Increased long-term failure risk associated with excessively thin cement mantle in cemented hip arthroplasty: a comparative in vitro study

An additively manufactured model for preclinical testing of cervical devices

Purpose

Composite models have become commonplace for the assessment of fixation and stability of total joint replacements; however, there are no comparable models for the cervical spine to evaluate fixation. The goal of this study was to create the framework for a tunable non-homogeneous model of cervical vertebral body by identifying the relationships between strength, in-fill density, and lattice structure and creating a final architectural framework for specific strengths to be applied to the model.

Methods

The range of material properties for cervical spine were identified from literature. Using additive manufacturing software, rectangular prints with three lattice structures, gyroid, triangle, zig-zag, and a range of in-fill densities were 3D-printed. The compressive and shear strengths for all combinations were calculated in the axial and coronal planes. Eleven unique vertebral regions were selected to represent the distribution of density. Each bone density was converted to strength and subsequently correlated to the lattice structure and in-fill density with the desired material properties. Finally, a complete cervical vertebra model was 3D-printed to ensure sufficient print quality.

Results

Materials testing identified a relationship between in-fill densities and strength for all lattice structures. The axial compressive strength of the gyroid specimens ranged from 1.5 MPa at 10% infill to 31.3 MPa at 100% infill and the triangle structure ranged from 2.7 MPa at 10% infill to 58.4 MPa at 100% infill. Based on these results, a cervical vertebra model was created utilizing cervical cancellous strength values and the corresponding in-fill density and lattice structure combination. This model was then printed with 11 different in-fill densities ranging from 33% gyroid to 84% triangle to ensure successful integration of the non-homogeneous in-fill densities and lattice structures.

Conclusions

The findings from this study introduced a framework for using additive manufacturing to create a tunable, customizable biomimetic model of a cervical vertebra.

Minimum 10-Year Follow-Up of Total Hip Arthroplasty With a Collarless Triple-Tapered Polished Cemented Stem With Line-to-Line Implantation Using a Direct Anterior Approach

BACKGROUND

The Trilliance stem (B. Braun-Aesculap, Tuttlingen, Germany), a novel collarless triple-tapered polished stem, was introduced in 2009. The aim of this study is to evaluate the long-term clinical and radiological results of the Trilliance stem with line-to-line implantation in primary total hip arthroplasty using a direct anterior approach.

METHODS

A consecutive retrospective series of 130 patients (151 hips) who underwent total hip arthroplasty between February 2009 and August 2011 were evaluated for a minimum of 10 years. Of these, 87.4% had a diagnosis of secondary osteoarthritis based on developmental hip dysplasia. Clinical and radiological results, complications were evaluated and survival analysis was performed.

RESULTS

The mean follow-up was 10.7 years (range, 10.0-12.1). Thirteen hips (13 patients, 6.8%) were lost to follow-up. Adequate cementation (Barrack grade A) was achieved in 136 hips (93.8%) 1 week post-operatively. Nearly all (144 hips, 99.3%) had been inserted within the range of 3°. No significant differences were identified between high- (≥30 procedures/year) and low- (<30 procedures/year) volume surgeons. The Kaplan-Meier survival analysis with revision of the femoral component for aseptic loosening, revision of the femoral component for any reason and revision of either component for any reason as the end points, cumulative survivorship was 100.0%, 97.6% (95% confidence interval (CI) 95.4-100.0) and 96.5% (95% CI 93.8-99.3) at 10 years, respectively.

CONCLUSION

The Trilliance stem with line-to-line implantation using a direct anterior approach has an excellent clinical and radiological outcome at a minimum of 10 years' follow-up.

LEVEL OF EVIDENCE

Level IV, Retrospective cohort study.

Short vs Standard-Length Femoral Stems Cemented According to the "French Paradox": A Matched Paired Prospective Study Using Ein Bild Roentgen Analyze Femoral Component at Two-Year Follow-Up

BACKGROUND

The purpose of this prospective matched paired study is to compare the in vivo migration patterns using Ein Bild Roentgen Analyze femoral component of shortened vs standard-length stems cemented line-to-line in primary total hip arthroplasty (THA) at 2-year follow-up.

METHODS

We prospectively included the first 50 consecutive primary cemented THAs in 50 patients using a 12% shortened stem (AmisK group) of which design was derived from the original Charnley-Kerboull (CK) femoral components. These 50 patients were matched paired to 50 patients from a historical series of patients who underwent primary THAs using standard-length CK stems (CK group) with available long-term results, including Ein Bild Roentgen Analyze femoral component data at 2-year follow-up.

