Biomechanical comparison of traditional anchors to all-suture anchors in a double-row rotator cuff repair cadaver model.

BACKGROUND: To further reduce the invasiveness of arthroscopic rotator cuff repair surgery the all-suture anchor has been developed. The all-suture anchor requires less bone removal and reduces the potential of loose body complications. The all-suture anchor must also have adequate biomechanical strength for the repair to heal. The hypothesis is there is no significant difference in the biomechanical performance of supraspinatus repairs using an all-suture anchor when compared to traditional solid-body suture anchors. METHODS: Using nine shoulders per group, the supraspinatus tendon was dissected from the greater tuberosity. The four different double row repairs tested were (medial row/lateral row): A: ICONIX2/ICONIX2; B: ICONIX2/Stryker ReelX 3.9mm; C: ICONIX2/Stryker ReelX 4.5mm; D: Arthrex BioComposite CorkScrew FT 4.5mm/Arthrex BioComposite SwiveLock 4.75mm. The ICONIX2 was the only all-suture anchor tested. Tendons underwent cyclic loading from 10 to 100N for 500 cycles, followed by load-to-failure. Data was collected at cycles 5, 100, 200, 300, 400, and 500. One-way ANOVA analysis was used to assess significance (P≤0.05). FINDINGS: The anchor combinations tested did not differ significantly in anterior (P>0.4) or posterior (P>0.3) gap formation, construct stiffness (P>0.7), ultimate load (P=0.06), or load to 5mm gap formation (P=0.84). INTERPRETATION: The all-suture anchor demonstrated comparable biomechanical performance in multiple double-row anchor combinations to a combination of traditional solid-body anchors. Thus it may be an attractive option to further reduce the invasiveness of rotator cuff repairs.

A biomechanical comparison of anterior cruciate ligament suspensory fixation devices in a porcine cadaver model.

BACKGROUND: Suspensory fixation use during anterior cruciate ligament reconstruction has increased due to ease of use and high pullout strength. We hypothesize that there are no significant differences in biomechanical performance among four types of suspensory fixation devices: Stryker VersiTomic G-Lok, Smith & Nephew Endobutton, Biomet ToggleLoc, and Arthrex RetroButton. METHODS: Forty fresh frozen porcine femurs and flexor digitorum profundus tendons were obtained. Each tendon graft was sized to 8.5mm or 9.0mm. Ten of each device were used to fix the grafts in the femur at the 2 o'clock (left) or 10 o'clock (right) position. The graft-femur complex was secured to a servohydraulic test machine in line with the femoral tunnel. The graft was cyclically loaded from 50 to 250 N for 1000 cycles at 1 Hz then loaded to failure at 20mm/min. Actuator load and displacement were recorded. Data were analyzed with multiple one-way ANOVA and Tukey HSD post-hoc tests. Bonferroni correction was applied resulting in P ≤ 0.005 considered statistically significant for ANOVA, P ≤ 0.05 for Tukey. FINDINGS: There were no significant differences in cyclic displacement among any of the groups (P=0.43). The only significant difference in failure properties is the Endobutton exhibited at least 50% greater displacement at failure than the other three devices. INTERPRETATION: Suspensory femoral soft tissue fixation devices are biomechanically similar with respect to failure load but differ in failure displacement. However, there was no significant difference in displacement after cyclic loading. All four fixation devices should withstand the forces associated with daily activities without failure.

Knotless single-row rotator cuff repair: a comparative biomechanical study of 2 knotless suture anchors.

The purpose of this study was to compare the gap formation during cyclic loading, maximum repair strength, and failure mode of single-row full-thickness supraspinatus repairs performed using 2 knotless suture anchors with differing internal suture-retention mechanisms in a human cadaver model. Nine matched pairs of cadaver shoulders were used. Full-thickness tears were induced by detaching the supraspinatus tendon from the greater tuberosity. Single-row repairs were performed with either type I (Opus Magnum PI; ArthroCare, Austin, Texas) or type II (ReelX STT; Stryker, Mahwah, New Jersey) knotless suture anchors. The repaired tendon was cycled from 10 to 90 N for 500 cycles, followed by load to failure. Gap formation was measured at 5, 100, 200, 300, 400, and 500 cycles with a video digitizing system. Anchor type or location (anterior or posterior) had no effect on gap formation during cyclic loading regardless of position (anterior, P=.385; posterior, P=.389). Maximum load to failure was significantly greater (P=.018) for repairs performed with type II anchors (288±62 N) compared with type I anchors (179±39 N). Primary failure modes were anchor pullout and tendon tearing for type II anchors and suture slippage through the anchor for type I anchors. The internal ratcheting suture-retention mechanism of type II anchors may have helped this anchor outperform the suture-cinching mechanism of type I anchors by supporting significantly higher loads before failure and minimizing suture slippage, potentially leading to stronger repairs clinically.

