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Prophylactic Screw Stabilization of Humeral Intracondylar Fissures
Humeral intracondylar fissures and the associated condylar fractures that ensue were initially a problem in the Spaniel breed dogs, but nowadays, other breeds such as the French Bulldog are also at risk. Humeral intracondylar fissure may be a cause of elbow pain and lameness or be an incidental finding. Insertion of a bone screw transversely through the condyle is performed as a prophylactic stabilization procedure to prevent development of a complete fracture.
Originally the bone screw was inserted into the lateral epicondylar region, and driven in a lateral-to-medial direction. This technique was partly selected for safety reasons, to avoid joint penetration by the screw because the lateral part of the condyle (capitulum) has a smaller diameter than the medial part (trochlea). However, several clinical publications reported that lateral-to-medial screw insertion was associated with higher rates of minor and major complications, especially surgical site infection and implant failure. Therefore, some surgeons switched to inserting the bone screw from the medial epicondyle in a medial-to-lateral direction. The choice of direction of screw insertion has been the subject of some controversy.
A recently published randomized, prospective clinical study from the United Kingdom found that the rates of postoperative surgical site infection after insertion of positional, cortical bones screws across humeral intracondylar fissures in a lateral-to-medial direction (12/37 procedures) and medial-to-lateral direction (4/36 procedures) were significantly different, but high with both techniques. By way of contrast, another United Kingdom clinical study (nonrandomized and retrospective) of the same problem found that the surgical site infection rates of lateral-to-medial screw insertion (4/15 procedures) and medial-to-lateral insertion (7/31 procedures) were both relatively high, but not significantly different.
One popular explanation for the higher rate of surgical site infection with lateral-to-medial transcondylar screws proposed that the skin and subcutaneous tissues overlying the screw head laterally could be more readily traumatized postoperatively, producing a seroma.
However, another and perhaps more likely explanation is that physical trauma and heat necrosis sustained by the tissues during surgical implantation of the transcondylar screw intraoperatively predispose to development to surgical site infection. The origins of the digital extensor muscles and the ulnaris lateralis muscle cover the lateral epicondyle, and these muscles are at risk of being physically traumatized (minced) by the rotating drill bits, especially the large 4.5-mm bits. By contrast, the medial epicondyle is not covered by any muscle in the region of drilling for insertion of medial-to-lateral screws. A second contributing factor to infection could be the heat necrosis of bone caused by drilling. Some surgeons place a transcondylar Kirschner wire initially to verify subsequent screw position. Bone of the humeral condyle afflicted by an intracondylar fissure is often dense and sclerotic, and Kirschner wires drilled into such dense bone generate considerable heat, with temperatures above 55°C causing bone necrosis. Moreover, cannulated drill bits are much less efficient at drilling dense bone compared with a sharp drill bit, so they also have the potential to cause bone necrosis. Flushing with saline during drilling of such bone is relatively ineffective at preventing heat necrosis of bone, especially with Kirchner wire insertion.
The pathogenesis of surgical site infection is complex and multifactorial. It is unlikely that the reason for the high rate of infection associated with transcondylar screw placement would be as simple as just the direction of the bone screw. Elucidation of this problem warrants further research.
Article published online:
06 November 2023
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- 1 Carwardine D, Mather A, Schofield I. et al. Medial versus lateral transcondylar screw placement for canine humeral intracondylar fissures: a randomized clinical trial. Vet Surg 2023; (e-pub ahead of print) DOI: 10.1111/vsu.13993.
- 2 Potamopoulou M, Brown G, Whitelock R. Correlation between the insertion side of a transcondylar screw for the surgical management of humeral intracondylar fissures in dogs and the incidence of postoperative surgical site infection. Vet Comp Orthop Traumatol 2023; 36 (06) 311-316
- 3 Woods JC, Cook JL, Bozynski CC, Tegethoff JD, Kuroki K, Crist BD. Does irrigating while drilling decrease bone damage?. Iowa Orthop J 2022; 42 (02) 22-29