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Plate and Screw Design in Fractures of the Hand and Wrist

Mudgal, Chaitanya, S; Jupiter, Jesse, B

Section Editor(s): Meals, Roy A MD, Guest Editor; Harness, Neil G MD, Guest Editor

Clinical Orthopaedics and Related Research: April 2006 - Volume 445 - Issue - p 68-80
doi: 10.1097/01.blo.0000205887.04200.21
SECTION I: SYMPOSIUM: Problem Fractures of the Hand and Wrist
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As internal fixation of fractures of the hand and wrist has evolved, so too have the implants used for the same purpose. Implants used for the first ½ of the 20th century were modeled on implants used to fix long bone fractures. Consequently, they were often bulky. In addition, they often were made of materials which were ill suited to the unique functional and biomechanical requirements of the hand and wrist. As a result, outcomes of internal fixation frequently were suboptimal and complication rates were high. In the past 40 years there has been an evolution in metallurgy, biomechanics, and implant design for fracture fixation in the hand and wrist, quite unlike any other anatomic location in the body. The principal purpose of this review is to highlight these very advances. Implants now are made of highly bio-compatible materials, have a low profile, can be contoured to suit individual anatomy, and provide considerably reduced rates of soft tissue irritation. These features afford surgeons the ability to fix complex injuries in a stable manner so as to institute early rehabilitation in an effort to maximize individual outcomes.

Level of Evidence: Level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

From the Orthopaedic Hand Service, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.

Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.

Correspondence to: Chaitanya S. Mudgal, MD, Yawkey Center, Suite 2100, Massachusetts General Hospital, Boston, MA 02114. Phone: 617-726-8530; Fax: 617-724-8532; E-mail: cmudgal@partners.org.

Internal fixation of the hand and wrist has changed tremendously during the past four decades. Essential to this change has been the acceptance of internal fixation as a safe, effective and viable alternative in the treatment of many fractures of the hand and wrist. It now is well recognized that early stable skeletal fixation in the setting of complex soft tissue injury, followed by early rehabilitation can lead to superior functional outcomes.13,23,39,51

Literature pertaining to internal fixation of fractures in the hand and wrist was reviewed carefully. Emphasis was placed on those articles that specifically dealt with plate and screw fixation of these fractures. It became apparent that when plate and screw fixation systems initially were developed for the hand, they simply were modeled after the large long-bone fracture fixation systems. However, with the passage of time and with a better understanding of the structural requirements of the hand skeleton, materials and technology, implants have been designed specifically for the hand and wrist.6,9,23,24,30,39,42-45,49,51,52

We will outline the advances in implant design and technology in the treatment of fractures of the hand and wrist and provide a unique step-wise, evidence-based perspective about this implant evolutionary process, along with a brief overview of salient historical aspects of internal fixation of the hand and wrist.

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HISTORY

The earliest description of plating fractures in the hand can be attributed to Albin Lambotte, a Belgian surgeon who described plating of a metacarpal fracture with an aluminum plate and cerclage wires in 1905.19,32 In 1909, Lane designed a plate-and-screw system in which the plates could be contoured, but were weak. Sherman, the chief surgeon for the Carnegie Steel Company in Pittsburgh, modified the Lane plate and made it stronger. Sherman also introduced self-tapping screws.19,32

The largest contribution to our current knowledge and to the development of implants specifically designed for use in the hand and wrist in the past 50 years has come from the Swiss group Arbeitsgemeinschaft für Osteosynthesefragen or Association for the Study of Internal Fixation (AO/ASIF). Founded in 1958 by Müller, Allgöwer, and Willenegger, this group defined principles of safe and stable internal fixation of fractures with the aim of restoration of anatomy and function of the injured extremity.19 The plate design of Bagby and Janes was modified and using the spherical gliding principle in a plate along with a hemispherical headed screw, compression plate osteo-synthesis as we know it today was born.19 Based on these principles and implant designs Heim and Mathys introduced a small fragment set in 1964 and a mini fragment set in 1970. The contributions of the AO/ASIF are seminal to our current understanding of the biology of bone healing, materials science, and biomechanical testing of implants and outcomes analysis.

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MATERIALS SCIENCE

There has been an evolution in materials used for implants during the last four decades.

Modern implants have been made out of alloys but this was not always the case and the earliest implants often were made of pure metals such as iron, gold, silver, and platinum.17 These materials were mechanically and biologically inadequate in vivo. Research was directed toward finding corrosion-resistant materials that would be able to withstand the mechanical stresses of the musculoskeletal system.

