Increased Risk of Periprosthetic Fractures and Revision Arthroplasty in Patients Undergoing Shoulder Arthroplasty With a History of Prior Fragility Fractures: A Matched Cohort Analysis.

INTRODUCTION: As rates of anatomic and reverse total shoulder arthroplasty (SA) continue to grow, an increase in the number of osteoporotic patients undergoing SA, including those who have sustained prior fragility fractures, is expected. The purpose of this study was to examine short-term, implant-related complication rates and secondary fragility fractures after SA in patients with and without a history of fragility fractures. METHODS: A propensity score-matched retrospective cohort study was done using the PearlDiver database to characterize the effect of antecedent fragility fractures in short-term complications after SA. Rates of revision SA, periprosthetic fractures, infection, and postoperative fragility fractures were evaluated using multivariate logistic regression analysis. Risks of these complications were also studied in patients with and without preoperative osteoporosis treatment. Statistical significance was set at P < 0.05. RESULTS: A total of 91,212 SA patients were identified, with 13,050 (14.3%) experiencing a fragility fracture within the 3 years before SA. Two years after SA, there were increased odds of periprosthetic fracture (odds ratio [OR] 2.24, 95% confidence interval [CI] 1.68 to 2.99), fragility fracture (OR 9.11, 95% CI 8.43 to 9.85), deep infection (OR 1.68, 95% CI 1.34 to 2.12), and all-cause revision SA (OR 1.68, 95% CI 1.44 to 1.96) within those patients who had experienced a fragility fracture within 3 years before their SA. Patients who were treated for osteoporosis with bisphosphonates and/or vitamin D supplementation before their SA had similar rates of postoperative periprosthetic fractures, fragility fractures, and all-cause revision SA to those who did not receive pharmacologic treatment. CONCLUSION: Sustaining a fragility fracture before SA portends substantial postoperative risk of periprosthetic fractures, infection, subsequent fragility fractures, and all-cause revision SA at the 2-year postoperative period. Pharmacotherapy did not markedly decrease the rate of these complications. These results are important for surgeons counseling patients who have experienced prior fragility fractures on the risks of SA.

Mechanisms by which electroacupuncture­mediated histone acetylation mitigates bone loss in rats with ovariectomy­induced osteoporosis.

The aim of the present study was to investigate the effectiveness of electroacupuncture (EA) on ovariectomy­induced osteoporotic rats to elucidate potential mechanisms by which EA regulates acetylation of histones in caput femoris. A total of 40 female Sprague­Dawley rats were randomly allocated into four groups: Sham operation, ovariectomy­induced osteoporosis (OVX), EA and 17ß­estradiol (E2) treatments. After 8 weeks of intervention, the trabecular morphology of each group was measured by micro­computed tomography. Biomarkers of bone metabolism in serum were detected. The protein expression of histone deacetylase 2 (HDAC2), histone H3, Ac­histone H3 and downstream cytokines involved in osteoblast and osteoclast differentiation were detected. The results showed that EA and E2 both prevented bone loss and improved trabecular morphology in OVX rats. EA was found to suppress the protein expression of HDAC2 and promoted the acetylation of histone H3 compared with the OVX model group. The results indicated that EA promoted the differentiation of osteoblasts, and suppressed that of osteoclasts, thereby improving the trabecular morphology. E2 was shown to regulate the expression of runt­related transcription factor 2 and receptor activator of nuclear factor­κB ligand without modulating the expression of HDAC2, and therefore diverged mechanistically from EA. Overall, the results of the present study suggested that the mechanisms through which EA improved bone mineral density and trabecular morphology may involve the modulation of histone H3 acetylation and regulation of osteoblast and osteoclast differentiation.

Hounsfield units value is a better predictor of pedicle screw loosening than the T-score of DXA in patients with lumbar degenerative diseases.

