Ultrasound-guided needle knife for releasing Osborne’s ligament: an anatomical study
Yunnan Li1
, Shiliang Li2,3
, Qiaoyin Zhou1, Yuyang Ou2,3
Contributions: (I) Conception and design: Q Zhou, S Li; (II) Administrative support: S Li; (III) Provision of study materials or patients: S Li; (IV) Collection and assembly of data: Y Li, Y Ou; (V) Data analysis and interpretation: Y Li; (VI) Manuscript writing: All authors.; (VII) Final approval of manuscript: All authors.
Background: There is a lack of effective clinical options for treating mild-to-moderate cubital tunnel syndrome (CuTS) that does not fulfill the surgical indications, as more conservative treatments are ineffective. In this study, we investigated the anatomical characteristics of a CuTS caused by ligament compression to propose a new procedure for incising Osborne’s ligament with a needle knife. We evaluated the safety and efficacy of Osborne’s ligament release under the guidance of ultrasound.
Methods: The study involved an anatomical examination of the cubital tunnel in 25 adult specimens to summarize the anatomical characteristics of the cubital tunnel. We examined the feasibility of using a needle knife to incise Osborne’s ligament. A comparison was made between the non-ultrasound-guided and ultrasound-guided procedures to assess the benefit of ultrasound guidance.
Results: The ultrasound-guided group (group U) consisted of 25 specimens, 3 of which displayed nerve or blood vessel injuries; meanwhile, the non-ultrasound-guided group (group N) consisted of 24 specimens, 6 of which displayed nerve injury. The effective rate of ligament release in group U was 80.00% while that in group N was 79.23%. The mean thickness of Osborne’s ligament was 0.050±0.026 mm, the mean width was 17.92±3.07 mm, and the mean actual length was 36.02±5.04 mm. The actual length of Osborne’s ligament was greater in males than in females (P=0.02); however, no statistically significant difference was found in terms of thickness or width between males and females or between the right and left hands. The contents of the cubital tunnel primarily consisted of the ulnar nerve and superior ulnar collateral artery. Nerves and blood vessels were predominantly present in the middle of Osborne’s ligament.
Conclusions: Ultrasound-guided needle knife for incising Osborne’s ligament is safe and effective. This can be a novel treatment option for CuTS that does not fulfill surgical indications.
Keywords: Ultrasound guidance; anatomy; Osborne’s ligament; needle knife; cubital tunnel syndrome (CuTS)
Submitted Jul 17, 2024. Accepted for publication Dec 06, 2024. Published online Jan 21, 2025.
doi: 10.21037/qims-24-1450
Introduction
Cubital tunnel syndrome (CuTS), a type of peripheral entrapment neuropathy, ranks second in terms of incidence after carpal tunnel syndrome. It usually occurs secondary to local trauma and long-term strain, along with acute and chronic bone, joint, and soft-tissue inflammation (1). There are several surgical indications for CuTS. (I) The early phase of CuTS can be treated with nonsurgical treatments, and surgery can be used when the numbness still cannot be relieved. (II) If there is a mass occupying the cubital tunnel, surgery can be used to remove the mass to relieve the compression. (III) If there is fracture and joint dislocation in the cubital tunnel, surgery can be applied to reset the fracture and the joint dislocation in order to release the compression on the nerve. For cases of CuTS that do not meet these indications, treatment primarily consists of rest, splinting, and steroid hormone injections, whose principal purpose is to provide relief in the acute phase (2). Osborne’s ligament is a fibrous tissue that extends from the ulnar to the radial heads of the flexor carpi ulnaris (FCU), forming the top of the cubital tunnel (3). It is a crucial factor in ulnar nerve entrapment and can also act as a causative site proximally (4). Ultrasound can be used to visualize the anatomy of the cubital tunnel and is effective in guiding treatment (Figure 1).
As a combination of a needle and a knife with high cutting efficacy, the needle knife is used for treating various osteoarticular and chronic soft-tissue diseases such as tenontothecitis stenosans (5) and scapulohumeral periarthritis (Figure 2). It has the advantages of small surgical incisions, ease of maneuvering, and low infection risk (6).
