Case Study - Equine Lameness Clinic 1

Feedback: The overall body condition was poor (2/5) and the horse was generally poorly muscled. Conformational abnormalities demonstrated that both forefeet had a long-toe/low heel conformation and broken back HPA (particularly the LF). When standing the horse stood toe-out, again especially on the LF, exacerbated by rotation of digit from LF fetlock. Long sloping pasterns on both forelimbs were visible.

Palpation
On palpation of the cervical spine a slight muscle swelling over the mid region on the left hand side was noted. The thoracolumbar spine was poorly muscled and a moderate pain response present in the caudal aspect and over gluteal region on both sides.
On the left fore the horn of the hoof appeared poor in quality. On foot examination the foot was fitted with short bars leading to inadequate heel support. Pain on hooftesters over medial/lateral quarters was noted.
On the right fore a medial firm, non-painful region (exostosis) was palpable on McII partially extending axially. Pain on extension of the right fore shoulder was also noted. Again there was poor heel support by the shoe present

Feedback: When examined in a straight line the horse was sound at the walk but 2/10 RF lameness at the trot. When lunged on the hard surface the horse was 3-4/10 RF on the left rein and 3/10 RF on the right rein. On the soft surface the horse was 4/10 RF on the left rein and 2/10 RF on the right rein
Flexion tests were performed. A slight positive response was seen following flexion of distal limb of the left fore. Flexion of the right fore also slightly positive response on left fore.

Feedback: A number of studies in the last 5-10 years have demonstrated the lack of specificity of distal limb blocks.

Feedback: Left fore: On the LM projection there is reverse rotation of the pedal bone in relation to the solar margin (i.e. the palmar aspect of P3 is lower than the dorsodistal region).Also evident is a moderate bony extension of the proximal margination of the navicular bone. This is relatively smooth and appears less radiodense that the main part of the navicular bone.
Right fore: On the LM view there is dorsopalmar imbalance showing as reverse rotation of the pedal bone (as described in the left fore). The toe region of the foot is moderately long leading to a centre of rotational axis of the DIP joint in the caudal third of the foot. There is obliquity of P2 on P3 through the DIP joint but this is likely due to the asymmetry of P2 as shown in the horizontal DP projection.

Feedback: LF - On the horizontal DP there is sloping of the lateral hoof wall and pedal bone laterally. There is a faint radiolucent line through the lateral third of the navicular bone with displacement and extension of the lateral wing slightly laterally and proximally.
RF-On the horizontal DP projection there is medial flaring of the hoof wall and sloping medially of the distal medial condyle of P2.

Feedback: LF - On the DPrPaDiO (P3) projection there is irregularity to the lateral wing of the navicular bone and a faint inverted Y-shaped radiolucent line in the lateral third of the bone. There are also increased circular lucencies along the distal border of the navicular bone. There is also some radiopaque material superimposed over the lateral, dorsal and possibly medial aspect of the hoof likely to be associated with dirt/poor foot preparation.
RF - On the DPrPaDiO (P3) projection there are 4-5 discrete radiolucencies present along the distal border of the navicular bone

Feedback: LF - On the DPrPaDiO (NB) projection there is a widened radiolucent line running from the proximal to distal border of the navicular bone in the lateral third of the bone. The lateral wing appears displaced proximally and laterally. There are 3-4 well described circular lucencies along the distal border of the navicular bone surround by a sclerotic rim. There is also some irregular modelling along the proximal border of the navicular bone.
RF - On the DPrPaDiO (NB) projection there are 4-5 radiolucencies in the distal margin of the navicular bone surrounded by moderate sclerosis

Feedback: LF - On the PaPrPaDiO projection there is severe distortion of the flexor cortex of the lateral half of the navicular bone. The flexor cortex from just medial of the sagittal ridge, along the ridge and laterally has an overall reduction in radiodensity with small punctuate lytic regions within the cortex. There is also irregularity along the endosteal cortex opposing this region. There is a radiolucent line through the lateral quarter of the navicular bone and rotation and alteration in the radiodensity of the lateral fragment (although the superimposition of the lateral palmar process makes this harder to appreciate and there is a degree of elongation of the image due to positioning)
RF - On the PaPrPaDiO projection there is irregularity along the endosteal aspect of the flexor cortex caused by endosteal new bone formation. There is a crescent shaped radiolucency in the sagittal ridge that is recognised as a normal variant.

Diagnosis

LF: chronic navicular bone fracture (lateral third wing displacement) and poor foot balance (dorsopalmar/mediolateral)
RF: navicular bone pathology and poor foot balance (dorsoplamar)

Feedback: This horse underwent corrective trimming and remedial farriery. Improvement in the dorsopalamr imbalance was performed by reducing the toe length and squaring the foot. A larger shoe size was placed on both front feet to increase heel support. These were in the form of central support shoes where the overall surface area of the shoe is increased leading to reduced force through the shoe and the breakover point is brought more caudally. 5° heel wedges were also placed.
Additionally the solar aspects of the feet were filled with isopolyurethane filler again to reduce concussive forces through the sole. The horse was also placed on a short course of phenylbutazone (1.1mg/kg sid 7 days) and advised initially to paddock rest (for 4 weeks) then to gradually return to light work.
Due to the presence of the navicular bone fracture in the left fore, the prognosis for return to athletic function was given as guarded.

Prognosis
Follow-up examination
On examination at the clinic approximately 6 months later the forelimb conformation and overall condition of the horse had significantly improved. The horse was sound in straight line and when lunged on the soft surface but bilaterally lame on the hard surface in the forelimbs (3/10 LF on the left rein and 2/10 RF on the right rein).

Further comments
This case presented with a history of an intermittent bilateral forelimb lameness of varying severity. On presentation to the clinic the horse was predominately right fore lame but became left fore following diagnostic anaesthesia of the right. Diagnostic anaesthesia of the right fore pointed towards the navicular apparatus but radiographical signs of classic navicular disease were not particulatly apparent and we know that diagnostic anaesthesia is less specific than originally thought. We also know that pain originating from the navicular region may not show overt radiographical signs but evidence of inflammation/osteonecrosis can be more apparent on MRI/scintigraphy and this horse, compounded by its poor foot balance, may have been overloading the right forefoot due to the chronic changes in the left.

Additionally the horse became markedly lame several hours after the left fore nerve block had been performed and was probably wearing off. The radiographic signs show the presence of a chronic navicular bone fracture with modelling and chronic changes within the bone and de-sensitising the region would have left the horse not protecting the region (unbeknown to use at the time!). It would have been interesting to image the DDFT and rest of the navicular apparatus in this case with MRI. This case however does demonstrate how important foot balance and support is since despite the poor radiological signs this horse did show signs of improvement by corrective farriery.