Pelvic fractures are common injuries in cats, most frequently affecting young males following trauma, such as road traffic accidents (Bookbinder and Flanders, 1992). A wide variety of fracture patterns are seen in various combinations (Figure 1).
Clinical examination and history
A thorough history and clinical examination are essential starting points in fracture assessment. Clinical examination should start with an assessment of the cardiovascular and neurological systems to identify any concomitant or life-threatening injuries that may have occurred (Box 1).
Common concomitant injuries or conditions seen with pelvic fractures
Assessment of the pelvis in the conscious, traumatised cat can be difficult. Palpation of the iliac crests and ischiatic tuberosities to determine whether they are aligned symmetrically as a rectangle allows assessment of the integrity of the pelvis with minimal patient discomfort. Similarly, the greater trochanter, ischiatic tuberosity and iliac crest should form a triangle on palpation and be symmetrical on each side. Finding crepitus or discomfort on manipulation of the hips is an indication of a probable injury of the coxofemoral joint.
A neurological examination will determine if there are neurological deficits present. The lumbosacral trunk and the sciatic nerve are particularly at risk in cats with pelvic fractures (Figure 2). The lumbosacral trunk passes ventral to the sacral wing, then medial to the iliac body. The sciatic nerve arises from the lumbosacral trunk to pass dorsal to the ischiatic notch of the pelvis, just caudal to the hip joint, to pass down the caudal aspect of the pelvic limb. The nerve is prone to damage during sacroiliac luxation and fracture of the iliac body, acetabulum or ischium and are seen in 13% of cats with pelvic fractures (Meeson and Geddes, 2017). Further damage may occur post-trauma because of fragment instability or during surgical repair. Sciatic neuropraxia is commonly seen, whereas sciatic neurotemesis is rare. It is important to establish that patients have conscious deep pain sensation and some spontaneous movement of the limb before fracture repair.
Abnormalities of tail tone, perineal sensation and the perineal reflex suggest damage to the sacral nerve segments, which can lead to urinary or faecal dysfunction or incontinence. These problems are commonly seen in cats with sacrococcygeal fracture and/or luxation or sacral fractures (Tatton et al, 2009). Where neurological deficits are identified, serial assessments should be performed to determine if the issues are static, deteriorating or improving. If cats have urinary dysfunction from cauda equina trauma, owners may wish to delay surgical treatment of pelvic fractures until there is some sign of neurological improvement, as some cats may remain permanently incontinent. Cats presented with shock or hypothermia often have obtundation of neurological reflexes and repeat neurological assessment should be made after correction of shock and hypothermia.
Following the examination and clinical history, initial supportive care should be provided with intravenous fluid therapy, analgesia and treatment of life-threatening injuries.
Diagnostic imaging
Orthogonal ventrodorsal and lateral view radiographs of the pelvis can be supplemented with a variety of oblique views; for example, tilting the pelvis to the left, right, cranially and caudally is useful to determine the configuration of the fracture and distribution of the fragments. Thoracic radiographs are recommended for traumatised patients in addition. It is also advisable to look for evidence of urinary tract trauma using retrograde urethrography with ultrasound of the kidneys, bladder and retroperitoneal space (Figure 3).
Computed tomography can allow an improved understanding of the fracture pattern and distribution of the fragments. This is especially useful in the assessment of fractures of the acetabulum and sacrum, where the complex anatomy can be difficult to interpret on radiographs (Draffan et al, 2009). It also facilitates indepth planning of the fracture repair.
Pelvic fracture assessment
The radiographs are carefully assessed to determine what fractures are present and whether the fracture is best treated surgically or can be adequately managed with conservative treatment (Box 2). The anatomy of the pelvis is arranged as an open-ended box with the sacrum forming the roof, the ilia and acetabulae forming the sides and the pubis and ischium forming the floor of the box. This configuration means that if one fracture is identified, at least one other fracture is likely to be present.
Conservative management of pelvic fractures
The concept of the weight-bearing axis in the pelvis is important in decision making. The forces of weight bearing will pass from the pelvic limb via the femoral head to the acetabulum, along the ilium, to the sacroiliac joint and then to the spine and body (Figure 4).
Fractures involving the weight-bearing axis are appropriate for surgical treatment because these fractures lead to pain and loss of function. An exception is minimally displaced sacroiliac fracture or luxation, which may be sufficiently stable to allow conservative management to be successful.
