The Medial Triquetrohamate Portal: A New Portal in Wrist Arthroscopy. Anatomical Study

Abstract

Introduction  Continuing advances in wrist arthroscopy and better understanding of carpal conditions have created the need to design new wrist access portals that facilitate the implementation of new surgical techniques. The aim of this study was to define and verify the safety of the medial triquetrohamate (MTH) portal.

Description of the technique  The MTH portal is located about 5-10 mm ulnar and 2-3 mm distal to the midcarpal ulnar portal, ulnar to the extensor digitorum communis (EDC) tendon of the fourth and fifth fingers, and radial to the extensor digiti quinti (minimi) (EDQ) tendon.

Methods  An anatomical study was performed on 15 upper limb specimens from 15 human cadavers. Iatrogenic injuries to potentially at-risk neurovascular and tendinous structures were assessed, and the distance from the portal to these structures was measured.

Results  There were no iatrogenic injuries to the structures at risk. Mean distances from the MTH portal to the EDC tendon of the fourth and fifth fingers and to the EDQ tendon were 4.67 ± 0.35 mm and 7.27 ± 0.18 mm, respectively. No differences were observed between the left and right wrists. The distance from the MTH portal to the dorsal sensory branch of the ulnar nerve was 15.07 ± 0.44 mm. The structure with the highest risk of injury was the EDC tendon of the fourth and fifth fingers, with a distance of less than 5 mm.

Conclusions  The MTH portal is safe, reproducible and facilitates the implementation of various techniques related to midcarpal pathology.

Most arthroscopic techniques can be performed properly using the classic dorsal wrist arthroscopic portals. ¹ Advances in wrist arthroscopy and the emergence of new surgical techniques and implants have created the need to design new portals to facilitate the implementation of these techniques. ² The development of surgical techniques to repair acute and chronic lesions of the intercarpal scapholunate ligament (SLL) and lunotriquetral ligament (LTL) prompted us to design a new dorsal portal at the midcarpal level and ulnar to the midcarpal ulnar portal that would facilitate the placement of implants and provide us with a third working portal in the midcarpal joint, avoiding damage to major structures. The medial triquetrohamate (MTH) portal allows better placement of the implants, with a better angle of attack and gives us a second working portal at the midcarpal level.

The aim of this study was to define the MTH portal, to specify the surgical techniques in which it may be useful, and to verify its safety with an anatomical study by measuring the distances to the main tendinous and neurovascular structures of the ulnar border of the wrist.

Surgical Technique. Creation of the Medial Triquetrohamate Portal

With the hand suspended from a traction tower with 5-6 kg of countertraction, standard dorsal midcarpal radial (MCR) and ulnar (MCU) portals are created. The MTH portal is located about 5-10 mm ulnar and 2-3 mm distal to the MCU portal, between the extensor digitorum communis (EDC) tendon of the fourth and fifth fingers and the extensor digiti quinti (minimi) (EDQ) tendon ( Fig. 1 ). To facilitate accurate localization, we created the portal with direct arthroscopic visualization from the MCR portal using an outside-to-inside technique with a needle located between the triquetral and hamate bones.

Fig. 1.

Anatomical references for the MTH portal in an arthroscopic procedure. 3-4 portal, 6-R portal, MC-R: Midcarpal radial portal, MCU: Midcarpal Ulnar portal. EDC: Extensor digitalis comunis, EDM: Extensor Digiti Minimi, LT: Lister Tubercle.

Methods

A total of 15 upper limb anatomical specimens from 15 frozen human cadavers were examined. Eight male and seven female cadavers were used. The study included nine right and six left wrists. None of the specimens had a history of upper limb sequelae or surgeries.

Standard wrist arthroscopy was performed and the MTH portal was created as described.

