The lifetime risk of revision following total hip arthroplasty

The effect of fixation type on periprosthetic fractures in high-risk patients who have osteoporosis undergoing total joint arthroplasty

Introduction

Minimizing the burden of periprosthetic fractures (PFF) following total joint arthroplasty (TJA) with regard to morbidity and mortality remains an outcome of interest. Patient and surgical risk factors, including osteoporosis and fixation type, have not truly been optimized in patients undergoing TJA as a means to reduce the risk of PFF. As such, we examined: (1) What percentage of patients who underwent THA and total knee arthroplasty (TKA) met the criteria for osteoporosis screening? (2) How did the 5-year rate of PFF and fragility fracture differ in the high-risk and low-risk groups for osteoporosis between the cemented and cementless cohorts? (3) What percentage of the aforementioned patients received a dual x-ray absorptiometry (DEXA) scan before THA or TKA?

Methods

We queried an all-payer, national database from April 1, 2016 to December 31, 2021, to identify high-risk and low-risk patients who underwent TJA with a cementless or cemented fixation. High-risk patients met at least one of the following criteria: men at least 70 years old, women at least 65 years old, or patients at least 60 years old who have the following: tobacco use, alcohol abuse, body mass index <18.5, prior fragility fracture, chronic systemic corticosteroids, or genetic condition affecting sex hormones or bone mineral density. Exclusion criteria were a diagnosis of malignancy, high-energy events (motor vehicle collision), those who underwent TJA indicated for fracture, patients less than 50 years old, those who had a prior diagnosis of or treatment for osteoporosis, and a minimum follow-up of less than 2 years.

Results

There were 384,783 patients (67.1 %) who underwent cementless TKA and 67,774 patients (11.8 %) who underwent cementless TKA who were considered high risk. Additionally, there were 62,505 patients (10.9 %) who underwent cemented THA and 58,667 patients (10.2 %) who underwent cementless THA and were considered high risk. The cementless cohort had a 5-year periprosthetic fracture risk following TKA of 7.8 % (95 % CI, 5.56 to 10.98) in comparison to 4.30 % in the cemented cohort (85 % CI, 3.98 to 4.65), P < 0.0001. The high-risk cementless cohort had a 5-year periprosthetic fracture risk following THA of 7.9 % (95 % confidence interval (CI), 6.87 to 9.19) in comparison to 7.78 % in the cemented cohort (85 % CI, 6.77 to 8.94), P < 0.0001.

Conclusion

There is an increased risk of PFF at 5 years following TKA in patients at high risk for osteoporosis undergoing cementless fixation in comparison to cemented fixation. There is an increased risk of PFF at 5 years following THA in patients at high risk for osteoporosis for both cementless fixation and cemented fixation, but no clinically meaningful difference between the two groups. Addressing the shortcomings of the underutilization of bone density scans and better selecting appropriate patients for TJA based on bone quality and fracture risk can help expedite the process of improving the current state of practice.

Contemporary Aseptic Revision Total Hip Arthroplasty in Patients ≤50 Years of Age: Results of >500 Cases

BACKGROUND

There has been a paucity of long-term outcomes data on aseptic revision total hip arthroplasties (THAs) in the young adult population. The purpose of this study was to evaluate implant survivorship, complications, and clinical outcomes in a large cohort of contemporary aseptic revision THAs in patients ≤50 years of age at the time of the surgical procedure.

METHODS

We identified 545 aseptic revision THAs performed at a single academic institution from 2000 to 2020 in patients who were 18 to 50 years of age. Patients who underwent conversion THAs and patients with a history of any ipsilateral hip infection were excluded. The mean age was 43 years, the mean body mass index (BMI) was 29 kg/m 2 , and 63% were female. The index indication for revision THA was aseptic loosening in 46% of cases, polyethylene wear or osteolysis in 28% of cases (all revisions of conventional polyethylene), and dislocation in 11% of cases. There were 126 hips (23%) that had undergone at least 1 previous revision (median, 1 revision [range, 1 to 5 revisions]). The mean follow-up was 10 years.

RESULTS

In the entire cohort, the 20-year survivorship free of any re-revision was 76% (95% confidence interval [95% CI], 69% to 82%). There were 87 re-revisions, with 31 dislocations, 18 cases of aseptic loosening of the femoral component, and 16 periprosthetic joint infections (PJIs) being the most common reasons for re-revision. Dislocation as the indication for the index revision was associated with an increased risk of re-revision (hazard ratio, 2.9; p < 0.001). The 20-year survivorship free of any reoperation was 73% (95% CI, 66% to 78%). There were 75 nonoperative complications (14%), including 32 dislocations. The mean Harris hip score significantly improved (p < 0.001) from 65 preoperatively to 81 at 10 years postoperatively.

CONCLUSIONS

Contemporary aseptic revision THAs in patients ≤50 years of age demonstrated a re-revision risk of approximately 1 in 4 at 20 years. Dislocation, aseptic loosening of the femoral component, and PJI were the most common reasons for re-revision. Index revision THAs for dislocation had a 3 times higher risk of re-revision.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Mechanobiochemical bone remodelling around an uncemented acetabular component: influence of bone orthotropy

Mechanical loosening of an implant is often caused by bone resorption, owing to stress/strain shielding. Adaptive bone remodelling elucidates the response of bone tissue to alterations in mechanical and biochemical environments. This study aims to propose a novel framework of bone remodelling based on the combined effects of bone orthotropy and mechanobiochemical stimulus. The proposed remodelling framework was employed in the finite element model of an implanted hemipelvis to predict evolutionary changes in bone density and associated orthotropic bone material properties. In order to account for variations in load transfer during common daily activities, several musculoskeletal loading conditions of hip joint corresponding to sitting down/up, stairs ascend/descend and normal walking were considered. The bone remodelling predictions were compared with those of isotropic strain energy density (SED)-based, isotropic mechanobiochemical and orthotropic strain-based bone remodelling formulations. Although similar trends of bone resorption were predicted by orthotropic mechanobiochemical (MBC) and orthotropic strain-based models across implanted acetabulum, more volume (10-20%) of bone elements was subjected to bone resorption for the orthotropic MBC model. Higher bone resorption (75-85%) was predicted by the orthotropic strain-based and orthotropic MBC models compared to the isotropic MBC and SED-based models. Higher bone apposition (35-160%) across the implanted acetabulum was predicted by the isotropic MBC model, compared to the SED-based model. The remodelling predictions indicated that a reduction in estrogen level might lead to an increase in bone resorption. The study highlighted the importance of including mechanobiochemical stimulus and bone anisotropy to predict bone remodelling adequately.