A second indication for surgery is involvement of the acetabulum. As an articular fracture, surgical treatment with perfect reduction and rigid internal fixation is recommended, to reduce the severity and speed of onset of osteoarthritis (Boudrieau and Kleine, 1988). Early repair results in less damage to the articular surfaces and improved outcome. However, it is important that life-threatening injuries are dealt with first, and the patient is sufficiently stable to undergo the anaesthetic and surgery. A successful outcome can often be achieved a week after fracture with primary repair, and salvage surgeries are not always required at this stage. Further delays will often lead to callus formation, fibrosis and difficulty achieving perfect reduction.
A third indication for surgery is narrowing of the pelvic canal (Figure 5). This tends to occur when there are fractures of the weight-bearing axis with medial displacement of the ilium or acetabulum. For cats, narrowing of the pelvic canal of 40–45% may be well tolerated (Hamilton et al, 2009). Cats with more than 40–45% narrowing are at higher risk of developing faecal retention, constipation, obstipation and megacolon. It is easier to prevent megacolon and obstipation than to treat them once they have become established. If conservative treatment is selected for fractures with moderate pelvic narrowing, it is advisable to repeat radiographs after 7–10 days to ensure that there has not been further medial displacement of the fracture segment when the cat starts to weight bear on the limb.
A final indication for pelvic fracture is neurological dysfunction as a result of nerve entrapment. This most commonly involves the lumbosacral trunk or the sciatic nerve. In most cases, the nerve is not entrapped but is bruised, leading to neuropraxia. These cases involve a loss of nerve function but are generally not extremely painful. Where extreme pain is observed, the nerve may be entrapped between fracture fragments, and pain can be difficult to control. This is an indication to explore and free the nerve while surgically stabilising the fracture. For cases with neuropraxia, functional recovery is seen in most cats, though this can take several weeks and may not be complete. Given the time needed for nerve recovery, it is not advised to delay surgical treatment until neurological function has recovered as fibrosis, contracture and callus formation will make surgery more challenging and increase the risk of further nerve damage during surgery.
While surgical treatment is considered the ideal for the fractures summarised in Box 3, conservative treatment might be the only option available as a result of financial and other constraints. Except in those cases with intractable pain, it is reasonable to try conservative treatment if the owner is informed of the limitations of this approach.
Fractures for which surgery should be the first choice
Considerations in feline pelvic fracture repair
Having determined that surgical repair is needed, fracture planning is essential before embarking on surgery. Good planning reduces surgical time, reduces intra-operative complications and allows the optimum surgical approach to be made. Reference to bone models can be useful for plate contouring and a better appreciation of the bony anatomy. A gluteal roll-down technique is used for iliac wing and sacroiliac fracture or luxation, a gluteal roll-up technique is used for iliac body fractures and a trochanteric osteotomy of the greater trochanter (or gluteal tenotomy) is used to approach acetabular fractures. The gluteal roll-up and trochanteric osteotomy approaches are easily combined for exposure of complex fractures involving the ilium and acetabulum. The biology of pelvic fractures is generally favourable, with an excellent blood supply from the muscles and soft tissues which surround the bones of the pelvis. Careful attention to preserving the soft tissues and vascular supply to the pelvis during the approach to the bone will help to ensure that healing progresses as expected. Particular attention should be paid to protecting the lumbosacral trunk and sciatic nerve.
The best time to repair the fracture is at the earliest opportunity once the cat is sufficiently stable and free of life-threatening conditions. Delay can lead to callus formation, fibrosis and contracture, which make fracture reduction difficult and risks further damage to the lumbosacral trunk or sacral nerve.
Where multiple fractures require repair (eg an acetabular fracture with a contralateral iliac body fracture or a sacroiliac luxation with a contralateral iliac body fracture), the fracture which requires the greatest degree of fragment mobility to allow reduction should be treated first. Often, repair of the first part of the pelvis will aid reduction of other fractures of the pelvis. For example, if a sacroiliac fracture luxation is initially reduced and stabilised, this will often help reduce a contralateral iliac fracture. If entrapment of the lumbosacral trunk or sciatic nerve is suspected, it is best to approach the suspected site of entrapment first and release the nerve before attempting reduction of other fractures.
An intact contralateral hemipelvis will significantly improve the general stability of the pelvis. Conversely, bilateral fractures at the same level such as bilateral iliac body fractures or bilateral acetabular fractures can provide a greater biomechanical challenge.
