28-mm Femoral Head Research Articles

Effect of femoral head size on risk of revision for dislocation after total hip arthroplasty

Background and purpose Previous population-based registry studies have shown that larger femoral head size is associated with reduced risk of revision for dislocation. However, the previous data have not included large numbers of hip resurfacing arthroplasties or large metal-on-metal (> 36-mm) femoral head arthroplasties. We evaluated the association between femoral component head size and the risk of revision for dislocation after THA by using Finnish Arthroplasty Register data.Patients and methods 42,379 patients who were operated during 1996–2010 fulfilled our criteria. 18 different cup/stem combinations were included. The head-size groups studied (numbers of cases) were 28 mm (23,800), 32 mm (4,815), 36 mm (3,320), and > 36 mm (10,444). Other risk factors studied were sex, age group (18–49 years, 50–59 years, 60–69 years, 70–79 years, and > 80 years), and time period of operation (1996–2000, 2001–2005, 2006–2010).Results The adjusted risk ratio in the Cox model for a revision operation due to dislocation was 0.40 (95% CI: 0.26–0.62) for 32-mm head size, 0.41 (0.24–0.70) for 36-mm head size, and 0.09 (0.05–0.17) for > 36-mm head size compared to implants with a head size of 28 mm.Interpretation Larger femoral heads clearly reduce the risk of dislocation. The difference in using heads of > 36 mm as opposed to 28-mm heads for the overall revision rate at 10 years follow-up is about 2%. Thus, although attractive from a mechanical point of view, based on recent less favorable clinical outcome data on these large heads, consisting mainly of metal-on-metal prostheses, one should be cautious using these implants.

Sex and Risk of Hip Implant Failure

The role of sex in relationship to implant failure after total hip arthroplasty (THA) is important for patient management and device innovation. To evaluate the association of sex with short-term risk of THA revision after adjusting for patient, implant, surgery, surgeon, and hospital confounders. A prospective cohort of patients enrolled in a total joint replacement registry from April 1, 2001, through December 31, 2010. Patients undergoing primary, elective, unilateral THA. Failure of THA, defined as revision procedure for (1) any reason, (2) septic reason, or (3) aseptic reason after the index procedure. A total of 35,140 THAs with 3.0 years of median follow-up were identified. Women constituted 57.5% of the study sample, and the mean (SD) patient age was 65.7 (11.6) years. A higher proportion of women received 28-mm femoral heads (28.2% vs 13.1%) and had metal on highly cross-linked polyethylene-bearing surfaces (60.6% vs 53.7%) than men. Men had a higher proportion of 36-mm or larger heads (55.4% vs 32.8%) and metal on metal-bearing surfaces (19.4% vs 9.6%). At 5-year follow-up, implant survival was 97.4% (95% CI, 97.2%-97.6%). Device survival for men (97.7%; 95% CI, 97.4%-98.0%) vs women (97.1%; 95% CI, 96.8%-97.4%) was significantly different (P = .01). After adjustments, the hazards ratios for women were 1.29 (95% CI, 1.11-1.51) for all-cause revision, 1.32 (95% CI, 1.10-1.58) for aseptic revision, and 1.17 (95% CI, 0.81-1.68) for septic revision. After considering patient-, surgery-, surgeon-, volume-, and implant-specific risk factors, women had a 29% higher risk of implant failure than men after THA in this community-based sample.

The 2012 John Charnley Award: Clinical Multicenter Studies of the Wear Performance of Highly Crosslinked Remelted Polyethylene in THA

Highly crosslinked polyethylene (HXLPE) in THA was developed to reduce particle-induced periprosthetic osteolysis. A series of clinical studies were initiated to determine the clinical efficacy as judged by patient-reported scores, radiographic osteolysis, and wear analysis of one form of HXLPE. The purposes of this series of studies were to (1) determine the wear rates of one form of HXLPE; (2) report long-term (7-10years) patient-reported outcome measures; (3) assess the effect of femoral head size on wear; and (4) determine the incidence of periprosthetic osteolysis. A single-center and two multicenter studies were conducted on 768 primary patients (head size 26-36mm) undergoing THA at eight medical centers. Patient-reported outcome scores, radiographic grading for osteolysis, and radiographic wear evaluation were performed. Serial plain radiographs showed no periprosthetic osteolysis in the three studies. The average femoral head penetration rates did not correlate with time in vivo for patients with standard femoral head sizes. Although there was an indication of higher wear in patients with 36-mm diameter femoral heads, it was below the threshold for producing osteolysis. The introduction of this HXLPE substantially improved the prognosis of patients after THA up to 13years as judged by clinical scores, incidence of osteolysis, and polyethylene wear measurements. Level III, therapeutic study. See the Guideline for Authors for a complete description of levels of evidence.

