Modern dual-mobility cup implanted with an uncemented stem: about 100 cases with 12-year follow-up

We report the results of a 12-year follow-up retrospective series of 100 total hip arthroplasties using cementless, press-fit, dual-mobility acetabular cups. The aim of our study was to evaluate the clinical and radiographic results of this acetabular cup at last follow-up. This continuous and homogeneous series included 100 primary total hip arthroplasties performed during the year 2000. The THA combined a Corail® stem (Corail®, Depuy, Warsaw, IN) with a stainless steel Novae Sunfit® (Serf, Decines, France) acetabular cup. Fifteen patients died and 2 were lost to follow-up. Two cases of early dislocation were observed, and 3 cases of aseptic loosening of the acetabular component were reported. The mean stem subsidence was 0.71 mm, the mean craniopodal acetabular migration was 1.37 mm, and the mean medio-lateral acetabular migration was 1.52 mm. The 12-year survivorship is comparable to the data from the literature. The low dislocation rate at 12 years confirms the long-term, high stability of dual mobility, which should be recommended in primary THA for patients at risk for postoperative instability. The absence of true intraprosthetic dislocation events at 12-year follow-up provides evidence of the good quality of the latest generation of polyethylene liners and the necessity of combining thin-mirror, polished femoral necks with dual-mobility cups.

[More muscle mass in men: explanatory model for superior outcome after total hip arthroplasty]

BACKGROUND

Men show better functional results after total hip arthroplasty (THA). The aim of this study was a patient-specific analysis of the hip joint muscles in comparison to the joint geometry.

METHODS

In this study 93 computed tomography (CT) scans of the pelvis (45 men, 48 women) were analyzed to determine hip joint geometry and the volume of the gluteus medius (GMV), gluteus maximus (GXV) and tensor fasciae latae (TFL) muscles. The abduction muscle volumes were analyzed with respect to patient-specific adduction moments.

RESULTS

The absolute total volume of the hip muscular system (TMV) was larger in men than in women (1913 ccm vs. 1479 ccm; p <0.0001). Men exhibited a more progressive increase of muscle volume as the adduction moment increases.

CONCLUSIONS

Men have a greater abduction muscle mass in order to balance adduction moments occurring in the hip joint and therefore have more muscle mass to compensate the inevitable intraoperative muscle damage during THA. This argument supports the extraordinary importance of muscle sparing surgical techniques in women.

The dual radius hemispherical 'Trident" cup: results based on 150 consecutive cases

INTRODUCTION

Initial stability with press-fit cups can be achieved in a number of ways based on the design of the cup. With line-to-line fit, screws fixation, press-fit of 1 to 2 mm which is obtained by an oversized hemispherical cup, initial stability can be achieved with the dual-radius press-fit cups, which have an equatorial diameter 1 to 2 mm greater than that of the polar diameter, to ensure a good press-fit and to provide adequate initial stability for bone ingrowth to occur reliably.

METHODS

Between January 2002 and January 2008, 400 total hip replacements (THRs) were carried out. We examined the first 150 consecutive primary THRs. In all hips, the acetabular component was the dual radius Trident AD shell (Stryker Orthopaedics, Mahwah, New Jersey).

RESULTS

The median duration of follow-up was 6,2 yrs (range, 5 to 7 yrs). The median post-operative Harris Hip Score for 150 hips was 90.5 (range, 51 to 98). At the time of the latest follow-up, there was a bony incorporation of all components; we found no definite evidence of radiographic loosening and no signs of radiolucency.

CONCLUSION

According to the encouraging results of the present study we conclude that the Trident cup is a valid choice for acetabular replacement.

[Arthroplasty registers as post-marketing surveillance systems: the Catalan Arthroplasty Register]

OBJECTIVE

The aim is to present the functioning and results of the Catalan Arthroplasty Registry (RACat).

MATERIAL AND METHOD

The RACat arose by the initiative of the Catalan Society of Orthopaedic Surgery and Traumatology, the Catalan Health Service (CHS) and the Catalan Agency for Health Information Assessment and Quality. Publicly funded hospitals sent information through the Internet (CHS Applications website) on knee and hip arthroplasties: patient identification, hospital, joint (hip/knee), type (primary/revision), side of operation, date of surgery and prosthesis (manufacturer's name and reference number). The quality of the data is analysed regularly. We estimate the risk of replacement by the Kaplan-Meier method.

