Acetabular fixation options: notes from the other side

Use of Porous Titanium Trabecular as a Bone Defect Regenerator: In Vivo Study

The application of porous materials is increasingly being used in orthopaedic surgery due to its good results. Bone growth within the pores results in excellent mechanical fixation with the bone, as well as good bone regeneration. The pores, in addition to being colonised by bone, produce a decrease in the modulus of elasticity that favours the transfer of loads to the bone. This research shows the results of an experimental study where we have created critical osteoperiosteal defects of 10 mm on rabbit’s radius diaphysis. In one group of 10 rabbits (experimental group) we have implanted a bioactive porous titanium cylinder, and in another group we have allowed spontaneous regeneration (control group). Mechanical tests were performed to assess the material. Image diagnostic techniques (X-ray, scanner and 3D scan: there are no references on the literature with the use of CT-scan in bone defects) and histological and histomorphometric studies post-op and after 3, 6 and 12 months after the surgery were performed. All the control cases went through a pseudoarthrosis. In 9 of the 10 cases of the experimental group complete regeneration was observed, with a normal cortical-marrow structure established at 6 months, similar to normal bone. Titanium trabecular reached a bone percentage of bone inside the implant of 49.3% on its surface 3 months post-op, 75.6% at 6 months and 81.3% at 12 months. This porous titanium biomaterial has appropriate characteristics to allow bone ingrowth, and it can be proposed as a bone graft substitute to regenerate bone defects, as a scaffold, or as a coating to achieve implant osteointegration.

Bead debonding from a modern cementless total hip femoral component with concomitant taper corrosion

We report a case of bead shedding from a cylindrical extensively porous-coated cementless femoral component with concomitant taper corrosion at the modular head-neck junction of a metal-on-polyethylene total hip prosthesis. The patient presented with chronic thigh pain 4 years after primary total hip arthroplasty, and radiographs revealed significant osteolysis and metallic debris around the femoral stem. Intraoperatively, the patient had a grossly loose femoral component with debonding of sintered beads from the femoral stem, as well as evidence of taper corrosion. We identify a failure of a modern beaded femoral component in conjunction with taper corrosion.

Bone loss around a stable, partly threaded hydroxyapatite-coated cup: a prospective cohort study using RSA and DXA

STUDY PURPOSE

Aseptic loosening of the acetabular component is the most common reason for revision after primary THA, and periprosthetic demineralisation has been described as a potential cause for this process. The trabeculae-oriented pattern (TOP)-cup is a flat, hydroxyapatite (HA)-coated titanium shell with a threaded rim that was developed in order to minimise periprosthetic bone loss. We hypothesised that this cup provides good primary stability and improves preservation of periprosthetic bone mineral density (BMD).

BASIC PROCEDURES

A prospective cohort study on 30 patients receiving the TOP cup was carried out. Preoperative total hip BMD and postoperative periprosthetic BMD in five periprosthetic regions of interest were investigated by dual energy radiographic absorptiometry (DXA), cup migration was analysed by radiostereometry (RSA), and the Harris hips score (HHS) was determined.

MAIN FINDINGS

Mean HHS increased from 49 (24-79) preoperatively to 99 (92-100) after two years. DXA after one year demonstrated substantial BMD loss in the proximal periprosthetic zones 1 (-18%), zone 2 (-16 %) and zone 3 (-9%, all p<0.001 when compared with baseline BMD determined immediately postoperatively). The bone loss in these regions did not recover after two years. RSA (performed on 16 patients) showed that only very limited micromotion of the implant occurred: Mean cranial migration was 0.01 mm (95% confidence interval (CI): -0.09-0.12) and mean inclination decreased by 0.02º (CI: -0.43-0.39) after two years.

CONCLUSION

We conclude that the TOP cup provides good primary stability in the short-term. However, substantial BMD loss in proximal periprosthetic areas indicates that the design of this cup cannot prevent periprosthetic bone loss that has also been observed around other uncemented cups.

Do tantalum and titanium cups show similar results in revision hip arthroplasty?

Porous surfaces are intended to enhance osteointegration of cementless implants. Tantalum has been introduced in an effort to enhance osseointegration potential of uncemented components. We therefore compared the clinical outcome of acetabular components with two different porous surfaces. We retrospectively reviewed 283 patients (295 hips) who underwent cementless revision hip arthroplasty with either an HA-coated titanium cup (207 patients, 214 hips) or porous tantalum cup (79 patients, 81 hips). The minimum followup was 24 months in both groups (titanium: average 51.8 months, range, 24-98 months; tantalum: average, 35.4 months, range, 24-63 months). The titanium and tantalum groups had a mechanical failure rate (clinical plus radiographic) of 8% and 6%, respectively. In hips with minor bone deficiency (type 1, 2A, 2B using the classification of Paprosky et al.), 6% of titanium cups and 4% of tantalum cups failed. In hips with major bone deficiency (type 2C, 3), 24% of titanium cups and 12% of tantalum cups developed failure. In the major bone deficiency group, the tantalum cups had fewer numbers of lucent zones around the cup. Eighty-two percent of titanium cups that failed did so at 6 months postoperatively or later, whereas 80% of tantalum cups that failed did so in less than 6 months. Radiographically in the major group, tantalum cups yielded better fixation.

LEVEL OF EVIDENCE

Level III, retrospective comparative study. See the Guidelines for Authors for a complete description of levels of evidence.

The development of a scanning strategy for the manufacture of porous biomaterials by selective laser melting

Porous structures are used in orthopaedics to promote biological fixation between metal implant and host bone. In order to achieve rapid and high volumes of bone ingrowth the structures must be manufactured from a biocompatible material and possess high interconnected porosities, pore sizes between 100 and 700 microm and mechanical strengths that withstand the anticipated biomechanical loads. The challenge is to develop a manufacturing process that can cost effectively produce structures that meet these requirements. The research presented in this paper describes the development of a 'beam overlap' technique for manufacturing porous structures in commercially pure titanium using the Selective Laser Melting (SLM) rapid manufacturing technique. A candidate bone ingrowth structure (71% porosity, 440 microm mean pore diameter and 70 MPa compression strength) was produced and used to manufacture a final shape orthopaedic component. These results suggest that SLM beam overlap is a promising technique for manufacturing final shape functional bone ingrowth materials.

Metallic Scaffolds for Bone Regeneration

Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

[Surgical treatment of hip osteoarthritis: update in total hip arthroplasty]

Total hip replacement is one of the most successful procedures in orthopaedic surgery. There are two different technologies for implant fixation in total hip replacement: cemented and cementless, both can be combined, which is called Hybrid arthroplasty. Long term implant stability results in long term function. The most important factor that limits longevity of well-fixed implants is the wear of the articular surfaces. Wear of the polyethylene from the acetabulum generates particles that access the implant bone or the implant-cement-bone interface. This produces an inflammatory reaction, osteolysis and implant loosening. Polyethylene of higher resistance to wear and prosthetic articulations without polyethylene (hard on hard bearings), have been introduced to improve wear particle generation. Minimally invasive surgical techniques minimize surgical trauma to sort tissue around the hip joint, facilitating a better and more rapid recovery.