William L. Jaffe

Total Hip Arthroplasty with Hydroxyapatite-Coated Prostheses

The use of hydroxyapatite-coated prosthesis for total hip arthroplasty began in 1985 and has gained favor with reports of prompt biological fixation and clinical success. The quality and quantity of the coating is sensitive to application techniques, metal substrate, and manufacturing controls—all important in creating a clinically successful coating. Bioactive coatings other than hydroxyapatite have had mixed success and are generally not available for clinical use at this time. Clinical experience with hydroxyapatite-coated hip implants have focused on the femoral component, where results approach the standard of cemented components. Acetabular components have been less impressive when hydroxyapatite is the primary source of fixation without macrostructured substrate or augmentation with screws. Analysis of sequential follow-up radiographs in patients with hydroxyapatite-coated hips consistently reveals the changes associated with prompt and tenacious biologic fixation of the femoral component. These changes are apparent at 6 months and persist beyond 8 years. While the optimal design of the components, the surface structure of the metal substrate, and the ideal application method are still evolving, the use of hydroxyapatite-coated prostheses for hip arthroplasty has been proven safe and successful for clinical use where biologically fixed components are indicated.

Current Concepts Review - Total Hip Arthroplasty with Hydroxyapatite-Coated Prostheses*

### History of the Use of Hydroxyapatite in Orthopaedics The term apatite was first applied to minerals by Werner45, in 1788. It now denotes a family of crystals with the formula M10(RO4)6X2, where M is usually calcium, R is usually phosphorus, and X is hydroxide or a halogen such as fluorine. The relationship to bone mineral was first suggested by Proust and Klaproth45, also in 1788. Only after the development and use of x-ray diffraction did Dejong confirm, in 1926, that the inorganic phase of bone was an apatite49. Bone mineral was found to be quite complex and included various types of hydrated calcium phosphates, the most common being calcium hydroxyapatite (Ca10[PO4]6[OH]2). To the best of our knowledge, the earliest use of calcium-phosphate materials in humans was as a powder of varying crystalline composition to improve bone-healing. Albee and Morrison, in 1920, reported accelerated formation of callus3, but others later observed no major advantage with use of the hydroxyapatite powder80,147. As a bulk implant, calcium-phosphate materials were first used for dental applications133, as reported in 1971. More recent reports in the dental literature have attested to the success of bulk calcium-phosphate materials composed of pure hydroxyapatite and used as a bone-graft substitute12,35,57,68,135,137. Patients who had hydroxyapatite grafts were followed for a maximum of seven years57 and were evaluated clinically12,35,57,137, radiographically12,35,57, and with computer-assisted densitometry68. In two studies135,137, biopsy specimens were obtained for histological analysis. In addition to impressive evidence of osseointegration, no adverse effects of hydroxyapatite …

Hydroxyapatite-coated femoral components: 15-year minimum followup.

Hydroxyapatite-coated femoral components were introduced to enhance fixation, but concerns were raised about whether the coating would be maintained over time. We therefore determined the long-term clinical and radiographic results of a proximally hydroxyapatite-coated femoral component and compared the mechanical failure rate to other fixation methods at similar lengths of followup. The study group, culled from a large, multicenter prospective study population, consisted of 146 patients (166 hips) with followup of 15 to 18 years. Average age at time of the index procedure was 51 years, and the most common diagnoses were osteoarthritis (71%) and osteonecrosis (11%). Average Harris hip scores were 42.7 preoperatively and 91.5 at most recent followup. Radiographically, one stem showed stable fibrous fixation, and all other unrevised stems were bony stable. Of 13 stem revisions in the study population, only one stem has been revised for aseptic loosening. Forty-nine percent of hips have an osteolytic lesion in proximal areas of Gruen Zones 1, 7, 8, or 14 only. Both the femoral aseptic revision and mechanical failure rates are 0.6% at 15-year minimum followup. The data demonstrate excellent long-term survivorship of this hydroxyapatite-coated femoral component used in a relatively young patient group.Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Hydroxylapatite-coated hip implants: Multicenter three-year clinical and roentgenographic results