The concept of alloying revolutionized modern implant design. Implants currently used in the hand and wrist most commonly are made from iron alloys such as stainless steel and titanium alloys.

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Stainless Steel

Currently, the most commonly used stainless steels are 316L and 22-13-5 as designated by the American Standard for Testing and Materials (ASTM). Stainless steel essentially is an iron alloy containing carbon, nickel and molybdenum. Low carbon contents reduce susceptibility to intergranular corrosion. Nickel and molybdenum improve strength while chromium imparts corrosion resistance in vivo, by developing an oxide film on the implant surface17,55 (Fig 1).

Fig 1

Fig 1

All contemporary orthopaedic implants are subjected to a process called as passivation or electropolishing. This enhances formation of the protective oxide film on the implant surface, cleans and reduces the surface roughness, and makes the implant smooth and highly resistant to corrosion.

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Titanium Alloys

The AO/ASIF introduced implants made out of commercially pure titanium. These were inert, but there were concerns about their mechanical strength. Soon they were replaced with titanium alloys, and the most commonly used alloys today are Ti-6Al-7Nb and Ti-6Al-4V. These alloys offer excellent corrosion resistance, biocompatibility and are stronger than commercially pure titanium. The oxygen content of the alloy controls the ductility and yield strength. The anodized surface finish seen in these implants increases the thickness of the protective oxide layer17,55 (Fig 2).

Fig 2

Fig 2

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Bioabsorbable Implants

The interest in the use of bioabsorbable implants in hand surgery largely is an extension of existing knowledge of the use of these implants in craniofacial surgery where they have been used extensively.2,3,53 However, they continue to remain an alternative mode of fixation.

The materials most commonly used include polylactic acid (PLA), polyglycolic acid (PGA) and their copolymers.59,60 The copolymers include PLGA 80/20, P(L/DL)LA and P(L/DL)LA 70/30. Self-reinforcing techniques in which the polymeric matrix is reinforced with fibers, fibrils or molecular chains of the same material, are used to produce ultra-high strength implants. These implants have been used in the fixation of metacarpal and phalangeal fractures.28,29,57,61 However, nonself-reinforced bioabsorbable plates and screws have been shown to have lower strength characteristics and higher failure rates in an experimental model.8

The modulus of elasticity in these implants is close to that of cortical bone. In addition compared to metallic implants, these implants are structurally less stiff. These features help to reduce stress shielding. It is now evident that any bony weakness deep to a plate is a representation of loss of periosteal vascularity rather than stress shielding. In addition, they degrade gradually while bony union and growth is occurring. The strength retention of these implants varies from six weeks to 36 weeks and complete absorption can take from 1 to 3 years.58

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IMPLANT DESIGN

Screws

The initial material from which a screw is manufactured is called bar stock and usually is purchased in the cylindrical rod form. The diameter of the rod closely approximates the largest diametric dimension of the screw being produced, and as a result, approximates the diameter of the screw head.17 The bar stock undergoes the first process of turning, in which the screw head and shank are turned to the screw specifications of length and size. This cylindrical piece is called a blank. The next step involves creation of the screw driver recess in the screw head. If necessary, the screw then is cannulated. This is done by a process called gun drilling.17

The cutting flutes are then machined for self-tapping screws. These usually are sharp and are cut at the leading edge to aid in screw insertion. Similar flutes are cut near the head of the screw in an opposite direction to aid in screw removal. These are called reverse cutting flutes. Now the blank is ready for external thread creation. Most orthopaedic screws have their threads produced by a process called cutting, which in itself can be done by turning, milling, or grinding. Grinding is the most common process. The screw is then subjected to electropolishing and passivation.17,55

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Screw Design

Most commonly, screws are used in the hand and wrist to compress fracture fragments using the lag screw principle or are applied through a plate. Screws rely on the mechanical advantage gained from the principle of an inclined plane, in the form of screw threads. As the screw is turned clockwise, an axial force is produced that helps to propel the screw along its inclined thread surfaces through the bone. The inclination of the thread should be small enough to prevent the screw from spinning in the bone and loosening, yet must be large enough to allow forward progress with a low number of turns.19,49 The distance between two threads is called the pitch, and screws with a high pitch (fine thread) commonly are used for cortical fixation whereas screws with a low pitch (coarse thread) are used for fixation in cancellous bone.