The original needle knife procedure involves perpendicular skin entry for releasing the ulnar and radial heads of the FCU and does not require ultrasound guidance (7), which is less safe and effective than the new ultrasound-guided procedure. In this study, we investigated the anatomical characteristics of the cubital tunnel and proposed a novel procedure for the release of Osborne’s ligament via needle knife. We also sought to determine whether application of needle knife guided by ultrasound is safe and effective for Osborne’s ligament release. We performed a simulation experiment and found that ultrasound-guided needle knife could accurately release Osborne’s ligament with good safety and efficacy. We present this article in accordance with the AQUA reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-1450/rc).
Methods
Source of specimens
In total, 49 cases of cubital tunnel (25 on the right side and 24 on the left side) fixed in 10% formalin antiseptic were obtained from cadaver specimen (13 males and 12 females) aged between 62 and 94 years (mean age 81.33±10.52 years). These specimens were acquired from the Beijing University of Traditional Chinese Medicine. The specimens did not involve any elbow injury, deformity, trauma, or obvious degeneration. This study was conducted from January to June 2023 in accordance with the Declaration of Helsinki (as revised in 2013). The requirement for informed consent and ethical approval was waived by the ethics committee of Beijing University of Traditional Chinese Medicine due to the use of cadavers and the educational purpose of the study.
Experimental instruments
The following instruments were used in this study: an ultrasonic instrument (uSmart 3300, Terason, Burlington, MA, USA) with a probe (12 MHz), a needle knife (50 mm in length and 1 mm in diameter; Hanzhang, brand Huayou, Beijing), electronic vernier calipers (accuracy 0.001 mm), scalpel, hemostatic forceps, metal protractor (accuracy 1°), marking pens, and a digital camera (Sony, Tokyo, Japan).
Division
After ultrasound examination, specimens were randomly divided into two groups: the ultrasound-guided group (group U) and the non-ultrasound-guided group (group N). Ultimately, 25 cases were included in group U and 24 cases in group N.
The ultrasound-guided procedure (group U) was conducted as follows. The bilateral upper arms were positioned in abduction and external rotation with the elbow joints flexed at 90° to make Osborne’s ligament more tense and amenable for incision via needle knife. The skin of the medial elbow was completely exposed, and Osborne’s ligament was kept tense. Bony landmarks, including the medial epicondyle and the olecranon, were palpated for anatomical localization. The highest aspect of the medial epicondyle was considered to be point a, whereas the highest aspect of the olecranon was considered to be point b. A parallel straight line was drawn 10 mm distal from the line ab to form line a’b’. Additionally, the range between the two lines was considered as the range of Osborne’s ligament (8). To ensure maximum release efficiency, the effective release was set at LU,N ≥3/2 L (LU “The cutting length of Group U” LN “The cutting length of Group N” L=10 mm; i.e., LU,N ≥15.00 mm). Damage to blood vessels or nerves will be counted in the injury rate. The formula for calculating the injury rate was as follows: injury cases/all cases in the group × 100%.
The ultrasound-guided needle knife was inserted at the distal end of the ab line. The location of the needle knife insertion was clearly determined based on the position of the a’b’ line. Thus, Osborne’s ligament was released under ultrasound (Figure 3).
The angle between the needle knife and skin was detected. The distance between the needle entry point and line ab, the shortest distance between the needle entry point and the highest aspect of the medial epicondyle, the angle made by the needle knife, and the ab line were measured. The average value of data was calculated, which provided the basis for the non-ultrasound-guided entry.
The non-ultrasound-guided procedure (group N) was conducted as follows. The average data value measured in group U was used to determine the entry point and the route of needle insertion to ensure consistency with group U. The highest aspect of the medial epicondyle was considered as the center, a circle with a radius of 20 mm was constructed, draw a vertical line of ab, the intersection of the circle and this line at the distal end (9 mm distant from ab) was considered the needle insertion point N. The angle of the needle knife to the skin was approximately 8°, whereas the angle of the needle knife to the ab line was approximately 72° (Figure 4).
The insertion was made quickly through the skin, which was followed by a slow exploration. If a sensation was felt at the tip of the needle touching the tough tissue, the needle was released three times (Figure 5).
