Proximal phalanx: fracture in Horses (Equis) | Vetlexicon
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Proximal phalanx: fracture

ISSN 2398-2977


Synonym(s): Split pastern

Introduction

Presenting signs

  • Acute onset of lameness in fore- or hindlimb.

Acute presentation

  • Lameness.
  • Swelling of pastern or fetlock regions.
  • Instability in the pastern region.

Geographic incidence

  • More common in regions of the world where there is racing.

Age predisposition

  • Foals or weanlings - palmar or plantar process fracture.
  • Yearlings - medial collateral ligament avulsion fracture.
  • Foals - proximal physeal fracture.

Breed/Species predisposition

  • Standardbreds Standardbred - proximal palmar or plantar chip fractures.
  • Thoroughbred Thoroughbred - sagittal fractures; distal frontal fractures.

Cost considerations

  • Costs of diagnosis and treatment can be substantial.
  • Costs of loss of use.
  • Costs of loss of horse.

Special risks

  • Recovery from anesthesia is crucial point in protecting any repair.

Pathogenesis

Etiology

  • Performance horses → repetitive concussive forces → fatigue fracture.
  • Stepped on by dam.
  • Pasture accident.

Predisposing factors

General

  • High speed galloping exercise, such as racing and eventing.

Specific

  • Direct trauma in foals.

Pathophysiology

Chip fractures of the proximal dorsal rim

  • Most common type of proximal phalangeal fracture.
    •    Hyperextension injury leading to compression of the dorsal proximal portion of P1 against the third metacarpal bone. Repeated trauma in this area leads to changes in the bone prior to fragmentation.
  • Racing and other performance horses, especially Thoroughbreds.
  • Intra-articular fracture, more commonly of the forelimb metacarpophalangeal joint.
  • Most common location is proximal medial eminence of the proximal phalanx; less commonly lateral aspect or both positions.
  • Require differentiation from rounded fragments seen in this area, particularly in young Warmblood horses which are part of developmental orthopedic disease and a separate entity. 

Axial osteochondral fragments of the proximal palmar/plantar aspect of the proximal phalanx

  • Found commonly in young Standardbreds and Warmbloods, and occasionally in other breeds Proximal phalanx: fracture.
  • Disputed etiology but they are thought to be avulsion fractures occurring during skeletal development.
  • Commonly identified in horses not started exercise. 
  • There may be no lameness, mild lameness or lameness only at high speed. Response to flexion and joint effusion is variable.
  • Most commonly found in plantar medial aspect of hindlimb fetlock joints.
  • Essential to assess their clinical significance as many are not causing problems. Intra-articualr analgesia Anesthesia: intra-articular is important to localize any lameness.
  • If significant, removal by arthroscopic surgery Joint: arthroscopy - overview is very effective.

Major fractures

  • Sagittal and sagittal-spiral fractures:
    • Mid-sagittal groove of proximal joint surface propagating distally in the sagittal or axial plane. Many propagate incompletely toward the lateral side of P1, at varying distances distally, some fracture completely through the lateral cortex, and others extend into the pastern joint. Propagation distally may be sagittal or spiral.
    • Usually minimal pre-existing changes in the fetlock cartilage and subchondral bone which improves the chances of a return to soundness after surgery. They are excellent cases for lag screw fixation. .
    • Compressive and torsional forces transmitted from the sagittal ridge of the cannon bone to the groove.
    • Forelimb > hindlimb.
    • Most commonly a racing injury, but occasionally occur at pasture.
  • Smaller proximal factures of P1 include:
    • Non-articular fractures of P1 in foals usually caused by the dam. Usually Salter-Harris type 2 fractures.
    • Palmar or plantar wing fractures (young horses).
    • Medial collateral ligament avulsion fractures in young horses such as yearlings; often derived from accidents at grass.
    • Incomplete short sagittal fractures about 1 cm long; in hindlimb subjected to more stress on rising from ground → displacement more likely.
    • Incomplete dorsal plane fractures occur usually in the proximal aspect of P1 in mainly the hindlimb of racing Thoroughbreds, probably due to additional hyperextension of the fetlock joint in these limbs. Often the fracture involves more of the dorsolateral (USA) or dorsomedial (UK) portions of P1 rather than being perfectly symmetrical. 
  • Complete dorsal or frontal plane fractures can occur in racehorses and pleasure horses.
  • Comminuted fractures:
    • Severely comminuted fractures: release of substantial internal energy → multiple fragmentation of the phalanx.
    • Variable conformation from simple three-piece fractures to 'bag of ice' injury.

