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Evaluation of two miniplate systems and figure-of-eight bandages for stabilization of experimentally induced ulnar and radial fractures in pigeons (Columba livid).

Abstract: Although plate fixation has advantages over other fixation methods for certain indications, it is rarely used in avian surgery, especially in birds that weigh less than 1000 g. Exceptionally small plating systems for these birds are required, which are relatively expensive and difficult to insert. To study avian fracture healing after repair using miniplates, we evaluated 2 steel miniplate systems in 27 pigeons (Columba livia) divided into 4 groups. In each pigeon, the left ulna and radius were transected and the ulna was repaired with a bone plate. In groups A and B, a 1.3-mm adaption plate was applied without and with a figure-of-eight bandage; in groups C and D, a 1.0-mm compression plate was applied without and with a bandage, respectively. Healing was evaluated with radiographs after 3, 14, and 28 days; flight tests were conducted after 14, 21, and 28 days; and the wing was macroscopically examined after euthanasia of birds on day 28. Fractures healed without bending or distortion of the plate in all 27 birds, and no significant differences in healing were found between treatment groups. At the end of the study, 23 pigeons (85.2%) showed good or very good flight ability. Results show the 1.3-mm adaption plate and the 1.0-mm compression plate meet the requirements for avian osteosynthesis and can be recommended for fracture repair of the ulna or other long bones in birds weighing less than 500 g. The application of a figure-of-eight bandage might be beneficial in fracture healing.

Key words: fracture, osteosynthesis, ulna, radius, 1.0-mm compression plate, 1.3-mm adaption plate, avian, pigeon, Columba livia

Introduction

Although plate fixation has advantages over other fixation methods for certain indications, it is rarely used in avian surgery, especially in birds with a body weight less than (1000) g. (1) In larger birds, plating appears to be used regularly because metal and acrylic plates are easily available in sizes that are useful for such animals. (2) Reported examples include a locking compression plate system used to treat a comminuted tarsometatarsal fracture with delayed union after 1 month of external coaptation in a bald eagle (Haliaeetus leucocephalus), (3) a 2.0-mm titanium miniplate successfully used in a blue-and-yellow macaw (Ara ararauna) with an old middiaphyseal fracture of the left tibiotarsus, (4) and a miniplate used in a goose (Anser anser) to stabilize a simple, complete, spiral-third fractured right tibia." In birds that weigh less than 1000 g, exceptionally small plating systems (ie, miniplate systems <2 mm) are required, which are relatively expensive and more challenging to insert. So far, none of the tested implants have proven entirely satisfactory for the use in small avian species. (1-2,6)

In a study in pigeons (Columba livia), Christen et al (7) used a maxillofacial titanium adaptation 1.0mm miniplate to treat induced ulnar and radial fractures; all implants bent, and callus formation was exuberant. The authors recommended the use of stronger and longer plates because an increase in plate size and length (plate : span ratio) may increase the strength of an implant and reduce the risk of fatigue failure. Gouvea et al (6) evaluated the use of titanium miniplates in the treatment of experimentally induced mid-diaphyseal fractures of the right tibiotarsus in pigeons. Results supported the hypothesis that longer plates may be more favorable. Although the forces acting on the pelvic limb differ from those acting on the thoracic limb, the most common complication in this study was bending of the implants; no implant loosening was observed. Best results were seen with the 1.0-mm titanium miniplate with 8 holes and a central spacer, resulting in bone healing within 27 days. Bending occurred in 20% of patients treated with the titanium miniplate with 8 holes and a central spacer compared with 60% of patients with the titanium miniplate with 6 holes and a central spacer and 40% of patients with the titanium miniplate with 8 holes without a central spacer.

Based on the results of Christen et al, (7) Gull et al (2) performed a study on ulnar fracture repair in pigeons using a longer 1,0-mm titanium miniplate (8 holes with a spacer) and compared it to a steel 1.3-mm adaptation plate. Bending occurred in all titanium miniplates. The steel plate was superior to the titanium plate with respect to bending; however, loosening of screws occurred. The authors concluded that the material of the plate, not the length of the plate, was crucial for the occurrence of bending. Regarding the risk of screw loosening, they recommended further trials with smaller drill bits and with screws having a smaller thread pitch to improve the system. In addition, the authors suggested the use of a postoperative figure-of-eight bandage to improve healing.

Recently a 1.0-mm steel compression plate system has been marketed that includes screws with a thread pitch as proposed by Gull et al. (2) The aim of the present study was to evaluate this new plate in comparison with the 1.3-mm adaptation plate used by Gull et al (2) to stabilize experimentally induced ulnar and radial fractures in pigeons. Additionally, the effect of a figure-of-eight bandage was tested. We predicted that fracture healing with less callus proliferation and better ability of flight could be achieved using a 1.0-mm compression plate compared with a 1,3-mm adaptation plate. Because of additional stability provided by a figure-of-eight bandage, we expected improved healing with either plate system in birds receiving a postoperative bandage compared with those treated without a bandage.

