What to expect before and after ACL reconstruction surgery

Written by Dr Sean Leo, a consultant orthopaedic surgeon whose clinical focus is the knee, sports injuries and the lower limb.

Last updated: 9 October 2026.

Anterior cruciate ligament (ACL) reconstruction can often be done as day surgery. Before any decision about surgery, the first step is an assessment. ACL reconstruction replaces the torn ligament with a graft. Return to high-risk pivoting sport is commonly around nine months or longer. That is a commonly used orientation, not a universal evidence-established minimum, and not a date.

Is ACL reconstruction day surgery?

Anterior cruciate ligament (ACL) reconstruction can often be done as day surgery. People with other medical conditions, or who need closer monitoring, may be advised to stay in hospital. The surgical team advises which applies to each patient.

• Return to high-risk pivoting sport is commonly around nine months or longer. That is a commonly used orientation, not a universal evidence-established minimum, and not a date.
• Progress is judged by milestones as well as time.
• There is no single best graft for everyone.

More on how this page is organised

The sections below follow the journey in order: the decision and preparation, the operation, how timing and graft are chosen, the first weeks, and the road back to sport. Reconstruction is one possible pathway. An ACL tear does not automatically mean that an operation is needed, and the right pathway depends on how the knee behaves, other injuries in the knee, the activities a person wants to return to, their health and their priorities.

What does this page cover?

• Is ACL reconstruction day surgery?
• What happens before surgery?
• What happens during surgery?
• How is the timing of surgery decided?
• Which graft is used?
• How long is recovery to sport?
• What are the early post-operative milestones?
• When is urgent help needed after knee surgery?
• What should I do next?

Owner clinical review required · not a release asset

What happens before surgery?

Before any decision about surgery, the first step is an assessment. The patient’s story and goals come first: what happened, when swelling developed, whether the knee gives way, and what has changed in everyday life, work or sport. The examination then looks at the whole knee, including possible injury to the menisci, cartilage or other ligaments.

• Imaging is used when it is useful. Magnetic resonance imaging (MRI) does not decide treatment by itself.
• An ACL tear may occur with other injuries. These can affect symptoms, timing, whether another procedure is considered, and how quickly weight-bearing or motion progresses.
• If reconstruction is considered, graft choice is discussed with the patient rather than assumed.
• Choosing reconstruction does not remove the need for rehabilitation.

More on preparing for the consultation and for cost

It may help to bring available imaging and reports and to think about the activities that matter most to the patient. An appointment should support an informed decision. It is not a commitment to surgery.

A cost estimate for surgery can be given only after a consultation and assessment, once a surgical plan has been developed.

What happens during surgery?

ACL reconstruction replaces the torn ligament with a graft. The surgeon creates bone tunnels and secures the graft so that it can serve as a new ligament while biological incorporation and rehabilitation progress. Reconstruction is typically carried out arthroscopically (keyhole surgery, through small cuts), and the operating time varies with the case.

• The exact technique depends on anatomy, graft choice, associated procedures and surgeon judgement.
• The operation does not restore a knee instantly, remove every future risk or guarantee a return to a particular sport. Reconstruction may improve stability in selected patients, but it does not guarantee return to sport. In the longer term, it has not been shown to lower the rate of osteoarthritis (wear-and-tear arthritis of the joint) compared with non-surgical treatment (Webster and Hewett, 2022).

Possible complications of reconstruction include infection, deep-vein thrombosis (a blood clot in a leg vein) or anaesthetic complications, loss of motion or arthrofibrosis (scar tissue that stiffens the knee), kneeling or donor-site pain, recurrent instability or graft retear (the graft tearing again), injury to nerves or blood vessels, and injury to the ACL in the other knee. Further procedures may sometimes be needed. The likelihood and relevance of each risk depend on the person, graft, associated injuries, procedure and rehabilitation.

How is the timing of surgery decided?

When reconstruction is indicated, timing is individual. The knee’s condition, motion, swelling, associated injuries and planned procedure all influence it.

The American Academy of Orthopaedic Surgeons (AAOS) clinical practice guideline “Management of Anterior Cruciate Ligament Injuries” (2022), as summarised by Brophy and Lowry (2023), gives a strong recommendation: “When surgical treatment is indicated for an acute isolated ACL tear, early reconstruction is preferred because the risk of additional cartilage and meniscal injury starts to increase within 3 months.” This applies most to younger and more active patients; it is less applicable to older and less active patients, who may do well with non-surgical treatment.

• That recommendation is a reason to discuss timing with a surgeon early.

Which graft is used?

Patellar-tendon, hamstring-tendon and quadriceps-tendon autografts (grafts taken from the patient’s own tendon) can all be considered. Patellar-tendon and hamstring grafts differ in donor-site symptoms and other trade-offs. Graft choice remains individual and requires an open discussion between patient and treating doctor.

• A systematic review focused on young or highly active patients found more failures with allograft (donor tissue) than with autograft (the patient’s own tissue).
• As summarised by Brophy and Lowry (2023), the AAOS guideline (2022) gives a strong recommendation that surgeons should consider autograft over allograft to improve patient outcomes and decrease ACL graft failure rate, particularly in young and/or active patients.

More on comparing graft types

A 2024 systematic review of seven randomised trials (trials in which people are assigned to a treatment by chance; 474 patients) found no detected difference between quadriceps- and hamstring-tendon grafts in patient-reported scores, graft failure or overall adverse events at 24 months. Donor-site (graft-harvest area) scores were lower with the quadriceps tendon in two of the studies, a borderline difference. The authors judged the evidence insufficient for a definitive conclusion. This does not establish a universal winner.

How long is recovery to sport?

