Aims

United Classification System (UCS) B2 and B3 periprosthetic fractures in total hip arthroplasties (THAs) have been commonly managed with modular tapered stems. No study has evaluated the use of monoblock fluted tapered titanium stems for this indication. This study aimed to evaluate the effects of a monoblock stems on implant survivorship, postoperative outcomes, radiological outcomes, and osseointegration following treatment of THA UCS B2 and B3 periprosthetic fractures.

Aims. Hip arthroplasty does not always restore normal anatomy. This is due to inaccurate surgery or lack of stem sizes. We evaluated the aptitude of four total hip arthroplasty systems to restore an anatomical and medialized hip rotation centre. Methods. Using 3D templating software in 49 CT scans of non-deformed femora, we virtually implanted: 1) small uncemented calcar-guided stems with two offset options (Optimys, Mathys), 2) uncemented straight stems with two offset options (Summit, DePuy Synthes), 3) cemented undersized stems (Exeter philosophy) with three offset options (CPT, ZimmerBiomet), and 4) cemented line-to-line stems (Kerboul philosophy) with proportional offsets (Centris, Mathys). We measured the distance between the templated and the anatomical and 5 mm medialized hip rotation centre. Results. Both rotation centres could be restored within 5 mm in 94% and 92% of cases, respectively. The cemented undersized stem performed best, combining freedom of stem positioning and a large offset range. The uncemented straight stem performed well because of its large and well-chosen offset range, and despite the need for cortical bone contact limiting stem positioning. The cemented line-to-line stem performed less well due to a small range of sizes and offsets. The uncemented calcar-guided stem performed worst, despite 24 sizes and a large and well-chosen offset range. This was attributed to the calcar curvature restricting the stem insertion depth along the femoral axis. Conclusion. In the majority of non-deformed femora, leg length, offset, and anteversion can be restored accurately with non-modular stems during 3D templating. Failure to restore hip biomechanics is mostly due to surgical inaccuracy. Small calcar guided stems offer no advantage to restore hip biomechanics compared to more traditional designs. Cite this article: Bone Jt Open 2021;2(7):476–485

Aims

We present the clinical and radiological results at a minimum follow-up of 20 years using a second-generation uncemented total hip arthroplasty (THA). These results are compared to our previously published results using a first-generation hip arthroplasty followed for 20 years.

Aims

For this retrospective cohort study, patients aged ≤ 30 years (very young) who underwent total hip arthroplasty (THA) were compared with patients aged ≥ 60 years (elderly) to evaluate the rate of revision arthroplasty, implant survival, the indications for revision, the complications, and the patient-reported outcomes.

