Radiographic structural abnormalities associated with premature, natural hip-joint failure

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1 Washington University School of Meicine Digital Open Access Publications 5-4- Raiographic structural abnormalities associate with premature, natural hip-joint failure John C. Clohisy Washington University School of Meicine in St. Louis Michael A. Dobson Washington University School of Meicine in St. Louis Jason F. Robison Washington University School of Meicine in St. Louis Lucian C. Warth University of Iowa School of Meicine Jie Zheng Washington University School of Meicine in St. Louis See next page for aitional authors Follow this an aitional works at: Part of the Meicine an Health Sciences Commons Recommene Citation Clohisy, John C.; Dobson, Michael A.; Robison, Jason F.; Warth, Lucian C.; Zheng, Jie; Liu, Steve S.; Yehyawi, Tameem M.; an Callaghan, John J.,,"Raiographic structural abnormalities associate with premature, natural hip-joint failure." The Journal of Bone an Joint Surgery.93,Supplement (). This Open Access Publication is brought to you for free an open access by Digital It has been accepte for inclusion in Open Access Publications by an authorize aministrator of Digital For more information, please contact

2 Authors John C. Clohisy, Michael A. Dobson, Jason F. Robison, Lucian C. Warth, Jie Zheng, Steve S. Liu, Tameem M. Yehyawi, an John J. Callaghan This open access publication is available at Digital

3 3 COPYRIGHT Ó BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Raiographic Structural Abnormalities Associate with Premature, Natural Hip-Joint Failure By John C. Clohisy, MD, Michael A. Dobson, MD, Jason F. Robison, MD, Lucian C. Warth, MD, Jie Zheng, MS, Steve S. Liu, MD, Tameem M. Yehyawi, MD, an John J. Callaghan, MD Investigation performe at Washington University School of Meicine, St. Louis, Missouri, an University of Iowa School of Meicine, Iowa City, Iowa Backgroun: Significant controversy exists regaring the causes of premature, natural hip-joint failure. Ientification of these causes may guie future investigations targeting prevention of this isorer. The aims of this stuy were to: (1) etermine an characterize structural abnormalities associate with premature, natural hip-joint failure, an () analyze isease progression in the contralateral hips of patients with femoroacetabular impingement eformities. Methos: We analyze 604 patients (710 hips) from three ifferent meical centers who unerwent primary total hip arthroplasty at or before fifty years of age (average age, forty years). Three hunre fourteen patients (5%) were male, an 90 patients (48%) were female. Results: The iagnoses associate with premature hip failure varie, but osteoarthritis an osteonecrosis were most common. Raiographic abnormalities associate with evelopmental hip ysplasia an femoroacetabular impingement were associate with the majority of osteoarthritic hips. Hips with femoroacetabular impingement eformities emonstrate istinct structural anatomy relative to asymptomatic hips, with a high prevalence of bilateral eformities. In a subgroup of seventy patients with femoroacetabular impingement eformities, contralateral raiographic isease progression or the nee for total hip arthroplasty was observe in 73% of hips. Conclusions: Osteoarthritis an osteonecrosis are the major causes of premature hip-joint failure in young patients. Femoroacetabular impingement abnormalities are usually bilateral an are commonly associate with progression of the isease to the contralateral hip. Level of Evience: Prognostic Level IV. See Instructions to Authors for a complete escription of levels of evience. Avariety of isorers, incluing osteoarthritis, osteonecrosis of the femoral hea, inflammatory arthritis, an posttraumatic conitions, can cause en-stage hip isease. For patients who are fifty years of age or younger, en-stage isease can be consiere premature an treatment is challenging ue to long life expectancies an potentially high activity levels. Thus, the concepts of early iagnosis an hip-joint preservation surgery have gaine increase attention 1,. While previous stuies have ocumente structural abnormalities associate with seconary osteoarthritis 3-6, there is a lack of comprehensive information regaring the causes of en-stage isease in the