An anatomical study was subsequently carried out after performing an ulnar-based dorsal skin flap to expose all the structures to be analyzed. Standard dissection instruments and retractors were used. The MTH portal and structures potentially at risk were marked: 1- EDC tendon of the fourth and fifth fingers; 2- EDQ tendon; and 3- dorsal sensory branch of the ulnar nerve (DSBUN) ( Fig. 2 and 3 ). All dissections were performed using 3.5× loupe magnification to avoid damaging the structures during dissection. Two data were recorded and analyzed: 1- the presence of any injury to the structures at risk; and 2- the distances to these structures from the MTH portal. These distances were measured as the shortest distance from the needle (located in the portal) to the structure at risk in a line perpendicular to the axis of the forearm. The measurements were taken by the same surgeon using a standard surgical ruler, observed by two other surgeons to ensure the quality of the measurements. All measurements were obtained after removing the retractors.

Fig. 2.

Anatomical dissection of the dorsal wrist. Dorsal view. ( a ) EDC tendon of the fourth and fifth fingers; ( b ) Medial Triquetrohamate portal; ( c ) EDQ tendon and ( d ) Dorsal sensory branch of the ulnar nerve.

Fig. 3.

Anatomical dissection of the dorsal wrist. Ulnar view. ( a ) EDC tendon of the fourth and fifth fingers; ( b ) Medial Triquetrohamate portal; ( c ) EDQ tendon and ( d ) Dorsal sensory branch of the ulnar nerve.

Statistical Analysis

We used SPSS software for Windows (version 28.0; SPSS, Chicago, IL) for the statistical analysis. This consisted of a descriptive analysis of the variables, calculating the frequency distribution for the qualitative variables and the arithmetic mean and standard error of the mean (SEM) for the quantitative variables. The values obtained for the different quantitative variables studied in relation to the independent variables (sex and laterality) were compared using the Mann-Whitney U test. Statistically significant differences were considered for p values <0.05.

Results

Anatomical dissection revealed no iatrogenic damage to the DSBUN, EDC or EDQ in any of the anatomical specimens.

The mean distances from the MTH portal to the DSBUN, EDC and EDQ were 15.07 ± 0.44 (range 12-18) mm, 4.67 ± 0.35 (range 3-7) mm and 7.27 ± 0.18 (range 6-8) mm, respectively ( Table 1 ). No statistically significant differences were found between the right and left sides for any of the measured distances. There were no statistically significant differences between sexes from the portal described to the DSBUN, EDC or EDQ.

Table 1. Mean distances from the MTH portal to the EDC, EDQ and RSNU.

SPECIMEN	LATERALITY	DISTANCES TO MTH PORTAL (mm)
		EDC	EDM	RSNU
Man 1	right	3	6	18
Man 2	right	4	7	17
Man 3	left	7	7	12
Man 4	left	5	8	14
Man 5	left	4	7	18
Man 6	right	5	7	14
Man 7	right	6	8	15
Man 8	left	7	8	14
Women 9	right	4	7	15
Women 10	right	3	6	13
Women 11	right	3	7	14
Women 12	left	6	8	15
Women 13	right	4	7	16
Women 14	right	5	8	16
Women 15	left	4	8	15
Mean		4.67	7.27	15.07
SEM		0.35	0.18	0.44

EDC, extensor digitorium comunis; EDM, extensor digitorium minimi; MTH, DSBUN, dorsal sensory branch of ulnar nerve; SEM, standard error of the mean.

Discussion

The MTH portal is a safe portal, as it is located at a sufficient distance from the tendinous and nerve structures that could potentially be injured at the midcarpal level. Although most wrist arthroscopy techniques can be performed through classic dorsal portals, ¹ having a second working portal at the midcarpal level is very useful in some cases. Access to the midcarpal joint at the volar level requires an approach with dissection and protection of the major neurovascular structures. ² Viegas ³ described the triquetrohamate (TH) portal, which enters the midcarpal joint at the level of the TH joint ulnar to the extensor carpi ulnaris (ECU) tendon. The entry site is ulnar and distal to the MCU and approximately 1 cm distal to the 6R accessory portal. This portal provides access to the TH joint and is useful for resection of the proximal pole of the hamate when there is HALT syndrome (hamate arthrosis lunotriquetal instability), ⁴ for arthroscopy-assisted internal fixation of displaced intra-articular fractures of the triquetrum, and for arthroscopic TH arthrodesis. ⁵ However, use of this portal puts the branches of the DSBUN at risk.

