Jared S. Johnson

Biomechanics of massive rotator cuff tears: implications for treatment.

BACKGROUND Some individuals with massive rotator cuff tears maintain active shoulder abduction, and some maintain good postoperative active range of motion despite high rates of repeat tears after repair. We devised a biomechanical rationale for these observations and measured the increases in residual muscle forces necessary to maintain active shoulder motion with rotator cuff tears of various sizes. METHODS A custom cadaver shoulder controller utilizing position and orientation closed-loop feedback control was used. Six cadaver glenohumeral joint specimens were tested in open-chain scapular plane abduction with equivalent upper extremity weight. The shoulder controller limited superior translation of the humeral head to 3.0 mm while maintaining neutral axial rotation by automatically controlling individual rotator cuff forces. Three-dimensional position and orientation and rotator cuff and deltoid force vectors were recorded. Specimens were tested with an intact rotator cuff and with 6, 7, and 8-cm tears. RESULTS All six specimens achieved full abduction with <or=3.0 mm of superior translation of the humeral head for all rotator cuff tear sizes. The effect of rotator cuff tear was significant for all tear sizes (p < 0.01). Compared with the intact condition, the subscapularis force requirements for the 6, 7, and 8-cm tears were increased by 30%, 44%, and 85%, respectively. For the combined infraspinatus and teres minor, the forces were increased by 32%, 45%, and 86%, respectively. The maximum deltoid force for the simulated tear condition never exceeded the deltoid force required at maximum abduction for the intact condition. However, between 10 degrees and 45 degrees of abduction, the average deltoid force requirement increased 22%, 28%, and 45% for the three tear sizes. CONCLUSIONS In the presence of a massive rotator cuff tear, stable glenohumeral abduction without excessive superior humeral head translation requires significantly higher forces in the remaining intact portion of the rotator cuff. These force increases are within the physiologic range of rotator cuff muscles for 6-cm tears and most 7-cm tears. Increases in deltoid force requirements occur in early abduction; however, greater relative increases are required of the rotator cuff, especially in the presence of larger rotator cuff tears.

Novel oxysterols have pro‐osteogenic and anti‐adipogenic effects in vitro and induce spinal fusion in vivo

Stimulation of bone formation by osteoinductive materials is of great clinical importance in spinal fusion surgery, repair of bone fractures, and in the treatment of osteoporosis. We previously reported that specific naturally occurring oxysterols including 20(S)‐hydroxycholesterol (20S) induce the osteogenic differentiation of pluripotent mesenchymal cells, while inhibiting their adipogenic differentiation. Here we report the characterization of two structural analogues of 20S, Oxy34 and Oxy49, which induce the osteogenic and inhibit the adipogenic differentiation of bone marrow stromal cells (MSC) through activation of Hedgehog (Hh) signaling. Treatment of M2‐10B4 MSC with Oxy34 or Oxy49 induced the expression of osteogenic differentiation markers Runx2, Osterix (Osx), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OCN), as well as ALP enzymatic activity and robust mineralization. Treatment with oxysterols together with PPARγ activator, troglitazone (Tro), inhibited mRNA expression for adipogenic genes PPARγ, LPL, and aP2, and inhibited the formation of adipocytes. Efficacy of Oxy34 and Oxy49 in stimulating bone formation in vivo was assessed using the posterolateral intertransverse process rat spinal fusion model. Rats receiving collagen implants with Oxy 34 or Oxy49 showed comparable osteogenic efficacy to BMP2/collagen implants as measured by radiography, MicroCT, and manual inspection. Histological analysis showed trabecular and cortical bone formation by oxysterols and rhBMP2 within the fusion mass, with robust adipogenesis in BMP2‐induced bone and significantly less adipocytes in oxysterol‐induced bone. These data suggest that Oxy34 and Oxy49 are effective novel osteoinductive molecules and may be suitable candidates for further development and use in orthopedic indications requiring local bone formation. J. Cell. Biochem. 112: 1673–1684, 2011.

