Angular and flexural limb deformities (Proceedings)
Foals are often afflicted with limb deformities, and they are classified as flexural or angular deformities. Occasionally, rotational deformities are also present. Many of the congenital angular limb deformities correct with no treatment or with only conservative treatment.
Foals are often afflicted with limb deformities, and they are classified as flexural or angular deformities. Occasionally, rotational deformities are also present.1,2 Many of the congenital angular limb deformities correct with no treatment or with only conservative treatment. In some cases of severe orthopedic disease in young horses, the supporting limb can develop an acquired angular deformity, but angular deformities are generally congenital or developmental. Flexural deformities are grouped into congenital and acquired deformities; congenital refers to deformities that are present at birth, while acquired deformities develop later in life.3 Both types of deformities will be discussed along available treatment options.
ANGULAR LIMB DEFORMITIES
Foals with angular limb deformities (ALD) have either a valgus or varus presentation. Valgus deformities deviate laterally distal to the origin of the deformity, while varus deformities deviate medially distal to the origin. Carpal valgus is the most common ALD seen, followed by fetlock varus.4,5 The etiology of ALD is not fully understood in every case and is likely multi-factorial. We do know that unequal growth can occur across the metaphyseal growth plate, or physis. Most of the long bone growth occurs at this level and with disparate growth, deformities can occur. It is theorized that perinatal as well as developmental factors can influence the occurrence of ALD.1 Trauma (or irregular pressure) across the physis may be a reason for incongruent growth rates. Abnormal pressure on the physis could occur due to joint laxity, malposititioning in utero, excessive exercise in young foals, or lameness in the opposite limb.1,5 It is also possible that nutritional factors may lead to excessive or anomalous growth in some cases. Another cause for ALD is incomplete ossification of the cuboidal bones. In premature or dysmature foals and in twins, the carpal or tarsal (cuboidal) bones may not be completely ossified. The carpal/tarsal structures consist of cartilage instead of bone when this occurs, and even normal weight bearing can deform the cartilage template. The bones then ossify in that crushed shape and the consequence can be an ALD of the carpus or tarsus.
Angular limb deformities are diagnosed based on physical exam. Examination of the leg or legs involved can be done from different angles to evaluate the deformity. Radiographs are also performed in most cases to determine the source(s) of the deformity as well as to determine if crushing of cuboidal bones is present. Manipulation of the limb can also aid in diagnosing joint laxity, or flaccid supporting structures. Most foals are born with some degree of angular deformity, and many will correct over time. Foals also have small chests and long legs, which make many foals appear "close-kneed" because of their toed-out posture. A good physical exam can determine if and where there is a serious deformity. Diagnosis of fetlock and phalangeal deformities should be made and treatment initiated as early as possible. The distal metacarpal or metatarsal physis has little remaining growth potential after 60-90 days. Moderate carpal or tarsal deformities with no cuboidal bone involvement can be treated at a later age, as the growth plates of the distal radius and tibia have substantial growth occurring for up to a year.
ALD: NON-SURGICAL MANAGEMENT
Conservative management can sometimes be very useful in treating foals with ALD. Stall rest or restricted exercise (small periods of turnout or hand walking with the mare) is a technique that will allow many, if not most foals to correct. Frequent hoof trimming is recommended for all cases, both surgical and non-surgical. Valgus cases should have the outside or lateral wall of the hoof trimmed slightly shorter (lower), while varus deformities need the medial aspect of the hoof slightly shorter. This results in the longer side of the foot hitting the ground first, and rotating it "away" from the deformity (i.e., medially for a valgus deformity). In addition, shoes or composite material may be used to extend the foot medially for valgus deformities and laterally for varus deformities. These extensions prevent wear on that aspect of the hoof as well as assisting in the foot contacting the ground first on that side. Splints and casts have limited use in foals with ALD unless they have incomplete ossification of the cuboidal bones, and decreasing weight-bearing in those cases has ideally been implemented before a significant ALD is present.
