Study design and participants
In this randomized open label controlled parallel groups clinical trial, among patients who attended to orthopedic clinic of Saadi and Kashani hospitals, affiliated to Isfahan University of Medical Sciences, Isfahan, Iran and undergone primary cementless THA between 2013-2018 and fulfilled our study inclusion criteria 67 patients/71 hips who consented to participate in the study were selected and randomized into two intervention groups, i.e. THA using cup positioning in true acetabulum technique or with cup positioning in false acetabulum technique. We included subjects with hip dysplasia at Crowe type III and IV according to the classification of Crowe (20) underwent THA. Crowe index is measured using an AP radiographs of the hip centered on pubic symphysis and including the iliac wings and indexes including: (1) the height of the pelvis; (2) the medial head-neck junction in the affected hip; and (3) the inferior margin of the acetabulum (the teardrop). Crowe score 1 is having less than 50% partial dislocation. Crowe score 2 is 50-75% partial dislocation while crowe score 3 is 75-100% partial dislocation. Type 4 is more than 100% partial dislocation (21). Other inclusion criteria were as absence of any other skeletal deformities, aged more than 18 years, hip dysplasia, having both true and false acetabulum in their hip and signing the written informed consent. We excluded those patients who refused to participate in the study, a history of pelvic trauma, previous pelvic surgery history of hip infection or tumor, lacks of data on main study outcomes during follow up, any affecting by unilateral or bilateral other CROWE types forms hip dysplasia, having neuromuscular diseases, lumbar spine stiffness (lumbar spine lateral curve <15°) or severe spinal deformity.
Study procedures and outcomes evaluation
We used direct lateral approach for all patients that is performed without trochanteric osteotomy. All osteophytes and soft tissues that interfered with our procedures were removed. For Crowe type IV DDH patients, resection of the hypertrophic capsule and femoral head was performed to expose the true acetabulum and proximal femur. Bone cup surface contact was >75% in patients. Stability of cup and superolateral side of the rim were evaluated by the surgeon during the surgical procedures and structural bone grafts were used in cases of insufficient bone cup coverage along with efforts to place the prosthesis in the medial location. The used devices in most patients were Triology acetabular system, M/L taper prosthesis, Aqulad wedge femoral stem and Coralli total hip system. All patients received 1 g of cephalexin administered 40– 60 min prior to surgeries.
Placement at true acetabulum
All the surgeries were conducted by a single surgeon in lateral position using direct lateral approach. Soft tissue dissection is conducted carefully keeping in mind that neurovascular bundle may not be present at normal anatomic place. The femoral neck is resected at around 1 cm proximal to lesser trochanter. Pushing down toward capsule and by direct palpation, the correct position of the true acetabulum is located. Although the precise position of acetabular component is well determined in preoperative radiographs, the whole process of finding the true acetabulum is monitored by image intensifier, after sufficient soft tissue dissection, the acetabulum is deepened and enlarged gradually with serial reaming at the desired angle of abduction and anteversion till anterior and posterior wall appear in order to fix a cement less component (size 40-44). After capturing a proportional press fit, the cup is tightened with long screws. (21). No structural bone grafts were used in this group.
Placement at false acetabulum
The direct lateral approach was used in each case. Joint capsulectomy, gluteal sling release, and iliopsoastenotomy was performed. The cup (range 44-52 mm) was implanted at the nonanatomic so called * False * 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 auto graft, cage or ring was used to support the acetabulum.
Placement of femoral prosthesis
After the cup implantation, the femur was internally rotated 90° and the femoral canal was prepared using the dedicated reamer for the 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 sub trochanteric or supra condylar osteotomy would be performed for femoral shortening.
Post operation assessments
Patients were visited by an expert orthopedist. All patients received antithrombotic prophylaxis using low-molecular-weight heparin (LMWH) (at half-dose 4–6 h after the procedure followed by full-dose the next day) postoperatively.
The severity of pain in patients was assessed daily using Visual Analog Scale (VAS) ranged from 0-10 in which no pain gets score (0) and highest pain gets score 10, during the period of hospitalization and an average score was obtained for each patient in both groups. We should note that patients were encouraged to conduct early mobilization and limb exercises in bed immediately after surgery, especially hip abduction function exercise. They walked with partial weight bearing for approximately 17 days, and then gradually progressive full weight bearing was allowed at 8-12 weeks after surgery. The immediate postoperative and most recent anteroposterior (AP) radiographs of the pelvis centered on the pubic symphysis and including the iliac wings were obtained for all patients and repeated in the first- third- sixth months after the surgery and also one year after surgery. Leg length discrepancy (LLD) was measured as the difference in distance between the tip of the lesser trochanter and the inter-teardrop line. The acetabular component was considered loosened in presence of a change in alignment of > 4° or migration of > 3 mm in the radiographic evaluation (22). Range of motion (ROM) of the involved joins was assessed by physical examinations 1 year after the surgery and included hip flexion, abduction, adduction, external rotation and internal rotation. The average degrees were calculated. Harris hip score (HHS) was measured for each patient after one year of surgery. This score evaluates patients’ pain, ability of walking, requirement of support when walking, distance for walking, claudication, sitting condition, ROM, ability of using the stairs, ability of using shoes or socks, gait, ability of using public transportation and scores from 0 to 100 (23). The other complications such as infection, need for revision and hip dislocation were assessed and evaluated during the 1 year study duration.
Basic data assessment on patients
We collected data from patients including age, sex, weight, height, body mass index (BMI) and involved side, Crowe type and also gait type. Patient’s gait was evaluated using scoring from 1 to 6. Normal gait scored 6, mild claudication but no usage of cane scored 5. Patients with the ability of long walks with one cane and mild disability of walking without cane scored 4. Score 3 were patients with limitation of walking with one cane and serious problems when walking without cane or standing up for a while. Serious disability of walking with or without one cane scored 2 and walking for only 2-3 meters or disability of walking or requiring to use 2 canes scored 1 (24) . Crowe's classification is based on easily identifiable anatomic landmarks based on AP radiography of pelvis. Type III and IV are the most severe types of DDH (8). Here patients with gait types 4 to 6 and Crowe types 3 and 4 were entered.
Statistical analysis
Continuous and categorical data were reported as mean ± Standard deviation (SD) and frequency (percentage), respectively. Normality of continuous was evaluated using Kolmogorov-Smirnov test and Q-Q plot. Continuous data were compared between groups using independent samples t-test and analysis of covariance (ANCOVA). ANCOVA was used when adjustment is need for potential confounding variables. Categorical data were compared between groups using chi-squared or Fisher exact tests. All statistical analyses were performed by using SPSS 20 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.).