Large Femoral Heads Decrease the Incidence of Dislocation After Total Hip Arthroplasty

The use of larger femoral heads has been proposed to reduce the risk of dislocation after total hip arthroplasty, but there is a lack of evidence to support this proposal. The aim of this multicenter randomized controlled trial was to determine whether the incidence of dislocation one year after total hip arthroplasty is significantly lower in association with the use of a 36-mm femoral head articulation as compared with a 28-mm articulation. Six hundred and forty-four middle-aged and elderly patients undergoing primary or revision arthroplasty were randomized intraoperatively to receive either a 36 or 28-mm metal femoral head on highly cross-linked polyethylene. Patients who were at high risk of dislocation (including those with dementia and neuromuscular disease) and those undergoing revision for the treatment of recurrent hip dislocation or infection were excluded. Patients were stratified according to other potential risk factors for dislocation, including diagnosis and age. Diagnosis of hip dislocation required confirmation by a physician and radiographic evidence of a dislocation. Overall, at one year of follow-up, hips with a 36-mm femoral head articulation had a significantly lower incidence of dislocation than did those with a 28-mm articulation (1.3% [four of 299] compared with 5.4% [seventeen of 316]; difference, 4.1% [95% confidence interval, 1.2% to 7.2%]) when controlling for the type of procedure (primary or revision) (p = 0.012). The incidence of dislocation following primary arthroplasty was also significantly lower for hips with a 36-mm femoral head articulation than for those with a 28-mm articulation (0.8% [two of 258] compared with 4.4% [twelve of 275]; difference, 3.6% [95% confidence interval, 0.9% to 6.8%]) (p = 0.024). The incidence of dislocation following revision arthroplasty was 4.9% (two of forty-one) for hips with a 36-mm articulation and 12.2% (five of forty-one) for hips with a 28-mm articulation; this difference was not significant with the relatively small sample size of the revision group (difference, 7.3% [95% confidence interval, -5.9% to 21.1%]) (p = 0.273). Compared with a 28-mm femoral head articulation, a larger 36-mm articulation resulted in a significantly decreased incidence of dislocation in the first year following primary total hip arthroplasty. However, before a 36-mm metal-on-highly cross-linked polyethylene articulation is widely recommended, the incidence of late dislocation, wear, periprosthetic osteolysis, and liner fracture should be established.

Twenty-three-Year Outcome of the Porous Coated Anatomic Total Hip Replacement

We previously reported the ten to fourteen-year results for 311 Porous Coated Anatomic total hip replacements that had been inserted by two surgeons in 279 patients. The purpose of the present report is to update that study and to report the outcome beyond twenty years. The patients were followed prospectively with clinical assessment with use of the Harris hip score and radiographic analysis, and the results were collected in a database. Two hundred and sixty-eight hips were functioning at the time of death or at the time of the latest follow-up. A total of forty-three hips (14%) underwent major revision for all causes, and an additional four hips underwent minor revision. At a mean of twenty-three years of follow-up, Kaplan-Meier analysis revealed a survival rate of 83% with revision for any reason as the end point. The survival rate was 95% for the femoral component and 88% for the acetabular component with revision for any reason as the end point. The rate of survival of the acetabular component was significantly higher in hips with a 26-mm femoral head than in those with a 32-mm femoral head (91% compared with 80%; p = 0.026).