Effects of SU5416 and a vascular endothelial growth factor neutralizing antibody on wear debris-induced inflammatory osteolysis in a mouse model.

BACKGROUND: The development of highly vascularized and inflammatory periprosthetic tissue characterizes the progress of aseptic loosening, a major complication of joint arthroplasty. Vascular endothelial growth factor (VEGF) is an important cell signaling protein involved in angiogenesis. The purpose of this study was to investigate whether R2/Fc (a VEGF neutralizing antibody) and SU5416 (a VEGF receptor II [Flk-1] inhibitor) could ameliorate particle-induced inflammatory osteolysis in a mouse model. METHODS: Ultrahigh molecular weight polyethylene (UHMWPE) particles were introduced into established air pouches in BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. Drug treatment was started 2 weeks after bone implantation, and mice without drug treatment were included as controls. Pouch tissues were harvested 4 weeks after bone implantation for molecular and histological analysis, and implanted bone degradation was analyzed by microcomputed tomography. RESULTS: Exposure to UHMWPE particles induced inflammatory osteolysis, which was associated with increased expression of VEGF/Flt-1 proteins. Treatment with R2/Fc significantly improved UHMWPE particle-induced inflammatory osteolysis, and reduced the expression of VEGF/Flt-1 proteins. However, SU5416 treatment showed no effect on UHMWPE particle-induced inflammatory osteolysis. CONCLUSION: Our findings indicate that VEGF signaling exerts a regulatory effect on the development of UHMWPE-induced inflammatory osteolysis, through its unique Flt-1, rather than Flk-1, receptor located on monocyte/macrophage cell lineages. These data provide a biological rationale for a VEGF/Flt-1-targeted treatment strategy, especially during the early stages of the wear debris-induced inflammatory response.

An in vivo evaluation of bone response to three implant surfaces using a rabbit intramedullary rod model.

Our study was designed to evaluate osseointegration among implants with three surface treatments: plasma-sprayed titanium (P), plasma-sprayed titanium with hydroxyapatite (PHA), and chemical-textured titanium with hydroxyapatite (CHA). Average surface roughness (Ra) was 27 microns for the P group, 17 microns for the PHA group, and 26 microns for the CHA group. Bilateral distal intramedullary implants were placed in the femora of thirty rabbits. Histomorphometry of scanning electron microscopy images was used to analyze the amount of bone around the implants at 6 and 12 weeks after implantation. Greater amounts of osseointegration were observed in the hydroxyapatite-coated groups than in the noncoated group. For all implant surfaces, osseointegration was greater at the diaphyseal level compared to the metaphyseal level. No significant differences were seen in osseointegration between the 6 and 12 week time points. Although the average surface roughness of the P and the CHA groups was similar, osseointegration of the CHA implants was significantly greater. The results of this in vivo lapine study suggest that the presence of an hydroxyapatite coating enhances osseointegration despite similarities in average surface roughness.

Efficacy of periprosthetic erythromycin delivery for wear debris-induced inflammation and osteolysis.

OBJECTIVES: We have reported that oral erythromycin (EM) inhibits periprosthetic tissue inflammation in a group of patients with aseptic loosening. The purpose of this study was to assess the efficacy of local, periprosthetic EM delivery in a rat model. METHODS: Uncoated Ti pins were press-fit into the right tibia of fourteen Sprague-Dawley rats following an intramedullar injection of UHMWPE (ultra high molecular weight polyethylene) particles. Revision surgeries were performed 2 months after the primary surgery. EM was applied to the Peri-Apatite™ (PA) layer of the titanium (Ti) pins. The previously implanted Ti pins were withdrawn and replaced with Ti pins coated either with (n = 7) or without (n = 7) EM. The rats were killed 1 month after "revision surgery". The EM efficacy was evaluated by (MicroCT) µCT and histology. RESULTS: µCT analysis showed that bone volume percentage (BV/TV) was significantly higher in the EM-treated group compared to the untreated group (p < 0.05). Histological analysis showed that EM treatment inhibits UHMWPE particle-induced periprosthetic tissue inflammation compared to the untreated group. CONCLUSION: This study demonstrated that periprosthetic EM delivery reduced periprosthetic inflammation and improved the quality of surrounding bone.