After the procedure, the highest aspect of the medial epicondyle was selected. An incision was made in the direction parallel to the longitudinal axis of the forearm. A vertical line perpendicular to this incision line was made beyond the highest aspect of the medial epicondyle. Additionally, another incision was made along the vertical line, which was located proximally to Osborne’s ligament, to prevent disruption. The fat layer was peeled, and the location of the FCU and its stopping point was determined. The humeral heads of the FCU were carefully dissected lay by layer of tissue until Osborne’s ligament was reached (Figure 6).
The needle knife passed through the following tissues in sequence: skin and subcutaneous fat, tendon membrane of the FCU, the FCU, and Osborne’s ligament (Figures 7,8).
Measurements
The width of Osborne’s ligament W was measured as the distance from the highest aspect of the medial epicondyle to the highest aspect of the olecranon. The actual length Lm and the thickness of the medial segment T were measured. The shortest distances of the ulnar nerve, superior ulnar collateral artery, and basilic vein from the highest aspect of the medial epicondyle were measured.
Statistical analysis
Data were analyzed with SPSS 26 (IBM Corp., Armonk, NY, USA). Count data are expressed as the percentage, and measurement data are expressed as . The Pearson chi-square test and independent samples t-tests were applied to analyze the data.
Results
Ultrasound-guided needle entry point measurements (Table 1)
Table 1
| Measurement | Minimum (mm/°) | Maximum (mm/°) | Average (mm/°, ) |
|---|---|---|---|
| Entry point U to ab (DU-ab) | 0.00 | 30.00 | 9.08±7.81 |
| Needle feed length (LeU) | 14.00 | 44.00 | 33.20±7.90 |
| U to ab (DU-a) | 9.00 | 35.00 | 19.68±7.01 |
| Angle between needle knife and ab (∠ab-Z) | 40.00 | 90.00 | 72.08±11.65 |
| Angle between needle knife and skin (∠S-Z) | 4.00 | 15.00 | 7.68±3.15 |
Statistical analysis indicated that the mean distance between the point U of the needle entry point and the ab line in group U was 9.08±7.81 mm. The mean shortest straight-line distance between entry point U and the highest aspect of the medial epicondyle (distance from U to a, DU-a) was 19.68±7.01 mm, the mean length of the entry needle (entry length of Group U, LeU) was 33.20±7.90 mm, the average angle of the needle knife to the ab line was 72.08°±11.65°, and the mean angle between the needle blade and the skin was 7.68°±3.15°.
Assessment of nerve and blood vessel damage
Incision marks were observed, and the injury rate for the nerves and blood vessels was calculated separately as follows: injury rate = number of injury cases/total number of cases ×100%. The criteria for safety assessment in terms of degree of damage were as follows: no damage; first degree, slight damage (only surface neurovascular damage and a length of the damage ≤1 mm); second degree, moderate damage (the neurovascular damage but not in all layers, with a length of the damage >1 mm); and third degree, severe damage (neurovascular damage or dissection to all layers).
Group U characteristics: There were 25 specimens in group U, which included 3 cases of neurovascular injury (injury rate 12%): 2 cases of nerve injury and 1 case of vascular injury. There was one case of first-degree damage, with a 0.5-mm cutting mark of the nerve and two cases of second-degree damage, with a 1.10 and 2.10 mm continuous incision of the nerve, respectively, which only damaged the superficial layer. All injuries were caused by unclear imaging in the specimen dehydration, which is not an issue in clinical treatment.
Group N characteristics: There were 24 specimens in group N, which included 6 cases of nerve injury (injury rate of 25%): 5 cases of second-degree nerve injury and 1 case of first-degree nerve injury. All 6 cases involved consecutive incisions, none of which penetrated the nerve. There is no statistically significant difference in the injury rate between Group U and N, but Group N has more injuries (100% more, 6 to 3) than Group U, which indicates the use of ultrasound is valuable.
Rate of Osborne’s ligament release in the two groups
The rate of ligament release was 80.00% in group U and 79.23% in group N. In terms of incision marks, Osborne’s ligament was thin, and the ligaments of both groups U and N were completely released. Both groups U and N are intermittent cutting. No statistically significant difference was found between the two groups (P=0.869) (Table 2).
