Biomechanical comparison of different rod-to-rod connectors to a conventional titanium- and cobalt chromium posterior spinal fixation system.

Introduction: Several types of rod-to-rod connectors are available for the extension of spinal fixation systems. However, scientific literature regarding the mechanical performance of different rod-to-rod connector systems is lacking. Research question: The goal of this study was to evaluate the mechanical characteristics of axial and lateral rod connectors in comparison to a conventional pedicle screw rod (titanium and cobalt chromium) construct. Material and method: Six types of instrumentations were investigated in a standardized test model to quantify the mechanical differences: 1: titanium rod; 2: titanium rod with axial connector; 3: titanium rod with lateral connector; 4: cobalt chromium rod; 5: cobalt chromium rod with axial connector; 6: cobalt chromium rod with lateral connector. All groups were tested in static compression, static torsion and dynamic compression and statistically compared regarding failure load and stiffness. Results: In static compression loading, the use of connectors increased the construct stiffness, but unaffected the yield load. The use of a cobalt chromium rod significantly increased by approximately 40% the yield load and stiffness in comparison to the titanium rod configurations. Under dynamic compression, a similar or higher fatigue strength for all tested groups in comparison to the titanium rod configuration was evaluated, with the exception of titanium rod with axial connector. Conclusion: Biomechanically, using rod connectors is a secure way for the extension of a construct and is mechanically equal to a conventional screw rod construct. However, in clinical use, attention should be paid regarding placement of the connectors at high loaded areas.

Management of Deep Spinal Wound Infections Following Instrumentation Surgery with Subfascial Negative Pressure Wound Therapy.

BACKGROUND AND STUDY AIMS: The treatment of infections following a spine surgery continues to be a challenge. Negative pressure wound therapy (NPWT) has been an effective method in the context of infection therapy, and its use has gained popularity in recent decades. This study aims to analyze the impact of known risk factors for postoperative wound infection on the efficiency and length of NPWT therapy until healing. PATIENTS AND METHODS: We analyzed 50 cases of NPWT treatment for deep wound infection after posterior and posteroanterior spinal fusion from March 2010 to July 2014 retrospectively. We included 32 women and 18 men with a mean age of 69 years (range, 36-87 years). Individual risk factors for postoperative infection, such as age, gender, obesity, diabetes, immunosuppression, duration of surgery, intraoperative blood loss, and previous surgeries, as well as type and onset (early vs. late) of the infection were analyzed. We assessed the associations between these risk factors and the number of revisions until wound healing. RESULTS: In 42 patients (84%), bacterial pathogens were successfully detected by means of intraoperative swabs and tissue samples during first revision. A total of 19 different pathogens could be identified with a preponderance of Staphylococcus epidermidis (21.4%) and S. aureus (19.0%). Methicillin-resistant S. aureus (MRSA) was recorded in two patients (2.6%). An average of four NPWT revisions was required until the infection was cured. Patients with infections caused by mixed pathogens required a significantly higher number of revisions (5.3 vs. 3.3; p < 0.01) until definitive wound healing. For the risk factors, no significant differences in the number of revisions could be demonstrated when compared with the patients without the respective risk factor. CONCLUSION: NPWT was an effective therapy for the treatment of wound infections after spinal fusion. All patients in the study had their infections successfully cured, and all spinal implants could be retained. The number of revisions was similar to those reported in the published literature. The present study provides insights regarding the effectiveness of NPWT for the treatment of deep wound infection after spinal fusion. Further investigations on the impact of potential risk factors for postoperative wound healing disorders are required. Better knowledge on the impact of specific risk factors will contribute to a higher effectiveness of prophylaxis for postoperative wound infections considering the patient-specific situation.

Impact of Obesity on Perioperative Complications on Treatment of Spinal Metastases: A Multicenter Surveillance Study from the German Spine Registry (DWG-Register).

