Distal insertional anatomy of the triceps brachii muscle: MRI assessment in cadaveric specimens employing histologic correlation and Play-doh(®) models of the anatomic findings

Does the articularis cubiti muscle really exist? Anatomical, histological, and magnetic resonance imaging study with a narrative review of literature

Although the term articularis cubiti muscle is incorporated in the official anatomical nomenclature, only sparse data about its appearance are available. It is usually described as few fibres originating from the medial head of the triceps brachii muscle and inserting to the capsule of the elbow joint. However, the most recent observations regarding the morphological relations in the posterior elbow region point towards the absence of a well-defined muscle. Therefore, this study was designed to verify the existence of the articularis cubiti muscle in question and to compile more data on the topographical features of the subtricipital area near the posterior aspect of the elbow. To address these questions, 20 embalmed upper limbs were dissected, and seven samples were collected for histological analysis. The laboratory findings were then correlated with 20 magnetic resonance imaging (MRI) scans of the elbow. Consequently, a narrative review of literature was performed to gain more information on the discussed muscle in a historical context. Upon the anatomical dissection, muscular fibres running from the posterior aspect of the shaft of the humerus to the elbow joint capsule and olecranon were identified in 100% of cases. Histologically, the connection with the joint capsule was provided via winding bands of connective tissue. On MRIs, the muscular fibres resembled a well-demarcated thin muscle located underneath the medial head of the triceps brachii muscle. Combined with the review of literature, we concluded that the constant articularis cubiti muscle originates from the posterior shaft of the humerus and attaches indirectly to the posterior aspect of the elbow joint capsule and directly to the superior portion of the olecranon. The obtained results slightly differ from the modern description, but are in agreement with the original publication, which has become misinterpreted throughout time. Presumably, the misused description has led to questioning the existence of an independent muscle. Moreover, our findings attribute to the articularis cubiti muscle, a function in pulling on the posterior aspect of the elbow joint capsule to prevent its entrapment, and possibly also a minor role in extension of the forearm. The presented results should be taken into consideration when intervening with the posterior aspect of the elbow joint because the articularis cubiti muscle poses a consistently appearing landmark.

Play in the reading room: Utilizing soft modeling compound to teach musculoskeletal anatomy and pathology

PROBLEM DESCRIPTION

Musculoskeletal (MSK) anatomy and pathology from a radiology perspective can be difficult to conceptualize and understand due to the challenge of visualizing 3D structures in stacks of 2D imaging. Consequently, trainees may benefit from inexpensive methods that can help trainees better visualize MSK anatomy and pathology. The purpose of this study is to provide proof of concept for inexpensive methodology to help learners such as radiology residents quickly and inexpensively understand musculoskeletal anatomy and pathology. This can help trainees become better at applying musculoskeletal knowledge to clinical practice.

INSTITUTIONAL METHODOLOGY

Soft-modeling compounds such as Play-Doh® was utilized in a variety of colors with pottery tools to recreate 3D models of challenging MSK anatomy and pathology for trainees. Qualitative feedback from the residents was collected.

RESULTS

Eighteen different pathological conditions across six major bone structures were modeled with a soft modeling compound. Residents qualitatively identified the experience as educational in terms of helping them better understand MSK pathology and positive in terms of making learning fun, less stressful, and memorable due to uniqueness of the learning modality. Residents report challenges modeling complex anatomical features and pathology via this methodology.

CONCLUSION

Radiology residents and other learners can enhance their knowledge of musculoskeletal anatomy and pathology via utilization of inexpensive soft modeling compounds. This may offer a cheaper and more time sensitive alternative to current 3-dimensional hardware and software technologies being developed for educational purposes. Additional work needs to be done to examine the utility of this methodology across larger and diverse groups of learners.

The anatomic - magnetic resonance imaging study of distal triceps brachii tendon

PURPOSE

The study aimed to describe the distal triceps brachii insertion on the olecranon and to correlate the findings with those seen in normal MR (Magnetic Resonance) anatomy of the triceps brachii insertion.