RESULTS

Body mass index was significantly higher (P = .007) in the AmisK vs the CK group. At the 2-year follow-up, the mean subsidence was 0.65 mm (0-1.40) in the AmisK group vs 0.68 mm (0.07-1.43) in the CK group (P = .73). When using a 1.5-mm threshold, none of the stems in either group was considered to have subsided. Femoral cortical thickening in zones 3 and 5 occurred in 6 of the 50 hips (12%) in the AmisK group vs 20 (40%) of the 50 hips in the CK group (P = .003).

CONCLUSION

Our study showed that a shortened highly polished double-tapered stem cemented line-to-line provided similar results including minimal subsidence as its standard-length counterpart, with significantly less distal femoral cortical thickening. However, longer term survival analysis still needs to be determined.

Current concepts and outcomes in cemented femoral stem design and cementation techniques: the argument for a new classification system

Cemented implant fixation design principles have evolved since the 1950s, and various femoral stem designs are currently in use to provide a stable construct between the implant-cement and cement-bone interfaces.Cemented stems have classically been classified into two broad categories: taper slip or force closed, and composite beams or shaped closed designs. While these simplifications are acceptable general categories, there are other important surgical details that need to be taken into consideration such as different broaching techniques, cementing techniques and mantle thickness.With the evolution of cemented implants, the introduction of newer implants which have hybrid properties, and the use of different broaching techniques, the classification of a very heterogenous group of implants into simple binary categories becomes increasingly difficult. A more comprehensive classification system would aid in comparison of results and better understanding of the implants' biomechanics.We review these differing stem designs, their respective cementing techniques and geometries. We then propose a simple four-part classification system and summarize the long-term outcomes and international registry data for each respective type of cemented prosthesis. Cite this article: EFORT Open Rev 2020;5:241-252. DOI: 10.1302/2058-5241.5.190034.

Standard and line-to-line cementation of a polished short hip stem: Long-term in vitro implant stability

The current trend is toward shorter hip stems. While there is a general agreement on the need for a cement mantle thicker than 2 mm, some surgeons prefer line-to-line cementation, where the mantle has only the thickness provided by the cement-bone interdigitation. The aim of this study was to assess if a relatively short, polished hip stem designed for a standard cementation can also be cemented line-to-line without increasing the risk of long-term loosening. Composite femurs with specific open-cell foam to allow cement-bone interdigitation were used. A validated in-vitro biomechanical cyclic test replicating long-term physiological loading was applied to femurs where the same stem was implanted with the Standard-mantle (optimal stem size) and Line-to-line (same rasp, one-size larger stem). Implant-bone motions were measured during the test. Inducible micromotions never exceeded 10 μm for both implant types (differences statistically not-significant). Permanent migrations ranged 50-300 μm for both implant types (differences statistically not-significant). While in the standard-mantle specimens there was a pronounced trend toward stabilization, line-to-line had less tendency to stabilize. The cement cracks were observed after the test by means of dye penetrants: The line-to-line specimens included the same cracks of the standard-mantle (but in the line-to-line specimens they were longer), and some additional cracks. The micromotions and cement damage were consistent with those observed in-vitro and clinically for stable stems, confirming that none of the specimens became dramatically loose. However, it seems that for this relatively short polished stem, standard-mantle cementation is preferable, as it results in less micromotion and less cement cracking. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2736-2744, 2018.

BIOMECHANICAL RATIONALE FOR CHOICE OF CEMENT MANTLE THICKNESS AROUND A FEMORAL STEM

The change in mechanical properties of the femoral bone tissue surrounding hip endoprosthesis stems during the post-operative period is one of the causes of implant instability, and the mathematical description of this phenomenon is the subject of much research. In the present study, a model of bone adaptation, based on isotropic Stanford theory, is created for further computer investigation. The results of implementation of such a mathematical model are presented regarding the choice of cement mantle rational thickness in cemented hip arthroplasties. The results show that for cement mantle thicknesses ranging from 1–1.5[Formula: see text]mm, a peak stress value in the proximal part of the mantle exceeds the limit of durability of bone cement. Moreover, results show that high reduction in the bone density of distal and proximal regions was observed in cases of cement mantle thicknesses varying from 1–3[Formula: see text]mm. No significant changes in bone density of the abovementioned regions were obtained for 4[Formula: see text]mm and 5[Formula: see text]mm. The outcome of numerical investigations can be treated as valuable and will lead to the improvement of cemented hip replacement surgery results.

