Controlled dynamic stability as the next step in “biologic plate osteosynthesis” - a pilot prospective observational cohort study in 34 patients with distal tibia fractures

Over the last decades, the state-of-the-art in plate osteosynthesis has evolved in parallel with the general understanding of bone healing. Fifteen years ago, Otmar Trentz postulated that “a fracture is defined as a soft tissue injury, in which we find an associated broken bone just by chance”. Against this backdrop, the technique of open and accurate reduction was gradually replaced by the minimally invasive bridging plate osteosynthesis. In 2003, Perren[1, 2] described the bridging plate technique by using angular stable implants. The aim of this technique consisted in preserving the local regeneration potency by protecting the soft tissue in order to reduce the high rate of local complications. This was a logical step towards a biological plate osteosynthesis. Absolute stability was replaced by relative stability and direct bone healing was replaced by indirect bone healing.

Goodship, Kenwright and other authors have analyzed the influence of micromovement upon the healing of tibial fractures. They has been able to demonstrate that the reduction of the axial stiffness leads to a significant increase of the rate of fracture healing[3‐12]. Potential changes in the construct, such as a longer plate, different screw configurations, or the variation of the number of cortices of fixation per screw have been proposed to alter the mechanical behavior of fracture fixation constructs and to affect micro-motion and callus formation[4, 5, 13, 14].

Especially simple fractures, i.e. oblique fractures of the distal tibia (AO 42 A2/A3 and AO 43 A1) present an unequal distribution of callus formation. In 2009, the clinical and biomechanical studies about delayed bone healing in distal femur fractures that had been carried out by Bottlang[1], proved that a continuous micro-movement in the fracture zone is necessary to enable sufficient callus formation. Figure 1 presents an example of a unsuccessful treatment of a distal tibia fracture with a low bend medial distal tibia LCP 3.5 (DePuy-Synthes, Zuchwil, Switzerland).

Recently, the Dynamic Locking Screw (DLS 3.7) has been developed by DePuy-Synthes, Zuchwil, Switzerland, to decrease the high rigidity of standard locking plate osteosynthesis Figures 2,3 and4.

The purpose of the present study was to show the safe use of a new implant (DLS 3.7) for the treatment of distal tibia fractures in a prospective non-controlled cohort study. The data were collected as part of a multi-center study. In this manuscript, we exclusively present the results obtained from the patients of our own center.

Between 03/2009 and 10/2010, a multi-centre study on the plating of acute traumatic distal tibia fracture with low bend distal medial tibia LCP and the DLS 3.7 was conducted. The purpose of this prospective, non-controlled cohort study consisted in evaluating the safe use of the new DLS 3.7. The patients were recruited in four centers (Munich/Germany, Berlin/Germany, Chur/Switzerland and Graz/Austria). Inclusion criteria were acute single fractures of the distal tibia according to the AO Classification (AO 43 A-C), age over 21 years at the time of the trauma, and full compliance to after-care and weight bearing restriction. Exclusion criteria were re-fracture, chronic inflammatory diseases, pregnancy, Hb serum level of less than 10 g/dl at the time of admission, cancer, admission of immune response-modulating drugs, HIV or chronic hepatitis B/C, osteitis or osteomyelitis, head injury, neurological deficit, allergic reaction to the Cobalt-Chromium-Molybdenum alloy (CoCrMo). Moreover, patients with an open fracture with a soft tissue injury worse than grade II according to the Gustilo and Anderson[15] classification were also excluded from our study. All participating patients signed an informed consent. Clinical and radiological follow-up exams were performed after 3, 6, 12, and 24 weeks. The fracture of each patient was classified according to the AO Classification of Fractures. The length of the plate, the type and the number of screws, as well the insertion performance of the DLS 3.7, which was rated as “excellent”, “good”, “satisfactory” or “poor” by the surgeon were documented.

For the evaluation of the safe use of the new implant, implant-specific complications i.e. screw loosening, screw breakage, and screw perforation, and general complications, i.e. pain perception according to the VAS (Visual-Analogue-Scale), were recorded.

For the evaluation of the status of fracture healing, the two-plane radiographs of each patient after 3, 6, 12 and 24 weeks were analyzed by two trauma surgeons who had not participated in the earlier stages of this study. The following parameters were assessed: callus formation at cis-cortex and trans-cortex (“minus”, “plus”, “plus/plus”) and status of consolidation of the fracture (“yes”, “no”). The pictures were blinded for the used implants or screws.

In total, 34 fractures in 34 patients were enrolled in our own center in the contest of the limited multi-center study. The follow-up was 6 months or obvious osseous consolidation at an earlier stage. 5 patients dropped out during the follow-up. In order to classify the fracture type, the AO Classification of Fractures was used. Three different types of fracture were included: AO 43 A (41%), AO 43 B (47%), and AO 43C (12%). The mean age of the patients was 51 years (SD ± 15 years) (44% male and 56% female). In 22 cases, the DLS 3.7 was used in the diaphyseal area only, whereas in 12 cases, DLS 3.7 was used in the proximal as well as in the distal area.

