What changes in the first hours after ACL reconstruction

The brake is the effusion

Harvesting the graft, drilling the bone tunnels and fixing the neo-ligament produce real tissue trauma, despite the two one-centimetre incisions of arthroscopy.

In the hours that follow, blood and exudate collect in the joint cavity.

That effusion distends the capsule, and a distended capsule reflexively inhibits recruitment of the quadriceps. However motivated the patient is, they cannot fully contract the quadriceps while the knee is full. This is the central mechanism behind delayed rehabilitation after knee surgery.

What plays out in the first hours is therefore not a question of comfort. It is the muscle's capacity to respond once rehabilitation begins.

What the two studies measured

Two studies approach the question from different ends. The first measured analgesic use and flexion. A French case-control study compared 39 patients operated on for an ACL reconstruction in the same centre, under an identical analgesic protocol: 20 on dynamic compression combined with cold, 19 on static compression combined with cold¹.

At discharge, cumulative tramadol consumption was 57.5 mg against 128.6 mg (p = 0.023), and morphine 0 mg against 1.14 mg (p < 0.05). Knee flexion measured at the same moment was 90.5 degrees against 84.5 (p = 0.0015)¹.

The second measured the effusion itself. A Korean study published in 2023 followed 56 patients after ACL reconstruction, half on cryocompression, half on ice packs, three sessions of 20 minutes a day until discharge².

Pain at day 4 was significantly lower in the cryocompression group (p = 0.001). Joint effusion, quantified by three dimensional MRI reconstruction rather than with a tape measure, was significantly reduced (p = 0.015)².

This is the most direct measurement available on that point: imaging shows that the intra-articular volume genuinely falls, and that volume is what locks the quadriceps.

Two measures, one signal

Murgier measures what is saved: the same level of comfort, reached on half the tramadol and with no morphine¹. Yang measures what is gained: lower pain at day 4 and a reduced effusion on imaging².

These are early phase data, from the phase where the need is greatest. They document a better starting point for rehabilitation.

Once the brake is off

Bringing the effusion down lifts the inhibition. Rebuilding the muscle is the role of electrical stimulation.

A systematic review published in 2025 pooled 11 randomised trials of electrical stimulation after ACL surgery³. Added to standard rehabilitation, it improves the recovery of quadriceps strength, in the short term and beyond.

The result that matters most for prescription comes from the subgroup analysis: when sessions start within the first week, the strength gain is markedly greater than when they start later (p < 0.001)³.

It is therefore advisable to start Compex® sessions early, alongside cryocompression, from the moment the patient leaves theatre. One contains the effusion and the pain, the other maintains recruitment while the knee is still responsive. The electrodes go on the quadriceps, away from the arthroscopy portals.

The protocol in practice

The useful window opens on leaving theatre and covers the first week, the one in which the effusion forms. After that, sessions are organised around physiotherapy: before, to mobilise a knee that hurts less, and after, to contain the response to the effort.

Precautions. As long as skin sensation has not returned after the block or the infiltration, shorten the sessions and monitor the skin. The dressing stays watertight and the wrap is applied over it.

Kolde at the patient's home

Kolde rents the Game Ready® GRPro 2.1 and the Compex® directly to the patient's home, with delivery, set-up and a hands-on walkthrough by a member of the team, and support reachable at any hour. It is the first week that needs to be equipped, not the one after. The strength gain from electrical stimulation started within the first seven days is markedly greater than that of a later start³.