young patient. Refinements in unerstaning the structural etiology of seconary osteoarthritis have highlighte evelopmental ysplasia of the hip an femoroacetabular impingement as possible precursors 1,. Femoroacetabular impingement has receive recent attention ue to improve methos of iagnosis an innovations in surgical treatment 7-1. Nevertheless, the role of femoroacetabular impingement in osteoarthritis remains controversial because a cause-an-effect relationship has not been rigorously establishe. Aitionally, the prevalence of femoroacetabular impingement abnormalities in hips with premature osteoarthritis is not known. The prevalence of bilateral isease, the fate of untreate femoroacetabular impingement eformities, an the prognostic factors for isease progression are topics of current controversy. Our stuy was esigne to analyze a large cohort of patients with premature, en-stage hip isease who unerwent primary total hip arthroplasty at or before fifty years of age. We performe a series of investigations to (1) etermine an characterize the Disclosure: In support of their research for or preparation of this work, one or more of the authors receive, in any one year, outsie funing or grants in excess of $10,000 from Zimmer, Inc. In aition, one or more of the authors or a member of his or her immeiate family receive, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provie such benefits from commercial entities (Zimmer, Inc., an DePuy). J Bone Joint Surg Am. ;93 Suppl :3-9 oi:10.106/jbjs.j.01734

4 4 structural abnormalities associate with premature, natural hipjoint failure an () analyze isease progression in the contralateral hips of patients with femoroacetabular impingement eformities. Materials an Methos Stuy Overview Aretrospective search was performe to ientify all patients who were treate with primary total hip arthroplasty at fifty years of age or younger by any of five orthopaeic surgeons at three meical centers. Six hunre an four patients (710 hips) with available meical recors an raiographs were ientifie an inclue. The total hip arthroplasties were performe between the years of 1975 an 005. The stuy protocol was approve by our institutional review boars. The average patient age at surgery was forty years (range, twelve to fifty); 314 patients (368 hips) were male, an 90 patients (34 hips) were female. All pertinent meical an surgical history information in conjunction with raiographic analysis of acetabular an proximal femoral anatomy were utilize to etermine the apparent cause of natural hip-joint failure. The cases were initially classifie into broa iagnostic categories, incluing osteoarthritis, osteonecrosis, inflammatory arthritis, posttraumatic isease, other conitions, an too far avance to etermine. Osteoarthritis cases were further evaluate to etermine associate structural abnormalities. These abnormalities were classifie as evelopmental ysplasia of the hip, slippe capital femoral epiphysis, Legg-Calvé- Perthes isease, or osteoarthritis of unknown etiology. Cases that were classifie as having an unknown etiology unerwent a comprehensive raiographic review to characterize the etaile structural anatomy an to ientify eformities consistent with femoroacetabular impingement. A subgroup of seventy patients with femoroacetabular impingement abnormalities an serial raiographs over time was ientifie an stuie to assess the prevalence of bilateral eformities an the risk of isease progression in the contralateral hip. Clinical an Raiographic Disease Classification Meical recor review inclue outpatient clinic notes, inpatient charts, an operative notes. Raiographic evaluation use all raiographs available. If multiple raiographs existe that spanne an extene time perio, the earliest were use to assess structural features of the hip so that any istortion cause by the presence of seconary osteoarthritis woul be minimize. Alternatively, the raiographs of highest quality were utilize. All cases were reviewe by the senior author (J.C.C.) to provie consistency with regar to isease classification. Cases categorize as osteoarthritis were further analyze for the presence of raiographic structural abnormalities. Measurements mae from the anteroposterior pelvic raiograph 13 inclue the lateral center-ege angle 14, the acetabular inex 15,16, the neck-shaft angle 17, the