In this study, we investigated the outcome related to the amount of stretch placed on the skin incision as measured by the ratio of the incision length in flexion to extension in patients undergoing primary TKA. Furthermore, we included the IS index as an assessment criterion to determine how the difference between EL and FL affected TKA’s outcomes. We compared VAS pain score, ROM, QS, knee circumference, and incision problems among groups. The present study revealed that pain feeling, ROM, QS, swelling, and incision problems were improved better two weeks after TKA with a decrease in IS index. These results showed that the closer the gap between EL and FL was, the less the incision stretching was,which benefit outcomes after TKA. Our present results suggested IS A was the optimal ratio between flexion and extension length in patients undergoing primary TKA. Given the above, during the study, we observed that such an incision (IS A) that the quadriceps tendon was incised 4 cm proximally above the upper border of the patella and distally along the medial side of the patellar tendon to the tubercle of the tibia could improve the results after TKA.
There are primarily three reasons that explain the above findings. Firstly, the strength of quadriceps is decreased by up to 60% after TKA, as the cutting of quadriceps muscle, eversion of the patella, and extreme knee flexion during TKA [18]. In addition to that, K. Chareancholvanich et al. reported that there is a significant effect of the length of surgical incision on the postoperative strength of quadriceps [18]. What’s more, the size of incision directly affects pain feeling and swelling as larger incision produces more inflammatory factors [16]. Less pain decreased swelling, and better strength of quadriceps makes patients relatively comfortable while they perform the functional exercise. Finally, IS C represents the ratio at the highest stretch level in comparison to IS A and B, which make surrounding tissue tolerate the largest tensile force, especially as the knee is in an extreme flexion intraoperatively. Made up of a complex network of collagen and elastin fibers, the skin has elastic characteristics and mechanical strength within its physiological limits [17]. However, previous studies indicated that the acute, purely reversible elastic response of stretched skin tissue, which is similar to the stretching process of the incision during TKA would be impaired to a certain extent if we stretched it beyond its physiological limits [17]. This impairment by releasing inflammatory elements and strain injury of nerves showed pain feelings, paresthesia, and tissue edema. Therefore, the contents above can help explain why IS A is the optimal ratio of the incision length in flexion to extension in patients undergoing primary TKA.
Clinically, more incision problems, even including skin necrosis, occurred as the incision was at higher stretch levels. Therefore, to avoid these problems, a decrease in incision stretching force by increasing its length in extension, which improves microcirculation of surrounding tissue, leads to a better incision healing, and hence it is clinically important. Our results may provide clinical evidence and basic data of the obvious effects of incision stretching on key outcomes after TKA, such as pain, ROM, QS, and swelling. Furthermore, our results reveal a greater surface area of sensory change in the front of the knee following TKA occurs in patients with incision at higher stretch level, since nerves around the knee which were stretched beyond physiological limits were shown to be impaired more widely due to the characteristic of the extensibility of the axon [1]. This greater alteration in skin sensation discounted the ability to kneel due to the fear of harming the prosthesis [1], combined a negative effect on subjective feelings such as titillation, results in patient dissatisfaction following TKA. That is, this study suggests that the length of incision, in extension, is possibly an effective treatment method, especially when patients perform the painful exercise, as appropriate incision stretching makes them comfortable by less pain and improved strength of quadriceps. It is conceivable and desirable that there were medical costs saved due to earlier recovery. Therefore, the findings in the present study suggest that selecting the optimal ratio of the incision length in flexion to extension in extension, which determines incision stretching would be significant in the clinical practice.
To our best knowledge, although there merely two studies involving the incision length in primary TKA. However, their results have a certain limitation. K. Chareancholvanich’s report only investigated the effect of the length of knee incision in full extension on quadriceps strength [16]. Despite elaborate data regarding quadriceps strength following TKA in his report, only different incision length in extension was discussed. However, incision length in flexion, namely the problem of incision stretching, did not be studied. By contrast, Roidis NT’s study paid close attention to the incision stretching in patients undergoing primary TKA [14]. He reported that the incision length was 5.7 cm longer in flexion than extension. The surgical incision site stretched an average of 23.6% in flexion compared to in extension [14]. However, what impact could incision stretching have on clinical outcomes after TKA, such as pain, ROM, and swelling, has not been investigated yet. Based on these two studies, our study further deepens the significance of incision stretching, and this is the first study to investigate that. A comprehensive understanding of the impact of incision stretching on TKA’s results may help surgeons to optimize clinical practice. This helps us know the effect of incision stretching on TKA’s results we interested in. Findings from this study can guide surgeons to attach importance to the length of incision in extension, which determines the stretching force of your incision. Despite being the seemingly minor problem, it is a real concern we should deliberate on. It becomes a well treatment of fast recovery from TKA with the circumstance of less incision stretching. We hope the present results could be helpful in optimizing TKA’s detail and perfect clinical outcomes.
Several limitations in this study warrant discussion. First, our data of incision stretching was obtained by calculating the self-designed formula: FL-EL/EL, and thus the examination of its real size was indirectly and relatively inaccurate. Second, no pathological examination was applied. However, that serves as the golden criterion, which demonstrates the incision stretching exists by the observation of changes in the microscopic structure, such as the disruption of skin collagen bundles. Third, our study employs many different combinations, and this made pain score evaluation accurate to a certain extent. Finally, relatively small sample results in less persuasive conclusions. Therefore, in the future study, we intend to quantitatively evaluate changes in the tissue under different stretching forces via microscopic examination and objective measurements such as a mechanical sensor.