Orthopedics · Medical Literature
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.
Abstract
Anterior 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? 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 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. https://clinicaltrials.gov/study/NCT03935750.
Clinical relevance
ACL reconstruction carries unacceptably high failure rates in young, active athletes (ages 14–25), leading to revision surgery, reduced quality of life, accelerated knee osteoarthritis, and significant socioeconomic burden. The STABILITY 2 trial addresses a critical evidence gap: whether stronger, stiffer graft choices (quadriceps tendon or bone-patellar tendon-bone) with or without lateral extra-articular tenodesis (LET) outperform the hamstring tendon graft paradigm established in STABILITY 1, including sex-specific subgroup analysis for females who exhibit quadriceps-dominant landing biomechanics. Clinicians managing high-risk ACL patients currently lack high-quality RCT evidence to guide graft selection, making this multinational protocol immediately relevant to orthopedic surgical practice.
Key findings
1. STABILITY 1 precedent (foundational data): Adding LET to hamstring tendon (HT) ACLR produced a Relative Risk Reduction (RRR) of 0.38 (95% CI 0.21–0.52; p<0.0001) in graft failure vs. HT alone, establishing LET augmentation as evidence-based in this cohort. 2. Graft hierarchy from meta-analyses: Existing meta-analytic data suggest bone-patellar tendon-bone (BPTB) grafts confer superior rotational stability compared to HT grafts, though with greater donor site morbidity; formal effect sizes from STABILITY 2 are not yet available (protocol paper). 3. Quadriceps tendon (QT) graft rationale: QT is hypothesized to match BPTB biomechanical properties (stiffness, cross-sectional area) while minimizing donor site morbidity, but no high-quality RCT has confirmed superiority or equivalence to BPTB prior to this trial. 4. Trial design and sample size: 1,292 patients across 31 international centers (9 Canadian, 8 European, 14 USA) will be randomized to QT±LET vs. BPTB±LET, powered to detect clinically meaningful differences in clinical failure rates at 2-year follow-up. 5. High-risk eligibility criteria (≥2 required): Grade ≥2 pivot shift, return to high-risk pivoting sport, generalized ligamentous laxity, or knee recurvatum ≥10°, enriching the sample for the population at greatest risk of re-rupture. 6. Planned pooled analysis: STABILITY 2 data will be combined with STABILITY 1 in a mixed-effects model (fixed effects: study, graft type, meniscal repair status, sex; random effects: time, patient, surgeon) to maximize statistical power and enable sex-stratified and cost-effectiveness sub-analyses.
Practice implications
Until STABILITY 2 results are available, surgeons should apply STABILITY 1 findings and consider LET augmentation for young athletes (ages 14–25) who meet ≥2 high-risk criteria (Grade ≥2 pivot shift, return to pivoting sport, ligamentous laxity, or recurvatum ≥10°) when using HT autografts, given the demonstrated RRR of 0.38 for clinical failure. Graft selection for high-risk patients should currently be individualized based on surgeon expertise, patient anatomy, and donor site morbidity considerations, with particular attention to sex-based biomechanical differences—females with quadriceps-dominant landing patterns may theoretically benefit from BPTB or QT grafts, a hypothesis this trial will formally test. Orthopedic surgeons and sports medicine physicians should monitor STABILITY 2 results to prospectively update their graft-selection algorithms, and eligible high-risk patients aged 14–25 should be referred to participating centers to support enrollment in this practice-changing multinational RCT (NCT03935750).