Materials and Methods

Thirty pigeons obtained from a private breeder were used in this study. Before surgery, all birds were examined and marked individually with colored plastic rings on the legs and a plumage color spray (RAIDEX Animal Marking Spray, RAIDEX Gmbh!, Dettingen/E., Germany). Bird weights ranged from 0.36 to 0.45 kg. The birds were kept in 2 aviaries (aviary size 2.5 X 1.5 X 2.4 m) on a commercial diet for homing pigeons (Vitabalance, Taubenfutter LJniversal, Meliofeed AG, Herzogbuchsee, Switzerland). Food and water were available ad libitum. All birds tested negative for Chlamydia psittaci and Salmonella species. Birds had been vaccinated by the breeder against paramyxovirus 1 (Nobilis, PARAMYXO P201, MSD Animal Health GmbH, Luzern, Switzerland). All pigeons were treated against trichomoniasis with dimetridazole (500 mg/L drinking water) for 6 days, once against ectoparasites with pyrethrum spray, and against coccidia with toltrazuril (75 mg/L drinking water for 5 days; Baycox, Provet SA, Lyssach, Switzerland). Radiographic examinations of the wings were performed and revealed no abnormalities.

All animal procedures were approved by the Animal Care and Use Committee. The animals were divided randomly into 4 groups of 7 pigeons each (groups A, B, C, and D). Two birds served as a control group with the physiologic ability of flight. Groups were arranged according to social interaction, with one control bird in each aviary. In group B, 1 pigeon died 2 days after surgery. Necropsy of this bird revealed severe gout of the viscera and kidneys.

The manual skills necessary for the intended surgery were acquired by the surgeon (B.B.) during a 2-month period at the Clinic for Small Animal Surgery of the Vetsuisse Faculty of the University of Zurich, followed by practicing the osteotomy and plate fixation on 17 dead pigeons and in a preliminary trial with 4 animals intended for euthanasia.

Approximately 30 minutes before surgery, the pigeons received tramadol (5 mg/kg IM) and meloxicam (2 mg/kg IM) and were then premedicated with ketamine (20 mg/kg IM) and medetomidine (0.2 mg/kg IM). Anesthesia was induced with 5% isoflurane via facemask, and birds were then intubated for anesthetic maintenance with isoflurane. An intravenous catheter was placed in the medial metatarsal or right basilic (ulnar) wing vein, and crystalloid fluids (10 mL/kg per hour, lactated Ringer's solution mixed equally with 5% dextrose) was administered during surgery. Patients were monitored by observation of reflexes, electrocardiography, auscultation of heart and respiration, pulse-oxymetry, and body temperature measurement.

Birds were placed in sternal recumbency and the wings and the head were kept slightly elevated by positioning the patient in a U-shaped board that provided a stable background. The covert feathers of the left distal wing were plucked from the dorsal side of the antebrachium. The surgical site was aseptically prepared and draped for surgery. At the completion of surgery, the pigeons received atipamezole (1 mg/kg 1M). In addition, doxycycline (75 mg/kg IV) in 4 mL 0.9% saline solution mixed equally with 5% dextrose was administered during surgery.

Surgeries were performed in a randomized order of birds from the different groups. Surgical procedures in the 4 groups differed in the type of implant and the use of a figure-of-eight bandage. In group A, birds were treated with an 8-hole, 3.3-cm-long, 1.3-mm stainless steel adaption plate (Synthes GmbH, Oberdorf, Switzerland) and 6 self-taping screws with a 1.3-mm thread diameter, 8-mm length, and 0.5-mm thread pitch. For drilling, a 1.0-mm drill bit was used with a mini air drill (Synthes). In group B, the same plate and screws were used, but additionally a figure-of-eight bandage was applied for 10 days after surgery. The figure-of-eight bandage, used to immobilize the elbow and carpal joint, (8) consisted of a precut (45 X 15 mm) nonadherent absorbent dressing (Telfa, Covidien LLC, Mansfield, MA, USA) applied directly on the suture line, followed by a nonprecut, simple layer of synthetic orthopedic soft bandage padding with a length of 600-630 mm and covered by a non-precut, simple layer of stretched cohesive bandage (Vetrap, Henry Schein Inc, Melville, NY, USA) with a length of 600-630 mm. In group C, birds were treated with an 8-hole, 3.5-cm-long 1.0-mm stainless steel compression plate (Veterinary Instrumentation, Sheffield, UK) and 6 self-taping screws with 1.0-mm thread diameter, 8-mm length, and 0.25-mm thread pitch. For drilling, a 0.7-mm drill bit was used. This drill bit was bought at a hardware store, because surgical drill bits in this size were not available for the miniature air drill used. In group D the same plate and screws were used, but additionally a figure-of-eight bandage as described above was applied for 10 days after surgery.

