Introduction:
Side strain is a condition diagnosed clinically, characterized by a sudden onset of pain and localized tenderness along the rib cage. This injury is commonly associated with sports such as cricket, javelin throwing, rowing, and ice hockey. While it is relatively rare, it is particularly impactful for elite athletes as it can lead to their exclusion from competitions and require an extended period of recovery.
Through MRI examinations of patients with side strain, we have identified that it typically results from a tear in the internal oblique muscle where it attaches to the rib or costal cartilage. The objective of the research was to document the imaging characteristics observed in athletes with side strain injuries.
The internal oblique muscle is part of the outer layer of the anterolateral abdominal wall, situated beneath the external oblique muscle. Its fibre originated from the inguinal ligament, iliac crest, and thoracolumbar fascia, with posterior fibres running upwards and forwards to attach to the lower four ribs and costal cartilages, eventually merging with the internal intercostal muscles. The upper fibres form a distinct super-medial border.
Clinical presentation:
A 27-year-old cricketer presented with complaints of pain and point tenderness at the right lateral thoracic wall following the match. So, the following MRI is taken.
Discussion:
Rib stress fractures previously observed in athletes like rowers, swimmers, golfers, and canoeists are believed to occur from repetitive strain on the internal oblique and serratus anterior muscles. These fractures typically manifest in the fifth to ninth ribs anterolateral to posterolateral regions. Additionally, elite ice hockey players may experience external oblique muscle strains in the groin, with timely diagnosis and treatment leading to swift recovery and restoration of full function. Our research indicates that side strain results from an acute tear in the internal oblique muscle where it attaches to the under surface of the ninth, tenth or eleventh rib. Athletes usually present with acute pain in the thoracic wall’s anterolateral or posterolateral regions, with movements resembling the initial injury often reproducing the pain along with deep breathing exacerbating it.
The mechanism behind internal oblique muscle strain involves sudden eccentric contraction leading to fibre rupture. Activities like cricket bowling, rowing, swimming, and golf involve muscle lengthening followed by eccentric contraction, making the muscle susceptible to tearing. MRI proves to be a sensitive tool for diagnosing side strain injuries, revealing abnormalities in patients with suspected muscle tears. Sagittal oblique muscle images derived from axial scans are particularly valuable for assessing the extent of muscle damage. Notably, technical considerations such as diaphragmatic splinting and the orientation of muscle fibres aid in the accurate diagnosis and differentiation between internal and external oblique muscles. Despite limitations like the absence of surgical or pathological confirmation, MRI findings correlated with patients’ symptoms and pain locations. Most patients returned to competition without functional impairment or strength loss after a recovery period of 6 to 10 weeks. Surgical intervention was required in one case to remove scar tissue, highlighting the importance of monitoring healing and muscle quality post-injury. In summary, side strain is an acute injury resulting from internal oblique muscle tearing, typically well-recognized by clinicians.
Conclusion:
MRI is capable of outlining the layers of muscle that form the lateral abdominal wall. Side strain injury occurs when the internal oblique muscle tears away from the under surface of one the lower four ribs or costal cartilages. MRI can pinpoint the location of the muscle tear, assess the extent of the injury, and track the healing process.
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Dr Kanagasabai Kamalasekar
Consultant Radiology
Kauvery Hospital, Chennai
Dr. Deepan
Post Graduate Resident – Radiology
Kauvery Hospital, Chennai