Biomechanics of a cemented short stem: Standard vs. line-to-line cementation techniques. A biomechanical in-vitro study involving six osteoporotic pairs of human cadaver femurs

BACKGROUND

Short-stem total hip arthroplasty (THA) potentially offers advantages compared to conventional THA, including sparing bone and soft tissue and being a facilitated and less traumatic implantation. However, the indication is limited to patients with sufficient bone quality. Cemented short-stem THA might provide an alternative to conventional cemented THA. To date, no cemented short stem is available on the market.

METHODS

In the present in vitro study, primary stability of a new cemented short stem was evaluated, comparing standard (undersized stem) versus line-to-line (same-sized stem) cementing techniques, using six pairs of human cadaver femurs. Primary stability, including reversible micromotion and irreversible migration, was assessed in a dynamic material-testing machine. Fracture load was tested and fracture pattern analyzed.

FINDINGS

Both cementation techniques (standard vs. line-to-line) displayed comparable results with respect to primary stability without any statistical differences (micromotion: 17.5 μm vs. 9.6 μm (p = 0.063); migration: 9.5 μm vs. 38.2 μm (p = 0.188)). Regarding fracture load, again, no difference was observed (3670 N vs. 3687 N (p = 0.063)). In all cases, proximal fractures of Vancouver type B3 occurred.

INTERPRETATION

The present in vitro study demonstrates that the line-to-line cementation technique, which is favourable regarding the philosophy of short stem THA, can be further pursued in the course of the development of a cemented short stem. Further investigations should address how well the cemented short stem compares to well-established cemented straight-stem designs.

Load transfer in the proximal femur and primary stability of a cemented and uncemented femoral stem: An experimental study on cadaver femurs

There are principally two fixation methods in total hip arthroplasty, cemented and uncemented. Both methods have in general good long-time survival. Studies comparing cemented and uncemented femoral stems indicate that the cemented stems perform somewhat better, at least in the elderly population. The aim of this study was to compare load transfer and the initial micromotion pattern for an uncemented and a cemented stem. A total of 12 human cadavers were tested in a hip simulator during single leg and stair climbing. Strain was measured on the proximal femur before and after implantation of the prostheses, and the values were presented as percentage of physiological strain. The micromovements between the stem and bone were measured and a total point motion was calculated. The results showed small statistically significant differences between the fixation methods, the largest difference being 8.1 percentage points. The uncemented stem had somewhat higher micromotion than the cemented stem, but less than 10 µm. Both stems thus had acceptable primary stability. The main finding of this study is the strain and micromotion pattern of a cemented and an uncemented stem of similar geometry is overall equal. There were small statistical significant differences between the two fixation methods regarding strain and micromotion levels. The differences are considered too small to be clinically relevant.

The effect of isotonic saline on the strength of bone cement during the polymerisation period

It is common practice to irrigate the wound in hip and knee replacement surgery during the working and setting phases of cement polymerisation. We sought to establish whether the addition of normal saline during the various stages of polymerisation would affect bone cement strength. Cement specimens were moulded to the dimensions defined in ISO 5833: 2002 and tested in an electro-mechanical test machine with a calibrated 50 kN load cell at a compression rate of 24 mm/min. The results suggest that the compressive strength of bone cement is not affected by the presence of saline following the initiation of polymerisation. However, saline added to the mix prior to the initiation of polymerisation increased its porosity and significantly decreased its strength. This may explain why vacuum mixing is important as it removes water vapour.

Effect of cement fill ratio in loosening of hip implants

Femoral loosening is one of the most prevalent causes of revision orthopedic surgeries. Cement mantle thickness has been directly correlated with femoral loosening. If the mantle is too thick, there is an increased risk of radiolucent lines and inconsistent densities. Also, the more bone that is reamed out during the procedure can lead to instability, especially if the quality of the bone is compromised due to osteoporosis. Too thin of a mantle can lead to a higher probability for cement fracture, loosening the prosthetic even further. This study has shown that there is an ideal thickness range between 2 to 5 mm that should be kept. From radiographic images one can measure the thickness of the cement mantle showing the loosening characteristics.

