Injectable calcium phosphate in the treatment of distal radial fractures

Outcome of tibial plateau fractures managed with calcium phosphate cement

OBJECTIVES

To compare the use of an injectable calcium phosphate cement (Skeletal Repair System (SRS), Norian corporation, Cupertino, CA) and minimal internal fixation with buttress plating and bone grafting for lateral tibial plateau fractures.

STUDY DESIGN

Retrospective analysis with 13 age, sex and fracture matched pairs of tibial plateau fractures.

METHODS

Thirteen patients with lateral tibial plateau fractures treated with buttress plating and bone grafting were matched with 13 patients treated using minimal internal fixation and an injectable calcium phosphate cement (SRS). All patients were followed for a minimum of one year. The operative time, quality of reduction, maintenance of reduction and development of post-traumatic osteoarthritis was compared in both groups.

RESULTS

The mean duration of surgery was 101 min in patients treated with buttress plating and bone grafting and 55 min in patients treated with SRS (P < 0.0001). Nine patients in the internal fixation and bone graft group had excellent anatomical reductions as judged on post-operative radiographs but some loss of reduction was observed in 8 of the 13 (61%) cases. All 13 patients from the SRS group had an excellent reduction on post-operative radiographs but 3 (23%) demonstrated some loss of reduction of the plateau. The mean residual plateau depression at one year was 4mm in the buttress plate group and 0.7 mm in the SRS group (P < 0.005). Two patients (15%) in the buttress plate group developed post-traumatic osteoarthritis and required knee arthroplasty.

CONCLUSIONS

The use of SRS was associated with more favourable anatomical results than conventional treatment with buttress plating and bone grafting for lateral tibial plateau fractures.

Corrective osteotomy of malunited distal radius fractures using carbonated hydroxyapatite as an alternative to autogenous bone grafting

PURPOSE

The purpose of the present study was to report on the author's experience using carbonated hydroxyapatite as a bony substitute in distal radius corrective osteotomies.

METHODS

Six patients had a corrective osteotomy for a malunited distal radius fracture using carbonated hydroxyapatite as an alternative to an autogenous bone graft. Internal fixation of the osteotomy was achieved by using 2 or 3 K-wires.

RESULTS

At an average follow-up evaluation of 33 months (range, 22-45 mo) all the osteotomies united. Wrist flexion-extension motion improved from 75 degrees to 110 degrees , forearm rotation increased from 116 degrees to 157 degrees , and grip strength had an average increase of 140% at the time of the final follow-up evaluation. All patients were satisfied and there were no reports of persistent pain. Radiographic evaluation showed an average volar tilt improvement from a preoperative dorsal angulation shifting into a neutral position in the sagittal plane; radial lengthening improved from an average of 4 mm (range, 2-6 mm) before surgery to 7 mm (range, 5-9 mm) after surgery, ulnar plus deformity improved by 5 mm. Radiographically the carbonated hydroxyapatite material was integrated completely into the bone tissue with evidence of progressive re-absorption and bony calcification over time. The Mayo wrist score system, according to Cooney and Krimmer modifications, improved by an average of 88 and 98 points (0-100 points), respectively.

CONCLUSIONS

On the basis of this preliminary experience it is reasonable to consider carbonated hydroxyapatite as a viable alternative to bone grafting in conjunction with surgical correction of a distal radius malunion. It must be augmented, however, with internal fixation.

Evaluation of an in situ setting injectable calcium phosphate as a new carrier material for gentamicin in the treatment of chronic osteomyelitis: Studies in vitro and in vivo

A study was performed to investigate the effectiveness of hydroxyapatite cement (HAC) as a new carrier system in the treatment of chronic, posttraumatic osteomyelitis. In the in vitro study, release of gentamicin from standard cylinders of HAC were measured by agar diffusion test. As a representative for mechanical properties, compression strength was measured in order to detect changes when mixing HAC with gentamicin. In the in vivo study, bone infection was induced according to the model of Norden by injection of 1 ml Na-morrhuat and 3 x 10(6)CFU Staphylococcus aureus. After 3 weeks, when chronic stage of infection was obtained, 17 animals were treated by debridement and filling the marrow either with HAC alone or HAC mixed with gentamicin (32 mg/g). Animals of the control groups were left untreated. After 6 weeks, all animals were sacrificed. Hematological, radiological, microbiological and histological examinations were carried out by covered investigation. Best evidence of the efficiency of treatment was observed in histopathological and microbiological findings. In all swabs of the control groups, taken 6 weeks following infection S. aureus were detected which were clonal to the strain used for induction of osteomyelitis. In HAC/gentamicin-treated animals, no growth was detectable after 7 days of culturing in BHI bouillon. In the HAC/gentamicin-treated group, there was no histopathological evidence of infection. In all other groups different stages of chronic osteomyelitis were found. No side effect was observed, neither locally nor systemically by HAC or gentamicin. Therefore, HAC is considered to be a very effective carrier for antibiotics in treatment of chronic, posttraumatic osteomyelitis.

Enhancement of initial stability of press-fit femoral stems using injectable calcium phosphate cement: an in vitro study in dog bones

In this in vitro study we evaluated the initial stability of cementless femoral stems using an injectable calcium phosphate (Ca-P) cement. The cement was not used to form a cement mantle as is routinely done in PMMA cemented prostheses but functioned as an additive to fill the small gaps that exist between a press-fit placed titanium plasma sprayed implant and the bone bed. Six pair of Beagle femora were used in this study. In a random fashion, one femur of each pair was used for placement of a prosthesis without Ca-P cement, the contralateral was used for press-fit placement after injection of the calcium phosphate cement into the intramedullary canal. The reconstructions were placed in a MTS testing machine, tilted 15 degrees in varsus and 15 degrees of endorotation to obtain a physiological load on the femoral head. The load was applied stepwise from zero to a maximum of 100, 250 and 400 N, respectively. At each loading step the load was applied dynamically at a frequency of 1 Hz for 30 min. Between the loading steps, the load was removed for 10 min to allow elastic recovery. The stability of the stems was determined at each loading step with roentgen-stereophotogrammetric analysis. Results showed that with the prostheses without Ca-P cement the most important displacements were movement into varus (max. 818 microm under 400 N) and subsidence (max. 587 microm under 400 N). The displacements showed large variation. After unloading some elastic recovery occurred. In the specimens with Ca-P cement, displacements were negligible. As determined by an F-test the variations found were significantly smaller for the press-fit+Ca-P cement relative to the press-fit prosthesis at all loading steps (p<0.05). A paired t-test revealed significant differences in the mentioned displacements between the press-fit- and press-fit+Ca-P cement prosthesis at a loading with 400 N (P<0.05). On the basis of these results we conclude that the use of Ca-P cement increases the initial stability of press-fit inserted plasma-sprayed femoral prostheses and corrects for the high variability in displacements found with press-fit insertion of these femoral hip prostheses.

