Low BMD affects initial stability and delays stem osseointegration in cementless total hip arthroplasty in women: a 2-year RSA study of 39 patients

Background and purpose

Immediate implant stability is a key factor for success in cementless total hip arthroplasty (THA). Low bone mineral density (BMD) and age-related geometric changes of the proximal femur may jeopardize initial stability and osseointegration. We compared migration of hydroxyapatite-coated femoral stems in women with or without low systemic BMD.

Patients and methods

61 female patients with hip osteoarthritis were treated with cementless THA with anatomically designed hydroxyapatite-coated femoral stems and ceramic-ceramic bearing surfaces (ABG-II). Of the 39 eligible patients between the ages of 41 and 78 years, 12 had normal systemic BMD and 27 had osteopenia or osteoporosis. According to the Dorr classification, 21 had type A bone and 18 had type B. Translational and rotational migration of the stems was evaluated with radiostereometric analysis (RSA) up to 2 years after surgery.

Results

Patients with low systemic BMD showed higher subsidence of the femoral stem during the first 3 months after surgery than did those with normal BMD (difference = 0.6, 95% CI: 0.1–1.1; p = 0.03). Low systemic BMD (odds ratio (OR) = 0.1, CI: 0.006–1.0; p = 0.02), low local hip BMD (OR = 0.3, CI: 0.1–0.7; p = 0.005) and ageing (OR = 1.1, CI: 1.0–1.2; p = 0.02) were risk factors for delayed translational stability. Ageing and low canal flare index were risk factors for delayed rotational stabilization (OR = 3, CI: 1.1–9; p = 0.04 and OR = 1.1, CI: 1.0–1.2; p = 0.02, respectively). Harris hip score and WOMAC score were similar in patients with normal systemic BMD and low systemic BMD.

Interpretation

Low BMD, changes in intraosseous dimensions of the proximal femur, and ageing adversely affected initial stability and delayed osseointegration of cementless stems in women.Cementless techniques in total hip arthroplasty (THA) were originally designed for patients with normal bone structure and normal healing capacity. Osseointegration of uncemented components is based on new bone ingrowth and ongrowth, which is inhibited by excessive micromotion (Pilliar et al. 1986). Thus, high initial stability is one of the key factors for rapid osseointegration of an implant. Along with biomechanically optimized implant designs and bioactive coatings for enhanced bone ingrowth, the indications have gradually been expanded to include even THAs in elderly patients with impaired bone quality and limited healing capacity (Keisu et al. 2001, Kelly et al. 2007, Meding et al. 2010, Mäkelä et al. 2010, Thillemann et al. 2010).Osteoporosis is common in postmenopausal women with osteoarthritis (OA) of the hip (Glowacki et al. 2003). Cementless THA techniques have never been systematically screened for appropriate indications in osteoporotic patients, although poor bone quality may jeopardize the initial stability of cementless stems. The bone-implant interface must withstand high shear stresses of physiological loading, and poor quality of periimplant bone may also jeopardize the long-term success of osseointegration (Gabet et al. 2010).We have used radiostereometric analysis (RSA) for evaluation of the success of cementless THAs in a population of female patients with primary OA of the hip. The study hypothesis was that the bone quality of postmenopausal women dictates the early stability of anatomically designed femoral stems.     

Prospective evaluation of total hip arthroplasty with a cementless, anatomically designed, porous-coated femoral implant: mean 11-year follow-up

The performance of an anatomically designed femoral implant with porous titanium mesh coating was assessed in patients undergoing total hip arthroplasty. The stem, with built-in 12 degrees anteversion, was implanted in neutral position relative to the long axis of the femur through a cementless press-fit application. The only requirement was the presence of sufficient thickness within the cortical bone of the femoral metaphysis to support the stem. Ninety-one evaluable patients were followed up for a minimum of 10 years. Patients tolerated weight-bearing activity within 24 hours after surgery. Only 1 femoral component required revision because of loosening. Most patients showed uniform bony ingrowth. Quality of life was markedly improved. The anatomically designed, porous-coated implant provides robust performance which has general utility in a wide range of patients.     