Background The spine is a common location for the development of primary and metastatic tumors, spinal metastases being the most common tumor in the spine. Spinal surgery in obesity is challenging due to difficulties with anesthesia, intravenous access, positioning, and physical access during surgery. The objective was to investigate the effect of obesity on perioperative complications by discharge in patients undergoing surgery for spinal metastases. Methods Retrospective analysis of data from the DWG-register on patients undergoing surgery for metastatic disease in the spine from January 2012 to December 2016. Preoperative variables included obesity (≥ 30 kg/m 2 ), age, gender, and smoking status. In addition, the influence of pre-existing medical comorbidity was determined, using the American Society of Anesthesiologists (ASA) score. Results In total, 528 decompressions with and without instrumentation undergoing tumor debulking, release of the neural structures, or tumor extirpation in metastatic disease of the spine were identified; 143 patients were obese (body mass index [BMI] ≥ 30 kg/m 2 ), and 385 patients had a BMI less than 30 kg/m 2 . The mean age in the group with BMI 30 kg/m 2 or higher (group 1) was 67 years (56.6%). In the group with BMI less than 30 kg/m 2 (group 2), the mean age was 64 years. Most of the patients had preoperatively an ASA score of 3 and 4 (patients with severe general disease). The likelihood of being obese in the logistic regression model seems to be protective by 47.5-fold for blood loss 500 mL or higher. Transfusions occurred in 321/528 (60.7%) patients (group 1, n = 122 and group 2, n = 299; p = 0.04). A total of 19 vertebroplasties with percutaneous stabilization (minimally invasive spine [MIS]), 6 vertebroplasties, and 31 MIS alone were identified. The variables between these groups, with exception of preoperative status (ASA-score; p = 0.02), remained nonsignificant. Conclusion Obese patients were predisposed to have blood loss more than 500 mL more often than nonobese patients undergoing surgery for spinal metastases but with perioperative blood transfusions, invasiveness, nor prolonged hospitalization. Early postoperative mobilization and a low threshold for perioperative venous thromboembolism (VTE) are important in obese patients to appropriately diagnose, treat complications, and minimize morbidity.

Invasiveness has no influence on the rate of incidental durotomies in surgery for multisegmental lumbar spinal canal stenosis (≥3 levels) with and without fusion: analysis from the German Spine Registry data (DWG-Register).

BACKGROUND: Nowadays, perioperative complications as dural tear (DT) with subsequent neurological deficits are documented in independent registers. However, the relationship of these complications with the grade of invasiveness (≥3 levels) is still unclear. The aim of this study was to evaluate perioperative complications, particularly DT with subsequent neurological deficits, between patients undergoing laminotomy and decompression and decompression and fusion in ≥3 levels. METHODS: Retrospective analysis of the data pool of the DWG register based on cases described by 10 clinics between January 2012 and December 2016 was performed. Surgically treated LSS in ≥3 segments were divided into decompression with or without instrumentation and fusion. Cases with intraoperative DT in both subgroups were analysed for risk factor occurrence. The Surgical Invasive Index (SII) was used. RESULTS: DT occurred in 102/941 (10.8%) patients. Difference in DT between groups was non-significant. The likelihood of DT increased by 2.12-fold with previous spinal surgery at the same level and by 1.9-fold for BMI 30-34 and >35 in comparison with BMI 26-29, respectively. Postoperative deep wound infection was increased by 2.39-fold after DT than without. Significance in outcomes between patients with/without DT was not found. The invasiveness index explained 48% of the variation in blood loss and 51% of the variation in surgery duration. CONCLUSIONS: The rate of incidental DT during decompression for LSS with and without fusion in ≥3 levels was associated with BMI and previous surgery at the same spinal level. Invasivness (SII) is valid rather for variables proper to surgery such as bledding and Op-time but no with incidence for DT and subsequent CSF-leackage.

There is no difference in perioperative results between posterior instrumentation with and without interbody cage and debridement in primary spondylodiscitis in adults: a multicenter surveillance study from the German Spine Registry (DWG Register).

