A Comparative Study Of Range Of Motion And Impingement In Patients With Low-dislocation Dysplastic Hips Underwent Arthroplasty

Objective:Both modular and non-modular stems are options for total hip arthroplasty(THA)in patients with Hartofilakidis type B developmental dysplasia of the hip(DDH).This study applied 3D reconstruction dynamic simulation techniques in functional pelvic positions to compare the postoperative range of motion(ROM)and impingement in patients with Hartofilakidis B DDH who underwent combined anteversion technique with modular and non-modular stems.And the study findings are expected to provide valuable references to the selection of prosthesis for DDH patients.Materials and methods:This retrospective study included 22 patients(25 hips)with Hartofilakidis type B DDH who underwent THA with combined anteversion technique in the Department of Bone and Joint Surgery,First Hospital of Jilin University between July 2020 and November 2022.There were 11 patients(12 hips)received the modular stem(the Mod group)and 11 patients(13 hips)received the non-modular stem(the Non-Mod group).Based on lateral pelvic radiographs in different functional positions,pelvic coordinate systems were established to simulate hip motion and impingement,including internal rotation at 75° flexion in relaxed sitting position,internal rotation at 90° flexion in flexed sitting position,and flexion,extension,and external rotation in standing position.Additionally,postoperative height and offset of rotation center,femoral offset restoration and leg length were compared to the contralateral side between the two groups.Results:The ROM from extension to flexion,internal rotation in relaxed sitting position and internal rotation in flexed sitting position were all higher in the Non-Mod group than in the Mod group(p=0.015;p=0.026;p=0.005).The Mod group exhibited a tendency of more prosthetic impingement during internal rotation in flexed sitting position and more bony impingement during extension compared to the Non-Mod group.No significant differences were observed between the two groups in the rotation center height difference,femoral offset restoration,cup offset restoration or leg length discrepancy(p=0.061;p=0.776;p=0.454;p=0.259).Conclusion:Both modular and non-modular stems can be utilized to achieve favorable clinical outcomes in patients with Hartofilakidis type B,even with differences in postoperative ROM and impingement.Ultimately,the selection of prosthesis still depends on the surgeon’s judgment and patient’s condition.