Comparisons among three approaches—two minimally invasive and one conventional—for total knee arthroplasty: a retrospective cohort study with minimum follow-up of 10 years




Few studies have investigated whether the mini-medial parapatellar (MMP) and quadriceps-sparing (QS) approaches have good long-term results compared to the conventional medial parapatellar (MP) approach in terms of clinical evaluations and radiographic assessments for total knee arthroplasty (TKA). The purpose of this study was to perform comparisons among the MMP, QS and MP approaches with a follow-up at 10 to 17 years.


This is a retrospective comparative study of 93 patients who underwent MMP TKA (32 TKAs), QS TKA (47 TKAs) or MP TKA (31 TKAs) with the same arthroplasty system. The clinical evaluations were performed according to the new American Knee Society score (KSS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the visual analogue scale (VAS), range of motion (ROM), incidence of anterior knee pain (AKP), the Feller patellofemoral score (PFS), the reoperation rate and the complication rates. Radiographic assessments included observation of the mechanical axis of the lower limb and calculations of the lateral distal femoral angle (LDFA), femoral flexion angle (FFA), medial proximal tibial angle (MPTA), tibial slope angle (TSA), lateral patella displacement (LPD), and lateral patella tilt (LPT).


There were no differences in the long-term follow-up results of the new KSS, WOMAC score, ROM, VAS, patellofemoral functions, reoperation rate or complication rates among the groups. In addition, no radiographic differences in terms of lower limb mechanical axis or femoral, tibial or patellar position were observed.


These results provide conclusive evidence that equivalent, long-term clinical results can be obtained using any one of these three approaches.


Total knee arthroplasty (TKA) is a safe and effective treatment for patients with end-stage knee osteoarthritis [1]; with the conventional medial parapatellar (MP) approach for TKA, good visualization of the knee can be obtained, helping to achieve correct osteotomy, proper ligament balance and good prosthesis position, which are all important for good long-term results [24]. To date, various types of minimally invasive approaches for TKA have been developed to improve functional recovery and rehabilitation and accelerate the return to the activities of daily life [5, 6]. Among them, two of the most commonly used minimally invasive procedures are the mini-medial parapatellar (MMP) and quadriceps-sparing (QS) approaches [79]. Some investigators have indicated that minimally invasive approaches may compromise the advantages of correct osteotomy, proper ligament balance and good prosthesis position to achieve potentially rapid rehabilitation [1012], potentially sacrificing the long-term clinical outcomes and survival of the prostheses [1316]. Thus far, to our knowledge, most of the studies of the MMP, QS and MP approaches have evaluated the follow-up of no more than five years, and there is a lack of data demonstrating the long-term results. Thus, we performed this study with a follow-up of 10 to 17 years to evaluate the post-TKA clinical and radiographic outcomes in patients who underwent MMP, QS or MP approaches for TKA. The primary hypothesis of this study is that the minimally invasive approaches would not compromise the clinical outcomes, lower limb mechanical axis or prosthetic positions evaluated by recently developed and validated outcome tools and that the reoperation and complication rates would be similar. A secondary hypothesis is that the two minimally invasive approaches may show superiority of patellofemoral functions in terms of anterior knee pain (AKP), Feller patellofemoral score (PFS), patellar physical examinations and patellar position.

Materials And Methods

This was a retrospective cohort study that was approved by the review board of our Hospital (IRB00006761-2011072), and informed consent was obtained from all patients. The inclusion criteria were patients who underwent primary TKA by one senior surgeon between November 2001 and June 2008 in our hospital. The exclusion criteria were patients with inflammatory arthritis (45 patients), patients with a history of previous knee surgery (67 patients), patients with neurological diseases (5 patients) and patients who received surgery with constrained TKA systems (8 patients). There were ninety-three patients (110 TKAs) enrolled in the final study. Data related to patient demographics, including affected side, gender, age, height, weight, body mass index (BMI), preoperative lower limb mechanical axis, Knee Society score (KSS) [17], range of motion (ROM) and visual analogue scale (VAS), were recorded. At the outpatient clinic, two independent observers performed all evaluations.

