Introduction. The use of stems in TKA revision surgery is well established. Stems off-load stress over a broad surface area of the diaphysis and help protect the metaphyseal interface areas from failure. Stems can provide an area of extra fixation. Uncemented Stems. Pros and Cons. Advantages. (1) Expeditious, (2) Compatible with intramedullary based revision instrumentation (3) Easy to remove if necessary (4) By filling diaphysis they help guarantee axial alignment. Disadvantages. (1) They help off load stress, but how much fixation do they really provide? (2) They don't fit all canal deformities, and under some circumstances can actually force implants into malalignment. (3) ? potential for end of stem pain. Cemented Stems. Pros and Cons. Advantages. (1) Cemented stem adds fixation in fresh metaphyseal and diaphyseal bone. (2) Proven 10-year track record. (3) Allow the surgeon to adjust for canal geometry abnormalities. Disadvantages. (1) More difficult to remove, if required. (2) They don't fill the canal so they don't guarantee alignment as well under most circumstances. Results. Favorable results with uncemented and cemented stems have been reported in several series. Cemented stems have longer term data. Technique Issues. Uncemented Stems. (1) Take advantage of offset bolts, tibial trays, stems to fit the stem/implant to the patient's anatomy. (2) Don't let the stem force you into suboptimal implant position. (3) Longer stems can be narrower but help engage more diaphysis. (4) Do a good job of restoring/uncovering cancellous bone in metaphysis for cement interdigitation. The cement provides the fixation. Cemented Stems. (1) Intra-operative x-ray with trials helps guarantee optimal alignment. (2) Use cement restrictors. (3) Cement tibia/femur separately. Metaphyseal Fixation. (1) Area of new emphasis. (2) Cones and sleeves can improve cemented and uncemented fixation

Introduction. The use of stems in TKA revision surgery is well established. Stems off-load stress over a broad surface area of the diaphysis and help protect the metaphyseal interface areas from failure. Stems can provide an area of extra fixation. Uncemented Stems: Advantages – Expeditious; Compatible with intramedullary based revision instrumentation; Easy to remove if necessary; By filling diaphysis they help guarantee axial alignment. Disadvantages - They help off load stress, but how much fixation do they really provide?; They don't fit all canal deformities, and under some circumstances can actually force implants into malalignment; ? potential for end of stem pain. Cemented Stems: Advantages - Cemented stem adds fixation in fresh metaphyseal and diaphyseal bone; Proven 10-year track record; Allow the surgeon to adjust for canal geometry abnormalities. Disadvantages - More difficult to remove if required; They don't fill the canal so they don't guarantee alignment as well under most circumstances. Results:. Favorable results with uncemented and cemented stems have been reported in several series; Cemented stems have longer term data. Technique Issues: Uncemented Stems - Take advantage of offset bolts, tibial trays, stems to fit the stem/implant to the patient's anatomy. Don't let the stem force you into suboptimal implant position; Longer stems can be narrower but help engage more diaphysis; Do a good job of restoring/uncovering cancellous bone in metaphysis for cement interdigitation. The cement provides the fixation. Cemented Stems - Intraoperative x-ray with trials helps guarantee optimal alignment; Use cement restrictors; Cement tibia/femur separately. Metaphyseal Fixation - Area of new emphasis; Cover and sleeves can improve cemented and uncemented fixation

Cementless femoral components have an excellent track record that includes efficient implantation and long-term survival, thus are the predominant stem utilised in North America. Femoral component stability and resistance to subsidence are critical for osseointegration and clinical success. Implant design, surgical technique, anatomic fit, and patient characteristics, such as bone quality, can all effect initial implant stability and resistance to subsidence. Variability in stem shape and in the anatomy of the proximal femoral metaphysis has been implicated in the failure of some stem designs. Biologic fixation obtained with osseointegration of cementless implants may improve implant longevity in young, active, and obese patients. Lack of intimate fit can lead to clinical complications such as subsidence, aseptic loosening, and peri-prosthetic fracture. Currently, there are several stem designs, all of which aim to achieve maximal femoral stability and minimal subsidence and include: Fit and Fill / Double Taper Proximally Porous Coated Stems; Parallel Sided Taper Wedge or “Blade” Stems; Wagner Style Conical Shape Splined Titanium Stems; Tapered Rectangular Cross-Section Zweymuller Stem; Fully-Porous Coated Stems; Modular Proximal Sleeve Fluted Stem; Anatomic Proximally Porous Coated Stems. The majority of patients with relatively straightforward anatomy can be treated with any of the aforementioned femoral implant types. However, more complicated femoral anatomy frequently requires a particular implant type to maximise stability and promote osseointegration. Stems with femoral deformity in the meta-diaphyseal region may require a shorter stem in order to avoid an osteotomy. Distorted femoral anatomy typically seen in childhood diseases, such as dysplasia, may require a modular proximal sleeve tapered fluted stem or Wagner style cone stem to impart optimal stem anteversion separate from the native femoral neck version. The most severe forms of dysplasia may require a shortening osteotomy and subsequent distal fixation and neck version flexibility, which can be addressed with a modular proximal sleeve fluted or fully porous coated stem. A stovepipe or osteoporotic femur may require a stem that engages more distally such as a conical splined tapered stem, a fully porous coated stem or even a cemented stem to achieve adequate stability. Finally, obese patients are a particular challenge and emerging data suggests that a morphologically based parallel-sided taper wedge stems may confer greater stability and resistance to subsidence in these patients. Ultimately, an appropriate selection algorithm will facilitate an appropriate match of the patient morphology with femoral implant geometry that facilitates stable fixation and osseointegration

