Surgical versus conservative management of patella fractures in cats: A retrospective study

Abstract

This study compared the clinical outcome in cats with patella fractures treated by surgery to those treated conservatively. Six cats with 9 patella fractures were treated. Six fractures were treated surgically and 3 were treated conservatively. Medical records of all 6 patients were reviewed for age, breed, gender, trauma, and fracture conformation. All patients had follow-up which consisted of a physical examination, radiographs, and an interview with the client between 1 and 4.5 y after surgery or diagnosis. All cats treated conservatively returned to normal activity with no gait abnormalities. In cats that had surgery, 4/6 had breakdown of the surgical repair but all cats went on to full recovery with normal activity and gait. The conclusions of this preliminary study are that surgical repair of cat patella fractures has a high rate of implant failure and that conservative management of cat patella fractures results in excellent clinical outcome.

Introduction

The patella is the largest sesamoid bone in the body located at the cranial aspect of the distal femur (1). It has a convex articular surface and is seated in the trochlear sulcus of the femur (2). The vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris form the quadriceps tendon that primarily attaches to the proximal portion of the patella (2). The tendon continues over the cranial surface of the patella to merge with the patellar ligament (2). The patellar ligament, a strong band of fibrous connective tissue, inserts on the tibial tuberosity (2). The patella is also held in place by the parapatellar fibrocartilage, which attaches the medial and lateral surfaces of the patella to the joint capsule (1,2). The fibrocartilage also articulates with the trochlear ridges and increases surface area and disperses forces of the quadriceps muscles (1,2). The patella plays an important role in the extensor mechanism of the stifle (1,2). As the quadriceps muscles contract the patella is pulled proximally and the stifle is extended (1,2).

Patella fractures are rare and have mostly been described in canines until recently. Canine patella fractures usually result from direct trauma and are most often associated with severe traction forces on the quadriceps as the stifle joint is extended to break a fall (3). Surgical intervention is recommended in canines because the fracture is caused by trauma which disrupts the surrounding soft tissue attachments to the patella making it very unstable. The treatment of choice for canine patella fractures is internal fixation with a tension band (3). The goals of treatment are to preserve the quadriceps extensor mechanism and to decrease the occurrence of degenerative joint disease. Patellectomy is only used as a salvage procedure, as it results in degenerative lesions of the stifle (3–5).

There is little information on the treatment of cat patella fractures, which are most commonly atraumatic (6,7). It is theorized that cat patella fractures that occur without known trauma are secondary to stress fatigue (6,7). Stress fatigue fractures occur due to repetitive, prolonged muscular action on a bone that has not accommodated itself to that action (6). The most common cat patella fracture is a transverse fracture (6,7). Surgical repair has been described using a tension band fixation; however, a recent publication reports increased failure with this repair and recommends treatment with a circumferential wire when surgical reconstruction is elected (6). Surgical repair has resulted in a high failure rate and very few cases go on to have radiographic evidence of healing (6). The hypothesis of this paper is that non-surgical management will result in the same clinical outcome as surgical management of cat patella fractures.

Materials and methods

Medical records of 6 cats with patella fractures (Table 1) were reviewed. Information obtained included age, breed, gender, housing environment, complete blood cell count and chemistry panel, and surgical procedure, if performed.

Table 1.

Summary of data from the medical records of 6 cats with patella fractures

Cat	Age (mo)	Gender	Degree of fracture displacement (cm)	Surgery	Time to failure	Revision surgery	Time to resolution of clinical signs (mo)	Total follow-up time
1	4.75	MI	0.2	No	NA	NA	1.5	2.4 y
2 Right	10	MC	0.8	Encircling #2 nylon	4 wk	No	6	4.5 y
2 Left	12	MC	0.3	No	NA	NA	2	4.5 y
3 Right	24	MC	0.5	Tension band (2 k-wires and #2 nylon)	2 wk-additional patella fracture	Revision-tension band	3	4 y
					6 wk after re-do surgery-implant failure	No
3 Left	30	MC	1.1	No	NA	NA	2	4 y
4 Left	96	MC	1	Tension band (2 k-wires and cerclage)	No failure	NA	5	4 y
4 Right	96	MC	0.2	Tension band (2 k-wires and cerclage)	4 wk, implant failure-displaced fracture	No	5	4 y
5 Left	84	FS	1.7	Tension band (2 k-wires and cerclage)	2 wk-implant failure displaced fracture	Yes; removed implants	3	1 y
6 Left	82	FS	2	Encircling cerclage wire	No failure	No	3	3.3 y

All the cats were domestic short hair except #5, which was Siamese. NA — not applicable. MI — male intact, MC — male castrated, FS — female spayed.

Patients were radiographed at the time of initial evaluation, after surgery (if surgery was performed), and at the time of this study (1 to 4.5 years after surgery). The degree of displacement and type of fracture were documented. The postoperative radiographs were evaluated for successful reduction, healing, and implant stability. The patients were evaluated for lameness, stifle pain, swelling, and crepitus. Owners were questioned as to function of the limb (lameness or gait abnormalities) and return to normal activity (difficulty or reluctance to jump).

