Inferior Check Ligament Desmotomy (PDF)

Inferior (Distal) Check Ligament Desmotomy Relevant Anatomy The inferior (distal) check ligament, also known as the deep digital flexor accessory ligament, originates from the palmar carpal ligament and joins the deep digital flexor tendon in the metacarpal regio...

Inferior (Distal) Check Ligament Desmotomy Relevant Anatomy The inferior (distal) check ligament, also known as the deep digital flexor accessory ligament, originates from the palmar carpal ligament and joins the deep digital flexor tendon in the metacarpal region. As described previously, the inferior check ligament functions as part of the stay apparatus in the horse to prevent overstretching of the flexor tendon and limit the amount of overextension possible in the metacarpophalangeal joint. Indications Inferior check ligament (deep digital flexor accessory ligament) desmotomy has been described as treatment for chronic desmitis of the deep digital flexor accessory ligament and chronic lameness associated with heel pain in horses. More commonly, this procedure is indicated as treatment for cases of flexure deformity of the distal interphalangeal (coffin) joint or metacarpophalangeal joint (fetlock) that involve contracture of the deep digital flexor tendon (DDF). This includes conditions such as clubfoot and some caudal foot lameness. Surgical treatment of flexural deformities is indicated only in cases that have not responded to conservative methods of therapy, which are described in detail in other texts. If after 1–2 months of conservative treatment methods are not successful, inferior check ligament desmotomy may be indicated. Flexure deformities may be congenital or acquired at any age in horses. Suggested causative factors for acquired flexure deformities included nutrition, genetics, and pain. Some authors have suggested that excessive feeding in some rapidly growing breeds may result in bone growth that exceeds the elongation rate of the associated tendons. Other potential causes of this disease are speculated to be pain and altered weight bearing associated with orthopedic disease, especially physeal dysplasia. In terms of function and cosmetics, inferior check desmotomy is a better technique than deep flexor tenotomy for the treatment of distal interphalangeal flexure deformities, except when the dorsal surface of the hoof is beyond vertical. An ultrasound-guided technique for inferior check desmotomy has been described as well. Suggested advantages to this procedure include selection of the incision site, a smaller incision, no subcutaneous suturing, and decreased tissue swelling after surgery. Anesthesia and Surgical Preparation Surgery is performed with the patient under general anesthesia and in lateral recumbency. A lateral or medial approach may be used, but the lateral approach avoids the medial palmar (common digital) artery on the medial side; it is the easiest approach and is recommended for the inexperienced surgeon. A medial approach has one advantage, however, in that, if a blemish develops, it will be on the medial side of the limb and may not be as obvious. If only one leg is affected, the animal is positioned so that the side of the leg to be operated on is uppermost. If both legs are affected, the horse is placed in dorsal recumbency and the legs are suspended from the ceiling. Then the carpometacarpal area is clipped and is surgically prepared. Instrumentation General surgery pack Surgical Technique A 3–4-cm incision is made over the cranial border of the DDF tendon centered at the junction of the proximal one-third and distal two-thirds of the cannon bone. The position of the incision is illustrated in Figure 9.3A, and the relevant anatomy is illustrated in Figure 9.3B. Following the skin incision, the loose connective tissue over the flexor tendons is dissected bluntly and the paratenon is incised (Figure 9.3C). The superficial and deep flexor tendons must be identified, but they need not be dissected from each other. Blunt dissection is directed craniad to expose the inferior check ligament, and a cleavage plane is identified between the proximal part of the DDF tendon and the inferior check ligament. This cleavage plane is used to separate the check ligament from the DDF tendon (Figure 9.3D). Forceps are inserted between the check ligament and the DDF tendon to separate the structures; then the check ligament is lifted from the incision and is incised with a scalpel (Figure 9.3E). The author prefers to remove a 1-cm segment of the check ligament. This surgical manipulation sometimes disrupts the synovial sheath of the carpal canal, the distal extremity of which extends most of the way down inside the cleavage plane. This event seems to be of little consequence, however. The foot of the patient is then extended manually. The ends of the check ligament become separated, and complete severance of all parts of the check ligament can be ascertained. The paratenon and superficial fascia are closed in a single layer with simple continuous sutures of synthetic, absorbable material. The skin is closed with nonabsorbable sutures in a suture pattern of the surgeon’s choice. Fig. 9.3. A–E. Inferior check ligament desmotomy. Postoperative Management A sterile dressing is placed over the incision, and the limb is bandaged from the proximal metacarpus to the coronary band. To apply more pressure over the surgical site (in an attempt to minimize swelling and reduce