Eighteen-Year Results of Cementless THA with Alumina-on-HXLPE Bearings in Patients <30 Years Old

Abstract

Abstract:

Despite overall good survivorship and clinical outcomes in the short term after total hip arthroplasty (THA) with use of alumina ceramic-on-highly cross-linked polyethylene (HXLPE) in patients younger than 30 years of age, there is a paucity of long-term data to evaluate the fixation of the components and the prevalence of osteolysis. We reviewed the records of 45 patients (54 hips) who had been included in a previous report to evaluate the long-term functional outcomes as well as radiographic and computed tomographic scan findings (particularly with regard to component fixation and osteolysis) after a mean duration of follow-up of 17.8 years. One femoral stem was revised because of aseptic loosening, and 2 acetabular components were revised because of recurrent dislocation. The survival rate at 17.8 years was 98% for the femoral component and 96% for the acetabular component.

Level of Evidence:

Therapeutic Level IV. See Instructions for Authors for a complete description of level of evidence.

Background

Although several short-term studies^1-3 have investigated the functional outcomes as well the radiographic results of total hip arthroplasty (THA) with use of alumina ceramic-on-highly cross-linked polyethylene (HXLPE) in younger patients, there is a paucity of long-term data to evaluate the fixation of the components and the prevalence of osteolysis associated with this prosthesis in patients younger than 30 years of age.

The aim of the present long-term report on patients who were included in a previous report¹ was to evaluate the long-term functional outcomes as well as the radiographic and computed tomographic (CT) scan results associated with the cementless ultra-short femoral stem (Immediate Postoperative Stability; DePuy) with a 28-mm alumina forte ceramic modular femoral head (BIOLOX forte; CeramTec) after a mean duration of follow-up of 17.8 years. A cementless Duraloc acetabular component (DePuy) with an HXLPE liner (Marathon; DePuy) (inner diameter, 28 mm) was used in all hips.

Methods

The records of 50 patients (60 hips) with a minimum duration of follow up of 10 years were entered into an ongoing computerized registry. All hips were reviewed by an orthopaedic surgeon who had not been involved with the original surgical procedure, and the data were entered into a computerized record. Routine follow-up evaluations were scheduled at postoperative intervals of 3 months, 1 year, and then every 2 or 3 years thereafter. At these intervals, the patients were evaluated clinically and radiographically. CT scans were obtained at the time of the latest follow-up. As described in the previous report¹, the Harris hip score⁴, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)⁵, and the University of California Los Angeles (UCLA) activity scores⁶ were recorded.

Radiographs and CT scans were evaluated by 1 independent observer for component stability^1,7,8, radiolucent lines, bone remodeling⁸, osteolysis¹, and loosening¹. To assess the location and extent of radiolucent lines and osteolysis, the zones described by DeLee and Charnley⁹ and those described by Gruen et al.¹⁰ were used. Osteolysis was defined as a radiolucent lesion with a minimum size of 0.5 cm² along with loss of the trabecular pattern that had not been observed on the immediate postoperative anteroposterior radiograph of the pelvis¹¹. The chi-square test with the Yates correction, 2-tailed Student t tests, and analysis of variance were used for statistical analysis. The level of significance was set at p < 0.05. Survival analysis was performed with use of Kaplan-Meier curves¹².

Results

Originally, THA was performed for 50 patients (60 hips). At the time of the present review, at a mean of 17.8 years (range, 17 to 19 years) postoperatively, 5 patients (6 hips) had been lost to follow-up. Forty-five patients (54 hips) with a mean age of 46.1 years (range, 39 to 47 years) were still living. At each follow-up, about 80% of the patients were captured; the remaining 20% were rescheduled to have a follow-up evaluation at the next visit. The patients included 31 men and 14 women with a mean body mass index of 27.5 kg/m² (range, 23 to 35 kg/m²). Demographic and clinical data on those who were lost to follow-up and those who stayed under observation are described in Table I.

TABLE I.

Demographic and Clinical Data^*

Parameters	Patients from Original Series Who Were Lost to Follow-up	Current Series
No. of patients (no. of hips)	5 (6)	45 (54)
Male:female ratio (no. of patients)	3:2	31:14
Interval between THA and loss to follow-up† (yr)	12.6 (11 to 14)	NA
Age at time of latest follow-up† (yr)	40.9 (32 to 43)	46.1 (39 to 47)
Body mass index† (kg/m2)	26.5 (22 to 36)	27.5 (23 to 35)
Harris hip score† (points)	95 (80 to 100)	94 (80 to 100)
WOMAC score† (points)	14 (10 to 17)	13 (9 to 15)
UCLA activity score† (points)	6.7 (5 to 8)	6.5 (4 to 8)
Polyethylene liner wear rate‡ (mm/yr)	0.033 ± 0.005 (0.02 to 0.05)	0.038 ± 0.006 (0.02 to 0.05)
Osteolysis (no. of hips)	0	0
Revision (no. of hips)
Acetabular component	0	2
Femoral component	0	1
Survivorship‡§
Acetabular component	100% (95% to 100%)	96% (93% to 100%)
Femoral component	100% (95% to 100%)	98% (95% to 100%)

^*WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index, UCLA = University of California Los Angeles, and NA = not applicable.

