Coxa profunda is not a useful radiographic parameter for diagnosing pincer-type femoroacetabular impingement

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1 Washington University School of Meicine Digital Open Access Publications 2013 Coxa profuna is not a useful raiographic parameter for iagnosing pincer-type femoroacetabular impingement Jeffrey J. Nepple Washington University School of Meicine in St. Louis Charles L. Lehmann Washington University School of Meicine in St. Louis James R. Ross Washington University School of Meicine in St. Louis Perry L. Schoenecker Washington University School of Meicine in St. Louis John C. Clohisy Washington University School of Meicine in St. Louis Follow this an aitional works at: Recommene Citation Nepple, Jeffrey J.; Lehmann, Charles L.; Ross, James R.; Schoenecker, Perry L.; an Clohisy, John C.,,"Coxa profuna is not a useful raiographic parameter for iagnosing pincer-type femoroacetabular impingement." The Journal of Bone an Joint Surgery.95, (2013). This Open Access Publication is brought to you for free an open access by Digital Commons@Becker. It has been accepte for inclusion in Open Access Publications by an authorize aministrator of Digital Commons@Becker. For more information, please contact engeszer@wustl.eu.

2 417 COPYRIGHT Ó 2013 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED Coxa Profuna Is Not a Useful Raiographic Parameter for Diagnosing Pincer-Type Femoroacetabular Impingement Jeffrey J. Nepple, MD, Charles L. Lehmann, MD, James R. Ross, MD, Perry L. Schoenecker, MD, an John C. Clohisy, MD Investigation performe at the Department of Orthopaeic Surgery, Washington University School of Meicine, St. Louis, Missouri Backgroun: Coxa profuna is commonly viewe as a raiographic parameter that is inicative of pincer-type femoroacetabular impingement, an this fining can impact iagnostic an surgical ecision-making. Valiation of coxa profuna as a measure of pincer-type femoroacetabular impingement has not been rigorously analyze. Our hypothesis was that coxa profuna is a very common raiographic fining in females an is not a fining that is specifically associate with pincer-type femoroacetabular impingement. Methos: A retrospective review was performe to etermine the prevalence of coxa profuna in four groups of hips: those with acetabular ysplasia (fifty-eight hips), femoroacetabular impingement (fifty hips), symptomatic resiual Legg- Calvé-Perthes eformities (sixteen hips), an asymptomatic hips (thirty-three). Coxa profuna was present when the floor of the acetabular fossa touche or was meial to the ilioischial line. The association between coxa profuna an hip isorer iagnosis, lateral center-ege angle, acetabular inclination, patient age, an sex was analyze. Results: Coxa profuna was seen in 55% of the 157 hips an was slightly less common in the hips with acetabular ysplasia or resiual Legg-Calvé-Perthes eformities (41% an 31%, respectively). Coxa profuna was evient in 76% of the thirty-three asymptomatic hips compare with 64% of the fifty hips with femoroacetabular impingement. Coxa profuna was more common in females than males (70% compare with 24%; p < 0.001). Acetabular overcoverage (a lateral centerege angle of >40 or acetabular inclination of <0 ) was seen in only 22% of hips with coxa profuna. Conclusions: Coxa profuna shoul be consiere a normal raiographic fining, at least in females. Coxa profuna is a nonspecific raiographic fining, seen in a variety of hip isorers an asymptomatic hips. The presence of coxa profuna is neither necessary nor sufficient to support a iagnosis of pincer-type femoroacetabular impingement. Level of Evience: Prognostic Level III. See Instructions for Authors for a complete escription of levels of evience. The refine unerstaning of femoroacetabular impingement as a source of hip pain in the young ault has ramatically change the evaluation an treatment of these patients 1-3. Accurate iagnosis relies heavily on clinical history, physical examination, an raiographic evaluation 1,2,4,5. Raiographic evaluation plays a role in supporting the clinical iagnosis an in ientifying anifferentiating among subtypes of femoroacetabular impingement. Cam, pincer, an combine types of femoroacetabular impingement can occur 2. Accurate ientification of hip pathomechanics is important as this may alter the iagnosis, preoperative planning, an surgical ecision-making relate to the treatment of prearthritic hip isorers. Pincer-type femoroacetabular impingement is characterize by a repetitive impaction type of injury between the prominent acetabular rim an the femoral hea-neck region 2. This type of