Stems provide short- and long-term stability to the femoral and tibial components. Poorer epiphyseal and metaphyseal bone quality will require sharing or offloading the femoral and tibial component interfaces with a stem. One needs to use stem technique most appropriate for each individual case because of variable anatomy and bone loss situations. The conflict with trying to obtain stability via the stem is that most stems are cylindrical but femoral and tibial metaphyseal/diaphyseal areas are conical in shape. Viable stem options include fully cemented short and long stems, uncemented long stems, offset uncemented stems, and a hybrid application of a cemented proximal end of longer uncemented diaphyseal engaging stems. Stems are not without their risk. The more the load is transferred to the cortex, the greater the risk of proximal interface stress shielding. A long uncemented stem has similar stress shielding as a short cemented stem. Long diaphyseal engaging stems that are cemented or uncemented have the potential to have end of stem pain, especially if more diaphyseal reaming is done to obtain greater cortical contact. A conical shaped long stem can provide more stability than a long cylindrical stem and avoid diaphyseal reaming. Use of long stems may create difficulty in placement of the tibial and femoral components in an optimal position. If the femoral or tibial components do not allow an offset stem insertion, using a long offset stem or short cemented stem is preferred. The amount of metaphyseal bone loss will drive the choice of stem used. Short cemented stems will not have good stability in poor metaphyseal bone without getting the cement out to the cortex. Long cemented stems provide satisfactory survivorship, however, most surgeons avoid cementing long stems due to the difficulty of removal, if a subsequent revision is required. If the metaphyseal bone is excellent, use of a short cemented stem or long uncemented stem can be expected to have good results. Long fully uncemented stems must have independent stability to be effective, or should be proximally cemented as a hybrid technique. Cases with AOI type IIb and III tibial and femoral defects are best managed with use of metaphyseal cones with short cemented stems or long hybrid straight or offset stems. Some studies also suggest that if the cone is very stable, no stem may be required. My preference is to use a short cemented stem or hybrid conical stem in patients with good metaphyseal bone. If significant metaphyseal bone loss is present, I will use a porous cone with either a short cemented stem, hybrid cylindrical or offset stem depending on the primary stability of the cone and whether the femoral or tibial component can be placed in an optimal position in patients with good metaphyseal bone

Stems are a crucial part of implant stabilization in revision total knee arthroplasty. In most cases the metaphyseal bone is deficient, and stabilization in the diaphyseal cortical bone is necessary to keep the implant tightly fixed to bone and to prevent tilt and micromotion. While sleeves and cones can be effective in revision total joint arthroplasty, they are technically difficult and may lead to major bone loss in cases of loosening or infection, especially if the stem is cemented past the cone. A much more conservative method is to ream the diaphysis to the least depth possible to achieve tight circumferential fixation, and to apply porous augments to the undersurface of the tibial tray or inner surface of the femoral component to allow them to bottom out against the bone surface and apply compressive load. If a robust, strong taper, stem and component combination is used, rim contact on only one side is necessary to achieve rigid permanent fixation. Porous and non-porous stems are available. The non-porous stems should have a spline surface that engages the diaphyseal bone and achieves rigid initial fixation but does not provide long-term axillary support. In that way the porous rim-engaging surface can bear compressive load and finally unload the stem and taper junction. Correctly designed stems do not stress relieve unless they are porous-coated. In situations where metaphyseal bone is not available, porous-coated stems that link to hinge prostheses are a very important part of the armamentarium in complex revision arthroplasty. Use of stems requires experience and special technique. Slight underreaming and initial scratch fit are necessary techniques. This does not result in tight fixation every time because split of the cortex does occasionally occur. In most cases these splits do not need to be repaired, but when there is a question, an intra-operative x ray should be taken and the surgeon should be prepared to repair the fracture. Stems are an essential part of revision total knee arthroplasty. A tightly fit stem in the diaphysis is necessary for fixation when metaphyseal bone is deficient. No amount of cement pressed into the deficient metaphyseal bone will substitute for rigid stem fixation

Little information exists regarding optimal tibial stem usage in revision total knee arthroplasty (rTKA) utilising a tibial trabecular metal (TM) cone. The purpose of this study was to compare 1) functional outcomes, 2) radiographic outcomes, and 3) implant survivorship in rTKA utilising TM cones combined with either short stems (SS) or long stems (LS) at minimum two-years clinical follow-up.