Modern modular revision stems employ tapered conical (TCR) distal stems designed for immediate axial and rotational stability with subsequent osseo-integration of the stem. Modular proximal segments allow the surgeon to achieve bone contact proximally with eventual ingrowth that protects the modular junction. The independent sizing of the proximal body and distal stem allows for each portion to obtain intimate bony contact and gives the surgeon the ability precisely control the femoral head center of rotation, offset, version, leg length, and overall stability. The most important advantage of modular revision stems is versatility - the ability to manage ALL levels of femoral bone loss (present before revision or created during revision). Used routinely, this allows the surgeon to quickly gain familiarity with the techniques and instruments for preparation and implantation and subsequently master the use for all variety of situations. This also allows the operating room staff to become comfortable with the instrumentation and components. Additionally, the ability to use the stem in all bone loss situations eliminates intra-operative shuffle (changes in the surgical plan resulting in more instruments being opened), as bone loss can be significantly under-estimated pre-operatively or may change intra-operatively. Furthermore, distal fixation can be obtained simply and reliably. Paprosky 1 femoral defects can be treated with a primary-type stem for the most part. All other femoral defects can be treated with a TCR stem. Fully porous coated stems also work for many revisions but why have two different revision stem choices available when the TCR stems work for ALL defects?. The most critical advantage is the ability to separate completely the critical task of fixation from other important tasks of restoring offset, leg length, and stability. Once fixation is secured, the surgeon can concentrate on hip stability and on optimization of hip mechanics (leg length and offset). The ability to do this allows the surgeon to maximise patient functionality post-operatively. Modular tapered stems have TWO specific advantages over monolithic stems in this important surgical task. The proximal body size and length can be adjusted AFTER stem insertion if the stem goes deeper than the trial. Further, proximal/distal bone size mismatch can be accommodated. The surgeon can control the diameter of the proximal body to ensure proper bony apposition independent of distal fitting needs. If the surgeon believes that proximal bone ingrowth is important to facilitate proximal bone remodeling, modular TCR stems can more easily accomplish this. The most under-appreciated advantage is the straightforward instrumentation system that makes the operation easier for the staff and the surgeon, while enhancing the operating room efficiency and reducing cost. Also, although the implant itself may result in more cost, most modular systems allow for a decrease in inventory requirements, which make up the cost differential. One theoretical disadvantage of modular revision stems is modular junction fracture, which can happen if the junction itself is not protected by bone. Ensuring proximal bone support can minimise this problem. Once porous ingrowth occurs proximally, the risk of junction fracture is eliminated. Even NON-modular stems fracture when proximal bone support is missing. Another theoretical issue is modular junction corrosion but this not a clinical one, since both components are titanium. One can also fail to connect properly the two parts during surgery

Modularity in femoral revision evolved to address the specific weaknesses in the execution and results of the early Wagner SL stem, namely dislocations and subsidence. With modularity, distal canal fit can be achieved independently, and the proximal geometry can be created to re-establish the leg length and offset. The benefits of modularity relate specifically to being able to modify a plan intra-operatively based on the conditions that are encountered in mid battle. Inherent in this concept is the principle of predictability. The extent to which the conditions of operation may change requires alternatives to manage those changes. More importantly we need to be able to predict how an implant will sit in the bone. At the inception and with subsequent manifestations of modular fluted stems, our ability to predict where the final implant will seat based on the trial options that existed was poor. For this reason, some modular stem designs offered no trial. This was part of the imperative for modularity, so that if the implant set too high it could be easily removed with reaming a little deeper and put back in. If the stem sat more deeply than had been anticipated, the change could be compensated by an alteration in the proximal modular segment. Reproducible mid- to long-term results have been published with this type of stem. Potential negatives of the modular junction include stem breakage, fretting and corrosion, cost, and the need to accommodate a large sized proximal segment within the proximal femur. The most important feature in modern non-modular implants will be predictability. We need to be able to predict that the final reamer will sit at a particular level in the femoral bone, and the trial will reproduce this level, and the final implant will reproduce this level. More importantly, we need to be able to predict that implants will remain where they are put, and not subside. Subsidence has been causally associated with implant under-sizing, which is an error in surgical execution. As such, design features that optimise the ability to achieve intimate and broad endosteal contact between the implant and the bone can help reduce subsidence. These include precise, sharp reamers, implants in 1 mm increments, and trials that reproduce the position of the final implant. A larger implant is less likely to break, and we recommend preparation for the largest implant that the diaphysis can accommodate, often evident in the tactile feedback from the reamer, and the quality of the reamed bone being removed. Reaming is performed eccentrically in the proximal femur, so as to engage the diaphysis optimally. The need for a kink in the stem is important for modular stems, which have bulky proximal segments that can create conflict with the peritrochanteric bone in smaller patients. Non-modular stems can have a smaller proximal diameter, such that a straight stem can be accommodated in most revision cases. Early follow-up of a modern non-modular stem has shown excellent clinical improvement and reproducible ingrowth. Subsidence of > 10 mm occurred in 6 hips (6%), which is a notable improvement in historical values for this stem type, but remain short of some reports with modular stems. Improvements in goals and techniques of reaming and implantation are surely part of the improvements that have been documented, as well as those yet to be realised. Predictability will lead to simplicity and intuitiveness

Tapered fluted titanium stems are increasingly used for femoral revision arthroplasty. They are available in modular and non-modular forms. Modularity has advantages when the bone loss is severe, the proximal femur is mis shapen or the surgeon is unfamiliar with the implant, but it introduces the risk of fracture of the stem at the junction between it and the proximal body segment. For that reason, and while awaiting intermediate-term results of more recently introduced designs of this junction, non-modularity has attracted attention, at least for straightforward revision cases.