Small and similar amounts of micromotion in an anatomical stem and a customized cementless femoral stem in regular-shaped femurs: A 5-year follow-up randomized RSA study

Background and purpose

High primary stability is important for long-term survival of uncemented femoral stems. Different stem designs are currently in use. The ABG-I is a well-documented anatomical stem with a press-fit design. The Unique stem is designed for a tight customized fit to the cortical bone of the upper femur. This implant was initially developed for patients with abnormal anatomy, but the concept can also be used in patients with normal femoral anatomy. We present 5-year radiostereometric analysis (RSA) results from a randomized study comparing the ABG-I anatomical stem with the Unique femoral stem.

Patients and methods

100 hips with regular upper femur anatomy were randomized to either the ABG-I stem or the Unique femoral stem. RSA measurements were performed postoperatively and after 3, 6, 12, 24, and 60 months.

Results

RSA measurements from 80 hips were available for analysis at the 5-year follow-up. Small amounts of movement were observed for both stems, with no statistically significant differences between the 2 types.

Interpretation

No improvement in long-term stability was found from using a customized stem design. However, no patients with abnormal geometry of the upper femur were included in this study.High mechanical stability is a crucial factor for correct performance of uncemented femoral stems. Micromovements along the implant-bone interface may prevent ingrowth of bone to the surface of the prosthesis, and it may lead to the formation of a fibrous membrane and eventually to loosening of the implant. The critical thresholds of micromovements that can be tolerated are not exactly known, but they are probably dependent on both patient- and implant-specific factors (Viceconti et al. 2006). It has been shown, however, that interfacial motion of around 40 μm leads to partial bone ingrowth whereas motions exceeding 150 μm completely prevent ingrowth of bone (Pilliar et al. 1986, Jasty et al. 1997).Uncemented, customized femoral stems are mainly designed and manufactured for patients with abnormal size and shape of the proximal femur, but this does not preclude their use in patients with regular-shaped proximal femurs. The requirement for maximum primary stability with uncemented off-the-shelf stems also applies to customized stems. The optimized fit and fill of a customized stem should theoretically promote even better mechanical fixation than with standard implants.Radiostereometric analysis (RSA) enables measurement of migration and rotation in the range of 0.1 mm and 0.05º, respectively (Selvik 1989, Kadar et al. 2011). There is a correlation between postoperative migration of femoral stems and early loosening (Freeman and Plante-Bordeneuve 1994, Linder 1994, Karrholm et al. 2006, Karrholm 2012). On the other hand, a new implant showing large degrees of micromovement should not necessarily be regarded as having a performance equivalent to long-term failure (Karrholm et al. 2006). Recently published studies reporting medium- to long-term RSA results will probably contribute to a better understanding of the topic (Nieuwenhuijse et al. 2012, Rohrl et al. 2012).This randomized study was performed as part of the clinical documentation of the Unique customized stem (Scandinavian Customized Prosthesis (SCP), Trondheim, Norway), to compare the migration pattern of the Unique stem with that of a standard anatomical uncemented stem with a clinically well-proven stem design (the ABG-I).Our aim was to measure migration of the Unique customized stem and the ABG-I stem using RSA. Our hypothesis was that there would be no difference in migration between the 2 types of uncemented femoral stems in patients with regular anatomy in the upper femur.     

Limited femorotomy: Removing a well-fixed,cementless femoral stem

We present a technique of a longitudinal posterior femorotomy that does not extend to the greater trochanter leaving the abductors intact. This technique allows safe, effective removal of well-fixed proximally coated cementless femoral stems with minimal bone loss and allows revision to metaphyseal fitting stems. We present results of this technique in 18 patients with a minimum 6-year follow-up. Harris hip scores increased from 68.2 to 92.4, all stems had evidence of good bony ingrowth, no evidence of migration, all femorotomies healed and there is no evidence of stress shielding or osteolysis. None required re-revision of femoral prosthesis.     

