This document describes a retrospective study evaluating a new surgical technique called subtotal (cranial wedge) ostectomy for treating impinging or overriding spinous processes in horses. The study reviewed 25 cases that underwent this procedure. Most horses had resolution of clinical signs and returned to full work following the procedure. The surgery time was short (median 30 minutes) and there were no complications. The procedure was found to maintain the contour of the back and produce functional outcomes similar to more invasive surgical techniques, but with fewer complications.

1. Descriptive Clinical Reports
A new technique for subtotal (cranial wedge) ostectomy in the
treatment of impinging/overriding spinous processes: Description
of technique and outcome of 25 cases
B. D. JACKLIN†
, G. J. MINSHALL and I. M. WRIGHT*
Newmarket Equine Hospital, Suffolk, UK.
*Correspondence email: ian.wright@neh.uk.com; Received: 19.03.13; Accepted: 05.11.13
†
Current Address: Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire AL9 7TA, UK.
Summary
Reasons for performing study: Surgical management for overriding spinous processes of the thoracolumbar vertebrae (SPs) is often favoured when
conservative therapies have failed, pathology is severe, or in competition horses constrained by drug withdrawal periods.
Objectives: To evaluate whether subtotal (cranial wedge) ostectomy represents an effective treatment for overriding SPs, with short surgery time and low
complication rates, maintains the contour of the spine and produces a functionally and cosmetically better outcome than previously reported surgical
techniques for management of overriding/impinging SPs.
Study design: Retrospective study.
Methods: A new technique is described and records were retrieved for 25 cases that had undergone the procedure at Newmarket Equine Hospital between
2009 and 2011. Case records were evaluated for anamnesis, clinical findings and details of surgical and post operative management. Outcome of surgery
was assessed by telephone questionnaire with owners, relating to both functional and cosmetic results.
Results: Of cases treated using the described technique, 78.9% had resolution of clinical signs and returned to full work and a further 18.2% were improved.
Outcome was unrelated to number of SPs resected or mean radiographic grade of impingement. Cosmetic outcome was described as excellent in 81.8% and
good in the remainder. Surgery time ranged from 20 to 70 (median 30) min and there were no intra- or post operative complications.
Conclusions: In contrast to previously described amputation techniques, subtotal (cranial wedge) ostectomy removes only impinging portions of SPs.
General anaesthesia and lateral recumbency facilitate access and enable a short surgery time. The procedure maintains the contour of the back and has
fewer complications, but produces functional outcomes similar to more invasive procedures.
Keywords: horse; spinous process; surgery; impinging; back
Introduction
The spinous processes (SPs) of the vertebrae of the thoracolumbar spine
are a frequently cited cause of back pain and poor performance in horses
[1–6]. However, back pain as a syndrome represents a challenge to the
equine clinician both in ascertaining presence and in localisation [7,8]. In
addition to overriding and impinging SPs, osseous pathology of the equine
spine includes osteoarthritis of the articular processes, spondylosis of the
vertebral bodies and a variety of less commonly encountered lesions,
including traumatic fractures of spinous processes or vertebral bodies and
laminar stress fractures of the vertebral bodies [2,9]. A variety of other
syndromes have been associated with back pain, including lameness
(particularly in the pelvic limbs) and sacroiliac pain [10,11].
A variety of therapeutic approaches to the treatment of overriding/
impinging SPs have been described, including conservative and surgical
options. Conservative treatment most often consists of rest, with systemic
and/or intralesional medication, and can be attempted prior to surgical
intervention as both therapeutic and diagnostic tools [6,12]. Extra-
corporeal shockwave/radial pressure wave therapy, acupuncture and
administration of systemic bisphosphonates have also been described, but
lack any data supportive of efficacy [7,8,13]. Systemic medication usually
consists of nonsteroidal anti-inflammatory drugs, but horses with back pain
may show little improvement [5,7]. Intralesional injection is most often with
corticosteroids, but may also include other agents such as Sarapin [7,8].
