Aims. The main advantage of 3D-printed, off-the-shelf acetabular implants is the potential to promote enhanced bony fixation due to their controllable porous structure. In this study we investigated the extent of osseointegration in retrieved 3D-printed acetabular implants. Methods. We compared two groups, one made via 3D-printing (n = 7) and the other using conventional techniques (n = 7). We collected implant details, type of surgery and removal technique, patient demographics, and clinical history. Bone integration was assessed by macroscopic visual analysis, followed by sectioning to allow undecalcified histology on eight sections (~200 µm) for each implant. The outcome measures considered were area of bone attachment (%), extent of bone ingrowth (%), bone-implant contact (%), and depth of ingrowth (%), and these were quantified using a line-intercept method. Results. The two groups were matched for patient sex, age (61 and 63 years), time to revision (30 and 41 months), implant size (54 mm and 52 mm), and porosity (72% and 60%) (p > 0.152). There was no difference in visual bony attachment (p = 0.209). Histological analysis showed greater bone ingrowth in 3D-printed implants (p < 0.001), with mean bone attachment of 63% (SD 28%) and 37% (SD 20%), respectively. This was observed for all the outcome measures. Conclusion. This was the first study to investigate osseointegration in retrieved 3D-printed acetabular implants. Greater bone ingrowth was found in 3D-printed implants, suggesting that better osseointegration can be achieved. However, the influence of specific surgeon, implant, and patient factors needs to be considered. Cite this article: Bone Joint Res 2021;10(7):388–400

Aims. Aseptic loosening is a leading cause of uncemented arthroplasty failure, often accompanied by fibrotic tissue at the bone-implant interface. A biological target, neutrophil extracellular traps (NETs), was investigated as a crucial connection between the innate immune system’s response to injury, fibrotic tissue development, and proper bone healing. Prevalence of NETs in peri-implant fibrotic tissue from aseptic loosening patients was assessed. A murine model of osseointegration failure was used to test the hypothesis that inhibition (through Pad4-/- mice that display defects in peptidyl arginine deiminase 4 (PAD4), an essential protein required for NETs) or resolution (via DNase 1 treatment, an enzyme that degrades the cytotoxic DNA matrix) of NETs can prevent osseointegration failure and formation of peri-implant fibrotic tissue. Methods. Patient peri-implant fibrotic tissue was analyzed for NETs biomarkers. To enhance osseointegration in loose implant conditions, an innate immune system pathway (NETs) was either inhibited (Pad4-/- mice) or resolved with a pharmacological agent (DNase 1) in a murine model of osseointegration failure. Results. NETs biomarkers were identified in peri-implant fibrotic tissue collected from aseptic loosening patients and at the bone-implant interface in a murine model of osseointegration failure. Inhibition (Pad4-/-) or resolution (DNase 1) of NETs improved osseointegration and reduced fibrotic tissue despite loose implant conditions in mice. Conclusion. This study identifies a biological target (NETs) for potential noninvasive treatments of aseptic loosening by discovering a novel connection between the innate immune system and post-injury bone remodelling caused by implant loosening. By inhibiting or resolving NETs in an osseointegration failure murine model, fibrotic tissue encapsulation around an implant is reduced and osseointegration is enhanced, despite loose implant conditions. Cite this article: Bone Joint J 2021;103-B(7 Supple B):135–144

Introduction. Patients with aseptic loosening, a cause of failure in uncemented total joint arthroplasty (TJA), often present with fibrous tissue at the bone-implant interface. 1. In this study, we characterize the presence of neutrophil extracellular traps (NETs) in the intramedullary fibrotic membrane of aseptic loosening patients. We further explore the role of NETs, mediated by peptidyl arginine deiminase (PAD4), in peri-implant fibrosis and osseointegration failure through a murine model of unstable tibial implantation. 2–4. Methods. Peri-implant membrane was retrieved from five patients during total hip revision surgery and analyzed for the presence of NETs (citH3+ with extracellular DNA) via immunofluorescence. A Ti-6Al-4V implant was inserted in an oversized drill-hole in the right proximal tibia of 8-week-old C57BL/6J and PAD4 knockout mice (n=3 per group). Fourteen days later, all mice were euthanized, and implanted tibias were dissected. Fibrosis and osseointegration at the bone-implant interface were assessed by micro-computed tomography (microCT) and hematoxylin and eosin (H&E) staining. H&E samples were scored blindly by the investigator and another observer for signs of poor (score=0) to excellent osseointegration (score=3) using a rubric established in our lab. Results. NETs were found in peri-implant membrane collected from aseptic loosening patients (Figure 1a) and at the bone-implant interface in a murine model (Figure 1b). Unstable implants in wild type mice failed to osseointegrate, indicated by presence of fibroblast-like cells (dashed arrow), immature bone matrix (Figure 1c), low bone volume fraction (BV/TV) and bone surface area (BS) (Figure 1e). Unstable implants in PAD4. −/−. mice showed signs of good osseointegration such as mature trabeculae (solid arrow) (Figure 1d), higher BV/TV (p<0.10) and BS (p<0.05) (Figure 1f). Histological osseointegration scoring indicated wildtype mice exhibited an average score of 0.83 and PAD4. −/−. exhibited an average score of 2.5 (p<0.05, weighted Cohen's kappa = 0.714) (Figure 1g). Conclusion. NETs were characterized in fibrotic tissue in both aseptic loosening patients and in a murine model of unstable tibial implantation. NET inhibition was able to successfully prevent peri-implant fibrosis and osseointegration failure, leading the way for a potential novel non-invasive therapeutic approach for the treatment of aseptic loosening. For any figures, tables, or references, please contact the authors directly