A randomized study on migration of the Spectron EF and the Charnley flanged 40 cemented femoral components using radiostereometric analysis at 2 years

Background and purpose We performed a randomized study to determine the migration patterns of the Spectron EF femoral stem and to compare them with those of the Charnley stem, which is regarded by many as the gold standard for comparison of implants due to its extensive documentation.Patients and methods 150 patients with a mean age of 70 years were randomized, single-blinded, to receive either a cemented Charnley flanged 40 monoblock, stainless steel, vaquasheen surface femoral stem with a 22.2-mm head (n = 30) or a cemented Spectron EF modular, matte, straight, collared, cobalt-chrome femoral stem with a 28-mm femoral head and a roughened proximal third of the stem (n = 120). The patients were followed with repeated radiostereometric analysis for 2 years to assess migration.Results At 2 years, stem retroversion was 2.3° and 0.7° (p < 0.001) and posterior translation was 0.44 mm and 0.17 mm (p = 0.002) for the Charnley group (n = 26) and the Spectron EF group (n = 74), respectively. Subsidence was 0.26 mm for the Charnley and 0.20 mm for the Spectron EF (p = 0.5).Interpretation The Spectron EF femoral stem was more stable than the Charnley flanged 40 stem in our study when evaluated at 2 years. In a report from the Norwegian arthroplasty register, the Spectron EF stem had a higher revision rate due to aseptic loosening beyond 5 years than the Charnley. Initial stability is not invariably related to good long-term results. Our results emphasize the importance of prospective long-term follow-up of prosthetic implants in clinical trials and national registries and a stepwise introduction of implants.

Dual Poly Liner Mobility Optimizes Wear and Stability in THA: Affirms

A dual-mobility acetabular component consists of a large, fixed, porous-coated acetabular component and a bipolar femoral component. These components are often called tripolar components. This configuration provides a stable, well-fixed implant platform against bone and 2 articular interfaces, a large polyethylene surface directly apposed to a highly polished metal implant, and a standard-sized (28- or 32-mm) femoral head captured within polyethylene. The dual-mobility cup appears to offer a safe, effective, durable solution to hip instability. The concept has extensive laboratory and clinical support. Although the long-term durability of these implants is unknown, the tested wear rates of a dual-mobility design with the current generation of highly cross-linked polyethylene are significantly lower than any previously reported wear rates. The recently introduced modular dual-mobility shell offers surgeons substantial flexibility in addressing the issue of hip instability with a cost-efficient, familiar option.

Dislocation Rate after Hip Arthroplasty within the First Postoperative Year: 36Mm versus 28Mm Femoral Heads

Dislocation is a common and important complication of total hip arthroplasty (THA). Larger femoral heads may reduce the risk of dislocation and improve the range of movement. The aim of this study was to compare the relative risk (RR) of dislocation during the first year after THA between implants with 28 mm and 36 mm femoral heads. 198 consecutive hips with 28 mm femoral head (Group-28) and 259 hips with 36 mm femoral head (Group-36) were studied. The patients were assessed preoperatively and periodically using the Harris hip score (HHS) and radiographic analysis. The relative risk (RR) of dislocation was calculated. The average HHS significantly improved from a preoperative baseline to the last follow-up at 82.1 months (28 mm) and 44.3 months (36 mm). No statistically significant differences were revealed between the two groups for HHS results and complications (p>0.05), but the difference in RR of dislocation within the first year between the two groups was 7.85 (95% CI: 1.34-46.03), p=0.046.Although dislocation is multifactorial in etiology, the two groups were homogenous for all principal contributing factors except the diameter of the femoral head. Therefore, the use of 36-mm heads can reduce the risk of dislocation following THA by a factor of 8 compared to conventional 28 mm heads.

Preliminary Clinical and Radiographic Results of Large Ceramic Heads on Highly Cross-Linked Polyethylene

Data are limited regarding large ceramic femoral heads with highly cross-linked polyethylene. We hypothesized that large ceramic head articulation with highly cross-linked polyethylene is safe with a low wear rate, comparable to metal-on-highly cross-linked polyethylene.The study group comprised 63 patients (72 hips) who had undergone total hip replacement (THR) with ceramic-on-highly cross-linked polyethylene between April 2006 and March 2007 with a minimum 2-year follow-up. Postoperative Western Ontario and Mc-Master Universities Arthritis Index (WOMAC) and Hospital for Special Surgery (HSS) scores were used for clinical assessment. Six-week and 2-year radiographs were analyzed by 2 independent observers using Roman 1.70 software. Twenty-six patients (29 hips) had 32-mm and 37 patients (43 hips) had 36-mm Biolox delta ceramic femoral heads (Ceramtec, Plochingen, Germany). Mean patient age was 60.9 ± 8.9 years, and mean follow-up was 2.9 ± 0.5 years. Mean postoperative WOMAC and HSS hip scores were 30.4 and 36.6, respectively. Mean wear at 1 and 2 years postoperatively was 0.06 ± 0.28 and 0.006 ± 0.12 mm/yr for all hips, respectively. Mean wear at 1 and 2 years postoperatively for the 32-mm femoral head was 0.063 ± 0.278 and 0.007 ± 0.126 mm/yr, respectively, and for the 36-mm femoral head was 0.057 ± 0.292 and 0.006 ± 0.118 mm/yr, respectively. No patient had any clinical complications, such as reoperation, infection, fractures, or radiographic evidence of osteolysis or loosening. The early results of THR with large ceramic heads demonstrate high safety and efficacy. Our data with 2-year follow-up show low wear rates, similar to published data for metal-on-highly cross-linked polyethylene.

