Survival of short hip stems with a modern, trochanter-sparing design-a systematic literature review, E Rometsch, PK Bos, BW Koes

Tags: stems, survival rate, systematic literature review, Hip Arthroplasty, survival results, Clin Orthop Relat Res, total hip arthroplasty, Wichtig Editore, stem, publications, femoral neck, revision, literature review, survival rates, National Joint Registry, presented, observational studies, observed component, total hip replacement, Barresi C. Perspectives, arthritis of the hip, Passariello R. Effect, Grandizio M. Preservation, replacement, greater trochanter, modern design, hip resurfacing, Arthroplasty, The Netherlands, Wohlrab D. Experience, Miller J. Medium, Sahlgrenska University Hospital, National Institute of Clinical Excellence U. Technology Appraisal Guidance, Annual Report, hip replacement surgery, subgroup, quality assessment, quality assessments, UK registry, subgroup analyses, OHS, component, patient populations, Rheumatoid arthritis, Patient population, National Institute of Clinical Excellence, Financial support, Osteoarthritis, implantation, arthritis, included patients, Murray D. Questionnaire
Content: Hip Int 2012 ; 22 ( 04 ): 344 - 354 REVIEW
DOI: 10.5301/HIP.2012.9472
Survival of short hip stems with a "modern", trochanter-sparing design - a systematic literature review Elke Rometsch 1,2, Pieter K. Bos 1, Bart W. Koes 2 1 D epartment of Orthopaedics, Erasmus Medical Centre, Rotterdam - The Netherlands 2 D epartment of General Practice, Erasmus Medical Centre, Rotterdam - The Netherlands Abstract: Modern total hip arthroplasty delivers excellent and reproducible results. New implant developments include a wide range of implants with a bone and tissue sparing design, including short femoral stems. This review was performed to provide an overview on the currently published survival results of short stems to allow comparison with the results of traditional hip stems. A literature search was performed to identify publications on short stems with a "modern" trochanter sparing design including implant survival information. Information was collected on the study population, follow-up time, implants used, implant survival and functional scores. The revision rate per 100 observed component years was calculated and compared to data presented in national arthroplasty registries. The methodological quality was assessed by employing a score specific to survival assessment of hip stems. In the course of 16 individual searches in EMBASE and Medline, 460 potentially eligible articles were identified. After thorough screening, 14 articles were deemed applicable. The variability in quality of the publications was high. No Association between survival outcome and publication quality was apparent. The total revision rate over all studies was found to be 0.38 per 100 component years with endpoint "stem revision for any reason". The survival rate of these stems is encouraging and appears to be comparable with that of more traditional uncemented stems. However, only few mid-term and long-term studies are available. Reports with longer follow-up are needed to draw further conclusions. Key words: Arthroplasty, Total hip replacement, Short stem, Systematic literature review Accepted: April 08, 2012
INTRODUCTION The good long-term results of total hip arthroplasty (THA) led to an extension of the procedure to younger patients, who frequently hold higher expectations. Such young patients hope to restore their quality of life, often including high-activity recreational interests (1), which may result in a number of revision procedures within their lifetime. Manufacturers have reacted to this by attempting to extend the
lifetime of implants and by developing bone preserving prosthetic designs. Bone preserving designs include hip resurfacing with epiphyseal anchorage, femoral neck prostheses with metaphyseal anchorage, and short stems with metaphyseal and limited diaphyseal anchorage (2). Short stems are anchored in the metaphysis of the femur and their distal part extends into the upper diaphysis. They may either be curved or straight and the straight ones may