The application of a thin coating of hydroxylapatite to total hip implants has provided the opportunity to realize stable fixation of a press-fit prosthesis without a porous coating or an intervening fibrous tissue layer. This series consists of 436 total hip arthroplasties, of which 320 cases have a minimum two-year follow-up period and 142 cases have a minimum three-year follow-up period. The femoral prosthesis used was a roughened titanium alloy with a 50-μ surface treatment of hydroxylapatite applied to the proximal one third. The acetabular components implanted included porous-coated implants (132), hydroxylapatite-coated acetabular shells of varying geometries (285), and bipolar implants (16). Analysis of the clinical results demonstrates a mean Harris Hip Score of 93 at six-months postarthroplasty, 95 at one and two years, and 96 at three years. At the three-year follow-up evaluation, 4.2% of patients complained of mild to moderate pain in the operative limb, whereas only 2.2% at two years and 1.4% at three years complained of activity-related thigh pain. The femoral mechanical loosening rate representing stems revised for aseptic loosening (two) plus roentgenographically unstable stems (zero) is 0.46%. Three hydroxylapatite-coated acetabular cups (1%) have shown measurable migration at two years, but none have been revised for aseptic loosening. The roentgenographic evaluation provides evidence for excellent proximal femoral fixation with distal stress transfer. Radiolucencies typically occur around the uncoated distal tip of the femoral stem (74%), but rarely in the proximal hydroxylapatite-coated anterior (3%) and lateral (2%) zones. Femoral cancellous condensation characteristically is seen at the transition zone of hydroxylapatite coated-to-uncoated stems (86%), whereas up to 32% of cases show cortical hypertrophy at the medial distal stem. These roentgenographic changes are progressive from one through three years postoperatively.

Effects of preheating of hip prostheses on the stem-cement interface

Background: Debonding of the cement from metal implants has been implicated in the loosening of cemented total hip prostheses. Strengthening of the stem-cement interface has been suggested as a way to prevent loosening of the component. Previously, it was reported that preheating the stem to 44°C reduced the porosity of the cement at the stem-cement interface. The purpose of this study was to determine the effect of stem preheating on the characteristics of the stem-cement interface. Methods: The effects of stem preheating, at temperatures of 37°C, 44°C, and 50°C, on the stem-cement interface were studied in a test model and a preparation that closely simulated the clinical situation. Static interface strength was determined initially and after the stems had been kept in isotonic saline solution at 37°C for two weeks. Fatigue lifetimes were measured, and the nature and extent of porosity at the interface were quantified. Results: Stem preheating had significant effects on the stem-cement interface. Stems preheated to 37°C had greater interface shear strength than stems at room temperature both initially (53% greater strength) and after simulated aging (155% greater strength). Fatigue lifetimes were also improved, and there was a >99% decrease in interface porosity. The setting time of the cement decreased 12%, and the maximum temperature at the cement-bone interface increased 6°C. Similar effects were found after preheating to 44°C and 50°C. Conclusions: Stem preheating had significant effects on the stem-cement interface, with significant improvements in the shear strength and cement porosity of the interface. Also, polymerization temperatures at the cement-bone interface increased. The possible biological effects of these increased interface temperatures at the cement-bone interface require further study.

Host—bone response to porous-coated cobalt—chrome and hydroxyapatite-coated titanium femoral components in hip arthroplasty: Dual-energy X-ray Absorptiometry Analysis of Paired Bilateral Cases at 5 to 7 Years

Uncemented porous-coated cobalt-chrome femoral stems have produced satisfactory short-term clinical results, although slightly inferior to the results of cemented total hip arthroplasty. Proximal femoral bone resorption, osteolysis and fibrous ingrowth have been reported with porous-coated stems. Hydroxyapatite-coated stems and titanium stems have been introduced to avoid these findings through improved fixation. Dual-energy x-ray absorptiometry allows quantitative examination of bone density changes after uncemented total hip arthroplasty. This study examines the host-bone response to hydroxyapatite-coated titanium and porous-coated cobalt-chrome stems of identical geometry in three paired bilateral cases at 5 to 7 years. Distinctly different patterns of femoral bone mineral density changes were observed with the two stem designs. The authors conclude that dual-energy x-ray absorptiometry is a promising technique allowing noninvasive analysis of uncemented stem fixation, and that the data from this study suggest improved fixation and stress transfer with hydroxyapatite-coated titanium stems.

