Clin Orthop Relat Res (2009) 467:2241–2250 DOI 10.1007/s11999-009-0853-3 SYMPOSIUM: PAPERS PRESENTED AT THE ANNUAL CLOSED MEETING OF THE INTERNATIONAL HIP SOCIETY Protrusio Acetabuli New Insights and Experience with Joint Preservation Michael Leunig MD, Shane J. Nho MD, MS, Luigino Turchetto MD, Reinhold Ganz MD Published online: 1 May 2009 Ó The Association of Bone and Joint Surgeons1 2009 Abstract Protrusio acetabuli is identified on anteropos- impingement. While the indication for joint-preserving terior (AP) radiographs of the pelvis with an acetabular line surgery currently consists primarily of a valgus femoral projecting medial to the ilioischial line. We documented osteotomy based on AP radiographs and patient age, this radiographic sign and additional radiographic param- modern decision making also relies on cartilage evaluation eters in 19 patients (29 hips) with protrusio and compared and requires advanced surgical techniques. We conclude the parameters to those of 29 older patients (29 hips) with joint-preservation surgery must be tailored to the individual advanced primary osteoarthritis (OA) but no protrusio and hip morphology. 12 younger patients (22 hips) with protrusio but no Level of Evidence: Level III, prognostic study. See advanced OA. A negative acetabular roof angle and par- Guidelines for Authors for a complete description of levels ticularly large acetabular fossa were more apparent in of evidence. younger patients; these hips suggest the destruction of a protrusio hip begins less in the medial joint area and more in the posteroinferior joint, and the mechanism is driven Introduction less by excessive medially directed forces but by a pincer The pathomorphology of an acetabulum protruding into the true pelvis was first described by Otto in 1816 [20]. During Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing the next 100 years, the interest in hip protrusion was arrangements, etc) that might pose a conflict of interest in connection focused on etiology and classification, while treatment with the submitted article. recommendations remained limited. In 1935, Overgaard Each author certifies that his institution either has waived or does not [21] presented the first useful classification into primary require approval for the human protocol for this investigation and that all investigations were conducted in conformity with ethical and secondary protrusio, which was later modified by principles of research. Gilmour [12] into the most commonly used classification today. It distinguishes between cases explained by an M. Leunig, S. J. Nho underlying disease (secondary) and those without such Hip Service, Schulthess Clinic, Zurich, Switzerland etiological explanation (primary). Today, the list of causes S. J. Nho (&) of secondary protrusion ranges widely from infection, Rush University Medical Center, 1725 West Harrison Street, trauma, and underlying metabolic, neoplastic, and genetic Suite 1063, Chicago, IL, USA diseases [7]. Bilateral manifestation with a female pre- e-mail: [email protected] dominance has typically been described for primary L. Turchetto protrusio [1, 12]. Heredity [6] and racial influence [4] have Orthopaedic Department, Veneto Regional Hospital, also been reported. A number of morphological arguments Portogruaro, Italy including accelerated epiphyseal growth and premature fusion of the triradiate cartilage have suggested a devel- R. Ganz Orthopaedic Department, University of Berne, Berne, opmental etiology [7] of primary protrusion; however, Switzerland these have not yet been substantiated. 123 2242 Leunig et al. Clinical Orthopaedics and Related Research The consequence of acetabular protrusio is secondary review the clinical and radiographic information of the osteoarthritis (OA) and has been characterized by a loss of young protrusion patients who underwent joint-preserving medial joint space, while the craniolateral (superior) joint surgery. space initially remains largely unaltered. The mechanism has been explained by higher load transmission through the medial aspect of the joint [5, 18]. Even in minimal primary Material and Methods protrusion the femoral head has been observed to migrate medially over time. We presume the acetabular morphol- We retrospectively compared the radiographic parameters ogy of the protrusion with OA differs from the classic OA in 19 patients (29 hips) with acetabular protrusio who patients. underwent total hip replacement for secondary OA (pro- The present standard surgical treatment in middle and trusio OA group) to those in two groups of patients: (1) 29 older age has been total joint replacement, while resection patients (29 hips) with OA (but no protrusio) who were arthroplasty and even arthrodesis