Surgical anatomy of the feline sacroiliac joint for lag screw fixation of sacroiliac fracture-luxation

Abstract

SummaryTwenty-eight feline pelves (56 hemipelves) were examined in order to identify the location for optimal sacroiliac screw placement in sacroiliac fracture-luxation repair. A drill hole was started on the median plane of the hemipelvis in the centre of the body of the first sacral segment until it penetrated the lateral cortex of the ilial wing, thus providing optimal drill hole placement. The position of the drill hole on the articular surface of the sacral wing and on the lateral surface of the ilial wing was measured. The distance of the drill hole from the cranial margin of the sacral wing was 51% of sacral wing length, just cranial to the crescent shaped hyaline cartilage. The distance from the dorsal margin was 47% of sacral wing height. The drill bit direction has to be adjusted to the cranio-caudal inclination (range 10° to 29°) and dorso-ventral inclination (range 2° to 25°) of the sacral wing. A notch in the cranial edge of the sacral wing was present, with variable position, in 34% of the specimens and is consequently not a useful landmark for sacroiliac screw placement. The drill hole on the lateral surface of the ilium was located in craniocaudal direction at a distance of 69% of sacral tuber length, measured from the cranial dorsal iliac spine. The dorso-ventral position of the drill hole was at a distance of 52% of ilial wing height measured from the sacral tuber. The ventral gluteal line, present in 93% of the cases, is a useful landmark to locate optimal screw hole position on the ilial wing.

Defining a safe corridor for trans‐iliac pin placement in cats

“…Previous studies have reported the same landmark when defining safe corridors for lag screw placement in cats. 3,19 Burger et al 3 described the sacral tuber as the reference for drilling the screw hole. The sacral tuber is straightforward to visualise intraoperatively and is delimited by the cranial dorsal iliac spine and the caudal dorsal iliac spine.…”

“…They also reported the ventral gluteal line as an additional landmark, which can also be useful when choosing the pin placement start point. 3,19 The distance between the DLVC-I is at its greatest at the most craniodorsal aspect of the iliac wing. Identifying this landmark guarantees the largest dorsoventral area to place the pin within the dHPC and avoids the vertebral canal ventrally.…”

“…20 However, the safe drill corridor is narrow at 0.5 cm 2 or less, and the drilling angles can be difficult to achieve. 3 One study showed that 12.5% of lag screws placed into the sacrum of 40 cats were found to be malpositioned, which can result in cauda equina injury, damage of the median sacral vessels and/or increase risk of screw loosening if the screw is less than 60% depth of the sacral width. 9 In comparison, trans-iliac pinning may be safer as the pin is positioned further away from major neurovascular structures.…”

“…P elvic fractures are common, accounting for 20%-32% of cat fractures, and 60% of these have a sacroiliac (SI) fracture luxation. [1][2][3] Unilateral SI luxation most commonly presents with other pelvic fractures (pelvic floor fracture and contralateral iliac body fracture) or symphyseal separation, 3 whereas bilateral SI luxation may occur in isolation. 2 Treatment options for SI luxation range from conservative management to bilateral surgical intervention.…”

“…16 Placement of lag screws through the ilium has been well described for both the canine and feline sacrum, including the anatomical differences, allowing for reliable and accurate screw positioning. 3,4,[17][18][19] The criteria for screw fixation in lag fashion for SI luxation repair were listed by Decamp and Braden, and these criteria are now used as a guide for the initial positioning of the screw. 20 Shales and Langley-Hobbs 17 suggested a ±4 margin of error for both the experimental measurements and operator error when driving screws into the sacrum at an angle specified but estimated 'by eye' of the surgeon.…”