Sonographic Anatomy or How Diagnostic Ultrasound is Becoming a Therapeutic Tool

Many physicians still believe it is lege artis to perform invasive pain therapy blind, simply based on “medical intuition”. The results that can be expected are usually limited [1] and are primarily related to placebo effects [2], with the procedure often being better described as “art” than precision, and a comparatively larger number of complications like (transient) neurological deficits, bleeding, severe ischemia (rarely even with spinal cord injury), and infections can be expected [3]. This is apparently also the reason for the classification of focal instillations as inferior in algorithms and guidelines for pain management. They are categorized as secondary to most other procedures and treatments and are described as an unreliable “last option” [4] [5].

The most important quality step was therefore the development of image-guided navigation: first fluoroscopy-guided and later CT-guided. Both options resulted in a striking improvement in the precision and reliability of focal instillations thus also yielding predictable effects, albeit with the use of ionizing radiation centered on bony landmarks [6]. The realization of this potential allowed focal-interventional pain therapies to become something for which they should be appreciated: precise procedures treating pain with marked clinical effects to focal high treatment doses without causing significant systemic side effects (as e. g. in the case of corticosteroids).

Compared to blind injections, the use of bony landmarks means a significant increase in quality (also in ultrasound; see below). They can be clearly defined, are easy to understand, and build confidence. For example, in cases of periradicular pain therapy (PRT) in the axial skeleton, they are sufficiently precise for reliable navigation [7]. However, even these landmarks only indicate relative proximity to the treatment site, with the actual target structures like nerves or nerve roots only being indirectly identified. However, these landmarks are identified in a standardized manner as e. g. in the case of bony neural foramina since these define the location of nerve roots and thus act as 1:1 indicators for precise targeting [7].

Many years ago, pioneers began using ultrasound (with actually low visualization power compared to today) to define and reproduce bony landmarks on B-mode images and thus to develop corresponding radiation-free imaging guidance in real-time. By and by the same quality and effectiveness as the gold standard CT was achieved and proven [8] [9] [10] [11], thereby offering equally reliable but incomparably faster and more efficient guidance, for example for PRT and focal facet joint instillations in all relevant segments of the spinal column. The significant equipment costs for fluoroscopy and CT were thus avoided, and ultrasound-guided focal pain therapies were conducted using standard equipment and presets directly as bedside-procedures and first-line procedures [8] [9] [10] [11] [12].

Technical developments of ultrasound imaging presented a fundamental challenge to ultrasound adopters imaging the musculoskeletal system, resulting in (micro-)anatomical knowledge becoming extremely more relevant: (micro-)anatomical structures or (micro-)topographies of smallest structures, which now became visualized for the first time, like nerves (branches), ligaments, tendons, muscles, and fascia including their functional interactions. Therefore, it has since become important for users to be familiar with countless structures in more and more increasing detail: the combination of growing precise knowledge and previously unimagined sonomorphological precision lastingly changed the requirements and even the terminology and the perceived “state of overall knowledge”. Pain or “disorders” previously dismissed as “possibly functional” were following, defined by high-frequency ultrasound, often also as morphological changes and thus understood for the first time, and pathological issues suspected to “function” were able to be provoked and thus comprehensibly defined. Particularly with respect to this “observing of functions and motions” in the musculoskeletal system, ultrasound imaging continues to be unrivaled [13] [14].

However, there is still further potential. Ultrasound is increasingly being used for diagnosis with previously unforeseen accuracy, for focused treatment of pain, and recently even as a primary surgical tool. Since the guidance of instruments beyond instillation needles in real-time is no longer a significant problem with robust, anatomical knowledge of a surgical area, these developments were conceivable. However, their sweeping success has still been surprising. In cases in which the release of pathological ligaments or fasciae is known to represent a lasting therapeutic solution, ultrasound imaging, combined with tiny stab incisions to insert special tools, yields results at least equal to open surgery performed by a surgeon in the stricter sense. Casually the further course of healing is also optimized. In contrast to relevant surgical counterparts, postoperative time-to-work is optimized, function is restored almost immediately, and patients can promptly resume at least their usual daily tasks. Ultrasound-guided carpal tunnel and cubital tunnel surgery, ultrasound-guided release for trigger fingers, and the correction of specific types of tenosynovitis are thus assumably first steps with the promise of more [15] [16] [17] [18] [19]. In any case, these procedures have already been able to greatly expand the spectrum of ultrasound-guided interventional treatments.

But what will become of targeted pain therapy? There are also new developments here. Damage to even the smallest cutaneous nerves [14] are presently visualized, and a clear morphological cause of symptoms can be determined [20] [21]. These nerves can be successfully blocked and/or focally treated in a highly targeted manner with incomparably low risks and impressive outcomes [22] [23] [24]. In addition to these usually corticosteroid-based instillation therapies [25], tiny thermo-ablation probes (with dimensions > 20 gauge), allowing ablation of small nerve branches [26], are currently providing new options. New developments in the understanding of pain-physiology and pain-processing are critical and allow optimization and adjustment with respect to more lasting ablation therapies (i. e., thermo-ablation, pRFA) basing again on very high accuracy, thereby promising improvement of therapeutic options for patients with very long lasting chronic pain [27] [28] [29].

And there is still more potential to be explored. We are excited to see where this exciting journey with “therapeutic ultrasound” will take us!

 

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Univ. Prof. Dr. Hannes Gruber

OÄ Dr. Elisabeth Skalla-Oberherber

Ass.-Prof. PD Dr. Alexander Loizides

Conflict of Interest

The authors declare that they have no conflict of interest.

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Publication History

Article published online:
02 April 2025