Late peri-prosthetic femoral fracture as a major mode of failure in uncemented primary hip replacement

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1 HIP Late peri-prosthetic femoral fracture as a major mode of failure in uncemented primary hip replacement M. R. Streit, C. Merle, M. Clarius, P. R. Aldinger From the University of Heidelberg, Heidelberg, Germany M. R. Streit, MSc, MD, Research Fellow C. Merle, MD, Research Fellow Department of Orthopaedic and Trauma Surgery University of Heidelberg, Schlierbacher Landstrasse 200a, Heidelberg, Germany. M. Clarius, MD, Head of Department of Orthopaedic and Trauma Surgery, Consultant Orthopaedic Surgeon Hospital for Orthopaedic and Trauma Surgery, Vulpiusklinik, Vulpiusstrasse 29, Bad Rappenau, Germany. P. R. Aldinger, MD, PhD, Professor of Orthopaedic Surgery, Head of Department of Orthopaedic and Trauma Surgery Orthopädische Klinik Paulinenhilfe, Diakonieklinikum, Rosenbergstrasse 38, Stuttgart, Germany. Correspondence should be sent to Professor P. R. Aldinger; peter.aldinger@diakstuttgart.de 2011 British Editorial Society of Bone and Joint Surgery doi: / x.93b $2.00 J Bone Joint Surg [Br] 2011;93-B: Received 31 January 2010; Accepted after revision 6 October 2010 Peri-prosthetic femoral fracture after total hip replacement (THR) is associated with a poor outcome and high mortality. However, little is known about its long-term incidence after uncemented THR. We retrospectively reviewed a consecutive series of 326 patients (354 hips) who had received a CLS Spotorno replacement with an uncemented, straight, collarless tapered titanium stem between January 1985 and December The mean follow-up was 17 years (15 to 20). The occurrence of peri-prosthetic femoral fracture during follow-up was noted. Kaplan-Meier survival analysis was used to estimate the cumulative incidence of fracture. At the last follow-up, 86 patients (89 hips) had died and eight patients (eight hips) had been lost to follow-up. A total of 14 fractures in 14 patients had occurred. In ten hips, the femoral component had to be revised and in four the fracture was treated by open reduction and internal fixation. The cumulative incidence of peri-prosthetic femoral fracture was 1.6% (95% confidence interval 0.7 to 3.8) at ten years and 4.5% (95% confidence interval 2.6 to 8.0) at 17 years after the primary THR. There was no association between the occurrence of fracture and gender or age at the time of the primary replacement. Our findings indicate that peri-prosthetic femoral fracture is a significant mode of failure in the long term after the insertion of an uncemented CLS Spotorno stem. Revision rates for this fracture rise in the second decade. Further research is required to investigate the risk factors involved in the occurrence of late peri-prosthetic femoral fracture after the implantation of any uncemented stem, and to assess possible methods of prevention. Peri-prosthetic femoral fracture after total hip replacement (THR) is associated with a poor clinical outcome and a high rate of postoperative complications. 1-6 Besides considerable loss of function, 7 it has a high mortality rate similar to that after fracture of the hip. 5,8 The incidence of peri-prosthetic femoral fracture seems to be increasing worldwide, 8-12 making it an important issue of health policy. It is difficult to estimate the true incidence of this fracture because of the heterogeneous case mix and differing periods of follow-up, with reported incidence ranging from 0.1% to 2.3%. 9,13-22 In a recent study a cumulative incidence of fracture of 3.5% was found at ten years after primary cemented THR, 15 suggesting that it is more common than was previously thought. Uncemented femoral implants of modern design show encouraging survival in the long term, with an excellent clinical outcome and persisting osseo-integration 23,24 even in young patients. 25 However, there have been few studies which have examined the incidence of periprosthetic femoral fracture after the implantation of uncemented stems, and to our knowledge, there have been no long-term studies. Our primary aim therefore was to investigate the cumulative incidence of periprosthetic femoral fracture after the insertion of one type of uncemented femoral stem commonly used for THR using long-term survivorship analysis. Patients and Methods We retrospectively reviewed a consecutive series of 326 patients (354 hips) who had undergone THR using an uncemented, straight, collarless tapered titanium stem (CLS Spotorno; Zimmer Inc., Warsaw, Indiana) between January 1985 and December 1989 to determine the occurrence of peri-prosthetic femoral fracture during the follow-up period. There were 178 hips in 166 men and 176 hips in 160 women with a mean age of 57 years (13 to 81). The mean body mass index was 27 kg/m 2 (19 to 40). The left hip was involved in 175 patients and the right in THE JOURNAL OF BONE AND JOINT SURGERY

