Prospective study of blackthorn injury and synovitis in 35 horses

The objective of this prospective clinical study was to investigate the cause and describe the presentation, diagnosis, treatment techniques and outcome of Prunus spinosa (blackthorn) injury and synovitis in the horse. In all cases presented with blackthorn injury and synovitis, surgical treatment was performed within 24 h, using a two-stage procedure: 1-Perisynovial technique using ultrasound guided electrosurgical dissection; 2-Endoscopic technique. The diagnosis was confirmed by retrieval of black plant material from or close to the affected synovial structure. Mean lameness score on presentation was 4/5 (range 1–5). The most commonly affected structures were extensor tendon sheaths (12/35) and fetlock joints (11/35). All cases had thorn material removed, 80% had thorn material removed at surgery and in 49% it was intra-synovial. On presentation, the mean synovial fluid total protein level (TP) was 47.6 g/L (range 18–66); mean total nucleated cell count (TNCC) was 176 × 10⁹ cells/L (range 12–312). Two days post-surgery, mean total protein levels were 33 g/L (range 16–52), mean TNCC was 13 × 10⁹ cells/L (range 1–35). At 5 days post-surgery, the mean total protein was 23 g/L (range 12–28) and TNCC was 5 × 10⁹ cells/L (range 1–12). All synovial fluid cultures were negative. Twenty-eight (80%) horses were sound 5 days post-operatively, seven (20%) were not lame in walk; they all returned to full work in an average time of 8 weeks (range 3–48 weeks). Surgery achieved accurate identification and removal of thorn material. In contrast to previous studies of synovial sepsis, these cases had a positive outcome despite high pre- and post-operative synovial fluid TP and TNCC. These findings suggest that Prunus spinosus (blackthorn) synovitis has a different aetiology to synovitis originating from sepsis or other types of contamination.