RESULTS

A total of 52 hospitals out of 62 send data to RACat, and information on 36,951 knee and 26,477 hip arthroplasties is available. Data quality improved between 2005 and 2010. In 2010 coverage exceeded 70%, with side of operation 97%, and prostheses identification of 80%. The risk of replacement at three years was 3.3% (95% CI:3.1-3.6) for knee, 2.9% (95% CI:2.5-3.3) for total hip, and 2.5% (95% CI:2.0-3.1) for partial hip.

DISCUSSION

Risk of replacement is higher than that observed in other registers, although data quality and its improvement over time should be taken into account.

CONCLUSIONS

The information available in the RACat will help to establish a standard that will enable hospitals to compare results.

Risk of cancer with metal-on-metal hip replacements: population based study

OBJECTIVE

To assess the risk of cancer associated with modern primary metal-on-metal hip replacements.

DESIGN

Population based study.

SETTING

Nationwide retrospective comparative register.

PARTICIPANTS

10,728 patients who underwent metal-on-metal total hip arthroplasty and 18,235 patients who underwent conventional metal-on-polyethylene, ceramic-on-polyethylene, and ceramic-on-ceramic total hip arthroplasty (the non-metal-on-metal cohort) in the Finnish Arthroplasty Register 2001-10. Data on cancer cases up to 2010 for these cohorts were extracted from the Finnish Cancer Registry.

MAIN OUTCOME MEASURES

The relative risk of cancer was expressed as the ratio of observed to expected number of cases from the Finnish population--that is, the standardised incidence ratio. The relative risk of cancer in the metal-on-metal cohort compared with the non-metal-on-metal cohort was estimated with analyses of these ratios and Poisson regression.

RESULTS

The overall risk of cancer in patients with metal-on-metal hip implants was similar to that in the Finnish population (378 observed v 400 expected, standardised incidence ratio 0.95, 95% confidence interval 0.85 to 1.04). The overall risk of cancer in patients with metal-on-metal hip implants was also no higher than in patients who had received non-metal-on-metal hip implants (relative risk 0.92, 0.81 to 1.05).

CONCLUSIONS

Metal-on-metal hip replacements are not associated with an increased overall risk of cancer during a mean follow-up of four years.

Hip resurfacing arthroplasty: short-term survivorship of 4,401 hips from the Finnish Arthroplasty Register

BACKGROUND AND PURPOSE

Population-based registry data from the Nordic Arthroplasty Register Association (NARA) and from the National Joint Register of England and Wales have revealed that the outcome after hip resurfacing arthroplasty (HRA) is inferior to that of conventional total hip arthroplasty (THA). We analyzed the short-term survival of 4,401 HRAs in the Finnish Arthroplasty Register.

METHODS

We compared the revision risk of the 4,401 HRAs from the Register to that of 48,409 THAs performed during the same time period. The median follow-up time was 3.5 (0-9) years for HRAs and 3.9 (0-9) years for THAs.

RESULTS

There was no statistically significant difference in revision risk between HRAs and THAs (RR = 0.93, 95% CI: 0.78-1.10). Female patients had about double the revision risk of male patients (RR = 2.0, CI: 1.4-2.7). Hospitals that had performed 100 or more HRA procedures had a lower revision risk than those with less than 100 HRAs (RR = 0.6, CI: 0.4-0.9). Articular Surface Replacement (ASR, DePuy) had inferior outcome with higher revision risk than the Birmingham Hip Resurfacing implant (BHR, Smith & Nephew), the reference implant (RR = 1.8, CI: 1.2-2.7).

INTERPRETATION

We found that HRA had comparable short-term survivorship to THA at a nationwide level. Implant design had an influence on revision rates. ASR had higher revision risk. Low hospital procedure volume worsened the outcome of HRA. Female patients had twice the revision risk of male patients.

Cross-sectional analysis of association between socioeconomic status and utilization of primary total hip joint replacements 2006-7: Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

The utilization of total hip replacement (THR) surgery is rapidly increasing, however few data examine whether these procedures are associated with socioeconomic status (SES) within Australia. This study examined primary THR across SES for both genders for the Barwon Statistical Division (BSD) of Victoria, Australia.