PURPOSE: To compare the performance of using Hounsfield units (HU) value derived from computed tomography and T-score of dual-energy X-ray absorptiometry (DXA) to predict pedicle screw loosening. METHODS: We reviewed 253 patients aged ≥ 50 years undergoing pedicle screw fixation for lumbar degenerative diseases (LDD). The evaluation of screw loosening: radiolucent zones of ≥ 1 mm thick in X-ray. The criterion for osteoporosis: the lowest T-score ≤ - 2.5. The average HU value of L1-L4 was used to represent lumbar bone mineral density (BMD). The area under receiver operating characteristics curve (AUC) was used to evaluate the performance of predicting screw loosening. RESULTS: One patient underwent reoperation for screw loosening at 9 months follow-up. At 12 months follow-up, the loosening rate was 30.6% (77/252) in the remaining 252 patients. Osteoporotic patients had higher loosening rate than non-osteoporotic patients (39.3% vs. 25.8%, P = 0.026). The T-score showed no significant difference between loosening group and non-loosening group (- 2.1 ± 1.5 vs. - 1.7 ± 1.6, P = 0.074), and so is the lowest lumbar BMD of DXA (0.83 ± 0.16 g/cm2 vs. 0.88 ± 0.19 g/cm2, P = 0.054). The HU value was lower in the loosening group (106.8 ± 34.4 vs. 129.8 ± 45.7, P < 0.001). The HU value (OR, 0.980; 95%CI 0.968-0.993; P = 0.002) was the independent influencing factor of screw loosening. The AUC of predicting screw loosening was 0.666 (P < 0.001) for HU value and 0.574 (P = 0.062) for T-score. CONCLUSIONS: HU value is a better predictor of pedicle screw loosening than T-score of DXA in patients aged ≥ 50 years with LDD. We should not only focus on the DXA measurements when making surgical plans concerning lumbar fixation. These slides can be retrieved under Electronic Supplementary Material.

Preoperative prone position exercises: a simple and novel method to improve tolerance to kyphoplasty for treatment of single level osteoporotic vertebral compression fractures.

BACKGROUND: The proper choice of anesthesia for kyphoplasty remains controversy. There are only a few clinical studies specially focusing on and giving detailed information about this treatment under local anesthesia with or without conscious sedation. To evaluate the effect of preoperative prone position exercises on patient tolerance to percutaneous kyphoplasty under local anesthesia. METHODS: Eighty-three patients with single level osteoporotic vertebral compression fractures were nonrandomly assigned to undergo percutaneous kyphoplasty under local anesthesia with preoperative prone position exercises or without. The number of procedure with or without a pause, need for intravenous sedation, and patient satisfactory were recorded and analyzed. Clinical outcomes were assessed using the visual analog scale and the Oswestry Disability Index. The follow-up time was 6 months. RESULTS: The baseline characteristics of both groups were comparable. The number of procedure without a pause in the exercises group was more than the control group (30/42 patients and 10/41 patients, respectively, P < 0.001), and fewer patients required intravenous sedation in the exercises group (7/42 and 28/41, respectively, P < 0.001). Patients in the exercises group were more satisfied compared to the control group (41/42 and 32/41, respectively, P < 0.01). There were no significant differences between the two groups with regard to improvement in pain and functional scores at all postoperative intervals. CONCLUSIONS: Prone position exercises may improve patient tolerance and satisfaction and reduce the need for intravenous sedation for those with single level vertebral compression fracture undergoing kyphoplasty under local anesthesia. We expect large sample size and multi-center randomized controlled trial studies to be conducted.

Effect of zoledronic acid on lumbar spinal fusion in osteoporotic patients.

