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BMJ Open. 2016; 6(3): e010472.
Published online 2016 Mar 23. doi:10.1136/bmjopen-2015-010472
PMCID: PMC4809092
PMID: 27009147
Loes W A H van Beers,1 Jakob van Oldenrijk,2 Vanessa A B Scholtes,1 Carel H Geerdink,3 Bob B A M Niers,3 Wouter Runne,1 Mohit Bhandari,4 and Rudolf W Poolman1
Author information Article notes Copyright and License information PMC Disclaimer
Abstract
Introduction
Answering the demands of an increasingly young and active patient population, recent developments in total hip arthroplasty (THA) have shifted towards minimising tissue damage. The Collum Femoris Preserving (CFP) stem was developed to preserve the trochanteric region of the femur, which potentially preserves the insertion of the gluteus musculature. This might accelerate early postoperative rehabilitation and improve functional outcome. Currently the functional results of the CFP stem have not been compared with conventional straight stems in a randomised controlled trial (RCT). The primary purpose of this trial is to compare the functional result of CFP stem THA with conventional uncemented straight stem THA, measured by the Dutch Hip disability and Osteoarthritis Outcome Score (HOOS) at 3-month follow-up.
Methods
A prospective blinded multicentre RCT will be performed. We aim to recruit 150 patients. The patients will be randomly allocated to a THA with a straight or a curved stem. All patients, research assistants, clinical assessors and investigators will be blinded for the type of prosthesis for 5 years. Clinical assessments and roentgenograms will be taken preoperative, at 6 weeks after surgery, at 1, 2, 3, 4 and 5 years after surgery. Patient reported outcome measures (PROMs) will be obtained at the same follow-up moments. In addition, the PROMs will also be sent to the patients at 3 and 6 months after surgery. The HOOS at 3-month follow-up will be our primary outcome.
Ethics and dissemination
This trial will be performed in accordance with the Declaration of Helsinki. A local ethics committee has approved this trial. Written informed consent will be obtained from all participating patients. All serious adverse events will be reported to the ethics committee.
Results
Results will be submitted for publication to an orthopaedics related journal.
Trial registration number
NTR1560.
Keywords: ORTHOPAEDIC & TRAUMA SURGERY
Strengths and limitations of this study
A good methodological quality, which reduces the risk of bias.
A multicentre randomised controlled trial.
Maximally blinded (patients, clinical assessors, investigators and data analysts are blinded for the type of implant).
A research assistant is hired for this study, to ensure that there will be complete data and a maximal follow-up.
Sealed envelopes instead of a digital system are used for the randomisation.
Introduction
For years, developments in total hip arthroplasty (THA) have focused mainly on improving implant survival, resulting in long-term survival rates of more than 90% for uncemented as well as cemented stems.1
There is a recent increase in uncemented hip replacements, especially in young and more active patients. Uncemented stems are currently the preferred implant of choice for these patients, providing that there is a good bone quality.2 The Zweymuller stem is a commonly used uncemented straight stem and studies have shown excellent 10-year survival rates of 90–100%.3–6 Weissinger et al7 have shown a reoperation rate of 6.8% after 20 years. Furthermore, stability of the implant was not affected by any proximal osteolysis.89 The proximal anchorage of this stem requires the use of a box chisel cutting a slot in the trochanteric fossa near the insertion of both the gluteus medius and the piriformis tendon to obtain entry in neutral alignment. A previous cadaver study by van Oldenrijk et al10 demonstrated a median gluteus medius midsubstance surface area damage of 22% (minimum 6, maximum 40%) after Zweymuller stem placement using a lateral transgluteus approach. Moreover, the external rotators were found to be unintentionally transected in one of five hips using this approach. Damage to the insertion of the gluteus musculature is an important cause of postoperative pain at the greater trochanter and reduced abductor strength, resulting in limping and a positive Trendelenburg gait.11–13
In the young and active patient population, recent developments have, therefore, shifted towards minimising tissue damage, thereby retaining normal bone physiology without compromising implant stability. This resulted in the modification of surgical techniques and the development of innovative bone and soft tissue-preserving implants, such as short stem hip arthroplasty. The aim of these developments was to accelerate early postoperative rehabilitation, improve functional outcome and preserve bone stock for future revisions.14
