The Role of Locking Technology in the Hand David E. Ruchelsman, MDa,b, Chaitanya S. Mudgal, MD, MS(Orth), MCh(Orth)a,b,c, Jesse B. Jupiter, MDa,b,* KEYWORDS Locking plates Metacarpal and phalanx fractures Hand trauma Internal fixation of the hand and wrist has evolved acute bone loss, periarticular and metaphyseal in the last 4 decades. It is well accepted that stable fractures, osteopenic bone) and complex recon- internal fixation in the setting of combined muscu- structions for malunion, nonunion, or posttrau- loskeletal injuries involving the osseous skeleton matic deformities. Locked plates in the hand and soft-tissue envelope facilitates early rehabili- confer rigid or relative stability based on the clin- tation and promotes improved functional ical scenario being addressed. outcomes.1–4 Plate and screw fixation systems in In appropriately selected cases, locking plate the hand and wrist were originally predicated on technology may be helpful in addressing a variety the larger long-bone fracture fixation systems. of extraarticular and periarticular problems in the Locked plating establishes a fixed-angle construct hand and wrist. Clinical experience with locking (ie, functions as an internal-external fixator). technology in hand trauma remains relatively Angular-stable fixation has begun to revolutionize limited compared with its application for fractures the operative management of complex metadia- about the proximal humerus,5–8 distal humerus,9 physeal long-bone trauma, as well as periarticular distal radius,10–14 distal femur,15,16 periprosthetic and periprosthetic fractures, and has acquired femur,17,18 tibial plateau,19 proximal,20 and distal a growing role in the hand as well. tibia.21 As hand surgeons become more familiar With the growth of hand surgery as a subspe- with locked plating, these plates may augment or cialty, and a better understanding of the structural replace the use of the technically demanding requirements of the hand skeleton and periarticu- fixed-angle blade plates used to stabilize periartic- lar soft tissues, an increasing number of commer- ular fractures and osteotomies. cially available hand fracture fixation systems that The current indications and impetus for locked incorporate fixed-angle technology into plate and (fixed-angle) plating, along with the pearls and screw designs have emerged. The multiple hand pitfalls of this technology are highlighted by fracture locking plate systems available reflect anatomic region in the hand. Results following the growing trend amongst hand surgeons to use the application of locking plate technology in the internal fixation for difficult acute fractures (ie, management of distal radius acute fractures10–14 a Hand and Upper Extremity Service, Yawkey Center, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Suite 2100, MA 02114, USA b Department of Orthopaedic Surgery, Harvard Medical School, Boston, 55 Fruit Street, Suite 2100, MA 02114, USA c Hand and Upper Extremity Surgery Fellowship, Harvard Medical School, 55 Fruit Street, Suite 2100, Boston, MA 02114, USA * Corresponding author. Hand and Upper Extremity Service, Yawkey Center, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Suite 2100, Boston, MA 02114. E-mail address: [email protected] Hand Clin 26 (2010) 307–319 doi:10.1016/j.hcl.2010.04.001 0749-0712/10/$ – see front matter ª 2010 Elsevier Inc. All rights reserved. hand.theclinics.com 308 Ruchelsman et al and malunion22,23 have been extensively reported. all screw-bone interfaces instead of that of a single A discussion of locked plating in the distal radius is component screw as in conventional plating. As beyond the scope of this article. The application of a result, the fixed-angle construct leads to a mech- locking technology in the distal ulna, metacarpals, anism of screw-purchase failure that is fundamen- and phalanges is discussed here. tally different from that of conventional unlocked screws. Locked screws act together in parallel, BIOMECHANICS whereas conventional screws act in series.35 Conventional Compression Plating With 3-point bending load application, screw hole track deformation occurs. Unlocked screws Conventional nonlocked plate/screw constructs toggle within the screw track and sequentially rely on frictional force created between the plate loosen. In contrast, with fixed-angle fixation, the and bone surface to neutralize the axial, torsional, plate/screw construct must fail as a unit. and 3-point bending forces experienced by the 24 Locked plates may be used in a bridging mode plate/screw/bone construct. Stability with stan- across an area of comminution and/or bone loss, dard plate/screw constructs is largely determined thereby avoiding fracture site compression. Bridge by screw