Surgical Techniques

All surgeries were performed by one senior surgeon who was experienced in MMP, QS and MP TKAs. For all TKAs, the Nexgen Legacy Posterior Stabilized-flex Prosthesis (Zimmer, Warsaw, Indiana, USA) was implanted in all patients in the three study groups with equal distribution, and a tourniquet was used during the procedure. For the MP and MMP groups, the operation was carried out through a midline incision and medial parapatellar arthrotomy. A quadriceps split approximately 4 centimeters (cm) above the superior pole of patella was used in the MP group, as described by Insall et al. [18], and a division of the quadriceps tendon extending 2 to 4 cm above the superior pole of the patella was used in the MMP group, as described by Tenholder et al. [19]. For the QS approach, a medial curved skin incision extending from the superior pole of the patella to the top of the tibial tubercle was made; the quadriceps tendon was divided no more than 2 cm within the vastus medialis obliquus muscle split if its insertion was attached to the medial edge of the patella, as described by Aglietti et al. [20]. During patellar resurfacing, the patella was dislocated and everted in the MP group and subluxed laterally with no eversion in the MMP or QS groups. The patella was removed at the same thickness as the components, and patellar resurfacing was performed in all patients with a cemented, three-pegged, all-polyethylene patellar component. The patellar tracking was examined by the no-thumb test.

According to the standard protocol, all patients received antibiotic prophylaxis for 48 hours (starting half an hour before skin incision) and thromboembolic prophylaxis for 20 days (starting on the first postoperative day). Meanwhile, the patients in our study underwent the same rehabilitation protocol. Ankle pump movement was initiated on the day of surgery, full weight-bearing under the supervision of a therapist was initiated on the first postoperative day, and ROM exercises were initiated on the fourth postoperative day, with increasing complexity according to the condition of the patients.

Clinical Evaluations

In each postoperative evaluation, the new KSS [21] was used to assess the knee score, satisfaction score, expectation score and functional activity score. The WOMAC and VAS scores were also used as patient-reported outcomes. Furthermore, ROM was also evaluated. During the ROM measurements, a goniometer was centered on the lateral femoral condyle with one arm placed along the long axis of the femur pointing to the greater trochanter and the other arm placed along the long axis of the tibia pointing to the lateral malleolus; thus, the ROM was obtained [22]. Meanwhile, the patellofemoral functions were evaluated and recorded. A standardized questionnaire including questions regarding the presence of AKP when climbing stairs, rising from a chair or exiting an automobile were also asked of all patients as a means of identifying symptoms related to the patellofemoral joint. In addition, a physician-rated Feller PFS and several physical examinations, including a patellar glide test (medial and lateral translations), a grind test (isometric quadriceps contraction with the patella immobilized and the knee in extension, thus forcing the patella into the trochlear groove) and patellar edge tenderness (isometric quadriceps contraction with the patella immobilized and the knee in extension while pressing sites around the patella), of every patient were measured and recorded, as well as measurement of thigh circumferences (15 cm above the proximal patella). Additionally, complications and revisions were determined based on both the inpatient and outpatient medical records of each patient.

Radiographic Assessments

Preoperative and postoperative long-standing films were obtained with subjects standing barefoot with the patella oriented forward according to Paley’s criteria [23]. Routine anteroposterior, lateral and standard skyline views were obtained thereafter. All of the following radiographic measurements are shown in Fig. 1. The hip-knee-ankle angle (HKA) was defined as the angle formed by the intersection of a line from the center of the head of the femur to the knee center landmark and a second line from the center of the ankle talus to the knee center landmark as described by McDaniel et al. [24]. The lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA) were measured as reported by Cip et al. and Chen et al. [25, 26], and the femoral flexion angle (FFA) and tibial slope were measured as described by Frederick et al. [27]. The lateral patellar tilt (LPT) and lateral patellar displacement (LPD) were evaluated as presented by Meftah et al. [28] and Laurin et al. [29]. The patellar height was determined by the Insall-Salvati ratio (IS). Aseptic loosening was indicated by the presence of radiolucent lines beyond 2 mm and gross shifting of components that caused subsidence or tilting [27]. HKA, LPT and LPD were measured before and after surgery. Evaluation of the radiographic assessments was performed using the picture Archiving and Communication System (PACS). The accepted values used in our study for the normal lower limb mechanical axis were (1) 0° ± 3° for HKA [26]; (2) 90° ± 3° for LDFA and MPTA [26]; (3) < 10° for LPT [30, 31]; (4) ≥ -5 mm and < 4 mm for LPD [30, 31]; and (5) ≥ 0.8 and ≤ 1.2 for IS. Two orthopedic surgeons skilled in TKA who were blinded to the surgical method performed the measurements, which were recorded with an accuracy of 0.1° and 0.1 mm. To test the reliability of these measurements, all variables were measured twice at 1-week intervals. For all measurements, the intraclass correlation coefficient of intraobserver reliability was > 0.92, whereas the intraclass correlation coefficient of interobserver reliability was > 0.86.

