Fractures involving the mandible or maxilla of cats are unique for no other reason than they are at least tenfold more common in the cat than in the dog.3 Vehicular trauma and high-rise syndrome are the most common causes of these fractures, which occur when the cat absorbs an impact face-first. Not surprisingly, such trauma is frequently associated with additional injuries, including broken teeth, thoracic injury, head trauma, and forelimb fractures. In a study of 45 cats treated for head trauma in the United Kingdom, 87% had mandibular fractures and 80% had skull fractures. Fractures in the nasopharynx, orbit, nose, upper jaw, intermaxillary suture, and zygomatic arch regions were likely to occur together.⁴ In another study of feline head trauma where all patients had computed tomography (CT) performed, most cases were due to vehicular trauma and multiple regions of the skull (mandible, upper jaw, craniofacial) were affected in 89% of cases.⁵ When compared with conventional radiography, CT may be superior for assessment, diagnosis, and treatment planning when head trauma is suspected.⁶

High-rise syndrome is the term for injuries sustained when a cat falls from a balcony or window of a tall building. Orofacial injuries are common and include hard palate fracture, mandibular fracture, mandibular symphyseal separation, dental trauma, and soft tissue trauma.⁷ Limb fractures also occurred in 46% and thoracic trauma in 34% of 119 cases in one study.⁸ Despite the multitude of possible injuries, survival rates for high-rise syndrome are >90%.^7,8

Details on treatment of mandibular and maxillary fractures are found in Chapter 24: Dental and Oral Diseases.

Patellar fractures in young adult cats can develop with no history or evidence of trauma. Lameness is acute but usually mild to moderate in severity. These have been characterized as stress fractures.9 Evidence for this pathogenesis includes the lack of known trauma in most cases and the presence of radiographic sclerosis of the fracture fragments. The fractures are simple transverse, involve the proximal one-third of the patella, and are bilateral in half of the cases. In one study of 34 cases, about half of the contralateral patellae subsequently fractured in a mean time of 3 months.⁹ In the same study, 10 cats with apparently atraumatic patellar fractures also had a history of previous, concurrent, or subsequent fracture of other bones.

Patellar fracture and dental anomaly syndrome (PADS) is seen in cats with atraumatic patellar ­fracture, retained deciduous teeth, and unerupted permanent teeth (Fig. 29.4). Previously known as “knees and teeth syndrome,” some affected cats also develop other abnormalities. In a series of 10 cases, imaging revealed marked bony and periosteal proliferation of the maxilla or mandible, hypodontia, tooth root resorption, and tooth root malformation.¹⁰ The mandibular and maxillary abnormalities may mimic neoplasia. Therefore, a thorough oral examination should be performed for cats with atraumatic patellar fracture. In one study of 191 cases of PADS, many cats suffered atraumatic fractures of other bones preceding or after their patellar fractures.¹¹

The etiology of atraumatic patellar fractures in cats is unclear. One case report presented evidence suggesting that some fractures may be due to osteochondrosis that is similar to a syndrome described in humans.12 In humans, there is a connection between dentinogenesis imperfecta, which involves several dental abnormalities, and osteogenesis imperfecta, a condition involving brittle, easily fractured bones that is also seen in cats (discussed later). It is also possible that PADS is similar to osteopetrosis in humans, which features persistent deciduous teeth and pathologic fractures. Interestingly, a case report describes a cat receiving long-term oral alendronate (an inhibitor of osteoclastic bone resorption) that developed bilateral patellar fractures with sclerosis of both patellae.¹³ Treatment of dental problems seen in PADS with antibiotics and anti-inflammatory drugs provides short-term improvement, but surgical extraction of retained deciduous and unerupted permanent teeth with débridement of proliferative and necrotic bone may be necessary for a good outcome.

Attempts at surgical repair of patellar fractures by pin and tension band wire have met with almost universal failure characterized by iatrogenic fracture of the remaining fragments, hardware failure, or, most often, nonunion. However, most cats regained reasonable function in the limb, with stiffness or intermittent lameness in about half of the cases.⁹ Conservative treatment of these patellar fractures would appear to be the most prudent course, especially if distraction of fracture fragments is mild to moderate. If fragments are significantly distracted, a circumferential wire may be preferred over an attempt to pass a pin through sclerotic bone. Alternatively, partial patellectomy may be performed.^14,15 Complete patellectomy does not usually produce satisfactory function.⁹

Fractures of the radius and ulna are relatively uncommon in cats, accounting for between 5% and 13.8% of feline fractures.16 Further, surgical repair of these fractures, especially when comminuted or open, is associated with a high complication rate.¹⁷ This appears to be primarily due to the cat’s ability to pronate the front limb and paw to a much greater degree than the dog. This increased mobility means the standard surgical approach in the dog of stabilizing only the radius when both bones are fractured may not confer enough stability to produce consistently good results in the cat. Adding an intramedullary pin or plate to the ulna in addition to the radial repair has been associated with increased strength of repair and more reliable surgical outcomes in cats.^17,18 In addition, the ulna, especially the proximal portion, has been identified as a common site of nonunion in the cat, which may be a significant contributing factor in surgical complication rates.¹⁶

