Periacetabular Osteotomy After Failed Hip Arthroscopy for Labral Tears in Patients with Acetabular Dysplasia

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1 57 COPYRIGHT Ó 011 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Periacetabular Osteotomy After Faile Hip Arthroscopy for Labral Tears in Patients with Acetabular Dysplasia By Michael S.H. Kain, MD, Euaro N. Novais, MD, Clarisa Vallim, MD, ScD, Michael B. Millis, MD, an Young-Jo Kim, MD, PhD Investigation performe at Chilren s Hospital, Boston, Massachusetts Backgroun: Chronic mechanical overloa of the acetabular rim may lea to acetabular labral isease in patients with hip ysplasia. Although arthroscopic ebriement of the labrum may provie symptomatic relief, the unerlying mechanical abnormality remains. There is little information regaring how the results of periacetabular osteotomy are affecte by a prior primary treatment for labral isease in the presence of acetabular ysplasia. Methos: In a retrospective matche-cohort stuy, seventeen patients who ha arthroscopic labral ebriement prior to periacetabular osteotomy (the arthroscopy group) were compare with a control group of thirty-four patients who i not unergo arthroscopic labral ebriement prior to periacetabular osteotomy (the non-arthroscopy group). Two control patients were ranomly matche to each experimental patient from a pool of controls. Functional outcomes were assesse with use of the Western Ontario an McMaster Universities Osteoarthritis Inex (WOMAC). Failure of periacetabular osteotomy was efine as conversion to a total hip replacement. Results: Changes in the preoperative an postoperative WOMAC scores of arthroscopy an non-arthroscopy patients were comparable, an the ifferences between the two treatment groups were not significant. We were unable to show a significant ifference between the seventeen arthroscopy an thirty-four non-arthroscopy patients with regar to the risk of having to unergo a total hip replacement. Conclusions: When arthroscopic labral ebriement fails to improve symptoms in patients with labral isease seconary to acetabular ysplasia, periacetabular osteotomy may still be consiere as a joint-preserving proceure that can achieve goo functional results. Level of Evience: Therapeutic Level III. See Instructions to Authors for a complete escription of levels of evience. Acetabular ysplasia is well recognize as the most common cause of seconary osteoarthritis of the hip 1,, with insufficient osseous coverage leaing to chronic mechanical overloa of the acetabular rim. The initial physiological response is hypertrophy of the labrum to compensate for the joint incongruence, but the mechanical overloa may ultimately result in egenerative cyst formation or a tear or etachment of the acetabular labrum, all of which are associate with progression of osteoarthritis 3. As the iagnosis an surgical treatment of acetabular labral tears have evolve, arthroscopic labral ebriement has gaine popularity an has been associate with overall favorable long-term results in the absence of arthritis 4. In the presence of acetabular ysplasia, however, arthroscopic labral ebriement may fail to provie long-term symptomatic relief an functional improvement if the unerlying abnormal hip mechanics are not aresse 5,6. Debriement of the labrum may further compromise hip stability because of resultant anterolateral migration of the femoral hea an increase shear stress in the acetabular margin 7,8. Periacetabular osteotomy has proven to be an effective treatment for symptomatic acetabular ysplasia 9-13.Establishe risk factors that have been associate with poor outcomes after periacetabular osteotomy inclue the presence of avance arthritis, increase patient age, a positive impingement test, the presence of a limp, a low Merle Aubigné an Postel score, an Disclosure: The authors i not receive any outsie funing or grants in support of their research for or preparation of this work. Neither they nor a member of their immeiate families receive payments or other benefits or a commitment or agreement to provie such benefits from a commercial entity. J Bone Joint Surg Am. 011;93 Suppl :57-61 oi:10.106/jbjs.j.01770

