Evaluation of fibrocartilage regeneration and bone response at full-thickness cartilage defects in articulation with pyrolytic carbon or cobalt-chromium alloy hemiarthroplasties

Promising results after hemi-shoulder arthroplasty using pyrolytic carbon heads in young and middle-aged patients

INTRODUCTION

The objective of this prospective cohort study was the assessment of short-term outcome results of shoulder hemiarthroplasty (HA) using pyrolytic carbon (PC) heads. PC has been introduced as a new material to avoid surgical revision due to glenoid erosion after HA. Glenoid erosion due to the use of metallic heads is known to reduce durability.

HYPOTHESIS

HA using PC heads shows comparable or better radiographic and clinical outcome compared to the conventional HA using metallic heads in the short-term.

PATIENTS AND METHODS

This study was conducted as a single center prospective cohort follow-up study including a total number of 16 consecutive HA with PC heads. Inclusion criteria were indication for HA, an intact rotator cuff, no proximal humeral fractures in patient's history and age>18years. Mean age at the time of arthroplasty was 52.8±10.8years. The mean follow-up was 24.3±8.1months. Baseline and follow-up Numeric Rating Scale (NRS), Constant Scores (CS), Range of Motion (ROM) and radiographs were assessed.

RESULTS

At a mean follow-up of 24.3months the mean CS (p<0.001), mean NRS (p<0.001) and mean ROM (p<0.05) improved statistically significant. Subgroup analysis revealed no differences between subgroups (sex, age, diagnosis, and handedness). Survival rate was high (94.1%). One periprosthetic fracture occurred as the only complication during follow-up. Radiographs showed glenoid erosion in one case and subacromial space reduction in two cases.

DISCUSSION

PC heads in HA show satisfying short-term results at a mean follow-up of two years, which are comparable to those of conventional HA. The clinical improvements were highly significant with good implant survival. However, long-term follow-up results are necessary, especially compared to conventional HA.

LEVEL OF EVIDENCE

IV; observational therapeutic cohort study.

Hemiarthroplasty implants should have very low stiffness to optimize cartilage contact stress

Hemiarthroplasty is often preferred to total arthroplasty as it preserves native tissue; however, accelerated wear of the opposing cartilage is problematic. This is thought to be caused by the stiffness mismatch between the implant and cartilage-bone construct. Reducing the stiffness of the implant by changing the material has been hypothesized as a potential solution. This study employs a finite element model to study a concave-convex hemiarthroplasty articulation for various implant materials (cobalt-chrome, pyrolytic carbon, polyether ether ketone, ultra-high-molecular-weight polyethylene, Bionate-55D, Bionate-75D, and Bionate-80A). The effect of the radius of curvature and the degree of flexion-extension was also investigated to ensure any relationships found between materials were generalizable. The implant material had a significant effect (P  < .001) for both contact area and maximum contact pressure on the cartilage surface. All of the materials were different from the native state except for Bionate-80A at two of the different flexion angles. Bionate-80A and Bionate-75D, the materials with the lowest stiffnesses, were the closest to the native state for all flexion angles and radii of curvature. No evident difference between materials occurred unless the modulus was below that of Bionate-55D (288 MPa), suggesting that hemiarthroplasty materials need to be less stiff than this material if they are to protect the opposing cartilage. This is clinically significant as the findings suggest that the development of new hemiarthroplasty implants should use materials with stiffnesses much lower than currently available devices.

Biological and functional evaluation of a novel pyrolytic carbon implant for the treatment of focal osteochondral defects in the medial femoral condyle: assessment in a canine model

Background

Osteochondral defects continue to be a clinical treatment challenge, and when left untreated, may cause pain and functional impairment. Pyrolytic carbon is a unique isotropic biomaterial used in heart valve and small joint replacements due to its excellent wear properties and biocompatibility with bone and articular cartilage. Therefore, a proposed solution is to utilize a focal pyrolytic carbon hemiarthroplasty implant as an alternative resurfacing treatment strategy for isolated cartilage lesions.

Methods

A canine model (n = 9) was used to evaluate the in vivo histologic response and function of a pyrolytic carbon implant replacing a full-thickness osteochondral defect in the medial femoral condyle (MFC) of the knee. The gross appearance and histologic results were compared to an identical cobalt-chromium (Co-Cr) alloy implant placed in a defect in the contralateral MFC and evaluated up to 52 weeks.

