Modular neck stems in total hip arthroplasty: current concepts

An Extended Trochanteric Osteotomy Is Necessary for the Removal of Broken Modular Metaphyseal Engaging Femoral Stems

BACKGROUND

Modular metaphyseal engaging (MME) femoral components in total hip arthroplasty (THA) allow optimized femoral length, offset, and anteversion and are useful in patients with unusual proximal femoral anatomy. Fretting, corrosion, and stem fractures above the modular sleeve are complications associated with these implants. The purpose of this study was to identify failure mechanisms of retrieved MME femoral components at our institution, identify all broken stem cases, and evaluate how often an extended trochanteric osteotomy (ETO) was required for removal.

METHODS

All consecutively retrieved MME femoral components from September 2002 to May 2023 were reviewed. Patient demographics, procedure information, component specifications, indications for removal, and requirements for further revision surgery were reviewed. Descriptive statistics were calculated for variables of interest.

RESULTS

There were 131 retrieved MME components. The mean age at surgery was 59 years (range, 28 to 75), 49% were women, mean body mass index was 29.4 (range, 20.7 to 33.3), and mean American Society of Anesthesiologists score was 2.4 ± 0.5. There were 102 (78%) stems of 1 design (stem A), and 29 (22%) stems of a different design (stem B). Of 131 components, 10 (7.6%) failed secondary to stem fracture proximal to the modular sleeve. Four of 102 (4%) of stem A and 6 of 29 (21% of stem B) fractured. All broken stems required additional intervention for removal during revision THA, using an ETO (N = 9) or cortical window (N = 1) in which an intraoperative proximal femoral fracture occurred.

CONCLUSIONS

Broken MME stems present a challenge for orthopaedic surgeons during revision THA. When a stem fracture occurs above the ingrown sleeve, the distal splines may have osseous interdigitation into the clothespin. Thus, when revising a broken MME stem, an ETO should be performed, and the segment should be long enough to allow distal access.

Mid-Term Outcomes of a Short Modular Neck-Preserving Cementless Hip Stem: A Retrospective Study With a 6-Year Minimum Follow-Up

BACKGROUND

The neck-preserving cementless short stem represents a valid therapeutic option for total hip replacement in high-functional-demand patients, but few studies are available about the use of modularity in the last-generation short stem. The aim of the study was to evaluate the mid-term survival of a specific implant design that combines partial collum short hip stem with neck modularity; assessing the functional status was the second endpoint.

METHODS

A retrospective single-center cohort study was conducted on 75 patients aged 35 to 80 years, with a minimum 6-year follow-up. Patients with neurological/rheumatic pathologies and previous hip surgeries were excluded. All the patients underwent total hip replacement with a short modular neck-preserving cementless hip stem. Clinical outcomes, complications, revisions, and the Western Ontario and McMaster Universities Osteoarthritis Index, Harris hip score, and Short Form 12-Item Health Survey (SF-12) questionnaires were evaluated. The results were compared with healthy population's data extracted from the literature, stratified by age.

RESULTS

The Kaplan-Meier analysis revealed a 10-year implant survival rate of 96.7%, coupled with a revision rate of 1.3%. Results showed a Harris hip score and physical SF-12 significantly lower and a mental SF-12 higher when compared to healthy population. No statistically significant differences emerged when comparing groups based on neck modularity.

CONCLUSIONS

The short modular neck-preserving cementless hip stem emerged as a reasonable choice for patients with elevated functional demands, ensuring good clinical outcomes while preserving bone integrity. The use of a modular neck in short stems didn't show any mechanical problems in the mid-term.

A review on manufacturing processes of cobalt-chromium alloy implants and its impact on corrosion resistance and biocompatibility

