Objective: To compare midvastus and subvastus approach regarding operative parameters(lateral retinacular release, operative time, neurovascular injury) and outcome (Knee Society Score, Straight Leg Raise) at 12 weeks in single stage bilateral total knee arthroplasty.

Study Design: Randomized clinical trial study

Place and Duration of Study: Institute of Orthopaedic Surgery and South City Hospital Karachi from 1st January 2016 to 31st December 2018.

Methodology: Fifty two patients of both genders ofmore than 50 years with osteoarthritis grade III or IV and bony changes confirmed by AP and lateral radiographs of knee were included. Patients with previous knee surgeries including high tibial osteotomy, deformities >20°(on mechanical axis), any neuromuscular problem and BMI ≥30 were excluded. Final assessment was done at 12 weeks. Isometric quadriceps strength was assessed by holding of contraction in seconds during the lifting (10cm above the plinth) phase of SLR (patient lying supine).Knee score (preoperative and final follow-up) was performed by Knee Society Score.

Results: Thirty five were females and 21 males with mean age 65.3 years (50-78 years). Mean body mass index was 27.8 Kg/m2 (26.4-29.9). In midvastus TKR, the mean operative time was 61.7 minutes (range 52-70) whereas the same was 68.3 minutes (range 58-74) in subvastus TKR with p value 0.002. Rate of lateral retinacular release (LLR) was significantly (p=0.011) different between the midvastus TKR 5 (8.9%) and subvastus TKR 11 (19.6%). Neither group had neurovascular injury or early infection of the knee. Active SLR in subvastus group was achieved in shorter time (mean 3.1 days) as compared to midvastus group (mean 4.7 days). There was no difference (p=0.173) in isometric quadriceps strength at 12 weeks between subvastus TKR (mean 18 seconds) and midvastus TKR (mean 17 seconds). Knee society pain and functional scores were comparable between the two approaches at final follow up.

Conclusion: Subvastus exposure has advantage of achieving active straight leg raise earlier while midvastus has lower frequency of lateral retinacular release. No difference in hospital stay and postoperative pain scores. Both subvastus and midvastus approaches are safe and offer comparable Knee Society Score outcomes.

Keywords: Midvastus, Subvastus, Total knee arthroplasty, Knee Society Score, Straight leg raise