In this retrospective, multi-centre study, patients undergoing TM cone utilising rTKA between 2008 and 2019 were included. Patients were divided into: SS group (no diaphyseal engagement), and LS group (diaphyseal engagement). All relevant clinical charts and post-operative radiographs were examined. Oxford Knee Score (OKS) and EuroQol-5D (EQ-5D-5L) data were collected at most recent follow-up.

In total, 44 patients were included: 18 in the SS group and 26 in the LS group. The mean time of follow-up was 4.0 years. Failure free survival was 94.5% for the SS group and 92.3% for the LS group. All failures were for prosthetic joint infections managed with debridement, antibiotics, and implant retention. At most recent follow-up, 3 patients demonstrated radiographic signs of lucency (1 SS 2 LS, p = 1) and the mean OKS were 37 ± 4 and 36 ± 6 (p = 0.73) in the SS and LS groups, respectively.

Tibial SS combined with TM cones performed as well as LS in rTKA at minimum two-years follow-up. A tibial SS in combination with a TM cone is a reliable technique to achieve stable and durable fixation in rTKA.

The demand for revision total knee arthroplasty (TKA) has grown significantly in recent years. The two major fixation methods for stems in revision TKA include cemented and ‘hybrid’ fixation. We explore the optimal fixation method using data from recent, well-designed comparative studies.

We performed a systematic review of comparative studies published within the last 10 years with a minimum follow-up of 24 months. To allow for missing data, a random-effects meta-analysis of all available cases was performed. The odds ratio (OR) for the relevant outcome was calculated with 95% confidence intervals. The effects of small studies were analyzed using a funnel plot, and asymmetry was assessed using Egger's test. The primary outcome measure was all-cause failure. Secondary outcome measures included all-cause revision, aseptic revision and radiographic failure.

There was a significantly lower failure rate for hybrid stems when compared to cemented stems (p = 0.006) (OR 0.61, 95% CI 0.42-0.87). Heterogeneity was 4.3% and insignificant (p = 0.39). There was a trend toward superior hybrid performance for all other outcome measures including all-cause re-revision, aseptic re-revision and radiographic failure.

Recent evidence suggests a significantly lower failure rate for hybrid stems in revision TKA. There is also a trend favoring the use of hybrid stems for all outcome variables assessed in this study. This is the first time a significant difference in outcome has been demonstrated through systematic review of these two modes of stem fixation. We therefore recommend the use, where possible, of hybrid stems in revision TKA.

There has been an evolution in revision hip arthroplasty towards cementless reconstruction. Whilst cemented arthroplasty works well in the primary setting, the difficulty with achieving cement fixation in femoral revisions has led to a move towards removal of cement, where it was present, and the use of ingrowth components. These have included proximally loading or, more commonly, distally fixed stems. We have been through various iterations of these, notably with extensively porous coated cobalt chrome stems and recently with taper-fluted titanium stems. As a result of this, cemented stems have become much less popular in the revision setting. Allied to concerns about fixation and longevity of cemented fixation revision, there were also worries in relation to bone cement implantation syndrome when large cement loads were pressurised into the femoral canal at the time of stem cementation. This was particularly the case with longer stems. Technical measures are available to reduce that risk but the fear is nevertheless there. In spite of this direction of travel and these concerns, there is, however, still a role for cemented stems in revision hip arthroplasty. This role is indeed expanding. First and foremost, the use of cement allows for local antibiotic delivery using a variety of drugs both instilled in the cement at the time of manufacture or added by the surgeon when the cement is mixed. This has advantages when dealing with periprosthetic infection. Thus, cement can be used both as interval spacers but also for definitive fixation when dealing with periprosthetic hip infection. The reconstitution of bone stock is always attractive, particularly in younger patients or those with stove pipe canals. This is achieved well using impaction grafting with cement and is another extremely good use of cement. In the very elderly or those in whom proximal femoral resection is needed at the time of revision surgery, distal fixation with cement provides a good solution for immediate weight bearing and does not have the high a risk of fracture seen with large cementless stems. Cement is also useful in cases of proximal femoral deformity or where cement has been used in a primary arthroplasty previously. We have learnt that if the cement is well-fixed then the bond of cement-to-cement is excellent and therefore retention of the cement mantle and recementation into that previous mantle is a great advantage. This avoids the risks of cement removal and allows for much easier fixation. Stems have been designed specifically to allow this cement-in-cement technique. It can be used most readily with polished tapered stems - tap out a stem, gain access at the time of revision surgery and reinsert it. It is, however, now increasingly used when any cemented stems are removed provided that the cement mantle is well fixed. The existing mantle is either wide enough to accommodate the cement-in-cement revision or can be expanded using manual instruments or ultrasonic tools. The cement interface is then dried and a new stem cemented in place. Whilst the direction of travel in revision hip arthroplasty has been towards cementless fixation, particularly with tapered distally fixed designs, the reality is that there is still a role for cement for its properties of immediate fixation, reduced fracture risk, local antibiotic delivery, impaction grafting and cement-in-cement revision