2 joint incongruence 11,13. Unlike the use of hip arthroscopy at the time of pelvic osteotomy, there is little information regaring how the results of periacetabular osteotomy are affecte by a prior treatment of the labral isease alone in ysplastic hips. We therefore esigne a case-control stuy (1) to evaluate if patients who ha hip arthroscopy for the treatment of labral isease prior to periacetabular osteotomy woul have functional outcomes worse than those of patients with a proven labral tear on magnetic resonance imaging (MRI) who ha not ha arthroscopy prior to periacetabular osteotomy, an () to analyze the rate of failure of periacetabular osteotomy, with failure efine as conversion to total hip replacement in these two groups. Materials an Methos Stuy Design an Population Using a retrospective matche-cohort esign, we compare the change in functional outcomes between patients who ha unergone arthroscopic labral ebriement prior to periacetabular osteotomy an patients who i not have arthroscopic labral ebriement but who ha MRI evience of labral pathology prior to periacetabular osteotomy. The two senior authors (M.B.M. an Y.-J.K.) performe all of the periacetabular osteotomy proceures. Between September 1991 an September 006, 741 periacetabular osteotomies were performe for symptomatic evelopmental acetabular ysplasia. A total of seventeen patients were ientifie who ha unergone hip arthroscopy for a labral tear as primary treatment but eventually unerwent periacetabular osteotomy (the arthroscopy group). These patients were referre to our institution after failure to achieve symptomatic an functional relief. From the remaining 74 periacetabular osteotomies, a pool of patients were ientifie that coul be use as matche controls. All subjects who were eligible to be use as a control ha unergone periacetabular osteotomy an ha a preoperative MRI that ocumente the presence of a labral tear. From this control pool, patients were matche with arthroscopy patients with use of the following criteria: ate of surgery, age, sex, an length of follow-up since the periacetabular osteotomy. Because all patients who ha unergone arthroscopic labral ebriement before periacetabular osteotomy were women, only female patients who ha not ha arthroscopic labral ebriement before periacetabular osteotomy were inclue in the control group. Two hunre an three patients were eligible to be use as controls on the basis of matching criteria. From this pool, controls were ranomly selecte until two control patients were foun for each arthroscopy patient, resulting in thirty-four control patients who i not unergo arthroscopy prior to periacetabular osteotomy (the non-arthroscopy group). Our institutional review boar approve this stuy. Raiographic Evaluation Preoperative an postoperative raiographs were evaluate by an inepenent observer (M.S.H.K.) who was not involve in the patient s care an was bline to group assignment. Preoperative an postoperative anteroposterior raiographs were evaluate subjectively for osteoarthritis by measuring the Tönnis grae 14 an the minimum joint-space with 15.Tönnis graing 14 was efine with use of the following criteria: a grae of 0 inicate a normal joint space with no egenerative changes or signs of osteoarthritis; a grae of 1 inicate subchonral sclerosis, with minimal joint-space narrowing an osteophyte formation; a grae of inicate a hip with subchonral cyst formation an moerate joint-space narrowing; a grae of 3 inicate a hip with severe or complete but localize joint-space narrowing; an a grae of 4 inicate hips with extensive or severe cartilage loss. Minimum joint-space with was measure at the point of the shortest raial istance between the femoral hea margin an the acetabulum. Normal space was efine as a joint space that was >.5 mm in with. Osteoarthritis was efine as a joint space that was between 1.5 an.5 mm in with, an efinitive osteoarthritis was efine as a joint space that was <1.5 mm in with. Acetabular ysplasia was measure with use of the lateral center-ege angle of Wiberg 16 an the Tönnis 14 acetabular angle on the anteroposterior part of the pelvis as well as the anterior center-ege angle as measure on the false-profile raiograph 17. Raiographic subluxation was evaluate preoperatively an postoperatively by ientifying whether or not the Shenton line was broken by 5 mm on the anteroposterior raiograph of the pelvis 18. Congruency was evaluate preoperatively with use of the Yasunaga 19 classification system, with measurements mae on an anteroposterior raiograph of the pelvis with the hip in slight abuction an internal rotation. The following four categories of congruency were efine: excellent, for ientical curvature of the acetabulum an femoral hea; goo, for curves that were not ientical but aequate joint space was maintaine an the lateral joint space was wier than the meial joint space; fair, for joints with partial narrowing of the joint space; an poor, when there was any loss of the joint space. Clinical Outcome Scores Patients were evaluate both preoperatively an postoperatively with the Western Ontario an McMaster Universities Osteoarthritis Inex (WOMAC) 