2 LATE PERI-PROSTHETIC FEMORAL FRACTURE AS A MAJOR MODE OF FAILURE IN UNCEMENTED PRIMARY HIP REPLACEMENT 179 Table I. Details of the diagnosis in the 354 hips Diagnosis Hips (%) Osteoarthritis 188 (53.1) Congenital hip dysplasia 85 (24.0) Avascular necrosis 39 (11.0) Post-traumatic osteoarthritis 21 (5.9) Rheumatoid arthritis 6 (1.7) Neck fracture 6 (1.7) Others 9 (2.5) Previous osteotomies 57 (16.1) The indications for using this implant were the absence of severe deformity of the femoral canal and adequate bone stock for uncemented fixation using the index of Singh, Nagrath and Maini, 31 as described by Spotorno et al. 32 We used either a modified Watson-Jones 33 or the transgluteal lateral approach according to Bauer et al 34 with the patient in the supine position. The surgical techniques and survival rates for this implant have been described previously. 23,25 The mean follow-up was 17 years (15 to 20). During this period, 86 patients (89 hips) died and eight patients (eight hips) were lost to follow-up, of whom four had moved abroad. At the time of the most recent review, 35 stems had been revised for isolated failure of the femoral component. Details of the diagnoses leading to THR are given in Table I. The patients were followed up at three and six months, at one year and yearly thereafter. Data were retrieved from a permanent continuous electronic database. Clinical and radiological data of all the patients with a peri-prosthetic femoral fracture were obtained directly from the medical records at our hospital or were acquired when revision surgery was performed elsewhere. The alignment of the stem in the coronal plane was determined on anteroposterior (AP) radiographs of the hip by measuring the angle formed between the long axis of the prosthesis and the long axis of the femur. 35 We also further evaluated the intramedullary position of the tip of the stem in the coronal and the sagittal planes on AP and lateral radiographs. Filling of the femoral canal, measured as the ratio of the width of the stem to the width of the medullary canal was determined at 3 cm below the lesser trochanter on the initial post-operative AP radiograph. 36 Subsidence of the stem was defined as distal migration of at least 5 mm of the distance between the proximal shoulder of the femoral component and the greater trochanter when the initial post-operative radiographs were compared with those taken at the follow-up by an author (MRS). The fractures were classified by two independent experienced orthopaedic surgeons (MC, PRA) according to the Vancouver classification, 37 which is reproducible and reliable. 38 Vancouver type-a fractures are located at the lesser trochanter (AL) and at the greater trochanter (AG). Type-B fractures are located around or just below a well-fixed stem (B1), around or just below a loose stem with adequate bone stock (B2), around or just below a loose stem with poor proximal bone stock (B3). Type-C fractures are located well below the stem. We included all types of fracture in the study. Minor trauma was defined as a fall to the floor at the same level on which the patient had been standing or sitting. Major trauma included traffic accidents and any other high-energy trauma. Spontaneous fractures were defined as those which occurred without a fall or obvious trauma. All the patients gave informed consent to participate in the study, which was approved by our institutional review board, and carried out in accordance with the Declaration of Helsinki, as revised in ,40 Statistical analysis. The Kaplan-Meier method using reoperation for a peri-prosthetic femoral fracture as the endpoint was used to calculate the cumulative incidence of fracture after primary THR, assessed with 95% confidence intervals (CI). The patients were censored at death, at revision of the stem