Effects of Systemic or Local Administration of Zoledronate on Implant Osseointegration: A Preclinical Meta-Analysis

Objective This study aims to investigate the effect of systemically administrated zoledronate on bone-implant fixation in animal models. Methods We searched MEDLINE, Embase, and EBSCO for studies that explore the role of systemic or local zoledronate delivery in implant osseointegration in animal models. The Review Manager software was used to analyze selected studies by using the weighted mean difference random-effects model. Analytical data are mainly about bone ingrowth, such as bone-to-implant contact (BIC), bone volume/total volume (BV/TV), and bone area. Results Twenty studies were selected from 182 publications. The mean quality score was 18/20 for all of the 20 studies (κ = 0.9). Despite differences in protocols, these studies showed consistent improvement of implant osseointegration with zoledronate administration. In addition, the osteoporotic animal model, systemic or local administration, sufficient drug dosage, and sample follow-up time were correlated with improved outcomes. Conclusion Systematic administration of zoledronate could improve the osseointegration of orthopedic implant in animal models. Results of this meta-analysis should be interpreted cautiously because of the inherent differences between preclinical and clinical subjects. For the local administration, there is a similar trend as well, but the results need to be confirmed and complemented with further analyses.


Introduction
Bone ingrowth into a prosthetic implant is crucial for the longevity of uncemented total hip arthroplasty (THA). Rapid and sound bone ingrowth can increase implant stability and improve long-term bone-implant fixation. In addition, adequate tissue ingrowth may protect the boneimplant interface against wear particle-induced osteolysis, which further decreases the risk of aseptic loosening [1]. erefore, how to improve bone-implant fixation is always a topic of great interest for joint surgeons.
Zoledronate (ZOL) is a new-generation intravenous bisphosphonate (BP) with the greatest affinity and longest retention for bone mineral, and it has been largely utilized in the treatment of osteoporosis and metastatic bone disease. It has a well-documented profile of possible side effects, such as initial influenza-like illness which has been documented with the first infusion of BPs. Renal failure has been noted in patients with cancer after repetitive high-dose infusions, and an association between BPs and osteonecrosis of the jaw after tooth extraction has been recorded as well [2,3]. ZOL is traditionally believed to be an antiresorptive agent; however, recent animal studies suggested that it could stimulate bone formation and improve implant mechanical fixation [4,5]. Meanwhile, there are clinical studies revealing that ZOL is associated with decreased early implant migration and reduced peri-implant bone loss [6,7]. Nevertheless, apart from these findings, because of small sample sizes and diverse study protocols of previous researches, the exact cellular and molecular mechanisms governing the improved bone content, structure, and strength, induced by the systemically or locally administered ZOL on implant osseointegration, have Li) independently applied the search strategy to select references from the aforementioned databases. e titles and abstracts were reviewed independently. When in doubt, the full-text articles were retrieved for further examination. ese two authors independently assessed each full report to evaluate fulfillment of the inclusion criteria, and corresponding authors were contacted for more information and clarification regarding their data, if necessary. Any disagreement was discussed with the senior author, and when consensus could not be established, that study was excluded.

Quality Assessment.
e methodological quality of included studies was assessed independently by two authors (Yao He and Xiang-Dong Wu) according to the ARRIVE guidelines which included title, abstract, background, objectives, ethical statement, study design, experimental procedures, experimental animals, housing and husbandry, sample size, allocation of animals to experimental groups, experimental outcomes, statistical methods, baseline data, numbers analyzed, outcomes and estimation, adverse events, interpretation/scientific implications, generalizability/translation, and funding. Each study was given a quality score out of a possible total of 20 points. Any disagreement was resolved by the senior author (Yao He).