New method of pediatric cranioplasty for skull defect utilizing polylactic acid absorbable plates and carbonated apatite bone cement

Cranial defect repair in the pediatric population requires a variety of special considerations. The pediatric skull has a dynamic nature that prohibits the use of rigid fixation, which is commonly applied in the adult population. A technique using a combination of polylactic acid plates and carbonated apatite bone cement has been devised by our group. Skull defects of varying sizes were repaired in 34 pediatric patients. Patients were examined on postoperative day 3 and at 3 months via three-dimensional computed tomography scans. Patients have been followed up to 60 months after surgery without complications or failures to date. This method benefits the pediatric patients undergoing cranioplasty by minimizing the insertion of long-term foreign bodies and allows the possibility for transformation of this construct into viable tissue.

The Use of Novabone and Norian in Cranioplasty: A Comparative Study

Bone replacement products have enhanced the ease of reconstructing bone while improving morbidity related to bone harvest. Although these products are successfully used, studies of bone healing and biomechanical strength are lacking. We aimed to compare how Norian CRS (cranial replacement substance) and Novabone C/M heal in a cranial defect. Adult New Zealand rabbits underwent removal of a critical size cranial defect. The defect was filled with Novabone (n = 8), Novabone plus demineralized bone matrix (n = 8), or Norian (n = 8), or it was left empty (n = 8). Rabbits were euthanized at 8 weeks. Cranial specimens were harvested and soft radiographs, contact microradiographs, and biomechanical testing were done. Soft radiographs revealed opacification like adjacent bone with Novabone, which was augmented when Novabone was combined with demineralized bone matrix. Norian maintained an opaque appearance. The control group did not heal. Contact microradiographs demonstrated bone within the healing defect with Novabone, which was augmented by demineralized bone matrix. Norian was not replaced with bone but served as a scaffold for bone formation. Biomechanical indentation testing demonstrated that the stiffness of Norian was the highest. Novabone plus demineralized bone matrix had a higher stiffness than Novabone alone. All experimental groups had a statistically significant difference compared with Norian. None of the groups achieved the strength of unoperated native bone. Studying two popular products, we found evidence that Novabone was incorporated into cranial bone, regenerating the bone. Novabone healed at a faster rate, creating a stronger product, with demineralized bone matrix. The biomechanical strength of the healed defect was higher in the Norian group, because the bone cement remained solid and was not incorporated, unlike crania reconstructed with Novabone.

Degradable injectable bone cement in maxillofacial surgery: indications and clinical experience in 27 patients

BACKGROUND

A carbonated apatite cement (NORIAN SRS) was used as a bone mineral substitute for the calvaria or viscerocranium in 27 patients. It has the consistency of a paste and hardens at physiologic pH and body temperature due to dahllite crystallization, which has the stoichiometric formula Ca(8.8)(HPO(4))(0.7)(PO(4))(4.5)(CO(3))(0.7)(OH)(1.3).

MATERIAL AND METHODS

The cement was used for posttraumatic bone defects in the orbital, periorbital or malar regions (nine patients), posttraumatic deformities of the frontal bone (six patients), tumour-dependent bony defects of the calvaria (two patients) and posttraumatic or cystic defects of the mandible (five patients). In another five patients, the material was used to augment the atrophic anterior mandible in combination with the insertion of dental implants. Follow-up varied between 6 and 40 months (mean: 29 months).

RESULTS

There was no inflammatory reaction surrounding the implanted material. There was no sign of infection in any of the patients and only one case of partial wound dehiscence with superficially exposed material. The defect fillings and augmentations were successful in all patients. None of the 19 dental implants which were inserted in combination with the material showed any sign of infection or loosening. Also, there was no loosening of the implants after loading (mean follow-up: 15 months). From the check-up radiographs, the material could be seen as a dense, radio-opaque structure. There were no material fractures or dislocations. Radiologically, the material seemed to be completely replaced by bony tissue after 30 months.

CONCLUSION

Our 5-year clinical experience suggests that the material is a suitable bone mineral substitute for cranio-maxillofacial surgery especially for moderate-sized defects of the calvaria and forehead bone. It has advantages over preformed, solid bone substitute materials, and, due to its initial plasticity and eventual great compressive strength, it can also stabilize dental endosseous implants in the atrophic mandible.

In vivo behavior of three different injectable hydraulic calcium phosphate cements

Two dicalcium phosphate dihydrate (DCPD) hydraulic cements and one apatite hydraulic cement were implanted in epiphyseal and metaphyseal, cylindrical bone defects of sheep. The in vivo study was performed to assess the biocompatibility of the DCPD cements, using the apatite cement as control. After time periods of 2, 4 and 6 months the cement samples were clinically and histologically evaluated. Histomorphometrically the amount of new bone formation, fibrous tissue and the area of remaining cement were measured over time. In all specimens, no signs of inflammation were detectable either macroscopically or microscopically. All cements were replaced by different amounts of new bone. The two DCPD-cements showed the highest new bone formation and least cement remnants at 6 months, whereas the apatite was almost unchanged over all time periods.

Augmentation expérimentale de la résistance du radius distal ostéoporotique par un ciment phosphocalcique

Diagnosis and treatment of osteoporosis are focused on demineralisation but bone mineral density is not directly correlated with bone strength. As with every material, the mechanical strength of bone depends upon its Young's modulus and its cross-sectional moment of inertia. In the clinical situation, bone strength can be quantified using peripheral quantitative computed tomography imaging (pQCT), a non-invasive imaging method, which allows calculation of a strength index. In this study, we tried to increase the fracture threshold of the distal radius by directly increasing bone strength rather than density. Twenty wrists in 10 cadavers were filled percutaneously with a calcium phosphate cement. Fluoroscopy and pQCT were performed twice, once before cementing and again 24 h after cement crystallisation to hydroxyapatite. We obtained measurements of trabecular and total bone density, and also stress strain index (SSI). Our results showed that trabecular bone density increased by a factor of 2.85, whereas total bone density increased by 1.61 and SSI by 1.99. Fluoroscopy showed two small leaks of cement at the point of injection. This study demonstrated that percutaneous injection of calcium phosphate cement increased distal radius strength, and consequently its fracture threshold. This technique could be employed in the future to prevent the occurrence of fractures in osteoporotic patients.