^†The values are given as the mean, with the range in parentheses.

^‡The values are given as the mean and the standard deviation, with the 95% CI in parentheses.

^§Survivorship was determined at a mean of 12.6 years for the patients who were lost to follow-up and at a mean of 17.8 years for the patients in the current study.

The Harris hip scores at the earlier follow-up interval (mean, 10.8 years) and the later interval (mean, 17.8 years) were 95 points (range, 85 to 100 points; 95% confidence interval [CI], 93 to 98 points) and 94 points (range, 80 to 100 points; 95% CI, 92 to 98 points), respectively. The WOMAC scores at the earlier and later intervals were 11 points (range, 8 to 13 points; 95% CI, 10 to 13 points) and 13 points (range, 9 to 15 points; 95% CI, 11 to 14 points), respectively. The UCLA activity scores at the earlier and later intervals were 6.7 points (range, 5 to 8 points; 95% CI, 5 to 8 points) and 6.5 points (range, 4 to 8 points; 95% CI, 5 to 8 points), respectively. The chance-corrected kappa coefficient that was calculated to determine the intraobserver agreement of the Harris hip, WOMAC, and UCLA activity scores was between 0.81 and 0.87.

Polyethylene liner wear was measured with use of AutoCAD software (release 13; Autodesk)^11,13 by 1 observer. The observer made 3 measurements on each radiograph. A flat-bed imaging scanner (ScanMaker 9600 XL; Microtek) was used to digitize the anteroposterior radiograph of the pelvis using 2-dimensional gray-scale arrays of 12-bit (256 gray-level) integers. The scanning resolution was 600 pixels per square inch. Penetration of the femoral head into the polyethylene liner was defined as polyethylene wear. The amount of penetration on radiographs made 6 weeks postoperatively was considered to be the “zero” position. The normal accuracy of measurement of this system was 0.002 mm. The chance-corrected kappa coefficient that was calculated to determine intraobserver agreement of wear measurements was 0.87. This evaluation technique is not able to differentiate between component penetration and actual material loss. This measurement compared favorably with those in previous reports^11,13. The mean HXLPE linear wear per year (and standard deviation) was 0.031 ± 0.004 mm (95% CI, 0.02 to 0.04 mm) at a mean of 10.8 years and 0.038 ± 0.006 mm (95% CI, 0.02 to 0.05 mm) at a mean of 17.8 years of follow-up. At a mean of 17.8 years, 6 hips were outliers for the so-called osteolysis threshold of 0.10 mm/yr^14-17, with the remaining 48 liners having a penetration rate below this level. No hip had evidence of acetabular or femoral osteolysis on radiographs or CT scans. In the 6 hips that were outliers for the osteolysis threshold, there was no evidence of acetabular or femoral osteolysis. With the numbers available, univariate regression analysis showed that age, sex, weight, patient activity, cup inclination, and cup anteversion had no influence on polyethylene liner penetration (Figs. 1-A and 1-B).

Figs. 1-A and 1-B Anteroposterior radiograph and CT scans of the right hip of a man who underwent THA for the treatment of osteonecrosis of the femoral head at the age of 27 years.

Fig. 1-A.

Anteroposterior radiograph of the right hip, made 18 years after surgery, demonstrating that the acetabular and femoral components are fixed in a satisfactory position. There is no evidence of a radiolucent line, polyethylene wear, or osteolysis about the acetabular or the femoral component.

Fig.1-B.

CT scans of the right hip, made 18 years after surgery, showing no evidence of osteolysis about the acetabular or the femoral component.

One femoral component was revised because of aseptic loosening, but no acetabular component was loose at 17.8 years postoperatively. Two acetabular components were revised because of recurrent dislocation at 3 and 6 months postoperatively. Kaplan-Meier survival analysis at 17.8 years, with aseptic loosening or revision as the end point for failure, showed that the survival rate of the femoral component was 98% (95% CI, 95% to 100%) and that of the acetabular component was 96% (95% CI, 93% to 100%) (Fig. 2).

Fig. 2.

Kaplan-Meier curves showing the survival rates for the acetabular and femoral components at 17.8 years, with revision or aseptic loosening as the end point.

Conclusions

The present study confirmed that cementless THA with use of alumina ceramic-on-HXLPE in patients younger than 30 years of age is a successful procedure that leads to improved Harris hip, WOMAC, and UCLA activity scores over the long term (mean, 17.8 years). These results are similar to those of previous studies^17-23.