Evidence for cemented TKA and THA based on a comparison of international register data

BACKGROUND

Hip and knee implants can either be fixed without cement, press-fit, or with bone cement. Real-world data from arthroplasty registers, as well as studies provide a broad database for the discussion of cemented versus uncemented arthroplasty procedures.

OBJECTIVE

What does current evidence from international arthroplasty registries and meta-analyses recommend regarding cemented or cementless fixation of hip and knee implants?

METHODS

A recommendation is generated by means of direct data comparison from the arthroplasty registries of eight countries (USA, Germany, Australia, UK, Sweden, Norway, New Zealand, Netherlands), the comparison of 22 review studies and meta-analyses based on registry data, as well as an evaluation of recommendations of healthcare systems from different nations. For this purpose, reviews and meta-analyses were selected where the results were statistically significant, as were the annual reports of the arthroplasty registries that were current at the time of writing.

RESULTS

For knee arthroplasties, long survival time as well as lower risk of revision can be achieved with the support of cemented fixation with antibiotic-loaded bone cement. In patients aged 70 years and older, cemented fixation of hip stem implants significantly reduces risk of intraoperative or postoperative periprosthetic fracture (quadruple). This applies both to elective total hip arthroplasties and to hemiarthroplasty after femoral neck fractures. Antibiotic-loaded bone cement significantly (p = 0.041) reduces the risk of periprosthetic infection, especially in patients with femoral neck fractures.

CONCLUSION

Total knee replacement with antibiotic-loaded bone cement is well established internationally and is evidence-based. Registry data and meta-analyses recommend cemented fixation of the hip stem in older patients. In Germany, USA and Australia these evidence-based recommendations still must be transferred to daily practice.

Evaluation of Proximal Femoral Bone Mineral Density in Cementless Total Hip Arthroplasty: A 3-Arm Prospective Randomized Controlled Trial

BACKGROUND

Femoral stem design affects periprosthetic bone mineral density (BMD), which may impact long-term survival of cementless implants in total hip arthroplasty (THA). The aim of this study was to examine proximal femoral BMD in 3 morphologically different uncemented femoral stem designs to investigate whether any particular design resulted in better preservation of BMD.

METHODS

A total of 119 patients were randomized to receive a proximally coated collarless dual-taper wedge stem, a proximally coated collarless anatomic stem, or a fully coated collarless triple-taper stem. All surgeries were performed via the posterior approach, with mobilization on the day of surgery. Dual x-ray absorptiometry scans (Lunar iDXA, GE Healthcare) assessed BMD across the 7 Gruen zones preoperatively and at 6 weeks and 2 years postoperatively; if available, the native contralateral femur was also assessed as a control. Patient-reported outcomes of pain, function, and health were also assessed at these follow-ups.

RESULTS

Averaged across all stems, BMD increased in zones 1 (2.5%), 2 (17.1%), 3 (13.0%), 5 (10%), and 6 (17.9%) at 2 years. Greater preservation of BMD was measured on the lateral cortex (zone 2) for both the dual-taper wedge and anatomic stems (p = 0.019). The dual-taper wedge stem also demonstrated preservation of BMD in the medial calcar (zone 7), while the anatomic and triple-taper stems declined in this region; however, the difference did not reach significance (p = 0.059). Averaged across all stems, BMD decreased in the mid-diaphysis region, distal to the stem tip (zone 4). All stems performed similarly at the time of final follow-up with respect to the patient-reported outcomes.

CONCLUSIONS

This study demonstrated maintenance of femoral BMD after use of 3 different cementless femoral stem designs, with all achieving excellent improvements in patient-reported outcomes. The stems designed to load the proximal metaphyseal region resulted in higher BMD in that region. No significant stress-shielding was observed; however, longer follow-up is required to elucidate the impact of this finding on implant survivorship.

LEVEL OF EVIDENCE

Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

[Register data on cemented arthroplasty : A proof for cementless fixation?]

BACKGROUND

Hip and knee implants can be either fixated without cement, press-fit, or with bone cement. Real-world data from arthroplasty registers, as well as studies, provide a broad database for the discussion of cemented versus uncemented arthroplasty procedures.

OBJECTIVES

What is the recommendation for cemented or cementless anchorage of hip and knee implants based on the current evidence from international arthroplasty registries and meta-analyses?

METHODS

A recommendation is generated by means of a direct comparison of data from the arthroplasty registries of eight different countries (USA, Germany, Australia, UK, Sweden, Norway, New Zealand, and The Netherlands), the comparison of 22 review studies and meta-analyses based on registry data, as well as the evaluation of the recommendation of healthcare systems of different nations. For this purpose, reviews and meta-analyses whose results were statistically significant were selected, as were the annual reports of the arthroplasty registries that were current at the time of writing.

RESULTS

For knee endoprostheses, a long survival time, as well as a lower risk of revision can be achieved with the help of cemented anchorage with antibiotic-laden bone cement. In patients aged 70 years and older, cemented anchorage of the hip stem implant significantly reduces the risk of intraoperative or postoperative periprosthetic fracture (times four), this applies both to elective total hip arthroplasties (TEPs) and to hemiarthroplasty after femoral neck fractures. Antibiotic-loaded bone cement significantly (p = 0.041) reduces the risk of periprosthetic infection, especially in patients with femoral neck fractures.

CONCLUSIONS

Total knee replacement with antibiotic-loaded bone cement is well established in Germany and evidence based. Registry data and meta-analyses recommend cemented fixation of the hip stem in older patients-in Germany the evidence-based recommendations must still be transferred to daily practice.

Extreme Serum Titanium Concentration Induced by Acetabular Cup Failure: Unveiling a Unique Scenario of Titanium Alloy Debris Accumulation

The majority of contemporary total hip arthroplasty (THA) implants are constructed from Ti alloys, which are generally believed to generate fewer adverse local tissue reactions (ALTRs) compared to CoCr alloys. This study presents a case of unusual primary THA failure where a substantial release of Ti alloy debris was observed. A 52-year-old active male underwent THA after post-traumatic aseptic necrosis of the femoral head in 2006. Seventeen years after the procedure, the patient presented with groin pain and a restricted range of motion. X-rays revealed the protrusion of the alumina ceramic head through the Ti6Al4V acetabular cup. Trace element analysis indicated significantly elevated levels of serum Ti, Al, and V. CT and MRI confirmed Ti alloy cup failure and a severe ALTR. During revision surgery, it was found that the worn-out ceramic head was in direct contact with the acetabular cup, having protruded through a central hole it had created over time. No acetabular liner was found. Histological analysis of his tissue samples showed wear-induced synovitis with areas of multinucleated foreign body giant cells and the accumulation of numerous metal particles but no acute inflammatory response. Six months after the revision THA, the patient has experienced favourable outcomes. This case provides an instructive illustration for studying the consequences of the substantial release of Ti alloy debris from orthopedic implants.