Mesotherapy and acupuncture have been described [5,7,14], but long-
term benefits have not been objectively assessed. One study reported that
19/24 cases treated with systemic and intralesional therapies returned to
work, but all needed repeated treatment [15]. Intralesional therapies in
competition horses also represent a concern with respect to withdrawal
periods of commonly used drugs. Surgical management is often favoured
when conservative therapies have failed, pathology is severe, or in
competition horses constrained by drug withdrawal periods. A variety of
surgical techniques have been described [16–22].
This study describes a new surgical approach for the management of
overriding SPs and reviews a series of 25 cases treated in this manner. The
authors hypothesised that previously described ostectomy techniques
were excessive and that reducing the bone mass removed, and hence the
dissection necessary, would optimise maintenance of spinal architecture
and support. As a consequence, a) surgery time would be short, b) the
functional outcome, c) cosmetic appearance and d) complication rate
would be equal to, or better than, those of previously reported techniques.
Materials and methods
Case records were retrieved for horses referred to Newmarket Equine
Hospital between 2009 and 2011 which underwent subtotal resection of
SPs of the thoracolumbar vertebrae, using a new surgical technique. Data
retrieved included age, gender and breed of horses, intended use,
duration of clinical signs, details of treatment prior to surgery, clinical
findings on presentation, details of diagnostics undertaken, number and
location of SPs resected, surgery time, anaesthesia time, antimicrobial and
analgesic regimes, time from surgery to discharge and details of post
operative complications.
Horses underwent radiographic examinations, which included
laterolateral views of the thoracolumbar spinous processes in all cases. In
9/25 (36%) horses, laterolateral views of the thoracic vertebral bodies and
ventrolateral–dorsolateral oblique views of the articular processes of
the thoracic vertebrae were also obtained. Radiographs were examined
retrospectively and graded from I–IV according to a published grading
system [7]. Grades were assigned to each affected interspinous space,
which were then used to generate total and mean scores for each horse.
When horses underwent diagnostic analgesia, impinging SPs were
identified and marked on the skin radiographically, using radio-opaque
markers with a clip patch and/or permanent marker pen. Following aseptic
preparation and local anaesthesia of the skin, a 2 inch, 19 gauge needle
was advanced to the left and right sides, adjacent to the interspinous
bs_bs_banner
Equine Veterinary Journal ISSN 0425-1644
DOI: 10.1111/evj.12215
339Equine Veterinary Journal 46 (2014) 339–344 © 2013 EVJ Ltd

2. space, from the dorsal midline and 10 ml 2.0% mepivacaine hydrochloride
injected on each side, throughout the dorsoventral extent of impingement,
as measured radiographically.
When nuclear scintigraphic evaluation was performed, horses were
injected i.v. with 99m Technetium methylene disphosphonate at
1 GBq/100 kg and given furosemide i.v. 90 min later; scintigraphic
examination was initiated 60 min after the diuretic injection. Images were
obtained on a gantry-mounted, rectangular field of view gamma cameraa
and then transferred to nuclear medicine softwareb
for interpretation.
Images were assessed retrospectively by 2 authors (B.J. and G.M.) and
categorised as having diffuse or focal increased radiopharmaceutical
uptake (IRU), which was then further categorised as being mild, moderate
or marked. The location of the IRU on the SPs was also recorded.
Ultrasonographic examination of the supraspinous and interspinous
ligaments (n = 1) was performed with a 10 MHz linear array probe, in both
transverse and longitudinal orientations.
Surgical technique
Horses were anaesthetised and positioned in left lateral recumbency.
Preoperatively, the SPs for resection, identified radiographically, were
marked with permanent marker pen. Once anaesthetised, surgical steel
skin staples were inserted adjacent to the marked sites and a laterolateral
radiograph was taken to confirm the location (Fig 1). The surgical field was
then aseptically prepared and draped.
