The prediction of failure of the stem in THR by measurement of early migration using EBRA-FCA. Einzel-Bild-Roentgen-Analyse-femoral component analysis

Biomechanics of a short stem: In vitro primary stability and stress shielding of a conservative cementless hip stem

Short stem prostheses provide conservative surgery and favorable metaphyseal load transmission. However, clinical long-term results are lacking. Therefore, in vitro trials can be used to predict bone-implant performance. In this in vitro study, primary stability and stress shielding of a new cementless short stem implant was evaluated in comparison to a straight stem using nine pairs of human cadaver femurs. Primary stability, including reversible micromotion and irreversible migration, was assessed in a hip simulator. Furthermore, changes in the pattern of cortical strain were evaluated. The short stem was more resistant to reversible micromotion and irreversible migration into retroversion. Axial stability was similar, with mean reversible micromotions of 9 µm for the short stem and 7 µm for the straight stem. Proximal load transmission was more physiological with the short stem, though both implants could not avoid stress shielding in Gruen zones 1 and 7. Primary stability of the short stem prosthesis was not negatively influenced compared to the straight shaft. Furthermore, proximal femoral strain pattern was more physiological after insertion of the short stem prosthesis.

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.

Migration analysis of a metaphyseal anchored short-stem hip prosthesis

BACKGROUND AND PURPOSE

Metaphyseal anchored short-stem hip implants were designed to improve load transmission and preserve femoral bone stock. Until now, only few outcome data have been available and migration studies are one of the few ways of obtaining data that are predictive of implant survival. We therefore evaluated a metaphyseal anchored short-stem hip implant by Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA).

PATIENTS AND METHODS

First, the EBRA-FCA method was validated for the short-stem hip implant. Then 80 of the first 100 consecutive implants were evaluated after at least 2 years. Clinical assessment was performed using the WOMAC and the UCLA score.

RESULTS

After 2.7 (2.0-4.2), years none of the implants had been revised and by that time the stems had subsided by a mean of 0.7 mm (SD 1.8) (95% CI: 0.3-1.1). Of the 80 implants, 78 were stable after 2 years, with 74 being primary stable and 4 showing secondary stabilization after initial subsidence. Continuous migration was seen in only 2 patients. The clinical outcome showed good results with a mean WOMAC of 11 (SD 13) and a mean UCLA score of 7.3 (SD 2.0).

INTERPRETATION

The metaphyseal anchored short-stem hip implant showed good functional results and a high degree of stability after 2 years. The outcome is comparable to that of clinically proven conventional hip implants and if the results are confirmed by long-term studies, short-stem hip arthroplasty might be an alternative for young patients requiring hip replacement.

[Implant position of total hip arthroplasty shafts. Establishment of a new method for comparison between planned and achieved shaft positions]

BACKGROUND

One of the main goals of the preoperative planning of hip prostheses is adequate shaft positioning with reconstruction of leg length and offset. The purpose of this study was to compare the planned and achieved shaft positions using a modified program for migration measurement.

METHODS

In 60 cases of total hip replacement the preoperative planning was compared with the postoperative radiograph using a modified version of the well-established EBRA-FCA program. The results of this new measurement were compared to conventional measurements. In 25 cases the intraobserver and interobserver reliability was determined.

RESULTS

The novel measurements correlated best with the measured distance between the greater trochanter and the center of rotation and yielded the best intraobserver and interobserver reliability. In general, cementless stems had a slightly more proximal position (0.65 mm) compared to cemented stems.

CONCLUSIONS

The modified program for migration measurement facilitates a reproducible and fast comparison of the planned and achieved shaft positions thus implementing an early and objective control of postoperative shaft position.

High incidence of migration with poor initial fixation of the Accolade stem

BACKGROUND

Numerous cementless femoral stem design variations are in clinical use. Because initial implant instability and micromotion are associated with aseptic loosening of the femoral component, migration analysis provides an early assessment of implant survivorship.

QUESTIONS/PURPOSES

We determined the (1) migration pattern of the Accolade cementless femoral stem; (2) clinical factors predisposing to stem migration; (3) self-reported patient outcomes; and (4) our current rate of aseptic stem loosening.

METHODS

We retrospectively analyzed 81 femoral stems for aseptic migration using Ein-Bild-Roentgen-Analyse-femoral component analysis. Postoperatively, patients completed the WOMAC and SF-12 questionnaires. We assessed radiographic factors potentially associated with subsidence: indices of bone shape and quality, canal fill of the implant, and radiographic signs of loosening. Minimum followup was 24 months (mean, 29 months; range, 24-48 months).

RESULTS

The average subsidence at 24 months was 1.3 mm (range, 0-1.5 mm). In the first 2 years, 36% of stems subsided more than 1.5 mm. Large stem size was associated with subsidence. Radiolucent lines (> 1.5 mm in three zones) were present in 10% of stems and associated with lower questionnaire scores. The 5-year survivorship for aseptic loosening of the 367 stems was 97% with revision as end point and 95% for radiographic failure.

