Abstract
Background
There are few reports including natural course of initial gap in total hip arthroplasty. The purpose of this study is to investigate the incidence of initial gap in the PSL type shells and its natural course.
Methods
Total of 386 THAs with Trident or TriAD PSL shells were performed between January 2000 and December 2014. Exclusion criteria were shells with screw fixations (n=189), previous pelvic osteotomy (n=15) and less than 3 years’ follow-up (n=11). Finally, our study included 171 hips. Average age was 56.8 (17∼83) years at THA and average follow-up time was 8.3 (3∼16.3) years; 112 (66%) were women; and 120 hips (70.2%) had osteoarthrosis. As radiographic evaluation, we checked presence or absence of initial gap, maximum size of it, gap filling and cup stability. The presence of initial gap was defined as gap present on post-operative anteroposterior X-ray measuring 1mm or greater. Gap filling was defined as confirmed trabecular formation between the cup and acetabular floor without cup migration. And we determined the time to gap filling. As clinical evaluation, we retrospectively checked Harris Hip Score (HHS) at pre-operative and final follow-up period, and presence of shell revision. Furthermore, we compared clinical results with or without initial gap.
Results
Initial gap was confirmed at 85 hips (49.7%) and mean maximum size was 2.1 (1∼6.3) mm. Mean gap filling occurred at 2.5 (± 1.4) years and there was no unstable cup. Comparing clinical results with or without initial gap, pre-operative HHS was not significantly associated with initial gap (57.8 and 56.3, respectively, p=0.41). HHS at final follow-up period was also not significantly associated with initial gap (88.4 and 87.5, respectively, p=0.49). There was no shell revision with or without initial gap.
Discussion
Initial gap of hemispherical type shell is reported that its incidence is 16∼38% and initial gap is not associated with clinical outcome. Our results show that PSL type shell occurs initial gap more frequently than hemispherical type shells.
Conclusion
Initial gap of PSL type shell was confirmed at 85 hips (49.7%) and mean gap filling occurred at 2.5 years. Initial gap did not affect shell revision and clinical outcome.