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. Methods. A retrospective review was conducted of all patients who underwent revision THA (rTHA) for periprosthetic UCS B2 and B3 periprosthetic fracture who received a single design monoblock fluted tapered titanium stem at two large, tertiary care, academic hospitals. A total of 72 patients met inclusion and exclusion criteria (68 UCS B2, and four UCS B3 fractures). Primary outcomes of interest were radiological stem subsidence (> 5 mm), radiological osseointegration, and fracture union. Sub-analysis was also done for 46 patients with minimum one-year follow-up. Results. For the total cohort, stem osseointegration, fracture union, and stem subsidence were 98.6%, 98.6%, and 6.9%, respectively, at latest follow-up (mean follow-up 27.0 months (SD 22.4)). For patients with minimum one-year of follow-up, stem osseointegration, fracture union, and stem subsidence were 97.8%, 97.8%, and 6.5%, respectively. Conclusion. Monoblock fluted stems can be an acceptable modality for the management of UCS B2 periprosthetic fractures in rTHAs due to high rates of stem osseointegration and survival, and the low rates of stem subsidence, and revision. Further research on the use of this stem for UCS B3 periprosthetic fractures is warranted to determine if the same conclusion can be made for this fracture pattern. Cite this article: Bone Jt Open 2023;4(8):551–558

Introduction. Modularity in femoral stem designs allow surgeons to independently control leg length, offset, and femoral version in revision or complex primary THA cases. Initial enthusiasm in these modular stems has been tempered by recognition of modular junction failures. This study evaluates mean 5-year clinical results and survival rates of a 3-part titanium alloy modular femoral implant with unique taper geometries and a metaphyseal plasma spray surface. The current results are presented after pre-market independent fatigue testing performed by Orthopaedic Laboratory (Greenwald) and previously published early clinical results in 2006. Low plasticity burnishing (LPB) was added in 2005 to further strengthen the neck metaphyseal modular junction. The modular stem component is a polished cylindrical splined clothespin design. Our hypothesis is that these unique modular junctions succeed in offering the advantages of modularity without failure at this midterm follow-up period. Methods. Between May 2010 and July 2016, 32 total hip arthroplasties were performed using a 3-part femoral stem with neck-metaphyseal-stem modular junctions. Surgeries were either the final stage of a two-stage revision for infection, revision THR for loosening, or a revision of a previous non-prosthetic replacement procedure. Patients were entered into an IRB-approved registry and followed with x-rays, HHS, Oxford scores, and patient satisfaction scores. Patients who failed to return for routine follow-up were contacted by phone or email. Two patients had died with their implants intact. Six patients could not be reached for an updated follow-up. One stem was revised for loosening at 33 months due to failed osseointegration in a patient with chronic renal failure. This removed stem was submitted for taper exam and sectioning. Results. There were 23 patients for evaluation at a mean 61 months (range 21–98). Mean patient age at implantation was 56 (range 25–88), BMI was 27 (range 20–40). There were no modular junction failures. Modular junctions examined in the retrieved implant did not demonstrate any abnormalities other than normal wear properties. HHS and OHS scores both improved between pre-op and final follow-up, 23 to 85 and 17 to 43, respectively. Average patient satisfaction score at final follow-up was 9.8 out of 10 (min 8, max 10). Radiographic examination showed stem subsidence > 2mm and radiolucencies around the metaphyseal cone in 1 patient, the same patient who required implant removal. Radiolucencies were seen along the polished stem tip in 43% of cases, spot welding at the distal metaphyseal cone in 67% of cases, and mild proximal-medial stress shielding in 33% of cases. Conclusion. This unique 3-part modular stem with metaphyseal fixation shows good functional and radiographic results at 5-year follow-up. There were no junctional failures. One stem was removed due to failure to osseointegrate and showed no worrisome taper abnormalities. Spot welding is common around the plasma spray metaphyseal cone. Implant removal, if necessary, only requires disruption of the metaphyseal fixation. Further follow-up will be important to confirm our confidence in this unique stem design

