Everything about musculoskeletal ultrasound

We as Radiologists and Physicians are particularly well clued to the concept of ALARA (as low as reasonably achievable) in terms of Radiation hazards awareness. Whilst investigating children for musculoskeletal ailments this gets translated into a very narrow range of availability of Cross-sectional modalities to arrive at a conclusive diagnosis. Radiographs of the affected part will always remain a very important investigation not just by virtue of its ease of availability but because of reasonable accuracy with which we get the bony pathology/detail. Despite the tag of "only one X-ray", we still need to carry a very conscious thought of harmful effects of radiation on growing, immature epiphysis. World over for the same reason the age limit of the Pediatric population has now been taken to 16 instead of 12 years.

Considerations of this order bring us closer to conclusively determining and weighing the advantages of a certain modality against the disadvantages it may extend and as clinicians, we need to offer the safest, quickest, radiation-free investigative modality to the patients in the management of pediatric illnesses, in particular, related to musculoskeletal pathologies.
Musculoskeletal ultrasound hence stands out as the modality of choice in Pediatric patients workup. In The US, the point of care management has taken on a new dimension where a super / sub-specialty is taking roots in form of ICU / emergency care through musculoskeletal ultrasound in neonates and have dedicated Consultants for neonatal MS-US for evaluation of pathologies related to bones and joint as soon as they are born.

When faced with a dilemma of choosing between the cross-sectional modalities in evaluation of musculoskeletal complaints in pediatric age group, the obvious choice begins with,

Plain Radiograph of the part affected: Adv: Ease of availability, reasonable bone detail and low radiation dose. Disadv: limited views, patient movement artifacts, masked soft tissue details, positional difficulties.

How can I tell good radiation exposure from bad radiation exposure?

The determination of radiation exposure being good or bad has more to do with how we each judge its benefit. Is it bad radiation exposure if you have an arm x-ray and it shows that no bones are broken? Or is that a good thing because now you know it is only a sprain? The reason for a person to receive a radiation dose from any source should be justified based on the expectation that the activity causing the radiation will benefit the individual exposed or society.

False negative situation too....!

CT scan: Poses the same difficulties as a plain radiograph since it is a radiation-based modality. In addition, fear of the gantry and radiation to the attendants needs to be accounted too, not to speak of the cost factor. Contrast reactions is an added concern if indicated.

People are exposed to ionizing radiation through medical imaging with X-rays, CT and nuclear medicine scans, including positron-emission tomography (PET). As there are no completed, large-scale epidemiological studies of cancer risk associated with CT, risk has been approximated using organ doses (or the distribution of dose in the organ) and application of organ-specific cancer incidence and mortality data derived from studies of atomic-bomb survivors on the peripheries of Hiroshima and Nagasaki. Risk estimates adjusted to take into account the greater use of CT since 2006 indicate that 1.5-2% of all cancers in the US may be due to radiation from CT. Estimating cancer risk from CT remains a contentious issue, and large-scale epidemiological studies are needed for a direct assessment of this risk
Concerns about exposure to ionizing radiation inducing cancer: Canadian Agency for Drugs and Technologies in Health. Appropriate Utilization of Advanced Diagnostic Imaging Procedures 2012.http://cadth.ca/media/pdf/PF%20DI%20ES%20Lit%20Scan%200%208.pdf.

Brenner DJ, Hall EJ. Computed tomography - an increasing source of radiation exposure. N Engl J Med 2007;357:2277-84. [PubMed]

MRI is safe and the ideal modality to be considered for MSK complaints. However, our needs to sedate the child and still remains clueless about the tissue-specific diagnosis add on to the difficulty of availability and cost factor. Bone evaluation remains suboptimal. Isotope scans have been considered but that is like killing are the ant with a cannonball!

Ultrasound, another imaging modality that does not use ionizing radiation, is the best modality for viewing dynamic images, separating solid from cystic masses and for viewing vascularity without the requirement for contrast media.

