Knee injuries are one of the most common reasons people visit an orthopaedic surgeon. But not all knee injuries are created equal. Some are straightforward and recover well with non-surgical care. Others are far more complex, involving multiple ligaments, joint instability, or even failed past surgeries.
If you’ve injured your knee or you’re still in pain after previous surgery, here’s how to understand what kind of knee injury you’re dealing with, and how treatment can differ.
First, though, let’s look at the knee itself.
Understanding the knee joint
The knee is one of the largest and most complex joints in the body. Its key structures include:
- Bones: The knee connects the thigh bone (femur) to the shin bone (tibia), with the kneecap (patella) sitting in front.
- Ligaments: The joint is supported by four main ligaments which keep the knee stable and properly aligned. These are the:
- Aanterior cruciate ligament (ACL)
- Posterior cruciate ligament (PCL)
- Medial collateral ligament (MCL)
- Llateral collateral ligament (LCL) and posterolateral corner (PLC)
- Menisci: Two C-shaped discs of cartilage that cushion your knee
- Nerves: Several nerves run through your knee, carrying messages between your body and brain.
- Cartilage: smooth, frictionless structure lining the articulating margins of the joint to enable painless movement.
Together, these structures allow the knee to bend, straighten, pivot, and absorb forces during movement.
Not all knee pain is the same
While some knee injuries respond well to rest, bracing, or physiotherapy, others are more complex, requiring surgical repair and longer-term rehabilitation.
Simple knee injury
Simple knee injuries:
- usually involve a single ligament, most commonly the ACL (anterior cruciate ligament) or MCL (medial collateral ligament)
- may also involve minor cartilage damage or swelling
- often respond well to conservative treatments but may require surgery, depending on your age, activity levels and joint stability
In contrast, a knee injury may be considered complex if affects more than one ligament, involves significant joint instability or bone fractures and includes damage to nerves or vascular structures.
Complex knee injuries more commonly require surgical intervention and are associated with a longer recovery timeline. Revision surgery (repeat surgery) is also considered complex.
ACL injuries: surgical vs. non-surgical options
One of the most common injuries we see is a torn ACL, but even here, treatment isn’t always one-size-fits-all. Depending on the degree of tear, an isolated ACL injury may respond to conservative treatment or may require surgery.
Non-surgical ACL rehab
Conservative treatment may:
- be considered for low-demand patients or those with partial tears
- be suitable for older some athletes provided their knee is stable
- focus on strengthening, bracing and proprioception training.
Surgical ACL reconstruction
ACL reconstruction surgery uses graft tissue to rebuild the damaged ligament. The decision to proceed with surgery involves assessing your age, the extent of your injury and your personal preferences.
Surgery may:
- be preferred for young, active patients, athletes, or those with persistent joint instability
- seeks to rebuild the ligament to allows return to sport or high-impact activity
- usually requires 9–12 months of structured ACL rehab
When it’s more than an ACL: multi-ligament knee injuries
But what if it’s not just the ACL? Some injuries affect several parts of the knee and that shifts the treatment approach significantly.
Multi-ligament knee injuries often occur in high-impact sports or traumatic events like motor vehicle accidents.
These are complex knee injuries that may involve:
- damage to more than one ligament, e.g. affecting both the front and back stabilisers of the knee
- combined cruciate and collateral ligaments
- dislocations, cartilage damage, or nerve involvement
These injuries typically require:
- specialised imaging (MRI scan)
- a highly structured, longer rehab timeline
- specialised, multi-disciplinary care
Revision ACL surgery: what if your last surgery didn’t work?
What happens if a previous ACL repair didn’t quite work? That’s where revision surgery comes in. It’s a more challenging procedure, but can offer a second chance at stability.
Revision ACL reconstruction may be needed when the:
- graft fails due to re-injury or poor healing
- knee remains unstable despite rehab
- original tunnel placement or technique was suboptimal
Revision cases are technically demanding and require:
- specialist imaging
- possible bone grafting
- rebuilding the joint with new grafts and advanced fixation techniques
Recovery is longer and more closely monitored than primary ACL reconstruction.
Why complex knee injuries often require surgery
When multiple structures are damaged, the knee loses its mechanical stability. Without surgical repair, this can lead to:
- long-term pain
- early arthritis
- limited mobility or activity
- poor quality of life
In these cases, surgery restores normal joint alignment, allows tissues to heal, and sets the foundation for rehabilitation.
Recovery and rehab: what to expect
The recovery timeline depends on the type and severity of injury, but here’s a general guide:
| Injury type | Surgery? | Return to sport | Rehab duration |
| Isolated ACL tear | Sometimes | 9–12 months | 6–9 months of rehab |
| Multi-ligament injury | Almost always | 12–18+ months | Structured, staged rehab |
| Revision ACL reconstruction | Yes | 12+ months | Closer monitoring, longer rehab |
Rehabilitation is essential for restoring strength, range of motion, and neuromuscular control. You’ll work closely with your physiotherapist and surgeon at every stage.
Final thoughts
Knee injuries can vary widely, from a partial tear in a single ligament to complex, multi-structure damage. Accurate diagnosis and tailored treatment help to avoid long-term complications and get you back to doing what you love.
I am a Perth-based orthopaedic surgeon with significant expertise in complex knee reconstruction and revision procedures. If you’re dealing with ongoing pain, instability, or concerns after previous knee surgery, please book a consultation to explore your options.
Disclaimer
All information is general and not intended as a substitute for professional advice. Any surgical or invasive procedure carries risks.
References
- Fortier LM, Stylli JA, Civilette M, et al. An Evidence-Based Approach to Multi-Ligamentous Knee Injuries. Orthopedic Reviews. 2022;14(3). doi:10.52965/001c.35825. PMID:35769647, [Accessed 29 January 2026]
- Zaffagnini, S., Lucidi, G.A., Pizza, N., Grassi, A., Dal Fabbro, G. (2024). Revision Anterior Cruciate Ligament Reconstruction. In: Doral, M.N., Karlsson, J. (eds) Sports Injuries. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-36801-1_424-1, [Accessed 29 January 2026]