Table 2
| Group | Average incision length (mm, ) | P | t |
|---|---|---|---|
| Ultrasound | 17.74±4.26 | 0.869 | −0.166 |
| None ultrasound | 17.96±4.91 |
Data for Osborne’s ligament
The width of Osborne’s ligament was considered the distance from the highest aspect of the medial epicondyle to the highest aspect of the olecranon (Table 3).
Table 3
| Measurement | Minimum (mm) | Maximum (mm) | Average (mm, ) |
|---|---|---|---|
| Thickness | 0.01 | 0.09 | 0.050±0.026 |
| Width | 13.00 | 28.00 | 17.92±3.07 |
| Actual length | 25.00 | 50.00 | 36.02±5.04 |
Notably, in the 25 specimens, the actual length of Osborne’s ligament was greater in males than in females. Nevertheless, no significant difference was found in the width (P=0.461) or thickness (P=0.233) of Osborne’s ligament between men and women. No significant difference was found in the actual length (P=0.759), width (P=0.164), or thickness (P=0.172) of the Osborne’s ligament between the right and left hands (Table 4).
Table 4
| Characteristics | Minimum (mm) | Maximum (mm) | Average (mm, ) | t | P |
|---|---|---|---|---|---|
| Men | 30.00 | 50.00 | 37.64±5.16 | 2.406 | 0.020 |
| Women | 25.00 | 42.00 | 34.33±4.41 | ||
| Left | 29.00 | 45.00 | 35.79±4.36 | −0.308 | 0.759 |
| Right | 25.00 | 50.00 | 36.24±5.70 |
Neurovascular alignment position measurements
The shortest distance between the ulnar nerve and the highest aspect of the medial epicondyle was measured. The mean value of the shortest distance between the ulnar nerve and the highest aspect of the medial epicondyle was 19.43±7.41 mm (Table 5).
Table 5
| Characteristics | Minimum (mm) | Maximum (mm) | Average (mm, ) | t | P |
|---|---|---|---|---|---|
| Men | 9.00 | 40.00 | 21.16±8.19 | 1.702 | 0.095 |
| Women | 10.00 | 32.00 | 17.62±6.16 | ||
| Left | 9.00 | 35.00 | 19.58±7.23 | 0.142 | 0.095 |
| Right | 10.00 | 40.00 | 19.28±7.73 |
The mean value of the shortest distance between the superior ulnar collateral artery and the highest aspect of the medial epicondyle was 22.33±7.84 mm. Furthermore, no significant difference was found between the average values of males and females or the right and left hands (Table 6).
Table 6
| Characteristics | Minimum (mm) | Maximum (mm) | Average (mm, ) | Z | P |
|---|---|---|---|---|---|
| Men | 11.00 | 40.00 | 23.67±8.21 | −1.283 | 0.200 |
| Women | 11.00 | 40.00 | 21.00±7.38 | ||
| Left | 11.00 | 40.00 | 23.08±8.52 | −0.403 | 0.687 |
| Right | 11.00 | 38.00 | 21.58±7.20 |
The mean value of the shortest distance between the basilic vein and the highest aspect of the medial epicondyle was 21.30±6.48 mm (Table 7).
Table 7
| Characteristics | Minimum (mm) | Maximum (mm) | Average (mm, ) | Statistic | P |
|---|---|---|---|---|---|
| Men | 14.00 | 34.00 | 22.77±6.06 | 1.145† | 0.263 |
| Women | 11.00 | 34.00 | 19.93±6.78 | ||
| Left | 12.00 | 32.00 | 20.31±6.28 | −0.707‡ | 0.687 |
| Right | 11.00 | 34.00 | 22.21±6.76 |
†, t-test. ‡, Z-test.
Discussion
The pressure within the cubital tunnel varies according to body position. In extension, the cubital tunnel appears circular in cross-section, whereas it becomes ovate during flexion. The greatest volume compression of the cubital tunnel is greatest at 135° of full flexion and the volume of cubital tunnel decreases by 55%, compares to the normal state (9). Meanwhile, the ulnar nerve is elongated by 8% when the elbow is at 90° of flexion (10). As the elbow flexion angle increases, the distance between Osborne’s ligament and the trochlea of the humerus decreases, while the ulnar nerve’s flattening rate increases (11). Muscle fibers and fat are found within the cubital tunnel, and their contraction during elbow flexion subsequently increases tunnel pressure in the cubital tunnel (12). Anatomical studies have indicated the presence of fat within the cubital tunnel, which contributes to an increase in pressure (Figure 9).