The Financial Burden of Patient Comorbidities on Total Hip Arthroplasties-A Matched Cohort Analysis of High Comorbidity Burden and Non-High Comorbidity Burden Patients

BACKGROUND

The impact of increased patient comorbidities on the cost-effectiveness of total hip arthroplasty (THAs) is lacking. This study aimed to compare revenue, costs, and short-term (90 days) surgical outcomes between patients who have and do not have a high comorbidity burden (HCB).

METHODS

We retrospectively reviewed 14,949 patients who underwent an elective, unilateral THA between 2012 and 2021. Patients were stratified into HCB (Charlson Comorbidity Index ≥ 5 and American Society of Anesthesiology scores of 3 or 4) and non-HCB groups, and were further 1:1 propensity matched based on baseline characteristics. Perioperative data, revenue, costs, and contribution margins (CMs) of the inpatient episode were compared between groups. Also, 90-day readmissions and revisions were compared between groups. Of the 11,717 patients who had available financial data (n = 1,017 HCB, n = 10,700 non-HCB), 1,914 patients were included in the final matched analyses (957 per group).

RESULTS

Total (P < .001) and direct (P < .001) costs were significantly higher for HCB patients. Comparable revenue between cohorts (P = .083) resulted in a significantly decreased CM in the HCB patient group (P < .001). The HCB patients were less likely to be discharged home (P < .001) and had significantly higher 90-day readmission rates (P = .049).

CONCLUSIONS

Increased THA costs for HCB patients were not matched by increased revenue, resulting in decreased CM. Higher rates of nonhome discharge and readmissions in the HCB population add to the additional financial burden. Adjustments to the current reimbursement models should better account for the increased financial burden of HCB patients undergoing THA and ensure access to care for all patient populations.

LEVEL OF EVIDENCE

III.

Does Time to Aseptic Failure After Primary Total Hip Arthroplasty Affect Clinical and Patient-Reported Outcomes?

BACKGROUND

Evidence on the effects of time-to-failure from primary total hip arthroplasty (THA) to aseptic first-revision on clinical results and patient-reported outcome measures (PROMs) is scarce. Therefore, we sought to compare demographics, operative times, lengths of stay, discharge dispositions, 90-day readmissions, re-revision rates, mortalities, and PROMs between early and late aseptic THA revisions.

METHODS

This study is a retrospective review of a prospectively collected institutional database of all elective hip procedures. In total, 572 patients who underwent aseptic revision after primary THA from August 2015 to December 2018 were analyzed. Patients were stratified into either early revision (<3-years; n = 176) or late revision (≥3-years; n = 396) cohorts.

RESULTS

Significantly more patients were revised earlier for bone-related (ie, periprosthetic fractures) (22.7% versus 8.3%) or other various complications (19.9% versus 5.8%), whereas more late revisions were performed to treat implant-related failures (6.8% versus 37.1%), respectively. Operative time was significantly shorter in early versus late revisions (133 versus 157 minutes). A significantly higher delta-change/improvement from baseline/preoperative to 1-year postoperative was found for hip disability and osteoarthritis outcome score physical function (HOOS-PS), veterans-RAND-12 physical and mental components (VR-12-PCS and MCS, respectively) of early revisions. However, HOOS-PS and HOOS-Pain at 1-year of follow-up were significantly worse in early revisions.

CONCLUSION

With exception of operative time, time-to-failure had no significant influence on clinical results. Despite greater improvements on PROMs from preoperative to postoperative, patients undergoing early revisions after primary THA perceive significantly higher levels of pain and worse physical functionality at 1-year of follow-up.

The different strategies in treating displaced femoral neck fractures: mid-term surgical outcome in a register-based cohort of 1,283 patients aged 60-69 years

BACKGROUND AND PURPOSE

In patients around retirement age controversy exists as to whether to treat displaced femoral neck fracture (dFNF) with internal fixation (IF) or arthroplasty. An arthroplasty in this age group may need revision due to a long expected remaining lifetime. IF carries a higher risk of early failure but a maintained native hip if healing occurs. We aimed to determine the cumulative 5-year rate of conversion to arthroplasty after IF and implant revision after primary total hip arthroplasty (THA), respectively.

PATIENTS AND METHODS

In this longitudinal cohort study, patients aged 60-69 years registered with a dFNF in the Swedish Fracture Register (SFR) 2012-2018 were cross-referenced with available data from the Swedish Arthroplasty Register (SAR) until December 31, 2019. Conversion to arthroplasty or revision were analyzed utilizing competing risk, with death as competing event.

RESULTS

At 5 years, the cumulative rate of conversion to arthroplasty after IF was 31% (95% confidence interval [CI] 26-37). For primary THA, the 5-year rate of revision was 4.0% (CI 2.8-5.8). The 5-year mortality did not differ, being 20% (CI 16-27) and 23% (CI 20-28) after IF and THA, respectively. Regression analyses did not identify any risk factors for conversion arthroplasty based on the variables in the register.

CONCLUSION

A follow-up of 5 years catches most reoperations after IF, resulting in a 31% conversion rate. The 4% revision rate at 5 years after primary THA should be seen as an intermediate result, as late complications may occur.

The lifetime revision risk of primary anatomic and reverse total shoulder arthroplasty

BACKGROUND

Implant survival in total shoulder arthroplasty (TSA) is currently defined with reference to a set time period (eg, 5-year implant survival). This is a difficult concept for patients to understand, especially for younger patients who have more years of life remaining. Our study aims to calculate a patient's lifetime revision risk after primary anatomic (aTSA) and reverse (rTSA) total shoulder arthroplasty-a more meaningful projection of revision risk over a patient's remaining lifetime.