Aims. Pelvic discontinuity is a rare but increasingly common complication of total hip arthroplasty (THA). This single-centre study evaluated the performance of custom-made triflange acetabular components in acetabular reconstruction with pelvic discontinuity by determining: 1) revision and overall implant survival rates; 2) discontinuity healing rate; and 3) Harris Hip Score (HHS). Methods. Retrospectively collected data of 38 patients (39 hips) with pelvic discontinuity treated with revision THA using a custom-made triflange acetabular component were analyzed. Minimum follow-up was two years (mean 5.1 years (2 to 11)). Results. There were eight subsequent surgical interventions. Two failures (5%) of the triflange acetabular components were both revised because of deep infection. There were seven (18%) patients with dislocation, and five (13%) of these were treated with a constraint liner. One patient had a debridement, antibiotics, and implant retention (DAIR) procedure. In 34 (92%) hips the custom-made triflange component was considered stable, with a healed pelvic discontinuity with no aseptic loosening at midterm follow-up. Mean HHS was 80.5 (48 to 96). Conclusion. The performance of the custom triflange implant in this study is encouraging, with high rates of discontinuity healing and osteointegration of the acetabular implant with no aseptic loosening at midterm follow-up. However, complications are not uncommon, particularly instability which we successfully addressed with constrained liners. Cite this article: Bone Jt Open 2022;3(11):867–876

Aims. BoneMaster is a thin electrochemically applied hydroxyapatite (HA) coating for orthopaedic implants that is quickly resorbed during osseointegration. Early stabilization is a surrogacy marker of good survival of femoral stems. The hypothesis of this study was that a BoneMaster coating yields a fast early and lasting fixation of stems. Methods. A total of 53 patients were randomized to be treated using Bi-Metric cementless femoral stems with either only a porous titanium plasma-sprayed coating (P group) or a porous titanium plasma-sprayed coating with an additional BoneMaster coating (PBM group). The patients were examined with radiostereometry until five years after surgery. Results. At three months, the mean total translation (TT) was 0.95 mm (95% confidence interval (CI) 0.68 to 1.22) in the P group and 0.57 mm (95% CI 0.31 to 0.83) in the PBM group (p = 0.047). From two to five years, the TT increased by a mean of 0.14 mm (95% CI 0.03 to 0.25) more in the P group than in the PBM group (p = 0.021). In osteopenic patients (n = 20), the mean TT after three months was 1.61 mm (95% CI 1.03 to 2.20) in the P group and 0.73 mm (95% CI 0.25 to 1.21) in the PBM group (p = 0.023). After 60 months, the mean TT in osteopenic patients was 1.87 mm (95% CI 1.24 to 2.50) in the P group and 0.82 mm (95% CI 0.30 to 1.33) in the PBM group (p = 0.011). Conclusion. There was less early and midterm migration of cementless stems with BoneMaster coating compared with those with only a porous titanium plasma-sprayed coating. Although a BoneMaster coating seems to be important for stem fixation, especially in osteopenic patients, further research is warranted. Cite this article: Bone Joint J 2022;104-B(6):647–656