Short stem THA aims to combine well-established anchoring principles with bone preservation. Pipino and Calderale 15 introduced the Biodynamic stem. This stem preserves the collum femoris, thereby preserving proximal bone stock for any future revisions. Furthermore, it preserves the trochanteric region of the femur. As such, it preserves the gluteal insertions on the greater trochanter, which may be beneficial as compared to a conventional stem, as this may potentially accelerate early postoperative rehabilitation. The Biodynamic stem, showing good medium and long-term survival rates,1617 was later modified into the collum femoris preserving (CFP) stem (Waldemar Link, Germany). A case series (mean follow-up of 5.1 years) demonstrated excellent integration and survivorship at medium follow-up (mean 5.1 years), with a revision rate of 0.21 per year.18–28 Clinical follow-up also showed good functional recovery and DEXA analysis of 10 patients showed minimal periprosthetic bone loss.1618 Two-year follow-up migration assessment using radiostereometry showed low migration, suggesting a favourable long-term outcome.2629 The quality of this currently available evidence is low, and no study has compared this stem with a conventional stem, so only a weak recommendation can be provided for clinical usage of these short stem designs.30 Stronger evidence is necessary, preferably prospective multicentre randomised trials, before widespread use can be recommended.30
Since the potential benefits of the CFP stem have not yet been compared with conventional straight stems in a randomised controlled trial (RCT), the potential additional benefit in terms of short-term rehabilitation remain to be determined. We aim to compare the early (3 month) and medium (up to 5 years) term functional result of a CFP stem THA to conventional straight stem THA. The primary purpose of this trial is to compare the functional result of CFP stem THA with conventional uncemented straight stem THA, measured by the Dutch version of the Hip disability and Osteoarthritis Outcome Score (HOOS)31 at 3-month follow-up.
The secondary objective will be an evaluation of secondary outcomes discussed in detail below. Since the CFP stem may require less dissection of the gluteal musculature off the greater trochanter, we expect to find a better short-term functional result after CFP stem THA compared with conventional straight stem THA, as reflected in higher HOOS.
Methods
Trial design
A prospective blinded randomised controlled multicentre trial with parallel groups will be performed at Onze Lieve Vrouwe Gasthuis (OLVG) in Amsterdam and at Ikazia hospital in Rotterdam, both in The Netherlands. A total of 100 patients from OLVG and 50 patients from Ikazia will be recruited. Three orthopaedic surgeons from OLVG, and two orthopaedic surgeons from Ikazia, participate in this trial. The allocation ratio between the two interventions will be 1:1, and a superiority design will be used. This trial is registered at the Dutch Trial Registry (Nederlands Trial Register, http://www.trialregister.nl) on 25 November 2008, file number NTR1560.
Participants
We will include patients between 18 and 70 years with osteoarthritis of the hip, who are not responding to conservative therapy, who meet the clinical criteria to undergo a cementless THA, and are willing to sign written informed consent. Consecutive patients from the waiting list for a total hip replacement will be approached for participating in this trial if they meet the inclusion criteria. Patients will be excluded when they: are not able to fill out the Dutch questionnaires; have morbid obesity with a body mass index of more than 40 mm Hg; have an altered anatomy resulting in impossibility for one of the procedures; have a life expectancy of <5 years; have had a lower extremity amputation; have a known alcohol or drugs abuse; have an active malignant disease or current cytostatic treatment; are participating in another clinical trial; have contralateral hip pain; have had a previous hip arthroplasty (ipsilateral or contralateral), or when they have avascular head necrosis due to sickle cell anaemia.
All orthopaedic surgeons will be informed about this trial through presentations, posters and newsletters. The orthopaedic surgeons will screen all patients in the outpatient clinic for eligibility, and they will inform eligible patients about the trial. A researcher will contact the patient by phone to resolve any questions. When the patient agrees to participate in this trial, informed consent has to be signed by both the orthopaedic surgeon or research assistant and the patient. After enrolment in this trial, patients will be assigned to a study identification number. Only the study identification number will be used on data forms and in the databases. The encryption between the study identification number and the personal information will only be accessible for the research coordinator of this trial.