the potential blemish) a 4-inch roll of gauze bandage is placed over the incision and is held in position with pressure from an overlying bandage. The hoof is trimmed to normal conformation. Phenylbutazone (1–2 g) is administered intravenously to reduce postoperative pain and to facilitate lowering of the heel. Antibiotics are not administered routinely. Toe extensions may be indicated in more severe cases. Sutures are removed at 12–14 days, and bandaging may be discontinued 3–4 days later. Complications and Prognosis Scarring at the incision site is a common complication of inferior check ligament desmotomies. Proponents of the ultrasound-guided technique for this procedure have reported a reduction in scarring when this method is used. Normal thickening of the check ligament occurs following desmotomy; however, this has not been shown to adversely affect tendon function after healing. Biomechanical studies show that following transection of the accessory ligament, the load is redistributed to the superficial flexor tendon and shifted to the deep digital flexor toward the end of the stance phase. Transfer of the load to the contralateral limb was not observed, and only minor hyperflexion of the metacarpophalangeal joint of the limb that received desmotomy occurred. Overloading of the flexor tendon during locomotion was not considered a concern assuming high-load situations following surgery are avoided, such as jumping. The results of athletic performance in horses afflicted with flexural deformities after surgery are favorable. A retrospective study of 40 horses treated for distal interphalangeal flexure deformities reported that 9 months to 4 years after surgery, 35 horses were not lame and were used as athletes. Of the other 7 horses, 6 had complications related to the deformity, whereas 1 had complications resulting from surgery. Another study reported that ultrasound-guided inferior check ligament desmotomy corrected 40 of 42 cases of clubfoot and both cases of fetlock deformities (2 horses). The prognosis for the horse returning to athletic function has been suggested to be correlated with the age of the horse receiving surgical treatment; Standardbred foals that received desmotomy at an older age had a decreased chance of racing and training soundly. Generally, the prognosis is poor for horses afflicted with desmitis of the deep digital flexor accessory ligament that is associated with adhesions or tendinitis of the superficial flexor tendon. Desmotomy of the accessory ligament has been shown to restore most of these horses to soundness and even use as a pleasure horse.  Superior Check Ligament Desmotomy (After Bramlage) Relevant Anatomy The superficial digital flexor muscle belly is located between the larger deep digital flexor muscle belly and the flexor carpi ulnaris on the caudal aspect of the forelimb. The superior check ligament (the accessory ligament of the superficial digital flexor muscle), which inserts on the caudal surface of the radius, functions in the stay apparatus in the horse. Together with the inferior check ligament (the accessory ligament of the deep digital flexor muscle), it prevents overextension of the fetlock during weight bearing. The cephalic vein runs superficially up the forearm and is used to locate the incision site in this procedure. Branches arising from this vein may require ligation. The brachial artery runs down the medial aspect of the humerus and gives rise to several branches. At the elbow, it becomes the median artery, which runs with the median nerve and courses under the flexor carpi radialis, giving rise to the common interosseous artery. Just proximal to the carpus, the median artery divides into three branches: the palmar branch; the radial artery; and the main branch, which runs through the carpal canal with the flexor tendons and becomes the medial palmar artery. The median nerve also divides proximal to the radiocarpal joint and gives rise to the medial and lateral palmar nerves. There is a nutrient artery that runs near the proximal aspect of the superior check ligament that should, if possible, be avoided. Indications Superior check ligament desmotomy was initially described as a surgical treatment for metacarpophalangeal flexural deformities in young horses. Reported results vary, however, and it is now recognized that the (SDF) tendon is not necessarily the primary unit in metacarpophalangeal flexural deformities. In cases where the SDF appears to be the most involved structure, superior check ligament desmotomy may be indicated. Superior check ligament desmotomy has been reported as a treatment for superficial digital flexor tendinitis in racehorses. The rationale for the surgery is that it interrupts the transfer of the weight-bearing load on the tendon to the distal radius, bringing the muscle and tendon proximal to the superior check ligament (and therefore enhanced elasticity to the functional unit) into use during weight-bearing. The technique described is a modification of that previously described. The approach is more caudal, and the limits of the superior check ligament are more easily defined. In addition, the closure of the medial wall of the flexor carpi radialis sheath facilitates elimination of dead space and minimizes the potential for hematoma formation and adhesions. Anesthesia and Surgical Preparation Surgery is performed with the patient under general anesthesia and either in lateral recumbency with the