PURPOSE: To investigate the effect of zoledronic acid (ZA) on lumbar spinal fusion in patients with osteoporosis. METHODS: This retrospective study includes 94 osteoporotic patients suffering from lumbar degenerative diseases or lumbar fracture who underwent lumbar spinal fusion in our institution from January 2013 to August 2014. They were divided into ZA group and control group according to whether the patient received ZA infusion or not. The patients in ZA group were given 5 mg intravenous ZA at the 3rd-5th days after operation. All patients took daily oral supplement of 600 mg calcium carbonate and 800 IU vitamin D during the follow-up after operation. The Visual Analogue Scale (VAS), Oswestry Disability Index (ODI), and Short Form 36 (SF-36) scores were recorded preoperatively and post-operatively to evaluate the clinic outcomes; the spinal fusion was assessed by X-ray or CT Scan. RESULTS: 64 patients finished the final follow-up, including 30 patients in ZA group and 34 patients in control group. No significant difference was observed in gender, age, and preoperative BMI VAS, ODI, and SF-36 scores between the two groups (P > 0.05). The post-operative VAS and ODI scores decreased rapidly at 3 and 6 months, but rose back slightly at 12 and 24 months in both groups. On the contrary, post-operative SF-36 scores increased rapidly at 3 and 6 months, while fell back slightly at 12 and 24 months, with a statistically significant difference between the two groups at 12 months, but not at 3 and 6 month post-operation. The spinal fusion rate in ZA group was 90% at 6 months, 92% at 12 months, while it was 75% at 6 months, 92.86% at 12 months in control group, significantly different between the two groups at 12 months, but not at 6 months. In the whole follow-up period, adjacent vertebral compressing fracture occurred in five patients in control group, none in ZA group. No pedicle screw loosening was observed in ZA group, with six in control group. CONCLUSIONS: Zoledronic acid accelerates spinal fusion, shortens the time of fusion without changing fusion rate, and also decreases the risk of adjacent vertebral compressing fracture and the rate of pedicle screw loosening, resulting in the improvement of clinical outcomes and quality of life.

Is pelvic fixation the only option to provide additional stability to the sacral anchorage in long lumbar instrumentation? A comparative biomechanical study of new techniques.

BACKGROUND: Supplementary iliac screws have the highest potential to protect S1-pedicle-screws from loosening in long fusion constructs. However, this technique bridges the iliosacral joint with potential disadvantages for the patient. This study aimed to evaluate if two different established fixation techniques can be used in addition to pedicle screws as alternative to iliac screws, and if these two techniques can provide similar stability when S1-pedicle-screws are loosened. METHODS: Flexibility testing with pure moments of 7.5Nm was performed with six human osteopenic/osteoporotic L4-pelvis specimens. The following conditions were investigated: 1. Intact; 2. Destabilization L5/S1; 3. Fixation with rigid L4-S1 pedicle-screw-system; 4. Condition 3- loosening of S1-screws; 5. Condition 4- L5-S2-lamina-hooks; 6. Condition 4- L5/S1-translaminar-screws; 7. Condition 4- S2-ala-ilium screws. FINDINGS: Application of compressive L5-S2-lamina-hooks or L5/S1-translaminar-screws next to pedicle screws in L5 and S1 was feasible in all specimens. L4-S1-pedicle-screw-instrumentation reduced the Range of Motion significantly compared to the destabilized condition. After simulation of S1 screw loosening, lamina hooks only reduced the Range of Motion in flexion/extension significantly. L5/S1-translaminar-screws had a higher stabilizing effect in lateral bending and axial rotation, but the effect of both systems was smaller than with an instrumentation extension to the os ilium. INTERPRETATION: In long lumbar pedicle screw instrumentations including L5/S1, additional ilium screws have the highest potential to protect the S1-anchorage. Additional L5/S1-translaminar-screws can increase stability of the lumbosacral junction without bridging the iliosacral joint, whereas lamina hooks showed no significant biomechanical benefit.

Medical Management of Osteoporosis for Elective Spine Surgery.

Over 50 million Americans have low bone mass. Poor bone quality is known to complicate spinal fusion surgery, which relies on strong bony purchase to be effective. Unfortunately, many spine surgeons do not perform routine workups for either osteoporosis or osteomalacia. Effective screening and risk factor assessment can allow for appropriate medical management of osteoporosis in the perioperative setting, improving outcomes. Medical management can be grouped into several different categories: vitamins and minerals, bisphosphonates, recombinant parathyroid hormone, estrogen replacement or modification, inhibitors of receptor activator of nuclear factor κ-B ligand (RANKL), and calcitonin. Calcium and vitamin D supplements are the least expensive to prescribe, with minimal side effects and promising animal studies, and thus should be provided to most osteoporotic patients. Recombinant parathyroid hormone can also be considered, as clinical studies have demonstrated impressive results in spine fusion patients. Bisphosphonates, estrogen therapy or selective estrogen receptor modulators, and calcitonin should all be avoided in this patient population given unproven benefit and potentially harmful side-effect profiles. Denosumab is potentially an option, but may not be first line given the general lack of supporting data for its use in perioperative management of spine surgery patients.

