The primary objective of this study is to determine in patients with non-acute Anterior Cruciate Ligament Deficiency (ACLD) whether a strategy of non-surgical management [Rehabilitation] (with option for later ACL reconstruction, only if required) is more clinically effective and cost effective than a strategy of surgical management [Reconstruction].

The ACL SNNAP study is a pragmatic multi-centre randomised controlled trial with two-arm parallel groups and 1:1 allocation ratio to compare non-surgical management (Rehabilitation) and surgical management (Reconstruction) options for patients with a symptomatic non-acute ACL deficient knee.

The objective is to determine, in patients with non-acute Anterior Cruciate Ligament Deficiency (ACLD), whether non-surgical treatment (with the option for later ACL reconstruction if required) is more effective than surgical ACL reconstruction (as measured by the Knee Injury and Osteoarthritis Outcome Score [KOOS4] at 18 months from randomisation).

Target sample size is 320 patients recruited from approx. 30 NHS orthopaedic units.

An internal pilot will be conducted with clear progression criteria regarding recruitment.

Both interventions are routine NHS treatments. Intervention content is based on a minimal set of pre-established criteria in order to ensure the integrity of the comparison while allowing for varying in practice in delivering the interventions between both surgeons and physiotherapists. This largely pragmatic approach will allow clinical management to reflect current practice and resource use within the NHS thus aiding generalisation.

Other than the allocated intervention, both groups will be followed-up in the same way to exclude bias. Follow up for study purposes will be by patient self-reported questionnaire completed using an electronic data capture collection system (a postal option will also be available). The questionnaire will include the outcomes indicated in section 4 and will be completed by participants at baseline, 6, 12 and 18 months. Non-response will be minimised through use of multiple reminders such as web based, phone and text.

Neither participants nor health care practitioners (surgeons and physiotherapists) can be blinded to receipt of the intervention.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study.
• Male or Female, aged 18 years or above.
• Symptomatic ACL deficiency of the native ligament1 (instability-episodes of frank giving way or feeling unstable) with ACL deficiency (either partial or complete tear) confirmed using clinical assessment and MRI scan.

Exclusion Criteria:

• Acute phase of primary ACL injury i.e. not recovered from any acute symptoms relating to their initial ACL injury.
• Previous knee surgery (other than diagnostic arthroscopy or partial meniscectomy) to index knee concomitant severe injury to contra-lateral knee.
• Meniscal pathology with characteristics that indicate immediate surgery i.e. locked knee, large bucket handle or complex cartilage tear producing mechanical symptoms.
• Knee joint status of grade 3 or 4 on the Kellgren and Lawrence scale,
• Grade 3 MCL/LCL injury, associated PCL/PLC injury
• Inflammatory arthropathy.
• Pregnancy.