Comparison of Subvastus and Medial Parapatellar Approaches in Total Knee Arthroplasty for Patients Aged Over 75 Years: Implications for Postoperative Rehabilitation and Early Mobilization

Introduction

Total knee arthroplasty (TKA) is a cornerstone treatment for severe knee osteoarthritis (OA) in older patients, improving pain and function [1]. Patients aged over 75 years face increased risks of immobilization-related complications, such as deep vein thrombosis (DVT) and pulmonary embolism (PE), due to comorbidities and reduced mobility [2]. In these patients, early functional milestones such as the ability to perform an active straight leg raise and achieving adequate knee range of motion within the first postoperative week are particularly meaningful. This population has reduced physiological reserve, higher prevalence of sarcopenia, and limited tolerance to prolonged immobilization. Delayed quadriceps activation and restricted early knee motion may hinder safe ambulation, delay physiotherapy participation, and increase the risk of immobilization-related complications and loss of functional independence. Therefore, surgical approaches that facilitate early quadriceps recovery and early knee motion may have a disproportionate clinical impact in this age group. The surgical approach in TKA influences recovery, with the medial parapatellar (MP) approach being standard due to its excellent exposure but potentially delaying mobilization by disrupting the quadriceps tendon [3]. Early achievement of active straight leg raise is especially critical in older patients, as it reflects preserved extensor mechanism function, which is essential for transfers, gait initiation, and fall prevention during the immediate postoperative period. The subvastus (SV) approach, which preserves the quadriceps mechanism, can reduce pain, enhance quadriceps function, and accelerate rehabilitation, which are critical for minimizing complications in older patients [4]. However, evidence specific to this age group is limited, and the SV approach’s technical demands may limit its adoption [5]. Comparisons of the subvastus and medial parapatellar approaches have largely focused on heterogeneous age groups or younger patient populations, typically defining “older” patients as those aged over 65 years. Moreover, many of these studies primarily relied on radiographic outcomes or knee-specific scores, with limited emphasis on baseline functional capacity. In contrast, the present study exclusively included patients aged over 75 years, a population characterized by reduced physiological reserve and higher vulnerability to immobilization-related complications. In addition, baseline functional status was objectively assessed using the 6-minute walk test and timed up and go test, allowing for a more precise comparison of early postoperative functional recovery between surgical approaches in a high-risk older population. The application of a strict age cutoff of 75 years allows this study to specifically examine a clinically distinct geriatric cohort that remains insufficiently represented in the subvastus versus medial parapatellar literature.

This study compared the SV and MP approaches in TKA for patients aged over 75 years, hypothesizing that the SV approach facilitates earlier mobilization, improves rehabilitation, and reduces immobilization-related complications.

Material and Methods

SURGICAL TECHNIQUE:

All procedures were performed by a single senior arthroplasty surgeon using the Zimmer Biomet Vanguard Knee System (posterior cruciate-sacrificing) prosthesis. All arthroplasties were made manually and cemented, no patellar resurfacing was performed, and the gap balancing method was used. The SV approach involved a midline incision, elevating the vastus medialis without tendon incision, and subluxating the patella laterally without eversion. The MP approach involved a midline incision with a quadriceps tendon incision along the muscle-tendon conjunction. Standardized anesthesia (spinal), multimodal analgesia, and the same rehabilitation protocols were applied. All surgeries were performed with tourniquet use and no intravenous tranexamid acid was used. None of the patients recieved postoperative nerve block for analgesia.

PRIMARY OUTCOMES: Time to active SLR (days), knee range of motion (ROM) at 1 week (degrees, all were measured by an surgical technique, blinded, and with a goniometer), VAS pain scores on hospital day 3 [7].

SECONDARY OUTCOMES:

Length of hospital stay (days), Knee Society Score (KSS) at 6 weeks, postoperative blood loss (mL, blood loss was estimated based on the sum of drain output within the first 24 hours combined with perioperative Hb changes; however, no standardized formula-based calculation was used), and immobilization-related complications (DVT, PE, pressure ulcers) within 30 days. DVT and PE were diagnosed using Doppler ultrasound on symptomatic cases. Data were collected preoperatively, perioperatively, and at 1 week, 30 days, and 6 weeks.

STATISTICAL ANALYSIS:

Continuous variables were compared using the independent-samples t test, and categorical variables were compared using Fisher’s exact test. Significance was set at P<0.05. Analyses were performed using SPSS version 27.

Results

PRIMARY OUTCOMES:

Time to SLR: The SV group achieved SLR earlier (mean 1.7±0.6 days vs 3.4±1.1 days, P=0.001).

Knee ROM at 1 week: The SV group had greater ROM (mean 94±7° vs 79±9°, P=0.008) (Figure 1). VAS Pain Scores at Day 3: The SV group reported less pain (mean 4.0±1.0 vs 6.0±1.3, P=0.02) (Table 2).

SECONDARY OUTCOMES:

Length of hospital stay: The SV group had a shorter stay (mean 5.0±1.2 days vs 6.7±1.6 days, P=0.03).

KSS at 6 weeks: No significant difference was observed (mean 81.2±8.9 vs 79.5±8.5, P=0.61).