CONCLUSIONS

The high incidence of migration and stems with radiographic failure raises concerns about patient clinical function and long-term survivorship of this stem design. This migration pattern may be due to poor initial stability with a subsequent lack of osseointegration. Our results differ from radiographic findings and clinical durability of other similar cementless stem designs.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

A preclinical study of stem subsidence and graft incorporation after femoral impaction grafting using porous hydroxyapatite as a bone graft extender

This preclinical in vivo screening study compared bone graft incorporation and stem subsidence in cemented hemiarthroplasty after femoral impaction bone grafting with either morselized allograft bone (n = 5, control group) or a 1:1 mix of allograft and porous hydroxyapatite ceramics (HA) granules (n = 5, HA group). At 14 weeks, there was excellent bone graft incorporation by bone, and the stems were well fixed in both groups. The median subsidence at the cement-bone interface, measured using radiostereometric analysis, was 0.14 and 0.93 mm in the control and HA groups, respectively. The comparable histologic results between groups and good stem fixation in this study support the conduct of a larger scale investigation of the use of porous HA in femoral impaction bone grafting at revision hip arthroplasty.

Digital comparison of planned and implanted stem position in total hip replacement using a program form migration analysis

AIM

One main goal in primary total hip replacement is the reconstruction of preoperative biomechanical conditions by adequate implant positioning. Our aim was to compare the planned and effectively implanted stem position in using a program for digital migration measurement.

PATIENTS

We examined 120 cases with this new method based on a modification of the EBRA-FCA program and compared these results to direct plain radiographic methods. In addition, the intra- and inter-observer reliability was determined in 50 cases.

RESULTS

We observed a rate of correct prediction of 80% for the size of the stem. The new method revealed a good correlation (0.95 and 0.64 for the position along the stem axis and 0.84 for the stem angle) to direct plain radiographic methods. Regarding the intraclass correlation coefficient for intra- and inter-observer reliability, the results were superior (0.97 vs. 0.81-0.84 and 0.90 vs. 0.74-0.88) compared with direct plain radiographic methods.

CONCLUSION

We concluded that the comparison of the planned and implanted stem position using a modified EBRA-FCA method is more reproducible than direct radiographic measurements.

The effect of abductor muscle and anterior-posterior hip contact load simulation on the in-vitro primary stability of a cementless hip stem

Background

In-vitro mechanical tests are commonly performed to assess pre-clinically the effect of implant design on the stability of hip endoprostheses. There is no standard protocol for these tests, and the forces applied vary between studies. This study examines the effect of the abductor force with and without application of the anterior-posterior hip contact force in the in-vitro assessment of cementless hip implant stability.

Methods

Cementless stems (VerSys Fiber Metal) were implanted in twelve composite femurs which were divided into two groups: group 1 (N = 6) was loaded with the hip contact force only, whereas group 2 (N = 6) was additionally subjected to an abductor force. Both groups were subjected to the same cranial-caudal hip contact force component, 2.3 times body weight (BW) and each specimen was subjected to three levels of anterior-posterior hip contact load: 0, -0.1 to 0.3 BW (walking), and -0.1 to 0.6 BW (stair climbing). The implant migration and micromotion relative to the femur was measured using a custom-built system comprised of 6 LVDT sensors.

Results

Substantially higher implant motion was observed when the anterior-posterior force was 0.6BW compared to the lower anterior-posterior load levels, particularly distally and in retroversion. The abductor load had little effect on implant motion when simulating walking, but resulted in significantly less motion than the hip contact force alone when simulating stair climbing.

Conclusions

The anterior-posterior component of the hip contact load has a significant effect on the axial motion of the stem relative to the bone. Inclusion of the abductor force had a stabilizing effect on the implant motion when simulating stair climbing.

Case report: Cementless stem stabilization after intraoperative fracture: a radiostereometric analysis

We present the case of a patient with intraoperative femoral fracture during THA, which was repaired using cerclage fixation and insertion of an hydroxyapatite-coated cementless stem. The patient was evaluated postoperatively using radiostereometry during a 2-year course, and despite a large amount of subsidence and rotation, stabilization occurred and was maintained by 6 months. By evaluating the pattern of stem migration after intraoperative fracture, this case shows, even in the presence of instability, a successful clinical outcome can be achieved using an hydroxyapatite-coated cementless stem.

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.

A prospective study of hip revision surgery using the Exeter long-stem prosthesis: function, subsidence, and complications for 57 patients

Background

The long-stem Exeter femoral component is commonly used in revision hip surgery. Subsidence of the femoral stem in primary hip arthroplasty has been studied extensively, but much less is known about its significance in revision surgery. This prospective study examined the relationship between radiological subsidence, Western Ontario and McMaster (WOMAC) osteoarthritis index pain score, patient satisfaction and complication rates for the long-stem Exeter hip prosthesis.

Materials and methods

Data was prospectively collected for a single-surgeon series of 96 patients undergoing revision surgery with a mean follow-up period of 36 months. Pre- and post-operative clinical evaluation was carried out using the validated WOMAC osteoarthritis index. Radiographic evaluation was carried out on magnification-adjusted digital radiographic images.

Results

Data from 57 patients were analysed. The mean rate of subsidence recorded was 0.43 mm/year, with a mean total subsidence of 0.79 mm [95% confidence interval (CI) 0.57–1.01] at 36.3 months. There was no correlation between subsidence and post-operative WOMAC score, complication rate or patient satisfaction. There was a statistically significant reduction between pre-operative and post-operative WOMAC scores, with means of 33.5 and 10.7, respectively (P < 0.001), and high patient satisfaction.

Conclusion

Our subsidence rates for long-stem revision femoral components are lower than the published data but demonstrate the same plateau. Radiographic subsidence does not appear to relate to functional outcome or complication rates in our data.