Randomisation and blinding
After signing the informed consent, the patient will be randomly allocated to THA with a straight stem or a curved stem. Stratified block randomisation will be used as allocation method. Blocks consist of 10 consecutive surgical procedures. At the end of each block an equal distribution of patients between the two groups will have been reached. Patient allocation will be stratified to surgeon, resulting in an equal distribution of surgical expertise and technique variation in each group. Randomisation will not be performed until the moment of surgery. The surgeon will, therefore, perform preoperative templating for both stems, and both stems and their instrumentation trays will be available in the surgery room. Since a digital randomisation system proved to be unsuccessful in our hospital due to technical difficulties, randomisation will be performed using envelopes. We will use randomisation envelopes that are sealed, sequentially numbered, opaque and blinded. An independent investigator will make these randomisation envelopes available to the surgeon in the operating room, after the patient is under anaesthesia, and just before incision. Both types of implants are ready to use in the operating room. All patients, researchers, clinical assessors and investigators will be blinded for the type of prosthesis for the total duration of the follow-up: 5 years. A pop-up message will be attached to the patient records in the electronically maintained hospital information system. This pop-up message is a reminder that the patient and clinical assessors are blinded, and therefore, the roentgenograms should not be shown. Only the orthopaedic surgeon will verify the roentgenograms, so in case there are any problems, they can be intervened. Data will be processed and analysed by blinded investigators. After finalising data analyses the blinding will be broken for publication purposes.
The number of deblinded patients will be recorded and presented in final reports.
Interventions
All participating surgeons should have gained experience with both implants. At least five procedures for both implants should have been performed prior to participating in the trial. The learning curve for the CFP stem is assessed in an earlier study,2832 and an acceptable level of proficiency is assumed after performing five procedures.
A lateral transgluteal approach in lateral decubitus position is used in all patients.
The same rehabilitation protocol will be used for both groups. Postoperatively, patients are allowed to fully weight bear with the use of crutches from the first postoperative day, continuing crutches if necessary during the first 6 weeks.
Straight stemmed THA
Patients randomised into the straight stem group will undergo surgery for THA where a straight, cementless, Alloclassic stem (Zimmer, Warsaw, Indiana, USA) will be used. This stem is inserted parallel to the longitudinal axis of the femur.
Curved stemmed THA
Patients randomised into the curved stem group will undergo surgery for THA where a curved, cementless, CFP stem (Waldemar Link, Hamburg, Germany) will be used. This stem follows the curvature of the remaining femoral neck. Two curvatures are available: A for coxa valga and norma, and B for coxa vara. The curvature will be assessed preoperatively by templating the hip.
Cup
A Trabeculae Oriented Pattern (TOP) cementless hemispheric cup (Waldemar Link, Hamburg, Germany) with a polyethylene liner will be used in both groups. The TOP cup has a biequatorial dissociation with a medial-caudal recess to allow a wider range of motion and an elevated cranial rim to reduce the risk of dislocation.17 A follow-up study of 301 TOP cups showed no detachment, migration or osteolysis after 7 years.18 All implants are positioned without the use of navigation.
Head
In both groups a 32 or 28 mm ceramic head is used.
Outcome measures
Primary outcome
The Dutch version of HOOS31 at 3 months postoperative, will be our primary outcome. The HOOS is a patient-reported outcome measure (PROM) that consists of five subscales; pain, other symptoms, function in daily living, function in sport and recreation and hip-related quality of life. Standardised answering options are given for each question (five Likert boxes) ranging from 0 to 4. A normalised score (100 indicating no symptoms and 0 indicating extreme symptoms) is calculated for each subscale.
Secondary outcomes
Secondary outcomes will be the amount of reoperations due to implant-related complications, for example, bleeding or vascular damage, neurogenic damage, fractures, dislocation, infection, loosening, deep venous thrombosis. Other secondary outcomes are pain in the ipsilateral and contralateral hip, knees and back, measured by a numeric rating scale (NRS), abductor strength measured by the Trendelenburg test,33 walking ability measured by the Timed Up and Go (TUG) test,3435 physical functioning measured by the Harris Hip Score (HHS),36 general health measured by the Short-Form 12 item (SF-12) questionnaire,37 quality of life by the EuroQol 5 Dimension (EQ-5D) questionnaire,38 and position of the prosthesis. The position of the prosthesis will be measured on weight-bearing anteroposterior pelvis with the patient's feet facing forward and hip faux profile roentgenograms. Preoperatively an X-ray will be taken which includes a ball of known diameter to enable calibration. Postoperatively X-rays are taken at day 1, 6 weeks, and annually up to 5 years after surgery. An assessor who is not involved with the surgical procedures will perform all measurements.
The clinical assessments, containing the range of motion of the hip, the Trendelenburg test, the TUG test, measuring leg length discrepancy and asking for the occurrence of any complications, will be performed at baseline (within 1 week prior to surgery), at 6 weeks after surgery, at 1, 2, 3, 4 and 5 years after surgery. A trained researcher will perform all clinical tests. Roentgenograms will be taken at the same time points.