affected leg down or in dorsal recumbency with the leg suspended. The latter position is preferable in terms of hemostasis. The leg is clipped from midradius to midmetacarpus. The medial side of the antebrachium is surgically prepared. Instrumentation General surgery pack Surgical Technique A 10-cm skin incision is made cranial to the cephalic vein, over the flexor carpi radialis tendon and extending from the level of the distal chestnut proximad. The incision is continued through the subcutaneous tissue and antebrachial fascia (Figure 9.4A). A transverse branch of the cephalic vein might require ligation (the incision can often be continued under it). The fascial sheath of the flexor carpi radialis is incised (Figure 9.4B), and Gelpi retractors are placed to expose the medial wall of the sheath, which adheres to the superior check ligament. A stab incision is made through the craniolateral wall of the sheath and superior check ligament (Figure 9.4C). The incision is continued proximad and distad to sever the ligament completely. Complete incision through the check ligament is evidenced by visualizing the muscular portion of the radial head of the deep digital flexor tendon beneath and separation of the superficial digital flexor muscle palmad (Figure 9.4D). An artery (nutrient artery for the superficial digital flexor tendon) may be present at the proximal border of the check ligament. After complete transection of the ligament, the membranous roof of the carpal synovial sheath is seen distally, and the muscle belly of the radial head of the deep digital flexor tendon is seen in central and proximal areas of the incision. The incision in the flexor carpi radialis sheath is closed with a simple continuous pattern using 2-0 synthetic absorbable material. The antebrachial fascia and subcutaneous tissue is closed with a continuous suture of 2-0 synthetic nonabsorbable material (Figure 9.4E). The skin is closed with interrupted sutures of 2-0 nonabsorbable material. Fig. 9.4. Superior check ligament desmotomy. Postoperative Management A sterile dressing is placed over the incision, and a pressure bandage is applied. Phenylbutazone is administered postoperatively, but antibiotics are not used routinely. Sutures are removed at 12–14 days, and bandaging may be discontinued 3–4 days later. Complications and Prognosis Biomechanical studies have suggested that superior check desmotomy used to treat horses with superficial flexor tendinitis may predispose these horses to developing suspensory desmitis. The superior check ligament plays a vital role in maintaining proper metacarpophalangeal and fetlock joint angles in the horse. Following superior check ligament desmotomy, these angles are decreased, which subsequently increases strain on the superficial digital flexure tendon and suspensory ligament and might predispose the horse to other injuries. In one study, Thoroughbred racehorses that received this procedure were shown to be 5.5 times more likely to develop suspensory desmitis than those that were treated nonsurgically. The efficacy of this procedure in returning racehorses inflicted with tendinitis to full athletic performance is controversial. Most clinical studies of superior check desmotomy have been conducted in Thoroughbred and Standardbred racehorses, despite the fact that superficial flexor tendinitis is common in all sport horses, especially jumpers and 3-day event horses. The prognosis in Standardbred racehorses appears to be slightly better for returning to athletic performance than that for Thoroughbreds, although the results are highly varied. One study showed that 50 of 61 Standardbred racehorses (83%) returned to racing after treatment for tendinitis. However, only 57% of the 61 horses went on to complete 20 or more starts. Similar results were found in another study, which reported that 35 of 38 (92%) horses returned to racing and 71% of horses started 5 or more races without recurring tendinitis. The prognosis for Thoroughbred racehorses is generally lower in the literature. Reported percentages of horses that returned to racing and completed multiple starts range from 53% to 73%. In some studies, these percentages have not substantially exceeded those calculated for Thoroughbred racehorses that are managed with minimal exercise and rehabilitation. A minimally invasive technique has been described using an arthroscope and a lateral approach. This technique provides a better cosmetic outcome and less postoperative care than the traditional open approach.  Palmar Digital Neurectomy Relevant Anatomy The lateral and medial palmar digital nerves are continuations of the lateral and medial palmar nerves. The palmar digital nerve is identified just palmar to the digital artery approximately 0.5 cm below the skin surface and deep to the ligament of the ergot. At the fetlock, the medial and lateral palmar nerves each give rise to dorsal branches. Indications Palmar, or posterior, digital neurectomy is used to relieve chronic heel pain. The most common indication is navicular disease that is not responsive to corrective shoeing and medical therapy, but it is also used in horses with fracture of the navicular bone, selected lateral-wing fractures of the distal phalanx, and calcification of the collateral cartilages of the distal phalanx. This surgical procedure is not benign, and it is not a panacea. A number of potential complications should be explained to the owner prior to surgery. In