torque generated. Osteopenia, metaphy- plating helps to preserve the vascularity of the seal bone, comminution, segmental bone loss, intercalary fracture fragments. Relative stability is and/or pathologic bone all affect maximal screw- achieved and allows enough strain at the fracture thread purchase and compromise the develop- site to promote secondary bone healing with callus ment of sufficient torque to establish absolute 37 24,25 formation. Alternatively, locked screws can be stability with compression plating. However, used to augment a standard compression plate/ the need to perform a more extensive soft-tissue screw construct to create hybrid fixation (ie, non- dissection to maximize the plate-bone contact locked and locked screws). In a hybrid construct, interface and coefficient of friction with conven- it is therefore essential to apply compression tional plating systems may adversely affect the across the fracture site using standard techniques fracture site and periosteal biology. before insertion of the locked screws. The use of hybrid fixation with bicortical locking screws is Locked Fixed-Angle Plating advantageous in osteopenic bone. Early attempts at improving fixation of conven- Indeed, current locked plate designs incorpo- tional plates to compromised bone have included rate combination-hole technology, which allows the use of bone cement to improve screw torque, surgeons to incorporate aspects of locked plating Schuhli nuts,26 and Zespol plates27 to create and compression plating into a single implant and a fixed-angle construct. Fixed-angle technology at each screw hole site. Combination plates are has been refined by the Arbeitsgemeinschaft fur helpful in select fracture patterns in which one Osteosynthesefragen (AO/ASIF) group.28–32 In aspect of the fracture would benefit from anatomic the Synthes (Paoli, PA, USA) fracture fixation reduction and compression (ie, simple intraarticu- system, the locking screw heads are conical with lar component), whereas another fracture compo- threads that lock into corresponding screw hole nent would benefit from bridging fixation (ie, threads that are recessed within the body of the comminuted metadiaphyseal portion). If cortical plate. A recent proliferation of locked plate designs contact can be achieved on the compression by several manufacturers has followed. Locking side, it is essential to complete maximal fracture technology aims to eliminate screw toggle and to compression before locked screws are inserted. create a fixed-angle single-beam construct.33 Endosteal fibula allograft augmentation34 has been described as a supplemental technique to INDICATIONS locked plating in larger long bones. Locked fixed-angle plate/screw constructs Current indications for locked plating in the hand function as an internal-external fixator. Locked include unstable distal ulna head/neck fractures plates preserve periosteal vascularity while main- associated with unstable fracture of the distal taining fixation by locking the fixation screws to radius, periarticular metacarpal and phalangeal the plate, which may be placed extraperiosteally. fractures, especially those with metaphyseal The angular stability of locked screws functions comminution, complex multifragmentary diaphy- to distribute the applied load more evenly across seal fractures with bone loss (ie, open, combined the component screws, thus avoiding significant injuries of the hand), osteopenic/pathologic frac- load concentration at a single screw-bone inter- tures, fixation for nonunions and corrective osteot- face.24,35,36 In a locked plate system, the overall omies in the hand, and arthrodeses of the small strength equals the sum of fixation strengths of joints of the hand. Locking Technology in the Hand 309 CONTRAINDICATIONS locations (ie, proximal and distal femur) (Fig. 1). The minicondylar plate was initially made of steel There are no absolute contraindications to the use and available in 1.5-mm and 2.0-mm sizes. It is of locked plates in the hand and wrist. However, currently also available in titanium. Blade length there are scenarios for which fixed-angle locked is determined by predrilling the blade pathway. plating is not essential. If open reduction internal The blade is then inserted and acts as a derotation fixation is selected for simple, displaced, diaphy- device and resists shear on the condylar frag- seal fractures of the short tubular bones in nonos- ments. Condylar fracture fragments can also be teopenic patients, compression or neutralization fixed and compressed with the supplemental with nonlocking plate fixation is all that is required. condylar screw. In addition, simple intraarticular split fractures do Proper insertion of this device remains technically