William N. Capello

The basis for a second-generation highly cross-linked UHMWPE

Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) decreases wear at the hip by more than 50% compared with conventional UHMWPE. However, melted highly cross-linked polyethylene may be susceptible to fatigue cracking, and annealed highly cross-linked polyethylene may be susceptible to in vivo oxidation. The second-generation highly cross-linked UHMWPE (X3 HXPE) uses a sequential irradiation and annealing process. It preserves mechanical strength properties and has the highest survivorship in functional fatigue testing. The free radical content is low, and its performance under accelerated aging is the same as virgin UHMWPE. Hip simulator studies with 32-mm acetabular components demonstrated 97% wear reduction compared with conventional UHMWPE, and 62% compared with a clinically successful first-generation annealed highly cross-linked polyethylene. The crystallinity, density, and tensile strength of the X3 HXPE material was unchanged by oxidative challenge. X3 HXPE material articulating on cobalt-chromium alloy yields a volumetric wear rate very similar to that of metal-on-metal articulations, but eliminates the concerns of metal ion release. Wear particles generated from the X3 HXPE were the same size as those produced from conventional UHMWPE. Preliminary results suggest X3 HXPE can be used for cups larger than 36 mm.

Morphologic features of the acetabulum and femur: Anteversion angle and implant positioning

Morphologic features of the hips, in particular those features germane to determination of acetabular and femoral anteversion angles and femoral head offset, were studied in 50 male and 50 female human skeletons with bilateral normal joints. Four distinct configurations were identified relative to the anterior acetabular ridge. The majority (121, 60.5%) were curved; 51 (25.5%) were angular; 19 (9.5%) were irregular; and nine (4.5%) were straight. The acetabular anteversion angle measured 19.9° ± 6.6° (range, 7°–42°) and was significantly larger in females (21.3° ± 7.1°) versus males (18.5° ± 5.8°). The notch acetabular angle, which can be identified easily intraoperatively, was defined as the angle created at the intersection of a line from the sciatic notch along the posterior acetabular ridge and a line from the posterior to the anterior acetabular wall. This angle is almost perpendicular (89.0° ± 3.5°) and, therefore, may provide an accurate estimate of acetabular anteversion during cup placement. Awareness of the anatomic differences between genders for acetabular anteversion angle, anterolateral bowing of the femur, and neck shaft angle may help reduce the relatively higher incidence of dislocation in females and may lead to different implant designs for male and female patients.

Alumina ceramic bearings for total hip arthroplasty: five-year results of a prospective randomized study.

Three hundred twenty-eight ceramic bearings were implanted by six surgeons in 316 patients as a part of a prospective randomized US Investigational Device Exemption study comparing alumina ceramic bearings with cobalt chrome-on-polyethylene bearings. There was no difference between the control metal-on-polyethylene and the alumina bearing couple patient cohorts regarding demographics or clinical scores through 7 years. Revision for any reason occurred in 2.7% of the patients with alumina bearings and 7.5% of the control patients with polyethylene bearings. Osteolysis was found in 1.4% of the patients with alumina bearings and in 14.0% of the control patients. At an average followup of 5.0 years (range, 1-86 months) no ceramic fractures or ceramic bearing failures have occurred. Results of this study suggest that alumina ceramics perform as well as the metal-on-polyethylene in clinical scores, but the patients with ceramic bearings had fewer revisions and less osteolysis. These results lead us to think that this new alumina ceramic bearing provides a safe option for younger and more active patients. Level of Evidence: Therapeutic study, Level I-1b (randomized controlled trial, no significant difference, but narrow confidence intervals). See the Guidelines for Authors for a complete description of levels of evidence.

Ceramic-on-ceramic total hip arthroplasty: update.

This prospective, randomized, multicenter study of alumina ceramic-on-alumina ceramic bearing couples includes 452 patients (475 hips). Their average age was 53 years with approximately two thirds men and 82% with osteoarthritis. At an average 8-year follow-up, clinical results were excellent and cortical erosions significantly less than in the conventional polyethylene-on-metal bearing group. Nine hips have undergone revision of one or both components for any reason. Of the 380 ceramic liners, 2 (0.5%) have fractured requiring reoperation, and 3 (0.8%) ceramic patients reported a transient squeaking sound, one of which had a head and liner change due to groin pain secondary to psoas tendinitis at 5 years. With no revisions for aseptic loosening and minimal cortical erosions, alumina-ceramic bearing couples are performing in a manner superior to the polyethylene-on-metal bearing in this young, active patient population.