BACKGROUND: Primary spondylodiscitis is a medically challenging disease that can lead to recurrent back pain, progressive kyphotic deformity, and neurologic deficits. The incidence rate of primary non-tuberculosis spondylodiscitis has been estimated from 2.2 to 2.4 cases per 100,000 person-years, and it has been reported to be increasing because of the aging population. The objectives were to determine the safety and efficacy of posterior instrumentation (PI) with and without interbody cage, bony attachment and debridement in the treatment of primary spondylodiscitis by comparing perioperative data, functional outcomes, and overall infection-free survival. METHODS: Analysis of data from the DWG Registry on patients who have undergone posterior instrumentation with and without interbody cage, bony attachment and debridement in primary spondylodiscitis from the thoracolumbar junction to S1 (Th10-S1) at 10 institutions from January 2012 to December 2016. RESULTS: In total, 420 posterior instrumentations with and without interbody cage, bony attachment and debridement in primary spondylodiscitis in the thoracolumbar junction to S1 were identified in the registry; N.=138 were exclusively percutaneous posterior instrumented (PPI), while N.=102 underwent open posterior instrumentation (OPI) without interbody cage, bony attachment and debridement and N.=180 OPI with interbody cage, bony attachment and debridement. Clinical evaluation after surgery did not show a significant difference between groups including improvement of the mobilization and infection-free survival. However, with PPI the duration of operation and blood loss was significantly less than OPI with and without interbody cage, bony attachment and debridement. CONCLUSIONS: The results suggest interbody cage, bony attachment and debridement as not indispensable for treatment in primary spondylodiscitis. Therefore, we encourage the use of posterior stabilization alone in the treatment of spondylodiscitis as less invasive procedure reducing costs in instrumentation.

Intra- and postoperative complications in the treatment of spinal metastases . A multicenter surveillance study from the German Spinal Registry (DWG-Register).

BACKGROUND: The incidence of spinal column tumors is estimated to be 0.62 per 100,000 individuals in the USA. It is especially important to understand the incidence and predictive factors for adverse events of surgery in spinal oncology patients, as a single complication may be associated with morbidity, mortality, and costs. The aim of the study was to use a large national registry to evaluate the perioperative cumulative incidence and predictors of major complications, for metastatic spinal tumors. METHODS: This study is a retrospective analysis of data from the DWG registry on patients who have undergone decompression with and without instrumentation undergoing tumor debulking, release of the neural structures, spinal stabilization or tumor extirpation in metastatic disease of the spine in 124 departments from January 2017 to January 2020, as well as vertebroplasty and percutaneous instrumentation. The outcomes evaluated were major complications defined by Finkelstein et al. as: death; cerebral (new postoperative coma or stroke), cardiac, pulmonary or renal complication; symptomatic venous thromboembolism; surgical site infection. RESULTS: In total, 1617 decompressions with and without instrumentation undergoing tumor debulking, release of the neural structures, spinal stabilization or tumor extirpation in metastatic disease in the spine were identified in the registry; N.=266 developed a major complication (group 2), while N.=1351 had no complication (group 1). The mean age in group 1 was 65 years (58.5%), in group 2 69 years (63.5%). In group 2, most of the patients had preoperatively an ASA Score of 3 and 4 (patients with severe general disease): 202/266 (75.9%) being significant. The overall prevalence of a major postoperative complication was 16.5% and for an intraoperative complication remained 8%. The likelihood ratio for major complications by blood loss greater than 500 mL were as follows: cardiovascular event with a likelihood of 4.22 pulmonary insufficiency 4.18 and cerebral 5.47. CONCLUSIONS: This analysis provides predictive models for surgeons to identify patients who may benefit from transitional care programs. Preoperative status, invasiveness, blood loss >500 mL and blood transfusions are independent predictors associated with higher risk of complication.

A Prospective, Randomized Study Evaluating Clinical and Radiographic Efficacy of Lumbar Interbody Fusion Performed Using a Truss Technology-Based Interbody Fusion Device With Homologous Bone or Bone Marrow Aspirate.

