Rib stress fracture in rowers

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Introduction

Stress fracture occurs when a bone fails to withstand repetitive bouts of mechanical loading. This loading results in bone strain, which on its turn may cause micro-damage. With normal physiological loading this micro-damage will be healed through the bone remodelling. With repetitive loading, however, an imbalance between the remodelling and micro-damage may occur, causing a stress fracture.

Epidemiology/Aetiology

Rib stress fracture is a frequently occurring pathology in the rower’s community, with an incidence of 6 to 12%. There are 2 sorts of causes which can lead to rib stress fractures: on the one hand there are factors which influence the rib loading, on the other hand, there are factors which influence the reaction to the rib loading.

Factors that affect rib loading

3 characteristics are distinctive to the loading stimuli, which determine the formation of micro-damage :

• The magnitude of load applied
• The rate at which the load is applied
• The number of loading cycles

Microdamages follow a threshold-principle: an increase in bone strain above a certain level leads to an increase in microdamages . Bone strains which are induced over a shorter period result in a significant increase in the development of microdamages. It could be concluded that factors increasing the magnitude and rate of rib loading contribute to the formation of microdamages, resulting in stress fractures. While rowing, there is only a small impact on the ribs therefore microdamages are the result of other sources than the forces associated with impact loading. Following sources will be discussed below: muscles, joints, rowing technique and rowing equipment

Muscles

• Abdominal muscles
  Pressure applied by the abdominal muscles on the sternum and lower ribs result in a loading of the entire ribcage.
  Radiological evidence shows a large amount of ribcage compression in the final stage of rowing, caused by the abdominal muscles .
• Serratus Anterior
  SA protects the ribs by resisting the abdominal rib loading at the end phase. Fatigue of the SA results in a decrease of force production, which leads to a decreased buffering of power applied by the abdominal muscles.

Joints

The costovertebral and costotransversal joints are the most important joints in the ribcage and form a mechanical connection between ribs and thoracic vertebrae. This mechanical connection enables the ribcage to provide protection to the thoracic region by redistributing the transmitted forces to the thoracic spine.

Technique and equipment

• Oar: since the 90’s, smaller and shorter oars made out of carbon are used. These oars are easier to use, but result in a larger loading since a greater force is generated at the handle when applying the same load. This exposes the ribs to a greater level of strain.
• Boat: larger boats increase the development of stress fractures. The larger the boat, the larger the water resistance and the bigger the oars needed to provide the necessary resistance due to leveraging.
• Positioning: bow rowers have a smaller chance at rib stress fractures because they have to apply a smaller force, at a lower rate.

Factors that affect the response to rib loading

The ability to resist loads and in that way limit formation of microdamages (skeletal factors):

1. The first skeletal factor which triggers the formation of rib stress fractures is the bone geometry. A narrower bone leads to a smaller cross-sectional area moment of inertia, which is an important factor in the ability of a bone to resist bending .
2. Second important skeletal factors are the properties of the bone material. A low bone density causes a decreased resistance against fatigue, resulting in the development of stress fractures.

The ability of the skeleton to recover from microdamages (training and gender):

Training

Rapid changes in the training modalities can interrupt the relative homeostasis between microdamages and the recovery of microdamages. This causes an increase in the amount of active remodelling units, which will result in a decrease of bone elasticity. This will result in an increased strain, causing an increase in microdamages.

Gender

women run an increased risk at stress fractures at any location of the body . This can be explained by gender-specific endocrine factors which alter the recovery response of the body to microdamages. We see that physically active women have a higher prevalence in menstrual disturbances causing a decrease in bone turnover and formation.

Characteristics/clinical presentation

The symptoms can range from a generalised pain in the rib area, persisting with activity and gradually becoming more specific, to a palpable bony callus with increased pain when pressure is applied. In the worst case the rower experiences pain when breathing deep or rolling over in bed. The fractures are often located on the antero- or posterolateral side of the ribs.

Diagnostic procedures

A bone scan or an MRI are the best ways to detect a stress fracture, although it may take a few months before there is real evidence of callus formation. A sonography or an RX can also be used to diagnose.

Physical therapy management

• The treatment consist of 4 up to 6 weeks of relative rest, where the rower is allowed to do everything within his pain threshold.
• Exercises on stability are very important.
• Strengthening exercises for the serratus anterior are recommended. Normally they should lead to increased power and additional loading on the rib cage.
• In the case of costovertebral and costostransverse joint stiffness, passive mobilisation of the thoracic spine and costovertebral joints is advised as treatment.
• Rowing is not advised, since it is often painful and since it is the cause of the fracture. When working on an ergometer, one must see at it carefully that the old flaws in technique are handled.
• Application of ice will diminish the pain, but does not heal the stress fracture.
  

Technique needs to be continuously fine tuned. Often, small flaws in technique can be a cause or related to the of stress fractures. Some examples of most occurring technique faults:

1. Bent arms: this occurs when the rower starts the leg drive with pulling theirs arms rather than pushing with both legs resulting in an increase of lactic acid in the arms and reduce of the oxygen supply
2. High pull: this occurs when the rower pulls the oar too high during the pull phase which results in their back leaning too far back and a higher energy consumption
3. Bending backwards too early: this occurs when the rower starts to lean back too early in the drive phase instead of driving back with his legs resulting in a weaker movement
4. Over-reaching: this occurs when the rower comes back in and stretches too far forwards pushing their shins passed the vertical position. This results in a weak starting position for the following drive phase, increasing the injury risk.

Rowers need good basic aerobic condition, mobility and flexibility of the trunk, arms and legs, and physical strength, speed and endurance. In general, the training programme consists for 60 to 70% of aerobic training and 30 to 40% anaerobic training.

Exercises

1. Serratus Strengthening: before starting the exercise it is very important to ensure that the patient is able to maintain the scapula in the proper position. Secondly we ask the patient to place his/her both hands, shoulder width, against the wall in an extended arm position. Then instruct the patient to pull the 2 margo medialis scapulae to each other and return to starting position. the intensity could be increased by either adding more repetitions or modifying the exercise into a weight bearing positions by placing both hands on the ground in a kneeling position. In the following stage we ask to the patient to lie down on his/her back, holding 2 dumbbells in hands with extended arms and perform scapular protraction. Starting with a light weight/high repetitions then progressing to heavier weight/few repetitions.
2. Furthermore, pull down exercises could be used: patient holds the bar with two hands in extended arm position. Trunk and arms should form an angle of 100° in starting position with legs in 15° flexion. We ask the patient to pull the bar in the direction of his thighs and back up. The back up phase should take a little longer (3 seconds) than the pulling phase (2 seconds).
3. Dumbbells pullover: patient lies down with his upper back across a bench and his body perpendicular to the bench. Both arms are extended above chest holding a dumbbell with both hands. The patient should lower his/her arms above the head and reverse the movement on the way back up. Using a medicine ball instead of a bench or raising the weight may increase the difficulty of this exercise.

References

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