We review the risks and causes of fracture of tapered titanium modular revision stems and present an argument in favour of the more selective use of modular designs.

Cite this article: Bone Joint J 2016;98-B(1 Suppl A):50–3.

The accurate reconstruction of hip anatomy and biomechanics is thought to be important in achieveing good clinical outcomes following total hip arthroplasty (THA). To this end some newer hip designs have introduced further modularity into the design of the femoral component such that neck­shaft angle and anteversion, which can be adjusted intra-operatively. The clinical effect of this increased modularity is unknown. We have investigated the changes in these anatomical parameters following conventional THA with a prosthesis of predetermined neck–shaft angle and assessed the effect of changes in the hip anatomy on clinical outcomes.

In total, 44 patients (mean age 65.3 years (standard deviation (sd) 7); 17 male/27 female; mean body mass index 26.9 (kg/m²) (sd 3.1)) underwent a pre- and post-operative three-dimensional CT scanning of the hip. The pre- and post-operative neck–shaft angle, offset, hip centre of rotation, femoral anteversion, and stem alignment were measured. Additionally, a functional assessment and pain score were evaluated before surgery and at one year post-operatively and related to the post-operative anatomical changes.

The mean pre-operative neck–shaft angle was significantly increased by 2.8° from 128° (sd 6.2; 119° to 147°) to 131° (sd 2.1; 127° to 136°) (p = 0.009). The mean pre-operative anteversion was 24.9° (sd 8; 7.9 to 39.1) and reduced to 7.4° (sd 7.3; -11.6° to 25.9°) post-operatively (p < 0.001). The post-operative changes had no influence on function and pain. Using a standard uncemented femoral component, high pre- and post-operative variability of femoral anteversion and neck–shaft angles was found with a significant decrease of the post-operative anteversion and slight increase of the neck–shaft angles, but without any impact on clinical outcome.

Cite this article: Bone Joint J 2015;97-B:1615–22.

Objectives

Third-body wear is believed to be one trigger for adverse results with metal-on-metal (MOM) bearings. Impingement and subluxation may release metal particles from MOM replacements. We therefore challenged MOM bearings with relevant debris types of cobalt–chrome alloy (CoCr), titanium alloy (Ti6Al4V) and polymethylmethacrylate bone cement (PMMA).

Non-modular tapered fluted, titanium stems are available for use in femoral revision. The combination of taper and flutes on the stem provides axial and rotational stability, respectively. The material and surface properties of the stem promotes bone on-growth. If the surgeon is confident and reasonably experienced in the surgical use of this sort of design and the case is relatively straightforward, a non-modular design is effective. It also potentially reduces implant inventory, and circumvents the potential problems of taper junction corrosion and fatigue fracture. There are reports of excellent survival, good clinical and functional results and evidence of subsequent increase in proximal bone stock.

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):56–9.

The “keel” is the relatively short part of the undersurface of the tibial component that extends into the medullary canal. Most knee replacement systems have the capacity to attach modular stem extensions for enhanced intra-medullary fixation for revision. Diaphyseal length, large diameter stems may also guide positioning of trial components and are ideal for accurate surgical technique, even if fully cemented stems are eventually implanted. Smaller diameter non-modular stem extensions may be used for fully cemented fixation. They do not however guide component position very accurately and do not make sense for uncemented fixation. Revision surgery is different from primary surgery and enhanced fixation with some type of intramedullary fixation is highly appropriate, especially if constrained devices might be required. Options for enhanced intramedullary fixation are: 1. Fully cemented metaphyseal or shorter stems; 2. Diaphyseal engaging press fit stems; and 3. Very short fully cemented stems with trabecular metal cone fixation. Metaphyseal length press fit stems do not provide reliable fixation in revision TKA. Revision with primary components or constrained components without any stem extension is not advised