METHODS

Using the Australian Orthopaedic Association National Joint Replacement Registry data for 2006-7, primary THR with a diagnosis of osteoarthritis (OA) among residents of the BSD was ascertained. The Index of Relative Socioeconomic Disadvantage was used to measure SES; determined by matching residential addresses with Australian Bureau of Statistics census data. The data were categorised into quintiles; quintile 1 indicating the most disadvantaged. Age- and sex-specific rates of primary THR per 1,000 person years were reported for 10-year age bands using the total population at risk.

RESULTS

Females accounted for 46.9% of the 642 primary THR performed during 2006-7. THR utilization per 1,000 person years was 1.9 for males and 1.5 for females. The highest utilization of primary THR was observed in those aged 70-79 years (males 6.1, and females 5.4 per 1,000 person years). Overall, the U-shaped pattern of THR across SES gave the appearance of bimodality for both males and females, whereby rates were greater for both the most disadvantaged and least disadvantaged groups.

CONCLUSIONS

Further work on a larger scale is required to determine whether relationships between SES and THR utilization for the diagnosis of OA is attributable to lifestyle factors related to SES, or alternatively reflects geographic and health system biases. Identifying contributing factors associated with SES may enhance resource planning and enable more effective and focussed preventive strategies for hip OA.

Failure rates of stemmed metal-on-metal hip replacements: analysis of data from the National Joint Registry of England and Wales

BACKGROUND

Total hip replacement (THR) is extremely common. Some prostheses fail, particularly in younger patients, and need to be revised, most commonly for loosening secondary to wear or dislocation. Surgeons have tried to address these problems by implanting large diameter metal-on-metal bearing surfaces. Our aim was to assess if metal-on-metal bearing surfaces lead to increased implant survival compared with other bearing surfaces in stemmed THR and, additionally, if larger head sizes result in improved implant survival.

METHODS

We analysed the National Joint Registry of England and Wales for primary hip replacements (402,051, of which 31,171 were stemmed metal-on-metal) undertaken between 2003 and 2011. Our analysis was with a multivariable flexible parametric survival model to estimate the covariate-adjusted cumulative incidence of revision adjusting for the competing risk of death.

FINDINGS

Metal-on-metal THR failed at high rates. Failure was related to head size, with larger heads failing earlier (3·2% cumulative incidence of revision [95% CI 2·5-4·1] for 28 mm and 5·1% [4·2-6·2] for 52 mm head at 5 years in men aged 60 years). 5 year revision rates in younger women were 6·1% (5·2-7·2) for 46 mm metal-on-metal compared with 1·6% (1·3-2·1) for 28 mm metal-on-polyethylene. By contrast, for ceramic-on-ceramic articulations larger head sizes were associated with improved survival (5 year revision rate of 3·3% [2·6-4·1] with 28 mm and 2·0% [1·5-2·7] with 40 mm for men aged 60 years).

INTERPRETATION

Metal-on-metal stemmed articulations give poor implant survival compared with other options and should not be implanted. All patients with these bearings should be carefully monitored, particularly young women implanted with large diameter heads. Since large diameter ceramic-on-ceramic bearings seem to do well we support their continued use.

FUNDING

National Joint Registry of England and Wales.

Combined multi-body and finite element investigation of the effect of the seat height on acetabular implant stability during the activity of getting up

An important question in assessing the stability of a total hip arthroplasty is the effect of daily physical activities of patients. The aim of this study is to examine these effects when standing up from three different seat heights. A musculoskeletal body model has been modified to simulate the three different seat heights. The calculated muscle forces have been transferred to a finite element model of a pelvis. The pelvis model was created from a hemipelvis CT dataset. As an implant component, a metal socket with a polyethylene insert was used. A primary implantation situation was modelled. For the analysed patient activities the highest hip contact forces and the highest micromotions occur at the beginning of the motion. The results of this study show that standing up from a certain seat height can have a significant influence on the micromotions in the implant-bone interface.

Distance visualization for interactive 3D implant planning

An instant and quantitative assessment of spatial distances between two objects plays an important role in interactive applications such as virtual model assembly, medical operation planning, or computational steering. While some research has been done on the development of distance-based measures between two objects, only very few attempts have been reported to visualize such measures in interactive scenarios. In this paper we present two different approaches for this purpose, and we investigate the effectiveness of these approaches for intuitive 3D implant positioning in a medical operation planning system. The first approach uses cylindrical glyphs to depict distances, which smoothly adapt their shape and color to changing distances when the objects are moved. This approach computes distances directly on the polygonal object representations by means of ray/triangle mesh intersection. The second approach introduces a set of slices as additional geometric structures, and uses color coding on surfaces to indicate distances. This approach obtains distances from a precomputed distance field of each object. The major findings of the performed user study indicate that a visualization that can facilitate an instant and quantitative analysis of distances between two objects in interactive 3D scenarios is demanding, yet can be achieved by including additional monocular cues into the visualization.

