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J Orthop Trauma. 2018 Jun;32(6):306-312. doi: 10.1097/BOT.0000000000001112.

Biomechanical Comparison of 3 Inferiorly Directed Versus 3 Superiorly Directed Locking Screws on Stability in a 3-Part Proximal Humerus Fracture Model.

Author information

1
Department of Orthopaedic Surgery, University of South Florida, Tampa, FL.
2
Foundation for Orthopaedic Research and Education, Tampa, FL.
3
Shoulder and Elbow Surgery Service, Florida Orthopaedic Institute, Tampa, FL.

Abstract

OBJECTIVE:

To quantify the stability of 3 points of inferiorly directed versus 3 points of superiorly directed locking screw fixation compared with the full contingent of 6 points of locked screw fixation in the treatment of a 3-part proximal humerus fracture.

METHODS:

A standardized 3-part fracture was created in 10 matched pairs (experimental groups) and 10 nonmatched humeri (control group). Osteosynthesis was performed using 3 locking screws in the superior hemisphere of the humeral head (suspension), 3 locking screws in the inferior hemisphere (buttress), or the full complement of 6 locking screws (control). Specimens were tested in varus cantilever bending (7.5 Nm) to 10,000 cycles or failure. Construct survival (%) and the cycles to failure were compared.

RESULTS:

Seven of 10 controls survived the 10,000-cycle runout (70%: 8193 average cycles to failure). No experimental constructs survived the 10,000-cycle runout. Suspension and buttress screw groups failed an average of 331 and 516 cycles, respectively (P = 1.00). The average number of cycles to failure and the number of humeri surviving the 10,000-cycle runout were greater in the control group than in the experimental groups (P ≤ 0.006).

CONCLUSION:

Data support the use of a full contingent of 6 points of locking screw fixation over 3 superior or 3 inferior points of fixation in the treatment of a 3-part proximal humerus fracture with a locking construct. No biomechanical advantage to the 3 buttress or 3 suspension screws used in isolation was observed.

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