Orthopaedic screws have gone through substantial changes in design over the last four decades. The next section will review these changes.

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The Screw Head

Traditionally bone screws had a vaulted head with a spherical undersurface (Fig 3A). This was well suited to the design of the dynamic compression plate (DCP), which relied on the spherical gliding principle for screw fixation through the plate.24,49 This head design allowed the insertion of a hexagonal headed screwdriver. To accommodate this driver and be able to withstand torque, the head had to be a certain size. Since 1984, this design was standard in screws developed by the AO/ASIF, and in fact replaced the Phillips head already in existence on smaller sized screws.24

Fig 3A

Fig 3A

However, the large head of the screw was prominent, and had a high profile, which interfered with gliding of soft tissues and were attributed to be the cause of extensor tendon irritation and excursion problems.6,39,45,51,52 To reduce screw head prominence, it has been recommended that the screw be countersunk.24 However, in soft cancellous bone, countersinking can lead to loss of fixation because of subsidence of the screw head. To prevent this subsidence, a washer has been recommended.24 During the last decade, there has been a revival in low profile screw heads, and currently screw heads are designed with a conical profile or a flat undersurface (Fig 3B).

The earliest orthopaedic screws had slotted heads and were largely modeled on machinery or wood screws. The slotted head was not suited for torque transmission and could strip easily. This head design was replaced by cruciate slotted heads that are more effective for torque transmission.54 The hexagonal head slot, which was introduced in large fragment screws, was applied to smaller screw heads in 1984.24 The hexagonal slot allows a strong connection capable of generating substantial torque without fear of stripping the screw head and is relatively insensitive to alignment.

Currently, screw head driving recesses are hexagonal, square or star shaped (Fig 4). The star shaped recesses offer improved torque, high strength, and self-retention of screws on the driver, in comparison with cruciate and hexagonal heads.63 An appropriately engaged screw in the driver allows a surgeon to exert a more suitable amount of manual axial force in its insertion, and can provide tactile feedback to the surgeon's hand.12

Fig 4A

Fig 4A

Headless screws were initially introduced by Herbert in 1984. Numerous features unique to this screw design enabled hand surgeons to securely fix fractures and start early mobilization in situations where previously it was not possible.25,26

The Herbert screw (Zimmer, Warsaw, IN) consists of a central portion or shaft that is smooth and there are threads at either end. The threads at each end have different pitches, with threads at the leading end being coarser than the trailing end. The leading threads advance more rapidly. When combined with the smooth shaft, this draws the two fracture fragments together generating compression across the fracture site (Fig 5). The small diameters of these screws allow for optimal positioning in small fragments. The lack of a protruding head, allows the screw to be buried completely and avoid soft tissue or joint irritation. Insertion is simplified by passing the screw through the same guide as the drills and tap.25,26 A potential disadvantage of the Herbert screw is that it needs tapping before insertion.

Fig 5

Fig 5

Headless screws were initially designed as differential pitch screws until the introduction of the Acutrak screw (Acumed, Hillsboro, OR). This design consisted of a variable pitch screw thread along a truncated cone. The tapered profile combined with the constant rate of thread pitch variation along the length of the screw allows for an accumulation of pitch differential, which leads to gradual compression across the fracture site (Fig 6).

Fig 6

Fig 6

The taper on the outer profile of the screws allows threads to constantly purchase new bone, which improves pull out strength. The design also allows screw threads across the fracture site, which is contraindicated in AO/ASIF screws. These self-tapping screws are made of a titanium alloy. The tapered design prevents cross threading and allows compression without using principles of lag screw fixation. The screws are cannulated, allowing percutaneous placement. This unique design has been noted in various biomechanical studies as a factor in the ability of the Acutrak screw to generate greater compression when compared with the Herbert screw and AO/ASIF cannulated screws.1,5,18,34,56,63

Conventional screws rely on compression of the plate against the bone to create friction. This, however, has an adverse effect on bony and periosteal biology. However, locking the screw head into the plate, creates a locked or fixed angle construct, allowing fixation only in the far cortex, but avoiding compression of the plate against the bone.

The locking screw heads are conical (Morse cone) with threads that lock into the body of the plate (Fig 7). These screws function more like unicortical bolts.41,49 Because these locking screws get fixation in only one cortex, it is critical that they be used in the diaphysis where the bony quality is better. An extension of this principle and that of a fixed angle device has been applied to screws placed through plates in the metaphyseal portion of the radius, metacarpals, and proximal phalanx. These screws simply lock into the plate, converting it to a fixed angle device and improving stability.

