Standing up all day can be tiring for us humans. This is because we need constant muscular effort in the form of our quadriceps muscles pulling our knee cap (patella) and in turn the patella ligament which attaches to the top of our shin bone. This keeps our leg straight!
Evolution has found a solution to this problem in horses and cows which need to support a lot of weight for a long time. Instead of a single patella ligament they have three, with the inner and middle ligaments forming a loop which can sit over a protrusion in the thigh bone. They can activate this system when needing to stand for prolonged periods so that their leg stays straight through the ligaments, rather than muscles, making it far easier.
Upward fixation of the patella is an uncommon problem where this mechanism cannot be released and predominantly affects horses. Owners will sometimes discover their horse unable to move a back leg. Usually walking them backwards will temporarily relieve the predicament. Surgery is required if the condition is recurrent.
Last month I came across the condition in a dairy cow. What started as an occasional inconvenience became a daily problem with the locking patella making walking very difficult. The cure is surgery to cut the inner ligament and therefore break the locking loop. It is a tried and tested procedure for horses but less so for cows.
I was therefore lucky that a dead cow donated her leg to veterinary science to enable me to practice!
With my anatomical knowledge strengthened, our hobbling cow was sedated and local anaesthetic used to numb the area. Despite difficult access, with the errant ligament on the inner surface of the back leg, the procedure was completed with the cow standing and a satisfying clunk as the ligament was released. Happily the cow recovered fully and is now grazing the spring grass uninhibited.
She owes a debt of gratitude to her fellow bovine who donated her leg to the furtherance of bovine surgery!
Richard Walters, Ivybridge