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. 2026 Feb 2;14(2):23259671251404069. doi: 10.1177/23259671251404069

Bare Area of the Proximal Radius and Its Relevance for Safe Repair of the Distal Tendon of the Biceps Brachii Muscle

Michal Benes *,†,‡, David Kachlik *,†, Marcos R Gonzalez §, Matous Kroupa *,†, Vojtech Kunc *,†,‡,‖,
PMCID: PMC12864697  PMID: 41640452

Abstract

Background:

Distal biceps tendon ruptures often require surgical repair to restore elbow flexion and forearm supination. However, the reinsertion procedure may be complicated by postoperative posterior interosseous nerve palsy caused by iatrogenic injury to the deep branch of the radial nerve (DBRN). While safe drilling trajectories for distal biceps tendon repair have been extensively studied, the potential influence of a bony gap between the insertion sites of the supinator muscle layers, referred to as the bare area of the proximal radius, has not been adequately addressed.

Purpose:

To determine the frequency, morphometrics, and topography of the bare area and to propose a safe bicortical drilling trajectory for single-incision distal biceps tendon repair that minimizes the risk of injury to the DBRN in the context of the bare area.

Study Design:

Descriptive laboratory study.

Methods:

A cadaveric dissection of 100 formalin-fixed upper limbs was conducted. Additionally, 1000 dry radii were examined for an osseous groove corresponding to the bare area. Furthermore, 10 fresh-frozen elbows were used for assessment of safe bicortical drilling trajectories in the presence of the bare area.

Results:

The bare area was present in 56.0% of cases, with no significant side or sex predominance. The bare area was 13.7 ± 5.2 mm long and 5.1 ± 1.6 mm wide, and occupied an area of 58.7 ± 33.8 mm2. Direct contact between the DBRN and the periosteum of the radius was noted in 28.6% of specimens. The extent of an osseous groove corresponding to the bare area overlapped with the radial tuberosity in 28.5% of the cases. Experimentally, bicortical drilling directed 30° ulnarly and 45° proximally ensured a safe distance from both the DBRN and the bare area.

Conclusion:

The frequent occurrence of the bare area should be a critical consideration during bicortical drilling for distal biceps tendon repair. Drilling angles directed ulnarly and proximally are recommended to minimize the risk of neural injury.

Clinical Relevance:

This study highlights the increased risk of DBRN injury during distal biceps tendon repair in individuals with the bare area and provides safe drilling trajectories to guide surgeons in reducing the likelihood of this neural injury.

Keywords: bare area, proximal radius, distal biceps rupture, distal biceps repair, deep branch of radial nerve, posterior interosseous nerve

Ruptures of the distal tendon of the biceps brachii muscle occur with an estimated incidence ranging from 1.2 to 2.6 per 100,000 patients annually.5,12 Surgical repair allows for successful restoration of elbow flexion and forearm supination but carries a risk of iatrogenic injury to the deep branch of the radial nerve (DBRN), which was reported at a 1.6% rate. 2 The mechanisms underlying this nerve injury involve direct trauma with a drill bit or surgical hardware, as well as ischemic damage due to retractor placement or upper limb positioning. Overall, postoperative posterior interosseous nerve (PIN) palsy occurs more frequently when using the single-incision technique, as it does not provide direct visualization of the anatomic structures coursing over the posterior cortex of the radius. 1 While the choice of fixation method has not been shown to influence the DBRN injury rate, 8 the risk of nerve damage may be exacerbated by individual anatomic variations, particularly as the nerve descends through the supinator canal.

Upon reaching the level of the radial neck, the DBRN enters the supinator canal underneath the arcade of Frohse. The DBRN then runs between the superficial and deep layers of the supinator muscle that form the supinator canal and provide a circumferential soft tissue corridor for the DBRN. However, the floor of the supinator canal may feature an osseous component, known as the bare area (BA) of the proximal radius. 6 This anatomic variation results from an incomplete connection between the insertion sites of the layers of the supinator muscle onto the radius, potentially exposing the DBRN to direct contact with the periosteum of the proximal radius. 20 In a landmark anatomic study of 21 upper limbs and 38 macerated bones, Davies and Laird 6 identified the BA in 57.1% of cases and described an osseous groove corresponding to the location of the BA in bony specimens. Although subsequent studies have briefly noted the potential contact between the DBRN and the periosteum of the radius, the anatomy of the BA has not been systematically investigated.4,9,13,16,23

Several authors attempted to define safe bicortical drilling trajectories to diminish DBRN injury during single-incision distal biceps tendon repair.3,4,7,14,15,19,22 However, the potential clinical impact of the BA in distal biceps tendon reinsertion has not been taken into consideration. Therefore, this present study aimed to (1) determine the frequency, morphometrics, and topography of the BA and (2) assess the drilling angles to define a safe trajectory that minimizes the risk of BA-related DBRN injury. We hypothesized that the presence of the BA increases the risk of iatrogenic DBRN injury during single-incision distal biceps tendon repair when drilling through the cortex contralateral to the radial tuberosity.