A longitudinal incision was made between the most cranial and caudal of
the affected SPs. In 2 cases, 2 separate incisions were made for treatment
of disparate SPs. The supraspinous ligament was divided sharply and
longitudinally along the length of the incision. The left and right portions of
the incised ligament were then elevated from their attachments to the SPs
and retracted abaxially using Gelpi retractors. The interspinous ligament
cranial to each affected SP was incised sharply at its insertion on the
affected portion of the process, in a craniodorsal–caudoventral direction,
in line with the shape of the apical portion of the thoracic SP. A pneumatic
oscillating sawc
was then used to resect the cranial portion of affected SPs,
by cutting in a caudodorsal–cranioventral direction (Fig 2). Resection was
undertaken with a trajectory as close to dorsoventral as possible, such that
the ventral extent of the resection emerged (distal to the site of
impingement) at the point at which the interspinous space diverged. This
most often involved initiating the resection at the junction of the cranial
and middle thirds of the dorsal length of the spinous process, but varied
depending on the shape of the spinous process in question. Fergusson’s
lion bone-holding forcepsd
were used to remove the resected portion of
the SP. If on digital palpation between SPs the wider/divergent ventral
interspinous space had not been reached, then further resection was
performed. This process was then repeated on the cranial edge of each SP
where impingement had previously been identified.
Once the resections were complete, the supraspinous ligament was
sutured using 5 metric polyglactin 910 (Vicryl)e
in a simple continuous
pattern. Skin was apposed using intradermal 3.5 metric polyglactin 910
(Vicryl)e
, in a continuous intradermal pattern, before closure with steel
staples. A gauze stent bandage was then sutured in place using 5 metric
sheathed braided polyamide sutures (Supramid)f
in an interrupted Lembert
pattern. Horses recovered from anaesthesia unaided.
Following discharge, horses received gradually increasing hand walking
or horsewalker exercise for 4 weeks, before a period of turnout of at least 2
months. Conditioning programmes of not less than 2 months followed.
Follow-up and data analysis
Outcomes were ascertained via telephone questionnaire. Clients were
asked whether they had experienced any complications following
discharge. They were then asked to describe the horse’s post operative
outcome as one of 5 categories: had the horse a) deteriorated since
surgery, b) made no improvement since surgery, c) improved in its clinical
signs since surgery and was in work but at a lower level than expected,
d) made a full recovery from clinical signs and was in full work or e) was
not in full work due to an unrelated problem? A Chi-square test for
independence was used to assess whether mean radiographic grade was
associated with outcome. Finally, owners were asked to describe the
cosmetic outcome of the surgery as: poor (significant evidence of surgical
intervention), good (mild evidence of surgical intervention) or excellent
(minimal or no evidence of surgical intervention).
Results
Case details
Case records were retrieved for 25 horses. Ages ranged from 5 to 16
(median = 9, interquartile range = 4.25) years. There were 18 geldings
Fig 1: Laterolateral radiographs of impinging SPs, a) with the horse standing (gantry
mounted generator at 110 kV and 20 mAs using Little Prism filter)j
and b) with the
horse in lateral recumbency (portable generator at 90 kV and 20 mAs). Skin staples
have been placed over the SPs to be removed.
Fig 2: Laterolateral radiographs illustrating subtotal (cranial wedge) ostectomy of 5
SPs, a) before surgery and b) 3 days post surgery. NB: this case was not included in the
current series because of insufficient follow-up time.
Subtotal (cranial wedge) ostectomy for impinging/overriding spinous processes B. D. Jacklin et al.
340 Equine Veterinary Journal 46 (2014) 339–344 © 2013 EVJ Ltd

3. (72%), 6 females (24%) and one male (4%). The horses comprised 6
Thoroughbreds, 6 Warmbloods, 5 Irish Sports Horses, 4 crossbreeds,
one Anglo-Arab, one Oldenburg and one Quarter Horse; breed was
unrecorded in one case. They were used for general riding purposes
(n = 6), eventing (n = 5), dressage (n = 5), showjumping (n = 4), western
reining (one), endurance (one), dressage and jumping (one); use was
unrecorded in 2 cases.
Anamnesis
Duration of clinical signs prior to referral was recorded in 22 cases and
ranged from 2 weeks to 2 years (median 14 weeks, IQR 13 weeks).
Seventeen (68%) horses were presented for evaluation of poor
performance and 10 (40%) had a history of bucking/bronking behaviour.
Four horses (16%) were reported to resent being tacked up.