Statistical Analysis

The descriptive statistics are summarized as the mean and standard deviation (SD). Analysis of variance with a post hoc test (Tukey’s method) was used to compare the continuous variances. The Chi-Square test was used to compare the nominal variables, including gender, affected side and outliers. The follow-up time was evaluated as a predisposing factor affecting the clinical outcomes using multiple regression analysis. Statistical analysis was performed using SPSS software (version 22.0; SPSS, Inc., Chicago, IL), and the normal distribution was assessed by the Kolmogorov-Smirnov test. P < 0.05 was considered statistically significant.


Overall, 93 patients (110 TKAs) were included for analysis of the clinical results at a follow-up of 10 to 17 years, which consisted of 28 patients (32 TKAs) in the MMP group, 39 patients (47 TKAs) in the QS group, and 26 patients (31 TKAs) in the MP group. Our follow-up rate was 73% for the MMP group, 78% for the QS group and 69% for the MP group. The mean follow-up for the MMP TKA group was 150.8 months (range, 124-171 months), 135.3 months (range, 120-151) for the QS TKA group, and 175.4 months (range, 150-203 months) for the MP TKA group; the differences among the three groups were statistically significant (P < 0.01). There were no significant differences among the three groups in terms of affected side, gender, age (at the time points of operation and follow-up), height, weight, BMI, or preoperative measurements, including HKA, LPT, LPD, KSS, ROM or VAS (Table 1).

Clinical outcomes

Clinical evaluations showed that there were no statistically significant differences among the three approaches for TKA (adjusted P >0.216) (Table 2). There were no differences in any section or in the total scores of the new KSS or WOMAC. The ROM, VAS and thigh circumference also did not differ among the three groups. Regarding the patellofemoral functions, including AKP, Feller PFS, and patellar physical examinations, no statistically significant differences were found based on the scores or records.

Complications and revisions

In the MP group, one patient developed deep vein thrombosis after surgery, which was suspected based on the swelling of the calf and was confirmed by venous ultrasound. In the QS group, one patient had a deep infection three months after the operation, which was successfully treated after surgical debridement and oral antibiotic therapy. No other intraoperative or postoperative complications were observed during follow-up in the MMP group. For the revision, one patient in the QS group had a revision of patella resurfacing due to patellar component loosening three years after her primary TKA, and one patient in the MMP group underwent a total revised TKA owing to aseptic loosening after 11 years, which was found at the follow-up. No revisions were required in the MP group. No significant differences among the three groups were found regarding complications and reoperation rate (P > 0.05).

Radiographic Results

The postoperative radiographic results are summarized in Table 3, and no statistically significant differences were detected among the three groups in the values of angles or the outliers with regard to lower limb mechanical axis, femoral or tibial component positions in the coronal or sagittal planes, or in patellar position.


Regarding the two hypotheses, relevant results showed that minimally invasive approaches would not yield better patellofemoral functions and no significant differences were found among the three groups in terms of clinical outcomes, radiographic evaluations, suggesting that no approach is superior to the other two regarding these results.

Compared with the MP approach, the MMP and QS approaches for TKA have two main differences in the present study. First, the arthrotomy extended into the quadriceps tendon less than 4 cm above the upper pole of the patella in the MMP and QS groups but extended 6-8 cm in the MP group; second, the patella was everted from the beginning of the femoral resection to the end when patella resurfacing was performed in the MP group, whereas in the MMP and QS groups, the patella was not everted during the surgery. Many comparative studies of the MMP, QS and MP approaches have reported good clinical results but inferior lower limb mechanical axis and malposition at the short-term follow-up for MMP [32, 33] and QS [8, 34-36] because of the limited working space compared with the MP approach. In addition, some studies indicated that the MP approach may affect patellar tracking, AKP and the patellar position [8, 34-36]. Therefore, we performed a comprehensive evaluation of patellofemoral function in addition to the overall knee score in the clinical investigations.