Revision for Recurrent Instability: What are the Predictors of Failure?

Dislocation is a common complication following total hip arthroplasty (THA). In this study, we evaluated treatment strategies in patients undergoing revision THA for instability. A total of 156 hips in 154 patients underwent revision THA for instability between 2000 and 2007 at our institution. Demographic data and surgical treatment used were analyzed to determine risk factors for failure. Revision treatments included acetabular components in 100 hips, liner exchange in 56 hips, and femoral and acetabular components in 13 hips. Thirty-three (21.2%) had further dislocation. Isolated liner revision ( P = .004), previous revision arthroplasty ( P < .05), and the use of a 28-mm femoral head were associated with higher failure rates. A total of 20.3% (12/59) of constrained liners failed. Isolated liner exchange, history of revision, and use of a 28-mm head were associated with failure in revision THA for instability.

Residual Groin Pain at a Minimum of Two Years After Metal-on-Metal THA with a Twenty-eight-Millimeter Femoral Head, THA with a Large-Diameter Femoral Head, and Hip Resurfacing

Groin pain may persist in up to 4.3% of patients after total hip arthroplasty and up to 18% of patients one year after hip resurfacing. The incidence of this problem after total hip arthroplasty with a large-diameter femoral head is unknown. We analyzed the natural history of groin pain and its clinical consequences during the first two years after three types of hip arthroplasty. Data were collected prospectively on 279 patients. Eighty-five patients had a polyethylene sandwich metal-on-metal total hip arthroplasty with a 28-mm-diameter femoral head, 105 had hip resurfacing, and eighty-nine had a total hip arthroplasty with a large-diameter femoral head component with three other cup designs (forty-nine in this group had the same monoblock acetabular cup design as those who had hip resurfacing). At the twenty-four-month follow-up evaluation, seventy-seven patients (28%) reported at least one painful area around the hip and thirty-four patients (12.2%) had pain at more than one location. At three months, the incidence of groin discomfort was significantly increased in those who had hip resurfacing (30.5%) and in those who had total hip arthroplasty with a large-diameter femoral head (30%) compared with those who had total hip arthroplasty with a 28-mm femoral head (18.3%). This incidence decreased at two years (14.9%, 16.9%, and 12.9%, respectively). At twenty-four months postoperatively, eleven (four who had hip resurfacing, six who had total hip arthroplasty with the large-diameter head, and one who had total hip arthroplasty with the 28-mm head) of forty-one patients who had groin pain had not reported groin pain at previous follow-up evaluations. Of the forty-one patients reporting groin pain at the time of the last follow-up, twenty-three patients (56%) did not seek further evaluation or treatment, nine had revision surgery (22%), and the remaining nine patients thought the pain was substantial enough to warrant further evaluation and treatment. When the exact source of groin pain cannot be found after total hip arthroplasty, careful follow-up should be done as local reactions to metal-on-metal implants and component loosening may take time to become apparent clinically or on imaging studies.