METHOD TO ANALYZE THE FATIGUE CRACKS IN ACRYLIC BONE CEMENT

Acrylic bone cement is a poly(methyl methacrylate)-based material that ensures short-term stability of orthopedic implants after surgery. Its long-term performance can be affected by many factors (e.g., composition, cement mixing and delivery method, temperature, humidity). Furthermore, patient activities produce a spectrum of cyclic loads that generate microdamage within the acrylic bone cement mantle. Therefore, pre-clinical studies on fatigue damage of acrylic bone cements are essential for predicting the long-term stability of cemented implants. There are several methods for analyzing damage of acrylic bone cement. However, they present a number of limitations. The aim of this study was to validate the use of a high-resolution scanner to analyze the presence of microcracks in acrylic bone cement. The proposed method met predetermined criteria to overcome limitations of previous methods, ensuring approximate spatial resolution of 5 microns, reduction of image acquisition time, and reduction of artifacts due to operator and/or environment during image acquisition. Additionally, the described method was applied to three types of acrylic bone cement specimens that previously were subjected to a fatigue test. The presented method enables the accurate assessment of fatigue damage induced during cycling loading, including quantification of the number, length, type and position of cement cracks.

Thermal effects of glenoid reaming during shoulder arthroplasty in vivo

BACKGROUND

Glenoid component loosening is a common cause of failure of total shoulder arthroplasty. It has been proposed that the heat generated during glenoid preparation may reach temperatures capable of producing osteonecrosis at the bone-implant interface. We hypothesized that temperatures sufficient to induce thermal necrosis can be produced with routine drilling and reaming during glenoid preparation for shoulder arthroplasty in vivo. Furthermore, we hypothesized that irrigation of the glenoid during reaming can reduce this temperature increase.

METHODS

Real-time, high-definition, infrared thermal video imaging was used to determine the temperatures produced by drilling and reaming during glenoid preparation in ten consecutive patients undergoing total shoulder arthroplasty. The maximum temperature and the duration of temperatures greater than the established thresholds for thermal necrosis were documented. The first five arthroplasties were performed without irrigation and were compared with the second five arthroplasties, in which continuous bulb irrigation was used during drilling and reaming. A one-dimensional finite element model was developed to estimate the depth of penetration of critical temperatures into the bone of the glenoid on the basis of recorded surface temperatures.

RESULTS

Our first hypothesis was supported by the recording of maximum surface temperatures above the 56°C threshold during reaming in four of the five arthroplasties done without irrigation and during drilling in two of the five arthroplasties without irrigation. The estimated depth of penetration of the critical temperature (56°C) to produce instantaneous osteonecrosis was beyond 1 mm (range, 1.97 to 5.12 mm) in four of these patients during reaming and one of these patients during drilling, and two had estimated temperatures above 56°C at 3 mm. Our second hypothesis was supported by the observation that, in the group receiving irrigation, the temperature exceeded the critical threshold in only one specimen during reaming and in two during drilling. The estimated depth of penetration for the critical temperature (56°C) did not reach a depth of 1 mm in any of these patients (range, 0.07 to 0.19 mm).

CONCLUSIONS

Temperatures sufficient to induce thermal necrosis of glenoid bone can be generated by glenoid preparation in shoulder arthroplasty in vivo. Frequent irrigation may be effective in preventing temperatures from reaching the threshold for bone necrosis during glenoid preparation.

Effect of undersizing on the long-term stability of the Exeter hip stem: A comparative in vitro study

BACKGROUND

Even for clinically successful hip stems such as the Exeter-V40 occasional failures are reported. It has been reported that sub-optimal pre-operative planning, leading to implant undersizing and/or thin cement mantle, can explain such failures. The scope of this study was to investigate whether stem undersizing and a thin cement mantle are sufficient to cause implant loosening.

METHODS

A comparative in vitro study was designed to compare hip implants prepared with optimal and smaller than optimal stem size. Exeter-V40, a highly polished cemented hip stem, was used in both cases. Tests were carried out simulating 24 years of activity of active hip patients. A multifaceted approach was taken: inducible and permanent micromotions were recorded throughout the test; cement micro-cracks were quantified using dye penetrants and statistically analyzed.

FINDINGS

The implants with an optimal stem size withstood the entire mechanical test, with low and stable inducible micromotions and permanent migrations during the test, and with moderate fatigue damage in the cement mantle after test completion. Conversely, the undersized specimens showed large and increasing micromotions, and failed after few loading cycles, because of macroscopic cracks in the proximal part of the cement mantle. While results for the optimal stem size are typical for stable hip stems, those for the undersize stem indicate a critical scenario.

INTERPRETATION

These results confirm that even a clinically successful hip prosthesis such as the Exeter-V40 is prone to early loosening if a stem smaller than the optimal size is implanted.

