Aust Vet J Vol 77, No 11,November 1999 713 Clinical Postoperative performance of racing horses with tearing of the medial palmar intercarpal ligament RC WHITTON a , NJ KANNEGIETER and RJ ROSE Department of Veterinary Clinical Sciences, The University of Sydney, New South Wales 2006 Objective To examine the relationship between medial palmar intercarpal ligament (MPICL) tearing and postopera- tive performance in racing horses. Materials and methods The postoperative performance of 42 horses in which the midcarpal joint was examined arthroscopically was followed prospectively. Intra-articular variables examined were the severity of MPICL tearing, subchondral bone damage and articular cartilage damage. Using a scoring system based on the class of race and the position in the race, a mean score was calculated for up to five races before and after surgery. The preoperative score was subtracted from the postoperative score to give a net score. Statistical analysis was by a Mann Whitney U test and multiple linear regression. Results Thirty-two (76%) raced postoperatively, 23 (55%) won at least one race and 12 of 26 (46%) performed at the same or higher level. Horses with grades 2 to 4 MPICL tearing had significantly lower net scores than those with grade 1 or no tearing. The severity of subchondral bone damage was the only variable on its own that was significantly correlated with net score (r 2 = 0.23, P<0.05). The addition of the grade of MPICL tearing to bone damage significantly improved the prediction of postoperative performance (P < 0.05). The inclusion of articular cartilage damage had no effect on the prediction of postoperative performance. Conclusion Tears involving more than one third of the MPICL as observed arthroscopically have a significant detri- mental affect on postoperative performance of racing horses. Aust Vet J 1999;77:713-717 Key words: Horse, carpus, ligament, performance. DMICL Dorsomedial intercarpal ligament MPICL Medial palmar intercarpal ligament O steochondral damage in the midcarpal joint is a well-estab- lished cause of clinical carpal disease and poor performance in racing horses. 1-4 However, the clinical signifi- cance of other intra-articular lesions is less well understood. Tearing of the MPICL 5,6 and enlargement of the DMICL 7 are both commonly observed in horses with midcarpal joint disease. It has been proposed that MPICL tearing causes instability in the midcarpal joint and contributes to osteochondral damage. 5 Previous studies have demon- strated a relationship between remod- elling of the dorsal aspect of the radial carpal bone and tearing of the MPICL, 6 and suggested that clinical signs of carpal disease were much more severe in joints with tearing than in joints with similar osteochondral damage but no ligament damage. 8 Enlargement of the DMICL has been proposed also as a primary cause of osteochondral damage in the midcarpal joint due to impinge- ment on the joint surface. 7 Although changes in these ligaments seem to be associated with midcarpal joint disease, there are also some ques- tions about their significance. A high prevalence of MPICL tearing has been observed in horses with no history of joint disease. 9 This suggests that MPICL tearing is not always clinically signifi- cant. We have also previously found no relationship between osteochondral damage and DMICL enlargement, chal- lenging its proposed role in midcarpal joint disease. 10 One way to determine the significance of intercarpal ligament lesions is to examine the postoperative performance of horses in which the midcarpal joint has been examined. Unfortunately, concurrent osteochondral damage also affects performance 3 and so comparison between horses is difficult. To our knowledge there is only one report of the postoperative performance in a number of horses with MPICL tearing: performance of horses with more than 50% of the MPICL torn was very poor. No consideration was made of concur- rent joint lesions. 8 In this prospective study we examined the postoperative performance of horses after the midcarpal joint was examined arthroscopically. The primary aim was to determine the effect of tearing of the MPICL and enlargement of the DMICL on postoperative performance, while taking into account other lesions identified in the joint at the time of surgery. Materials and methods All racing horses undergoing midcarpal joint arthroscopy at The University of Sydney Veterinary Teaching Hospital between April 1993 and April 1995 were included in the study. The indications for surgery were intra-articular osteochondral fragments observed on radiographs, areas of subchondral lucency and/or lameness localised to the midcarpal joint with intra-articular anaesthesia. Arthroscopic surgery was performed using previously described techniques. 11 All articular surfaces of the bones of the midcarpal joint were closely examined. Cartilage damage was graded from 0 to 3. a Present address: Newcastle Equine Centre, PO Box 123, Broadmeadow, New South Wales 2242