Norian SRS cement compared with conventional fixation in distal radial fractures. A randomized study

BACKGROUND

A prospective, randomized multicenter study was conducted to evaluate closed reduction and immobilization with and without Norian SRS (Skeletal Repair System) cement in the management of distal radial fractures. Norian SRS is a calcium-phosphate bone cement that is injectable, hardens in situ, and cures by a crystallization reaction to form dahllite, a carbonated apatite equivalent to bone mineral.

METHODS

A total of 323 patients with a distal radial fracture were randomized to treatment with or without Norian SRS cement. Stratification factors included fracture type (intra-articular or extra-articular), hand dominance, bone density, and the surgeon's preferred conventional treatment (cast or external fixator). The subjects receiving Norian SRS underwent a closed reduction followed by injection of the cement percutaneously or through a limited open approach. Wrist motion, beginning two weeks postoperatively, was encouraged. Control subjects, who had not received a Norian SRS injection, underwent closed reduction and application of a cast or external fixator for six to eight weeks. Supplemental Kirschner wires were used in specific instances in both groups. Patients were followed clinically and radiographically at one, two, four, and between six and eight weeks and at three, six, and twelve months. Patients rated pain and the function of the hand with use of a visual analog scale. Quality of life was assessed with use of the Short Form-36 (SF-36) health status questionnaire. Complications were recorded.

RESULTS

Significant clinical differences were seen at six to eight weeks postoperatively, with better grip strength, wrist range of motion, digital motion, use of the hand, and social and emotional function, and less swelling in the patients treated with Norian SRS than in the control group (p < 0.05). By three months, these differences had normalized except for digital motion, which remained significantly better in the group treated with Norian SRS (p = 0.015). At one year, no clinical differences were detected. Radiographically, the average change in ulnar variance was greater in the patients treated with Norian SRS (+2.0 mm) than in the control group (+1.4 mm) (p < 0.02). No differences were seen in the total number of complications, including loss of reduction. The infection rate, however, was significantly higher (p < 0.001) in the control group (16.7%) than in the group treated with Norian SRS (2.5%) and the infections were always related to external fixator pins or Kirschner wires. Four patients with intra-articular extravasation of cement were identified; no sequelae were observed at twenty-four months. Cement was seen in extraosseous locations in 112 (70%) of the SRS-treated patients; loss of reduction was highest in this subgroup (37%). The extraosseous material had disappeared in eighty-three of the 112 patients by twelve months.

CONCLUSIONS

Our results indicate that fixation of a distal radial fracture with Norian SRS cement may allow for accelerated rehabilitation. A limited open approach and supplemental fixation with Kirschner wires are recommended. Additional or alternate fixation is necessary for complex articular fractures.

Palmar plating with calcium phosphate bone cement for unstable Colles' fractures

A prospective study was done in 20 patients with unstable Colles' fractures with metaphyseal bone defects and who were treated with palmar plating combined with injectable calcium phosphate bone cement. The patients were three men and 17 women with a mean age of 69 years (range, 65-86 years) at the time of the injury. The followup after the operation ranged from 6 to 24 months (mean, 12 months). Union was gained in all the patients. The records of radiographic parameters, including the palmar tilting angle, radial inclination, radial length, and ulnar variance had been maintained since the surgery. According to the rating scale of Gartland and Werley, 16 patients had excellent results and four had good results. There were no neurovascular and tendon injuries as complications.

Severely impacted valgus proximal humeral fractures. Results of operative treatment

BACKGROUND

The functional results associated with nonoperative treatment of severely impacted valgus fractures of the proximal part of the humerus are poor, and these injuries are difficult to treat with minimally invasive percutaneous fixation techniques. The aim of this study was to review the functional and radiographic results and complications of a new operative technique in a series of twenty-five patients.

METHODS

Over a two-year period, we treated twenty-nine patients with a severely impacted valgus fracture of the proximal part of the humerus. Three patients were lost to follow-up and one died, leaving twenty-five patients who were available for the study. In all of the fractures, the head-shaft angle had been tilted into > or = 160 degrees of valgus and the greater tuberosity was displaced by >1 cm. All patients were treated with open reduction of the fracture, and the space created behind the humeral head was filled with Norian Skeletal Repair System (SRS) bone substitute. The fractures were stabilized with either screws or buttress plate fixation. Associated rotator cuff tears were repaired. All patients underwent functional outcome assessment with use of the Constant, DASH (Disabilities of the Arm, Shoulder and Hand), and SF-36 (Short Form-36) scores at one year, and twelve patients were followed for two years.

RESULTS

All fractures united within the first year, all reductions were maintained, and no patient had signs of osteonecrosis of the humeral head on the latest follow-up radiographs. At one year, the median Constant score was 80 points and the median DASH score was 22 points. The functional results continued to be satisfactory in the twelve patients who were followed for two years. The results in our series were better than those achieved in studies of nonoperative treatment of similar fracture configurations. There were six clinically relevant complications, although none required a reoperation and all six patients had a satisfactory short-term functional outcome.

CONCLUSIONS

Internal fixation of severely impacted valgus fractures of the proximal part of the humerus, supplemented by Norian SRS bone substitute to fill the proximal humeral metaphyseal defect, produces good early functional and radiographic outcomes. Additional follow-up will be required to assess whether these initially satisfactory outcomes are maintained over the longer term.

