Electrocautery Damage Can Reduce Implant Fatigue Strength: Cases and in Vitro Investigation

Fracture of Contemporary Femoral Stems: Common Trends in This Rare Occurrence

BACKGROUND

Fracture of contemporary femoral stems is a rare occurrence in total hip arthroplasty (THA). A knowledge gap remains regarding manufacturing, patient, and surgeon factors that may contribute to the increased risk of this complication.

METHODS

We analyzed 13 contemporary fractured porous coated femoral stems of various designs to determine cause and contributing factors of mechanical failure. Cases included 12 men and one woman who had an average age at index surgery of 53 years (range, 34 to 76). There were ten of 13 patients who had a body mass index (BMI) greater than 30 (obese); 3 of the 10 had a BMI greater than 40. The mean time to fracture was 7.6 years (range, 7 months to 12 years).

RESULTS

There were four titanium alloy stems that fractured an average of 3.6 years post-revision surgery for head/cup exchange, and had associated iatrogenic mechanical and electrocautery damage to the femoral neck at fracture initiation sites. There were six modular stems that failed at the stem-sleeve or stem-neck interfaces with evidence of fretting corrosion. For two stem-neck fractures, mis-matched head/stem combinations from different manufacturers resulted in untested mechanical offsets and loading. There were two proximal neck fractures and one mid-shaft fracture of coated cobalt-chromium alloy stems that occurred in three obese men. The neck fractures (10 to 12 years) were well-fixed stems. Lack of proximal fixation contributed to the mid-shaft fracture (7 months).

CONCLUSION

While rare, femoral stem fractures pose catastrophic outcomes in primary and revision THA. Manufacturing, patient, and surgical factors contributing to stem failures were identified, including patient obesity, heat-treatment reduction of mechanical properties, iatrogenic implant damage, and mixing of different vendor stems and heads.

Mechanical failure of total hip arthroplasties and associated risk factors

INTRODUCTION

Mechanical failure of total hip arthroplasties is a rare but devastating complication. With increasing numbers in primary arthroplasty implantation, revision surgeries are indicated more often. Therefore, understanding the mechanism and the location of failure is essential in determining proper treatment. Aim of this study was to identify mechanical failures of all total hip arthroplasties performed in a major academic center as well as the associated risk factors such as BMI and sports.

METHODS

A retrospective trial was conducted using our prospective arthroplasty database. Database was searched for all patients presenting with mechanical failures of total hip arthroplasty (THA) to the emergency department between 2011 and 2019. All medical charts and radiographs as well as surgical reports were analyzed to identify demographics, implant choice in addition to location of failure and subsequent treatment.

RESULTS

In total, 13 patients suffering from mechanical total hip implant failure were found. The femoral neck (conus) was broken in four patients, the stem in five cases, one broken inlay, two cup failures and one conus dislocation. The mean BMI was 31.42 ± 5.29 kg/m² including five patients who have obesity class II. In all cases, revision surgeries were indicated. No structural causes or underlying risk factors such as repeated physical load (i.e. in sports) were identified.

CONCLUSION

Implant failure does not seem to correlate with participation in sports or BMI. Catastrophic failure of implants is a technical challenge requiring special extraction instruments that can be difficult even for experienced surgeons. It should be noted that functional outcome is often worse for this group of patients after surgery than comparing against those revised for loosening.

LEVEL OF EVIDENCE

III, Retrospective Trial.

Metallic Implants Used in Lumbar Interbody Fusion

Over the last decade, pedicle fixation systems have evolved and modifications in spinal fusion techniques have been developed to increase fusion rates and improve clinical outcomes after lumbar interbody fusion (LIF). Regarding materials used for screw and rod manufacturing, metals, especially titanium alloys, are the most popular resources. In the case of pedicle screws, that biomaterial can be also doped with hydroxyapatite, CaP, ECM, or tantalum. Other materials used for rod fabrication include cobalt-chromium alloys and nitinol (nickel-titanium alloy). In terms of mechanical properties, the ideal implant used in LIF should have high tensile and fatigue strength, Young's modulus similar to that of the bone, and should be 100% resistant to corrosion to avoid mechanical failures. On the other hand, a comprehensive understanding of cellular and molecular pathways is essential to identify preferable characteristics of implanted biomaterial to obtain fusion and avoid implant loosening. Implanted material elicits a biological response driven by immune cells at the site of insertion. These reactions are subdivided into innate (primary cellular response with no previous exposure) and adaptive (a specific type of reaction induced after earlier exposure to the antigen) and are responsible for wound healing, fusion, and also adverse reactions, i.e., hypersensitivity. The main purposes of this literature review are to summarize the physical and mechanical properties of metal alloys used for spinal instrumentation in LIF which include fatigue strength, Young's modulus, and corrosion resistance. Moreover, we also focused on describing biological response after their implantation into the human body. Our review paper is mainly focused on titanium, cobalt-chromium, nickel-titanium (nitinol), and stainless steel alloys.