impingement can occur as a result of several istinct structural abnormalities, incluing acetabular retroversion, focal anterosuperior overcoverage, or global acetabular overcoverage. Raiographic parameters of pincer-type femoroacetabular Disclosure: One or more of the authors receive payments or services, either irectly or inirectly (i.e., via his or her institution), from a thir party in support of an aspect of this work. One or more of the authors, or his or her institution, has ha a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomeical arena that coul be perceive to influence or have the potential to influence what is written in this work. No author has ha any other relationships, or has engage in any other activities, that coul be perceive to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitte by authors are always provie with the online version of the article. J Bone Joint Surg Am. 2013;95:

3 418 impingement are evaluate on anteroposterior pelvic raiographs. Parameters reporte in the literature are variable an inclue the crossover sign, ischial spine sign, posterior wall sign, lateral center-ege angle, acetabular inex, acetabular rim osseous apposition, acetabular protrusio, an coxa profuna 4,6. Among these parameters, coxa profuna has the least ocumente valiation. Coxa profuna is efine as being present when the floor of the acetabular fossa touches or is meial to the ilioischial line 4,7. In istinction, acetabular protrusio is present when the femoral hea projects meial to the ilioischial line. A hip with coxa profuna is classically referre to as a eep hip or eep socket. 8 Alternative efinitions of coxa profuna base on quantitative parameters (generally the lateral center-ege angle) have occasionally been utilize in the literature an are a source of confusion. Clearly, there is a nee to better characterize the clinical importance of coxa profuna an the association of this fining with femoral hea coverage. It is our clinical impression that coxa profuna is not a useful marker of pincer-type femoroacetabular impingement because we commonly observe this fining in a wie variety of hip isorers as well as in patients without hip pathology. Aitionally, we have note this fining to be particularly common in females. The purpose of the present stuy was to etermine the prevalence of coxa profuna in (1) hips with acetabular ysplasia, (2) hips with femoroacetabular impingement (all subtypes), (3) hips with symptomatic resiual Legg-Calvé-Perthes eformities, an (4) asymptomatic hips. Aitionally, we investigate the association of coxa profuna with the lateral center-ege angle, acetabular inclination, an patient age an sex. Materials an Methos We performe a retrospective review of anteroposterior pelvic raiographs of 157 patients (157 hips) to etermine the prevalence of coxa profuna in four ifferent subgroups. The four subgroups inclue (1) hips with acetabular ysplasia (fifty-eight), (2) hips with symptomatic femoroacetabular impingement (fifty), (3) hips with resiual Legg-Calvé-Perthes eformities (sixteen), an (4) a comparison group of asymptomatic hips (thirty-three). The stuy was approve by the institutional review boar at our institution. The comparison group of asymptomatic hips has been previously escribe 9. These patients were evaluate in clinic by one of the senior authors (J.C.C.) after the completion of hip raiographs. Nevertheless, after a complete history an physical examination, the patients ha no symptoms consistent with hip pathology. All of the patients presente with back or leg pain an ha no evience of intra-articular hip isease. None of the patients ha evience of hip irritability on examination, an none ha a positive impingement sign. All patients ha signs an symptoms of isorers not involving the hip. The other patient cohorts were establishe by searching our hip preservation surgery atabase (February 2008 to February 2011). Diagnoses were establishe on the basis of clinical history, physical examination, an raiographic finings by one of the senior authors, with extensive experience treating prearthritic hip isease, incluing ysplasia, femoroacetabular impingement, an resiual Legg-Calvé-Perthes eformities 3,10. The subtype of femoroacetabular impingement (cam, pincer, or combine) was etermine by one of the senior authors. Raiographic finings of coxa profuna were not consiere inicative of any iagnosis. Consecutive surgical patients with symptomatic acetabular ysplasia unergoing periacetabular osteotomy, those with symptomatic femoroacetabular impingement (any type) unergoing arthroscopy or open surgical islocation, an those with resiual Legg-Calvé- Perthes