Use of injectable calcium-phosphate cement for the fixation of titanium implants: an experimental study in goats

This in vivo study evaluated the fixation of two types of titanium implants with the use of an injectable calcium-phosphate (CaP) cement. The cement was either used to create a cement mantle (Type A implant) or as an additive to press-fit placed titanium plasma sprayed implants (Type B implant). The implants were placed in trabecular bone of the medial femoral condyle of goats and left in place for 2 and 10 weeks. Mechanical evaluation of the implant fixation was done by torque testing. This showed that for the Type A implants the calcium-phosphate cement's performance was significantly inferior (P < 0.05) to that of polymethylmethacrylate cement fixation. For the two-week Type B implants a significant increase (P < 0.05) in failure load was found for calcium-phosphate cemented implants compared with just press-fitted Type B implants. Histological evaluation revealed that for Type A implants, failure during torque testing occurred at the implant-cement interface. In contrast, for Type B implants, failure occurred in the bone-implant interface for press-fit-placed devices and in the cement layer for CaP-cemented devices. Further, the CaP cement was found to be overgrown with new formed bone already after 2 weeks of implantation. The cement showed resorption due to regular bone remodeling. On the basis of these observations, it was concluded that the use of injectable CaP cement might facilitate earlier loading of press-fit inserted titanium implants. Nevertheless, the results have to be confirmed in dynamical mechanical as well as loaded in vivo studies.

An injectable calcium phosphate cement as a bone-graft substitute in the treatment of displaced lateral tibial plateau fractures

In the treatment of displaced tibial plateau fractures, filling the resultant metaphyseal defect is essential for maintaining reduction. This study reports on 14 patients with an average age of 53 (range 34-63) years who sustained such a fracture and whose tibial defect was augmented with an injectable calcium phosphate cement under arthroscopic and fluoroscopic control. Eight fractures were treated with subcortical percutaneous screw fixation, plates were used in four cases and two fractures were treated with bone cement only. Full weight-bearing was allowed after 6-12 weeks. At the last follow-up which averaged 28 (range 18-47) months, the reduction achieved at the index operation was not altered in any of the patients except one. Most patients recorded little or no pain with an average VAS score of 1.2 (0-3.4). Ten patients had no limitation of their walking distance. Patient satisfaction was good or excellent in 12 cases. Flexion averaged 140 degrees (range 130-150 degrees ) and extension was unlimited in 13 patients. The Lysholm knee score averaged 80 and the Knee Society score 180 (range 127-195). In our opinion the injectable calcium phosphate cement used here is a promising alternative for filling metaphyseal defects in the treatment of displaced tibial plateau fractures.

Reconstruction of the immature craniofacial skeleton with a carbonated calcium phosphate bone cement: interaction with bioresorbable mesh

Calcium phosphate cements have been recently introduced for use in craniofacial reconstruction. In the clinical setting, however, pulsations of the underlying brain and dura may interfere with the crystallization of these cements, thereby rendering their use in cranioplasty problematic. To circumvent such problems, many clinicians have interposed synthetic resorbable plates or mesh between the dura and the cement. At the present time, however, little is known about the influence of such materials or their breakdown products on the fate of calcium phosphate cements. The specific aim of this project was to evaluate the biocompatibility, osteoconductivity, and remodeling capacity of a calcium phosphate cement after implantation into experimental calvarial defects when combined with a resorbable mesh underlay. Four 10-mm diameter full-thickness calvarial defects (two frontal, two parietal) were created in each of six 3-week-old Yorkshire pigs. The defects were treated as follows: 1) empty control, 2) macroporous polylactic acid (70/30 L/DL polylactic acid [PLA]) mesh, 3) Norian CRS calcium phosphate cement, and 4) Norian CRS over PLA mesh underlay. Animals were divided into two groups. Half of the animals were killed 30 days after surgery, and half were killed 180 days after surgery, and the graft recipient sites were examined histologically. At 30 days, minimal bone ingrowth was observed in untreated calvarial defects or in those that were treated with PLA plates alone. Defects treated with the cement alone demonstrated a modest amount of new woven bone deposition, primarily at the periphery of the implants. Defects treated with calcium phosphate cement over PLA mesh underlays were characterized by remodeling and woven bone deposition at 30 days, with complete or near-complete osseous bridging of the ectocranial implant surfaces. Progressive bone ingrowth was noted in all defects at 180 days, with near-complete replacement of all Norian CRS implants by host bone. The PLA mesh remained incompletely resorbed at 180 days. No inflammatory response to the implants was observed at either time point. Calcium phosphate cement may be safely used for craniofacial reconstruction in the presence of PLA implants without compromise to its biocompatibility, osteoconductivity, or remodeling capacity.

A biomechanical analysis of fixation of intra-articular distal radial fractures with calcium-phosphate bone cement

BACKGROUND

Calcium phosphate cement has been used to treat unstable fractures of the distal end of the radius with the intent of avoiding the stiffness and morbidity associated with prolonged immobilization in a cast or external fixation. The purpose of this study was to compare the stability of the fracture fragments after fixation with augmented calcium phosphate cement with that after alternative methods of percutaneous fracture treatment.

METHODS

Both an osteotomy and osteoclasis were used to create a model of an intra-articular fracture of the distal part of the radius (AO type C2) with dorsal bone loss in seven pairs of fresh-frozen upper extremities. One wrist from each pair was fixed with an external fixator and three Kirschner wires, and the contralateral wrist was fixed with calcium phosphate cement (Norian SRS) and three Kirschner wires (augmented calcium phosphate cement). Sequentially increasing loads, up to a total of 100 N, were then applied to the major flexors and extensors of the wrist. Fracture fragment motion was measured by the Optotrak three-dimensional system.

RESULTS

Fixation with cement alone failed at the bone-cement interface at <80 N in all specimens. With use of an analysis of variance, augmented external fixation was found to provide significantly increased stability to the radial fragment compared with that provided by augmented calcium phosphate cement in four of the six axes tested (e.g., mean motion [and standard deviation] in flexion-extension was 3.0 degrees +/- 2.93 degrees versus 11.1 degrees +/- 13.08 degrees, respectively; p = 0.001). Augmented calcium phosphate cement was found to provide greater stability for the radial fragment than were Kirschner wires alone in three axes (e.g., mean motion in flexion-extension was 11.1 degrees +/- 13.08 degrees versus 36.5 degrees +/- 13.03 degrees, respectively; p = 0.001).

CONCLUSIONS

Calcium phosphate cement alone is insufficient to withstand physiologic flexion-extension motion of the wrist without supplemental wire fixation. When supplemented with Kirschner wires, fixation with bone cement is more stable than are Kirschner wires alone, but it is significantly less stable than augmented external fixation.

