The 2012 Mark Coventry Award: A Retrieval Analysis of High Flexion versus Posterior-stabilized Tibial Inserts

• Published in: Clinical orthopaedics and related research Vol. 471; no. 1; pp. 56 - 63
• Main Authors: Paterson, Nicholas R., Teeter, Matthew G., MacDonald, Steven J., McCalden, Richard W., Naudie, Douglas D. R.
• Format: Journal Article
• Language: English
• Published: New York Springer-Verlag 01-01-2013; Lippincott Williams & Wilkins Ovid Technologies
• Subjects: Aged; Aged, 80 and over; Arthroplasty, Replacement, Knee - instrumentation; Awards and Prizes; Conservative Orthopedics; Equipment Failure Analysis; Female; Humans; Knee; Knee Prosthesis; Male; Medicine; Medicine & Public Health; Middle Aged; Orthopedics; Patient Satisfaction; Prosthesis Design; Prosthesis Failure; Sports Medicine; Surgery; Surgical Orthopedics; Symposium: Papers Presented at the Annual Meetings of the Knee Society; Tibia - surgery; Tibial Insert; Flexion Angle; High Flexion; Damage Score; Post Damage
• ISSN: 0009-921X; 1528-1132
• DOI: 10.1007/s11999-012-2387-3

Background
High flexion (HF) implants were introduced to increase ROM and patient satisfaction, but design changes to the implant potentially have deleterious effects on polyethylene wear. It is unclear whether the HF implants affect wear.
Questions/purposes
We therefore examined whether the design changes between HF and posterior-stabilized (PS) tibial inserts would affect overall damage or damage on their articular surface, backside, and tibial post and whether flexion angle achieved related to damage.
Methods
We matched 20 retrieved HF inserts to 20 retrieved PS inserts from the same implant system on the basis of duration of implantation, body mass index, and age. Inserts were divided into 16 zones and a microscopic analysis of surface damage was carried out. Five inserts were scanned using micro-CT to further quantify instances of severe post notching. We determined overall damage with a scoring system.
Results
We found greater backside and post damage in the HF group but no difference in the articular surface or overall damage scores. Backside and post damage scores correlated to flexion angle in the HF group. There was no flexion/damage correlation in the PS group. Notch depths around the post in both groups ranged from 0.6 to 1.9 mm.
Conclusions
HF inserts are more susceptible to post damage, possibly as a result of higher contact stresses from greater flexion. The increased backside damage was unexpected because the two groups have the same tibial component, locking mechanism, and sterilization method.
Clinical Relevance
The introduction of a highly crosslinked HF insert will require close scrutiny as a result of the potential for post damage demonstrated in this series.