One of the important issues for anaesthesia/analgesia in bone fractures is sensory innervation of the periosteum. Thus, also innervation of adjacent joints as well as nerves entering the bone via nutritional foramina has to be considered (see below for reasons).

Historical glimpse on research for bone and periosteal innervation: It was as early as in 1784 that a ‘bone nerve’ entering the humeral diaphysis was described¹. First assumptions of nerves to the periosteum of tibia and fibula date back to 1791², such were proven (microscopically) in 1839³. More details of periosteal supply and mention of sympathetic filaments joining the above came up between 1843 and 1863^4–11. Finally, from 1868–1870, all nerves to long bones of upper and lower extremity were described and illustrated in incredible detail^{12 13}. Unfortunately, this does not apply to the clavicle, although first details of nerves to the periosteum on its sternal end can be found in a work from 1857 (dealing with articular nerves of the human body)¹⁴. Intriguingly, its complete innervation is still causing controversy!¹⁵

Necessary general considerations: the periosteum is richly innervated¹⁶. These fibers stem from different sources: 1. Terminal branches of motor nerves** (‘Muscle-Areas’ of periosteum). 2. Terminal branches of joint nerves (‘Capsule-Adjacent-Areas’). 3. Branches of cutaneous nerves (‘Muscle-Free-Areas’) and 4. Branches of nerves following nutrient arteries (‘Nutrient-Foramina-Areas’). Well-known examples are: ventral periosteum of femur for 1. (motor branches from the femoral nerve to three vasti). Periosteum of greater tubercle of humerus for 2. (axillary nerve). Periosteum of medial malleolus for 3. (saphenous nerve) and periosteum in the vicinity of the proximal nutrial foramen of radius (‘bone nerves’ from anterior interosseous nerve). [** it is crucial to mention that a motor or ‘muscle-nerve’ is in reality always a mixed nerve! ¹⁶]

If we apply the above general principles to the CLAVICLE, it comes to involvement of the following NERVES: a) the medial and intermediate supraclavicular nerves, b) subclavian nerve, c) lateral pectoral nerves, d) trapezius branch of cervical plexus, e) accessory nerve and f) suprascapular nerve. Unlike other bones (e.g. the fibula) the clavicle has a considerable ‘muscle-free-area’ (see above), especially anterior and superior: domain of a). the subclavius extensively attaches to the undersurface of the shaft: b). At the acromial end, c) (is also responsible for the ‘nutrient-foramen-area’) and d) are the main players. e) gets especially important if d) lacks. So both, undersurface and acromial end are classic examples of ‘muscle-areas’. Not so the sternal end, where again a) – the medial ones¹⁴- count. the long thoracic nerve, although repeatedly named¹⁷, is not involved! the same applies to the lateral supraclavicular nerves in most cases, as ‘lateral’ is just an ill-fated misnomer of newer terminology (their original description was Nn. supraacromiales!! ¹⁸). Finally, f) contributes to the periosteal innervation of the undersurface near the AC joint, representing the ‘capsule-adjacent-area’. However, supply of the capsule itself is predominant.

It is well known that sensory innervation in general has a wide range of individual variability^{19 20}. Not surprisingly, this is also true for the periosteum and may therefore be assumed for the clavicle too. Especially the ‘muscle-areas’ can stay as a case in point: we are well aware of the great differences concerning the area of major muscle attachments to this bone²¹. Accordingly, areas of periosteal innervation will adapt.

What are the practical consequences/options from a more detailed knowledge of innervation as shown here for ANAESTHESIA/ANALGESIA? To date, a combination of an interscalene (ISPB) or superior trunk (STBP) block with additional blocking the a) (as part of a cervical plexus block, CPB, — more often — or, unfortunately seldom, separately) is suggested²². Considering the above, this seems reasonable at first sight, because involved nerves from the brachial plexus are most often covered with an ISPB/STBP: b), c) and f). With a CPB, a) are included. But whatever combination, blocking nerves other than the above may easily happen (e.g. phrenic). on the other hand, important ones may be missed, e.g. d)! (The latter is most often not even mentioned anatomically.) From an anatomical standpoint, we could state it that way: best use a STBP block, taking care that it is done as close to the offspring of f) as possible; and combine with a (low volume) CPB if d) is considered important (e.g. involvement of acromial end of clavicle); combine with blocking a) separately (sparing the rest of the CP) if not. the author has other possible (unpublished) options in his quiver that will be presented at the very end of the lecture. These should be considered as an outlook and stimulus for further research, respectively.

References (more detailed bibliographic data for 1–14. available from the author on request)

1. J. Klint, commentatio anatomica de nervis brachii, Goett

2. J.L. Fischer, descriptio anatomica nervorum lumbalium, sacralium et exrtremitatis inferioris, Lipsiae

3. J.E. Purkinje, Jahrbücher der Medizinischen Fakultät, Krakau

4. G. Pappenheim, Müller’s Archiv, Berlin

5. G.L. Kobelt, Arnold’s Lehrbuch der Anatomie

6. B. Beck, über einige in Knochen verlaufende und an der Markhaut verzweigte Nerven, Freiburg

7. J. Halbertsma, Müller’s Archiv, Berlin

8. J. Engel, Zeitschrift der Wiener Aerzte

9. A. Kölliker, Verhandlungen der physikalisch-medizinischen Gesellschaft, Würzburg

10. H. v. Luschka, Die Nerven des menschlichen Wirbelkanals, Tübingen.

11. N. Rüdinger, die Verbreitung des Sympathicus in der animalen Röhre, Rückenmark und Gehirn, München.

12. A. Rauber, Nerven der Knochenhaut und Knochen des Vorderarmes und Unterschenkels, München.

13. A. Rauber, Über die Knochen-Nerven des Oberarm- und Oberschenkelknochens, München.

14. N. Rüdinger, Gelenknerven des menschlichen Körpers, München.

15. R. Schuitemaker et al., the Pecs II block as a major analgesic component of clavicle operation: a description of 7 case reports.

16. J.C.B. Grant (1948) in Method of Anatomy, Toronto.

17. D.Q. Tran et al., Analgesia for clavicular fracture and surgery: call for evidence. Reg Anest Pain Med (2013), 38(6).

18. C. Elze (1940) in H. Braus (Hrsg.) Anatomie des Menschen, 4. Band, Nn. supraclaviculares.

19. M. Keplinger et al., Cutaneous innervation of the hand: clinical testing in volunteers shows high laterality and inter-individual variability. BJA (2017), accepted Sept 19.

20. E. Gardner, the innervation of the hip joint. Anat Rec (1948), 101.

21. W. Platzer (2009) in Taschenatlas der Anatomie, Band 1 Bewegungsapparat.

22. O. Balaban et al., Ultrasound-Guided Combined Interscalene-Cervical Plexus Block for Surgical Anesthesia in Clavicular Fractures: a Retrospective Observational Study. Anesth Res Pract (2018).