Surgical repair was performed by 1 of 3 surgeons using a tension band fixation technique or circumferential wire. One stifle was placed in a bandage and 3 others were placed in anterior orthoplast splints after surgery. Conservative management consisted of 8 wk of restricted activity (crate confinement) and pain medications. One cat was treated with buprenorphine (Buprenex; Bedford Laboratories, Bedford, Ohio, USA) 0.01 mg/kg body weight (BW) buccally q8h as needed for pain. Meloxicam (Metacam; Boehringer Ingelheim, St. Joseph, Missouri, USA), 0.05 mg/kg BW, PO, q24h) was prescribed for 1 patient to be given as needed for pain. Two cats were treated with a fentanyl patch (12.5 mg) (Fentanyl transdermal system; Mylan pharmacy, Morgantown, West Virginia, USA), and 2 cats were given meloxicam (0.05 mg/kg BW, PO, q24h), and buprenorphine (0.01 mg/kg BW, buccally, q8h) as needed for pain. None of the cases that were managed conservatively were placed in additional coaptation.

Results

Three of the 6 cats in the study had bilateral patella fractures for a total of 9 patella fractures. Six patella fractures were treated surgically. The mean age of the 6 cats was 48.6 mo (range: 4.75 to 96 mo) and their mean weight was 4 kg (range: 3.3 to 5.8 kg). There were 3 male castrated cats, 1 male intact cat, and 2 female spayed cats. Breeds included 1 Siamese and 5 domestic short hair. No trauma was documented in any case. No cat had bilateral patella fractures at initial presentation. For those with bilateral fractures, the average interval between fractures was 15 wk (range: 2 wk to 9 mo). Initial radiographs showed transverse proximal 1/3 patella fractures in all cats with the least displacement being 0.2 cm and the most 2 cm (Figure 1).

Figure 1.

Preoperative feline patellar fracture.

Tension band fixation (k-wire and cerclage wire in a figure of 8 pattern) was used in 4 cases (Figure 2). One case was treated with an encircling wire around the patella (Figure 3) and 1 case was treated using an encircling suture of #2 nylon. One cat that was repaired with a tension band was repaired bilaterally and placed in anterior splints postoperatively. This cat had a left patella fracture on presentation, but by the time surgery was scheduled the cat was acutely lame on the right side and was diagnosed with bilateral patella fractures.

Figure 2.

Postoperative feline patella fracture repaired with a tension band.

Figure 3.

Feline patella fracture repaired with an encircling cerclage wire.

There was a 67% (4/6) failure rate in cases treated surgically and in 17% (1/6) of all cases there was an additional fracture of the same patella noted on follow-up radiographs. The earliest documented failure was 2 wk after surgery and the longest time to failure was 4 wk after initial surgery. One surgically treated fracture had radiographic evidence of bony union, however 83% (5/6) had no radiographic evidence of healing. One surgical case was taken back to surgery and the implants were removed. One case that failed was taken back to surgery and was revised with a tension band. This case failed again 6 wk after the second surgery.

All clients were contacted at the time of the study (1 to 4.5 y from the time of surgery). No owners reported any problems or gait abnormalities. All the cats were able to run and jump normally. All owners were happy with the clinical outcome. No evidence of degenerative joint disease was noted in any cat.

None of the 3 cats that were treated conservatively had evidence of radiographic healing or of degenerative joint disease. All cases were re-evaluated at the time of this study (1 to 4.5 y after initial presentation). All cats had good range of motion, with no crepitus of the stifle joint and no evidence of lameness.

Discussion

It is thought that cat patellar fractures that are not associated with trauma are a result of stress fatigue (6). None of the cats in this study had a history of trauma. The most common fracture location in our study was a proximal 1/3 transverse patella fracture, which is consistent with previous studies (3,6,7). No radiographic evidence of bony union was noted in 8 of the 9 cases. In a previous study only 1/52 cat patella fractures had radiographic evidence of fracture healing (6). This lack of radiographic union is because sesamoid bones produce a fibrous rather than an osseous union (7) and so clinical outcome may be more important than radiographic union in these cases.

All cats in this study returned to normal function with no clinical abnormalities. One would suspect that as the quadriceps muscles contract the fragments would be displaced further if the patella is not surgically stabilized. Because the fractures in this study and in previous studies were not associated with trauma, the soft tissues around the patella may be intact and may help in counteracting the forces by the quadriceps muscles, thereby preventing further displacement (6).

The results of this study suggest that internal fixation may not be the treatment of choice given the high failure rate of surgery and the excellent clinical outcome in cases treated conservatively. A previous study indicated that conservative management can be considered if there is no or minimal displacement of the fragments, and no or mild clinical signs (6). However the cases that were treated conservatively in our study all had clinical signs of lameness at presentation and a mild to moderate amount of displacement. Despite the displacement and clinical signs all cats had an excellent clinical outcome.

Further studies with larger numbers of cats that have patella fractures are necessary to determine appropriate treatment recommendations; however, based on this study conservative treatment of cats with patella fractures should be considered. The authors acknowledge that the number of cases evaluated was small due to the rare occurrence of this type of fracture. No radiographic evidence of underlying pathology was noted; however, histopathological evaluation of the patella may provide further information regarding underlying bone disease causing these types of fractures. The cats in this study did not have any evidence of dental anomalies or additional fractures, although osteogenesis imperfecta has been postulated as a possibility in cats with patella fractures (6).