Which structures may be causing your knee pain (and how to stop it)

Knee pain is a very common complaint, becoming more common the older we get. This is because the knee is a large weight-bearing joint that has to deal with some demanding forces whilst we walk, run, jump etc. Each decade over the age of 30, we lose 8% of our strength, this means that by the age of 80, you could have potentially have lost 40% of your strength (CSP). This is why falls occur more in the elderly population. It is also why the knee can pick up injuries far more easily as we get older. Muscular control around a joint as big as the knee is vital in protecting the structures in and around it. It is the muscles that should take the forces travelling through a joint, and when they take this stress, the structure within the knee are protected and secure. However, if muscular strength is lost, (as is the case in those who do not complete regular strengthening exercises), the knee joint is exposed to the forces transmitted through the knee and the structures, resulting in a higher incidence of injury.

Knee pain can come on suddenly or gradually, and sometimes seemingly for no reason. Physiotherapy assessments can accurately identify which structures which may be implicated and help guide the best treatment approach. Often, if function is adequate, conservative management with manual therapy and strengthening has the best outcomes.

The most common structures injured in the knee are:

Menisci

The correct term for the cartilage in the knee- there is a larger medial meniscus (on the inside), and a smaller lateral meniscus (on the outside) within the joint. These structures act as shock absorbers within the knee, and are very good at dealing with compressive forces travelling through the knee. What the menisci are not good at tolerating are the torsional forces that come when a knee is twisted. This tends to happen when the knee is walking on uneven ground and there is not enough muscular stability to control the hip and/or knee joint. Injury to this area will often result in some swelling, and severe injury can cause the knee to give way and lock. Strengthening the quadriceps after meniscal injury can help to stabilise the knee, allowing inflammation to settle and reduces the torsional forces that can prevent an meniscus from healing.

Medial Collateral Ligament (MCL)

This is a large ligament on the inside of the knee which stops valgus stresses on the knee (collapsing inwards). Ligaments are slightly elastic in nature, so they have the ability to stretch a little, but overstretching will cause injury and in the worst cases, rupture. This ligament will usually be injured if a knee is twisted or knocked and the inside is stressed with some force. It will usually result in fairly moderate-severe swelling when injured.

Anterior Cruciate Ligament (ACL)

This is the ligament that athletes dread injuring. It stops the anterior slip of the tibia (shin bone sliding forwards) and the posterior slip of the femur (thigh bone sliding backwards). Rupture will often come if an athlete lands awkwardly and the knee collapses inwards, or if the knee is forced into hyperextension. Most people describe a popping noise, significant pain and swelling after ACL rupture. A full ACL rupture will often need surgical repair if aiming to get back to high level sport, but many surgeons will ask that a good time has been spend on pre-operative rehab to give the best chance of success. Rehab after ACL repair can take between 9-12 months to get back to high level sport. All ACL injuries should have a full course of regular physiotherapy rehab to reduce the chance of osteoarthritis, re-rupture of the graft, and other unwanted complications. Strength of the hip stabilisers and hamstrings are particularly important.

Lateral Collateral Ligament (LCL)

This is a smaller ligament on the outside of the knee which helps to stop varus deformity (collapsing outwards). This ligament is less commonly injured.

Posterior Cruciate Ligament (PCL)

This ligament stops the posterior slip of the tibia (shin bone sliding backwards), and the anterior slip of the femur (thigh bone sliding forwards). It is less often injured than the ACL, and less often repaired because it does not provide the knee with so much day-to-day support.

Patellofemoral pain (PFPS)

The patellofemoral joint is where the patella (knee cap) runs over the front of the knee. This occurs when the quadriceps (thigh) muscles get weak, tight or imbalanced, and often the hip will have dysfunction as well. The pain is thought to come on when there is improper or over-loading of the patellofemoral joint

Sciatic nerve

Sciatica can be an incredibly painful source of pain which stems from the large sciatic nerve running down the back of the leg. It can manifest itself as posterior knee pain (pain in the back of the knee), but actually be originating from the hip or lower back. Branches of the sciatic nerve also supply the front of the lower leg so pain can also radiate into these regions. Sciatica responds very well to physiotherapy, as we can de-sensitise the nerve and also work on improving the underlying cause of the pain at its origin.

Other injuries or causes of pain that do very well with physiotherapy management are patella tendinopathy, ITB syndrome, osteoarthritis, muscular strain to name just a few.

Many injuries to the knee can be avoided completely by strengthening the hip and knee, teaching improved biomechanics and movement patterns. A well-structured strengthening programme should be done a couple of times a week to reduce the chance (or at least slow the progression) of osteoarthritis (wear and tear), and greatly reduce the chance of injury within the knee joint by up to 50% (FIFA). Prevention is better than cure for knee pain!

Furthermore, even if an injury does occur any of the above structures, often they will not need surgery, and most good bodies of evidence now champion physiotherapy over surgical intervention when it comes to long-term outcomes. Surgery can often give good short-term results, but for many this can lead to inferior outcomes in the future, with long-term issues arising like osteoarthritis. If you have knee pain- whether and acute injury which has come on from trauma, or whether a chronic pain that has come on over time, you should have a thorough physiotherapy assessment to identify which of the above structures may be the culprit, and this will identify whether physiotherapy is the best solution, or whether surgery is warranted. Surgery can of-course not always be prevented and in many cases, a prompt referral to an orthopaedic surgeon is needed.