Corrosion in modular taper connections of total joint replacement has become a hot topic in the orthopaedic community and failures of modular systems have been reported. The objective of the present study was to determine in vivo titanium ion levels following cementless total hip arthroplasty (THA) using a modular neck system. A consecutive series of 173 patients who underwent cementless modular neck THA and a ceramic on polyethylene bearing was evaluated retrospectively. According to a standardized protocol, titanium ion measurements were performed on 67 patients using high-resolution inductively coupled plasma-mass spectrometry. Ion levels were compared to a control group comprising patients with non-modular titanium implants and to individuals without implants. Although there was a higher range, modular-neck THA (unilateral THA: 3.0 μg/L (0.8–21.0); bilateral THA: 6.0 μg/L (2.0–20.0)) did not result in significant elevated titanium ion levels compared to non-modular THA (unilateral THA: 2.7 μg/L (1.1–7.0), p = 0.821; bilateral THA: 6.2 μg/L, (2.3–8.0), p = 0.638). In the modular-neck THA group, patients with bilateral implants had significantly higher titanium ion levels than patients with an unilateral implant (p < 0.001). Compared to healthy controls (0.9 μg/L (0.1–4.5)), both modular THA (unilateral: p = 0.029; bilateral p = 0.003) and non-modular THA (unilateral: p < 0.001; bilateral: p < 0.001) showed elevated titanium ion levels. The data suggest that the present modular stem system does not result in elevated systemic titanium ion levels in the medium term when compared to non-modular stems. However, more outliner were seen in modular-neck THA. Further longitudinal studies are needed to evaluate the use of systemic titanium ion levels as an objective diagnostic tool to identify THA failure and to monitor patients following revision surgery

Wear debris associated with CoCr bearings has been implicated in the development of adverse soft tissue reactions and pseudotumors following THA with large metal heads and following hip resurfacing. Additional concerns have been raised regarding trunion fretting and corrosion. Most recently, the neck-stem junction of some modular femoral stem designs have come under additional scrutiny. We undertook a review of patients who had undergone THA with a proximal modular junction stem design in order to ascertain the state of the junction in early follow up. We examined the records of all patients in our practice who had undergone uncomplicated, unilateral THA with the ARC stem (OmniLife Science, East Taunton, MA, USA) between April 2010 and April 2012. Office records, radiographs and laboratory data were included. Serum or blood cobalt and chromium ion levels were obtained at the one-year post-op visit or later or if the patient had unexpected pain. The test obtained (serum or blood) was dependent on the lab performing the study. In the study period 100 patients met the inclusion criteria and had metal ion levels available for review. No patient required revision for adverse soft tissue reaction or elevated metal ion levels. Cobalt levels fell with the normal lab ranges in the majority of patients with a very small percentage demonstrating levels slightly above the normal range. Chromium levels all fell within the expected normal range. One patient had a neck exchange for mechanical reasons at 8 weeks following primary THA. This patient went on to develop elevated serum cobalt levels and a large hip effusion. The hip was revised at one year to a non-modular stem. A modular proximal stem offers the advantages of addressing variable anatomy and allowing less soft tissue dissection. Some designs have enjoyed success while others have been withdrawn from the market due to fatigue failure, dissociation or metal-associated adverse reactions. Modular junction designs vary greatly which can impact their inherent stability and their ability to resist micro-motion. In this patient group the junction has shown good stability in early follow up as judged by clinical and laboratory data. Cobalt levels were all normal or well below the range considered suspicious for adverse reaction. Chromium levels all fell within the normal range. A case of an exchanged neck with retention of the stem was associated with high cobalt levels. We discuss several junction designs and their characteristics