Data Extraction.
A data extraction form was designed and agreed by the authors, and a pilot test of five articles was performed to ensure their consistency. Initially, two authors (Yao He and Xiang-Dong Wu) independently extracted the data, which were later reviewed jointly to produce the agreed accurate data. Disagreements were resolved by consensus or consultation with the senior author. e extracted data included study design, animal species, implantation site, implant characteristics (material, shape, and coating), ZOL route and dosage, follow-up time, and outcome measurements (BIC, BV/TV, and bone area). In all studies, BIC was calculated as the length percentage of the direct bone-implant interface to the total implant surface, BV/TV was defined as the percentage of mineralized bone volume to total bone tissue volume in the peri-implant region, and bone area was evaluated as the percentage of bone tissue area to the total area of the bone and implant.
2.6. Statistical Analysis. Review Manager (RevMan version 5.0, e Cochrane Collaboration in 2008) was used to analyze the included studies. e primary outcome was the BIC between treatment and control groups. From a clinical point of view, the authors (Yao He and Xiang-Dong Wu) performed subgroup analyses according to the animal model (osteoporotic or normal), animal species, and drug dosage and frequency, as well as follow-up time. In case of multiple treatment groups next to a control group within one trial, the animal number in the control group was divided equally by the number of treatment groups. For each arm in a particular study, continuous data were expressed as means and standard deviations (SDs), and dichotomous data were expressed as proportions or risks. For continuous outcomes, we calculated the mean differences (MDs) with 95% confidence interval (CI). For dichotomous outcomes, we estimated the relative risks' 95% CI. Statistical heterogeneity was assessed by using the value of I 2 and the result of the chisquare test. An I 2 value >50% suggests statistical heterogeneity, which prompts a random-effects modeling estimate. Otherwise, a fixed-effects approach was used. A P value <0.05 was determined as statistically significant.

Characteristics of Enrolled Studies.
e sample size ranged from 10 to 64. In twelve studies, rats were used as animal models; in other seven studies, rabbits were utilized as animal models; and in the last one study, dogs were used as animal models. e follow-up time ranged from 10 days to 1 year. e tail vertebra was used as the implantation site in one study; in another four studies, the femoral condyle was operated on; the remaining 15 studies all selected the proximal tibia as the surgical site. Out of 20 studies, one used the tantalum as the implant, another used the calcium phosphate bone cement, and the remaining eighteen studies used the titanium implant (Table 1).
Animal model (osteoporotic vs. normal) was initially used for subgroup analysis. e results showed that more effects of ZOL were seen improving BV/TV in osteoporotic animals (MD, 22.28; 95% CI, 11.98-32.58; P � 0.0004). With regard to animal species, ZOL significantly increased BV/TV in rats (MD, 18.60; 95% CI, 4.59-32.60; P � 0.009) and rabbits (MD, 8.00; 95% CI, 3.47-12.53; P � 0.0005). Finally, similar effects of ZOL on Potentially relevant references identified and screened for retrieval (n = 182) References retrieved for more detailed evaluation (n = 89) References to potentially appropriate randomized controlled trials to be included in the meta-analysis (n = 35) Randomized controlled trials with usable information (n = 20) References excluded (n = 93) (implants were embedded in the mandible or maxilla) References excluded (n = 54) (outcomes did not include pertinent information regarding bone ingrowth) References excluded (n = 15) (there were no specific values for bone ingrowth)

Discussion
THA is an effective technique owing to its ability to reduce pain, correct deformity, and improve function. However, its longevity is always an unsolved issue. According to previous reports, the most common reason of implant failure is aseptic loosening, which is caused by implant micromotion, prosthesis-related stress shielding, disuse osteoporosis, and wear-debris-induced osteolysis [6]. us, a simple, low-cost, and readily available method for improving implant fixation and decreasing periprosthetic bone loss is considerably important. Over the recent years, some animal study data proposed that ZOL might increase peri-implant bone stock and improve biological implant fixation, whereas other studies have denied this effect [14]. By pooling the currently available animal study data, the present meta-analysis provides evidence-based information about the positive effects of ZOL on implant osseointegration. In addition, our results indicated that the animal model, drug dosage, and follow-up time might influence study outcomes, which suggests possible reasons for the diversity of previous studies and gives insights into the design of future research.
Although bisphosphonates are well-known osteoclast inhibitors, they could reduce bone resorption by inhibiting and promoting apoptosis of osteoclasts [28,29]. Several in vitro studies have demonstrated that they could also stimulate osteoblast function [30,31]. However, according to our results, ZOL could only significantly improve implant osseointegration in osteoporotic animals but not in normal ones, which indicates that this effect was mediated mainly by decreasing the abnormal bone turnover rate rather than directly stimulating bone formation. Meanwhile, caution should be taken when interpreting this result. In the experimental animals, osteoporosis was acquired mainly by ovariectomy and was the only systemic condition. Nevertheless, in clinical settings, osteoporotic patients are usually old aged and sometimes diabetic. It has already been reported that aging and chronic hyperglycemia would lead to accumulation of advanced glycation end products (AGEs), which could negatively influence bone metabolism, and thus, the effect of ZOL may be less promising in clinical settings than in laboratories [32,33].
In view of the widespread use of bisphosphonates and the increase in bisphosphonate-related cases of osteonecrosis of the jaw, some studies have shown that osteonecrosis with dental implants may be a side effect of treatment with BP. e incidence of bisphosphonate-related osteonecrosis of the jaws is accelerated at the end of or during BP treatment. Serra et al. [34] suggested the avoidance of Table 2: Quality assessment score of enrolled studies.

