The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 89, Issue 1

Scientific Articles | January 01, 2007

Alendronate Improves Screw Fixation in Osteoporotic Bone

Antonio Moroni, MD¹; Cesare Faldini, MD¹; Amy Hoang-Kim, BSCH¹; Francesco Pegreffi, MD¹; Sandro Giannini, MD¹

¹ Rizzoli Orthopaedic Institute, University of Bologna, Via G.C. Pupilli 1, 40136 Bologna, Italy. E-mail address for A. Moroni: a.moroni@ior.it

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Disclosure: The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at the Rizzoli Orthopaedic Institute, University of Bologna, Bologna, Italy

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2007 Jan 01;89(1):96-101. doi: 10.2106/JBJS.F.00484

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Abstract

Background: Animal studies have demonstrated the efficacy of the use of bisphosphonates to enhance screw fixation in bone. In this prospective, randomized study of pertrochanteric fractures treated with external fixation, we tested whether systemic administration of bisphosphonates would improve the fixation of hydroxyapatite-coated screws implanted in osteoporotic bone.

Methods: Sixteen consecutive patients with a pertrochanteric fracture were selected. Inclusion criteria were female gender, an age of at least sixty-five years, and a bone mineral density T-score of less than —2.5 standard deviations. Exclusion criteria included bisphosphonate treatment during the two-year period prior to the fracture. Fractures were fixed with a pertrochanteric fixator and four hydroxyapatite-coated pins. Two pins were implanted in the femoral head (pin positions 1 and 2), and two were placed in the femoral diaphysis (pin positions 3 and 4). The patients were randomized either to therapy with alendronate for a three-month postoperative period (Group A) or to no therapy (Group B). The Group-A patients received an oral dose of 70 mg of alendronate per week. The fixators were removed after three months.

Results: All of the fractures healed, and no loss of reduction, nonunion, or delayed union was observed. The combined mean extraction torque (and standard deviation) of the pins implanted at positions 1 and 2 (cancellous bone) was 2558 ± 1103 N/mm in Group A and 1171 ± 480 N/mm in Group B (p < 0.0005). The combined mean extraction torque of the pins implanted at positions 3 and 4 (cortical bone) was 4327 ± 1720 N/mm in Group A and 4075 ± 1022 N/mm in Group B.

Conclusions: These data show that weekly systemic administration of alendronate improves pin fixation in cancellous bone in elderly female patients with osteoporosis. We observed a twofold increase in extraction torque with the pins implanted in cancellous bone. These results support the use of alendronate in the treatment of osteoporotic pertrochanteric fractures to improve screw fixation in the femoral head.

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

Figures in this Article

Osteoporosis compromises the structural strength of the bone, thus making it more prone to fracture. Furthermore, osteoporotic bone, especially in the metaphyseal areas, can fail to provide adequate screw purchase. As a consequence, there is a high rate of screw loosening, which can lead to fracture malunion and nonunion¹.

To reduce these complications, fixation augmentation techniques with polymethylmethacrylate, bone grafts, calcium phosphate ceramics, or hydroxyapatite-coated screws have been proposed^2-5. The rationale for the use of hydroxyapatite-coated screws is based on the abilities of hydroxyapatite to bind to metals and to integrate well with the bone. Several animal and clinical studies have described better fixation and lower rates of pin-track infection with use of hydroxyapatite-coated screws^5-12. In a previous clinical comparative study of hydroxyapatite-coated and uncoated external fixation screws, the extraction torque of the hydroxyapatite-coated screws in cortical bone was two times higher than that of the uncoated screws. In the same study, the extraction torque of the hydroxyapatite-coated screws in cancellous bone was sixty times greater that that of the uncoated screws¹³. However, the extraction torque of the hydroxyapatite-coated screws implanted in cancellous bone was remarkably lower than it was in cortical bone, and the rate of pin-track infection of the hydroxyapatite-coated screws implanted in cancellous bone was three times higher than it was in cortical bone. Therefore, there is still a clear need for further improvement in the fixation of hydroxyapatite-coated screws when they are implanted in cancellous bone.