Methods

Anatomic Dissection

Following institutional review board approval, a total of 100 formalin-fixed upper limbs of deceased body donors (54 right and 46 left) were obtained from the donation programs of the First, Second, and Third Faculty of Medicine, Charles University, Prague, Czech Republic. In total, 51 upper limbs had been isolated from the corpses of unknown sex, and the remaining 49 upper limbs (32 male and 17 female) were dissected from the whole cadavers. All specimens showed no evidence of previous surgery or trauma. The same 2 authors (M.B. and M.K.) conducted all dissections according to the following protocol. All forearms were dissected of skin and subcutaneous tissue. The supinator muscle was accessed via the anterolateral approach. 24 An interval between the brachioradialis and extensor carpi radialis longus muscles was used to expose the DBRN, entering the supinator canal underneath the tendinous arch of the supinator muscle (arcade of Frohse) and leaving below the distal arcade. The superficial layer of the supinator muscle was carefully incised along the course of the DBRN to ascertain the content of the supinator canal.

In cases where the BA was present, the following measurements were taken. Length (proximodistal extent), width (mediolateral extent), and area of the BA were digitally measured from the obtained photographs using a computer-assisted image analysis software Fiji ImageJ v. 2.0.0 (National Institutes of Health). When taking the photographs, a ruler was placed next to the BA to provide a reference scale. Consequently, the scale was calibrated using the known distance between marks on the ruler, allowing for simple and accurate translation of pixel differences into the metric system. Then, the software was able to calculate the distance between 2 points, such as length and width, and the area of the marked surface. Furthermore, the distance from the proximal margin of the articular circumference on the radial head to the most proximal and distal tips of the BA was measured with the use of a digital caliper with a manufacturer-guaranteed accuracy of ± 0.2 mm (Extol Craft).

In addition to the morphometric measurements, the DBRN was morphologically assessed for direct contact with the periosteum of the proximal radius due to the BA. The forearm was maintained in a neutral position during the fixation process in formalin, leading to stiffness and immobility. This approach ensured a consistent forearm position and avoided skewing of the periosteal contact due to the DBRN movement during pronation and supination.10,11

Osteology

A total of 1000 dry radii (455 right and 545 left) were analyzed for the presence of an osseous groove corresponding to the location of the BA. The bones were acquired from the osteological collections of the First, Second, and Third Faculty of Medicine in Prague, the Faculty of Medicine in Pilsen, and the Faculty of Medicine in Hradec Králové, Charles University, Czech Republic. All bones were unpaired, and the sex and age remained unknown. The osseous groove that corresponded with the location of the BA was visually and palpably identified and subsequently compared with the extent of the radial tuberosity.

Experimental Setup

Nineteen fresh-frozen upper limbs (10 right, 9 left), obtained from the donation program of the Second Faculty of Medicine, Charles University, Prague, Czech Republic, were allowed to thaw overnight before the experiment. The upper limbs belonged to 6 female and 4 male body donors (mean age 68.4 ± 10.1 years). The presence of the BA was assessed through a posterior approach to the proximal forearm. Following a longitudinal skin incision, starting from the lateral epicondyle of the humerus and extending one-third of the way down the forearm, a superficial dissection was performed. The plane between the extensor carpi radialis brevis and extensor digitorum muscles was used to visualize the supinator muscle. The exit point of the PIN from the supinator canal was noted to estimate the course of the DBRN within the canal. The superficial layer of the supinator muscle was carefully incised with special attention not to disturb the natural course of the DBRN, and the presence of the BA was assessed. Ten upper limbs (52.6%) were found to have the BA (6 right, 4 left) and were further used for the experiment.

