Episode 10 | Ask the Expert | Guest: Ben Saldivar MCSP, HCPC – ACL Rehabilitation Physiotherapist, Founder of ACL Rehab Online
Mention an ACL injury and most people think of a professional footballer going down in agony, or a Six Nations player being stretchered off. What fewer people know is how common these injuries are in amateur and recreational sport, how much variation exists in how they are managed, and how significantly the quality of rehabilitation affects the outcome – regardless of whether surgery takes place.
In this episode of the London Bridge Sports Medicine podcast, Dr Ajai Seth is joined by Ben Saldivar, a physiotherapist who specialises exclusively in ACL rehabilitation and runs an online service supporting patients from diagnosis through to return to sport. What follows is a comprehensive guide to ACL injuries for athletes and active people at every level.
What is the ACL?
The anterior cruciate ligament (ACL) sits inside the knee joint, connecting the underside of the thigh bone (femur) to the top of the shin bone (tibia). Its primary job is to stabilise the knee – preventing the shin from sliding forward and the knee from giving way during movement.
An important point Ben makes early: a significant number of people can function normally – including playing sport – without an intact ACL, depending on the strength and control of the surrounding muscles. This is relevant to the later discussion about surgery, but it establishes from the outset that the ACL is not the sole stabiliser of the knee.
How does an ACL injury happen?
ACL injuries most commonly occur in what Ben calls “level one sports” – those involving high-speed change of direction: football, basketball, rugby, netball, gymnastics, skiing. The injury typically happens not through direct contact to the knee, but through an uncontrolled movement at speed – planting the foot in a slightly awkward position, with the knee collapsing inward in a way that places excessive stress on the ligament.
The key point is that athletes perform these movements thousands of times without injury. ACL injuries are multifactorial – a combination of factors converging at a particular moment. Risk factors include:
- Velocity: most ACL injuries require high-speed movement; the ligament is under much greater stress at pace
- Unexpected environmental factors: an opposing player appearing suddenly, an uneven surface, or an unexpected change in ground conditions
- Previous injury or compensation: loading the knee differently due to a niggle elsewhere changes movement patterns and can increase stress on the ACL
- Fatigue and general condition: there is some research showing a small cluster of pain or discomfort in the days before an ACL injury, suggesting altered movement patterns may be a contributing factor
- Sex: female athletes face approximately 15–17 times greater ACL injury risk, likely related to a combination of anatomical, hormonal, and training history factors. Ben notes that girls have historically had less exposure to strength training and rough-and-tumble physical play, meaning less time developing the muscle strength and movement coordination that protects the knee
- Age: ACL injuries peak between approximately 14 and 30, coinciding with the years of highest participation in high-speed, high-contact sport
Despite extensive research, injury rates are not falling. “We still have a lot to learn,” says Ben. Predicting who will be injured and when remains very difficult.
How to recognise an ACL injury
Not every knee injury is an ACL tear – and an ACL tear is often accompanied by other injuries, most commonly to the meniscus (the knee’s shock-absorbing cartilage). The signs that suggest an ACL injury rather than a more minor issue:
- An instability episode: the knee gives way during a movement
- A pop: a loud or significant pop at the moment of injury is strongly associated with ACL tears
- Inability to play on: having to come off immediately
- Rapid swelling: the ACL has a significant blood supply; significant swelling within the first 24 hours is a classic sign
- Loss of range of motion: difficulty fully straightening or bending the knee
An MRI scan is the gold standard for confirming the diagnosis. A clinical assessment by a sports medicine doctor or specialist physiotherapist will be very informative, but imaging gives definitive clarity. For more information on meniscal tears, which often occur alongside ACL injuries, the LBSM website has a dedicated guide.
What to do immediately after the injury
The instinct to rest completely is understandable but counterproductive. Muscle wasting (atrophy) begins within days of an injury if the limb is not being used. Starting active management early – even in the first few days – significantly affects how good a position you will be in for either rehabilitation or surgery.
Immediate priorities:
- Reduce swelling: compression garments, ice packs, or a cryo-compression device (such as a Game Ready). Elevate the leg to help fluid drain.
- Restore knee extension: getting the knee fully straight is the first functional goal. A bent, stiff knee at rest causes problems that compound over time.
- Start quadriceps activation: simple muscle contractions in the early days keep the quad from switching off. Quadricep wasting after ACL injury is visible and significant.
