Screwed Up? Radiographs Might Be Jumping the Gun on Joint Penetration in Dogs

Detection of intra-articular implant penetration of the canine stifle with radiography: A cadaveric study

Ryan G. Philips, Richard M. Jerram, Damian Chase

Background
The placement of metal implants near joints is a common aspect of orthopedic surgery in veterinary medicine. One significant complication is the unintended entry of an implant into the joint space, which can lead to pain, reduced joint function, degenerative joint disease, and may necessitate additional surgery. This issue, referred to as intra-articular implant penetration, is not well studied in dogs. Postoperative imaging, particularly radiographs, is commonly used to evaluate the position of implants. However, the reliability of radiographs in detecting whether an implant has entered the joint space in the canine knee (stifle) remains unclear. This study aimed to evaluate whether standard radiographic views can accurately detect implant penetration into the joint when the implant is placed at known depths relative to the joint surface.

Methods
This was an experimental study conducted using five adult dog cadavers, providing a total of nine usable knee joints. Surgical screws made of stainless steel were inserted into the upper part of the tibia bone and aimed either toward the inner side (medial) or outer side (lateral) of the joint. Each screw was placed at a precise depth relative to the joint surface: either 2 millimeters below, exactly at, or 2 millimeters above the surface. After placement, standard radiographs were taken of each joint from two angles. A total of 54 veterinary experts in surgery and imaging independently reviewed 104 radiographic cases. They were asked to determine whether the screw had penetrated the joint, based solely on the radiographic images.

Results
The study found that the overall accuracy of radiographs in detecting whether an implant had entered the joint was 78 percent. When the implant truly had entered the joint, it was correctly identified in 97 percent of cases. However, when the implant did not enter the joint, it was incorrectly identified as penetrating the joint in approximately 32 percent of cases. This overestimation was especially common when screws were directed toward the outer (lateral) side of the joint, as opposed to the inner (medial) side. Screws placed exactly at the joint surface or slightly below it were the most difficult to classify correctly. Despite these challenges, there was a moderate to high level of agreement among different reviewers, particularly when screws were clearly inside or clearly outside the joint space.

Limitations
This study was conducted using cadaver limbs rather than live animals, so the clinical relevance of some findings may be limited. The small number of cadavers and reviewers could also restrict the generalizability of the results. Additionally, implant placement was not guided by a fixed positioning tool, introducing variability in how and where the screws exited the bone. Radiographs themselves were subject to slight differences in limb angulation, which may have affected how the screw appeared. Since joint cartilage does not show up on X-rays, some reviewers may have incorrectly judged screws that were near or in the subchondral bone as being within the joint space.

Conclusions
This study provides evidence that standard radiographs are reasonably effective in detecting when an implant has entered the joint space in the canine knee. However, radiographs also have a tendency to incorrectly suggest joint penetration when the implant is close to but not actually within the joint, particularly when aimed laterally. These misinterpretations could lead to unnecessary repeat surgeries. Therefore, surgeons should be cautious when interpreting postoperative radiographs, and consider additional imaging techniques such as computed tomography or fluoroscopy for improved accuracy in evaluating implant placement. Further research is warranted to explore the clinical effects of implants located near but not within the joint space.

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