Thomas Jakobsen

The effect of pretreating morselized allograft bone with rhBMP-2 and/or pamidronate on the fixation of porous Ti and HA-coated implants.

BMPs stimulate new bone formation, but may also accelerate bone resorption. We added rhBMP-2 and pamidronate to morselized bone allograft packed around uncemented HA-coated and non-coated porous Ti implants in sixteen dogs. Each dog received four implants where the allograft was added (1) nothing, (2) BMP, (3) BP, and (4) BMP+BP. After four weeks, the untreated control implants had better mechanical fixation than all other treatment groups. The rhBMP-2-treated group had abundant formation of new bone on and around the implant. However, almost all allografts were resorbed, rendering the implant mechanically unstable. In the pamidronate-treated group the allograft was preserved, but the implants were covered by fibrous tissue and there was almost no new bone formation. This was also the case for the combined BMP+BP group, although fibrous tissue was absent on these implants. The HA-coated implants had more than twice as good mechanical fixation and improved osseointegration compared to the corresponding Ti implants. RhBMP-2 raised the total metabolic turnover of bone within the allograft with a net negative result on implant fixation. Pamidronate virtually blocked bone metabolism, also when combined with rhBMP-2. The results warrant a conservative approach and emphasize the importance of identifying a therapeutic window for these substances prior to clinical use.

Local Bisphosphonate Treatment Increases Fixation of Hydroxyapatite-Coated Implants Inserted with Bone Compaction

It has been shown that fixation of primary cementless joint replacement can independently be enhanced by either: (1) use of hydroxyapatite (HA) coated implants, (2) compaction of the peri‐implant bone, or (3) local application of bisphosphonate. We investigated whether the combined effect of HA coating and bone compaction can be further enhanced with the use of local bisphosphonate treatment. HA‐coated implants were bilaterally inserted into the proximal tibiae of 10 dogs. On one side local bisphosphonate was applied prior to bone compaction. Saline was used as control on the contralateral side. Implants were evaluated with histomorphometry and biomechanical push‐out test. We found that bisphosphonate increased the peri‐implant bone volume fraction (1.3‐fold), maximum shear strength (2.1‐fold), and maximum shear stiffness (2.7‐fold). No significant difference was found in bone‐to‐implant contact or total energy absorption. This study indicates that local alendronate treatment can further improve the fixation of porous‐coated implants that have also undergone HA‐surface coating and peri‐implant bone compaction.

Bone healing after median sternotomy: A comparison of two hemostatic devices

BackgroundBone wax is traditionally used as part of surgical procedures to prevent bleeding from exposed spongy bone. It is an effective hemostatic device which creates a physical barrier. Unfortunately it interferes with subsequent bone healing and increases the risk of infection in experimental studies. Recently, a water-soluble, synthetic, hemostatic compound (Ostene®) was introduced to serve the same purpose as bone wax without hampering bone healing. This study aims to compare sternal healing after application of either bone wax or Ostene®.MethodsTwenty-four pigs were randomized into one of three treatment groups: Ostene®, bone wax or no hemostatic treatment (control). Each animal was subjected to midline sternotomy. Either Ostene® or bone wax was applied to the spongy bone surfaces until local hemostasis was ensured. The control group received no hemostatic treatment. The wound was left open for 60 min before closing to simulate conditions alike those of cardiac surgery. All sterni were harvested 6 weeks after intervention.Bone density and the area of the bone defect were determined with peripheral quantitative CT-scanning; bone healing was displayed with plain X-ray and chronic inflammation was histologically assessed.ResultsBoth CT-scanning and plain X-ray disclosed that bone healing was significantly impaired in the bone wax group (p < 0.01) compared with the other two groups, and the former group had significantly more chronic inflammation (p < 0.01) than the two latter.ConclusionBone wax inhibits bone healing and induces chronic inflammation in a porcine model. Ostene® treated animals displayed bone healing characteristics and inflammatory reactions similar to those of the control group without application of a hemostatic agent.

Hydroxyapatite nanoparticles in poly-D,L-lactic acid coatings on porous titanium implants conducts bone formation.

