Failure of the Patellar Tendon with the Patella Everted versus Noneverted in a Matched-Pair Cadaver Model

James A. Ryan, MD
Department of Orthopaedic Surgery, Hospital for Special Surgery

Kathleen N. Meyers, MS
Department of Biomechanics, Hospital for Special Surgery

Paolo DiBenedetto, MD
Clinic of Orthopaedics and Traumatology, University of Udine

Steven B. Haas, MD
Steven B. Haas, MD

Chief of Knee Service, Hospital for Special Surgery
Attending Orthopedic Surgeon, Hospital for Special Surgery

Timothy Wright, PhD

Senior Scientist, Hospital for Special Surgery
F.M. Kirby Chair, Orthopaedic Biomechanics


Avoidance of patellar eversion during total knee arthroplasty may help to prevent injury to the patellar tendon. The purpose of this study was to compare the load-to-failure of the everted versus the noneverted patella in a cadaveric model. Fourteen cadaver knees (seven pairs) were loaded to failure with the patella everted in one knee and not everted in the other. Mean load-at-ultimate failure in the patella-everted group was 1,111 ± 572 N, and in the patella-noneverted group was 1,621 ± 683 N (p = 0.01). Additionally, loads-at-initial-partial failure were lower (p = 0.04) in the patella-everted compared to the patella-noneverted group, 573 ± 302 N versus 1,115 ± 358 N, respectively. A partial failure of the patellar tendon occurred in 100% of the everted specimens, whereas only 57% of the noneverted specimens had partial failure. These findings suggest patella eversion may lead to failure of the patellar insertion at lower loads than when the patella is not everted.

This article appears in HSS Journal: Volume 6, Number 2.
View the full article at

About the HSS Journal

HSS Journal, an academic peer-reviewed journal, is published twice a year, February and September, and features articles by internal faculty and HSS alumni that present current research and clinical work in the field of musculoskeletal medicine performed at HSS, including research articles, surgical procedures, and case reports.


Related Conditions

Back in the Game Patient Stories: