Electromyographic comparison of the mid-vastus and sub-vastus approaches to total knee arthroplasty

Background To date there has been no study using robust surface electromyographic methods to compare the effect of sub-vastus and mid-vastus approaches to total knee arthroplasty on quadriceps activity. This study was done to ascertain if the sub-vastus technique would result in greater postoperative muscle activity than a vastus splitting approach as measured by electromyography and an earlier achievement of a straight leg raise. Methods This was a prospective comparative study of the sub-vastus and mid-vastus approaches on vastus medialis and vastus lateralis muscle activity measured by electromyography and time to straight leg raise in 18 patients (7 men and 11 women) after a primary total knee arthroplasty. Results A statistically significant difference in the number of days taken to achieve straight leg was noted between the mid-vastus and subvastus groups (mid-vastus=2.0 days, 95% CI, 1.43 to 2.56; subvastus =1.25 days, 95% CI, 0.93 to 1.57; P=0.045). There were no statistical differences (P>0.05) between the two techniques in electromyography or any of the secondary outcomes at 5 days, 6 weeks and 3 months after surgery. There was no significant correlation (P>0.05) between the earlier return of straight leg raise in the sub-vastus technique and increased quadriceps activation. Conclusions This study did not find any statistically significant differences in electromyographic data between the two approaches, suggesting no evidence of denervation of the vastus medialis, although thesub-vastus technique led to an earlier single-leg raise. ©Lippincott Williams & Wilkins.