Cobalt-Chromium (CoCr) alloys are currently used for various cardiovascular, orthopedic, fracture fixation, and dental implants. A variety of processes such as casting, forging, wrought processing, hot isostatic pressing, metal injection molding, milling, selective laser melting, and electron beam melting are used in the manufacture of CoCr alloy implants. The microstructure and precipitates (carbides, nitrides, carbonitrides, and intermetallic compounds) formed within the alloy are primarily determined by the type of manufacturing process employed. Although the effects of microstructure and precipitates on the physical and mechanical properties of CoCr alloys are well reviewed and documented in the literature, the effects on corrosion resistance and biocompatibility are not comprehensively reviewed. This article reviews the various processes used to manufacture CoCr alloy implants and discusses the effects of manufacturing processes on corrosion resistance and biocompatibility. This review concludes that the microstructure and precipitates formed in the alloy are unique to the manufacturing process employed and have a significant impact on the corrosion resistance and biocompatibility of CoCr alloys. Additionally, a historical and scientific overview of corrosion and biocompatibility for metallic implants is included in this review. Specifically, the failure of CoCr alloys when used in metal-on-metal bearing surfaces of total hip replacements is highlighted. It is recommended that the type of implant/application (orthopedic, dental, cardiovascular, etc.) should be the first and foremost factor to be considered when selecting biomaterials for medical device development.

Fracture of femoral neck in modular total hip arthroplasty: a systematic review of the literature

BACKGROUND

Modular femoral stems have the advantage of anatomic hip reconstruction by restoring the femoral offset thus minimising the bearing surface wear, implant loosening and dislocation.

AIM

This study aims to investigate the existing literature on modular neck fractures, to identify predisposing factors and guide the decision-making process in the management of these difficult cases.

METHODS

A systematic literature review was conducted until July 2022. PRISMA guidelines were followed, eligibility criteria were set, and methodology assessment of included studies was conducted based on MINORS criteria, size and primary outcome. Data were extracted and analysed thoroughly.

RESULTS

5657 studies were initially screened; the full texts of 124 records were assessed and finally, 32 reports were included. There were 7 clinical studies and 25 case reports. A total of 4825 patients (5204 hips) with a mean age 62.38 years and a mean BMI 29.06 kg/m2 were analysed in the 7 clinical studies. The reported overall weighted revision rate was 0.86%, while the weighted mean modular neck fracture rate was 0.26%. The usual history was sudden experience of hip pain and instability. The average time interval to neck fracture was 4.57 (range 3-4.7) years and a long modular neck was identified in 91.17% of them. Data from case reports showed a mean age and average BMI of 55.85 and 31.63 kg/m2. 82.35% of the patients were male. Necks were fractured after an average time interval of 64.5 ± 8.8 months.

CONCLUSIONS

The incidence of modular neck fracture is significant. The profile of a male, obese patient with a long modular neck increased risk of neck fracture. Microstructural investigation of the retrieved implants demonstrated a higher incidence of fracture line in the base of the neck junction and at its anterolateral distal part. Surgeons should be aware of this complication while using or revising such protheses.

Mid-term results of titanium-titanium modular neck femoral stem in primary total hip arthroplasty

BACKGROUND

Modular neck femoral stems are advantageous because they can accurately restore the ideal hip geometry using various options in terms of offset, length, and version. However, there are concerns regarding junctional problems. Despite several reports on such issues, there is a lack of study on mid- to long-term results of these stems. The current study evaluated the mid-term results of patients who underwent primary total hip arthroplasty using a titanium-titanium (Ti-Ti) modular neck femoral stem.

METHODS

In total, data on 47 hips (42 patients) that could be followed-up for ≥ 5 years after primary total hip arthroplasty using the Ti-Ti modular neck femoral stem from 2011 to 2015 were reviewed. There were 22 male and 20 female patients, and their mean age was 56.3 (range: 31-76) years. The mean follow-up period was 8 (range: 5-12) years. Functional and radiological outcomes, complications, and reoperations were investigated. In addition, we conducted a comparative analysis of the outcomes between those who underwent surgery using the Ti-Ti modular neck femoral stem and 41 hips (35 patients, 19 males and 16 females) that underwent primary total hip arthroplasty using nonmodular femoral stems as a control.

RESULTS

In all Ti-Ti cases, the mean Harris Hip Scores were 50.6 (range: 6-59) preoperatively and 92.7 (range: 78-99) at the last follow-up (P < 0.001). Regarding the neck component's modularity, straight neck components were used in all Ti-Ti cases, and an anteverted or a retroverted neck was not used in any case. Stem revision was performed in one hip due to aseptic loosening. One hip underwent open reduction and internal fixation due to periprosthetic fracture without stem loosening. There were no cases of osteolysis and periprosthetic joint infection and clinically detectable junctional problems. The stem survival rate, with any stem revision as the endpoint, at 12 years was 96.6%. No significant difference was observed in the functional and radiological outcomes beween the Ti-Ti and nonmodular groups.