Fracture of a titanium femoral neck after revision total hip arthroplasty

We report a case of a fractured titanium alloy (Ti6Al4V) femoral stem 2 years after revision (debridement, antibiotics and implant retention due to periprosthetic joint infection) total hip arthroplasty (THA). Material analysis revealed a superficial abnormality on the upper neck surface caused by local melting with electrocautery probably acting as a stress amplifier. This lesion presumably was the trigger of a fatigue fracture with typical features on the fracture surface. Electrocautery should therefore be avoided in case of revision THA or used with utmost care to avoid contact with the femoral stem.

Electrocautery-induced molten metal particle generation from total joint replacements: Morphology and chemistry

Electrosurgical techniques are used during surgery to cauterize, and their damaging effects have primarily been documented in terms of tissue necrosis, charring, and localized heat accumulation. Metallic implants as well as the surgical blade can experience incidental electrosurgical current arcing that results in the generation and transfer of melted metallic particles. This work examines the composition, particle size distribution, and chemical state of the melted alloy surfaces and particles produced in vitro. Using scanning electron microscopy and energy dispersive spectroscopy, a flash-melting particle generation phenomenon between source 304 SSL blades and polished cobalt-chromium-molybdenum (CoCrMo) and titanium-6-aluminum-4-vandaium (Ti6Al4V) surfaces was documented where 304 SSL mixed heterogeneously with the CoCrMo and Ti6Al4V ejecting "splatter" particles from the cautery site. The spherical micron-sized particles were embedded with sub-micron-sized particles with 42% of the total sample population measuring between 0.25 and 0.35 μm in diameter. CoCrMo-304 SSL particles were principally made of high concentrations of iron, oxygen, and nickel with embedded sub-micron-sized particles containing oxygen, chromium, and cobalt with lower concentrations of iron and molybdenum. Ti6Al4V-304 SSL interactions resulted in similar micron-sized particles made up of high concentrations of iron, nickel, and chromium with embedded sub-micron-sized particles containing titanium, oxygen, and small amounts of aluminum. X-ray photoelectron spectroscopy of damaged CoCrMo surfaces confirmed the presence of chromium (VI) following dry electrocautery contact in coagulation mode. The structural effects of electrocautery-induced damage are becoming visible in retrieval analysis, but the long-term physiological implications during the lifetime of the implant from this damage mode have yet to be defined.

Femoral Stem Fracture in Hip Revision Arthroplasty: A Systematic Literature Review of the Real-World Evidence

Background Total hip arthroplasty (THA) presents as an excellent treatment for the osteoarthritic hip, demonstrating good survival rates. However, aseptic loosening and infection are the main causes of operative revision. The methods used in revision surgery are non-modular or modular THA implants. In addition to the abovementioned revision reasons for THA, this treatment could be associated with the possibility of femoral stem fracture, especially in the modular system. The topic of material failure has been focused on in the public media. The question arises as to how such media reports correlate with the published literature. The observed mentioned number of cases concerning a femoral stem fracture vary between one single case and up to 18.5% within a clinical study, thus presenting an inhomogeneous data situation with a large span. The specific aim of this systematic review is to establish facts and clarify the number of unforeseen events of a femoral stem fracture based on peer review articles and registry data. This clarification is important to us, as these media reports have led to uncertainty among patients.

Methods A systematic review was performed in accordance with the PRISMA statement. Peer review articles in English and German, presenting original articles, meta-analyses, or case reports, were searched from the turn of the millennium up to December 2019. Only articles that reported a femoral stem component fracture, with content of clinical data as well as register data, were included. Relevant papers published after the defined research time frame were taken into account within the discussion.

Results In total, 218 fractures of a femoral stem (141 primary and 77 revision THA) component could be identified within the selected literature. Most cases of a femoral stem fracture occurred in the modular THA implants compared to the non-modular stems. Regarding revision THA, in summary, 77 implants, presenting 23 non-modular and 54 modular implants, failed by means of femoral stem fracture. A review of 11 National Joint Registries shows a revision rate between 0.04 and 0.05% in only 2 registers according to the specific subject of a femoral stem fracture. For the remaining 9 registers, however, detailed information is lacking and only nonspecific information such as a generic “implant failure” or “other reason” (which can cover a multitude of causes) is supplied.

