RESUMO
Background: Deviation from planned component placement with robot-assisted total hip arthroplasty (RA-THA) may differ based on surgical approach. The purpose of this study was to compare radiographic accuracy and precision of acetabular component position using RA-THA with the direct anterior approach (DAA) or posterior approach (PA). Methods: Between 2016 and 2019, 134 PA RA-THA patients were matched to 134 DAA RA-THA patients based on age (±10 years), body mass index (±5 kg/m2), and sex (exact). Acetabular component position was assessed using (1) planned position on preoperative computed tomography, (2) intraoperative position, and (3) position on 6-week postoperative radiographs using the digital Ein Bild Röntgen Analyse system. Results: Accuracy of acetabular component inclination in the PA cohort was lower than that in the DAA cohort (PA: 4.3° ± 2.8° vs DAA: 3.1° ± 2.4°, P = .001). Inclination precision was not statistically different (PA: 3° ± 2.4° vs DAA: 2.5° ± 1.8°, P = .071). Anteversion accuracy was not statistically different (PA: 4.1° ± 3.7° vs DAA: 3.5° ± 2.5°, P = .091). Acetabular component anteversion was more precise with DAA (PA: 4.1° ± 3.7° vs DAA: 2.9° ± 2.0°, P = .001). Radiographic outliers (anteversion or inclination was >10° or <-10° from the planned target) were significantly more prevalent in the PA cohort than in the DAA cohort (12 vs 3, P = .016). Conclusions: The acetabular component can be positioned with excellent precision and accuracy when using RA-THA regardless of approach. Although the DAA resulted in a slight increase in precise placement of cup anteversion and more accurate placement of cup abduction with fewer outliers, these small differences may not be clinically meaningful.
RESUMO
AIMS: This combined clinical and in vitro study aimed to determine the incidence of liner malseating in modular dual mobility (MDM) constructs in primary total hip arthroplasties (THAs) from a large volume arthroplasty centre, and determine whether malseating increases the potential for fretting and corrosion at the modular metal interface in malseated MDM constructs using a simulated corrosion chamber. METHODS: For the clinical arm of the study, observers independently reviewed postoperative radiographs of 551 primary THAs using MDM constructs from a single manufacturer over a three-year period, to identify the incidence of MDM liner-shell malseating. Multivariable logistic regression analysis was performed to identify risk factors including age, sex, body mass index (BMI), cup design, cup size, and the MDM case volume of the surgeon. For the in vitro arm, six pristine MDM implants with cobalt-chrome liners were tested in a simulated corrosion chamber. Three were well-seated and three were malseated with 6° of canting. The liner-shell couples underwent cyclic loading of increasing magnitudes. Fretting current was measured throughout testing and the onset of fretting load was determined by analyzing the increase in average current. RESULTS: The radiological review identified that 32 of 551 MDM liners (5.8%) were malseated. Malseating was noted in all of the three different cup designs. The incidence of malseating was significantly higher in low-volume MDM surgeons than high-volume MDM surgeons (p < 0.001). Pristine well-seated liners showed significantly lower fretting current values at all peak loads greater than 800 N (p < 0.044). Malseated liner-shell couples had lower fretting onset loads at 2,400 N. CONCLUSION: MDM malseating remains an issue that can occur in at least one in 20 patients at a high-volume arthroplasty centre. The onset of fretting and increased fretting current throughout loading cycles suggests susceptibility to corrosion when this occurs. These results support the hypothesis that malseated liners may be at risk for fretting corrosion. Clinicians should be aware of this phenomenon. Cite this article: Bone Joint J 2020;102-B(7 Supple B):20-26.