Which criterion is commonly used to determine return-to-sport readiness after ACL reconstruction?

• A. Time since surgery 9 months
• B. Limb symmetry index (LSI) of hop tests ≥ 90% and adequate strength
• C. Full ROM bilaterally
• D. Pain-free at rest

Answer: (B)

The key idea is that returning to sport after ACL reconstruction is best guided by objective functional performance rather than just how long it has been since surgery or how the knee feels at rest. A primary criterion used is the limb symmetry index from hop tests, aiming for at least 90%. This means the injured leg should perform at a level close to the uninjured leg when doing dynamic tasks that mimic sport demands. Hop tests are dynamic, explosive measures of power, control, and confidence on one leg, and they challenge the knee under functional loads that resemble real activity. When this symmetry is accompanied by adequate overall strength—typically quadriceps (and often hamstring) strength comparable to the other leg—the knee is better prepared to handle the forces of sport and less likely to fail under return-to-play conditions.

Why the other considerations aren’t as strong on their own: simply having time elapsed since surgery, even at several months, doesn’t guarantee that muscle strength, neuromuscular control, or functional stability have recovered. Full range of motion on both sides is important, but it doesn’t guarantee that the knee can tolerate high-load activities or that there’s balanced strength and control. Being pain-free at rest is helpful, but pain during movement or under load often reveals deficits that could predispose to re-injury if return to sport is attempted.

So, the best-supported criterion combines functional performance with symmetry (the 90% LSI on hop tests) and adequate strength, signaling the knee has regained sufficient dynamic function for safe return to activity.