Conclusion A femoral stem fracture presents a devastating complication for the patient, the surgeon as well as for the manufacturer of the implant. Modular THA implants play an increasingly valuable role concerning restoration of individual anatomy in modern THA revision surgery, especially within complex cases. Regarding revision procedures, data suggests a lower risk of femoral stem fracture for modular implants compared to primary procedures, while the risk of fracture for non-modular implants seems to increase during revision. Ultimately, it cannot be proven whether this is actually applicable, since the absolute number of implanted prosthesis systems is not known. Various implant-, patient-, and surgeon-related factors may lead to these reported femoral stem fractures. However, this systematic review suggests that this is, in general, a rare complication.

Removal of an osteointegrated broken uncemented femoral stem after hip arthroplasty-technical note

Broken stems are particularly challenging in revision hip arthroplasty, as no standard extraction instruments fit anymore. Well-integrated uncemented stem remnants can be particularly arduous to remove. Stem fatigue failure is not rare with modular stems. Since these are particularly useful in revision hip arthroplasty, increasing numbers of broken stems are to be expected. Usually applied techniques using cortical fenestration distally to the tip of the stem or using an extended transfemoral approach cause supplementary bone defects impairing reconstruction. We present a relatively simple and reproducible revision technique, using a limited standard approach and only regular orthopedic instruments, to extract the remnants of broken uncemented femoral stems in hip arthroplasty. This technique was applied successfully and without complications in 6 cases, permitting eventually the reimplantation of even shorter stems.

Fatigue fracture of an uncemented Zweymüller femoral stem at the neck-shoulder junction

A fracture through the neck of the femoral stem in total hip arthroplasty is extremely rare. We report a neck fracture of a cementless Zweymüller stem, one of the most implanted stems worldwide. According to our knowledge, this is the first thorough case description of a neck fracture of a cementless Zweymüller stem. The case concerns a 53-year-old man, with a body weight of 103 kg and a body mass index of 31. We consider potential risk factors for a femoral stem fracture, such as patient-related factors, suboptimal implant positioning, surgical technique and implant characteristics.

Additively Manufactured Tantalum Implants for Repairing Bone Defects: A Systematic Review

Tantalum has unique advantages as a biomaterial for repairing bone defects due to its outstanding bioactivity, excellent corrosion resistance, and mechanical properties. Ideal implants for bone repair should be of good biocompatibility and bioactivity, as well as ability to simulate the microstructure and mechanical environment of human bone tissues. Additive manufacturing can facilitate freedom of design for the macrostructure/microstructure of bone implants with controlled mechanical properties; thus, this method has great potential. Additively manufactured tantalum implants provide a novel alternative for bone repair and are gaining increasing attention. This systematic review aims to comprehensively summarize the subsistent evidence from physicochemical, cellular, animal, and clinical studies on additively manufactured tantalum implants in repairing bone defects, for the first time. This work may provide researchers an essential grasp on the advances of additively manufactured tantalum implants. Impact statement Tantalum has unique advantages as a biomaterial. Additive manufacturing facilitates design freedom and additively manufactured tantalum is a novel alternative for bone repair. Studies on additively manufactured tantalum progress greatly, while no review summarizing the progresses was published.

Debridement, antibiotic pearls, and retention of the implant in the treatment of infected total hip arthroplasty

In this article the authors describe a modified surgical technique developed to enhance the classical irrigation and debridement procedure to improve the possibilities of retaining a total hip arthroplasty (THA) undergoing acute periprosthetic joint infection (PJI). This technique, debridement antibiotic pearls and retention of the implant (DAPRI), aims to remove the intra-articular biofilm allowing a higher and prolonged local antibiotic concentration by using calcium sulphate antibiotic-added beads. The combination of 3 different surgical techniques (tumour-like synovectomy, Argon Beam application and chlorhexidine gluconate brushing) might enhance the disruption and removal of the bacterial biofilm which is the main responsible of antibiotics and antibodies resistance. The timing of the diagnosis (6 weeks from the original surgery or 1 week from clinical symptoms appearance in the case of an hematogenous infection) and the preoperative isolation of the germ are fundamental in order to obtain a satisfactory outcome. A 12-week course of postoperative antibiotic therapy (6 weeks I.V. and 6 weeks oral) complete the postoperative protocol used by the authors.The DAPRI technique might represent a safe and more conservative treatment for acute and early hematogenous PJI.