In these 10 upper limbs with the BA, an additional curved incision was made 2 cm below and parallel to the cubital flexion crease, continuing distally along the medial margin of the brachioradialis muscle. After sharp dissection of the subcutaneous tissue, the tendon of the biceps brachii muscle was identified and detached from its insertion to simulate tendon rupture.

Subsequently, full supination was strictly maintained, and the radial tuberosity was brought into view. A 3.2-mm drill bit was used to create a bicortical drill hole, starting at the center of the radial tuberosity. Based on previous studies,3,4,7,14,15,19,22 9 drilling trajectories were defined: (1) aiming 45° distally and 30° radially, (2) aiming 45° distally and copying the long axis of the radius, (3) aiming 45° distally and 30° ulnarly, (4) aiming perpendicular to the long axis of the radius and 30° radially, (5) aiming perpendicular to both the long and short axes of the radius, (6) aiming perpendicular to the long axis of the radius and 30° ulnarly, (7) aiming 45° proximally and 30° radially, (8) aiming 45° proximally and copying the long axis of the radius, and (9) aiming 45° proximally and 30° ulnarly. The desired trajectory was confirmed with a protractor. The shortest distance from each exit point of the drill bit to the DBRN was measured with the same digital caliper as described above. Moreover, the relationship of the drill bit to the BA was recorded.

Statistical Analysis

Categorical variables are presented as counts with percentages. Normality of continuous data distribution was assessed using the Shapiro-Wilk test. Normally distributed variables are reported as means with standard deviation, while nonnormally distributed variables are presented as medians with interquartile ranges. The chi-square test was used to compare categorical variables. Differences between groups were compared either by the t test or the Mann-Whitney U test for normally and nonnormally distributed continuous variables, respectively. Statistical significance was set at P≤ .05. Data were analyzed using GraphPad Prism v. 10.4.0 (GraphPad Software).

Results

Cadaveric Observations of Preserved Forearms

A gap between the insertions of the superficial and the deep layer of the supinator muscle, forming the BA, was found in 56 of 100 dissected upper limbs (56.0%) (Figure 1). In all cases, the BA featured an elongated elliptical shape with pointed ends, with the proximal end oriented anteriorly and the distal end pointing posteriorly. The difference in frequency of the BA between the right (31 upper limbs; 57.4%) and left (25 upper limbs; 54.3%) sides was not significant (P = .729). Similarly, there was no statistically significant difference between male (15 upper limbs; 46.9%) and female (13 upper limbs; 76.5%) specimens (P = .061).

Figure 1.

Surgeon examines a right forearm anatomy showing supinator canal, nerves, and muscles with labeled parts like biceps brachii, brachialis, and radial nerve branches.

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Cadaveric dissection of a right forearm demonstrating the opened supinator canal with the bare area of the proximal radius (asterisk). The deep branch of the radial nerve (DBRN) lies on the deep layer of the supinator muscle (DLSM) and thus is not in contact with the periosteum. BBM, biceps brachii muscle; BM, brachialis muscle; Dist., distal; ECRBM, extensor carpi radialis brevis muscle; ECRLM, extensor carpi radialis longus muscle; Lat., lateral; Med., medial; Prox., proximal; SBRN, superficial branch of the radial nerve; SLSM, superficial layer of the supinator muscle.

The BA measured 13.7 ± 5.2 mm in length and 5.1 ± 1.6 mm in width, occupying an area of 58.7 ± 33.8 mm2. The proximal tip of the BA was 36.7 ± 8.1 mm distant from the radial head, and the distance between the distal tip and the radial head was 50.2 ± 10.5 mm. No statistically significant difference was found in the morphometric parameters between sides and sexes (Table 1).

Table 1.

Morphometric Properties of the Bare Area of the Proximal Radius a

Measurement Overall (n = 56) Right (n = 31) Left (n = 25) P Value Male (n = 15) Female (n = 13) P Value
Length 13.7 ± 5.2 13.9 ± 5.8 13.4 ± 4.2 .735 15.1 ± 4.5 13.2 ± 4.9 .675
Width 5.1 ± 1.6 5.0 ± 1.8 5.1 ± 1.4 .602 5.2 ± 1.5 4.7 ± 1.2 .224
Area 58.7 ± 33.8 59.7 ± 35.1 57.2 ± 32.4 .835 70.9 ± 39.2 49.0 ± 18.9 .199
Distance between radial head and proximal tip 36.7 ± 8.1 38.5 ± 7.6 34.0 ± 8.3 .715 37.5 ± 6.7 34.0 ± 7.8 .460
Distance between radial head and distal tip 50.2 ± 10.5 52.0 ± 9.5 47.7 ± 11.6 .860 51.7 ± 10.3 46.8 ± 10.8 .581
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a

Values are presented as mean ± standard deviation.