Treating the Aging Spine.

Demographic trends make it incumbent on orthopaedic spine surgeons to recognize the special challenges involved in caring for older patients with spine pathology. Unique pathologies, such as osteoporosis and degenerative deformities, must be recognized and treated. Recent treatment options and recommendations for the medical optimization of bone health include vitamin D and calcium supplementation, diphosphonates, and teriparatide. Optimizing spinal fixation in elderly patients who have osteoporosis is critical; cement augmentation of pedicle screws is promising. In the management of geriatric odontoid fractures, nonsurgical support with a collar may be considered for low-demand patients, whereas surgical fixation is favored for high-demand patients. Management of degenerative deformity must address sagittal plane balance, which includes consideration of pelvic incidence. Various osteotomies may prove helpful in this setting.

[PREPARATIONS OF PAMIDRONOVIC ACID IN COMPLEX TREATMENT ON OSTEOGENESIS IMPERFECTA].

Modern view of drug therapy in the complex treatment of orthopedic manifestations of osteogenesis imperfecta (OI) was submitted. Developed and tested system of drug correction of structural and functional state of bone tissue (BT) using drugs pamidronovic acid, depending on osteoporosis severity and type of disease. Such therapy is appropriate to apply both independently and in conjunction with surgery to correct deformations of long bones of the lower extremities. Effectiveness and feasibility of the proposed methods of drug therapy was proved, most patients resume features walking and support.

Fragility fracture programs: are they effective and what is the surgeon's role?

Fragility fractures are occurring at an ever-increasing rate, creating an enormous economic and societal impact. Outpatient-based fragility fracture programs have been developed to identify at-risk patients, initiate effective treatment of metabolic bone disease, and improve coordination between members of the patient's care team with the goal of reducing future fractures. Inpatient programs focus on effective, efficient management of patients presenting with acute fractures. Both have proven successful in reducing the impact of fragility fractures, but many challenges exist. The orthopedic surgeon, as part of an integrated team of providers, is integral in identifying at-risk patients, ensuring appropriate care of acute fractures, and initiating treatment protocols to reduce the risk of further injuries.

Hinged external fixation for complex fracture-dislocation of the elbow in elderly people.

The authors report their experience of treating complex elbow fracture-dislocations in elderly people, using a minimally-invasive approach with a new articulated external fixator that is associated with minimal internal fixation. The clinical results for 19 patients are presented according to outcome factors, such as range of motion, pain and function, rate and type of complications, and reoperation rate. The results indicate that this treatment strategy should be considered as a good alternative to other treatment options reported in the literature, including conservative treatment, ORIF with angular stable plates and total elbow arthroplasty.

Drynaria total flavonoids decrease cathepsin K expression in ovariectomized rats.

This study investigated the effects of Drynaria total flavonoids on cathepsin K serum concentrations and gene expression, biomechanics and bone mineral density (BMD) of the tibial shaft in ovariectomized rat models of osteoporosis, and mechanism in the prevention and cure of osteoporosis. Seventy-two female Sprague-Dawley rats were divided into six groups. The rats in each group were subjected to gastric lavage after the model was established. The tibial shaft of the right hindlimb was obtained to measure the BMD. Serum cathepsin K concentrations were determined. The cathepsin K mRNA expression was also determined using fluorescent quantitative polymerase chain reaction. The three-point bending method was performed to measure the maximum bending load of the tibial shaft. The total flavonoid and normal groups had significant differences in serum cathepsin K concentrations compared with that in the estrogen group (P<0.05). The total flavonoid and sham-operated groups also showed significant differences in cathepsin K mRNA expression compared with that in the normal group (P<0.01). The maximum bending load of the rats in the total flavonoid group was significantly different from that in the estrogen group (P<0.05) and the sham-operated and normal groups (P<0.01). The high-dose total flavonoid group elicited a better effect on BMD than that by the medium- and low-dose groups (P<0.05). Thus, Drynaria total flavonoids inhibited the serum cathepsin K concentration and increased the maximum bending load of the tibial shaft in ovariectomized rats.