Foals with incomplete ossification of the cuboidal bones must be on strict stall rest, and in some cases sleeve casts, splints, braces or slings may be warranted. These adjunctive therapies may help reduce weight-bearing and deformation of cartilage template as mentioned above. Most neonatal specialists advocate repeated radiographs every 2 weeks to monitor ossification of the bones.
If the bones are ossified, foals with carpal or tarsal deformities can be treated with stall rest and trimming for several months if there is no worsening of the condition. If the foals are improving with stall rest and limited turnout (from one to a few hours a day), even 4-6 months is an acceptable period to wait. I have treated foals as old as 9 months of age, and still had successful results after transphyseal bridging in those that did not eventually correct with conservative management. It typically takes foals of this age longer to correct. It must be noted however, that it is important to identify foals with cuboidal bone abnormalities, joint laxity, and deformities that worsen over time to recommend a different course of treatment than only conservative management for this length of time.
In foals that have fetlock deformities, surgical treatment is encouraged early (~ 3-4 weeks of age), as the window for manipulating growth with surgical procedures is much smaller. As such, we generally do not recommend stall rest as a treatment option in these cases. Foot trimming and extensions, if warranted, are included in the treatment for these cases as well.
ALD: SURGICAL TREATMENT
Surgical management of ALD cases is most common for the carpal region; up to 85% of those referred for surgery are carpal deformities.4 Options for surgical treatment include growth acceleration or growth retardation. Growth acceleration is carried out on the lateral side of the physis for valgus deformities, and retardation on the medial side. This can be thought of as increasing growth on the "short" side or decreasing growth on the "long" side. Some clinicians have used both techniques in the same case.
Growth acceleration became very popular and was widely accepted after the mid-80s.4,6,7 The technique is named hemicircumferential transection of the periosteum and periosteal elevation (HCPTE), and is commonly known as periosteal stripping. Despite its popularity, the true efficacy of this technique is controversial, and in a recent study, periosteal stripping was no more effective in correcting experimentally induced angular limb deformities than stall rest and hoof trimming alone.8 In another study, there was no difference between medial and lateral growth rates at the proximal or distal end of the radius in foals that had received HCPTE or those used as controls.9 In addition, the study that introduced HCPTE for use in foals was an experimental model using six pony foals. The study was not blind, and there was no significant difference in growth at the distal radial physis after the procedure in principal limbs compared with controls.6 Differences in angulation of the limbs were found to be significantly different; the greatest difference during the study in average angulation between control and principal limbs was 3.2 degrees. It was concluded that an angulation was created in the principal limbs beyond that of the control limbs. In contrast, much of the literature concerning this procedure claims that a limb cannot be overcorrected with this procedure. Most of the measured angulations throughout that study were within what are considered normal ranges.10 Furthermore, all the foals were 60 days of age or less, and most were 45 days of age or less. This is an age range when it is expected that there is a change in angulation as the foal matures.1,6,11 There are also no studies comparing growth retardation directly with HCPTE. The two procedures are sometimes used in combination, usually when the clinician decides the deformity is severe or the foal is older and has less growth potential.1
Though abandoned by many, the procedure for HCPTE is still practiced and will be described. An approximately 3 centimeter skin incision is made on the concave aspect of the limb over the physis starting about 4-5 cm proximal to the physis. The incision is continued to the level of the periosteum. After reflecting the tendons, in inverted T shaped incision is made in the periosteum. An elevator is used elevate 2 triangular flaps that this creates. After elevation, the periosteum is laid back onto the bone, and the subcutaneous tissues and skin are closed with absorbable suture. Bandaging and after the procedure is routine, and this is usually performed on farm, or on an outpatient basis. Hoof trimming and restricted exercise is recommended as discussed above in non-surgical management.
Growth retardation is also called transphyseal bridging. There are several different procedures that can be employed to retard growth on one side of the physis. Placement of two cortical screws and figure-eight cerclage wires, transphyseal staples, or single transphyseal screws are all viable options. Using an implant to bridge the physis may result in overcorrection of the deformity (resulting in the opposite deformity) if the implant is not removed when the leg is straight. Thus, owners should be educated about monitoring and making an appointment for removal when transphyseal bridging is used. All of these techniques are performed on the "long" or convex side of the deformity (across the medial physis for a valgus deformity).