In 16 upper limbs with the BA (28.6%), the DBRN laid directly on the periosteum of the proximal radius. However, in most cases with the BA (40 upper limbs; 71.4%), the DBRN was separated from the periosteum by either the muscular fibers of the deep layer of the supinator muscle or a thin layer of connective tissue at the attachment site of the deep muscular layer. There were no statistically significant differences in the size of the BA between the periosteal contact group and the noncontact group (Figure 2).

Figure 2.

Boxplot depicting nonsignificant dimension differences in bare area between periosteal and noncontact groups, with specific boxplots labeled for length, width, and area comparisons.

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Boxplot showing the nonsignificant differences in dimensions of the bare area between the periosteal contact group and the noncontact group.

Osteological Observations

Analysis of the dry radii revealed an osseous groove in 383 of 1000 cases (38.3%) (Figure 3). The groove exhibited the same elliptical shape as the BA in cadaveric upper limbs, except the pointed ends faded peripherally. Moderate prominences were present at the attachment sites of the superficial and deep layers of the supinator muscle, marking the boundaries of the groove. The alignment of the prominences with the insertion sites of the supinator muscle was confirmed in cases of extensively dissected upper limbs, where remnants of the muscle's insertions were preserved (Figure 4).

Figure 3.

A right proximal radius bone illustrating an osseous groove bordered by moderate prominences, with directional labels for distal, lateral, medial, proximal, radial tuberosity.

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Right proximal radius demonstrating the osseous groove bordered by the moderate prominences (white arrowheads). Dist., distal; Lat., lateral; Med., medial; Prox., proximal; RT, radial tuberosity.

Figure 4.

An extant forearm showcases the attachment points of the supinator muscle, with white and black arrows indicating the deep and superficial layers, annotated with the directional indicators.

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Extensive cadaveric dissection of a right proximal forearm demonstrating the attachment sites of the deep (white arrowheads) and superficial (black arrowheads) layer of the supinator muscle. Ant., anterior; Dist., distal; Post., posterior; Prox., proximal; RH, radial head; RT, radial tuberosity.

The groove always extended below the level of the radial tuberosity (383 cases; 100%). However, the proximal entrance of the groove was variable. Most commonly (274 cases; 71.5%), the whole groove was located below the radial tuberosity. In 104 cases (27.2%), the entrance was within the extent of the radial tuberosity, and in 5 cases (1.3%), the entrance was located above the radial tuberosity. Therefore, in 109 cases (28.5%), the extents of the BA and the radial tuberosity overlapped.

Vulnerability of the DBRN During Bicortical Drilling in the Presence of the Bare Area

During the experiment using fresh-frozen specimens, the most dangerous drilling trajectories were those aimed perpendicular to the long axis of the radius and 30° radially (7 cases of DBRN injury; 70%) (Figure 5) and those aimed 45° distally and copying the long axis of the radius (5 cases of DBRN injury; 50%). No contact between the drill bit and the DBRN was observed in any of the remaining trajectories. The safest drilling angle, ensuring the greatest distance from the DBRN, was achieved by aiming the drill bit 45° proximally and 30° ulnarly (31.2 ± 5.8 mm). Complete results are shown in Table 2.

Figure 5.

Simulated deep branch of radial nerve injury during radial bone drilling simulation in vivo. Anatomical orientation indicated with labels.

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Simulated injury to the deep branch of the radial nerve (DBRN) after drilling perpendicular to the long axis of the radius and at a 30° radial angle. Ant., anterior; Dist., distal; Post., posterior; Prox., proximal.

Table 2.

