Splints : If a horse is worked too hard while young and immature extra pressure is put on the splint and cannon bones on the inside of the foreleg. This can lead to a tear in the fiborous ligament resulting in a soft swelling that develops into a bony lump called a splint.
The cannon and splint fuse naturally in a young horse between the ages of 5 and 7 so splints are unlikely to occur in older horses.
Spavins: Bone Spavins are an osteoarthritic condition of the hocks resulting in a bony enlargement on the inside of the hock often caused by strain and /or poor conformation of the hock.
A Bog Spavin is a swelling of the tibiotarsal joint of the hock caused by strain to the synovial bursa , the membrane surrounding a joint. A swelling is caused when the membrane is stretched and it fills with synovial fluid.