Screws and cerclage wires have been widely used for growth retardation. Two 4.5 mm cortical screws are placed through stab incisions; one is made in the center of the epiphysis, and one proximal to the physis – or one screw on either side of the physis. They are inserted in routine fashion, but not tightened. The soft tissues between the stab incisions are elevated, and a wire loop is inserted and hooked over the distal screw head. The wire ends are twisted together and tightened at the proximal screw head. The screws are then tightened and the stab incisions are closed with single interrupted sutures.
Transphyseal staples have been used since the late seventies after being adapted from human techniques for deformities in children. Staple placement was compared to screw and wires in a retrospective study published in 1978.12 From this study it was concluded that the overall success rate did not differ, but surgical complications were greater with staple application. The authors reported marked blemishes, wound dehiscence, staple spreading and staple extrusion requiring reinsertion.12 The staples used in that study were vitallium staples originally manufactured for use in humans. The complications described in this study have lead to a negative view of using staples for transphyseal bridging. This technique has been seldom recommended, and is widely not considered as secure as screws and wire. In contrast, transphyseal stapling has met with success at our clinic.13 However, we use custom made staples which makes them more secure than the vitallium staples. Staples can be readily made by any practitioner with materials that are readily available. Surgery time is short using this method, and the cosmetic result is excellent in almost all cases. We experience very few incisional complications; the staples stay in place and are easy to remove.
Steinmann pins of 7/64 inch diameter are used to make staples. A 90 degree angle is bent in the end of the Steinmann pin with heavy pliers at approximately 1.25 inches from the end. An identical bend is placed approximately 1.25 inches from the first, and the pin is cut with sidecutters at approximately 1.25 inches from the second bend. The cut end is sharpened on a bench grinder. This yields a U-shaped staple approximately 1.25 inches on all three sides. The same procedure is repeated on the other end of the pin, and thus two staples are made from one pin. The staples are sterilized individually or in pairs in an autoclave and stored until use. Smaller staples can be made in the same manner with smaller Steinmann pins for distal metacarpal (metatarsal) physis or miniature horses.
When performing this surgery, we use towel clamps to retract skin dorsally. This is an important step as it allows the skin incision, when released, to not be directly over the staple. The skin incision is made centered over the widest part of the physeal area through the skin and subcutaneous tissues. The incision is approximately 4 cm in length. The physis is identified using a needle, the antebrachial carpal or fetlock joint identified via palpation, and the staple is centered over the physis. The staple is inserted into the bone using a hammer. The proximal end is not driven down flush with bone, leaving it slightly "proud". This makes palpation and elevation of the proximal edge of the staple easier during removal. It is possible to take intraoperative radiographs or use fluoroscopy to verify placement of the staple at this point in the surgery, but with experience, this is not necessary. The skin is released and it is closed with absorbable suture (usually Monocryl) continuous horizontal mattress or subcuticular pattern. The leg is bandaged, and the feet are trimmed if necessary before moving to recovery.
Recently, a technique has been developed for transphyseal bridging using a single screw. This initial report describes the use of a lag screw technique to correct tarsal valgus deviation with a screw across the growth plate of the medial malleolus of the tibia.14 Lag screws were initially used, but a position, or neutral, screw technique is currently utilized because excessive tension lag screws result from limb growth.15 This leads to difficult removal or potential screw breakage. The technique has been described.15 The screw is placed via a stab incision across the physis. The screw should be backed out and tightened several times to seat and prevent over tightening to facilitate removal. Placement of screw can be confirmed with intra-operative radiographs or fluoroscopy. A single suture is used to close the skin, although some practitioners leave the incision open.15 Bandaging is routine.
