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Use of Grid Coordinate Technique for Implant and Foreign Body Removal

Arnold S. Lesser, VMD

A method of accurately marking the location of surgical implants for their removal was devised with the use of a sterile radiopaque grid. This grid enables the surgeon to mark the incision site while maintaining sterility, thereby, decreasing tissue dissection and exploration. Four surgical cases are presented which demonstrate types of implants that can be removed with the help of this technique.

Introduction

The use of metallic implants with internal fixation in orthopedics usually necessitates the eventual removal of these implants through a second surgical procedure. Since this need for a separate procedure is often cited as a disadvantage (especially with the use of more intricate implants such as plate and screws), a technique for simplifying the removal procedure was sought by the author. 1

The key appeared to be in accurately locating the implant so that only a minimal incision was necessary and extensive surgical exploration could be avoided. In some instances, especially where pins are used, the implant can be palpated through the skin and located easily. Often, however, fibrous connective tissue covers the ends of these pins, making palpation difficult. Also, irregular callus formation can mimic implant ends. When screws are used they are even more difficult to palpate since they are usually flush with the bone.

The implants can easily be seen on radiographs, but a method was needed to locate them in relation to the planned incision site, and to mark this site while maintaining sterility.

Methods and Materials

Radiopaque grids have been available in medicine for the measurement of internal organs and the locating of foreign bodies, 2 but in this case a sterile metal grid was used to delineate the exact location of an implant on radiographs.

Two sizes of grids were chosen for this study - 1/8 inch and ¼ inch, although only the ¼ inch grid appears in the cases presented. The grids were sterilized using ethylene oxide. They were malleable enough to be contoured to the limb so that movement was avoided between radiography and the marking of the incision site. The technique is simpler if a system is available for taking radiographs during surgery [Figure 2]. In this case, the patient is prepared and draped for surgery and the sterile grid is applied over the area, fastened to the limb with stay sutures, and radiographs are taken [Figure 1]. From the developed plate, it is simple to locate the implant by counting horizontal and vertical bars [Figure 3]. This is repeated on the grid, and a small stab incision is made through the grid at the proper site [Figure 4]. The grid is removed and the incision is enlarged to facilitate the removal of the implant [Figures 5 and 6].

If equipment is not available for in-surgery radiography, then the area is clipped and cleaned and the grid is applied in radiology. After locating the incision site, a hypodermic needle can be used to mark the site. The animal is then taken to surgery and the area is surgically prepared. The needle is removed before surgically scrubbing the area, but there is usually some bleeding, especially over a joint, so the site is still obvious. The use of an indelible dye, (such as methylene blue) also can b e used to mark the site before surgical scrub.

Case Studies

Case 1 - This case involves a three-month-old German shepherd with a medial condylar fracture of the elbow [Figure 8A]. The fracture was reduced and fixed with two compression screws [Figure 8B]. At three weeks, the fracture was considered healed radiographically, and the animal was admitted for screw removal. This was the first case in which this technique was used, so the grid had not been obtained. Therefore, a makeshift screen was prepared with orthopedic wire [Figure 8C]. The screws were marked with two needles and the grid and needles were removed before surgical preparation of the leg. Even after surgical scrubbing of the elbow, the two pin holes were easily identifiable. A small stab incision and blunt dissection were all that was necessary to find the screws and remove them.

Case 2 - A distal, femoral, epiphyseal fracture in an eight-month-old mixed breed was cross-pinned with small Steinmann pins [Figures 9A and 9B]. At seven weeks, the pins were removed form the lateral side using a sterile grid and radiographs [Figure 9C]. In this case, it was possible to apply the grid after surgical preparation of the site. The pin was located easily, even though it was not palpable. With this technique available, it is now possible to cut the ends of the cross pins closer to the bone. This reduces soft tissue irritation from joint movement during the healing process.

Case 3 - A slipped capital epiphyseal fracture in a one-year-old golden retriever was repaired with a single 35 mm cancellous screw [Figures 10A and 10B]. Compression was gained by overdrilling the hole in the femoral neck. With the use of a grid, it was possible to remove the screw at seven weeks using a stab incision, even though the screw was not palpable through the skin [Figure 10C].

Case 4 - A mixed-breed dog of unknown age was presented with an untreated nonunion of the femur [Figure 11A]. A six-hole DCP plate was used to fix the fracture under compression [Figure 11B]. The plate was removed at nine months with the use of the grid technique [Figure 11C]. IN previous plate removals, it was always necessary to make a large incision at least half the length of the plate to accomplish removal. With the grid, it was possible to remove the plate with a stab incision over each screw, and a 1 cm incistion at the distal end of the plate [Figure 11D].

Discussion

This method has proved to be very helpful in the accurate location and subsequent removal of internal fixation devices. As illustrate in the preceding cases, the technique can b e applied to numerous forms of implant; however, this technique has many other potential uses. Any time there is a radiopaque object to be pinpointed in the body, such as a migrating needle, the grid can be utilized. Also, if a pin or Kirschner wire migrate out of the bone into the surrounding tissue, it can be difficult to locate. Anteroposterior and lateral radiographs incorporating the grid will greatly simplify retrieval. Bone sequestra, joint mice, and osteomyelitic cavities are other instances where the grid technique can reduce surgical exploration and dissection. The grid technique can be used in place of or in conjunction with the more elaborate equipment and techniques available in human medicine. These include fluoroscopy, xeroradiography, electronic auscultation, stereotaxic apparatus, and metal detectors. 2,3,4,5 With the advent of gas sterilization, there are many materials that can be used for the grid and many situations that are adaptable to its use in veterinary surgery.