Fixation of Acetabular Cups without Cement in Total Hip Arthroplasty. A Comparison of Three Different Implant Surfaces at a Minimum Duration of Follow-up of Five Years*

We evaluated 377 patients (428 hips) who had been managed, by a total of fourteen surgeons at twelve clinical sites in the United States and Europe, with a porous-coated press-fit acetabular cup, a hydroxyapatite-coated threaded screw-in cup, or one of two similar designs of hydroxyapatite-coated press-fit cups between April 1987 and November 1992. The same type of hydroxyapatite-coated femoral stem was inserted without cement in all patients. After a minimum duration of follow-up of five years (mean, 7.9 years; range, 5.3 to 9.1 years), one (1 per cent) of the 131 hydroxyapatite-coated threaded cups, two (2 per cent) of the 109 porous-coated press-fit cups, and twenty-one (11 per cent) of the 188 hydroxyapatite-coated press-fit cups had been revised because of aseptic loosening. A common radiographic sign of impending failure of the hydroxyapatite-coated press-fit cups was radiolucency at the interface between the implant and the subchondral bone beneath it. This radiolucency usually was seen initially more than two years after implantation. Radiographic evaluation of the 383 acetabular implants that were in situ at the time of the most recent follow-up showed that 123 (99 per cent) of the 124 hydroxyapatite-coated threaded cups, 101 (98 per cent) of the 103 porous-coated cups, and 139 (89 per cent) of the 156 hydroxyapatite-coated press-fit cups were stable with osseous ingrowth (as indicated by the absence of radiolucency at the interface and the absence of migration within the acetabulum). The probability of revision due to aseptic loosening was significantly greater for the hydroxyapatite-coated press-fit cups than it was for the hydroxyapatite-coated threaded cups or the porous-coated press-fit cups (p < 0.001 for both comparisons). Within the group of patients who had a hydroxyapatite-coated press-fit cup, the probability of revision due to aseptic loosening was significantly greater in association with a young age (p = 0.003), female gender (p = 0.02), the use of a femoral head with a diameter of thirty-two millimeters (p = 0.018), and the use of a thin polyethylene liner (p < 0.001). We found that the hydroxyapatite-coated threaded cups and the porous-coated press-fit cups continued to perform well more than five years after the operation. The hydroxyapatite-coated press-fit cups that were revised probably failed because the fixation interface beneath the cup could not sustain the tensile stresses that were imposed between the cup and the bone by the activity of the patient. Our data suggest that, in the specific biomechanical environment of the acetabulum, physical interlocking between the cup and the supporting bone beneath it may be a prerequisite for long-term stability.

Hydroxyapatite in total hip arthroplasty: Clinical results and critical issues

Surgeons who perform arthroplasties have posed some critical questions about hydroxyapatite. Does hydroxyapatite coating enhance bone ingrowth or ongrowth? Will hydroxyapatite lead to increased polyethylene wear or an increased incidence of osteolysis? Will the hydroxyapatite coating disappear, and if so, what will be left to maintain implant fixation? A multicenter study of 316 hips (282 patients) with a proximally hydroxyapatite coated stem and either a hydroxyapatite or porous coated cup were followed up 8.1 years (range, 5.6-9.9 years). The average patient age was 50 years (range, 16-81 years), and 61% of the patients were male. One (0.3%) stem, three (2.7%) porous coated cups, and 25 (11.9%) hydroxyapatite coated cups were revised for aseptic loosening. Disappointing results on the acetabular side indicate that substrate design is critical. There were no cases of intramedullary femoral osteolysis, and the incidence of acetabular and proximal femoral osteolysis and polyethylene wear was no greater than that seen with other cementless or cemented components. Based on these clinical results and a critical review of the literature, it is concluded that hydroxyapatite coated hip components do enhance ingrowth or ongrowth with no increased incidence of osteolysis for as many as 10 years. Concern about the disappearance of the hydroxyapatite coating with time seems moot in light of the above clinical findings.

Hydroxyapatite femoral stems for total hip arthroplasty 10- to 13-year followup

Three hundred eighty hydroxyapatite-coated titanium alloy stems were implanted in a young and active patient population from 1987 through 1990. Within the population, 274 patients (314 hips) had a minimum 10-year and maximum 13-year followup. The average age of the population was 51 years. Thirty-seven percent of the population was 50 years or younger when operated on (average age, 39 years). Osteoarthritis was seen in 63.7% and avascular necrosis in 16.6% of patients. Fifty-four percent of patients were men. Clinically, these patients had early pain relief and rapid restoration of function. The Harris hip score averaged 92 points, and only 1.6% of patients had mild or moderate activity-related thigh pain. Radiographically, progressive remodeling occurred around the implants, 100% were bone stable, and no patient had endosteal distal osteolysis. Two patients had revision surgery for aseptic loosening: one at 2 years postoperative because of a nonunion of a concomitant subtrochanteric osteotomy and one at 9.5 years postoperative because of polyethylene wear and progressive osteolysis. The mechanical failure rate was 0.5%. The results show excellent lasting fixation of this tapered titanium alloy stem coated proximally with a thin, dense layer of hydroxyapatite. The stem has performed well in a young, active, high-risk population and in the hands of various surgeons.

