An anterior cruciate ligament (ACL) injury can turn a routine match, run or awkward landing into months of uncertainty. A swollen knee, a “pop” and difficulty putting weight through the leg may raise suspicion, but symptoms alone cannot confirm exactly what has been damaged. This guide explains assessment, rehabilitation, surgery decisions and realistic return-to-sport expectations for UK readers.
Unsure what to do after an ACL injury?
Your free initial consultation lets you meet the physiotherapist, describe your symptoms and understand the YourPhysio service before choosing whether to have any paid treatment. Paid physiotherapy sessions are optional and secondary.
What is the ACL?
The ACL is a strong band of tissue inside the knee that connects the thighbone to the shinbone and helps control stability. It can be injured when the knee twists, when someone lands awkwardly, or during a sudden stop or change of direction. Contact injuries can also damage it.
An ACL injury may be partial or complete. Other structures can be injured at the same time, including the meniscus, cartilage or other ligaments. That is one reason a prompt, skilled assessment matters: “ACL tear” does not describe the whole knee.
Common ACL injury symptoms
People often report a pop or snap, immediate pain and swelling that develops quickly. Weight-bearing may be difficult. Once the first painful phase settles, the main problem may become instability: the knee feels loose, wobbly or gives way when turning, landing or changing direction.
These symptoms can overlap with a meniscus tear, patellar dislocation, fracture or another ligament injury. A clinician will ask how the injury happened, examine the knee and decide whether imaging or orthopaedic review is needed. MRI is commonly used to confirm ACL damage and identify associated injuries, but it should be interpreted alongside the history and examination.
What should you do in the first few days?
Protect the knee from movements that make it give way. Crutches or a brace may be advised, depending on the injury and clinical assessment. Relative rest, elevation, compression and a wrapped cold pack can help manage pain and swelling. Do not place ice directly on the skin, and ask a pharmacist or clinician about suitable pain relief if needed.
Complete immobilisation is rarely the goal unless a clinician has given specific restrictions. Gentle movement and gradual loading are usually introduced as symptoms allow. Early priorities often include reducing swelling, regaining knee straightening, restoring comfortable bending, waking up the quadriceps and returning towards a normal walking pattern.
Does every ACL tear need surgery?
No. The NHS states that not all ACL injuries require an operation. Some people can manage well with rehabilitation and changes to activity. Surgery is more likely to be discussed when the knee continues to give way, when the person wants to return to pivoting or high-intensity sport, when the job is physically demanding, or when another part of the knee also needs repair.
The British Orthopaedic Association describes symptomatic instability as the main indication for ACL reconstruction and recommends an individual decision after discussing operative and non-operative options. Age alone does not make the decision. Your sport, occupation, instability, associated damage, goals and willingness to complete a long rehabilitation programme all matter.
An orthopaedic surgeon should lead the decision about surgery. Physiotherapy can help you understand function and build capacity, but it cannot decide from a video call whether a ligament needs reconstruction.
Why rehabilitation matters with or without surgery
Rehabilitation is central whether the ACL injury is managed without surgery or with reconstruction. Before an operation, “prehabilitation” aims to settle swelling, restore movement — especially full extension — and rebuild quadriceps control. A calmer, more mobile knee is generally a better starting point for surgery.
After surgery, the graft needs time to heal while the knee regains movement, strength and control. The exact plan depends on the graft, any meniscal repair, the surgeon’s instructions and the person’s progress. Someone who has also had a meniscus repair may have different weight-bearing or range-of-motion restrictions, so a generic ACL timeline should never override the surgical plan.
What does ACL rehabilitation include?
Restore movement and reduce swelling
Early rehabilitation usually targets comfortable knee straightening and gradually improving flexion. Swelling can inhibit the quadriceps and alter walking, so it is monitored rather than ignored. A sudden increase after exercise is a reason to review the dose.
Rebuild strength
Progressive strengthening commonly addresses the quadriceps, hamstrings, calves, hips and trunk. Exercises may move from simple contractions and supported movements to squats, step work, leg press, split squats and heavier resistance. Selection and loading depend on the stage of recovery and any surgical precautions.
Train balance, landing and direction changes
Strength alone does not prepare someone for football, rugby, netball, skiing or another change-of-direction sport. Later rehabilitation may include single-leg control, jumping, landing, deceleration, cutting, reactive drills and sport-specific fatigue. Each layer should be earned through good movement quality and an appropriate response afterwards.
Build confidence
Fear of reinjury is common and relevant. A good plan uses graded exposure to feared movements, clear milestones and honest feedback. Confidence should grow alongside physical capacity rather than being treated as a final checkbox.
How long does ACL recovery take?
Recovery varies. After reconstruction, the NHS advises that it can take several months or longer, and up to a year to return to sport. British Orthopaedic Association guidance says return to sport should rarely be before nine months after surgery because of reinjury risk. Some NHS services advise that pivoting-sport rehabilitation is likely to take at least a year.
Calendar time is only one part of the decision. Progress should be criteria based. Before unrestricted sport, assessment may include knee symptoms, full movement, strength testing, hop tests, landing quality, change-of-direction ability, fitness, psychological readiness and the demands of the specific sport. Passing tests cannot remove all risk, but returning because a date has arrived gives too little information.
When can you start running?
There is no universal week that suits every ACL injury. After reconstruction, some protocols consider straight-line jogging from around three months when movement is restored and single-leg control is good, but many people need longer. Meniscal repair, graft choice, swelling, pain and strength can change the plan.
Running should normally begin as a progression: walk-jog intervals, controlled straight-line running, gradual volume, then speed, curves and direction changes later. The knee’s response over the following 24 hours helps guide the next step. New swelling, instability or loss of movement suggests that the load needs review.
Can online physiotherapy help?
Online physiotherapy can support education, exercise coaching, programme progression and regular review. A video appointment can show walking, squats, step control and selected exercises, and it can help adapt a home or gym programme. It can also make follow-up easier when travel is difficult.
ACL care may also require hands-on examination, imaging, strength equipment and formal return-to-sport testing. YourPhysio should work alongside the fracture clinic, orthopaedic team or local physiotherapy service when those are needed. If your injury also involves locking or suspected meniscal damage, our guide to meniscus tear symptoms and recovery provides additional context.
ACL injury red flags and urgent symptoms
Use NHS 111 if the knee is very painful, badly swollen or misshapen; you cannot move it or put weight through it; it locks; or it repeatedly gives way. A hot, red knee with fever or shivering needs urgent assessment because infection is possible. After a major injury, seek urgent help if there is numbness, a cold or pale foot, or severe worsening pain.
After ACL surgery, contact NHS 111 or seek an urgent GP appointment for worsening wound redness, discharge or pus, fever, or new throbbing pain and swelling in the leg. Call 999 for leg pain or swelling with chest pain or breathing difficulty, as this could indicate a pulmonary embolism.
Questions to ask at your next appointment
- Is the ACL diagnosis confirmed, and are the meniscus or other ligaments involved?
- What activities should I avoid while the knee is unstable?
- What are my current movement, swelling and strength goals?
- Would rehabilitation alone be reasonable for my work and sport?
- If surgery is planned, what graft and post-operative restrictions are expected?
- Which objective tests will be used before running and return to sport?
Discuss your ACL rehabilitation goals
The free initial consultation lets you meet the physiotherapist, describe your symptoms and understand how the service works before choosing paid treatment. Any paid sessions are optional and secondary to the free conversation.
Sources and further reading
Sources checked 29 October 2026. This article provides general information and cannot replace an individual assessment or your surgeon’s instructions.