It is well established in the field of biomaterials that hydroxyapatite (HA) may provide interesting osteoconductive properties. In this study, we investigated the osseointegrational effect of a 50/50 vol % composite of HA nanoparticles and poly-D,L-lactic acid (PDLLA) coated on model titanium bone implants in an in vivo animal model. The aim is to evaluate how the addition of HA to PDLLA may improve the bone formation and initial fixation of the implant. Two titanium implants coated with the PDLLA/HA composite and pure PDLLA, respectively, were implanted bilaterally in proximal part of humeri with a 2-mm peri-implant gap in 10 sheep. After 12 weeks, the remains of the coatings were present on 20.3 and 19.8% of PDLLA/HA composite- and PDLLA-coated implants, respectively. It was observed that newly formed bone (39.3%) and fibrous tissue (58.3%) had replaced the PDLLA/HA composite, whereas pure PDLLA was replaced almost completely by fibrous tissue (96.2%). Consequently, the PDLLA/HA composite-coated implants were better fixated as confirmed by push-out tests. Using quantification of peri-implant tissue and implant fixation as parameters, the present findings, therefore, clearly reveal that the addition of nanoparticulate HA to a PDLLA coating on titanium implants increases osseointegration.

Strontium doping of bone graft extender

Background and purpose Allografts are often used during revision hip replacement surgery for stabilization of the implant. Resorption of the allograft may exceed new bone formation, and instability of the prosthesis can develop. We investigated whether strontium could regulate the imbalance of fast resorption of allograft and slower formation of new bone, because it is both an anabolic and an anticatabolic agent. Method Strontium was added to the implant interface environment by doping a hydroxyapatite bone graft extender. 10 dogs each received 2 experimental titanium implants. The implants were inserted within a 2.7-mm concentric gap in cancellous bone. The gap was filled with 50% (v/v) allograft mixed with 50% bone graft extender. The extender either had 5% strontium doping (SrHA) or was undoped (HA). After 4 weeks, osseointegration and mechanical fixation were evaluated by histomorphometry and by push-out test. Results SrHA bone graft extender induced a 1.2-fold increase in volume of new bone, a 1.2-fold increase in allograft remaining in the gap, and a 1.4-fold increase in surface area of the bone graft extender material in contact with new bone compared to HA bone graft extender. All these increases were statistically significant. SrHA bone graft extender did not significantly improve ongrowth of bone onto the implants or improve any of the mechanical push-out parameters compared to HA bone graft extender. Interpretation Doping of the HA bone graft extender with 5% strontium increased gap healing, preserved more of the allograft in the gap, and increased the ongrowth of bone onto the bone graft extender material, but did not improve mechanical fixation.

Biomechanical implant fixation of CoCrMo coating inferior to titanium coating in a canine implant model

The use of CoCrMo in orthopedic surgery is not new, and CoCrMo (cobalt-chromium-molybdenum) is well tolerated. Nevertheless, the alloy is still considered less biocompatible than titanium. We therefore wanted to explore the biocompatibility of CoCrMo by investigating the biomechanical implant fixation and implant osseointegration of CoCrMo (ASTM F-75) porous bead-coated and titanium (ASTM F-136) porous bead-coated implants. In 10 dogs, the two implant types were inserted into the proximal part of the humerus. Implant sites were overdrilled, leaving an empty 0.75-mm gap between implant and surrounding bone. The implants were observed for 6 weeks and were evaluated by biomechanical push-out test and histomorphometry. We found a statistically significant 40% decrease in the biomechanical fixation of CoCrMo porous bead-coated implants compared with titanium porous bead-coated implants. Implant osseointegration was comparable between the two implants; however, a slight decrease in bone volume density around CoCrMo implants was observed. Insertions of CoCrMo implants are associated with a disturbance of the delicate peri-implant milieu. Even from implants not subjected to any mechanical forces, metal ions are liberated and result in intra- and extracellular accumulation in the immediate implant vicinity, presenting a likely explanation for our findings. A 40% reduction of initial implant fixation could prove to be serious because initial implant fixation is critical for long-term performance. The choice between titanium alloy and CoCrMo should, however, ultimately be governed by a comprehensive review of all factors influencing clinical implant survival. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Effects of gold coating on experimental implant fixation

