Authors of section

Authors

Jörg Auer, Larry Bramlage, Patricia Hogan, Alan Ruggles, Jeffrey Watkins

Executive Editor

Jörg Auer

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Growth retardation

1. Principles

Mechanism of growth retardation

Growth retardation involves the insertion of implants across the physis of the longer side of the bone (in a valgus deformity the lateral side) and the maintenance of these implants until the shorter side has caught up and the deformity is corrected. At this point in time the implants are removed.

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Overview of techniques

Growth retardation can be accomplished using one of four techniques:

  1. Staples
  2. Screws and cerclage wire
  3. Screws and small plate
  4. Transphyseal screw

Note: techniques 2 and 3 are basically the same and only the bridging implant is different. Using the plate prevents the complication of wire breakage and premature loss of the growth retardation effect.

Note: the different techniques of growth retardation will be explained at the distal McIII only. The technique itself does not change if it is applied in any of the different anatomic locations where angular limb deformities can occur, only the local anatomical considerations do.

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2. Anatomical landmarks

When using staples

The center of the supracondylar fossa can be identified by drawing a line from the top of the dorsal condyle articular surface to the proximal palmar eminence of the proximal phalanx.
This is less important in cases where a staple is inserted as this device is centered over the physis, which is an easy landmark to identify.

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When using screws and wires

The center of the supracondylar fossa can be identified by drawing a line from the top of the dorsal condyle articular surface to the proximal palmar eminence of the proximal phalanx. The screw location is half way along this line.

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3. Positioning

This procedure is performed with the patient placed in lateral recumbency.

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4. Skin incision

Stab incisions

A small skin stab incision is performed directly over the location where each screw is inserted. If a staple is inserted the skin incision is centered over the physis and adjusted in length according to the length of the staple.
All incisions are carried down to the underlying bone.

When using screws and wires

The stab incision for the distal screw is placed over the center of the lateral supracondylar fossa (in a varus deformity).
The stab incision for the proximal screw is placed approximately 2 cm proximal to the growth plate.

Note: the level of the growth plate is easily recognized as the widest diameter of the distal McIII/MtIII (see insert drawing).

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When using screws and plate

The stab incision for the distal screw is placed over the center of the lateral supracondylar fossa.
The plate is held with the distal most screw hole over the distal stab incision and the stab incision for the proximal screw is placed at the level of the proximal most screw hole in the plate.

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When using transphyseal screws

A 1 cm skin incision is made 3 cm proximal to the growth plate on the lateral side of the bone (in a varus deformity).

Note: The level of the growth plate is easily recognized as the widest diameter of the distal third metacarpal/metatarsal bone (see insert drawing).

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5. Staples

Placing the staples

The staple is secured in the applicator.
The limbs of the staple are positioned equidistant from the level of the growth plate.

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The limbs are driven into the bone with the help of a mallet applied to the top end of the applicator.

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Closure

The subcutaneous tissues and the skin are closed in two layers using simple continuous suture patterns. The skin sutures should be placed intradermally for a better cosmetic appearance.

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6. Screw and cerclage wire

Screw insertion

A 26 mm 4.5 mm cortex screw is inserted using routine technique parallel to the growth plate through each stab incision. The screw is not tightened yet and the screw head should protrude slightly over the skin surface.

Note: the thread hole is a blind hole so it should be drilled to a depth of approximately 30 mm.

Note: the procedure can also be performed with 3.5 mm cortex screws. However these screws are more difficult to remove, especially with hex design of the propulsion device in the screw head, because of potential failure.

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Cerclage application

A 15 mm long 1.25 mm diameter cerclage wire is bent in the center and the two limbs crossed over each other. The loop is introduced through the proximal incision and carefully pushed distally.
Another option is to introduce a curved hemostat through the distal incision, grab the wire loop and pull it distally.

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The loop is positioned over the protruding screw head located in the distal incision.

The wires are crossed over the proximal screw head, such that a figure-8 configuration is achieved.

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The two wire limbs are crossed above the proximal screw head and with flat-nosed pliers twisted evenly around each other until tight.

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The wire ends are cut 1 cm away from the proximal screw head and the remaining end pressed down onto the bone. The two screws are subsequently fully tightened. This provides additional compression across the growth plate by the wire loops moving along the screw heads proximally and distally, respectively.

Each stab incision is closed with one or two interrupted sutures.

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Postoperative radiographs are taken to confirm proper seating of the implants and to provide base data for evaluation of the progress on correction.

Left: preoperative appearance of the hind legs without implants.

Right: radiographic appearance of the left MtIII

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Left: appearance of the limb following correction of the deformity at 6 weeks postoperativley.

Right: 6-week follow up radiograph with implants still in place showing good correction of the deformity. The implants were subsequently removed.