Results

Extensive bone incorporation to the stem portion was observed for both implant types. The total mean histologic score for the cartilage of the MFC surrounding the pyrolytic carbon implants was significantly improved compared to that of the Co-Cr alloy implants at all evaluation periods (p < 0.05). Histologic grading and gross observations at 52 weeks for pyrolytic carbon implants were similar to those of Co-Cr alloy implants at 24 weeks. At 24 weeks, the mean total histologic score for Co-Cr alloy implants was 11.6 ± 0.7 (0–16 range point; 16 = normal appearance), while at 52 weeks, the mean total score for the pyrolytic carbon implants was 11.7 ± 1.3. Mean total histologic score of opposing medial tibia cartilage for the pyrolytic carbon implants was superior to that of the Co-Cr alloy group at all evaluation periods and significantly improved over the Co-Cr alloy implant group at 24 weeks (p = 0.001) and 52 weeks (p < 0.001).

Conclusions

Use of a pyrolytic carbon implant for reconstruction of a focal cartilage defect demonstrated effective implant fixation and superior in vivo response compared to an identical Co-Cr alloy implant.

ESTABLISHING A LIVE CARTILAGE-ON-CARTILAGE INTERFACE FOR TRIBOLOGICAL TESTING

Mechano-biochemical wear encompasses the tribological interplay between biological and mechanical mechanisms responsible for cartilage wear and degradation. The aim of this study was to develop and start validating a novel tribological testing system, which better resembles the natural joint environment through incorporating a live cartilage-on-cartilage articulating interface, joint specific kinematics, and the application of controlled mechanical stimuli for the measurement of biological responses in order to study the mechano-biochemical wear of cartilage. The study entailed two parts. In Part 1, the novel testing rig was used to compare two bearing systems: (a) cartilage articulating against cartilage (CoC) and (b) metal articulating against cartilage (MoC). The clinically relevant MoC, which is also a common tribological interface for evaluating cartilage wear, should produce more wear to agree with clinical observations. In Part II, the novel testing system was used to determine how wear is affected by tissue viability in live and dead CoC articulations. For both parts, bovine cartilage explants were harvested and tribologically tested for three consecutive days. Wear was defined as release of glycosaminoglycans into the media and as evaluation of the tissue structure. For Part I, we found that the live CoC articulation did not cause damage to the cartilage, to the extent of being comparable to the free swelling controls, whereas the MoC articulation caused decreased cell viability, extracellular matrix disruption, and increased wear when compared to CoC, and consistent with clinical data. These results provided confidence that this novel testing system will be adequate to screen new biomaterials for articulation against cartilage, such as in hemiarthroplasty. For Part II, the live and dead cartilage articulation yielded similar wear as determined by the release of proteoglycans and aggrecan fragments, suggesting that keeping the cartilage alive may not be essential for short term wear tests. However, the biosynthesis of glycosaminoglycans was significantly higher due to live CoC articulation than due to the corresponding live free swelling controls, indicating that articulation stimulated cell activity. Moving forward, the cell response to mechanical stimuli and the underlying mechano-biochemical wear mechanisms need to be further studied for a complete picture of tissue degradation.

Longitudinal instability of the forearm

The Essex Lopresti lesion is a rare triad of injury to the radial head, interosseous membrane of the forearm and distal radio-ulnar joint, which results in longitudinal instability of the radius. If unrecognized this leads to chronic pain and disability which is difficult to salvage. Early recognition and appropriate treatment is therefore desirable to prevent long-term problems. The aim of this article is to review the pathoanatomy of longitudinal radius instability and use the existing literature and authors' experience to provide recommendations for recognition and treatment of acute and chronic forearm instability, including description of the author's technique for interosseous membrane reconstruction.

Preclinical evaluation of a novel implant for treatment of a full-thickness distal femoral focal cartilage defect

A novel, nonresorbable, monolithic composite structure ceramic, developed using a partially stabilized zirconia ceramic common to implantable devices, was used in a cementless weight-bearing articular implant to test the feasibility of replacing a region of degenerated or damaged articular cartilage in the knee as part of a preclinical study using male mongrel dogs lasting up to 24 weeks. Gross/histological cartilage observations showed no differences among control, 12-week and 24-week groups, while pull-out tests showed an increase in maximum pull-out load over time relative to controls. Hence, the use of a novel ceramic implant as a replacement for a focal cartilage defect leads to effective implant fixation within 12 weeks and does not cause significant degradation in opposing articular cartilage in the time frame evaluated.