The general aspects of surgical procedure were according to the studies of Christen et al (7) and Gull et al. (2) A dorsal approach to the radius and ulna was used. The skin incision was made just cranial to the insertion point of the secondary flight feathers of the left ulna. The fractures were produced by transecting the diaphysis of the radius and the ulna with an oscillating bone saw (blade width 6 mm, thickness 0.25 mm) (Synthes). The ulnar osteotomy was stabilized by using one of the plate systems while the radius was not stabilized. The skin was closed with a single interrupted suture using 5-0 polydioxanone (PDS*II, Ethicon GmbH, Norderstedt, Germany).

After surgery, the birds had individual cage rest (cage size 0.6 X 0.6 X 0.4 m) for up to 14 days. The birds were handled as little as possible and only while being wrapped in a towel to minimize uncontrolled wing movements. Postoperative analgesia was provided with tramadol (5 mg/kg IM q12h) for 1 day and meloxicam (2 mg/kg PO q12h) for 5 days. If the bird did not receive intravenous doxycycline intraoperatively as described above, oral doxycycline (250 mg/L drinking water) was administered for 7 days. If signs of pain were observed (such as fluffed feathers, hunched posture, shivering slightly with the left wing), analgesic treatment was prolonged. Supplemental food (12 mL PO q12h. Recovery Formula, Harrison's Bird Foods, West Palm Beach, FL, USA) was given by gavage in addition to the regular diet if a bird lost more than 10% of its body weight.

Figure-of-eight bandages in groups B and D were changed after 3 days with birds under general isoflurane anesthesia. After removing the bandage, the limb was carefully stretched to reduce the risk of shortening of the propatagium and the wound was treated with a topical wound disinfectant (Octenisept farblos/incolore, Schtilke & Mayr GmbH, Norderstedt, Germany). Mobilization included stretching the elbow and carpal joints to the maximum extension possible 4 times and holding in this position for 30 seconds. Bandage changes with disinfection of the wound and mobilization of the joints were repeated under general isoflurane anesthesia according to necessity, onaverage 2 (1-7) times per bird.

The position of the affected wing was noted every other day during cage rest and at days 10, 14, and 28 after surgery. Mediolateral and caudocranial radiographic studies of the wing were taken at 3, 14, and 28 days after surgery. For evaluation and measurements, a dedicated DICOM-viewer (OsiriX Foundation, Geneva, Switzerland) was used. All radiographs were assessed by one specialist (P.K.) without any information regarding bandage application or the healing process of pigeons. Because the plates could be differentiated easily by appearance in the radiographic study, there was no blinding regarding the treatment groups. The length of the radius and ulna, the step between the fracture margins of the ulna, and the maximal fracture gap were measured. The percentage of pigeons in a group in which all screws were bicortical was evaluated. Signs of osteomyelitis (bone lucency, irregular fracture margins, periosteal reactions), occurrence of synostosis, loosening of screws, or additional fractures were noted. The angle of the fracture ends (alignment) of the ulna was measured at the intersection of a line from the distal metaphyseal corticalis of the ulna to the distal corticalis of the osteotomy site, and a line from the corticalis of the osteotomy site to the metaphyseal corticalis of the proximal ulna. The apposition of the fracture ends of the radius and the ulna was evaluated. The width of the mineralized callus, classified as callus width, was measured at the caudal surface of the ulna and radius at the fracture site. The bone width was measured at the distal end of the ulna and radius, classified as distal bone width. The ratio of the callus width to the distal bone width was calculated and recorded as callus ratio.

Flight ability was assessed by two methods. At least twice daily, the birds in the aviaries were checked and it was noted if a pigeon perched in the upper half of the aviary (at 110-240 cm) was one that had not been seen there before. Additionally, 2 cameras (Day & Night Color CCD Camera, 3.6-mm lens, Visor Tech, PEARL GmbH, Buggingen, Germany) linked to a video recorder (D7704HT, Visor Tech, PEARL) were installed in each aviary, one pointing at the feeding/drinking station at 110 cm height and the ground, the other pointing at the upper perches. Flight ability at 14, 21, and 28 days after surgery was classified into 4 categories: very good, equal to the physiologic flight ability of the control animals (no problems reaching perches located at a height of 220 cm); good (no problems reaching perches located at 200 cm); moderate, (no problems reaching perches located at 30-110 cm); and poor (not reaching a height of 30 cm).