acetabular epth (coxa profuna or protrusio) 13, an the Tönnis osteoarthritis grae 18. A hip was classifie as coxa profuna if the meial wall of the acetabulum abutte or traverse the ilioischial line an/or ha a lateral center-ege angle of 40, an it was classifie as coxa protrusio if the meial aspect of the femoral hea crosse the ilioischial line 13. Femoral hea sphericity was ocumente 19. Characterization of acetabular version was accomplishe by examining for the acetabular crossover sign 13,0. This was recore an analyze only when the anterior an posterior lips of the acetabulum coul be visualize an the pelvic raiograph emonstrate no pelvic rotation an tilt 17,0. From the cross-table lateral projections, hea-neck offset an hea-neck offset ratio were measure with use of the technique escribe by Eijer et al. 1,. Hea sphericity was also note on the lateral projections 19. For cases that ha a false-profile raiograph 3, the anterior center-ege angle was measure 13,15,16. All raiographic measurements were performe or supervise by one senior author (J.C.C.). Specific raiographic features were consiere inicators of associate structural hip isease. Developmental ysplasia of the hip was consiere to be the primary iagnosis for hips with a lateral center-ege angle of <0 an an acetabular inclination of >15. In the absence of structural features for evelopmental ysplasia of the hip, hips with ecrease hea-neck offset (<9 mm) 19,1,, ecrease hea-neck offset ratio (<0.17), or aspherical femoral heas 19,1, were classifie as having a cam impingement eformity. Similarly, retroverte acetabula, coxa profuna, or coxa protrusio were ientifie as pincer impingement eformities 1,8,10,1,13,4. Hips exhibiting features of both cam an pincer impingement were consiere combine impingement eformities 8. Femoroacetabular Impingement: Prevalence of Bilateral Deformities an Disease Progression in the Contralateral Hip Hips with raiographic finings of femoroacetabular impingement were stuie in etail to etermine the prevalence of bilateral femoroacetabular impingement eformities an the risk of isease progression in the contralateral hip over time. The 118 hips with femoroacetabular impingement were screene to ientify patients who ha aequate serial raiographs (at least two istinct time points) that spanne a minimum of four years. This yiele seventy hips for inclusion in this aspect of the investigation: fifty (71.4%) in men an twenty (8.6%) in women. The average age at the time of inex arthroplasty was forty-four years (range, twenty-three to fifty years). The contralateral hip (not unergoing initial arthroplasty) was the focus of this portion of the stuy. Raiographic parameters analyze inclue age, sex, type of impingement, alpha angle 5, hea-neck offset ratio, functional hea-neck offset ratio, acetabular version, lateral center-ege angle, acetabular inclination, Tönnis osteoarthritis grae, an minimum joint-space with 6. All raiographic measurements were mae with use of establishe raiographic parameters with the exception of the measurement for functional hea-neck offset ratio, which was mae as previously escribe for hea-neck offset ratio 1 except that the most anterior or anterolateral aspect of the femoral hea was etermine by incluing osteophytes an/or reactive bone superimpose on a visible femoral neck cortex. The investigators who mae the raiographic measurements were bline to patient name, film ate, an clinical status. The clinical an raiographic isease progression was etermine by objective en points, incluing subsequent total hip arthroplasty or the progression of raiographic osteoarthritis grae. The average time from the first raiograph to the last raiograph was 8.8 years (average, 0.3 to 30.5 years). Subjects were efine as having an event if they unerwent total hip arthroplasty or showe progression of Tönnis osteoarthritis grae uring the follow-up time perio. Statistical analysis was performe to etermine the factors associate with an event. Structural Hip-Anatomy Comparison Group A comparison group was establishe as previously escribe an consiste of patients who were fifty years or younger who presente to one author s clinic (J.C.C.) with complaints of back or leg pain an ha a complete raiographic hip series prior to clinical evaluation. History an physical examination reveale no signs or symptoms of