Management of Complications in Lunate Facet Fracture Fixation

10 Management of Complications in Lunate Facet Fracture Fixation

Simon B.M. MacLean and Greg I. Bain

Abstract

The lunate facet represents the “critical corner” of the distal radius, and the main load-bearing area. The injury may be overlooked by an inexperienced surgeon. Lunate facet fractures can be one of five types: (1) a volar ulnar corner fracture (VUC) as an isolated fragment, (2) VUC fragment with extension radially to involve the radiocarpal ligaments (the entire volar rim), (3) VUC fragment as one component of a metaphyseal fracture, (4) VUC fragment as part of a high-energy “pilon-type” fracture, or (5) in combination with a greater arc injury. Standard locking volar distal radius plates often provide inadequate support to and fixation of this fragment and each subtype requires separate consideration for management.

In this chapter we will outline the anatomy of the fracture. We will discuss treatment principles including imaging, surgical approach, and fixation techniques. We will cover salvage procedures, rehabilitation, and tips and tricks to ensure satisfactory treatment of this injury.

Keywords: lunate facet fracture, volar marginal rim fractures, distal radius, volar plate, fragment-specific fixation, complications

10.1 Definition and Problem

The volar marginal rim of the distal radius owes its importance to both loadbearing function as well as the attachment of the radiolunate ligaments, which prevent volar subluxation and ulnar translocation of the carpus.1^,² The centroid of force application is volarly on the lunate facet, and because it is offset in a palmar direction relative to the radial shaft, this area transmits high loads and is difficult to stabilize.² The volar marginal rim, or “lunate facet” fracture, therefore, is an important subset of fractures, which may not be adequately fixed with traditional volar-locking plate technology. Specific volar rim plates have been designed to sit distal to the watershed line of the radius and contain this critical fragment. Despite fragment-specific technology however, hardware positioning can be challenging, and fixation may be inadequate to stabilize this challenging injury. The lunate facet fracture may be only one component of a more extensive distal radius or carpal injury, and poor outcomes may result from treatment of this fracture in isolation.

10.2 Anatomy of the Fracture

The importance of the ligamentous attachments of the distal radius was described by Melone and Medoff.³^,⁴ Melone specifically described the role of the two medial fragments for articular function, and their strong ligamentous attachments.³^,⁵ Medoff recognized the contribution of these ligaments to fracture displacement, radiocarpal instability, and the contribution of ligament avulsion to the creation of “rim” fragments leading to catastrophic failure of fixation.⁴

All low-energy injuries occur between ligaments on the distal radius, and each fragment is likely to have an attached ligament.⁶ We describe this as the “osteoligamentous concept of distal radius fracture” (Fig. 10‑1).

Fig. 10.1 Osteoligamentous concept.⁷ (a) Diagram of osteoligamentous unit, (b) Isolated volar ulnar corner fracture. Copyright Dr. Gregory Bain, with permission.

Physiological extension of the wrist creates tension on the volar radiocarpal ligaments and acts as a tension band, increasing contact pressure on the lunate facet. Following impact on an outstretched hand, forced hyperextension and axial compression causes a fracture of the subchondral bone plate and avulsion of the lunate facet with the attached short radiolunate ligament (SRLL). The wrist settles in volar subluxation with this fragment. If the force propagates radially to include the scaphoid facet, then the long radiolunate ligament (LRLL) will also avulse, leading to ulnar translocation.⁸

10.3 Treatment: Management of Volar Rim Fractures

All patients require computed tomography (CT) scanning as well as plain radiographs. Critical review of these is imperative to identify other fractures of the carpus and ulnar styloid, as well as assessment for carpal alignment and carpal instability.

Volar rim fractures of the lunate facet may occur in isolation or may be one component of a distal radius fracture with comminution. Identifying this will aid in determining the fixation system required. We have a low threshold for performing diagnostic and/or therapeutic arthroscopy at the time of fixation if preoperative imaging suggests this may be beneficial.

Before deciding on management, the type of volar rim fracture should be determined. From our clinical experience, we have determined five main fractures of the distal radius involving the volar rim (Fig. 10‑2).

Fig. 10.2 (a-e)Classification system for volar marginal rim fractures of the distal radius. Copyright Mr. Simon MacLean, with permission.