Fig 7A

Fig 7A

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The Shaft of the Screw

The addition of the partially threaded screw allowed lag screw fixation even in metaphyseal regions. The shaft of the screw has a diameter less than the widest diameter of the screw thread. This design allows it to automatically function as a lag screw.24,49 However, because there are no reverse cutting flutes, removal can be difficult, especially with the passage of time when the portion of the screw hole around the shaft will fill in with new bone.19 Partially threaded screws are now available in sizes as small as 2.4 mm (Synthes, Paoli, PA).

Locking headed screws with smooth shafts, also referred to as bolts or buttress pins, have also been used in fixation of fractures of the distal radius (Synthes; Hand Innovations, Miami, FL),36,64 and in the hand in conjunction with the mini condylar plate. These lock into the plate and essentially perform a buttressing function for the articular surface. The design of the screw allows smooth and easy insertion of the screw into bone, especially in the presence of comminution, without disturbing any fracture fragments. These screws may also be available as partially threaded screws that engage the dorsal cortex of the radius and provide fixation in addition to the buttressing effect (Fig 8).

Fig 8

Fig 8

Cannulation of screws has simplified numerous procedures. Smaller incisions, less soft tissue dissection, and accurate percutaneous screw placement over a guide wire have allowed many procedures to be performed simply, effectively, and expeditiously. Biologically, when cannulation is combined with a headless screw, it creates a minimally invasive procedure with an extremely low profile implant. The Herbert-Whipple screw (Zimmer) is cannulated with a wider shaft than its noncannulated counterpart. Unlike the Herbert screw, it is self-tapping.

Biomechanically, although cannulated screws have less material in the cross section of the shaft, they have a larger shaft diameter. This actually makes them far stronger than a noncannulated cortical or cancellous screw of a similar size.54 This is because of the increase in stiffness of a cylinder, which is a function of the third power of its radius. While theoretically this increased shaft diameter reduces its thread depth and may therefore reduce holding power in bone, there is no clinical evidence to support this concern.

Screws with fine and coarse pitches have been used in cortical and cancellous bone respectively. Changes in screw pitch affect the performance of screws in in vivo conditions due to the thread shape factor. The thread shape factor is calculated by adding 0.5 to the product of a constant with the ratio of thread depth to pitch. Theoretically, this implies that as pitch increases, the thread shape factor increases. It has been shown in numerous studies that increasing the pitch improves holding power and increases pullout strength.15,20 However, an increase in thread shape factor beyond a certain point implies a reduction in thread thickness, allowing threads to fail by bending rather than by shear. In clinical practice, most screws used in fractures of the hand have a high pitch to improve their holding power and increase pullout strength.

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The Tip of the Screw

The most clinically relevant change in screw design has been the introduction of self-tapping screws. These are screws that are inserted directly into a predrilled hole without first tapping a thread. Heim and Pfeiffer24 have noted that, “even with small screws it is necessary to tap the drill hole, so that the screw can seat properly in the bone and function correctly.” They go on to say, “ … also, the frictional heat generated by driving a screw into an untapped hole can cause thermal necrosis that predisposes to loosening. The ASIF has always been very skeptical toward the use of self-tapping screws in cortical bone.”

However, the AO/ASIF since has revised its stance on self-tapping screws based on on-going research. There is data to suggest that there is no difference in the pullout strength of tapped and untapped screws.4,50 In addition, self-tapping screws have been shown to perform excellently in the clinical setting.7

The screw tip of self-tapping screws can differ greatly. The tip itself may be tapered or sharp. The number and depth of flutes can differ. The flutes may have a positive, neutral, or negative rake. The rake is the angle subtended by the edge of the screw with a line passing through the center of the screw shaft and perpendicular to its long axis.4,54 Currently available screws usually have two or three large cutting flutes with a positive rake angle. The volume and number of the cutting flutes is important in the management of bone debris generated as the screw tip cuts its way through the bone (Fig 3A).