Twenty-eight days after surgery, the pigeons were anesthetized with ketamine (25-30 mg/kg IM) and medetomidine (0.25-0.30 mg/kg IM) before euthanasia with pentobarbital (750 mg/kg IV). The treated wings were dissected, and signs of distortion and bending of the plate, osteomyelitis, and the callus formation were noted.

Groups were compared by 1-way ANOVA with Sidak post hoc tests if data were normally distributed and by the Kruskal-Wallis test and subsequent pair-wise Mann-Whitney U tests (with Sidak adjustment for multiple testing) if data were not normally distributed. All analyses were performed in SPSS 21.0 (SPSS Inc, Chicago, IL, USA). Significance was set as P = .05.

Results

All birds survived surgery and all implants were successfully applied. In the subjective opinion of the surgeon (B.B.), the surgical technique differed only minimally between the plate systems, but the ease in plate application differed. Because the tip of the 1.0-mm cruciate screwdriver has a taper fit that holds the screw without a sleeve, the screws used to install the 1,0-mm compression plate were prone to falling off the screwdriver. Despite this, both mean duration of anesthesia (87.2 [+ or -] 14.9 min) and mean duration of surgery (51.7 [+ or -] 12.0 min) did not differ significantly between groups ([F.sub.3,23] = 0.341, P = .8 and [F.sub.3,23] = 1.022, P= .4) (Table'1).

Several difficulties occurred during surgery (Table 1). In 1 pigeon from group B, an axis deviation of 1 screw resulted in a fracture of the ulna, and 4 instead of 6 screws were used in this animal. In 5 birds in groups A and C, screw holes needed to be redrilled after applying the plate (1 bird in group A, 4 in group C). In 3 pigeons (one each in groups B. C, D), the position order of 1 screw each had to be changed.

After surgery, additional fractures of the ulna occurred in 3 birds. One pigeon each in groups A and C were euthanatized because they suffered from comminuted fractures due to wing flapping during handling. One bird in group C fell on the left wing during recovery from anesthesia; because it had a monocortical stable fracture, it remained a participant of the study. One pigeon in group A developed instability of the ulna and required prolonged cage rest until day 14 after surgery. By 28 days after surgery, the fractures of all remaining birds were stable on palpation of the wing. Two pigeons (one each in groups B and C) exhibited depression and anorexia after surgery and were housed separately for a prolonged period. Their flight ability was not evaluated.

Radiographic evaluation (Figs 1 through 4; Table 1) revealed no signs of plate bending or screw loosening. All screws remained bicortical until the end of the study except for 1 screw each in 1 pigeon of groups B and D. The pigeon in group B was the bird that suffered from a comminuted fracture during surgery. In this bird, 1 screw was unicortical at radiographs taken 14 days after surgery and remained in that position until the end of the study. In the pigeon in group D, the screws were bicortical, including in all radiographs taken before day 28 after surgery, but 1 screw was unicortical on the radiographs at 28 days after surgery. The wings of these birds were stable on palpation.

[FIGURE 1 OMITTED]

Results of radiographic measurements are summarized in Table 2. Only the difference in maximal callus width of the radius was significant by ANOVA (Table 1); however, in the post hoc comparisons, only the difference between groups B and C tended toward significance (P = .07). The callus ratios of radius or ulna did not differ between groups, but across all animals, the mean ratio of the ulna was significantly smaller than that of the radius (Table 2; paired t test, t = 3.782, P = .001, n = 25).

The length of the ulna remained unchanged, whereas the length of the unfixed radius was reduced by 2.0 mm at 28 days after surgery (Table 2), because the radial fracture ends were dislocated in most birds (4 birds group A; 4 birds group B; 5 birds group C; 5 birds group D).

Postoperative signs of fractures or fissures occurred in 8 (30%) pigeons (2 birds group A; 2 birds group B; 3 birds group C; 1 bird group D). This led to euthanasia of 2 birds (one pigeon each, groups A and C). Cage rest of the other birds was prolonged until 14 days after surgery, but no further treatment was needed. The wings of these birds were stable on palpation. Radiographically, 1 bird of group A showed signs of osteomyelitis and 1 bird of group D showed development of a synostosis between radius and ulna.

Thirteen pigeons (6 birds group B; 7 birds group D) were treated with a figure-of-eight bandage. The position of the left wing differed significantly at day 10 after surgery (Kruskal-Wallis test, P = .04) between groups C and D. The wing tip of pigeons of group D touched the ground or the pigeons let their left wing droop mildly without the wing tip touching the ground, whereas pigeons of group C held their wings in physiologic position or let their left wing droop mildly without the wing tip touching the ground. However, this difference was no longer evident at 14 or 28 days after surgery, when most of the pigeons showed only a slight drop of the wing without the wing tip touching the ground or held the wing in physiologic position. No correlation was found between slight wing drop or physiologic wing position and flight ability.

