Reasons and Countermeasures for the Failure of Locking Compression Plate

As an internal fixator, the compression plate has always played significant roles in the fracture treatment. In recent years, the concept of minimally invasive osteosynthesis has been deeply understood and applied, gradually shifting from the previous emphasis on machinery mechanics of internal fixator to emphasis on biological fixation, which not only focuses on protection of bone and soft tissue blood supply, but also promotes the improvements in surgical techniques and internal fixator. Locking Compression Plate (LCP) is a brand new plate fixation system, which is developed on the basis of dynamic compression plate (DCP) and the limited contact dynamic compression plate (LC-DCP), and combined with the clinical advantages of the AO’s point contact plate (PC-Fix) and Less Invasive Stabilization System (LISS). The system started to be used clinically in May 2000, had achieved better clinical effects, and many reports have given highly appraisals for it. Although there are many advantages in its fracture fixation, it has higher demands on technology and experience. If it is improperly used, it might be counterproductive, and result in irretrievable consequences.

1. Biomechanical Principles, Design and Advantages of LCP
The stability of ordinary steel plate is based on the friction between the plate and the bone. The screws are required to be tightened. Once the screws are loose, the friction between the plate and the bone will be reduced, the stability will also be decreased, resulting in failure of internal fixator. LCP is a new support plate inside the soft tissue, which is developed by combining the traditional compression plate and support. Its fixation principle does not rely on the friction between the plate and bone cortex, but relies on the angle stability between the plate and locking screws as well as the holding force between the screws and bone cortex, in order to realize fracture fixation. The direct advantage lies in reducing the interference of periosteal blood supply. The angle stability between the plate and screws has greatly improved the holding force of screws, thus the fixation strength of the plate is much greater, which is applicable to different bones. [4-7]

The unique feature of LCP design is the “combination hole”, which combines the dynamic compression holes (DCU) with the conical threaded holes. DCU can realize axial compression by using the standard screws, or the displaced fractures can be compressed and fixed via the lag screw; the conical threaded hole has threads, which can lock the screw and nut’s threaded latch, transfer the torque between the screw and plate, and the longitudinal stress can be transferred to the fracture side. In addition, the cutting groove is design below the plate, which reduces the contact area with the bone.

In short, it has many advantages over the traditional plates: ① stabilizes the angle: the angle between the nail plates is stable and fixed, being effective for different bones; ② reduces the risk of reduction loss: there is no need to conduct accurate pre-bending for the plates, reducing the risks of the first-phase reduction loss and the second-phase of reduction loss; [8] ③ protects the blood supply: the minimum contact surface between the steel plate and the bone reduces the losses of plate for the periosteum blood supply, which is more aligned with principles of minimally invasive; ④ has a good holding nature: it is especially applicable to the osteoporosis fracture bone, reduces the incidence of screw loosening and exiting; ⑤ allows the early exercise function; ⑥ has a wide range of applications: the plate type and length are complete, the anatomical pre-shaped is good, which can realize the fixation of different parts and different types fractures.