eformities unergoing open surgical islocation with or without periacetabular osteotomy were inclue. Subtypes of femoroacetabular impingement inclue cam type (72%; thirty-six of fifty hips), pincer (2%; one hip), an combine (26%; thirteen hips). For analysis, subtypes of femoroacetabular impingement were groupe into femoroacetabular impingement with (fourteen hips) an without (thirty-six hips) a component of pincer-type femoroacetabular impingement. Hips with resiual Legg-Calvé-Perthes eformities were inclue because of the common ifficulty in istinguishing unerlying etiology between instability an impingement in these patients 11. Patients with a history of previous pelvic osteotomy or substantial osteoarthritis (a Tönnis grae 12 of 2) were exclue. Anteroposterior pelvic raiographs were performe with the patient in the supine position with 15 of internal rotation of the lower extremities accoring to a stanarize protocol previously escribe 4. The raiograph tubeto-film istance was 120 cm. The x-ray beam was perpenicular to the x-ray table an centere miway between the superior borer of pubic symphysis an anterior superior iliac spines. Patient iagnosis, age, an sex were recore. Raiographic evaluation of coxa profuna was performe by a single iniviual (J.J.N.) with experience in the raiographic evaluation of the young ault hip but not involve in the clinical care of the patients. Coxa profuna was efine as present when the floor of the acetabular fossa touche or was meial to the ilioischial line 4,7 (Figs. 1, 2, an 3). Raiographic analysis was performe with the evaluator bline to the iagnosis, age, an sex of the patient. Fig. 1 An example of an asymptomatic hip without coxa profuna in the control group emonstrating the meial acetabular fossa (blue) an ilioischial line (re).

4 419 Fig. 2 An example of a ysplastic hip with coxa profuna emonstrating the meial acetabular fossa (blue) touching the ilioischial line (re). However, the complete anteroposterior pelvic raiograph was reviewe, which in some cases woul allow the iagnosis to be inferre. The intraobserver an interobserver reliability of etermination of coxa profuna was assesse using a subset of twenty raiographs (incluing hips from all four cohorts) an one aitional reaer (J.C.C.). Intraobserver an interobserver reliability was perfect (kappa of 1.0). Coxa profuna was also assesse in the contralateral hip (n = 150), with seven contralateral hips being exclue because of prior surgery. Measurements of the lateral center-ege angle 13 an acetabular inclination 12 were performe by the same iniviual (J.J.N). Both measurements utilize a horizontal reference between the inferior aspects of the ischial tuberosities. The lateral center-ege angle was efine as the angle between a line perpenicular to the horizontal reference through the center of the femoral hea an a line connecting the femoral hea center to the most lateral aspect of the acetabular sourcil. The acetabular inclination was efine as the angle between the horizontal reference an a line connecting the most lateral an meial aspects of the sourcil. The intraobserver an interobserver reliability of the lateral center-ege angle an acetabular inclination has been previously shown to be excellent 14,15. Analysis of the association of coxa profuna with other parameters of excessive acetabular coverage was performe on the combine normal an femoroacetabular impingement subgroups. A lateral center-ege angle of >40 an acetabular inclination of <0 were efine as acetabular overcoverage 4,6,16. A power analysis was performe for the primary comparison of interest (femoroacetabular impingement group versus comparison group). For a large effect size, an alpha of 0.05, an a power of 0.9, forty-three subjects were require between the two groups combine. Statistical analysis was performe using the chi-square test, Fisher exact test, or Mann-Whitney U test. Source of Funing Funing for the stuy inclue the Curing Hip Disease Fun an NFL Charities Grant. The funing sources playe no role in the investigation. Results Table I summarizes the emographic ata for each cohort. Overall, 68% of the 157 patients were female. Female patients were more common than males in all but the cohort with resiual Legg-Calvé-Perthes eformities. The average age of the patients in the stuy was 30.5 years (range, 13.7 to 50.9 years). The cohort with resiual Legg-Calvé-Perthes eformities tene to be slightly younger, while the asymptomatic cohort was slightly oler. Fig. 3 An example of an asymptomatic control hip with coxa profuna emonstrating the meial acetabular fossa (blue) projecting meial to the ilioischial line (re).