Nine horses had received veterinary treatment prior to referral
which included phenylbutazone (n = 5), perilesional corticosteroid
administration in combination with extracorporeal radial pressure wave
therapy (n = 3), perilesional corticosteroid administration alone (n = 1)
and i.v. bisphosphonate infusion combined with both extracorporeal
radial pressure wave therapy and perilesional corticosteroids (n = 1).
Phenylbutazone had improved clinical signs in 2 of 5 cases. In all 5 cases
where perilesional corticosteroids were used, clinical signs improved, but
these returned in all horses after varying periods of time. In 3 of 5 cases
they were used in conjunction with extracorporeal radial pressure wave
therapy and in one of these cases also with i.v. bisphosphonate. Six horses
had received physiotherapy without lasting improvement.
Clinical signs
Eight horses were admitted to Newmarket Equine Hospital for orthopaedic
and/or poor performance investigations, 7 of which were seen ridden by
the owner/rider. The owner of the remaining case refused to ride the horse
because of the incited behaviour. Seventeen cases were admitted for
surgery, following work-up by referring veterinary surgeons. Of the cases
seen ridden, all demonstrated a fixed thoracolumbar spine and reduced
stride phases in all gaits. Five were agitated with inconsistent contact, poor
transitions and sudden movements without rider request, 4 resisted
working forward and 3 adopted a kyphotic posture. Additional features
included bucking (n = 2), bronking (n = 2) and rearing (one).
Clinical examination revealed pain on firm digital pressure over the
thoracolumbar spine in 12 (48%) horses. One horse was found to have a low
grade concurrent right hindlimb lameness, but lameness was not recorded
in any other case.
Diagnostic procedures
All horses underwent radiographic examination of the thoracolumbar
spine. This revealed one or more radiological abnormalities, affecting at
least one SP in all cases. Abnormalities included reduced interspinous
space, osteolysis, entheseous new bone, opacification and alteration to
the shape of the SP. The number of affected SPs ranged from 1 to 4
(median = 2, IQR = 2). There was no relationship between the number of
affected SPs and their location. Radiographic grades for individual
interspinous spaces ranged from grades 1 to 4 (median = 2, IQR = 1). Total
radiographic grades for horses ranged from 1 to 9 (median = 4, IQR = 3),
while mean radiographic grades ranged from grades 1 to 4 (mean 1.89, s.d.
0.89). The locations of affected SPs are shown in Figure 3.
Eleven cases (44%) underwent scintigraphic examination of the
thoracolumbar spine which revealed increased radiopharmaceutical
uptake associated with all of the radiologically affected SPs in each case.
This was described as mild in 3 (27.2%), moderate in 6 (54.5%) and marked
in one (9.1%), and classified as focal in 7 (63.6%) and diffuse in 3 (27.2%)
horses. In all cases the uptake was located in the dorsal component of the
SPs. One horse (subsequently referred to as Horse X) had a combination of
a single focal area of marked IRU over the dorsal aspect of the spinous
processes of the 14th and 15th thoracic vertebrae and a further area of
mild diffuse uptake over the dorsal aspects of the 15th thoracic to the first
lumbar vertebrae.
One horse underwent ultrasonographic examination of the
thoracolumbar spine which revealed disruption to the echo structure of
the supraspinous ligament at multiple sites in the caudal thoracic spine.
Ten horses (40%), including 7 at Newmarket Equine Hospital, underwent
perispinous local anaesthesia of the affected SPs, which produced
improvement in exhibited clinical signs in all cases.
Surgery and post operative care
Median surgical time was 30 (range = 20–70, IQR = 15) min and median
duration of anaesthesia (measured from induction to return to recovery
box) was 60 (range = 45–85, IQR = 20) minutes. Horses had between one
and 4 SPs resected (median = 2, IQR = 2). Two horses had SPs resected
through 2 separate incisions, as sites of impingement were disparate.
Radiologically affected SPs were all resected in all but one case. This horse
(Horse X) had marked focal IRU associated with T14/T15, which correlated
with a radiological grade 2 lesion. However, SPs T15–L1 were described as
radiological grade 1 lesions and were associated with mild diffuse IRU.
Following discussion, owners elected for single site resection of the grade
2 lesion in this case.