10.3.1 Surgical Approach

Surgical approach is determined by the type of fracture. If the lunate facet fracture is an isolated injury we prefer a volar ulnar approach. This allows direct access to the lunate facet. We then proceed with fragment-specific fixation. This approach can also be extended into the palm, past the distal transverse wrist crease if concomitant carpal tunnel decompression is required.⁹^,¹⁰

If the lunate facet fracture is one component of a distal radius fracture or there is more radial extension of the marginal rim fracture, we prefer a distal flexor carpi radialis (FCR) approach with oblique extension past the distal wrist crease, which allows excellent access to the radial metaphysis, as well as both the scaphoid and lunate facets.

Volar-Ulnar Approach

An incision is made between FCU and palmaris longus to the distal transverse wrist crease. The interval between the ulnar neurovascular bundle and the carpal tunnel contents is used, and these structures are protected with right-angled retractors. If an extensile incision is used, the distal wrist crease is crossed obliquely and extended longitudinally in line with the ring finger. The flexor retinaculum is released completely. The pronator quadratus (PQ) is elevated from the radial aspect of the distal radius. The volar-ulnar fragment is then exposed. Small K-wires can be used as a joystick, then temporarily secure the fragment. Alternatively, sutures at the bone-ligament junction can be used to reduce the fracture (Fig. 10‑3).

Fig. 10.3 The extended volar-ulnar approach to the distal radius used to fix a type 2 fracture. (a) The ulnar neurovascular bundle is retracted ulnarly, and the flexors with median nerve are retracted radially. The pronator quadratus (PQ) is exposed. (b) The PQ is released from radial to ulnar. A fine needle is used to identify the radiocarpal joint. (c) A buttress pin is used to fix the lunate facet fragment. Small all-suture anchors are used to repair the adjacent radial capsule with the long radiolunate ligament (LRLL), which has avulsed from the marginal rim of the distal radius. Copyright Mr. Simon MacLean, with permission.

Distal FCR Approach

The incision is based over the FCR tendon, and the skin incision proceeds obliquely for 1 cm over the distal wrist crease in a radial direction. The sheath of the tendon is opened and the FCR tendon retracted ulnarly. The posterior bed of the sheath is released to expose the deep volar compartment. We do not specifically identify the median nerve but retract the flexors with the nerve ulnarly. A right-angled retractor is used to protect the radial artery. The PQ is released. We routinely release the distal insertion of brachioradialis by sharp dissection. This allows pronation of the distal fragment to aid anatomical reduction. The components of the distal radius fracture are identified, and each separate component reduced. We proceed with reduction of the intermediate column, including the lunate facet. Next the radial column is reduced. These components are held with K-wires or buttressed with the chosen plate for fixation. Lastly, the ulnar column is reduced and fixed if required.

10.3.2 Fixation Techniques

Lunate facet fractures represent avulsion of an osteoligamentous unit in the “critical corner” of the distal radius.11 Strain energy from wrist hyperextension causes progressive lengthening of the SRLL before avulsion of the fragment, as the ultimate tensile strength of the distal radius bone is usually reached before that of the ligament. Radiocarpal dislocations can occur without fracture however, and these injuries represent failure at the junction of the bone and the ligament (osteoligamentous junction). A marginal rim fracture therefore can occur together with avulsion of the adjacent radiocarpal ligaments, including the LRLL and radioscaphocapitate ligament (RSCL) (type 2). The size of the fragment and any adjacent injury to the radiocarpal ligaments determine the type of fixation used.

Direct vision and fluoroscopy are used to determine anatomical reduction. In isolated type 1 fractures we prefer a fragment-specific plate. If the fragment is particularly small, a volar buttress pin (Fig. 10‑4) provides rigid fixation without the risk of further comminution to the fragment. If the fragment is larger, we prefer a fragment-specific volar buttress plate. If there is adjacent capsular injury (type 2), this should be repaired. Our preference is to use two to three all-suture anchors. These are positioned along the marginal rim, under subchondral bone, and the capsule is repaired (Fig. 10‑5).

Fig. 10.4 Type 1 injury involving an isolated avulsion fracture to the volar ulnar corner. Stability is achieved by stable fixation to the fragment. Copyright Dr. Gregory Bain, with permission.

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