Only one patient out of five achieves symmetrical knee function 6 months after primary anterior cruciate ligament reconstruction

Key points

1. 01Symmetrical function meant a Limb Symmetry Index of at least 90% on all three tests: quadriceps strength, hamstring strength, and single-leg hop.
2. 02Only 693 of 3541 patients (19.6%) reached that bar on all three tests at 6 months.
3. 03Quadriceps strength was the hardest to recover, with only 35.7% reaching 90% symmetry, versus 47.3% for hamstrings and 67.9% for the hop test.
4. 04Being 30 or older and having meniscus surgery lowered the odds of full recovery; a hamstring tendon graft raised the odds compared with a patellar tendon graft.
5. 05The findings support counseling patients that full symmetry by 6 months is the exception, not the rule.

How it was conducted

Design

Retrospective single-clinic cohort study using a database from 2000 to 2015 (Level III evidence)

Participants

4093 patients after primary ACL reconstruction (54.3% male, mean age 28.3 plus or minus 10.7 years); 3541 had data for all three tests

Tests

Isokinetic quadriceps and hamstring peak torque on a Biodex at 90 degrees per second, plus single-leg hop (best of 3 trials)

Definition

Symmetrical knee function defined as Limb Symmetry Index of 90% or more on all three tests compared with the other leg

Analysis

Multivariate logistic regression to identify factors affecting the odds of symmetrical function

What they found

• Only 693 of 3541 patients (19.6%) had a Limb Symmetry Index of 90% or more on all three tests at 6 months.
• Individual test pass rates: quadriceps strength 35.7%, hamstring strength 47.3%, single-leg hop 67.9%.
• Age 30 or older reduced the odds of symmetrical function (OR 0.50).
• Medial meniscus resection (OR 0.75) and medial meniscus repair (OR 0.63) reduced the odds.
• A hamstring tendon autograft increased the odds compared with a bone-patellar tendon-bone graft (OR 2.28).

Limitations

• Retrospective database design, which limits control over data quality and unmeasured confounders.
• Single clinic with one standardized rehabilitation and graft protocol, so results may not transfer to other settings.
• Symmetry is measured against the patient's other leg, which may itself be weakened after injury, so a 90% index does not guarantee full pre-injury strength.
• Outcomes captured only at the 6-month time point, with no later follow-up on eventual recovery.

Why it matters

For patients

If you are recovering from ACL surgery, expect that most people do not have fully symmetrical knee strength by 6 months, so do not rush a return to sport based on time alone.

For clinicians

Use limb symmetry testing rather than time since surgery to gauge readiness, and counsel older patients and those with meniscus surgery that recovery to symmetry may take longer.

For readers

Returning to symmetrical knee function 6 months after ACL reconstruction is achieved by only about 1 in 5 patients, with quadriceps strength the slowest to come back.