The PROMs, containing the HOOS, NRS, HHS, SF-12 and EQ-5D, can be filled out using either pen and paper or web-based forms. The PROMs will be sent to the patient's home address (including prestamped return envelopes) or e-mail address. Patients are asked to fill out the PROMs at the same follow-up moments as the clinical assessments. In addition, the PROMs will also be sent to the patients 3 and 6 months after surgery. All follow-up moments are presented schematically in table 1. Every patient will receive a reminding card containing the date of surgery and the subsequent months/years of clinical follow-up. For every follow-up visit, patients will be contacted by phone to make an appointment. Patients who have not responded to the PROMs, are contacted by phone as a reminder. Patients will be kept informed about the trial by sending them newsletters, approximately twice a year. In addition, every patient chart has a note for doctors, that in case of any complication the research coordinator should be contacted.
Table1
Follow-up moments
| Preoperative | Postoperative | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Baseline | 6 Weeks | 3 Months | 6 Months | 1 Year | 2 Years | 3 Years | 4 Years | 5 Years | |
| PROMs | X | X | X | X | X | X | X | X | X |
| Clinical tests | X | X | X | X | X | X | X | ||
| Roentgenograms | X | X | X | X | X | X | X | ||
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PROMs, patient-reported outcome measures.
Sample size
Sample size calculation is based on the HOOS pain subscale, to detect a difference between the two groups at 3 months postoperative. De Groot et al31 found a mean HOOS pain score of 65.4 points with an SD of 14.3 in patients 9.5 months after THA. We consider a 10% difference in outcome clinically relevant, resulting in a seven-point difference.39 Based on these assumptions, setting α at 0.05 and the power level at 80%, a sample size of 67 patients in each group is required to detect a statistically significant difference.
We expect a maximum drop-out rate of 10%, resulting in a total of 150 patients (75 patients in the curved stem group and 75 patients in the straight stem group).
We expect to recruit the 150 patients within a period of 2 years.
Statistical analyses
To investigate the effect of both implants, we will use generalised estimating equations (GEE) for longitudinal analysis in SPSS. All patients who withdraw from the trial after surgery, and patients who undergo a revision surgery, will be included in an intention-to-treat analysis. Both intention-to-treat analysis and per-protocol analysis will be performed. This method takes into account the dependency of observations within a patient, and the fact that not all patients may be assessed at each time point (missing data).
Primary analyses
In the primary GEE model, the outcome variable studied (eg, physical function on the HOOS) will be analysed as a dependent variable, using implant allocation (1, CFP; 0, Zweymuller) and time as key independent variables. The primary endpoint of the study is on the effect at 3 months, but all time moments will be analysed in the same GEE model.
Secondary analyses
In the secondary GEE model, the outcome variables studied (eg, physical function on the HHS, general health on the SF12, quality of life on the EQ5D, walking ability on the TUG, pain on the NRS, hip range of motion, abductor strength on the Trendelenburg test, position of the prosthesis and leg length discrepancy on the roentgenograms, satisfaction) will be analysed in a similar way. To evaluate whether the two implant groups differed in change over time, the interaction term of group and time (group×time) will be assessed. Time will be included as a dummy variable (reference=baseline T0), and seven interaction terms will be analysed (T1 6 weeks×group, T2 3 months×group; T3 6 months×group; T4 1 year×group, T5 2 years×group, T6 3 years×group, T7 4 years×group, T8 5 years×group). All models will be corrected for centre of inclusion and surgeon. In additional analysis, we will investigate the possible confounding effect (defined as more than 10% change in the parameter estimate for group×time) of several variables (body mass index, gender, ASA-classification, comorbidity, mental health, other joint pain). At the following time points following the surgery (T4, T5, T6, T7 and T8), we will describe the incidence of reoperations (both implant groups) using descriptives. For all analysis, a two-tailed value of p<0.05 is considered to be significant.
Data storage
Data will be entered into a digital database (SPSS), and after the data entry, paper data collection forms will be stored in an archive. Both paper forms and digital databases will be accessible only to the research coordinator.
Steering and data monitoring committee
No official steering committee has been appointed for this study. The following representatives from the participating organisations are involved in the project oversight and control: RWP (principal investigator and sponsor), JvO, CHG, BBAMN, VABS and LWAHvB. All study-related problems or (serious) adverse events will be discussed with the principal investigator RWP, and researchers VABS, LWAHvB and JvO. SAEs will be officially reported to the ethical committee. The ethical committee judges whether the safety of the patients is jeopardised, and whether the trial can be continued or not.