Development and delivery of patient treatment in the Trondheim Hip Fracture Trial. A new geriatric in-hospital pathway for elderly patients with hip fracture.

BACKGROUND: Hip fractures are common among frail elderly persons and often have serious consequences on function, mobility and mortality. Traditional treatment of these patients is performed in orthopedic departments without additional geriatric assessment. However, studies have shown that interdisciplinary geriatric treatment may be beneficial compared to traditional treatment. The aim of the present study is to investigate whether treatment of these patients in a Department of Geriatrics (DG) during the entire hospital stay gives additional benefits as compared to conventional treatment in a Department of Orthopaedic Surgery (DOS). FINDINGS: A new clinical pathway for in-hospital treatment of hip fracture patients was developed. In this pathway patients were treated pre-and postoperatively in DG. Comprehensive geriatric assessment was performed as an interdisciplinary, multidimensional, systematic assessment of all patients focusing on each patient's capabilities and limitations as recommended in guidelines and systematic reviews. Identification and treatment of co-morbidities, pain relief, hydration, oxygenation, nutrition, elimination, prevention and management of delirium, assessment of falls and osteoporosis were emphasized. Discharge planning started as early as possible. Initiation of rehabilitation with focus on early mobilisation and development of individual plans was initiated in hospital and continued after discharge from hospital. Fracture specific treatment was based upon standard treatment for the hospital, expert opinions and a review of the literature. CONCLUSION: A new treatment program for old hip fracture patients was developed, introduced and run in the DG, the potential benefits of which being compared with traditional care of hip fracture patients in the DOS in a randomised clinical trial.

Future perspectives: the need for large clinical trials.

Fragility fractures represent a growing problem with large economic and patient burdens that are likely to increase as the population ages. The elderly patient with osteopenic bone presents a unique surgical challenge with appreciable risks associated with each surgical treatment option. As demonstrated in this supplement, the current evidence suggests that the best surgical treatment options for patients with fragility fractures remains largely unknown. Additional evidence, from large clinical trials, is required before definitive treatment recommendations can be made in many cases. In this article, we review the example of the femoral neck fracture to illustrate this point.

Augmentation of pedicle screw stability with calcium sulfate cement in osteoporotic sheep: biomechanical and screw-bone interfacial evaluation.

STUDY DESIGN: Augmentation of pedicle screws with calcium sulfate cement (CSC) was performed in osteoporotic sheep. Biomechanical tests, micro-computed tomography (CT) analysis, and histological observation were performed. OBJECTIVE: To investigate the long-term biomechanical performance of pedicle screws augmented with CSC in vivo and evaluated the screw-bone interfacial bonding with micro-CT and histological techniques. SUMMARY OF BACKGROUND DATA: There is little information on the long-term biomechanical performance and screw-bone interfacial bonding of pedicle screws augmented with CSC in osteoporosis in vivo. METHODS: Twelve months after ovariectomy, bilateral pedicles of lumbar vertebrae (L1 to L5) of 6 female sheep were fixed with pedicle screws. One pedicle of each vertebral body was treated with a screw augmented with CSC (CSC group) and the contralateral pedicle was treated with a screw without any augmentation (control group). Three months later, the sheep were killed and biomechanical tests, micro-CT analysis, and histological observation were conducted on the isolated specimen vertebrae. RESULTS: Twelve months after ovariectomy, animal model of osteoporosis was established successfully. Both the axial and vertical stabilities of the pedicle screws in CSC group were significantly enhanced compared with those in the control group (P<0.05). Micro-CT reconstruction and analysis showed that there were more bone trabeculae around the screws in CSC group compared with those in control group (P<0.05), and the bone trabeculae were significantly denser than those in control group (P<0.05). Histological observation showed that CSC was completely degradated and bone trabeculae around the screws in CSC group were more and denser than that in the control group. Bone trabeculae held the screws tightly without any interspaces between screw and bone, which formed strong bonding between bone and screw. CONCLUSIONS: CSC can significantly improve screw-bone interfacial bonding and strengthen the long-term stability of pedicle screws in osteoporotic sheep. Augmentation with CSC may be a potentially useful method to increase the stability of pedicle screws in patients with osteoporosis.

