements` antibacterial effectiveness. Such modified cements may be a new solution for medical applications.

Hip Spacers in Two-Stage Revision for Periprosthetic Joint Infection: A Review of Literature

Infection after total hip arthroplasty (THA) is a devastating complication with significant consequences for patients. In literature, single and two-stage revision, irrigation and debridement, Girdlestone resection arthroplasty, and arthrodesis and amputation are reported as possible treatments. Recently, two-stage revision has become popular as the gold standard treatment for chronic hip joint infections after THA. In this review, we evaluate the current literature about microbiology of periprosthetic joint infections and the use of antibiotic-loaded cement spacers. We aim to give an overview about indications, clinical results, and mechanical complications for spacers implantation, evaluating also selection criteria, pharmacokinetic properties, and systemic safety of the most frequently used antibiotics.

Optimisation of a Reinforced Cement Spacer in Total Hip Arthroplasty

Infections total hip arthroplasty (THA) are common and can lead to serious complications for patients. Newly developed antibiotic spacers successfully eradicated infection in more than 90 percent of patients. However, the low mechanical strength of the orthopedic cement can be a serious handicap for the success of the surgical operation. The reinforcement of cement spacers with high strength materials can improve the efficiency of this type of surgery. In this study, the three-dimensional finite element method (FEM) is coupled with the experimental design method (EDM) to optimize the geometrical and mechanical properties of the reinforcement that can be applied to cements spacers. The obtained results show that the full stem reinforcement in bio-ceramic with a thickness of 8.2 mm can represent the optimal model to ensure good mechanical resistance of the cement spacer.

Two-stage protocol and spacer implantation in the treatment of destructive septic arthritis of the hip joint

INTRODUCTION

The ideal treatment of the destructive septic arthritis of the hip joint remains controversial. The aim of the present retrospective study was to report on our experience about the use of antibiotic-loaded cement spacers in the treatment of destructive bacterial coxitis.

MATERIALS AND METHODS

22 consecutive patients (11 male, 11 female, mean age 59.7 years) have been treated with a two-stage protocol and implantation of an antibiotic-loaded cement spacer. All patients' records have been retrospectively evaluated with regard to comorbidities/predisposing factors, infection cause, causative pathogen organism, presence of a psoas abscess, surgical time of spacer implantation, duration of spacer implantation, spacer articulation, impregnation of bone cement, systemic antibiotic therapy, surgical time of prosthesis implantation, implant type, complications, and infection control rate.

RESULTS

The most common identified organism was Staphylococcus aureus (73 %). The mean duration of spacer implantation was 88 days. Spacer-specific complications were observed in 23 % of the cases and spacer non-specific ones in 50 % between stages. The mortality rate after the first stage was 18 %. Prosthesis implantation was performed in 16 cases. At a mean follow-up of 44.8 (12-120) months, the primary infection control rate (after one spacer implantation) was 87 % (13/15) and the secondary infection control rate (after two spacer implantations) 100 %.

CONCLUSIONS

Two-stage treatment and spacer implantation is associated with a high rate of infection control but also with a high mortality rate between stages.

Mechanical complications with one hundred and thirty eight (antibiotic-laden) cement spacers in the treatment of periprosthetic infection after total hip arthroplasty

PURPOSE

Periprosthetic infection after total hip arthroplasty is a devastating complication. A two-stage protocol with the temporary insertion of an antibiotic-laden cement spacer is the gold standard treatment for chronic infections (Clinics (Sao Paulo) 62:99-108, 2007; Clin Orthop Relat Res 427:37-46, 2004; J Arthroplast 14:175-181, 1999; Clin Orthop Relat Res 467:1848-1858, 2009; J Arthroplast 20:874-879, 2005; J Arthroplast 24: 607-613, 2009; Clin Orthop Relat Res 469:1009-1015, 2011; Hip Int 20:26-33, 2010; J Arthroplast 24:1051-1060, 2009; J Bone Joint Surg Br 91:44-51, 2009). Some authors, however (Int J Med Sci 6(5):265-73, 2009), report mechanical complication rates with spacers in excess of 50%.Therefore, the aim of this study is to determine (1) the mechanical complications associated with enclosed articulating partial load-bearing spacers when treating periprosthetic hip infections and (2) possible factors of influence.

METHODS

Between 2000 and 2011, 138 patients received an antibiotic-laden cement spacer as part of a two-stage protocol. The overall frequency of complications (spacer fracture, dislocation, femoral fracture with enclosed spacer, spacer fracture with dislocation, protusion into the pelvis) was recorded. Potential influencing factors ('mould spacer' vs. handmade spacer, Steinmann pins as an endoskeleton, addition of vancomycin into the spacer) were analysed.

RESULTS

The mean age at the time of the first stage operation was 69.3 ± 10.5 years. Overall, 27 of 138 patients suffered one of the above-mentioned complications (19.6%). Spacer fracture occurred in 12 cases (8.7%) and dislocation in another 12 (8.7%). There was also one periprosthetic femoral fracture with a spacer in situ, one dislocation with a simultaneous spacer fracture, and one protrusion into the pelvis (0.7% each).

CONCLUSIONS

Our data revealed an overall complication rate of 13.2% with a mould spacer enclosing a Steinman pin. The mechanical complication rate of over 50% reported by some authors cannot be confirmed. As a consequence, we recommend using a mould spacer with an enclosed Steinman pin as an endoskeleton to minimize the complication rate.

[Hip joint infections - Results of a questionnaire among 28 university orthopedic departments]

BACKGROUND

Despite numerous prophylactic measures infections still remain a hazardous complication in orthopedic surgery.

