Patellar Fracture Risk Is Not Affected by Harvest Length During Bone–Patellar Tendon–Bone Harvest: A Biomechanical and Ultimate Load-to-Failure Analysis

Purpose

To biomechanically assess the impact of different patellar defect sizes on the ultimate load to failure (ULTF) and fracture risk immediately after bone–patellar tendon–bone harvest.

Methods

Twelve fresh-frozen mid femur to mid tibia–fibula cadaveric specimens (8 female specimens) with an average age of 75 years (range, 64-88 years) were randomly assigned to a defect length of 20 or 25 mm. A triangular wedge bone block was harvested from the patella, and the defect was measured. The extensor mechanism was loaded until failure with the knee in 30° of flexion. ULTF and failure modes were recorded. Statistical analyses were performed between the 2 groups to identify significance (P < .05).

Results

Analyses were performed on 10 specimens because 2 were excluded. The average ULTF was not significantly different between the 20- and 25-mm groups (2,313 ± 863 N and 2,443 ± 839 N, respectively; P = .815) despite a significantly different percentage of total patellar defect length between the 2 groups (39.5% ± 3.9% and 49.1% ± 4.1%, respectively; P = .005). In 7 specimens, the first point of bony failure was at the patella, whereas in the remaining 3 specimens, it was distal to the patella.

Conclusions

The results of this biomechanical study show that up to a 25-mm-long patellar bone block harvest can be performed safely with a low risk of patellar fracture.

Clinical Relevance

There is concern for complications including an increased risk of patellar fracture at the harvest site after bone–patellar tendon–bone autograft harvest. The risk of this complication based on patellar harvest size is not well understood. This study provides biomechanical insights into assessing fracture risk of patellar harvest between 20 and 25 mm in length.