Surface properties of calcium phosphate particles for self setting bone cements

Calcium phosphate cements (CPC), consist of multicomponent powder mixtures of calcium orthophosphates with grain sizes in the region of 1-20 microm. Due to the small particle sizes surface properties as the zeta potential and adsorption processes play a significant role during manufacturing and application. In the context of this work zeta potentials of different calcium phosphates, like dicalcium phosphate anhydride (DPCA) tetracalcium phosphate (TTCP) and hydroxyapatite were measured in various organic/aqueous media with different pH values. The results show a strong dependency of the zeta potential on the kind of suspension medium used associated with different milling properties. The addition of sodium phosphate leads to a pH value dependent stabilization of the particles in the liquid phase; the zeta potential of the surface increases from about -15 to -18 mV in water and from -35 to -45 mV in 0.05 mol/l sodium phosphate solution. Besides the interaction of particles with various antibiotics was determined on the basis of the zeta potential of the surface. The substances partly cause a tremendous change of the surface load. This is accompanied by a change of the rheological properties of the cement paste, the morphology of the hardened cement matrix and a significant deterioration of the application-relevant properties as setting time or mechanical strength.

Trabecular bone response to injectable calcium phosphate (Ca-P) cement

The aim of this study was to investigate the physicochemical, biological, and handling properties of a new developed calcium phosphate (Ca-P) cement when implanted in trabecular bone. Ca-P cement consisting of a powder and a liquid phase was implanted as a paste into femoral trabecular bone of goats for 3 days and 2, 8, 16, and 24 weeks. The cement was tested using three clinically relevant liquid-to-powder ratios. Polymethylmethacrylate bone cement, routinely used in orthopedics, was used as a control. The Ca-P cement was easy to handle and was fast setting with good cohesion when in contact with body fluids. X-ray diffraction at the different implantation periods showed that the cement had set as an apatite and remained stable over time. Histological evaluation after 2 weeks, performed on 10 microm un-decalcified sections, showed abundant bone apposition on the cement surface without any inflammatory reaction or fibrous encapsulation. At later time points, the Ca-P cement implants were totally covered by a thin layer of bone. Osteoclast-like cells, as present at the interface, had resorbed parts of the cement mass. At locations where Ca-P cement was resorbed, new bone was formed without loss of integrity between the bone bed and the cement. This demonstrated the osteotransductive property of the cement, i.e., resorption of the material by osteoclast-like cells, directly followed by the formation of new bone. Histological and histomorphometrical evaluation did not show any significant differences between the Ca-P cement implanted at the three different liquid/powder ratios. The results indicate that the investigated Ca-P cement is biocompatible, osteoconductive, as well as osteotransductive and is a candidate material for use as a bone substitute.

Calcium phosphate bone cement for treatment of distal radius fractures: a preliminary report

Distal radius fractures in osteoporotic patients are often complicated with a residual deformity and a subsequent stiff and painful wrist. The aim of this study was to evaluate the usefulness of calcium phosphate bone cement (CPC95) in the treatment of these fractures. Seven Colles type fractures in seven patients (all female; average age, 58 years) were treated. After a closed reduction, the fractures were fixed either by percutaneous pinning or by external skeletal fixation. The CPC95 was then injected into the cancellous bone defect through a small dorsal incision. The functional and radiological results were evaluated for up to 1 year. All patients were graded as good or excellent within 3 months, and all were graded as excellent at the final follow-up. The average duration of immobilization was 3.5 weeks. The overall shortening of the radius was 2.3 mm. In one patient, CPC95 extruded into the extensor tendon sheath and was surgically removed. Injection of CPC95 is a promising augmentation of osteosynthesis for distal radius fractures, although a prospective control study is mandatory to prove the usefulness of this material. The equipment and surgical technique should be refined to avoid the extrusion of CPC95.

Use of an injectable calcium phosphate bone cement in the treatment of tibial plateau fractures: a prospective study of twenty-six cases with twenty-month mean follow-up

OBJECTIVE

To evaluate the potential benefit of a new injectable mineral bone cement (Norian SRS, Cupertino, CA, USA) for the treatment of tibial plateau fractures OTA types 41.B2-B3 and C3.

DESIGN

Prospective study with established protocol.

SETTING

University hospital; university teaching hospital.

PATIENTS

Twenty-six patients gave informed consent to participate in this study and were available for follow-up examinations. All patients had sustained intraarticular tibial plateau fracture types OTA B2-B3 and C3. All cases were followed with a mean follow-up time of 19.7 months (6 to 36 months, median eighteen months).

INTERVENTION

Twenty-five cases were treated with open reduction, osteosynthesis with screws or plate, and injection of Norian SRS in the subchondral bone defect. One case had closed reduction, screw osteosynthesis, and percutaneous cement injection.

MAIN OUTCOME MEASUREMENTS

Radiographs in two planes were evaluated prospectively at six, twelve, and twenty-six weeks postoperatively and at last follow-up using Rasmussen's radiologic score. Clinical parameters were measured at the same time intervals using Lysholm's and Tegner's knee scores.

RESULTS

Two cases required early wound revisions because of sterile drainage. Two cases developed partial loss of reduction of the fracture between four and eight weeks after surgery, requiring revision surgery in one case (total complication rate 15.3 percent). No other patients had complications, and all other fractures healed without any displacement. The high mechanical strength of the cement allowed early weight bearing after a mean postoperative period of 4.5 weeks (1 to 6 weeks).

CONCLUSIONS

An injectable mineral bone cement with high initial mechanical strength was used to fill bone defects in unstable tibial plateau fractures with good success. This material offers new perspectives in the treatment of tibial plateau fractures.

Use of injectable calcium phosphate in the treatment of intra-articular distal radius fractures

This study reviewed 19 patients with intra-articular fractures of the distal end ofthe radius treated with augmented external fixation and injectable calcium phosphate (Norian SRS; Norian Corp, Cupertino, Calif) between November 1997 and July 2000. Average patient age was 52 years, and average follow-up was 16.3 months. Patients were evaluated clinically and radiographically using the modified Mayo Wrist Score and Knirk and Jupiter's criteria, respectively. Overall results are comparable to those from other studies of intra-articular distal radius fractures in which other grafts have been used.