Surgical treatment outcome evaluation of hip joint acetabular fracture

Since November 1989 till the end of 2007 year we have been operatively treating 752 of acetabular hip fractures. We have analised 750 operated patients, two patients bilateral fractures. The follow up span lasts from 2 till 20 years. The age of treated patients is from 14 till 79 years old. These fractures were divided into those operated to 21 days after trauma--569 operated acetabulum. And those operated after 21 days after trauma--183 patients with the delayed reconstruction of acetabular fractures from 22 till 229 days. Both groups were provided detailed assesement. And next we compared fracture reduction of broken acetabulum and assesement of clinical treatment. The types of fractures were defined according to classification of Judet-Letournel. The criteria of fracture reduction due to Letournel. The clinical result was based on Merle d'Aubigne-Matta scale. In the group of treated patients till 3 weeks after trauma, we have received 83.8% of very good and good results, 6.9% fair results and 9.3% poor results. During fracture reduction: 75% very good, 4% in secondary joint congruence, 17.8% fair and 3.2% poor. After fair reduction there was always the right congrugence between the head and acetabulum. The displacements to 3 mm were left in more cases as a part after weight-bearing area. In trauma fracture trated after 3 weeks, the result was very good and good 66.1%, fair 14.8% and poor 19.1%. During fracture reduction: 49.7% very good, 4.4% secondary joint congruence, 32.8% fair and 13.1% poor. We have noticed the crucial corelation between fracture reduction and the final result of treatment. Additional traumae, especially head with long time loss of consciousness and the traumae of chest with insufficient breathing have indirect infulence on treatment results causing the longer operation waiting. The complexity fractures also indirectly influence on the result of treatment decreasing the chances on anathomical fracture reduction.

[Survivorship of the cemented hip prosthesis]

OBJECTIVES

To asses a survival-time of the cemented hip prostheses and to find factors causing its loosening.

MATERIALS AND METHODS

211 patients (282 hip prostheses) were analyzed, of the 1693 patients (2096 hip prostheses) treated between 1970-2000. The follow-up ranged from 7 to 34 years (mean: 12.2 ++/- 5.4 years). The age of the patients at the operation procedure ranged from 25 to 74 years (mean 52 +/- 12 years). Only aseptic prosthesis loosening were considered and Kaplan-Meyer method was used for the prosthesis survivorship assessment.

RESULTS

Of the 282 prostheses, implant exchange was performed in 39 cases, where in 15 cases only cup was revised, in 5 cases the stem exclusively, and in 19 patients the whole implant was exchanged. Only 1.1% of implants were exchanged during first 5 years after surgery but from the 6th year the percentage of loosening increased several percents each year. Respectively 88.6, 70 and 65% survivorship of prosthesis was found after 10, 15, 20 years of follow-up. In the group of bilateral prosthesis implantation, the first implanted prosthesis was more susceptible for loosening. Seven cases of aseptic loosening (5.4%) of the 129 prostheses implanted between 1974 and 1995, occurred within 7 years after initial surgery where only one prosthesis (0.7%) was revised of the 152 implanted between 1996-2000 in the same time of follow-up. The age, growth, weight, BMI and sex did not influence the risk of implant loosening.

CONCLUSION

The mean survivorship of the hip prosthesis is 65% in 20- years follow up. When a proper initial fixation of the cemented hip prosthesis is performed, the risk of implant loosening increases gradually especially from the 6th year after surgery. The modern implants are less susceptible for loosening.