Effects of hydroxyapatite on titanium foam as a bone ingrowth surface in acetabular shells: a canine study.

This study investigated a highly porous titanium foam with and without a PeriApetite coating as an alternative surface for implant fixation. Twelve mongrel canines received staged total hip replacements under International Animal Care and Use Committee (IACUC) approval from our institution. Animals were randomly placed in three- or six-month groups for sacrifice. Seventeen total hips were available for evaluation. The area and depth of ingrowth was measured by SEM. At three months, PeriApetite Ti foam had 37% more depth and almost 10% more bone ingrowth. Both groups were found not to be different at the six-month mark with over 36% of ingrowth calculated on SEM. The results prove not only that titanium foam is a viable ingrowth surface but also that PA coating can enhance the time to bony incorporation.

Inhibitory effects of erythromycin on wear debris-induced VEGF/Flt-1 gene production and osteolysis.

OBJECTIVES: A highly vascularized and inflammatory periprosthetic tissue augments the progress of aseptic loosening, a major clinical problem after total joint replacement. The purpose of this study is to investigate the effect of erythromycin (EM) on ultra high molecular weight polyethylene (UHMWPE) particle-induced VEGF/VEGF receptor 1 (Flt-1) gene production and inflammatory osteolysis in a mouse model. METHODS: UHMWPE particles were introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. EM treatment started 2 weeks after bone implantation (5 mg/kg day, i.p. injection). Mice without drug treatment as well as mice injected with saline alone were included. Pouch tissues were harvested 2 weeks after bone implantation. Expression of VEGF, Flt-1, RANKL, IL-1, TNF and CD68 was measured by immunostain and RT-PCR, and implanted bone resorption was analyzed by micro-CT (muCT). RESULTS: Exposure to UHMWPE induced pouch tissue inflammation, increase of VEGF/Flt-1 proteins, and increased bone resorption. EM treatment significantly improved UHMWPE particle-induced tissue inflammation, reduced VEGF/Flt-1 protein expression, and diminished the number of TRAP(+) cells, as well as the implanted bone resorption. CONCLUSION: This study demonstrated that EM inhibited VEGF and Flt-1 gene expression. The molecular mechanism of EM action on VEGF/Flt-1 signaling-mediated osteoclastogenesis warrants further investigation.

Long-term evaluation of a calcium phosphate bone cement with carboxymethyl cellulose in a vertebral defect model.

We investigated histological and compressive properties of a calcium phosphate bone cement (BoneSource (CPC); Stryker Orthopaedics, Mahwah, New Jersey) plus carboxymethyl cellulose (CMC) using a sheep vertebral bone void model. Bone voids were surgically created in L3 and L5 in each of 40 sheep, and the voids were filled with the cement. Histological and radiographic evaluations were performed on one vertebral body from each animal at either: 0, 3, 6, 12, 24, or 36 months after surgery; mechanical testing was performed on operated and non-operated vertebral bodies from 35 sheep. Undecalcified sections were digitized, and the area of the original defect, new bone formation, empty space, fibrous tissue, and residual cement were quantified with histomorphometry. Decalcified sections were evaluated qualitatively. The cement was biocompatible, extremely osteoconductive and underwent steady resorption and replacement by bone and bone marrow. Histomorphometry showed variations in the rate of cement remodeling among animals in each time group, but on average, at 36 months the original defect area was occupied by approximately 14% bone, 82% cement, and 4% bone marrow. Even in animals that had greater resorption of cement, there was good bone ingrowth with no fibrous tissue. Compressive testing did not reveal a significant difference in the mechanical properties between vertebral bodies augmented with cement and non-augmented controls, irrespective of the postoperative time. BoneSource mixed with CMC had adequate osteoconductivity, biocompatibility, and adequate compressive strength. There was variability among animals, but histology suggests that considerable cement was still present in most samples after 36 months.

Blockade of vascular endothelial growth factor activity suppresses wear debris-induced inflammatory osteolysis.

