New plating techniques, such as non-contact plates, have been introduced in acknowledgment of the importance of biological factors in internal fixation. Knowledge of the fixation stability provided by these new plates is very limited and clarification is still necessary to determine how the mechanical stability, e.g. fracture motion, and the risk of implant failure can best be controlled. The results of a study based on in vitro experiments with composite bone cylinders and finite element analysis using the Locking Compression Plate (LCP) for diaphyseal fractures are presented and recommendations for clinical practice are given. Several factors were shown to influence stability both in compression and torsion. Axial stiffness and torsional rigidity was mainly influenced by the working length, e.g. the distance of the first screw to the fracture site. By omitting one screw hole on either side of the fracture, the construct became almost twice as flexible in both compression and torsion. The number of screws also significantly affected the stability, however, more than three screws per fragment did little to increase axial stiffness; nor did four screws increase torsional rigidity. The position of the third screw in the fragment significantly affected axial stiffness, but not torsional rigidity. The closer an additional screw is positioned towards the fracture gap, the stiffer the construct becomes under compression. The rigidity under torsional load was determined by the number of screws only. Another factor affecting construct stability was the distance of the plate to the bone. Increasing this distance resulted in decreased construct stability. Finally, a shorter plate with an equal number of screws caused a reduction in axial stiffness but not in torsional rigidity. Static compression tests showed that increasing the working length, e.g. omitting the screws immediately adjacent to the fracture on both sides, significantly diminished the load causing plastic deformation of the plate. If bone contact was not present at the fracture site due to comminution, a greater working length also led to earlier failure in dynamic loading tests. For simple fractures with a small fracture gap and bone contact under dynamic load, the number of cycles until failure was greater than one million for all tested constructs. Plate failures invariably occurred through the DCP hole where the highest von Mises stresses were found in the finite element analysis (FEA). This stress was reduced in constructions with bone contact by increasing the bridging length. On the other hand, additional screws increased the implant stress since higher loads were needed to achieve bone contact. Based on the present results, the following clinical recommendations can be made for the locked internal fixator in bridging technique as part of a minimally invasive percutaneous osteosynthesis (MIPO): for fractures of the lower extremity, two or three screws on either side of the fracture should be sufficient. For fractures of the humerus or forearm, three to four screws on either side should be used as rotational forces predominate in these bones. In simple fractures with a small interfragmentary gap, one or two holes should be omitted on each side of the fracture to initiate spontaneous fracture healing, including the generation of callus formations. In fractures with a large fracture gap such as comminuted fractures, we advise placement of the innermost screws as close as practicable to the fracture. Furthermore, the distance between the plate and the bone ought to be kept small and long plates should be used to provide sufficient axial stiffness.

Biomechanical testing of the LCP--how can stability in locked internal fixators be controlled?

Objective To summarize the surgical experience and clinical results of the first 89 fractures of the proximal tibia treated with the Less Invasive Stabilization System (LISS; Synthes, Paoli, PA). Design Retrospective analysis of prospectively enrolled patients into a database. Setting Academic level I trauma center. Subjects/participants Eighty-seven consecutive patients with 89 proximal tibia fractures (AO/OTA type 41 and proximal type 42 fractures) treated by 2 surgeons. Seventy-five patients with 77 fractures were followed until union. The mean follow-up was 14 months (range: 3-35 months). There were 55 closed fractures and 22 open fractures. Intervention Surgical reduction and fixation of fractures, followed by rehabilitation. Main outcome measurements Perioperative and postoperative complications, postoperative alignment, loss of fixation, time to full weight bearing, radiographic union, and range of motion. Results Seventy of 77 fractures healed without major complications (91%). There were 2 early losses of proximal fixation, 2 nonunions, 2 deep delayed infections, and 1 deep peroneal nerve palsy. Other complications included a superficial wound infection and 3 seromas. Postoperative malalignment occurred in 7 patients with 6 degrees to 10 degrees of angular deformity (6 flexion/extension and 1 varus/valgus malalignments), and an eighth patient had a 15 degrees flexion deformity. In 4 patients, the hardware was removed at an average of 13 months because of irritation (5%). The mean time for allowance of full weight bearing was 12.6 weeks (range: 6-21 weeks), and the mean range of final knee motion was 1 degrees to 122 degrees . Conclusions The LISS provides stable fixation (97%), a high rate of union (97%), and a low (4%) rate of infection for proximal tibial fractures. The technique requires the successful use of new and unfamiliar surgical principles to effect an accurate reduction and acceptable rate of malalignment.