for reasons unrelated to their fracture or at final follow-up, whichever came first. Differences in the cumulative incidence between different groups of patients were tested for statistical significance using the two-sided log-rank test. Continuous variables were compared using a two-sided Student t-test. We considered a p- value 0.05 to be significant. Data were recorded and analysed using SPSS version 17.0 (SPSS Inc., Chicago, Illinois) and Graphpad Prism version 5.0 (Graphpad Software, San Diego, California) software. Results During the follow-up period, 14 peri-prosthetic femoral fractures occurred in 14 patients (Fig. 1). There were seven men with a mean age of 52.4 years (47 to 59) and seven women with a mean age of 60.3 years (47 to 70). The distribution of the type of fracture according to the Vancouver classification was as follows: AG (1), B1 (3), B2 (7), B3 (2) and C (1). An operation was required in all 14 patients. Ten stems were found to be loose at operation and were therefore revised. The other four stems were well-fixed despite the femoral fracture which was treated by open reduction and internal fixation. None of these four stems had required subsequent revision by the final follow-up (Fig. 2). The Kaplan-Meier survival analysis showed no significant difference in the incidence of fracture according to gender or age at THR (Table II, Fig. 3). The mean time from primary THR to fracture was 11.7 years (3.4 to 18.2). In all, 12 of the 14 fractures occurred more than eight years after primary THR. The mean age at fracture in all cases was 68.2 years (56 to 87). In females it was 72 years (60 to 87) and in males it was 64.4 years (56 to 69), but this difference was not significant (Student s t-test, p = 0.08). There was no significant difference in the mean interval between THR and fracture in relation to gender (11.6 years (4.7 to 18.2) versus 11.8 years (3.4 to 17.2) for male and female patients, respectively; Student s t-test, p = 0.94). VOL. 93-B, No. 2, FEBRUARY 2011

3 180 M. R. STREIT, C. MERLE, M. CLARIUS, P. R. ALDINGER Original series 354 hips No stem revision, no fracture 307 hips Stem revision or peri-prosthetic fracture 39 hips Lost to follow-up 8 hips Aseptic loosening 17 hips Peri-prosthetic fracture 14 hips Infection 8 hips Stem unstable, stem revision 10 hips Stem stable, open reduction and internal fixation 4 hips Fig. 2a Fig. 2b Fig. 1 Diagram showing the distribution of hips evaluated at a mean of 17 years (15 to 20) post-operatively. There was also no significant difference in the mean age at the time of THR between patients with a subsequent fracture and those without (56.4 years (47 to 70) versus 56.1 years (13 to 81), respectively; Student s t-test, p = 0.93). In ten patients the fracture was caused by minor trauma, and in three by major trauma. In one patient it occurred spontaneously on turning while standing on the affected limb. In all cases, the peri-prosthetic femoral fracture was the only injury sustained. At the last follow-up before fracture, the stem was considered to be stable in all the patients and there were no planned stem revisions. No patient with this fracture reported any problems related to the hip before the fracture. The mean interval between last review and fracture was 3.1 years (0.5 to 11.3). Of the stems with a peri-prosthetic femoral fracture, four had a varus alignment of > 2. None had varus alignment of > 5 or valgus alignment of > 2. The intramedullary position of the tip of the stem was central in eight hips, lateral in two, anterolateral in one, posterolateral in one hip and posterior in one. In the remaining hip we could not accurately determine the position of the tip in the sagittal plane because of an inadequate lateral radiograph. There was no significant difference in the mean filling of the canal for hips with and without a fracture (81.0% (69.6% to 100.0%) vs 83.3% (52.2% to 100.0%), respectively; Student s t-test, p = 0.37). Of the hips evaluated radiologically at a minimum of 15 years, one hip had > 2 mm of subsidence of the stem. In this case, the stem showed early subsidence, which stabilised at 12 months after operation without further clinical or radiological signs of loosening at follow-up. In the patients who sustained a peri-prosthetic femoral fracture, subsidence had not been found at the last follow-up before the fracture occurred. Fig. 