Bony Ingrowth of Coil-Type Open-Architecture Anchors Compared With Screw-Type PEEK Anchors for the Medial Row in Rotator Cuff Repair: A Randomized Controlled Trial.

PURPOSE: To evaluate outcomes of screw-type and coil-type open-architecture suture anchors with respect to bony ingrowth, release of biological markers, and patient-reported outcome measures when used in rotator cuff repair (RCR). METHODS: Forty patients undergoing arthroscopic RCR for full-thickness rotator cuff tears were enrolled and prospectively randomized to receive a screw-type (19 patients) or coil-type (21 patients) suture anchor for the medial row during repair. All repairs used a transosseous-equivalent configuration with footprint anchors laterally. Marrow elements released during surgery were evaluated for 9 cytokine markers (insulin-like growth factor 1, fibroblast growth factor 2, bone morphogenetic proteins 7 and 2, platelet-derived growth factors AA and BB, epidermal growth factor, transforming growth factor beta1, and vascular endothelial growth factor). Postoperative computed tomography scans were performed at 6 months. Range of motion, strength, and validated patient-reported outcome measures (Simple Shoulder Test, Single Assessment Numeric Evaluation, visual analog scale, and American Shoulder and Elbow Surgeons scores) were gathered before the operation and at 6 months and 1 year postoperatively. RESULTS: Bone mineral density surrounding the coil-type anchor was significantly greater than that surrounding the screw-type anchor (P = .005). Bone mineral density values within the coil-type and screw-type anchors were comparable (P = .527); however, a larger amount of total bone mineral mass (in milligrams) was shown within the coil-type anchor owing to its larger volume (P < .01). Marrow elements released at the repair site were similar between groups (P > .05). Postoperatively, no statistically significant difference was found between groups for clinical outcome measures at 6 months or 1 year. Retear and complication rates were similar between groups (P > .05). CONCLUSIONS: Both the coil-type and screw-type anchors can be reliably used for RCR and produce similar clinical outcomes. The coil-type anchor resulted in superior bony growth surrounding the anchor and a larger total bone mineral mass within the anchor owing to its larger volume. LEVEL OF EVIDENCE: Level II, randomized prospective comparative study.

Synthetic bone mimetic matrix-mediated in situ bone tissue formation through host cell recruitment.

Advances in tissue engineering have offered new opportunities to restore anatomically and functionally compromised tissues. Although traditional tissue engineering approaches that utilize biomaterials and cells to create tissue constructs for implantation or biomaterials as a scaffold to deliver cells are promising, strategies that can activate endogenous cells to promote tissue repair are more clinically attractive. Here, we demonstrate that an engineered injectable matrix mimicking a calcium phosphate (CaP)-rich bone-specific microenvironment can recruit endogenous cells to form bone tissues in vivo. Comparison of matrix alone with that of bone marrow-soaked or bFGF-soaked matrix demonstrates similar extent of neo-bone formation and bridging of decorticated transverse processes in a posterolateral lumbar fusion rat model. Synthetic biomaterials that stimulate endogenous cells without the need for biologics to assist tissue repair could circumvent limitations associated with conventional tissue engineering approaches, including ex vivo cell processing and laborious efforts, thereby accelerating the translational aspects of regenerative medicine.

Callus stimulation in distraction osteogenesis.

Distraction osteogenesis has been described as in vivo tissue engineering. The ability to stimulate this process for the repair of bony defects or lengthening of congenitally shortened facial structures is likely to significantly impact the field of craniofacial surgery. The purpose of this study was to determine whether mechanical stimulation of the distracted rabbit mandible would accelerate the maturation of the bony callus when applied during the early consolidation period. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A uni-directional internal distractor device (Synthes, Paoli, Pa.) was positioned along a plane perpendicular to the line of osteotomy. After a 7-day latency period, distraction was commenced at a rate of 1.0 mm/day for 12 days in all animals. In a control group of 10 rabbits, a consolidation period of 8 weeks was observed before they were killed. In the experimental group of 10 rabbits, daily alternate compression and distraction of 1 mm (sequential compression and distraction) was performed for 3 weeks followed by a 5-week period of rigid fixation. Each animal received a dose of a fluorescent label at three different time points during the study: at the end of the distraction period, 3 weeks after the completion of the distraction phase, and 3 days before it was killed. All animals were killed 8 weeks after the completion of the distraction phase. Undecalcified histologic analysis and 3-point bending tests to failure were performed on the extracted mandibles. The results of the experimental and control groups were compared. Four animals in the control group and three animals in the experimental group were excluded from the study because of screw loosening resulting in distractor dislodgment or because of infection. On histologic analysis, cortical thickness at the center of the callus was found to be significantly greater in the experimental group compared with the control group when normalized to the contralateral hemimandible (83 percent versus 49 percent, respectively; p < 0.007). The ratio of cortical to cancellous bone in the distracted callus was uniformly found to be greater in the experimental specimens. The mineral apposition rate was calculated by using fluorescence microscopy and found to be significantly greater in the experimental group both during the period of sequential compression and distraction (3.2 microm/day versus 2.1 microm/day, p = 0.02) and after the period of sequential compression and distraction (1.4 microm/day versus 1.1 microm/day, p = 0.006). Mechanical testing revealed no significant differences in bending strength or stiffness between experimental or control groups (p = 0.54 and 0.47, respectively). This study has demonstrated that daily alternating compression and distraction of 1 mm amplitude during the early consolidation period has a stimulatory impact on callus formation with respect to osteoblastic activity, remodeling, and maturation of bone. Optimal timing and amplitude of sequential movement, long-term biomechanical differences, and molecular pathways have yet to be elucidated.