The Canadian Association of Radiologists. Diagnostic Imaging Referral Guidelines, a Guide for Physicians. Saint-Laurent, Quebec: Legal Deposit, Bibliothèque Nationale du Québec, 2005. (accessed 9 August 2012)

So when we consider ultrasound as the modality of choice, we are yet again reminded of the caveat: Bones are impervious to ultrasound. Fact, yet an as the loyal MS-US resource, we also know that most of the bones with pathologies end up creating micro cracks in the cortex which act as the perfect window to give us a peep into the pathological process leading to a conclusive diagnosis. Soft tissue and muscle planes are superbly accessible to evaluation by ultrasound. But what stands out above all other modalities is the clear differentiation between the joint, articular cartilage, epiphysis, growth plate, metaphyseal region and diaphysis in one sweep of the probe. Visualization of the ossific nucleus with the cartilaginous epiphysis and comparing it with unaffected other limb gives a radiologist a very strong clue to the pathology. DDH is a perfect example of this.

Ref: Government of Western Australia, Department of Health. Diagnostic Imaging Pathways. General Principles of Requesting Imaging Investigations 2011.

Added to this a friendly environment with the patient in the lap of parents (preferably less than 12yrs!), both the parents and child feeling safe and less intimidated by the surrounding environ, utilizing a non-radiation dependent modality, no possibility of contrast reactions (as color Doppler app. steps in perfectly in place of contrast study), ease of availability, cost-effective and interventional ease, if required saving time too. That it is, dynamic and real-time study, adds to the gamut of advantages that ultrasound stands for.

Last but not the least, one can repeat ultrasound for follow up studies as many times as the need may be without fearing any side effects.

The indications for which High-frequency ultrasound in pediatric age group can be requisitioned for, broadly are:-

1. DDH- Developmental dysplasia of hip


2. Joint effusions


3. Trauma
   
   
   
   • Negative Radiograph - occult fracture.
   
   
   • Epiphyseal injuries.
   
   
   
   


4. Transient synovitis.


5. Skeletal dysplasia (Limited )


6. Osteomyelitis (Acute )


7. Foreign bodies -commonest splinter.


8. Pulled Elbow/Shoulder


9. Abscess


10. Chronic osteomyelitis (Koch's)


11. Pulled Elbow/Shoulder


12. Pott's abscess


13. Multiple fractures in various stages of healing


14. Vascular malformation/Lymphangioma.

Epiphyseal cartilage appears as empty spaces on radiographs, seen filled up hypoechoic tissue on ultrasound for evaluation. Ossific nuclei are echogenic blobs surrounded by the hypoechoic unossified cartilage

In end, children must not be examined with the premise of being "small adults"

Ultrasound provides a safe, cost-effective and rapid means of assessing MSK abnormalities. This review has emphasized the role of ultrasound examination as the primary imaging investigation in the initial evaluation of MSK diseases. In most aspects of assessment of MSK diseases US is comparable to or even better than the expensive imaging techniques such as MRI. The combination of high-frequency probes and improved power Doppler technology provides a great opportunity to study image aspects of inflammatory conditions such as tenosynovitis and enthesitis that were traditionally considered difficult to image. Recent advances in technology such as three-dimensional ultrasound and contrast agents have potential to play a major role in early detection and monitoring of inflammatory arthritis in the future. The long learning curve remains an important limiting factor to the widespread use of US in routine clinical practice study.

Ref: Role of diagnostic ultrasound in the assessment of musculoskeletal diseases Pravin Patil and Bhaskar Dasgupta

Bianchi S., Martinoli C., Sureda D., Rizzatto G. (2001) Ultrasound of the hand. Eur J Ultrasound 14: 29-34 [PubMed]

Dr. Nidhi Bhatnagar

The author is M.D., Radio-diagnosis, Ph.D. ( Hony. Seoul) and Assistant Professor, General Secretary, Musculoskeletal Ultrasound Society, Dept of Radiologist and Ultrasonologist, She is a member Editorial Board, Radiology at Specialty Medical Dialogues.