Aims. Uncemented metal acetabular components show good osseointegration, but material stiffness causes stress shielding and retroacetabular bone loss. Cemented monoblock polyethylene components load more physiologically; however, the cement bone interface can suffer fibrous encapsulation and loosening. It was hypothesized that an uncemented titanium-sintered monoblock polyethylene component may offer the optimum combination of osseointegration and anatomical loading. Methods. A total of 38 patients were prospectively enrolled and received an uncemented monoblock polyethylene acetabular (pressfit) component. This single cohort was then retrospectively compared with previously reported randomized cohorts of cemented monoblock (cemented) and trabecular metal (trabecular) acetabular implants. The primary outcome measure was periprosthetic bone density using dual-energy x-ray absorptiometry over two years. Secondary outcomes included radiological and clinical analysis. Results. Although there were differences in the number of males and females in each group, no significant sex bias was noted (p = 0.080). Furthermore, there was no significant difference in age (p = 0.910) or baseline lumbar bone mineral density (BMD) (p = 0.998) found between any of the groups (pressfit, cemented, or trabecular). The pressfit implant initially behaved like the trabecular component with an immediate fall in BMD in the inferior and medial regions, with preserved BMD laterally, suggesting lateral rim loading. However, the pressfit component subsequently showed a reversal in BMD medially with recovery back towards baseline, and a continued rise in lateral BMD. This would suggest that the pressfit component begins to reload the medial bone over time, more akin to the cemented component. Analysis of postoperative radiographs revealed no pressfit component subsidence or movement up to two years postoperatively (100% interobserver reliability). Medial defects seen immediately postoperatively in five cases had completely resolved by two years in four patients. Conclusion. Initially, the uncemented monoblock component behaved similarly to the rigid trabecular metal component with lateral rim loading; however, over two years this changed to more closely resemble the loading pattern of a cemented polyethylene component with increasing medial pelvic loading. This indicates that the uncemented monoblock acetabular component may result in optimized fixation and preservation of retroacetabular bone stock. Cite this article: Bone Joint J 2021;103-B(5):872–880

To evaluate the effects of 6 and 18 months of abaloparatide (ABL) compared with placebo (PBO) on bone mineral density (BMD) in the acetabular regions of postmenopausal women with osteoporosis (OP). Acetabular bone loss, as may occur in OP, increases risk of acetabular fragility fractures. a. In total hip arthroplasty (THA), low acetabular BMD adversely affects primary stability, osseointegration, and migration of acetabular cups. c. ABL is an osteoanabolic agent for the treatment of men and postmenopausal women with OP at high risk for fracture. Effects of ABL on acetabular BMD are unknown. Hip DXA scans were obtained at baseline, 6, and 18 months from a random subgroup of postmenopausal women (aged 49–86 y) from the phase 3 ACTIVE trial randomized to either ABL 80 µg/d or PBO (n=250/group). Anatomical landmarks were identified in each DXA scan to virtually place a hemispherical shell model of an acetabular cup and define regions of interest corresponding to DeLee & Charnley zones 1 (R1), 2 (R2), and 3 (R3). BMD changes compared to baseline were calculated for each zone. Statistical P values were based on a repeated mixed measures model. BMD in all zones were similar at baseline in the ABL and PBO groups. BMD significantly increased in the ABL group at 6 and 18 months compared with PBO (all P<0.0001 vs PBO). BMD in the PBO group was relatively stable over time. ABL treatment resulted in rapid and progressive increases in BMD of all 3 acetabular zones. Increasing acetabular BMD has the potential to improve acetabular strength, which may reduce risk of acetabular fragility fractures. In bone health optimization prior to THA, increased acetabular BMD via ABL may provide better primary stability and longevity of acetabular cups in postmenopausal women with OP

Subsidence remains a concern when utilizing modern tapered fluted titanium (TFT) femoral stems and may lead to leg length discrepancy, impingement, instability and failure to obtain stem osseointegration. This study aims to compare stem subsidence across three modern TFT stems. Our secondary aim was to investigate the influence of bicortical contact or ‘scratch fit’ on subsidence, as well as the role of intraoperative imaging in maximizing this bicortical contact and preventing stem subsidence. A retrospective review of 271 hip arthroplasties utilizing modern TFT stems in a single institution was performed. Three stem designs were included in the analysis: one monoblock TFT stem (n=91) and two modular TFT stems (Modular A [n=90]; Modular B [n=90]). Patient demographics, Paprosky femoral bone loss classification, bi-cortical contact, utilization of intra-operative imaging and stem subsidence (comparison of initial post-operative radiograph to the latest follow up radiograph - minimum three months) were recorded. There was no statistically significant difference in the amount of subsidence between the three stems (Monoblock: 2.33mm, Modular A: 3.43mm, Modular B: 3.02mm; p=0.191). There was no statistical difference in subsidence >5mm between stems (Monoblock: 9.9%, Modular A: 22.2%, Modular B: 16.7%). Subgroup analysis based on femoral bone loss grading showed no difference in subsidence between stems. Increased bicortical contact was strongly associated with reduced subsidence (p=0.004). Intra-operative imaging was used in 46.5% (126/271) of cases; this was not correlated with bicortical contact (p=0.673) or subsidence (p=0.521). Across all groups, only two stems were revised for subsidence (0.7%). All three modern TFT stems were highly successful and associated with low rates of subsidence, regardless of modular or monoblock design. Surgeons should select the stem that they feel is most clinically appropriate