No complications were encountered intraoperatively. Haemorrhage was
mild, readily controlled using diathermy and did not hinder surgical
progress in any case. Spinous processes were noted in all cases to be more
widely spaced with horses in lateral recumbency than in standing on the
basis of qualitative radiographic assessment (Fig 1).
All horses received antimicrobial drugs commencing preoperatively and
continuing for between 3 and 10 (median = 5, IQR = 2) days. Twenty-one
horses received enrofloxacin (Baytril 10%)g
at 5 mg/kg bwt i.v. q. 24 h, 2
horses received a combination of sodium benzyl penicillin (Crystapen)h
at
22,000 iu/kg bwt i.v. q. 8 h and gentamicin sulphate (Genta Equine 10%)i
at
2.2 mg/kg bwt i.v. q. 8 h. In 2 horses antimicrobials were changed from
enrofloxacin to sodium benzyl penicillin and gentamicin sulphate 3 days
after surgery, following increased swelling with resentment to digital
pressure in both horses and an increased surface temperature in one
animal. In both horses swelling resolved uneventfully. Two horses
developed a mild plaque of swelling around the incision which resolved
without treatment. A further horse developed a serous discharge from the
caudal incision which lasted 24 h and resolved without treatment. Stents
were removed at between 3 and 7 (median = 5, IQR = 1) days following
surgery. Two horses displayed mild transient signs of colic post operatively;
one was treated with fluids administered via nasogastric intubation and
the other resolved without treatment.
Horses received between 3 and 20 (median 8, IQR 3) days of
phenylbutazone (between 2.2 mg/kg bwt s.i.d. and 4.4 mg/kg bwt s.i.d.)
post operatively, initially i.v. and then orally once i.v. catheters were
removed. Horses were hospitalised post operatively for a median of 9
(range 3–13, IQR 3) days, depending on case progression and owner
preference.
Case follow-up
Twenty-three (92%) cases were available for follow-up. Time of follow-up
ranged from 316 to 1156 days post surgery (median = 506 days, IQR = 180
days). No owners reported any complications following discharge. At the
time of follow-up, 3 horses were out of work for reasons unrelated to the
0
2
4
6
8
10
12
T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18 L1 L2 L3 L4
Fig 3: Histogram to show the location of affected SPs in the current series.
B. D. Jacklin et al. Subtotal (cranial wedge) ostectomy for impinging/overriding spinous processes
341Equine Veterinary Journal 46 (2014) 339–344 © 2013 EVJ Ltd

4. SP surgery. One had developed hindlimb proximal suspensory ligament
desmitis and was put in foal; one developed bilateral forelimb foot
lameness and one was retired having developed hindlimb lameness
associated with both tarsi. One horse was subjected to euthanasia 4
months post operatively having sustained a catastrophic scapular fracture
as a result of a kick. None of these horses exhibited any clinical signs of
back pain at the time of follow-up, but because they had not returned to
full work they were excluded from the final analysis.
Of the remaining 19 horses with follow-up, 15 horses (78.9%) were
described as having complete resolution of clinical signs and returned to
full work. Three horses (15.8%) were described as improved but not able to
undertake an expected level of full work. Combining these categories
revealed that 94.7% of horses (18/19) either improved or recovered
completely following surgery. Horse X, which had a single (grade 2) SP
resected, but also had multiple grade 1 SPs affected along the length of the
thoracolumbar spine (T15–L1), made no improvement post operatively and
was subjected to euthanasia 6 months after surgery.
Horses that made a full recovery and returned to work had a mean
radiographic grade of 1.92 (s.d. 1.33) compared to horses that did not
make a full recovery which had a mean radiographic grade of 2.06 (s.d.
0.88). These were not significantly different (P = 0.13).
Eighteen of 22 (81.8%) of owners described the cosmetic outcome as
excellent and 4/22 (18.2%) as good. Three of these 4 horses were reported
to have a small lump at the surgery site and 2 were said to have a small
number of white hairs. No horses had a poor cosmetic outcome.
