Bone Ingrowths to Press-Fit and Loose-Fit Implants: Comparisons between Titanium and Hydroxyapatite

Short to Midterm Follow-Up of Periprosthetic Bone Mineral Density after Total Hip Arthroplasty with the Ribbed Anatomic Stem

Background

Femoral bone remodeling around hip prosthesis after total hip arthroplasty (THA) is definite but unpredictable in time and place. This study aimed to investigate the implant-specific remodeling and periprosthetic bone mineral density (BMD) changes after implantation of the Ribbed anatomic cementless femoral stem.

Methods

After power analysis, 41 patients who had undergone primary unilateral THA with the Ribbed anatomic cementless stem were included. BMD of the seven Gruen zones was measured by dual-energy X-ray absorptiometry, and the contact, fitness, and fixation of the femoral stem and proximal femur were analyzed by X-ray. Additional clinical outcome parameters were also recorded.

Results

Compared with the contralateral unoperated side, significant reductions of BMD were detected in the distal zone (Gruen zone 4: 1.665±0.198 versus 1.568±0.242 g/cm², P=0.001) and middle distal zone (Gruen zone 5: 1.660±0.209 versus 1.608±0.215 g/cm², P=0.026) on the prosthetic side, but no significant differences in BMD were detected in other zones (Gruen zones 1, 2, 3, 6, and 7). Subgroups analyses indicated no significant correlation between periprosthetic BMD changes and clinical factors including primary disease and body mass index. Visible areas of bone ingrowth indicated solid fixation of the femoral stem and there was no case of loosening. Clinical and functional outcome scores were excellent with mean HHS of 93.13 points and mean WOMAC score of 5.20 points, and three patients described intermittent mild thigh pain at the final follow-up.

Conclusions

For the Ribbed femoral stem, the periprosthetic BMD was well maintained in the proximal femur, while periprosthetic BMD was significantly reduced in the distal and middle distal zones of the femur. Further clinical investigations are required to examine the efficacy of the Ribbed stem, particularly with regard to long-term survival. This trial is registered with ChiCTR1800017750.

Osteolysis in Total Ankle Replacement: How Does It Work?

Aseptic loosening of implants remains the most common reason for revision surgery for hip, knee, or ankle prostheses. Although a great scientific effort has been made to explain the underlying mechanisms it remains poorly understood, complex, and multifactorial. Many factors, including age, body weight, activity lesions, implant design, fixation methods, material proprieties, immunologic responses, and biomechanical adaptations to total ankle replacement all contribute to the development of periprosthetic osteolysis.

The Absence of Hydroxyapatite Coating on Cementless Acetabular Components Does Not Affect Long-Term Survivorship in Total Hip Arthroplasty

BACKGROUND

Hydroxyapatite (HA) has been applied to joint prostheses as a bioactive coating to prolong their durability. However, HA benefits for cup survival in total hip arthroplasty (THA) remain controversial. In this study, we compared the survival of cups with and without HA coating during a minimum follow-up of 18 years.

METHODS

In total, 183 THA cases in 163 patients were analyzed, including 73 cups with HA coating (HA(+) group) and 110 without HA coating (HA(-) group); otherwise, the cups had identical titanium-sprayed rough surfaces and were fixed with screws. In both groups, the same conventional polyethylene liners were applied. Zirconia and alumina ceramic heads were used in the HA(+) and HA(-) groups, respectively. We retrospectively analyzed cup survival based on cup revision for any reason or aseptic loosening as end points.

RESULTS

In total, 7 and 8 revisions were performed in the HA(-) and HA(+) groups with survival rates of 86.3% and 90.1%, respectively. Among them, 3 cups in the HA(-) group and 1 cup in the HA(+) group were revised for aseptic loosening in 20 years (survival rates 94.1% and 98.7%, respectively). No significant difference was detected in cup survival rates between the groups based on both end points. There were no stem revisions during the observation period.

CONCLUSION

The results suggested that HA coating did not have either beneficial or adverse effects on the long-term cup survival in primary cementless THA.

Fabrication, Properties and Applications of Dense Hydroxyapatite: A Review

In the last five decades, there have been vast advances in the field of biomaterials, including ceramics, glasses, glass-ceramics and metal alloys. Dense and porous ceramics have been widely used for various biomedical applications. Current applications of bioceramics include bone grafts, spinal fusion, bone repairs, bone fillers, maxillofacial reconstruction, etc. Amongst the various calcium phosphate compositions, hydroxyapatite, which has a composition similar to human bone, has attracted wide interest. Much emphasis is given to tissue engineering, both in porous and dense ceramic forms. The current review focusses on the various applications of dense hydroxyapatite and other dense biomaterials on the aspects of transparency and the mechanical and electrical behavior. Prospective future applications, established along the aforesaid applications of hydroxyapatite, appear to be promising regarding bone bonding, advanced medical treatment methods, improvement of the mechanical strength of artificial bone grafts and better in vitro/in vivo methodologies to afford more particular outcomes.

Calcium Orthophosphate-Based Bioceramics

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells.

Calcium orthophosphates as bioceramics: state of the art

In the late 1960s, much interest was raised in regard to biomedical applications of various ceramic materials. A little bit later, such materials were named bioceramics. This review is limited to bioceramics prepared from calcium orthophosphates only, which belong to the categories of bioactive and bioresorbable compounds. There have been a number of important advances in this field during the past 30-40 years. Namely, by structural and compositional control, it became possible to choose whether calcium orthophosphate bioceramics were biologically stable once incorporated within the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of calcium orthophosphate bioceramics-which is able to promote regeneration of bones-was developed. Presently, calcium orthophosphate bioceramics are available in the form of particulates, blocks, cements, coatings, customized designs for specific applications and as injectable composites in a polymer carrier. Current biomedical applications include artificial replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery. Exploratory studies demonstrate potential applications of calcium orthophosphate bioceramics as scaffolds, drug delivery systems, as well as carriers of growth factors, bioactive peptides and/or various types of cells for tissue engineering purposes.

Two Human Hydroxyapatite-Coated Dental Implants Retrieved After a 14-Year Loading Period: A Histologic and Histomorphometric Case Report

BACKGROUND

Controversy over the long-term clinical effectiveness of hydroxyapatite (HA)-coated dental implants still persists, despite numerous clinical studies documenting high survival rates. Concerns about the degradation of the coating over the years have been raised; it has been speculated that resorption of the HA could produce a space between the implant and the bone with a resultant mechanical instability.

METHODS

Two HA-coated implants were retrieved due to a fracture of the abutment screws after a loading period of 14 years and were treated to obtain thin ground sections for histologic evaluation.

RESULTS

At low-power magnification, it was possible to observe that the HA coating was in contact with mature bone. No gaps or connective fibrous tissue was found at the implant-bone interface. No epithelial downgrowth was present. No acute or chronic inflammatory cell infiltrate was present at the implant-bone interface. No foreign body reaction was present in the peri-implant tissues. Some osteocytes were in direct contact with the coating. For implant 1, the percentage of bone-titanium contact was 25% +/- 2.1%, and the percentage of bone-HA contact was 35% +/- 1.4%. The total bone-implant contact was approximately 60%. The HA coating appeared to be resorbed in 46% +/- 3.2% of the implant perimeter, especially in the coronal portions of the implant. For implant 2, the mean percentage of bone-HA contact was 13% +/- 1.8%, and the mean percentage of bone-titanium contact was 15% +/- 2.3%. The total bone-implant contact was approximately 28%. The HA coating appeared to be resorbed for a mean of 68% +/- 4.1% of the implant perimeter, especially in the coronal portion of the implant.

CONCLUSIONS

No acute or chronic inflammatory cell infiltrate was present in the peri-implant tissues. No signs of coating infection, fatigue, or failure were observed in two specimens. The HA coating may not be susceptible to degradation or dissolution under long-term function.