Different techniques have been described to address massive bone loss of the acetabulum in revision hip surgery. aMace has gained popularity as it provides customization aiming to restore hip centre and provide good initial stability in cases of large non-contained defects. It takes into account quality of host bone. Its porous defect filling scaffold provides an excellent surface for osteointegration. Our aim was to assess the short and mid-term outcomes of patients who underwent revision surgery using aMace system. Ethical approval was obtained. A retrospective study included all patients who had aMace between June 2013 and October 2022 allowing for a minimum of 12-months follow-up. Patients’ demographics, indication, bone-loss severity, reconstruction details, re-operation, complications, mortality, pain and function were assessed. 52 cases were performed by 13 surgeons with median 51 months follow-up. Median age was 72.7 years. 86.5% were female. Average BMI was 25.3. Average ASA grade was 3. 65% were classified as Paprosky IIIB and 32% were IIIA. 73% were found to have poor bone quality on CT. Main indication for aMace was massive bone loss/discontinuity secondary to aseptic loosening in 88.5%. 77% underwent single-stage revision. 53.8% had 2 or more previous revisions. 71% underwent stem revision in the same setting. 77% received a dual mobility bearing. Re-operation rate was 5.7% for instability and femoral PPF. LLD was reported in 9.6%. Permanent Sciatic nerve palsy occurred in 3.8% of the cases. 30-days mortality was 1.9%. Statistically significant post-op improvements in pain and mobility were reported (p<0.001). None of the acetabular components have been revised. Our study shows satisfactory surgical outcomes with a relatively low complication rate and significant pain and mobility improvements in the early to mid-term stages. We recommend these costly cases to be done in highly specialist centres adopting MDT approach

3D printing acetabular cups offers the theoretical advantage of enhanced bony fixation due to greater design control of the porous implant surfaces. Analysing retrieved 3D printed implants can help determine whether this design intent has been achieved. We sectioned 14 off-the-shelf retrieved acetabular cups for histological analysis; 7 cups had been 3D printed and 7 had been conventionally manufactured. Some of the most commonly used contemporary designs were represented in both groups, which were removed due to either aseptic loosening, unexplained pain, infection or dislocation. Clinical data was collected for all implants, including their age, gender, and time to revision. Bone ingrowth was evaluated using microscopic assessment and two primary outcome measures: 1) bone area fraction and 2) extent of bone ingrowth. The additively manufactured cups were revised after a median (IQR) time of 24.9 months (20.5 to 45.6) from patients with a median (IQR) age of 61.1 years (48.4 to 71.9), while the conventional cups had a median (IQR) time to revision of 46.3 months (34.7 to 49.1, p = 0.366) and had been retrieved from patients with a median age of 66.0 years (56.9 to 68.9, p = 0.999). The additively and conventionally manufactured implants had a median (IQR) bone area fraction of 65.7% (36.4 to 90.6) and 33.9% (21.9 to 50.0), respectively (p < 0.001). A significantly greater amount of bone ingrowth was measured into the backside of the additively manufactured acetabular cups, compared to their conventional counterparts (p < 0.001). Bone occupied a median of 60.0% and 5.7% of the porous depth in the additively manufactured and conventional cups, respectively. 3D printed components were found to achieve a greater amount of bone ingrowth than their conventionally manufactured counterparts, suggesting that the complex porous structures generated through this manufacturing technique may encourage greater osteointegration

Aims. The diversity of femoral morphology renders femoral component sizing in total hip arthroplasty (THA) challenging. We aimed to determine whether femoral morphology and femoral component filling influence early clinical and radiological outcomes following THA using fully hydroxyapatite (HA)-coated femoral components. Methods. We retrospectively reviewed records of 183 primary uncemented THAs. Femoral morphology, including Dorr classification, canal bone ratio (CBR), canal flare index (CFI), and canal-calcar ratio (CCR), were calculated on preoperative radiographs. The canal fill ratio (CFR) was calculated at different levels relative to the lesser trochanter (LT) using immediate postoperative radiographs: P1, 2 cm above LT; P2, at LT; P3, 2 cm below LT; and D1, 7 cm below LT. At two years, radiological femoral component osseointegration was evaluated using the Engh score, and hip function using the Postel Merle d’Aubigné (PMA) and Oxford Hip Score (OHS). Results. CFR was moderately correlated with CCR at P1 (r = 0.44; p < 0.001), P2 (r = 0.53; p < 0.001), and CFI at P1 (r = − 0.56; p < 0.001). Absence of spot welds (n = 3, 2%) was associated with lower CCR (p = 0.049), greater CFI (p = 0.017), and lower CFR at P3 (p = 0.015). Migration (n = 9, 7%) was associated with lower CFR at P2 (p = 0.028) and P3 (p = 0.007). Varus malalignment (n = 7, 5%), predominantly in Dorr A femurs (p = 0.028), was associated with lower CFR at all levels (p < 0.05). Absence of spot welds was associated with lower PMA gait (p = 0.012) and migration with worse OHS (p = 0.032). Conclusion. This study revealed that femurs with insufficient proximal filling tend to have less favourable radiological outcomes following uncemented THA using a fully HA-coated double-tapered femoral component. Cite this article: Bone Joint Res. 2020;9(4):182–191