There are a number of studies that have compared the clinical and radiographic differences among the MMP, QS and MP approaches [34, 37, 41-44], but few of them had a follow-up of at least 10 years. In a retrospective study with a mean follow-up of 5 years, Huang et al.[37] reported that the MMP and QS approaches led to more appropriate LPT and LPD than the conventional MP approach did. Chiang et al.[8] conducted a prospective and randomized study with a mean follow-up of 2 years and reported that patients undergoing QS and MP TKA had comparable clinical outcomes, and that the QS TKA was more time consuming surgically and resulted in a less accurate prosthesis position. In a retrospective study with a mean follow-up of 2 years, Lin et al.[45] showed that the QS approach provided inferior radiographic results with similar clinical outcomes when compared with the MP approach. In 2018, Kazarian et al. [46] conducted a meta-analysis of randomized controlled trials (RCTs) of the QS approach and MP approach, in which all the studies were no more than 2 years long ,and reported that the QS approach to TKA failed to demonstrate clinically significant advantages but showed increased lower limb mechanical axis and femoral and tibial prothesis frontal position. Our study is a more than 10-year study aimed at the long-term results, showing no statistically significant differences among the three approaches for TKA in terms of clinical outcomes, radiographic outcomes and prothesis survival rate.

Some studies have shown that the MP approach affects patellar tracking, AKP and the position of the patella [37-40] because the MMP and QS approaches preserve the majority of the extensor mechanism. Some studies have indicated that the position of the femoral and patellar protheses, especially when poor rotational alignment occurs, can lead to AKP [47]. AKP is a common reason for reoperation or revision [40]. Therefore, we conducted the current study and included the AKP questionnaire, Feller PFS, and patella physical examinations. Nevertheless, we did not find a statistically significant difference among them, which was consistent with the radiographic assessments. Furthermore, weakness of the quadriceps muscle is associated with patellofemoral function [48]. When patients are discharged from the hospital and reexamined in outpatient clinics, we always advise them to exercise the quadriceps muscle, usually by squatting. There is a rough estimate that the amount of quadriceps atrophy is indicative of the amount of weakness present [49], so we measured the thigh circumference of every patient, and no statistically significant difference was noticed, which was consistent with the results of patellofemoral function.

Longevity is one of the concerns in TKA, and the survivorship of implants is dependent on the patient demographics, the surgical technique and implant-related factors [50, 51]. Incorrect positioning of the implant and improper mechanical axis of the lower limb can lead to accelerated implant wear and loosening, as well as suboptimal function. Aseptic loosening, instability, and malalignment were the most common reasons for late revision [52-55]. In this study, no differences were found in the value of or in the outliers of the radiographic assessment angles. We believe that the MMP and QS approaches not only do not increase the risk of malalignment and malposition of the components but also do not increase the reoperation rate of TKA. Our results are consistent with those from other studies [34, 56], indicating that radiographic outcomes were not compromised with the MMP and QS approaches. King et al. [44] demonstrated that a substantial learning curve (fifteen procedures) may be required for surgeons before reaching steady results using the QS approach, so we recommend that surgeons gradually decrease quadriceps exposure in order for patients to gain advantages of the TKA procedure.

In the present study, we conducted long-term follow-ups for a minimum of 10 years in which detailed evaluations of the postoperative clinical outcomes and radiographic assessments were measured. The new KSS system [21] has been recognized as a more efficient method to primarily differentiate the activities contributing to the function score compared with the old KSS system. In addition, some studies have demonstrated that the knee function score declines gradually [21] and that the alignment and prothesis position worsen during the long-term postoperative period [38], so we performed a multiple regression analysis, and the results were the same.