Distal radius fractures in adults

Although distal radius fractures are a common injury in the elderly and young adult population, the classification, treatment options, and assessment of outcomes of these fractures remain controversial. Since there is no uniform fracture classification system, it is difficult to compare studies. An evidence-based model of management needs to be developed.

First histological observations on the incorporation of a novel calcium phosphate bone substitute material in human cancellous bone

Calcium phosphates are frequently used as bone substitute materials because of their similarity to the mineral phase of bone, absence of antigenicity, and excellent osteoconductivity. However, in most currently available mineral substitutes, resorption occurs slowly if at all. In contrast, calcium phosphate cements have shown rapid resorption and remodeling in animal studies. In two prospective studies, a novel amorphous calcium phosphate cement (Biobon) was implanted in human patients for the first time. After 2-12 months, ten biopsies were obtained from nine individuals during secondary surgical interventions, for example, for implant removal. In all specimens, partial replacement of the material by new bone was observed, while residues of the cement were still visible. Undecalcified sections revealed extensive bone formation in immediate contact to the cement without fibrous interface. Polynucleated cells and superficial lacunae were indicative of resorptive activity, but inflammatory tissue response was absent. The new bone displayed regular trabecular and osteonal patterns. The histologic findings are in accordance with the excellent biocompatibility observed in the clinical follow-up. Though still incomplete, the resorbability of this cement appears superior to sintered calcium phosphates in these biopsy specimens. Presumably this is due to its amorphous crystalline structure. Biobon merits further studies as a promising substance for bone defect reconstruction in non-stress-bearing areas.

Radiostereometric analysis of distal radial fracture displacement during treatment: a randomized study comparing Norian SRS and external fixation in 23 patients

In a randomized study, we included 23 osteoporotic patients with a distal radial fracture and loss of reduction after 1 week. The facture was re-reduced. In one group, a self-setting hydroxyapatite, Norian SRS, was injected into the fracture and the wrist was immobilized for 2 weeks with a dorsal splint (n 12). In the other group, the fracture was immobilized for 5 weeks with an external fixator (n 11). During the operation, the fracture fragments were marked with tantalum markers, so that loss of reduction during the immobilization and after mobilization could be studied with radiostereometric analysis (RSA). We found some recurrence of compression in the fracture in both groups during immobilization. After mobilization, the motion of the fracture, measured by displacement of the fragments along the longitudinal axis, was less than 2 mm, except in 3 cases treated with Norian SRS. A compression along the longitudinal axis of less than 2 mm is not likely to cause any problem in the long term. From the first to the last investigation, 7/12 patients with Norian SRS and 4/11 with external fixation lost more than 2 mm of the reduction along the longitudinal axis. We conclude that 5 weeks of immobilization is sufficient for healing with external fixation in this age group. This immobilization time might be reduced to 2 weeks for fractures treated with Norian SRS, but additional hardware should be used to ensure stability of the fracture system.

Injectable biodegradable materials for orthopedic tissue engineering

The large number of orthopedic procedures performed each year, including many performed arthroscopically, have led to great interest in injectable biodegradable materials for regeneration of bone and cartilage. A variety of materials have been developed for these applications, including ceramics, naturally derived substances and synthetic polymers. These materials demonstrate overall biocompatibility and appropriate mechanical properties, as well as promote tissue formation, thus providing an important step towards minimally invasive orthopedic procedures. This review provides a comparison of these materials based on mechanical properties, biocompatibility and regeneration efficacy. Advantages and disadvantages of each material are explained and design criteria for injectable biodegradable systems are provided.

Biomechanical evaluation of calcium phosphate cement-augmented fixation of unstable intertrochanteric fractures

OBJECTIVE

The purpose of this study was to evaluate the mechanical effects of using an injectable calcium phosphate cement, Norian Skeletal Replacement System (SRS), which is replaced by the native remodeling process, to augment sliding hip screw fixation of unstable intertrochanteric fractures in a cadaver model.

DESIGN

Ten matched pairs of human cadaver femora were used. One randomly selected femur from each pair was designated as experimental, whereas the contralateral femur served as the control.

SETTING

Testing was performed in the Orthopaedic Research Laboratories, The University of Michigan, Ann Arbor, Michigan, U.S.A.

PATIENTS/PARTICIPANTS

Femora with no radiographic evidence of pathology and with below-normal bone mineral density in the neck region were accepted into the study.

INTERVENTION

Three-part, intertrochanteric fractures were repaired by using a sliding hip screw and sideplate, without replacement of the posteromedial fragment. In the experimental side of each pair, SRS was used to grout the hip screw and to fill the posteromedial defect.

MAIN OUTCOME MEASUREMENTS

Femora were subjected to simulated single-leg stance loading to approximately one body weight in a servohydraulic testing machine. Measurements of stiffness, medial bone surface strain, hip screw displacement, and sideplate strain were made in fractured femora. Stiffness and medial bone surface strain baseline data were obtained in the intact bone before fracture creation as well.

RESULTS

Augmenting fixation with Norian SRS increased the fracture construct stiffness and minimized sliding hip screw displacement. It also maintained medial bone surface strain closer to the intact state and lowered sideplate strain relative to controls. However, there was no difference in the load to failure between SRS-augmented and control femora.

CONCLUSIONS

SRS augmentation of unstable, intertrochanteric fractures significantly improved overall stability, facilitated load transfer across the fracture, and decreased both shortening of the proximal femur and stress on the sliding hip screw.

Bone cells and matrices in orthopedic tissue engineering

The ability to harvest and manipulate osteogenic cells gives clinicians the opportunity to harness capacity of these cells for targeted regeneration and repair of skeletal tissues. Further opportunities to optimize use of cells exist in the ability to design specialized matrices that act as conductive scaffolds. Realization of the full potential of engineered matrix materials and cell-matrix composites can provide new solutions to many clinical problems in skeletal reconstruction.

