Arch Orthop Trauma Surg DOI 10.1007/s00402-007-0543-0
ORTHOPAEDIC SURGERY
Revascularisation during fracture healing with soft tissue injury Mark Melnyk · Thomas Henke · Lutz Claes · Peter Augat
Received: 30 July 2007 © Springer-Verlag 2007
Abstract Introduction The purpose of our study was to quantitatively assess changes in the revascularisation process in the fracture gap and in adjacent regions during the course of healing of diaphyseal fractures with and without closed soft tissue injury. Methods In a rat model (fracture n = 26; fracture with closed soft tissue crush n = 26) revascularisation was assessed in a long-term study with regional mapping by laser Doppler Xowmetry, the healing outcome being mechanically tested after 4 weeks. Fracture and soft tissue crush were performed by modiWed controlled impact device. Results No diVerences in blood circulation were observed at the fracture gap between the study groups up to day 28. In the proximal region of the fracture, the blood circulation in the group with additional soft tissue trauma was down to the baseline throughout the investigation period while the values in the fracture group led to a hyperperfusion after 3 and 7 days. In the distal part at day 1, the blood Xow was strongly depressed after fracture, while microcirculation with an additional soft tissue trauma showed only a moderate
M. Melnyk (&) · L. Claes Institute of Orthopaedic Research and Biomechanics, University of Ulm, Helmholtzstrasse 14, 89081 Ulm, Germany e-mail:
[email protected] P. Augat Biomechanics Laboratory, Trauma Center Murnau, Prof. Küntscher Str. 8, 82418 Murnau, Germany e-mail:
[email protected] T. Henke Department of Orthopaedic Surgery, Military Hospital Ulm, Oberer Eselsberg 40, 89081 Ulm, Germany
decline. The reduction of blood circulation in the soft tissue corresponded to the extent of trauma. Mechanical testing demonstrated no signiWcant diVerence in failure load or in Xexural rigidity. Conclusion Our results indicate that damage severe soft tissue does not adversely aVect the fracture healing process. Furthermore, the present Wndings suggest that a partly destroyed bone–soft tissue interaction resulting in only a temporary and slight reduction of the extraosseous blood supply might have no deteriorating eVect on fracture healing outcome. A possible delay in healing is not observed during the Wrst 4 weeks. Therefore, soft tissue damage without destruction of the bone–soft tissue interface is likely to have only a limited eVect on fracture healing. Keywords Fracture healing · Extensive soft tissue injury · Revascularisation · Laser Doppler Xowmetry · Rat
Introduction Successful fracture healing requires suYcient mechanical stability and an eYcient restoration of vascularity [17]. Intact bone blood Xow is generally oriented from the medullary area into the cortex, whereas in case of bone failure blood Xow direction is changed from centrifugal to centripetal [26, 37]. This centripetal blood Xow by periosteum and muscular tissue has shown a substantial role in initiating the fracture healing process. Particularly the soft tissue, with its supply of undiVerentiated mesenchymal cells, which possess a high-osteogenic potential, serves as an essential promoter for tissue regeneration after fracture trauma [9]. Severe injuries like complex fractures of the lower limb are generally associated with destruction of the soft tissue
123
Arch Orthop Trauma Surg
and periosteum, leading to tissue necrosis and an increased risk of healing complications [15]. From a clinical point of view, only qualitative descriptions of the relationship between soft tissue crush and fracture outcome are available. Most empiric studies concordantly indicate that severe soft tissue injury is associated with delayed healing or pseudarthrosis after fracture trauma [8, 11, 15, 22]. However, most of these studies lack in clear diVerentiation with respect to severity of fracture and soft tissue injury, respectively. Also, no information about the vascular situation of the investigated fractures was reported. In contrast to the clinical studies, experimental investigations have shown conXicting results. Histological and biomechanical Wndings in a rat model suggested that a severe soft tissue crush leads to transient delay in early fracture healing, however, without aVecting the Wnal healing outcome [7, 30]. The authors explained the transient retardation of the healing process by an initial decline of blood supply as a result of the soft tissue damage. Admittedly, partial loss of soft tissue around the fracture gap resulted in delayed fracture healing process [42]. However, the remaining question about the quantitative impact of a soft tissue deterioration on the blood supply in fractured bone has not yet been answered. In this study, we intended to measure diVerences in blood supply during fracture healing after soft tissue injury. Although the problem of blood Xow measurement in vivo has not been completely solved, a few measurement methods have been established to evaluate vascularity in bone and soft tissue. Microsphere investigations were able to detect blood Xow changes, particularly in cortical bone and at the bone–soft tissue interface [24]. In vivo Xuorescence microscopy provides a very detailed view on local circulatory activity in soft tissue and periosteum [29, 44]. However, this method is particularly sensitive to variations in capillary density, microvascular diameter and the behaviour of individual leucocytes. Both methods are invasive, time-consuming and can only be performed at the termination of the study. Laser Doppler Xowmetry (LDF) has been established for in vivo blood Xow investigations and permits a noninvasive measurement at diVerent locations in a short time frame during the whole healing period [18]. Moreover, methods to determine the depth of the laser light emission into the tissue has been developed [5, 21, 31]. Despite extensive work on fracture healing, the role of angiogenesis in diVerent regions of healing bone after soft tissue injury remains ambiguous. The purpose of our study was to quantitatively assess changes in the blood Xow during the course of healing of diaphyseal fractures with and without soft tissue injury. We were particularly interested in the revascularisation process in the fracture gap and in adjacent regions and therefore performed blood Xow measurements at various regions of the fractured leg.
123
Materials and methods Study groups and animal preparation Fifty-two Wistar rats (Charles River Laboratories, Maastricht, Netherlands), 77 days old, weighing 390 g (375– 400 g) were used. All rats were pre-medicated with atropine sulfate (Atropin® 0.05 mg/kg body weight; Braun, Germany) and anaesthetised by intraperitoneal injection with xylazine hydrochloride (Rompun® 12 mg/kg body weight, Bayer, Erlangen, Germany) and ketamine hydrochloride (Ketamin® 75 mg/kg; WDT, Garbsen, Germany). In this context, it is important to note that ketamine has only shown to result in a minor venular vasospasm [33], whereas other potential anaesthetic drugs, such as sevoXurane and halothane or fentanyl, increase leukocyte rolling and adherence [20] and induce leukocyte rolling [14], respectively. Therefore, a substantial eVect caused by the applied ketamine on the blood circulation can be neglected. The rats were randomly divided into a fracture group (n = 26) and a fracture with a soft tissue crush group (n = 26). The protocol was in accordance to the principles of the Guide for the Care and Use of Laboratory Animals and was approved by the Animal Care and Use Committee (Tübingen, No. 707). Experimental model Prior to the creation of a closed tibia fracture and a closed soft tissue trauma in all rats, a steel wire (diameter 0.7 mm, length 4 § 0.3 cm; Mizuho Medical Co., Tokyo, Japan) was inserted into the medullary cavity of the right tibia and afterwards removed up to the Wrst one-third of the length of the tibia in order to create a fracture without bending the induced Kirschner wire. This procedure ensured an uncomplicated redrilling of the wire without any additional destruction of the cortical bone structure. No medullary reaming was performed. A closed fracture was created by three-point bending of the tibia, applying an impact velocity of 1.6 m/s by dropping a weight of 650 g from a height of 13 cm [1, 7]. This controlled-impact device, for the creation of the fracture as well as for the soft tissue trauma, showed a high reproducibility of the extent of the induced trauma. The fracture level was set about 2–3 mm proximally of the connection of tibia and Wbula. The fracture was stabilised by advancing the previously retracted Kirschner wire through the intramedullary canal to the distal fragment. To maintain rotational stability, a second wire with a length of 2.5 § 0.2 cm was inserted proximally while the broken Wbula was not Wxed. Exact postoperative pin placement was conWrmed in all rats by radiographs (25 kV, 3 mA, 5 min exposure time; 43805 N X-ray, Hewlett-Packard, Palo Alto, USA).
Arch Orthop Trauma Surg
The creation of the soft tissue trauma and the fracture included a two-step procedure, whereby the production of the soft tissue trauma was followed by the creation of the fracture. In order to inXict the soft tissue trauma, the fracture apparatus was modiWed. The lower leg rested on a Xat bearing and was injured by a blunt impactor. The impact velocity was adjusted to 6 m/s by dropping a weight of 170 g from a height of 180 cm in order to generated a deep impact trauma with destruction of muscle and surrounding fascia, however, without causing a compartment syndrome. Compared to previous studies which crushed soft tissue in a selective way with a minor extent [29, 44] or indeWnite impact [42], we created the impact to the lateral and medial aspect of the tibia at the level of the planned fracture before that fracture was created in a second step. This procedure caused an extensive, closed, soft tissue trauma, which may reXect a more clinical situation than the aforementioned studies [29, 42, 44] did. The distance between the support and the impactor was experimentally determined in a pilot study to result in a closed soft tissue trauma corresponding to a grade 2 trauma according to the Oestern and Tscherne classiWcation [22]. Blood Xow analysis Blood Xow was measured by laser Doppler Xowmetry (OptoXow Lea, Gießen, Germany), which is a generally accepted method [13, 21, 31, 36]. Instead of the microsphere method or intravital microscopy, LDF is noninvasive and unaVected by Xow changes due to the injected tracers and surgical intervention, respectively. A suYcient reproducibility of measurement (