BACKGROUND: Our group used vertebral bone marrow aspirate (BMA) with an anterior truss-based interbody implant to promote fusion. This implant has biomechanical characteristics that may enhance bone on-growth and through-growth and allow for the use of BMA clot alone. The primary end point was comparison of the proportion of patients who achieved fusion with the implant packed with either crushed cancellous homologous bone chips (CCB) alone or with BMA clot alone. METHODS: Patients were randomized to receive either BMA clot or CCB in the implant. Both groups also had supplemental fixation. Clinical assessments were performed preoperatively and postoperatively at 3, 6, and 12 months, including for the Oswestry Disability Index, leg and back visual analog scale, EQ5-D, reoperations, complications, and adverse events. Radiographs were obtained prior to discharge and at 3, 6, and 12 months postoperatively. A computed tomography scan was performed 3 months postoperatively. Radiographs were assessed by an independent radiologist to determine fusion status and evidence of subsidence. RESULTS: Between January 2015 and February 2016, 42 consecutive patients were randomized into 1 of the 2 study groups. There were significant postoperative changes within both groups in pain improvement across all outcome scales. There were no significant differences between groups in change scores from preoperative to assessments at any follow-up time point, with the exception of the change in EQ-5D and visual analog scale at 6 months; however, there was no difference at 3 or 12 months. There were no device-related adverse events in either group. All patients achieved grade II fusion at 3 months postoperatively. There was no significant difference in implant subsidence between groups or smokers versus nonsmokers. CONCLUSIONS: The clinical outcomes of this study suggest that reliable fusion can be obtained using an anterior truss-based implant with either CCB or BMA alone. LEVEL OF EVIDENCE: 2.

Carbon fiber-reinforced pedicle screws reduce artifacts in magnetic resonance imaging of patients with lumbar spondylodesis.

The study investigated whether the use of carbon fiber-reinforced PEEK screw material (CF-PEEK) can reduce magnetic resonance imaging (MRI) artifact formation. Two consecutive groups of patients were treated for degenerative spinal disorders of the lumbar spine with dorsal transpedicular spinal fusion. The first group (n = 27) received titanium pedicle screws. The second group (n = 20) received CF-PEEK screws. All patients underwent an MRI assessment within the first four postoperative weeks. For each operated segment, the surface of the artifact-free vertebral body area was calculated as percentage of the total vertebral body. For each implanted segment, the assessability of the spinal canal, the neuroforamina, and the pedicle screws, as well as the surrounding bony and soft-tissue structures was graded from 1 to 5. A mean artifact-free vertebral body area of 48.3 ± 5.0% was found in the in the titanium group and of 67.1 ± 5.6% in the CF-PEEK group (p ≤ 0.01). Assessability of the lumbar spine was significantly improved for CF-PEEK screws (p ≤ 0.01) for all measurements. CF-PEEK pedicle screws exhibit smaller artifact areas on vertebral body surfaces and their surrounding tissues, which improves the radiographic assessability. Hence, CF-PEEK may provide a diagnostic benefit.

Clinical Outcome After Anterior Lumbar Interbody Fusion With a New Osteoinductive Bone Substitute Material: A Randomized Clinical Pilot Study.