Study or subgroup
Systemic Ayan et al. [8] Cardemil et al. [9] Carvas et al. [10] Chen et al. [11] Dikicier et al. [12] Li et al. [13] de Oliveira et al. [14] Qi et al. [ Test for subgroup differences: chi 2 = 0.00; df = 1 (P = 0.99); I 2 = 0% result in osteonecrosis. However, the duration of their follow-up was short. Najeeb et al. [42] believe that these results should be confirmed by more in-depth research before the dental implant can be used in the clinic. is is also the reason that one of the exclusion criteria is the implants embedded in the mandible or maxilla in our study.
Rats are the most commonly used animal model for osteoporosis studies because the ovariectomized rat exhibits most of the characteristics of human postmenopausal osteoporosis. However, the lack of intracortical remodeling process in this animal compromises the physiologic investigation of the cortical bone. By contrast, rabbits do have some inherent advantages as the osteoporosis animal model. For example, they achieve skeletal maturity shortly after reaching complete sexual development and show significant intracortical remodeling [43]. us, some researchers prefer rabbits as their ideal model. With respect to our results, studies with rats or rabbits have achieved similar yet slightly different outcomes, indicating that different animal models  Ayan et al. [8] 27. 38  Test for subgroup differences: chi 2 = 13.62; df = 1 (P = 0.0002); I 2 = 92.7% may influence implant osseointegration characteristics. However, because of the limited number of included studies, drawing the final conclusion now is too early. e dosage and frequency of ZOL delivery varied among the included studies, and the best medication administration protocol remains unclear. According to the present study, administration frequency does not exert much influence as long as drug dosage exceeds 0.1 mg/kg. is information is quite important because concerns about the safety of long-term bisphosphonate usage are always present. If single and multiple administrations have similar osseointegrationimproving effects, long-term usage would be unnecessary, thus avoiding the risk of complications, such as osteonecrosis of the jaw or stress fracture [44].
is meta-analysis has several limitations. Firstly, because of the small number of included studies and the limited animal sample sizes, conclusions from this metaanalysis should be interpreted cautiously and should be substantiated by larger studies. Secondly, because of the diverse study characteristics, animal populations, and treatment protocols, significant heterogeneity existed among the included studies. Nevertheless, because the main focus of preclinical meta-analysis is to generate hypotheses, the existence of heterogeneity is quite rational Arnoldi et al. [18] Bobyn et al. [25] Gao et al. [20] Miettinen et al. [19] Sörensen et al. [24] Stadlinger et al. [22] Ying et al. [22] Subtotal (95% CI) Figure 6: Forest plot of comparison for bone area between control and treatment groups. 8 BioMed Research International and could provide insight into the design of future clinical trials [45].

Conclusions
In conclusion, current animal studies demonstrate that both systemic and local administration of ZOL could improve the osseointegration of the orthopedic implant in animal models. An appropriate animal model (osteoporotic), sufficient drug dosage (exceeding 0.1 mg/kg, only in the method of systemic administration), and enough follow-up time (more than eight weeks) are crucial influencing factors, which should be given particular attention in future animal or clinical studies. Nonetheless, caution should be taken when interpreting the results of this meta-analysis because of inherent differences between preclinical and clinical subjects.

Additional Points
Strengths and Limitations of is Study. is metaanalysis should be considered cautiously and should be substantiated by larger studies. (5) Results of this metaanalysis should be interpreted cautiously because of the inherent differences between preclinical and clinical subjects.