2c Anteroposterior radiographs of a 77-year-old man showing a) total hip arthroplasty after 20 years at the last follow-up four months before the fracture, b) a Vancouver type-b1 fracture with a well-fixed stem after minor trauma, c) a well-fixed stem without subsidence four years after treatment by open reduction and internal fixation. Table II. Cumulative incidence with 95% confidence intervals with the p-value at ten and 17 years Cumulative fracture incidence (%) Variable 10 years 17 years Overall 1.6 (0.7 to 3.8) 4.5 (2.6 to 8.0) Gender Male 2.0 (0.6 to 6.1) 4.8 (2.1 to 10.4) 0.74 Female 1.2 (0.3 to 4.8) 4.3 (1.9 to 9.6) Age (yrs) (0.5 to 5.1) 5.9 (3.1 to 11.2) 0.36 > (0.4 to 5.7) 2.3 (0.8 to 7.2) p-value (log-rank test) Discussion As stated in the introduction, the true incidence of periprosthetic femoral fracture after THR may have been underreported. We found a cumulative incidence of 4.5% (95% CI 2.6 to 8) at 17 years after primary uncemented THR. The rate of fracture was low until the eighth post-operative year THE JOURNAL OF BONE AND JOINT SURGERY

4 LATE PERI-PROSTHETIC FEMORAL FRACTURE AS A MAJOR MODE OF FAILURE IN UNCEMENTED PRIMARY HIP REPLACEMENT 181 Cumulative incidence (%) Cumulative incidence (%) Aseptic loosening Peri-prosthetic femoral fracture Time (yrs) Fig Time (yrs) Number at risk Inverted Kaplan-Meier plot showing peri-prosthetic fracture and aseptic loosening as major modes of failure with comparable cumulative incidence at 17 years after primary uncemented total hip replacement (4.5% (95% CI 2.6 to 8.0) and 5.7% (95% CI 3.5 to 9.3), respectively). Fig. 3 Inverted Kaplan-Meier plot showing an increasing rate of periprosthetic femoral fracture in the second decade after primary uncemented total hip replacement. The pick marks indicate censored data. and showed a continuous rise thereafter into the second decade (Fig. 3). These findings suggest that peri-prosthetic femoral fracture becomes an increasingly relevant mode of failure in the long term. In our present series, we found that there were two main modes of failure around uncemented tapered stems, which were aseptic loosening 23 and periprosthetic femoral fracture, which had a similar cumulative incidence at 17 years after primary THR (Fig. 4). The lower incidence of peri-prosthetic femoral fracture in previous studies may have been due to failure to use survivorship analysis to evaluate the fracture rate over time which extended to a maximum of 15 years in these reports, and failure to include all types of fracture. 14,16,19,21,41-43 Additionally it is possible that not all the information was included in registry reports, as surgeons may have considered some femoral fractures to be unrelated to the implant. In many follow-up studies, revision of the stem is applied as the endpoint but not re-operation related to peri-prosthetic femoral fracture when the stem is well fixed. In our study, we chose a consecutive series of primary THRs with one type of femoral component, thereby avoiding any confounding due to differences in the design, and analysed the incidence of fracture using the Kaplan-Meier method of estimating survival. Recent studies have contributed to a better understanding of the aetiology and risk factors for peri-prosthetic femoral fractures. 27 The Swedish Hip Registry has identified minor trauma as a major risk factor, accounting for approximately 75% of late peri-prosthetic femoral fractures, 22 a finding reflected in our study. Furthermore, aseptic loosening has been shown to be an important risk factor for this fracture after cemented THR. 2,22,41,44-46 Although two hips showed significant osteopenia of the proximal femur at the time of fracture, in our study using uncemented stems we did not find pre-fracture evidence of loosening of the femoral component at the last follow-up examinations. At the last clinical and radiological evaluation before peri-prosthetic femoral fracture, all the stems were considered to be well fixed. No patient reported any problems related to the hip before the fracture while those with late aseptic loosening often described the sudden onset of pain. 23 The mean filling of the canal in hips with a peri-prosthetic femoral fracture was not significantly different from that in hips without a fracture. It has been reported previously with this stem that aseptic loosening rarely occurs when the stem is not undersized. 