One important issue related to cementless THA in younger patients is the long-term fixation of the components. Adelani et al.¹⁸ concluded that the revision rate among young patients undergoing THA decreased substantially with the advent of contemporary surgical techniques and implants. Wangen et al.¹⁹ demonstrated excellent 10 to 16-year results for a fully hydroxyapatite (HA)-coated femoral stem in patients younger than 30 years of age; however, they reported a high rate of aseptic loosening of the HA-coated press-fit acetabular component. D’Ambrosi et al.²¹ reported that no ceramic-on-ceramic or ceramic-on-HXLPE bearings were revised at a mean of 12.5 years (range, 10 to 17 years) following THA without cement in patients younger than 20 of age. Finkbone et al.²² reported promising short to intermediate-term results, with a 96% survival rate, following THA without cement with use of a ceramic-on-ceramic bearing. Clohisy et al.²³ demonstrated that contemporary THA in patients ≤25 years of age was associated with solid fixation of uncemented implants at early follow-up. They suggested that cementless fixation combined with improved bearing materials provided good long-term survival even in the young patient population. In the current study, we obtained good fixation in the majority of patients, which we attributed to improved implant design (metaphyseal fitting, pronounced lateral flare, anteroposterior buildup, and a short and narrow polished distal end of the stem), the surgical technique for implantation of the cementless stem, the strong trabecular bone in young patients, the utilization of an alumina forte ceramic femoral head and an HXLPE acetabular liner, and a cohort of small and light patients.

Bitsch et al.² reported that, after a mean duration of follow-up of 5.8 years (range, 5.0 to 7.7 years), the mean femoral head penetration was 0.031 mm/yr (range, 0.04 to 0.196 mm/yr) in hips with a Marathon HXLPE liner (DePuy) and 0.104 mm/yr (range, 0.04 to 0.916 mm/yr) in hips with an Enduron polyethylene liner (DePuy). Osteolysis was not observed in any of the hips with a Marathon HXLPE liner. Engh et al.²⁴ reported a 95% reduction in the mean wear rate for Marathon HXLPE liners in comparison with that for Enduron liners (0.01 ± 0.12 compared with 0.19 ± 0.12 mm/yr). Kim et al.³ observed that the mean polyethylene penetration rate for Marathon HXLPE liners was 0.05 ± 0.02 mm/yr and that no hip had aseptic loosening or osteolysis in young patients with femoral head osteonecrosis. The mean HXLPE wear per year (and standard deviation) was 0.031 ± 0.04 mm at a mean of 10.8 years in our previous report¹, compared with 0.038 ± 0.06 mm at a mean of 17.8 years of follow-up in the current study. For all but 6 hips in our study, the penetration rate of Marathon HXLPE was below the osteolysis threshold (0.1 mm/yr)³. No detectable osteolysis was observed on radiographs or CT scans in any hip in our study; this finding was consistent with those of other studies^3,24. In these 6 hips, the excessive polyethylene wear seems to have been due to the bedding-in period during the first 1 to 2 years after THA rather than consistent elevated wear.

Contrary to initial concern about fatigue crack propagation resistance of HXLPE raised by Bradford et al.²⁵, no hip had an HXLPE liner fracture due to the reduction in fatigue, tensile, and toughness properties of HXLPE. We speculate that the use of an adequate thickness of HXLPE liner (>6.0 mm) and optimal cup orientation of the acetabular component led to an absence of polyethylene liner fracture. Fracture of the alumina femoral head has been reported in the literature^26,27. In the current series, possible contributing factors to the absence of ceramic head fracture include the tight fit of the ceramic head to the taper of the stem, the fact that a short neck was not used, and the inclusion of patients who were light and small. In our previous report on ultra-short uncemented femoral stem using an alumina delta ceramics, no alumina delta ceramic head or alumina delta ceramic liner fracture was observed²⁸.

The strengths of the present study are as follows. First, although the first generation of HXLPE was claimed to have reductions in fatigue, tensile, and toughness properties²⁵, the present long-term study of active and younger patients demonstrated no evidence of fracture of the HXLPE due to reductions in these properties. Second, although there has been some concern that smaller polyethylene wear particles are produced with HXLPE than with conventional polyethylene, leading to a higher functional biological activity²⁹, the present long-term study of active and younger patients did not show any evidence of osteolysis due to the biological activity of HXLPE debris. Our study has also had some limitations. First, although the clinical and radiographic data were analyzed prospectively, there was no randomization. Second, the performance of all operations by a single surgeon may introduce bias. Third, our study population had low body mass index, and this factor might limit general applicability to other patients or practice settings. On the other hand, the patients in the current study engaged in a high level of activities such as farming, squatting, and lifting. Fourth, the hip scoring system and the measurement of HXLPE wear are prone to intraobserver variability. However, the chance-corrected kappa coefficient that was calculated to determine intraobserver agreement of hip scoring and wear measurement was between 0.81 and 0.87. Fifth, 9 patients (20%) had bilateral THA. Finally, the study design was a prospective case series with 90% follow-up at nearly 18 years; the study design could be improved by comparing the study group with a control population with a conventional polyethylene bearing.

In conclusion, contemporary cementless acetabular and femoral components with alumina forte ceramic-on-HXLPE bearings have functioned well when used in patients younger than 30 years of age, with no osteolysis or fracture of the ceramic head or Marathon HXLPE liner after a mean duration of follow-up of 17.8 years. We found no factors limiting the longevity of the prosthesis at the time of our follow-up. We recommend continued use of this prosthesis.