OBJECTIVE: Aseptic loosening is a common complication of total joint replacement in humans. Our study examined the hypothesis that wear debris may influence vascular endothelial grow factor (VEGF) expression, and that blocking VEGF bioactivity might improve wear debris-induced inflammatory osteolysis in a mouse model. METHODS: Ultra high molecular weight polyethylene (UHMWPE) particles were introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. Mice were treated with recombinant VEGF, or VEGF inhibitor (VEGF R2/Fc chimera) or vehicle control, and mice without UHMWPE stimulation were also included. Pouch tissues were harvested 2 weeks after bone implantation for molecular and histological analyses. RESULTS: Exposure of UHMWPE particles increased VEGF expression at both mRNA and protein levels in pouch tissues. Immunostaining revealed intense VEGF staining predominantly in UHMWPE deposit foci surrounded by inflammatory cells. VEGF inhibitor treatment strongly attenuated tissue inflammation (cellular infiltration, membrane proliferation, and expression of interleukin 1beta and tumor necrosis factor-alpha in UHMWPE-stimulated pouch tissues). Further, VEGF inhibitor treatment caused a significant reduction in the number of TRAP+ cells, and effectively prevented UHMWPE particle-induced bone resorption of implanted calvaria (assessed by extent of collagen depletion and frequency of bone erosions). CONCLUSION: The observation that VEGF inhibitor treatment prevented UHMWPE particle-induced inflammatory osteolysis opens new possibilities for treatment of aseptic loosening, especially at an early stage.

Ectopic bone formation using osteogenic protein-1 carried by a solution precipitated hydroxyapatite.

Solution precipitation of calcium and phosphate is a technique to generate hydroxyapatite [Peri-Apatitetrade mark (PA), Stryker Orthopaedics, Mahwah, NJ] on metal substrate. This study was carried out to determine the capacity of PA to adsorb osteogenic protein-1 (OP-1) and the time course of release, and to determine the osteoinductive activity of OP-1. The adsorption and release studies were conducted with (125)I-labeled OP-1- and PA-coated titanium alloy disks. The results indicate that the adsorption of OP-1 on the PA-coated disks is linear with the concentration of OP-1 up to 5 mg/mL. There is an initial release of 75% to 80% of adsorbed OP-1 within the first hour, and 92% of OP-1 is released in 3 days. The osteoinductive activity of OP-1 was determined in the rat intramuscular ectopic bone formation assay. A total of 24 titanium alloy disks were evenly divided into 3 groups with different treatments for implantation, plain disks (group A), disks coated with PA (group B), and disks coated with PA plus 40 microg OP-1 (group C). Osteogenic protein-1, 40 microg in solution, was injected into the muscle pouch in animals of group D (n = 8). The rats were sacrificed 3 weeks postoperatively and the implants were retrieved. Ectopic bone formation was evaluated with radiography and histology. Results demonstrated that OP-1 induced ectopic bone in all the animals of group C and group D. The titanium alloy disks were surrounded by trabecular bone and marrow tissue. None of the animals of group A or group B showed any evidence of osteoinduction. Our findings indicate that PA can deliver OP-1 directly to titanium alloy implants and maintain the osteoinductive activity of OP-1.

Osteogenic protein-1 enhances osseointegration of titanium implants coated with peri-apatite in rabbit femoral defect.

This study evaluated the effect of osteogenic protein-1 (OP-1) carried by Peri-Apatite (PA) on bone healing in the gap surrounding implants in a rabbit model. Cylindrical titanium implants (3 x 9 mm) were uniformly coated with PA precipitated from a calcium and phosphate solution. OP-1 solution containing 60 microg OP-1 was directly loaded on the implants immediately before implantation for the experimental group, whereas buffer solution was loaded on the implants for the control. The implant was placed in the distal femur and surrounded by a 1-mm gap. The implants were retrieved and examined 6 weeks after implantation. Mechanical testing (push-out) data showed that OP-1 enhanced implant fixation by 80%. Histomorphometric measurements indicated that bone ingrowth in the initial gap expressed as a percentage of the whole gap was significantly higher in the specimens treated with OP-1 than the control group (25.4% vs. 8.9%, p < 0.05). The percentage of the surface of implants, which was covered by bone, was significantly higher in the OP-1-treated group compared to the control group (65% vs. 25%, p < 0.05). This study suggests that OP-1 can be loaded on orthopedic implants through PA to enhance the osseointegration of orthopedic implant.