Wrist arthroscopy portals

Introduction

Since its inception, wrist arthroscopy has continued to evolve. The initial emphasis on viewing the wrist from the dorsal aspect arose from the relative lack of neurovascular structures and the familiarity of most surgeons with dorsal approaches to the radiocarpal joint. Anatomical studies have provided a better understanding of both the interosseous ligaments and carpal kinematics, which has led to the development of midcarpal arthroscopy along with a number of volar portals that are discussed in this chapter.

Indications

The standard dorsal portals are used as a part of the initial arthroscopic survey of the wrist ( Video 1-1 ). These include the 3,4 portal, the 4,5 portal, and the 6 radial (6R) and 6 ulnar (6U) portals. Typically, the 3,4 and 4,5 portals are used interchangeably for visualizing the radiocarpal joint and for instrumentation. The 4,5 portal and the 6R portal are used to access the ulnocarpal joint. The 6U portal is typically used for outflow. However, with careful attention to surface landmarks, any portal can be used for viewing or instrumentation.

Midcarpal arthroscopy is essential in making the diagnosis of scapholunate and lunotriquetral instability. The Geissler classification of intercarpal ligaments provides a means of staging the degree of instability in order to provide an algorithm for treatment. Midcarpal arthroscopy is also useful for the assessment and treatment of chondral lesions of the proximal hamate. The triquetro-hamate joint can also be accessed through another special-use midcarpal portal.

Volar portals for wrist arthroscopy have certain advantages over the standard dorsal portals for visualizing dorsal capsular structures and the palmar aspects of the carpal ligaments. The volar radial portal is relatively easy to use and is an ideal portal for evaluation of the dorsal radiocarpal ligament (DRCL) and the palmar subregion of the scapholunate interosseous ligament (SLIL). It facilitates the identification and repair of DRCL tears. ^, The VR portal also facilitates arthroscopic reduction of intraarticular fractures of the distal radius by providing a clear view of the dorsal rim fragments.

The volar radial midcarpal (VRM) portal is an accessory portal for visualizing the palmar aspects of the capitate and hamate in cases of avascular necrosis or osteochondral fractures ( Video 1-2 ). This portal allows for visualization of the palmar aspect of the capitohamate interosseous ligament (CHIL), which is important in minimizing translational motion and has an essential role in providing stability to the transverse carpal arch. It can also be used to visualize the dorsal intercarpal ligament (DIC), the ulnar part of the arcuate ligament, and the stalk of the midcarpal dorsal ganglia.

The volar ulnar portal can be used to view the dorsal radioulnar ligament, the dorsal ulnar wrist capsule, and the palmar aspects of the lunotriquetral interosseous ligament (LTIL). It also aids in the repair or debridement of dorsally located triangular fibrocartilage (TFC) tears because the proximity of the 4,5 and 6R portals makes triangulation of the instruments difficult. The volar aspect of the distal radioulnar joint can be visualized through the volar distal radial ulnar (VDRU) distal radioulnar joint (DRUJ) portal to assess the foveal attachment of the TFC in cases of suspected peripheral detachment of the TFC.

Corella et al. recently described a volar central portal that allows access to the radiocarpal and midcarpal portals.

Two dorsal DRUJ portals may be used to assess the status of the articular cartilage of the ulnar head and sigmoid notch. This information may be useful in cases of DRUJ instability or when there is the suspicion of early osteoarthritis, in which case arthroscopy may differentiate between the need for DRUJ stabilization or ulnar head excision and arthroplasty. The two dorsal DRUJ portals can be used for an arthroscopic synovectomy of the DRUJ and for arthroscopic wafer resections of the ulnar head when combined with the volar DRUJ portal.

Contraindications

Contraindications to the use of dorsal or volar portals include any cause of marked swelling that distorts the topographic anatomy, large capsular tears that might lead to extravasation of irrigation fluid, neurovascular compromise, bleeding disorders, and infection. Unfamiliarity with the regional anatomy is a relative contraindication.

Relevant anatomy

( Video 1-1 ) The standard portals for wrist arthroscopy are largely dorsal ( Fig. 1.1 ). The dorsal radiocarpal portals are so named in relation to the tendons of the dorsal extensor compartments. For example, the 1,2 portal lies between the first extensor compartment, which include the extensor pollicis brevis (EPB) and the abductor pollicis longus (APL), and the second extensor compartment, which contains the extensor carpi radialis brevis and longus (ECRB/L).