In the proximal part, this resulted in the use of three DLS 3.7 (range: 0 to 4) on average per patient. In the distal part, the mean number of DLS 3.7 per patient was 0.8 (range: 0 to 6). The mean number of LHS 3.5 per patient was 5 (range: 0 to 7). Finally, the mean number of cortical screws was 0.1 (range: 0 to 3) per patient. The distribution of the plate length was 239 mm in 24% of the patients, 213 mm in 26% of the patients, 208 mm in 3% of the patients, 198 mm in 12% of the patients, 187 mm in in 26% of the patients, and 171 mm in 9% of the patients.

The bone quality, which was assessed by the surgeon (1–5, 1 meaning “very good” and 5 meaning “poor”), was classified as follows: 1: 35% of the subjects, 2: 44% of the subjects, 3: 6% of the subjects, 4: 12% of the subjects, and 5: 3% of the subjects. The insertion of the DLS 3.7 was excellent in 50% of the patients, good in 32% of the patients, satisfactory in 15% of the patients, and poor in 3% of the patients. Six weeks after surgery, the mean VAS was 1.4 (SD ± 0.9). At the time of the 3 months follow-up, it had slightly deteriorated to 1.6 (SD ± 1.1). At the time of the 6 months follow-up, it had improved again to 1.5 (SD ± 1.3). After 6 weeks, however, the differences between the three follow-ups were not significant. The radiological assessment by the surgeon was union in 27% and non-union in 73% of the cases. After three months, 78% of the fractures were assessed as union and after 6 months, even 100% of the fractures were assessed as union. The assessment by the observers (authors) that was based on callus formation, led to the following results: After 6 weeks, callus formation was observed in 35% of the fractures. After 3 months, it was even visible in 96% of the fractures. However, after 6 months, callus formation was only visible in 83% of the fractures. This difference can be explained with the dropout of 5 patients who had exhibited callus formation after 3 months which could no longer be examined during the follow-up after 6 months.

In this study, we present the first clinical experiences with the use of the DLS 3.7 in distal tibia fractures and the technical innovations of this novel screw type in comparison to the well-known small-fragment Locking Head Screw (LHS 3.5). The aim of the study was to figure out the safety and effectiveness of the new DLS 3.7 in a limited clinical trial. The data were collected as part of a multi-center study. In this manuscript however, we only present the analysis of the results of the patients from our own center.

Concerning the problem of high stiffness in locking plate systems, different solutions have been presented in the past ten years[2, 12‐14, 16‐22]. However, the problem concerning the modulation of the fracture site movement in order to achieve the same range of motion despite the differences concerning the diameter of the treated bone and the length of the used screws remains unsolved. To date, the most extensive investigations about axial stiffness in locking plates have been carried out by Bottlang et al., Gardner et al., Duda et al., Cleas et al., Doebele et al., and Stoffel et al.[4, 5, 13, 16‐18, 22]. In these studies, two questions of critical importance have been addressed:

They found out that the interfragmentary motion of locked plates is asymmetrical: fragment motion in the cis-cortex region where the plate is located remains below the motion of 0.2-1 mm which is known to promote callus formation by continuous callus massage[9, 16, 23, 24]. This is possibly one reason for the high rate of non-union (19%) and delayed union (37%) which has been found in studies describing distal femur fractures treated with locked plating osteosynthesis[20, 25].

In order to solve the problem of an asymmetrical fracture motion of locked plating systems, several techniques have been introduced by different work group, like for example Far Cortical Locking, Dynamic Locking Screw, and near cortical slotted holes[16‐18], with each technique having various advantages and disadvantages.

In a biomechnical study, Doebele et al.[16] have demonstrated in a biomechanical set-up that axial stiffness is reduced by using the DLS 3.7. In the same study, they have proven that a controlled symmetrical motion can be achieved, even if a bicortical fixation is required. This concept has promised to provide an interfragmentary motion of 0.45 mm, which is considered to be the ideal stimulus level for the promotion of secondary bone healing[3, 6]. With the DLS 3.7, the established concept of the locking-plate osteosynthesis has remained untouched[16].

In the present study, all analyzed distal tibia fractures consolidated after at least 6 months. In spite of the limited number of 34 patients, these results are remarkable and better than those that can be found for the use of the LHS 3.5 with rates of delayed union or non-union up to 19%[19, 25‐27].

This pilot observational cohort study could show that the DLS 3.7 in combination with locking compression plates provides a secure and easy application. According to the recent literature, adequate inter-fragmentary micro-motion is one evident goal to increase the reliability in fracture healing. The new DLS 3.7 with a maximum micro-motion of 0.2 mm combines the advantage of micro-motion with the well-known advantages of angular stable plate fixation.