0 to assess their functional outcome. The WOMAC is compose of three sections: pain, stiffness, an function. Each section is score separately. Pain ranges from 0 (no pain) to 0 (extreme pain), stiffness ranges from 0 (no stiffness) to 8 (worst possible stiffness), an function ranges from 0 (no functional eficit) to 68 (worst possible functional eficit). The WOMAC scores use for comparison were the preoperative score recore closest to the ate of periacetabular osteotomy an the most recent follow-up scores. Our primary outcomes were changes in the three categories making up the WOMAC an the seconary outcome was the occurrence of total hip arthroplasty following periacetabular osteotomy. Hips that neee total hip replacement were consiere to be failures. The time to failure was efine as time to known ate of total hip replacement. To evaluate the percentage of patients in the control group who unerwent total hip replacement, we looke at the number of total hip replacements that occurre in the 03 patients who were eligible to be control subjects, as this appeare to represent a more accurate representation of the prevalence of total hip replacement for a female patient with ysplasia an a labral tear prior to a periacetabular osteotomy. Statistics Baseline characteristics of the two groups were summarize with use of means (an stanar eviations) or meians (an interquartile ranges) for continuous measures, an proportion for categorical measures. Comparisons across treatment groups of continuous an categorical measures were performe with use of exact conitional score tests obtaine in a conitional logistic regression base on the true permutation istribution. Although sample-size ecisions were base on feasibility issues an not on stuy power, after the stuy was performe we assesse the minimum etectable ifferences in patients who i or i not unergo arthroscopy by looking at the ifference between the preoperative an postoperative WOMAC scores of the seventeen patients who unerwent arthroscopy an the thirty-four patients who i not. For these power analyses, we use as baseline parameters the mean an the variance of the changes of the arthroscopy patients. We assume constant variances for the two treatment groups. For correlation coefficients across each triplet of patients (i.e., those who unerwent arthroscopy an their two ranomly matche control patients) ranging from 0.3 to 0.7, in a two-sie, paire t test with 80% power an an alpha level of 0.05, the minimum etectable ifference woul be.7 to 4.1 for pain, 0.9 to 1.4 for stiffness, an 6.8 to 10.4 for function. Analyses were performe with use of Spotfire S1, version 8.0 (TIBCO Spotfire, Somerville, Massachusetts). Results Baseline Demographic Characteristics an Raiographic Examinations The arthroscopy group comprise seventeen female patients (mean age, thirty-one years; range, fourteen to forty-nine years), an the non-arthroscopy group comprise thirty-four female patients (mean age, thirty-one years; range, sixteen to forty-eight years). The two treatment groups were comparable

3 TABLE I Demographic an Raiographic Characteristics for Each Group Arthroscopy Group (N = 17) Non-Arthroscopy Group (N = 34) P Value Demographic variables Mean age ± stanar eviation (range) (yr) 31 ± 10 (range, 14 to 49) 31 ± 10 (range, 16 to 48) 0.86 Preoperative raiographic measurements Tönnis grae 0.3 ± ± Minimum joint-space with (mm) 4.6 ± ± Crossover sign (Yes = 1; No = 0) 41.% 3.5% 1.0 Posterior wall sign (Yes = 1; No = 0) 76.5% 85.3% 0.68 Shenton line broken (Yes = 1; No = 0) 35.3% 44.1% 0.79 Lateral center-ege angle (eg) 10.0 ± ± Tönnis angle (eg) 18.9 ± ± Anterior center-ege angle (eg) 9.4 ± ± Joint congruency 3.1 ± ± Postoperative raiographic measurements Tönnis grae 0.4 ± ± Minimum joint-space with (mm) 4.1 ± ± Crossover sign (Yes = 1; No = 0) 11.8% 8.8% 0.6 Posterior wall sign (Yes = 1; No = 0) 3.5% 5.9% 0.16 Shenton line broken (Yes = 1; No = 0) 0% 5.9% 0.90 Lateral center-ege angle (eg) 8. ± ± Tönnis angle (eg) 4.7 ± ± Anterior center-ege angle (eg) 6.3 ± ± with respect to all matche baseline characteristics (Table I). With regar to raiographic finings, there were no clinically relevant ifferences between the two treatment groups, espite the significant ifference recore between the lateral centerege angle of patients who ha arthroscopy (10.0 ) an those who i not (5.1 )(p= 0.049; paire t test). In both groups, the acetabulum was clearly ysplastic an, with the reporte intraobserver rate of variation of approximately 4 in the measurement of the center-ege angle 1, we believe this to be clinically insignificant. Clinical Outcomes In the arthroscopy group, the functional outcome of two patients was unknown. To the best of our knowlege, neither ha unergone total hip replacement; however, because they i not have complete WOMAC scoring available, these two patients were exclue from the clinical outcomes analyses. Two other patients unerwent total hip replacement but ha no preoperative scores because we began routinely using the WOMAC at our institution subsequent to those periacetabular osteotomies. One other patient in the arthroscopy group ha a WOMAC postoperative score of zero; however, no preoperative WOMAC score was recore. This left twelve patients with complete preoperative an postoperative WOMAC scores in the arthroscopy group. Preoperative WOMAC scores in the arthroscopy group were comparable with those in the nonarthroscopy group, although patients in the non-arthroscopy group ha lower stiffness scores than those of patients in the arthroscopy group. Changes in the preoperative an postoperative WOMAC scores of patients in the arthroscopy an non-arthroscopy groups were comparable, an the ifference between the two treatment groups was not significant (Table II). This may suggest that arthroscopic labral ebriement prior to periacetabular osteotomy has no significant effect on the short-term functional outcomes after periacetabular osteotomy, as measure with use of the WOMAC. We also compare the groups with use of unpaire t tests, an the ifference between the preoperative scores an the postoperative scores with regar to pain, stiffness, an function showe no statistical ifference. Differences between the two treatment groups were also not significant in paire analysis of inepenent t tests for pain (p = 0.405), stiffness (p = 0.71), an function (p = 0.394). In the arthroscopy group, a total of three (17.6%) of the seventeen patients ha a subsequent total hip replacement at 3.6, 3.8, an 6.7 years, respectively, following periacetabular osteotomy. One patient (.9%) in the non-arthroscopy group went on to total hip replacement at.6 years following the periacetabular osteotomy. In aition, of the 03 eligible hips to be use as controls in the non-arthroscopy group, twelve (5.9%) unerwent total hip replacement, with the average time to total hip replacement being 4. years (range, 0.8 to 7.8 years). With regar to the risk of having a total hip replacement, there was no significant ifference between the seventeen patients who unerwent arthroscopy an the thirty-four patients who i not (p = 0.09, Fisher exact test; an p = 0., exact conitional logistic regression test).

4 TABLE II WOMAC Scores for the Twelve Patients with Complete Information about Scores an Their Respective Matche Controls* WOMAC Scores Patients in the Arthroscopy Group (N = 1) Ranomly Matche Patients in the Non-Arthroscopy Group (N = 4) P Value Preoperative Pain 10.9 ± ± Stiffness 4.1 ± ± Function 9 ± 16.0 ± Postoperative Pain 5.8 ± ± Stiffness.6 ± ± Function 17.7 ± ± Preoperative compare with postoperative Pain 5. ± ± Stiffness 1.5 ± ± Function 9.3 ± ± *Except for p values, the ata are given as the mean an the stanar eviation. P values were generate with use of estimate exact tests of a conitional logistic regression that mae use of the true permutation istribution (LogXact 8.0; Cytel, Cambrige, Massachusetts). Calculations were base on the twenty-four patients in the non-arthroscopy group who coul be paire with the twelve patients who ha complete information. Discussion Acetabular ysplasia is known to moify the normal biomechanics of the hip joint. One of the consequences of the shallow acetabulum is an increase mechanical overloa of the acetabular margin, which results in labral lesions 3,5. Periacetabular osteotomy is a recognize metho of treatment of symptomatic hip ysplasia that can correct the pathologic mechanical environment that is responsible for the evelopment of osteoarthritis 3,4. On the other han, isolate treatment of the labral lesion in the presence of unerlying hip ysplasia may carry a high risk of failure to improve symptoms an function in the long term because the abnormal mechanics are not change 5,8,5,6. In this investigation, the functional outcome following a periacetabular osteotomy in hips that were not converte to an arthroplasty was not affecte, at an average of forty-one months, by a previous hip arthroscopy for labral ebriement. The effectiveness of arthroscopic labral ebriement in proviing relief of symptoms in patients with acetabular ysplasia is controversial. Byr an Jones 5 reporte on fortyeight patients who unerwent arthroscopic labral ebriement of a ysplastic hip. At a mean follow-up of twenty-seven months (range, twelve to sixty months), the average functional score