Study of strength of fumeral bone of rats after filling bone tissue defects with bone cement based on tricalcium phosphate

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Study of strength of fumeral bone of rats after filling bone tissue defects with bone cement based on tricalcium phosphate

V.A. Filipenko, K.S. Poplavska, O.D. Karpinska, M.Yu. Karpinsky

Abstract

There are bone defects that do not heal on their own, despite the ability of bone tissue to fully regenerate. These defects occur due to degenerative-dystrophic diseases, injuries, resections of tumors and tumor-like formations, metastatic lesions, as a result of the development of aseptic instability after primary arthroplasty. Autogenous material for transplantation is the most acceptable, but its use depends on the quality of the bone. Allografts have compensated for the shortcomings of autografts, but the risk of infection and ethical issues limit the use of this material. The group II cement that we offer retains the properties of tricalcium phosphate-based materials: high biocompatibility, osteoconductive and osteointegrative qualities, and, due to strengthening by HA whiskers, it has higher strength and slower biodegradation time.

Key words: bioceramics, a-tricalcium phosphate, calcium phosphate cement, orthopedic surgery, bone regeneration.

Анотація

Дослідження міцності стегнових кісток щурів після заповнення дефектів кісткової тканини кістковим цементом на основі трикальційфосфату

В.А. Філіпенко, К.С. Поплавська, О.Д. Карпінська, М.Ю. Карпінський

Існують дефекти кістки, які не загоюються самостійно, незважаючи на здатність кісткової тканини до повної регенерації. Ці дефекти виникли внаслідок дегенеративно-дистрофічних захворювань, травм, резекцій пухлин і пухлиноподібних утворень, метастатичних уражень, у результаті розвитку асептичної нестабільності після первинного ендопротезування. Аутогенний матеріал для трансплантації є найбільш прийнятним, але його використання залежить від якості кістки. Аллотрансплантати скомпенсували недоліки аутотрансплантатів, але ризик інфекційного ураження й етичні питання обмежують застосування цього матеріалу. Цемент ІІ групи, який пропонуємо ми, лишив у собі характеристики, що притаманні матеріалам на основі трикальційфосфату: високі біосумісні, остеокондуктивні й остеоінтегративні якості, та, за рахунок зміцнення гілками гідроксіапатиту отримав вищу міцність, і більш повільний час біодеградації. Ці характеристики як час перебудови імплантованого матеріалу та його витривалість при навантаженні, напряму мають вплив на можливість здійснення навантаження в більш ранній післяопераційний період.

Ключові слова: біокераміки, а-трикальційфосфат, кальцій-фосфатний цемент, ортопедичні операції, регенерація кістки.

Introduction

The study is an initiative. The relevance of the study of osteoplastic materials is due to the occurrence of such bone defects that do not heal on their own, despite the ability of bone tissue to fully regenerate. These include defects caused by degenerative-dystrophic diseases, injuries, resections of tumors and tumor-like formations, metastatic lesions, as well as in the case of aseptic instability after primary arthroplasty [1-3]. Autogenous material for transplantation is the most suitable, mainly because it meets certain requirements: it contains osteogenic stem cells, has osteoinductive growth factors and plays the role of the osteoconductive matrix. However, its use is limited by the amount of material, reduced bone quality of some dystrophic diseases, additional injuries and the pain present in the donor site. [4, 5].

Allografts, having become available in the surgeon's arsenal, have partially compensated for the shortcomings of autografts. However, antigenic properties, the risk of infection (viral diseases), ethical issues limit the use of this material. Given that, allografts lose their osteoconductive and osteoinductive properties while being manufactured, sterilized and stored, they cannot be considered the “gold standard” [4]. Xenotransplants are characterized by a slowed-down reconstruction, compared to other bone materials as well as by the risk of infections of viral origin (Kreutzfeldt-Jakob, etc.) [6, 7].

Synthetic materials, such as calcium-phosphate bioceramics, have high biocompatible, osteoconductive and osteointegrative properties, and their composition is close to the bone matrix, which causes the gradual replacement of bone tissue [8, 9]. In addition, the variety of forms in which bioceramics (powder, granules, blocks of different porosity) are presented, expands the range of uses, even if defects of different configurations are present [8]. Due to the difficulties for the surgeon in filling defects of irregular shape, it has become important to create a material with osteoinductive and osteoconductive properties, which is introduced into the cavity in a liquid state and which hardens quickly while meeting the required strength values close to the bone. Unfortunately, the fragility and the low compressive strength of this material, as well as the rather rapid biodegradation, limit its use. It is expected that the addition of certain reinforcing impurities (in the form of HA whiskers) will significantly improve the mechanical properties of cement, slow down its degradation. It is desirable that such particles have bioactive properties similar to the quality of cement. A minor modification of the material can significantly change its properties, which makes it necessary to study the experimental biological properties of the studied material.

The purpose of the study was to determine the strength limits of the femurs of rats after filling their cavity defects with bone types of cement, based on a-tricalcium phosphate at different times after surgery.

Materials and methods

In the laboratory of the biomechanics of the State Institution “Sytenko Institute of Spine and Joint Pathology at the National Academy of Medical Sciences of Ukraine” experimental studies of the strength of the femurs of rats after filling the cavity defects with bone cement were conducted at different times after surgery. The study was performed on 20 laboratory rats of the population of the Institute of Spine and Joint Pathology (ISJP). A cavity defect in the proximal part of the left femur was formed in all the rats with the dental boron. This defect was filled with bone cements based on tricalcium phosphate (TCP). Two types of bone cements were used: aTCP was used for group I (comprising 10 rats), and aTCP reinforced with hydroxylapatite (HA) whiskers were used for group II (comprising the other 10 rats). Animals were removed from the experiment after 1 month and 3 months after the surgery, 5 rats from each group.

