Feline knees and teeth syndrome is an association of nontraumatic patellar fractures and persistent deciduous teeth. This pathologic syndrome may include persistence of deciduous teeth, unerupted permanent teeth, and insufficiency fractures of the patella.1,2 Other fractures, including in the long bones and pelvis, and spinal abnormalities have also been reported.3,4 Pathologic fractures of the tibia and fibula can occur up to 10 years after diagnosis.2
Feline knees and teeth syndrome was first identified in the United States, but affected cats have since been identified in South America and the United Kingdom.2,5 This syndrome was believed to be a manifestation of osteogenesis imperfecta, but another mechanism is currently supported,6,7 as patellar fractures showing radiographic evidence of sclerosis and generalized osteosclerosis have been seen in both humans and cats.8 In humans, osteomyelitis of the jaw associated with osteopetrosis and dental pathology has been reported.8-10 In addition, fractures of the patella and other bones have been associated with generalized osteopetrosis.8-10 Patellar sclerosis has similarly been observed in some cats with knees and teeth syndrome.2,4,11
Feline knees and teeth syndrome is typically recognized in young cats, with male cats more frequently affected than female cats.2,12 The mean age of onset of pelvic limb lameness or radiographic diagnosis is 28 months (range, 4 months-8 years).5 Physical examination findings typically reveal persistent deciduous teeth, pelvic limb lameness, and swelling of the distal quadriceps muscle; concurrent paronychia has also been reported.2,4 Intraoral and whole-body orthopedic radiography, with particular attention given to the pelvic limbs, should be performed for evaluation. In some cases, lameness and quadricep swelling precede visible radiographic fractures.2,4
Failure of deciduous tooth exfoliation in cats is rare and most often the result of an altered eruption path of the permanent tooth (see Take-Home Messages). Persistence of deciduous cheek teeth was reported in 40 of 60 cats with patellar fractures in one case series.2 Another series of 191 cats with various fractures reported that 48% had dental anomalies possibly related to knees and teeth syndrome.4 Extraction of both the persistent deciduous teeth and the impacted adult teeth is key, as proliferative osteomyelitis, dentigerous cysts, and jaw deformation may develop when these teeth are left in situ (see Treatment at a Glance).2,11,13,14 A careful, meticulous technique is required to avoid mandibular fracture due to the space occupancy of the impacted teeth in the mandible/mandibular canal.2
Although surgical reduction of patellar fractures may seem like a good option, surgical failure was reported in 86% of cats with feline knees and teeth syndrome.15 Therefore, nonsurgical, conservative approaches should be considered.15 Fractures in these patients may heal or the patient may adapt to the fractures and function normally even without surgical management; other cats may develop a plantigrade gait.2 A study of cats with knees and teeth syndrome that developed humeral fractures lacked sufficient data to determine the long-term prognosis for surgical repair, suggesting that many of these fractures may heal with medical management alone.3
Most cats that sustain pathologic fractures of the patellae related to knees and teeth syndrome adapt with good return to function. Cats with persistent deciduous cheek teeth should be closely monitored because development of pathologic insufficiency fractures of the patellae and other bones may be anticipated.