A Bridge Too Far.
The following pages contain a copy of the case report that I wrote whilst
on elective. The research was taken as part of a grant that was given to the
hospital. This case report has been submitted to Injury journal for publication.
A bridge too far: Less Invasive Stabilization System (LISS) for fractures of the proximal tibia – a case of nonunion.
P. Satya, B. O’Toole, R.M. Smith
Orthopedic Trauma Service, 15 Parkman Street, WACC 525, Boston, Massachusetts USA, 02114-3117.
1. Introduction
Surgical treatment of proximal tibia fractures are associated with problems of non fixation and significant complication rates [1]. Plating techniques have developed from traditional direct reduction using invasive techniques to more modern indirect reduction using a minimally invasive approach. This illustrates the use of biological techniques to facilitate union and the use of locking plates in fixation. Less Invasive Stabilization System (LISS) represents a major advance in management by combining both a minimally invasive approach and a fixed angle plate. LISS has been shown to be an effective bridging technique in multifragmented displaced fractures with a view to biological healing. However although rare the use of this bridging technique can result in nonunion according to Perren’s hypothesis regarding motion at the fracture site [2,3]. We report a case of mid diaphyseal nonunion following treatment of a proximal tibia fracture by LISS. This illustrates an interesting failure mode which can demonstrate the biomechanical features of a LISS plate and the mode of bony healing.
2. Case Report
A 60-year-old grave digger was referred to us with a grade 3B open left tibial fracture following a severe crush injury sustained at work. He underwent an initial irrigation and debridement with the application of external fixation. A separate procedure involving additional irrigation and debridement and open reduction and internal fixation with the application of a 13-hole LISS plate was then performed (figure 1).
Three months later he presented in routine follow up with a segmental defect at the fracture site and demonstration of tibial nonunion (figure 2). This was a 2 centimeter defect with a displaced tibial segment which was united to the proximal part of the tibia.
The LISS was well fixed to the bone, but the long unfixed segment was flexible such that it was possible to move the bone significantly with the LISS retaining good hold. The nonunion therefore seemed to result from a combination of segmental injury, low bone healing potential and the motion. The bone was also generally healthy and only a few small areas needed debridement.
A cancellous bone graft and additional external fixation was performed (figure 3). Local bone was trimmed to remove the prominent segment and maximal bone graft was harvested from the left and right anterior iliac crests.
The whole construct was then stiffened with three screws passed into the LISS to hold the largest central segments which was now well healed proximally. However significant movement of the distal segment remained due to flexion within the LISS device itself. A single bar external fixation frame was then applied to the medial side of the tibia to additionally stiffen the construct and to facilitate incorporation of the bone graft.
Postoperative recovery was uneventful and the patient was discharged on the fourth day. Five months later radiographs showed osseous healing with a moderate-sized osseous bridge and the external fixator was removed. Six weeks later the tibia was found to be clinically and radiologically healed and the patient was able to progressively increase his activity and he was then discharged from our service three months later.
Figure 1. Postoperative anteroposterior radiograph showing application of LISS plate.
Figure 2. 3 Month postoperative anteroposterior radiograph showing tibial nonunion.
Figure 3. Postoperative anteroposterior radiograph showing additional external fixation of LISS plate.
3. Discussion
LISS represents a move towards the concept of bridging and the advantages of a minimally invasive operative technique. This illustrates the concept of biological plating by minimizing damage to the blood supply and periosteum when compared to conventional plating techniques and the technique is associated with fewer postoperative complications [4].
The fixed angle LISS plate uses locking screws to prevent tilting and aim to stabilize the proximal fragment. In a case of nonunion the findings are typical to those of a loose plate, however a the LISS was well attached to the proximal segment and was flexible. This may represent the LISS plate being made of titanium which can afford some flexibility when compared with stainless steel plating.
This demonstrated the concept of motion at a fracture site that can result in nonunion. [2,3]. The resulting flexibility caused a stress concentration at the site of nonunion had to therefore be stiffened with additional external fixation which resulted in subsequent healing.
Thus although LISS represents a technique that minimizes complications postoperatively the case of nonunion can result from stresses caused by motion in a fixed angle LISS plate. Combined with a large segmental injury resulting in reduced ossification potential the length of the bridging gap with regards to frame stiffening of the LISS should be considered.
References