the hands of a good operator, however, palmar digital neurectomy is a form of long-term relief from the pain of those conditions just listed. Anesthesia and Surgical Preparation Neurectomy may be performed under local analgesia with the animal standing or under general anesthesia. If the surgery is performed with the animal standing, it is preferable to inject the local analgesic agent over the palmar nerves at the level of the abaxial surface of the sesamoid bones. The nerves can be palpated in this area, and the infiltration of this area avoids additional trauma and irritation at the surgery site. If neurectomy is performed in a field situation immediately following the use of a diagnostic block of the palmar digital nerve, however, this same block may be used for the surgical procedure. However, the author generally recommends waiting for 10 days after performing a palmar digital nerve block before performing a neurectomy in order to reduce inflammation in the region. General anesthesia is convenient to use, and for the more involved technique of epineural capping, it is certainly indicated. The area of the surgical incision is clipped, shaved, and prepared for surgery in a routine manner. Plastic adhesive drapes are useful to exclude the hoof as a source of contamination. Instrumentation 1. General surgery pack 2. Iris spatula (epineural capping technique) 3. CO₂ laser Surgical Technique In both the simple guillotine method and the technique of epineural capping, the approach to the nerve is the same. In the simple guillotine technique, an incision 2 cm long is made over the dorsal border of the flexor tendons (Figure 9.7A). If epineural capping is to be performed, the incision is generally 3–4 cm long and is continued through the subcutaneous tissue. It is important that the tissues be subjected to minimal trauma. An incision over the dorsal border of the flexor tendons generally brings the operator close to the palmar digital nerve. Variation exists, but the relationship of vein, artery, nerve, and the ligament of the ergot assists the surgeon’s orientation (Figure 9.7B). At this stage of the dissection, the surgeon should look for accessory branches of the palmar digital nerve. These branches are commonly found near the ligament of the ergot. If an accessory branch is found, a 2-cm portion is removed using a scalpel. B A C Fig. 9.7. A–C. Palmar digital neurectomy. Guillotine Technique The nerve is identified and is dissected free of the subcutaneous tissue. The structure can be identified as nerve if it puckers after it is stretched, if scraping its surface reveals the longitudinal strands of the axons, or if a small incision into the nerve body reveals cut transverse sections of bundles of nerve fibers. The nerve is severed at the distal extremity of the incision. Then a hemostat is placed on the nerve, which is stretched while being cut with a scalpel or CO₂ laser at the proximal limit of the incision (Figure 9.7C). This sharp incision is made in such a fashion that the proximal portion of the nerve springs up into the tissue planes and out of sight. It is believed that the severance of untraumatized nerve and its retraction up into the tissue planes helps reduce the problems of painful neuromas. The concept behind using the CO₂ laser is that it seals the nerve ending, even further reducing the possibility of a painful neuroma. The skin is closed with interrupted sutures of nonabsorbable material. Pull-Through Technique The pull-through technique is an extension of the Guillotine technique. The first part of the procedure is performed as previously described. The main difference is that, instead of transecting the nerve at the proximal site of the incision as in the guillotine technique, traction is placed on the distal nerve, and a second incision of 1 cm is made over the nerve at the base of the proximal sesamoid bone. The digital nerve is then pulled through the proximal incision and a guillotine technique is used to transect the nerve. Postoperative Management Antibiotics are not used routinely. A sterile dressing is placed on the incision, and a pressure bandage is maintained on the leg for at least 21 days. To minimize postoperative inflammation, 2 g of phenylbutazone are administered daily following surgery for 5–7 days. Sutures are removed 10 days after the operation, and the horse is rested for 60 days. Complications and Prognosis Complications of neurectomy include painful neuroma formation, rupture of the deep digital flexor tendon, reinnervation, persistence of sensation because of failure to identify and sever accessory branches of the nerve, and loss of the hoof wall. Neuromas are the most common complications and can arise when the axons in the proximal stump regenerate axon sprouts, which cause pain and hypersensitivity. One retrospective study of 50 horses that received palmar digital neurectomies, the majority by transection and electrocoagulation, reported that 17 horses (34%) had complications, with recurrence of heel pain being the most common. Only 3 of the 17 horses developed neuromas, although this number may have been higher due to undetectable painful neuromas that could not be palpated. In 2 years, 63% of all the horses that received neurectomies were still sound. More recently, a study of 24 horses that received neurectomies using the guillotine technique reported no postoperative complications. The majority of these horses (22 of the 24) were treated for lameness associated with abnormal radiographic findings of the navicular bone and associated structures; the collateral cartilages of the hoof, or in one case, pedal osteitis. Twenty-two of these horses returned to full athletic performance, including jumping, dressage, camp drafting, cutting, and endurance competition. When using the pull-through technique, 88% of the horses were sound at one year post surgery.  