Next to hand fractures, the hand tendon injuries are considered the most common hand injuries with open and penetrating injuries specifically reported as the commonest type of injuries rather than dull avulsions and disrupted pulley system .
Hand tendon injuries are considered serious injuries especially if involving the flexor tendons and need to be carefully evaluated and skillfully managed by reconstructive hand surgeries, so a meticulous imaging workup should be employed for this purpose including the HRUS or MRI examination; the former has the advantage of being cheaper and could be complemented by dynamic maneuvers; additionally, a side to side comparison to the contralateral unaffected hand could be performed [15, 16].
In concordance with Hall study  which had included a sample of population in an age group close to our study population, there was male gender predominance in both studies and this could be attributed to the more frequent male involvement in the manual occupations.
Hand tendons tears were present in 56.7% of our cases, of which 33.3% had a complete tear while 23.33% had a partial tear; this was matching Lee et al.’s study that had reported a predominance of the full thickness tears in their cases by ultrasonography and had been confirmed during surgery .
Regarding the type of tendon affection, our study had shown more affection of the flexor tendons (63.3%) (Fig. 4), mismatching the Hall study, where the extensor tendon injuries were more frequently seen .
In another study by Lee et al., among 24 patients, the most commonly affected tendon was the extensor pollicis longus tendon, being found in 11 of their patients, where the thumb was the most commonly affected finger ; we do not have an explanation for such difference between the three studies; however, there were no selection criteria for our patients regarding the type of the tendon affection.
By HRUS, our results had revealed that the tendon tears were the predominating features among injuries (17 cases; 56%) followed by the abnormal mobility (15 cases; 50%), and then a gap between the torn tendon ends (10 cases; 33.3%); post-reconstructive tendon integrity was present in 13 cases (44%), while re-tear (re-rupture) had existed in four cases (13.3%). A tendon callus was present in only two cases (6.66%) (Figs. 3 and 6); these findings were greatly matching Lee et al.’s study, where they had found that among the sonographic findings of tendon injuries, a tendon tear was the salient ultrasound finding, being noticed in 23 of 24 cases followed by the gapping tendons (18 cases), and then the abnormal motion (14 cases). The decreased echogenicity of the tendon was seen in 11 of 24 cases. Out of all (24 cases), only nine cases had a tendon callus, while tenosynovitis was present in seven cases .
Contradicting Lee et al.’s study, the hypoechoic areas were seen only in four of our cases (13.33%) compared to 11 in theirs; our explanation for this mismatch is attributed to the timing of the postoperative scanning, where the immediate postoperative examination could reveal some transient ultrasound findings, as the presence of peritendinous hypoechoic thin rind of simple fluid (described as minimal simple tenosynovitis) had faded spontaneously after a few days on ultrasound follow-up examination and this was considered an acceptable postoperative reactive process; also, we had noticed that the presence of intra-tendinous hypoechoic areas but with no associated fiber discontinuity or abnormal mobility of the affected tendons had disappeared completely and spontaneously on follow-up examinations; thus, it was considered a reactive process or subsiding postoperative edema.
However, any persistent intra-tendinous hypoechoic areas, especially if associated with abnormal mobility or fiber discontinuity, were considered postoperative significant findings and could be a partial tear that might necessitate a follow-up examination.
Many works of the literature had reported superiority of the ultrasound examination in the assessment of hand tendon injuries especially in the postoperative evaluation and in the detection of tenosynovitis with a diagnostic capability that may exceed the computed tomography examinations and might emulate the MRI with contrast, as it can alleviate the metallic artifacts that are frequently encountered in postoperative orthopedic patients [19,20,21].
In a consensus study based on a Delphi process done by the European Society of Musculoskeletal Radiology (ESSR), experts of musculoskeletal imaging had recommended US as the first-choice technique for assessment of hand and finger injuries, including the intrinsic muscles and bones when the other imaging modalities could not be used and for foreign body detection [22, 23]; moreover, the consensus has been recently updated in the image-guided interventions as well .
Intra-tendinous foreign bodies were found in two of our cases by ultrasound examination, and this was considered an important finding, as the retained foreign bodies (Fig. 4) can induce inflammatory reaction and superadded soft tissue infections might supervene . However, within the repaired tendons, the surgical materials (sutures and staples) could be seen (Fig. 3) and should be carefully interpreted to avoid unnecessary interventions.
Like MRI, HRUS can depict an avulsed bony fragment attached to the injured tendon with fairly good visualization of the irregular bony cortex of the parent bone, allowing the differentiation from a dystrophic intra-tendinous calcification in long-standing tendon injuries .
The role of the dynamic ultrasound examination for torn tendons had been emphasized by many studies over the static examination, especially in the tendon tears, where the retracted torn ends are being more appreciated and the limitation of the tendon movement could be obviously seen , and this was supported by our results (Table 3).
Being in close anatomical proximity, nerves may be involved in traumatic affection of the hand tendons; this was found in two of our cases (6.66%), in agreement with Rajesh Kumar et al.; the ultrasound had a great diagnostic value in the evaluation of the nerve injury as regards the extent and the level of the lesion as much as a twofold confirmation of the clinical examination and the nerve conduction studies. By HRUS examination, the torn nerve may show a discontinuity along its trunk with a hypoechoic mass-like area (stumps) (Fig. 7) which might be seen. As a result of the inflammatory changes, marked tenderness and neurogenic (electric) pain could be elicited by probing this lesion; a finding that is known as sonographic Tinel’s sign (Table 3) [16, 27].
A recent study by Albano et al. has emphasized the promising role of the HRUS and the ultra-HRUS (frequencies 22–70 MHz) in delineating the anatomical details and the ultrastructural changes of the very superficial nerves, pulley systems, retinacula, and the tendons .
We agreed that HRUS examination of the hand tendon injuries had proved a high diagnostic value (Tables 4 and 5), especially, in postoperative tendon repair and cases of retained foreign bodies; moreover, its availability, its relatively low-cost, and the high spatial resolution of the obtained images could provide wide popularity for its use.
Some limitations were met in this work: First is the use of two gold standards (operative and MRI evaluation); however, this was justified that not all of our patients were candidates for surgery or accepting it; thus, we used the MRI examinations as a complementary study that support our HRUS findings. The second was the concept that ultrasound is an operator-dependent technique and this is usually compensated by frequent practice under the supervision of the experienced seniors and the second-look examination if there was a need for this. The third one was being a single-center study with a relatively small sample size for the recruited patients, so the statistical analysis was not so robust. And the last one is the lack of the long-term follow-up examinations (about 1-year duration study) for most of the repaired lesions; thus, we recommend a long-term follow-up for postoperative cases in the future researches.