BIOMECHANICS
Foot fault: the common trigger for a wide range of sport injuries
This is the first of two articles aiming to provide athletes and coaches with sufficient information to use orthotic therapy for the treatment and prevention of sports injuries as well as for performance enhancement.
This first article looks at the basic anatomical and biomechanical dysfunctions that often lead to overuse injuries in the musculoskeletal system.
Sports injuries can be divided into two major categories; macro-trauma and micro-trauma. Macro-traumatic injuries involve a single traumatic event resulting in acute injury1. Examples include:
- spraining an ankle in a football tackle;
- straining a muscle/tendon during competitive weightlifting;
- incurring broken bones or severe bruising as a result of a rugby tackle.
Micro-traumatic injuries involve much smaller, repetitive traumatic events that impact on the soft tissues surrounding and supporting joints. In these circumstances, an athlete may not even be aware that there is a problem until the accumulated damage results in sufficient tissue disruption, swelling, and irritation to cause pain.
Nevertheless, these repetitive small injuries to the muscles and tendons in the feet, ankles, knees, legs, hips, pelvis, and spine can lead to chronic injuries that will compromise performance and eventually become disabling.
Examples of this type of injury include shin splints, foot arch pain, runner’s knee, jumper’s knee, ilio-tibial band syndrome (ITBS), sacro-iliac joint dysfunctions (SIJD), and chronic low back pain.
Such injuries are often tricky to treat as the biomechanical mechanism of injury can be difficult to ascertain. Furthermore, while standard sports medicine treatment – involving rest, ice, physiotherapy, stretching exercises, proprioceptive retraining and other rehabilitative procedures – will often resolve the acute symptoms, if the underlying biomechanical fault is not identified and corrected, the injury will simply recur when regular training is resumed.
This is where functional orthotic therapy comes into play. Foot orthoses, more commonly known as ‘orthotics’, are valuable tools for treating chronic overuse injuries in the weight-bearing joints of the body that result from faulty foot mechanics.
In simple terms, orthotics are inserts that are placed in the shoe to support the joints and soft tissues of the foot. There are a wide variety of options, ranging from very simple foam arches, available over-the-counter from your local chemist, to highly sophisticated devices prescribed by musculoskeletal professionals, using such technological assessment tools as video gait and/or digital pressure plate analysis.
To help you make an informed decision about how best to obtain proper orthotics for yourself or the athletes you work with, we need to review some of the basic principles about foot structure and function. We’ll also look at how dysfunction of the foot places abnormal stresses on the structures of the leg, pelvis and spine.
There are three arches in the foot: the medial longitudinal arch (MLA), the lateral longitudinal arch (LLA) and the transverse metatarsal arch (TMA)2. These three arches (illustrated in figure 1) allow the foot to absorb shock at impact with the ground and facilitate propulsion when the foot is pushing off.
As the foot hits the ground and the pressure shifts from the heel, over the arches and onto the forefoot, there is also a pressure transition from the outside to the inside of the foot, and back again 3. So, as the foot is moving from heel to toe, it is also rolling inwards (known as pronation) and outwards (supination). Thus, if you were to draw a line along the bottom of the foot that outlines the center of pressure from heel to toe, it would have an S-shape, as shown in figure 2.
As the foot pronates and supinates through the gait cycle it creates torsional (twisting) movements in the foot, ankle, knee, hip, pelvis and spine. In the normal foot, as the heel strikes the ground it pronates approximately 6°. As the body weight then shifts directly over the longitudinal arches, pronation through the MLA causes a controlled collapse of the arch. These two events allow for shock absorbency as weight is transferred onto the foot.
As the body weight shifts further forwards over the ball of the foot, the heel and MLA supinate (roll out) to reform the arch and prevent excessive torsion in the leg. While the body weight is over the ball of the foot, the TMA also collapses and rebounds to facilitate shock absorbency and propulsion in the late phase of the gait cycle (see figure 3).
However, some people’s feet are abnormal in that they have a tendency to over-pronate, leading to excessive rolling in of the heel and collapse of the MLA 4. This can result in abnormal and repetitive stresses to the ligaments, tendons and other connective tissue in the sole of the foot5. It can also create excessive torsional forces through the leg, causing stress to the ligaments and tendons supporting the knee and the soft tissue in the hip, sacro-iliac and spinal joints (see figure 4) 6.
