The most important finding in our research was that when forgetting the artificial joint after TKA is the ultimate target, better QOL can be acquired by performing TKA via a MMV approach. In addition, compared with the MPP approach, the MMV approach may offer less pain and a faster recovery.
There are multiple approaches to minimally invasive TKA, including the MMV approach, the quadriceps-sparing approach, the mini-subvastus approach, and the limited MPP approach . However, because of the difficulty of the operation, the long learning curve , and the difficulty of preserving the extensor mechanism , few surgeons currently use the quadriceps-sparing approach and the mini-subvastus approach. Thus, we used FJS to study whether the MMV approach can be successfully used routinely as a minimally invasive TKA approach.
Several authors have attempted to compare the MMV approach and the MPP approach with conventional scores such as the VAS, the HSS (Hospital for Special Surgery) score, and the KSS, and only found differences in short-term outcomes, but this early clinical advantage has seemed to disappear over time [5-7]. Some authors even found no differences in clinical outcomes during the follow-up period [20-22]. A more responsive joint-specific score, such as the FJS, can provide a clearer assessment of patients' postoperative satisfaction, and our study highlighted differences for the first time between the two approaches during a follow-up of at least 3 years. This shows that the FJS is an appropriate tool to evaluate patients' satisfaction, which can reflect patients' satisfaction well not only in the early postoperative period but also in the medium-term postoperative period when KSS cannot detect differences.
The FJS has been a highly rated scoring method over the last few years, and is often used to measure the ability of patients to forget joint awareness or joint arthroplasty . Even if the patient's knee function is improved and no pain is felt, the FJS score will be lower if the patient is “aware of” the presence of their artificial joint in daily life. As a result, minor complaints that are not identified by specific questions (such as “can you participate in sports?”) are called “aware” joints, which may more sensitively reflect postoperative patient satisfaction and reduce the ceiling effect [12, 23]. Ozaki et al. believed that the FJS is a scoring system that can express “sense of stability” as “awareness” . Morten et al. believed that the FJS combines factors such as stiffness, pain, ability of daily activities, and patients’ expectations to reflect patients’ ability to forget artificial joints during activity, and therefore this scoring system may be the best tool to evaluate the results after TKA . Another study found that when using the FJS scoring system to evaluate the difference in knee awareness of patients who underwent patellofemoral arthroplasty, unicompartmental knee arthroplasty, and TKA, they found that patients who underwent different joint arthroplasties had large differences in the FJS .
Hiyama et al. found that quadriceps strength and pain were the main factors affecting joint awareness after TKA . Quadriceps weakness is the main obstacle to patients' functional recovery after TKA, and pain is usually one of the main criteria for success or failure after TKA. Quadriceps weakness and pain are closely related to disability , patient satisfaction , and QOL [29, 30].
One of the greatest advantages of TKA via the MMV approach is that it retains the extensor mechanism as much as possible during the operation. Therefore, it can reduce the perioperative pain and help the patients recover quickly. However, it has been pointed out that the standard MPP approach may decrease the strength of the quadriceps measured by isokinetics as much as 30.7% in the 2 years after TKA, and excessive damage to the extensor mechanism may be permanent . Retaining the extensor mechanism as much as possible was the main reason why the MMV approach enabled patients to achieve faster functional recovery and higher satisfaction [8, 32]. Our study adds to these findings by investigating the effects of quadriceps weakness and pain on joint awareness after TKA.
Some studies indicated that the performance of a postoperative straight leg raise reflects the recovery of quadriceps muscle strength [33, 34]. Schroer and Nestor measured the pre- and postoperative muscle strength of their patients who underwent TKA via the MMV approach and reported that patients had regained their preoperative quadriceps muscle strength in a short period, and even exceeded those levels by 30% at 3 to 6 months [35, 36]. Similar results were found in our research. In the present study, the time to be able to perform a postoperative straight leg raise in patients who underwent TKA via the MMV approach was much earlier than in patients who underwent TKA via the MPP approach. This difference in quadriceps muscle strength is essential for patients to resume daily activities. As reported in previous studies [37, 38], we also found that the MMV approach can shorten the length of the skin incision compared with the traditional MPP approach. In addition, a shorter skin incision may produce a better aesthetic effect, which can improve patients' satisfaction.
However, it has been pointed out that during the TKA with minimally invasive surgery, such as the MMV approach, the complex manipulation and poor exposure can lead to malalignment of the components [34, 39], which may lead to failure of TKA . However, in our study, no significant differences in postoperative complications were found in the patients until the final follow-up. Consequently, the MMV approach that protected the extensor mechanism may be a good choice in TKA.
The limitation of this study was that it had a retrospective mid-term follow-up design. Prospective and longer-term studies should be performed to confirm these findings.