Distances Between the Deep Branch of the Radial Nerve and the Drill Bit and Frequencies of the Drill Bit Contact With the Nerve and the Bare Area

Drill Trajectory Distance Between Drill Bit and Deep Branch of the Radial Nerve, Mean ± SD, mm Contact of Drill Bit With Deep Branch of the Radial Nerve, No./Total No. (%) Contact of Drill Bit With Bare Area, No./Total No. (%)
1. 45° distally and 30° radially 6.9 ± 2.8 0/10 (0%) 10/10 (100%)
2. 45° distally 2.7 ± 2.1 5/10 (50%) 8/10 (80%)
3. 45° distally and 30° ulnarly 11.8 ± 3.8 0/10 (0%) 0/10 (0%)
4. 30° radially 1.2 ± 1.9 7/10 (70) 4/10 (40)
5. perpendicular 10.4 ± 4.5 0/10 (0) 2/10 (20)
6. 30° ulnarly 17.5 ± 4.3 0/10 (0) 0/10 (0)
7. 45° proximally and 30° radially 20.3 ± 5.0 0/10 (0) 0/10 (0)
8. 45° proximally 22.3 ± 5.1 0/10 (0) 0/10 (0)
9. 45° proximally and 30° ulnarly 31.2 ± 5.8 0/10 (0) 0/10 (0)
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The drill bit always exited through the BA when aiming 45° distally and 30° radially (10 cases; 100%) (Figure 6). Conversely, drilling in the ulnar and proximal direction did not interfere with the BA in any case. The standard anatomic drilling technique (aiming perpendicular to the long and short axes of the radius) resulted in 2 cases (20%) of contact between the BA and the drill bit.

Figure 6.

Surgical incision on a person's radial forearm. Drill bit exits from the raw area at a 45-degree angle distally and a 30-degree angle radially. Anterior, proximal, posterior, distal.

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Exit of the drill bit through the bare area (BA) of the proximal radius after drilling 45° distally and 30° radially. Ant., anterior; Dist., distal; Post., posterior; Prox., proximal.

Direct DBRN injury due to the BA (drill bit caused DBRN injury and simultaneously made contact with the BA) was observed in 5 cases (50%) when drilling at a 45° distal angle. Additionally, direct BA-related DBRN injury occurred in 4 cases (40%) when the drill bit was aimed perpendicular to the long axis of the radius and 30° radially.

Discussion

The principal finding of this study was the identification of the BA in more than half of the dissected upper limbs. Furthermore, this study revealed direct contact between the DBRN and the periosteum of the proximal radius in nearly one-third of these cases with the BA. While several previous studies have investigated safe drilling trajectories for single-incision distal biceps tendon repair, they have largely overlooked the presence of the BA. The current study experimentally confirmed the risk of iatrogenic DBRN injury in those with the BA during bicortical drilling for anatomic reinsertion of the distal biceps tendon, providing evidence for safe drilling angles. Understanding the topographic relationship between the radial tuberosity and the adjacent contents of the supinator canal may help enhance safety and promote better functional outcomes for patients undergoing distal biceps tendon repair.

PIN palsy is a major complication after distal biceps tendon repair, often related to surgical technique and anatomic considerations. The PIN innervates the extensor muscles of the hand and is susceptible to injury during surgical dissection or bicortical drilling as it traverses the supinator canal. Literature indicates that nerve injury can occur due to direct trauma, compression from hematoma formation, or excessive retraction of surrounding structures during the procedure.17,18 Clinically, the PIN palsy manifests as wrist drop and inability to extend the metacarpophalangeal joints, significantly impairing hand function. 20 Early recognition and appropriate management of this complication are crucial for optimizing recovery and restoring functionality. Although some cases tend to resolve spontaneously, additional surgical intervention may be necessary.1,17 Current reports suggest that meticulous surgical technique can mitigate the risk of nerve injury; therefore, this study explores an overlooked anatomic variation within the supinator canal to refine the single-incision reinsertion technique.

Despite the extensive research on the topography of the DBRN, the osseous area within the floor of the supinator canal has been rarely reported. The original study by Davies and Laird 6 identified the BA in 57% of 21 upper limbs. Based on the findings of Lawton et al, 13 the BA appeared in 71% of their 24 upper limbs. Most recently, Gilan et al 9 declared its presence in 10% of 40 upper limbs. These substantial differences may be attributed to the low sample sizes of the aforementioned studies. Our results, based on a significantly larger sample, indicate that the BA was present in 56.0% of cases. Moreover, the corresponding groove on the proximal radius was found in 38.3% of cases, similar to the 36.8% figure reported in the only study documenting this osseous structure. 6 Relevant to the distal biceps tendon repair, the overlap between the osseous groove and the radial tuberosity occurred in 28.5% of the observed dry radii containing the groove. This overlap, especially when combined with direct periosteal contact of the DBRN, puts the nerve at greater risk of iatrogenic injury.