Self-tapping increases the torque of screw insertion by 35% to 40%.4 The increase in torque, however, generates heat. Using saline as a lubricant reduces the heat. If the cutting flutes have a positive rake, the cutting force required is less and consequently the heat generated is also less.49,54

Most importantly clinically, self-tapping screws reduce the need for an additional operative step and operating time. This is critical in small fragments where an additional step could involve a loss of reduction. It is important to remember that because the last millimeter of a self-tapping screw is bereft of any threads, it has no purchase in the far cortex. It is therefore critical to place a screw that is slightly longer than the measured size so as to achieve fixation in the far cortex. This is even more critical when using it as a lag screw.4,49,54

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Plates

Currently, plates are tailored to suit local anatomy, functional requirements after surgery, and to withstand loading during early mobilization. They have not only reduced in size but have also been reduced in profile and have incorporated design features used in implants for fractures in other anatomical locations.

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Plate Design in the Hand

The earliest plates formally designed for use in the hand were 2.7 mm plates.24 Most of these implants were made of stainless steel. The implants tended to be stiff, could not be contoured closely to fit bony anatomy, and were thick. Early reports on internal fixation in the hand using these implants reported extremely high implant related complication rates.6,39,52 In addition, fixation of periarticular fractures was challenging because of the limited plates available.

Some authors believed the implants were too large for the hand skeleton, and interference with extensor excursion was often noted.6,39,45,52 Contouring was difficult and to place these implants precisely, often the degree of soft tissue dissection led to additional soft tissue injury.6,39,45,52 However, these reports,6,39,45,52 also dealt with fractures involving significant soft tissue injury. Therefore, we think, as do some of the aforementioned authors, that the problems noted may be largely related to the soft tissue injury and not to implant design and placement. There is now growing evidence to support the definitive role of newer designs in stable fracture fixation and early mobilization with a reduction in the previously noted implant related complications.6,23,44,49,51

In 1987, Buchler and Fischer9 reported their early experiences with a new mini condylar plate. The blade plate that they used was similar in design to fixed angle devices used for periarticular fractures in other anatomical locations (Fig 9). The mini condylar plate was initially made of steel and available in 1.5 and 2.0 mm sizes and is now available in titanium. The blade can be cut as needed and the shaft section is notched for ease of contouring. It was designed for use in periarticular fractures of the metacarpals and phalanges. It was believed this implant would be ideal for use in intercondylar fractures of the proximal phalanx by placing it laterally. This would allow the blade to act as an antirotation device and resist shear on the condylar fragments. The condylar fragments could also be compressed with the condylar screw. The authors emphasized the critical need for pre-operative planning and precise placement of this implant.9,38 The insertion technique is demanding and authors of subsequent reports noted high complication rates related to its insertion.38,39

Fig 9

Fig 9

As the limitations of existing implants were identified, a newer generation of implant evolved based on pre-existing implants used in maxillofacial surgery.44 Leibovic30 introduced these mini-plates in 1984 for maxillofacial use and in 1992 introduced a set of implants specifically designed for the hand as their Profyle set, complete with self-tapping screws.30 These pre-contoured titanium implants had a lower modulus of elasticity, and could be contoured to individual bony anatomy. These plates were also thinner and were combined with screws that had flat conical heads that tightened flush to the plate. Plates are available in 1.2, 1.7, and 2.3 mm sizes. The height of these plates after screw placement ranges from 0.76 to 1.34 mm.30

The AO/ASIF introduced their own version of a modernized small and mini-fragment fixation system in 1997 with the advent of the Modular set (Synthes). These titanium, low-profile implants are used with self-tapping screws. Four plate sizes are available and include 1.3-mm, 1.5-mm, 2.0-mm, and 2.4-mm plates. Plate thickness varies from 0.7 to 1.25 mm30 (Fig 10).

Fig 10

Fig 10

Plates are available in Y, T, and H shapes as well as straight plates. Both systems have plates that are notched in the shaft portion of the plates, which allows the plate to be cut to size easily, and contoured to fit individual anatomy. The low profile and precontoured design allow periosteal closure over the plate, preventing any contact with the extensor mechanism with consequently reduced problems with extensor excursion.

Finally, both systems have plates with fixed angle designs available, in the form of mini condylar plates, and locking plates (Synthes). Plates in this system are available with limited contact dynamic compression (LC-DCP) designs.

