Summary

Strong mechanical fixation is critical to the success of rotator cuff repairs. In this comparative study in cadaveric shoulders, single-tendon full-thickness supraspinatus tears were repaired using two different types of PEEK knotless suture anchors-ReelX STT (Stryker) and Opus Magnum PI (Arthrocare)-using a single-row technique in both instances. Cyclic testing was performed followed by loading until mechanical failure. No significant difference was observed in gap formation, measured as the distance between the supraspinatus tendon and bone at the repair site, during cyclic loading. However, the maximum load was statistically higher for repairs with the ReelX anchor.

Introduction

Clinical studies have shown distinct differences in later-onset idiopathic scoliosis (IS) between men and women, including curve severity, stiffness, and ease of operative intervention. Therefore, significant scoliosis in men was used as criteria to create a phenotypical subset of families with IS. The goal of this study is to identify genetic determinants that relate specifically to men with a scoliotic curvature of 30° or more.

Pyrocarbon has been used for over 25 years in finger joint replacements. Excellent biocompatibility, material and wear properties make pyrocarbon ideal for an orthopaedic device.

Pyrocarbon implants incur significantly less wear to articular cartilage than metal implants. The pyrocarbon implant replacement device (PIR) was developed to treat focal chondral and osteochondral defects of the femoral condyles. The PIR is intended to treat defects not amenable to microfracture or similar regenerative techniques and those for which unicompartmental or total knee arthroplasty is not yet indicated. The purpose of this study was to evaluate the in vivo articular response to the PIR device and compare it to a similar device made from cobaltchromium (CoCr) device. In addition, bone fixation of the PIR device with and without hydroxyapatite (HA) coating was evaluated.

Nine adult bred-for-purpose beagles received bilateral 6mm medial condyle full thickness osteochondral defects. One defect was treated with a PIR device and the other an identical CoCr device. In addition, one HA-coated and one non-HA coated PIR device was placed unicortically in the lateral distal femurs of each animal. Three animals each were terminated at 12, 24, and 52 weeks postoperative. Non-decalcified histologic sections of the implanted condyles and decalcified sections of the medial tibia and meniscus were evaluated. The femoral condyle sections were graded using a modified scale of Kirker-Head (2006). Additionally, the bone– implant contact area was quantified. The tibia-meniscus sections were evaluated utilising a modified version of the ICRS Histological Visual Scale (2002). The lateral distal femur implants were mechanically tested in axial push-out to compare the bone-implant interface strength between the HA-coated and non-HA coated PIR devices.

The mean histologic grades for the tibia and meniscus were superior for surfaces that articulated against the pyrocarbon PIR device compared to the CoCr device at 12, 24 and 52 weeks. Over time, the mean histologic grades decreased with both materials; however, tibias that articulated with the CoCr device had the lowest mean grade at 52 weeks. There were little difference in bone contact 12 and 24 weeks between the pyrocarbon and the CoCr devices. At 52 weeks, less bone contact was observed compared to 12 and 24 weeks. Mechanical testing demonstrated that the HA-coating imparted a statically significant improvement in interface strength as well as greater direct bone contact to the implant.

The results of this study confirm that pyrocarbon provides an ideal surface for an implant that articulates with cartilage of the knee. Although adequate direct bone contact was observed, the addition of HA-coating imparted both superior initial and long term bone fixation. The PIR device is suitable for restoration of focal defects of the knee.

An unconstrained, articulating pyrocarbon cervical total disc replacement (TDR; Rescue, Biomet, US) has been developed. Pyrocarbon is a chemically inert form of carbon with an elastic modulus similar to bone. The long-term durability and wear resistance of pyrocarbon has been demonstrated in other orthopaedic devices. The purpose of this study was two-fold: to compare the wear of identical disc reaplcements fabricated from cobalt chrome (CoCr) and ultrahigh-molecular-weight-polyethylene (UHMWPE) to pyrocarbon and to compare the motion at index and motion segments before and after Rescue TDR.

