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The hip-spine relationship is a critical consideration in total hip arthroplasty (THA) procedures. While THA is generally successful in patient, complications such as instability and dislocation can arise. These issues are significantly influenced by the alignment of implant components and the overall balance of the spine and pelvis, known as spinopelvic balance. Patients with alteration of those parameters, in particular rigid spines, often due to fusion surgery, face a higher risk of THA complications, with an emphasis on complications in instability, impingement and dislocation. For these reasons, over the years, computer modelling and simulation techniques have been developed to support clinicians in the different steps of surgery. The aim of the current review is to present current knowledge on hip-spine relationship to serve as a common platform of discussion among clinicians and engineers. The offered overview aims to update the reader on the main critical aspects of the issue, from both a theoretical and practical perspective, and to be a valuable introductory tool for those approaching this problem for the first time., (© 2024. The Author(s).)

Purpose: The purpose of this study is to estimate the effect of unilateral hip osteoarthritis (OA) on hip muscle volume and fatty infiltration and to evaluate changes of muscles after total hip arthroplasty (THA) surgery., Methods: A retrospective analysis was conducted on patients with unilateral hip OA subjected to THA with perioperative pelvic girdle 1.5 T magnetic resonance imaging (MRI). Thirty-five patients were included. Ten of these have also postoperative MRIs. Medius gluteus (MG) and iliopsoas (IP) muscles were manually segmented on the MRI scans, the corresponding 3D muscle geometries were reconstructed, and the volumes extracted. Muscle quality was assessed using the Goutallier classification on coronal MRI images. Volume and muscle quality differences were calculated between healthy and affected side., Results: Pre-operatively, MG and IP on the affected side presented a mean muscle volume 17.5 ± 18% (p < 0.001) and 14.4 ± 15.8% (p < 0.001) smaller than the healthy counterpart, respectively. Muscles on the affected side showed a significant higher grade of fatty infiltration compared to the healthy side (p < 0.05 for MG; p < 0.001 for IP). At an average follow-up of 13 ± 5.3 months after THA, MG, and IP muscles of the affected hip showed an average 22.8% (p < 0.001) and 28.2% (p < 0.001) volume increase after THA. Also, the healthy side showed a significant increase of muscle volume for IP (17.1% p < 0.001). No significant change for MG muscle was observed., Conclusions: The study demonstrated preoperative reduced muscle volume and higher fatty infiltration at the muscles of the OA hip compared to the contralateral healthy one. A significant positive effect of THA on hip muscle volume was observed. These findings give an interesting insight on muscle deconditioning and recovery in patients undergoing THA., (© 2023. The Author(s) under exclusive licence to SICOT aisbl.)