Changes in Invasiveness and Latent Infection Rate Associated with Switching the Approach in Total Hip Replacement.

Purpose: Muscle-sparing approaches for total hip replacement (THR) involve learning curves. This study aimed to clarify changes in invasiveness and infection rate with changes in approach.

Methods: One surgeon changed the approach of THR from Dall's approach (Dall) to anterolateral modified Watson-Jones approach (OCM). Another changed from Dall to a direct anterior approach (DAA). Another 3 surgeons changed from posterolateral approach (PL) to OCM. Subjects were 150 cases, comprising the last 25 cases with conventional approaches and the first 25 cases with new approaches (Dall to OCM: 25 + 25; Dall to DAA: 25 + 25; PL to OCM: 25 + 25 cases). Differences in operative time, bleeding volume, hospital stay, haemoglobin (Hb), white blood cell count, lymphocyte count, creatine kinase (CK) and C-reactive protein (CRP) were investigated.

Results: In the change from Dall to OCM, only hospital stay decreased. In the change from Dall to DAA, hospital stay and CRP decreased, but bleeding volume increased. In the change from PL to OCM, operative time, CRP and CK decreased, but Hb also decreased. Cases with lymphocyte count <1000/μL or lymphocytes comprising <10% of total white blood cells at around day 4 after surgery were defined as latent infection cases. In these cases, operative time was longer, Hb was lower and CK was higher.

Conclusion: Introducing muscle-sparing approaches improved many markers of invasiveness, but some items deteriorated. In the early stages of introducing a new approach, choosing cases without obesity and without high muscle volume may reduce the risk of infection.