Activity Characteristics Of The Sagittal Plane Of The Spinopelvic In Patients With Developmental Dysplasia Of The Hip Undergoing Total Hip Arthroplasty

Background:Correct acetabular cup positioning and restoration of normal hip dynamics play a key role in the stability of the implanted prosthesis and they are important factors affecting the outcome of total hip arthroplasty(THA).It has been shown that spinopelvic deformities and abnormal spinopelvic mobility may lead to poor outcomes after THA,including instability,higher risk of revision and poorer clinical outcomes.Also patients with developmental dysplasia of the hip(DDH)have abnormal spinal alignment and an anterior pelvic tilt.And while spinopelvic deformities and abnormal pelvic mobility in patients with total hip arthroplasty(THA)have received increasing attention in recent years,the spinopelvic imaging features of patients with DDH are not fully understood.Therefore,the spinopelvic radiographic characteristics in patients with developmental dysplasia of the hip(DDH)have not been fully understood.The objectives of this study were 1)to observe the morphological characteristics of the sagittal plane of the spinopelvic and the changes in the mobility of the spine,pelvis and hip joints between different functional positions in patients with DDH before and after surgery,2)to investigate the preoperative and postoperative spine,pelvic and hip mobility of DDH patients with different degrees of dislocation,and 3)to compare these characteristics with those of patients with osteonecrosis of the femoral head(ONFH).Methods:This was a retrospective cohort study.Thirty patients with DDH(42 hips;31 hips were dysplasia,8 hips were low dislocation,and 3 hips were high dislocation)and 30patients(39 hips)with steroid-induced ONFH undergoing total hip arthroplasty(THA)were enrolled in the case group and the control group,respectively.The lateral radiographs in standing,relaxed-seated and deep-flexed-seated positions of all patients were taken.The preoperative and 3-month postoperative pelvic incidence(PI),lumbar lordosis(LL)and sacral slope(SS),and 3-month postoperative acetabular anteversion(AA)of the two groups were measured,and the changes of these parameters between different functional positions were documented as delta values.The change in sacral slope(ΔSS),the change in lumbar lordosis(ΔLL)and the change in acetabular anteversion(Δ AA)are used to represent the changes in these angles under dynamic conditions.Results:In the low dislocation subgroup,a sightly lower PI was observed.In the high dislocation subgroup,a wide range of PI was noted,with PI of 51.0°±13.3°in the standing position,47.8°±6.8°in the relaxed-seated position,and 41.6°±7.7°in the deep-flexed-seated position.The SSs were abnormal in patients with stiff spine.Six patients in the DDH group were found to have stiff spine before surgery and 4 of them were relieved after surgery,but none in the ONFH group had stiff spine.The preoperative and postoperative LLs of the DDH group at different positions were significantly greater than those of the ONFH group.The postoperative AAs of the DDH group at different positions were significantly smaller than those of the ONFH group.In the DDH group,the Δ SSs from relaxed-seated to standing and from deep-flexed-seated to standing increased significantly after surgery(p = 0.001 and p <0.001,respectively).There were no significant differences in the preoperative and postoperative Δ SSs between the DDH group and the ONFH group.In the DDH group,the ΔLLs from deep-flexed-seated to standing increased significantly after surgery(p = 0.007).Conclusions:The spinopelvic mobility of DDH patients was significantly improved by THA.The incidence of stiff spine in the DDH group was higher than that in the ONFH group,which was relieved after surgery.The PI of the low dislocation subgroup was slightly lower.Compared with patients with ONFH,patients with DDH had higher lumbar lordosis and lower postoperative acetabular component anteversion.