What's next? Alternative materials for articulation in total joint replacement

The use of an artificial joint is always related to a certain amount of wear. Its biological effects, e.g., the osteolysis potential, are a function of the bulk material as well as its debris. Following comprehensive experiences with polyethylene (PE) wear, material science is tracking two ways to minimize the risk of a particle-induced aseptic implant loosening: (i) reduction of the PE debris by a low-wearing articulation partner; and (ii) replacement of the PE by other materials. Therefore, new ceramics (e.g., ZTA, Si(3)N(4)), as well as coatings (e.g., TiN, "diamond-like" carbon) and modifications of a bulk metal (e.g., oxidizes zirconium) or cushion bearings (polyurethane, hydrogels), are currently available for total joint replacements or have been used for pre-clinical testing. This review gives a brief overview and evaluates the potential of those that have recently been published in literature.

Pyrolytic carbon endoprosthetic replacement for osteonecrosis and femoral fracture of the hip: a pilot study

Hemiarthroplasty in young patients has the potential for eliminating bearing wear, but has the disadvantage of cartilage wear. Low-temperature isotropic (LTI) pyrolytic carbon reportedly reduces cartilage wear in canine hemiarthroplasties. We therefore initiated a study in humans when it was released for human use. However, we observed failures in some patients. We therefore document and report the high failure rate observed in a subset of patients treated with an LTI pyrolytic carbon femoral head for osteonecrosis. We conducted a prospective pilot study of 17 patients treated with a titanium stem and an LTI pyrolytic carbon femoral head bearing surface for unipolar hemiarthroplasty for either femoral neck fracture (10 patients) or osteonecrosis (seven patients). One of 10 patients in the fracture group underwent conversion to THA as a result of arthritic progression compared with six of seven patients with osteonecrosis who underwent conversion to THA as a result of acetabular wear and severe groin pain. In this small series, patients with osteonecrosis had a higher rate of revision compared with the patients treated for femoral neck fracture.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Enhancement of the fixation of pyrolytic carbon implants by using atomic oxygen texturing

The purpose of this study was to examine the effect on the biocompatibility and biologic fixation of atomic oxygen-textured pyrolytic carbon. The implants consisted of unalloyed pyrolytic carbon rods, with half the length of the rod textured by atomic oxygen, and the other half retaining the as-deposited surface that normally occurs during the manufacturing process. The rods were implanted transcortically across the distal portion of the femurs of 6 adult male rabbits for 8 weeks. The implants were assessed mechanically by measuring the interface strength between the implant and the bone. The implant-bone interface was also examined by light microscopy. No adverse reaction to either the as-deposited or the textured pyrolytic carbon was seen. Percent bone apposition was greater for textured implants than for the as-deposited implants; however, it was not significant. The bone apposition efficiency factor, calculated by dividing the interface strength by the fraction of bone apposition, was greater for the textured implants than for the as-deposited implants. This indicates that the fixation obtained was more effective for the textured implants. The findings of this study suggest that biologic fixation of pyrolytic carbon implants can be enhanced by surface texturing by using direct exposure to atomic oxygen, without compromising its biocompatibility.

Factors influencing changes in articular cartilage following hemiarthroplasty in sheep

This study examined the relationship between acetabular cartilage properties after hemiarthroplasty surgery and surgical variables including femoral head size and position. Nineteen sheep received unilateral hip arthroplasties and were euthanized one year post-operatively to harvest the femora and acetabula. Cartilage histology, biochemistry and material properties were determined from samples located in the superior load-bearing region. Femoral head size mismatch, leg length difference, anterior-posterior and medial lateral offset and anteversion were measured. In the acetabulum. substantial cartilage degradation occurred with widespread librillation and significant changes in the biochemical and material properties compared to the intact contralateral joint. Regression analyses on the surgical variables explained 75-80% of the changes in tissue biochemistry but did not explain the material changes. Head size mismatch and leg length difference were the most significant contributors of the five variables examined and therefore may be critical to successful outcome in hemiarthroplasty.