Tibial component overhang following unicompartmental knee replacement--does it matter?

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Medical Device Design

Background:

• Implant sizing is crucial in joint replacement surgery, with component fit impacting patient outcomes.
• Tibial component sizing in unicompartmental knee replacement (UKR) presents a dilemma between overhang and underhang.
• Overhang can cause soft tissue irritation and pain, while underhang risks component loosening.

Purpose of the Study:

• To evaluate the long-term effects of tibial component overhang and underhang in Oxford UKR.
• To determine the optimal sizing strategy for tibial components in UKR to maximize patient outcomes.

Main Methods:

• A retrospective study of 160 Oxford UKR procedures was conducted.
• Patients were categorized into three groups: minor tibial overhang (<3 mm), major tibial overhang (>=3 mm), and tibial underhang.
• Patient outcomes, including Oxford Knee Scores (OKS) and pain levels, were assessed one and five years post-surgery.

Main Results:

• No significant outcome differences were observed between groups at one year post-surgery.
• Five years after surgery, patients with major tibial overhang (>=3 mm) reported significantly worse OKS and pain scores compared to other groups.
• The difference in OKS was substantial, averaging 10 points, indicating a clinically significant impact.

Conclusions:

• Tibial component overhang of 3 mm or more in UKR severely compromises long-term patient outcomes and should be avoided.
• While minor overhang and underhang showed no significant difference at five years, significant underhang is not recommended due to the theoretical risk of component loosening and subsidence.