This project was supported by Hoof wall wound repair the Rural Industries Research and Development Corporation (RIRDC) of Australia. C. C. Pollitt and M. Daradka Summary Reasons for performing study: Surgical stripping of the hoof wall results in a wound that heals remarkabley well. In contrast, lamellae recovering from laminitis are often deformed. Investigating lamellar wound healing may aid understanding of laminitis. Objectives: To document temporal changes in the lamellar basement membrane (BM), dermis and epidermis after surgery. Methods: Wall strips were made in the dorsal hoof wall midline of 6 mature horses. Immunohistochemistry was used to document changes in the basement membrane (BM) and detect proliferation of epidermal cells in lamellar tissues harvested at intervals. A conforming metal plate was screwed to the hoof wall to maintain alignment of the wound edges. Results: Wall stripping caused lamellar tips to snap and remain behind in the dermis along with the majority of the lamellar BM and some lamellar basal cells. Three days later the BM was intact and new lamellae had been reconstructed by proliferation of surviving epidermal cells. By 5 days the surface of the stripped zone was covered with yellow epidermis that subsequently thickened and hardened. Eventually the hoof wall deficit was replaced by new wall growing down from the coronet. The conforming metal plate and post operative analgesic ensured minimal lameness. Conclusions and potential relevance: In wall stripped lamellae the BM survives virtually intact and is used as a template for proliferating cells, from snapped-off lamellar tips, to migrate and quickly achieve repair to near normality. In laminitis epidermal dysadhesion and lamellar BM destruction occurs and lack of a functional BM template may explain the prolonged and abnormal repair of affected lamellae. Introduction The removal of hoof wall strips to facilitate repair of cracks and to remove underlying foreign bodies and tumours is an established surgical technique (White and Moore 1998). The post surgical deficit in the hoof wall heals remarkably well (Pollitt 1995). After a few days the surface of exposed lamellar corium dries and hardens but is never replaced from within by new hoof wall. Instead, new hoof wall, generated at the coronet, grows slowly downwards, over the superficially keratinised lamellar surface, until the hoof wall deficit disappears. How the lamellae of the hoof wall recover from wall stripping has never been reported. Here we investigate wall strip wound healing to better understand the biology of hoof lamellae and therefore the pathophysiology of laminitis. Materials and methods Six healthy, Standardbred racehorses aged 4–8 years, with clinically normal hooves, were used for this study. Horses weighed 370–427 kg, were housed in stables on rubber matting and fed a maintenance diet. The protocol for the experiments was approved by The University of Queensland Animal Experimentation Ethics Committee and, after surgery, all horses were inspected by the committee’s veterinary officer. Horses were walked twice daily to evaluate lameness. A notch (20 mm wide) was made in the distal hoof wall toe and the adjacent sole of the front hooves using a hoof knife and hoof nipper (Fig 1a). Two parallel lines (10 mm apart), aligned with the notch, were marked on the hoof wall from coronet to bearing border. A standard, side-clipped horseshoe was fitted to reduce foot expansion. A metal plate, to support the dorsal hoof wall post operatively, was shaped to conform to the dorsal hoof wall (Fig 1d). Holes (3 x 6 mm), corresponding with the holes in the plate, were drilled in the hoof wall of the standing, unsedated horse. The plate was then screwed to the hoof prior to the wall strip operation. The wall strips (one per fore foot) were made at different times to enable wounds of different ages to be harvested for analysis. Each horse was anaesthetised using 1.1 mg/kg bwt xylazine HCl (Xylazil) and, after 5 mins, 2.2 mg/kg bwt ketamine HCl (Ketamine injection) i.v. The duration of anaesthesia was 20–25 mins providing enough time for the procedure. The hooves were scrubbed with a povidone iodine solution (Iovone) and the pre- positioned, hoof wall plate was removed. Esmarch’s bandage was applied to the distal limb to control haemorrhage. The oscillating blade of a plaster cast-cutting saw was placed over the lines marked on the dorsal hoof wall and cuts were made through the wall to a level just deeper than the stratum internum (Fig 1a). The blade of the saw was cooled with cold saline. The wall between the parallel cuts became mobile when the saw-cuts were complete and sufficiently deep. A special wall stripping tool was made from standard nail clenchers; a sharp edged hook was forged into the lower straight jaw (Fig 1b). The hook was inserted in the notch between the hoof wall and the sole, at the level of the white line, and the handles of the tool were grasped firmly. Rolling upwards toward the coronet, the pressure applied by the