State of the Art Lecture - Pelvic Fractures in Cats - WSAVA 2015 Congress

State of the Art Lecture - Pelvic Fractures in Cats

World Small Animal Veterinary Association World Congress Proceedings, 2015

S. Langley-Hobbs¹

¹School of Veterinary Sciences, University of Bristol, Langford, Bristol, UK

The majority of pelvic fractures in cats occur after significant trauma and the animal should be assessed and investigated carefully for life threatening diseases such as thoracic or urinary tract problems.

The aim of this lecture is to help in the decision making as to whether repair is necessary and if necessary which bone(s) need repair and finally how these are best repaired.

Whether to Repair or Not?

Most pelvic fractures will heal, however without surgical reduction malunion is common and this can result in significant morbidity to the cat particularly if it affects the ability to defaecate.

The main aim with pelvic fracture repair in cats is to restore:

Pelvic canal diameter

The weight bearing axis

Joint surfaces - by repairing articular (acetabular) fractures

When fracture fragments are minimally displaced, the acetabulum is intact and the cat is weight bearing then surgery may not be necessary. Even with acetabular fractures it may not be necessary to repair them as, if necessary, salvage surgery such as a femoral head and neck excision (or a hip replacement) can be performed at a later date.

Sacroiliac Luxation

Fracture/luxation of the sacroiliac joint is a common injury in the cat. The injury is seen both unilaterally and bilaterally, there will usually be concurrent pelvic floor injuries however other significant fractures are not always present. Diagnosis of a sacroiliac luxation is made from the radiograph. The ilium displaces in a cranial dorsal direction, this displacement is the most important aspect to assess. An apparent widening of the sacroiliac joint can be seen if the pelvis is not straight on the radiograph, if there is no cranial displacement of the ilial wing it is unlikely to have fractured. Minimally displaced sacroiliac luxations can be treated without surgery. Those that benefit from reduction and stabilisation are those injuries that are significantly displaced, and where the cat is lame or unable to weight bear on the affected limb. If injuries are bilateral then repair is usually beneficial.

Sacroiliac Repair

There are a variety of repair techniques described in the literature. One of the most commonest techniques is a lag screw repair. This is performed through a dorsal surgical approach. A skin incision is made midway between the dorsal spinous processes and ilial wing centred at the level of the sacrum, dissection continues via fascial incision and then through the middle gluteal and epaxial muscles; there is often significant tearing of muscle and elevation of skin from the underlying subcutis. Expose the articular surface of the sacrum and place a small Hohmann retractor under the ventral edge to level the ilial wing ventrally. Gently clean up the sacrum with a periosteal elevator and identify the small crescenteric shaped region of hyaline cartilage. Drill a 2.0 mm hole in the bone just cranial and marginally dorsal to the centre of the cartilage.¹ Angle the drill at 90° to the sacrum surface & perpendicular to the dorsal spinous processes. Drill through approximately 60% of the sacrum, measure the depth of the hole. Tap a few turns in the sacrum. Locate the articular surface on the medial aspect of the ilium. Using a pair of bone holders such as Kerns retract the ilium caudally to reduce the luxation; the addition of a small Hohmann retractor placed caudal to the sacral articular face and used to lever the sacrum cranially can help reduction. Tunnel through the middle gluteal muscle down onto the lateral aspect of the ilium. Drill a 2.7 mm hole through the ilium opposite the articular surface on the medial ilium - a curved mosquito can be placed on the medial ilium to identify this point and as a reference point to drill towards. Measure depth of hole. Estimate length of screw required from addition of the two measurements (usually 22–26 mm). Place a 2.7 mm screw through hole in ilium until tip protruding through medial cortex. Retract ilium until screw tip is in line with hole in sacrum. Insert screw, sacroiliac joint should compress as screw tightened.

Ilial Fractures

Ilial fractures are common in cats. There are three main indications for repairing such fractures, narrowing of the pelvic canal and disruption of the weight-bearing axis and sciatic nerve entrapment or impingement. The preferred surgical option is plate and screw fixation. Screw loosening is a possible complication^2,3 and it is recommended that a minimum of six cortices engage either side of the fracture and 2.0 mm screws appear to be are preferable to 2.7 mm. Cuttable plates and dynamic compression plates are the most useful implants, T plates and locking plates have also been used. When using the 7 and 8 hole 2.0 mm DCPs select the slightly thicker implants (1.5 mm rather than 1 mm). Try and engage the sacrum with at least one screw to improve bone purchase and decrease the risk of implants pulling out.

A gluteal roll up technique is my preferred surgical approach for lateral plating.³ If the fracture is caudal or there is an acetabular fracture then it may be necessary to perform gluteal tenotomies (or a greater trochanter osteotomy). Reduce the fracture using a combination of levers and bone holders. The plate should be contoured to the shape of the ilium using the radiograph as a guide, 'over bend' the plate to ensure the caudal ilial fragment is pulled laterally enough. Applying the plate to the caudal fragment first and the application of bone holders to either the ischium or greater trochanter can aid lateralisation of the medially displaced caudal fragments. In cats it is possible to apply a dorsal plate instead of a lateral one.⁴ The 7 or 8 hole 2.0 mm (1.5 mm thick) plates are most useful with 2.0 mm screws. The advantage of the dorsal position is longer screws are used, usually 16–18 mm in length, as compared to 6–10 mm with a lateral plate³ and this reduces the chance of screw loosening and back out. The plate is also best positioned to resist medial displacement of the caudal ilial fragments, which minimises pelvic canal narrowing. If the fracture extends to the acetabulum use a gluteal roll up and gluteal tenotomies. For dorsal plating a gluteal roll down approach can be used. Additionally the cat can be placed in sternal recumbency enabling sacroiliac repair and a contralateral ilial wing repair with no requirement to reposition the cat. Minimally displaced ilial fractures in young cats may be managed conservatively but plate and screw fixation can give an earlier return to function and better pain relief.

Another stabilisation option for pelvic fractures is the use of ESF, however reduction of fracture fragments is not always accurate, there is morbidity associated with the pins going through large muscle masses and close to major nerves & implant removal is always necessary.

Ischial Fractures

Historically it was not thought necessary to repair ischial fractures as they do not occur on the weight bearing axis so they tended to be ignored. However ischial fractures in cats that occur in the region between the acetabulum and ischial tuberosity will benefit from stabilisation. These fractures can result in significant medial displacement with obvious consequences. Repair can be achieved by intramedullary pin or plate and screw fixation.

Acetabular Fractures

Simple acetabular fractures in cats can be repaired using a variety of techniques including the pin/screw/wire composite technique. Physeal fractures seen in young kittens do well after a simple tension band technique.⁵ The dorsal acetabulum in the cat is actually quite a flat bone and it is possible to use straight plates (2.0 mm DCP) rather than curved acetabular plates. Great care should be taken when retracting the feline sciatic nerve as it is very susceptible to traction injuries. Some acetabular fractures can be treated conservatively and if pain and lameness occur subsequent to arthritis then femoral head and neck excision can be performed at a later date.

Complications

Pelvic canal narrowing after conservative management and even surgical management of pelvic fractures is one of the most common complications. This can lead to constipation, obstipation and ultimately megacolon. Generally if the pelvic canal narrowing is not addressed early on then the prognosis is guarded for reversal of any colonic enlargement and colonic resection may be indicated. Narrowing of more than 45% of the pelvic canal diameter was associated with constipation and obstipation in one study³ so narrowing of this degree or more is a good indication to recommend surgical repair to owners. Skin avulsion is common after pelvic fractures in cats and this can result in skin necrosis and local slough⁶.