Diagnosis

Presenting problems

  • Forelimb lameness.
  • Hindlimb lameness.

Client history

  • Sudden onset of lameness.

Clinical signs

  • See:
  • Chip fractures:
    • Usually occurs during fast exercise with clinical signs most evident in the few days thereafter.
    • Synovial effusion in fetlock.
    • Varying degrees of lameness, but usually mild to moderate.
    • Local dorsal soft tissue swelling.
    • Pain on joint flexion.
    • May be no clinical signs and lesions is incidental on radiographs.
    • Clinical signs decrease with rest but become apparent again with exercise.
    • Uni- and bilateral cases are recorded.
  • Sagittal or sagittal-spiral fractures:
    • Pain on flexion.
    • Pain on digital palpation.
    • Lameness improves on nerve block at abaxial sesamoid level, blocks at low palmar ring block.
  • Palmar or plantar wing fractures: may have less dramatic clinical signs compared to some other P1 fractures.
  • Medial collateral ligament avulsion fractures:
    • Severe lameness.
    • Marked joint effusion.
    • Pain on direct palpation.
    • Fractures may not be recognized in foals and weanlings and heal by fibrous union with limited clinical signs. They are then sometimes detected on screening radiographs prior to sale as a yearling or adult.
  • Incomplete dorsal frontal fractures:
    • Clinical signs are dependent on the degree of fracture displacement.
    • Mild to moderate lameness in non-displaced fractures.
    • May be difficult to localize.
  • Complete dorsal frontal fractures:
    • These are larger and more displaced and therefore more painful and lame.
    • May present similarly to the complete sagittal fractures.
  • Incomplete short sagittal fractures extend 1-2 cm from the sagittal groove distally:
    • Usually pain on flexion.
      •    Sensitive to direct palpation over the proximal dorsal aspect of P1.
      •    Lameness is often improved by an abaxial sesamoid local analgesia or a low palmar ring block Forelimb: perineural analgesia Hindlimb: perineural analgesia but if there is a suspicion of a fracture these should not be undertaken prior to imaging of the region.
  • Comminuted fractures:
    • Non-weight bearing lameness.
    • Pastern instability on manipulation.

Diagnostic investigation

Radiography

  • Radiography of the forelimb Forelimb: radiography / hindlimb Hindlimb: radiography.
  • Take at least four views: LM, DP and two oblique (compare with normal Proximal phalanx: normal - LM radiographProximal phalanx: normal - DPa radiograph) as a minimum with additional views if warranted by specific variations in type of fracture.
  • Chip fractures:
    • May be incidental finding.
    • Osteochondral fragments.
  • Sagittal:
    • Dorsopalmar view - for fracture line Proximal phalanx: fracture 04 - DPa radiographMiddle phalanx: fracture 01 - radiograph.
    • Fracture extends distally toward proximal interphalangeal joint or deviate obliquely at the mid-diaphysis towards the lateral cortex Proximal phalanx: fracture 05 - DPa radiograph.
  • Palmar or plantar wing fractures Proximal phalanx: fracture 02 - DLPaMO radiograph: seen most clearly on appropriate oblique views.
  • Medial collateral ligament avulsion fractures:
    • Triangular fragment involving proximal joint surface of P1.
    • Best seen on dorsopalmar or dorsoplantar views for fractures involving the dorsal bundle of collateral ligament fibers. Oblique views are best at highlighting the palmar/plantar bundle associated fractures.
  • Incomplete dorsal frontal fractures:
    • Dorsal proximal aspect of phalanx in a frontal plane and slightly more lateral in the USA and more medial in the UK.
    • Best shown on lateral-medial and dorsomedial-palmarolateral (USA) or dorsolateral-palmaromedial (UK) oblique views.
  • Complete dorsal frontal fracture: best shown on the lateral and oblique views.
  • Short sagittal fractures:
    • Well-exposed dorsopalmar view (slightly dorsal to proximal) and a slightly underexposed lateral view are helpful in identifying the fracture line and associated dorsal callus formation just below the fetlock joint, respectively. 
    • Only 1-2 cm long, stable Proximal phalanx: fracture 13 - DP radiograph.
    • Radiographs taken within 1-2 days of the fracture occurring may be inconclusive. Repeat views at 10-14 days may be required.
  • Comminuted fractures:
    • Three piece fracture - 'bag of ice' Proximal phalanx: fracture 07 - comminuted - DPa radiograph.
    • Look for intact proximo-distal strut fragment Proximal phalanx: fracture 06 - comminuted - LM radiographspanning the length of P1.
    • Take full radiographic series to support surgical planning.
    • Computed tomography (CT) Computed tomography, magnetic resonance imaging (MRI) Magnetic resonance imaging and 3D fluoroscopy are very helpful in planning any surgical repair.