METHODS

The New Zealand Joint Registry (NZJR) and national death data was used to calculate the incidence of revision and mortality in all patients who underwent primary aTSA and rTSA in New Zealand between 1999 and 2021. Lifetime revision risk was calculated using previously described methods, and this risk was stratified by age (46-90 years, 5-year bins), sex, and procedure type (aTSA and rTSA).

RESULTS

In total, there were 4346 patients in the aTSA cohort and 7384 patients in the rTSA cohort. Lifetime revision risk was highest in the youngest age group (46-50 years) at 35.8% (95% CI 34.5%-37.0%) for aTSA and 30.9% (95% CI 29.9%-32.0%) for rTSA, with risk decreasing with increasing age. Across all age groups, the lifetime revision risk was higher for aTSA compared to rTSA. By sex, females reported higher lifetime revision risk for each age group in the aTSA cohort whereas males reported higher lifetime revision risk for each group in the rTSA cohort.

CONCLUSIONS

Our study demonstrates that younger patients have higher lifetime revision risk after total shoulder arthroplasty. Our results highlight the long-term revision risks associated with the trend of offering shoulder arthroplasty to younger patients. The data may be used among various health care stakeholders to inform the surgical decision-making process and plan for future health care resource use.

Mortality and re-revision following single-stage and two-stage revision surgery for the management of infected primary hip arthroplasty in England and Wales

We compared the risks of re-revision and mortality between two-stage and single-stage revision surgeries among patients with infected primary hip arthroplasty. Patients with a periprosthetic joint infection (PJI) of their primary arthroplasty revised with single-stage or two-stage procedure in England and Wales between 2003 and 2014 were identified from the National Joint Registry. We used Poisson regression with restricted cubic splines to compute hazard ratios (HRs) at different postoperative periods. The total number of revisions and re-revisions undergone by patients was compared between the two strategies. In total, 535 primary hip arthroplasties were revised with single-stage procedure (1,525 person-years) and 1,605 with two-stage procedure (5,885 person-years). All-cause re-revision was higher following single-stage revision, especially in the first three months (HR at 3 months = 1.98 (95% confidence interval (CI) 1.14 to 3.43), p = 0.009). The risks were comparable thereafter. Re-revision for PJI was higher in the first three postoperative months for single-stage revision and waned with time (HR at 3 months = 1.81 (95% CI 1.22 to 2.68), p = 0.003; HR at 6 months = 1.25 (95% CI 0.71 to 2.21), p = 0.441; HR at 12 months = 0.94 (95% CI 0.54 to 1.63), p = 0.819). Patients initially managed with a single-stage revision received fewer revision operations (mean 1.3 (SD 0.7) vs 2.2 (SD 0.6), p < 0.001). Mortality rates were comparable between these two procedures (29/10,000 person-years vs 33/10,000). The risk of unplanned re-revision was lower following two-stage revision, but only in the early postoperative period. The lower overall number of revision procedures associated with a single-stage revision strategy and the equivalent mortality rates to two-stage revision are reassuring. With appropriate counselling, single-stage revision is a viable option for the treatment of hip PJI.

Which Unified Classification System type B periprosthetic fractures around cemented polished tapered stems should not be fixed?

The Unified Classification System (UCS), or Vancouver system, is a validated and widely used classification system to guide the management of periprosthetic femoral fractures. It suggests that well-fixed stems (type B1) can be treated with fixation but that loose stems (types B2 and B3) should be revised. Determining whether a stem is loose can be difficult and some authors have questioned how to apply this classification system to polished taper slip stems which are, by definition, loose within their cement mantle. Recent evidence has challenged the common perception that revision surgery is preferable to fixation surgery for UCS-B periprosthetic fractures around cemented polished taper slip stems. Indications for fixation include an anatomically reducible fracture and cement mantle, a well-fixed femoral bone-cement interface, and a well-functioning acetabular component. However, not all type B fractures can or should be managed with fixation due to the risk of early failure. This annotation details specific fracture patterns that should not be managed with fixation alone.

Proanthocyanidins Inhibit Osteoblast Apoptosis via the PI3K/AKT/Bcl-xL Pathway in the Treatment of Steroid-Induced Osteonecrosis of the Femoral Head in Rats

BACKGROUND

Steroid-induced osteonecrosis of the femoral head (SONFH) is a common clinical disease caused by massive or prolonged use of steroids. Its pathogenesis is unclear, but its incidence is increasing annually. It is characterized by an insidious and rapid onset, and high disability rate, causing a great burden on patients' daily life. Therefore, clarifying its pathogenesis and providing early and effective treatment for steroid osteonecrosis is important.

METHODS

In vivo, we used methylprednisolone (MPS) to construct a SONFH rat model and employed Mirco-ct, Hematoxylin and eosin (H&E) staining, and TdT-mediated dUTP nick end labeling (TUNEL) staining analysis to evaluate the therapeutic effects of proanthocyanidins (PACs). Network pharmacology analysis was conducted to mine targets associated with femoral head necrosis, and PACs analyzed possible molecular mechanisms. In vitro, PACs were added at different doses after treatment of cells with dexamethasone (DEX), and human osteoblast-like sarcoma(MG-63) cell apoptosis was determined by Annexin V-FITC-PI. The mechanisms by which PACs regulate bone metabolism via the Phosphoinositide 3-kinase(PI3K)/protein kinase B(AKT)/Recombinant Human B-Cell Leukemia/Lymphoma 2 XL(Bcl-xL) axis were explored by Western blotting.

RESULT

In vivo studies showed that PACs prevented SONFH in rat model. The PI3K/AKT/Bcl-xL signaling pathway was selected by network pharmacology approach; in vitro studies showed that proanthocyanidin-activated AKT and Bcl-xL inhibited osteoblast apoptosis.

CONCLUSIONS

PACs can inhibit excessive osteoblast apoptosis in SONFH via the PI3K/AKT/Bcl-xL signaling axis and have potential therapeutic effects.

Surgeon Estimations of Acetabular Cup Orientation Using Intraoperative Fluoroscopic Imagining Are Unreliable

Background

Accurate acetabular cup orientation is associated with decreased revision rates and improved outcomes of primary total hip arthroplasty. This study assesses surgeon's ability to estimate both the acetabular component inclination and anteversion angles via intraoperative fluoroscopy (IF) images.

Methods

We surveyed orthopedic surgeons to estimate acetabular component inclination and anteversion based on 20 IF images of total hip arthroplasty through a direct anterior approach. Postoperative computed-tomography scans were used to calculate the true inclination and anteversion component angles. The absolute difference between the true and estimated values was calculated to determine the mean and standard deviation of the survey results. Interrater reliability was determined through interclass correlation coefficients.