Early Failure of a Modular Femoral Neck Total Hip Arthroplasty Component

The PROFEMUR Z modular total hip arthroplasty component (Wright Medical Technology, Arlington, Tennessee) is a primary total hip replacement system that offers surgeons the ability to alter the length and version of the femoral neck after the femoral stem has been implanted. The modularity is achieved through taper interfaces at the distal and proximal ends of the femoral neck. The proximal femoral neck taper engages with the femoral head, and the distal taper engages with the femoral stem. In this report, we present the case of a patient who twice underwent total hip arthroplasty revision surgery. The first revision was due to a fractured ceramic femoral head. The second revision was due to a complete fracture of the modular femoral neck. This report will focus on the second revision, and, specifically, the failure of the modular femoral neck at the junction of the neck to the femoral stem. The patient was informed that data concerning the case would be submitted for publication, and he consented. A sixty-two-year-old man (height, 181 cm; weight, 84 kg; body mass index, 25.6 kg/m2) presented with severe primary osteoarthritis of the left hip. He underwent uneventful primary total hip replacement surgery in November 2006. The components implanted were a 58-mm Lineage cup fixed with two screws; a size-5 PROFEMUR Z modular stem with a modular, long, 8° retroverted neck; a 32-mm ceramic femoral head with a +3.5-mm offset; and a ceramic Transcend liner (Wright Medical Technology). The patient recovered well with no postoperative complications. In February 2007, the patient presented to the emergency department with a painful left hip. Radiographs revealed superior migration of the femoral head, and a fracture of the ceramic head was suspected. The patient was hospitalized, and revision total hip arthroplasty was performed. During the procedure, the head was found …

Dislocation after total hip arthroplasty with 28 and 32-mm femoral head

BackgroundDislocation after primary total hip arthroplasty (THA) is a significant complication that occurs in 2–5% of patients. It has been postulated that increasing the femoral head diameter may reduce the risk of dislocation. The purpose of this paper is to report our experiences with a change from a 28 to a 32-mm femoral head.Materials and methodsThe retrospective cohort study includes 2572 primary THA performed with a 28 or 32 mm diameter femoral head in the period February 2002 to July 2009. All patients were operated with a posterolateral approach, and all except 18 were operated because of osteoarthritis. Cemented stems were used in 1991 cases and uncemented stems in 581 cases. Cemented cups were used in 2,230 cases and uncemented cups in 342 cases. The patients have been routinely followed for 1–8 years in the 28-mm femoral head group and from 0.5–7.5 years in the 32 femoral head group. We defined a dislocation as an event in which the hip required reduction by a physician.ResultsDislocation occurred in 49 hips with a 28-mm femoral head and in 4 hips with a 32-mm femoral head with an odds ratio of 6.06 (95% CI = 2.05–17.8) (P < 0.001). Otherwise, there were no significant associations between sex, age, diagnosis and type of prosthesis.ConclusionsMultivariate analyses of patients operated at our hospital indicate a significant association between femoral head diameter and dislocation after THA. There were no significant associations between dislocation and sex, age, diagnosis, or type of prosthesis.

Bedding-in and true wear in two different generations cementless porous-coated acetabular cups

Radiographic measurement of polyethylene wear cannot distinguish between so-called bedding-in and true wear in porous-coated cups. In this study, sequential wear performance was compared in two different generations of two cementless porous-coated cups. Group 1 consisted of 42 Harris-Galante I cups (HG I; 32-mm femoral head) and 37 Harris-Galante II cups (HG II; 28 mm); group 2 comprised 30 ACS liners using Profile or Trilock cups (32 mm) and 53 Duraloc cups (28 mm). All liners were made of conventional polyethylene sterilised by gamma irradiation in air. All cups showed radiographic bone ingrowth. Follow-up ranged from 5 to 17 years. Anteroposterior pelvic radiographs were scanned digitally and sequential femoral head penetration was estimated using a software package based on Kim's method. Bedding-in was 0.17 ± 0.09 mm for HG I and 0.09 ± 0.02 for HG II cups (p=0.035) in group 1, and 0.60 ± 0.50 for the ACS liners and 0.11 ± 0.41 for the Duraloc cups (p<0.01) in group 2. Femoral head penetration at the end of follow-up was 1.50 ± 0.28 mm for HG I (mean 14 years) and 0.85 ± 0.01 for HG II (8 years) in group 1, and 2.86 ± 0.68 for ACS (12 years) and 0.90 ± 0.41 for Duraloc (8 years) in group 2. Mean wear was 0.09 mm/year for HG I and 0.10 for HG II in group 1, and 0.20 for the ACS liners and 0.09 for the Duraloc cups in group 2. In conclusion, sequential femoral head penetration using Kim's digitised method allows us to distinguish between bedding-in and true wear.