The shortest distance between the ulnar nerve and the vessel, measured from the highest aspect of the medial epicondyle, ranges from 9 to 11 mm, with an average width of Osborne’s ligament being approximately 17.92±3.07 mm. Based on these measurement data and observations, we inferred that the ulnar nerve and vessel are situated within the middle of the cubital tunnel.
Inflammation can be attributed to various factors, with tissue damage being a significant contributor. Prolonged chronic tissue damage can induce inflammation, which in turn, may exacerbate tissue damage (13). Prolonged chronic entrapment and stretching of nerves within the cubital tunnel can cause inflammatory exudation, resulting in tissue adhesion or fibrosis of the tissues (14).
The primary treatment concept for CuTS involves ulnar nerve decompression, which encompasses different surgical techniques such as decompression in situ (15) and transpositional decompression (16). Presently, options for minimally invasive treatment of the CuTS are limited to in situ ulnar nerve decompression. Endoscopic approaches offer less invasiveness and lower complication rates as compared with open surgical treatment (17), which may indicate that minimally invasive CuTS treatment is preferable. Decompression of Osborne’s ligament enhances the stability of the ulnar nerve (18). Ultrasound-guided in situ ulnar nerve decompression has proven to be an effective method (19), as ultrasound allows for accurate and comprehensive assessment of nerve compression status and stability, facilitating precise minimally invasive treatment (20,21).
Based on this, we hypothesized that ultrasound-guided needle knife release of Osborne’s ligament could relieve pressure on the ulnar nerve and promote inflammatory exudation, thus promoting the healing of CuTS. Compared with other surgical instruments, the needle knife offers minimal incisions and involves a low risk of infection and low cost; furthermore, it is easy to perform and train personnel in this procedure.
Currently available needle knife procedures for CuTS typically involve the release of the ulnar and radial heads of the FCU, without addressing Osborne’s ligament, which only provides limited benefit. Our newly developed procedure includes the lateral release of Osborne’s ligament with ultrasound guidance, which can prevent damage to tightly adhering nerves and blood vessels.
We performed a study of fixed specimens to examine the anatomical characteristics associated with the cubital tunnel and to assess the potential feasibility of ultrasound-guided needle knife treatment. However, this study was accompanied by certain limitations which should be considered. Due to this being a cadaveric study, the data may be prone to inaccuracies due to specimen dehydration, which could particularly affect thickness measurements. Since the source of the specimens was donation, we were not able to accurately find specimens with CuTS, but this technique still holds important theoretical and research implications. Furthermore, in terms of clinical application, although a limited number (12 cases) of experimental treatments were performed, patients reported that the treatment was rapid and effective, with no adverse effects. Nevertheless, the study lacked a sufficient number of patients to confirm the long-term efficacy of this treatment, and our clinical study is ongoing. We found that ultrasound-guided ligament release does not cause any nerve or vascular injury in clinical practice. All injuries caused in the ultrasound group in this study were due to poor visualization caused by severe dehydration of some specimens, and the use of ultrasound in clinical practice should be safer than treatment without ultrasound. Moreover, due to the limitations associated with small-sized surgical equipment, the incisions of extremely thick lesion ligaments have limited effectiveness, and the effect of release is less than that of open treatment; however, there is almost no risk of infection. Finally, the sample size in this study was small, which might have produced measurement bias. Therefore, further studies should be performed to validate the findings of this study.
Conclusions
In 20% of CuTS, releasing the ligament is ineffective. However, ultrasound-guided needle knife provides good safety and efficacy in the release of Osborne’s ligament and may thus represent a novel treatment option for CuTS caused by ligament compression.
Acknowledgments
None.
Footnote
Reporting Checklist: The authors have completed the AQUA reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-24-1450/rc
Funding: None.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-1450/coif). The authors have no conflicts of interest to declare.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The requirement for informed consent and ethical approval was waived by the ethics committee of Beijing University of Traditional Chinese Medicine due to the use of cadavers and the educational purpose of the study.
Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.
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