25 Therefore we assume that the ten stems found to be loose intra-operatively had traumatic loosening, although pre-fracture loosening after the last follow-up cannot be excluded completely. The importance of aseptic loosening as a predisposing factor for peri-prosthetic femoral fracture may differ between cemented and uncemented THR. Other generally accepted risk factors for these fractures are osteoporosis, 26,43,47-50 osteolysis, 7,44,51 revision procedures, 1,42,50 and several pre-operative diagnoses, in particular rheumatoid arthritis, 22,50,52 and hip fracture as indication for the original THR. 50,52 Other factors such as age, 10,15,26,50,52 gender, 10,15,44 the type of implant 15,22 and the method of fixation used 14,53 show no consistency in the literature as risk factors. In our study, no significant difference in the incidence of peri-prosthetic femoral fracture in relation to gender or age at the time of primary THR was found. We could not find a relationship between the intramedullary position of the tip or alignment of the stem and the incidence of fracture. However, the primary weakness of VOL. 93-B, No. 2, FEBRUARY 2011

5 182 M. R. STREIT, C. MERLE, M. CLARIUS, P. R. ALDINGER our study is its relatively low power to reveal relevant risk factors because of the small number of fractures and a relatively small series of 354 hips compared with various national registries. Findings in our study suggest that minor trauma resulting from a fall plays the most important role in the pathogenesis of peri-prosthetic femoral fracture after uncemented THR. The same mechanism is known to account for approximately 90% of hip fractures in the elderly. 54 As the risk of falling established in previous research varies from 28% to 70% per year among subjects aged 65 years and older and the incidence of falls rise with increasing age, 60,61 we believe that this accounts for the rising incidence of periprosthetic femoral fracture in the second decade after primary THR. The findings of our study may not apply to all types of cementless stem. The CLS Spotorno stem is designed to achieve press-fit fixation in the proximal femur, so it could be speculated that proximal stress concentration during a fall involving impact may be a pathogenic factor, especially in an ageing skeleton. Implant-related bone remodelling may also have some relevance. Further studies are necessary to decide whether the design of the implant has an influence on the incidence of fracture in the long term after the implantation of uncemented stems. In conclusion, our findings indicate that, besides aseptic loosening, peri-prosthetic femoral fracture is a major mode of failure in the long term after an uncemented THR. Rates of revision for this problem rise in the second decade. It is likely that longer periods of follow-up will show more fractures in the third decade. We believe that at this time there is insufficient evidence available to conclude whether or not cemented or cementless fixation makes a difference regarding the incidence of such fractures in the long term. Despite this important complication, the 17-year re-operation rate for all problems related to the femoral component is still low and the device remains in continued use for uncemented THR. Further evaluation should focus on the risk factors for these fractures after uncemented THR and the development of prevention strategies. Listen live Listen to the abstract of this article at We thank the non-commercial research fund Deutsche Arthrose-Hilfe e.v. for supporting this study. The author or one or more of the authors have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. In addition, benefits have been or will be directed to a research fund. References 1. Lewallen DG, Berry DJ. Periprosthetic fracture of the femur after total hip arthroplasty: treatment and results to date. Instr Course Lect 1998;47: Tower SS, Beals RK. Fractures of the femur after hip replacement: the Oregon experience. Orthop Clin North Am 1999;30: Laffargue P, Soenen M, Pinoit Y, Migaud H. Periprosthetic fractures around total hip and knee arthroplasty: mortality, morbidity and prognostic factors of periprosthetic femoral fractures following hip arthroplasty: multicentric prospective assessment of 115 cases. Rev Chir Orthop Reparatrice Appar Mot 2006;92(Suppl2)):64-9 (in French). 