Biomechanical studies have shown that these low profile designs do withstand bending forces well.14,35 However, their thin design does leave them susceptible to torsional forces. Therefore, this weakness to torsional forces has been countered by imparting a precontour to these plates, which allows them to be fixed in more than one dimension especially in periarticular fractures. This design has been shown to increase the stiffness of constructs.42,43

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Plate Design in the Wrist

There has been an intense amount of interest in fixation of fractures of the distal radius. The increased awareness of certain fracture patterns, limitations of casting, pins, and external fixation,62 better imaging and understanding of fracture geometry, and the concept of not bridging the wrist31 in an attempt to improve functional outcomes, were instrumental in getting this implant design evolution started. The concepts of subchondral bone support,21 fragment specific fixation,33 multidimensional fixation,26,46-48 locked screw plating to provide a fixed angle construct,36,47,48 and finally columnar fixation27,33,46 all have provided the design of implants with new features that appear to improve fixation and affect outcomes positively. The seminal feature of all these concepts and the effect they have on implant design has been the desire to have the implant support and recreate individual anatomy without sacrificing stability.33,36,46-48

The earliest plates available for fixation of fractures of the distal radius were designed by the AO/ASIF and were 3.5-mm T-shaped plates. They were made of steel, had no ability to be customized or contoured, and were designed to be used on the dorsal aspect of the distal radius for dorsally angulated fractures and the volar aspect of the radius for volar marginal or shearing fractures.24,55 These plates often were inadequate in fixing comminuted fractures of the distal radius. The 3.5-mm screws were too large and had prominent heads. The plates interfered with extensor function over the dorsal distal radius. The screws often did not get purchase in the soft, fragmented periarticular bone.

The concept of subchondral bone support was suggested in 1995 by Gesensway et al21 when they presented their design of a fixed angle device to apply to the dorsal aspect of the radius. In 1996, the AO/ASIF introduced a plate design shaped like the Greek letter pi. It was designed by their Hand Study Group for internal fixation of complex distal radius fractures and was designed for dorsal application.47,48

At the same time a volar plate with similar design features was developed to address volar marginal fractures. These low profile plates incorporated the concept of locking screws into the plate to provide a fixed angle construct. The distal portion of the pi plate is contoured to fit the anatomy of the distal radius, and screws can be placed subchondrally in different angles to provide multiplanar fixation in comminuted fractures. The screw holes are designed to accept traditional screws and threaded buttress pins (bolts). The screw holes are recessed, allowing the screws to sit flush with the plate and reduce the profile of the construct. There are two proximal limbs and these are meant to reduce bending stress on the construct and by making them narrow, they are meant to limit the amount of bony devascularization under the plate. These plates also had the ability to have a drill guide screwed in to the screw hole for precise placement of the locking buttress pins. The notched design of these plates meant that they could be additionally contoured to individual anatomy or cut to size as necessary.47,48

Shortly thereafter, other plates for dorsal fixation of distal radius fractures were commercially available.10,21 Although the development of low-profile, locking, subchondral-bone-supporting systems was a notable advance in fixation of distal radius fractures, numerous investigators reported a high incidence of implant related complications and need for implant removal.10,24,47,48 These problems were, however, noted very infrequently with volarly placed plates. To date, only one report has identified serious problems with the flexor pollicis longus after volar plating of distal radius fractures.16 It seems that meticulous plate placement, followed by careful repair of the pronator quadratus, has reduced the possibility of flexor tendon irritation or rupture to a minimum.

During the last decade, as the emphasis on internal fixation of the distal radius has increased, volar fixation of dorsally displaced distal radius fractures appears to have acquired a popular following. The volar fixation of these fractures is based on the premise that a strong volar locking plate that functions as a fixed-angle device essentially would function as an internal fixator to restore length and buttress the subchondral region to facilitate early motion while obviating chances of future collapse and length loss.36,64 Fragment-specific and columnar fixation are also growing in popularity.22,33,46,64 All of these popular fixation systems have certain design features in common.

Volar implants on the distal radius have traditionally been T shaped and current designs have not digressed from this concept (Fig 11). The T shape allows fixation in the distal fragment of the distal radius with multiple fixation points. Some designs offer a simple T configuration with rounded edges on the distal limb of the T (Hand Innovations; Acumed), while others have the distal limb placed at an oblique angle to follow the anatomic ulnar inclination of the radial articular surface (Synthes).

Fig 11

Fig 11

Most implant designers are cognizant of fracture patterns and have developed specially designed extensions to cover the volar surface of the lunate facet and radial styloid. Plates developed by the AO/ASIF can also be contoured with the help of locking drill guides being used as benders. Because the holes are undercut they are protected to some extent from distortion after contouring. Also, because these plates are placed volarly in dorsally comminuted fractures they are subjected to considerable bending forces. Therefore, most manufacturers have reinforced this portion of the plate by increasing its thickness.