When these excessive torsional forces are asymmetrical – ie one leg is more affected than the other – this will cause biomechanical problems in the pelvis and spine – a phenomenon known as ‘bilateral asymmetrical pronation syndrome’.
A number of common musculoskeletal sports injuries are linked with faulty foot mechanics starting with over-pronation, and can be treated and prevented with orthotics. Those described below are the most common:
- Plantar fasciitis (PF): foot arch pain
The plantar fascia is a connective tissue that is a cross between a tendon and a ligament. It attaches to the bottom of the heel and then spans the length of the foot, spreading out like a fan to attach at the base of each toe. Its function is to support the MLA and control the collapse of that arch during normal pronation.
When over-pronation occurs, the plantar fascia is repetitively and excessively stressed, causing pain in the arch of the foot, which is felt most keenly on the bottom of the heel close to the medial longitudinal arch, although it can also extend the full length of the foot. 7 A classic sign of this condition is severe pain on walking in the morning.
Plantar fasciitis is very common among runners, walkers, aerobic dancers, and athletes involved in jumping sports. Its onset can be triggered by changes in the surface used for training or competition – eg from track to grass or vice versa – or a change in footwear. Another common trigger for plantar fasciitis is a change in training; the addition of hills, stairs or sprints, for example, can cause overuse of the plantar fascia, leading to inflammation and injury.
If an athlete develops plantar fasciitis for the very first time as a result of changes in training surface or methods, the condition will usually respond readily to standard treatments. However, a recurrence of the condition, despite treatment protocols suggests an underlying mechanical fault.
- Medial tibial stress syndrome (shin splints)
Pain on the inside of the tibia (shin) is commonly referred to as ‘shin splints’. There is a long tendon that runs along the back and medial (inside) aspect of the tibia called the posterior tibialis. This tendon then passes behind the inside ankle bone (medial malleolus), and underneath the MLA, with several attachments onto the underside of the bones of the foot, allowing it to support the MLA like a stirrup.
When the MLA over-pronates and collapses excessively, there is a consequent overstretching of the posterior tibialis muscle and tendon. This causes pain, particularly in the lower third of the tibia where the tendon attaches.
This injury is most prevalent in long distance runners, but is also common in other sports, especially those that involve jumping. As with plantar fasciitis, if an athlete develops this condition for the very first time following abrupt changes to training surface or methods, it will respond readily to standard treatment.
However, if the condition is unresponsive to treatment, or recurs subsequently, there may well be an underlying biomechanical weakness in the foot, which will benefit from orthotic treatment.
3) Patello-femoral tracking syndrome(runner’s knee)
This condition arises as a result of the kneecap gliding abnormally between the femoral condyles (a groove at the bottom end of the thigh bone) as the knee bends and straightens.
The four major muscles in the thigh (quadriceps) share a common tendon that attaches just below the knee and encases the kneecap. Therefore the contraction of the quadriceps has an impact on how the kneecap glides in this groove. If there is abnormal pulling of the quadriceps on the kneecap, this can cause the kneecap to grind rather than glide in the groove, leading to inflammation and pain.
This condition is common in long distance runners (hence ‘runner’s knee’), particularly in women, who have wider hips than men and are therefore comparatively knock-kneed.
Apart from abnormal bone/joint structure and alignment, other factors that predispose athletes to runner’s knee include previous trauma and muscle imbalance, as well as abnormal foot biomechanics.
When the foot over-pronates, this creates a twisting, or torsional, force which extends up into the knee, causing the top of the tibia to twist inwards, changing the way the quadriceps pulls against the kneecap, with the painful consequences described above.
4) Iliotibial band syndrome (lateral knee tendonitis)
The iliotibial band (ITB) is a very long tendon extending from the tensor fascia latae muscle, which lies on the side of the hip. The ITB spans the length of the upper leg, crosses the knee and attaches below it. The contraction of this muscle controls the movements of both the hip and the knee, stabilising them during walking and running.
Injury to this tendon is very common in long distance runners and practitioners of sports requiring a lot of lateral motion, such as tennis or squash. Common triggers of injury include radical changes to the intensity, frequency or duration of training and/or changes in the training surface. And in such cases most athletes will respond to physiotherapy.
However, if the condition proves chronic and recurrent, an underlying biomechanical abnormality is the likely culprit. In some athletes, a minor biomechanical weakness will not cause injury as long as the training regimen remains below their threshold of tolerance. But an increase in training load may be enough to trigger a strain injury to the ITB.