For high-risk pivoting sport, return is commonly around nine months or longer. That is a commonly used orientation, not a universal evidence-established minimum. Return to sport should not be decided by time alone; the treating team also considers how the knee has healed, the person’s circumstances and any other injuries (Meredith et al., 2021). This is not automatic clearance.

• A practical pathway is better described as overlapping phases than as a guaranteed calendar. The phases are orientation, not clearance dates.
• Nine months is not automatic clearance, and passing a test battery does not guarantee that reinjury will not occur.
• Return to some sport is more common than return to the preinjury or competitive level (Ardern et al., 2014).

The international Panther consensus describes a continuum from return to participation, to return to sport, and finally return to performance. It recommends moving away from decisions based only on elapsed time and considering examination findings, function, psychological readiness, biological healing, associated injuries and the activity context.

More on the later phases

• In typical rehabilitation protocols, graded running often begins only after adequate motion, minimal pain and swelling, strength and single-leg control, and tolerance of preparatory loading. Calendar time alone is insufficient.
• In typical protocols, power, landing, change-of-direction and sport-specific capacity are then developed where relevant, once strength, control and test criteria are met, as decided by the treating team. These stages are protocol orientation, not clearance dates.
• A prospective cohort of 106 people returning to high-risk pivoting sports found that later return, up to nine months, was associated with fewer knee reinjuries over two years. This was a small, non-randomised study.
• Group findings cannot predict what one person will achieve.

What are the early post-operative milestones?

Exercise-based rehabilitation is the mainstay after ACL reconstruction. It should respond to the graft, associated procedures, swelling, pain, motion, strength, function and the person’s goals. In a typical pathway, rehabilitation starts soon after surgery, as directed by the surgical team.

• Early on: settle swelling and pain, regain full knee extension, activate the quadriceps and establish safe mobility.
• Next: restore movement and gait while progressively rebuilding strength, balance and tolerance for daily activity.
• Progress may pause or move backwards if symptoms increase or a milestone is not met. A meniscal repair, cartilage procedure or other associated injury may alter weight-bearing, motion, running and sport timelines.

More on the first weeks

Walking aids can be reduced when gait is safe and without a limp, subject to surgical and associated-injury restrictions. A general webpage is not a self-directed rehabilitation prescription, so a rehabilitation programme should come from the surgical and physiotherapy team.

For more on recovering well, see post-surgery recovery.

When is urgent help needed after knee surgery?

What should I do next?

For anyone thinking about ACL reconstruction, or already advised to have it, an assessment is a sensible next step. It brings together the patient’s story, an examination and any tests that help, so that the patient and clinician can decide what to do next. An appointment supports an informed decision. It is not a commitment to surgery.

Many people aim to return to the activities they enjoy.

• Read how an ACL injury is assessed and how the treatment options compare on the ACL reconstruction surgery page.
• Arrange a knee assessment when you are ready.
• Browse the Knee Hub for other knee problems, or more articles.
• Read about the treatment options for an ACL tear, including rehabilitation.
• Read about which ACL injuries suit repair rather than replacement.
• Read about tips for recovering after ACL surgery.
• Read more about Dr Sean Leo, who is named as the author of this page.

References

1. American Academy of Orthopaedic Surgeons. Management of Anterior Cruciate Ligament Injuries: Evidence-Based Clinical Practice Guideline. Rosemont (IL): AAOS; published 22 August 2022 (replacing the 2014 edition). Available from: https://www.aaos.org/aclcpg
2. Brophy RH, Lowry KJ. American Academy of Orthopaedic Surgeons Clinical Practice Guideline Summary: Management of Anterior Cruciate Ligament Injuries. J Am Acad Orthop Surg. 2023;31(11):531-537. doi:10.5435/JAAOS-D-22-01020. PMID:36727995.
3. Diermeier TA, Rothrauff BB, Engebretsen L, Lynch A, Svantesson E, Hamrin Senorski EA, et al. Treatment after ACL injury: Panther Symposium ACL Treatment Consensus Group. Br J Sports Med. 2021;55(1):14-22. doi:10.1136/bjsports-2020-102200. PMID:32661128.
4. Meredith SJ, Rauer T, Chmielewski TL, Fink C, Diermeier T, Rothrauff BB, et al. Return to sport after anterior cruciate ligament injury: Panther Symposium ACL Injury Return to Sport Consensus Group. J ISAKOS. 2021;6(3):138-146. doi:10.1136/jisakos-2020-000495. PMID:34006577.
5. Wasserstein D, Sheth U, Cabrera A, Spindler KP. A Systematic Review of Failed Anterior Cruciate Ligament Reconstruction With Autograft Compared With Allograft in Young Patients. Sports Health. 2015;7(3):207-216. doi:10.1177/1941738115579030. PMID:26131297.
6. Raj S, Ridha A, Searle HKC, Khatri C, Ahmed I, Metcalfe A, et al. Quadriceps tendon versus hamstring tendon graft for primary anterior cruciate ligament reconstruction: a systematic review and meta-analysis of randomised trials. Knee. 2024;49:226-240. doi:10.1016/j.knee.2024.07.002. PMID:39043018.
7. Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med. 2016;50(13):804-808. doi:10.1136/bjsports-2016-096031. PMID:27162233. PMCID:PMC4912389.
8. Ardern CL, Taylor NF, Feller JA, Webster KE. Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors. Br J Sports Med. 2014;48(21):1543-1552. doi:10.1136/bjsports-2013-093398. PMID:25157180.
9. Webster KE, Hewett TE. Anterior Cruciate Ligament Injury and Knee Osteoarthritis: An Umbrella Systematic Review and Meta-analysis. Clin J Sport Med. 2022;32(2):145-152. doi:10.1097/JSM.0000000000000894. PMID:33852440.