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or may not have a reduced shoulder. The latter typically require straight rasping, which involves a similar amount of bone loss in the trochanteric region as traditional straight stems. This leads to less tissue sparing at the abductor insertion on the greater trochanter, but they conserve a considerable amount of bone distally. It remains unclear whether these implants perform as well as traditional hip stems, and randomised controlled trials (RCTs) are scarce. At present, only one RCT on short stems has been published (3). The "Guidance On The Selection Of Hip Prostheses" issued by the National Institute of Clinical Excellence in the UK defines a benchmark performance of 90% cumulative survival at 10 years in combination with a significant improvement in pain and mobility (4). Survival is usually measured with cumulative survival functions or with calculations of survival per 100 observed component years. Pain and mobility are typically measured in combined functional scores such as the Harris hip score (HHS) (5), the Merle D'Aubignй score (MDA) (6) or the Oxford Hip Score (OHS) (7). The objective of this systematic literature review was to summarise the survival and the functional results of short hip stems with a "modern design" and put the survival results in relation to information published in independent national registries. A quality assessment of the identified literature was performed and the potential influence of study quality on the reported survival rates was assessed. MATERIALS AND METHODS Literature selection We concentrated on short stems with a "modern", trochanter- sparing design, defined as being uncemented, with a proximal metaphyseal and short diaphyseal anchorage, typically not extending beyond 12 cm in the majority of sizes, with a trochanter sparing resection (i.e. no straight rasping), and with or without a neck-sparing resection. Current brands that meet these criteria include the Mayo (Zimmer, Warsaw, USA), CFP (Waldemar Link, Hamburg, Germany), Taperloc Microplasty (Biomet, Warsaw, USA), Fitmore (Zimmer, Warsaw, USA), Nanos (Smith & Nephew, London, UK), Metha (B. Braun, Melsungen, Germany), M/L taper (Zimmer, Warsaw, USA) and Proxima (De Puy, Warsaw, USA).
We did not include short stems requiring straight rasping, as well as femoral neck prostheses. For prostheses where classification did not seem straightforward, we referred to other authors' classifications, e. g. the ESKA CUT (ESKA Implants) has previously been classified as a "neck prosthesis" and was thus not considered (8). A literature search was performed in EMBASE and Medline in August 2010 to identify publications on short stems with a "modern" trochanter sparing design that present information about the survival of these types of implants. Initially, generic Search Terms ("short stem") and all brand names of potentially eligible stems that were known to the authors were used. All potentially eligible brand and generic names mentioned in the identified literature not previously considered were then searched for. Finally, after determination of eligibility, the reference lists of all eligible articles was screened for further potentially eligible Peer Reviewed journal publications. Details on the search strategy are given in Table I.
TABLE I - SEARCH STRINGS AND NUMBER OF RESPECTIVE HITS USED DURING THE LITERATURE SEARCHES IN EMBASE AND MEDLINE WHICH TOOK PLACE AUGUST 24, 2010
Hip OR Arthroplasty AND "Short stem" Hip OR Arthroplasty AND (Conservative AND Stem) Hip OR Arthroplasty AND CFP Hip OR Arthroplasty AND Fitmore Hip OR Arthroplasty AND Metha Hip OR Arthroplasty AND Microplasty Hip OR Arthroplasty AND Nanos Hip OR Arthroplasty AND Pipino Hip OR Arthroplasty AND Proxima Hip OR Arthroplasty AND ESKA(df) (Hip OR Arthroplasty AND ("m/l" AND taper)) OR (Hip OR Arthroplasty AND ("m l" AND taper)) OR (Hip OR Arthroplasty AND (ml AND taper)) "Tri lock" OR "Tri-lock" OR Trilock ((Mayo AND Arthroplasty) AND Hip) NOT "mayo clinic" "Mayo Hip" OR "Mayo stem"
50 hits 100 hits 25 hits 10 hits 11 hits 4 hits 2 hits 46 hits 11 hits 38 hits 7 hits 22 hits 108 hits 26 hits
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Two authors independently determined eligibility of publications based on the information given in the title or abstract. In cases where this was problematic, the full text was obtained to allow a valid decision. A consensus method was used to resolve disagreement concerning eligibility. Publications were regarded as eligible when they met the following inclusion criteria: 1.design of the stem was "modern", trochanter sparing, as described above; 2.a minimum of 20 hips were included at the start of the study; 3.a minimum mean follow-up time of one year was pre- sented; 4.information on survival or information facilitating calcu- lation of survival was presented; 5.articles were in English, Spanish, Dutch or German. In case of duplicate or near duplicate studies (i.e. studies dealing with the same population but with different follow up times or different outcome measures), only the study with the longer follow-up time and/or more detailed presentation of the relevant outcomes was included in the review. Data extraction Information was collected on the study population, followup time, implants, survival of the implant and functional scores, using a standardised data extraction form. Data on