Removal of each of these implants can be done standing in the sedated animal. The occasional foal is too fractious or not well-trained enough to stand for this. I like to sedate the smaller foals and lay them on a padded table. We have owners bandage the legs for 2 weeks after insertion, and for 1-2 weeks after removal. Cosmetic results with any of the above surgical procedures are excellent in most cases. Occasionally, foals that have transphyseal bridging surgeries develop scar tissue over the implant, but the scar tissue usually remodels after removal and is aesthetically acceptable when the foal is mature. A retrospective of foals that had transphyseal stapling over 6 years (2000-2006) showed few incisional complications.13 Incisional complications were encountered in 6 out of 63 total cases (9.5%). All were minor complications that resolved with bandaging and conservative management. Two foals had seromas; these were resolved with drainage and bandaging. One foal's bandages were not maintained by the owner after surgery, and the surgical incisions dehisced. The foal was returned to our clinic, and with bandaging, the wounds healed. The staples remained in place during this time. One foal had severe valgus deformities, and when bandaging was discontinued by the owner, the distal radii rubbed together and caused some dehiscence of the surgical sites. This also resolved with bandaging. One foal had drainage at one of the surgery sites at the time of staple removal. The staples were removed, and the infected side was left partially open. One foal had some scar tissue at the previous surgery site noted during a recheck a month and half after staple removal.
FLEXURAL LIMB DEFORMITIES
A flexural limb deformity is a deviation of a limb in the sagittal plane. Congenital deformities are present at birth; acquired deformities occur later in life. These deformities are usually manifested in hyperextension or hyperflexion of the metacarpophalangeal or distal interphalangeal joints.16 Hyperflexion also occurs, but less frequently, in the carpus. Hyperextension of the limb is often called laxity. Congenital hyperflexion is usually incorrectly termed "contracted tendons". More correct terminology for these conditions is flexural deformity of the metacarpophalangeal joint or distal interphalangeal joint. However, the tendons are not actually contracted, but are short relative to the skeletal structure.16 Most clients and practitioners call acquired hyperflexion of fetlock area 'knuckling over' and deformity at coffin joint a 'club foot'.
FLD: CONGENITAL DEFORMITIES
The severity of congenital FLD can span from mild flexion of a joint to extreme flexion of more than one joint that prevents the foal from standing. The reason for occurrence of a congenital FLD is usually unknown. Anecdotally, it has been noted that mares with a higher body condition score are more likely to give birth to a foal with a congenital FLD. Other causes that have been implicated include intrauterine positioning or crowding, teratogens, congenital hypothyroidism, and influenza.16 Some of the purported causes lack evidence supporting them as an etiologic agent, and it is quite possible that many cases have multifactorial origins.
CONGENITAL FLD: DIAGNOSIS
Congenital FLD are easy to identify after birth, and diagnosis is made on physical exam. Foals should be palpated, and the leg manipulated so that the examiner can determine if the deformity is manually reducible. The ability to manually correct the deformity indicates a good prognosis. Severe cases of hyperflexion (90 degree angle or less of the carpus) that are not correctable during the exam have a poor prognosis and are often humanely euthanized soon after birth.17 Hyperextension cases are most noticeable when the foal is standing, and some degree of flaccidity is very common in newborn foals. However, some cases of hyperextension require treatment.
Rupture of the common digital extensor tendon is seen commonly in conjunction with FLD. It is also seen sometimes in otherwise normal foals. Although this condition requires no treatment other than protection of the skin on the knees and fetlocks if the foal has trouble standing at first, and is not a flexural limb deformity, it bears mention here. Affected foals exhibit swelling over the carpus, and sometimes fling the forelimbs forward while walking, or buckle over while standing or walking. The swelling can be differentiated from swelling within the joint because it is oriented proximal to distal along the tendon sheath, instead of across the carpus as for joint effusion. The tendon ends can often be palpated within the sheath to aid in diagnosis.
CONGENITAL FLD: NON-SURGICAL MANAGEMENT
Most congenital FLD can be successfully treated without surgery. Rarely, carpal contracture or severe distal limb cases may warrant surgical intervention (see below). Foals with FLD of the carpus, metacarpophalangeal or distal interphalangeal joints are painful, especially as we treat them and try to "force" the leg into a more normal conformation. Pain management using non-steroidal antiinflammatories and/or opioids is warranted in almost every case.