The preparations of the operated and contralateral femurs of the laboratory animals were tested. The preparations of the femurs were tested for strength under the vertical compressive load. The loading scheme is shown in fig. 1.

Fig. 1 Scheme of the experiment, F - compressive force; D - dynamometer

Also, the study of compressive strength was performed on samples of bone cement columns. In total, 5 samples of each type of cement were made. The samples were made cylindrical with the diameter of 5 mm and with the length of 10 mm. According to the results of tests of the cement samples, the strength limit was calculated according to the formula [9]: where F is the magnitude of the force at which the destruction of the sample we observed; S is the cross-sectional area of the sample.

During the tests, the values of the compressive force that provoked the destruction of the sample were recorded using the strain gauge SBA-100L and a CAS recording device type CI-2001A.

The test results were processed using statistical methods. The mean (M), standard deviation (SD) as well as the minimum and the maximum values of the experimental data samples for cement samples of different types and each of the groups of bone preparations of experimental animals were calculated. The comparison of the strength limits of the cement samples and the femoral preparations was performed using one-dimensional analysis of variance (ANOVA) and a posteriori Duncan test. The data processing was performed in the IBM SPSS Statistic 20.0 application package [11].

Results of the study and their discussion

The first stage of the study was the one of the compressive strength of dry samples of the bone cement. The cement samples were produced in the laboratory in the manner similar to other experiments: the dry sample was mixed with the solidifying liquid at the room temperature. To give the cement a shape suitable for the strength assessment experiment, it was placed in insulin syringes and then removed.

The results of the tests showed that the cement samples with the addition of hydroxylapatite whiskers have statistically significantly higher strength (p=0.021), as evidenced by the indicators of their strength limit - (15.41±1.93) MPa against (10.57+1.67) MPa of the cement samples not reinforced with hydroxylapatite whiskers. endoprosthesis allotransplant bone calcium

The clear idea of the ratio of the values of the compressive strength of the bone cement samples can be obtained using the diagram shown in fig. 2.

Fig. 2 The diagram of the strength limit of the bone cement samples

The second stage of the work was performed to test the strength of the femoral preparations of the laboratory rats with bone defects, which is filled with the above-mentioned cements. The main parameters that characterize the suitability of the cement for practical use are the cement setting time and the compression strength. The CPC needs to set relatively slowly so that the surgeon has enough time to perform the implantation but at the samtime it has to set quickly enough to prevent the unjustified prolongation of the surgery. The setting time of TCP-based cement is usually several tens of minutes.

According to the studies, a month after filling the bone defect with cement, the strength of the operated bones is determined to be statistically significantly lower than intact bones in both groups. There was no statistically significant difference between the groups depending on the type of the cement (p=0.699), but the average value of the destructive force for the second group of drugs with cement mixed with HA (204+40) H is slightly lower than for the cements without it (214+40) N.

In the diagram in fig.3 you can see the more detailed comparison of the magnitudes of the destructive force due to which the destruction of the femurs of the laboratory animals a month after filling bone defects with bone cements took place. Three months after the surgery, there is a statistically significant difference (p=0.010) in the strength of the intact and the operated bones in the first group of the cements. In the other group of animals, the difference in strength between the intact and the operated bones is determined at the significance limit (p=0.055). Similar to the study a month after the surgery, in terms of the type of the cement used, the statistical significance of the strength was not detected in the groups of the preparations (p=0.932), but the mean values of the destructive force are slightly higher in group I cements (230+70) H against (226+70) H in the second group.

To visually compare the magnitude of the destructive force at which the destruction of the femoral preparations of the laboratory animals three months after filling the bone defects with bone cements took place, a diagram was constructed, which is shown in fig. 4.

Fig. 3 Demonstrates the diagram of the values of the load at which the destruction of the femurs of the laboratory animals a month after filling bone defects with the bone cement took place.

Fig. 4 Demonstrates the diagram of the values of the load at which the destruction of the femurs of laboratory animals three months after filling bone defects with TCP-based cements took place.

Table 1 shows the results of the comparative analysis of the changes in the strength of the preparations of the femurs of rats, depending on the time period after the surgery.

Table 1 The evolution of changes in the strength of the preparations of the femurs of rats, depending on the time period after the surgery

Conclusions

The studied cement from group II, with impurities of HA whiskers has the primary strength limit (15.41±1.93) MPa, which is statistically significantly higher than the strenth limit of the cement from group I (10.57+1.67) MPa. One month after filling the defects of bone tissue with cements based on TCF, the strength of the operated bones is determined to be statistically significantly lower than the intact bones in both groups. There was no statistically significant difference between the groups in terms of the type of cement (p=0.699). Three months after the surgery, the strength of both operated and intact bones increased, but the difference in strength of the intact and the operated bones is not statistically significant. Between the groups of the preparations of the operated bones, in terms of the type of the cement used, the statistical significance of strength was also not determined (p=0.932). From the above-mentioned list, we can conclude that by reinforcing the cement by adding HA whiskers based on aTKP, we increase its strength properties, and to some extent, we slow down the restructuring of the material implanted in the defect of the bone tissue. TCP-based materials are well restructured, but biodegradation is too rapid to form a strong block of bone-implanted material, and they have a fragile structure, which is extremely important for the patient in the postoperative period in terms of the load on the operated limb.

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