- Restore normal walking mechanics: as soon as pain allows, working on how you walk – not just whether you can walk – sets the foundation for everything that follows.
Both Ben and Dr Seth emphasise: the weeks immediately after injury are probably the most important of the entire rehabilitation process, and the ones most often wasted. Starting a structured programme in the first few days changes the trajectory of recovery significantly.
Surgery or no surgery: the million dollar question
This is the question every ACL patient asks, and the honest answer is that it depends on the individual. Ben is clear that non-surgical management is a genuinely valid option for many people – not a compromise or a lesser path.
The key Frobell paper (2013) followed a group of young, athletic, level-one sport participants after ACL injury. Half had surgery; half did not. At both two and five years, functional outcomes were equivalent between the groups. Some of the non-surgical group eventually required surgery – but even those who delayed surgery had the same long-term outcomes as those who had it immediately.
Factors that favour non-surgical management:
- Older age with lower sporting ambitions
- Primarily linear sports or activities (running, cycling)
- Partial rather than complete tear
- A knee that feels stable enough to manage daily activities and lower-impact sport
Factors that favour surgical management:
- Desire to return to level-one sports (football, rugby, basketball, netball)
- Associated injury to the meniscus or other structures that require surgical attention
- Persistent instability that prevents engagement with rehabilitation
On the question of whether not having surgery leads to more wear and tear over time: recent evidence suggests that osteoarthritis risk is elevated after an ACL injury regardless of whether surgery takes place. The surgery does not prevent long-term joint changes – but what both approaches share is the importance of strong, well-conditioned muscles around the knee.
Ben’s important practical point for anyone facing NHS waiting times: use that time. The best predictor of surgical outcome is the state of the knee going into surgery. A patient who has spent six months building strength, restoring movement, and conditioning the supporting muscles will have significantly better results than one who waited passively.
What good rehabilitation looks like
ACL rehabilitation is not a fixed-length programme. It is a process of reaching specific functional milestones – and only progressing when those milestones are met. Ben recommends working backwards from the end goal: if the aim is to return to football, what does a fully rehabilitated athlete look like? What are the measurable strength, power, and stability criteria for return to play? Setting those benchmarks early gives the process structure and makes it less overwhelming.
The broad phases of rehabilitation:
Early phase (weeks 1–6)
Swelling management, restoring full knee extension, reactivating the quadriceps, restoring normal gait. The aim is to get the knee calm and functional before loading it.
Mid phase (weeks 6–16 approximately)
Progressive strength loading in the gym – squats, deadlifts, leg press, hamstring work. Building the quadriceps, hamstrings, glutes, and calves systematically. Consistency here is the critical variable: “Consistency is king,” says Ben. Dipping in and out of the programme slows progress significantly.
Later phase (months 4–9+)
Once specific strength milestones are met, introducing impact work: jumping, landing, running. Then change of direction, agility, and sport-specific movement. This phase is often under-resourced in standard physiotherapy pathways – Ben recommends working with someone who has specific experience in late-stage ACL rehabilitation and return to sport, or pairing a physiotherapist with a strength and conditioning coach for this phase.
Return to training and play
Ben recommends returning to training at least two to three months before returning to full match play, building back gradually – starting at around 25% of normal training load and increasing by approximately 20% per week. Only once strength, power, stability, and coordination criteria are all met should the athlete return to competitive sport.
Timeline varies enormously. For many amateur athletes returning to level-one sport, nine to twelve months is realistic. Rushing this process – particularly the later stages – significantly increases the risk of re-injury.
The bottom line
An ACL injury is not the end. Many people return to the same level of sport, often in better physical condition than before, because the rehabilitation process demands a level of strength and conditioning work that their previous training never included. But the outcome depends heavily on what happens in the days, weeks, and months after injury – and on finding people who can guide that process well.
“Find someone that you can work with that will give you support throughout the whole process,” is Ben’s one golden tip. “Going through it on your own is really, really tough. Make sure you’ve got a good support team – surgeon, doctor, physio, family. You can come back from it and get back to the things you love.”
Ben Saldivar (MCSP, HCPC) is a specialist ACL rehabilitation physiotherapist and founder of ACL Rehab Online, providing structured online rehabilitation support from diagnosis through to return to sport. Find out more at aclrehab.com.
If you have suffered a knee injury and would like a clinical assessment, the LBSM team can help. Visit lbsm.co.uk/booking to book an appointment.
Listen to the full episode below ↓