Results

A majority of surgeons preferred the direct anterior approach (83.3%) and utilized IF during surgery (70%). Surgeons surveyed were on average 5.9° away from the true value of inclination (standard deviation = 4.7) and 8.8° away from the true value of anteversion (standard deviation = 6.0). Respondents were within 5° of both inclination and anteversion in 19.7% of cases, and within 10° in 57.3% of cases. All surgeons were determined to have poor reliability in estimating anteversion (interclass correlation coefficient < 0.5). Only 2 surgeons were determined to have moderate reliability when estimating inclination.

Conclusions

Surgeons, when solely relying on IF for the estimation of anteversion and inclination, are unreliable. Utilization of other techniques in conjunction with IF would improve observer reliability.

The promising role of bacteriophage therapy in managing total hip and knee arthroplasty related periprosthetic joint infection, a systematic review

PURPOSE

Total hip and knee arthroplasty periprosthetic joint infection (PJI) poses a management dilemma owing to the emergence of resistant organisms. A promising option is Bacteriophage therapy (BT) was used as an adjuvant for PJI management, aiming at treating resistant infections, decreasing morbidity, and mortality. The current review aimed to demonstrate the role and safety of using BT as an adjuvant to treat PJIs.

METHODS

A systematic search was performed through four databases (Embase, PubMed, Web of Science, and Scopus) up to March 2022, according to the predetermined inclusion and exclusion criteria.

RESULTS

Our systematic review included 11 case reports of 13 patients in which 14 joints (11 TKAs and three THAs) were treated. The patients' average age was 73.7 years, underwent an average of 4.5 previous surgeries. The most common organism was the Staphylococcus aureus species. All patients underwent surgical debridement; for the 13 patients, eight received a cocktail, and five received monophage therapy. All patients received postoperative suppressive antibiotic therapy. After an average follow-up of 14.5 months, all patients had satisfactory outcomes. No recurrence of infection in any patient. Transaminitis complicating BT was developed in three patients, needed stoppage in only one, and the condition was reversible and non-life-threatening.

CONCLUSION

BT is a safe and potentially effective adjuvant therapy for treating resistant and relapsing PJIs. However, further investigations are needed to clarify some BT-related issues to create effective and reproducible therapeutics. Furthermore, new ethical regulations should be implemented to facilitate its widespread use.

Mid- to late-term follow-up of primary hip and knee arthroplasty: the UK SAFE evidence-based recommendations

To review the evidence and reach consensus on recommendations for follow-up after total hip and knee arthroplasty. A programme of work was conducted, including: a systematic review of the clinical and cost-effectiveness literature; analysis of routine national datasets to identify pre-, peri-, and postoperative predictors of mid-to-late term revision; prospective data analyses from 560 patients to understand how patients present for revision surgery; qualitative interviews with NHS managers and orthopaedic surgeons; and health economic modelling. Finally, a consensus meeting considered all the work and agreed the final recommendations and research areas. The UK poSt Arthroplasty Follow-up rEcommendations (UK SAFE) recommendations apply to post-primary hip and knee arthroplasty follow-up. The ten-year time point is based on a lack of robust evidence beyond ten years. The term 'complex cases' refers to individual patient and surgical factors that may increase the risk for arthroplasty failure. For Orthopaedic Data Evaluation Panel (ODEP) 10A* minimum implants, it is safe to disinvest in routine follow-up from one to ten years post-non-complex hip and knee arthroplasty provided there is rapid access to orthopaedic review. For ODEP 10A* minimum implants in complex cases, or non-ODEP 10A* minimum implants, periodic follow-up post-hip and knee arthroplasty may be required from one to ten years. At ten years post-hip and knee arthroplasty, clinical and radiological evaluation is recommended. After ten years post-hip and knee arthroplasty, frequency of further follow-up should be based on the ten-year assessment; ongoing rapid access to orthopaedic review is still required. Complex cases, implants not meeting the ODEP 10A* criteria, and follow-up after revision surgery are not covered by this recommendation.

HUCMSC-derived Exosomes Suppress the Titanium Particles-induced Osteolysis in Mice through Inhibiting CCL2 and CCL3

OBJECTIVE

Wear particles induce inflammation and the further osteolysis around the prosthesis, has been proven to be the main cause of aseptic hip joint loosening. In this research, we aimed to clarify whether human umbilical cord mesenchymal stem cells (HUCMSCs) could inhibit the titanium particles-induced osteolysis and shed light upon its mechanism.

METHODS

The expression of chemokine (C-C motif) ligand 2 (CCL2), chemokine (C-C motif) ligand 3 (CCL3) and chemokine (C-C motif) ligand 5 (CCL5) were examinjed in clinical specimens of aseptic hip prosthesis loosening patients. Local injection of lentivirus that knocked down CCL2 or CCL3 in a cranial osteolysis mice model were used to exam the effect of CCL2 and CCL3 on titanium particles-induced osteolysis in vivo. Transwell assay was used to examine the effect of CCL2 and CCL3 on titanium particles-induced activation of macrophage in vitro. Furthermore, the therapeutic effect of HUCMSCs, and exosomes from HUCMSCs were also examed in vivo and vitro. Immunohistochemical and real-time PCR were used to examine the expression of relative pathways. Analysis of variance (ANOVA) and Student-Newman-Keuls post hoc t test were used to analyze the results and determine the statistical significance of the differences.

RESULTS

Results showed that titanium particles caused the osteolysis at the mice cranial in vivo and a large number of macrophages that migrated, while local injection of HUCMSCs and exosomes did inhibit the cranial osteolysis and migration. An exosome inhibitor GW4869 significantly increased the osteolysis area in the mice cranium osteolysis model, and increased the number of migrated macrophages. Immunohistochemical results suggested that the expression of CCL2, CCL3 and CD68 in the cranial in Titanium particles mice increased significantly, but was significantly reduced by HUCMSCs or exosomes. HUCMSC and exosomes down-regulate the expression of CCL3 in vitro and in vivo.

CONCLUSION

HUCMSCs and HUCMSC-derived exosomes could suppress the titanium particles-induced osteolysis in mice through inhibiting chemokine (C-C motif) ligand 2, chemokine (C-C motif) ligand 3.