Conventional uncemented femoral implants provide dependable long-term fixation in patients with a wide range of functional requirements. Yet challenges associated with proximal–distal femoral dimensional mismatch, preservation of bone stock, and minimally invasive approaches have led to exploration into alternative implant designs. Short stem designs focusing on a stable metaphyseal fit have emerged to address these issues in total hip replacement (THR). Uncemented metaphyseal-engaging short stem implants are stable and are associated with proximal bone remodeling closer to the metaphysis when compared with conventional stems and they also have comparable clinical performances. Short stem metaphyseal-engaging implants can meet the goals of a successful THR, including tolerating a high level of patient function, as well as durable fixation.

Cite this article: Bone Joint J 2013;95-B, Supple A:57–62.

Following the recall of modular neck hip stems in July 2012, research into femoral modularity will intensify over the next few years. This review aims to provide surgeons with an up-to-date summary of the clinically relevant evidence. The development of femoral modularity, and a classification system, is described. The theoretical rationale for modularity is summarised and the clinical outcomes are explored. The review also examines the clinically relevant problems reported following the use of femoral stems with a modular neck.

Joint replacement registries in the United Kingdom and Australia have provided data on the failure rates of modular devices but cannot identify the mechanism of failure. This information is needed to determine whether modular neck femoral stems will be used in the future, and how we should monitor patients who already have them implanted.

Cite this article: Bone Joint J 2013;95-B:1011–21.

Tapered, fluted, modular, titanium stems have a long history in Europe and are increasing in popularity in North America. We have reviewed the results at our institution looking at stem survival and clinical outcomes. Radiological outcomes and quality of life assessments have been performed and compared to cylindrical non-modular cobalt chromium stems. Survival at five years was 94%. This fell to 85% at ten years due to stem breakage with older designs. Review of radiology showed maintenance or improvement of bone stock in 87% of cases. Outcome scores were superior in tapered stems despite worse pre-operative femoral deficiency. Tapered stems have proved to be a useful alternative in revision total hip arthroplasty across the spectrum of femoral bone deficiency.

We reviewed 123 second-generation uncemented total hip replacements performed on 115 patients by a single surgeon between 1993 and 1994. The acetabular component used in all cases was a fully porous-coated threaded hemispheric titanium shell (T-Tap ST) with a calcium ion stearate-free, isostatically compression-moulded polyethylene liner. The titanium femoral component used was a Taperloc with a reduced distal stem. No patient was lost to follow-up. Complete clinical and radiological follow-up was obtained for all 123 hips at a mean of 14 years (12 to 16). One femoral component was revised after a fracture, and three acetabular components for aseptic loosening. No additional femoral or acetabular components were judged loose by radiological criteria. Mild proximal femoral osteolysis was identified in two hips and minor acetabular osteolysis was present in four. The mean rate of penetration of the femoral head was 0.036 mm/year (0.000 to 0.227).

These findings suggest that refinements in component design may be associated with excellent long-term fixation in cementless primary total hip replacement.

Pre-operative computerised three-dimensional planning was carried out in 223 patients undergoing total hip replacement with a cementless acetabular component and a cementless modular-neck femoral stem. Components were chosen which best restored leg length and femoral offset. The post-operative restoration of the anatomy was assessed by CT and compared with the pre-operative plan.

The component implanted was the same as that planned in 86% of the hips for the acetabular implant, 94% for the stem, and 93% for the neck-shaft angle. The rotational centre of the hip was restored with a mean accuracy of 0.73 mm (sd 3.5) craniocaudally and 1.2 mm (sd 2) laterally. Limb length was restored with a mean accuracy of 0.3 mm (sd 3.3) and femoral offset with a mean accuracy of 0.8 mm (sd 3.1).

This method appears to offer high accuracy in hip reconstruction as the difficulties likely to be encountered when restoring the anatomy can be anticipated and solved pre-operatively by optimising the selection of implants. Modularity of the femoral neck helped to restore the femoral offset and limb length.