The screws that are placed in the distal portion follow some common concepts. Most designs offer locking screws distally, recessed into screw holes to create a low profile. The screws in the distal portion are angulated so as to provide a subchondral bone fixed angle support. The screws are angulated distally (Hand Innovations; Acumed) or proximally (Synthes) (Fig 12). Some designs also offer a further unique ability to place the locking screw into a volar bearing that is capable of locking into the distal screw holes. As the screw is tightened into the bearing, this design offers the possibility of changing the angle at which the screw and bearing are tightened to the plate, allowing the surgeon to further dial in the reduction more accurately (TriMed, Valencia, CA).

Fig 12A

Fig 12A

Screws are placed in the distal limb in a more anatomic pattern to try and match normal anatomical contours of the distal radius so as to optimize subchondral bone support. Screws can be placed in two sets of rows, so as to provide support to different portions of the subchondral plate, in a three-dimensional scaffolding fashion (Fig 12A) (Hand Innovations).

Screws placed into the lunate facet and styloid are placed at an angle to additionally increase the length of the screw in the bone and augment its holding power. This also fulfills the rationale for columnar fixation by getting purchase in the styloid and lunate facet, which form parts of the radial and intermediate column (Fig 13). All the distal screws can be placed as locking screws. The screw holes are drilled with special targeting devices that lock into the screw holes in the plate.

Figure 13A

Figure 13A

These targeting devices are available as individual units (Hand Innovations; Synthes) or as a single unit that mimics the geometry of the entire plate (Acumed). Provisional fixation with Kirschner wires allows the surgeon to assess the inclination of the distal locking screws and move the plate distally to optimize subchondral bone support or proximally to avoid intra-articular screw placement.

The subchondral bone support pegs are designed to transfer axial loads across the fracture while achieving fixation in weak metaphyseal bone. This is meant to allow early motion despite comminution and, because of the fixed angle construct, eliminates the need for bone grafting of compacted metaphyseal bone. However, careful placement immediately adjacent to subchondral bone must be emphasized to avoid any possibility of settling of the articular fragments, especially in patients with osteoporosis.

Most plates are designed to fit the volar anatomy of the distal radius and come precontoured. The volar inclination of the distal radius is matched with an angle in the plate between the distal end and the shaft which measures between 18° and 20°. The distal edges of the plate are beveled or rounded to reduce soft tissue irritation. The oblong hole in the shaft allows the plate to be fixed provisionally until final adjustments can be made. Some designs offer the choice of using additional screw holes to produce compression at the fracture, while at the same time retaining the ability to alternatively place a locking screw through the same hole.

This feature of a combination hole in the plate is unique to the Locking Compression Plates developed by the AO/ASIF, and has a distinct role in osteoporotic bone (Synthes). These particular plate designs also incorporate features of the limited contact-dynamic compression plate, which was also designed by the AO/ASIF. The plates have evenly distributed undercuts to reduce contact with the bone and thereby improve blood supply. The holes are also undercut so as to allow tilting of a screw up to 40° along the long axis of the plate. The undercuts also allow contouring to occur between holes and thereby do not distort locking screw holes.

Columnar plates are largely linear in shape. However, in profile the plates designed to be placed on the radial column are precontoured to this anatomical profile, to provide a buttressing effect (Synthes). While some allow placement of wires through the distal holes in the styloid portion, others are designed to accept locking screws and Kirschner wires that can be placed at angles of up to 40° off the central axis of the pin hole (Trimed).

Columnar plates also come in straight profiles for placement on the dorsal aspect of the radius. They are available in L and oblique L shapes and in various lengths. This allows them to be customized and contoured additionally, minimizing the need to cut a plate, which may be associated with tendon irritation (Fig 14).

Fig 14

Fig 14

These plates are placed in an orthogonal fashion (ie, 50° to 70° to each other). The placement of these low profile implants not only reduces overall implant bulk in the confines of the extensor surface of the distal radius but also improves torsional stability by fixation in different planes.40 This allows stable fixation and early motion and in the experience of most authors has been associated with satisfactory outcomes.22,46 The need to remove implants because of tendon irritation, however, continues to remain a concern.

