Application value of the oval fossa in total hip arthroplasty for ankylosing spondylitis patients with bony ankylosis of the hip

WANG Dong-dong; PEI Li-jia; LIU Yang; LU Shan; WU Kui; CAO Wei; ZHOU Xin-she

doi:10.3969/j.issn.2095-252X.2025.12.009

Abstract：Objective To investigate the application value of the oval fossa in total hip arthroplasty(THA)for patients with ankylosing spondylitis(AS)complicated by bony hip fusion.Methods A retrospective analysis was conducted on the clinical data of 23 patients with AS complicated by bony hip fusion who were admitted to the First Affiliated Hospital of Bengbu Medical University and Suzhou First People's Hospital between January 2023 and April 2024.The patients were divided into an oval fossa group(n=11)and a conventional positioning group(n=12)based on whether the oval fossa was used as a positioning landmark during surgery.All patients underwent preoperative imaging examinations,including hip X-ray,CT,and MRI.In the oval fossa group,the oval fossa was used as an anatomical reference marker for installing the acetabular prosthesis and restoring the hip joint rotation center during surgery,while in the conventional positioning group,prosthesis center positioning relied on conventional landmarks such as the acetabular rim,anterior and posterior acetabular columns,and obturator foramen.The operative time and intraoperative blood loss were recorded for both groups,along with postoperative measurements of abduction angle,anteversion angle,changes in lower limb length discrepancy,and horizontal acetabular cup coverage.Hip joint function was assessed using the Harris Hip Score(HHS),and activity-related pain was evaluated with the Visual Analogue Scale(VAS).Comparative analysis was performed between the two groups.Results The operative time for patients in the oval fossa group was(145.55±11.35)min,while that for patients in the conventional positioning group was(117.33±12.62)min.The intraoperative blood loss in the oval fossa group was(329.55±52.61)ml;compared to(283.42±45.27)ml in the conventional positioning group,the differences were statistically significant(P<0.05).The postoperative abduction angle in the oval fossa group was(39.09±3.05)°,while that in the conventional positioning group was(42.25±3.11)°,and the differences were statistically significant(P<0.05).There was no statistically significant difference in the postoperative anteversion angle between the two groups(P>0.05).The postoperative HHS in the oval fossa group was(89.64±3.91)points,while that in the conventional positioning group was(80.58±4.12)points,and the differences were statistically significant(P<0.05).The postoperative VAS score during activity in the oval fossa group was(1.27±0.47)points;compared to(3.58±1.00)points in the conventional positioning group,the differences were statistically significant(P<0.05).The postoperative total horizontal coverage rate of the acetabular cup in the oval fossa group was(97.18±1.25)%,while that in the conventional positioning group was(93.58±1.98)%,and the differences were statistically significant(P<0.05).The postoperative lower limb length discrepancy in the oval fossa group was(0.92±0.30)cm;compared to(2.12±0.65)cm in the conventional positioning group,the differences were statistically significant(P<0.05).Conclusions The oval fossa serves as an anatomical reference marker for restoring the hip joint rotation center and holds significant application value in positioning the acetabular prosthesis during THA for AS patients with ankylosed hips.Although the oval fossa positioning technique increases operative time and intraoperative blood loss,it optimizes acetabular cup placement by reducing the postoperative abduction angle and lower limb length discrepancy.This approach significantly improves hip joint function,enhances total acetabular cup coverage,alleviates postoperative pain,and ultimately demonstrates superior clinical outcomes.