For most revision total knee replacement there is associated soft tissue and bone loss. A constrained condylar implant can be useful in improving the stability of the knee after revision. Augmentation is commonly used to deal with bone loss on the femoral and tibial side of the joint. Stems are known to reduce the load at the interface of the femoral and tibial component and transfer the load into the medullary canals. There are problems with using stems in the revision setting however, which include: (1) increased cost, (2) difficulty with removal should further revision be necessary, (3) violation of the intramedullary canals if infection occurs, (4) increased operating time. For these reasons a CCK implant was developed without stems in 1998. The use of this device must be very selective and it is primarily used for severe valgus deformity in elderly patients. In a revision setting where there is good preservation of femoral and/or tibial bone but the need for increased constraint is present (e.g. unicompartmental, cruciate retaining knee) a CCK without stems can be used with good results. We retrospectively reviewed 36 primary constrained condylar knee implants without stem extensions from 1998 to 2000 in 31 patients with knees in 15 degrees valgus or greater. All patients were followed up for a minimum 10 years (range, 10 to 12 years). One patient had aseptic loosening and needed to be revised with stemmed components at 9 years post-surgery. Wear was found in two patients. One patient, with severe rheumatoid arthritis, had infection and required a two-stage re-implantation procedure. Patients who are very active or heavy body weight where stresses may be excessive at the implant bone interface should have stems utilised

For most revision total knee replacement there is associated soft tissue and bone loss. A constrained condylar implant can be useful in improving the stability of the knee after revision. Augmentation is commonly used to deal with bone loss on the femoral and tibial side of the joint. Stems are known to reduce the load at the interface of the femoral and tibial component and transfer the load into the medullary canals. There are problems with using stems in the revision setting, however, which include: (1) increased cost, (2) difficulty with removal should further revision be necessary, (3) violation of the intramedullary canals if infection occurs, (4) increased operating time. For these reasons a CCK implant was developed without stems in 1998. The use of this device must be very selective and it is primarily used for severe valgus deformity in elderly patients. In a revision setting where there is good preservation of femoral and/or tibial bone but the need for increased constraint is present (e.g. unicompartmental, cruciate retaining knee) a CCK without stems can be used with good results. We retrospectively reviewed 36 primary constrained condylar knee implants without stem extensions from 1998 to 2000 in 31 patients with knees in 15° valgus or greater. All patients were followed up for a minimum 10 years (range, 10 to 12 years). One patient had aseptic loosening and needed to be revised with stemmed components at nine years post-surgery. Wear was found in two patients. One patient, with severe rheumatoid arthritis, had infection and required a two-stage re-implantation procedure. Patients who are very active or heavy body weight where stresses may be excessive at the implant bone interface should have stems utilised

For most complex primary total knee replacement there is associated soft tissue and bone loss. A constrained condylar implant can be useful in improving the stability of the knee after revision. Augmentation is commonly used to deal with bone loss on the femoral and tibial side of the joint. Stems are known to reduce the load at the interface of the femoral and tibial component and transfer the load into the medullary canals. There are problems with using stems in the complex primary knee setting however, which include: (1) increased cost, (2) difficulty with removal should further revision be necessary, (3) violation of the intramedullary canals if infection occurs, (4) increased operating time. For these reasons a CCK implant was developed without stems in 1998. The use of this device must be very selective and it is primarily used for severe valgus deformity in elderly patients. In a revision setting where there is good preservation of femoral and/or tibial bone but the need for increased constraint is present (e.g. unicompartmental, cruciate retaining knee) a CCK without stems can be used with good results. We retrospectively reviewed 36 primary constrained condylar knee implants without stem extensions from 1998 to 2000 in 31 patients with knees in 15 degrees valgus or greater. All patients were followed up for a minimum 10 years (range, 10 to 12 years). One patient had aseptic loosening and needed to be revised with stemmed components at 9 years post surgery. Wear was found in two patients. One patient, with severe rheumatoid arthritis, had infection and required a two-stage re-implantation procedure. Patients who are very active or heavy body weight where stresses may be excessive at the implant bone interface should have stems utilised