Introduction. Pelvic discontinuity is a challenging complication. One treatment option that has garnered enthusiasm is acetabular distraction. This method obtains stability via distraction of the discontinuity and placement of an oversized socket (± augments) and elastic recoil of the pelvis. The aims of this study were to report implant survivorship, radiographic results, clinical outcomes, and complications of acetabular distraction for pelvic discontinuity in the largest series to date. Methods. We retrospectively identified all revision THAs with a Paprosky 3B defect and pelvic discontinuity between 2005 and 2017. Of the 162 patients, 32 were treated with distraction. The mean distraction achieved was 5mm (range, 3–8mm). In addition to distraction with a hemispherical cup, augments were utilized in 3 and cages in 19. The mean age at revision was 68 years with 75% female. Mean follow-up was 3 years. Results. The 2-year survivorships free from revision for aseptic loosening, revision, and reoperation were 95%, 75%, and 69%, respectively. There were 3 revisions including one for instability, one for infection, and one for aseptic loosening. At last follow-up, 16 patients had radiographic evidence of cup osteointegration to ilium and ischium, 13 to ilium only, and 3 without evidence of osteointegration (two distracted 3mm and one distracted 6mm). 19 discontinuity lines persisted while 13 had radiographically healed. Only those with osteointegration to both ilium and ischium had evidence of bone graft consolidation and discontinuity line healing. Mean HHS improved from 43 preoperatively to 77 postoperatively (p<0.0001). The most common complication was a postoperative sciatic nerve plasy in 4 patients (13%) of which 3 partially recovered. Conclusion. Pelvic discontinuities treated with acetabular distraction had a 2-year survivorship free from aseptic looseing of 95%. While nearly 2/3. rd. of discontinuity lines persisted, 91% of patients had radiographic evidence of osteointegration of the acetabular component. However, 13% of patients had a sciatic nerve palsy. For any tables or figures, please contact the authors directly

Introduction. As new innovations are developed to improve the longevity of joint replacement components, preclinical testing is necessary in the early stages of research into areas such as osseointegration, metal-cartilage wear and periprosthetic joint infection (PJI). Large-animal studies that test load-bearing components are expensive, however, requiring that animals be housed in special facilities that are not available at all institutions. Comparably, small animal models, such as the rat, offer several advantages including lower cost. Load-bearing implants remain difficult to manufacture via traditional methods in the sizes required for small-animal testing. Recent advances in additive manufacturing (3D metal-printing) have allowed for the creation of miniature joint replacement components in a variety of medical-grade metal alloys. The objective of this work is to create and optimize an image-based 3D-printed rat hip implant system that will allow in vivo testing of functional implant properties in a rat model. Methods. A database of n=25 previously-acquired, 154μm micro-CT volumes (eXplore Locus Ultra, GE Medical) of male Sprague-Dawley rats (390–610g) were analyzed to obtain spatial and angular relationships between several anatomical features of the proximal rat femora. Mean measurements were used to guide the creation of a femoral implant template in computer-aided design software (Solidworks, Dassault Systemes). Several different variations were created, including collarless and collared designs, in a range of sizes to accommodate rats of various weights. Initial prototypes were 3D-printed 316L stainless steel with subsequent iterations printed in Ti6Al4V titanium and F75 cobalt-chrome. Implants were post-processed via sandblasting, hand-polishing, ultrasonic bath, and sterilization in an autoclave. Innate surface texturing was left on manufactured stems to promote osseointegration. Surgical implantation was performed in three live Sprague-Dawley rats (900g, 500g, 750g) with preservation of muscle attachments to the greater trochanter. Micro-CT imaging and X-ray fluoroscopy were performed post-operatively on each animal at 1 day, and 1, 3, 9 and 12 weeks to evaluate gait and component positioning. Results. Implantation of components was successful and each animal was observed to ambulate on its affected limb immediately following recovery from surgery. The 900g rat, given a collarless 316L stainless steel component, was kept for 11 months post-implantation before succumbing to old age. Micro-CT and fluoroscopic findings revealed no evidence of implant subsidence. The 500g animal, given a collarless 316L stainless steel implant, showed evidence of implant subsidence at 3 weeks, with full subsidence and hip dislocation at 12 weeks. The 750g rat, given a collared F75 cobalt-chrome implant, was observed ambulating on its affected limb, but experienced implant rotation and failure at 9 weeks. Conclusions. We report the first hip hemi-arthroplasty in a rat using a 3D-printed metal implant. This model aims to provide a low-cost platform for studying osseointegration, metal-cartilage interactions, and PJI using a functional, loaded implant. Efforts to further optimize the surgical approach will be made to reduce early implant loosening. A study with larger sample sizes is needed to determine if implants can be installed repeatedly, without complications, before the utility of this approach can be validated. Future work will include surface preparations on implant stems, with micro-CT to longitudinally track changes at the bone-metal interface, and gait analysis on a radiolucent treadmill to quantify post-operative kinematics

