Novel technique for prevention of rotation of the distal phalanx relative to the hoof wall in horses with acute laminitis

Abstract

OBJECTIVE To determine the holding capacity of a 5.5-mm-diameter cortical bone screw when placed in the third phalanx (P3) of horses and assess whether screw placement through the dorsal hoof wall into P3 would be tolerated by clinically normal horses and would alleviate signs of pain and prevent P3 rotation in horses with oligofructose-induced laminitis. ANIMALS 40 limbs from 10 equine cadavers and 19 clinically normal adult horses. PROCEDURES In part 1 of a 3-part study, a 5.5-mm-diameter cortical bone screw was inserted by use of a lag-screw technique through the dorsal hoof wall midline into P3 of 40 cadaveric limbs and tested to failure to determine screw pullout force. In part 2, 6 horses had 5.5-mm-diameter cortical bone screws placed in both forefeet as described for part 1. Screws were removed 4 days after placement. Horses were monitored for lameness before and for 2 weeks after screw removal. In part 3, 13 horses were randomly assigned to serve as controls (n = 3) or undergo screw placement without (group 2; 6) or with (group 3; 4) a washer. Following the acquisition of baseline data, horses were sedated and administered oligofructose (10 g/kg) via a stomach tube. Twenty-four hours later, screws were placed as previously described in both forefeet of horses in groups 2 and 3. Horses were assessed every 4 hours, and radiographic images of the feet were obtained at 96 and 120 hours after oligofructose administration. Horses were euthanized, and the feet were harvested for histologic examination. RESULTS The mean ± SD screw pullout force was 3,908.7 ± 1,473.4 N, and it was positively affected by the depth of screw insertion into P3. Horses of part 2 tolerated screw placement and removal well and did not become lame. All horses of part 3 developed signs of acute lameness, and the distance between P3 and the dorsal hoof wall increased slightly over time. The change in the ratio of the dorsal hoof wall width at the extensor process of P3 to that at the tip of P3 over time was the only variable significantly associated with treatment. CONCLUSIONS AND CLINICAL RELEVANCE Placement of a 5.5-mm-diameter cortical bone screw through the dorsal hoof wall into P3 had sufficient holding power to counteract the pull of the deep digital flexor tendon in approximately 500-kg horses, and placement of such a screw was well tolerated by clinically normal horses but did not alleviate signs of pain in horses with oligofructose-induced laminitis. Further research is necessary before this technique can be recommended for horses with naturally occurring acute laminitis.

Evaluation of locking compression plate fixation of the distal phalanx to the hoof wall as a potential therapy for laminitis

“…Carmalt (2019) reported on the effects of a single, unicortical screw fixation in an experimental laminitis model in a small group of horses (10 treated and 3 control) with inconclusive results. Potential limitation of that study include, mechanical testing of the construct was limited to screw pullout force, the screw was placed 24 h after the administration of oligofructose (at which time histological damage is already present 3 ), the lamellar histology was only subjectively described and the laminitis pathology not severe enough to adequately evaluate the effects of fixation on DP displacement 7 . Further studies designed to carefully test the mechanical effects of different fixation constructs as well as the consequences of DP fixation on lamellar microvascular perfusion and mechanostasis are warranted before any additional interventional studies in experimental laminitis models (or natural laminitis cases) are conducted.…”

“…6 An invasive, yet potentially more effective approach is surgical fixation of the DP to the hoof. Carmalt et al (2019) reported on fixation of the DP to the dorsal hoof wall (DHW) using a single 5.5 mm cortical bone screw. 7 That fixation method did not appear to alter the course of experimentally induced laminitis; however, the study did not establish whether the construct effectively stabilised the DP relative to the DHW.…”

“…Carmalt et al (2019) reported on fixation of the DP to the dorsal hoof wall (DHW) using a single 5.5 mm cortical bone screw. 7 That fixation method did not appear to alter the course of experimentally induced laminitis; however, the study did not establish whether the construct effectively stabilised the DP relative to the DHW. A four screw locking compression plate (LCP) could provide rigid fixation between the DP and DHW, relieving the tensile and shear stresses acting on the SADP during weight bearing and ambulation.…”

“…However, considering the clinical tolerance in vivo and efficacy of the LCP construct ex vivo in the current study, further investigations may be warranted to optimise the technique. Less rigid fixation may prevent disturbances of microvascular perfusion or mechanostasis, yet still be adequate to prevent DP displacement in the face of SADP failure Carmalt (2019). reported on the effects of a single, unicortical screw fixation in an experimental laminitis model in a small group of horses (10 treated and 3 control) with inconclusive results.…”