Flexibility and joint laxity

Flexibility refers to the range of motion possible at a joint or throughout a series of joints. It is influenced by several factors, including the type of joint, its structure (e. g. the position of ligaments, etc) and the position and tension of the muscles and tendons that cross it. A range of motion that is greater than that which is considered normal is known as hypermobility. A joint is ‘lax’ if the ligaments do not hold the bones and hence the joint together particularly well, allowing considerable joint play.

It is not unusual for hypermobility and joint laxity to go together and the freedom of movement at such a joint means that it is far easier to sublux or dislocate this type of joint. A good general level of flexibility is required in most sports and some sports and activities (such as gymnastics and ballet) require extreme ranges of motion. However, if the muscles cannot control the limbs and joints throughout this extreme range of motion and the joint is lax, then the risk of injury is greatly increased.

The ability to control movement throughout its full range is often referred to as joint stability. A history of joint dislocations (for example, at the shoulder) or general ‘looseness’ reported by a sports performer indicates that the joint may be lax and potentially unstable. Joint stability may be improved by developing the strength and control of specific muscles acting at the joint. Malalignment Everyone has a slightly different joint configuration that falls within a normal range. However, when bones and joints develop in certain ways, they are often referred to as being malaligned.

At the foot and ankle, there are numerous shapes and configurations that a specialist (such as a podiatrist) may recognise and name. For example, at the ankle, there can be an increased ‘inward’ movement and a ‘rolling’ in of the foot, most noticeable when the foot contacts the ground during running. This is known as excessive pronation (hyperpronation). In turn, this means that the forces going through the foot, ankle, knee and leg change. As a consequence, some muscles need to work harder than they would do normally (usually those of the lower leg) to control and stabilise the foot and ankle.

In addition, some tendons are placed in lengthened or slightly twisted positions (such as the Achilles) as their muscles contract. The end result of superimposing training on these abnormal biomechanical movements and stresses can often be an overuse injury. Overuse injuries associated with excessive pronation include stress fractures of the tibia, inflammation of the tibial periosteum (‘medial tibial stress syndrome’ often referred to as ‘shin splints’) and Achilles tendonitis.

Furthermore, because excessive pronation can cause the lower leg to rotate inwards, this may change the forces that go through the knee and overuse injuries to structures of the knee (such as the patella tendon at the front of the knee, resulting in patellar tendonitis) may also occur. Similarly, certain knee joint configurations commonly referred to as ‘knock knees’ (genu valgus) or ‘bow legs’ (genu varus) plus specific hip and pelvis angles can increase the risk of overuse injury.

A hip joint that naturally rotates inwards (femoral anteversion) for example, or a pelvis that tilts forwards excessively (anterior tilt) can also contribute to overuse injuries of the knee and/or contribute to injuries to any of the many muscles attached to the pelvis, hip and thigh. A pelvis with excessive anterior tilt usually leads to an increase in the curve in the lower back (lordosis) and occasionally a compensatory curve in the opposite direction in the mid-spine known as a kyphosis.

However, there are many sportsmen and women with less than perfect joint mechanics who do not suffer from overuse injuries. The important point is that if you suffer an overuse injury, particularly one that re-occurs, you should seek appropriate treatment. Abnormal lower limb biomechanics can often be improved through specific conditioning and rehabilitation approaches and/or custom made inserts (orthotics) once an athlete’s gait and movement mechanics have been evaluated. Gender

The generally wider pelvis of the female compared with the male means that the angle of the thigh relative to the knee is different. In turn, this means that the relationship between the line of pull of the front thigh muscles (the quadriceps) and the angle of the quadriceps tendon (patellar tendon) also differs. The greater the angle between the line of pull of the quadriceps and the patellar tendon (known as the Q angle), the greater the risk of injury at the knee during running and jumping activities.

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