STUDY DESIGN: Pilot, single-center, single-blinded, parallel-group, randomized clinical study. OBJECTIVE: The aim of this study was to pilot a randomized clinical study to evaluate whether instrumented anterior lumbar interbody fusion (ALIF) with a new nanocrystalline hydroxyapatite embedded in a silica gel matrix (NH-SiO2) leads to superior radiologic and clinical outcomes at 12-month follow-up compared with instrumented ALIF with homologous bone. SUMMARY OF BACKGROUND DATA: ALIF completed with interbody cages is an established technique for performing arthrodesis of the lumbar spine. There is ongoing discussion about which cage-filling material is most appropriate. This is the first study to assess the efficacy of NH-SiO2 in ALIF surgery. MATERIALS AND METHODS: This randomized, clinical, pilot trial included 2 groups of 20 patients with monosegmental or multisegmental degenerative disease of the lumbar spine who were suitable to undergo monosegmental or bisegmental ALIF fusion at the level L4/L5 and L5/S1 with a carbon fiber reinforced polymer ALIF cage filled with either NH-SiO2 or homogenous bone. Primary outcome was postoperative disability as measured by the Oswestry Disability Index (ODI). Secondary outcomes were postoperative radiographic outcomes, pain, and quality of life. Patients were followed 12 months postoperatively. RESULTS: Mean (±SD) 12-month ODI was 24±17 in the NH-SiO2 group and 27±19 in the homologous bone group (P=0.582). Postoperative radiography, functional outcomes, and quality-of-life indices did not differ significantly between groups at any of the regularly scheduled follow-up visits. CONCLUSIONS: This clinical study showed similar functional, radiologic, and clinical outcomes 12 months postoperatively for instrumented ALIF procedures with the use of NH-SiO2 or homologous bone as cage filling. In the absence of any relevant differences in outcome, we postulate that the pivotal clinical study should be designed as an equivalence trial.

Radiological evaluation of kyphoplasty with an intravertebral expander after osteoporotic vertebral fracture.

Spinal deformities due to osteoporotic vertebral compression fractures can be reduced by balloon kyphoplasty, but the correction may be partly lost when the balloon is deflated. The present study aimed to evaluate an intravertebral expander developed to reduce and maintain vertebral body height while cement is injected to correct spinal deformities due to osteoporotic vertebral fractures. The study included 31 osteoporotic vertebral body fractures in 31 patients, classified as A1 according to the AO classification, who underwent kyphoplasty using an intravertebral expander. The kyphosis angle was significantly corrected from 13.4 degrees prior to kyphoplasty to 10.8 degrees (p < 0.01) after surgery, but this correction was lost at 12 months (13.3 degrees). The correction of the kyphosis angle best correlated with the pre-operative mobility of the fracture (r = 0.59, p < 0.01), and the loss of the kyphosis improvement correlated with the amount of correction (r = 0.49, p = 0.01). All patients, except for six with adjacent vertebral fractures, experienced significant pain reduction (VAS 8.7 pre-operatively and 2.0 at 12 months; p < 0.01), and the pain was not affected by the correction of the spinal deformity or the loss of correction in the follow-up period. These results suggest that the mobility of the fracture mainly determines the extent of deformity correction rather the device used for reduction, and greater corrections are at increased risk for losing the improvement. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:457-465, 2019.

Anterior cement augmentation of adjacent levels after vertebral body replacement leads to superior stability of the corpectomy cage under cyclic loading-a biomechanical investigation.

BACKGROUND: In the operative treatment of osteoporotic vertebral body fractures, a dorsal stabilization in combination with a corpectomy of the fractured vertebral body might be necessary with respect to the fracture morphology, whereby the osteoporotic bone quality may possibly increase the risk of implant failure. To achieve better stability, it is recommended to use cement-augmented screws for dorsal instrumentation. Besides careful end plate preparation, cement augmentation of the adjacent end plates has also been reported to lead to less reduction loss. PURPOSE: The aim of the study was to evaluate biomechanically under cyclic loading whether an additional cement augmentation of the adjacent end plates leads to improved stability of the inserted cage. STUDY DESIGN/SETTING: Methodical cadaver study. MATERIALS AND METHODS: Fourteen fresh frozen human thoracic spines with proven osteoporosis were used (T2-T7). After removal of the soft tissues, the spine was embedded in Technovit (Kulzer, Germany). Subsequently, a corpectomy of T5 was performed, leaving the dorsal ligamentary structures intact. After randomization with respect to bone quality, two groups were generated: Dorsal instrumentation (cemented pedicle screws, Medtronic, Minneapolis, MN, USA)+cage implantation (CAPRI Corpectomy Cage, K2M, Leesburg, VA, USA) without additional cementation of the adjacent endplates (Group A) and dorsal instrumentation+cage implantation with additional cement augmentation of the adjacent end plates (Group B). The subsequent axial and cyclic loading was performed at a frequency of 1 Hz, starting at 400 N and increasing the load within 200 N after every 500 cycles up to a maximum of 2,200 N. Load failure was determined when the cages sintered macroscopically into the end plates (implant failure) or when the maximum load was reached. RESULTS: One specimen in Group B could not be clamped appropriately into the test bench for axial loading because of a pronounced scoliotic misalignment and had to be excluded. The mean strength for implant failure was 1,000 N±258.2 N in Group A (no cement augmentation of the adjacent end plates, n=7); on average, 1,622.1±637.6 cycles were achieved. In Group B (cement augmentation of the adjacent end plates, n=6), the mean force at the end of loading was 1,766.7 N±320.4 N; an average of 3,572±920.6 cycles was achieved. Three specimens reached a load of 2,000 N. The differences between the two groups were significant (p=.006 and p=.0047) regarding load failure and number of cycles. CONCLUSIONS: Additional cement augmentation of the adjacent end plates during implantation of a vertebral body replacement in osteoporotic bone resulted in a significant increased stability of the cage in the axial cyclic loading test.