CONCLUSIONS

The Ti-Ti modular neck femoral stem had comparable results with broadly used nonmodular femoral stems; hence, it can be a reliable option in primary total hip arthroplasty. However, in terms of the modularity itself of the modular neck femoral stem, whether the modular neck femoral stem is useful in uncomplicated primary total hip arthroplasty is unclear.

Modular Well-Fixed Hip Revision Stem Fracture: A Case Report and Literature Review

This study presents a case of repeated prosthetic fractures in a modular hip prosthesis in a 56-year-old male patient. After the initial implantation of a modular total hip prosthesis in 2006, the patient experienced two instances of prosthetic implant fractures over seventeen years. In this study, we analyze the clinical case, explore potential underlying causes of this complication, and delve into current indications and strategies for the revision of fractured prosthesis stems. The discussion is informed by a literature review and underscores the significance of selecting appropriate revision techniques to address this challenge.

A Modular Head-Neck Adapter System and Ceramic Heads in Revision Hip Arthroplasty: A Registry Study on 354 Implants

BACKGROUND

Five- to 10-year outcomes of a modular head-neck adapter system with ceramic heads in revision hip arthroplasty on large populations are still lacking. A registry study about modular adapter system with Delta ceramic head in revisions was designed, aiming to assess (1) the survival rates of the device, (2) the reasons for re-revisions of the device, and (3) a comparison to factory assembled titanium sleeve and Delta head cohort in revision hips.

METHODS

Using a regional arthroplasty registry, we investigated the modular adapter system with a ceramic head in revision hips. Demographics, implant features, and reasons for revision were recorded. Survival rates and reasons for re-revision were assessed. The modular adapter system with the ceramic ball was compared to a factory-assembled ceramic titanium-sleeved head in revisions, acting as a control group. There were 354 revisions included at a mean follow-up of 5 years (range, 0 to 13).

RESULTS

The 5- and 7-year survival rates were 87.9% and 86.9%, respectively. Dislocations (2.8%) and cup aseptic loosening (4.2%) were the 2 most frequent reasons for re-revision. No breakage of the adapter system or the ceramic head occurred. A femoral neck failed (0.3%). No implant features, offset (P = .088) or skirted (P = .870) tapers, impacted on failures. No differences between the 2 cohorts were found regarding survival rates (P = .696) and reasons for re-revision (dislocations, P = .983; cup aseptic loosening, P = .296).

CONCLUSION

The modular head neck adapter system with a ceramic head seems to be a valid option in revisions at 5 and 7 years, without additional risk of implant breakage in this registry.

Mechanisms of Premature Fracture in Modular Neck Stems Made of CoCrMo/Ti6Al4V and Ti6Al4V/Ti6Al4V Alloy

In this paper, we present the mechanisms of premature fracture of modular neck stems in two case studies: (I) when the neck and stem are both made of the same Ti6Al4V alloy, and (II) when the neck and stem are made from two different alloys, CoCrMo and Ti6Al4V alloy. Our study integrates two orthopedic patients who have undergone primary uncemented THA for usual indications in two orthopedic centers (Community Health Centre and University Medical Centre). Both centers are part of the national public health care system. Both surgeries were performed by two skilled orthopedic surgeons with more than 10 years of experience in THA. The survivorship of the modular neck of cast CoCrMo alloy was 24 months. The survivorship of the modular neck from Ti6Al4V alloy was 84 months. Multivariate analyses were performed to assess the differences in the fretting, corrosion, and fatigue of the two prematurely failed modular neck stems: stereo light microscopy (SLM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). Patient demographic information, including sex, age, body mass index, survivorship of implants, and reason for the revision, was collected from medical records. We found that fretting and fatigue occurred on both neck-stem retrievals due to additional galvanic corrosion, but the CoCrMo/Ti6Al4V alloy system suffered more corrosion due to additional galvanic corrosion and fractured earlier than the Ti6Al4V/Ti6Al4V metal alloy system. Both metallic alloy systems used in this application are known to be highly corrosion-resistant, but the bio-tribo-corrosion processes need to be understood in detail and characterized so that appropriate improvements in design and materials can be made.

Bimodular femoral stems in primary total hip arthroplasty

INTRODUCTION

This review critically examines the efficacy of dual-modular stems in primary total hip arthroplasty. Given the variability and non-comparability of certain femoral stem designs and stem-neck couplings, with some even being withdrawn from the market, this review offers an in-depth analysis of predominant implant performances.