4. Lindahl H, Oden A, Garellick G, Malchau H. The excess mortality due to periprosthetic femur fracture: a study from the Swedish national hip arthroplasty register. Bone 2007;40: Young SW, Walker CG, Pitto RP. Functional outcome of femoral periprosthetic fracture and revision hip arthroplasty: a matched-pair study from the New Zealand Registry. Acta Orthop 2008;79: Zuurmond RG, van Wijhe W, van Raay JJ, Bulstra SK. High incidence of complications and poor clinical outcome in the operative treatment of periprosthetic femoral fractures: an analysis of 71 cases. Injury 2010;41: Schmidt AH, Kyle RF. Periprosthetic fractures of the femur. Orthop Clin North Am 2002;33: Bhattacharyya T, Chang D, Meigs JB, Estok DM 2nd, Malchau H. Mortality after periprosthetic fracture of the femur. J Bone Joint Surg [Am] 2007;89-A: Berry DJ. Epidemiology: hip and knee. Orthop Clin North Am 1999;30: Lindahl H, Garellick G, Regnér H, Herberts P, Malchau H. Three hundred and twenty-one periprosthetic femoral fractures. J Bone Joint Surg [Am] 2006;88-A: Berry DJ. Periprosthetic fractures associated with osteolysis: a problem on the rise. J Arthroplasty 2003;18(Suppl 1): Meek RM, Norwood T, Smith R, Brenkel IJ, Howie CR. The risk of peri-prosthetic fracture after primary and revision total hip and knee replacement. J Bone Joint Surg [Br] 2011;93-B: DeFrances CJ, Hall MJ National Hospital Discharge Survey. Adv Data 2004;342: Lindahl H. Epidemiology of periprosthetic femur fracture around a total hip arthroplasty. Injury 2007;38: Cook RE, Jenkins PJ, Walmsley PJ, Patton JT, Robinson CM. Risk factors for periprosthetic fractures of the hip: a survivorship analysis. Clin Orthop 2008;466: Lowenhielm G, Hansson LI, Karrholm J. Fracture of the lower extremity after total hip replacement. Arch Orthop Trauma Surg 1989;108: Morrey BF, Kavanagh BF. Complications with revision of the femoral component of total hip arthroplasty: comparison between cemented and uncemented techniques. J Arthroplasty 1992;7: Crockarell JR Jr, Berry DJ, Lewallen DG. Nonunion after periprosthetic femoral fracture associated with total hip arthroplasty. J Bone Joint Surg [Am] 1999;81- A: Havelin LI, Engesaeter LB, Espehaug B, et al. The Norwegian Arthroplasty Register: 11 years and 73,000 arthroplasties. Acta Orthop Scand 2000;71: Lucht U. The Danish Hip Arthroplasty Register. Acta Orthop Scand 2000;71: Sarvilinna R, Huhtala HS, Puolakka TJ, Nevalainen JK, Pajamaki KJ. Periprosthetic fractures in total hip arthroplasty: an epidemiologic study. Int Orthop 2003;27: Lindahl H, Malchau H, Herberts P, Garellick G. Periprosthetic femoral fractures: classification and demographics of 1049 periprosthetic femoral fractures from the Swedish National Hip Arthroplasty Register. J Arthroplasty 2005;20: Aldinger PR, Jung AW, Breusch SJ, Ewerbeck V, Parsch D. Survival of the cementless Spotorno stem in the second decade. Clin Orthop 2009;467: Muirhead-Allwood SK, Sandiford N, Skinner JA, et al. Uncemented custom computer-assisted design and manufacture of hydroxyapatite-coated femoral components: survival at 10 to 17 years. J Bone Joint Surg [Br] 2010;92-B: Aldinger PR, Jung AW, Pritsch M, et al. Uncemented grit-blasted straight tapered titanium stems in patients younger than fifty-five years of age: fifteen to twenty-year results. J Bone Joint Surg [Am] 2009;91-A: Wu CC, Au MK, Wu SS, Lin LC. Risk factors for postoperative femoral fracture in cementless hip arthroplasty. J Formos Med Assoc 1999;98: Franklin J, Malchau H. Risk factors for periprosthetic femoral fracture. Injury 2007;38: Foster AP, Thompson NW, Wong J, Charlwood AP. Periprosthetic femoral fractures: a comparison between cemented and uncemented hemiarthroplasties. Injury 2005;36: Benum P, Aamodt A. Uncemented custom femoral components in hip arthroplasty: a prospective, clinical study of 191 hip followed for at least 7 years. Acta Orthop 2010;81: Radl R, Aigner C, Hungerford M, Pascher A, Windhager R. Proximal femoral bone loss and increased rate of fracture with a proximally hydroxyapatite-coated femoral component. J Bone Joint Surg [Br] 2000;82-B: Singh M, Nagrath AR, Maini PS. Changes in trabecular pattern of the upper end of the femur as an index of osteoporosis. J Bone Joint Surg [Am] 1970;52-A: Spotorno L, Romagnoli S, Ivaldo N, et al. The CLS system: theoretical concept and results. Acta Orthop Belg 1993;59(Suppl 1): THE JOURNAL OF BONE AND JOINT SURGERY