Bone ingrowth is desired with uncemented hip implants. Infection is clearly undesirable. We have worked on developing a nanofiber coating for implants that would enhance bone formation while inhibiting infection. Few studies have focused on developing an implant surface nanofiber (NF) coating to prevent infection and enhance osseointegration by local drug release. In this study, coaxial doxycycline (Doxy)-doped polycaprolactone/polyvinyl alcohol (PCL/PVA) Nanofibers were directly deposited on the titanium (Ti) implant surface during electrospinning. The interaction of loaded Doxy with both PVA and PCL NFs was characterized by Raman spectroscopy. The bonding strength of Doxy-doped NF coating on Ti implants was confirmed by a stand single-pass scratch test. The improved implant osseointegration by PCL/PVA NF coatings in vivo was confirmed by scanning electron microscopy, histomorphometry and micro computed tomography at 2, 4 and 8 weeks after implantation. The bone contact surface (%) changes of NF coating group (80%) is significantly higher than that of no NF group (< 5%, p<0.05). Finally, we demonstrated that Doxy-doped NF coating effectively inhibited bacterial infection and enhanced osseointegration in an infected (Staphylococcus aureus) tibia implantation rat model. Doxy released from NF coating inhibited bacterial growth up to 8 weeks in vivo. The maximal push-in force of Doxy-NF coating (38 N) is much higher than that of NF coating group (6.5 N) 8 weeks after implantation (p<0.05), which was further confirmed by quantitative histological analysis and micro computed tomography. These findings indicate that coaxial PCL/PVA NF coating doped with Doxy and/or other drugs have great potential in enhancing implant osseointegration and preventing infection

Background. The acknowledged benefit of the direct anterior (DA) approach is early functional return. Most surgeons in the U.S. use cementless femoral replacement given the negative track record of some cemented designs. However, delayed osseointegration of a femoral stem typically seen in older patients with poor bone quality will delay recovery, diminishing the benefits of the DA approach. Registry studies have shown a higher revision rate and complications in this patient population leading to a renewed interest in cemented fixation. Questions posed. To achieve the functional benefits of the DA approach and the fixation benefits of cemented replacement, this study combined the 2 techniques posing the following questions:1) Does the limited access of the DA approach adversely affect the cement technique? 2) Does such a cementing technique reduce the incidence of cementless complications?. Methods. A consecutive series of 341 patients (360 hips) receiving the DA approach between 2016–2018 were reviewed. There were 203 cementless stems and 157 cemented stems. Mean age was 75 in the cementless group and 76 in the cemented group, 70% females. Femoral complications were compared between the 2 groups using the T-test. Results. The cementless group had a higher rate of femoral complications (8 versus 0, P=0.011). There were 2 loose stems and 6 fractures, all requiring revision. Fractures occurred about 14.5 days and loosening about 10 months postoperatively. Conclusion. A higher rate of complications occurred with cementless stems. Cemented stems are protective in patients above 70 and can be safely done through the DA approach