5 420 TABLE I Demographics of Cohorts Cohort Description No. of Hips No. of Hips in Female Patients Mean Age (yr) 1 Dysplasia (71%) Femoroacetabular impingement (72%) Resiual Legg-Calvé-Perthes eformities 16 5 (31%) Asymptomatic (73%) 38.2 Combine (68%) 30.5 TABLE II Prevalence of Coxa Profuna by Cohort an Sex Hips with Coxa Profuna Cohort Description All Hips (%) Females (%) Males (%) Comparison of Male an Female Patients (p value) 1 Dysplasia < Femoroacetabular impingement Resiual Legg-Calvé-Perthes eformities Asymptomatic Combine <0.001 Coxa profuna was seen in 55% (eighty-six) of all 157 hips. Coxa profuna was less common in the cohort with ysplasia (41%; twenty-four of fifty-eight hips; p = 0.002) an the cohort with resiual Legg-Calvé-Perthes eformities (31%; five of sixteen hips; p = 0.003) than in the comparison group (76%; twenty-five of thirty-three hips). Coxa profuna was evient in 64% (thirty-two) of fifty hips with femoroacetabular impingement, which i not iffer significantly from the comparison group (p = 0.258). Coxa profuna was much more common in females (70%; seventy-four of 106 hips) than males (24%; twelve of fifty-one hips) (p < 0.001). For the entire cohort, coxa profuna was three times more likely in females (95% confience interval [CI]: 1.8, 4.9) than males. This was true for each cohort (Table II). Coxa profuna was seen in 88% of females in the comparison group compare with 44% of males in this group. Coxa profuna was seen in 78% of females with femoroacetabular impingement an 29% of males with femoroacetabular impingement. Coxa profuna was seen in 79% (eleven) of fourteen hips with pincer-type or combine femoroacetabular impingement compare with 58% (twentyone) of thirty-six hips with isolate cam-type femoroacetabular impingement. This ifference was not significant (p = 0.181). No significant association between age an the presence of coxa profuna was observe (p = 0.152). Patients with coxa profuna were an average of 31.6 years ol compare with patients without coxa profuna who were an average of 29.2 years ol. In the entire cohort, 5% (four) of eighty-six hips with coxa profuna ha a lateral center-ege angle of >40 an 21% (eighteen) ha an acetabular inclination of <0. Of all eighty-six hips with coxa profuna, only 22% (nineteen) ha evience of acetabular overcoverage (a lateral center-ege angle of >40 an/ or acetabular inclination of <0 ). Among the asymptomatic an femoroacetabular impingement cohorts combine, the meian lateral center-ege angle of hips with coxa profuna was 29.7 compare with 28.4 for hips without coxa profuna (p = 0.569) (Table III). Similarly, the meian acetabular inclination of hips with coxa profuna was 2.7 compare with 2.9 for hips without coxa profuna (p = 0.579). A lateral center-ege angle of >40 was foun in 5% (three) of fifty-seven hips with coxa profuna an 4% (one) of twenty-six hips without coxa profuna. An acetabular inclination of <0 was seen in 30% (seventeen) of fifty-seven hips with coxa profuna an 19% (five) of twenty-six hips without coxa profuna (p = 0.310). Acetabular overcoverage (a lateral center-ege angle of >40 or acetabular inclination of <0 ) was present in 30% of hips with coxa profuna an 19% of hips without coxa profuna (p = 0.310). Table III shows the measurements of acetabular coverage by group. The presence of coxa profuna was highly associate between the inex, or affecte, hip an the contralateral hip (p < 0.001). Of the eighty-three patients with coxa profuna in the affecte hip, seventy-one (86%) ha evience of coxa profuna in the contralateral hip. Of the sixty-seven patients without coxa profuna in the affecte hip, forty-six (69%) ha no evience of coxa profuna in the contralateral hip. Specifically in the femoroacetabular impingement group, coxa profuna in one hip was highly associate with evience of it in the contralateral hip (p < 0.001). Among the thirty-two patients (thirty-two hips) in the femoroacetabular impingement group with coxa profuna, twenty-nine (91%) ha evience of coxa profuna in the contralateral hip. Among the eighteen patients (eighteen hips) in the femoroacetabular impingement group without coxa profuna, fifteen (83%) ha no evience of coxa profuna in the contralateral hip.

