Level V Evidence The “50% Rule” in Arthroscopic and Orthopaedic Surgery

The “50% rule” is used commonly to guide treatment of partial tears of tendons and ligaments. The purpose of this study was to examine the history and validity of the 50% rule in arthroscopic and orthopaedic surgery. A PubMed search yielded 1,039 articles that were reviewed to identify the origins of the 50% rule for hand flexor tendon lacerations, partial anterior cruciate ligament tears, partial-thickness rotator cuff tears, and partial injuries of the long head of the biceps tendon. The rule appears to have evolved from the hand literature toward somewhat arbitrary application for other orthopaedic conditions. Little scientific information is available to support the 50% rule for these disparate entities. In our Level V opinion, the 50% rule allows surgeons to use subjective discretion in the management of prevalent orthopaedic conditions but there is very little scientific support for this ubiquitous decision-making criterion.