Comparison of the model-based and marker-based roentgen stereophotogrammetry methods in a typical clinical setting

Roentgen stereophotogrammetric analysis (RSA) is an established method for the precise measurement of implant migration. Model-based RSA (MBRSA) alleviates the need to attach tantalum markers to the prosthesis, which has prevented wider application of RSA. The goal of this study was to investigate the equivalence of both methods for the clinical measurement of implant migration. Tibial component migration was measured in 24 patients using both methods from the same set of radiographs. The maximum agreement interval, mean (+/-2 standard deviations), of the difference between both methods was modest, at 0.002 mm (0.144 mm) and -0.078 degrees (0.782 degrees ). The results suggest that MBRSA can be used interchangeably with the marker-based method and that the advantages of MBRSA do not come at the cost of a loss in accuracy.

The effect of a single infusion of zoledronic acid on early implant migration in total hip arthroplasty. A randomized, double-blind, controlled trial

BACKGROUND

Aseptic loosening is the most frequent cause of implant failure in total hip arthroplasty. While a direct link between aseptic loosening and periprosthetic bone loss remains elusive, there is plentiful evidence for a close association with early implant migration. The present trial was primarily designed to evaluate whether a single infusion of 4 mg of zoledronic acid prevented early implant migration in patients with osteonecrosis of the femoral head.

METHODS

Fifty patients were consecutively enrolled to receive either zoledronic acid or saline solution after cementless total hip arthroplasty. Radiographs, biochemical parameters of bone turnover, and the Harris hip-rating score were determined preoperatively and at each follow-up examination at seven weeks, six months, one year, and yearly thereafter. The median follow-up period was 2.8 years.

RESULTS

We found a significant subsidence of the stem of up to a mean (and standard deviation) of -1.2 +/- 0.6 mm at two years within the control group, and the cups had a mean medialization of 0.6 +/- 1.0 mm and a mean cranialization of 0.6 +/- 0.8 mm (p < 0.001). Treatment with zoledronic acid effectively minimized the migration of the cups in both the transverse and the vertical direction (mean, 0.15 +/- 0.6 mm and 0.06 +/- 0.6 mm, respectively; p < 0.05), while only a trend to decreased subsidence of the stem was detected. Finally, the Harris hip score rapidly increased over time in both treatment groups, although this increase was significantly more pronounced in the zoledronate-treated group than in the control group (analysis of variance, p = 0.008).

CONCLUSIONS

A single infusion of zoledronic acid shows promise in improving initial fixation of a cementless implant, which may improve the clinical outcome of total hip arthroplasty in patients with osteonecrosis of the femoral head.

Aseptic stem loosening in primary THA: migration analysis of cemented and cementless fixation

Early migration has reportedly been predictive for later implant failure. Using four different migration patterns, this study aimed to analyse migration behaviour of the two types of implant fixation--cemented and cementless--throughout the process of loosening. Migrational behaviour of 69 revised stems (49 cemented, 20 uncemented) was analysed retrospectively with EBRA-FCA (Einzel-Bild-Röntgen-Analyse, Femoral Component Analysis). Uncemented stems failed after early and late onset migration alike, while late migration was the predominant pattern in cemented stems. Mean prosthetic failure after early migration occurred 5.8 (+/-4.4) years postoperatively due to insufficient primary stability. Initially stable stems with late onset migration were revised after 12.4 (+/-4.5) years. Measurement of early migration was found to be a valuable tool to screen short-term and mid-term failure. In the long run the method's sensitivity decreased. Late onset migration, however, preceded long-term failure by a mean of three years.

Accuracy of model-based RSA contour reduction in a typical clinical application

Marker-based roentgen stereophotogrammetric analysis (RSA) is an accurate method for measuring in vivo implant migration, which requires attachment of tantalum markers to the implant. Model-based RSA allows migration measurement without implant markers; digital pose estimation, which can be thought of as casting a shadow of a surface model of the implant into the stereoradiographs, is used instead. The number of surface models required in a given clinical study depends on the number of implanted sizes and design variations of prostheses. Contour selection can be used to limit pose estimation to areas of the prosthesis that do not vary with design, reducing the number of surface models required. The effect of contour reduction on the accuracy of the model-based method was investigated using three different contour selection schemes on tibial components in 24 patients at 3 and 6 month followup. The agreement interval (mean +/- 2 standard deviations), which bounds the differences between the marker-based and model-based methods with contour reduction was smaller than -0.028 +/- 0.254 mm. The data suggest that contour reduction does not result in unacceptable loss of model-based RSA accuracy, and that the model-based method can be used interchangeably with the marker-based method for measuring tibial component migration.

Early outcome of a modular femoral component in revision total hip arthroplasty

Forty-six hips in 42 patients underwent revision surgery with a modular femoral component (ZMR; Zimmer, Warsaw, Ind). Thirty-nine hips with 2 to 5 years' follow-up were evaluated radiographically and clinically by the Harris hip score and WOMAC pain/stiffness/function scores. The Harris hip score improved from 47.4 to 72.3 (P<.001), with significant improvements in the WOMAC pain/stiffness/function scores. The mean subsidence was 4.4 mm, with 5 hips demonstrating significant subsidence of more than 5 mm. Four hips required reoperation, 1 due to failure of the femoral component. No early complications were encountered regarding the modular junction. Modular, cementless, extensively porous, coated femoral components have demonstrated early clinical and radiographic success. Distal intramedullary fit helps ensure initial stability; proximal modularity further maximizes fit while optimizing hip offset and length.