Platelet-rich plasma use for hip and knee osteoarthritis in the United States

BACKGROUND

Hip and knee osteoarthritis (OA) are rising in prevalence and increasingly affecting younger patients. There is a rising demand for therapeutics to address its growing disease burden. Platelet-rich plasma (PRP) therapy has been used to treat various musculoskeletal conditions, but its role in OA treatment is not well understood. Even still, there is significant interest in this biologic for treatment of OA. The purpose of this study was to determine the PRP utilization trends in the United States for hip and knee OA.

METHODS

This was a retrospective review from the PearlDiver Patient Record Database. International Classification of Diseases and Current Procedural Terminology codes were used to identify patients who had received PRP injections for hip and knee OA from 2010 to 2018. Injection incidence was evaluated on an annual basis and by patient demographics, geographic distribution, and medical specialty under which the treatment was administered.

RESULTS

A total of 3,884 PRP injections were administered over the study period, 15% for hip OA and 85% for knee OA. PRP injections per 100,000 patient cases increased by an average year-over-year percentage of 53% and 12% for hip and knee OA, respectively. The highest injection incidences were observed in patients younger than 44 years of age. 58% of both hip and knee PRP injections were administered in general orthopaedic practices.

CONCLUSION

These findings show that PRP is increasingly being used as a treatment modality for hip and knee OA. There is a need for further research on its long term outcomes.

Systematic review on the application of 3D-bioprinting technology in orthoregeneration: current achievements and open challenges

BACKGROUND

Joint degeneration and large or complex bone defects are a significant source of morbidity and diminished quality of life worldwide. There is an unmet need for a functional implant with near-native biomechanical properties. The potential for their generation using 3D bioprinting (3DBP)-based tissue engineering methods was assessed. We systematically reviewed the current state of 3DBP in orthoregeneration.

METHODS

This review was performed using PubMed and Web of Science. Primary research articles reporting 3DBP of cartilage, bone, vasculature, and their osteochondral and vascular bone composites were considered. Full text English articles were analyzed.

RESULTS

Over 1300 studies were retrieved, after removing duplicates, 1046 studies remained. After inclusion and exclusion criteria were applied, 114 articles were analyzed fully. Bioink material types and combinations were tallied. Cell types and testing methods were also analyzed. Nearly all papers determined the effect of 3DBP on cell survival. Bioink material physical characterization using gelation and rheology, and construct biomechanics were performed. In vitro testing methods assessed biochemistry, markers of extracellular matrix production and/or cell differentiation into respective lineages. In vivo proof-of-concept studies included full-thickness bone and joint defects as well as subcutaneous implantation in rodents followed by histological and µCT analyses to demonstrate implant growth and integration into surrounding native tissues.

CONCLUSIONS

Despite its relative infancy, 3DBP is making an impact in joint and bone engineering. Several groups have demonstrated preclinical efficacy of mechanically robust constructs which integrate into articular joint defects in small animals. However, notable obstacles remain. Notably, researchers encountered pitfalls in scaling up constructs and establishing implant function and viability in long term animal models. Further, to translate from the laboratory to the clinic, standardized quality control metrics such as construct stiffness and graft integration metrics should be established with investigator consensus. While there is much work to be done, 3DBP implants have great potential to treat degenerative joint diseases and provide benefit to patients globally.

The prevalence and risk factors of dislocation after primary total hip arthroplasty

This study aimed to investigate the occurrence of dislocation and risk factors following primary total hip arthroplasty (THA). Retrospective analysis was done on the clinical data of 441patients with primary total hip arthroplasty who were admitted to our hospital between May 2018 and early December 2020. A total of 294 patients without posterior soft tissue repair were included as control group, and a total of 147 patients with repair of the short external rotator muscle and joint capsule were assigned to the repair group. All operated patients were observed to analyze the occurrence and risk of early postoperative dislocation. Within 6 months after hip arthroplasty, the early hip dislocation rate in the repair group was 0.68%, which was significantly lower than that in the control group (4.78%) (P < 0.05). The results of multifactorial analysis showed that age ≥75 years, combined limb or mental illness, artificial femoral head diameter <30 mm, posterolateral approach and prosthesis placement outside the safety zone, and improper handling were risk factors for dislocation (P < 0.05); The incidence of re-dislocation was lower in the targeted intervention group (P < 0.05). The occurrence of dislocation after THA is related to age, gender, and type of orthopedic disease. The risk factors should be explored to develop targeted intervention protocol, decreasing the dislocation rate and improving the prognosis.

Mid-Term Survival of Total Hip Arthroplasty in Patients Younger Than 55-year-old

BACKGROUND

Survivorship of total hip arthroplasty (THA) in younger patients is concerning given the inverse relationship between age and lifetime risk for revision. The purpose of this study is to determine if risk of revision has improved for patients aged 55 years or younger who undergo primary THA using modern polyethylene liners.

METHODS

A retrospective review identified 2,461 consented patients (2,814 hips) with minimum 2-year follow-up who underwent primary THA at our institution between September 2007 and August 2014 using components from a single manufacturer (Zimmer Biomet), all with vitamin E-infused highly crosslinked polyethylene acetabular inserts. There were 561 patients (643 THA; 23%) aged 55 or younger and 1,900 (2,171 THA; 77%) older than 55.

RESULTS

Mean follow-up was 5.0 years for both groups. There were more male patients in the younger (55%) than older (41%) group. Body mass index (BMI) was higher in younger patients independent of gender. Improvement in Harris hip score (HHS) was similar between groups. Kaplan-Meier survival to endpoint of all cause revision was similar between groups at 12 years (P = .8808) with 97.5% (95% CI: ±0.7%) for younger versus 97.1% (95% CI: ±0.6%) for older patients. Most frequent reason for revision overall was periprosthetic femoral fracture (21; 0.75%); univariate analysis revealed risk factors were female gender (P = .28) and age ≥65 years (P = .012).

CONCLUSION

Use of modern polyethylene, such as vitamin E-stabilized highly cross-linked, liners during THA may improve survivorship in younger patients undergoing THA. Younger patients undergoing primary THA with highly cross-linked polyethylene liners had no increased rate of revision at mid-term follow-up.

The lifetime revision risk of unicompartmental knee arthroplasty

AIMS

Unicompartmental knee arthroplasty (UKA) has a higher risk of revision than total knee arthroplasty (TKA), particularly for younger patients. The outcome of knee arthroplasty is typically defined as implant survival or revision incidence after a defined number of years. This can be difficult for patients to conceptualize. We aimed to calculate the 'lifetime risk' of revision for UKA as a more meaningful estimate of risk projection over a patient's remaining lifetime, and to compare this to TKA.