Discussion
The vertebral skeleton of the horse generally consists of 7 cervical, 18
thoracic, 6 lumbar, 5 sacral and 15–21 caudal vertebrae. Variations are not
uncommon and most frequently involve the presence of only 5 lumbar
vertebrae, which is more common in Arabian horses [23]. Less frequently,
horses are encountered with 17 or 19 thoracic vertebrae [24] and 4 or 6
sacral vertebrae [25]. In the midline on the dorsal aspect of each vertebra
lies an SP which projects dorsally and varies considerably in size along the
length of the spine. It is minimal in size in the cervical region, with the
exception of the 2nd and 7th vertebrae. The SPs increase in dorsoventral
length/height up to the 4th or 5th thoracic vertebrae and reduce in size to
the 15th or 16th vertebra. From this point caudad they are roughly equal in
height, up to the final lumbar and first sacral vertebrae, which are
somewhat shorter. The cranial thoracic SPs are inclined in a dorsocaudal
direction, to a decreasing degree moving caudally. The spinous process of
the 15th or 16th thoracic vertebra is vertical and known as the anticlinal
vertebra, caudal to which the processes are inclined dorsocranially
[7,8,25–27]. At the lumbosacral junction this alters as the first sacral
vertebra is inclined dorsocaudally, leaving a significant space between the
SPs of L6 and S1. In the caudal thoracic spine the dorsal components of the
SPs become more beak-shaped, usually between T11 and T18 [26].
The thoracolumbar vertebrae articulate with one another in 2 ways.
First, by the articular processes, of which each vertebra possess a cranial
and a caudal pair and which form the synovial articular facet joints. These
facet joints comprise the caudal pair of articular processes of one vertebra
with the cranial pair of articular processes from the adjacent caudad
vertebra. Second, the vertebral bodies articulate via amphiarthroses with
intervening intervertebral discs [28]. The discs are variably described as
possessing a nucleus pulposus, but most descriptions regard it as less
distinct than in other species, or even absent [12,23,26,28]. Dorsal to the
thoracolumbar vertebrae lies a strong fibrous supraspinous ligament
attached to the summits of the SPs and extending cranially to form the
funicular component of the nuchal ligament. The SPs are attached to one
another via the interspinous ligaments which fill the interspinous spaces
and consist of oblique fibres directed craniodorsal to caudoventrally, with
the exception of the ligament between T1 and T2 whose fibres run
cranioventrally to caudodorsally [28]. The vertebral bodies are supported
ventrally by the ventral spinous ligament and dorsally by the dorsal spinous
ligament, the latter of which forms the ventral surface of the spinal canal.
In most horses, including all in the current series, the thoracolumbar
interspinous spaces are more widely separated in the ventral two-thirds of
the SPs, while this space narrows in its dorsal one third. It is in this region
that SPs are in closest proximity and where impinging lesions are usually
encountered.
Overriding SPs represent a common radiographic and post mortem
finding and have been identified in skeletons of an extinct and
undomesticated species of equid [29]. Post mortem studies of horses
without clinical evidence of back pain reveal a high prevalence (86–92%) of
overriding SPs [30,31]. Lesions are frequently seen radiographically in
apparently clinically normal horses, and one radiographic study of 110
apparently normal horses revealed 37% of horses to have evidence of
overriding SPs [1,4]. Despite this, overriding SPs are frequently cited as a
common cause of back pain and poor performance in the horse [8]. While
the presence of radiographic abnormalities alone is poorly associated with
clinical disease, radiographic changes of greater severity correlate
well with the presence of clinical signs and a variety of grading systems
have been described in an attempt to demonstrate this relationship
[2,7,8,20,30]. It is recognised that, radiographically, overriding SPs tend to
be less severe and of lower radiological grade in apparently clinically
normal horses, with a fewer number of SPs affected [2,6,32]. The advent of
nuclear scintigraphy has enabled clinicians to evaluate metabolic activity
associated with radiographic lesions, although the relationship is not
absolute. Areas of increased radiopharmaceutical uptake in the spine of
clinically normal horses are very common, with reported prevalences
of 73–79% [33,34]. However, areas of IRU in the spines of clinically
affected animals are encountered with greater frequency, with studies
demonstrating 95–100% of horses with signs of poor performance or back
pain having one or more areas of IRU [15,35,36]. The correlation of areas
of IRU with clinical signs of back pain has yet to be fully elucidated, and
opinions vary [7], but one recent study demonstrated a strong association
between the maximum and total scintigraphic grade of IRU in the
thoracolumbar spine and the presence of clinical signs of back pain [6]. In
horses with areas of IRU in the region of the SPs, between 83% and 98%
have been shown to have radiographic evidence of overriding SPs
[6,15,33,35]. In the current series, all horses that underwent scintigraphic
evaluation had increased radiopharmaceutical uptake in radiologically
affected SPs.