intrinsic hip isease. Specifically, no patient ha groin pain, hip-joint irritability, asymmetric or iminishe range of hip motion, or a positive impingement test. The majority of these patients ha signs an symptoms consistent with lumbar spinal isease in the absence of hip involvement. Thirty-five patients (forty-two hips) with an average age of 38.5 years (range, eighteen to fifty years) were ientifie an use as the comparison group. The raiographic ata from twenty-two of these patients have been publishe previously.elevenpatients (fourteen hips) were male an twenty-four patients (twenty-eight hips) were female. Statistical Analysis All ata are reporte as the mean plus the stanar eviation for continuous variables an the number of patients (an the percentage of the group) for categorical variables. When the baseline characteristics an raiographic parameters were compare between the ifferent groups separately (comparison group vs. combine groups, patients with subsequent total hip arthroplasty surgery vs. patients without subsequent total hip arthroplasty surgery), chisquare tests were use for categorical variables an unpaire t tests were use for continuous variables. Raiographic parameters of the comparison group an combine impingement groups were analyze by sex. For categorical variables, if the cell count was too low (n < 5), the Fisher exact test was use instea. Among the seventy patients with femoroacetabular impingement, logistic regression moels were use to etermine if any preictors were associate with raiographic outcomes. Os ratios an the corresponing 95%

5 5 TABLE I Diagnostic Categories an Patient Characteristics for 604 Patients (710 Hips) with Premature Hip-Joint Failure Accoring to Sex Number of Hips* Age of Patients (yr) Diagnosis Female (N = 34) Male (N = 368) Overall (N = 710) Female (N = 34) Male (N = 368) Overall (N = 710) Osteoarthritis 190 (55.6%) 147 (40%) 337 (47.5%) 40.9 ± ± ± 8.0 Osteonecrosis 63 (18.4%) 14 (38.6%) 05 (8.9%) 35.8 ± ± ± 7.6 Posttraumatic isease 3 (9.4%) 9 (7.9%) 61 (8.6%) 41.8 ± ± ± 8.1 Inflammatory arthritis 36 (10.5%) 19 (5.%) 55 (7.7%) 36.4 ± ± ± 9. Too far avance 14 (4.1%) 7 (7.3%) 41 (5.8%) 38.6 ± ± ± 8.4 Other 7 (.1%) 4 (1.1%) 11 (1.5%) 31.0 ± ± ± 11.5 *The values are expresse as the number an percent of patients. The values are expresse as years of age an the stanar eviation. A significant ifference (p < 0.01) was seen between men an women within the same isease group. A significant ifference (p < 0.05) was seen between men an women within the same isease group. TABLE II Raiographic Parameters of Hips Accoring to Sex* Osteoarthritic Hips Variables Asymptomatic Hips (Comparison Group) With Cam-type or Combine Impingement Deformity P Value With Pincer-type or Combine Impingement Deformity P Value Sex = male n = 14 n = 83 n = 6 Age (yr) 41.4 ± 6.4 (n = 14) 44.4 ± 5.1 (n = 83) ± 5. (n = 6) LCE angle (eg) 31.4 ± 7.1 (n = 14) 6.9 ± 9.6 (n = 8) ± 8. (n = 6) Acetabular inclination (eg) 7.5 ± 7.0 (n = 14) 10.4 ± 7.3 (n = 8) ± 7.0 (n = 6) Neck-shaft angle (eg) 136 ± 5(n= 14) 137 ± 7(n= 8) ± 8(n= 6) ACE angle (eg) 31.8 ± 9.9 (n = 9) 7.4 ± 15.9 (n = 1) ± 9.3 (n = 3) Hea-neck offset ratio 0.18 ± 0.05 (n = 13) 0.09 ± 0.11 (n = 58) < ± 0.11 (n = ) Crossover sign n = 14 n = n = No 9 (64%) 19 (63%) 3 (3%) Yes 5 (36%) 11 (37%) 10 (77%) Femoral hea sphericity n = 14 n = n = Aspherical 0 0 (36%) 9 (43%) Spherical 14 (100%) 35 (64%) 1 (57%) Sex = female n = 8 n = 8 n = 17 Age (yr) 37.0 ± 10.4 (n = 8) 43.5 ± 5.3 (n = 8) ± 4.9 (n = 17) LCE angle (eg) 31. ± 6.9 (n = 8) 31.8 ± 10.6 (n = 7) ± 13.1 (n = 17) 0.0 Acetabular inclination (eg).64 ± 5.80 (n = 8) 8.59 ± 5.9 (n = 7) < ± 6.45 (n = 17) Neck-shaft angle (eg) 136 ± 5(n= 8) 134 ± 6(n= 7) ± 6(n= 17) 0.31 ACE angle (eg) 3. ± 7.0 (n = 0) 35.1 ± 15.9 (n = 11) ± 17.0 (n = 7) 0.5 Hea-neck offset ratio 0.19 ± 0.05 (n = 6) 0.10 ± 0.09 (n = 3) < ± 0.10 (n = 17) Crossover sign n = 8 n = n = 11 <0.001 No 6 (93%) 7 (47%) 3 (7%) Yes (7%) 8 (53%) 8 (73%) Femoral hea sphericity n = 8 n = 0.01 n = Aspherical 0 5 (3%) 3 (3%) Spherical 8 (100%) 17 (77%) 10 (77%) *Unless otherwise inicate, the values are expresse as the mean plus the stanar eviation for continuous variables an the number of patients (an the percentage of the group) for categorical variables. LCE = lateral center-ege, an ACE = anterior center-ege.