Grit-blasted titanium femoral stem in cementless primary total hip arthroplasty: a 5- to 10-year multicenter study

A total of 133 cementless primary total hip arthroplasties using the Zweymuller-Alloclassic grit-blasted titanium tapered stem were performed in 3 institutions. The patient cohort was divided into 2 subgroups, nonselected and selected, on the basis of excellent bone stock and age (<65 years old at surgery). Acetabular components were all cementless, and bearing surfaces were all alumina-ceramic on polyethylene. After a 7.3-year average follow-up period (range, 5-10 years), 118 primary femoral replacements in 109 patients could be reviewed fully. Mean age at surgery was 55.7 years (range, 27-84 years). According to the Merle d'Aubigne and Charnley rating system, clinical results were graded excellent and good in 89% of hips and fair in 11%. Radiologically, early subsidence >2 mm could be detected in 4 hips (3.4%). Calcar atrophy and spot welds were noted in 77% and 82% of hips. Femoral osteolysis granuloma was noted in 4 hips (3.4%). There has been no stem fracture and no ceramic head breakage. The survivorship at 10 years with definite femoral aseptic loosening (radiographic failure) as the endpoint was 100% (95% Wilson confidence interval, 78.4%-100%; worst scenario, 95.4%). A significant difference between the nonselected and selected patient subgroups was observed only for early reoperation (P =.03) and proximal stress shielding (P =.01). Press-fitting but not filling the femoral canal with a rough titanium, straight, tapered femoral component represents, at intermediate follow-up, a promising cementless option in primary total hip arthroplasty.     

Early migration characteristics of a hydroxyapatite-coated femoral stem: an RSA study

Measurement of early stem subsidence can be used to predict the likelihood of long-term femoral component loosening and clinical failure. Data that examines the early migration pattern of clinically proven stems will provide clinicians with useful baseline data with which to compare new stem designs. This study was performed to evaluate the early migration pattern of a hydroxyapatite-coated press-fit femoral component that has been in use for over ten years. We enrolled 30 patients who underwent THA for osteoarthritis. The median age was 70 years (range, 55–80 years). Patients were clinically assessed using the Harris hip score. Radiostereometric analysis was used to evaluate stem migration at three to four days, six months, one year and two years. We observed a mean subsidence of 0.73 mm at six months, 0.62 mm at one year and 0.58 mm at two years and a mean retroversion of 1.82° at six months, 1.90° at one year and 1.59° at two years. This data suggests that subsidence is confined to the first six months after which there was no further subsidence. The results from this study can be compared with those from novel cementless stem designs to help predict the long-term outcome one may expect from new cementless stem designs.     

Fit and fill analysis of a newly designed femoral stem in cementless total hip arthroplasty for patients with secondary osteoarthritis

The fit and fill of the femoral canal are critical to the success of cementless femoral stems in total hip arthroplasty. It is difficult for conventional stems to provide a good fit and fill for the femora of patients with secondary osteoarthritis. Based on measurements of 100 femora of these patients, we designed two types of Fukui Medical School (FMS) stems with a proximal lateral flare that differed in the medial radius. We compared the fit and fill of the FMS stems with those of four conventional stems, using computer simulation. The mean proximal fit and total fit of the FMS stems were 46% and 53% respectively, a significant improvement compared with the other stems examined. The mean fill of FMS stems was 82% at the lower end of the lesser trochanter and 84% at the upper end of the isthmus, values that were significantly higher than those of the other stems. Since September 1995, we have implanted FMS stems in 15 hips with secondary osteoarthritis. Radiographic evaluations showed that the canal fill of the FMS stems was significantly greater in the proximal femur compared with other stems previously inserted at our department. A summary of this paper was presented at the 9th Symposium on Computer-Assisted Radiology; June 1995, Berlin, and at the 8th International Symposium on Technology in Arthroplasty; September 1995, Puerto Rico.     