Another innovative approach to enhance implant fixation is the administration of bisphosphonates. Bisphosphonates inhibit the activity, recruitment, and survival of the osteoclasts, thus reducing bone resorption⁶. There is also evidence suggesting that some bisphosphonates may prevent osteocyte and osteoblast apoptosis¹⁴. Other effects include the induction of osteoblast proliferation and the inhibition of inflammatory cells¹⁴. In clinical practice, bisphosphonates are used as antiresorptive agents in a variety of skeletal conditions, including osteoporosis, osteogenesis imperfecta, Paget disease, and metastatic bone lesions^15-18.

Bisphosphonate therapy has also been used to enhance early fixation of total joint prostheses⁷ and to improve their clinical survival by reducing bone loss around the implant¹⁹. Another application of bisphosphonates is improvement of screw fixation^6-9. In a murine study, the local delivery of ibandronate resulted in a substantial increase of 60% in the removal torque of stainless-steel screws two weeks after implantation in the tibia⁸. In the same study, the authors found an increase of 30% in the pull-out force at the same period of time following systemic treatment with ibandronate. In another murine study of external fixation with the use of stainless-steel screws and systemic administration of alendronate, histological analysis performed five weeks postoperatively showed inhibition of bone resorption at the bone-screw interface⁶. Furthermore, in a canine study, enhancement of bone growth into porous metal implants was found following a single systemic dose of zoledronic acid^6,9. In a recent study, implants coated with hydroxyapatite and impregnated with zoledronate showed better fixation in osteoporotic murine bone than that seen in the control group⁷. However, we are unaware of any study evaluating bisphosphonates as a means to improve screw fixation in a clinical setting.

Given the encouraging results of these animal studies, we thought that alendronate therapy could be a viable augmentation to improve screw fixation in osteoporotic bone in the clinical setting. Therefore, we assessed whether hydroxyapatite-coated screw fixation could be further improved by postoperative systemic alendronate therapy in osteoporotic patients with a pertrochanteric fracture.

Materials and Methods

Materials and Methods | Results | Discussion | Appendix | References

This study design was approved by our ethics committee. Sixteen consecutive female patients with a pertrochanteric fracture in osteoporotic bone were identified. Inclusion criteria were female gender, an age of at least sixty-five years, an AO/OTA type-A1 or A2 fracture according to the Orthopaedic Trauma Association classification system²⁰, a pertrochanteric fracture resulting from a minor trauma, no evidence of dementia, the ability to walk unassisted prior to the injury, and a bone mineral density T-score of less than —2.5 standard deviations for the contralateral hip. After the patient was admitted to the hospital, radiographs were made and bone mineral density was measured with a Norland XR-36 scanner (Norland, Fort Atkinson, Wisconsin) in the same ward. Exclusion criteria included a previous hip fracture, an open fracture, a fracture secondary to a malignant tumor, infection at the fracture site, chemotherapy, multiple fractures, and bisphosphonate treatment during the two-year period prior to the fracture. As the patients were enrolled in the study, the objectives and randomization process were explained and informed consent was obtained. The patients were randomized by a computer-generated list to receive either postoperative alendronate therapy (Group A) or no therapy (Group B). At the time of patient enrollment, envelopes containing the group assignment were opened by the investigator.

The mean age (and standard deviation) was 83 ± 7 years in Group A and 86 ± 4 years in Group B. In Group A, six patients had an AO/OTA type-A1 fracture and two had an AO/OTA type-A2 fracture. In Group B, three patients had an AO/OTA type-A1 fracture and five had an AO/OTA type-A2 fracture. The average bone mineral density was 493 ± 173 mg/cm² in Group A and 490 ± 122 mg/cm² in Group B. With regard to comorbidities, no significant difference between the two groups was detected with use of the American Society of Anesthesiologists (ASA) scale.