Again, abnormal foot mechanics are often to blame: over-pronation followed by twisting of the tibia causes the ITP to pull away from its attachments on the outside of the tibia, causing strain, irritation and ultimately pain or dysfunction.
5) Sacroiliac joint syndrome (sacroiliitis or sciatica)
The sacroiliac joint (SIJ) is a very complicated mechanical system, and sports injuries occurring here can be difficult to diagnose and treat.
Affected athletes tend to feel pain and/or stiffness over the region of the SIJ and may also experience pain in the groin or buttock, or radiating down the thigh (8). In more severe cases, this pain can radiate into the lower leg and foot, and be accompanied by numbness and tingling.
Like any other joint, the SIJ can become inflamed and irritated as a result of acute trauma from a fall or impact. More commonly, however, this inflammation is a manifestation of overuse caused by faulty biomechanics (9).
If the foot is over-pronating and the tibia is twisting inwards, the torsional forces at the knee will ultimately result in twisting of the thigh bone (femur), which leads, in turn, to twisting of the ilium (hip bone). This creates stress at the SIJ – the joint between the ilium and the sacrum at the base of the spine. And this stress leads, in turn, to irritation of the ligaments, tendons and muscles that stabilise the joint.
As this joint is anatomically close to the sacral nerves that pass into the leg, irritation to the SIJ can ultimately cause pain in the leg, although this would normally be a late development (8-10). More commonly, athletes will notice an achy sensation and stiffness around the sacroiliac joint with extreme ranges of motion.
Injuries to the SIJ are common in a wide range of sports and are frequently misdiagnosed as a simple strain or sprain, although in most cases there is no history of trauma to support such a diagnosis.
6) Lumbar facet syndrome (low back pain)
Low back pain is a very common problem in athletes which, as with SIJ injury, is often misdiagnosed as a strain or sprain. For this reason, athletes with back problems are well advised to consult sports medicine therapists with experience of treating pelvic and spinal conditions.
The lumbar spine comprises the bottom five vertebrae, connected by 10 joints (five on either side of the spine) and five inter-vertebral discs. Thus there are 15 joints and multiple ligamentous tendons and muscles that facilitate stability and movement in this area.
These joints, like any other joints in the body, can be damaged by macro- or micro-trauma. In the absence of biomechanical faults in the leg or foot, acute injury to the lumbar spine should respond to standard treatments. However, underlying biomechanical faults will compromise the healing of an acute injury, and can lead to chronic overuse injury.
As with SIJ syndrome, over-pronation of the foot can set off a chain of abnormal stresses that can eventually affect the lumbar spine joints (see figure 5). This can result in chronic low back pain that is aggravated by standing, walking or running for any length of time.
Typically, an affected athlete will feel a bit better after relative rest and/or treatment, but will experience a recurrence of the condition with return to full activity.
In summary, then, a range of common and apparently unrelated sports injuries can be triggered by the same mechanical fault – a tendency of one or both feet to pronate to an abnormal extent.
In my next article, I will take a look at the main treatment options for each of the conditions considered above, including physiotherapy, manipulation, stretching, proprioceptive retraining, athletic taping and, of course, orthotics.
I will also offer guidance on orthotic therapists and products as well as taking a look at how orthotic therapy can enhance performance.
References:
- Hammer, WI (1999) Functional Soft Tissue Examination and Treatment by Manual Methods, 2nd edition, Aspen Publishers, Maryland
- Moore, K & Dalley, A (1999) Clinically Oriented Anatomy, 4th edition, Lippincott, Williams and Wilkins, Pennsylvania.
- Magee, DJ (2002) Orthopaedic Physical Assessment, 4th edition, p.661 WB Saunders Company, Pennsylvania
- Clinical Journal of Sport Medicine 8(1), 38-42
- Naughton KM (2001) Running Injuries – Starting off on the Right Foot, Part 1, chiroweb.com
- Charschan W (2001) Simplifying Lower Extremity and Lower Back Diagnosis by Understanding the Effects of Foot Overpronation. chiroweb.com
- Souza, T (2001) Differential Diagnosis and Management for the Chiropractor, 2nd edition, Aspen Publishers, Maryland
- The American Journal of Orthopedics, 475-478, 1995
- Movement, Stability & Low Back Pain, (ed by Vleeming A, Mooney V, Dorman T, Snijders CJ, Stoeckart R.), pp. 53-71. Churchill Livingstone
- Journal of Bodywork and Movement Therapies, 5(4), 227-229