Arthroscopy

Scintigraphy

  • Scintigraphy Bone: scintigraphy is useful for initial localization of non-displaced and incomplete fractures with limited localizing signs such as incomplete dorsal frontal and short incomplete sagittal.

CT

  • CT Computed tomography is very useful in complicated types of fractures particularly when comminuted in the surgical treatment planning.

Confirmation of diagnosis

Discriminatory diagnostic features

  • History and clinical signs.
  • Localization of the site of pain by diagnostic local or intra-articular analgesia techniques may be necessary to assess the significance of chip fragments which are present without localizing signs.

Definitive diagnostic features

Differential diagnosis

Treatment

Standard treatment

Overview

Use a spray rather than syringe to deliver antibiotic to fracture site.

Chip fractures

  • Medical:
    • Topical therapy, intra-articular medications, rest, reduced training load.
    • Small non-displaced fragments do not heal but they can develop a fibrous union which helps stabilize them and decrease clinical signs.
  • Surgical:
    • Arthroscopy Joint: arthroscopy - overview.
    • Remove fragment if causing clinical signs.
    • This is the treatment of choice, but some owners/trainers delay the surgery and treat the case conservatively whilst attempting to continue training and/or racing.
    • Post-operative bandaging is maintained for 2 weeks, changed every 2-3 days.

Palmar or plantar wing fractures

  • Screw fixation only in acute cases:
    • Larger fragments may allow the use of 4.5 mm screws, but 2 x 3.5 mm screws are usually required. Screws must be directed slightly distally to avoid the sagittal groove.
    • Non-displaced fractures can be repaired via stab incisions and radiographic control
    • Displaced fractures require an arthrotomy.
    • Recovered in a bandage for the fore limbs but usually a cast in the hindlimbs.
    • Box rest for 4 months before return to exercise.
  • Many cases occur as foals or weanlings and may heal conservatively.
  • Some cases are developmental in origin and heal by fibrous union: these types of cases are unlikely to benefit from internal fixation.

Medial collateral ligament avulsion fractures

  • Usually require open reduction as arthroscopic manipulation is difficult.
  • Locate the correct position for the implant to be placed in fragment with a needle and intra-operative imaging.
  • With an open reduction, make a 3-4 cm incision over the medial aspect of the proximal phalanx.
  • Deepen incision into fracture line.
  • Debride and reduce at the joint surface.
  • Trim any avulsed cartilage so there is no risk of a loose flap developing in the joint.
  • Maintain reduction with forceps.
  • Insert 1-2 x 3.5 mm lag screws or for small rotationally unstable fragments, use a single screw and a 2 mm pin. Exact screw placement is essential to avoid interference with the distal metacarpal/metatarsal condyle.
  • Close wound.
  • Cast or use rigid boot for anesthetic recovery.
  • Box/stall rest for 3 months or until fracture is healed.
  • Total of 6 months rest before beginning exercise.

Dorsal frontal fractures

  • For non-displaced short incomplete fractures, make stab incisions guided by radiography.
  • Place 1-2 x 3.5 mm lag screws via the incisions, to the side of the midline away from the sagittal groove. More complex fractures will require additional screws; larger fractures will require more and larger screws.
  • For displaced fractures:
    • Acute injuries should be assessed and reduced, preferably with arthroscopic guidance Joint: arthroscopy - overview, but chronic injuries may require an arthrotomy for debridement and reduction.
    • Internal fixation using the same principles as in the repair of sagittal fractures.
    • Recovery in a light bandage with fracture healing in four months; screws do not require removal in most cases.
    • More complex dorsal fractures can be repaired by lag screw fixation if the fracture can be accurately defined beforehand. CT and arthroscopy can be useful in guiding the repair.

Short sagittal fractures

  • Many of these fractures are inherently stable and are unlikely to displace in the box/stall. Rest, with stall confinement for 3-4 months is often adequate for healing. Persistence of the radiolucency is common.
  • There are advantages to placing screws across the fracture line to compress the fracture and enhance bone healing, and also to decrease fracture propagation at the time of return to work. Comparison between conservative and surgical treatments have, as yet, not been published.

Long, non-displaced sagittal fractures

Surgically prepare limb, place skin staples at incision site and radiograph before anesthesia to save intra-operative time; alternatively use intra-operative needles and radiography to locate fracture.

  • Repaired using standard lag screw technique Bone: slab fracture repair - lag screw.
  • Stab incisions: use single 1 cm incision down to bone, oblique and parallel to the extensor branch of the suspensory ligament.