Some DEFINITIONS are necessary: “STEMS” refers to “intramedullary stem extensions”, which may be of a variety of lengths and diameters, fixed with cement, porous coating or press fit alone and which may be modular or an inherent part of the prosthesis. The standard extension keel on the tibia does not qualify as a “stem (extension)”. COMPLEX implies multiple variables acting on the end result of the arthroplasty with the capability of inducing failure, as well as necessary variations to the standard surgical technique. A lesser degree of predictability is implied. More specifically, the elements usually found in an arthritic knee and used for the arthroplasty are missing, so that cases of COMPLEX primary TKA include: Soft tissue coverage-(not relevant here), Extensor mechanism deficiency-patellectomy, Severe deformity, Extra-articular deformity, Instability: Varus valgus, Instability: Plane of motion, Instability: Old PCL rupture, Dislocated patella, Stiffness, Medical conditions: Neuromuscular disorder, Ipsilateral arthroplasty, Prior incisions, Fixation hardware, Osteopenia, Ipsilateral hip arthrodesis, Ipsilateral below knee amputation, etc. Complexity includes MORE than large deformity, i.e., success with large deformity does NOT mean success with constrained implants regardless of indication. In addition, the degree of constraint must be specified to be meaningful. NECESSARY presumably this means: “necessary to ensure durable fixation in the face of poor bone quality or more mechanically constrained” and SUFFICIENT suggests that stems, by themselves or in some shape of form, by themselves “will ensure success (specifically here) of fixation”. If we can start with the second proposal, that STEMS are SUFFICIENT for success the answer is: “NO”, many more aspects of surgical technique and implant design are required. Even if all other aspects of the technique are exemplary, some types of stems or techniques are inadequate, e.g., completely uncemented, short stem extensions. The answer to the first proposal is: “YES, in many cases”. The problem will be to determine which cases. There are philosophical analogies to this question that we already know the answer to. ANALOGY: Is a life-raft necessary on a boat? Yes, you may not use it, but it is considered necessary. Is a life-raft “sufficient” on a boat? No, other problems may occur. Are seat belts necessary? Are child seats necessary? The AAOS already has a position on child restraints, an analogous situation, where a party who cannot control their situation (anesthetised patient/ child) functions in the care of a responsible party. The objection may be argued in terms of cost saving by NOT using increased fixation. A useful analogy, (that would of course require specific analysis), is that of patellar resurfacing: universal resurfacing is cost-effective when considering the expense of even a small number of secondary resurfacings. Of course a complex arthroplasty that requires a revision procedure is far more expensive than secondary patellar resurfacing and so universal use of the enhanced fixation in the face of increased constraint makes sense. The human cost of revision surgery tips the balance irrefutably. DANGER-We must avoid the glib conclusion, often based on poor quality data, that constrained implants do not need additional intramedullary fixation (with stem extensions). When “complexity” is involved, complex analysis is appropriate to select the best course

There is renewed concern surrounding the potential for corrosion at the modular head-neck junction to cause early failure in modern hip implants. Although taper corrosion involves a complex interplay of many factors, previous studies have correlated decreasing flexural rigidity of the femoral trunnion with an increased likelihood of corrosion at retrieval. A multicenter retrieval analysis of 85 modular femoral stems was performed to calculate the flexural rigidity of various femoral trunnions. Stems were implanted between 1991–2012 and retrieved between 2004–2012. There were 10 different taper designs from 16 manufacturers. Digital calipers were used to measure taper geometries by two independent observers. Mean flexural rigidity was 262 Nm. 2. , however there was a wide range of values among the various stems spanning nearly an order of magnitude between the most flexible (80 Nm. 2. ) and most rigid (623 Nm. 2. ) trunnions, which was due in part to the taper geometry and in part to the material properties of the base alloy. There was a modest but significant negative correlation between flexural rigidity of the trunnion and release date of the stem. This wide variability in flexural rigidity may predispose particular stem designs to an increased risk of corrosion at the modular head-neck taper, and may in part explain why taper corrosion is being seen with increasing frequency in modern hip arthroplasty