Ten pyrocarbon and three CoCr-UHMWPE TDRs were subjected to 10 million cycles in 20 degrees of flexion–extension with 155N axial load in serum solution at 4.0Hz. One additional CoCr-UHMWPE couple was immersed in serum and loaded to 155 N. TDRs and serum solution were examined at 0, 2.5, 5, 7.5 and 10 million cycles to characterize wear. The surfaces were measured with a coordinate measuring machine prior to and after 10 million cycles. Serum solutions and time controlled serum-only controls were characterized for the quantity of wear debris using particle analysis. Nine cadaver cervical spines were placed through dynamic 2Nm cycles of flexion, extension, and lateral bending. Electromagnetic sensors recorded the motion of each vertebral body in response to applied loads. Total range of motion at the index and adjacent levels were determined for the intact spine and after TDR.

There was no significant difference in the pyrocarbon surface geometry after 10 million cycles or in the number of particles generated during testing compared to baseline (p > 0.05).

However, CoCr-UHMWPE devices displayed classic patterns of total joint wear. CoCr-UHMWPE wear couples had an initial increase in serum particles, followed by lower particle producing rates that gradually increased. The difference in mean UHMWPE wear particles at each interval was significantly greater than with the pyrocarbon TDR (all p< 0.05).

The mean total and dynamic ranges of flexion-extension and lateral bending after implantation of the Rescue TDR at the index level were not statistically significantly different from that of the intact spine (ANOVA: p > 0.05). Similarly, at the superior and inferior adjacent levels, the mean total and dynamic range of flexion-extension and lateral bending after implantation of the Rescue device were not statistically significantly different from the intact spine (ANOVA: p > 0.05).

Introduction: The use of adjunctive techniques such as electrical stimulation may improve the rate of successful anterior lumbar interbody fusion. The purpose of this study was to determine if supplemental direct current electrical stimulation of a titanium anterior spinal fusion device increases the incidence and extent of bony fusion in a nonhuman primate model.

Methods: Anterior lumbar interbody fusion was performed at the L5–L6 level in 35 adult pigtail macaque monkeys with iliac crest graft and either a titanium fusion device or a femoral allograft ring. The fusion devices of some animals received either high current (100μA) or low current (28μA) electrical stimulation using an implanted generator for the duration of the 12- or 26- week evaluation period. All animals were studied using AP and lateral radiographs, CT imaging, nondestructive mechanical testing, and qualitative and quantitative histology. Specimens were scored for presence of fusion according to a semi-quantitative scale (0 = No healing, 1 = Minimal consolidation, 2 = Consolidation, 3 = Bridging callus, 4 = Bridging callus with trabeculations, 5= Evidence of bony remodeling of callus). A similar scale was used to score the extent of fusion.

Results: As shown in Table 1, both low and high current stimulation groups had generally increased incidence of bony fusion compared to the non-stimulated and femoral allograft ring groups. At 26 weeks, the extent of bony fusion increased with the devices from 43% to 75% in a dose-dependent fashion, compared to 25% with the femoral rings. Mechanical testing also demonstrated similar increases in mechanical stiffness in a dose-dependent fashion.

Discussion: Adjunctive electrical stimulation of an anterior titanium spinal fusion device improved success rate and overall fusion quality compared to non-stimulated devices and femoral allograft rings. Stimulated devices may be particularly beneficial in patients with known risk factors for nonunion.

INTRODUCTION: The use of adjunctive techniques such as electrical stimulation may improve the rate of successful anterior lumbar interbody fusion. The purpose of this study was to determine if supplemental direct current electrical stimulation of a titanium anterior spinal fusion device increases the incidence and extent of bony fusion in a nonhuman primate model.

METHODS: Anterior lumbar interbody fusion was level in 35 adult pigtail macaque performed at the L₅–L₆ monkeys with iliac crest graft and either a titanium fusion device or a femoral allograft ring. The fusion devices of some animals received either high current (100 μA) or low current (28 μA) electrical stimulation using an implanted generator for the duration of the 12- or 26-week evaluation period. All animals were studied using AP and lateral radiographs, CT imaging, nondestructive mechanical testing, and qualitative and quantitative histology. Specimens were scored for presence of fusion according to a semi-quantitative scale (0 = No healing, 1 = Minimal consolidation, 2 = Consolidation, 3 = Bridging callus, 4 = Bridging callus with trabeculations, 5= Evidence of bony remodeling of callus). A similar scale was used to score the extent of fusion.

RESULTS: As shown in Table 1, both low and high current stimulation groups had generally increased incidence of bony fusion compared to the non-stimulated and femoral allograft ring groups. At 26 weeks, the extent of bony fusion increased with the devices from 43% to 75% in a dose-dependent fashion, compared to 25% with the femoral rings. Mechanical testing also demonstrated similar increases in mechanical stiffness in a dose-dependent fashion.