Evaluation of flight ability on day 28 after surgery in 23 birds (6 birds group A; 5 birds group B, 5 birds group C; 7 birds group D) is represented in Tables 1 and 3. There were no significant differences in flight ability between the treatment groups at any time point and the day when the pigeons were first observed in the upper half of the aviary. The combination of both methods assessing flight ability (personal observation and video observation) allowed defining the mean number of days when the pigeons were seen in the upper half of the aviary for the first time (21.7 [+ or -] 5.9 days after surgery) (Table 3). Interestingly, the results gained by camera observation differed from those gained during approaching/handling of the birds at 28 days after surgery (Table 1). In the presence of a person, 12 (52%) and 11 (48%) birds showed very good and good flight ability, respectively.

At necropsy, no significant differences were found among the treatment groups. The bones of 3 pigeons macroscopically revealed signs of osteomyelitis (1 bird group A; 2 birds group C). In 7 birds, the implant was still visible (2 birds group B; 2 birds group C; 3 birds group D); in 15 birds, the plate and screws were only partially visible (6 birds group A; 4 birds group B; 2 birds group C; 3 birds group D); and in 3 birds, no implant was visible because of callus formation (2 birds group C; 1 bird group D). In 1 pigeon of group D, the synostosis diagnosed by radiography was confirmed.

Discussion

In this study, we evaluated 2 different miniplates in the repair of ulnar fractures with and without use of a postoperative figure-of-eight bandage for birds weighing less than 500 g. Taking into account the results described above, we found no significant difference between the treatment groups. There was no evidence that fracture healing with less callus proliferation and better ability of flight could be achieved using a 1.0-mm compression plate compared with a 1.3-mm adaptation plate. The use of a figure-of-eight bandage for 10 days after surgery did not improve fracture healing.

[FIGURE 2 OMITTED]

In contrast to results of similar studies, (7-9) there was neither distortion nor bending of the plates in the present study (Fig 5). This finding is explained by the material of the different plate systems. The compact 1.0-mm maxillofacial miniplate with 11 holes evaluated by Gull et al (2) consisted of titanium, whereas the 1.3-mm adaption plate as well as the 1.0-mm compression plate evaluated in the present study consisted of stainless steel. Taking into account the results of all studies (2,7) evaluating these plates for their applicability for wing fracture repair, we conclude that stainless steel plates are required to sustain the stresses for fracture repair of the ulna in pigeons in vivo. Stainless steel plates as implanted in the present study are suited for single plating of fractures of the avian antebrachium. With respect to plate choice, the compression plate system used in this study provides fracture fixation with equal clinical results at an economically preferable price compared with the adaption plate system.

An additional finding of our study is the importance of screw length and number of screws. In the study performed by Gull et al, (2) 1 group of 6 pigeons was treated with an 8-hole 1.3-mm adaption plate, using 4 screws of 6-mm length. In that study, 1 of 6 pigeons was euthanatized due to screw loosening, and 3 of 6 pigeons had screws that were not bicortical. In our study, the same plate was used, but with 6 screws of 8-mm length (group A). Screw loosening was observed in only 1 of 7 pigeons, and all screws were bicortical. Therefore, we recommend longer screws to ensure bicortical placement. This is especially critical when performing surgery in small animals, as no depth gauge is available for such small implants that would allow measuring the length of the screw holes intraoperatively.

[FIGURE 3 OMITTED]

In contrast to the predictions of Gull et al, (2) thread pitch of screws was not as critical as screw length. In our study, screws with a thread pitch of 0.25 and 0.5 mm were used. Gull et al (2) suggested that the use of screws with a thread pitch of less than 0.5 mm may be preferable due to better holding power. However, in our study, no differences in holding power were observed clinically. Nevertheless, the screws with a thread pitch of 0.25 mm may prove to be advantageous in birds with a thinner cortex than the ones used in this study.