Challenges to bone formation in spinal fusion

Spinal arthrodesis continues to expand in clinical indications and surgical practice. Despite a century of study, failure of bone formation or pseudarthrosis can occur in individual patients with debilitating clinical symptoms. Here we review biological and technical aspects of spinal fusion under active investigation, describe relevant biomechanics in health and disease, and identify the possibilities and limitations of translational animal models. The purpose of this article is to foster collaborative efforts with researchers who model bone hierarchy. The induction of heterotopic osteosynthesis requires a complex balance of biologic factors and operative technique to achieve successful fusion. Anatomical considerations of each spinal region including blood supply, osteology, and biomechanics predispose a fusion site to robust or insufficient bone formation. Careful preparation of the fusion site and appropriate selection of graft materials remains critical but is sometimes guided by conflicting evidence from the long-bone literature. Modern techniques of graft site preparation and instrumentation have evolved for every segment of the vertebral column. Despite validated biomechanical studies of modern instrumentation, a correlation with superior clinical outcomes is difficult to demonstrate. In many cases, adjuvant biologic therapies with allograft and synthetic cages have been used successfully to reproduce the enhancement of fusion rates observed with cancellous and tricortical autograft. Current areas of investigation comprise materials science, stem cell therapies, recombinant growth factors, scaffolds and biologic delivery systems, and minimally invasive surgical techniques to optimize the biologic response to intervention. Diverse animal models are required to approach the breadth of spinal pathology and novel therapeutics.

The effect of needle size inducing degeneration in the rat caudal disc: evaluation using radiograph, magnetic resonance imaging, histology, and immunohistochemistry

BACKGROUND CONTEXT The rat caudal disc has been increasingly used in studying of disc degeneration because of its simplicity, low cost, and efficiency. However, the reproducibility and standardization are essential to facilitate the investigations of biologic therapeutics at different stages of degeneration. PURPOSE To identify the effect of different needle gauges to the degenerative response in rat caudal discs and to examine its pathogenesis by looking at the cellular and matrix changes. STUDY DESIGN In vivo study of injury-induced rat caudal disc degeneration using needle puncture. PATIENT SAMPLE Thirty-six Lewis rats aged 12-14 weeks. OUTCOME MEASURES The induced degenerative discs were analyzed by plain radiograph, magnetic resonance imaging (MRI) and histological examination. Proteoglycan content was assessed by alcian blue stain. Immunohistochemistry using aggrecan, collagen II, and Sox-9 was also evaluated to investigate cell differentiation and matrix changes. METHODS All rats were divided into three groups according to different needle gauges (18G, 20G, and 22G). Caudal discs were punctured percutaneously under image guidance. Radiographs and MRI were obtained at 2 weeks interval until 8 weeks. At each time point, three rats from each group were sacrificed for histological analysis and immunohistochemistry. RESULTS Larger needle gauges, especially 18G, produced more deterioration of the disc when compared with smaller sizes, particularly with time. Significant differences were identified in almost all parameters compared between 18G and 22G at the 8-week time point. For the effect of time in the same needle size, the differences occurred between 2- or 4-week and 8-week time point in the 18G and 20G groups. The proteoglycan and aggrecan stain gradually decreased over time. Chondrogenic differentiation was identified within the degenerative disc by detecting Sox-9 positive cells and collagen II accumulation increased as degeneration progressed. CONCLUSIONS The puncture-induced degenerative changes in rat caudal discs can imitate the human degenerative cascade as observed in plain radiograph, MRI, histology, and immunohistochemistry. We suggest that needle size affects the occurrence of progression of degeneration; thus, the large needle size was required to accelerate the deterioration. The size of needle and time point after injury should be considered when investigating the effect of therapeutic materials to retard degeneration or regenerate the intervertebral disc.

Surgical management of PCL injuries: indications, techniques, and outcomes

The ideal treatment for posterior cruciate ligament (PCL) injuries is controversial and remains an active area of orthopedic research. The indications for surgery and the ideal method of reconstruction continue to be evaluated in biomechanical and clinical studies. Recent research has provided information on the anatomy and biomechanics of the PCL, and the merits and drawbacks of the transtibial compared with the tibial inlay technique, the use of single vs double-bundle reconstruction, and different graft options for reconstruction. This review discusses important factors in the surgical treatment of PCL injuries, with attention to the most current literature on these topics.