Strontium ranelate treatment enhances hydroxyapatite-coated titanium screws fixation in osteoporotic rats.

Increased bone turnover with excessive bone resorption and decreased bone formation is known to impair implant fixation. Strontium ranelate is well known as an effective antiosteoporotic agent by its dual effect of antiresorbing and bone-forming activity. This study was designed to evaluate the effect of systemic strontium ranelate (SR) treatment on fixation of hydroxyapatite (HA)-coated titanium screws in ovariectomized (OVX) rats. Twelve weeks after being OVX (n=30) or sham (n=10) operated, 40 female Sprague-Dawley rats received unilateral implants in the proximal tibiae. The OVX rats were randomly divided into the following groups: OVX, OVX+SRL ("L" refers to low SR dose of 500 mg/kg/day), OVX+SRH ("H" refers to high SR dose of 1000 mg/kg/day).Twelve weeks after treatment, bone blocks with implants were evaluated with micro-CT and biomechanical push-out tests. Compared to OVX animals, SR treatment increased the bone volume ratio by 51.5% and 1.1-fold, the percentage osteointegration by 1.0-fold and 1.9-fold in micro-CT evaluation, and the maximal force by 1.9-fold and 3.3-fold in biomechanical push-out test, for the low and high dose of SR, respectively. Significant correlation between micro-CT and biomechanical properties demonstrated that trabecular parameters played an important role in predicting the biomechanical properties of implant fixation. Our findings suggest that SR treatment can dose-dependently improve HA-coated screw fixation in OVX rats and facilitate the stability of the implant in the osteoporotic bone.

[Kyphoplasty in osteoporotic spinal fractures]. / Kyphoplastie bei osteoporotischen Wirbelfrakturen.

Kyphoplasty has been the standard procedure for osteoporotic fractures for more than 5 years but the material costs are still very high. The aim of this study was to clarify whether pain reduction could be achieved without increasing the rate of new fractures and also in what areas costs could possibly be reduced. From 15.01.2007 until 15.01.2008, a total of 100 patients with 126 recent osteoporotic spinal fractures were treated by kyphoplasty with an average operation time of 38 min and follow-up times up to 12 months. During this follow-up period 15 lateral and 2 dorsal cement leakages remained asymptomatic and 1 dorsal leakage caused an incomplete paraparesis, which was finally cured completely. All patients were very content and pain measured on the visual analogous scale could be lowered from 8.0 before the operation to 2.7 points after the operation. With material costs of 3,056 Euro, there were additional operation costs of 247 Euro per case. The average effective weight was 2.84. On average 7,810 Euro returns could be achieved, deducting material and operation costs left 4,507 Euro per case. More than 40% of gains were reinvested in operation and material costs. Within 12 months 6 new fractures occurred despite medicinal prophylactic treatment which could also be successfully treated by kyphoplasty. The average visual analogous scale after 12 months was 2.1 points.Kyphoplasty still causes financial deficits due to high material costs, however, patients benefit from a reduction of pain.

The use of calcium sulfate and calcium phosphate composite graft to augment screw purchase in osteoporotic ankles.

BACKGROUND: Screws placed in the distal fibula may not have satisfactory purchase during internal fixation of an osteoporotic ankle fracture. Tibia-pro-fibula screws that extend from the fibula into the distal tibial metaphysis provide additional purchase. The purpose of this study was to investigate if purchase of these screws can be enhanced further by injecting calcium sulfate and calcium phosphate composite graft into the drill holes prior to insertion of the screws. MATERIALS AND METHODS: Bone density was quantified using a DEXA scan in paired cadaver legs. One leg from each pair was randomly selected for injection of composite graft into the screw holes before insertion of the screws. Two screws were inserted through the fibula into the distal tibial metaphysis in each leg, at the level of the syndesmosis under fluoroscopy in a standardized fashion in an MTS machine. RESULTS: After testing 4 pairs of cadaver legs, a statistically significant difference was noted in displacement (p = 0.018 distal, p = 0.0093 proximal), failure load, (p = 0.0185 distal, p = 0.0238 proximal), and failure energy (p = 0.0071 distal, p = 0.0115 proximal) between augmented and non-augmented screws, with the augmented screws being considerably stronger. CONCLUSION: Screws augmented with composite graft provide significantly greater purchase in an osteoporotic fibular fracture model. CLINICAL RELEVANCE: Composite graft augmented screws inserted into the distal tibia from the fibula may enhance the stability of internal fixation of an osteoporotic ankle fracture. This may enable earlier weightbearing and return to function which is important in elderly patients.