AREAS COVERED

The paper explores a brief historical summary related to dual-modular stems, including the complications associated with their use, diagnostic tools for evaluation, analysis of both recalled and currently available models, as well as alternative therapeutic options. This information is pertinent for both clinical and research domains.

EXPERT OPINION

While dual-modular systems were initially touted to offer several advantages, the evidence substantiating these benefits has been ambiguous. Further, these systems introduce the risk of alternative complications. In specific cases involving patients with developmental hip dysplasia and certain proximal femoral deformities requiring complex reconstructions, dual-modular systems might be relevant. Nonetheless, the use of long interchangeable necks in patients with a body mass index above 30 kg/m2 is discouraged, and pairing a long varus-oriented neck with an extra-long femoral head should be avoided in all patients.

Dual-Modular Versus Single-Modular Stems for Primary Total Hip Arthroplasty: A Long-Term Survival Analysis

Background and Objectives: Increased revision rate of dual-modular (DM) femoral stems in primary total hip arthroplasty (THA) because of modular-neck breakage and adverse local tissue reactions (ALTRs) to additional junction damage products is well established and some designs have been recalled from the market. However, some long-term studies of specific DM stems did not confirm the inferiority of these stems compared to standard single-modular (SM) stems, and a head-to-head comparison THA is missing. The objectives of this multicentre study were to determine the survivorship and complication rates of a common DM stem design compared to a similar SM stem. Materials and Methods: In a time frame from January 2012 to November 2015, a cohort of 807 patients (882 hips) consecutively underwent primary cementless THAs at two orthopaedic centres. 377 hips were treated with a Zweimüller-type DM stem THA system and 505 hips with a similar SM stem THA system, both including a modern press-fit acetabulum. Kaplan-Meier survivorship and complication rates were compared between both groups in a median follow-up of 9.0 years (maximum, 9.9 years). Results: The 9-year survivorship of the DM stem THA system (92.6%, 95% CI 89.9-95.3) was significantly lower than that of the SM stem THA system (97.0%, 95% CI 95.2-98.8). There were no differences in revision rates for septic loosening, dislocation, and periprosthetic fractures between the two groups. One ceramic inlay and one Ti-alloy modular neck breakage occurred in the DM stem THA system group, but the main reason for revision in this group was aseptic loosening of components. Conclusions: The survivorship of the DM stem THA system was lower than the similar SM stem THA system in a comparable clinical environment with long-term follow-up. Our results confirmed that no rationale for stem modularity exists in primary THAs.

Comparison of single taper and dual taper versions of the same stem design in total hip arthroplasty for primary osteoarthritis

BACKGROUND

In total hip arthroplasty (THA), the outcomes of single taper (ST) and dual taper (DT) versions of the same stem design have been scarcely studied. A registry study comparing ST and DT versions of the same stem design was designed, aiming to assess: (1) the survival rates and the hazard ratios for failure; (2) the survival rates and the hazard ratios for failure using stem-focused endpoints.

MATERIAL AND METHODS

A regional arthroplasty registry was interrogated about stem designs with ST and DT versions in cementless THAs performed for primary osteoarthritis. Only the same cup and ceramic-on-ceramic bearings were included: the DT stems had a titanium-on-titanium modularity. Demographic and implant features were recorded. Survival rates and hazard ratios were evaluated and compared. Stem-focused endpoints were also investigated.

RESULTS

A total of 5359 THAs were included, with three stem designs. The two versions of every stem showed different demographics and implant-related features: ST versions were preferentially implanted in heavier young men. For each stem, the two versions had similar survival rates at 5 years (p = 0.076; p = 0.319; p = 0.616) and similar adjusted hazard ratios for failures (p = 0.084; p = 0.308; p = 0.729). When stem-focused endpoints were adopted, the ST and DT versions of the three stems achieved similar survival rates (p = 0.710; p = 0.784; p = 0.983) and similar adjusted hazard ratios (p = 0.647; p = 0.858; p = 0.787). Three neck breakages occurred (0.0007% of all the modular implants).

CONCLUSIONS

ST and DT versions of the same stem design did not show any differences in terms of survival rates and hazard ratios for failures at 5 years.

LEVEL OF EVIDENCE

IV.