Femoral revision with taper stems: results at ten years follow-up

In the case of extensively damaged meta-diaphyseal femoral bone with cortices thinning and widened femoral canal, tapered stems allow a good primary fixation and early weight-bearing. A retrospective review was conducted to evaluate long-term results of modular revision taper stems implanted from March 1999 to December 2002. Sixty-five consecutive hip revision surgeries were performed, mostly for aseptic loosening (75% of the cases). Femoral bone stock defects were classified according to AAOS's criteria and consisted mainly in type II (cavitary defects, 44.6%) and type III (combined defects, 33.9%). A trochanteric osteotomy was performed in 25 cases (38%) to remove primary implants that were cemented in 35 cases (54%). The mean postoperative follow-up was 109 months (range, 76 to 131 months). Clinical assessment at follow-up showed a significantly improved mean Harris Hip Score from 42 points preoperatively to 81 points postoperatively, while the x-ray examination did show a satisfactory distal integration of the stem in all cases and satisfactory reconstitution of the femoral bone stock in 47% of cases. The average subsidence of the stem at follow-up was less than one millimeter. According to data analysis, a leg-length discrepancy exceeding 15 millimeters caused significantly worse functional outcome and pain.

[Revision arthroplasty of the hip: modularity of neck and metaphyseal components]

BACKGROUND

Modular parts in femoral components used for hip arthroplasty are reported to be predilection sites for mechanical failure. The possible benefit of their use is therefore controversial.

PATIENTS AND METHOD

We report the outcome of 97 revision hip arthroplasties using a non-cemented femoral component with a modular metaphyseal part and an interchangeable neck (Profemur). The femoral defects treated included Paprosky types I-III. The average follow-up was 5 years (range 3-10 years).

DISCUSSION

No mechanical failure of the modular parts and taper connections has been observed so far. The percentage of patients with a balanced leg length increased from 32% preoperative to 65% postoperative. The mean leg length discrepancy could be reduced from 1.4 cm preoperative to 0.5 cm postoperative. A total of 5 re-revisions were required, including 2 cases of infection. The cumulative survival of the implants due to aseptic loosening was 96.5%.

CONCLUSION

Because of the achieved results the use of the modular stem investigated in this study can be classified as safe and effective for revision hip arthroplasty. The interchangeable neck proved to be a useful completion of the revision system.

Ceramic on crosslinked polyethylene in total hip replacement: any better than metal on crosslinked polyethylene?

The authors evaluated the use of ceramic femoral heads on crosslinked polyethylene bearing couples versus metal on crosslinked polyethylene couples in a consecutive series of hips performed by a single surgeon over a one year interval. Ceramic femoral heads and more extensively crosslinked polyethylene were used more commonly in the younger aged patients with utilization of ceramic heads in patients average age 50.2 versus 63.9 for metal heads, and utilization of more extensively crosslinked polyethylene in patients average age 54.1 versus 77.2 years for patients receiving less extensive crosslinked polyethylene. The authors explain the cost effectiveness of this approach where the difference in cost is approximately 36%.

Cementing the metaphyseal stem in metal-on-metal resurfacing: when and why

Initial fixation of the femoral component in hip resurfacing is key to the enduring survival of the prosthesis. Cementing the metaphyseal stem increases the interface area between bone and cement. We compared the clinical and survivorship results of two groups in a cohort of 1000 hips (838 patients) implanted with Conserve((R)) Plus hip resurfacing; one group was resurfaced with a cemented metaphyseal stem (400 hips; Group 1) and the other with a press-fit stem (600 hips; Group 2). We carried out a time-dependent analysis to determine the indications for cementing the stem. The 5-year Kaplan-Meier survival estimate was 98.2% for Group 1 and 94.4% for Group 2, using any revision as an endpoint. Femoral aseptic failure was reduced in Group 1 compared to Group 2. Cementing the metaphyseal stem is particularly effective for hips with a small femoral component size (< 48 mm) and hips with large femoral defects (> 1 cm). There was no difference between groups in incidence of femoral neck narrowing or femoral neck fractures. Longer followup is needed to determine if cementing the stem can be detrimental to the long-term durability of the femoral implant.

LEVEL OF EVIDENCE

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

Cost drivers in total hip arthroplasty: effects of procedure volume and implant selling price

Total hip arthroplasty (THA), though a highly effective procedure for patients with end-stage hip disease, has become increasingly costly, both because of increasing procedure volume and because of the introduction and widespread use of new technologies. Data regarding procedure volume and procedure costs for THA were obtained from the National Inpatient Sample and other published sources for the years 1995 through 2005. Procedure volume increased 61% over the period studied. When adjusted for inflation, using the medical consumer price index, the average selling price of THA implants increased 24%. The selling price of THA implants as a percentage of total procedure costs increased from 29% to 60% during the period under study. The increasing cost of THA in the United States is a result of both increased procedure volume and increased cost of THA implants. No long-term outcome studies related to use of new implant technologies are available, and short-term results have been similar to those obtained with previous generations of THA implants. This study reinforces the need for a US total joint arthroplasty registry and for careful clinical and economic analyses of new technologies in orthopedics.