Good performance of a titanium femoral component in cementless hip arthroplasty in younger patients

We performed 97 uncemented primary total hip arthroplasties in 80 patients having an average age of 50 years. The femoral implant was a titanium stem with a proximal circumferential plasma spray-coating. Three different acetabular components were used: a threaded and partly porous-coated design in 70% of the cases. The average follow-up period was 8 years. 1 stem was revised 9 years after insertion due to a comminuted fracture of the proximal femur, 1 stem was revised 9 years after insertion due to a deep infection. No stem revisions were due to aseptic loosening. 1 femora had areas of distal osteolysis associated with a deep infection, but no signs of proximal loosening. 3 femora had areas of minor proximal osteolysis. 16 acetabular components (14 threaded) had been revised in 13 patients. The average Harris hip score was 91 points at the latest follow-up We conclude that the uncemented titanium femoral component with a circumferential porous coating performed well in these patients, most of whom were young. As reported previously, aseptic loosening of threaded acetabular components was common.     

Total hip arthroplasty using cementless grit-blasted femoral component: a minimum 10-year follow-up study

The grit-blasted cementless Spotorno (CLS) stem, which has excellent survival rates up to 10 years, is widely used in total hip arthroplasty (THA). We investigated the survivorships of CLS stems in THA at a minimum follow-up of 10 years and sought to identify factors that influence outcomes. A total of 227 hips of 191 patients who underwent cementless THA with a CLS stem were retrospectively reviewed at a mean follow-up of 12.3 years. All patients were evaluated clinically and radiographically according to implant type and surgery-related and patient-related factors. Survivorship was 97.2% when femoral revision for any reason was defined as the end point. Femoral revisions were performed in 3 hips because of periprosthetic fractures. Survivorship for all hips, using revision for any reason as the end point, was 92.6%. Two metal-on-metal THAs were revised because of aseptic loosening or osteolysis around the cup. No significant differences were evident for type of stem, type of bearing surface, stem alignment, or patient-related factors. However, a canal fill index of 80% or less was found to affect cortical remodeling, subsidence, and a change in stem position of 5° or more, which indicates that care must be taken not to undersize stems. In addition, in view of the revisions performed, bearing surfaces appear to importantly influence THA survivorship.     

The ESOP-HA modular cementless femoral stem: a study of the results of 165 hip arthroplasties with a minimum of 10-year follow-up

The authors report on more than 10 years’ experience of using a cementless femoral stem, with a two-piece modular design, for indications of primary prosthetic replacement. One hundred and sixty-five prostheses, inserted between 06/11/1991 and 31/12/1994, were reviewed. No patient was lost to follow-up. The probability of 10-year survival of these hip prostheses was assessed using the actuarial Kaplan–Meier method (the endpoint was revision of the arthroplasty regardless of the reason: failure of the femoral or acetabular component, fracture of one piece of the implant etc.). The mean age of the 165 patients (84 women, 81 men) was 64 years. The clinical results were excellent or good in 87.2% of hips. There was no instance of post-operative thigh pain (apart from one case), because of the primary stability of the hydroxyapatite-coated metaphyseal part where stress transmission occurs, while the diaphyseal part, selected in accordance with requirements and smaller in diameter than the femoral canal, remained free in the diaphysis. No significant difference in the results was noted in accordance with the pattern of femoral anatomy encountered; however, the cylindrical femur yielded slightly inferior results (PMA score). Radiological follow-up showed that femoral fixation had been obtained, generally accompanied by obvious signs of bone fixation (endosteal ossification, radiolucencies indicating condensed bone in the smooth zone). A high number of cortical changes was not noted. Two stems were the cause of revision surgery, one because of thigh pain without sealing, the other because the stem fractured. Six acetabular implants were removed without interfering with the femoral stem, because of localised osteolysis around an expandable peg. Two other acetabular implants were replaced: one because poor positioning resulted in recurrent luxation and the other for premature wear of the polyethylene after 7 years. The grounds for revision were failure of the acetabular implant in 8 cases out of 10. Thus, there is sufficient justification for the use of this modular two-piece stem, which has fulfilled its purpose in the majority of patients, enabling us to extend with confidence indications for the cementless stem to all the anatomical types of femur encountered. Our series of patients included almost 78.7% of what are known as “normal” femurs, but in the remaining cases (21.3%) or in more than one in five instances, the modular stem made it possible to extend the indications for a cementless prosthesis to all the patterns of femur encountered, in particular to young adults, who often have femoral dysplasia or a cylindrical femur. The survival curve reflects the life of the implant: implant survival is 96.3%. If acetabular revisions are not included it is 98.8%. Conclusions: A modular system then, consisting of a metaphyseal and diaphyseal part, appears to be a first-rate component which optimises the indication for implantation of a cementless femoral prosthesis in order to obtain the correct performance of a medical service as the survival curve demonstrates.     