6 6 confience intervals were reporte. A p value of <0.05 was use to etermine significance. All analyses were performe with use of SAS statistical software (Version 9; SAS Institute, Cary, North Carolina). Source of Funing This stuy was supporte in part by a grant from the Curing Hip Disease Fun, which was utilize for research personnel salary an ata analysis. Results Etiologies of Premature Degeneration of the Hip Joint The iagnoses associate with premature failure of the hip joint varie, yet osteoarthritis an osteonecrosis were the ominant conitions associate with hip replacement surgery (Table I). Of the 710 hips, 337 (47.5%) ha osteoarthritis, 05 (8.9%) ha osteonecrosis, sixty-one (8.6%) ha posttraumatic isease, fifty-five (7.7%) ha inflammatory arthritis, an forty-one (5.8%) ha isease too far avance to allow accurate measurements or classification. Within the osteoarthritis group, 163 (48.4%) hips were classifie as having evelopmental ysplasia of the hip, thirty-two (9.5%) as having Legg-Calvé- Perthes isease, twenty-one (6.%) as having slippe capital femoral epiphysis, an 11 (35.9%) as having an unknown etiology. Raiographic Abnormalities Associate with Osteoarthritic Hips with Unknown Etiology Detaile raiographic analysis of osteoarthritic hips with an unknown etiology emonstrate a high prevalence of structural abnormalities associate with femoroacetabular impingement. Analysis of the 11 hips in which the cause of isease was unclear reveale that seventy-six hips (6.8%) ha raiographic features consistent with cam impingement; seven (6%), with pincer impingement; an thirty-five (30%), with combine cam an pincer impingement. These patients with femoroacetabular impingement eformities were more likely to be male (71.4%) compare with the total hip arthroplasty group as a whole (5% male) (p = ). We analyze the same raiographic parameters in reference to our comparison group of asymptomatic hips. To separately analyze cam an pincer abnormalities, all hips with cam eformities (cam only an combine cam an pincer cases) were groupe together (n = 111) as were all hips with pincer eformities (pincer only an combine cam an pincer) (n = 43) (Table II). Hips were also analyze accoring to sex to control for sex-specific morphologies. Male patients with cam impingement eformities ha structural ifferences when analyze with the comparison group (Table II). These inclue a ecrease hea-neck offset ratio (p < ) an a higher percentage of hips with an aspherical femoral hea (p = 0.007). Female patients with cam impingement eformities ha an increase acetabular inclination (p < 0.001), a ecrease heaneck offset ratio (p < 0.001), a higher percentage of hips with a crossover sign (p = 0.001), an a higher percentage of hips with an aspherical femoral hea (p = 0.01). Male patients with pincer eformities emonstrate reuce hea-neck offset ratio (p = 0.014) an a higher percentage of hips with an aspherical femoral hea (p = 0.005; Table II). When analyze with the comparison group, female patients with a pincer eformity emonstrate an increase lateral center-ege angle (p = 0.0), an increase acetabular inclination (p = 0.019), an a ecrease hea-neck offset ratio (p = 0.009) an compose a higher percentage of hips with a crossover sign (p < 0.001) an an aspherical femoral hea (p = 0.07). TABLE III Baseline Characteristics of the Seventy Patients with Femoroacetabular Impingement Accoring to the Nee for Subsequent Contralateral Total Hip Arthroplasty (THA)* Variables Patients without Subsequent Contralateral THA (N = 44) Patients with Subsequent Contralateral THA (N = 6) P Value Age (yr) 43.5 ± ± Alpha angle (eg) 76.6 ± ± 15.5 <0.001 LCE angle (eg) 8.3 ± ± 7.3 <0.001 Acetabular inclination (eg) 7.74 ± ± Hea-neck offset ratio 0.11 ± ± Functional hea-neck 0.07 ± ± offset ratio Joint-space with (mm) 0.06 ± ± 0.0 <0.001 Percent (no.) of female hips 5.0 (11) 34.6 (9) Impingement type (percent [no.]) 0.33 Cam 70.5 (31) 84.6 () Pincer 6.8 (3) 0 Both.7 (10) 15.4 (4) *Unless otherwise inicate, the values are expresse as the mean plus the stanar eviation for continuous variables an the number of patients (an the percentage of the group) for categorical variables. LCE = lateral center-ege.