METHODS

Incidence of revision and mortality for all primary UKAs performed from 1999 to 2019 (n = 13,481) was obtained from the New Zealand Joint Registry (NZJR). Lifetime risk of revision was calculated for patients and stratified by age, sex, and American Society of Anesthesiologists (ASA) grade.

RESULTS

The lifetime risk of revision was highest in the youngest age group (46 to 50 years; 40.4%) and decreased sequentially to the oldest (86 to 90 years; 3.7%). Across all age groups, lifetime risk of revision was higher for females (ranging from 4.3% to 43.4% vs males 2.9% to 37.4%) and patients with a higher ASA grade (ASA 3 to 4, ranging from 8.8% to 41.2% vs ASA 1 1.8% to 29.8%). The lifetime risk of revision for UKA was double that of TKA across all age groups (ranging from 3.7% to 40.4% for UKA, and 1.6% to 22.4% for TKA). The higher risk of revision in younger patients was associated with aseptic loosening in both sexes and pain in females. Periprosthetic joint infection (PJI) accounted for 4% of all UKA revisions, in contrast with 27% for TKA; the risk of PJI was higher for males than females for both procedures.

CONCLUSION

Lifetime risk of revision may be a more meaningful measure of arthroplasty outcomes than implant survival at defined time periods. This study highlights the higher lifetime risk of UKA revision for younger patients, females, and those with a higher ASA grade, which can aid with patient counselling prior to UKA. Cite this article: Bone Joint J 2022;104-B(6):672-679.

Does Dosage or Duration of Concurrent Oral Corticosteroid Influence Elevated Risk of Postoperative Complications After Total Joint Arthroplasty?

BACKGROUND

This report seeks to clarify whether the dosage and duration of preoperative concurrent corticosteroid use influence postoperative complications after primary total joint arthroplasty (TJA).

METHODS

This retrospective single institutional study enrolled 1128 primary TJA cases, including 905 total hip arthroplasties and 223 total knee arthroplasties at a minimum 6 months of follow-up. Mean follow-up period was 51.9 ± 34.1 months (range 6-146). Of all joints, 120 joints (10.6%) were associated with chronic concurrent oral corticosteroid use. Multivariate analysis was performed to identify whether chronic concurrent oral corticosteroid use elevated the risk of postoperative complications including surgical site infection/periprosthetic joint infection, delayed wound healing, periprosthetic fracture, and implant loosening. For chronic concurrent oral corticosteroid user, we determined whether the dosage and duration of preoperative concurrent corticosteroid use influenced postoperative complications and have an effective threshold for postoperative complications using receiver operating characteristic curve analysis.

RESULTS

The multivariate analysis revealed that American Society of Anesthesiologist Physical Status 3 was an independent risk factor for postoperative complications, while concurrent oral corticosteroid use was not an independent risk factor. When we compared joints with (n = 13) and without (n = 107) postoperative complications in chronic concurrent oral corticosteroid user, there was no statistical difference in the dosage (P = .97) and duration (P = .69) between the 2 groups. Area under the curve values for the oral corticosteroid dosages and duration were 0.482 and 0.549, respectively.

CONCLUSION

This study revealed that neither dosage nor duration of concurrent oral corticosteroid use was predictive of postoperative complications after TJA. American Society of Anesthesiologist Physical Status 3 is a major factor in postoperative complications after TJA.

UK poSt Arthroplasty Follow-up rEcommendations (UK SAFE): what does analysis of linked, routinely collected national data sets tell us about mid-late term revision risk after hip replacement? Retrospective cohort study

OBJECTIVE

To identify patients at risk of mid-late term revision of hip replacement to inform targeted follow-up.

DESIGN

Analysis of linked national data sets from primary and secondary care (Clinical Practice Research Datalink (CPRD-GOLD); National Joint Registry (NJR); English Hospital Episode Statistics (HES); Patient-Reported Outcome Measures (PROMs)).

PARTICIPANTS

Primary elective total hip replacement (THR) aged≥18.

EVENT OF INTEREST

Revision surgery≥5 years (mid-late term) after primary THR.

STATISTICAL METHODS

Cox regression modelling to ascertain risk factors of mid-late term revision. HR and 95% CI assessed association of sociodemographic factors, comorbidities, medication, surgical variables and PROMs with mid-late term revision.

RESULTS

NJR-HES-PROMs data were available from 2008 to 2011 on 142 275 THR; mean age 70.0 years and 61.9% female. CPRD GOLD-HES data covered 1995-2011 on 17 047 THR; mean age 68.4 years, 61.8% female. Patients had minimum 5 years postprimary surgery to end 2016. In NJR-HES-PROMS data, there were 3582 (2.5%) revisions, median time-to-revision after primary surgery 1.9 years (range 0.01-8.7), with 598 (0.4%) mid-late term revisions; in CPRD GOLD, 982 (5.8%) revisions, median time-to-revision 5.3 years (range 0-20), with 520 (3.1%) mid-late term revisions.Reduced risk of mid-late term revision was associated with older age at primary surgery (HR: 0.96; 95% CI: 0.95 to 0.96); better 6-month postoperative pain/function scores (HR: 0.35; 95% CI: 0.27 to 0.46); use of ceramic-on-ceramic (HR: 0.73; 95% CI: 0.56 to 0.95) or ceramic-on-polyethylene (HR: 0.76; 95% CI: 0.58 to 1.00) bearing surfaces.Increased risk of mid-late term revision was associated with the use of antidepressants (HR: 1.32; 95% CI: 1.09 to 1.59), glucocorticoid injections (HR: 1.33; 95% CI: 1.06 to 1.67) and femoral head size≥44 mm (HR: 2.56; 95% CI: 1.09 to 6.02)No association of gender, obesity or Index of Multiple Deprivation was observed.

CONCLUSION

The risk of mid-late term THR is associated with age at primary surgery, 6-month postoperative pain and function and implant factors. Further work is needed to explore the associations with prescription medications observed in our data.

The lifetime risk of revision following total knee arthroplasty : a New Zealand Joint Registry study

AIMS

The success of total knee arthroplasty (TKA) is usually measured using functional outcome scores and revision-free survivorship. However, reporting the lifetime risk of revision may be more meaningful to patients when gauging risks, especially in younger patients. We aimed to assess the lifetime risk of revision for patients in different age categories at the time of undergoing primary TKA.