The surgery time in this study was comparable to that in the study by Gull et al. (2) The mean surgery time in our study was increased by 15 minutes, which is explained by the fact that 2 more screws were applied. These additional screws seem to have had an effect on fracture stability and facture healing, which resulted in less callus formation. The comparison of the 4 experimental groups of the present study with group A of Gull et al (2) with respect to the ulnar callus ratio at 28 days after surgery (Fig 6) revealed a significant difference between the treatments (ANOVA [F.sub.4,25] = 4.210, P = .01). Sidak post hoc tests revealed significant differences between group A of Gull et al (2) (3.41 [+ or -] 1.47) and groups B (2.09 [+ or -] 0.12), C (1.78 [+ or -] 0.62), and D (2.10 [+ or -] 0.45) of the present study. Avian fractures heal with the same physiologic processes as in mammals but do so more quickly, and callus formation appears to be similar in birds and in mammals. (8,10) First bridging occurs in the periphery in the callus, where tissue strain is the lowest. (11) Instability of the chosen fixation of the fracture leads to interfragmentary motion." The more interfragmentary motion occurs, the more callus is formed at the fracture side. (11) Therefore it is not surprising that the callus ratio of the unfixated radius of all pigeons at 28 days after surgery was significantly larger (2.4 [+ or -] 0.5) than that of the fixated ulna (2.0 [+ or -] 0.4; t = 3.782; P = .001) of all pigeons (Figs 1 through 4).

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

If removal of an implant is recommended (eg, in birds intended for release in the wild), this study offers information regarding the time-point. At day 28 after surgery in 15 birds, the plate was only partially visible and in 3 birds the plate was completely covered by callus. In these birds, plate removal would have been very challenging if not impossible. We therefore conclude that implant removal is recommended earlier than day 28 after surgery with the plate systems used in this study.

The use of a figure-of-eight bandage did not result in a significant difference regarding speed of healing and callus formation. The more pronounced wing droop shown by the birds of group D at 10 days after surgery was resolved by day 14 after surgery. In addition, these pigeons showed no statistically relevant impairment in their flight ability.

Therefore, one may deduct that the use of a figure-of-eight bandage does not bring any advantages. Nevertheless, we consider the application of a figure-of-eight bandage to be an advantage for two reasons. At necropsy, signs of osteomyelitis were only found in groups treated without the bandage. This finding might indicate that the application of dressings is advantageous to reduce the risk of infection and the development of bacterial osteomyelitis. The figure-of-eight bandage may also have reduced the risk of fracture occurrence after surgery. No bird of groups B and D suffered from additional fractures due to wing flapping while handling or recovery from anesthesia, whereas 2 birds treated without bandage were euthanatized because of additional fractures.

[FIGURE 6 OMITTED]

Based on these observations, we do recommend the use of a figure-of-eight bandage for up to 10 days after surgery, although the small sample size of the present study is a limiting factor and prevents a definitive conclusion. We recommend that the bandage should be changed every 2 to 3 days for inspection of the wound. In the present study, the treated wings were gently stretched and mobilized during bandage changes under general anesthesia. Thus, physical therapy (eg, as described by Wimsatt et al (12)) should take place during each bandage change session to prevent complications from immobilization such as muscle atrophy, joint ankylosis, tendon contraction, and patagial constriction.

Results of this study revealed that radiography only detected osteomyelitis in 1 out of 3 birds. This finding emphasizes that it may take days or weeks until bacterial osteomyelitis becomes evident with plain radiography. (13)

In the postsurgical radiographic examinations, 8 (29.6%) pigeons of our study showed fissures or fracture lines. Fissures may occur intraoperatively during manipulation with surgical equipment and implants. Because the avian bone with its specific structure is more brittle than a mammalian bone, one may easily damage the thin avian cortical bone while placing the screws or pins. (8,14-16) A common reason for fracture formation are screws that are larger than 40% of the bone diameter. However, this was not the case in this study because the diameter of the ulna was approximately 5 mm. Postoperatively, suboptimal placement of the implant may result in too high of a strain on the bone due to wrong positioning or inappropriate size of the implant. A recently stabilized bone may fracture due to a trauma in the recovery and convalescence period as described for the 4 birds mentioned earlier. Unnoticed trauma due to too much pressure on the stabilized bone after surgery, maybe during handling, cannot be ruled out completely for the 4 remaining pigeons but seemed less likely. A limitation of the study was that the first postoperative radiographs were not taken until 3 days after surgery, thus these possible reasons could not be definitely narrowed down further.

The occurrence of iatrogenic fracture formation as a result of pin insertion was reported by Ferraz et al. (17) In that study, 18 experimentally induced distal fractures of the humerus of 12 pigeons were stabilized with an articulated external fixator consisting of 3 titanium rods with 6-mm diameter and 5 (3 humeral placed, 2 ulnar placed) Shunz pins with 1-mm or 1.5-mm diameters. Iatrogenic fractures of the humerus, ulna, or both occurred in 33.3% of cases during pin insertion. The authors concluded that the large pin size was the most likely cause for the iatrogenic fractures. This could be the case in our study as well, as the ulnar diameter varied according to the size of the individual pigeon.