were historical treatment age-, gender-, and To¨nnis scale [30] matched (OA Control options. Anterior acetabuloplasty was first performed by group), and (2) 12 young (\ 43 years of age) patients (22 Smith-Petersen [28] to increase motion in older patients hips) with protrusio being evaluated for possible joint- with marked stiffness. Surgical closure of the triradiate preserving surgery (protrusio joint preservation group). cartilage has been proposed for the skeletally immature hip The 19 patients with protrusio included all those patients [29]; however, this approach has not been widely adopted, between 35 and 81 years who had undergone total hip in part because of the inability to predict which hips will arthroplasty. Protrusio was defined by an acetabular line undergo progressive protrusion. Valgus intertrochanteric crossing the ilioischial line by 3 mm (male) or 6 mm osteotomy has also been recommended in the young adult (female) on the anteroposterior (AP) view (Fig. 1A–C) under the age of 40 years without the presence of arthritic [2, 13, 31]. changes [7, 19, 24]. The patient demographic information was recorded The aims of this paper were: (1) to compare the mor- including the age, gender, hip involvement (unilateral or phology using preoperative radiographs in an arthroplasty bilateral), type (primary or alternate diagnosis), and sub- database of a cohort of patients with acetabular protrusion sequent surgical procedures. with osteoarthritis to an age- and gender-matched cohort All patients of both groups had a standard AP radio- with classic osteoarthritis; (2) to characterize the mor- graph of the pelvis with the patient in a supine position and phology of young patients with acetabular protrusion and cross-table lateral views. All radiographs were performed to compare these patients to the patients with acetabular with the coccyx positioned in the midline, about 1 cm protrusion with osteoarthritis; and (3) to retrospectively above the pubic symphysis (neutral tilt) and the obturator Fig. 1 (A) In a normal hip, the acetabulum sufficiently covers the being medial to the anterior and posterior acetabular walls. (Reprinted femoral head. (B) In coxa profunda, the head is more medial with the with permission from Leunig, M., Huff, T., Ganz, R. Femoroacetabular acetabular fossa being at or medial to the ilioischial line. (C) In protrusio, impingement: Treatment of the acetabular side. In: Azar FM, O’Connor the femoral head is close, at or medial to the ilioischial line and the MI (eds). Instructional Course Lectures 58. Rosemont, IL: American acetabular roof is negatively tilted with the center of the femoral head Academy of Orthopaedic Surgeons; 2009:223–229.) 123 Volume 467, Number 9, September 2009 Protrusio Acetabuli 2243 foramina and the greater trochanter symmetrical (neutral extrusion, neck-shaft angle) between protrusio OA and rotation) [26]. All radiographs were graded using tools to protrusio joint preservation cohorts using one-way measure length (mm) and angles (°) provided by the PACS ANOVA with Bonferroni post-hoc analysis. Analysis was by one orthopaedic surgeon (SJN). The joint space was performed using SPSS software (SPSS, Inc., Chicago, IL). measured at two points, medial and superior. The following parameters were measured: To¨nnis angle [30], Sharp’s angle [25], the lateral center edge (LCE) angle of Wiberg Results [32], femoral head extrusion index, neck-shaft angle, cross- over sign, posterior wall sign [23], ilioischial line relative We observed a number of radiographic differences to acetabular fossa, center of rotation of femoral head between protrusion hips and the OA control group. relative to the top of the trochanter [32]. Although the degree of joint degeneration was similar According to availability, additional information from between the two cohorts (Table 1), the pattern of joint the radiographic studies was also recorded including false space narrowing differed markedly (Tables 2, 3). In the profile radiographs [15], computer tomography, and mag- protrusio group, the medial joint space was decreased and netic resonance (MR) arthrography [17]. These studies the superior joint space was increased when compared to have been used to determine whether pathomorphological the OA control group. The acetabular morphology also aspects can be better visualized than with AP pelvic differed between the two groups. All hips in the protrusio radiographs alone and have currently been used to guide group had an ilioischial line lateral to the acetabular fossa, treatment for joint-preservation surgery [19, 21, 22]. Fur- whereas the opposite was observed in the hips of the OA thermore, the radiographic findings of previously operated control group. The posterior