Results of a tapered cementless femoral stem implanted in varus

Varus placement of the femoral component in total hip arthroplasty has been associated with poor outcomes. The purpose of this study was to examine results of total hip arthroplasty with varus alignment of a tapered titanium femoral prosthesis (Alloclassic; Sulzer, Zurich, Switzerland) at a minimum 5-year follow-up. Of a consecutive series of 585 patients, 23 met the inclusion criteria. Harris hip scores averaged 97, and all implants were clinically and radiographically stable at the most recent follow-up. In this series of patients, varus alignment of the prosthesis did not have an adverse effect on outcome. Although malalignment of the femoral prosthesis may compromise the results of some designs, the Alloclassic prosthesis has proved to be reliable and forgiving despite varus malalignment at 5 to 11 years' follow-up.     

Good stability but high periprosthetic bone mineral loss and late-occurring periprosthetic fractures with use of uncemented tapered femoral stems in patients with a femoral neck fracture: A 5-year follow-up of 31 patients using RSA and DXA

Background and purpose

We previously evaluated a new uncemented femoral stem designed for elderly patients with a femoral neck fracture and found stable implant fixation and good clinical results up to 2 years postoperatively, despite substantial periprosthetic bone mineral loss. We now present the medium-term follow-up results from this study.

Patients and methods

In this observational prospective cohort study, we included 50 patients (mean age 81 (70–92) years) with a femoral neck fracture. All patients underwent surgery with a cemented cup and an uncemented stem specifically designed for fracture treatment. Outcome variables were migration of the stem measured with radiostereometry (RSA) and periprosthetic change in bone mineral density (BMD), measured with dual-energy X-ray absorptiometry (DXA). Hip function and health-related quality of life were assessed using the Harris hip score (HHS) and the EuroQol-5D (EQ-5D). DXA and RSA data were collected at regular intervals up to 4 years, and data concerning reoperations and hip-related complications were collected during a mean follow-up time of 5 (0.2–7.5) years.

Results

At 5 years, 19 patients had either passed away or were unavailable for further participation and 31 could be followed up. Of the original 50 patients, 6 patients had suffered a periprosthetic fracture, all of them sustained after the 2-year follow-up. In 19 patients, we obtained complete RSA and DXA data and no component had migrated after the 2-year follow-up. We also found a continuous total periprosthetic bone loss amounting to a median of –19% (–39 to 2). No changes in HHS or EQ-5D were observed during the follow-up period.

Interpretation

In this medium-term follow-up, the stem remained firmly fixed in bone despite considerable periprosthetic bone mineral loss. However, this bone loss might explain the high number of late-occurring periprosthetic fractures. Based on these results, we would not recommend uncemented femoral stems for the treatment of femoral neck fractures in the elderly.In Sweden, cemented stems have been used primarily for patients with a femoral neck fracture (FNF), but with the introduction of modern hydroxyapatite- (HA-) coated implants, uncemented fixation has increased in popularity (Garellick et al. 2011). Excellent long-term results have been reported for patients with primary osteoarthritis (OA) of the hip (Boden et al. 2006a). The concept of inserting an uncemented femoral component is attractive to many surgeons, as the cementing procedure can induce cardiac arrhythmia and/or cardiorespiratory collapse (Parvizi et al. 1999). However, a recent report from the Swedish Hip Arthroplasty Register indicated that uncemented implants used for patients with an FNF are associated with a 20-fold higher risk of reoperation due to periprosthetic fracture than cemented matte stems (Leonardsson et al. 2012).We have already published an evaluation of a new uncemented femoral stem designed for elderly patients with an FNF; this showed good clinical results and stable implant fixation up to 2 years after surgery despite substantial periprosthetic bone loss (Sköldenberg et al. 2011). We now present the medium-term follow-up from this study.     

