Side strain

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Side strain or oblique abdominal muscle strain refers to a tear or strain type muscle injury of the oblique abdominal muscles seen in certain sports.

Epidemiology

Side strain is a rather uncommon injury mostly seen in certain athletes .

Risk factors

Sports or activities that increase the likelihood of sustaining a side strain include :

  • javelin throwing
  • cricket
  • ice hockey
  • golf
  • swimming
  • bowling
  • rowing

Clinical presentation

The main symptom will be a sudden onset of pain in the anterolateral or posterolateral thoracic wall associated with point tenderness. Pain is typically worse with deep inspiration and can be re-created by movements similar to the causative motion .

Pathology

The pathological correlate of a side strain injury can be defined as a partial or complete discontinuity of muscle fibers of the internal or external oblique abdominis muscle along their course or at their insertion site.

Mechanism

The underlying mechanism is supposedly a sudden eccentric contraction associated with initial muscle lengthening followed up by a superimposed contraction.

Location

This type of strain injury has been most often reported for the internal oblique abdominis muscle at its insertion of the 9 to 12 rib or the costal cartilage. However, oblique abdominal muscle injuries can also happen at other locations and were reported in one case for internal oblique and external oblique abdominis muscle at the iliac crest .

Radiographic features

A typical radiographic feature of muscle strains is fluid-signal tracking along and around the muscle fibers. Side strain injuries can be suitably assessed with ultrasound and MRI. Plain radiographs and CT might be obtained to search for or rule out associated injuries or differential diagnosis.

Plain radiograph

Plain radiographs of the ipsilateral hemithorax might be obtained to rule out a fracture.

Ultrasound

A side strain injury can be detected on ultrasound by hypoechoic or anechoic gaps at the costal or chondral attachment site and a loss of the normal fibrillar pattern.  In addition, hypoechoic or anechoic areas may be found between the internal and external oblique muscles reflecting hemorrhage .

During the acute phase of the injury, there should not be any increased neovascularization on color Doppler.

CT

A CT might be only obtained to rule out rib fractures or to rule out differential diagnosis e.g. in case a retroperitoneal origin of flank pain is suspected.

MRI

Side strain injuries can be detected with MRI, furthermore, the severity of the injury can be outlined and healing can be monitored. Sagittal oblique images are apparently most suitable for evaluation .

Side strain injuries can be graded into partial or complete tears. Partial tears can appear as feathery fluid-like signal intensity on fat-saturated T2 weighted or intermediate weighted images as well as fluid tracking between the myofibrils.  A complete tear can be assumed when a discontinuity of the fibers is present along the proximal muscle fibers or a detachment at their costal or costochondral insertion site .

Radiology report

The radiological report should contain a description of the following:

  • location and extent of the muscle strain
  • affected muscle
  • associated injuries

Treatment and prognosis

Muscle strains can be managed conservatively with activity modification and pain control followed up with physiotherapy and rehabilitation aimed in regaining mobility and strength .

Side strain injuries can go along with a prolonged convalescence of up to 10 weeks, which precludes athletes from competition during that period .

Differential diagnosis

The differential diagnosis of side strain includes the following:

​See also