MATERIAL AND METHODS

A questionnaire about hip joint infections was sent to all university orthopedic departments in Germany and Austria. The questionnaire included 33 questions with respect to demographic data, causative organisms, diagnostic measures, treatment options for early and late infections, antibiotic therapy and prosthesis reimplantation.

RESULTS

The participation rate was 70%. The most frequent primary surgical indication was primary total hip replacement and Staphylococcus aureus and S. epidermidis were the most common pathogens identified. All departments performed a joint aspiration for diagnosis confirmation but for other diagnostic measures a great discrepancy could be observed. In the treatment of early infections removable components were always exchanged, whereas a local antibiotic therapy was not always employed. With regard to late infections a two-stage protocol was more frequently used than a one-stage treatment, whereby the implantation of a cement spacer was more commonly performed than a resection arthroplasty. The time between stages varied between 6 and 12 weeks and systemic antibiotics were administered for a mean time of 6 weeks. For prosthesis reimplantion cementless components were mostly used but no clear tendency could be determined for systemic antibiotic therapy.

CONCLUSION

Treatment of hip joint infections among German and Austrian university orthopedic departments is only partly carried out in a similar manner.

The effect of endoskeleton on antibiotic impregnated cement spacer for treating deep hip infection

Backgrounds

A two-stage revision arthroplasty was suggested optimal treatment for deep infections in hip joint. The effect of endoskeleton of cement spacers on the interim function and infection control remains unclear.

Methods

From Jan. 2004 to Dec. 2007, we collected a prospective cohort of consecutive 34 patients who treated with two-stage revision total hip arthroplasty for deep infection of hip joint. In group 1, fifteen patients were treated by a novel design augmented with hip compression screw while nineteen patients were treated by traditional design in group 2.

Results

No fracture of cement spacer occurred in group 1 while 6 cases developed spacer failure in group 2. (p < 0.05) There were significant differences in bodily pain and general health perception between groups (p < 0.05).

Conclusions

Patients being treated for deep infection of hip joint using cement spacer augmented with stronger endoskeleton have lower pain levels and better joint function between stages.

Preformed gentamicin spacers in two-stage revision hip arthroplasty: functional results and complications

Two-stage revisions with antibiotic-loaded spacers have gained popularity for treating infected hip-joint arthroplasties. The aim of this prospective study was to assess patient functionality between stages and treatment impact on duration of hospital stay and to describe related complications. Sixty-one consecutive patients with infected hip arthroplasties underwent two-stage revision with preformed spacer implantation. Mean Harris Hip and Merle d'Aubigné scores between the two stages were 39.9 and 7.6, respectively. Forty-six patients (75.4%) were able to leave hospital between stages. Spacer dislocation occurred in 16.4%. No cases of spacer breakage were noted. Preformed cement spacers provide acceptable functional outcome between revision hip arthroplasty stages and facilitate the surgical procedure without increasing mechanical complication rates.

Mechanical behaviour of standardized, endoskeleton-including hip spacers implanted into composite femurs

Two-stage reconstruction using an antibiotic loaded cement spacer is the preferred treatment method of late hip joint infections. Hip spacers maintain stability of the joint and length of the limb during treatment period. However, as the material strength of bone cement (PMMA) is limited, spacer fractures led to serious complications in the past. This study investigated the load capacity of custom made hip spacers, developed at the 'Klinik für Orthopädie und Orthopädische Chirurgie' (Universitätsklinikum des Saarlandes, Homburg/Saar, Germany), and implanted into composite femurs. In a quasi-static test, non-reinforced spacers tolerated hip joint loads of about 3000 N, whereas reinforced spacers with titanium-grade-two endoskeletons doubled this load up to 6000 N. Even for cyclic loading, endoskeleton-including hip spacers tolerated loads of >4500 N with 500,000 load cycles. Thus, an endoskeleton-including spacer should provide a mobile and functional joint through the treatment course. A generated FE-model was used to determine the fracture stresses and allows for further sensitivity analysis.

Complications after spacer implantation in the treatment of hip joint infections

The aim of this retrospective study was to identify and evaluate complications after hip spacer implantation other than reinfection and/or infection persistence. Between 1999 and 2008, 88 hip spacer implantations in 82 patients have been performed. There were 43 male and 39 female patients at a mean age of 70 [43-89] years. The mean spacer implantation time was 90 [14-1460] days. The mean follow-up was 54 [7-96] months. The most common identified organisms were S. aureus and S. epidermidis. In most cases, the spacers were impregnated with 1 g gentamicin and 4 g vancomycin/80 g bone cement. The overall complication rate was 58.5% (48/82 cases). A spacer dislocation occurred in 15 cases (17%). Spacer fractures could be noticed in 9 cases (10.2%). Femoral fractures occurred in 12 cases (13.6%). After prosthesis reimplantation, 16 patients suffered from a prosthesis dislocation (23%). 2 patients (2.4%) showed allergic reactions against the intravenous antibiotic therapy. An acute renal failure occurred in 5 cases (6%). No cases of hepatic failure or ototoxicity could be observed in our collective. General complications (consisting mostly of draining sinus, pneumonia, cardiopulmonary decompensation, lower urinary tract infections) occurred in 38 patients (46.3%). Despite the retrospective study design and the limited possibility of interpreting these findings and their causes, this rate indicates that patients suffering from late hip joint infections and being treated with a two-stage protocol are prone to having complications. Orthopaedic surgeons should be aware of these complications and their treatment options and focus on the early diagnosis for prevention of further complications. Between stages, an interdisciplinary cooperation with other facilities (internal medicine, microbiologists) should be aimed for patients with several comorbidities for optimizing their general medical condition.