curved upper jaw of the tool caused the hoof wall to bend and lift easily from the underlying dermal lamellae and coronet. The corium of the lamellae and coronet invariably separated cleanly from the horn of the hoof wall. The wound was dressed with 10 mm wide, saline soaked wound dressings, the steel plate was screwed back into place (Fig 1d) and the foot wrapped, first with cotton wool and then adhesive bandage. Parenteral post operative penicillin, 12 mg/kg i.m. (Depocillin) and a phenylbutazone/sodium salicylate mixture, 4.5 mg/kg and 1.2 mg/kg i.v. respectively (Butasyl) were administered, daily for 5 days. The wound was gently irrigated with normal saline and the dressing changed every second day without removing the steel hoof plate. No medicament was applied to the wound. One horse, with 3 and 5 day wall strips, was injected with the thymidine analogue 5-bromo-2’-deoxyuridine (BRdU) to detect basal cell proliferation (Daradka and Pollitt 2004). The wall strip zone was photographed with a digital camera. The 6 horses were subjected to euthanasia by barbiturate overdose and lamellar tissue from the 12 wall stripped hooves were cut and harvested using the method of Pollitt (1996). Wall stripped tissue 1–10 days post surgery came from 5 horses while 4–6 month tissue came from one horse. Hoof wall specimens taken at the time of wall stripping were also harvested. The specimens were fixed, processed and stained (Pollitt and Daradka 1998; Daradka and Pollitt 2004). Results The wall strip procedure was completed in less than 20 mins and all wounds healed without sepsis or other complications. The metal, hoof wall plate, in conjunction with the side-clipped shoe, stabilised the hoof wall post operatively, kept the edges of the wall strip parallel, resulting in only slight post operative lameness. Pre-drilled holes in the hoof wall, using the plate as a template, ensured that the normal shape and distance between the cut edges was maintained. This, in conjunction with daily administration of the phenylbutazone/sodium salicylate mixture, ensured no significant, post operative lameness when the horses were evaluated at the walk. The veterinary officer of the Animal Experimentation Ethics Committee was satisfied that the procedure and the standard of post operative care caused no compromise to the welfare of the horses. Day 0 (specimens taken at the time wall stripping) Immunostained sections from stripped hoof wall showed small portions of the BM still attached to epidermal basal cells (Fig 2a). Apparently most of the BM, along with some basal cells, had been torn from the hoof wall during its removal and remained in the dermis. One day after surgery In all cases, stripping the hoof wall caused the tips of the lamellae to snap at the same point and remain behind in the dermis in their original, prestripping, positions (Fig 2b). The majority of the lamellar basement membrane (BM) and some secondary epidermal lamellar (SEL) basal cells was with the dermis (Fig 2c). The BM, once bordering SELs, had collapsed inwards, no longer supported by epidermal cells (Figs 2b,c). It had a bi-layered appearance where opposite sides of now empty SELs were apposed. However, in most apparently empty SELs, a few basal and suprabasal cells, usually at SEL tips, had survived stripping and were still attached to the BM (Fig 2c, inset). Laminin and collagen type IV immunostaining was of normal density around blood vessels, nerves and the PEL tip but much denser elsewhere. Many haemorrhagic areas were present in and around empty PELs (Fig 2d). Polymorphonucleocytes (PMNs) were within capillaries but many had migrated to epidermal compartments, especially in sections close to the tip of the PDL(Fig 2d). Gaps (green arrow in Figs 2d and 3a) in the continuity of the lamellar BM were present where portions were torn away during the operation. The gaps corresponded with remnants of BM that had remained with the ablated epidermis (Fig 2a). Some epidermal basal cells had rounded, instead of oval, nuclei (Figs 2d, 3a) and were no longer attached to the BM. They appeared to be migrating into the empty lamella; surviving SEL basal cells and the snapped off PEL tip appeared to be the source of the migrating cells (Fig 3a). Two days after surgery Within 48 h of wall strip surgery, re-epithelisation of PELs and SELs was well underway (Fig 3b). The immunostained BM was fully restored and gaps in its continuity could no longer be found. The epidermal compartments no longer had a collapsed appearance and were repopulated with new basal cells. Many of the basal cells appeared to have reattached to the lamellar BM. They had the oval nucleus of normal lamellar basal cells. The shape of the SELs was more rounded and lobulated than normal. The point where the PEL snapped during the wall strip operation could still be located (Fig 3b, red asterisks). Blood and serum were still oozing from the stripped surface and there was no evidence of epithelialisation (Fig 4a).  