The optimal drilling angles for single-incision distal biceps tendon repair remain a subject of debate. Bain et al 3 advised against directing the drill distally and radially and recommended a perpendicular anterior-to-posterior drilling. However, this recommendation has since been reconsidered. Lo et al 14 suggested drilling perpendicular to the long axis of the radius and aiming 0° to 30° ulnarly. Similarly, Saldua et al 19 and Thumm et al 22 found that a 30° ulnar drilling angle maintained a sufficiently safe distance from the DBRN. Duncan et al 7 suggested drilling 0° to 20° toward the radiocapitellar joint. Becker et al 4 recommended avoiding perpendicular bicortical drilling in favor of a more proximal and ulnar drilling angle. Based on our results, proximally and ulnarly oriented drilling is the safest approach due to longer distances from both the DBRN and the BA. Although the selection of fixation techniques does not significantly affect postoperative PIN palsy rates, the use of a cortical button introduces an additional risk of the DBRN injury during both its deployment and seating. Lynch et al, 15 in their cadaveric study, reported direct contact between the cortical button and the DBRN in 50% of cadaveric cases during deployment, with 1 case of DBRN entrapment after its seating when aiming the drill bit 30° in the ulnar direction. Such a high incidence of neural contact was explained by deployment of the cortical button transversely to the long axis of the radius. Therefore, deploying and seating the cortical button parallel to the radial shaft was advised.

Periosteal contact of the DBRN within the supinator canal has been reported with an incidence ranging from 2% to 83.3%.6,9,13,16,23 Our findings indicate a 28.6% incidence of contact between the periosteum of the proximal radius and the DBRN in a neutral position of the forearm. Importantly, the DBRN is not fixed within the supinator canal but moves dynamically during supination and pronation of the forearm. Based on the study by Hackl et al, 10 the DBRN moves proximally with forearm pronation, while supination causes distal shift of the nerve. Therefore, any hardware protruding above the cortex within the BA may cause chronic irritation of the DBRN as the forearm moves, potentially manifesting as a delayed PIN palsy. To mitigate this risk, fixation techniques that avoid perforating the far cortex from the radial tuberosity should be considered. 21

This study has several limitations inherent to its cadaveric design. The sex and age of most anatomic specimens and all bones were unknown, preventing a reliable analysis of the sex- and age-related differences. Additionally, the number of specimens used for the experiment is relatively low; however, it is similar to that used in previous studies. Furthermore, while great care was taken to preserve the natural anatomy of the contents of the supinator canal during the experiment, the initial posterolateral approach might have caused minor structural displacement. Moreover, the location of the DBRN in relation to the BA detected in our cadaveric observations of preserved forearms in the neutral position may differ from the actual intraoperative positioning because the surgery is typically performed in hypersupination of the forearm. Despite these limitations, this study provides valuable data that the variable BA may be a risk factor for postoperative PIN palsy after distal biceps tendon repair.

Conclusion

This study identified the BA in 56.0% of the dissected upper limbs, with direct periosteal contact between the DBRN and the proximal radius in 28.6% of these cases. On dry radii, the BA was most commonly located below the radial tuberosity; however, in 28.5% of cases, it overlapped with the extent of the radial tuberosity. Thus, this topographical relationship places the DBRN at risk for iatrogenic injury during distal biceps tendon repair. Furthermore, this study identified an optimal drilling trajectory to reduce the risk of DBRN injury during bicortical drilling for distal biceps tendon repair. By aiming the drill bit ulnarly and proximally, the exit point is reliably distant from both the DBRN and the BA, mitigating the risk of direct neural injury and chronic irritation of the DBRN, respectively. Understanding these safe trajectories and the anatomic nuances of the supinator canal is essential for minimizing major neural complications after single-incision distal biceps tendon repair.

Acknowledgments

The authors sincerely thank those who donated their bodies to science so that anatomic research could be performed. Results from such research can potentially increase humankind's overall knowledge that can then improve patient care. Therefore, these donors and their families deserve our highest gratitude. The authors thank Lada Eberlova, Petr Hajek, Anastasya Lagutina, and Ondrej Nanka for access to the anatomic specimens.

Footnotes

Final revision submitted October 2, 2025; accepted November 6, 2025.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

This study was supported by the Charles University Grant Agency (GAUK; No. 174523).

Ethical approval for this study was obtained from Ethics Committee for Multi-Centric Clinical Trials of the University Hospital Motol and Second Faculty of Medicine, Charles University in Prague (No. EK-1107/22).

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