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To hear a lion roar once again - the Tawny Eagle case

I woke up this morning with a lioness roaring close by. She bump-started an especially early dawn chorus, to be followed by the nightjars’ closing remarks. Then George rang out his territory call, then Girl, and then Helen (all Crowned Eagles) and finally the old male Augur Buzzard. Embarrassingly late, the Robin Chats wrapped it up with the cacophony of other small birds. I got up but it was still dark and cold outside with a half moon sweeping on sickle wings away from Venus in a clear sky. Far too early to get up so went back to bed and rolled over smiling and finally caught up with a good solid sleep that I had missed throughout the night.

It had been a bad night. I was anxious about our future. The future of the centre, the birds even of raptor conservation itself. But my immediate worry was about keeping alive an eagle that many would have euthanized. The reason I finally slept well during the dawn chorus was that this eagle had lived to hear a lion roar once again. And too few do.

The day before ( 7th Dec 2023) Dr Juliet Waiyaki, Mwanzia and I had operated on two eagles. One a Tawny Eagle that had come from the Mara with a shattered wing that had mud crushed into its bones. After nearly a year we had to amputate the wing entirely. This, after a succession of failures in trying to keep the wing through the use of internal prosthesis was a bitter disappointment. The other was a Southern Banded Snake Eagle, an obscure species I had never handled previously. Its jaw was badly broken and we were lucky to resolve it (see previous blog post).

The Tawny Eagle case

We had tried to clean out the bones and remove all the maggots and make as sterile a surgery as possible but the entire midsection of the humerus (upper arm bone) ultimately died. It took two operations to know just how much had to be removed and there came a time when there was only the top end of the humerus and the bottom end joint at the elbow. One overriding concern in amputating a wing is balance. If one wing is complete and the other missing the bird will, when it tries to jump, beat both wings. This spins the bird over onto its side or back. In some cases amputating both wings allows the bird to jump and clamber around like a penguin or a biped. Therefore all effort is needed to keep the wing, even if it doesn’t function, if only to keep balance.

In order to keep the wing we planned to stick in a mid section humerus prosthesis. But after waiting months to get bone cement from abroad the nature of the injury was getting worse and we had little left to work with. We had waited too long and when it finally did arrive it proved to set like stone in less than a minute especially if injected down a 1mm tube. It was nothing like as easy to work with as my first efforts some 25 years ago with a different cement.

The Juvenile Tawny Eagle on the 11th April 2023 being rescued. Unfortunately the method of handling was less than ideal and the wound was infected with maggots.

Placing an internal mid section prosthesis is tricky at the best of times but it goes like this. 1. Remove all the non viable bone taking care not to severe nerves, arteries and muscle attachments. 2. Make sure the joints on either end of the bone are not injured otherwise arthritis will occur. 3. Fill both ends of the hollow bones near the joints with cement. 4. Place a telescopic stainless steel or titanium pin inside both ends, slide an external trans-cutaneous stabilising pin into the bone and hollow of the inside pin before the cement sets and seat them exactly in place. 5. Wait till it sets. 6. Sew it all back together again. 7. Rigorous antibiotic treatment followed by months of physiotherapy.

Now that’s not easy. The various muscles, and nerves and blood vessels need to be on the right sides of this new prosthesis so that they can function as they should. Placing the prosthesis inside this narrow tunnel can take as much as 20 minutes even if things work smoothly. We opted for stainless steel as there was no need for osseointegration given the bone cement. When flustered by a cement that heats up (beyond the temperature that can kill tissue) and cures in less than a minute to a consistency that is hopeless for the task, then the end result is going to be less than optimal. That this bone cement costs more than a Landcruiser’s tyre for 40 grams makes for overly cautious frugal use again resulting in less than ideal outcome. Given its use in humans one can imagine many surgeons break down in tears of frustration as they rush slapping things together on the operating table. Over 25 years ago I used a bone cement that was cheap, flowed easily, took 20 mins to set and had a low exothermic temperature.

The use of stents was required to align the skin under much pressure over the internal prosthesis. This was a few weeks after surgery and looked good and allowed partial function of the entire wing.

The result ultimately was not good. Months later the prosthesis implant wriggled its way to the surface requiring yet another operation to seat it in the middle of the muscles. The eagle was frightened of people but was happy with two other Tawny Eagles in a big breeding enclosure. Months later his wing hung at a bad angle and I took the prosthesis out to find it had glass smooth knobs of cement that had absolutely no adhesive qualities. This is a well known property of bone cement, yet it would seem logical if it was a little more adhesive friendly. The glass smooth surface has nothing for the new bone to “grip” at all when inside the medulla of the bone. Annoyed, I finally tracked down a cement of exactly the same polymer and monomer, yet 15 times less expensive (used in the dental practice). This plus about ¼ calcium phosphate and a small amount of antibiotic mixed in would replicate the exorbitant human bone cement and function well. It also set slower, and had less exothermic heat and could be pushed down a 1mm tube without problems. Whether or not this mixture will osseointegrate remains to be seen but it is certainly biocompatible and an easier to use option.

I spent a whole day making a new telescopic prosthesis. As luck would have it, the X-rays we had to rely on had waited nearly 3 weeks due to a government take-over of the hospital that scanned them. The plates were very grainy and missed the key areas, most notably the elbow end. There had been a succession of bad luck but we were determined to change this around.

Then the day arrived and Juliet and I, armed with a new prosthesis, a detailed plan and the new improved bone cement set to work with Mwanzia holding the anaesthetised eagle. But to our dismay the wing showed no discernible elbow section to drill out and place the implant. This was now to be Juliet’s first amputation or euthanasia. I hate euthanasia as today eagles are rare and after so long he had settled in well and was part of the family. So we amputated. He had previously shown clotting problems, an eagle haemophiliac, so we had to take special care. A lot of ligatures later the wing was removed and we placed a stainless steel ITAP with a threaded tip into the stump with the intent to one day screw on an external wing prosthesis. Nothing fancy, just something he could use as a counter weight.

He was removed from the table as an anaesthetised Southern Banded Snake eagle was slid on. While preparing the snake eagle Juliet reappeared with the Tawny as it had “sprung a leak” - the trauma surgeon’s understatement of an arterial blow out. The table now had two eagles on it. I diligently remained focused on mine while Juliet focused on hers.

This is about as intense an ER situation can get and although unplanned Dr Juliet Waiyaki and I were able to fix both eagles without a problem.

Twenty minutes after being put back in his enclosure he ran up to his nest 15 feet high and fed ravenously. Raptors are truly incredible, bouncing back from the most extreme operations to apparent full health in minutes.

The bump is the distal end of a metal implant that enters the humerus. In time we aim to add a wing prosthesis, not so he can fly, but so he can better balance.


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Kenya Bird of Prey Trust

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