In our previous large study performed on anteroposterior and lateral X-ray images of 2413 elbows of the Central European population there was no os supratrochelare anterius found unlike all other types of the accessory ossicle around the elbow joint [1], which make this accessory ossicle very rare and interesting when observed.
Simril and Trotter in 1949 presented probably the first well documented case of the os supratrochleare anterius in a dissected cadaver, seen in the both upper limbs of an Afroamerican male, in front of the coronoid and radial fossae of the humerus, approximately 24 mm wide (transverse plane) and 6 mm thick (sagittal plane) on the left (oblong shape), and 14 mm wide (transverse plane) and 8 mm thick (sagittal plane) on the right (nearly round shape), visible on the lateral radiographs and also confirmed by dissection. They used the term “os cubiti anterius”. Histological examinations revealed true, mature and viable bone, arthritic changes (frayed articular cartilage) and extension of subchondral bone into the cartilaginous matrix (no resemblance to either loose bodies of osteochondritis dissecans or other clinical entities resulting in a joint mouse were noted). Moreover, bilaterally there were arthritic changes in the whole elbow, long and narrow olecranon and the olecranon fossa of the humerus presented a transverse bony ridge [4]. In an appended note, they offered a personal communication of Edward A. Holyoke (Nebraska) who definitely encountered such case in an Afroamerican male in his laboratory in 1947 [4].
Schwarz in 1957 reported probably the first case of the os supratrochleare anterius diagnosed in a life patient, present in the both upper limbs of an American white female, within the coronoid fossa of the humerus, approximately 6 x 11 mm large, visible on the radiographs [5]. He used the term “antecubital bone/ossicle” but proposed a new term for this variant – “fabella cubiti“– based on the opinion that it is most likely a sesamoid bone within the brachialis muscle tendon and thus analogous to the fabella. In the Introduction, Schwarz offered a personal communication of Birkner who “possibly encountered similar two cases“ but no further data are available and we were unfortunately not able to find closer information [5].
Ochsenschläger in 1959 described a case of an aseptic necrosis of the bony septum between the coronoid and olecranon fossae of the humerus (supratrochlear septum) in the left upper limb of a German female. The original X-rays are neither of good contrast nor performed in standard
projections. After application of previously defined three radiographic criteria for accessory bones it fulfils two out of three: ovoid and regular shape, and smooth margins. The third criterion of regular cortical-to-medullary ratio cannot be assessed duo to the low quality of radiographs. Nevertheless,
it is probably a case of the os supratrochleare anterius, although this conclusion is not fully certain [6]. Gudmundsen and Østsensen in 1987 reported three cases (collected in previous years) which they considered to be the potential os supratrochleare anterius. Unfortunately, their conclusions are based on low quality or even missing radiographs. The first case (male) featured three additional bony particles in the coronoid fossa of the right humerus (no X-ray available) after 7-years-period of increasing pain and limitation of motion and then a suffered minor trauma. The second case (male) one year after minor trauma presented with increasing pain and limitations of motion and small oval ossicles were removed from both the coronoid and olecranon fossae of the humerus (X-ray of low quality do not allow us to decide whether the ossicle is pathological or accessory). Third case (male) after 20-years-period of pain and disturbed motion with no history of trauma (no X-ray available) featured a large ossicle with clear bony structure in the coronoid fossa and two small ossicles in the olecranon fossa of the right humerus. Unfortunately, this last case which is probably an example of the os supratrochleare anterius but it cannot be verified on the X-ray image [2].
We stated in our previous article [1] that “three cases of os supratrochleare anterius are described in the literature” [3] but this information was based on a wrong translation of the original Spanish text and no such is reported in their work. After recent deeper analysis we can in total present two well documented bilateral cases [4, 5], one probable unilateral case [6], one unilateral case with scarce data and no image [2] and three potentially bilateral cases reported by personal communication with neither evidence nor image [4, 5]. There have been no recent reports from 1987 to 2022 which makes this anatomical unit very rare (see Table 1) – 13 bones in 8 individuals (including ours) – and thus important to point at to get larger medical public acquainted with such existing anatomical variant. All three well described cases ([4, 5]; ours) were intra-articular which was observed directly. The joint capsule inserts onto the humerus above the coronoid fossa that is why the entire fossa is intra-articular. However, the accessory ossicle may be imbedded within the capsule or rests on the external surface of the capsule and still may produce similar picture on X-ray [5]. Based on this opinion, the imaging method of choice to visualize and differentiate this accessory bone is definitively the magnetic resonance.
Differential diagnosis
It is necessary to thoroughly consider each case of bony fragment found around the elbow. Either it is an accessory bone/ossicle (typical ovoid shape, smooth margins, cortex ratio) or a pathological structure (quite irregular shape and size, calcifications, can be multiple). The closest accessory bones are the os supratrochleare posterius, much more common, located within the olecranon fossa of the humerus and first described by Pfitzner in 1892 as “sesamum cubiti”, and the os sesamoideum brachiale within the insertional tendon of the brachialis muscle, also considered a separated/persistent ossification centre of the coronoid process of the ulna by some authors [5, 7, 8] and called “accessory coronoid ossicle” [9].
These three bones located very close to each other can be mistaken in the anteroposterior projection of the X-ray examination and they can also cause similar symptoms such as limitation of elbow range of motion and pain, and often have to be surgically removed [9].
Both the ossa supratrochlearia have been postulated to arise from separate ossification centres [9]. Another theory is that the os supratrochleare is as an accessory “bone nucleus” separated from the olecranon [10].
The pathological situations comprise cases of the osteochondritis dissecans of the supratrochlear septum of the humerus but also other pathological processes (degenerative changes, occult and avulsion fractures, gout, Panner's disease, synovial chondromatosis, primary tumours – chondrom, nidus of an osteoid osteoma – or metastatic tumours) which may feature similar clinical symptoms (pain, limited movements). Entrapment neuropathy concerning the ulnar nerve around the elbow, bursitis, tendinitis, epicondylitis, entesopathy may also coexist with the bone. All these situations can mimic an accessory ossicle and it is necessary to thoroughly judge each case. For critical and uniform decision process we have created a three-step-protocol. Morphological features of a true accessory bone were defined as: 1) regular ovoid shape; 2) smooth margins; and 3) regular cortical to medullar ratio throughout the circumference [1].
Limitations
First limitation is done by the terminological inconsistence in existing literature concerning both the accessory ossicles and pathological structures which may cause that some relevant article have been skipped. Second limitation is the low quality of X-rays in older articles which did not allow us to clearly differentiate between the accessory and pathological structures. Third limitation is the difficult application of our three criteria as there often appear degenerative and traumatic changes influenced by avulsion of the coronoid process of the ulna as well as the olecranon. Fractures of the os supratrochelare posterius have been described [10].