In the MTH portal, all the dorsal neurovascular structures are protected by tendinous structures, giving access to the midcarpal joint. The EDC tendon of the fourth and fifth fingers protects the terminal branches of the posterior interosseous nerve that run over the MCU portal, ⁶ while the EDQ tendon protects the DSBUN.

The description of this new MTH portal could improve the instrumentation of lesions at the TH joint level, in addition to providing optimal orientation for placing implants and performing volar capsulodesis of the SLL and LTL at the midcarpal level ( Figs. 4 and 5 ). Use of the MTH portal as a second instrumentation portal facilitates the performance of surgical techniques. In fact, at the radiocarpal level, we have five dorsal portals that can be used for viewing and instrumentation, depending on the pathology.

Fig. 4.

Arthroscopic view of the establishment of the medial triquetrohamate portal (MTH). (TQ) Triquetrum bone. (SL) Lunate bone; (CP) Capitate bone; Lunotriquetral ligament (LTL).

Fig. 5.

Arthroscopic view from the radial midcarpal portal. Use of the MTH portal in a volar lunotriquetral capsulodesis. (TQ) Triquetrum bone. (SL) Lunate bone; (CP) Capitate bone; Lunotriquetral ligament (LTL).

In this study, we observed that the MTH portal was located at a mean distance of between 5 and 15 mm away from the three tendinous and nerve structures that could potentially be injured, the structure at greatest risk being the EDC of the fourth and fifth fingers, with the smallest distance from the portal recorded in the 15 wrists studied. Despite the small distance, this risk is minimal, since when making the incision for the portal vertically along the direction of the tendons, in case of injury, this would produce a vertical lesion that would not entail functional impairment. Based on the study findings, we can say that this portal is safer than the TH portal in terms of possible damage to the DSBUN.

Since Slutsky ⁷ published his summary of all the midcarpal portals, no new dorsal portals have been described, which explains the few advances that have emerged in surgical techniques in this joint.

In 2016, Pan and Hung ⁸ studied the distances between the posterior interosseous nerve (PIN) and the dorsal portals. The distances between the MCU portal and the PIN or its closest terminal branch was a mean of only 1.6 mm. In 15 of the 28 specimens studied, the PIN was found directly over the MCU portal, or the portal was located between the terminal branches of the PIN. However, the MTH portal being 5-10 mm from the MCU portal minimizes the risk of injury to the terminal branches of the PIN.

Falcochio and Brunelli ⁹ used the TH portal as a novel way to facilitate and improve anterior midcarpal debridement in four-corner arthrodesis, ³ with a risk of damage to the DSBUN. ¹⁰ Accordingly, our portal can also be used in this technique, minimizing the risk of iatrogenic nerve damage.

Midcarpal access from the MTH portal reduces the risk of damaging the dorsal nerves. The risk of injury to the DSBUN is much lower and allows better triangulation in the midcarpal space by having a third portal. The techniques in which this portal is most frequently used are the volar reinsertions associated with capsulodesis of the SLL and LTL, treatment of chondral lesions in HALT syndromes and joint resections in four-corner arthrodesis.

Another advantage in arthroscopic capsuloligamentous sutures of the volar SLL and LTL is that it provides optimal orientation for creating the tunnels on the volar surface of the lunate and for inserting the implant.

Conclusions

The MTH portal is a safe, reproducible portal that facilitates the implementation of various techniques related to midcarpal pathology. Furthermore, this portal makes it possible to have a third working portal at the level of the midcarpal joint, with the nerve structures at risk being at a safe distance to avoid being damaged.