7 7 TABLE IV Os Ratios of Risk Factors for Subsequent Contralateral Total Hip Arthroplasty in the Seventy Patients with Femoroacetabular Impingement Variable Os Ratio (95% Confience Interval) P Value Alpha angle* 1.98 (1.33,.95) LCE angle 0.87 (0.79, 0.95) 0.00 Acetabular inclination 1.1 (1.0, 1.) 0.01 Hea-neck offset ratio* 0.3 (0.07, 0.8) 0.04 Functional hea-neck 0.4 (0.10, 0.55) offset ratio* Joint-space with 0.53 (0.38, 0.73) <0.001 Both/pincer versus cam (cam was reference group) 0.43 (0.13, 1.51) *The os ratio of the alpha angle was base on a 10 increase; the os ratios of the hea-neck offset ratio an the functional hea-neck offset ratio were base on a 0.1 increase. LCE = lateral center-ege. Contralateral Disease Progression in Patients with Femoroacetabular Impingement Screening of the 118 hips that ha structural eformities consistent with femoroacetabular impingement ientifie seventy with aequate serial raiographs spanning a minimum of four years or until contralateral total hip arthroplasty. The average uration of raiographic monitoring of the contralateral hip was 8.8 years (range, 0.3 to 30.5 years). Structural abnormalities were foun in the contralateral hips of all seventy patients with femoroacetabular impingement eformities. Of the seventy contralateral hips analyze, fifty-one (73%) unerwent subsequent total hip arthroplasty or emonstrate a progression in osteoarthritis grae. Twenty-six (37%) of the seventy hips unerwentsubsequenttotalhiparthroplastyatanaverageof 5.1 years (range, zero to nineteen years) after the initial total hip arthroplasty in the other limb. Twenty-five (36%) of the seventy hips emonstrate progression of the Tönnis osteoarthritis grae at an average of 8.4 years (range, 0.6 to twenty-one). Analysis of baseline characteristics (Table III) inicate that patients unergoing total hip arthroplasty ha major ifferences in structural hip anatomy compare with the anatomy in patients who i not require surgery. Os ratio analysis for subsequent total hip arthroplasty reveale that an increase alpha angle an acetabular inclination were the strongest preictors of subsequent total hip arthroplasty (Table IV). These finings inicate that a more severe cam eformity (increase alpha angle) an milly increase acetabular inclination were preictors of isease progression in the contralateral hip. Discussion The current stuy was esigne to analyze a large cohort of patients who ha premature, en-stage hip isease an who unerwent primary total hip arthroplasty at or before fifty years of age. Our goals were to etermine an characterize structural abnormalities associate with premature, natural hip-joint failure an to analyze isease progression in the contralateral hips of patients with femoroacetabular impingement eformities. Our ata are unique because we focuse specifically on a young patient population, investigate all causes of en-stage isease, utilize contemporary techniques to measure the structural anatomy of the hip, examine a comparison group of patients without hip symptoms, an analyze serial raiographs to etermine preictors of progression of joint isease in the contralateral hip in patients with femoroacetabular impingement eformities. Our finings emonstrate that osteoarthritis an osteonecrosis are the major causes of en-stage egeneration of the hip joint in young patients. In-epth raiographic analysis of osteoarthritic hips highlighte evelopmental ysplasia of the hip an femoroacetabular impingement as the preominant structural abnormalities associate with osteoarthritis. Hip eformities ue to slippe capital femoral epiphysis an Legg-Calvé-Perthes isease commonly have the pathomechanical characteristics of hipimpingement isease an can be consiere severe forms of femoroacetabular impingement 7. When we combine the cases in which these isorers were present an the cases in which femoroacetabular impingement eformities were present, we foun that seconary osteoarthritis was associate with evelopmental ysplasia of the hip an femoroacetabular impingement abnormalities in near equal proportions (48.4% an 50.7%, respectively) an that they collectively accounte for 99% of hips with premature arthritis. In the thir portion of this stuy, we investigate the fate of the contralateral hip in patients with avance seconary osteoarthritis an associate femoroacetabular impingement eformities. Our ata inicate that contralateral hip eformities were present in all cases an that progression of osteoarthritic isease was very common in the contralateral hip. Specifically, at an average of 8.8 years of surveillance, 37% of hips ha unergone total hip arthroplasty an an aitional 36% of hips emonstrate raiographic progression of isease. The nee for surgical intervention