A matched comparison was made between femoral neck-preserving short, tapered stems (n = 50) and conventional length femoral stems (n = 50) in cementless total hip arthroplasty between January 2008 and January 2012. Patients were matched for age, sex, body mass index, height, surgical approach, and surgeon. In group A, mean preoperative HHS and WOMAC scores of 55.0 and 53.0, respectively, improved to mean postoperative scores of 98.6 and 3.3, respectively, at an average follow–up of 37.2 months. In group B, mean preoperative HHS and WOMAC scores of 53.0 and 49.5, respectively, improved to mean postoperative scores 97.8 and 4.4, respectively, at an average follow–up of 35.3 months. In addition, no significant differences in mean postoperative HHS (P = 0.168) or WOMAC scores (P = 0.158) were observed between the two groups according to the independent sample t-test. Table 1 shows two stems (4%) located in valgus (greater than 5° from neutral). The mean preoperative and postoperative HHS and WOMAC scores were similar to those of stems neutrally located in group A. All group A stems displayed bone bridging and endosteal spot welds distributed in Gruen zones 2 and 6 as evidence of bony ingrowth with no radiolucencies (Fig. 1). Two patients in group B had the slight decrease in bone density, mostly in Gruen zone 1 and 7. No radiographic evidence of osteolytic lesions, cortical hypertrophy, or acetabular fractures was detected in either group. Furthermore, no patient required revision surgery for aseptic loosening. The chi–square (Fisher's exact) test showed no significant difference between the two groups with respect to patient complications (Table 2). One patient in group A with a CCD angle of 135° had subsidence (greater than 2 mm, P =0.313) that displayed bony ingrowth with no further progression of subsidence at final follow-up. An intraoperative minor femur neck fracture (P =1.00) occurred in two patients (one in group A and one in group B). These patients were treated by cerclage wires without further incident. Three patients (two in group A: valgus and a CCD angle 135°, and one in group B: varus) had malalignment (P = 0.554) that was not associated with loosening. One patient in group A with a CCD angle of 135° had greater than 1 cm leg length discrepancy (shortening, P = 0.313). Two patients in group B had thigh pain (P = 0.151) that disappeared after a few months. Three patients (one in group A and two in group B) had heterotopic ossifications (P = 0.554) that were categorized as Brooker class I in two patients and class II in one patient without limiting their activities. In conclusion, no significant differences in the clinical and radiographic outcomes as well as component-specific complications were observed between the two groups, showing satisfactory performance at the 5-year follow-up. Group A had a higher incidence of malalignment and subsidence and a lower incidence of thigh pain and proximal bone resorption than group B.

Shoulder arthroplasty is effective at restoring function and relieving pain in patients suffering from glenohumeral arthritis; however, cortex thinning has been significantly associated with larger press-fit stems (fill ratio = 0.57 vs 0.48; P = 0.013)1. Additionally, excessively stiff implant-bone constructs are considered undesirable, as high initial stiffness of rigid fracture fixation implants has been related to premature loosening and an ultimate failure of the implant-bone interface2. Consequently, one objective which has driven the evolution of humeral stem design has been the reduction of stress-shielding induced bone resorption; this in-part has led to the introduction of short stems, which rely on metaphyseal fixation. However, the selection of short stem diametral (i.e., thickness) sizing remains subjective, and its impact on the resulting stem-bone construct stiffness has yet to be quantified.

Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized and 2mm ‘oversized’ short-stemmed implants. Standard stem sizing was based on a haptic assessment of stem and broach stability per typical surgical practice. Anteroposterior radiographs were taken, and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of compressive loading representing 90º forward flexion to simulate postoperative seating. Following this, a custom 3D printed metal implant adapter was affixed to the stem, which allowed for compressive loading in-line with the stem axis (Fig.1). Each stem was then forced to subside by 5mm at a rate of 1mm/min, from which the compressive stiffness of the stem-bone construct was assessed. The bone-implant construct stiffness was quantified as the slope of the linear portion of the resulting force-displacement curves.

The metaphyseal and diaphyseal fill ratios were 0.50±0.10 and 0.45±0.07 for the standard sized stems and 0.50±0.06 and 0.52±0.06 for the oversized stems, respectively. Neither was found to correlate significantly with the stem-bone construct stiffness measure (metaphysis: P = 0.259, diaphysis: P = 0.529); however, the diaphyseal fill ratio was significantly different between standard and oversized stems (P < 0.001, Power = 1.0). Increasing the stem size by 2mm had a significant impact on the stiffness of the stem-bone construct (P = 0.003, Power = 0.971; Fig.2). Stem oversizing yielded a construct stiffness of −741±243N/mm; more than double that of the standard stems, which was −334±120N/mm.

The fill ratios reported in the present investigation match well with those of a finite element assessment of oversizing short humeral stems3. This work complements that investigation's conclusion, that small reductions in diaphyseal fill ratio may reduce the likelihood of stress shielding, by also demonstrating that oversizing stems by 2mm dramatically increases the stiffness of the resulting implant-bone construct, as stiffer implants have been associated with decreased bone stimulus4 and premature loosening2. The present findings suggest that even a small, 2mm, variation in the thickness of short stem humeral components can have a marked influence on the resulting stiffness of the implant-bone construct. This highlights the need for more objective intraoperative methods for selecting stem size to provide guidelines for appropriate diametral sizing.

For any figures or tables, please contact the authors directly.

Revision surgeries for orthopaedic infections are done in two stages – one surgery to implant an antibiotic spacer to clear the infection and another to install a permanent implant. A permanent porous implant, that can be loaded with antibiotics and allow for single-stage revision surgery, will benefit patients and save healthcare resources. Gyroid structures can be constructed with high porosity, without stress concentrations that can develop in other period porous structures [1] [2]. The purpose of this research is to compare the resulting bone and prosthesis stress distributions when porous versus solid stems are implanted into three proximal humeri with varying bone densities, using finite element models (FEM).

