Quantitative analysis of the patella following the harvest of a quadriceps tendon autograft with a bone block.
OBJECTIVE
The objective of this study was to determine parameters associated with patellar fracture after quadriceps tendon autograft harvest.


METHODS
Thirteen non-fractured and five fractured patella surface models were created based on patient data obtained from a prospective randomized clinical trial in order to assess geometric parameters and bending stress. Measurements that describe the bone block harvest site geometry were used to calculate three normalized parameters. The relative depth parameter describes the thickness of the bone block harvest site with respect to the thickness of the patella at the harvest site. The asymmetry parameter defines the medial-lateral location of the bone bock harvest site. The normalized bending stress parameter assesses the bending stress experienced by the remaining bone beneath the bone block harvest site.


RESULTS
The relative depth of the bone block harvest site in the non-fractured patellae was 27 ± 12 % and for the fractured patellae was 42 ± 14 % (p < 0.05). With a value <1 indicating a more lateral location of the harvest site, asymmetry for the non-fractured group was 1.0 ± 0.5 and 0.7 ± 0.4 for the fractured group (n.s.). The maximum bending stress experienced by the non-fractured patellae was (1.8 × 10(-3) ± 1.3 × 10(-3)) mm(-3) × M and for the fractured patellae was over three times greater (6.3 × 10(-3) ± 3.7 × 10(-3)) mm(-3) × M (p < 0.05).


CONCLUSIONS
Based on the non-uniform geometry of the patella, an emphasis should be made on harvesting a standard percentage of patella thickness rather than a fixed depth. In order to minimize the incidence of a patellar fracture, bone blocks should not be taken laterally and should not exceed 30 % of the total patella thickness at the harvest site.
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, 300 Technology Drive, 306 CNBIO, Pittsburgh, PA, 15219, USA.
Gerald A
GA
Ferrer
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, 300 Technology Drive, 306 CNBIO, Pittsburgh, PA, 15219, USA.
R Matthew
RM
Miller
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, 1010 Kaufmann Building, Pittsburgh, PA, 15213, USA.
Christopher D
CD
Murawski
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, 1010 Kaufmann Building, Pittsburgh, PA, 15213, USA.
Scott
S
Tashman
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, 1010 Kaufmann Building, Pittsburgh, PA, 15213, USA.
James J
JJ
Irrgang
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, 300 Technology Drive, 306 CNBIO, Pittsburgh, PA, 15219, USA.|Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, 1010 Kaufmann Building, Pittsburgh, PA, 15213, USA.
Volker
V
Musahl
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA.|Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, 1010 Kaufmann Building, Pittsburgh, PA, 15213, USA.
Freddie H
FH
Fu
Orthopaedic Robotics Laboratory, Pittsburgh, PA, USA. genesis1@pitt.edu.|Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, 300 Technology Drive, 306 CNBIO, Pittsburgh, PA, 15219, USA. genesis1@pitt.edu.|Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, 1010 Kaufmann Building, Pittsburgh, PA, 15213, USA. genesis1@pitt.edu.
Richard E
RE
Debski
D016118:Anterior Cruciate Ligament / Q000601:surgery; D050723:Fractures, Bone / Q000209:etiology; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control*; D007718:Knee Injuries / Q000150:complications; D010329:Patella / Q000601:surgery*; D052097:Quadriceps Muscle; D016032:Randomized Controlled Trials as Topic; D012189:Retrospective Studies; D013710:Tendons / Q000637:transplantation*; D014182:Transplantation, Autologous / Q000379:methods*
ACL reconstruction; Patella fracture; QTB autograft; Quadriceps tendon