was consiere fair for patients with labral excision (Harris hip scores change from 5 preoperatively to 76 postoperatively). Parvizi et al. 7 reporte on thirty-four patients who ha unerlying morphologic abnormality of the hip an who unerwent arthroscopic treatment of a labral tear. Although there was significant improvement in functional scores as measure at six weeks, arthroscopic treatment ha faile to control symptoms in twenty-four patients at an average follow-up time of 3.5 years after treatment (range, one to seven years). Pain relief following labral ebriement may mask the mechanical abnormality that may lea to progressive amage to the anterolateral acetabular articular cartilage. The progression of osteoarthritis an anterolateral migration of the femoral hea has been escribe following arthroscopic labral ebriement in hips with unerlying ysplasia 7,8. The temporary relief of pain following arthroscopy may prolong the interim between the onset of symptoms an the time of periacetabular osteotomy, allowing unrecognize progression of osteoarthritis. Patients with hip ysplasia who unergo arthroscopic ebriement of a labral tear nee to be carefully watche, an earlier intervention with a periacetabular osteotomy shoul be consiere. Arthroscopic labral ebriement may provie short-term symptomatic improvement but shoul not be recommene alone 5,6. Periacetabular osteotomy may still provie goo functional outcomes after the failure of arthroscopic labral ebriement, with the avantage of reestablishing hip mechanics 4. With regar to the risk of total hip replacement following periacetabular osteotomy, there was no statistically significant ifference seen between patients who unerwent previous arthroscopic labral ebriement an patients with MRI-proven labral tear. Three (18%) of the seventeen patients in the arthroscopy group require a total hip replacement after periacetabular osteotomy. The rate of total hip replacement in the entire group of potential controls was lower (6%), but not significantly ifferent. Nevertheless, further investigation is neee as our numbers are small an we ha insufficient power for this specific analysis. The previously reporte rate of total hip replacement after faile arthroscopic labral ebriement range from 4% 5 to 9% 7. In a systematic literature review, failure of periacetabular osteotomy with conversion to total hip replacement was note in 0% to 17% of cases 7. The higher percentage of total hip replacement but similar WOMAC scores

5 of patients with unerlying acetabular ysplasia who unergo hip arthroscopy for labral tears suggests that if the periacetabular osteotomy is successful, the patient may achieve similar clinical results to those of patients who i not unergo a prior arthroscopy. The small number of patients with a prior hip arthroscopy in our stuy limits our ability to truly assess the ifference between the arthroscopy group an the non-arthroscopy group. The retrospective nature of our stuy is also a limiting factor, as the arthroscopies that were performe on the patients in the arthroscopy group were one by various surgeons, resulting in the use of various techniques at various institutions, an the patients were only seen after the arthroscopy faile to relieve their symptoms. Because this group consists of a ranom group of patients for whom arthroscopic treatment faile, we coul not compare these patients with similar patients who ha goo outcomes after arthroscopic treatment. Although our results emonstrate that prior arthroscopic labral treatment may not have a negative effect on the functional outcome of a subsequent periacetabular osteotomy in patients with hip ysplasia, we believe that the surgeon shoul procee with caution when consiering the use of arthroscopic treatment of the labrum alone in a ysplastic hip. As pointe out by Wenger et al. 6, if hip ysplasia is the preisposing factor to the evelopment of the labral lesion, isolate ebriement of the labrum may provie some relief, but this relief may be incomplete or temporary because the unerlying conition remains. Therefore, a thorough physical examination an raiographic evaluation shoul be performe before consiering arthroscopic treatment, an arthroscopy shoul not be the primary treatment moality for symptomatic acetabular ysplasia. If patients with acetabular ysplasia are experiencing symptoms an o unergo arthroscopic treatment of a labral tear, careful follow-up is essential. When arthroscopic labral ebriement fails to improve symptoms, periacetabular osteotomy may be consiere as a joint-preserving proceure that can achieve goo functional results. n NOTE: The authors thank Catherine Matero, BA, Patricia Connell, MPH, an Joseph A. Janicki, MD, for their help in preparing this manuscript. Michael S.H. Kain, MD Department of Orthopaeic Surgery, Lahey Clinic, 41 Mall Roa, Burlington, MA Euaro N. Novais, MD Clarisa Vallim, MD, ScD Michael B. Millis, MD Young-Jo Kim, MD, PhD Department of Orthopaeic Surgery (E.N.N., M.B.M., an Y.