All fractures were fixed within forty-eight hours following the injury. Intramuscular cephalosporin was given preoperatively and then every eight hours for three days. All patients received spinal anesthesia.

The fractures were reduced under fluoroscopy on a fracture table and then were fixed with an Orthofix pertrochanteric fixator and four 6/5-mm-diameter hydroxyapatite-coated tapered pins (Orthofix, Bussolengo, Italy) (Fig. 1). These pins are slightly tapered with a diameter of 6 mm at the shank and 5 mm at the tip^10,21. The distal part of the pin is threaded to ensure appropriate fixation into the bone. The hydroxyapatite coating was applied by plasma spraying, and it had a mean thickness (and standard deviation) of 56 ± 19 µm. All of the patients received the same pin type. Pins numbered 1 through 4 were implanted from proximal to distal. After predrilling, with a 4.8-mm-diameter drill, two pins were implanted in the femoral head (pin positions 1 and 2) and two were placed in the femoral diaphysis (pin positions 3 and 4). Pins 1 and 2 were implanted to a depth of 2 to 4 mm below the femoral head contour, and pins 3 and 4 were implanted to a depth of two screw threads beyond the opposite bone cortex. A torque wrench was connected to each pin, the torque was applied and measured, and then the fixator was mounted. When the fixators were mounted, care was taken not to bend or twist the pins so as not to place them under undue stress.

The patients were randomized either to therapy with alendronate (Fosamax; Merck, Rahway, New Jersey) for a three-month postoperative period (Group A) or to no therapy (Group B). The patients in Group A received a 70-mg oral dose of alendronate per week starting the first week after surgery. At discharge, Group-A patients were given a three-month prescription and instructions on how to take the alendronate. We monitored compliance by a monthly telephone call to the patients to ask them to count the number of pills taken.

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Fig. 1: A pertrochanteric fracture in an eighty-nine-year-old woman who was treated with external fixation. A: Preoperative radiograph. B: Radiograph made immediately postoperatively. C: Radiograph made three months after fixation removal.

On the first postoperative day, the patients were mobilized and full weight-bearing with a walker or crutches was encouraged. Pin sites were cleaned twice a week with saline solution. After the patients were discharged from the hospital, follow-up visits were scheduled at one and three months. All fixators were removed at three months, without local anesthesia. At the time of fixator removal, the pin-extraction torque was measured and radiographs were made. When the fixators were removed, the pin tracks were classified according to the Checketts and Otterburn system²², in which pin-track infections are graded on a scale of 1 through 6. It is generally necessary to remove affected pins when the infection is grade 4 or higher and to perform additional surgery to eradicate the infection.

Radiographic union was defined as the presence of trabeculae bridging the fracture site or obvious periosteal callus in the fracture line²³. Radiographic analysis also included measurement of the femoral neck-shaft angle. Standard antero-posterior radiographs were made immediately after surgery and again at three months. The femoral neck-shaft angle was measured, and a comparison was made between the three-month and the immediate postoperative angles.

Statistical Analysis

All continuous data were expressed as the mean and standard deviation of the mean. One-way analysis of variance was performed to test hypotheses about the means of different groups. When the Levene test for homogeneity of variances was significant (p < 0.05), the Mann-Whitney U test (evaluated by the Monte Carlo method) was used to check the results of the analysis of variance. The Pearson chi-square test, calculated by the Monte Carlo method, was performed to investigate the relationships between grouping variables. For all tests, p < 0.05 was considered significant. Statistical analysis was carried out with the Statistical Package for the Social Sciences (SPSS) software (version 9.0; SPSS, Chicago, Illinois).

Results

Materials and Methods | Results | Discussion | Appendix | References

In the alendronate-treated group (Group A), no adverse reaction to the drug occurred. All of the patients followed our instructions on drug administration. All of the fractures healed, and there was no loss of reduction, nonunion, or delayed union. No pin loosening or infection occurred. The mean reduction of the femoral neck-shaft angle over time was 2° ± 1° in Group A and 3° ± 2° in Group B.