Hyperextension is caused by flaccid flexor muscles and is almost always corrected with exercise.16 Stall rest is contraindicated in these foals. Rasping the hooves often greatly improves these cases as well. The foot should be rasped to provide a flat base of support as well as moving the base of support caudally. Rasping the wall back to the widest part of the frog increases weight bearing in that part of the foot. Infrequently, shoes or extensions that project caudally are needed to help further shift weight-bearing. This also lifts the fetlock further from the ground and can prevent abrasions from contact with the ground. Some foals may need their fetlocks bandaged to help protect the skin though one must resist the urge to bandage them snuggly to "support" the fetlock as that is counter-productive.
Intravenous oxytetracycline is a popular treatment for congenital hyperflexion (contracted tendons). The exact mechanism by which oxytetracycline could cause relaxation is not known. Chelation of Ca2+ and subsequent decrease in available calcium for striated muscle contraction has been theorized,18 but there is no evidence for this in the veterinary literature. Indeed, even at high doses, calculations that estimate the amount of chelation based on oxytetracycline pharmacokinetics and the known association constant reveal that only a modest decrease in serum calcium would occur and that there would be no chelate left after 24 hours.19 Another article described oxytetracycline as a neuromuscular blocking agent.20 However, other muscle groups do not appear to be affected when this therapy is employed. The 2 studies that introduced the use of this antibiotic to treat FLD were both simply descriptive case series by one author.21,22 Foals were less than 14 days of age, those that had more severe deformities were not treated (each foal had to be able to place some part of the foot on the ground), and splinting was also used in some cases.22 The author opined that oxytetracycline therapy was not effective for severe deformities. A controlled study showed that metacarpophalangeal and distal interphalangeal joint angles did decrease by an average of 4.25 degrees after treatment with 44 mg/kg of oxytetracycline as compared to control groups (saline or oxytetracycline vehicle).19 The change was short-term though; joints returned to pre-treatment values by 96 hours.19 Any effect that oxytetracycline has in congenital FLD may be due to a temporary decrease in joint angle which makes it easier for the foal to move about and exercise, stretching the muscle-tendon unit. This stretching appears to also happen in some mild cases that spontaneously resolve. The most common amount of oxytetracycline given is 2-3 grams slowly IV, which is approximately the dose described above.
The use of splints and casts are also regularly used to correct FLD. Their use is contraindicated in those foals with hyperextension, as they will only lead to more flaccidity. Most veterinarians prefer to use splints instead of casts. They can be placed on the foal easily, and can be removed for periods of time to allow for examination of the skin for rub sores, and to relieve the foal. Splinting foals with FLD is painful for them, and a schedule that allows for at least 12 hours on, 12 hours off is ideal.23 In more severe cases that necessitate more pressure being placed on the leg, I sometimes shorten the time period with the splints on to as little as 6 or 8 hours. Splints should be applied to the palmar or plantar aspect of the leg in order to be most effective. Splints applied dorsally stop putting tension on the flexor structures when the leg reaches a straight conformation. In addition, the bandaging material used to hold the splint on is pulling against (and possibly damaging) the dorsal structures instead of the flexor tendons. There are many materials that splints can be made from, but PVC is the most common. It can be cut to the appropriate width, and heated to create a bend. An even better material is Orthoplast II (3M, St. Paul, MN). It can be cut, heated and shaped to fit any leg, and then can be reheated and reshaped as needed. When splinting FLD, care should be taken to adequately pad the leg. Combiroll (Butler, Dublin, OH) cotton bandaging material is ideal. Splint sores can occur in severity from small swellings and skin erosions to life-threatening full thickness wounds entering joints, tendon sheaths, and other structures. Bandages should not be too thick though, as the splint will be less effective and they can slip more. Splints tend to shift, and many times they must be reset several times a day. Splints that have shifted should not be left in place, as they can cause sores. The outer wrap that holds splints in place should be durable and we prefer a reusable wrap. Splints held on with duct tape, white tape, or similar tapes are secure, but harder to reset if the need arises. Ace wraps (BD, Franklin Lakes, NJ) are most often used in our clinics. They are economical, can be applied tightly over the bandage and splint, and can be reset and reused many times.