Resorbable calcium phosphate bone substitute

The in vitro and in vivo properties of a novel, fully resorbable, apatitic calcium phosphate bone substitute (ABS) are described. The ABS was prepared from calcium phosphate precursors that were hydrated to form an injectable paste that hardens endothermically at 37 degrees C to form a poorly crystalline apatitic calcium phosphate (PCA). The PCA reaction product is stable in vivo as determined by FTIR and XRD analysis of rabbit intramuscular implants of ABS retrieved 4, 7, and 14 days postimplantation. Bone formation and resorption characteristics of the ABS material were characterized in a canine femoral slot defect model. Femoral slot defects in dogs were filled with either autologous bone implants or the ABS material. Sections of femoral bone defect site from animals sacrificed at 3, 4, 12, 26, and 52 weeks demonstrated that new bone formation proceeded similarly in both autograft and ABS filled slots. Defects receiving either material were filled with trabecular bone in the first 3 to 4 weeks after implantation; lamellar or cortical bone formation was well established by week 12. New bone formation in ABS filled defects followed a time course comparable to autologous bone graft filled defects. Histomorphometric evaluation of ABS resorption and new bone formation indicated that the ABS material was greater than 99% resorbed within 26 weeks; residual ABS occupied 0.36+/-0.36% (SEM, n = 4) of the original defect area at 26 weeks. Quantitatively and qualitatively, the autograft and ABS were associated with similar new bone growth and defect filling characteristics.

Use of an osteoconductive agent (Norian) in anterior surgical management of odontoid fractures

Odontoid fractures can be successfully treated with anterior screw fixation. Odontoid fractures commonly occur in older patients who may have significant osteopenia. The authors examined the use of a bone substitute to overcome limitations encountered during a procedure in which anterior odontoid screw fixation is performed.

Two elderly patients with displaced, reducible acute odontoid fractures underwent anterior odontoid screw fixation. The intraoperative failure of the anterior vertebral cortex from osteopenic bone and failure to achieve complete contact between the dens and axis were encountered. The defects were supplemented by using the osteoconductive agent Norian. Outcome was evaluated to determine the utility of this method.

Occasional intraoperative failure of anterior odontoid screw fixation may be encountered. Supplementation of bone defects with this osteoconductive agent may facilitate successful bone union in selected patients.

Open reduction and augmentation of internal fixation with an injectable skeletal cement for the treatment of complex calcaneal fractures

OBJECTIVES

To describe the surgical handling, potential complications, and remodeling of an injectable, osteoconductive calcium phosphate cement (Norian SRS) for joint depression-type calcaneal fractures in humans, and to illustrate the clinical efficacy of this cement with special reference to early postoperative full weight bearing.

DESIGN

Prospective cohort study.

SETTING

Level I trauma centers in Bochum and Leipzig, Germany.

INTERVENTION

Thirty-six joint depression type calcaneal fractures in thirty-two patients were augmented with the calcium phosphate cement after standard open reduction with internal fixation. Postoperative full weight bearing was allowed progressively earlier, and as the study progressed, the last patients were bearing full weight as early as three weeks postoperatively. Biopsies for histologic analysis were performed at time of hardware removal after one year (seven biopsies) or in case of infection at time of debridement (five biopsies).

MAIN OUTCOME MEASURES

Clinical outcome was evaluated according to a calcaneal scoring system. Data were compared and statistically analyzed between patients with postoperative full weight bearing after eight to twelve weeks and three to six weeks, respectively. Histologic findings are described.

RESULTS

Cement injection averaged ten cubic centimeters and could easily be performed under fluoroscopic control. Progressively earlier full weight-bearing was achieved without loss of reduction. There was no statistical difference in clinical outcome scores in patients with full weight bearing before or after six weeks postoperatively. The infection rate was 11 percent, possibly related to the skin incisions. The biopsies from clinically satisfactory cases showed nearly complete bone apposition, areas of vascular penetration, and reversal lines illustrating progressive cycles of resorption and new bone formation. Biopsy specimens from infected cases showed bone and cement surrounded by either fibrous tissue or acute inflammation without extensive bone apposition.

CONCLUSIONS

Calcium phosphate cement augmentation of standard open reduction with internal fixation in joint-depression type calcaneal fractures allows postoperative full weight bearing as early as three weeks postoperatively. The injectable bone cement can easily be handled surgically under fluoroscopic control and has proved to be remodelable.

Upper extremity disorders in women

Carpal tunnel syndrome, Colles' fracture, and osteoarthritis of the basilar joint of the thumb are only three of the many upper extremity conditions that preferentially affect women. With more and more women entering the workplace, these conditions become more disruptive of patients' lifestyles and even may be increasing in incidence. Orthopaedic surgeons traditionally have focused on the surgical treatment of patients with these conditions, but it is becoming increasingly clear that surgeons also must focus on delineating pathophysiology to better identify those individuals at risk and help prevent these potentially disabling disorders.

alpha-BSM: a biomimetic bone substitute and drug delivery vehicle

alpha-BSM is a biomimetic endothermically setting apatitic calcium phosphate bone substitute material. Its injectability and ability to harden at body temperature in the presence of physiologic saline, and other buffering agents, makes it an attractive clinical bone substitute and delivery vehicle for therapeutic agents in orthopaedic and dental applications. In osseous tissue, alpha-BSM alone remodels into bone and promotes bone healing. alpha-BSM treatment has been shown in several animal models to be effective in promoting healing of surgically created critical size defects and restoring bone biomechanical strength to values equal to or greater than values achieved with autograft controls. In vitro studies with alpha-BSM containing gentamicin show that antibiotics can be incorporated stably into alpha-BSM and that the release kinetics can be controlled with the appropriate formulation and preparative procedures. Growth factors and enzymes also are compatible with the alpha-BSM setting reaction. The incorporation of recombinant human bone morphogenetic protein-2 with alpha-BSM was shown to be effective in stimulating bone formation and accelerating restoration of the differentiated phenotype in an osteotomy model. Clinical trial investigators in Europe currently are using alpha-BSM implantations for treatment of fractures and other indications.

Osteoconductive materials and their role as substitutes for autogenous bone grafts

The term osteoconduction applies to a three-dimensional process that is observed when porous structures are implanted into or adjacent to bone. Capillaries, perivascular tissues, and osteoprogenitor cells migrate into porous spaces and incorporate the porous structure with newly formed bone. The observed process is characterized by an initial ingrowth of fibrovascular tissue that invades the porous structure followed by the later development of new bone applied directly within it. This article reviews observations of commonly used osteoconductive matrices to increase understanding of this process.