There were no significant differences in pin insertion torque between the two groups. The combined mean extraction torque of the pins implanted at positions 1 and 2 (cancellous bone of the femoral head) was 2558 ± 1103 N/mm in Group A and 1171 ± 480 N/mm in Group B (p < 0.0005). The combined mean extraction torque of the pins implanted at positions 3 and 4 (cortical bone of the femoral diaphysis) was 4327 ± 1720 N/mm in Group A and 4075 ± 1022 N/mm in Group B; the difference was not significant.

In Group A, fixation of the pins implanted at positions 1 and 2 improved over time as shown by the mean pin extraction torque, which was higher than the corresponding insertion torque (p < 0.0005) (Table I).

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TABLE I Pin Insertion and Extraction Torque in Cancellous and Cortical Bone

	Pin Insertion Torque^*(N/mm)	Pin Extraction Torque^*(N/mm)	P Value†
Cancellous bone (pin positions 1 and 2)
Group A	1250 ± 439	2558 ± 1103	<0.0005
Group B	1125 ± 291	1171 ± 480	NS
Cortical bone (pin positions 3 and 4)
Group A	4021 ± 1563	4327 ± 1720	NS
Group B	3800 ± 880	4075 ± 1022	NS

The values are given as the mean and the standard deviationNS = not significant

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TABLE I Pin Insertion and Extraction Torque in Cancellous and Cortical Bone

	Pin Insertion Torque^*(N/mm)	Pin Extraction Torque^*(N/mm)	P Value†
Cancellous bone (pin positions 1 and 2)
Group A	1250 ± 439	2558 ± 1103	<0.0005
Group B	1125 ± 291	1171 ± 480	NS
Cortical bone (pin positions 3 and 4)
Group A	4021 ± 1563	4327 ± 1720	NS
Group B	3800 ± 880	4075 ± 1022	NS

The values are given as the mean and the standard deviationNS = not significant

In Group B, fixation of the pins implanted at positions 1 and 2 was maintained over time, but it did not improve, as no significant difference was detected between the mean pin extraction and insertion torque (Table I).

Discussion

Materials and Methods | Results | Discussion | Appendix | References

Implant loosening is one of the major problems in both trauma and reconstructive surgical procedures. On implantation of screws and joint prostheses, the bone matrix and cells are damaged and an inflammatory response occurs. Around a recently inserted implant there is osteocyte apoptosis and osteoclast activation with a risk of rapid bone resorption, fibrous tissue formation, and consequently deterioration of implant fixation⁸. It has been shown that screw fixation deteriorates quite rapidly^24,25. Similarly, early loss of fixation has been identified as a key factor for prosthesis loosening in the long term^26-29.

Implant fixation can be improved by calcium phosphate coatings. Prostheses coated with hydroxyapatite are considered to be an improved type of uncemented fixation³⁰. Similarly, screws coated with hydroxyapatite have shown improved fixation and a reduced complication rate in a variety of animal and clinical studies of internal and external fixation. Although the coated implants are very effective, a further improvement of fixation would be of great value, particularly for cancellous bone. This could be particularly beneficial in patients with a substantial risk of implant loosening, such as those with osteoporosis⁷.

Recent animal studies have described positive results for implant fixation with use of either local or systemic administration of bisphosphonates in normal and osteoporotic bone (see Appendix). Because bisphosphonates have a particular affinity for hydroxyapatite as well as for areas of increased bone turnover around skeletal fracture areas, we compared the fixation of osteoporotic pertrochanteric fractures with hydroxyapatite-coated screws with and without the systemic administration of alendronate^{5,10,11,21,31-36}. We decided to use alendronate because it is indicated in these patients, regardless of its effect on implant fixation, since it improves bone quality and is effective in reducing the prevalence of secondary fractures¹⁷. Unlike previous animal studies, we evaluated implant fixation in a clinical setting, under load and in osteoporotic bone^6,8,9,37-40, which enhances the value of our results.