Using the Oxford Foot Model to determine the association between objective measures of foot function and results of the AOFAS Ankle-Hindfoot Scale and the Foot Function Index: a prospective gait analysis study in Germany.

OBJECTIVE: After cross-cultural adaption for the German translation of the Ankle-Hindfoot Scale of the American Orthopaedic Foot and Ankle Society (AOFAS-AHS) and agreement analysis with the Foot Function Index (FFI-D), the following gait analysis study using the Oxford Foot Model (OFM) was carried out to show which of the two scores better correlates with objective gait dysfunction. DESIGN AND PARTICIPANTS: Results of the AOFAS-AHS and FFI-D, as well as data from three-dimensional gait analysis were collected from 20 patients with mild to severe ankle and hindfoot pathologies.Kinematic and kinetic gait data were correlated with the results of the total AOFAS scale and FFI-D as well as the results of those items representing hindfoot function in the AOFAS-AHS assessment. With respect to the foot disorders in our patients (osteoarthritis and prearthritic conditions), we correlated the total range of motion (ROM) in the ankle and subtalar joints as identified by the OFM with values identified during clinical examination 'translated' into score values. Furthermore, reduced walking speed, reduced step length and reduced maximum ankle power generation during push-off were taken into account and correlated to gait abnormalities described in the scores. An analysis of correlations with CIs between the FFI-D and the AOFAS-AHS items and the gait parameters was performed by means of the Jonckheere-Terpstra test; furthermore, exploratory factor analysis was applied to identify common information structures and thereby redundancy in the FFI-D and the AOFAS-AHS items. RESULTS: Objective findings for hindfoot disorders, namely a reduced ROM, in the ankle and subtalar joints, respectively, as well as reduced ankle power generation during push-off, showed a better correlation with the AOFAS-AHS total score-as well as AOFAS-AHS items representing ROM in the ankle, subtalar joints and gait function-compared with the FFI-D score.Factor analysis, however, could not identify FFI-D items consistently related to these three indicator parameters (pain, disability and function) found in the AOFAS-AHS. Furthermore, factor analysis did not support stratification of the FFI-D into two subscales. CONCLUSIONS: The AOFAS-AHS showed a good agreement with objective gait parameters and is therefore better suited to evaluate disability and functional limitations of patients suffering from foot and ankle pathologies compared with the FFI-D.

Small cavity creation in the vertebral body reduces the rate of cement leakage during vertebroplasty.

Cement leakage is the most common complication during vertebroplasty and may result in serious morbidity. Measures to reduce the rate of cement leakage are valuable ways to improve vertebroplasty safety. The present study aimed to evaluate whether creating a small cavity in the vertebral body prior to cement injection would reduce the rate of cement leakage during vertebroplasty. The study included 36 consecutive patients with 42 painful osteoporotic vertebral body compression fractures that were classified as A1 fractures according to AO classification. Patients were randomly assigned to receive either treatment with vertebroplasty (control) or with a procedure termed cavuplasty, in which a small cavity was created in the vertebral body prior to cement injection. CT scanning was performed to detect cement leakage. Cement leakage was observed in 14 (66.6%) of the 21 vertebral bodies treated with vertebroplasty and 5 (23.8%) of the 21 vertebral bodies treated with cavuplasty (p = 0.012). These results suggest that the creation of a small cavity in the vertebral body prior to cement injection is an effective way to reduce cement leakage during vertebroplasty. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:154-159, 2017.

