Functional and Radiological Results of the Subvastus Versus Medial Parapatellar Method in Total Knee Arthroplasty: A Randomized Controlled Cohort

Introduction

Total knee arthroplasty (TKA) remains a standard surgical treatment for advanced knee osteoarthritis, providing substantial improvements in pain and function. It provides substantial pain relief, improved function, and durable implant survival ^[1]. The medial parapatellar method remains the cornerstone surgical approach, offering consistent joint exposure and allowing effective mobilization of the patella. However, this technique requires incision through the extensor mechanism and may potentially compromise the patellar blood supply ^[2]. In contrast, the subvastus method involves dissection beneath the vastus medialis yet maintains the quadriceps tendon and extensor mechanism. This preservation has the potential to facilitate early quadriceps recovery and rehabilitation ^[3]. Previous comparative studies have reported advantages of the subvastus method in select early post-operative findings, such as quadriceps recovery, range of motion (ROM), and early functional recovery. However, the subvastus method can be technically more challenging and may provide more limited exposure and difficulty with patellar eversion, particularly in patients with large or stiff knees.

Despite the hypothetical advantages of maintaining the extensor mechanism, the clinical superiority of the subvastus method over the conventional medial parapatellar method remains uncertain. In a study of 90 patients, Bourke et al. ^[4] showed no significant difference in functional scores between the two methods. However, patients assigned to the subvastus method achieved straight-leg raising earlier, although the method was associated with greater technical difficulty for surgeons. Similarly, systematic reviews and meta-analyses have demonstrated some early post-operative advantages with the subvastus method but have not consistently demonstrated clinically important differences in overall functional outcomes ^[5]. Furthermore, evidence directly evaluating both functional and radiological outcomes remains limited. This uncertainty provides a rationale for further prospective comparative evaluation of these two commonly used methods. This study compared functional, pain, and radiological outcomes among the subvastus and medial parapatellar methods.

Materials and Methods

Results

Discussion

Post-operative pain plays a critical role in early recovery and rehabilitation after TKA. The VAS score was 6.74 ± 0.94 and 7.00 ± 0.95 (P = 0.172) in the subvastus and medial parapatellar groups. Patients in the subvastus group had considerably reduced VAS scores during the initial 3 post-operative days compared with those in the medial parapatellar group (P <0.05). Similarly, another study found a trend of lower post-operative VAS scores in subvastus patients compared to medial parapatellar patients up to 6 months ^[6,7]. The study by Shah et al. ^[8] reported significantly lower VAS scores among patients undergoing the subvastus method. Moreover, patients treated with this technique required approximately 40% less post-operative analgesic compared to those who underwent the conventional medial parapatellar method. The meta-analysis of 10 studies revealed that patients undergoing the subvastus method required less analgesic medication within 24 h ^[9,10] and experienced less pain during the first 1–3 post-operative days ^[11,12], although two studies did not observe a contrast in post-operative pain scores between the methods ^[12,13]. The decreased pain observed with the subvastus method may be ascribed to the maintenance of the extensor mechanism and the avoidance of quadriceps tendon transection, thereby reducing soft-tissue trauma ^[14].

Post-operative ROM is an influential indicator of functional recovery following TKA. In our trial, at the 2-week follow-up, the subvastus patients demonstrated greater mean ROM of 82.56° ± 9.11° compared with 78.02° ± 7.33° in the medial parapatellar patients (P = 0.007). This advantage remained at 6 weeks (subvastus: 98.14° ± 10.38° and medial parapatellar: 92.86° ± 5.20°; P = 0.002). However, at 3 months, ROM was comparable between the two groups (P = 0.333), suggesting that the subvastus method may primarily offer an advantage in early post-operative functional recovery. These outcomes are in line with those of Bridgman et al. ^[13], who stated better ROM for subvastus patients 1 week postoperatively. Similarly, Bourke et al. ^[4] reported better mean flexion of subvastus patients compared to medial parapatellar patients up to discharge, while Lingayat et al. ^[15] observed better ROM at 3 months. The preservation of the quadriceps integrity in the subvastus method likely contributes to reduced post-operative stiffness and earlier initiation of active knee motion.

The objective and functional KSS values improved progressively after surgery in both patient groups. At the 6-month follow-up, the groups showed comparable outcomes, with no statistically significant difference (P = 0.280). Our study findings are supported by those of Mathew et al. ^[16]. Bourke et al. ^[4] conducted a study with longer-term follow-up and reported that the American KSS functional scores at 12 (P = 0.032) and 18 months (P = 0.028) favored the medial parapatellar method. Similarly, Teng et al., ^[17] in their meta-analysis, reported significantly better KSS functional scores at 4–6 weeks and higher knee scores at 12 months among patients treated with the subvastus approach. These findings suggest that the early advantage of the subvastus method arises from enhanced quadriceps activation and reduced trauma to the extensor mechanism, promoting faster restoration of independent ambulation.

Radiological findings revealed comparable results between the subvastus and medial parapatellar groups regarding coronal or sagittal alignment. Similarly, post-operative HKA angles were comparable, indicating accurate mechanical axis restoration in both groups. Thus, surgical proficiency and attention to technique are critical determinants of component placement accuracy, irrespective of the method.

Post-operative complications were minimal and comparable between the two methods. Deep wound infections occurred in 2 (4.0%) subvastus patients and 3 (6.0%) medial parapatellar patients. Wound dehiscence occurred in 1 (2.0%) patient in both the subvastus and medial parapatellar groups. No cases of DVT were reported. These outcomes agree with observations of Wu et al., ^[18] who also observed comparable rates of infection and DVT between the methods. The findings of Hu et al. ^[14] emphasized the role of surgeon experience in preventing complications, particularly in obese patients or patients with limited pre-operative knee flexion.

This study has several limitations. First, the relatively small sample size (100 patients) may have limited statistical power to detect differences in clinical outcomes and complications. Second, the single-center design may limit generalizability to other institutions and patient populations. Third, the absence of reported blinding may have introduced assessment or reporting bias. Fourth, allocation based on odd and even UHID numbers was predictable and may have introduced selection bias. Fifth, the 6-month follow-up was insufficient to evaluate long-term functional outcomes, implant survival, and revision rates. Sixth, radiological measurements were assessed by a single observer, preventing evaluation of interobserver reliability and reproducibility. Seventh, the reported statistical power of 70% may have been inadequate to detect smaller but clinically meaningful differences. Eighth, the effects of surgeon experience, the learning curve, and technical difficulty were not formally assessed. Ninth, the small sample size and low complication rates limited reliable comparisons of uncommon adverse events between the two approaches. Larger multicenter studies with longer follow-up, concealed random allocation, blinded outcome assessment where feasible, and standardized radiological evaluation are warranted.

Conclusion

The subvastus method was associated with better early post-operative pain relief and ROM, while functional and radiological outcomes were comparable at later follow-up.

Clinical Message

Both the subvastus and medial parapatellar methods are viable methods for total knee arthroplasty. Selection of methods should be tailored to the individual patient, taking into account patient-specific factors, the operator’s experience, and the extent of exposure required for optimal implant positioning.

References

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About the Authors

• 

  Jayvirsinh Solanki

• 

  Mukesh Yadav

• 

  Amit Kumar Jha

• 

  Swaroop Patel

• 

  S K Singh