There were many clinical studies on the relationship between obesity and THA, in which several different perspectives have been proposed[18–25]. However, there was still no unified conclusion on whether obesity had a negative impact on THA. This was conflicting evidence as to whether, how, and to what degree obesity may negatively influence the outcomes of THA. For a more in-depth discussion, we have provided this idea as to whether there was a factor closely related to but not absolutely consistent with, obesity that led to this result. Our prospective study explored the factor of AO to prove it.
Our research identified no significant difference between AO and non-AO patients in terms of their hip function 3-year following their THA, the preoperative scores of the two groups were significantly improved. There was no significant difference between the two groups in acetabular anteversion, inclination and patients’ satisfaction. However, there were significant differences in the improvement of walking ability and the relief of hip pain between the two groups. The improvement of walking ability in non-AO group was significantly higher than that in AO group. In terms of walking ability, AO had a certain impact on patients after THA. This was the same as Samantha Haebich's conclusion on the impact of obesity on THA in 2019. This seemed to corroborate the hypothesis proposed in this article. The relationship between AO index and degree of influence has not been discussed in depth in this study. The patient mentioned in our results who underwent revision surgery due to prosthesis infection was in non-AO group, the cause may be postoperative trauma infection. There was no significant difference in BMI between the two groups in this study, and the influence of obesity on the experimental results was ruled out.
A study by Purcell in 2016 showed that the infection rate of deep and superficial wounds in obese patients increased during THA. In this study, there was no significant relationship between the occurrence of infection and AO, which seemed to indicate that the increase in the infection rate in obese patients was not related to AO. However, it was worth noting that the surgical method used a direct anterior approach with a specific surgical auxiliary machine. During the operation, we took some approaches to the abdomen of patients with AO to reduce the influence of abdominal fat on the operation and prevent it from affecting the surgical field of vision. This may be the reason we had fewer complications.
In a large cohort study of 124368 patients undergoing THA, the authors found that in patients undergoing total hip replacement surgery, obesity increased the risk of various complications and correction rates. For overall complications, 1-year revision surgery, and 90-day surgery complications, the risk increased with increasing body mass index (BMI). In a prospective study, Chee et al.compared the matching of 55 consecutive THAs in morbidly obese patients with a set of 55 THAs in non-obese patients. The authors found that the incidence of all types of complications was significantly higher in obese patients. However, there were no significant differences in the risk of superficial and deep wound infection and dislocation between the two groups. In our study, AO did not significantly add the incidence of pulmonary complications. All patients have achieved satisfactory results, and postoperative pain, hip joint function, and walking ability have all been greatly improved.
AO was a component of the metabolic syndrome and was a predictor of exercise performance during the 6-minute walk test. AO had a significant impact on sports performance and physical activity. The blood flow of the calf was significantly reduced, which increased the risk of thrombosis in surgical patients. However, there was no significant statistical difference in the 6wt preoperative baseline data of the two groups in this study. The specific reason is not yet clear. Perhaps the pain of the hip and limited movement of the lower limbs covered the impact of AO on walking ability. This requires further research. In terms of the 6wt improvement of the two groups, the AO group was significantly lower than the non-AO group, and the two groups’ data were statistically significant(p<0.001). However, it cannot be ruled out that the impact of AO on walking ability would appear after the elimination of hip pain and limited movement of lower limbs. No patient with thrombosis was found in this study. The specific reason may be the current general use of “Low Molecular Weight Heparin Sodium Injection” in THA. The impact of the reduction of peripheral circulation on the recovery of the soft tissues of the lower extremity wounds was not mentioned in this study due to the long follow-up time.
As far as we know, there are few studies on AO for the prognosis of THA. The surgical method used in this study was a direct anterior approach, and some additional measures were taken during the operation for patients with AO. This is not shown in other studies, which may be the reason our results conflict with other studies. The follow-up time of this study was about 3 years, which is relatively short compared with other studies. To understand the long-term effects of AO on THA surgery, longer follow-up is needed. This study only counted the patient's weight and abdominal circumference before surgery but did not consider the patient's weight and abdominal circumference changes during the follow-up period.
In conclusion, AO does not increase the complications after THA, nor does it have a significant impact on the function after THA. However, it seems to have a negative effect on the improvement of walking ability and the relief of hip pain, slowing down the time to recover from pain and reducing the patient's postoperative walking speed. However, multicentre study with larger sample sizes is needed to further confirm the impact of AO on THA.