6 LATE PERI-PROSTHETIC FEMORAL FRACTURE AS A MAJOR MODE OF FAILURE IN UNCEMENTED PRIMARY HIP REPLACEMENT Vicar AJ, Coleman CR. A comparison of the anterolateral, transtrochanteric and posterior surgical approaches in primary total hip arthroplasty. Clin Orthop 1984;188: Bauer R, Kerschbaumer F, Poisel S, Oberthaler W. The transgluteal approach to the hip joint. Arch Orthop Trauma Surg 1979;95: Min BW, Song KS, Bae KC, et al. The effect of stem alignment on results of total hip arthroplasty with a cementless tapered-wedge femoral component. J Arthroplasty 2008;23: Garcia-Cimbrelo E, Cruz-Pardos A, Madero R, Ortega-Andreu M. Total hip arthroplasty with use of the cementless Zweymuller Alloclassic system: a ten to thirteen-year follow-up study. J Bone Joint Surg [Am] 2003;85-A: Brady OH, Garbuz DS, Masri BA, Duncan CP. Classification of the hip. Orthop Clin North Am 1999;30: Brady OH, Garbuz DS, Masri BA, Duncan CP. The reliability and validity of the Vancouver classification of femoral fractures after hip replacement. J Arthroplasty 2000;15: Rickham PP. Human experimentation code of ethics of the World Medical Association: Declaration of Helsinki. Br Med J 1964;2: No authors listed. World Medical Association Declaration of Helsinki: ethical principles for medical research involving human subjects web/ / (date last accessed 23 December 2010). 41. Fredin HQ, Lindberg H, Carlsson AS. Femoral fracture following hip arthroplasty. Acta Orthop Scand 1987;58: Kavanagh BF. Femoral fractures associated with total hip arthroplasty. Orthop Clin North Am 1992;23: Beals RK, Tower SS. Periprosthetic fractures of the femur: an analysis of 93 fractures. Clin Orthop 1996;327: Tsiridis E, Haddad FS, Gie GA. The management of periprosthetic femoral fractures around hip replacements. Injury 2003;34: Beathea JS 3rd, DeAndrade JR, Fleming LL, Lindenbaum SD, Welch RB. Proximal femoral fractures following total hip arthroplasty. Clin Orthop 1982;170: Harris B, Owen JR, Wayne JS, Jiranek WA. Does femoral component loosening predispose to femoral fracture?: an in vitro comparison of cemented hips. Clin Orthop 2010;468: Learmonth ID. The management of periprosthetic fractures around the femoral stem. J Bone Joint Surg [Br] 2004;86-B: Hsieh PH, Chang YH, Lee PC, Shih CH. Periprosthetic fractures of the greater trochanter through osteolytic cysts with uncemented MicroStructured Omnifit prosthesis: retrospective analyses of 23 fractures in 887 hips after 5-14 years. Acta Orthop 2005;76: Kelley SS. Periprosthetic femoral fractures. J Am Acad Orthop Surg 1994;2: Lindahl H. The periprosthetic femur fracture: a study from the Swedish National Hip Arthroplasty Register [Abstract] ?locale=en (date last accessed 26 October 2010). 51. Pazzaglia U, Byers PD. Fractured femoral shaft through an osteolytic lesion resulting from the reaction to a prosthesis: a case report. J Bone Joint Surg [Br] 1984;66- B: Sarvilinna R, Huhtala H, Pajamaki J. Young age and wedge stem design are risk factors for periprosthetic fracture after arthroplasty due to hip fracture: a case-control study. Acta Orthop 2005;76: Robinson CM, Adams CI, Craig M, et al. Implant-related fractures of the femur following hip fracture surgery. J Bone Joint Surg [Am] 2002;84-A: Baker SP, Harvey AH. Fall injuries in the elderly. Clin Geriatr Med 1985;1: Tinetti ME, Speechley M, Ginter SF. Risk factors for falls among elderly persons living in the community. N Engl J Med 1988;319: Blake AJ, Morgan K, Bendall MJ, et al. Falls by elderly people at home: prevalence and associated factors. Age Ageing 1988;17: Campbell AJ, Borrie MJ, Spears GF. Risk factors for falls in a community-based prospective study of people 70 years and older. J Gerontol 1989;44:M Gryfe CI, Amies A, Ashley MJ. A longitudinal study of falls in an elderly population. I: incidence and morbidity. Age Ageing 1977;6: Tinetti ME. Factors associated with serious injury during falls by ambulatory nursing home residents. J Am Geriatri Soc 1987;35: Campbell AJ, Spears GF, Borrie MJ. Examination by logistic regression modelling of the variables which increase the relative risk of elderly women falling compared to elderly men. J Clin Epidemiol 1990;43: Wickham C, Cooper C, Margetts BM, Barker DJ. Muscle strength, activity, housing and the risk of falls in elderly people. Age Ageing 1989;18: VOL. 93-B, No. 2, FEBRUARY 2011