Alendronate prevents femoral periprosthetic bone loss following total hip arthroplasty: prospective randomized double-blind study.

Following total hip arthroplasty (THA), femoral periprosthetic bone undergoes a remodeling process that results in bone loss in its proximal regions that may compromise the long-term outcome of THA. Periprosthetic bone loss mainly occurs during the first postoperative months. The question is whether a postoperative treatment with alendronate is effective in reducing periprosthetic bone loss and which doses and duration of treatment are required. In a 12-month prospective, randomized double-blind study, 51 patients undergoing cementless THA were treated postoperatively either with a daily dose of 20 mg alendronate for 2 months and 10 mg for 2 months thereafter (group I), with 20 mg of alendronate for 2 months and 10 mg for 4 months thereafter (group II), or treated with placebo (group III). Proximal femoral bone mineral density (BMD) was measured with dual-energy X-ray absorptiometry (DEXA) and serum biochemical markers of bone turnover bone specific alkaline phosphatase, osteocalcin, and C-terminal telopeptides (CTX-I) were assayed. Six months of alendronate treatment significantly reduced (p<0.001) bone loss in proximal medial region (-10%) compared with placebo (-26%). All biochemical markers of bone turnover were suppressed by alendronate. These data suggest that alendronate administered for the first 6 postoperative months following THA was effective in preventing early periprosthetic bone loss.

PMMA-hydroxyapatite composite material retards fatigue failure of augmented bone compared to augmentation with plain PMMA: in vivo study using a sheep model.

Polymethylmethacrylate (PMMA) is the most commonly used void filler for augmentation of osteoporotic vertebral fracture, but the differing mechanical features of PMMA and osteoporotic bone result in overload and failure of adjacent bone. The aim of this study was to compare fatigue failure of bone after augmentation with PMMA-nanocrystalline hydroxyapatite (HA) composite material or with plain PMMA in a sheep model. After characterization of the mechanical properties of a composite material consisting of PMMA and defined amounts (10, 20, and 30% volume fraction) of HA, the composite material with 30% volume fraction HA was implanted in one distal femur of sheep; plain PMMA was implanted in the other femur. Native non-augmented bone served as control. Three and 6 months after implantation, the augmented bone samples were exposed to cyclic loading and the evolution of damage was investigated. The fatigue life was highest for the ovine native bone and lowest for bone-PMMA specimens. Bone-composite specimens showed significantly higher fatigue life than the respective bone-PMMA specimens in both 3- and 6-month follow-up groups. These results suggest that modification of mechanical properties of PMMA by addition of HA to approximate those of cancellous bone retards fatigue failure of the surrounding bone compared to augmented bone with plain PMMA.

Nanocrystalline hydroxyapatite facilitates bone apposition to polymethylmethacrylate: histological investigation using a sheep model.

Polymethylmethacrylate (PMMA) is the most commonly used bone void filler for vertebral augmentation in osteoporotic fracture. It provides mechanical stability and immediate pain relief; however, PMMA is not osteointegrated and is separated from the surrounding bone tissue by a thin fibrous layer. The aim of this study was to investigate the effect of nanocrystalline hydroxyapatite (HA) on osteointegration of PMMA in a sheep model. A composite material, consisting of PMMA and nanocrystalline HA (70:30, v/v), was implanted in one distal femur, with pure PMMA in the other femur as a control. Three and 6 months after implantation, the distal femora were histologically investigated. All composite implants exhibited a tight junction to the surrounding bone tissue, with minimal bone ingrowth into the outer surface of the implant. In comparison, with use of the control implants, we observed an overall bone resorption around pure PMMA, with fibrous connective tissue encapsulating the implant. These results suggest that nanocrystalline HA enables osteointegration of PMMA in bone tissue, which might alter the biomechanical characteristics of the osteoporotic vertebral body after augmentation.