2. Indications of LCP
LCP can be used either as a conventional compressing plate or as an internal support. The surgeon can also combine both, so as to greatly expand its indications and apply to a great variety of fracture patterns.
2.1 Simple Fractures of Diaphysis or Metaphysis: if the damage to soft tissue is not severe and the bone has good quality, simple transverse fractures or short oblique fracture of long bones are required to cut and accurately reduction, and the fracture side requires strong compression, thus LCP can be used as a compression plate and plate or neutralization plate.
2.2 Comminuted Fractures of Diaphysis or Metaphyseal: LCP can be used as the bridge plate, which adopts the indirect reduction and bridge osteosynthesis. It does not require anatomical reduction, but merely recovers the limb length, rotation and axial force line. Fracture of the radius and ulna is an exception, because the rotation function of forearms depends largely on normal anatomy of radius and ulna, which is similar to the intra-articular fractures. Besides, anatomical reduction must be carried out, and shall be stably fixed with plates..
2.3 Intra-articular Fractures and Inter-articular Fractures: In the intra-articular fracture, we not only need to carry out the anatomical reduction to recover the smoothness of articular surface, but also need to compress the bones to achieve stable fixation and promote bone healing, and allows the early functional exercise. If the articular fractures have impacts on the bones, LCP can fix the joint between the reduced articular and diaphysis. And there is no need to shape the plate in the surgery, which has reduced the surgery time.
2.4 Delayed Union or Nonunion.
2.5 Closed or Open Osteotomy.
2.6 It is not applicable to the interlocking intramedullary nailing fracture, and LCP is a relatively ideal alternative. For example, LCP is inapplicable to marrow damage fractures of children or teenagers, people whose pulp cavities are too narrow or too wide or malformed.
2.7 Osteoporosis Patients: since the bone cortex is too thin, it is difficult for the traditional plate to obtain reliable stability, which has increased the difficulty of fracture surgery, and resulted in failure due to easy loosening and exiting of postoperative fixation. LCP locking screw and plate anchor form the angle stability, and the plate nails are integrated. In addition, the mandrel diameter of locking screw is large, increasing the gripping force of the bone. Therefore, the incidence of screw loosening is effectively reduced. Early functional body exercises are permitted in post-operation. Osteoporosis is a strong indication of LCP, and many reports have given it a high recognition.
2.8 Periprosthetic Femoral Fracture: periprosthetic femoral fractures are often accompanied by osteoporosis, elderly diseases and serious systemic diseases. The traditional plates are subject to extensive incision, causing potential damages to blood supply of the fractures. Besides, the common screws require bicortical fixation, causing damages to bone cement, and the osteoporosis gripping force is also poor. LCP and LISS plates solve such problems in a good way. That is to say, they adopt the MIPO technology to reduce the joint operations, reduce the damages to blood supply, and then the single cortical locking screw can provide sufficient stability, which will not cause damages to bone cement. This method is featured by simplicity, shorter operation time, less bleeding, small stripping range and facilitating the fracture healing. Therefore, periprosthetic femoral fractures are also one of the strong indications of LCP. [1, 10, 11]

3. Surgical Techniques Related to Use of LCP
3.1 Traditional Compression Technology: although the concept of AO internal fixator has changed and the blood supply of protection bone and soft tissues won’t be neglected due to overemphasis of the mechanical stability of fixation, the fracture side still requires compression to obtain fixation for some fractures, such as intra-articular fractures, osteotomy fixation, simple transverse or short oblique fractures. Compression methods are: ① LCP is used as a compression plate, using two standard cortical screws to eccentrically fix on the plate sliding compression unit or using the compression device to realize fixation; ② as a protection plate, LCP uses the lag screws to fix the long-oblique fractures; ③ by adopting the tension band principle, the plate are placed on the tension side of the bone, shall be mounted under tension, and cortical bone can obtain compression; ④ as a buttress plate, LCP is used in conjunction with the lag screws for the fixation of articular fractures.
3.2 Bridge Fixation Technology: Firstly, adopt the indirect reduction method to reset the fracture, span across the fracture zones via the bridge and fix both sides of fracture. Anatomic reduction is not required, but only requires recovery of the diaphysis length, rotation and force line. Meanwhile, bone grafting can be performed to stimulate callus formation and promote fracture healing. However, the bridge fixation can just achieve the relative stability, yet the fracture healing is achieved through two calluses by second intention, so it is only applicable to comminuted fractures.
3.3 Minimally Invasive Plate Osteosynthesis (MIPO) Technology: Since the 1970s, AO organization put forward the principles of fracture treatment: anatomical reduction, internal fixator, blood supply protection and early painless functional exercise. The principles have been widely recognized in the world, and the clinical effects are better than the previous treatment methods. However, to obtain the anatomic reduction and internal fixator, it often requires extensive incision, resulting in the reduced bone perfusion, decreased blood supply of fracture fragments and increased risks of infection. In recent years, domestic and overseas scholars pay more attention to and put more emphasis on the minimally invasive technology, protecting the blood supply of soft tissue and bone in the meantime of promoting internal fixator, not stripping off the periosteum and soft tissue on the fracture sides, not forcing anatomical reduction of the fracture fragments. Therefore, it protects the fracture biological environment, namely the biological osteosynthesis (BO). In the 1990s, Krettek proposed the MIPO technology, which is a new progress of fracture fixation in recent years. It aims at protecting the blood supply of protection bone and soft tissues with the minimum damages to the largest extent. The method is to build a subcutaneous tunnel through a small incision, place the plates, and adopt the indirect reduction techniques for fracture reduction and internal fixator. The angle between LCP plates is stable. Even though the plates do not fully realize anatomical shaping, the fracture reduction can still be maintained, so the advantages of MIPO technology are more prominent, and it is a relatively ideal implant of MIPO technology.

4. Reasons and Countermeasures for the Failure of LCP Application
4.1 Failure of Internal fixator
All implants have the loosening, displacement, fracture and other risks of failures, locking plates and LCP are no exceptions. According to the literature reports, failure of internal fixator is not mainly caused by the plate itself, but because the basic principles of fracture treatment are violated due to insufficient understanding and knowledge of the LCP fixation.
4.1.1. The selected plates are too short. The length of plate and screw distribution is key factors affecting the fixation stability. Prior to emergence of IMIPO technology, the shorter plates can reduce the incision length and the separation of soft tissue. Too short plates will reduce the axial strength and torsion strength for the fixed overall structure, resulting in failure of internal fixator. With the development of indirect reduction technology and the minimally invasive technology, the longer plates will not increase the incision of soft tissue. The surgeons should select the plate length in accordance with the biomechanics of fracture fixation. For simple fractures, the ratio of ideal plate length and the length of whole fracture zone should be higher than 8-10 times, whereas for the comminuted fracture, this ratio should be higher than 2-3 times. [13, 15] The plates with long enough length will reduce the plate load, further reduce the screw load, and thereby reduce the failure incidence of internal fixator. According to the results of LCP finite element analysis, when the gap between the fracture sides is 1mm, the fracture side leaves one compression plate hole, stress at the compression plate reduces 10%, and stress at the screws reduces 63%; when the fracture side leaves two holes, stress at the compression plate reduces 45% reduction, and stress at the screws reduces 78%. Therefore, to avoid stress concentration, for the simple fractures, 1-2 holes close to the fracture sides shall be left, whereas for the comminuted fractures, three screws are recommended to be used at each fracture side and 2 screws shall get close to the fractures.
4.1.2 The gap between plates and bone surface is excessive. When LCP adopts the bridge fixation technology, the plates are not required to contact the periosteum to protect the blood supply of fracture zone. It belongs to elastic fixation category, stimulating the second intension of callus growth. By studying the biomechanical stability, Ahmad M, Nanda R [16] et al found that when the gap between LCP and bone surface is greater than 5mm, axial and torsion strength of plates is significantly decreased; when the gap is less than 2mm, there is no significant decrease. Therefore, the gap is recommended to be less than 2mm.
4.1.3 The plate deviates from the diaphysis axis, and the screws are eccentric to fixation. When LCP is combined MIPO technology, plates are required percutaneous insertion, and it is sometimes difficult to control the plate position. If the bone axis is unparallel with the plate axis, the distal plate may deviate from the bone axis, which will inevitably lead to eccentric fixation of screws and weakened fixation. [9,15]. It is recommended to take an appropriate incision, and X-ray examination shall be made after the guide position of finger touch is proper and Kuntscher pin fixation.
4.1.4 Fail to follow the basic principles of fracture treatment and choose wrong internal fixator and fixation technology. For intra-articular fractures, simple transverse diaphysis fractures, LCP can be used as a compression plate to fix the absolute fracture stability via the compression technology, and promote primary healing of fractures; for the Metaphyseal or comminuted fractures, the bridge fixation technology should be used, pay attention to the blood supply of protection bone and soft tissue, permit the relatively stable fixation of fractures, stimulate callus growth to achieve healing by the second intension. On the contrary, the use of bridge fixation technology to treat simple fractures may cause unstable fractures, resulting in delayed fracture healing; [17] comminuted fractures’ excessive pursuit of anatomical reduction and compression at fracture sides can cause damages to blood supply of bones, resulting in delayed union or nonunion.

