2025 ISAKOS Congress in Munich, Germany

2025 ISAKOS Biennial Congress Paper


Biomechanical Comparison of Anteromedialization Type Tibial Tubercle Osteotomy Using the Modified Fulkerson or Multi-Directional Tibial Tubercle Transfer Techniques

Stewart Bryant, MD, Palo Alto, CA UNITED STATES
Ian Hollyer, MD, Stanford, CA UNITED STATES
Calvin Chan, MS, Palo Alto, California UNITED STATES
Ran Atzmon, MD, Ashdod ISRAEL
John P. Fulkerson, MD, Litchfield, CT UNITED STATES
Seth L. Sherman, MD, Redwood City, California UNITED STATES

Stanford University, Stanford, CA, UNITED STATES

FDA Status Cleared

Summary

This study compared the biomechanical strength and failure modes of the MD3T system to the modified Fulkerson technique for anteromedialization tibial tubercle osteotomy, finding that both techniques provide comparable strength, with the MD3T offering more consistent completion rates in simulated activities.

Abstract

Purpose

The modified Fulkerson technique remains the gold standard for anteromedialization (AMZ) type of tibial tubercle osteotomy (TTO). This procedure traditionally relies on freehand cuts and is somewhat limited by surgeon experience, pre-determined cut angle, and fairly extensive soft tissue dissection for neurovascular protection. To mitigate these and other risks, the multi-directional tibial tubercle transfer system (MD3T) was introduced, utilizing a guided system that offers the possibility of precise, reproducible, and modular tubercle transfer. The MD3T technique also minimizes cortical disruption and soft tissue dissection. This study aimed to compare the biomechanical strength and failure modes of the MD3T system to the modified Fulkerson technique for AMZ TTO.

Methods

Sixteen composite tibia models underwent cyclic biomechanical testing simulating walking and chair rising, followed by load-to-failure testing. Eight models underwent AMZ TTO using the MD3T system, and eight underwent modified Fulkerson AMZ. Ultimate failure load, failure mechanisms, and completion rates for simulated activities were recorded. Statistical comparisons between the two groups were performed. Power analysis showed that three specimens would be needed in each group to detect a difference in ultimate failure strength between specimens at 80% power and 0.05 significance level.

Results

Both techniques demonstrated comparable biomechanical strength. The average maximum load to failure was 1459N (+/- 552N) versus 1201 (+/- 565N) for the MD3T and modified Fulkerson techniques, respectively. There were no significant differences in ultimate failure load. Seven out of eight (88%) of the MD3T models versus 3 of 8 (38%) of the Fulkerson models completed simulated walking and chair rise. The modified Fulkerson most commonly failed during simulated chair rising via fracture propagation through the proximal aspect of the osteotomy. In contrast, MD3T constructs most commonly failed during load-to-failure via distal screw breakage.

Conclusion

The MD3T technique provides comparable biomechanical strength to the modified Fulkerson technique for AMZ TTO. Future clinical studies are needed to evaluate patient outcomes and to validate the comparative clinical benefit of the novel MD3T technique.