-J.K.) an Clinical Research Program (C.V.), Chilren s Hospital Boston, Hunnewell 5, 300 Longwoo Avenue, Boston, MA aress for Y.-J. Kim: young-jo.kim@chilrens.harvar.eu References 1. Aronson J. Osteoarthritis of the young ault hip: etiology an treatment. Instr Course Lect. 1986;35: Stulberg SD, Corell LD, Harris WH, Ramsey PL, MacEwen GD. Unrecognize chilhoo hip isease: a major cause of iiopathic osteoarthritis of the hip. Paper presente at: Thir Open Scientific Meeting of the Hip Society 1975; St. Louis, MO. 3. Klaue K, Durnin CW, Ganz R. The acetabular rim synrome. A clinical presentation of ysplasia of the hip. J Bone Joint Surg Br. 1991;73: Byr JW, Jones KS. Hip arthroscopy for labral pathology: prospective analysis with 10-year follow-up. Arthroscopy. 009;5: Dorrell JH, Catterall A. The torn acetabular labrum. J Bone Joint Surg Br. 1986; 68: Wenger DE, Kenell KR, Miner MR, Trousale RT. Acetabular labral tears rarely occur in the absence of bony abnormalities. Clin Orthop Relat Res. 004;46: Parvizi J, Bican O, Bener B, Mortazavi SM, Purtill JJ, Erickson J, Peters C. Arthroscopy for labral tears in patients with evelopmental ysplasia of the hip: a cautionary note. J Arthroplasty. 009;4(6 Suppl): Yamamoto Y, Ie T, Nakamura M, Hamaa Y, Usui I. Arthroscopic partial limbectomy in hip joints with acetabular hypoplasia. Arthroscopy. 005;1: Clohisy JC, Barrett SE, Goron JE, Delgao ED, Schoenecker PL. Periacetabular osteotomy for the treatment of severe acetabular ysplasia. J Bone Joint Surg Am. 005;87: Crockarell J Jr, Trousale RT, Cabanela ME, Berry DJ. Early experience an results with the periacetabular osteotomy. The Mayo Clinic experience. Clin Orthop Relat Res. 1999;363: Matheney T, Kim YJ, Zurakowski D, Matero C, Millis M. Intermeiate to longterm results following the Bernese periacetabular osteotomy an preictors of clinical outcome. J Bone Joint Surg Am. 009;91: Siebenrock KA, Leunig M, Ganz R. Periacetabular osteotomy: the Bernese experience. Instr Course Lect. 001;50: Steppacher SD, Tannast M, Ganz R, Siebenrock KA. Mean 0-year followup of Bernese periacetabular osteotomy. Clin Orthop Relat Res. 008;466: Tönnis D. Congenital ysplasia an islocation of the hip in chilren an aults. New York: Springer Verlag; Jacobsen S, Sonne-Holm S, Søballe K, Gebuhr P, Lun B. Raiographic case efinitions an prevalence of osteoarthrosis of the hip: a survey of subjects in the Osteoarthritis Substuy of the Copenhagen City Heart Stuy. Acta Orthop Scan. 004;75: Wiberg G. Stuies on ysplastic acetabula an congenital subluxation of the hip joint. With special reference to the complication of osteoarthritis. Acta Chir Scan. 1939;83(Suppl 58): Lequesne M, e Sèze S. [False profile of the pelvis. A new raiographic incience for the stuy of the hip. Its use in ysplasias an ifferent coxopathies]. Rev Rhum Mal Osteoartic. 1961;8: French. 18. Cooperman DR, Wallensten R, Stulberg SD. Acetabular ysplasia in the ault. Clin Orthop Relat Res. 1983;175: Yasunaga Y, Ikuta Y, Kanazawa T, Takahashi K, Hisatome T. The state of the articular cartilage at the time of surgery as an inication for rotational acetabular osteotomy. J Bone Joint Surg Br. 001;83: Bellamy N, Buchanan WW, Golsmith CH, Campbell J, Stitt LW. Valiation stuy of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic rug therapy in patients with osteoarthritis of the hip or knee. J Rheumatol. 1988;15: Omeroglu H, Bicximoglu A, Agusx H, Tümer Y. Measurement of center-ege angle in evelopmental ysplasia of the hip: a comparison of two methos in patients uner 0 years of age. Skeletal Raiol. 00;31:5-9.. Bombelli R, Santore RF, Poss R. Mechanics of the normal an osteoarthritic hip. A new perspective. Clin Orthop Relat Res. 1984;18: Ganz R, Klaue K, Vinh TS, Mast JW. A new periacetabular osteotomy for the treatment of hip ysplasias. Technique an preliminary results. Clin Orthop Relat Res. 1988;3: Leunig M, Siebenrock KA, Ganz R. Rationale of periacetabular osteotomy an backgroun work. Instr Course Lect. 001;50: Byr JW, Jones KS. Hip arthroscopy in the presence of ysplasia. Arthroscopy. 003;19: Wenger DR, Bomar JD. Human hip ysplasia: evolution of current treatment concepts. J Orthop Sci. 003;8: Clohisy JC, Schutz AL, St John L, Schoenecker PL, Wright RW. Periacetabular osteotomy: a systematic literature review. Clin Orthop Relat Res. 009;467:041-5.