Porous humeral stems were constructed in a gyroid structure at porosities of 60%, 70%, and 80% using computer-aided design (CAD) software. These CAD models were analyzed using FEM (Abaqus) to look at the stress distributions within the proximal humerus and the stem components with loads and boundary conditions representing the arm actively maintained at 120˚ of flexion. The stem was assumed to be made of titanium (Ti6Al4V). Three different bone densities were investigated, representing a healthy, an osteopenic, and an osteoporotic humerus, with an average bone shape created using a statistical shape and density model (SSDM) based on 75 cadaveric shoulders (57 males and 18 females, 73 12 years) [3]. The Young's moduli (E) of the cortical and trabecular bones were defined on an element-by-element basis, with a minimum allowable E of 15 MPa. The Von Mises stress distributions in the bone and the stems were compared between different stem scenarios for each bone density model.

A preliminary analysis shows an increase in stress values at the proximal-lateral region of the humerus when using the porous stems compared to the solid stem, which becomes more prominent as bone density decreases. With the exception of a few mesh dependent singularities, all three porous stems show stress distributions below the fatigue strength of Ti-6Al-4V (410 MPa) for this loading scenario when employed in the osteopenic and osteoporotic humeri [4]. The 80% porosity stem had a single strut exceeding the fatigue strength when employed in the healthy bone.

The results of this study indicate that the more compliant nature of the porous stem geometries may allow for better load transmission through the proximal humeral bone, better matching the stress distributions of the intact bone and possibly mitigating stress-shielding effects. Importantly, this study also indicates that these porous stems have adequate strength for long-term use, as none were predicted to have catastrophic failure under the physiologically-relevant loads. Although these results are limited to a single boney geometry, it is based on the average shape of 75 shoulders and different bone densities are considered. Future work could leverage the shape model for probabilistic models that could explore the effect of stem porosity across a broader population. The development of these models are instrumental in determining if these structures are a viable solution to combatting orthopaedic implant infections.

The 2021 Australian Orthopaedic Association National Joint Replacement Registry report indicated that total shoulder replacement using both mid head (TMH) length humeral components and reverse arthroplasty (RTSA) had a lower revision rate than stemmed humeral components in anatomical total shoulder arthroplasty (aTSA) - for all prosthesis types and diagnoses. The aim of this study was to assess the impact of component variables in the various primary total arthroplasty alternatives for osteoarthritis in the shoulder.

Data from a large national arthroplasty registry were analysed for the period April 2004 to December 2020. The study population included all primary aTSA, RTSA, and TMH shoulder arthroplasty procedures undertaken for osteoarthritis (OA) using either cross-linked polyethylene (XLPE) or non-cross-linked polyethylene (non XLPE). Due to the previously documented and reported higher revision rate compared to other anatomical total shoulder replacement options, those using a cementless metal backed glenoid components were excluded. The rate of revision was determined by Kaplan-Meir estimates, with comparisons by Cox proportional hazard models. Reasons for revision were also assessed.

For a primary diagnosis of OA, aTSA with a cemented XLPE glenoid component had the lowest revision rate with a 12-year cumulative revision rate of 4.7%, compared to aTSA with cemented non-XLPE glenoid component of 8.7%, and RTSA of 6.8%. The revision rate for TMH was lower than aTSA with cemented non-XLPE, but was similar to the other implants at the same length of follow-up. The reason for revision for cemented aTSR was most commonly component loosening, not rotator cuff deficiency.

Long stem humeral components matched with XLPE in aTSA achieve a lower revision rate compared to shorter stems, long stems with conventional polyethylene, and RTSA when used to treat shoulder OA. In all these cohorts, loosening, not rotator cuff failure was the most common diagnosis for revision.

This study used model-based radiostereometric analysis (MBRSA) to compare migration of a recently introduced cementless hip stem to an established hip stem of similar design. Novel design features of the newer hip stem included a greater thickness of hydroxyapatite coating and a blended compaction extraction femoral broach.

Fifty-seven patients requiring primary total hip arthroplasty (THA) were enrolled at a single centre. Patients were randomized to receive either an Avenir collarless stem and Trilogy IT cup (ZimmerBiomet) or a Corail collarless stem and Pinnacle cup (DePuy Synthes) via a posterior or lateral approach. Both stems are broach-only femoral bone preparation. RSA beads (Halifax Biomedical) were inserted into the proximal femur during surgery. Patients underwent supine RSA imaging a 6 weeks (baseline), 6, 12, and 24 months following surgery. The primary study outcome was total subsidence of the hip stem from baseline to 24 months as well as progression of subsidence between 12 and 24 months. These values were compared against published migration thresholds for well-performing hip stems (0.5mm). The detection limit, or precision, of MBRSA was calculated based on duplicate examinations taken at baseline. Patient reported outcome measures were collected throughout the study and included the Oxford-12 Hip Score (OHS), EuroQoL EQ-5D-5L, Hip Osteoarthritis Score (HOOS) as well as visual analogue scales (VAS) for thigh pain and satisfaction. Analysis comprised of paired and unpaired t-tests with significance set at p≤0.05.