survival were independently extracted by two authors. A consensus method was used to resolve disagreement. The remaining information was extracted by one author. Data synthesis For the calculation of prosthesis survival, cumulative survival (Kaplan Meier) is seen as the Gold Standard. However, calculation of revisions per 100 observed component years is also a valid instrument and may have advantages when the available follow-up time is short. This method is used in the Australian Orthopaedic Association National Joint Registry (AOANJRR) besides cumulative survival estimations, but Kaplan-Meier survivorship is the method of choice for survival or revision rate calculation by both the Swedish Arthroplasty Register and the National Joint Registry of England and Wales. Since very few publications presented information on cumulative survival, we resorted to calculating survival
per 100 component years. The rate of revisions per 100 component years for all explantations, for aseptic loosening and for periprosthetic fractures was calculated as a total over all studies as well as for the individual studies. An overall mean follow-up time was calculated for all studies combined by dividing the total observed component years by the number of patients included. For the purpose of comparison, information regarding survival of similar patient populations was extracted form the latest Annual Reports of the Australian National Joint Replacement Registry (AOANJRR) (9), the Swedish Hip Arthroplasty Register (10) and the National Joint Registry for England and Wales (11). All of these registries present several subgroup analyses, going into detail and resembling the populations subject to this review in varying degrees. In all these subgroup analyses, no differentiation between stem and cup revision is made. For our comparison, we chose the subgroup we found to match our population most closely. In the Australian registry, this was the subgroup of patients of an age between 55 and 64 with a primary diagnosis of osteoarthritis and uncemented fixation. In the UK registry, this was the subgroup of patients of an age between 55 and 64 with uncemented implants. In the Swedish registry, the subgroups of patients of an age between 50 and 59 as well as those of an age between 60 and 75 with all diagnoses and uncemented fixation were deemed of interest; hence the weighted mean of the age group between 50 and 75 was calculated. The AOANJRR is the only registry providing the survival information on subgroups of patients as figures, the other reports only presenting the subgroup analyses in graphs. When this information was solely available on a graph, approximate values extrapolated from the graphs were employed. Assessment of methodological quality Most current quality assessments are designed for RCTs. However, only one of the publications identified in this literature search was an RCT (3). All other articles were observational studies, not uncommon in orthopedics. Recently, a quality assessment list applicable to observational studies in orthopedics was published by Huisstede et al in the context of interventions for radial tunnel syndrome (12). We slightly modified this score, adapting it to the needs spe-
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cific to survival assessment of hip stems. The score (18 items) consists of five domains containing individual items as follows: Study population 1 Inclusion and exclusion criteria described explicitly 2 Sufficient description of baseline characteristics 3 Number of cases 50 4Same implants used in all patients Interventions 5 detailed description of surgical technique 6 Description of implants used: 6a) Information on which cup used 6b) Information on which articulation used study design 7 prospective study design 8 Loss to follow-up/drop-outs: 8a) Information given about reasons for loss to follow-up/ drop-outs 8b) No drop-outs or <2% of loss to follow-up/drop-outs per year 8c) N o drop-outs or item 8a positive and information given about completers versus loss to follow up/dropouts 9Mean follow up time clearly stated as 2 years Outcome measurements 10 Explantation information: 10a) Information on survival provided 10b) In case of explantations: information on causes of ex- plantations provided 11 Description of adverse events provided 12 Interval between measurements identical for all pa- tients 13Standardised or valid measurements used Analysis 14 Cumulative survival calculation presented Two authors independently assessed the quality of each study. A consensus method was used to resolve disagreement. Each item was scored as positive (+), negative (-), or unclear (?) and was given one point when the reviewer assigned a positive (+) score (maximum overall score, 18 points).