MATERIALS AND METHODS

14 un-paired fresh frozen elbows were included according to the institution guidelines and dissected. Histologic examination was performed to the distal triceps brachii insertion. The dimension of the distal triceps brachii tendon insertion was measured and defined based on its layer. The measurement of distal triceps brachii insertion was performed with image processing program (Image J, National Institute of Health, Bethesda, Maryland). T1-weighted elbow MR images (3.0 T) of a 102 patients were acquired and analyzed according to its sagittal plane.

RESULTS

All specimens shows that distal triceps brachii tendon is with three distinct insertional areas in the olecranon which are: (1) capsular, (2) deep muscular, (3) superficial tendinous insertion with the areas of 80.7 mm², 56.4 mm², and 175.2 mm², respectively. The superficial tendinous insertion was observed with a thickened portion, the "central cord" with 0.5 occupation ratio. MR analysis showed that 30% (31/102) of the distal biceps brachii insertion was with a cleft between the bipartite insertion of the superficial tendinous and the deep muscular insertion on olecranon which designated as the "lacuna" which was also found in 35% (5/14) of the specimens.

CONCLUSIONS

The distal triceps brachii has three distinct insertion on the olecranon. The superficial tendinous layer was separated with the deep muscular layer by a cleft in one third of the cases. Knowledge of this anatomy will help surgeon to understand the partial triceps injury and to avoid iatrogenic injury to the distal triceps tendon during surgery.

Anatomic evaluation of the triceps tendon insertion at the proximal olecranon regarding placement of fracture fixation devices

PURPOSE

Olecranon fractures, especially with a small proximal fragment, remain a surgical challenge. Soft tissue irritation and affection of the triceps muscle bear a risk of complications. In order to find an area for a soft-tissue sparing placement of implants in the treatment of olecranon fractures, we aimed to define and measure the segments of the proximal olecranon and evaluate them regarding possible plate placement.

METHODS

We investigated 82 elbow joints. Ethical approval was obtained from the local ethics committee, After positioning in an arm holder and a posterior approach we described the morphology of the triceps footprint, evaluated and measured the surface area of the triceps and posterior capsule and correlated the results to easily measurable anatomical landmarks.

RESULTS

We found a bipartite insertional footprint with a superficial tendinous triceps insertion of 218.2 mm² (± 41.2, range 124.7-343.2), a capsular insertion of 159.3 mm² (± 30.2, range 99.0-232.1) and a deep, muscular triceps insertion area of 138.1 mm² (± 30.2, range 79.9-227.5). Olecranon height was 26.7 mm (± 2.3, range 20.5-32.2), and olecranon width was 25.3 mm (± 2.4, range 20.9-30.4). Average correlation between the size of the deep insertion and ulnar (r = 0.314) and radial length (r = 0.298) was obtained.

CONCLUSIONS

We demonstrated the bipartite morphology of the distal triceps footprint and that the deep muscular triceps insertion area by its measured size could be a possible site for the placement of fracture fixations devices. The size correlates with ulnar and radial length.

Biceps, Brachialis, and Triceps

Tendon injuries at the elbow affect mostly the distal biceps and can progressively degenerate over time or rupture in an acute event. The degree of retraction may depend on the integrity of the lacertus fibrosus, a fibrous expansion that merges with the forearm flexor fascia. Biceps disorders are frequently associated with fluid or synovitis of the adjacent bicipital bursa; primary bursal disorders (primary inflammatory synovitis) can also be observed. Distal triceps is less frequently injured than the distal biceps, and tears usually manifest as distal ruptures with avulsion of a small flake of bone from the tip of the olecranon. Brachialis injuries are uncommon and the consequence of sudden muscle stretching during forced elbow hyperextension, as in posterior elbow luxation.

Imaging of Elbow Injuries

Familiarity with throwing mechanics during elbow range of motion allows accurate diagnosis of sports-related elbow injuries, which occur in predictable patterns. In addition, repetitive stress-related injuries are often clinically apparent; however, imaging plays an important role in determining severity as well as associated injuries that may affect clinical management. A detailed understanding of elbow imaging regarding anatomy and mechanism of injury results in prompt and precise treatment.