Polymethylmethacrylate: properties and contemporary uses in orthopaedics

Polymethylmethacrylate (PMMA) has been used in orthopaedics since the 1940s. Despite the development and popularity of new biomaterials, PMMA remains popular. Although its basic components remain the same, small proprietary and environmental changes create variations in its properties. PMMA can serve as a spacer and as a delivery vehicle for antibiotics, and it can be placed to eliminate dead space. Endogenous and exogenous variables that affect its performance include component variables, air, temperature, and handling and mixing. PMMA is used in hip arthroplasty and vertebral augmentation, notably, vertebroplasty and kyphoplasty. Cardiopulmonary complications have been reported.

Anatomic stem design reduces risk of thin cement mantles in primary hip replacement

PURPOSE

To analyse the influence of femoral stem design in the lateral plane (anatomic vs. straight) on the cement mantle quality.

METHOD

In this consecutive multi-surgeon radiographic study we determined, Dorr grading, cement mantle quality (Barrack) and mantle thickness using Gruen zones 1–14 in 280 primary cemented total hip replacements, divided into two groups (140 anatomic Biomet Olympia, 140 straight Exeter Universal Series).

RESULTS

Twenty-three per cent of the straight Exeter Universal stems had a cement mantle of <2 mm thickness in Gruen zone 8 and 25% in Gruen zone 9, compared to 0.7% of the anatomical Olympia stems in Gruen zone 8 and 1.4% in Gruen zone 9. The difference between the two groups was statistically significant (P < 0.001). In all other zones no significant differences were found.

CONCLUSION

This radiological study confirms that femoral stems with an anatomical curve in the lateral plane carry a lower risk of thin cement mantles (especially in Gruen zones 8 and 9) than straight stems. Cement mantle analysis in one radiographic plane only is insufficient.

The cement mantle of femoral hip implants is more influenced by stem-broach sizing than by shape: an in vitro CT analysis of straight Charnley-Kerboul and anatomic Lubinus SPII stems

INTRODUCTION

Both, the stem shape and the implantation technique could influence the quality of the cement mantle surrounding femoral hip implants. We investigated which of these two factors is most important for the stem-cement-bone construct.

METHODS

We compared morphological data of 22 straight Charnley-Kerboul and 18 anatomic Lubinus SPII plastic replicas implanted line-to-line with the broach or one size undersized in paired cadaver femora. Specimens were CT scanned and assessed with validated segmentation software.

RESULTS

According to a general linear model, the canal-filling capacity of the stem, the cement thickness, the amount of thin and deficient cement and cortical support to areas of weak cement, were exclusively related to the implantation technique. The anatomic shape of Lubinus stems did not improve centralization or alignment.

CONCLUSION

Stem shape was the most obvious difference between Lubinus SPII and Chanrley-Kerboul implants. However, comparing both, stem-broach sizing was the most important determining factor for the cemented stem construct.

Effect of long-term physiological activity on the long-term stem stability of cemented hip arthroplasty: in vitro comparison of three commercial bone cements

Long-term endurance of the cement mantle is fundamental for the survival of cemented hip prostheses. Current protocols to characterize bone cements are unsuitable to predict the actual clinical outcome. The aim of this study was to assess if it is possible to rank cement types having diverse clinical outcome by using a simplified in vitro physiological test. Composite femurs were implanted with identical stems (Lubinus-SPII), using different commercial cement types: CMW1 to represent cement with poor clinical outcome; Simplex-P and Cemex-RX to represent cements with a positive clinical outcome. Implanted femurs were subjected to a validated protocol that simulated a demanding but physiological loading spectrum. Inducible micromotions and permanent migrations were recorded throughout the test. After test completion, the cement mantles were sectioned and inspected with dye penetrants to quantify the fatigue-induced cracks. Micromotions did not differ significantly between cement types (possibly because a successful prosthesis was chosen that is very stable in the host bone). Significant differences were observed in terms of cement cracks: CMW1 induced significantly more numerous and larger cracks than Simplex-P and Cemex-RX; no difference was observed between Simplex-P and Cemex-RX. This indicates that this protocol: (a) can discriminate between ‘good’ and ‘bad’ cements and (b) yields consistent results when comparable cements are tested. The proposed protocol overcomes the limitations of existing standardized material tests for bone cements. New cements can be assessed in comparison with other cements with known (positive/negative) clinical outcome, tested with the same protocol.