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DISCUSSION

Our purpose has been to provide an overview of the advances in implant design and technology used in contemporary fixation of fractures of the hand and wrist. It is by no means the intention of this review to suggest that current implant designs and studies dealing with these implants are not without their own shortcomings. Implant-related complications are well documented in fractures of the hand and wrist.10,11,24,39,45,47,48 The single criticism that can be applied to the current generation of implants used for distal radius fracture fixation is the widespread use of various designs in the absence of carefully controlled randomized prospective trials that document their efficacy in treating a particular fracture pattern and show the superiority of any one particular implant design. Although authors of biomechanical studies have compared the in vitro behaviors of some distal radius implants, most published clinical studies pertain to the relative merits and demerits of a specific implant, and infrequently provide comparative data in the in vivo setting, about similar implants used to treat similar fracture patterns.21,22,33,40,46-48

In fractures of the distal radius, fixation with pins or with external fixation has its limitations.62 As with any periarticular fracture, the goal of treatment should be restoration of anatomy to allow early motion and optimize outcome. Dorsal plate designs have helped to achieve this goal but have presented their own unique set of problems. It appears that volar fixation of fractures of the distal radius may reduce a number of these problems. This in no way suggests that volar fixation is the panacea for fractures of the distal radius. Fragment-specific fixation and columnar fixation have their own roles in carefully selected fracture patterns.

Authors of biomechanical studies support the use of volar fixation of dorsally angulated fractures using fixed angle devices.21,36,37 In addition, biomechanical studies have also shown that columnar or double-plating techniques have superior stiffness when compared with some other dorsal plating techniques.40 Results of fixation with these multiple new plate and screw systems appear to be comparable. It is critical to understand fracture geometry and use implants appropriately to neutralize various fracture fragments. At this time no single system or approach has shown a clear superiority over the others.

Complex fractures in the hand and wrist are often associated with joint stiffness, tendon adhesion, and soft tissue edema. The goal of treatment of unstable fractures in the hand and wrist is to provide anatomic restoration in an attempt to institute early motion with an optimal functional outcome being most desirable. Stable internal fixation is critical in achieving this goal provided it is combined with judicious rehabilitation. It must be understood that implant design is merely one facet of the overall treatment program and that numerous other factors can lead to a suboptimal outcome despite suitable fixation.

Indeed, Page and Stern,39 reporting complications after plate fixation of metacarpal and phalangeal fractures, commented that “the lack of improvement in our complication rates between our 1987 series and the present series can be explained as follows: the advances in plate design are inadequate to prevent problems associated with plate fixation; the complications and poor results often associated with plate fixation are not so much the result of the implants and techniques associated with plate fixation, but rather stem from the frequent use of plates in situations with many factors associated with poor outcome.”

These sentiments have been echoed by other authors.12,47 It seems that metacarpal fractures have a more favorable outcome after plating than do phalangeal fractures.13,39,50 This in no way implies that plating of phalangeal fractures is inadvisable. On the contrary, it indicates a need for judicious patient selection, and outcomes have been noted to be excellent in carefully selected patients,13,23,39,50 which implies that in patients with severe injuries, it is all the more critical to have implants that are specifically designed for use in the hand and fulfill certain criteria that would allow for stable fixation and early mobilization. Earlier implants failed to fulfill many of these criteria and in part may have been responsible for at least some of the suboptimal outcomes.

It is clearly evident that an ideal implant for use around the hand and wrist must fulfill a few basic criteria. It must be small, yet strong enough to withstand the considerable bending, axial, and torsional forces. It must be low profile to avoid soft tissue irritation. It should be biocompatible and inert, with a high and consistently reproducible manufacturing quality. Its clinical use should be simplified for widespread use, inventory should be limited, and modularity is optimal. Finally, its cost should not be prohibitive.

There has been a considerable evolution in implant design for fractures around the hand and wrist. With a greater understanding of fracture mechanisms and musculoskeletal biology, emphasis has been placed on anatomical restoration. Advances in materials science and implant design have helped us to fix fractures in a stable manner and provide our patients with a chance at early mobilization in an effort to optimize outcomes. These represent a quantum leap in fracture management when compared with earlier treatment methods and outcomes. However, additional advances with biomaterials and low profile, modular implants may reduce some of the problems that we still continue to encounter.

Furthermore, carefully controlled prospective studies which highlight analysis of fracture geometry and careful implant selection in the appropriate setting would certainly help to diminish adverse outcomes which may ensue from inappropriate use of an implant in a setting for which it is not designed.

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