Long term survival analysis of cementless Spotorno femoral stem in young patients

Objective

The aim of this study was to analyze the survivorship and clinical outcome of Cementless Spotorno (CLS) stem in young patients.

Efforts to improve cementless femoral stems in THR: 2- to 5-year follow-up of a high-offset femoral stem with distal stem modification (Secur-Fit Plus)

A retrospective review of 81 sequential primary total hip arthroplasties using a cementless, high-offset femoral stem was performed. Follow-up was 24 to 60 months. The average age at the time of surgery was 54 years. The femoral bone types were: 36% Dorr A, 51% Dorr B, and 13% Dorr C. The mean postoperative Harris Hip Score was 95. The mean postoperative Oxford score was 17. Eighty-five percent had no clinical leg-length difference. All stems were radiographically stable. The stem features of hydroxyapatite coating on a rough circumferential titanium arc-deposit proximal surface in conjunction with distal flutes seem to provide immediate stability, making this implant clinically versatile. Potential benefits of increased offset include improved joint stability and avoidance of leg lengthening.     

Isolated revision acetabuloplasty using a porous-coated cementless acetabular component without removal of a well-fixed femoral component: A 3- to 9-year follow-up study

The results of isolated acetabular revision performed in 31 patients (32 hips) were monitored for between 3 and 9 years. All femoral components were well fixed and not removed or revised at the time of index surgery. There were 4 hips with little or no acetabular bony defect, 2 hips with pure segmental defects (type I), 10 hips with cavitary defects (type II), 15 with combined segmental cavitary defects (type III), and 1 with pelvic discontinuity (type IV). All revision acetabular implants were cementless, using a porous-coated hemispheric cup with or without bone-graft. There were four grade I reconstructions, 16 grade II reconstructions, and 12 grade III reconstructions. At final follow-up evaluation 94% of the cups were judged to be stable. Two hips required a second revision acetabuloplasty because of loss of fixation of the cup. The 2 repeat revisions were also done without removal of the femoral component. One acetabular component had evidence of rotational migration, which stabilized and remained nonprogressive. There were no cases of femoral component radiographic or clinical failure. The mean pre and postoperative hip scores were 44 and 83, respectively. The pre- and postoperative pain scores were 12 and 42, respectively. The findings of this study suggest that isolated acetabular revision, using a cementless porous-coated hemispheric cup, can be successfully performed without removing or revising a well-fixed femoral stem and not compromise the final outcome.     

Behaviour of the ultra-short anatomic cementless femoral stem in young and elderly patients

Purpose

The question arises as to whether it is possible to obtain rigid fixation of the ultra-short metaphyseal-fitting anatomic cementless stem without diaphyseal fixation in the elderly as well as younger patients. We investigated whether ultra-short, metaphyseal-fitting anatomic cementless femoral stem would provide similar functional improvements in the younger and elderly patients, radiographically secure implant fixation would be achieved in both groups, the bone content would be preserved in both groups, and complication rates would be similar in both groups.

Methods

A total of 100 patients (114 hips) in the younger patient group and 100 patients (112 hips) in the elderly patient group were included in the study. Their mean age was 43.9 ± 6.11 years (range, 31–65 years) in the younger patient group and 78.9 ± 12.1 years (range, 66–91 years) in the elderly patient group. The mean duration of follow-up was 7.5 years (range, six to nine years) in the younger patient group and 7.6 years (range, six to nine years) in the elderly patient group.