Proximal loading of the femur leads to low subsidence rates: first clinical results of the CR-stem

INTRODUCTION

A new femoral stem was developed with a design that leads to compression of cancellous bone in the calcar region which results in proximal loading. The cross-sectional design of the implant provides rotational stability.

MATERIALS AND METHODS

In the first clinical investigation ten patients underwent uncemented total hip arthroplasty between January 1999 and May 1999 using the CR-stem((R)) (Implantcast GmbH, Buxtehude, Germany). Results were investigated using the Harris-hip-score (HHS) and antero-posterior and lateral radiographs. Migration was evaluated with the EBRA-FCA-method with a follow-up of 7 years.

RESULTS

We demonstrated a mean subsidence rate of 2.23 +/- 1.13 mm 7 years after implantation thus providing basic data for extensive testing in a clinical environment.

DISCUSSION

As small subsidence rates are regarded as predictor for superior long-term results in uncemented total hip arthroplasty according to the literature, the CR-stem shows promise for excellent long-term results.

Migration of the Duraloc cup after 5 years

The Duraloc cup is a frequently used metal-backed, porous-coated, hemispherical, press-fit acetabular component. Published data on loosening rates are contradictory. In this study we investigated migration patterns with computer-assisted Einzel-Bild-Roentgen-Analyse (EBRA) of 67 Duraloc 100 cups. Cup migration and clinical scores were analysed over a 5-year follow-up period. Median total migration of the Duraloc 100 cup was 1.21 mm at 5 years. Seventy-five percent of implants were radiologically stable at 2 years and 90% at 4 years. One cup loosened aseptically at 60 months, requiring revision. Cup diameters > or = 54 mm migrated significantly more than cups < 54 mm in diameter (p = 0.029 at 4 years). There was a significant correlation between high polyethylene wear and further migrating cups within the first post-operative year (p = 0.035 at 12 months). Our analysis revealed significantly higher wear in males (p = 0.029 at 4 years). Radiological loosening at two years could be calculated using receiver-operating characteristic curve analysis, and 1.2 mm as an adequate threshold value (sensitivity = 100%, specificity = 89%).

Hip arthroplasty with proximal transmission of force: first clinical results with a new partially cemented femoral stem

BACKGROUND

Proximal stem fixation by partial cementing is a new concept in hip arthroplasty. We conducted a prospective clinical and radiological analysis to evaluate the preliminary outcome of this new technique with the Option 3000 stem (Mathys Orthopaedics, Bettlach, Switzerland).

METHODS AND FOCUS

One hundred and thirty-three hip replacements in 123 patients have been performed between 1996 and 2003: All of them were followed up regularly both clinically and radiological and 53 were analysed with the EBRA-FCA method. Eighty-six patients with 95 hips could be seen in August 2004. At this point of time, the mean follow-up time was 61 months (5.08 years) with a maximum of 100 months (8.33 years)

RESULTS

The clinical data reported an average Harris Hip Score of 85.5. Nine stems had to be exchanged over the period of study. The EBRA-FCA analysis reported a mean subsidence less than 1.5 mm after 2 years, then an average stable subsidence of 2.4 mm. So the results are similar to the early results obtained with other fixation concepts and the long-term results appear promising.

Proximal cement fixation in total hip arthroplasty--first results with a new stem design

Stem loosening and stress-shielding are problems encountered in cemented hip arthroplasty. Could proximal stem fixation by partial cementing solve the problem? More physiological transmission of forces with only proximal cement fixation seems to be possible with this recent development (Z-stem, Option 3000, Mathys Orthopaedics, Bettlach, Switzerland). In a prospective clinical trial, this new implant was used for total hip arthroplasty in human patients. One hundred and thirty-three (133) total hip replacements in 123 patients were performed between April 1996 and January 2003. All of them were followed up regularly; 53 were analysed with the EBRA-FCA method (Einzel Bild Röntgen Analyse--femoral component analysis), whereas the rest were analysed using conventional follow-up X-rays. Eighty-six (86) patients with 95 hips could be examined in August 2004 to obtain mid-term results. At this stage, the mean follow-up time was 61 months (5.08 years), with a maximum of 100 months (8.33 years). Up to October 2004, nine cases needed a revision. The clinical data collected reported an average Harris Hip Score of 89.3 (good). The EBRA-FCA analysis reported a mean subsidence of less than 1.5 mm after the first two years, under the EBRA threshold of predicted loosening. At the latest follow-up (at an average of 61 months), there was an average stable subsidence of 2.4 mm in general. Eight (8) patients presented with subsidence of more than 5 mm. The results of the new implant seem to be encouraging. Finally, comparing our results to other fixation concepts will require longer follow-up periods.

No increased stem subsidence after arthroplasty in young patients with femoral head osteonecrosis: 41 patients followed for 1-9 years

BACKGROUND

Poor bone stock in patients with osteonecrosis of the femoral head may be a reason for poor outcome after hip replacement. One way of studying bone quality is to measure implant migration. We thus investigated the clinical and radiographic results of cementless THR in younger patients with femoral head osteonecrosis.