There is no official data monitoring committee. Data entry will be performed by one of the researchers (LWAHvB). All entered data will be checked and cleaned (LWAHvB and VABS) according to the quality handbook of the emgo+institute for health and care research (http://www.emgo.nl/kc). In addition, a random sample of 20% of the data will be re-entered by another researcher (JvO) to check for inconsistencies. A third researcher (VABS) will be involved with the data processing and analysis, which will be performed without knowledge of the allocation key. All data analysis (VABS) will be discussed with the researchers (RWP, JvO and LWAHvB) prior to deblinding, before final presentation of the results.
Interim analysis will be performed after 2 years. Data analysts and researchers are still blinded to the type of prosthesis at that time point. Results of the interim analysis will be discussed with the researchers.
Ethics and dissemination
This trial will be performed in accordance with the Declaration of Helsinki. All substantial amendments to the protocol will be notified to the ethics committee and to the competent authority. Non-substantial amendments will not be notified to the accredited METC and the competent authority, but will be recorded and filed by the sponsor. Written informed consent will be obtained from all participating patients. The research coordinator will report all serious adverse events within 24 h after noticing any, using the online submission system of the ethics committee. The ethical committee judges whether the safety of the patients is jeopardised, and whether the trial can be continued or not. Results will be submitted for publication to an orthopaedics-related journal.
Protecting against sources of bias
Selection bias
In this trial, the risk of selection bias is reduced by approaching all consecutive eligible patients.
Furthermore, randomisation will not be performed until the moment of surgery. This will prevent selecting patients for a specific type of prosthesis.
Performance bias (blinding)
Unblinded patients allocated to an intervention which they do not prefer, may feel resentful. This may lead to performance bias.4041 In this trial, all patients will be blinded to the type of prosthesis, reducing the risk of performance bias.
Performance bias (surgeon expertise)
Requiring a minimum number of procedures prior to initiating the trial reduces the risk of performance bias.
Detection bias
The clinical assessors who will perform the clinical tests will be blinded, to reduce the risk of detection bias.
Attrition bias
To reduce attrition bias, a blinded research assistant is the direct contact person for all trial patients. Efforts are undertaken to minimise the amount of patient drop-out or lost to follow-up. Moreover, all PROMs and clinical assessment data is verified to prevent incomplete data.
Publication bias
By publishing this protocol, we would like to prevent publication bias. Results of this trial will be submitted for publication in a peer-reviewed journal.
Minimising cointerventions and contamination
Crossover between intervention groups can occur, for instance, when a revision surgery will be performed and another type of stem will be implanted. All patients will be analysed in the group to which they were allocated following the intention-to-treat analysis. Additionally, we can perform per-protocol analysis.
Discussion
Authors of surgical RCTs often fail to report measures to prevent bias.42–46 Several reviews of RCTs in orthopaedic surgery have studied the reporting of bias prevention. They found that this is often not well reported. Blinding of outcome assessors, concealment of allocation, and intention-to-treat analysis are types of bias preventions that are often not reported.404147 In this trial, extensive measures will be taken to reduce the risk of bias. It will be a challenge to keep all involved persons, patients as well as research staff, blinded for 5 years. These strenuous measures to reduce the risk of bias may serve as a model for future implant-related orthopaedic RCTs. This trial will be the first RCT that compares the early and medium-term functional results of the CFP stem THA with conventional straight stem (Zweymuller) THA. Herewith, this trial can contribute to the clinical evidence around short stem THA.
At first sight, 3 months follow-up might not be the most clinically relevant time point to evaluate. This time point was chosen as it best reflects the timing to evaluate the theoretical advantage of the CFP stem as compared with the Zweymuller stem; for example, that the gluteal musculature might be less damaged. This preserving of gluteal musculature might be beneficial for the acceleration of rehabilitation/improved physical functioning of the patients, in particular, in the first months after surgery. The intention of this trial is to evaluate whether the theoretical advantages of the CFP stem do really result in better physical functioning, compared to the Zweymuller. For that reason, we choose 3-month follow-up as our primary end point. Naturally, mid-term and long-term results of prosthetic stems are valuable. For that reason, we will follow all patients up to 5 years after surgery.