CONGENITAL FLD: SURGICAL MANAGEMENT
Cases with distal limb deformities that do not respond to non-surgical management can be salvaged for breeding or pasture soundness. Transection of the affected tendon(s) (or, occasionally the suspensory ligament as a last resort) is carried out under general anesthesia. This procedure, especially the suspensory desomotomy, will make the patient painful and analgesic therapy should be employed.
Mild carpal contracture that does not improve with exercise and splinting can be treated surgically. It is indicated to evaluate the carpus radiographically to insure that the contracture is not secondary to carpal bone malformation. Tenotomy of the flexor carpi ulnaris and ulnaris lateralis is performed with the foal under general anesthesia and in lateral recumbency. An incision is made 2.5-4 cm above the accessory carpal bone near the caudal aspect of the leg in the depression between the two tendons. A hemostat is used to elevate each tendon out of the incision, where they are transected with a scalpel. Alternatively, a bistoury can be inserted into the incision and used to transect the tendons. Identification of the tendons is made easier if tension is placed on the leg during the procedure. Skin sutures using absorbable suture are placed in the incision, and the leg is bandaged. A splint can be used post-operatively to help extend the leg if necessary.
FLD: ACQUIRED DEFORMITIES
As with the previous deformities discussed here, acquired FLD are probably multifactorial and the complete etiopathogenesis is unknown at this time. Most published factors are speculative, but the theories that have the widest acceptance are mismatch in bone and soft tissue growth, and pain causing contraction of the muscle-tendon unit.23 The bone growth hypothesis is plausible to some degree, because the onset of these FLD are commonly seen at a predictable age.16 The relatively inelastic inferior and superior check ligaments may contribute to the deep and superficial digital flexor muscle-tendon units' inability to elongate during these growth spurts. Rapid growth may also contribute to pain. FLD of the distal interphalangeal (DIP) joint, or club foot, is usually seen between 1-6 months of age.23 Metacarpophalangeal (MCP) joint FLD, or knuckling over at the fetlock, usually occurs between 10-18 months.23 Many times, acquired FLD are reported by the owner to have an acute onset (24-48 hours). Acquired FLD can develop over time in horses with decreased weight-bearing due to painful conditions such as physitis, arthritis, or a fracture that is being treated conservatively.
ACQUIRED FLD: DIAGNOSIS
Diagnosis is based on physical exam findings. DIP joint deformities have a "boxy" or club foot, characterized by an upright dorsal hoof wall angle and short toe. Classification of DIP deformities has been described, in which stage I deformities have a dorsal hoof wall angle of less than 90 degrees, and stage II deformities' dorsal hoof wall is greater than 90 degrees or beyond vertical.16 Horses with acquired FLD of the MCP display straight or upright conformation of the fetlock; some cases pop or knuckle over when fatigued. In the more severe cases, knuckling of the fetlock is seen at rest. The limb can be palpated and manipulated while weight bearing and non-weight bearing to help determine which structures are involved. Prognosis is usually poorer with increased duration and severity of MCP deformity. The great majority of DIP deformities have a good to excellent prognosis.
ACQUIRED FLD: NON-SURGICAL MANAGEMENT
Non surgical management of FLD is limited due to a lack of efficacy. Various splints have been fashioned in attempts to correct MCP deformities with little success. Some very mild cases of MCP deformity may respond to a strict diet (to decrease rapid growth and weight gain), controlled exercise (to help stretch the limb, but prevent overly fatiguing the horse, which leads to worsening of knuckling), and physical therapy. Hopping the horse on one leg and passive stretching may or may not be of benefit. Non-steroidal antiinflammatories are useful if conservative management is employed because horses are usually painful. Although counterintuitive, elevation of the heel may actually help settle the fetlock back. This type of shoeing is often combined with superior check ligament desmotomy (see below) for moderate to severe MCP deformities. Toe extensions are sometimes used in DIP deformities, but are really of benefit only if surgery is to be performed and the toe is already worn off. Trimming the heels down in horses with DIP without performing concurrent surgery is contraindicated as it makes them more painful, does not resolve the condition, and over time, can lead to damage or tearing of the laminae.