Insertions of orthopedic implants are traumatic procedures that trigger an inflammatory response. Macrophages have been shown to liberate gold ions from metallic gold. Gold ions are known to act in an antiinflammatory manner by inhibiting cellular NF-kappaB-DNA binding and suppressing I-kappa B-kinase activation. The present study investigated whether gilding implant surfaces augmented early implant osseointegration and implant fixation by its modulatory effect on the local inflammatory response. Ion release was traced by autometallographic silver enhancement. Gold-coated cylindrical porous coated Ti6Al4V implants were inserted press-fit in the proximal part of tibiae in nine canines and control implants without gold inserted contralateral. Observation time was 4 weeks. Biomechanical push-out tests showed that implants with gold coating had approximately 50% decrease in mechanical strength and stiffness. Histomorphometrical analyses showed gold-coated implants had a decrease in overall total bone-to-implant contact of 35%. Autometallographic analysis revealed few cells loaded with gold close to the gilded implant surface. The findings demonstrate that gilding of implants negatively affects mechanical strength and osseointegration because of a significant effect of the released gold ions on the local inflammatory process around the implant. The possibility that a partial metallic gold coating could prolong the period of satisfactory mechanical strength, however, cannot be excluded.

Absence of a Tourniquet Does Not Affect Fixation of Cemented TKA: A Randomized RSA Study of 70 Patients

We aimed to determine whether not using a tourniquet in cemented TKA would affect migration of the tibial component measured by radiosterometric analysis (RSA). Seventy patients were randomized into a tourniquet group and a non-tourniquet group and using model-based RSA, the migration of the tibial component was analyzed. Primary and secondary outcome measures were maximum total point motion (MTPM) and translations and rotations. Follow-up period was 2 years. The tibial component was well fixated in both groups and no significant difference in migration between the two groups was detected (P=0.632). Mean MTPM (SD) was 0.47 mm (0.16) in the tourniquet group and 0.45 mm (0.21) in the non-tourniquet group. Absence of tourniquet indicates that stable fixation of the tibial component can be achieved in cemented TKA.

The effect of adding an equine bone matrix protein lyophilisate on fixation and osseointegration of HA‐coated Ti implants

Joint replacements should be firmly anchored in vital bone to avoid early implant subsidence and late aseptic loosening. We investigated whether the fixation of orthopedic implants could be improved by adding an osteoinductive extract of lyophilized equine bone matrix proteins (Colloss E, Ossacur AG, Germany), between the implant and the surrounding bone. Eighteen uncemented HA-coated implants were inserted pairwise in the proximal tibia of nine dogs. All implants were surrounded by a 2 mm concentric defect. In each dog, the intervention implant was added 20 mg protein lyophilisate. The contralateral control implant was inserted untreated. After four weeks, the treated HA-coated implants had better mechanical fixation than the untreated control implants. The treated implants were better osseointegrated, there was more newly formed bone around these implants, and fibrous tissue was eliminated. The mechanical implant fixation had a strong positive correlation to new bone formation on and around the implant, and a strong negative correlation to fibrous tissue encapsulation. The results suggest that bone protein extracts such as the Colloss E device may augment early implant fixation of even HA-coated Ti implants and thereby reduce the risk of long-term failure. This may be particularly useful in revision arthroplasty with bone loss.

Local delivery of zoledronate from a poly (D,L-lactide)-Coating increases fixation of press-fit implants.

Early secure fixation of total joint replacements is crucial for long‐term survival. Antiresorptive agents such as bisphosphonates have been shown to increase implant fixation. We investigated whether local delivery of zoledronate from poly‐D, L‐lactide (PDLLA)‐coated implants could improve implant fixation and osseointegration. Experimental titanium implants were bilaterally inserted press‐fit into the proximal tibiae of 10 dogs. On one side the implant was coated with PDLLA containing zoledronate. The contralateral implant was uncoated and used as control. Observation period was 12 weeks. Implant fixation was evaluated with histomorphometry and biomechanical push‐out test. We found an approximately twofold increase in all biomechanical parameters when comparing data from the zoledronate group with their respective controls. Histomorphometry showed increased amount of preserved bone and increased bone formation around the zoledronate implants. This study indicates that local delivery of zoledronate from a PDDLA coating has the potential to increase implant fixation.