Footnotes
Contributors: All authors contributed to the design of this trial protocol. LWAHvB, JvO, VABS and RWP contributed to writing the manuscript. VABS, LWAHvB and JvO contributed to the data analysis plan. All authors contributed to the manuscript and read and approved the final manuscript.
Funding: The department of orthopaedic surgery of the Onze Lieve Vrouwe Gasthuis receives funding from Link Nederland. This financial support is used for personnel costs to carry out this trial. Link Nederland was not involved in writing this protocol and will not have authority over the data analysis or publications.
Competing interests: None declared.
Patient consent: Obtained.
Ethics approval: Medical Research Ethics Committees United and Verenigde Commissies Mensgebonden Onderzoek, Nieuwegein, The Netherlands approved the trial on 16 September 2008, file number NL21637.100.08.
Provenance and peer review: Not commissioned; externally peer reviewed.
References
1. Morshed S, Bozic KJ, Ries MD et al.. Comparison of cemented and uncemented fixation in total hip replacement: a meta-analysis. Acta Orthop2007;78:315–26. 10.1080/17453670710013861 [PubMed] [CrossRef] [Google Scholar]
2. Kynaston-Pearson F, Ashmore AM, Malak TT et al.. Primary hip replacement prostheses and their evidence base: systematic review of literature. BMJ2013;347:f6956 10.1136/bmj.f6956 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
3. Baumann B, Hendrich C, Barthel T et al.. 9- to 11-year results of cemented titanium mueller straight stem in total hip arthroplasty. Orthopedics2007;30:551–7. [PubMed] [Google Scholar]
4. Garcia-Cimbrelo E, Cruz-Pardos A, Madero R et al.. Total hip arthroplasty with use of the cementless Zweymuller Alloclassic system. A ten to thirteen-year follow-up study. J Bone Joint Surg Am2003;85-A:296–303. [PubMed] [Google Scholar]
5. Pieringer H, Auersperg V, Griessler W et al.. Long-term results with the cementless Alloclassic brand hip arthroplasty system. J Arthroplasty2003;18:321–8. 10.1054/arth.2003.50045 [PubMed] [CrossRef] [Google Scholar]
6. Pieringer H, Auersperg V, Böhler N. Long-term results of the cementless ALLOCLASSIC hip arthroplasty system using a 28-mm ceramic head: with a retrospective comparison to a 32-mm head. J Arthroplasty2006;21:967–74. 10.1016/j.arth.2005.08.027 [PubMed] [CrossRef] [Google Scholar]
7. Weissinger M, Helmreich C, Pöll G. Results covering 20 years use of the cement-free Zweymuller Alloclassic total endoprosthesis of the hip joint. Acta Chir Orthop Traumatol Cech2010;77:186–93. [PubMed] [Google Scholar]
8. Vervest TM, Anderson PG, Van HF et al.. Ten to twelve-year results with the Zweymüller cementless total hip prosthesis. J Arthroplasty2005;20:362–8. 10.1016/j.arth.2004.11.017 [PubMed] [CrossRef] [Google Scholar]
9. Wick M, Lester DK. Radiological changes in second- and third-generation Zweymuller stems. J Bone Joint Surg Br2004;86:1108–14. 10.1302/0301-620X.86B8.14732 [PubMed] [CrossRef] [Google Scholar]
10. van Oldenrijk J, Hoogland PV, Tuijthof GJ et al.. Soft tissue damage after minimally invasive THA. Acta Orthop2010;81:696–702. 10.3109/17453674.2010.537804 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
11. Baker AS, Bitounis VC. Abductor function after total hip replacement. An electromyographic and clinical review. J Bone Joint Surg Br1989;71:47–50. [PubMed] [Google Scholar]
12. Pfirrmann CW, Notzli HP, Dora C et al.. Abductor tendons and muscles assessed at MR imaging after total hip arthroplasty in asymptomatic and symptomatic patients. Radiology2005;235:969–76. 10.1148/radiol.2353040403 [PubMed] [CrossRef] [Google Scholar]
13. Stähelin T.[Abductor repair failure and nerve damage during hip replacement via the transgluteal approach. Why less invasive methods of joint replacement are needed, and some approaches to solving the problems]. Orthopade2006;35:1215–24. 10.1007/s00132-006-1003-1 [PubMed] [CrossRef] [Google Scholar]