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Treatment of proximal tibia fractures using the less invasive stabilization system: surgical experience and early clinical results in 77 fractures

The Locking Compression Plate (LCP) is a new screw-plate system that offers the possibility of inserting conventional and locking head screws into the specially designed combination holes. It represents a further development of the PC-Fix and the LISS and was released for clinical application in March 2000. In a prospective multicentre study, the new system was used to treat 144 patients (f: 67, m: 77; average age: 51.4 years) with 169 fractures: of these, 57 were tibial fractures, 45 humerus, 19 radius and 18 femoral. After one year, clinical and radiological follow-up assessment was carried out on 127 patients with 151 fractures (88%). In 130 fractures (86%), healing took place within the expected period and without complication or secondary dislocation ("uneventful healing"). In 19 patients, a total of 27 unexpected complications occurred ("adverse events"), in which 18 revision operations were necessary in 13 patients: five for implant loosening/pull-out, four for plate failure, one for non-union, five for secondary fractures immediately adjacent to the implant after a subsequent injury and two for infection. Analysis by a committee of experts indicated that mechanical complications arose entirely from technical errors of application (incorrect fixation technique, incorrect choice of plate). No purely implant-related complications were observed. The new system can be regarded as technically mature. It offers numerous fixation possibilities and has proven its worth in complex fractures situations and in revision operations after the failure of other implants. A good knowledge of biomechanics is essential as well as precise preoperative planning.

First clinical results of the Locking Compression Plate (LCP)

Background: The care of the patient with the fractured femur entails a multiple surgical team approach. Healing of the fracture and expediency in the operating room are both important. We sought to determine the results of the treatment of fractures of the femoral shaft with interlocking femoral nails inserted with closed techniques, and to compare the outcomes of fractures nailed by using a fracture table with those stabilized with the leg draped free on a radiolucent table. Methods: Eight hundred eighty-two consecutive patients with fractures of the femoral shaft treated with a first-generation intramedullary nail at the authors' institution during the years 1986 to 1996 were identified. Five hundred fifty-one fractures in 515 patients met the inclusion criteria. Results: Treatment with an intramedullary nail led to a union rate of 98.9%. There were six infections, all occurring in closed fractures. Thirty-eight percent of the fractures had hardware removed, most commonly because of pain. One nail and 13 locking bolts broke. Four hundred eighteen fractures had adequate radiographs available to assess fracture alignment. No fracture healed with more than 10 degrees of angulation in either plane. Forty-four fractures healed with more than 5 degrees of angulation. A distal third fracture was found to be associated with an increased incidence of malalignment. There were no differences in outcomes between fractures stabilized with or without a fracture table. Conclusion: Reamed intramedullary nailing of femoral shaft fractures results in a low rate of nonunion, malunion, infection, and hardware failure. There is no difference in the outcomes of fractures treated with and without the use of a fracture table. This is particularly useful in the patient with multiple injuries for whom transfer to a fracture table may not be time effective.

Reamed intramedullary nailing of the femur : 551 cases

Objectives:Locked plating constructs may be too stiff to reliably promote secondary bone healing. This study used a novel imaging technique to quantify periosteal callus formation of distal femur fractures stabilized with locking plates. It investigated the effects of cortex-to-plate distance, bridg

Locked Plating of Distal Femur Fractures Leads to Inconsistent and Asymmetric Callus Formation

The LISS-DF (Less invasive stabilization system-distal femur) is a new type of implant system for the treatment of distal femoral fractures according to the principles of "Minimally Invasive Surgery". A plate, pre-contoured to the anatomy, is inserted through a minimally invasive incision into the epiperiosteal space by means of an aiming device after indirect, closed fracture reduction. The implant is stabilized by insertion of screws which lock into the plate holes and prevent tilting. This is performed with the aid of an aiming device and through stab incisions. It is not necessary for a large area to be exposed at the fracture site. As part of an AO prospective multicenter study, the new system was applied to 112 patients with 116 fractures. The time to follow-up was on average 13.7 months (minimum 7 months, maximum 33 months). Fractures treated were distal femoral shaft and supracondylar femoral fractures. Eight patients died during the study of causes unrelated to the implant. Of the remaining 104 patients with 107 fractures, 96 patients with 99 fractures were available for complete follow-up (93% follow-up rate). In 90% of all cases treated and followed up, the fracture had consolidated during the period of observation. Twenty-three revision operations were necessary in 21 patients. In two cases, implant failure occurred as the result of a pseudarthrosis. The complications can be attributed in nearly all cases to the severity of the trauma and/or a lack of experience when applying the new style implant to a wider range of indications. The results of the study show that with a sound knowledge of the operative technique and careful preoperative planning this system represents an excellent, safe procedure for the treatment of almost all distal femoral fracture types including periprosthetic fractures of the distal femur. There is generally no need for primary cancellous bone grafting.

Minimally invasive fracture stabilization of distal femoral fractures with the LISS: a prospective multicenter study. Results of a clinical study with special emphasis on difficult cases.

Grundlagen: Das Hauptproblem konventioneller Plattenosteosynthesen ist die durch den Vaskularitatsschaden unter der Platte bedingte Osteoporose. Die vorliegende Studie zeigt die Ergebnisse mit dem neuen Stabilisationssystem LISS-DF (Fixateur intern), welches die Anforderungen eines optimierten Knochen-Implantat-Kontaktes und zusatzlich die Moglichkeit einer minimal invasiven Chirurgie konsequent umsetzt.

P. Regazzoni

Papers

Minimally invasive fracture stabilization of distal femoral fractures with the LISS: a prospective multicenter study. Results of a clinical study with special emphasis on difficult cases.

Minimal invasive Frakturstabilisierung von distalen Femurfrakturen mit dem LISS-System — Ergebnisse einer prospektiven Multizenter-Studie