Changes of femoral periprosthetic bone mineral density 6 years after treatment with alendronate following total hip arthroplasty.

Earlier osteodensitometric results of femoral periprosthetic bone showed that postoperative antiresorptive treatment with alendronate following total hip arthroplasty (THA) reduces the periprosthetic bone loss that commonly occurs in the first months after surgery. However, whether alendronate can prevent periprosthetic bone loss over the long term, or if bone loss occurs after discontinuing alendronate is unknown. Femoral periprosthetic bone mineral density (BMD) was assessed in 49 patients 6 years after cementless total hip arthroplasty using dual energy X-ray absorptiometry. Twenty-nine patients were treated postoperatively with alendronate and 20 control patients received no treatment. All patients were followed up at 12 months after surgery in a prospective randomized study. The bone mineral density was evaluated in 7 regions of interest according to the Gruen protocol. Six years after total hip arthroplasty, no significant changes were detected in femoral periprosthetic BMD when compared with results at 1 year, and the bone loss in patients with postoperative alendronate treatment was still significantly less than those without treatment. These results suggest that the prevention of femoral periprosthetic bone loss following THA achieved by postoperative antiresorptive treatment with alendronate is of long-standing effect, and further bone loss does not occur after the first postoperative year.

Changes of the biochemical markers of bone turnover and periprosthetic bone remodeling after cemented hip arthroplasty.

Do periprosthetic bone loss and postoperative levels of the biochemical markers of bone turnover correlate? The femoral bone mineral density of 53 patients was measured by dual-energy x-ray absorptiometry 1 week and 2, 4, 6, and 12 months after cemented total hip arthroplasty (THA). Biochemical markers of bone turnover were assayed preoperatively and 3, 8, 16, and 24 weeks post-THA. Greatest bone loss was detected in the calcar region (region of interest 7), on average, 16% after 1 year. A marker of bone resorption, C-terminal telopeptides of type I collagen, increased 21% 3 weeks after THA. A significant correlation between periprosthetic bone loss in region of interest 7 after 1 year and type I collagen at 3 weeks was seen (r = -0.42, P = .003). Data suggest that periprosthetic bone loss is induced by an early postoperative high activity of osteoclasts. Counteracting this osteoclast activity with a limited and timely postoperative antiresorptive treatment may be concluded for clinical application.

Bone strength influences periprosthetic bone loss after hip arthroplasty.

UNLABELLED: Our primary question was whether bone strength at the time of surgery, reflected by the lumbar spine T-score and femoral cortical thickness, influences periprosthetic bone loss after a total hip arthroplasty. Using dual energy xray absorptiometry we preoperatively and postoperatively examined 38 consecutive patients having cementless total hip arthroplasties for their bone density. Bone strength was estimated using lumbar spine bone mineral density and the ipsilateral diaphyseal cortical thickness of the femur measured on radiographs. Periprosthetic femoral bone mineral density was measured with dual energy xray absorptiometry within 1 week postoperatively and at 2, 4, 6, 9, 12, and 24 months thereafter. Periprosthetic bone loss was influenced by the patient's bone strength at the time of surgery. Bone loss in the calcar femoris (as much as 54% after 2 years) was greater in patients with a low lumbar spine T-score or low femoral cortical thickness. Preoperative assessment of bone strength (ie, lumbar spine bone mineral density and femoral cortical thickness on radiographs) served as a reliable indicator in predicting the extent of periprosthetic bone loss after total hip arthroplasty. LEVEL OF EVIDENCE: Prognostic Study, Level I (high quality prospective study-all patients were enrolled at the same point in their disease with > or = 80% followup of enrolled patients). See the Guidelines for Authors for a complete description of levels of evidence.