A Novel Osteogenic Oxysterol Compound for Therapeutic Development to Promote Bone Growth: Activation of Hedgehog Signaling and Osteogenesis through Smoothened Binding

Osteogenic factors are often used in orthopedics to promote bone growth, improve fracture healing, and induce spine fusion. Osteogenic oxysterols are naturally occurring molecules that were shown to induce osteogenic differentiation in vitro and promote spine fusion in vivo. The purpose of this study was to identify an osteogenic oxysterol more suitable for clinical development than those previously reported, and evaluate its ability to promote osteogenesis in vitro and spine fusion in rats in vivo. Among more than 100 oxysterol analogues synthesized, Oxy133 induced significant expression of osteogenic markers Runx2, osterix (OSX), alkaline phosphatase (ALP), bone sialoprotein (BSP), and osteocalcin (OCN) in C3H10T1/2 mouse embryonic fibroblasts and in M2‐10B4 mouse marrow stromal cells. Oxy133‐induced activation of an 8X‐Gli luciferase reporter, its direct binding to Smoothened, and the inhibition of Oxy133‐induced osteogenic effects by the Hedgehog (Hh) pathway inhibitor, cyclopamine, demonstrated the role of Hh pathway in mediating osteogenic responses to Oxy133. Oxy133 did not stimulate osteogenesis via BMP or Wnt signaling. Oxy133 induced the expression of OSX, BSP, and OCN, and stimulated robust mineralization in primary human mesenchymal stem cells. In vivo, bilateral spine fusion occurred through endochondral ossification and was observed in animals treated with Oxy133 at the fusion site on X‐ray after 4 weeks and confirmed with manual assessment, micro‐CT (µCT), and histology after 8 weeks, with equal efficiency to recombinant human bone morphogenetic protein‐2 (rhBMP‐2). Unlike rhBMP‐2, Oxy133 did not induce adipogenesis in the fusion mass and resulted in denser bone evidenced by greater bone volume/tissue volume (BV/TV) ratio and smaller trabecular separation. Findings here suggest that Oxy133 has significant potential as an osteogenic molecule with greater ease of synthesis and improved time to fusion compared to previously studied oxysterols. Small molecule osteogenic oxysterols may serve as the next generation of bone anabolic agents for therapeutic development.

Synergistic effect of bone morphogenetic proteins 2 and 7 by ex vivo gene therapy in a rat spinal fusion model.

BACKGROUND Previous studies have suggested that the co-expression of two different bone morphogenetic protein (BMP) genes can result in the production of heterodimeric BMPs that may be more potent than homodimers. In this study, combined BMP-2 and BMP-7 gene transfer was performed ex vivo to compare the resulting new bone formation with that of single-BMP gene transfer in a rat spinal fusion model. METHODS Forty-four athymic rats underwent posterolateral fusion at L4-L5 and were implanted with a collagen sponge containing human adipose-derived stem cells. Group A received untreated cells, and the remaining groups received cells transfected with various genes in a lentivirus vector. The transferred genes were GFP (green fluorescent protein) in Group B, BMP-2 in Group C, BMP-7 in Group D, and both BMP-2 and BMP-7 in Group E. In vitro production of BMP-2 and BMP-7 was quantified by means of an enzyme-linked immunosorbent assay (ELISA) specific to BMP-2 or BMP-7. Osseous fusion was quantified with use of radiography and microcomputed tomography. RESULTS ELISA demonstrated that Group E, which was treated with both BMP-2 and BMP-7, produced less than one-fourth as much BMP as the groups treated with a single transfected BMP (Groups C and D). Radiographs showed that all of the spines in Groups C, D, and E appeared to be fused by eight weeks; the spines in Groups A and B showed minimal evidence of new bone formation. Measurements confirmed that the mean bone formation area was significantly greater in Groups C, D, and E compared with Groups A and B (p < 0.001). In addition, the bone formation area was significantly greater in Group E compared with Groups C and D (p < 0.001). CONCLUSIONS Combined BMP-2 and BMP-7 ex vivo gene transfer was found to be significantly more effective for inducing new bone formation compared with ex vivo gene transfer of an individual BMP in a rat spinal fusion model. CLINICAL RELEVANCE Combined BMP-2 and BMP-7 therapy may lead to efficient bone regeneration.