Three days after surgery By 72 h post surgery most of the lamellar BM had been restored to a near normal SEL shape and density (Fig 3d) and the PEL had attained the thickness of a normal PEL. Many of the new cells showed positive BRdU immunostaining (Fig 3c), indicating that proliferation as well as migration had occurred. In contrast, the snapped off lamellar tip contained no proliferating cells (Fig 3c, inset) except at the break point, the source of the new cells that had migrated to fill empty lamellae. Four days after surgery Sections from tissue 4 days after wall strip surgery appeared similar to tissue at 3 days. The wound caused by the oscillating saw cut showed the poorest healing response. In one horse the saw cut had penetrated deep into the dermis causing severe anatomical disruption. Even normal lamellae adjacent to stripped zone showed pathology. Six days after surgery By Day 6 the stripped zone was covered with a layer of yellowish material with a striped appearance (Fig 4b). Examination of the corresponding tissue sections showed that the yellow material was neo-epithelium that had proliferated outwards, past parallel rows of PDLs, hence the striped appearance. In some sections, where the BM was damaged extensively at the time of wall stripping, re-establishment of normal lamellar anatomy had not occurred. If the BM template was faulty then the resultant reconstruction was compromised. There were many distorted SEL shapes and islands of epidermal cells not connected to PELs. The epidermal islands appeared to have arisen from SEL tip basal cells that survived wall stripping. Some of the isolated pockets of epidermal cells resembled hoof wall tubules, never usually present at the tips of lamellae (data not shown). Ten days after surgery Reconstruction of the hoof wall lamellae to near normal anatomy was virtually complete 10 days after surgery. The neo-epithelium that was growing past the tips of the PDLs was now a thick keratinised layer (arrows in Fig 4b) that protected the underlying corium. Only the saw cuts left a legacy of pathological anatomy. Four to 6 months after surgery Four months after surgery the surface of the wound was covered with a hard dry keratinised layer (Fig 4c). The layer remained the same thickness at subsequent examinations. The new hoof wall, generated by the coronet, progressively covered the keratinised lamellar layer and replaced the hoof wall deficit from above. There was minimal scarring or evidence that a deficit had existed (Fig 4d). However, despite outward appearances, the new hoof wall did not have a normal relationship with the distal phalanx beneath. This was shown by examination of a sagittal foot section from the hoof wall stripped 6 months previously. There was a wedge of keratinised lamellar material between the new hoof wall and the distal phalanx. However, sections 2 mm abaxial to the wall strip site showed normal anatomy indicating that the wedge was confined to the stripped zone. Stabled horses were virtually pain free after the wall strip surgery. If the metal plate became loose and the edges of the cut hoof wall collapsed inwards lameness developed. This occurred in one horse approximately 2 months after surgery. Reinforcing the plate with fibre-glass cloth and polymethylmethacrylate resin resolved lameness.  a) b) c) d) Fig 1: Before wall stripping, a 2 cm notch (red arrow in (a) and (b)) was made in the distal, midline, dorsal hoof wall toe, and sole; then an oscillating plaster cutting saw (a) was used to cut through the hoof wall and a stripping tool (b) was used to peel the wall from the underlying corium (c). Damage to the hoof epidermal lamellae (white arrow) and the corresponding dermal lamellae (yellow arrow) appears to be minimal. Finally, using predrilled holes, a stabilising steel plate (d) was screwed to the hoof wall. a) b) c) d) Fig 2: In stripped away hoof lamellae (a) there are remnants of brown, immunostained BM (red arrows), between SEL bases. One day after surgery (b) BM of stripped lamellae (red arrows) and the tips of 2 snapped-off PELs (black arrows) are isolated in the dermis. Empty SELs (c) have a bi-layered appearance (red arrows) but contain basal cells (inset; black arrows). Gaps in the continuity of the lamellar BM (d) are mainly at SDL tips (green arrow). Capillaries and all lamellar compartments contain PMNs (yellow arrows). Surviving basal cells have rounded nuclei and are not attached to the BM (black arrows). BM = basement membrane; PEL= primary epidermal lamella; SEL= secondary epidermal lamella; SDL= secondary dermal lamella; PMNs = polymorphonuclear cells; V= veins. Bars = 100 µm.  a) b) c) d) Fig 3: Lamellar dermis with immunostained BM. One day after surgey (a) mobilised basal cells, with rounded nuclei (black arrow), are beside the stump of the snapped-off PEL tip. There is a gap in the BM (green arrow). Two days after surgery (b) the stumps of the snapped-off PELs (red asterisks) have merged with re-epithelised PELs and SELs. Three days after surgery (c) many of the cells have dark brown nuclei showing positive BRdU immunostaining (arrows). In contrast, the snapped-off lamellar tip contains no proliferating cells (inset). At 4 days (d), lamellae have a near normal appearance. Bars = 100 µm. a) b) c) d) Fig 4: Exudate oozes from the surface of stripped lamellar corium 2 days after surgery (a). By Day 6 (b) exudation has stopped and most of the corium is covered with a striped (arrowed), yellow epidermis. Two months after surgery (c) the surface of the wound is covered with a dry, keratinised layer and a 15 mm long, new hoof wall (*). Four months after surgery (d) the keratinised layer is no thicker but the new hoof wall (*) is 30 mm long. Discussion Analysis of wall strips, performed in the midline of the dorsal hoof wall of 6 mature Standardbred horses, documented healing of lamellar tissues after wounding. The gross appearance and histology of the wall stripped