Surface Oxidized Zirconium Total Hip Arthroplasty Head Damage Due to Closed Reduction Effects on Polyethylene Wear

Recent case studies of surface oxidized zirconium THA heads removed after attempted, closed reduction have shown significant surface damage that has been suggested as potentially deleterious to polyethylene wear. We obtained 4 clinically retrieved specimens, produced well-characterized surface damage on additional heads, and tested them on a hip simulator. After 1 million cycles, the amount of polyethylene wear was related to the extent of surface damage, the most damaged clinical specimen showing more than 50 times more wear than a new head. Although all heads after failed attempted closed reduction(s) should be replaced, surface oxidized zirconium heads are of particular concern; those patients with a successful, simple closed reduction should be monitored for excessive wear.

Ceramic-on-ceramic total hip arthroplasty early dislocation rate.

Wear debris from metal-on-polyethylene articulation in conventional total hip arthroplasty can limit the implants longevity. Modern ceramic material with high wear resistance and low fracture risk has the potential to extend the lifetime of total hip arthroplasty, which makes the procedure potentially more suitable for young, active patients. Concerns with brittle ceramic material include fracture risk, the “squeak” phenomenon, and potentially a higher dislocation rate secondary to limited neck lengths and liner options. We therefore determined the early dislocation rate in modern ceramic-on-ceramic total hip arthroplasty. In 1635 total hip arthroplasties performed over the 9-year period (1996-2005), we observed three anterior and 15 posterior dislocations (1.1%). All were treated successfully, one with a revision and 17 with closed reduction under general anesthesia. Ceramic-on-ceramic total hip arthroplasty can be a good alternative bearing surface with a low dislocation rate.Level of Evidence: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Total Hip Arthroplasty in Sickle Cell Hemoglobinopathies

Abstract Advances in medical treatment have led to improved life expectancy in patients with sickle cell hemoglobinopathies. Improved life expectancy has, in turn, led to an increasing number of patients with osteonecrosis requiring total hip arthroplasty. Patient evaluation begins with understanding the extent of the disease process and the patients musculoskeletal manifestations (ie, pyogenic infection, marrow hyperplasia, osteonecrosis). A multidisciplinary approach to implementing effective preoperative treatment strategies increases the likelihood of a successful surgical outcome. Intraoperatively, consideration of bone stock, bone quality, and method of component fixation may help minimize the risk of eccentric reaming, perforation or fracture of either the acetabulum or the femur, and loosening. The optimal mode of acetabular and femoral fixation in these patients has not been conclusively determined, but recent results of cementless total hip arthroplasty have been encouraging. Although patients with sickle cell disease are at increased risk of medical and surgical complications, total hip arthroplasty in the appropriately selected patient can provide significant pain relief, restoration of function, and patient satisfaction.

The effect of surface roughness on the stress adaptation of trabecular architecture around a cylindrical implant.

The effect of implant-bone bonding and the effect of implant surface roughness on bone remodeling near the bone-implant interface were studied by using a surface remodeling theory and the boundary element method. The study has shown that implant attachment plays an important role in bone remodeling near the implant. It has been observed in animal experiments and in clinical situations that the remodeled trabecular bone architecture around a cylindrical implant could vary, on one hand, from a hub surrounding the implant with a set of external spokes to, on the other hand, a hubless situation in which a set of spokes attach directly to the implant. It is shown here that the difference in these structures may be attributed to differences in implant attachment. The results show that the bone with perfect bonding or roller boundary condition without a gap remodeled to a hubless spoke trabecular bone architecture. On the other hand, the roller boundary condition with a specified gap yielded a spoke trabecular architecture with a hub or ring surrounding the implant. These quantitative results mirror the experimental and clinical observations. It is concluded that the hub is a consequence of the gap and not a consequence of the lack of friction between the implant and the bone.