Hemiarthroplasty of the hip for fracture-what is the appropriate sized femoral head?

INTRODUCTION

Caliper measurement of the excised femoral head is a standard technique for determination of prosthetic head size during hemiarthroplasty for displaced femoral neck fractures.

OBJECTIVES

To evaluate the accuracy of the caliper method of hemiarthroplasty head sizing by comparing it to the native joint congruency (JC) at the weight bearing surface.

MATERIALS AND METHODS

The diameters of femoral heads in 10 cadaver hip joints were measured by using a caliper at the head equator. Cast moulds were prepared from both the acetabulum and the femoral head in each joint. Every mould's exact spherical diameter at the weight bearing region was measured by a computerised coordinate measuring machine (MNC B231 MITUTOYO). All specimens were coded to ensure that future examination was carried out in a blind manner. Native JC mismatch was determined by subtracting the diameter of the femoral cement mould from that of the acetabular one. Similarly, JC mismatch was calculated for the caliper measurements.

RESULTS

The average native JC mismatch (0.36+/-0.29mm, range 0.03-0.82mm, median 0.29mm) was found significantly smaller (p=0.03) than following caliper measurements (0.72+/-0.37mm, range 0.37-1.46mm, median 0.6mm). Routine caliper measured downward size rounding enhanced (p=0.004) this mismatch (0.98+/-0.44mm, range 0.37-1.96mm, median 1.01mm), while upward rounding (0.48+/-0.46mm, range -0.06 to 1.15mm, median 0.41mm) helped mitigate this tendency.

CONCLUSIONS

Caliper measurements tend to undersize the actual sphere diameter of the femoral head at the weight bearing region. Upward rounded prosthesis should be selected in order to compensate for this propensity.

Acetabular augmentation ring for recurrent dislocation of total hip arthroplasty: 60% stability rate after an average follow-up of 74 months

Between 1988 and 2002, 47 patients (50 hips) were treated with acetabular shell augmentation arthroplasty for recurrent idiopathic dislocation of their total hip arthroplasty. Apparent causes for dislocation such as deep infection, component malposition, or polyethylene wear were excluded. Follow-up averaged 74 months (range, 12-178 months), and clinically, 30 hips (60%) did not present a subsequent dislocation at most recent follow-up. In five hips (10%), deep infection after the augmentation procedure necessitated removal of the entire prosthesis. In our opinion, this technique cannot be recommended as it has an unacceptable failure and high infection rate.

[Effects of hospital and surgeon procedure volume on outcome in total hip replacement]

AIM

According to the "practice makes perfect" hypothesis, the mortality rates of many surgical procedures are inversely related to hospital and surgeon procedure volume. Currently there is a discussion regarding the implementation of high-volume centres for total hip replacement. Nevertheless, the body of evidence describing such an association is weak. Therefore the American National Cancer Policy Board came up with four evidence criteria describing a valid association between volume and outcome: 1) the association must be logical, 2) the association must be consistent in all studies, 3) the size of the measured effect must be substantial and clinically relevant and 4) the effect has to be reproducible in clinical studies.

METHOD

We searched MEDLINE and EMBASE (1996 until November 2006) using the following "medical subject headings" (MeSH): "Arthroplasty, Replacement, Hip" or "Hip Prosthesis" and "Volume". We searched for full articles that reported on an association between hospital and surgeon procedure volume and outcome after total hip replacement. No language restriction was applied.

RESULTS

We found 17 relevant studies in MEDLINE and EMBASE. The outcome after primary hip prosthesis and revision hip prosthesis was better when performed in high-volume hospitals or by high-volume surgeons. Depending on the cut-off for the definition of "high volume" and "low volume" the results could be statistically significant.

CONCLUSION

Many of the included studies were of minor quality, the data were often not comparable between studies. Therefore, the results are not directly transferable to our medical system in Germany. Applying the criteria designed by the American National Cancer Policy Board on the studies about procedure volume and outcome after total hip replacement yields the following result: 1) the association must be logical: Yes. 2) The association must be consistent in all studies: Yes. 3) The size of the measured effect must be substantial and clinically relevant and has to be analysed using validated statistical criteria: No. 4) The effect has to be reproducible in clinical studies: No.