4.1.5 Choose the inappropriate screw types. LCP combination hole can be screwed in four types of screws: the standard cortical screws, the standard cancellous bone screws, the self-drilling/self-tapping screws and self-tapping screws. Self-drilling/self-tapping screws are usually used as a unicortical screws to fix the normal diaphyseal fractures of bones. Its nail tip has the drill pattern design, which is easier to pass through the cortex usually without necessity of measuring the depth. If the diaphyseal pulp cavity is very narrow, screw nut may not fully fit the screw, and the screw tip touches the contralateral cortex, then the damages to fixed lateral cortex affect the gripping force between screws and bones, and bicortical self-tapping screws shall be used at this time. The pure unicortical screws have good gripping force towards the normal bones, but the osteoporosis bone usually has weak cortex. Since the operation time of screws reduces, the moment arm of screw resistance to bending decreases, which is easily resulting in screw cutting bone cortex, screw loosening and secondary fracture displacement. [18] Since the bicortical screws have increased the screws’ operation length, the gripping force of bones also increase. Above all, the normal bone might use the unicortical screws to fix, yet the osteoporosis bone is recommended to use bicortical screws. In addition, the humerus bone cortex is relatively thin, easily causes incision, so the bicortical screws are needed to fix in treating the humeral fractures.
4.1.6 Screw distribution is too dense or too little. Screw fixation is required to comply with the fracture biomechanics. Too dense screw distribution will result in local stress concentration and fracture of internal fixator; too less fracture screws and insufficient fixation strength will also result in failure of internal fixator. When the bridge technology is applied to fracture fixation, the recommended screw density should be below 40% -50% or less. [7,13,15] Therefore, the plates are relatively longer, so as to increase the balance of mechanics; 2-3 holes should be left for the fracture sides, in order to allow greater plate elasticity, avoid stress concentration and reduce the incidence of internal fixator breakage [19]. Gautier and Sommer [15] thought that at least two unicortical screws shall be fixed at both sides of fractures, the increased number of fixed cortex will not reduce the plates failure rate, thus at least three screws are recommended to be sued at both sides of fracture. At least 3-4 screws are required at both sides of humerus and forearm fracture, more torsion loads have to be carried.
4.1.7 Fixation equipments are incorrectly used, resulting in failure of internal fixator. Sommer C [9] visited 127 patients with 151 fracture cases who have used LCP for one year, the analysis results show that among the 700 locking screws, only few screws with diameter of 3.5mm are loosened. The reason is the abandoned use of locking screws sighting device. In fact, the locking screw and the plate are not completely vertical, but show 50 degrees of angle. This design aims at reducing the locking screw stress. Abandoned use of sighting device may change the nail passage and thus cause damage to fixation strength. Kääb [20] had conducted an experimental study, he found the angle between screws and LCP plates is too large, and thus the gripping force of screws is significantly decreased.
4.1.8 Limb weigh loading is too early. Too much positive reports guide many doctors to excessively believe the strength of locking plates and screws as well as fixation stability, they mistakenly believe that the strength of locking plates can bear early full weight loading, resulting in plate or screw fractures. In using the bridge fixation fractures, LCP is relatively stable, and is required to form callus so as to realize the healing by second intension. If the patients get out of bed too early and load excessive weight, the plate and screw will be broke or unplugged. Locking plate fixation encourages early activity, but complete gradual loading shall be six weeks later, and x-ray films show that the fracture side presents significant callus. [9]
4.2 Tendon and Neurovascular Injuries:
MIPO technology requires percutaneous insertion and to be placed under the muscles, so when the plate screws are placed, the surgeons could not see the subcutaneous structure, and thereby the tendon and neurovascular damages are increased. Van Hensbroek PB [21] reported a case of using LISS technology to use LCP, which resulted in anterior tibial artery pseudoaneurysms. AI-Rashid M. [22] et al reported to treat delayed ruptures of extensor tendon secondary for distal radial fractures with LCP. The main reasons for damages are iatrogenic. The first one is direct damage brought by screws or Kirschner pin. The second one is the damage caused by the sleeve. And the third one is thermal damages generated by drilling self-tapping screws. [9] Therefore, the surgeons are required to get familiar with the surrounding anatomy, pay attention to protecting the nervus vascularis and other important structures, fully conduct blunt dissection in placing the sleeves, avoid compression or nerve traction. In addition, when drilling the self-tapping screws, use water to reduce heat production and decrease heat conduction.
4.3 Surgical Site Infection and Plate Exposure:
LCP is an internal fixator system occurred under the background of promoting the minimally invasive concept, aiming at reducing damages, reducing infection, nonunion and other complications. In the surgery, we should pay particular attention to soft tissue protection, especially the weak parts of soft tissue. Compared with DCP, LCP has larger width and greater thickness. When applying the MIPO technology for percutaneous or intramuscular insertion, it may cause soft tissue contusion or avulsion damage and lead to wound infection. Phinit P [23] reported that LISS system had treated 37 cases of proximal tibia fractures, and the incidence of postoperative deep infection was up to 22%. Namazi H [24] reported that LCP had treated 34 cases of tibial shaft fracture of 34 cases of metaphyseal fracture of tibia, and the incidences of postoperative wound infection and plate exposure were up to 23.5%. Therefore, prior to operation, opportunities and internal fixator shall be awfully considered in accordance with the damages of soft tissue and complexity degree of fractures.
4.4 Irritable Bowel Syndrome of Soft Tissue:
Phinit P [23] reported that the LISS system had treated 37 cases of proximal tibia fractures, 4 cases of postoperative soft tissue irritation (the pains of subcutaneous palpable plate and around the plates), in which 3 cases of plates are 5mm away from the bone surface and 1 case is 10mm away from the bone surface. Hasenboehler.E [17] et al reported LCP had treated 32 cases of distal tibial fractures, including 29 cases of medial malleolus discomfort. The reason is that the plate volume is too large or the plates are placed improperly and the soft tissue is thinner at the medial malleolus, so the patients will feel uncomfortable when the patients are wearing high boots and compress the skin. The good news is that the newly distal metaphyseal plate developed by Synthes is thin and adhesive to bone surface with smooth edges, which has effectively solved this problem.

4.5 Difficulty in Removing the Locking Screws:
LCP material is of high strength titanium, has high compatibility with the human body, which is easy to be packed by callus. In removing, first removing of the callus leads to increased difficulty. Another reason for removing difficulty lies in the over-tightening of the locking screws or nut damage, which is usually caused by replacing the abandoned locking screw sighting device with self-sighting device. Therefore, the sighting device shall be used in adopting the locking screws, so that the screw threads can be precisely anchored with the plate threads. [9] Specific wrench is required to be used in tightening screws, so as to control the magnitude of force.
Above all, as a compression plate of AO’s latest development, LCP has provided a new option for modern surgical treatment of fractures. Combined with the MIPO technology, LCP combines reserves the blood supply at fracture sides to the largest extent, promotes fracture healing, reduces the risks of infection and re-fracture, maintains fracture stability, so it has broad application prospects in fracture treatment. Since the application, LCP has obtained good short-term clinical results, yet some problems are also exposed. Surgery requires a detailed preoperative planning and extensive clinical experience, chooses the right internal fixators and technologies on the basis of features of specific fractures, adheres to the basic principles of fracture treatment, uses the fixators in a correct and standardized manner, in order to prevent the complications and get the optimal therapeutic effects.