ACQUIRED FLD: SURGICAL MANAGEMENT
DIP Deformity (club-foot)
Inferior check ligament desmotomy is the preferred surgical treatment for DIP deformity and it has been described.24 The approach can be performed from the lateral or medial side, but we prefer the medial approach. There is always at least a small scar from the skin incision and there is usually some additional soft tissue scarring and proliferation. The medial approach usually makes the surgery site appear more cosmetic after healing. The foal is placed in lateral recumbency. A skin incision of about 5 cm length is made starting at the distal margin of the carpus. It should be made on the approximate cranial border of the deep digital flexor tendon (DDFT).24 An incision is then made through the thick, fibrous paratenon. Blunt dissection is used to isolate a plane between the check ligament and the suspensory ligament and then between the check ligament and the DDFT. The inferior check ligament is elevated into the incision using a forceps or scissors, and transected with a scalpel. This is facilitated by flexing the foot to reduce tension on the flexor structures. Before transection, the superficial and deep digital flexor tendons should be identified by palpation or visualization to reduce the chance of cutting the DDFT. The large metacarpal vessels both medially and laterally (when elevating the check ligament) should be avoided. Care should also be taken to transect the entire check ligament; leaving a substantial portion of it could result in failure to correct the deformity. The size of the inferior check ligament is sometimes surprising; it is usually at least the size of the DDFT. The paratenon is closed in a continuous pattern with absorbable suture, and skin sutures are placed. The foot should always be trimmed after surgery so that the heels are lowered. The owner should be instructed to carry out controlled exercise and frequent hoof care to keep the heels lowered. In some instances excessive toe wear prior to surgery may dictate the need for shoeing with toe plates or augmenting the toe with hoof composites in order to rebuild the toe to allow proper weight bearing. This management will help allow the muscle-tendon unit to stretch after release of the inferior check ligament. Bandaging should be continued for at least 2 weeks.
In severe cases of DIP deformity or those that do not respond to an inferior check ligament desmotomy, a deep digital flexor tenotomy can be performed. This must be considered a "salvage" procedure and may well preclude an athletic career. The surgery can be performed mid-cannon, or in the pastern region. The deep digital flexor tendon is isolated and elevated into the incision, and transected as described for the check ligament. Skin closure and bandaging are routine.
MCP Deformity (knuckling over at fetlock)
A superior check ligament desmotomy can be used to treat horses with fetlock FLD. The surgery can be performed using an open technique or by tenoscopic access to the carpal sheath.24,25 The tenoscopic approach uses a camera portal approximately 2 cm proximal to the distal radial physis between the tendons of the ulnaris lateralis and the lateral digital extensor muscle.25 After the ligament is identified, it is transected with a meniscectomy knife, Beaver blade, or arthroscopic hook knife. The camera and instrument portals are closed with single sutures. The open approach is performed from the medial aspect of the limb. A 10 cm incision is made just dorsal to the cephalic vein from the level of the distal chestnut proximally.24 The incision is continued through fascia and the carpal sheath. The proximal check ligament is identified and cut. The muscular radial head of the deep digital flexor can be seen behind the check ligament after the desmotomy. An artery courses through the proximal margin of the check ligament and is often accidently severed during the procedure; it should be avoided as it decreases visualization during both approaches. The sheath and skin are closed with absorbable suture. Bandaging is routine in both cases as required by the respective incisions. It may be prudent to perform both an inferior and superior check ligament desmotomy in those cases that appear to have involvement of both superficial and deep flexor tendons. For refractory cases whose owners desire breeding salvage, superficial digital flexor tenotomy or suspensory desmotomy can be performed, but should be considered a last resort.
Veterinarians in equine practice should be able to diagnose, treat, and refer horses with angular and flexural limb deformities. Unique characteristics of each type of deformity dictate the treatment that will be applied to these cases. Many cases can be corrected with appropriate conservative management or surgical treatment. Exact cause is often unknown, and ongoing research is needed to help answer questions about etiopathogenesis and the efficacy of some popular treatments.
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