Comparing the results of our study with those of the study by Ferraz et al (17) in regard to flight ability is interesting as well because study designs were similar. In the previous study, flight capacity in all 6 birds was adequate by at least 13 weeks after surgery, 2 weeks after being put in aviaries (2.5 X 2.5 X 3 m) allowing unrestricted movement. In our study, the mean number of days for pigeons evaluated to regain good flight ability was 21.8 [+ or -] 4.4 days after surgery, 11.8 [+ or -] 4.4 days after being put in aviaries allowing unrestricted movement.

The two methods to evaluate flight ability in our study yielded different results, with direct observation scoring birds better in flight ability than did camera observation. This possibly reflects the tendency of birds to conceal a weakened condition in the presence of a possible threat such as the sight of humans approaching, even though the pigeons used in this study were raised as companion animals. These differences would possibly be even more distinct in a wild bird with no possibility of becoming familiar with the housing and might confuse clinical assessment of the patient, thus provoking a premature release. This discrepancy could be minimized by examination without human input, such as by installing cameras in the aviaries in question, thereby reducing the influence of stress on the evaluated behavior.

The present data suggest that stainless steel miniplate systems using screws with a thread pitch of either 0.25 mm or 0.5 mm are suitable for fracture repair of the ulna in birds weighing less than 500 g. If plates are to be removed, this must be done before day 28 after surgery. The use of a postoperative figure-of-eight bandage for up to 10 days may be advantageous and appears to reduce the risk of postoperative wound infection. When evaluating flight ability after surgery, birds may feign better flight ability, which is of special concern in birds that are not accustomed to human observation.

Acknowledgments: We thank Marcus Clauss for his assistance during manuscript preparation; the keepers and the students of the Clinic for Zoo Animals, Exotic Pets and Wildlife for their help in the care for the animals; the technicians of the Division of Diagnostic Imaging for their practical advice; and Urs Freiburghaus for providing the animals, as well as Lukas Sprenger for his technical advice regarding the video observation. We would also like to acknowledge the financial support by the Schwyzer-Stiftung and the Baugarten-Stiftung.

References

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Beatrice M. Bennert, Dr Med Vet, Patrick R. Kircher, Prof Dr Med Vet, PhD, Dipl ECVDI, Andreas Gutbrod, Dr Med Vet, Dipl ECVS, Juliane Riechert, PhD, and Jean-Michel Hatt, Prof Dr Med Vet, MSc, Dipl ACZM, Dipl ECZM (Avian)

From the Clinic for Zoo Animals, Exotic Pets and Wildlife (Bennert, Hatt), the Division of Diagnostic Imaging (Kircher), and the Clinic for Small Animal Surgery (Gutbrod), Department of Small Animals, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 260, CH-8057, Zurich, Switzerland; and Hauptstr. 18, CH-8415 Berg am Irchel, Switzerland (Riechert).
Table 1. Results of fracture repair in 4 groups of pigeons after
fractures of the radius and the ulna were experimentally induced and
the ulna was repaired with a bone plate (Ap = 1.3-mm adaption plate or
Cp = 1.0-mm compression plate) with (+) or without (-) a
figure-of-eight bandage applied after surgery.

                           Days after          Group A, Ap-
Parameter                   surgery               (n = 7)

Surgical time (mean            --            50.6 [+ or -] 6.7
  [+ or -] SD), min
Surgical procedure             --       Redrill of holes necessary,
  problems                                  soft tissue trauma

Euthanized due to             1-28                   0
  screw loosening, %
Euthanized due to             1-28                  14
  fracture, %
Plate bent and twisted,        14                    0
  %                            28                    0
Maximal callus width           14       Signs of bone remodelling,
  (mean [+ or -] SD), mm                    but not measurable
   Radius                      28            5.9 [+ or -] 0.9
   Ulna                                      9.5 [+ or -] 1.9
Flight ability, %b
  Very good                    28                 43#/71
  Good                         28                 29#/14
  Moderate                     28                  0#/0
  Poor                         28                  14#/0
  Not evaluated                28                 14#/14
Signs of osteomyelitis         28                   14
  at necropsy, %

                                   Group B, Ap+
Parameter                             (n = 6)

Surgical time (mean              45.3 [+ or -] 3.1
  [+ or -] SD), min
Surgical procedure          Accidental fracture while
  problems                      inserting 1 screw,
                           variation in order of screws
Euthanized due to                        0
  screw loosening, %
Euthanized due to                        0
  fracture, %
Plate bent and twisted,                  0
  %                                      0
Maximal callus width        Signs of bone remodelling,
  (mean [+ or -] SD), mm        but not measurable
   Radius                        7.1 [+ or -] 1.0
   Ulna                          9.6 [+ or -] 0.5
Flight ability, %b
  Very good                           17#/17
  Good                                50#/67
  Moderate                             17#/0
  Poor                                 0#/0
  Not evaluated                       17#/17
Signs of osteomyelitis                   0
  at necropsy, %