No differences in clinical outcomes, such as fracture-healing or loss of fixation, were found between the two groups. However, these should be addressed in a study with a larger number of patients, as the sample size of the present study was selected to assess whether alendronate therapy would improve screw fixation and not clinical outcomes.

As has been shown in previous studies, the fixation of the hydroxyapatite-coated screws was well maintained, if not improved, over time. This confirms that hydroxyapatite-coated screws are very well fixed, even under load, in osteoporotic bone. However, a further improvement of fixation in cancellous bone was seen in the alendronate-treated group. This result is particularly important because it was seen with already well-fixed screws and showed the powerful effect of alendronate, thus opening the way for further studies and clinical applications of this drug, particularly when dealing with orthopaedic implants inserted in osteoporotic cancellous bone.

Our results indicated a twofold increase in fixation in the screws implanted in the cancellous bone of the femoral head. The improved fixation in cancellous bone confirms the results reported in the study by Miyaji et al.⁶, in which alendronate was administered systemically. Screw fixation in cancellous bone was also greater than previously observed in a similar study of the Orthofix pertrochanteric fixator and hydroxyapatite-coated screws in which alendronate was not administered¹⁰. The positive effect of alendronate on screw fixation is confirmed by the increase over time of the fixation of the screws implanted in the cancellous bone of the femoral head as shown by a screw extraction torque that was higher than the corresponding screw insertion torque. This result was not observed in the control group.

In cortical bone, the difference in fixation between the treated patients and the control group was not significant. We believe that this is because of the very high fixation achieved by the hydroxyapatite-coated screws alone in cortical bone. In previous animal studies of stainless-steel screws and hydroxyapatite-coated titanium implants, improvement of fixation in cortical bone was found at two and three weeks, respectively, following the local delivery of ibandronate and zoledronate^8,12. In our study, the longer period of alendronate administration (three months) might have also contributed to the absence of a significant increase in fixation for the screws implanted in cortical bone. We maintain that, in osteoporotic bone, the need to improve fixation is certainly more important in cancellous bone than it is in cortical bone because implant-loosening in the former is far more frequent than it is in the latter.

Concerns have been raised about the negative impact of bisphosphonate therapy on fracture-healing in elderly patients with osteoporosis⁴⁰. Despite the large number of patients treated with bisphosphonates, the effect of these drugs on fracture-healing has not been extensively investigated in humans. However, according to Morris and Einhorn: "On the basis of the evidence available from preclinical investigations, it may be reasonable to suggest that, at doses comparable with those used in the treatment of osteoporosis, administration of a bisphosphonate in the presence of a fracture will not inhibit healing, although the remodeling of the callus may be mildly delayed."¹⁵ In our study, we did not find any healing complications.

The limitations of this study include the small sample size, and therefore the study does not demonstrate the value of alendronate therapy as a tool to reduce the prevalence of fixation failure in osteoporotic pertrochanteric fractures, as all of the fractures healed. Furthermore, the rate and strength of fracture-healing were not rigorously addressed.

In conclusion, our study showed that alendronate, which has well-known systemic effects on bone quality and secondary fracture prevention, is also effective in improving screw fixation in the cancellous bone of osteoporotic patients with a hip fracture.

Appendix

Materials and Methods | Results | Discussion | Appendix | References

A table summarizing recent animal studies on this subject is available with the electronic versions of this article, on our web site at (go to the article citation and click on "Supplementary Material") and on our quarterly CDROM (call our subscription department, at 781-449-9780, to order the CD-ROM). ?

References

Materials and Methods | Results | Discussion | Appendix | References

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Topics

osteoporosis ; alendronate ; bisphosphonates ; fracture ; bone nails ; bone screws ; durapatite ; hydroxyapatites ; torque ; external fixation devices

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Antonio Moroni, Cesare Faldini, Amy Hoang-Kim, Francesco Pegreffi, Sandro Giannini; Alendronate Improves Screw Fixation in Osteoporotic Bone. The Journal of Bone & Joint Surgery. 2007 Jan;89(1):96-101.

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