Postoperative blood loss: Blood loss was slightly higher in the SV group, but the difference was not signifiant (mean 360.5±45.2 mL vs 340.2±42.7 mL, P=0.76).

Complications: Immobilization-related complications occurred in 1 patient (3.3%, DVT) in the SV group and in 3 patients (10%, 2 DVT, 1 PE) in the MP group (P=0.24). No pressure ulcers were reported.

Operative time: The SV approach had a longer operative time (mean 110.2±11.8 minutes vs 92.7±10.3 minutes, P=0.008) (Table 3).

Discussion

This study demonstrated that the SV approach in TKA for older patients with end-stage OA significantly enhances postoperative rehabilitation and early mobilization compared to the MP approach.

The SV group’s earlier SLR (1.7 vs 3.4 days), greater ROM at 1 week (94° vs 79°), lower pain scores (4.0 vs 6.0), and shorter hospital stay (5.0 vs 6.7 days) underscore its advantages. These findings align with studies highlighting the SV approach’s preservation of quadriceps function by avoiding tendon incision and minimizing patellar eversion [4–6]. The study’s strengths include standardized prosthesis, a single surgeon, independent radiologist staging, and comparable preoperative physical conditions (ASA, CCI, 6MWT, TUG), ensuring robust internal validity.

The earlier SLR in the SV group reflects preserved extensor mechanism integrity, which is critical for older patients to initiate physiotherapy promptly and reduce immobilization-related complications like DVT and PE [2]. The 15° ROM advantage at 1 week likely results from reduced quadriceps trauma, enabling more effective rehabilitation and minimizing stiffness [8]. The lower pain scores in the SV group may be due to less soft-tissue disruption, enhancing patient compliance with physiotherapy [8]. These factors contributed to a 1.7-day reduction in hospital stay, potentially lowering healthcare costs and risks of hospital-acquired infections [9].

Although immobilization-related complications were not significantly different (3.3% vs 10%, P=0.24), the trend favors the SV approach, likely due to earlier ambulation reducing venous stasis [10]. The slightly higher blood loss in the SV group (360.5 vs 340.2 mL, P=0.76) may reflect the approach’s technical demands, requiring careful hemostasis during vastus medialis elevation. The lack of statistical significance and no increase in transfusion rates suggest this difference is clinically negligible, consistent with recent findings [11]. The absence of KSS differences at 6 weeks aligns with studies showing comparable midterm functional outcomes between approaches, indicating that the SV approach’s benefits are most pronounced in the early postoperative period [12].

The SV approach’s longer operative time (110.2 vs 92.7 minutes) is a notable limitation, potentially increasing intraoperative risks in older patients with comorbidities [5]. This highlights the need for surgeon expertise to optimize outcomes. The subvastus technique presents more difficulty in joint visualization and demands advanced surgical expertise [9]. However, the SV approach’s learning curve may hinder its adoption in lower-volume centers, necessitating training to ensure proficiency [13]. In this study, the senior surgeron had used both approaches in over 100 surgeries annually, so this would not be a limitation. The slightly higher blood loss, although not significant, warrants further study in larger cohorts, particularly in patients with preoperative anemia or coagulopathy.

Limitations include the small sample size, which may have underpowered detection of rare complications like PE. The short follow-up time is also another main limitation. Globally, TKA utilization is rising in older populations, and optimizing surgical approaches can significantly impact healthcare systems [1]. The SV approach’s ability to expedite recovery may align with enhanced recovery after surgery (ERAS) protocols, which prioritize early mobilization and reduced hospital stays [14]. However, its technical complexity requires careful patient selection and surgeon training to balance benefits against operative time and potential blood loss. Another limitation is that, although continuous variables were analyzed using parametric statistical methods, formal testing for normality was not systematically performed for all variables, which may affect the robustness of the statistical assumptions. Second, no a priori power or sample size calculation was conducted, which is inherent to the retrospective design of the study. Consequently, the study may be underpowered to detect differences in less frequent outcomes, particularly postoperative complications. These limitations should be considered when interpreting the results. The retrospective, non-randomized nature of the study introduces a potential risk of selection bias, as the choice of surgical approach was not randomly assigned and may have been influenced by unmeasured factors. Future research should explore long-term outcomes, such as patellar tracking and anterior knee pain, which may differ between approaches [15]. Incorporating objective measures of mobilization (eg, wearable sensors for step counts) and cost-effectiveness analyses could further validate the SV approach’s benefits [16]. Multicenter trials with diverse patient populations and extended follow-up are needed to enhance generalizability and assess the approach’s scalability across different healthcare settings.

Conclusions

This study demonstrates that the use of the subvastus approach was associated with earlier achievement of straight leg raise, greater knee range of motion at 1 week, lower early postoperative pain scores, and shorter hospital stay in patients aged over 75 years undergoing total knee arthroplasty. Although the subvastus approach was also associated with slightly longer operative time and marginally higher blood loss, these differences were not clinically significant. Overall, the findings suggest that the subvastus approach is a valuable surgical option for older patients when performed by experienced surgeons. These findings support broader adoption of the SV approach in this high-risk population, with further research needed to optimize its implementation.