                                   Group C, Cp-
Parameter                             (n = 7)

Surgical time (mean             56.7 [+ or -] 16.4
  [+ or -] SD), min
Surgical procedure          Redrill of holes necessary,
  problems                 variation in order of screws

Euthanized due to                        0
  screw loosening, %
Euthanized due to                       14
  fracture, %
Plate bent and twisted,                  0
  %                                      0
Maximal callus width        Signs of bone remodelling,
  (mean [+ or -] SD), mm        but not measurable
   Radius                        5.8 [+ or -] 0.8
   Ulna                          7.9 [+ or -] 2.6
Flight ability, %b
  Very good                           14#/43
  Good                                14#/29
  Moderate                             29#/0
  Poor                                14#/ 0
  Not evaluated                       29#/29
Signs of osteomyelitis                  29
  at necropsy, %

                                   Group D, Cp+               P
Parameter                             (n = 7)               value

Surgical time (mean             53.1 [+ or -] 15.2          .4 (a)
  [+ or -] SD), min
Surgical procedure              Soft tissue trauma,
  problems                 variation in order of screws

Euthanized due to                        0                    --
  screw loosening, %
Euthanized due to                        0                    --
  fracture, %
Plate bent and twisted,                  0                    --
  %                                      0
Maximal callus width        Signs of bone remodelling,
  (mean [+ or -] SD), mm        but not measurable
   Radius                        6.8 [+ or -] 0.6          .023 (a)
   Ulna                          9.4 [+ or -] 1.6          .36 (a)
Flight ability, %b
  Very good                           14#/43                  --
  Good                                14#/57                  --
  Moderate                             43#/0                  --
  Poor                                 29#/0                  --
  Not evaluated                        0#/0                   --
Signs of osteomyelitis                   0                    --
  at necropsy, %

(a) ANOVA.

(b) Observations gained by video observation/direct observation in 23
pigeons; not evaluated refers to pigeons euthanatized or housed in
outside aviaries.

Note: Observations gained by video observation/direct observation in 23
pigeons are indicated with #.

Table 2. Mean radiographic values from 4 groups of pigeons (A: n = 7,
B: n = 6, C: n = 7, D: n = 7) following experimental fracture of the
radius and the ulna.

                                  Days          Mean [+ or -] SD
                              after surgery

Length of radius, mm               0           53.3 [+ or -] 2.2 A (a)
                                   3           50.5 [+ or -] 2.2 (b)
                                  28           51.3 [+ or -] 1.8 (c)
Length of ulna, mm                 0           59.5 [+ or -] 2.2
                                   3           59.1 [+ or -] 2.2
                                  28           59.5 [+ or -] 1.8
Maximal fracture gap of the
  ulna, mm                         3            0.2 [+ or -] 0.17
Step between the fracture
  margins of the ulna, mm         28            0.6 [+ or -] 0.7
Alignment of the fracture
  ends of the ulna, degrees        3          165.9 [+ or -] 4.7
                                  14          163.6 [+ or -] 4.9
                                  28          162.6 [+ or -] 4.9
Callus ratio ulna                 28            2.0 [+ or -] 0.4
Callus ratio radius               28            2.4 [+ or -] 0.5

Callus ratio indicates ratio of the callus width to the distal bone.

(a) Different letters indicate significant differences (paired l test
with Sidak adjustment) in the length of the radius; there were no
significant differences in the length of the ulna.

Table 3. Mean [+ or -] SD days after surgery by experimental
group until pigeons were seen in the upper half of the
aviary after experimental fracture of the radius and ulna
and surgical repair by different miniplate systems.

Group       Good flight ability          Very good flight ability

               Days         % Pigeons          Days         % Pigeons

A       19.9 [+ or -] 4.4     100       23.6 [+ or -] 4.4     83.3
B       21.2 [+ or -] 1.1      83.3     24.5 [+ or -] 4.9     40
C       22.4 [+ or -] 4.0      83.3     25.7 [+ or -] 2.5     60
D       23.4 [+ or -] 6.1     100       25.0 [+ or -] 5.2     42.9
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Title Annotation:Original Study
Author:Bennert, Beatrice M.; Kircher, Patrick R.; Gutbrod, Andreas; Riechert, Juliane; Hatt, Jean-Michel
Publication:Journal of Avian Medicine and Surgery
Article Type:Report
Date:Jun 1, 2016
Words:7074
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