was strongly associate with severity of the impingement eformity (Tables III an IV). These ata suggest that femoroacetabular impingement eformities are commonly bilateral an that the long-range prognosis for the contralateral hip is guare. Other investigators have escribe structural eformities associate with osteoarthritis. In general, these stuies analyze patients of all ages an utilize less sophisticate raiographic measures to assess the structural anatomy. In 1965, Murray 5 stuie 00 cases of primary osteoarthritis an reporte that up to 65% ha an unerlying abnormality. Stulberg et al. reporte on seventy-five cases of iiopathic osteoarthritis in all age groups an, using lateral raiographs, ientifie the pistolgrip eformity in 40% an acetabular ysplasia in an aitional 39% 6. Gosvig et al. 8 ientifie a eep acetabular socket an pistol-grip eformities as risk factors for osteoarthritis in a large-population stuy. These stuies are consistent with our observations on young patients with premature osteoarthritis

8 8 in that nearly all such patients have an associate structural eformity. A contrasting theory, as presente by Resnick 9, suggests that femoroacetabular impingement eformities of the femur are seconary to a remoeling phenomenon in the osteoarthritic hip. More recent stuies have further aresse the issue of bilaterality of femoroacetabular impingement in osteoarthritic hips in the early stages of isease. In their recent analysis of a cohort of patients with femoroacetabular impingement, Allen et al. 30 reporte bilateral eformities in 78% an bilateral symptoms in 6% of patients. Similarly, we have recently reporte on joint-preservation surgery with a combine arthroscopic an limite anterior approach 31. In our series, 75% of patients ha bilateral raiographic eformities an 34% ha symptoms in the contralateral hip. The finings from these two recent stuies emphasize that, in aition to hips with femoroacetabular impingement an en-stage isease, prearthritic hips an hips with early stage arthritis commonly emonstrate bilateral eformities an symptoms. Although the current investigation presents unique ata on a large group of young patients with en-stage hip isease, there are weaknesses. First, the patients presente over a thirtyyear time interval an it is possible that the etiology of enstage isease varie uring this time frame. For example, the introuction of screening protocols for evelopmental ysplasia of the hip an the availability of antirheumatoi meications may have impacte the proportion of hips with en-stage arthritis that were attribute to those causes. Seconly, the raiographic protocols, the images obtaine, an the quality of raiographs varie at the ifferent institutions an over the time course of the stuy. We have obtaine ata from all raiographs for which positioning an image quality was aequate, but the ataset is imperfect in that all cases i not have the same aequate raiographs. Aitionally, inaequate visualization of osseous lanmarks ue to seconary osteoarthritic changes occurre with some raiographs. Thirly, we acknowlege that the femoroacetabular impingement cases in this cohort likely represent major impingement isease, as these patients all require total hip arthroplasty at a young age. Therefore, our finings of bilateral eformities in hips in all cases an the common observation of isease progression may not be applicable to patients with miler forms of femoroacetabular impingement. Finally, it shoul be note that our ata escribe associations an o not present evience of a true cause-aneffect relationship between structural eformities an enstage isease. Collectively, these ata expan on previous observations regaring natural hip-joint failure. Finings inicate that femoroacetabular impingement eformities are associate with premature osteoarthritis; thus, investigations to enhance early iagnosis an analyze joint preservation treatments are appropriate. Aitionally, femoroacetabular impingement shoul be approache as bilateral hip isease an patient monitoring an/ or patient eucation regaring early symptoms an preventive treatments shoul be consiere. n John C. Clohisy, MD Michael A. Dobson, MD Jason F. Robison, MD Jie Zheng, MS Department of Orthopaeic Surgery (J.C.C., M.A.D., an J.F.R.) an Department of Biostatistics (J.Z.), Washington University School of Meicine, 1 Barnes-Jewish Hospital Plaza, St. Louis, MO aress for J.C. Clohisy: jclohisy@wustl.eu Lucian C. Warth, MD Steve S. Liu, MD Tameem M. Yehyawi, MD John J. Callaghan, MD Department of Orthopaeic Surgery, University of Iowa School of Meicine, 00 Hawkins Drive, Iowa City, IA 54 References 1. Ganz R, Leunig M, Leunig-Ganz K, Harris WH. 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