Surgical resection of SPs was first described by Roberts [18], who
performed transverse amputation of the dorsal component of SPs in 29
horses via a cresentic paramedian incision under general anaesthesia. He
reported that 24/29 (82.8%) recovered fully and the remainder improved. A
subsequent series of 14 cases of chronic back pain treated in the same way
via a midline incision reported that 11/14 (78.6%) horses returned to work
improved, with no adverse effects of the surgery encountered [21].
Another study reported 8/10 (80%) horses returning to work following the
procedure [15]. The largest series published to date using the modified en
bloc resection technique consisted of 215 cases, all of which had both
responded to local anaesthesia and failed to respond to conservative
management [20]. In this series, surgery involved complete transverse
amputation of the full craniocaudal width of affected SPs to an unspecified
dorsoventral extent, as well as the dorsal 1 cm of adjacent SPs, using an
oscillating saw. It reported 72% of horses returning to full work, with a
further 9% improved (compared with 79% and 16%, respectively, in the
current series). Horses with higher radiographic grades of overriding SPs
were associated with a poorer outcome, but the number of processes
resected did not affect outcome. In the current series no association was
found between number of SPs affected or mean radiographic grade, and
outcome. This may reflect the targeted, less radical excision employed,
and thus greater preservation of normal architecture and anatomy using
the technique described in the current series. It is noted that Horse X, in
which there was a debate over the number of SPs to resect, was the one
horse which failed to have a successful outcome in the series. A limitation
of the current series is that not all horses underwent both nuclear
scintigraphy and diagnostic anaesthesia in conjunction with radiography. A
more rigorous evaluation of the described technique would be obtained if
all included horses had undergone all 3 diagnostic procedures.
One study has reported successful outcomes via resection of SPs in the
conscious standing animal [17], with 9/9 (100%) animals having a successful
outcome. However, 5/9 of these were cases of fistulous withers [37,38] and
the different aetiology of these cases makes comparison difficult. The
surgical technique described in this series involved the resection of the
entire dorsal component of affected SPs, with 2 oblique cuts made using
Subtotal (cranial wedge) ostectomy for impinging/overriding spinous processes B. D. Jacklin et al.
342 Equine Veterinary Journal 46 (2014) 339–344 © 2013 EVJ Ltd

5. either an osteotome or an oscillating saw, first craniodorsal–caudoventrally
and then caudodorsal–cranioventrally. The pointed apex of the remaining
stump was then rounded using rongeurs and bone curettes. This is similar
to the Roberts en bloc technique in dissecting through and removing
considerable amounts of unaffected tissues.
A special device has been designed for use in human surgery, known as
the Destandau Endospine, which permits the creation of a working space
via a stab incision and access to the surgical site via instrument, camera
and egress ports [39,40]. One case series described the use of this device
for endoscopic resection of SPs in 10 horses which had failed to respond to
conservative management [16]. The technique involved resection of the
cranial and caudal aspects of SPs rather than en bloc or subtotal resection
of the entire SP. The series reports 8/10 (80%) horses returned to previous
levels of work, but neither scintigraphy nor diagnostic analgesia were used
in the diagnosis of any of these cases.
A recent study has described a novel treatment for overriding SPs which
involved desmotomy of the interspinous ligaments between impinging
processes [22]. Eighty-two per cent of surgically treated horses in that
study returned to normal function. A high proportion of these horses (16/
35–46%) went on to experience lameness after surgery, which was not
identified preoperatively; 6 of these (17.1%) failed to resume normal work.