RESULTS Eligible literature Based on the literature search, a total of 460 potentially eligible articles were identified. After screening of titles and abstracts, 46 potentially eligible full papers were ordered, except for one article which could not be ordered through our library (13). The ordered articles were further assessed and after application of inclusion and exclusion criteria, 13 articles were deemed appropriate for inclusion. The reference lists of these publications were scanned for further potentially eligible citations which led to identification of another three eligible articles. Screening for overlapping patient populations led to exclusion of two articles as they were considered duplicates (3, 14). Thus, 14 publications were included in this review. Quality assessment The variability in quality was high and ranged between five and 15 on a scale with an 18 point maximum. Table II presents the results of the quality assessment score of each study per domain. Eight of 14 articles scored 50% or more ( 9 points) of the maximum attainable score. No association between survival outcome and methodological quality became apparent when displayed on a scatter plot (Fig. 1). Study population A sufficient description of population baseline characteristics including age, gender distribution and diagnoses was given in 13 of the 14 citations, whereas only five explicitly described inclusion and exclusion criteria for study participation. The same implant was used in all patients in only seven studies, whereby different curvatures of the same stem brands were not considered as different implants. In nine publications, the patient number included at the start was 50 or higher. Intervention A detailed description of the surgical technique which described the approach was given in eight citations. Whilst eleven publications presented information on the em-
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TABLE II - SCORES ON THE METHODOLOGICAL QUALITY ASSESSMENT
Ref.
Population
Interventions
Study design
Outcome measurements
Total Analysis score
1 2 3 4 5 6a 6b 7 8a 8b 8c 9 10a 10b 11 12 13 14
Pipino 2000* 21 - + - + - + - - - + - + - - - - +
-
6
Morrey 2000* 28 + + + - + + - + + + - + + + + + +
+
15
Pipino 2004* 22 - + + - + + - - - - - - + + + - +
-
8
Buecking 2006 25 + + - ? - - - + - + - - + - + + +
-
8
Rцhrl 2006
23 - + - + + + + + + + - + + - + + +
-
13
Falez 2008
17 - + + + - - - - - + - + + + + - +
-
9
Gill 2008
27 + + + + - + + + + + - + + + + - +
+
15
Hagel 2008
20 - - + ? - - - - - - - + + + - - +
-
5
Gilbert 2009 19 - + - + + + - - + + - + + + + - +
-
11
Goebel 2009 15 - + - + + + - + - ? ? + + + + + +
-
11
Synder 2009 24 - + + - - + + - - + - - + - - + +
-
8
Ghera 2009
18 - + + - + + + + + + - - + - + + +
-
12
Briem 2011
26 + + + + + + - - + + - + + + + - +
+
14
Pons 2010
29 + + + - + + + ? + + - + + + + + +
-
14
*Publication with designing surgeon involvement.
Study design As few as six of the studies described a prospective study design. Information on reasons for loss to follow-up was presented in half of the citations. In eleven studies, the rate of loss to follow- up was not higher than 2% per year. None of the studies provided information on the characteristics of study completers compared to those patients who were lost to follow up. In ten studies, the mean follow-up time was clearly stated to be at least two years.
Fig. 1 - Stem revision rate with endpoint "revision for any reason" plotted against quality rating. ployed cup, information on the type of the articulation was given in only five articles. Interestingly, only in one study did a surgeon mention changing strategy intraoperatively to implant a conventional stem. This was made necessary by a patient's unusual anatomy that did not allow implantation the smallest size in the intended manner (15).
