Differences in fixation stability between spacer plate and plate fixator following high tibial osteotomy

Purpose Since in vivo stability following high tibial osteotomy is unknown, surgeons customize the postoperative rehabilitation to the assumed implant stability, leaving us with numerous rehabilitation protocols. The purpose of the study is to quantify the fixation stability of different open-wedge high tibial osteotomy implants. It is hypothesized that the higher fixation stability of a plate fixator justifies early weight bearing. Methods In this prospective 30-subject clinical trial, fixation stability was determined over a 2-year period using radiostereometric analysis (RSA). Patients were assigned to two angle-stable osteotomy plates: a spacer plate with 6 postoperative weeks of feather-touch weight bearing versus a plate fixator with 2 postoperative weeks of feather-touch weight bearing. Results Postoperative RSA data showed a significant higher lateral translation of the distal tibia and a significantly increased subsidence, varus and internal rotation of the tibial head in the spacer plate compared to the plate fixator group. Weight bearing following spacer plate fixation induced significant micromotion 6 weeks after surgery. Three months after surgery, bone healing was achieved regardless of the used implant. Conclusions Early weight bearing is appropriate for plate fixator fixation. The 6-week period of delayed weight bearing following spacer plate fixation is inadequate and should be prolonged presumably up to 8–10 weeks to avoid pseudarthrosis and/or recurrence of varus angulation. Level of evidence Level II, diagnostic study—investigating a diagnostic test.