PATIENTS AND METHODS

We studied hips in 41 patients (mean age 48 (25-63) years) with a cementless hip arthroplasty after late stage osteonecrosis. Clinical evaluation was by the Harris hip score, the WOMAC score and the SF-36 score. Stem subsidence was measured with the Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA) at 3, 12, 24, 60, and 72 months after operation. The average duration of follow-up was 7(1-9) years, with less than 2 years for 2 patients.

RESULTS

There was no revision of any hip. No radiographic or clinical stem loosening was seen. After 60 months, the cementless stems showed a median subsidence of -0.7 mm (95% CI: -0.9 to -0.2). No femoral osteolysis occurred. Femoral radiolucent lines, all < 1 mm, were seen in 10 hips. At the latest follow-up the Harris hip score was 83 (23-100) points.

INTERPRETATION

Our findings for porous-coated stems in patients with femoral osteonecrosis indicate no greater risk of stem subsidence and rate of osteolysis after an average of 7 years follow-up. Thus, we continue to use uncemented stems in younger patients with femoral osteonecrosis. However, continued follow-up will be necessary to evaluate the long-term outcome.

[The cemented MS-30 stem. A multi-surgeon series of 333 consecutive cases]

INTRODUCTION

So far there is only one peer-reviewed long-term publication from the inventors' clinic for the MS-30 stem.

MATERIAL AND METHODS

In a retrospective study we followed the first 333 consecutive MS-30 stems. All patients with 5- to 11-year follow-up were clinically and radiographically evaluated. At the time of implantation the criteria of modern cementing techniques were not implemented. Clinical evaluation was done using the scores of Harris and Merle d'Aubigné and Postel. Radiographic evaluation included quality of the cement mantle (true lateral radiographs taken under fluoroscopy), stem subsidence, loosening signs, and the risk for pending failure.

RESULTS

At follow-up 12 hips had undergone femoral revision: 3 for aseptic loosening, 6 for infection, 1 for periprosthetic fracture, and 2 for recurrent dislocation. The overall survival for all reasons at 10 years was 96.1%; survival with aseptic loosening as an end point was 99.0%. The median Harris Hip Score at follow-up was 80 (26-100) points. Radiological evaluation revealed a thin cement mantle (<2 mm) in approximately 2/3, predominantly on the lateral views (Gruen zones 8/9). One-third of all reviewed prostheses were considered at risk for pending failure, which strongly correlated with the initial quality of the cement mantle.

CONCLUSION

Midterm results with the MS-30 stem are encouraging and an even better long-term outcome can be expected with a better cement technique.

[Clinical evaluation tools of total hip arthroplasties]

Total hip arthroplasty is one of the most efficient hip surgery procedures enabling improved function in the vast majority of operated patients. The major long-term complication is aseptic loosening due to an inflammatory response to particle wear debris coming from the bearings. Polyethylene is the key culprit. Currently two solutions are proposed: eliminating polyethylene from the prosthetic articulation or reducing material wear. This leads to the need for reliable tools for evaluating short-term results, predictive of long-term outcome. When the innovation concerns reduction of polyethylene wear, short-term wear should be measured with software methods or radiostereometry. If the innovation concerns improvement of polyethyleneless implants, then short-term migration should be measured with EBRA or radiostereometry. In addition, the long-term retrospective evaluation of large series of patients remains of major interest provided that it is performed with survival analysis. These different methods are detailed in this study, indicating the pros and cons for each solution.

Migration and cyclic motion of a new short-stemmed hip prosthesis--a biomechanical in vitro study

BACKGROUND

Uncemented, short-stemmed hip prostheses have been developed to reduce the risk of stress shielding and to preserve femural bone stock. The long-term success of these implants is yet uncertain. Prerequisite for osseointegration is sufficient primary stability. In this study the cyclic motion and migration patterns of a new short-stemmed hip implant were compared with those for two clinically successful shaft prostheses.

METHODS

The prostheses were implanted in paired fresh human femura and loaded dynamically (gait cycle) with increasing load (max 2,100 N) up to 15,000 cycles. Relative displacements between prosthesis and bone were recorded using a 3D-video analysis system.

FINDINGS

The short stem displayed a biphasic migration pattern with stabilisation at maximum load. Initial migration was predominantly into varus and was greater than that for the shaft prostheses. Failure occurred in cases of poor bone quality and malpositioning. Cyclic motion of the short prosthesis was less than that for the shaft prostheses. Surface finish showed no effect. System stiffness for the new stem was lower than for the shaft prostheses.

INTERPRETATION

The new stem tended to migrate initially more than the shaft prostheses, but stabilised when cortical contact was achieved or the cancellous bone was compacted sufficiently. Bone quality and correct positioning were important factors for the short stem. The lower cyclic motion of the new stem should be favourable for bony ingrowth. The lower system bending stiffness with the new implant indicated a more physiological loading of the bone and should thereby reduce the effects of stress shielding.

