The most important finding in our research is that when forgetting the artificial joint after TKA is the ultimate target, better QOL can be acquired by performing TKA via MMV approach. In addition, compared with MPP approach, the MMV approach could offer less pain and faster recovery.
Several authors attempted to compare MMV approach and MPP approach with conventional scores such as the VAS, HSS (Hospital for Special Surgery) score and KSS, and found only differences in short-term outcomes, but this early clinical advantage seemed to disappear over time [5-7]. Some authors even found no differences in clinical outcomes during follow-up period [16-19]. A more responsive joint specific score, such as FJS, can provide a clearer assessment of patients' postoperative satisfaction and it observed differences for the first time between the two approaches during the follow-up for at least 3 years. This shows that 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 can not detect the differences.
The FJS is a highly evaluated scoring method in last few years, which 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 artificial joints in daily life. As a result, minor complaints that are not identified by specific issues (such as “Can you do sports?”) are called “aware” joints, which may more sensitively reflect postoperative patient satisfaction and reduce the ceiling effect [12,20].
Hiyama Y 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 , patients' satisfaction  and QOL [24,25].
One of the greatest advantages of TKA via 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 decreased the strength of quadriceps measured by isokinetic as much as 30.7% in two years after TKA, and excessive damage to the extensor mechanism may be permanent . This was the main reason why MMV approach enabled patients to achieve faster functional recovery and higher satisfaction [8, 27]. Our study add to these findings by investigating the effects of quadriceps weakness and pain on joint awareness after TKA.
In our study, no significant correlation was found in regard to age, gender and BMI with the FJS. However, the MMV approach were positively correlated with the good outcome of FJS. This demonstrated that the FJS is optimally adapted to compensate for age, gender and obesity covariates .
Some studies indicated that the performance of postoperative straight leg raise reflects the recovery of quadriceps muscle strength [29, 30]. Schroer and Nestor measured the pre and postoperative muscle strengths of their patients who underwent TKA via MMV approach and reported that patients had gained their preoperative quadriceps muscle strength in a short period and even exceeded those levels by 30% in 3 to 6 months [31,32]. The similar results were found in our research. This difference in quadriceps muscle strength is essential for patients to resume daily activities. As reported in previous studies [33, 34], we also found that MMV approach can shorten the length of skin incision compared with traditional MPP approach. In addition, shorter skin incision could produce better aesthetic effect, which could improve patients' satisfaction.
It has been pointed out that during the operation, complex manipulation and poor exposure would lead to the malalignment of the components [31, 35], which might lead to the failure of TKA . However, in our study, no significant postoperative complications were found in all patients until the last follow-up. Consequently, the MMV approach which protected the extensor mechanism might be a good choice to perform TKA.
The limitation is that this research was a retrospective mid-term follow-up design, which has its potential weaknesses. A prospective and long term research should be established to confirm these findings.