Mind over matter: knee and shoulder injuries are avoidable

Poor technique, biomechanics, deconditioning and ageing: knee and shoulder injuries are avoidable

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Whether because of poor technique and biomechanics, deconditioning or ageing, many knee and shoulder injuries are avoidable

When we start exercising, it’s our knees and shoulders that are most susceptible to injury. This is confirmed by a review of the top 100 cited articles in clinical sports medicine, which shows a heavy leaning towards the topic of knees and shoulders.¹ But if we take the time to understand why these injuries occur so commonly, we can often prevent them.

KNEES

The knee has a complex range of movements within the restrictions of a hinge joint, in addition to suffering the stresses of weight bearing. Hence it is no surprise this joint is such a common site of injury. Most knee injuries are chronic minor irritations that develop slowly, and are often ignored. It is this chronic low­ grade irritation that makes knee injuries so potentially sinister, and healing can be protracted.

We know that age, body weight and previous injury need to be factored into the advice we give about physical activity. Older age and a greater BMI are independently associated with accelerated knee osteoarthritis, and increase the risk of injury.² So what can we tell our patients?

High-impact options such as burpees (a combination of squats, press-ups and jumps) and tuck jumps and/or high intensity interval training are an obvious no-no when trying to go from older, overweight and unfit to Member of the Month at the local gym.

The result could be patellar tendonitis/bursitis – ‘jumper’s knee’ – essentially, an overuse injury in a joint that has exceeded its stress capacity.

Significant factors in knee injury predisposition are an individual’s balance and level of motor skill. True of both children and adults, these factors are, however, not clear­cut. Research indicates that poor balance is a consistent predictor of traumatic injuries.

When it comes to good motor performance – core stability, vertical jump, shuttle run – there is a positive association with both traumatic and overuse injuries, and a negative association – assessed by single leg hop – with traumatic injuries.⁴ This study indicates there’s a mix of important influences on injury risk that need to be factored into the advice and support patients are given about how to exercise. This is particularly so when people are starting out.

As compared what some weekend warriors appear to believe, possessing great physical ability and confidence is not a safeguard against injury. This same study found that previous injury doesn’t guarantee that people subsequently take more care when resuming exercise following a further injury. This disconnect between previous experience and subsequent action is an important warning sign that can highlight those very susceptible to significant injury if not appropriately guided.

In addition to co-ordination and attitude, individual biomechanics can have a massive effect on injury. This muddies the water when it comes to group-based physical activity because people have different needs based on factors such as body shape, flexibility and the relative balance of muscle development. Chondromalacia might technically be the result of roughened knee cartilage and a poorly tracking patella.

However, it’s the upstream causative elements of this condition, such as weak gluteal muscles and or a tight iliotibial band, that need to be considered. This means providing careful advice about how to reduce lower limb impact during those activities requiring knee flexion. Such tweaking can often be overlooked or difficult to achieve in group-based activities so raising individual awareness is key.

Anterior cruciate ligament (ACL) injuries usually have a traumatic onset but this may be as simple as jumping or twisting when changing direction, or an awkward fall. While the relationship between non-contact anterior cruciate ligament injuries and the underlying biomechanics are still unclear, researchers have identified certain patterns of skeletal alignment as predictors of increased injury risk.

A study of 53 non­contact anterior cruciate ligament injuries among male athletes found the injury was significantly correlated to decreased range of motion in ankle dorsiflexion, hip internal rotation and increased hip anteversion.⁵ In another study, analysis revealed that higher ground reaction force, lower hip flexion and higher hip extension movement were correlated with higher peak strain. In short, it was intrinsic anatomical factors that accounted for most of the variance in strain. With respect to extrinsic variables, it was hip and trunk flexion angles that were the most significant contributors to the strain.⁶

These studies add further grist to the one-size-does-not-fit ­all mill. They emphasise the importance of taking the time to understand each person’s starting point for exercise, by knowing what’s happened in the past, and then carefully mapping out the best options going forward.