In vitro cyclic testing of the Exeter stem after cement within cement revision

Cement-within-cement (C-C) revision arthroplasty minimizes the complications associated with removal of secure polymethylmethacrylate. Failure at the interfacial region between new and old cement mantles remains a theoretical concern. This article assesses the cyclic fatigue properties of bilaminar cement mantles after C-C revision in vitro with the Exeter stem. Seven Exeter stems were cemented into Sawbone femurs and removed, and new undersized stems were cemented into the preserved mantle. The new constructs were loaded for 1,000,000 cycles at body temperature. Cement mantles were inspected postcycling. In no case was there delamination or failure of the cement mantle. The findings support the hypothesis that use of a thin revision cement mantle in conjunction with a polished double-tapered stem is not detrimental to the overall success of the implant. In the presence of a secure cement-bone interface in suitable patients, we recommend C-C revision techniques using double-tapered polished femoral stems.

The condition of the cement mantle in femoral hip prosthesis implantations--a post mortem retrieval study

Despite numerous studies demonstrating the characteristics of the optimal cement mantle in joint replacement, the clinical state of the cement mantle is rarely assessed. A random sample of 214 cemented implanted femoral hip components was retrieved post mortem from Hamburg, Germany, and sectioned to investigate the quality of the cement mantle. The most common observation made in at least one measured region per retrieval was debonding (82% of stems), followed by a thin cement mantle (74%), stem-bone contact (48%), soft tissue at the stem interface (44%), no cement-bone interdigitation (30%), a gap at the stem interface (28%), voids in the cement (22%) and cracks and blood in the cement mantle (<10%). 21% of stems demonstrated complete debonding of the interface. However, distributions of all other defects were local, with less than 10% of stems demonstrating any imperfection in more than 21% of the regions assessed. No progressive damage was observed with implantation duration. The results suggest that current implantation technique may be adequate for proper implant function over the service life in the older patient population. However, for younger and more active patients, perfection of the cementation technique is crucial, particularly in modern implant systems such as resurfacing. The frequency of almost all defects could be further reduced by careful implantation technique, providing the increased service life necessary for the ever younger, more physically demanding, patient population.

Effect of modular neck variation on bone and cement mantle mechanics around a total hip arthroplasty stem

BACKGROUND

Total hip arthroplasty carried out using cemented modular-neck implants provides the surgeon with greater intra-operative flexibility and allows more controlled stem positioning.

METHODS

In this study, finite element models of a whole femur implanted with either the Exeter or with anew cemented modular-neck total hip arthroplasty (separate, neck and stem components) were developed.The changes in bone and cement mantle stress/strain were assessed for varying amounts of neck offset and version angle for the modular-neck device for two simulated physiological load cases: walking and stair climbing. Since the Exeter is the gold standard for polished cemented total hip arthroplasty stem design, bone and cement mantle stresses/strains in the modular-neck finite element models were compared with finite element results for the Exeter.

FINDINGS

For the two physiological load cases, stresses and strains in the bone and cement mantle were similar for all modular-neck geometries. These results were comparable to the bone and cement mechanics surrounding the Exeter. These findings suggest that the Exeter and the modular neck device distribute stress to the surrounding bone and cement in a similar manner.

INTERPRETATION

It is anticipated that the modular-neck device will have a similar short-term clinical performance to that of the Exeter, with the additional advantages of increased modularity.

The importance of a thick cement mantle depends on stem geometry and stem—cement interfacial bonding

The thickness of the cement mantle around the femoral component of total hip replacements is a contributing factor to aseptic loosening and revision. Nevertheless, various designs of stems and surgical tooling lead to cement mantles of different thicknesses. Opinion is divided on whether a thick mantle enhances implant longevity. This study investigates the effect of cement mantle thickness on accumulated damage in the cement, and how this is influenced by the presence or absence of a proximal collar and on whether the stem—cement interface remains bonded. Three-dimensional finite element simulations incorporating creep and non-linear damage accumulation were performed to investigate cracking in the cement mantles around Stanmore Hips under physiologically informed stair-climbing and gait loads. Cement mantle thickness, stem—cement interfacial bonding, and collar design were varied to assess the interactive effects of these parameters. In all cases, damage levels were three to six times higher when the stem—cement interface remained bonded. Cement mantle thickness had little effect on cement damage accumulation around debonded collared stems but was critical in both bonded and collarless cases, where a thicker mantle reduced cement cracking. Damage around a smooth debonded stem with a collar is thus much less sensitive to cement thickness than around bonded or collarless stems.