Effects of the bone morphogenetic protein binding protein spp24 (secreted phosphoprotein 24 kD) on the growth of human lung cancer cells.

Bone morphogenetic proteins (BMPs) and transforming growth factor‐beta (TGF‐β) contribute to the growth of some skeletal metastases through autocrine stimulation. Secreted phosphoprotein 24 kDa (spp24) has been shown to bind to both BMP‐2 and TGF‐β and to markedly inhibit the osteogenic properties of rhBMP‐2. We hypothesized that the addition of spp24 would sequester autocrine growth factors (especially BMP‐2) and reduce tumor growth in a system (A549 human non‐small cell lung cancer cell line) where autocrine stimulation by BMP‐2 is known to be important. A549 cells were injected into two sites (subcutaneous and intraosseus) in SCID mice with and without the co‐injection of BMP‐2 and spp24. Tumor growth after 8 weeks was assessed through gross examination, radiological imaging, and histological analysis. Spp24 attenuated the tumor growth enhancing effects of rhBMP‐2 and reduced the tumor growth when added to tumor cells that were not treated with BMP‐2. We conclude that spp24 can reduce A549 cell tumor growth in both soft tissue and intraosseus environments. We hypothesize that the mechanism for this inhibition is interruption of autocrine stimulation through the sequestration of BMP‐2. Spp24 can be developed into a therapeutic agent that can be employed in clinical situations where the inhibitions of BMPs and related proteins is advantageous.

Anterior fusion alone compared with combined anterior and posterior fusion for the treatment of degenerative cervical kyphosis

We evaluated the efficacy of anterior fusion alone compared with combined anterior and posterior fusion for the treatment of degenerative cervical kyphosis. Anterior fusion alone was undertaken in 15 patients (group A) and combined anterior and posterior fusion was carried out in a further 15 (group B). The degree and maintenance of the angle of correction, the incidence of graft subsidence, degeneration at adjacent levels and the rate of fusion were assessed radiologically and clinically and the rate of complications recorded. The mean angle of correction in group B was significantly higher than in group A (p = 0.0009). The mean visual analogue scale and the neck disability index in group B was better than in group A (p = 0.043, 0.0006). The mean operation time and the blood loss in B were greater than in group A (p < 0.0001, 0.037). Pseudarthrosis, subsidence of the cage, and problems related to the hardware were more prevalent in group A than in group B (p = 0.034, 0.025, 0.013). Although the combined procedure resulted in a longer operating time and greater blood loss than with anterior fusion alone, our results suggest that for the treatment of degenerative cervical kyphosis the combined approach leads to better maintenance of sagittal alignment, a higher rate of fusion, a lower incidence of complications and a better clinical outcome.

Enhancement of recombinant human BMP‐7 bone formation with bmp binding peptide in a rodent femoral defect model

Bone morphogenetic binding peptide (BBP) is an 18.5 kDa fragment of a bone matrix protein peptide. A rat femoral defect model was used to test the effect of BBP combined with recombinant human bone morphogenetic protein‐7 (rhBMP‐7) to induced bone healing. Two doses of BBP (500 and 1000 µg) were tested with two doses of rhBMP‐7 (2 and 5 µg), and the results were compared with a positive control (10 µg rhBMP‐7). Bone healing was evaluated by radiology, manual palpation, microcomputed tomography, and histology. The high dose of 10 µg of rhBMP‐7 resulted in a consistent 100% bone union rate and a mature histological appearance on histology, and was used as a positive control. When 1000 µg of BBP was combined with lower doses of BMP‐7 (2 µg rhBMP‐7 or 5 µg rhBMP‐7) significant differences were seen in radiographic scores, manual palpation, and bone volume, when compared to 2 µg rhBMP‐7 or 5 µg rhBMP‐7 alone. The combination of 1000 µg of BBP and 5 µg rhBMP‐7 also achieved 100% fusion rate, induced a larger amount of bone formation, and yielded similar maturity of bone marrow when compared with the high dosage 10 µg rhBMP‐7 group. This study demonstrated that when combined together, BBP can enhance the bone healing of rhBMP‐7. Improved healing imparted by the addition of BBP may result in lesser amounts of rhBMP‐7 needed to achieve union in the clinical setting.