Results

The mean postoperative Harris hip scores (95 points versus 91 points), WOMAC scores (11 points versus 15 points), thigh pain (none in either group), UCLA activity scores (6.5 points versus 4.5 points), and radiographic results were not significantly different between the two groups. No hip in either group had an aseptic loosening. No hip in either group had clicking or squeaking sounds or ceramic fractures.

Conclusion

The cementless ultra-short, metaphyseal-fitting anatomic cementless femoral component provides stable fixation without any need of diaphyseal fixation in both younger and elderly patients. Despite the concern, the poor bone quality in elderly patients did not compromise the stability, and osseointegration of this ultra-short, anatomic cementless femoral stem was achieved in all elderly patients.     

The migration pattern of the Charnley femoral stem: a five-year follow-up RSA study in a well-functioning patient group

Background

Implant stability is considered vital to long-time implant survival in total hip arthroplasty (THA), since loose implants are reported to be a major cause of hip revision. There is an association between early implant micromotion and increased risk of revision. More implant-specific data are needed to establish acceptable levels of early implant movement.

Materials and methods

Thirty-five patients (36 hips) undergoing Charnley THA were followed with repeated clinical, radiographic, and radiostereometric analysis (RSA) over 5 years. Twenty-three patients attended 5 years postoperatively.

Results

The patient group was well functioning based on the radiological and clinical evaluations. The stems constantly moved up to 5 years postoperatively, with subsidence, retroversion, and varus tilt, based on the RSA.

Conclusion

Continuous movement of the Charnley stem was observed up to 5 years postoperatively in a well-functioning patient group. The migration data presented herein could be useful when defining acceptable migration limits for certain types of cemented femoral stems.     

The 6-year migration characteristics of a hydroxyapatite-coated femoral stem: a radiostereometric analysis study

A prospective cohort of 30 patients undergoing primary total hip arthroplasty for treatment of osteoarthritis was enrolled in a study to characterize the migration behavior of a clinically successful cementless stem. At 6 years, the mean subsidence of the stem was 0.63 mm (range, -0.33 to 3.68 mm); the mean rotation into retroversion was 1.41° (range, -1.33° to 7.48°). No stems had additional subsidence of more than 0.25 mm between 6 months and 6 years. The resultant mean subsidence between 2 and 6 years was 0.03 mm, which is below the limit measurable by radiostereometric analysis. The data demonstrate that subsidence of this cementless stem occurs within the first 6 months, after which there is persistent stabilization.     

Revision of failed acetabular components utilizing a cementless oblong cup: an average 9-year follow-up study

Introduction  Failure of acetabular components often leads to bone loss with extensive elongated defects in the surrounding bone. In these cases, reconstruction is challenging and stable fixation of the revision implant difficult. The use of an oblong cup has been described as an option for acetabular reconstruction in such revisions. We report the first long-term results obtained with this implant to date. Materials and methods  Fifty-six longitudinal oblong revision cups (LOR™) were evaluated clinically and radiologically after a follow-up of 8–12 years (average 9 years). The defects treated with the LOR™ cup ranged from Paprosky type 1–3. Allogenic cancellous bone chips were additionally used in 31 reconstructions to fill cavitary defects. Results  Based on radiological criteria, 50 acetabular implants underwent osseointegration without any definitive signs of loosening; 2 consistently exhibited zonal radiolucent lines that were always smaller than 2 mm, 1 migrated by around 3 mm. None of these cases exhibited any clinical symptoms. In 11 cases where acetabular defects manifested postoperatively, 8 were remodeled completely and 3 partially at final follow-up. Three revision implants migrated farther than 5 mm and had to be revised before 32-month follow-up. In addition, 1 septic implant failure occurred. After an average follow-up of 9 years, 93% of the investigated implants remained in situ without further revision and 95% without aseptic implant failure. Conclusion  This 12-year clinical study demonstrates that the LOR™ cup offers a successful concept for the revision of failed acetabular components that also promotes the biological reconstruction of bony defects. Compared with other methods with similarly long follow-ups, our long-term results prove this procedure has a very low rate of revision and aseptic implant failure.