Outcome measurements All but one study made explicit statements about survival or explantations, but only nine gave details about the reasons for explantation. Reasons for explantation were periprosthetic fractures in 0-50% and aseptic loosening in 0-100% of all revisions. In eleven publications, a description of adverse events was given and all studies used standardised instruments to evaluate outcome. However, only half of the studies provided information that all patients were seen at the same time points after surgery.
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Analysis Cumulative survival was only presented by three of the 14 publications. OUTCOME Patient population In most articles, patients were in their late fifties or early sixties. In less than half of the publications, the gender distribution was close to equal, whereas in the majority of the remaining studies more women than men were included. Only in two studies the proportion of men was significantly higher than that of women. In nine of the 13 publications, osteoarthritis was the main indication for surgery in 80% of the population (Tab. III).
femoral bone during implantation, load the neck and metaphysis in a near physiological way, construct a biomechanically favorable offset without unduly lengthening the leg and favour less invasive soft tissue handling during implantation" (16). Most of these claims are taken into account when designing the type of implants which were the subject of this review, namely short hip stems with a "modern" trochanter-sparing design. Our study systematically reviewed and assessed the performance of all available studies presenting survival of these types of stems with a minimum follow-up time of one year and a minimum of 20 patients included at the start of the study. Since nearly all of these studies were observational, a special methodological quality assessment tool for observational studies in the orthopedic field was adapted specifically to the needs of survival assessment of hip stems. Identified studies/quality of studies
Clinical performance Survival rates and functional outcome are depicted in Table IV. The postoperative functional scores all demonstrated a significant improvement and range in the upper quintile of the attainable ranges. The revision rates per 100 component years ranged between zero and 3.6. The total revision rate per 100 component years over all studies, based on a total of 7387 observed component years and a mean follow-up time of 4.5 years, was found to be 0.38 with endpoint "stem revision for any reason" of 0.18 for "stem revision for aseptic loosening (AL)" and 0.09 for revision due to periprosthetic fracture. In order to facilitate comparison, survival rates of selected subgroups of patients from the latest annual reports of the major independent national registries are presented in Table V (9-11). Only the Australian registry presents revisions per 100 component years. Even though this is not presented in the other national registries, it may still act as a proxy for cumulative revision rates. DISCUSSION Current developments in the design of hip stems postulate that "a modern femoral implant should spare healthy
Most of the currently available short stems with a "modern", trochanter-sparing design are relatively new. Therefore it was not surprising that even with low entry criteria like a minimum follow- up time of one year and a minimum number of 20 patients at the start of the study, we failed to identify articles on all brands that could have been included in this review had there been any studies published, and we did not identify any studies on Nanos, Taperloc Microplasty, Fitmore and M/L taper. One RCT was identified in the course of the literature search (3). This RCT compared the functional results of the Mayo and the ABG stem three months after surgery and found them to be significantly in favor of the Mayo stem. Since the same group of researchers published a longerterm study on the Mayo stem with an overlapping recruitment period and a larger number of included patients, this RCT is not presented in this review. In many of the studies, important information was not available. Frequently, the description of criteria for study inclusion was unclear (15, 17-24) or information on reasons for loss to follow up was not provided (15, 17, 20-22, 24, 25). Only in half of the studies was it clear that the same implants, including cup and articulation, were used in all patients (15, 17, 19, 21, 23, 26, 27). In some cases no information on cup or articulation was given at all (15, 17, 19-22, 25, 26, 28), and in many publications several types of cups or articulations were used (18, 22, 24, 28, 29), rendering the study groups rather heterogeneous.
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TABLE III - PATIENT POPULATION PARAMETERS OF THE ELIGIBLE PUBLICATIONS
Author Pipino*
Year 2000
Morrey* 2000
Pipino* 2004
Buecking 2006
Rцhrl
2006
Falez
2008
Gill
2008
Hagel
2008
Gilbert 2009 Goebel 2009
Ref.