Sacroiliac fracture/luxation
Surgical treatment of sacroiliac luxation is recommended when it results in pelvic narrowing, is moderately or markedly displaced, is palpably unstable or there is evidence of entrapment of the lumbosacral trunk. While conservative treatment can result in a successful outcome, recovery is faster and associated with reduced discomfort if surgical stabilisation is achieved. Placement of a transiliosacral lag screw (usually a 2.4 mm or 2.7 mm cortical screw) traversing at least 60% of the width of the sacral body is recommended. The surgeon should be familiar with the appropriate drill start point on the articular surface of the sacral wing (Figure 6) and the angle that the drill should be directed relative to the sacral wing, which is tilted in both the sagittal and transverse planes (Figure 7) (Shales et al, 2009).
There is a narrow safe corridor for screw placement in the sacral body, which is bordered by the spinal canal dorsally, pelvic canal ventrally and lumbosacral intervertebral disc cranially. The glide hole in the wing of the ilium should be drilled at the location shown in Figure 6. Use of a large smooth washer under the head of the screw to spread the load applied by the screw head over a wider area of the iliac wing reduces the chance of fracture of the thin bone. Where available, fluoroscopic guidance or the use of a 3D-printed guide can improve the chances of placing the screw in the correct orientation and reduce the chance of complications.
Iliac body factures
Iliac body fractures are most commonly oblique from cranioventral to dorsocaudal with medial displacement of the caudal fragment. These are frequently treated with a laterally applied bone plate and screws via a gluteal roll-up approach. The fracture is reduced following exposure of the fracture fragments. The thin mediolateral dimension of the bone can make application of boneholding forceps across the fracture difficult. Use of bone-holding forceps attached to the greater trochanter of the femur or to the ischiatic tuberosity via a small caudal incision directly over the tuberosity can allow easier manipulation of the caudal bone fragment (Figure 8).
Bone stock available for implant placement can be limited when applying a plate on the lateral aspect of the ilium. The bone of the iliac body and especially the wing is thin with few screw threads engaging in the bone, making screws in this area prone to loosening. Strategies to improve screw holding in the ilium include:
Iliac body fractures commonly occur close to the acetabulum. It is important to avoid placement of screws into the acetabulum, leaving a small region of bone cranial to the acetabulum for screw placement. Strategies to overcome this problem include:
Acetabular fractures
The goal of acetabular fracture repair, like other articular fractures, is to achieve perfect apposition, ensure joint congruency and to apply rigid internal fixation. This can be achieved with a dorsally applied acetabular plate designed for the purpose (Figure 10).
A trochanteric osteotomy approach is used to allow access to the bone cranial and caudal to the acetabulum. This also helps to retract the sciatic nerve out of the surgical site. Reduction of the fracture can be challenging, and use of reduction forceps attached to the femur and ischiatic tuberosity can be useful to help lateralise and rotate the caudal fragment. Once the fracture is reduced, reduction can be maintained with pointed reduction forceps placed from cranial to caudal with or without a temporary arthrodesis wire. If pointed reduction forceps are difficult to retain in the correct position, then drilling small holes cranial and caudal to the proposed plate location can be useful to stabilise the points of the reduction forceps. If the joint capsule is not already torn or avulsed, then it is useful to make a small arthrotomy at the level of the fracture to allow visualisation of the femoral head and the dorsal acetabular rim. Use of locking acetabular plates significantly facilitates fixation because of the reduced need for perfect contouring of the plate to the dorsal acetabulum (Figure 10). Use of a longer plate to bridge from the cranial ilium to the ischium (Figure 11) can be especially useful where there are comminuted fractures involving the acetabulum and the ilium or ischium. Acetabular fracture repair can be particularly demanding as a result of difficulties obtaining adequate exposure for plate application and the biological cost inherent in the surgical approach. For complex acetabular fractures, alternative approaches such as conservative treatment with femoral head and neck excision or total hip replacement can be considered as salvage procedures if function is poor.
Postoperative management
Following surgery, cats should receive appropriate postoperative management similar to the conservative treatment outlined in Box 2. It is important that the patient has adequate analgesia and is sufficiently rested and restricted to allow bone healing to occur. However, early mobilisation and weight bearing are desirable to prevent joint stiffness, loss of muscle mass and fibrosis. Physiotherapy when tolerated by cats is very useful to help speed up and maximise the quality of recovery
Conclusions
A systematic and logical approach to pelvic fractures will help to identify those cases which can be treated successfully with a conservative approach and which cases will benefit from surgery.