Locking compression plate (LCP) is a new type of internal fixator combining traditional power compression hole and locking screw hole, which has been in multicenter clinical application since 2000 with satisfactory results. Since its use in China, it has been reported more frequently, but there have been no reports of LCP failure. We collected 5 cases of LCP failure from January 2005 to October 2007, and combined with the related literature reports, this paper will introduce some practical experience and tips on how to avoid the failure of locking plate surgery.
Discussion
Although locking plates are widely used and have many indications, they are not suitable for all types of fractures. Without understanding the mechanics of locking plates and mastering the technique of locking plate surgery, blind use of locking plates may lead to failure of internal fixation and bone nonunion. Through the discussion of the above cases and the analysis of the current causes of LCP failure after combining the relevant literature, we believe that: the main cause of internal fixation failure is the incorrect surgical technique, not the plate itself. Specifically, it can be divided into the following aspects: failure in the selection of internal fixation principle, failure in the selection and application of plate screws, failure in the surgical operation technique and failure in the judgment of skin and soft tissue.
1, the choice of internal fixation principle
Mistakes in the selection of internal fixation principles are often caused by the confusion of the surgeon with the theory of the role of LCP and traditional internal fixation. Generally speaking, there are three basic principles of internal fixation of fractures: interfracture compression fixation, bridging fixation and joint fixation principles, each of which has its own suitable application.
The traditional compression plate is required to extensively expose the fracture end, the plate is shaped and placed snugly, the screw fixes the plate with the fracture end under pressure, and the fixation effect is produced by the mocha force between the plate and the bone, which can be effectively fixed for simple type fractures with good bone condition; however, for comminuted fractures relying on simple compression fixation, the effect is poor, and then the bridging joint technique can be chosen, and the fracture is fixed elastically. The blood flow and soft tissue destruction at the fracture end are reduced, and the fracture is easily healed by bone scab formation in phase II. The combined principle is a biomechanical mixture of compression and bridging principles in a single plate and is used for simple fractures at one level combined with comminuted fractures at another level.
The LCP, due to its unique screw hole design, allows the choice of the compression principle, the bridging principle, or a combination of both, depending on the fracture. When treating simple fractures or intra-articular fractures, the compression principle is used as in the case of traditional splints, with anatomical repositioning; when used to treat comminuted fractures the bridging technique can be chosen, using the MIPPO technique, which reduces the stripping of soft tissues at the fracture end and the impact on the fracture blood flow, which facilitates the fixation and healing of the fracture; the combined technique is only used in two cases.
1, intra-articular fractures combined with extra-articular comminuted fractures, intra-articular using compression technique and extra-articular using bridging technique;
2. multi-segment fractures combining two fracture types: compression fixation is used for simple fractures and bridging technique is used for comminuted fractures. When the locking plate is used as an internal fixation brace for simple fractures in violation of the above treatment principles, it may increase the possibility of bone nonunion.
There are three types of screws that accompany locking plates: self-tapping locking nails, self-tapping self-drilling locking nails, and plain screws. To reduce complications, the type of screw and the principle of unicortical or bicortical fixation must be followed.
Self-tapping self-drilling screws are designed for unicortical fixation. The drill-like design of the nail tip allows easy penetration into the bone without generating high heat, avoiding damage to the ipsilateral bone cortex when the medullary cavity is narrow, while if they are used for bicortical fixation, the sharp drill bit may damage the adjacent vascular nerves and soft tissues after penetrating the contralateral bone cortex.
Self-tapping type can be used for unicortical or bicortical fixation, and since the tip does not have a drill-like design, it is less likely to damage soft tissues after penetrating the contralateral cortex. There is a risk of unicortical fixation with self-tapping screws: if the screw is too long when the medullary cavity is small, the head of the screw may be blocked by the contralateral cortex when it reaches the contralateral cortex, damaging the tapped proximal cortex and making the head of the locking screw not completely screwed into the locking hole; if the screw is too short, the tapped threads of the proximal cortex cannot be screwed into the screw well and the locking structure of the nail plate is subjected to repeated loading. If the screw is too short, the tapping threads of the proximal cortex cannot screw into the screw well, and the locking structure of the nail plate is subjected to repeated loading, and failure is likely to occur.
The decision to choose single or double cortical screws depends on the quality of the bone and the size of the rotational violence at the fracture end. In general, in the treatment of fractures with good bone quality, a single screw is sufficient to provide adequate stability. However, in osteoporotic and especially predominantly torsionally resistant sites (e.g., humerus), the working length of a single screw is greatly reduced and is insufficient to provide stability. Therefore, double cortical fixation with self-tapping screws is preferred to provide adequate working length in osteoporotic fractures.
From a purely mechanical point of view, two single cortical screws per major fracture block are sufficient to provide structural stability, but this stability is easily lost. Therefore, this structure should only be used when the bone is in good condition or when the surgeon is confident that all screws are properly fixed.
For safety reasons, 3 screws per major fracture block are necessary. In general, for weight-bearing femoral and tibial fractures, which are primarily resistant to axial loading, 2 or 3 screws are used on each side of the fracture area; for fractures of the humerus and forearm, which are primarily resistant to torsion, 3-4 screws are required for each major fracture fragment. The screw density = the number of screws driven / the number of holes in the joint plate (2-3, in simple fractures to > 8-10), while in the fracture area to leave a long enough plate without screws (at least 2-3 screws), in order to reduce the local load of the plate.
4.Mistake in surgical operation technique
Failure of surgical operation technique is also often one of the main reasons for the failure of locking plate, LCP requires the surgeon to master its principle based on a detailed understanding of its operation technique.
Since the locking screw does not have fracture repositioning function, once the locking screw is screwed into the bone through the plate, the fracture end of this segment cannot be repositioned by screwing in additional screws or by using compression instruments. Therefore, the order of screwing in is crucial. If a combination of locking screws and common screws is required intraoperatively, the common screws must be repositioned first, followed by locking screw reinforcement, or if locking screws have been used for fixation, the locking screws must be loosened and then the common screws must be pressurized, otherwise poor repositioning will result.
Locking hole does not allow the screw to change the angle of screwing in, if the screw diagonally into the screw hole, the screw locking thread alignment is poor, will lead to screw loosening and reset lost, if the screw screwing in too tight, may lead to thread wrong buckle, later internal fixation out can lead to the failure of internal fixation due to the fusion between the internal fixation locking screw and the steel plate. Therefore, screw screwing must be carefully operated, the correct use of the guide, locking screws placed along the axis of the locking hole, otherwise the correct locking effect can not be achieved.
5.Skin soft tissue condition
The skin soft tissue condition is also a key factor affecting success or failure after surgery. Whether the traditional compression technique is used to treat simple fractures or the bridging technique is used to treat complex fractures, the local soft tissue condition must be considered and the swelling must subside for cases such as swelling at the fracture site and tension blister formation. Although tension blisters do not necessarily increase the risk of infection, they should still be used with caution, otherwise they may lead to local skin ischemic necrosis and plate exposure and failure. In the follow-up of 34 patients with tibial fractures fixed with conventional incisional LCP, there were 8 cases with severe soft tissue injury and plate exposure, which required flap repair.