Bedding-in and true wear in two different generations cementless porous-coated acetabular cups

Radiographic measurement of polyethylene wear cannot distinguish between so-called bedding-in and true wear in porous-coated cups. In this study, sequential wear performance was compared in two different generations of two cementless porous-coated cups. Group 1 consisted of 42 Harris-Galante I cups (HG I; 32-mm femoral head) and 37 Harris-Galante II cups (HG II; 28 mm); group 2 comprised 30 ACS liners using Profile or Trilock cups (32 mm) and 53 Duraloc cups (28 mm). All liners were made of conventional polyethylene sterilised by gamma irradiation in air. All cups showed radiographic bone ingrowth. Follow-up ranged from 5 to 17 years. Anteroposterior pelvic radiographs were scanned digitally and sequential femoral head penetration was estimated using a software package based on Kim's method. Bedding-in was 0.17 ± 0.09 mm for HG I and 0.09 ± 0.02 for HG II cups (p=0.035) in group 1, and 0.60 ± 0.50 for the ACS liners and 0.11 ± 0.41 for the Duraloc cups (p<0.01) in group 2. Femoral head penetration at the end of follow-up was 1.50 ± 0.28 mm for HG I (mean 14 years) and 0.85 ± 0.01 for HG II (8 years) in group 1, and 2.86 ± 0.68 for ACS (12 years) and 0.90 ± 0.41 for Duraloc (8 years) in group 2. Mean wear was 0.09 mm/year for HG I and 0.10 for HG II in group 1, and 0.20 for the ACS liners and 0.09 for the Duraloc cups in group 2. In conclusion, sequential femoral head penetration using Kim's digitised method allows us to distinguish between bedding-in and true wear.

Do large femoral heads reduce the risks of impingement in total hip arthroplasty with optimal and non-optimal cup positioning?

The purpose of this study was to assess whether large femoral heads (36-38 mm) improve the range of motion in total hip arthroplasty compared to standard (28-32 mm) femoral heads in the presence of optimal and non-optimal cup positioning. A mathematical model of the hip joint was generated by using a laser scan of a dried cadaveric hip. The range of motion was assessed with a cup inclination and anteversion of reference and with non-optimal cup positions. Large femoral heads increased the range of motion, compared to the 28-mm femoral head, in the presence of a hip prosthesis correctly implanted and even more so in the presence of non-optimal cup positioning. However, with respect to the 32-mm femoral head, large femoral heads showed limited benefits both in the presence of optimal and non-optimal cup positioning.

Serum metal ion levels after second-generation metal-on-metal total hip arthroplasty

Metal-on-metal bearings for total hip arthroplasty are increasing in popularity. However, metal ion toxicity, metal hypersensitivity, and metal carcinogenicity are the causes concern for patients with metal-on-metal hip replacement. We investigated serum levels of cobalt and chromium ions in patients with successfully implanted second-generation metal-on-metal total hip arthroplasty (THA) using PINNACLE-A (DePuy, Warsaw, IN, USA). Thirty-three patients underwent primary cementless THA with the use of a 36-mm femoral head PINNACLE-A with a metal-on-metal articulation. Blood samples were taken preoperatively, at 3 months, and at 1 year, and levels of cobalt and chromium were determined. At 3 months, levels of both cobalt and chromium had increased significantly compared with preoperative levels. There were no significant differences between levels of either metal at 3 months and 1 year. Patients with metal-on-metal THA had higher circulating levels of metal ions than before arthroplasty at 3 months, with no additional significant increases at 1 year in this study.

Letter to the Editor: Clinical Comparison of Polyethylene Wear with Zirconia or Cobalt-Chromium Femoral Heads