Fatigue strength reduction of Ti-6Al-4V titanium alloy after contact with high-frequency cauterising instruments

Contact of implants with high-frequency cauterising instruments has serious implications for patient safety. Studies have reported a possible direct connection of fatigue failure of Ti-6Al-4V implants with electrocautery contact. Such contacts were observed at the polished neck of titanium hip stems, which are subjected to high-tension loads. Evidence of electrocautery contact has also been found on a retrieved spinal fixator with a rough surface; however, no fatigue failure related to electrocautery contact has been reported thus far. The influence of the heat-affected zone caused by flashover on the mechanical behaviour of the Ti-6Al-4V titanium alloy is not yet fully understood. Then, the aim of this study was to investigate whether the polished areas of Ti-6Al-4V implants are especially susceptible to fatigue failure after electrocautery contact. Flashovers caused by electrocautery contact were induced on titanium specimens with different surface roughnesses. These specimens were subjected to cyclic loading in a four-point-bending test setup, which represented the stress resulting from physiological loading activities (~861 MPa). In this test setup, electrocautery contact was found to reduce the fatigue strength of the titanium alloy significantly-by up to 96%-as revealed from the median value of the cycles to failure. Cycles to failure showed a dependence on the flashover duration, with a flashover for 40 ms leading to fatigue fracture. Despite the lower fatigue strength of a rough polished surface in the undamaged state, it is less prone to the damaging effect of flashover than a smooth polished surface.

Mechanical failure of 113 uncemented modular revision femoral components

Aims

We evaluated a large database with mechanical failure of a single uncemented modular femoral component, used in revision hip arthroplasty, as the end point and compared them to a control group treated with the same implant. Patient- and implant-specific risk factors for implant failure were analyzed.

Methods

All cases of a fractured uncemented modular revision femoral component from one manufacturer until April 2017 were identified and the total number of implants sold until April 2017 was used to calculate the fracture rate. The manufacturer provided data on patient demographics, time to failure, and implant details for all notified fractured devices. Patient- and implant-specific risk factors were evaluated using a logistic regression model with multiple imputations and compared to data from a previously published reference group, where no fractures had been observed. The results of a retrieval analysis of the fractured implants, performed by the manufacturer, were available for evaluation.

Results

There were 113 recorded cases with fracture at the modular junction, resulting in a calculated fracture rate of 0.30% (113/37,600). The fracture rate of the implant without signs of improper use was 0.11% (41/37,600). In 79% (89/113) of cases with a failed implant, either a lateralized (high offset) neck segment, an extralong head, or the combination of both were used. Logistic regression analysis revealed male sex, high body mass index (BMI), straight component design, and small neck segments were significant risk factors for failure. Investigation of the implants (76/113) showed at least one sign of improper use in 72 cases.

Conclusion

Implant failure at the modular junction is associated with patient- and implant-specific risk factors as well as technical errors during implantation. Whenever possible, the use of short and lateralized neck segments should be avoided with this revision system. Implantation instructions and contraindications need to be adhered to and respected. Cite this article: Bone Joint J 2020;102-B(5):573–579.

Impact of Electrocautery on Fatigue Life of Spinal Fusion Constructs-An In Vitro Biomechanical Study

Instrumentation failure in the context of spine surgery is attributed to cyclic loading leading to formation of fatigue cracks, which later propagate and result in rod fracture. A biomechanical analysis of the potential impact of electrocautery on the fatigue life of spinal implants has not been previously performed. The aim of this study was to assess the fatigue life of titanium (Ti) and cobalt-chrome (CoCr) rod-screw constructs after being treated with electrocautery. Twelve spinal constructs with CoCr and Ti rods were examined. Specimens were divided into four groups by rod material (Ti and CoCr) and application of monopolar electrocautery on the rods' surface (control-group and electrocautery-group). Electrocautery was applied on each rod at three locations, then constructs were cyclically tested. Outcome measures were load-to-failure, total number of cycles-to-failure, and location of rod failure. Ti-rods treated with electrocautery demonstrated a significantly decreased fatigue life compared to non-treated Ti-rods. Intergroup comparison of cycles-to-failure revealed a significant mean decrease of almost 9 × 105 cycles (p = 0.03). No CoCr-rods failed in this experiment. Electrocautery application on the surface of Ti-rods significantly reduces their fatigue life. Surgeons should exercise caution when using electrocautery in the vicinity of Ti-rods to mitigate the risk of rod failure.