A quantitative anatomical and kinematic comparison of the subvastus versus medial parapatellar approach in total knee arthroplasty: A cadaveric study

Abstract

Background: Surgical exposure is critical in total knee arthroplasty for accurate implant alignment and function. The medial parapatellar (MPP) approach, the conventional technique, involves a longitudinal quadriceps split, whereas the subvastus (SV) approach preserves the extensor mechanism. Aims and Objectives: This study aimed to quantify and compare dissection parameters, patellar kinematics, and structural risks associated with the SV and MPP approaches. Materials and Methods: A comparative anatomical study was performed on 16 knees from 8 formalin-embalmed adult cadavers. A paired contralateral design was adopted, with each cadaver’s knees randomly assigned to either MPP or SV, thereby controlling for inter-individual variability. Before dissection, 20 flexion-extension cycles were performed to reduce embalming-induced stiffness. Recorded parameters included incision lengths, capsulotomy, intra-articular exposure, patellar eversion angle, and time to full visualization. Results: The SV approach required a longer deep fascia incision (16.8±1.28 cm vs. 13.4±1.27 cm; P<0.001), greater skin incision extension (P=0.003), and longer exposure time (17.8±4.33 vs. 10.9±3.31 min; P=0.003). Intra-articular exposure was comparable between groups. The MPP approach achieved significantly higher patellar eversion angles (96.8°±17.6° vs.60.6°±9.80°; P<0.001), with full eversion in 87.5% of MPP knees, but none in SV. Vastus medialis obliquus (VMO) fiber tearing occurred in two SV specimens. Conclusion: Both approaches provide equivalent joint exposure; however, MPP is more efficient in dissection parameters, procedural time, and patellar kinematics. While SV preserves the extensor mechanism, it necessitates greater soft-tissue dissection and may increase the risk of VMO traction injury.