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.

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.