Overexpression of DMP1 accelerates mineralization and alters cortical bone biomechanical properties in vivo.

Dentin matrix protein-1 (DMP1) is a key regulator of biomineralization. Here, we examine changes in structural, geometric, and material properties of cortical bone in a transgenic mouse model overexpressing DMP1. Micro-computed tomography and three-point bending were performed on 90 femora of wild type and transgenic mice at 1, 2, 4, and 6 months. Fourier transform infrared imaging was performed at 2 months. We found that the transgenic femurs were longer (p<0.01), more robust in cross-section (p<0.05), stronger (p<0.05), but had less post-yield strain and displacement (p<0.01), and higher tissue mineral density (p<0.01) than the wild type femurs at 1 and 2 months. At 2 months, the transgenic femurs also had a higher mineral-to-matrix ratio (p<0.05) and lower carbonate substitution (p<0.05) compared to wild type femurs. These findings indicate that increased mineralization caused by overexpressing DMP1 led to increased structural cortical bone properties associated with decreased ductility during the early post-natal period.

Biomechanical effect of the C2 laminar decortication on the stability of C2 intralaminar screw construct and biomechanical comparison of C2 intralaminar screw and C2 pars screw.

BACKGROUND: There have been no reports of biomechanical stability of C1-2 constructs after decortication of the C2 lamina. In addition, few studies have compared the stability of C2 laminar screw and pars screw constructs. OBJECTIVE: To compare the biomechanical stability of 3 different C1-2 construct conditions (C2 pars screw, C2 intralaminar screw, C2 intralaminar construct with C2 laminar decortication). METHODS: Fourteen fresh-frozen cadaveric cervical specimens (C1-3) were used. In 7 specimens, pure moments of 1.5 Nm were applied in flexion/extension, lateral bending, and axial rotation. Each specimen was tested in the normal state, in the destabilized state (after odontoidectomy and resection of transverse atlantal ligament), and after application of constructs. After kinematic study, these 7 specimens underwent axial pullout strength testing of pars screw and 50% decorticated C2 intralaminar screws. In another 7 specimens, insertion torque and pullout strength were measured to compare the pars screw and intact C2 intralaminar screw. RESULTS: : There were no statistically significant differences between the intact C2 intralaminar and 50% decorticated C2 intralaminar screw constructs in terms of range-of-motion limitations. The C2 pars screw construct was significantly superior to the C2 laminar screw construct in lateral bending (P < .01) and axial rotation (P < .01) and equivalent to the C2 laminar screw construct in flexion/extension (P = .42). There was no significant pullout strength difference between the 3 kinds of C2 screw. CONCLUSION: The C1 lateral mass-C2 pars screws construct was stronger than the C1 lateral mass-C2 intralaminar screw construct. Decortication of C2 laminar (up to 50%) did not affect the immediate stability of the C1-2 construct.

Three-dimensional morphology and kinematics of the craniovertebral junction in rheumatoid arthritis.

STUDY DESIGN: A case-series study. OBJECTIVES: To measure the 3-dimensional (3D) morphology and kinematics of the craniovertebral junction (CVJ) using a 3D computed tomography (CT) model; to reveal abnormal patterns and the relationships between pathology and kinematics. SUMMARY OF BACKGROUND DATA: Evaluations using radiography, 2-dimensional (2D) CT and magnetic resonance imaging have limitations because of the complex 3D structure of the CVJ. METHODS: Twenty-four rheumatoid arthritis patients (21 females, 3 males) with cervical involvement underwent CT scanning of the cervical spine from the basilar process of the occipital bone to the first thoracic vertebra in neutral and flexed positions. The 3D morphology of the occipital condyle, atlas, and axis were classified based on the type of deformity observed. Periodontoid lesions (continuous bony lesions between the atlas and the odontoid process) were also noted. The 3D kinematics in the atlanto-occipital and atlantoaxial joints were evaluated using the volume merge method. RESULTS: Deformities in the atlanto-occipital joints appeared more frequently than those in the atlantoaxial joints. The most common instability pattern was flexural rotation during flexion at the CVJ. The direction of translational motions during flexion was posterior in the atlanto-occipital joint and anterior and caudal in the atlantoaxial joint. CONCLUSION: The results suggest that bilateral occipital condyle deformation, unilateral and bilateral mass collapse, and periodontoid lesions may affect flexion/extension rotational instability in the atlantoaxial joint. In addition, unilateral occipital condyle deformation and atlantoaxial joint stability may affect sagittal translational instability to the posterior side in the atlanto-occipital joint. The noninvasive 3D CT imaging technique employed here would be useful for predicting the prognosis of patients with rheumatoid deformities at the CVJ.