This study has several limitations. First, this study was limited by its retrospective design. Second, although we conducted a multiple linear regression, the significant difference in the follow-up time among groups could still introduce some degree of bias. Third, the small cohort sizes led to insufficient observations to determine the level of statistical significance. Fourth, only approximately 65% of the patients were able to directly be evaluated at the long-term follow-up. However, this follow-up rate is typical of the follow-up rate for TKA performed in elderly people [58, 59] due to a high number of patients faced with nonrelated TKA, including back pain, hip and ankle disease.

This study also has several strengths. This study is one of the few studies to report long-term postoperative clinical and radiographic outcomes for these three approaches to TKA. All surgeries were performed at a single center by the same surgical team using only one type of TKA, which allowed for better consistency among these three groups. Our study used the new KSS to assess the clinical outcomes, which provides sufficient detail to evaluate the functional capabilities of the knee [21].


In conclusion, our study demonstrated that no one approach for TKA was superior to another. Successful survival for these three clinical approaches was achieved. The choice of approach depended on the status of patient and the surgeon’s preference.


MMP: mini-medial parapatellar; QS: quadriceps-sparing; MP: medial parapatellar; TKA: total knee arthroplasty; KSS: new American Knee Society score; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index; VAS: visual analogue scale; ROM: range of motion; AKP: anterior knee pain; PFS: patellofemoral score; LDFA: lateral distal femoral angle; FFA: femoral flexion angle; MPTA: medial proximal tibial angle; LPD: lateral patella displacement; LPT: lateral patella tilt; BMI: body mass index; HKA: hip-knee-ankle angle; TSA: tibial slope angle; PACS: picture Archiving and Communication System; SD: standard deviation; RCTs: randomized controlled trials; IS: Insall-Salvati   


Ethical Approval and Consent to participate

This retrospective study was approved by the Ethics Committee of the Peking University Third Hospital (IRB00006761-2011072). Written informed consent was obtained by all participants.

Consent for publication

Not applicable.

Availability of data and materials

The datasets analyzed during the current study are available from the corresponding author upon reasonable request.

Competing interests

The authors declare that they have no competing interests.


Not applicable.

Authors’ contributions

Conception and design: YFZ, YJK. Analysis and interpretation of the data: YFZ, SZW, FBS. Drafting of the article: YFZ, SZW, ZJY. Critical revision of the article for important intellectual content: YJK, JD. Final approval of the article: YFZ, SZW, YJK. All authors read and approved the final manuscript.


This study was funded by the National Key R&D Program of China (2017YFB1303000).


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Table 1 Baseline characteristics and preoperative comparisons [mean (SD/range)]



(n = 32)


(n = 47)


(n = 31)












Age at operation

63.2 (4.9)

64.4 (6.0)

63.1 (5.2)


Age at follow-up

75.5 (5.5)

75.5 (6.0)

77.0 (4.9)


Height (cm)

160.2 (8.6)

160.4 (6.7)

162.9 (7.1)


Weight (kg)

72.4 (12.2)

70.7 (11.5) 

69.0 (12.9)



28.2 (4.1)

27.5 (4.3)

29.9 (3.9)


Preoperative HKA

7.7 (7.5)

9.4 (7.1)

10.3 (7.1)


Preoperative HKA outliers





Patellar position





Preoperative LPT

2.2 (3.7) 

3.0 (2.9)

3.0 (3.0)


Preoperative LPT outliers

0 (0%)

1 (2.1%)

1 (3.2%)


Preoperative LPD 

1.2 (3.6)

0.0 (2.7)

0.1 (3.5)


Preoperative LPD outliers

1 (3.1%)

2 (4.3%)

1 (3.2%)


Preoperative KSS 





Knee score

49.1 (11.2)

52.1 (9.3)

50.5 (9.5)


Function score

53.1 (6.8)

55.3 (11.2)

52.4 (10.4)



104.2 (14.7)

106.8 (15.3)

105.9 (12.6)


Preoperative ROM

102.3 (9.0)

101.2 (8.2)

101.9 (9.6)


Preoperative VAS

6.6 (1.0)

6.6 (0.9)

6.5 (0.9)


Follow-up time (months) 

150.8 (124 172)

135.3 (120 151)

175.4 (150 203)

< 0.01


Table 2 Postoperative clinical data [mean (SD/range)]


Group MMP

(n = 32)

Group QS

(n = 47)