Differences in Rupture Patterns and Associated Lesions Related to Traumatic Distal Triceps Tendon Rupture Between Outstretched Hand and Direct Injuries

BACKGROUND

Traumatic distal triceps tendon rupture results in substantial disability in the absence of an appropriate diagnosis and treatment. To the best of our knowledge, differences in the degree of injury according to the injury mechanisms and associated lesions are not well known.

QUESTIONS/PURPOSES

In this study, we asked: (1) What differences are seen in triceps tear patterns between indirect injuries (fall on an outstretched hand) and direct injuries? (2) What are the associated elbow and soft tissue injuries seen in indirect and direct triceps ruptures?

METHODS

Between 2006 and 2017, one center treated 73 elbows of 72 patients for distal triceps tendon rupture. Of those, 70% (51 of 73 elbows) was excluded from this study; 8% (6 of 73) were related to systemic diseases, 59% (43 of 73) sustained open injuries, and 3% (2 of 73) were related to local steroid injections. We retrospectively collected data on traumatic distal triceps tendon rupture in 30% (22 of 73) of elbows at a single trauma center during a 10-year period. A fall on an outstretched hand was the cause of injury in 15 patients and direct blow by object or contusion were the cause in seven. MRI and surgery were performed in all patients. Traumatic distal triceps tendon rupture was classified by the Giannicola method, which is classified according to the depth and degree of the lesion based on MRI and surgical findings. Associated fractures and bone contusions on MRI were characterized. Ligament injuries on MRI was divided into partial and complete rupture. Agreement between the MRI and intraoperative findings for the presence of a traumatic distal triceps tendon rupture was perfect, and the Giannicola classification of traumatic distal triceps tendon rupture was good (kappa = 0.713).

RESULTS

In the indirect injury group (fall on an outstretched hand), 15 of 15 patients had injuries that involved only the tendinous portion of the distal triceps, but these injuries were not full-thickness tears, whereas in the direct injury group, three of seven patients had a full-thickness rupture (odds ratio [OR] 1.75 [95% CI 0.92 to 3.32]; p = 0.02). The direct injury group had no associated ligamentous injuries while 14 of 15 patients with indirect injuries had ligamentous injuries (OR 0.13 [95% CI 0.02 to 0.78]; p < 0.001; associated injuries in the indirect group: anterior medial collateral ligament [14 of 15], posterior medial collateral ligament [7 of 15], and lateral collateral ligament complex [2 of 15]). Similarly, one of seven patients in the direct injury group had a bone injury (capitellar contusion), whereas 15 of 15 patients with indirect ruptures had associated fractures or bone contusions (OR 16.0 [95% CI 2.4 to 106.7]; p < 0.001).

CONCLUSION

A fall on an outstretched hand may result in an injury mostly to the lateral and long head of distal triceps tendon and an intact medial head tendon; however, direct injuries can involve full-thickness ruptures. Although a traumatic distal triceps tendon rupture occurs after a fall on an outstretched hand, radial neck, capitellar, and medial collateral ligament injury can occur because of valgus load and remnant extensor mechanisms. Based on our finding, the clinician encountering a distal triceps tendon rupture due to a fall on an outstretched hand should be aware of the possibility of remaining elbow extensor mechanism by intact medial head tendon portion, and associated injuries, which may induce latent complications.

LEVEL OF EVIDENCE

Level III, prognostic study.

Magnetic resonance imaging of the elbow

Elbow pain can cause disability, especially in athletes, and is a common clinical complaint for both the general practitioner and the orthopaedic surgeon. Magnetic resonance imaging (MRI) is an excellent tool for the evaluation of joint pathology due to its high sensitivity as a result of high contrast resolution for soft tissues. This article aims to describe the normal imaging anatomy and biomechanics of the elbow, the most commonly used MRI protocols and techniques, and common MRI findings related to tendinopathy, ligamentous and osteochondral injuries, and instability of the elbow.