6 421 TABLE III Parameters of Acetabular Overcoverage All Hips Dysplasia Femoroacetabular Impingement Asymptomatic Coxa profuna Present Absent Present Absent Present Absent Present Absent No. of hips Lateral center-ege angle Meian (eg) >40 (% of hips) Acetabular inclination Meian (eg) <0 (% of hips) Lateral center-ege angle of >40 or acetabular inclination of <0 (%) Discussion Coxa profuna, efine as the acetabular fossa touching or projecting meial to the ilioischial line, has been viewe as one of the finings associate with pincer-type femoroacetabular impingement since its original escription 2. Beck et al. 8 viewe coxa profuna as typical of pincer impingement. Prospective longituinal stuies emonstrating the long-term implications of coxa profuna have not been performe. Numerous authors have continue to view coxa profuna as evience of pincer-type impingement 6,8, We also viewe this raiographic parameter as an inicator of femoroacetabular impingement 4. The results of our stuy strongly question the clinical utility of coxa profuna as a raiographic marker of pincer-type femoroacetabular impingement. Previous authors have questione the clinical utility of coxa profuna 30,31, even before a refine unerstaning of femoroacetabular impingement. In 1978, Armbuster et al. 30 reporte the results of a etaile stuy of raiographic anatomy pertaining to coxa profuna. They foun the presence of the acetabular line crossing the ilioischial line (coxa profuna) to be strongly associate with sex, as it was seen in 71% of females compare with 19% of males. They also foun it to be more common in iniviuals less than forty years ol compare with oler iniviuals. Aitionally, the prevalence of coxa profuna in females has been shown to be approximately 50% in one large stuy 32. In our stuy (combining cohorts), we foun a prevalence of 70% in females an 24% in males. We i not observe a significant association between coxa profuna an age, although patients in our stuy tene to be younger. Only about 20% of our cohort was over the age of forty years. Corten et al. 17 investigate a cohort of 148 hips with femoroacetabular impingement an the association of coxa profuna with acetabular rim osseous apposition on raiographs an magnetic resonance imaging (MRI) scans. The authors implie that appositional bone growth at the acetabular rim is inicative of pincer-type femoroacetabular impingement. They foun a 52% incience of coxa profuna in female patients with femoroacetabular impingement. They foun osseous apposition in 29% of hips with coxa profuna compare with 8% of hips without coxa profuna. The authors conclue that coxa profuna is a useful parameter of pincertype femoroacetabular impingement, except in hips with a center-ege angle <20, although there was no control population for comparison. In our stuy, coxa profuna was common (41%) even in the most shallow hips being treate for symptomatic acetabular ysplasia. After excluing cohorts associate with acetabular ysplasia, the presence of coxa profuna was not strongly associate with other markers of acetabular overcoverage. Only about 30% of hips with coxa profuna in our stuy ha other evience of raiographic acetabular overcoverage. There is variation in efinitions of pincer-type femoroacetabular impingement in the literature. Femoroacetabular impingement is commonly subcategorize as cam, pincer, or combine types. The combine type of femoroacetabular impingement has been generally reporte to be the most common 8. However, many of these stuies utilize coxa profuna as a marker of pincer morphology. The prevalence of coxa profuna in groups of patients with symptomatic femoroacetabular impingement has been reporte to range from 14% to 58% 8,18, Given the results of the current stuy, if the presence of coxa profuna is interprete as pincer-type femoroacetabular impingement, then nearly two-thirs of cam-type eformities woul be classifie as combine femoroacetabular impingement. Further research is inicate to better efine the prevalence of femoroacetabular impingement subtypes, with the exclusion of coxa profuna as a iagnostic parameter. Allen et al. 20 previously reporte a significantly higher lateral centerege angle in hips with coxa profuna. In their stuy, hips with coxa profuna ha a mean lateral center-ege angle of 38.7 (range, 29 to 56 ) compare with those without coxa profuna or acetabular retroversion (mean lateral center-ege angle, 33.6 ). Combining the femoroacetabular impingement group an comparison group, we foun no significant ifference in

