Various authors40-43 have described alternative fixation methods for the palmar lunate facet fragment. Jupiter and Marent-Huber42 described 2.4-mm locked-plate fixation with either a standard palmar plate or T- or L-plates for cases in which the palmar lip fragment is very distal and small. In fact, some newer anatomical distal radius implants include features designed to target these fragments (Figures 7A, 7B). An alternative fixation method involves use of a 26-gauge stainless steel wire passed through drill holes in the metaphysis 1 cm proximal to the fracture and then passed through the palmar capsule just distal to the fragment and secured in figure-8 fashion while the fragment is manually held reduced.41 Still others have recommended limited internal fixation of the sustentaculum lunatum through an ulna-sided palmar approach to the distal radius (between the ulnar neurovascular bundle and the flexor tendons) combined with external fixation to restore length and palmar tilt in highly comminuted fractures.40,43
A method involving arthroscopically assisted reduction and fixation of the lunate facet has also been described, though this procedure is technically demanding and has limited indications.44 It uses a Freer elevator passed through the standard 3-4 portal after initial visualization and evacuation of hematoma. The Freer elevator is used to disimpact the sustentaculum lunatum and to elevate it from its depressed position. With the dorsal lunate facet left displaced to facilitate access to the palmar fragment, a nerve hook retractor is used to reduce the palmar facet to the radial styloid, and Kirschner wires are used to achieve interfragmentary fixation. The dorsal lunate fragment is then pieced back to the articular segment, and the entire construct is fixed to the radial metaphysis with additional Kirschner wires.
Discussion
Given the increasing incidence of fractures of the distal radius, internal fixation of these injuries will continue to be relevant. American Academy of Orthopaedic Surgeons guidelines recommend operative fixation for fractures with postreduction radial shortening of more than 3 mm, dorsal tilt of more than 10°, or intra-articular displacement or step-off of more than 2 mm.45 Dr. Eglseder and Dr. Pensy indicate operative treatment of any incongruity of more than 2 mm in a young, active adult with a fracture of the distal radius. For the multifragmentary distal radius being treated operatively, attempts are made to achieve reduction more accurate than this, but formal dorsal exposure or direct visualization of the joint surface via dorsal capsulotomy is carefully chosen based on age, activity level, and bone quality. Recent high-level evidence46 showed that closed treatment of unstable fractures of the distal radius results in good outcomes in the elderly. However, it is important to note that fractures displaced in a palmar direction and palmar shear patterns were excluded from that work. It is widely accepted that palmar carpal translation should be addressed with internal fixation, and specific attention must therefore be paid to the lunate facet as the cornerstone of the distal radius. Furthermore, high-energy comminuted fractures in young patients still necessitate internal fixation of fragments to restore alignment and articular congruity.
Conclusion
The importance of the palmar lunate facet in providing support and restraint to palmar carpal translation and the key role of this facet in restoring the anatomy of the distal radius have been known. This fragment deserves special attention because failure to adequately stabilize it results in loss of fixation and carpal subluxation. Various approaches and fixation techniques have been recommended, including the method we prefer and have described here. Our newly proposed term, sustentaculum lunatum, our review of its structure and function, and our descriptions of fixation techniques are intended to promote awareness of this fragment in the treatment of fractures of the distal radius.