STABILITY 2: A protocol for a randomised trial in orthopaedic surgery to determine whether anterior cruciate ligament (ACL) reconstruction using a patellar or quadriceps tendon autograft with or without lateral extra-articular tenodesis is more effective at reducing the incidence of recurrent instability in young, active athletes.

introductionAnterior cruciate ligament reconstruction (ACLR) is complicated by high failure rates in young, active individuals, which is associated with worse outcomes and higher rates of osteoarthritis (OA). Failure of ACLR limits activity, reduces quality of life and substantially increases socio-economic costs. Thus, strategies to reduce ACLR failure are imperative. In the STABILITY 1 trial, we showed that adding a lateral extra-articular tenodesis (LET) to ACLR with a hamstring tendon (HT) graft provided greater stability than HT alone (Relative Risk Reduction (RRR)=0.38; 95% CI 0.21 to 0.52; p<0001). Recent meta-analyses suggest patellar tendon (bone patellar tendon bone (BPTB)) grafts provide better stability than HT although with greater donor site morbidity. Recently, the quadriceps tendon (QT) graft has become popular, claiming similar stability to BPTB without donor site morbidity. However, no high-quality studies have shown it to be better and no study has determined if the reduced rate of ACLR failure seen with the addition of a LET to a HT graft is still present when using stronger, stiffer BPTB or QT grafts. Therefore, this study will evaluate whether in patients at high risk of rerupture, graft type (QT, BPTB, HT) with or without a LET offers a greater reduction in rate of clinical failure, better performance-based function and patient-reported symptoms, function and quality of life or higher rates of return to sport 2 years after ACLR. And does graft type±LET affect muscle strength recovery or increase the risk of donor site morbidity or lateral compartment articular cartilage degeneration? Do females, who are more often quadriceps dominant in their landing biomechanics, experience better outcomes if their ACLR uses a BPTB and/or QT autograft compared with a HT+LET autograft? Finally, is a particular graft type±LET a more cost-effective approach to ACLR? METHODS AND ANALYSIS: Across 31 centres (9 Canadian, 8 European, 14 USA), we will randomly assign 1292 patients with an ACL rupture who are at high risk of failure to either QT (±LET) or BPTB (±LET). Eligible participants will be 14-25 years of age, with at least two of the following: (1) Grade 2 pivot shift or greater; (2) returning to high-risk pivoting sport; (3) generalised ligamentous laxity; or (4) knee recurvatum of 10 degrees or more. Surgeons with similar expertise and no preference for either graft type will use traditional randomisation; two centres will use an expertise-based approach. Outcomes include ACLR clinical failure, patient-reported outcomes that assess symptoms, activity, participation and quality of life, measures of impaired range of motion and muscle function (quadriceps and hamstring strength), performance-based measures of physical function (hop tests, drop vertical jump), return to preinjury sports, adverse outcomes, intervention-related donor site morbidity and complications. Clinical failure and performance-based outcomes will be assessed by blinded evaluators over 2 years following ACLR. Analyses will combine STABILITY 2 and STABILITY 1 data in a mixed effects model where fixed effects include study, graft type, meniscal repair status and sex, while time, patient and surgeon are random effects variables. ETHICS AND DISSEMINATION: Ethics approval was granted for each centre prior to beginning recruitment. If successful, the results of this study will inform the optimal treatment of ACL rupture in young athletes, and women specifically, who are at risk for persistent rotational laxity/instability and graft rerupture. Reducing the risk of ACLR clinical failure will reduce the need for revision ACLR and the associated decreased quality of life and socio-economic burden that occurs because of ongoing knee instability and the increased risk for OA. TRIAL REGISTRATION NUMBER: https://clinicaltrials.gov/study/NCT03935750.