Migration of two different cementless hip arthroplasty stems in combination with two different heads: a biomechanical in vitro study

The aim of the present in vitro study was to evaluate migrational characteristics of cementless primary hip arthroplasty stems in combination with a diameter 50 mm head (hemiarthroplasty) and a diameter 28 mm head in and with a polyethylene cup (total hip arthroplasty) in fresh-frozen human specimens. Two different types (Endo SL, FMT) were implanted into seven pairs of fresh-frozen human femoral specimens. The implanted stems were combined with a diameter 50 mm head (hemiarthroplasty) on one side and with a polyethylene cup and a 28 mm head (total hip arthroplasty) on the other side. Dynamic mechanical loading was applied for 50,000 cycles while recording relative motions between stem and bone stock using a 3-D motion analysis system. The Endo SL stem showed a significantly higher amplitude of relative motion in all translational and rotational components regardless of the head used. In both stem types a strong tendency for higher axial migration with the diameter 50 mm head in comparison to the THA head was found. The lowest axial migration was found in the FMTstem in combination with the small head and a PE cup. The highest axial migration was found in the Endo SL stem combined with the diameter 50 mm head. Our results indicate that the head might play an important role for axial migration of cementless stems.

Cementless hemiarthroplasty in femoral neck fractures: evaluation of clinical results and measurement of migration by EBRA-FCA

Aim of the present study was to evaluate migration rates of cementless primary hemiarthroplasty in acute femoral neck fractures. In a longitudinal, prospective study 46 patients were treated by cementless hemiarthroplasty. Clinical follow up was correlated with the EBRA-FCA method. In 30% of all patients stem migration amounted to more than 2 mm; further, these patients were seen to have a high level of activity. A high degree of migration in more than 30% of all patients requires critical scepticism toward further use of the investigated cementless stem as hemiarthroplasty. According to literature, migration of more than 2 mm suggests a high probability of early aseptic loosening. In patients with a low degree of activity good results could be observed; nevertheless, in patients with a high level of activity the combination of the investigated cementless stem with a solid fracture head cannot be recommended.

Modes of failure of a threaded acetabular cup : a radiographic study with EBRA of 42 revised cups

A radiographic study of a singular type of threaded cup, revised due to aseptic loosening, was performed with Einzel-Bild-Roentgen-Analyse (EBRA) to detect eventual risk factors and patterns of loosening. Fifty-three cups of 50 patients were revised. Forty-two cups could be measured with EBRA. No cup had obvious osteolysis, 33 cups demonstrated early migration, and all cups had migrated at the time of revision. Twenty-eight of the cups had a change of inclination and 21 of anteversion, respectively. The mean migration was 1.9 mm in the medial and 7.9 mm in the cranial direction; the mean wear rate was 0.2 mm/year. Cups with early migration had a higher migration rate. All male patients had early migration; medially placed cups had less migration than the other cups. Wear was not significantly affected by the migration of the implant. No cup had a complete radiolucent line, and the only radiographic sign for loosening was the change of position of the cup. Medial placement showed less migration in case of loosening. Regular radiographic follow-up is recommended for the examined implant, and the cup should not be used in the future.

Biomechanics of a new short-stemmed uncemented hip prosthesis: An in-vitro study in human bone

The migration pattern, cyclic motion, system stiffness and failure load of a new short-stemmed hip prosthesis were compared to a clinically successful shaft prosthesis during the initial loading phase. The influence of implant-sizing on mechanical stability was also investigated for the new stem, in particular with relation to the bone quality. Prostheses were implanted in paired human femora and loaded cyclically up to 3515 cycles. Relative displacements between prosthesis and bone were measured using a 3D-camera and reflective marker system. Migration of the new stem was predominantly into varus and was higher than for the shaft prosthesis. The test set-up was proposed to simulate a worst-case loading scenario since muscle forces, which tend to reduce bone deformation, were not simulated. It could therefore be expected that clinical migration of the implants would be less pronounced than that observed in this study. Cyclic motion for the new stem was similar to that for the clinically successful shaft prosthesis, suggesting that bone ingrowth could be expected for the new stem. No significant difference in fracture load was observed between the implants. The system stiffness with the new stem was lower than for the shaft prosthesis, indicating more physiological load transfer. Smaller implant sizing with 'cancellous' fixation seems favourable, as it led to similar migration and smaller cyclic motion values than with 'cortical' fixation. A trend for higher cyclic motion and migration was observed in femora with poor bone quality. Hence, sufficiently good bone stock is necessary, when implanting the new short-stemmed prosthesis.

Stair climbing is more critical than walking in pre-clinical assessment of primary stability in cementless THA in vitro

Pre-clinical testing of hip endoprostheses is a mandatory requirement before clinical release. Inadequate loading conditions may lead to lower elastic and plastic interface movements than those occurring post-operatively in vivo. This study investigated the influence of patient activity on the primary stability of cementless prostheses with a special emphasis on active simulation of muscle forces. A loading setup, based on validated musculo-skeletal analyses, was used to generate the hip contact force during walking and stair climbing by transmitting muscle forces through the femur. In addition, a loading configuration which only generated the hip contact force occurring during stair climbing at the prosthesis head was simulated. CLS prostheses were implanted in 18 composite femora and subjected to cyclical loading. The relative micro-movements at the bone-prosthesis interface were determined and appeared to be extremely sensitive to the specific patient activity. Compared to walking, stair climbing generated higher micro-movements, with pronounced axial and rotational components. Stair climbing with the femur loaded by the resultant hip contact force only exhibited a characteristic valgus tilt of the stem with significantly lower interface micro-movements than under active simulation of muscle forces. The analyses suggest that stair climbing induced the highest mechanical instability at the bone-prosthesis interface, a level which may compromise the necessary osseointegration process. Active simulation of muscle forces considerably affects the primary stability of cementless hip endoprostheses. Pre-clinical in vitro tests should therefore simulate stair climbing and include muscle activity in the assessment of initial implant stability, otherwise micro-movements may be underestimated and the primary stability overestimated.