Reconstruction of bone using calcium phosphate bone cements: a critical review

The calcium phosphate cements (CPCs) are rapidly emerging as a new technology in craniofacial surgery and will soon impact many areas of orthopedic and maxillofacial reconstructive surgery as well. These materials are, in many ways, substantially different from the previously marketed dense, crystalline, hydroxyapatite (HA) ceramic materials of the 1980s. The CPCs are blends of amorphous and crystalline calcium phosphate compounds and set to produce HA. These materials 1) have x-ray diffraction spectra similar to the mineral phase of bone, 2) set endothermically at body temperature, 3) are capable of being injected into fractures or bone defects, 4) have compressive strengths equal to or greater than bone, 5) form chemical bonds to the host bone, and 6) may exhibit osteoconductive properties. This review provides an overall commentary on the different types of CPCs, emphasizing those materials currently on the market or soon to emerge in the marketplace.

Biphasic calcium phosphate/hydrosoluble polymer composites: a new concept for bone and dental substitution biomaterials

Calcium phosphate materials have been increasingly employed in orthopedic and dental applications in recent years and are now being developed for use in noninvasive surgery or as carriers for drug delivery systems. We developed an injectable bone substitute (IBS) constituted of biphasic calcium phosphate and a hydrosoluble polymer as a carrier. In vivo biocompatibility and biofunctionality of IBS were tested in rabbits using implants in osseous and nonosseous areas. The results obtained demonstrated that the concept of IBS, a filler without initial mechanical properties but able to be rapidly resorbed and replaced by newly formed bone, can be applied to new surgical applications in orthopedic surgery, maxillofacial surgery, and dentistry for pulp capping and root filling.

Biomechanical evaluation of fixation of intra-articular fractures of the distal part of the radius in cadavera: Kirschner wires compared with calcium-phosphate bone cement

BACKGROUND

The purpose of this study was to compare the biomechanical efficacy of an injectable calcium-phosphate bone cement (Skeletal Repair System [SRS]) with that of Kirschner wires for the fixation of intraarticular fractures of the distal part of the radius.

METHODS

Colles fractures (AO pattern, C2.1) were produced in ten pairs of fresh-frozen human cadaveric radii. One radius from each pair was randomly chosen for stabilization with SRS bone cement. These ten radii were treated with open incision, impaction of loose cancellous bone with use of a Freer elevator, and placement of the SRS bone cement by injection. In the ten control specimens, the fracture was stabilized with use of two horizontal and two oblique Kirschner wires. The specimens were cyclically loaded to a peak load of 200 newtons for 2000 cycles to evaluate the amount of settling, or radial shortening, under conditions simulating postoperative loading with the limb in a cast. Each specimen then was loaded to failure to determine its ultimate strength.

RESULTS

The amount of radial shortening was highly variable among the specimens, but it was consistently higher in the Kirschner-wire constructs than in the bone fixed with SRS bone cement within each pair of radii. The range of shortening for all twenty specimens was 0.18 to 4.51 millimeters. The average amount of shortening in the SRS constructs was 50 percent of that in the Kirschner-wire constructs (0.51+/-0.34 compared with 1.01+/-1.23 millimeters; p = 0.015). With the numbers available, no significant difference in ultimate strength was detected between the two fixation groups.

CONCLUSIONS

This study showed that fixation of an intra-articular fracture of the distal part of a cadaveric radius with biocompatible calcium-phosphate bone cement produced results that were biomechanically comparable with those produced by fixation with Kirschner wires. However, the constructs that were fixed with calcium-phosphate bone cement demonstrated less shortening under simulated cyclic load-bearing.

Norian SRS versus external fixation in redisplaced distal radial fractures. A randomized study in 40 patients

We compared Norian SRS, an injectable calcium phosphate bone cement, with external fixation in the treatment of redisplaced distal radial fractures by a prospective randomized study in 40 patients (women 50-80 years or men 60-80 years). After rereduction, the fracture was either stabilized by injection of SRS and immobilized with a cast for 2 weeks, or externally fixed with Hoffman's bar for 5 weeks. Each patient was evaluated at 2, 5, 7 weeks and at 3, 6 and 12 months. Functional parameters were grip strength, range of motion and pain. Radiographic parameters were radial angle, ulnar variance and dorsal tilt. The chosen primary effect variable was grip strength at 7 weeks. Patients treated by injection of SRS apatite had better grip strength, wrist extension and forearm supination at 7 weeks. There was no difference in functional parameters at 3 months or later. None of the methods could fully stabilize the fracture: radiographs showed a progressive redislocation over time. The results indicate that SRS can be used in the treatment of unstable distal radial fractures. The more rapid recovery of grip strength and wrist mobility in the SRS group appears to be due to the shorter immobilization time.

Superior compressive strength of a calcaneal fracture construct augmented with remodelable cancellous bone cement

Twenty-six paired, fresh-frozen cadaveric feet were disarticulated at the ankle joint, and the dome of the talus was potted. Stress-risers were placed along the medial, lateral, and posterior aspects of the calcaneus, and the specimen was loaded rapidly to failure in a testing machine to produce a type-IIB displaced intra-articular fracture according to the classification system of Sanders et al. One specimen of each pair was treated with standard internal fixation with bone-grafting (the control group), and the other was treated with similar fixation but with SRS (Skeletal Repair System) calcium phosphate bone cement placed in any osseous defect. All of the specimens were cured for twenty-four hours in a bath of saline solution at 37 degrees Celsius. The specimens were tested cyclically for ten cycles from zero to 100 newtons at one hertz and for 1010 cycles from zero to 350 newtons at one hertz. The deformation per cycle (millimeters per cycle), first-cycle deformation (millimeters), number of cycles to failure, and number of specimens withstanding the cyclical testing were calculated. The specimens were examined radiographically before and after fracture and after reconstruction and testing. A large difference in the results of the cyclical testing was noted. The specimens that had been augmented with the SRS bone cement had an average deformation of 0.00195 millimeter per cycle compared with 1.013 millimeters per cycle in the control group (p < 0.005). A similar magnitude of difference was noted when the results were stratified for good and poor-quality bone. Visual examination and radiographs demonstrated that a type-IIB displaced intra-articular fracture had been created reproducibly, and computed tomographic scans showed that nearly anatomical reconstruction had been achieved in all of the specimens. The computerized tomographic scans revealed good filling of the osseous voids and no evidence of failure of the cement after cyclical loading.