METHODS

The New Zealand Joint Registry database was used to obtain revision rates, mortality, and the indications for revision for all primary TKAs performed during an 18-year period between January 1999 and December 2016. Patients were stratified into age groups at the time of the initial TKA, and the lifetime risk of revision was calculated according to age, sex, and the American Society of Anesthesiologists (ASA) grade. The most common indications for revision were also analyzed for each age group.

RESULTS

The overall ten-year survival rate was 95.6%. This was lowest in the youngest age group (between 46 and 50 years) and increased sequentially with increasing age. The lifetime risk of requiring revision was 22.4% in those aged between 46 and 50 years at the time of the initial surgery, and decreased linearly with increasing age to 1.15% in those aged between 90 and 95 years at the time of surgery. Higher ASA grades were associated with increased lifetime risk of revision in all age groups. The three commonest indications for revision were aseptic loosening, infection, and unexplained pain. Young males, aged between 46 and 50 years, had the highest lifetime risk of revision (25.2%).

CONCLUSION

Lifetime risk of revision may be a more meaningful measure of outcome than implant survival at defined time periods when counselling patients prior to TKA. This study highlights the considerably higher lifetime risk of revision surgery for all indications, including infection, in younger male patients. Cite this article: Bone Joint J 2022;104-B(2):235-241.

Revision Risk in a Cohort of US Patients Younger Than 55 Undergoing Primary Elective Total Hip Arthroplasty

BACKGROUND

As indications for elective total hip arthroplasty (THA) expand to younger patients, we sought to (1) compare revision risk following primary elective THA in patients <55 years at the time of their THA to patients aged ≥65 years and (2) identify specific risk factors for revision in patients <55 years.

METHODS

A Kaiser Permanente's total joint replacement registry was used to conduct a cohort study including primary elective THA patients aged ≥18 (2001-2018). In total, 11,671 patients <55 years and 53,106 patients ≥65 years were included. Multiple Cox regression was used to evaluate cause-specific revision risk, including septic revision, aseptic loosening, instability, and periprosthetic fracture. Stepwise Cox regression was used to identify patient and surgical factors associated with cause-specific revision in patients <55 years.

RESULTS

Patients <55 years had a higher risk of septic revision (hazard ratio [HR] = 1.30, 95% confidence interval [CI] = 1.02-1.66), aseptic loosening (HR = 2.60, 95% CI = 1.99-3.40), and instability (HR = 1.35, 95% CI = 1.09-1.68), but a lower risk of revision for periprosthetic fracture (HR = 0.36, 95% CI = 0.22-0.59) compared to patients aged ≥65 years. In the <55 age group, risk factors for septic revision included higher body mass index, drug abuse, and liver disease. Hypertension, anterior approach, and ceramic-on-ceramic were associated with aseptic loosening. White race, American Society of Anesthesiologists classification ≥3, smoker, paralysis, posterior approach, ceramic-on-ceramic, and smaller head diameter were associated with instability.

CONCLUSION

Identified risk factors varied depending on the cause for revision. Although septic revisions were related to patient characteristics, more modifiable factors, such as implant or surgical approach, were associated with revision due to aseptic loosening and instability.

LEVEL OF EVIDENCE

III.

Outcomes of primary total hip arthroplasty using 3D image-based custom stems in unselected patients: a systematic review

To report clinical and radiographic outcomes of primary THA using three-dimensional (3D) image-based custom stems.

This systematic review was performed according to PRISMA guidelines and registered with PROSPERO (CRD42020216079). A search was conducted using MEDLINE, Embase and Cochrane. Clinical studies were included if they reported clinical or radiographic outcomes of primary THA using 3D image-based custom stems. Studies were excluded if specific to patients with major hip anatomical deformities, or if not written in English.

Fourteen studies were eligible for inclusion (n = 1936 hips). There was considerable heterogeneity in terms of manufacturer, proximal geometry, coating and length of custom stems. Revision rates ranged from 0% to 1% in the short-term, 0% to 20% in the mid-term, and 4% to 10% in the long-term, while complication rates ranged from 3% in the short-term, 0% to 11% in the mid-term and 0% to 4% in the long-term. Post-operative Harris hip scores ranged from 95 to 96 in the short-term, 80 to 99 in the mid-term, and 87 to 94 in the long-term. Radiographic outcomes were reported in eleven studies, although none reported 3D implant sizing or positioning, nor compared planned and postoperative hip architecture.

Primary THA using 3D image-based custom stems in unselected patients provides limited but promising clinical and radiographic outcomes. Despite excellent survival, the evidence available in the literature remains insufficient to recommend their routine use. Future studies should specify proximal geometry, length, fixation, material and coating, as well as management of femoral offset and anteversion. The authors propose a classification system to help distinguish between custom stem designs based primarily on their proximal geometry and length.

Cite this article: EFORT Open Rev 2021;6:1166-1180. DOI: 10.1302/2058-5241.6.210053

Pro-Angiogenic and Osteogenic Effects of Adipose Tissue-Derived Pericytes Synergistically Enhanced by Nel-like Protein-1

An important objective of vascularized tissue regeneration is to develop agents for osteonecrosis. We aimed to identify the pro-angiogenic and osteogenic efficacy of adipose tissue-derived (AD) pericytes combined with Nel-like protein-1 (NELL-1) to investigate the therapeutic effects on osteonecrosis. Tube formation and cell migration were assessed to determine the pro-angiogenic efficacy. Vessel formation was evaluated in vivo using the chorioallantoic membrane assay. A mouse model with a 2.5 mm necrotic bone fragment in the femoral shaft was used as a substitute for osteonecrosis in humans. Bone formation was assessed radiographically (plain radiographs, three-dimensional images, and quantitative analyses), and histomorphometric analyses were performed. To identify factors related to the effects of NELL-1, analysis using microarrays, qRT-PCR, and Western blotting was performed. The results for pro-angiogenic efficacy evaluation identified synergistic effects of pericytes and NELL-1 on tube formation, cell migration, and vessel formation. For osteogenic efficacy analysis, the mouse model for osteonecrosis was treated in combination with pericytes and NELL-1, and the results showed maximum bone formation using radiographic images and quantitative analyses, compared with other treatment groups and showed robust bone and vessel formation using histomorphometric analysis. We identified an association between FGF2 and the effects of NELL-1 using array-based analysis. Thus, combinatorial therapy using AD pericytes and NELL-1 may have potential as a novel treatment for osteonecrosis.