OTSR - 2026-07-11 - Journal Article
Thick metal augmentation is associated with inferior implant survival compared with structural allografts in Anderson Orthopaedic Research Institute Type 2A uncontained medial tibial bone loss.
Song SJ, Kim MS, Park CH
Topics
Key Takeaway
For AORI Type 2A uncontained medial tibial bone loss, structural allograft achieved 97.0% 10-year tibial implant survival versus 83.6% with thick metal augments (≥10 mm), a statistically significant difference (P=0.015).
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Summary
This study compared tibial implant survival in revision TKA for AORI Type 2A uncontained medial tibial bone loss managed with thick metal augments (≥10 mm) versus structural allografts, all with cemented tibial stems. Tibial component loosening occurred in 14.3% of the metal augment group versus 8.1% of the allograft group (P=0.294 for incidence), but Kaplan-Meier survival at 10 years was significantly inferior in the metal augment group (83.6% vs 97.0%; P=0.015). Stress shielding-induced bone resorption was identified radiographically in all loosening cases in the metal augment group, while no allograft resorption was observed in allograft failures.
Key Limitation
The metal augment group had significantly shorter follow-up (6.0 vs 8.2 years), which likely underestimates the true long-term loosening rate in that cohort and may confound the survival curve comparison.
Original Abstract
BACKGROUND
Anderson Orthopaedic Research Institute (AORI) type 2A uncontained medial tibial bone loss can be managed using either thick modular metal augments or structural allografts in revision total knee arthroplasty (TKA). This study evaluated tibial implant survival in revision TKA with either thick metal augments (≥10 mm thickness) or structural allografts for AORI type 2A uncontained medial tibial loss.
HYPOTHESIS
Stress shielding associated with metal augmentation or allograft resorption could adversely affect implant survival, potentially contributing to differences in survival between the two bone loss management strategies.
METHODS
Among revision TKAs with AORI type 2A uncontained medial tibial bone loss, 70 cases using only thick metal augments (group M) and 74 cases using only structural allografts (group A) were retrospectively reviewed. Cemented tibial stems were used in all cases. Failure was defined as reoperation due to loosening of the tibial component, and all patients with radiographic evidence of loosening underwent reoperation. The aseptic survival of the tibial implants was also analyzed. Stress shielding-induced bone and allograft resorption were assessed radiographically.
RESULTS
Demographic characteristics, polyethylene inserts, and tibial stem characteristics were not significantly different between groups. The average thickness of the structural allografts in group A was significantly greater than that of the metal augments in group M (12.5 mm vs 17.1 mm, P<0.001). The average follow-up period was significantly longer in group A (6.0 vs 8.2 years, P=0.031). The incidence of tibial component loosening was 14.3% (10/70) in group M and 8.1% (6/74) in group A (P = 0.294). The 5-, 10-, and 15-year survival rates were 87.2%, 83.6%, and 83.6%, in group M respectively, and 97.0%, 97.0%, and 92.6% in group A, respectively (P = 0.015). Stress shielding-induced bone resorption was observed in all loosening cases in group M. No allograft resorption was observed in any of the failure cases in group A.
CONCLUSION
Thick metal augmentation may be associated with inferior implant survival compared to structural allografts for AORI type 2A uncontained medial tibial bone loss. Stress shielding-induced bone resorption should be carefully considered when thick metal augments are used for AORI type 2A medial tibial bone loss.
LEVEL OF EVIDENCE
IV.