Purpose: Most displaced olecranon fractures can be treated with ORIF. However with severe comminution or bone loss, excision of the fragments and repair of the triceps to the ulna is recommended. The triceps can be reattached to either the anterior or posterior aspect of the ulna. The purpose of this in-vitro study was to determine the effect of triceps repair technique on elbow laxity and extension strength in the setting of olecranon deficiency. Method: Eight unpreserved cadaveric arms were used (age 75 ± 11 years). Surface models were generated from CT images and sequential olecranon resections in 25% increments were performed using real-time navigation. Muscle tendons (biceps, brachialis, brachioradialis and triceps) were sutured to actuators of an elbow motion simulator, which produced active extension. A tracking system recorded kinematics in the varus and valgus positions. A triceps advancement was performed using either an anterior or posterior repair to the remaining olecranon in random order. Triceps extension strength was measured in the dependent position with the elbow flexed 90° using a force transducer located at the distal ulnar styloid, while triceps tension was increased from 25–200 N. Outcome variables included maximum varus-valgus elbow laxity and triceps extension strength. Two-way repeated measures ANOVAs were performed for laxity comparing resection level and repair method. Three-way repeated measures ANOVAs were performed for triceps extension strength comparing triceps tension, resection level and repair method. Significance was set at p < 0.05. Results: Progressive olecranon resection increased elbow laxity (p < 0.001). Although the posterior repair produced slightly greater laxity for all but the 50% resection, this difference was not significant (p = 0.2). The posterior repair provided greater extension strength than the anterior repair at all applied triceps tensions and for all olecranon resections (p = 0.01). The initial 0% resection reduced extension strength for both repairs (p < 0.01), however, there was no effect of progressive olecranon resections (p = 0.09). Conclusion: There was no significant difference in laxity between the anterior and posterior repairs. Thus even for large olecranon resections, the technique of triceps repair does not have significant influence on joint stability. Extension strength was not reduced by progressive olecranon resections, perhaps due to wrapping of the triceps tendon around the trochlea putting it in-line with the ulna and giving it a constant moment arm. Triceps extension strength was higher for the posterior repair. This is likely due to the greater distance and hence moment arm of the posterior repair to the joint rotation center. Conversely, the anterior repair brings the triceps insertion closer to the joint center, reducing the moment arm. Since there was no significant difference in laxity between the repairs, the authors favour the posterior repair due to its significantly higher triceps extension strength