zone, studied over 10 days in both fore hooves of 5 horses and 4 and 6 months in one horse, showed the sequence of hoof wound healing. Immunohistochemistry with anti-type IV collagen and antilaminin enabled tracking of subtle changes in BM structure. BRdU, injected into one horse, and detected in its lamellar tissues with an anti BRdU, indicated the location of epidermal cell proliferation in wounded lamellar tissues. The discovery that stripping the equine hoof wall causes the tips of the PELs to snap and remain embedded in the dermis has not been reported before. Wall stripping, despite gross appearances, does not completely separate epidermal from dermal lamellae. In the process of peeling the hoof wall from the underlying corium the PEL tips snap, at the weakest point of their anatomy, where the keratinised axis of the PEL ends. Also, most of the lamellar BM separates from the lamellar epidermis, remains in the dermis and small gaps are quickly repaired. Only fragments of the lamellar BM could be detected in lamellar hoof material stripped from the hoof at the time of surgery. Basal cells, migrating from the stumps of PEL tips, transformed the empty, collapsed, BM shells of the stripped lamellae, filling them with new keratinocytes. Remarkably, the new lamellae had near normal anatomy. The source of new cells appeared to be the stumps of PEL tips and SEL basal cells that had not been stripped away during surgery. The repaired lamellar BM acted as a template over which migrating keratinocytes reconstructed the lamellae. Damaged BM, that was unable to repair along anatomical lines, gave rise to bizarre shaped lamellae. BM enclosed islands of epidermal cells, not connected to the PEL, were present in badly damaged zones. Immunostaining with anti BRdU detected proliferation amongst migrating mid-lamellar basal cells. This contrasts with the results of BRdU staining of normal mid-lamellar tissue that showed virtually no proliferation (Daradka and Pollitt 2004). Therefore, lamellar wounding triggers lamellar proliferation. The parallel saw cuts made in the hoof wall at the time of surgery caused the greatest amount of damage. Care should be taken when performing wall strips to prevent deep penetration of the saw blade into the dermis. The conforming steel plate that was screwed to the hoof wall surface immediately after surgery successfully stabilised the toe and prevented significant post operative lameness. Reinforcing the steel plate with fibreglass and polymethylmethacrylate resin improved stability and allowed one horse a successful long term recovery, unrestained in a paddock. Rapid and uncomplicated healing occurred with a post operative treatment regime of parenteral penicillin, analgesia, irrigation of the wounds with normal saline and the application of non absorbent dressings without ointments or antiseptics. The application of topical antibacterial ointments and creams to healing wounds is controversial. Delayed epithelialisation, leucocyte migration and healing result when they are used (Vijanto 1980; Lee et al.1984, 1986; Zamora 1984; Swaim and Lee 1987; Lee and Bishop 1997), results vindicated by this study. Dressings and bandages had a beneficial effect on the wounds. They provided protection from contamination, absorbed wound exudate, increased wound temperature and reduced wound pH (Stashak 1991). Months after stripping, beneath the stripped zone, there was a small wedge of keratinised material resembling the so- called ‘lamellar wedge’ of chronic laminitis. The proliferation of lamellar basal cells in the stripped zone, shown to occur by Day 3 in this study, apparently continues indefinitely to produce the lamellar wedge. The lamellar wedge that follows wall stripping is not likely to be a long term problem because of the support offered by the normal lamellae on either side of the stripped zone. The results suggest that activation of basal cell proliferation is likely to be a feature of chronic laminitis where the unpredictable size and growth rate of the lamellar wedge is a significant problem. The growth of the lamellar wedge of chronic laminitis could be studied using the BRdU method described here. The wall strip experiments reveal a key difference between lamellae affected by laminitis and wall stripped lamellae. In the former, epidermal cells leave their BM (Pollitt 1996) or lose it completely due to lysis (Pollitt and Daradka 1998) and without an intact BM nearby the lamellar epithelium repairs poorly. However, after wall stripping, the BM survives virtually intact and is quickly and effectively repaired. In addition, a source of new cells is available (the stump of the snapped off PEL and surviving SEL cells) and, using the BM as a template a lamellae are quickly reepithelialised. Unlike skin, which can recruit basal cells from hair follicles and sweat glands, healing lamellae cannot access keratinocytes from other sources. Uniquely, the act of tearing away the hoof, whether by accident or the intent of the surgeon, automatically invokes a mechanism that provides not only a source of cells but a BM template on which they can rapidly migrate. This option is not available to laminitis affected tissue. In laminitis the pathology is reversed; the lamellar tips and the BM template are far removed from each other making anatomical reconstitution difficult. Perhaps this explains the irreversible nature of chronic laminitis and why cases of full recovery are so rare.