Maintain location of the holes by leaving a pin in place when changing guides and drills.

  • 4.5 mm lag screws: proximal screw 5-8 mm distal from the distal extent of the sagittal groove and in the thickest dorsopalmar part of the bone (on the dorsal margin of the extensor process of the suspensory ligament); second screw inserted less than 2 cm distal to the first screw, palmar or plantar to the extensor branch. 5.5 mm screws can also be used either initially or if the 4.5 mm screws strip their thread.
  • The number of screws required depends on the length of the fracture. It is important not to place any screws distal to the visible fracture line.
  • Check position of screws radiographically Middle phalanx: fracture 02 - repair - radiographin two planes.
  • Stab incisions are closed routinely. 
  • Recover from general anesthesia in a Robert Jones bandage for the forelimb and a cast or boot for the hindlimb. The cast is removed immediately after recovery and replaced by a Robert Jones bandage. The horse is kept in the bandage for 2-3 weeks with changes as necessary. A light bandage is kept in place for a further 1-2 weeks.
  • Keep horse in a stall/box for 4 weeks followed by 4 weeks of box rest and hand walking. Then 4 weeks of small pen turnout. Post-operative radiographs at 12 weeks. If evidence of good healing start 12 weeks of graduated exercise. If the fracture line is still present at 12 weeks, then an additional 6 weeks of pen rest is indicated. A faint radiolucent line at the joint margin may persist indefinitely in some horses and is not a reason to delay a graduated exercise program.
    •    Screws rarely have to be removed.

Standing repair

Displaced sagittal and oblique fractures

  • Require anatomical reduction and fixation with lag screws. Acute fractures can be reduced under arthroscopic control. If this is not possible, then open reduction is required. A 2 cm dorsal incision over the fracture line at the proximal articular surface is usually adequate. Extend along fracture line, if necessary in older fractures, by splitting the extensor tendon.
  • Use curettes to separate fracture fragments and debride hematoma and other debris.
  • Use large, pointed reduction forceps to maintain fracture while lag screws are inserted through separate stab incisions.
  • Close stab incisions with simple interrupted non-absorbable sutures or staples.
  • Place fiberglass cast, boot or splinted bandage for recovery.
  • Post-operative care is similar to non-displaced fractures.

Comminuted fractures

  • Surgical reconstruction if: fracture is closed, and there is an intact proximal-dorsal strut of bone; and if transfixation techniques are combined with internal fixation and at least 80% of cortices can be realigned.
  • Not recommended if fracture is open.
  • Lateral recumbency with most comminuted surface uppermost.
  • Open reduction, exposed proximal joint surface to ensure accurate reconstruction.
  • Make a curvilinear incision from 2 cm distal to the end of the splint bone over dorsal midline of the fetlock and proximal phalanx then toward the proximal lateral margin of the middle phalanx.
  • Incise through subcutaneous tissues to extensor tendon and joint capsule, retract skin and subcutaneous tissues together.

H-shaped or 'barn door' incisions repair less successfully.

  • Expose the palmar pouch of the fetlock by transecting the collateral sesamoidean ligament.
  • Continue incision around the condyle at the joint, severing the collateral ligament and joint capsule to the proximal dorsal margin of the fracture.
  • Split extensor tendon distally by inserting scalpel through it into the fracture line.
  • Elevate the edges of the fragments (leverage with a Hohmann retractor may assist dissection.)
  • Luxate the fetlock to expose the joint surface.
  • Debride fracture ends and remove hematoma.
  • Repair deepest and most proximal fragment first.
  • Use 4.5 mm screws for large fragments and 3.5 mm screws for smaller fragments. 5.5 mm screws may split fragments.
  • Secure wing fragments with lag screws 1 cm distal to joint surface.
  • Repair sagittal fractures with lateral to medial screws, avoiding the sagittal groove.
  • Place most distal screws guided by radiography.

Reduction and fixation should be as accurate as possible to prevent fracture collapse within the cast.

  • Repair collateral ligament with resorbable suture.
  • Appose joint capsule and extensor tendon with interrupted or tension sutures.
  • Cast extending to proximal metacarpus.
  • Minimally invasive techniques can be used to reconstruct mildly displaced 3-to-5-piece fractures, especially if pre-operative CT imaging is available combined with intra-operative fluoroscopy or digital radiography. Arthroscopy is used to verify accuracy of articular realignment.
  • Assisted recovery is essential.
  • Leave cast in place for 6 weeks. In many cases, a change at 10-14 days under GA is required. Further periods of casting may be required in severely damaged cas