AAEP Rounds case 10-15-07 HIGH RINGBONE By Anna Thompson-Kelley On Sept. 17th,  a 15 year old American Quarter Horse gelding presented to the LATH with a 2 year history of lameness on his forelimb.  About one week prior to the visit, his shoeing had changed to a rocker-toe shoe probably to aid in shortening the breakover duration of his stride and stress on those affected ligaments and tendons. In the physical exam, everything was normal except a bony enlargement located on his left pastern joint.  A lameness exam was performed revealing him to test positive on his left forelimb on a scale of 3/5 on baseline and eventually a 4/5 after flexion of the lower limb.  At this point, a Palmar Digital nerve block was performed, blocking the lowest region of the limb, which indicated no change in lameness.  Next, a Lower Abaxial nerve block was performed,  blocking  the proximal and distal interphalangeal joints, which indicated an 80% improvement in lameness. At this point, radiographs were taken of the pastern joint (proximal interphalangeal joint). His radiographs showed exostosis (new bone growth out from a bony surface, and enthesiophyte (areas of muscle or ligament insertion to bone that have undergone calcification) formation which indicate progression of an existing problem.  His diagnosis of High Ringbone is confirmed by the extraarticular and periarticular bone deposits involving the proximal interphalangeal joint.  Due to the significant changes in the radiographs degenerative joint disease is also present. This horse’s lesion is secondary probably due to post traumatic osteoarthritis.  Since he has a lot of bony proliferation on the eminences of his proximal phalanx where the collateral ligaments attach, there’s reason to believe he could have injured himself in the past and caused instability to the joint.   Ideally once a joint has started new bone growth and degenerative changes, it begins to naturally fuse itself together and can be very painful for the horse.  In the case of High Ringbone it doesn’t always occur, so surgical intervention is usually the preferred treatment.  The procedure for this horse is called a Pastern Arthrodesis where the surgeon transfixes the pastern joint with multiple screws that remain in the proximal and middle phalanx permanently.  Eventually these two bones form a single phalanx over time and rid the horse of pain in that joint space. On Sept. 19th,  the gelding was premedicated with 2 grams of Bute (Phenylbutazone) , 22 mL of Kpen (Potassium Penicillin), 30 mL of Gentamicin, and given Tetanus Toxoid.  Bupivacaine, a potent local anesthetic, was given as a 4 point perineural block.  Cefotaxime, a 3rd Generation Cephalosporin antibiotic that kills Pseudomonus, gram - , and some gram + was given as regional limb perfusion.  The surgery involved the removal of as much articular cartilage from the proximal interphalangeal joint space as possible allowing close apposition of the two phalanges. A drill was used to place the precise size holes for the compression screws. The hole drilled through the middle phalanx must be small enough so the screw can pull it tight up against the proximal phalanx without stripping through the bone. The size screws used are typically 5.5 mm cortical screws in a parallel fashion because 2 of these screws when compared to the alternative 4.5 mm 3 screw or crossing technique showed better healing, greater tensile breaking strength, and holding power.  This overall gives a more stable internal fixation of the joint.  In this particular surgery, the surgeon also decided to remove a lot of the bony proliferation on the dorsal surface of the joint margins of bone and apply a bone plate held in by screws.  Hopefully this will decrease the excess bony proliferation and add to joint stability, or what will now be bone stability. In his recovery from surgery, he encountered some respiratory distress due to edema, possibly from being recumbent and increased hydrostatic pressure.  He was given Prednisolone (Corticosteroid) to decrease pulmonary inflammation, and 10 mL of Lasix (Furosemide) a diuretic, which helps to mobilize lung extravascular water and decrease the nasal edema. A cast was placed distal to his carpus and his medications were continued.  The next day an Ultimate Shoe was placed on his contralateral hoof.  He was closely monitored in a stall for signs of colic, standing vs. lying down, and changes to the cast.  Possible complications must be considered, the screws could break or an infection could set in.  The screws may break immediately when in recovery or longterm.  They could possibly bend out of place or slightly move and never cause any problems. Eventually new bone will grow over them.  An infection can start at any time.  You will usually see post-op peripheral new bone growth sooner than expected, a draining sinus may be present, heat, swelling, or increased lameness. The cast must be felt everyday for increased heat and antibiotics are given to help the horse’s immune system. Post-op radiographs were taken to confirm screws still intact after recovery. Gastroguard (Omeprazole) was then given to him BID for any potential gastroinestinal ulcers he may have accumulated.  The cast was daily monitored for heat and a strike through, the point at which the cast will feel moist due to liquid passing from the inside and making its way to the outside of the material. The liquid can be fluid from blood, exudate, or tissue fluid. Five days after the surgery his pain had decreased and he was using his limb more freely in the stall.  The Bute was decreased and the antibiotics discontinued.  His cast was changed and his catheter was removed. Over the next week he developed a warm, moist strike through area located on the palmar aspect of the fetlock region. When the cast was changed, sores were noted and treated on the distal fetlock and proximal metacarpus.  The incision site was granulating in and the skin sutures were removed. He is currently still in a cast and on low amounts of Bute and Gastroguard.  His screws and bone plate seem to be without infection and staying fixed. FYI: If you look closely at the oblique radiographs, the proximal bony eminences where the extensor tendon attaches contains radiolucency and the edges are not very smooth.  Dr. Downs stated that these were very important views to evaluate in pre-purchase exams and those types of changes shouldn’t be missed. Bute= Non-Steroidal Anti-inflammatory Drug that can interact with Gentamicin and increase nephrotoxicity) Kpen=kills some Streptococci, Staphylococci,  and anaerobes Gentamicin = Aminoglycoside, kills gram - , enteric pathogens (E.coli, Pseudomonus) Tetanus Toxoid = attacks Clostridium tetani toxins References: Case Information and Radiographs provided by Dr. Downs AAEP Rounds 10/15/07 And the Case Binder Records Adams’ Lameness in Horses, 5th Ed.  By Ted S. Stashak. 2002.

High Ringbone