14. van Oldenrijk J, Molleman J, Klaver M et al.. Revision rate after short-stem total hip arthroplasty: a systematic review of 49 studies. Acta Orthop2014;85:250–8. 10.3109/17453674.2014.908343 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
15. Pipino F, Calderale PM. Biodynamic total hip prosthesis. Ital J Orthop Traumatol1987;13:289–97. [PubMed] [Google Scholar]
16. Pipino F, Molfetta L, Grandizio M. Preservation of the femoral neck in hip arthroplasty: results of a 13–17-year follow-up. J Orthop Traumatol2000;1:31–9. 10.1007/s101950070026 [CrossRef] [Google Scholar]
17. Pipino F, Keller A. Tissue-sparing surgery: 25 years' experience with femoral neck preserving hip arthroplasty. J Orthop Traumatol2006;7:36–41. 10.1007/s10195-006-0120-2 [CrossRef] [Google Scholar]
18. Pipino F.CFP prosthetic stem in mini-invasive total hip arthroplasty. J Orthop Traumatol2004;5:165–71. 10.1007/s10195-004-0065-2 [CrossRef] [Google Scholar]
19. Hutt J, Harb Z, Gill I et al.. Ten year results of the collum femoris preserving total hip replacement: a prospective cohort study of seventy five patients. Int Orthop2014;38:917–22. 10.1007/s00264-013-2212-y [PMC free article] [PubMed] [CrossRef] [Google Scholar]
20. Briem D, Schneider M, Bogner N et al.. Mid-term results of 155 patients treated with a collum femoris preserving (CFP) short stem prosthesis. Int Orthop2011;35:655–60. 10.1007/s00264-010-1020-x [PMC free article] [PubMed] [CrossRef] [Google Scholar]
21. Gill IR, Gill K, Jayasekera N et al.. Medium term results of the collum femoris preserving hydroxyapatite coated total hip replacement. Hip Int2008;18:75–80. [PubMed] [Google Scholar]
22. Kendoff D, Egidy C, Gehrke T.C.. F.P. In: Jerosch J, ed.. Kurzschaftendoprothesen. Wo liegen die Unterschiede. Cologne: Deutscher Ärzte-Verlag GmbH, 2013:48. [Google Scholar]
23. Kress AM, Schmidt R, Nowak TE et al.. Stress-related femoral cortical and cancellous bone density loss after collum femoris preserving uncemented total hip arthroplasty: a prospective 7-year follow-up with quantitative computed tomography. Arch Orthop Trauma Surg2012;132:1111–19. 10.1007/s00402-012-1537-0 [PubMed] [CrossRef] [Google Scholar]
24. Nowak M, Nowak TE, Schmidt R et al.. Prospective study of a cementless total hip arthroplasty with a collum femoris preserving stem and a trabeculae oriented pressfit cup: minimun 6-year follow-up. Arch Orthop Trauma Surg2011;131:549–55. 10.1007/s00402-010-1189-x [PubMed] [CrossRef] [Google Scholar]
25. Pons M.Learning curve and short-term results with a short-stem CFP system. Hip Int2010;20(Suppl 7):S52–7. 10.5301/HIP.2010.4443 [PubMed] [CrossRef] [Google Scholar]
26. Röhrl SM, Li MG, Pedersen E et al.. Migration pattern of a short femoral neck preserving stem. Clin Orthop Relat Res2006;448:73–8. 10.1097/01.blo.0000224000.87517.4c [PubMed] [CrossRef] [Google Scholar]
27. Schmidt R, Gollwitzer S, Nowak TE et al.. [Periprosthetic femoral bone reaction after total hip arthroplasty with preservation of the collum femoris: CT-assisted osteodensitometry 1 and 3 years postoperatively]. Orthopade2011;40:591–8. 10.1007/s00132-011-1745-2 [PubMed] [CrossRef] [Google Scholar]
28. van Oldenrijk J, Schafroth MU, Bhandari M et al.. Time-action analysis (TAA) of the surgical technique implanting the collum femoris preserving (CFP) hip arthroplasty. TAASTIC trial identifying pitfalls during the learning curve of surgeons participating in a subsequent randomized controlled trial (an observational study). BMC Musculoskelet Disord2008;9:93 10.1186/1471-2474-9-93 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
29. Lazarinis S, Mattsson P, Milbrink J et al.. A prospective cohort study on the short collum femoris-preserving (CFP) stem using RSA and DXA. Primary stability but no prevention of proximal bone loss in 27 patients followed for 2 years. Acta Orthop2013;84:32–9. 10.3109/17453674.2013.765623 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
