A horse with an avulsion fracture of the third metatarsal bone in combination with a proximal suspensory desmitis is described. The horse was presented to the clinic with a lameness history of 4 years. With several local anaesthetic techniques the lameness was localized in the area of the proximal metatarsus. The radiological evaluation clearly showed a bone fragment in the area of the origin of the suspensory ligament and with computertomographic examination the position of the fragment was exactly defined and described. A proximal suspensory desmitis was diagnosed by ultrasonographic and computer-tomographic means. Treatment consisted of local injections and slow rehabilitation work over 5 months, but did not show any improvement. After the surgical treatment by osteostixis and fasciotomy, performed in the proximal metatarsus, the horse became sound after 5 months. The problems of diagnosing the suspensory desmitis is described and a possible surgical technique, the osteostixis, as treatment is discussed.