SHOULDERS

Shoulders sacrifice stability for mobility, which makes this joint particularly vulnerable to injury from trauma, overuse or chronic degeneration. Rotator cuff injuries, especially involving the supraspinatus muscle, are so common that this injury has its own smartphone app.⁸

Overhead movements such as those involved in swimming, throwing, and shoulder presses are the main culprit in rotator cuff injuries. The result is a painful tendinopathy. One expert, physiotherapist Sonja Schulze⁹ distinguishes between two types of tendinopathy. Primary tendinopathy is due to overuse or incorrect technique, where repetitive or end of range positions have constantly loaded the rotator cuff.

This type of injury is preventable. Secondary tendinopathy is a result of inefficient shoulder biomechanics, shoulder instability or anatomical abnormalities. Unfortunately, these may not be realised until after an initial injury has occurred. These can be treated but require an informed exercise strategy to ensure recovery and prevent reoccurrence.

Optimal shoulder performance requires the balanced activation of muscles responsible for strength, mobility and functional stability. However, shoulders are frequently exercised in a very unbalanced way, which predisposes to injury. Often there is a strong bias in favour of the better known ‘global’ muscles, such as latissimus dorsi and pectoralis major, while the ‘helper’ muscles, which include the supraspinatus, infraspinatus, subscapularis, and rear deltoid, essential to keeping the joint in needed balance with the global muscles, are somewhat neglected.

By focusing exercises on these large muscles of the chest and back, the shoulder becomes internally rotated. The smaller external rotators, such as infraspinatus and rear deltoid, require only the use of light weights and resistance bands. These types of exercise are relatively easy to do but lack the grunt and showmanship of the loaded up lateral pulldown in the gym. However, strengthening these lesser-known muscles is the key to better exercise performance and injury prevention.

Adopting a balanced approach to exercising the shoulder by safely including the rotator cuff muscles provides all-important shoulder joint stability.¹⁰

Such balanced activation of these muscles centres the humeral head into the glenoid fossa, facilitating efficient force during arm elevation and overhead activities.¹¹ Failing to learn good techniques at the start of a sport or exercise can lead to the inability to stabilise the shoulder girdle. This contributes to the commonly seen elevated or hunched shoulders, both during activities of daily living and exercise. Learning how to ‘set’ the scapulae is essential to improving scapula stability, which reduces neck and back pain, and ensures the right muscles are activated to the right degree during exercise. For example, the aforementioned lateral pulldown exercise should see movement from the shoulder joint not the shoulder girdle, so that the target muscles latissimus dorsi and teres major are correctly activated.

Even if an exerciser’s focus is a throwing sport or increasing upper body muscle mass, it’s important to understand that the human body does not compartmentalise. The shoulders are inextricably linked to the rest of the body, so the torso and lower limbs must be trained too. Adequate trunk and leg flexibility, strength and power must be ensured as over 50% of shoulder force is generated through the trunk and legs. A good exercise program will combine functional movements such as extension and rotation of the hips and trunk with the shoulder complex.

In addition to linking the upper extremity and trunk, the scapula provides insertion points for several muscles involved in scapulohumeral and scapulothoracic motions.¹² During rotational movements, a coordinated balance between mobility and functional stability is essential for the safe transmission of the high forces placed on the shoulder complex.

Repetitive, vigorous activities have the potential to chronically overload the rotator cuff causing a kinetic chain “breakage”.¹³ The combined effect of glenohumeral internal­rotation deficit, rotator cuff strength imbalance, scapular dyskinesis, thoracic spine stiffness and hyperkyphosis, lumbar core instability, and hip range of motion and strength deficits, can cause a “cascade to injury”.¹⁴ The high occurrence of rotator cuff injuries highlights the need for better implementation of sound training strategies, injury prevention and rehabilitation. GPs are an important link in this injury prevention chain.

Rachel Livingstone is Director, The Health Hub, Sydney

References

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2. Dr. Benjamin Koh. Exercise Scientist and Sports Doctor. University Of Technology, Sydney.
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