30. Khanuja HS, Banerjee S, Jain D et al.. Short bone-conserving stems in cementless hip arthroplasty. J Bone Joint Surg Am2014;96:1742–52. 10.2106/JBJS.M.00780 [PubMed] [CrossRef] [Google Scholar]
31. de Groot IB, Reijman M, Terwee CB et al.. Validation of the dutch version of the hip disability and osteoarthritis outcome score. Osteoarthritis Cartilage2007;15:104–9. 10.1016/j.joca.2006.06.014 [PubMed] [CrossRef] [Google Scholar]
32. Van Oldenrijk J, Schafroth MU, Rijk E et al.. Learning curve analysis of the Collum Femoris Preserving total hip surgical technique. Hip Int2013;23:154–61. 10.5301/hipint.5000013 [PubMed] [CrossRef] [Google Scholar]
33. Hardcastle P, Nade S. The significance of the Trendelenburg test. J Bone Joint Surg Br1985;67:741–6. [PubMed] [Google Scholar]
34. Podsiadlo D, Richardson S. The timed “Up & Go”: a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc1991;39:142–8. 10.1111/j.1532-5415.1991.tb01616.x [PubMed] [CrossRef] [Google Scholar]
35. Mathias S, Nayak US, Isaacs B. Balance in elderly patients: the “get-up and go” test. Arch Phys Med Rehabil1986;67:387–9. [PubMed] [Google Scholar]
36. Harris WH.Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am1969;51:737–55. [PubMed] [Google Scholar]
37. Ware J Jr, Kosinski M, Keller SD. A 12-Item Short-Form Health Survey: construction of scales and preliminary tests of reliability and validity. Med Care1996;34:220–33. 10.1097/00005650-199603000-00003 [PubMed] [CrossRef] [Google Scholar]
38. EuroQol Group. EuroQol--a new facility for the measurement of health-related quality of life. Health Policy1990;16:199–208. 10.1016/0168-8510(90)90421-9 [PubMed] [CrossRef] [Google Scholar]
39. Norman GR, Sloan JA, Wyrwich KW. Interpretation of changes in health-related quality of life: the remarkable universality of half a standard deviation. Med Care2003;41:582–92. 10.1097/01.MLR.0000062554.74615.4C [PubMed] [CrossRef] [Google Scholar]
40. Boutron I, Ravaud P, Nizard R. The design and assessment of prospective randomised, controlled trials in orthopaedic surgery. J Bone Joint Surg Br2007;89:858–63. 10.1302/0301-620X.89B7.19440 [PubMed] [CrossRef] [Google Scholar]
41. Poolman RW, Struijs PA, Krips R et al.. Reporting of outcomes in orthopaedic randomized trials: does blinding of outcome assessors matter?J Bone Joint Surg Am2007;89:550–8. 10.2106/JBJS.F.00683 [PubMed] [CrossRef] [Google Scholar]
42. Agha R, Cooper D, Muir G. The reporting quality of randomised controlled trials in surgery: a systematic review. Int J Surg2007;5:413–22. 10.1016/j.ijsu.2007.06.002 [PubMed] [CrossRef] [Google Scholar]
43. Chess LE, Gagnier J. Risk of bias of randomized controlled trials published in orthopaedic journals. BMC Med Res Methodol2013;13:76 10.1186/1471-2288-13-76 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
44. Poolman RW, Struijs PA, Krips R et al.. Does a “Level I Evidence” rating imply high quality of reporting in orthopaedic randomised controlled trials?BMC Med Res Methodol2006;6:44 10.1186/1471-2288-6-44 [PMC free article] [PubMed] [CrossRef] [Google Scholar]
45. Soucacos PN, Johnson EO, Babis G. Randomised controlled trials in orthopaedic surgery and traumatology: overview of parameters and pitfalls. Injury2008;39:636–42. 10.1016/j.injury.2008.02.011 [PubMed] [CrossRef] [Google Scholar]
46. van Oldenrijk J, van Berkel Y, Kerkhoffs GM et al.. Do authors report surgical expertise in open spine surgery related randomized controlled trials? A systematic review on quality of reporting. Spine (Phila Pa 1976)2013;38:857–64. 10.1097/BRS.0b013e31827ecb1c [PubMed] [CrossRef] [Google Scholar]
47. Bhandari M, Richards RR, Sprague S et al.. The quality of reporting of randomized trials in the Journal of Bone and Joint Surgery from 1988 through 2000. J Bone Joint Surg Am2002;84-A:388–96. [PubMed] [Google Scholar]
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