The 3,4 portal is named for the interval between the third dorsal extensor compartment, which contains the extensor pollicis longus tendon (EPL), and the fourth extensor compartment, which contains the extensor digitorum communis (EDC) tendons. In a similar vein, the 4,5 portal is located between the EDC and the extensor digiti minimi (EDM). The 6R portal is located on the radial side of the extensor carpi ulnaris (ECU) tendon, compared with the 6U portal (which is located on the ulnar side).

The midcarpal joint is assessed through two portals, which allows triangulation of the arthroscope and the instrumentation. The midcarpal radial portal (MCR) is located 1 cm distal to the 3,4 portal and is bounded radially by the ECRB and ulnarly by the EDC. The midcarpal ulnar portal (MCU) is similarly located 1 to 1.5 cm distal to the 4,5 portal and is bounded by the EDC and the EDM.

Dorsal portals

Dorsal radiocarpal portals

Abrams et al. performed anatomical dissections on 23 unembalmed fresh cadaver extremities and measured the distances between the standard dorsal portals and the contiguous neurovascular structures. The 1,2 portal was found to be the most perilous. The radial sensory nerve exits from under the brachioradialis approximately 5 cm proximal to the radial styloid and bifurcates into a major volar and a major dorsal branch at a mean distance of 4.2 cm proximal to the radial styloid ( Fig. 1.2 ). Branches of the superficial radial nerve (SRN) that were radial to the portal were within a mean of 3 mm (range 1–6 mm), whereas branches that were ulnar to the portal were at a mean of 5 mm (range 2–12 mm).

The radial artery was found at an average of 3 mm radial to the portal (range 1–5 mm). Either partial or complete overlap of the lateral antebrachial cutaneous nerve (LABCN) with the SRN occurs up to 75 percent of the time. In an anatomical study by Steinberg et al., the LABCN was present within the anatomical snuffbox in 9 of 20 (45%) specimens. Based on these findings, they recommended a more palmar, proximal portal in the snuffbox that was no more than 4.5 mm dorsal to the first extensor compartment and within 4.5 mm of the radial styloid.

Branches of the SRN that were radial to the 3,4 portal were located at a mean distance of 16 mm (range 5–22 mm). In one specimen, an ulnar branch of the SRN was found 6 mm ulnar to the portal. The distance to the radial artery was a mean of 26.3 mm (range 20–30 mm). Sensory nerves were remote to the 4,5 portal, except in one case in which an aberrant SRN branch was found 4 mm radial to the portal.

The dorsal cutaneous branch of the ulnar nerve (DCBUN) arises from the ulnar nerve an average of 6.4 cm (SD = 2.3 cm) proximal to the ulnar head and becomes subcutaneous 5 cm proximal to the pisiform. It crosses the ulnar snuffbox and gives off three to nine branches that supply the dorsoulnar aspect of the carpus, small finger, and ulnar ring finger. The mean distance of the DCBUN to the 6R portal was 8.2 mm (range 0–14 mm). Transverse branches of the DCBUN were found in 12 of 19 specimens and were noted to be within 2 mm of the portal (range 0–6 mm). The mean distance of branches of the DCBUN that were radial to the 6U portal was 4.5 mm (range 2–10 mm), whereas branches that were ulnar to the portal ranged from 1.9 to 4.8 mm. Any transverse branches of the DCBUN were generally proximal to the portal, at an average of 2.5 mm.

Dorsal midcarpal portals

Branches of the SRN were found radial to the MCR portal at a mean of 7.2 mm (range 2–12 mm; SD = 2.7 mm). Two specimens contained SRN branches ulnar to the portal at 2 and 4 mm. Branches of the SRN were generally remote from the MCU portal except in one specimen (1 mm). Branches of the DCBUN were found at a mean distance of 15.1 mm (range 0–25 mm; SD = 4.6 mm).

Triquetro-hamate portal

This portal enters the midcarpal joint at the level of the triquetro-hamate (TH) joint ulnar to the ECU tendon. The entry site is both ulnar and distal to the MCU. Branches of the DCBUN are most at risk ( Fig. 1.3 ) ( Video 1-3 ).

Dorsal radioulnar portals

These portals lie between the ECU and the EDM tendons. Transverse branches of the DCBUN were the only sensory nerves in proximity to the dorsal radioulnar portal at a mean of 17.5 mm distally (range 10–20 mm) ( Fig. 1.4 ).