RCT or pro/ retrospective
21 retrospective
28 prospective
22 retrospective 25 prospective 23 prospective 17 nd
27 prospective
20 retrospective 19 retrospective 15 prospective
Diagnosis Coxarthrosis 93% Rheumatoid arthritis 5% Dysplastic coxarthrosis 2% Osteoarthritis 62% Osteonecrosis 14% Developmental dysplasia 9% Rheumatoid arthritis 8% Traumatic arthritis 4% Slipped epiphysis 3% Coxarthrosis 82% Necrosis of the femoral head 8% Coxarthrosis and dysplasia 6% Other 4% Degenerative coxarthrosis and AVN [no figures given] Osteoarthritis 92% Osteoarthritis following Perthes 4% Osteoarthritis following dsyplasia 4% Primary arthritis: 81% Osteonecrosis: 9% Post-traumatic arthritis: 6% CHD (Crowe type 1) 2% Failed osteosynthesis of proximal femur 1% Failed resurfacing arthroplasty 1% Osteoarthritis 74.67% Rheumatoid arthritis 10.67% Avascular necrosis 4.0% Perthes 2.67% SUFE 2.67% Post Traumatic OA 2.67% DDH 1.33% Psoriatic arthritis 1.33% "We favour this implant for younger patients (<70 years) with good bone quality and normal anatomical conditions" Osteoarthritis: 89.8% Rheumatoid arthritis: 10.2% "Severe primary or secondary osteoarthritis"
Synder 2009 24 prospective
Ghera 2009 18 nd
Briem
2011
26 retrospective
Pons
2010 29 retrospective
Primary coxarthrosis 58% Dysplastic coxarthrosis 22% Post-traumatic coxarthrosis 12% Aseptic femoral head necrosis 8% Osteoarthritis 87.7% AVN 10.8% Fracture 1.5% Osteoarthritis 54.8% Dysplasia 14.8% AVN 14.2% Post-traumatic necrosis 5.2% Coxa vara 5.2% Coxa valga 3.2% Rheumatoid arthritis 1.9% Perthes disease 0.7% Osteoarthritis in 84.8% [no further information given]
*Publication with designing surgeon involvement.
Hips Gender 56 18 men 26 women
Mean age (years) 62.5 (59-69)
162 74 men 72 women
50.8 (19-72)
Implant Bio dynamic (CoCrMd) Mayo
82 220 men
60
CFP
148 women
29 13 men 16 women 26 11 men 15 women 160 nd
54.7 (38-65) median age 54 (40-66) 63.4 (42-83)
Metha CFP Mayo
75 33 men
52
CFP
36 women (13*-75)
316 nd
*13 year old excluded from analysis
nd
Mayo
49 21 men
57.8
21 women (44-74)
30 8 men
57.4
18 women (36-79)
50 12 men
43
28 women (21-59)
Mayo Mayo Metha
65 20 men 45 women 155 80 men 75 women
70.1 (46-87) 59.3±9.9 (27-77)
Proxima CFP
138 90 men
57.1
CFP
38 women (22-76)
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TABLE IV - SURVIVAL RATES AND FUNCTIONAL OUTCOMES PRESENTED IN THE ELIGIBLE PUBLICATIONS
Author
Year Ref.