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7. Screws and plate

Plate selection and preparation

Usually, a 6-7-hole 2 mm small animal cuttable plate is used for this technique. This can be an old used plate and it is advisable to enlarge the most distal and most proximal plate holes with a 3.5 mm metal drill bit before sterilization of the plate.
These plates can be bent by hand immediately before introduction.

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Plate insertion

A curved hemostatic forceps is introduced through the proximal stab incision and pushed distally. The proximal plate end is grabbed and the hemostatic forceps is withdrawn through the proximal stab incision introducing the plate into its location.

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Securing the plate

A 26 mm 3.5 mm cortex screw is inserted using routine technique parallel to the growth plate through the distal most plate hole. The screw is not tightened completely.

Note: The thread hole is a blind hole so it should be drilled to a depth of approximately 30 mm.

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The plate is pulled proximally and the proximal screw inserted through the proximal most plate hole applying the identical technique as for the distal screw. Both screws are tightened.
Each stab incision is closed with one or two interrupted sutures.

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Radiographs

Postoperative radiographs are taken to confirm proper seating of the implants and to provide base data for evaluation of the progress on correction.

The image shows:

Left: preoperative radiograph without implants.
Right: 2-months follow up radiograph with implants still in place showing good correction of the deformity. The implants were subsequently removed

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8. Transphyseal screw

Needle placement

A hypodermic needle is inserted parallel to the metacarpo-/metatarsophalangeal joint space at the distal most aspect of McIII/MtIII. Care is taken not to injure the articular cartilage.

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Placement of the transphyseal screw

The 3.2 mm thread hole for the transphyseal 4.5 mm screw is drilled in distomedial direction across the physis into the epiphysis. It should cross the growth plate at approximately one quarter of its width.

Note: drilling should be started in parallel direction to the growth plate (1) and while drilling the drill should gradually be rotated proximally until it comes to lie flat on the bone (2).

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Periodically, the drill bit should be withdrawn, cleaned and placed in front of the limb to gauge the penetration depth needed to engage the physis but avoid penetration of the joint.
The hypodermic needle helps to identify the level of the joint.

Another option involves taking of a dorsopalmar/dorsoplantar intraoperative radiographic view with the drill bit in place. If needed, the drill bit can be further advanced until it reaches a level approximately 5-8 mm short of the radiographic articular joint space.

Note: the radiographic articular joint space consists of 2 articular cartilage layers and the microscopic joint space.

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The depth of the hole is determined, the threads are cut and a 4.5 mm cortex screw 4 mm shorter than the depth of the hole is inserted and tightened. Tightening should be stopped when the side of the screw head makes contact with the bone. This leaves the screw head distant from the onset of the screw hole.

Note: the countersink is not used to facilitate recognition of the screw head for screw removal and to avoid making a bigger defect on the bone surface, which may develop a periosteal reaction that may be seen at a pre-purchase examination.

Tightening the screw until the screw head meets the onset of the screw hole leads to bending of the screw, which provides a risk for screw breakage during its removal.

The use of 3.5 mm screws bears the risk of screw breakage, especially if the screw is bent.

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The stab incision is closed with one or two interrupted sutures.
Postoperative radiographs are best taken while the foal is still under anesthesia to document correct placement of the implants. Any potential adjustment to the implants such as redirection can then still be accomplished without re-anesthetizing the foal.

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Treatment of a severe bilateral metacarpophalangeal varus deformity with the help of transphyseal screws.

The images show: preoperative, slightly oblique radiographic views of deformed areas.

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Immediate postoperative radiographs following insertion of 4 mm cancellous screw across each physis.

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4-months follow up dorsopalmar radiographic views of the same foal showing good correction of the deformities. The screws were subsequently removed.

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9. Aftercare

The limb is covered with a tight bandage up to the carpus/tarsus. The bandage is changed every 4 days.
The foal is kept with the mare in a box stall for two weeks. Ideally, a continuous intradermal suture pattern using a resorbable material is used. In this case, no sutures have to be removed. Otherwise, when regular skin sutures or staples are used, these devices are removed at 10 days postoperatively.
A light bandage is reapplied and left in place for 4 more days. After that the foal can go on pasture.

additional material

Correction of the angular limb deformity is observed visually and once the limb is straight follow up radiographs should be taken.
If the radiographs confirm optimal correction...

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...the implants should be removed immediately.

See the additional material on staple and other implant removal.

Note: in an animal with a bilateral deformity it may be necessary to remove the implants in two steps. If one limb is straight the implants should be removed. It is not recommended to wait until the second limb is also straight because at that time the first limb may already be overcorrected. It is strongly advised to do the best for the foal and not to take compromises.

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