Personalizing the Quadriceps Tendon Graft in Anterior Cruciate Ligament Reconstruction: A Novel, Continuous Method to Predict Graft Size Using Preoperative MRI.
Orthopaedic journal of sports medicine · 2026
A new MRI formula predicts QT graft diameter within 1mm in 90% of cases, but the screening cutoff for 'small grafts' has only 39% specificity.
The paper
Retrospective cross-sectional diagnostic accuracy study, n=130, mostly adolescent patients (mean age 16.4) undergoing primary ACL reconstruction with quadriceps tendon autograft at one tertiary centre.
What they found
A preoperative QT thickness cutoff of <8.3 mm predicted a final graft diameter <10 mm with AUC 0.818, sensitivity 98.2% but specificity only 39.1%. A continuous formula (2 x sqrt(WT/pi)) predicted actual graft diameter within +/-1.0 mm in 90% of cases.
Study design
Single-centre retrospective cross-sectional diagnostic accuracy study, Level of evidence 3, n=130, predominantly adolescent/young athletic patients (59 female, 71 male) who had QT autograft ACLR between January 2022 and July 2025.
Methodology
Two reviewers measured QT thickness on MRI blinded to outcome, which limits detection bias in the measurement step, and ROC/AUC analysis is an appropriate way to derive the cutoff. But this is retrospective single-surgeon/single-institution data with a specific MRI protocol and scanner, so selection and measurement technique may not transfer elsewhere. Interrater reliability was listed as a stated aim but no ICC or kappa values appear in the abstract, so a clinician can't yet judge how reproducible the measurement itself is between observers. The diameter formula also assumes a circular tendon cross-section, a geometric simplification that may explain the 10% of cases falling outside +/-1.0 mm.
The appraisal
The AUC of 0.818 looks respectable, and the 98.2% sensitivity at this threshold makes it a decent rule-out test: a QT thickness of 8.3mm or higher makes an inadequately small graft (<10mm) unlikely. The trade-off is a specificity of only 39.1%, so as a rule-in test the cutoff is weak, a good chunk of patients whose graft would actually turn out an adequate size still get flagged by it, and the paper doesn't report how common small grafts were in this cohort, so we can't say precisely how many flagged patients would be false alarms in practice. The continuous formula's 90% hit rate within 1mm is more clinically interesting for preoperative planning, but this is associational, single-centre, retrospective evidence, not a validated predictive tool ready for generalisation.
The gap
No external validation across institutions, scanners, or an adult population, and the promised interrater reliability data for both methods isn't reported in the abstract, so reproducibility of the core measurement is unknown.
Landmark context
This sits within the broader literature documenting quadriceps strength deficits after QT graft harvest relative to hamstring or BTB grafts, which is the rationale for trying to personalise harvest width; it extends existing dichotomous MRI cutoff methods into a continuous prediction formula rather than overturning any single landmark trial.
What to do Monday
This is a surgeon's preoperative planning tool, not something physiotherapists or S&C coaches apply directly, there's no protocol change here. The transferable point for the rest of the team is the reminder baked into the study's own rationale: QT autograft carries a real donor-site quadriceps strength penalty, regardless of what the final graft diameter turns out to be. That's worth flagging in the post-op handover so quad strength gets monitored more closely, and earlier, than it might with a hamstring or BTB graft. The formula itself needs external validation before anyone builds a pathway around it.
In practice
Nothing here changes what a surgeon does on Monday, let alone a physio or S&C coach, this is an imaging-measurement study, not an outcomes study. What it's genuinely useful for is a prompt: QT autograft is known to cost quad strength at the donor site more than hamstring or BTB grafts, and that's true whatever the harvested diameter ends up being. In the clinic, that means QT autograft patients shouldn't be defaulted onto the same quad-strength timeline as other graft types, benchmark quad strength objectively (Single Leg Extension or Single Leg Press) from around 12 weeks and again before RTS testing, and hold them to the same ≥90% limb symmetry index before clearing cutting or jumping sport rather than assuming it'll catch up on schedule. On the S&C floor, that means prioritising unilateral knee extension loading through the mid-late rehab phase for QT graft athletes and being realistic with return-to-full-training timelines for this group specifically. The paper itself doesn't test the strength-outcome link, that's context from the wider literature it cites, so treat this as a reason for closer quad monitoring in QT autograft patients generally, not a reason to change today's testing battery based on predicted graft size.
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