Hydroxyapatite-Coated Total Hip Femoral Components in Patients Less Than Fifty Years Old. Clinical and Radiographic Results after Five to Eight Years of Follow-up*

One hundred and thirty-three patients (152 hips) who were an average of thirty-nine years old (range, sixteen to forty-nine years old) received a proximally hydroxyapatite-coated femoral prosthesis as part of a total hip arthroplasty and were followed for a minimum of five years (average, 6.4 years; range, five to 8.3 years) or until revision. The average Harris hip score was 47 points (range, 22 to 77 points) preoperatively and 93 points (range, 49 to 100 points) at the time of the latest clinical evaluation. Two patients who had a well fixed femoral implant had activity-limiting pain in the thigh at the time of the most recent examination. Radiographic changes consistent with bone-remodeling (cortical hypertrophy and bone condensation) typically were seen around the mid-part of the shaft of the prosthesis. Forty-eight (32 per cent) of the 148 hips that were included in the radiographic analysis demonstrated a small amount of erosive scalloping in either zone 1 or zone 7 of Gruen et al., and intramedullary osteolysis was suspected in only one hip. All stems were radiographically osseointegrated according to a modification of the criteria described by Engh et al. Four stems were revised, but none of the revisions were performed because of mechanical failure (two stems were revised in conjunction with a revision of the cup because of pain; one, because of an infection; and one, after a traumatic femoral fracture that occurred six years postoperatively). Thus, the rates of aseptic and mechanical failure were both 0 per cent. The combined rate of failure, which included the two stems that were revised because of pain and the two stems that were associated with pain that limited activity, was 2.6 per cent (four of 152 stems). The over-all clinical results associated with hydroxyapatite-coated femoral components were excellent in this group of young patients after intermediate-term follow-up. A review of serial radiographs showed mechanically stable implants with osseous ingrowth, evidence of stress transmission at the middle part of the stem, and minimum endosteal osteolysis.

Remodeling of bone around hydroxyapatite-coated femoral stems.

Two hundred and twenty-four total hip arthroplasties were performed in 201 patients with use of a femoral component with hydroxyapatite coating of the proximal portion of the stem. The mean duration of follow-up was seventy-one months (range, fifty-eight to eighty-seven months). Of the 224 arthroplasties, 208 (93 per cent; 190 patients) yielded a good or excellent clinical result. Four patients (2 per cent) reported mild-to-moderate activity-related pain in the thigh, and two (1 per cent) had aseptic loosening. The radiographic findings of progressive new-bone formation (cancellous condensation and cortical hypertrophy) throughout the zones adjacent to the middle and distal portions of the stem were evidence of early, extensive proximal fixation of the implant, with distal stress transfer through the implant, which is stiffer than the surrounding bone. Remodeling of the femur began early, was predictable, and progressed throughout the follow-up period. Cortical hypertrophy about the middle and distal portions of the stem occurred predominantly in the mediolateral plane (in 105 hips [47 per cent], compared with thirteen hips [6 per cent] in the anteroposterior plane), and it was more common in patients who had had poorer bone quality preoperatively. Intramedullary osteolysis was present in one femur (0.4 per cent) at five years; the osteolytic area was less than five millimeters in its greatest dimension and had not progressed at the time of the six-year follow-up evaluation. This low rate of osteolysis suggests that a circumferential coating of hydroxyapatite may effectively minimize migration of wear debris along the femoral stem. The progressive remodeling of the femur about the middle and distal portions of the stem, as evidenced by cancellous condensation and cortical hypertrophy, has not, to our knowledge, been described previously to this magnitude in association with proximally coated (porous or hydroxyapatite-coated) femoral implants.

Ten-year results with hydroxyapatite-coated total hip femoral components in patients less than fifty years old. A concise follow-up of a previous report.

Abstract: We report the results of total hip arthroplasty with use of a proximally hydroxyapatite-coated femoral component after a minimum follow-up of ten years in a group of patients who were less than fifty years old at the time of the primary procedure. In the five years since the original publication of our study, two additional stems have undergone revision. Thus, a total of six stems have been revised. A small amount of erosive scalloping of the proximal part of the femur was seen in nearly one-half of the hips; however, all unrevised stems were radiographically stable and no hip had intramedullary osteolysis. The revision rate because of aseptic loosening of the stem was 0.9%, which compares favorably with that for other stems and other fixation methods in young patients at this point in time. This stem is currently being paired with a highly cross-linked polyethylene liner because of cup failures and the need for reoperation secondary to excessive polyethylene wear and proximal femoral osteolysis. Level of Evidence: Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.