Forty-eight patients (30 males) were included for analysis; 7 patients received a non-study hip stem intra-operatively, 1 patient suffered a traumatic dislocation within three weeks of surgery, and 1 patient died within 12 months post-surgery. RSA data was obtained for 45 patients as three patients did not receive RSA beads intra-operatively. Our patient cohort had a mean age of 65.9 years (±;7.2) at the time of surgery and body mass index of 30.5 kg/m2 (±;5.2). No statistical difference in total stem migration was found between the Avenir and Corail stems at 12 months (p=0.045, 95%CI: −0.046 to 0.088) and 24 months (p=0.936, 95% CI: −0.098 to 0.090). Progression of subsidence from 12-24 months was 0.011mm and 0.034mm for the Avenir and Corail groups which were not statistically different (p=0.163, 95%CI: −0.100 to 0.008) between groups and significantly less than the 0.5mm threshold (pNo statistically significant differences existed between study groups for any pre-operative function scores (p>0.05). All patients showed significant functional improvement from pre- to post-surgery and no outcome measures were different between study groups with exception of EQ-5D-5L health visual analogue scale at 12 months which showed marginally superior (p=0.036) scores in the Avenir group. This study was not powered to detect differences in clinical outcomes.

This study has demonstrated no statistical difference in subsidence or patient-reported outcomes between the Corail hip stem and the more recently introduced Avenir hip stem. This result is predictable as both stems are of a triple-tapered design, are coated with hydroxyapatite, and utilize a broach-only bone preparation technique. Both stem designs demonstrate migration below 0.5mm suggesting both are low-risk for aseptic loosening in the long-term.

ZrN-multilayer coating is clinically well established in total knee arthroplasty [1-3] and has demonstrated significant reduction in polyethylene wear and metal ion release [4,5].

The goal of our study was to analyze the biotribological behaviour of the ZrN-multilayer coating on a polished cobalt-chromium cemented hip stem.

CoCr28Mo6 alloy hip stems with ZrN-multilayer coating (CoreHip®AS) were tested versus an un-coated version. In a worst-case-scenario the stems with ceramic heads have been tested in bovine serum in a severe cement interface debonding condition under a cyclic load of 3,875 N for 15 million cycles. After 1, 3, 5, 10 & 15 million cycles the surface texture was analysed by scanning-electron-microscopy (SEM) and energy-dispersive x-ray (EDX). Metal ion concentration of Co,Cr,Mo was measured by inductively coupled plasma mass spectroscopy (ICP-MS) after each test interval.

Based on SEM/EDX analysis, it has been demonstrated that the ZrN-multilayer coating keeps his integrity over 15 million cycles of severe stem cemented interface debonding without any exposure of the CoCr28Mo6 substrate.

The ZrN-multilayer coated polished cobalt-chromium cemented hip stem has shown a reduction of Co & Cr metal ion release by two orders of a magnitude, even under severe stem debonding and high interface micro-motion conditions.

ZrN-multilayer coating on polished cobalt-chromium cemented hip stems might be a suitable option for further minimisation of Co & Cr metal ion release in total hip arthroplasty. Clinical evidence has to be proven during the next years.

Increasing femoral offset in total hip replacement (THR) has several benefits including improved hip abductor strength and enhanced range of motion. Biomechanical studies have suggested that this may negatively impact on stem stability. However, it is unclear whether this has a clinical impact. Using data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), the aim of this study was to determine the impact of stem offset and stem size for the three most common cementless THR prostheses revised for aseptic loosening.

The study period was September 1999 to December 2020. The study population included all primary procedures for osteoarthritis with a cementless THR using the Corail, Quadra-H and Polarstem. Procedures were divided into small and large stem sizes and by standard and high stem offset for each stem system. Hazard ratios (HR) from Cox proportional hazards models, adjusting for age and gender, were performed to compare revision for aseptic loosening for offset and stem size for each of the three femoral stems.

There were 55,194 Corail stems, 13,642 Quadra-H stem, and 13,736 Polarstem prostheses included in this study. For the Corail stem, offset had an impact only when small stems were used (sizes 8-11). Revision for aseptic loosening was increased for the high offset stem (HR=1.90;95% CI 1.53–2.37;p<0.001).

There was also a higher revision risk for aseptic loosening for high offset small size Quadra-H stems (sizes 0-3). Similar to the Corail stem, offset did not impact on the revision risk for larger stems (Corail sizes 12-20, Quadra-H sizes 4-7). The Polarstem did not show any difference in aseptic loosening revision risk when high and standard offset stems were compared, and this was irrespective of stem size.

High offset may be associated with increased revision for aseptic loosening, but this is both stem size and prosthesis specific.