Osseointegration of hollow cylinder based spinal implants in normal and osteoporotic vertebrae: a sheep study.

INTRODUCTION: Osteoporosis is not only responsible for an increased number of metaphyseal and spinal fractures but it also complicates their treatment. To prevent the initial loosening, we developed a new implant with an enlarged implant/bone interface based on the concept of perforated, hollow cylinders. We evaluated whether osseointegration of a hollow cylinder based implant takes place in normal or osteoporotic bone of sheep under functional loading conditions during anterior stabilization of the lumbar spine. MATERIALS AND METHODS: Osseointegration of the cylinders and status of the fused segments (ventral corpectomy, replacement with iliac strut, and fixation with testing implant) were investigated in six osteoporotic (age 6.9 +/- 0.8 years, mean body weight 61.1 +/- 5.2 kg) and seven control sheep (age 6.1 +/- 0.2 years, mean body weight 64.9 +/- 5.7 kg). Osteoporosis was introduced using a combination protocol of ovariectomy, high-dose prednisone, calcium and phosphor reduced diet and movement restriction. Osseointegration was quantified using fluorescence and conventional histology; fusion status was determined using biomechanical testing of the stabilized segment in a six-degree-of-freedom loading device as well as with radiological and histological staging. RESULTS: Intact bone trabeculae were found in 70% of all perforations without differences between the two groups (P = 0.26). Inside the cylinders, bone volume/total volume was significantly higher than in the control vertebra (50 +/- 16 vs. 28 +/- 13%) of the same animal (P<0.01), but significantly less (P<0.01) than in the near surrounding (60 +/- 21%). After biomechanical testing as described in Sect. "Materials and methods", seven spines (three healthy and four osteoporotic) were classified as completely fused and six (four healthy and two osteoporotic) as not fused after a 4-month observation time. All endplates were bridged with intact trabeculae in the histological slices. CONCLUSIONS: The high number of perforations, filled with intact trabeculae, indicates an adequate fixation; bridging trabeculae between adjacent endplates and tricortical iliac struts in all vertebrae indicates that the anchorage is adequate to promote fusion in this animal model, even in the osteoporotic sheep.

Pedicle screw motion in the osteoporotic spine after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement: a comparative analysis.

STUDY DESIGN: A biomechanical study addressing the motion of pedicle screws in a human cadaveric, osteoporotic spine model. OBJECTIVES: To compare the fixation of pedicle screws in an osteoporotic spine model after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement and to determine the kinematic patterns of these screws. SUMMARY OF BACKGROUND DATA: Numerous techniques exist for improving the quality of fixation within the osteoporotic spine, including supplementing the construct with laminar hooks, sublaminar wires, or calcium phosphate cement. Direct comparisons of these practices, however, are lacking. METHODS.: Twenty-four cadaveric lumbar vertebrae were instrumented with a pedicle screw and rod construct augmented with laminar hooks, sublaminar wires, or calcium phosphate cement. The screws were tested cyclically with physiologic loads. Rigid body motions of the screws were measured using an optoelectronic camera system, and the motion at the screw tip and at the screw head were calculated. Screw motions were compared using nonparametric paired statistical analysis. RESULTS: Between augmentation groups, there were no significant differences in the magnitude of motion at the screw head and at the screw tip. After calcium phosphate cement supplementation, screw motion was predominantly rotational in nature, whereas rigid body translation of the screw was more common with sublaminar wires or laminar hooks. CONCLUSIONS: The three augmentation techniques were similar in their ability to enhance the rigidity of fixation of the pedicle screws. Differences did exist, however, in the patterns of pedicle screw motion, with the calcium phosphate cement augmentation resulting in less rigid body translation than the other two techniques.