Increased bone formation using calcium sulfate-calcium phosphate composite graft.

Calcium phosphates (CaPO4) and faster-resorbing calcium sulfate (CaSO4) are successfully employed as synthetic bone grafts for treatment of contained defects. We used a canine critical-sized bone defect model to study an injectable CaSO4/CaPO4 composite graft that incorporated a matrix of CaSO4 and dicalcium phosphate dihydrate into which beta-tricalcium phosphate granules were distributed. The area fraction, ultimate compressive stress, and elastic modulus of restored bone and the relative rates of material resorption were compared between the CaSO4/CaPO4 composite graft and pure CaSO4 pellets and to normal canine bone. The area fraction of bone in stained sections and the ultimate compressive stress of the regenerated bone were greater using the CaSO4/CaPO4 composite graft compared to pure CaSO4 pellets after 13 and 26 weeks and were greater than normal bone. The elastic modulus of restored bone in defects treated with CaSO4/CaPO4 composite graft was greater than in defects treated with CaSO4 pellets after 26 weeks, but similar to specimens of normal bone. A small amount of CaSO4/CaPO4 composite graft and no CaSO4 pellets remained after 13 or 26 weeks. This novel CaSO4/CaPO4 composite holds promise for clinical applications where a strong, injectable, slower-resorbing, and biocompatible bone graft substitute would be advantageous.

Role of guided bone regeneration principle in preventing fibrous healing in distraction osteogenesis at high speed: experimental study in rabbit mandibles.

The formation of fibrous tissues at the distraction gap may result from the accumulation of rapidly migrating fibroblasts at the site of an osteotomy, especially when distraction is rapid. Addition of osteopromotive membranes could theoretically prevent fibroblasts from entering the distraction gap, allowing the osteotomy site to be filled with only osteogenic cells. This study is an attempt to achieve a rapid successful distraction without fibrosis through the use of collagen membranes. Sixteen skeletally mature New Zealand white rabbits were used in this study. They were divided into two groups. One rabbit from each group was excluded from the study because of dislodgement of the distractors. In one group (n = 7), distraction was done as usual. In the other group (n = 7), a collagen membrane surrounded the osteotomy site to be distracted. After a 7-day latency period, distraction started at a rate 2 mm once per day for 5 days. The distractor was left in place for 4 weeks to allow consolidation. Results showed osteogenesis in both groups. Whereas addition of the membrane to distraction increased the quantity of bone formed, absence of the membrane allowed early mineralization (better quality of bone regarding the density). Neither of the two groups showed significant fibrosis or cartilage formation. The endosteum served as a source of blood supply when the periosteum was excluded. The periosteum served as a membrane for guided bone regeneration. Membranes for guided bone regeneration can be used with distraction when the periosteum is lost from trauma or is broken from fast distraction.

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.

Spring-mediated mandibular distraction osteogenesis.

Successful performance of distraction osteogenesis requires rigorous patient compliance with a daily activation regimen of a percutaneous screw. Previous clinical studies have found that failure of patient compliance with this regimen is the most common complication leading to technical failure of the distraction process. The authors have developed an internalized spring-mediated device for mandibular distraction osteogenesis that can potentially abrogate the risks associated with patient compliance by allowing for automated distraction across an osteotomy. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A segment of nickel-titanium shape memory alloy reinforced at both ends with a pinball was fashioned into an inferiorly based arc and secured to the mandible with stainless steel wire. On postoperative day 12, spring activation commenced by cutting a wire binding the two pinballs to one another. Animals were observed for 6 weeks before they were killed. Radiographic studies and decalcified histologic analysis were performed on extracted mandibles. Temperature- and displacement-dependent properties of the shape memory alloy were also examined. Five animals were excluded from the study due to infection, nonunion, or device failure. A mean distraction of 1.2 mm in the distracted hemimandible relative to the nonoperated hemimandible was found (P <.001, two-tailed paired t test). The maximum distraction achieved in an experimental specimen using the spring distractor was 3.7 mm. There were no other histologic or radiographic differences found between study specimens and specimens subjected to traditional distraction methods. Biomechanical testing of the shape memory alloy revealed a temperature-dependent increase in force at body temperature compared with room temperature and a reduction in force with increased displacement of the spring. This study demonstrates the feasibility of spring-mediated distraction osteogenesis across an osteotomy. As the field of distraction osteogenesis matures, the next level of sophistication in the clinical development of devices will incorporate technology that permits fully internalized and automated distraction to occur.