Survival of cementless femoral components after osteonecrosis of the femoral head with different etiologies

We reviewed 41 patients with 55 cementless total hip arthroplasty operated for advanced osteonecrosis. Patients were divided into 2 groups according to etiology of the osteonecrosis. The first group included 17 cases with osteonecrosis without a systemic disease and the second group 38 cases with osteonecrosis associated with a systemic disease. The follow-up was on average 6.4 years (range, 2-12.8). Eight (15.4%) stem revisions had to be performed; all of them were in the patients with a systemic disease. Ten-year survival rates with femoral revision as the endpoint were in the first group 100% and in the systemic disease group 68% (P = .03). The data of this retrospective study indicate a correlation between the survival of the femoral component and the etiology of the osteonecrosis.

Clinical correlation of femoral component migration in hip resurfacing arthroplasty analyzed by Einzel-Bild-Röntgen-analyze-femoral component analysis

Hip resurfacing arthroplasty using metal-on-metal bearings has become increasingly popular. Wear of these bearings has been imperceptible on plain radiographs. Migration analysis studies may represent the opportunity to detect early failures and evaluate long-term prosthetic survival. The authors retrospectively reviewed 29 hips in a consecutive series of metal-on-metal hip resurfacing arthroplasties with a long-term clinical follow-up (average 8.7 years) to analyze the femoral component migration pattern by means of Einzel-Bild-Röntgen-Analyze-femoral component analysis (EBRA-FCA). Femoral component migrations at 2 years and latest follow-up were compared with the known clinical outcomes. The authors' findings add validity to EBRA-FCA as a means to monitor femoral component migration and the clinical outcome of metal-on-metal hip resurfacing arthroplasty.

Subsidence of titanium straight stems in combination with highly viscous bone cement

Varying results and a high rate of subsidence have been reported for the straight femoral stem (M.E. Muller) made of titanium alloy. We examined subsidence in 135 titanium-alloy straight stems implanted with high viscosity cement after 68.8+/-11.5 months using a digital high-precision method (EBRA-FCA). One revised implant showed a subsidence of 14.6 mm and another 2.5 mm over 5 years. A third implant without migration was found to be loose. The 122 implants without loosening showed a mean subsidence of 0.1+/-0.1 mm, and focal osteolysis was seen in two. Altogether, we found subsidence of the titanium stems very small. The small subsidence may be related to the use of high viscosity bone cement.

Higher failure rate and stem migration of an uncemented femoral component in patients with femoral head osteonecrosis than in patients with osteoarthrosis

BACKGROUND

Several authors have found poorer outcome after hip replacement for osteonecrosis than after hip replacement for arthrosis. In a retrospective study we evaluated the performance of an uncemented femoral component in patients with osteonecrosis and arthrosis of the hip.

PATIENTS AND METHODS

31 patients operated for osteonecrosis, and 49 patients operated for osteoarthrosis were included. The median follow-up time was 6.1 (2-11) years for the patients with osteonecrosis, and 5.9 (4-8) for the arthrosis patients.

RESULTS

Migration analysis performed by the Einzel-Bild-Roentgen Analysis (EBRA) technique revealed a median stem migration of 1.5 (-8.8-0) mm in the patients with osteonecrosis, but only 0.6 (-2.8-0.7) mm in the patients with arthrosis (p < 0.001). Survivorship analysis with stem revision as endpoint for failure was 74% (95% CI: 55-94) in the osteonecrosis, and 98% (95% CI: 94-100) in the arthrosis group (p = 0.01).

INTERPRETATION

We suggest that the higher failure rate and stem migration of uncemented total hip replacement in the patients with osteonecrosis is a consequence of the disease. On the basis of these findings, we recommend close monitoring of the patients with osteonecrosis, which should include migration measurements.

Validation d’une méthode de mesure de l’enfoncement d’un implant fémoral cimenté de type Exeter

PURPOSE OF THE STUDY

Total hip arthroplasty has become one of the most common procedures in orthopedic surgery. These patients must nevertheless be followed with care due to the risk of instability. Knowledge of early migration behavior can provide an indirect assessment of implant fixation. The purpose of this work was to develop a new measurement tool for early assessment of the femoral component.

MATERIAL AND METHODS

We analyzed the x-rays of ten Exeter stems (Stryker-Howmedica) implanted between 1996 and 2001 using a simple software designed to calculate the vertical subsidence of each implant. The technical precision and inter-observer reproducibility were checked.

RESULTS

The software provided a precision of 0.14-0.3 millimeters. The overall precision of the technique was 1.2 millimeters. There was no statistically significant inter-observer variability. We observed a mean subsidence of 1.3+/-0.7 millimeters at six Months, followed by no further migration.

DISCUSSION AND CONCLUSION

This new method was found to be reliable. It is useful for identifying implant migration at different bone-cement-implant interfaces. The time course of subsidence appears to be important to determine threshold values for failure. This tool provides an easy-to-use method for both retrospective and prospective analysis. With minor modifications of the software program, this tool can be used for other types of implants.