FUP [m]
Hips at start
Hips at FUP
Stem revisions / 100 comp.-years
total for
for
fracture AL
Pipino* 2000 21 180 56
44 0.0
0.0
0.0
Morrey* 2000 28 78.0 162 159 0.5
0.2
0.3
Pipino* 2004 22 48.0 390 353 0.1
0.1
0.0
Buecking 2006 25 12.0 29
29 0.0
0.0
0.0
Rцhrl 2006 23 24.0 26
26 0.0
0.0
0.0
Falez 2008 17 56.4 160 160 0.5
0.1
0.3
Gill
2008 27 43.0 75
66 0.0
0.0
0.0
Hagel 2008 20 83.6 316 270 0.3
0.0
0.3
Gilbert 2009 19 37.2 49
49 3.6
1.4
0.7
Goebel 2009 15 81.0 30
26 1.7
0.0
0.0
Synder 2009 24 13.0 50
50 0.0
0.0
0.0
Ghera 2009 18 20.4 64
63 0.0
0.0
0.0
Briem 2011 26 74.3 155 151 0.1
0.0
0.1
Pons 2010 29 38.3 138 138 0.5
0.2
0.0
Cumulative survival
Functional Functional score score preop last FUP
nd
nd
HHS
excellent 16 (37%)
good
20 (45%)
fair
6 (14%)
poor
2 (4%)
for AL: 98.2% at 5 and 10 years
mean HHS: 66.3
mean HHS incl. revised: 90.4 mean HHS excl. revised: 92.5
nd
nd
HHS
excellent 321 (90.9%)
good
20 (5.7%)
fair
8 (2.3%)
poor
4 (1.1%)
nd
mean HHS: mean HHS at 12m:
50
97 (67-100)
nd
mean HHS: mean HHS:
42
93
"survivorship" after nd
nd
a mean of 4.7 yrs:
97.5%§
"cumulative survival" median HHS: median HHS:
at 3 years : 100%§ 50
99
"average" survival rate at 83.6 months: 98.1%
mean HHS: 44.79
mean HHS: 93.58
nd
mean OHS: mean OHS:
43.4 (22-52) 19.6 (12-46)
nd
MDA: 6
MDA at 72m: 16.3
100%
mean HHS: 54 (46-75)
mean HHS at 12m: 97 (94-98)
nd
mean HHS: mean HHS:
51 (36-64)
91 (50-99)
mean OHS: mean OHS:
42.5
12.4
99.4%, CI (95%) 96-100 (max. FUP time: 94 m)
mean HHS: 65.5 ± 15.3
mean HHS: 96.3 ± 7.4
nd
mean HHS: mean HHS:
30.2 (18-48) 92 (88-100)
*Publication with designing surgeon involvement. no censoring used; only patients available for FUP included. information presented as graph, not as figures, therefore approximation. § calculation method not described. nd: not documented.
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TABLE V - SURVIVAL RATES OF SELECTED SUBGROUPS OF PATIENTS WITH UNCEMENTED FIXATION OF THE JOINT ARTHROPLASTY REGISTRIES FROM AUSTRALIA, SWEDEN AND England & Wales
Registry Australia Sweden England & Wales
Primary Age Group Diagnosis
55-64 50-75 55-64
Osteoarthritis all diagnoses all diagnoses
1 yr 98.6 98.6 98.8
Cumulative percent survival
3 yrs 5 yrs 7 yrs 9 yrs
97.2
96.4
95.3
94.4
97.5
96.5
93.8
90.7
97.4
96.4
nd
nd
Revisions per 100 observed component years 0.8 nd nd
Fig. 2 - Stem revision rate with endpoint "revision for any reason" plotted against quality rating. The mean follow-up times were relatively short. Only one article on a brand that is no longer available published on a follow-up time greater than ten years (21). This publication had the second lowest quality ranking. Another four articles published on follow-up times greater than five years. Three of these articles can be considered high quality with a quality ranking of eleven or higher (15, 20, 28). No clear association of the studies' quality and the presented survival rates was apparent as illustrated in Figure 2. Performance/comparison to registry data In order to determine performance, survival rates and functional scores were extracted from the literature. Functional scores appear to be very good at follow-up and range in the upper quintiles of the attainable ranges of the respective scores, representing a significant improvement in pain and function. Based on the lack of data on cumulative survival, we resorted to calculating revisions per 100 component years. Whereas cumulative survival always refers to a specified
time interval, revision rates calculated per component years do not refer to a specified time interval but to the product of the number of implants and the time they spent in situ. Thus, comparing different cumulative survival rates is usually a valid comparison, whilst a comparison of revision rates per component years only seems justified when the follow up- times of the populations are similar and the time pattern for revision is comparable. For this reason, we calculated the overall follow-up time in the population, even though this calculation method does not allow taking into account any time effects. Many factors may have an influence on survival of THA. Both the Swedish Registry (30) and the AOANJRR (9) have identified a wide range of predictive factors for early prosthesis failure. These include young age, male gender, and certain types of secondary arthritis. In order to compare the results found in this review with data from the registries in the best possible way, access to raw data facilitating application of the Cox- models presented in the registries to our patient populations would have been needed. Since this possibility was not available to us, the present comparison