We retrospectively compared the radiographic parameters in 19 patients (29 hips) with acetabular protrusio who underwent total hip replacement for secondary OA (protrusio OA group) to those in two groups of patients: (1) 29 patients (29 hips) with OA (but no protrusio) who were age-, gender-, and Tönnis scale [30
] matched (OA Control group), and (2) 12 young (< 43 years of age) patients (22 hips) with protrusio being evaluated for possible joint-preserving surgery (protrusio joint preservation group). The 19 patients with protrusio included all those patients between 35 and 81 years who had undergone total hip arthroplasty. Protrusio was defined by an acetabular line crossing the ilioischial line by 3 mm (male) or 6 mm (female) on the anteroposterior (AP) view (Fig. A–C) [2
Fig. 1 (A) In a normal hip, the acetabulum sufficiently covers the femoral head. (B) In coxa profunda, the head is more medial with the acetabular fossa being at or medial to the ilioischial line. (C) In protrusio, the femoral head is close, at or medial to (more ...)
The patient demographic information was recorded including the age, gender, hip involvement (unilateral or bilateral), type (primary or alternate diagnosis), and subsequent surgical procedures.
All patients of both groups had a standard AP radiograph of the pelvis with the patient in a supine position and cross-table lateral views. All radiographs were performed with the coccyx positioned in the midline, about 1 cm above the pubic symphysis (neutral tilt) and the obturator foramina and the greater trochanter symmetrical (neutral rotation) [26
]. All radiographs were graded using tools to measure length (mm) and angles (°) provided by the PACS by one orthopaedic surgeon (SJN). The joint space was measured at two points, medial and superior. The following parameters were measured: Tönnis angle [30
], Sharp’s angle [25
], the lateral center edge (LCE) angle of Wiberg [32
], femoral head extrusion index, neck-shaft angle, cross-over sign, posterior wall sign [23
], ilioischial line relative to acetabular fossa, center of rotation of femoral head relative to the top of the trochanter [32
According to availability, additional information from the radiographic studies was also recorded including false profile radiographs [15
], computer tomography, and magnetic resonance (MR) arthrography [17
]. These studies have been used to determine whether pathomorphological aspects can be better visualized than with AP pelvic radiographs alone and have currently been used to guide treatment for joint-preservation surgery [19
]. Furthermore, the radiographic findings of previously operated hips from this group have been correlated to the intraoperative pathology observed during routine surgical hip dislocation [9
]. False profile views to show the posteroinferior joint space [15
] were available from seven hips. Computer tomography was performed in four patients and MR arthrography was available from seven hips.
At the time of surgery, the amount and location of cartilage injury was recorded. Except for one hip with reversed periacetabular osteotomy only, the first step of surgery was surgical dislocation [9
], followed by global or localized trimming of the acetabular rim, and/or relative neck lengthening [10
], and/or reversed periacetabular osteotomy (PAO) [27
] and/or valgus intertrochanteric osteotomy. In a reversed PAO, the protrusio acetabulum was reoriented with flexion and internal rotation of the acetabular fragment to allow impingment-free motion in flexion and internal rotation.
Histograms were performed to determine whether the data were normally distributed. Superior joint space and the medial joint space measurements were the only measurements that did not follow a normal distribution and for these we used nonparametric tests. We determined differences in superior joint space and medial joint space between all groups using the Kruskal-Wallis tests and performed post-hoc analysis with Tukey test to compare between protrusio OA and control OA cohorts and between protrusio OA and protrusio joint preservation cohorts. We determined differences in radiographic morphology (Tönnis angle, Sharp’s angle, LCE angle, FH extrusion, neck-shaft angle) between protrusio OA and control OA cohorts using one-way ANOVA with Bonferroni post-hoc analysis. We also determined differences in radiographic morphology (Tönnis angle, Sharp’s angle, LCE angle, FH extrusion, neck-shaft angle) between protrusio OA and protrusio joint preservation cohorts using one-way ANOVA with Bonferroni post-hoc analysis. Analysis was performed using SPSS software (SPSS, Inc., Chicago, IL).