Radiographic evaluation of Charnley cups used in first-time revision: repeated observations for 7-15 years

The radiographs of 46 consecutive polyethylene cups used in cemented first-time revision of the acetabulum were studied up to a mean of 10.7 years (range, 0.5-16.3 years). Six cups developed loosening, of which 2 were revised. New radiolucent lines appeared mainly up to the 3 years follow-up. Progression of radiolucencies to new regions was noted in 28 (61%) cups. This progression occurred as an increase in extension from the periphery to the central region of the interface, whereas the width only showed minor changes. Our findings indicate that even radiolucent lines with a width <1.0 mm should be given attention because these lines can surround the cup before significant migration (>5 mm) is established. True lateral radiographs exposed to visualize the interface add information concerning presence of loosening. According to our opinion, complete radiolucent lines on either the anterior-posterior or lateral view, with a width of 0.3 to 0.5 mm or more, should be regarded as radiographic failure.

Automated image analysis technique for measurement of femoral component subsidence in total hip joint replacement

A new technique for the measurement of subsidence of the femoral components is proposed. The method relies on the implantation of two ball markers around the femoral stem. A single radiographic image of the hip is analysed using image-processing techniques to minimize subjectivity related to manual identification of landmarks. Dimensions of the stem are used to correct for magnification and out-of-plane rotations resulting from radiographic positioning. This technique has been applied to a specific design of implant (Exeter). A study of the effect of radiographic positioning has been conducted using a cadaveric bone phantom. Results for the variation in the measurement of axial migration compared to the neutral position (in millimetres) were: 0.942 (10 degrees extension); 0.347 (20 degrees flexion); -0.435 (40 degrees internal rotation); 0.187 (30 degrees external rotation) for distances measured between the bone marker and the implant. Results for distances measured between the implant and the cement centralizer were: 0.107 (10 degrees extension); -0.277 (20 degrees flexion); 0.085 (40 degrees internal rotation); 0.280 (30 degrees external rotation). The variations from within a more realistic range of positions demonstrate that axial migration measurements of ca. 0.5 mm between the bone and implant, and less than 0.3 mm between the implant and the bone cement, may be expected.

Pose estimation of artificial hip joint using a single radiographic projection

Total hip joint arthroplasty is commonly used in cases of osteoarthritis and rheumatoid arthritis. A hip joint prosthesis consists of a cup and a stem. The relative pose (position and orientation) of the prosthesis, when the patient is standing naturally, is planned pre-operatively; however, there is no guarantee that the pre-operatively planned pose will be accurate. Prosthesis component malposition, which is inadequate positioning of the acetabular or femoral component, results in limited joint movement and a large prosthetic joint contact area, and this can cause dislocation of the femoral head from the cap. Because the range of motion after total hip joint arthroplasty is determined by the relative pose of the cup and the stem, it is important to know the relative pose after hip arthroplasty. Several pose estimation methods using single-plane fluoroscopy or conventional roentgenography have been proposed. Because a conventional radiograph system is commonly used at small cost, a method using conventional radiograms is desirable for use in a clinical setting. In this study, a pose estimation method using conventional radiography is proposed, and an in vitro experiment is performed to evaluate its accuracy. The rotational errors of the relative pose of the cup with respect to the stem were smaller than 2.3 degrees.

Direct plain radiographic methods versus EBRA-Digital for measuring implant migration after total hip arthroplasty

We aimed to determine whether the precision and sensitivity of migration measurements after total hip arthroplasty (THA) using direct plain radiographic techniques could be made comparable to those of digital methods (EBRA-Digital; University of Innsbruck, Innsbruck, Austria) by careful control of radiographic technique and use of modern measuring tools. Precision was examined by analysis of consecutive radiographs taken after repositioning in 20 patients after hybrid THA. The precision (95% confidence interval) of measurements for cup migration using direct methods was +/-1.11 to 3.07 mm (x-axis) and +/-1.28 to 1.92 mm (y-axis). The precision of EBRA for cup measurements was +/-1.00 mm (x-axis) and +/-0.82 mm (y-axis). The precision of stem y-axis migration measurements was +/-1.12 to 6.91 mm using direct methods and +/-0.80 mm using EBRA. Migration of the stem (1.53 mm subsidence; P<.01) and the cup (0.53 mm cranial migration, P<.05) was detected using EBRA in 10 patients followed for 6 months after hybrid THA, but significant migration was not detectable using the most precise of the direct methods. Careful measures to standardize plain radiographs improve precision of direct radiographic measurements; however, their long-term sensitivity remains inferior to methods that employ quality control and measurement algorithms to measure migration from digitized radiographs.

Precision of EBRA-Digital software for monitoring implant migration after total hip arthroplasty

We assessed the precision of the EBRA-Digital software (EBRA, University of Innsbruck, Innsbruck, Austria) for measuring implant migration after total hip arthroplasty. Study subjects (n = 29) underwent consecutive, standardized, plain radiographic examinations of the hip on the same day after repositioning. The resulting radiograph pairs were digitized and analyzed using EBRA. The precision (95% confidence interval) of the method for measuring migration and wear was <+/-0.9 mm for both implant components. The 95% confidence intervals for measurement of cup inclination and anteversion and femoral stem/shaft angle were <+/-1.7 degrees. Measurement precision was not strongly related to patient gender, digitization method, or observer. The EBRA-Digital method has sufficient precision to detect clinically relevant migration to allow individual patient monitoring after total hip arthroplasty. The method requires careful patient positioning and radiographic technique to produce consistently images suitable for analysis.