To the Editor: We read with interest the October 2009 article by Stilling et al. [9] entitled “Clinical Comparison of Polyethylene Wear with Zirconia or Cobalt-Chromium Femoral Heads.” The authors compared linear wear rates from zirconia or cobalt-chromium alloy femoral heads with gamma-irradiated but not remelted polyethylene (PE) liners, finding no difference after a minimum of 5 years in vivo. In their discussion, Stilling et al. noted a limitation of their study was the tetragonal-to-monoclinic phase transformation associated with yttria-stabilized zirconia [1], suggesting the increased “Zr surface roughening and grain pullout provides the potential for accelerated PE wear” and thus explains the similar wear performance between yttria-stabilized zirconia and cobalt-chromium alloy femoral heads. We have observed similar phase transformation and roughening of yttria-stabilized zirconia in retrieval series [8] and in artificial aging studies [7]. However, not all zirconia degrades in vivo. Magnesia-stabilized zirconia [2] also is available for clinical use. Although the tetragonal and monoclinic phases also are present in medical-grade magnesia-stabilized zirconia, its microstructure mainly consists of tetragonal precipitates in a cubic matrix, which tends to inhibit tetragonal-to-monoclinic phase transformation [5]. Magnesia-stabilized zirconia has proven to be stable and free from degradation and roughening in retrieval series [8] and in artificial aging studies [7]. In addition, hip wear simulator data in our laboratory comparing 28-mm femoral heads of different materials with 10-Mrad cross-linked/remelted PE revealed wrought cobalt-chromium alloy [3, 4] femoral heads produce higher gravimetric wear at 3 M cycles [6]. We continued this simulator study to 7 M cycles and found the difference in gravimetric wear between cobalt-chromium alloy and magnesia-stabilized zirconia to increase and have submitted a manuscript based on these data to a journal for review. Finally, Stilling et al. [9] use unnecessarily broad language in their final two paragraphs, repeatedly using the abbreviation Zr to refer to all zirconia, not the unstable yttria-stabilized form examined in their study. For example, the statement that “Zr femoral heads were withdrawn from the commercial market in 2001 owing to incidents of head fracture” is not entirely accurate, because only certain batches of yttria-stabilized zirconia manufactured by Saint Gobain Desmarquest (Evreux, France) were recalled. Magnesia-stabilized zirconia was not affected by the recall, and no cases of magnesia-stabilized zirconia fracture have been reported. Although yttria-stabilized zirconia is susceptible to low-temperature degradation and has all but completely disappeared from the market, magnesia-stabilized zirconia has proven to be stable and safe in clinical use. Our hip simulator data suggest the use of magnesia-stabilized zirconia femoral heads will lead to a reduction in wear in vivo compared with cobalt-chromium alloy heads, even with cross-linked acetabular liners.

Activities of daily living after total hip arthroplasty. Is a 32-mm femoral head superior to a 26-mm head for improving daily activities?

Range of motion (ROM) of the hip joint after total hip arthroplasty (THA) could be increased by using a larger prosthetic femoral head, but it is not known whether the activities of daily living (ADL) are influenced by THA with different head sizes. Our objective was to compare postoperative ADL in patients who underwent THA using a head diameter of 26mm or 32mm. We assessed the range of motion and the mode of ADL after cementless primary THA. Comparison was performed between 25 joints of 24 patients who underwent THA with a 26-mm femoral head (26-mm group) and 24 joints of 20 patients with a 32-mm head (32-mm group). The postoperative range of flexion and abduction was significantly larger in the 32-mm group than in the 26-mm group. With respect to the mode of performing selected ADL such as putting on and removing pants, socks, and cutting toenails, many patients adopted the compensatory position of lumbar flexion with hip flexion plus knee extension in the 26-mm group, while a majority of the patients from the 32-mm group employed the mode of hip flexion with knee flexion. Patients with the 32-mm head showed better postoperative ADL of the ipsilateral side compared with the 26-mm head.

Two-Year Radiostereometric Analysis Evaluation of Femoral Head Penetration in a Challenging Population of Young Total Hip Arthroplasty Patients

This prospective, randomized protocol evaluated femoral head penetration after total hip arthroplasty in a young population. Forty-five patients randomly received either a cross-linked or conventional ultrahigh-molecular-weight polyethylene (UHMWPE) liner in a noncemented hemispheric cup (Trilogy, Zimmer, Warsaw, Ind) with a 28-mm femoral head. Radiostereometric analysis film pairs, Harris hip, UCLA, SF-12, and Western Ontario and McMaster Universities scores were obtained through 2 years. Median femoral head penetration was less among cross-linked compared to conventional liners as follows: 0.06 mm (0.04-0.08 mm) vs 0.08 mm (0.02-0.19 mm) at 6 months, 0.07 mm (−0.14 to 0.16 mm) vs 0.11 mm (0.01-0.27 mm) at 1 year, and 0.065 mm (−0.04 to 0.193 mm) vs 0.169 mm (0.09-0.22 mm) at 2 years. Clinical outcomes were similar between the groups. Highly cross-linked UHMWPE demonstrated 55% less femoral head penetration compared to conventional polyethylene at 2 years. Despite improvements in the manufacturing process and sterilization of conventional UHMWPE, the femoral head penetration rate is unchanged from historical standards.