Quadriceps strength at 3 months tracks two-year outcome after quadriceps tendon ACL reconstruction

Design

Case series, level of evidence 4

Population

100 patients after primary quadriceps tendon autograft ACL reconstruction, mean age 25

Primary outcome

IKDC and Lysholm scores at mean 2 years

Effect

3-month isometric quadriceps LSI: beta 3.9, adjusted R² 0.36 for IKDC

This case series followed 100 patients, mean age 25, after primary ACL reconstruction with quadriceps tendon autograft, tested for limb symmetry in strength and function at 3, 6 and 9 months, with knee scores at a mean of two years.

Quadriceps strength symmetry lagged, reaching only 77% to 81% by 9 months, while hamstring symmetry was near 100%. After adjustment for age, sex and BMI, isometric quadriceps symmetry at 3 months was associated with the two-year IKDC knee score and explained about a third of its variation. Fast isokinetic quadriceps symmetry at 9 months was associated with both IKDC and Lysholm scores. Patients who reached an acceptable symptom state had generally achieved 60% to 70% quadriceps symmetry by 3 months.

This is a single-series, level 4 study without a comparison group. It shows association, not that pushing early quadriceps strengthening will improve the outcome.

The practical point is that quadriceps recovery is slow after this graft and that a 3-month strength test may flag patients who need more rehabilitation attention.

• Measure isometric quadriceps strength symmetry at about 3 months after quadriceps tendon ACL reconstruction.
• Flag patients below about 60% quadriceps symmetry at 3 months for closer rehabilitation review.
• Expect quadriceps symmetry to remain below 85% at 9 months with this graft.
• Do not use hamstring symmetry as reassurance: it recovers early and predicts less.

Why it matters

Quadriceps tendon grafts are increasingly used, and the quadriceps deficit they leave is easy to underestimate when hamstring strength looks normal.

Don't overread it

This level 4 case series shows association only; it does not show that targeting the 3-month number changes the outcome.

The statistics, in plain English

An adjusted R² of 0.36 means the 3-month quadriceps measure explained about 36% of the variation in two-year IKDC scores; the rest depends on other factors. In a case series without controls, the association may partly reflect patients who were doing well in every respect.

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