Table 4

Examples of outcome measurements and considerations for follow-up time

Outcome categoryExample of specific outcomeComment follow-up time
Adverse events
  • Intraoperative complications

Usually less than 1-year follow-up required to detect these outcomes. When identifying adverse events, these should be reported as soon as possible, regardless of the minimum time lapsed from treatment start
  • Surgery- or device-related complications

  • Infections

  • VTE

  • Re-operation

  • Validated knee-specific outcome scores

Depending on study purpose, population and the specific outcome tool used. Generally, at least 1-year follow-up is required to obtain meaningful measures for interpretation of treatment effect, preferably 2 years. However, for the IKDC-SKF and the KOOS, the 1- and 2-year results have been reported equivalent.94 117 Patients could be followed over several years to detect changes over time and to compare short-, mid- and long-term results
  • Psychological measures

  • HRQoL

  • Activity level

  • Return to sport

ACL failure and recurrent ligament disruption
  • Graft rupture/failure

The follow-up time must allow for sufficient time to detect events such as re-rupture and ACL revision. These events tend to occur after the patient returns to knee-strenuous activities, which means that a 2-year follow-up should be a minimum
  • ACL revision

  • Contralateral ACL injury

Clinical measures of knee function and structure
  • Strength testing

Largely depending on the specific outcome and the study purpose. However, care should be taken not to draw conclusion about the short-term treatment result until a 2-year follow-up is obtained. Functional performance tests, knee joint laxity and range of motion assessments are preferably performed in multiple follow-ups prior to the 2-year follow-up for changes over time. Osteoarthritis assessment should have at least 5-year follow-up. Concomitant knee joint injuries should be reported whenever identified
  • Hop testing

  • Performance testing

  • Knee joint laxity

  • Range of motion

  • Imaging

  • Osteoarthritis

  • Concomitant knee joint injuries

  • ACL, anterior cruciate ligament; HRQoL, health-related quality of life; IKDC-SKF, International Knee Documentation Committee Subjective Knee Form; KOOS, Knee injury and Osteoarthritis Outcome Score; PRO, patient-reported outcome; VTE, venous thromboembolism.