After the Institutional Review Board approval, we retrospectively reviewed 242 consecutive patients (305 hips) affected by Crowe type IV DDH who underwent primary THA with modular cementless stem (S-ROM, DePuy, Warsaw, Indiana) from April 2008 to May 2019 in our institution. Exclusion criteria were (1) previous femoral osteotomy, or (2) previous hip pyogenic arthritis, or (3) proximal placement of the cup component, or (4) use of conical sleeve, or (5) inadequate postoperative anteroposterior (AP) radiographs. Finally, a total of 182 patients (232 hips) were included in the study (Fig. 1).Demographics and clinical information including age, gender, weight, height, and operative note were collected from our electronic medical records.
Standardized digital, calibrated AP hip and full-length standing AP radiographs were acquired both preoperatively and postoperatively .The performance of subtrochanteric osteotomy was validated by osteotomy line on images of the second day after surgery and also by reference to operative notes (Fig.2). Radiographic assessment contained the recognition of false acetabulum and the measurement of distalization of greater trochanter. The presence of false acetabulum was defined as a fossa that obstructs the femur from higher dislocation and does not overlap with the true acetabulum (Fig.3). The distalization of greater trochanter was calculated by vertical height difference between the pre- and postoperative tip of the greater trochanter, which was perpendicular to the inter-teardrop line. Before initiation of the study, all observers reached an agreement on criteria for radiographic assessment. Removing all identifying marks, each part of radiographic assessment was accomplished by two observers independently in random order, who were not involved in index surgery. Then at least one month later, observers repeated their readings without knowledge of the previous results. All measurements were conducted by using Digimizer v5.4 (Acacialaan, Belgium). Inter-observer variability was measured by comparing the mean value of two observers on each occasion, while intra-observer reliability was determined by comparing the two reviews of each observer.
All operations were performed by one senior surgeon under general anesthesia in the lateral decubitus position. The posterolateral approach was used in each case. Joint capsulectomy, gluteal sling release, and iliopsoastenotomy was performed. In order to use ceramic on ceramic bearing, the cup (range 44-46 mm) was implanted at the anatomic position by reaming the acetabulum posteriorly and inferiorly . Two or three screws were used to augment primary stability of the cup. No additional stabilization such as femoral head autograft, cage or ring was used to support the acetabulum. After the cup implantation, the femur was internally rotated 90° and the femoral canal was prepared using the dedicated reamer for the S-ROM stem. First, we reamed the femoral canal until the maximum cortical contact was reached distally. Then conical and triangular reaming of the metaphysis was performed to prepare for the proximal sleeve. With trial seated in the femur, we measured the final vertical distance from femoral head to cup under constant and vigorous traction. If hip reduction with a femoral trial stem was impossible, a subtrochanteric osteotomy would be performed for femoral shortening. The osteotomy position was planned to be adjacent enough to the end of the proximal sleeve, approximately corresponding to 1-2 cm beneath the lesser trochanter, which was able to provide sufficient engagement of the implant to stabilize the osteotomy site. Prophylactic cerclage wires were placed both proximally and distally around the fragment of the planned osteotomy. Also, a longitudinal line along the femoral diaphysis was marked by electrocautery prior to osteotomy to determine the rotation. After removing the trial, a transverse osteotomy was performed, by resection of a length of the femur below the lesser trochanter. The length of the removed bone stock was based on the distance we measured before, leaving a scope of 1-1.5 cm with surgeon’s discretion. After completion of osteotomy, a final preparation of the femur including repeated reaming and broaching was undertaken, until optimal cortical contact was achieved especially distal to the osteotomy site. Then trial reduction was performed again. If impossible, additional bone was incrementally resected at the osteotomy site until reduction was achieved. After trial reduction, stability, limb length and soft tissue tension were evaluated. Intraoperative measurement of limb length discrepancy (LLD) was performed by palpating the inferior point of bilateral patella. Mild LLD could be adjusted by means of the modifications of head/neck length and stem depth in femur. Finally, the definitive femoral component was implanted with the rotational alignment of femoral stem adjusted to allow approximately 30-50° of combined anteversion. During the stem insertion, compression of the osteotomy site was obtained without any gaps and no rotational adjustment of the bone segment was performed. At the end of the surgery, motion in abduction was assessed to evaluate the necessity of a percutaneous partial adductor tenotomy. Postoperatively, patient’s hip and knee were maintained in flexion for several days to relax the sciatic nerve and reduce tension of soft tissue. In cases of bilateral Crowe type IV dysplasia, apart from consideration for safe reduction, limb length would be equalized through the amount of bone resection and the modularity of implant.
Patients were followed up in regular intervals at 3 months, 6 months, and yearly after surgery. Clinical information was collected including LLD measured on full-length standing AP radiograph (from the base of teardrop to the center of plafond), and occurrence of nerve injury and dislocation.
All statistical analyses were performed using SPSS version 26.0 (IBM Inc., Armonk, New York) and Microsoft Excel. Assessment of inter- and intra-observer consistency was accomplished by the use of the intraclass correlation coefficient (ICC). Agreement was graded as slight (ICC = 0 to 0.2), fair (ICC = 0.21 to 0.40), moderate (ICC = 0.41 to 0.60), substantial (ICC = 0.61 to 0.80) or almost perfect (ICC = 0.81 to 1.0). Categorical variables were presented as frequencies and continuous variables as means with ranges or median with interquartile range (IQR). Continuous variables were assessed using t-test or Mann-Whitney test, whereas categorical variables were analyzed using Chi-square test or Fisher’s exact test. Receiver operating characteristic (ROC) curves were generated to determine the predicting value of each indicator for the assessment of subtrochanteric osteotomy. The area under the curve (AUC) and 95% confidence interval (CI) were calculated. The discriminatory value of curves was interpreted as excellent (0.9 to 1), good (0.8 to 0.89), fair (0.7 to 0.79), poor (0.6 to 0.69), or as failing or having no discriminatory capacity (0.5 to 0.59). The comparison of AUCs was analyzed by Z test. The optimal threshold for indicator as a predicting tool for subtrochanteric osteotomy was determined using the Youden index. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the indicators were calculated. P value of <0.05 was considered significant.