DISCUSSION: Adjunctive electrical stimulation of an anterior titanium spinal fusion device improved success rate and overall fusion quality compared to non-stimulated devices and femoral allograft rings. Stimulated devices may be particularly beneficial in patients with known risk factors for nonunion.

Growth factors hold great promise for the treatment of various musculoskeletal conditions. Growth factors are small proteins that serve as signaling agents for cells. The discovery of these substances revolutionized the field of cell biology by revealing the mechanism of regulation of cell activities. Growth factors are present in plasma or tissues at concentrations measured in billionths of a gram yet they are the principal effector of such critical cellular functions such as cell division, matrix synthesis and tissue differentiation.

Several growth promoting substances have been identified in bone matrix and at the site of healing fractures. Among these are the transforming growth factor beta’s, bone morphogenetic proteins, fibroblast growth factors, insulin like growth factors and platelet derived growth factor. These growth factors are mainly produced by osteoblasts and incorporated into the extracellular matrix during bone formation. Small amounts of the growth factors can also be trapped systemically from serum and be incorporated into matrix. The present hypothesis is that growth factors are located within the matrix until remodeling or trauma causes solubilization and release of the proteins.

The discovery of growth factors and their study in in vitro cultures has allowed an understanding of the mechanism of the regulation of a broad range of cell activities. However, their presence in plasma and tissues in minute quantities limited their evaluation in vivo and precluded clinical application of the natural purified products. Advances in recombinant DNA methodology have allowed sufficient quantities of these materials to be produced and many are in various stage of in vivo pre-clinical and clinical evaluation.

Extensive efforts have been made to find methods by which growth factors can be used to stimulate local bone healing and bone formation in a variety of clinical models. The growth factors TGF-α, BMP and basic FGF are the only growth factors that have been demonstrated to possess substantial in vivo bone stimulatory capacity. The growth factors BMP-2 and BMP-7, also known as osteogenic protein-1, are in the final stages of pivotal human trials.

There are many challenges to the clinical application of growth factors. It is unlikely that cell signaling molecules act independently of each other or are present in isolation from each other at their sites of action. The therapeutic application of growth factors must also accommodate the fact that most factors have a widespread and varied distribution of target cells. A growth factor administered to elicit a desired response from one cell type may also influence other cell types possible in unintended or undesirable ways. Finally, in the current era of cost consciousness in health care, a growth factor treatment must demonstrate cost effectiveness along with clinical efficacy.

Osteogenic proteins (OPs), also referred to as bone morphogenetic proteins (BMPs), are a family of bone-matrix polypeptides isolated from a variety of mammalian species. These proteins are members of the transforming growth factors-beta superfamily of molecules that contain a highly conserved 7 cysteine transforming growth factor domain in their C-termini. Implantation of osteogenic proteins induce a sequence of cellular events that leads to the formation of new bone.

In preclinical studies, the implantation of recombinantly produced human osteogenic protein-1 (OP-1, also referred to as BMP-7) in conjunction with bovine bone derived Type 1 collagen or various nonproteinaceous biodegradable carriers into surgically created, critical size diaphyseal segmental defects resulted in the regeneration of new bone that was fully functional biologically and biomechanically. Injection of an OP-1 solution into a fresh fracture model accelerated the bone repair process compared with control fracture healing. Significantly increased biomechanical strength was the result of greater and earlier new bone formation. Further study has demonstrated that OP-1 can be used as a bone graft substitute to promote spinal fusion, aid in the incorporation of metal implants, and improve the performance of autograft and allograft bone. OP-1 has also shown promise as an agent for the repair of osteochondral defects.

Clinical study of the OP-1 device for the treatment of tibial nonunion fractures has shown healing characteristics similar to that obtained with autogenous iliac crest bone graft. The randomized, prospective clinical evaluation included 30 patients with 31 tibal nonunion fractures. The mean time from injury was 27.2 months (minimum 9 months). All patients were treated with reamed intramedullary rods. At the 9 month evaluation 14 of 16 OP-1 and 14 of 15 autograft treated fractures were clinically and radiographically healed. Advantages of OP-1 included no donor site complications, less blood loss, an a shorter operative time.