The results are comparable with those of other surgical techniques;
however, case selection is open to criticism as no horses underwent either
scintigraphy or local anaesthesia, ‘all narrowed spaces were treated’ and
the study did not report lesion grades. For these reasons, the authors do
not believe that meaningful conclusions or comparisons with other studies
can be made.
The technique described in this paper is based on surgical first principles
of minimising trauma, removing only affected and preserving normal
tissue. With the exception of Desbrosse et al. [16], previously described
techniques fail to address the dorsoventral location of lesions on the SPs.
In the authors’ experience, the interspinous space between SPs is most
commonly narrowed or lost in its most dorsal one third. This reflects the
most common thoracolumbar SP shape, whereby the ventral two-thirds of
the SPs are more widely separated (Figs 1–3) [25]. The authors reason that
it is therefore only necessary, in most cases, to remove bone associated
with the proximal one-third of each SP. Removal of elements of the dorsal
spine not associated with impingement or pathological bone requires
greater dissection, increased tissue trauma and haemorrhage. The
technique described can be performed with minimal dissection, while
maximising preservation of normal spinal architecture, thereby reducing
surgical times and predisposing factors for post operative complications.
The outcome of cases in the current series is similar to those of other
published series and supports its efficacy in managing cases of
impinging/overriding SPs.
The authors consider that the increase in interspinous space associated
with lateral recumbency aids surgical access and, in turn, tissue trauma
and dissection. Surgical time in the current series was short and less than
the authors’ previous experiences of transverse amputation of SPs under
general anaesthesia and resection under standing sedation. One study
reported the benefit of reduced haemorrhage when performing standing
surgery. This has not been the authors’ experience, as in the standing
animal blood pools in the surgical field, obscuring visibility. In the current
series, intraoperative haemorrhage did not represent a concern or
encumbrance in any case, nor was this reported in the largest series of SP
surgery under general anaesthesia published to date [20].
Cosmesis has not been reported in previous studies, precluding
comparison. However, the cosmetic outcomes reported in this series
support the technique’s principles of minimising tissue trauma and
maximising conservation of normal supporting tissues.
Previously reported complications of surgical management have
included intraoperative haemorrhage and incisional infection [16–18,20].
In the largest case series, 7/215 cases experienced incisional infection
(3.3%) comparable to rates of infection in human spinal surgery [20,41,42].
In human spinal surgery, minimally invasive approaches are associated
with reduced risk of infection, but 1/10 of an equine minimally invasive case
series developed infection [16]. The current group did not have any
incidence of incisional infection, although with only 25 cases this is not
statistically comparable with other series. Further cases are required to
determine whether this is a genuine finding.
Antimicrobial selection in the current case series was based on a local
policy formed from perioperative morbidity monitoring within the hospital.
This rationale is population specific and in other circumstances other
antimicrobial regimes may be more appropriate.
Conclusion
The current series supports the reported technique as an effective method
of treating impinging and/or overriding SPs, with functional outcomes
comparable to those of previously reported amputation techniques.
Additionally, surgical time is short and the technique is less invasive, with
minimal complications and favourable cosmetic results.
Authors’ declaration of interests
No competing interests have been declared.
Ethical animal research
Ethical review not currently required by this journal: retrospective clinical
study.
Source of funding
None.
Acknowledgements
The authors gratefully acknowledge the contributions to patient care of the
interns, nurses and stable staff at Newmarket Equine Hospital.
Authorship
All authors collectively designed and executed this study. The manuscript
was written in combination and approved for submission as a group.
Manufacturers’ addresses
a
Bartec Technologies, Camberley, Surrey, UK.
b
Hermes Nuclear Diagnostics, Gravesend, Kent, UK.
c
De Soutter Medical Limited, Aston Clinton, Buckinghamshire, UK.
d
Thackray Instruments, Leeds, Yorkshire, UK.
e
Ethicon, Livingston, UK.
f
SMI, Hünningen, Belgium.
g
Bayer Animal Health, Newbury, UK.
h
MSD Animal Health, Milton Keynes, Buckinghamshire, UK.
i
Dechra, Shrewsbury, Shropshire, UK.
j
Octostop, Laval, Canada.
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