Introduction. Patients undergoing primary total hip arthroplasty (THA) following pelvic radiation have historically had poor survivorship free of aseptic acetabular component loosening. However, several series have reported improved results with tantalum acetabular components. The purpose of this study was to assess implant survivorship, radiographic results, and clinical outcomes of contemporary, non-tantalum, porous acetabular components in the setting of prior pelvic radiation. Methods. We retrospectively reviewed 33 patients (38 hips) with prior therapeutic pelvic radiation between 2006 and 2016 who underwent primary THA. The mean overall pelvic radiation dose was 6300 cGy with a mean latency period to THA of 5 years. The most common acetabular component was Pinnacle (Depuy-Synthes) in 76%, followed by Trident (Stryker) in 8%, Tritanium (Stryker) in 8%, Trilogy (Zimmer-Biomet) in 5%, and G7 (Zimmer-Biomet) in 3%. Eighty-seven percent of cups were fixed with screws, of which the mean number used was 3. The mean age at primary THA was 74 years, 76% were male, and the mean BMI was 30 kg/m. 2. Mean follow-up was 5 years. Results. The 10-year survivorship free of revision for aseptic loosening, free of any revision, and free of any reoperation were 100%, 89%, and 89%, respectively. There were three revisions; one each for taper corrosion, recurrent dislocation, and infection. Radiographically, all cups had evidence of osteointegration and none had radiographic evidence of loosening. The mean Harris hip score improved from 50 to 84 postoperatively (p<0.0001). Conclusion. Contemporary non-tantalum porous acetabular components with supplemental screws provided excellent implant fixation in patients with prior therapeutic pelvic radiation. At 10 years, 100% of these components were free of revision for aseptic loosening and 100% were radiographically well-fixed. Summary. Contemporary non-tantalum porous uncemented acetabular cups provided 100% survivorship free from revision for aseptic loosening for patients undergoing THA following therapeutic pelvic radiation

Reconstruction of massive acetabular bone defects in primary and revision THA is challenging for reconstructive joint surgeons. The use of porous metal augments is one of the options. The advantages of porous metal augments are easy to use, modularity and lack of resorption. We investigated the radiological results of porous metal augments used for massive acetabular bone defects in primary and revision THA. Forty-one hips in forty patients had porous metal augments between 2011 and 2016. Thirty of the procedures were revision arthroplasties and 11 were primary procedures (Crowe type III in 5 hips, Crowe type IV in 3, septic hip sequalae in 2 and RA in one). Four of the revisions were second-stage reimplantation after infection. The Paprosky classification for revision was 2B in 4 hips, 2C in one, 3A in 3 and 3B in 22. Regenerex augments were used in 39 hips and trabecular metal augments were used in 2. Thirty-six cups were cemented and 5 cups were uncemented. Mean follow-up was 37.6 months (range, 1–82). Radiographic findings of osteointegration between host bone and the porous metal augments were assessed. The presence or absence of radiolucent lines between cement or cup/host bone and augment/host bone interface was noted. Two revisions were performed due to infection, one month and 66 months after operation. The other implants were stable without any complications. Osteointegration between host bone and the porous metal augments were recognized in 36 hips. Radiolucent lines between cement/host bone interface, less than 1 mm in width, were visualized in 2 hips. Porous metal augments are convenient and our short-term results showed excellent radiological results for massive acetabular bone defects in primary and revision THA

Revision total hip arthroplasty (THA) is challenging when there is severe loss of bone in the proximal femur. The purpose of this study was to evaluate the clinical and radiographic outcomes of revision THA in patients with severe proximal femoral bone loss treated with a fluted, tapered, modular femoral component. Between January 1998 and December 2004, 92 revision THAs were performed in 92 patients using a single fluted, tapered, modular femoral stem design. Pre-operative diagnoses included aseptic loosening, infection and peri-prosthetic fracture. Bone loss was categorised pre-operatively as Paprosky types III-IV, or Vancouver B3 in patients with a peri-prosthetic fracture. The mean clinical follow-up was 6.4 years (2 to 12). A total of 47 patients had peri-operative complications, 27 of whom required further surgery. However, most of these further operations involved retention of a well-fixed femoral stem, and 88/92 femoral components (97%) remained in situ. Of the four components requiring revision, three were revised for infection and were well fixed at the time of revision; only one (1%) was revised for aseptic loosening. The most common complications were post-operative instability (17 hips, 19%) and intra-operative femoral fracture during insertion of the stem (11 hips, 12%). Diaphyseal stress shielding was noted in 20 hips (22%). There were no fractures of the femoral component. At the final follow-up 78% of patients had minimal or no pain. . Revision THA in patients with extensive proximal femoral bone loss using the Link MP fluted, tapered, modular stem led to a high rate of osseointegration of the stem at mid-term follow-up. Cite this article: Bone Joint J 2015; 97-B:312–17