7 422 lateral center-ege angle among hips with an without coxa profuna (mean, 30.1 an 29.2, respectively). Similarly, no significant ifferences in acetabular inclination were etecte. Coxa profuna was seen in 76% of hips in the asymptomatic comparison group. However, the comparison group in our stuy may not represent a cohort of truly asymptomatic, so-calle control patients, as they presente for clinical evaluation an ha a raiographic hip series followe by a complete orthopaeic history an physical examination 9. One of the senior authors (J.C.C.) evaluate these patients an thought there was no clinical evience of intrinsic hip isease. Nevertheless, there exists the possibility that some of these patients coul have ha structural hip isease (femoroacetabular impingement or acetabular ysplasia) with an atypical clinical presentation. If this were the case, it woul be in a small minority of these patients an unlikely to change the finings of the stuy. However, our control group oes represent a group of patients without an abnormality of the hip who may present for possible hip pathology an unergo raiographs. In this sense, this group ieally represents patients in whom the presence of coxa profuna shoul not be overemphasize. This stuy has limitations. First, pelvic tilt was not assesse as part of the raiographic analysis. The position of the sacrococcygeal joint an/or coccyx on the anteroposterior pelvic raiograph provies an estimate of pelvic tilt, although a true lateral raiograph of the sacrum is require for accurate etermination of pelvic tilt 33,34. The effect of changes that pelvic tilt has on the appearance of coxa profuna is unknown. However, changes in pelvic tilt have a minimal effect on the measurement of the lateral center-ege angle an acetabular inclination 33. Aitionally, the patient cohorts were establishe accoring to the iagnoses assigne by one of the senior authors. While misiagnoses may have occurre, this author has extensive experience in the evaluation of prearthritic hip isease 3-5,10. Raiographic review was part of this clinical evaluation an is an aitional potential source of bias. However, in etermining the clinical iagnoses, the presence of coxa profuna alone was not viewe as consistent with femoroacetabular impingement. Aitionally, only about one-thir of the hips with femoroacetabular impingement ha a pincer component on the basis of the treating surgeon s assessment. Thus, the number of hips with femoroacetabular impingement an pincer-type morphology was somewhat limite. However, coxa profuna was common in this subgroup (79%), but a similar rate was also observe in the asymptomatic control group (76%). Finally, our stuy utilize the classic efinition of coxa profuna, in which the acetabular fossa touches or is meial to the ilioischial line. Determination of whether the acetabular fossa touches the ilioischial line in subtle cases may be more subjective. This etermination woul influence the relative prevalence of these finings to some egree. The presence of coxa profuna on anteroposterior pelvic raiographs has historically been consiere an inicator of a eep hip socket. The recent unerstaning of femoroacetabular impingement has le to the inclusion of coxa profuna as a marker of pincer-type eformity, with little valiation. In light of our ata, the presence of coxa profuna can be a normal fining. The presence of coxa profuna appears to have a very limite role in the raiographic ientification of pincer-type eformity. Alternative parameters of pincer-type femoroacetabular impingement, incluing the crossover sign, posterior wall sign, lateral center-ege angle, anterior center-ege angle, an acetabular inclination, shoul be utilize collectively to assess femoral hea overcoverage. Importantly, the final iagnosis an treatment ecision-making for a given patient is erive from multiple factors incluing emographics, history, physical examination, raiographs, an avance imaging (compute tomography an MRI). n Jeffrey J. Nepple, MD Charles L. Lehmann, MD James R. Ross, MD Perry L. Schoenecker, MD John C. Clohisy, MD Department of Orthopaeic Surgery, Washington University School of Meicine, 660 South Eucli Avenue, West Pavilion 11300, St. Louis, MO aress for J.C. Clohisy: clohisyj@wuosis.wustl.eu References 1. Ganz R, Leunig M, Leunig-Ganz K, Harris WH. The etiology of osteoarthritis of the hip: an integrate mechanical concept. Clin Orthop Relat Res Feb;466(2): Epub 2008 Jan Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res Dec;(417): Clohisy JC, Knaus ER, Hunt DM, Lesher JM, Harris-Hayes M, Prather H. 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