has the underlying assumption that patient populations are comparable with regard to outcome predictors. Over all studies, we found a total revision rate of 0.38 per 100 observed component years. Only the AOANJRR presents survival rates per 100 observed component years. Most patients in the studies presented in this review were in their late fifties or early sixties, so we selected the age group of patients aged 55-64 having received uncemented implants as the best possible comparator from the AOANJRR. For this age and implant subgroup, the registry only presents data for the indication `osteoarthritis' with a revision rate of 0.8 per 100 observed component years. Considering that in the registry only combined revision rates of stem and cup are presented, the survival rate
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of the types of short stems in our review seem to match this figure well. Given that some other indications which are positive predictors for early revision are also represented in our patient populations, using this subgroup as a comparator may even have produced a conservative estimate. From the registry of England and Wales, data of the same age and implant group, but for all diagnoses, was available, which we believe matches our population best. From the Swedish registry, the age grouping is different, so we chose to present the weighted mean value of the age groups of 50-59 and 60-75. Neither the arthroplasty registry of Sweden nor that of England and Wales present survival rates per 100 observed component years. However, the differences in the presented cumulative survival rates of uncemented stems in the respective patient subgroups compared to those of the AOANJRR are marginal up to 5 years after surgery, so it seems safe to assume that the revision rates per 100 observed component years would be similar, too. The overall mean follow-up time in the studies we present is limited to 4.5 years, so any interpretation of revision rates beyond this time frame would be difficult anyway.
geon. Finally and most important, the majority of studies only presented short- term results, and, for the evaluation of the performance of hip implants long term results are essential. CONCLUSION In this literature review, 14 publications on short stems with a "modern" trochanter sparing design were identified. The quality of the studies varied, but no association of the studies' quality and presented survival rates was found. Even though the early survival rates of these types of stems appear to be comparable to those of other uncemented stems, most of the publications present only short term data. Given that a wide range of short stems have recently been introduced on a large scale without sufficient clinical documentation, it is clear that a stepwise market introduction has not been carried out. Since a minimum of ten-year survival is needed to evaluate the performance of a THA, further well-conducted prospective studies with much longer follow up times are needed to draw final conclusions.
Limitations Our review has several limitations. On one hand, RCTs are barely available, so we had to rely on observational studies with the inherent possibility of confounding by indication. This may also include a selection bias for patients with good bone quality and uncomplicated anatomy. On the other hand, the comparison with registry data also presents several issues. Firstly, we could only compare with published information of pre-defined subgroups, which obviously does not allow any matching for predictive factors. Secondly, most results generated in this review were only available as revisions per 100 observed component years. With this unit, the possibility to compare implants is limited and time effects cannot be accounted for. Thirdly, some of the comparative figures from the registries had to be extrapolated from graphs and may therefore lack precision. Furthermore, a comparative analysis of joint arthroplasty outcome has shown that often results generated by the inventor of the prosthesis cannot be reproduced in independent registries (31). Of the 14 publications we present in this review, three were published by a designing sur-
Financial support: No financial support of third parties has been received for this piece of research. Conflict of interest: None of the authors has any conflict of interest to declare. Address for correspondence: Ms. Elke Rometsch Talackerstr. 54, CH-8404 Winterthur, Switzerland [email protected]
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Survival of short hip stems - a systematic literature review
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