Group MP

(n = 31)







Pain score (25)

23.7 (3.0)

22.7 (2.8)

22.2 (4.1)


Satisfaction score (40)

36.8 (4.5)

35.0 (5.6)

33.6 (7.7)


Expectation score (15)

13.9 (1.7)

13.0 (1.9)

12.8 (3.5)


Walking/Standing score (30)

22.2 (7.4)

21.2 (7.9)

19.5 (6.5)


Standard activities score (30)

24.5 (4.7)

23.3 (3.8)

21.9 (7.1)


Advanced activities score (25)

15.7 (6.7)

13.9 (6.0)

13.3 (7.7)


Discretionary activities score (15)

6.4 (3.4)

5.7 (2.7)

5.5 (2.1)



148.2 (18.4)

150.7 (19.1)

144.2 (16.9)








1.4 (3.7)

0.8 (1.8)

3.0 (7.0)



1.1 (1.6)

0.4 (1.2)

1.7 (4.6)



15.7 (11.5)

17.9 (15.4)

22.5 (20.2)



19.3 (2.7)

18.6 (4.5)

21.2 (3.7)


Range of motion

119.7 (5.9)

118.3 (7.7)

115.5 (9.5)


Visual analogue scale

0.6 (1.2)

1.1 (1.2)

1.3 (1.6)


Thigh circumference

49.0 (3.8)

48.8 (3.7)

47.7 (4.1)


Patellofemoral functions





Anterior knee pain





Are you aware of your anterior knee pain when

Climbing stairs? 

3 (9.4%)

8 (17.0%)

4 (12.9%)


Rising from a chair?

4 (12.5%)

8 (17.0%)

44 (12.9%)


Exiting an automobile?

4 (12.5%)

8 (17.0%)

44 (12.9%)


Feller PFS





Anterior knee pain (15)

13.7 (2.5)

12.9 (3.1)

13.0 (2.6)


Quadriceps strength (5)

3.9 (1.0)

3.7 (1.2)

3.6 (0.9)


Ability to rise from chair (5)

4.3 (1.6)

4.2 (1.7)

4.1 (1.5)


Stair climbing (5)

4.3 (1.4)

4.5 (1.8)

4.3 (1.4)



32.7 (4.6)

32.1 (4.1)

31.8 (4.0)


Patellar glide test pain

2 (6.3%)

3 (6.4%)

0 (0%)


Patellar grind test pain

2 (6.3%)

3 (6.4%)

0 (0%)


Patellar edge tenderness

1 (3.1%)

3 (6.4%)

4 (12.9%)



Table 3 Postoperative radiographic data [mean (SD/range)]



(n = 32)


(n = 47)


(n = 31)


Lower limb mechanical axis





Hip-knee-ankle angle

2.4 (3.0)

3.5 (3.2)

3.0 (1.9)


Hip-knee-ankle angle outliers

14 (43.8%)

16 (34.0)

11 (35.5%)


Femoral position





Lateral distal femoral angle

90.2 (1.6)

89.7 (1.8)

90.5 (2.0)


Lateral distal femoral angle outliers

1 (3.1%)

3 (6.4%)

3 (9.7%)


Femoral component flexion angle

88.6 (1.6)

89.4 (2.0)

88.9 (1.9)


Tibial position





Medial proximal tibial angle

88.3 (3.0)

89.0 (3.5)

88.0 (2.2)


Medial proximal tibial angle outliers

9 (28.1%)

12 (25.5%)

7 (22.6%)


Tibial component slope angle

84.5 (1.9)

84.5 (2.8)

84.7 (2.0)


Patellar position





Lateral patellar tilt

2.6 (3.6)

3.2 (3.6)

3.0 (3.3)


Lateral patellar tilt outliers

1 (3.1%)

1 (2.1%)

1 (3.2%)


Lateral patellar displacement

0.9 (4.2)

-0.8 (3.7)

-0.1 (3.6)


Lateral patellar displacement outliers

8 (25.0%)

7 (14.9%)

4 (12.9%)


Insall-Salvati ratio

1.08 (0.12)

1.05 (0.14)

0.93 (0.17)


Insall-Salvati ratio outliers

6 (18.8%)

13 (27.7%)

10 (32.3%)