Percutaneous osteosynthesis is a very new technique that consists of inserting screws into bone structures through a very small skin incision (of less than 10mm). The technique is now performed percutaneously by interventional radiologists due to the development of cannulated screws that can be inserted coaxially over a guide pin, and due to the level of accuracy possible with CT- or flat panel-guidance, writes Frédéric Deschamps.
Metastatic bone disease is a very common clinical occurrence in cancer patients. A pathological fracture can result in significant pain and loss of function. Prophylactic fixation before a fracture occurs is an issue of utmost importance. In addition, insufficiency fractures can occur in cancer patients because of osteoporosis, which may be primary (related to age) or secondary (related to the use of steroids, radiation of pelvic malignancies, etc). Percutaneous osteosynthesis is a very new technique that consists of inserting screws into bone structures through a very small skin incision (of less than 10mm). This technique was initially developed by orthopaedic surgeons to stabilise non-displaced bone fractures during open surgery. The technique is now performed percutaneously by interventional radiologists due to the development of cannulated screws that can be inserted coaxially over a guide pin, and thanks to the level of accuracy possible with CT- or flat panel-guidance. The procedures can be performed under general anaesthesia or conscious sedation by an interventional radiologist, either in an interventional CT-room or in an angiosuite equipped with a cone-beam CT.
Fig 1 The cannulated screw (black arrows) is advancing a Kirschner wire (white arrows) thanks to a cannulated screwdriver (black arrow heads) through a small skin incision.
The interventional radiologist first drills a Kirschner wire across the fracture/the tumour under CT-fluoroscopy guidance or under cone-beam CT guidance, using dedicated guidance-software. A 3D image must then be obtained via CT or cone-beam CT to assess the proper direction of the track and to measure the appropriate length of the screw to be inserted. Ideally, the screw should be long enough to reach the distal subchondral bone. The 8mm cannulated self-drilling tapping screw (Asnis III cannulated screws; Stryker) is placed over the Kirschner wire and slid down to the cortical bone with the use of a cannulated screw driver (Fig 1). Once the proper positioning of the screw is confirmed by a new 3D acquisition, the Kirschner wire is withdrawn and the skin entry point is sutured.
The indications for percutaneous osteosynthesis are twofold: firstly, it is a palliative technique for patients suffering from pathological or non-pathological non-displaced fractures and, secondly, it provides prophylactic consolidation, in association with cementoplasty, for patients with impending pathological fractures due to osteolytic metastases.
Fig 2 Palliation of a non-pathologic fracture of the pubic ramus in a patient suffering from prostate cancer. VAS score decreased from 8 to 0 at day three.
Palliation of pathological or non-pathological fracture
For patients suffering from pathological or non-pathological fractures, the goal of percutaneous osteosynthesis is to achieve stabilisation of the fractures, which will result in pain palliation. Ideally the fracture should be non-displaced because is not possible to provide a percutaneous anatomic reduction of fracture fragments. However, in certain cases, namely in non-surgical patients, stabilisation of a displaced fracture was performed without reduction. Technically, the screws must be inserted perpendicularly to the fracture and across the fracture. Typically, fractures that can be fixed using percutaneous osteosynthesis are located in the sacrum, the iliac crest, the acetabulum roof, the pubic ramus (Fig 2) and the proximal femur We currently do not perform cementoplasty in association with fracture stabilisation because there is a risk of cement leakage through the fracture line, and because the mechanical property of the cement is not appropriate in locations submitted to torsion forces. However, in certain cases, small amounts of cement were injected through a second puncture in order to improve the screw tip’s anchorage (Fig 3).
Fig 3: Palliation of a post-ablation insufficiency fracture of the sternum (A1 and A2) stabilised by percutaneous osteosynthesis (B1 and B2). Cementoplasty was performed in association at the end of the procedure to improve the screw anchorage (C1 and C2). VAS score decreased from 9 to 1 at day two.
Prophylactic consolidations of osteolytic metastases
For patients with impending osteolytic metastases, the decision to perform percutaneous osteosynthesis plus cementoplasty instead of cementoplasty alone is driven by the fact that the strengthening properties of the cement are strong in compression but weak for tensile or shear stresses. This explains why cementoplasty alone is only appropriate for the consolidation of osteolytic metastases located in the cotyle and in the vertebrae. Technically, we insert the screws across the osteolytic metastases first and then inject the cement into the osteolytic metastases. For good consolidation, the screws must enter a strong bone cortical and their tips must be advanced as far as possible, ideally reaching the distal subchondral bone. We then use a dedicated cementoplasty needle for injecting cement. This needle is inserted through the same track of the screws in parallel. We start the injection close to the tips of the screws and continue the injection during the removal of the needle. We always try to fill the entire osteolytic metastases. Typically, the impending osteolytic metastases that can be consolidated using percutaneous osteosynthesis plus cementoplasty are located in the iliac crest (Fig 4) and in the proximal femur.
In conclusion, percutaneous osteosynthesis provides pain palliation for pathological and non-pathological fractures, as well as prophylactic consolidation of osteolytic metastases in bone cancer patients. The technique must be considered as part of the therapeutic arsenal of interventional radiologists for two main reasons. First, because it is a minimally invasive procedure that avoids extensive surgical exposure, and second, because the accuracy made possible by CT- or flat panel-guidance results in high technical success rates and very low complication rates for screw placement.
Fréderic Déschamps is an interventional radiologist at the Gustave Roussy Cancer Campus, Villejuif, France. He has reported no disclosures pertaining to the article