Capital femoral epiphysis fractures (Salter-Harris type 1) are a common traumatic injury in cats, but it appears many cases arise without a traumatic episode (Fig. 29.5).^19–22 This is called slipped capital femoral epiphysis (SCFE), also known as feline capital physeal dysplasia syndrome and spontaneous femoral capital physeal fracture. In these atraumatic fractures, there is a unilateral or bilateral displacement of the capital femoral epiphysis from the proximal femoral metaphysis through the growth plate. Affected cats usually present with acute hind limb lameness, although the lameness may be mild and chronic in some instances. Published reports suggest that between 24% and 38% of cats with SCFE will develop bilateral fractures.^{19–21,23–25}

The first report of SCFE described it as metaphyseal osteopathy of the femoral neck, which was thought to result from an aseptic necrosis, not unlike Legg–Calve-–Perthes disease in the dog.21 However, research suggests the etiopathogenesis of SCFE involves abnormalities of the physis. Radiographically, cats with SCFE have abnormally wide physes that remain open long after expected closure. As the disease progresses, the abnormal physis is not able to resist mechanical stress and the femoral neck is displaced. Metaphyseal bone remodeling and metaphyseal and epiphyseal sclerosis may be seen. Histologically, the physes are characterized by an irregular arrangement of chondrocytes rather than the normal columnar appearance, which has resulted in the use of the term “physeal dysplasia” to describe the process.

The disease has mainly been reported in Siamese, Maine Coon, and domestic shorthair cats.^{20,21,25–27} Various factors may play a role in SCFE, such as genetics, obesity, endocrine imbalances, neutering, and patient sex. Mature, neutered, overweight male cats are most commonly affected.^19–21 Although neutering at an early age has been shown to delay physeal closure times in the cat, this effect is only present in male cats and only in some physes, not including the capital femoral physis.²⁸ A similar syndrome occurs in young, overweight adolescent humans, especially those that are hypothyroid, are receiving growth hormone supplementation, or have hypogonadism.²⁹ Hypothyroidism may also be a predisposing factor in cats. One case report describes bilateral SCFE in a 4-year-old domestic shorthair cat with congenital primary hypothyroidism.²⁴

Surgical treatment is recommended for most cases to avoid nonunion and impaired function. Femoral head and neck excision (FHNE) will produce a return to normal function in the majority of cases.^30,31 Primary repair techniques with Kirschner wires and total hip replacement (THR) have been described for SCFE^32–34 but these procedures have greater potential for complications than FHNE, with few, if any, demonstrable advantages.

Pelvic fractures are extremely common in the cat, especially after vehicular trauma (Fig. 29.6). It is important to evaluate the whole patient as concurrent injuries to the abdomen and thorax are common.³⁵ In one study of 112 cats with pelvic trauma, 19% required a blood transfusion so treatment of pelvic fractures may have to wait until the patient has been thoroughly assessed and stabilized.³⁶ Most pelvic fractures are multiple, with 90% involving the pelvic floor, 60% with sacroiliac luxation, and almost 50% involving ilial fractures.³⁷ Regardless, most will heal with conservative therapy. However, the issue is not whether they will heal but rather the severity and consequences of the malunion that almost invariably results with conservative management. Although surgery can be considered for any case to hasten pain relief and return to function, there are two primary indications for surgery: displaced acetabular fractures and pelvic canal narrowing.

Any degree of fracture malunion in the coxofemoral joint will lead to degenerative joint disease (DJD) and pain. Such a fracture can be addressed near the time of the initial trauma by primary fixation methods that include plates, screws, and tension band wires. Traditionally, caudal acetabular fractures have been treated conservatively because this area of the acetabulum was not considered to be weight bearing. However, it is now recognized that the central and caudal portions of the acetabulum are the major weight-bearing regions within the coxofemoral joint of the cat.38 In a study of 16 cats with acetabular fractures undergoing surgical stabilization, all cats returned to full or acceptable function.³⁹ Neurologic deficits were common preoperatively, but most resolved following treatment. If primary repair of acetabular fractures is not possible and there is evidence of ongoing disability, FHNE can be performed several days or weeks later once the patient’s condition has stabilized.

Ilial and acetabular fractures commonly displace axially, producing a narrowing of the pelvic canal. This can have immediate traumatic effects on bladder and bowel function, but the greater concern is the prospect of chronic constipation or obstipation which is extremely frustrating to treat and much better prevented. Standard recommendations are that pelvic fractures producing more than 25% to 30% narrowing of the pelvic canal are best treated surgically. However, one study could not find a correlation between the degree of pelvic canal narrowing and whether the case was treated conservatively or surgically with the likelihood of the development of constipation or obstipation.⁴⁰

Surgical repair, in most cases utilizing bone plates, is best performed within 5 days of the initial trauma. After that time, it becomes more difficult to break down fibrous tissue and reduce the fractures. Complication rates with surgical repair have been reported as about 20% with transient sciatic neuropraxia, screw loosening, and pelvic canal narrowing being most common.^37,40 These complications did not impair long-term mobility in 86% of cases.^37,40 Procedures to widen the pelvic canal such as pelvic symphyseal osteotomy or triple pelvic osteotomy can be performed if constipation has been present for less than 6 months. If constipation has been present for more than 6 months, colon function is often beyond reclamation and subtotal colectomy should be performed.^41,42

Cats may be characterized as the perfect orthopedic patient because their straight bones, lightweight frames, and legendary healing abilities have resulted in many amazing outcomes in fracture cases. However, complications are a reality of fracture repair. Major complications include: