Growth acceleration involves a trauma at approximately 2 cm proximal to the physis at the shorter side of the bone (in a valgus deformity the medial side). No implants are inserted and therefore no implants have to be removed once the deformity has corrected.
Negative feedback mechanism
The trauma to afferent blood vessels to this side of the physis initiates a negative feedback mechanism within the physis coupled by the Ihh/PTHrP/PTHR (indian hedge hog parathyroid hormone related protein/parathyroid hormone receptor) cascade, resulting in accelerated cell division within the physis and associated faster growth of this side of the bone.
Overview of techniques
The trauma to initiate growth acceleration can be induced through different techniques such as:
Inverted “T” incision (described technique)
(Needle trauma /not shown in the figure)
(Shockwave therapy / not shown in the figure)
Note: only technique 1 and 3 will be described at the distal McIII. The techniques themselves do not change if they are applied in any of the different anatomic locations where angular limb deformities can occur, only the local anatomical considerations do.
An approximately 1.5 cm long incision is performed parallel to the long axis of the bone starting at a level 2 cm proximal to the level of the physis in proximal direction. The incision is carried down to the underlying bone.
Note the vertical incision should end below the level of the distal end of the vestigial metacarpal/metatarsal bone.
Preparing the horizontal incision
At the distal end of the vertical incision a curved hemostat is inserted perpendicular between the subcutaneous tissues and the periosteum in dorsal direction to separate the tissues from the periosteum.
The hemostat is elevated at the handle and spread to facilitate insertion of the No. 12 scalpel perpendicular to the vertical incision.
By pressing the tip of the scalpel across the periosteum and pulling the scalpel handle backwards the periosteum is transected. The horizontal transection should connect to the distal end of the vertical incision.
Note: it is prudent to protect the caudal skin with the periosteal elevator in case the scalpel tip gets temporarily caught in the bone surface and the increased traction momentarily releases the scalpel tip resulting in an accidental horizontal skin incision because the accelerated movement cannot be counteracted in time.
The same procedure is performed at the palmar/plantar aspect of the vertical incision resulting in an inverted “T”-incision of the periosteum. The horizontal incision extends approximately around ¼ to 1/3 of the circumference of McIII/MtIII centered on the midline. Care must be taken to avoid opening of the palmar pouch of the metacarpo-/metatarsophalangeal joint capsule.
Note: in the “+” incision the cuts are about half the size of the incisions described above and the horizontal incision is centered in the center of the vertical incision.
Creating a periosteal flap
A periosteal elevator is inserted under the periosteum staring at the “T” intersection in proximal direction at a 45 degree angle and subsequently elevated separating the periosteum from the underlying bone. The periosteal flap is subsequently carefully placed back onto the bone surface. The other flap is elevated using identical technique.
The separated part of the periosteum is subsequently repositioned onto the underlying bone resulting in a gap between the flaps of several mm.
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. The effect of periosteal stripping lasts approximately two months. If needed, the procedure can be repeated.
Note: overcorrection of the deformity is not an issue.
Transcutaneous horizontal incision
The skin at the surgical site is rolled horizontally backwards with the help of the thumb.
Note: this should be done at a level distal from the distal end of the vestigial metacarpal/metatarsal bone on that side.
The tip of the No. 12 scalpel blade is pressed down to the bone creating a puncture of the skin. The skin is now rolled back in cranial direction as much as possible. At the same time the scalpel handle is pulled forward at the same speed creating a horizontal periosteal transection through a small puncture wound. With this technique the periosteum is not elevated and ideally no sutures are needed.
The surgical site is covered with a pressure bandage for 4 days. The bandage is changed and left in place for a week. No additional bandaging is needed.
The foal is kept in a restricted area with limited exercise until the majority of the deformity is corrected.
Left: 1-month old Arabian foal with a marked bilateral varus deformity at the distal McIII. Right: dorsoplamar radiographic view of the left metacarpophalangeal region showing a 7°varus deformity and new bone proliferation at the physis.
Left: appearance of the limbs 75 days postoperatively showing good correction of the deformities. Right: 75-day follow up dorsoplamar radiographic view of the left metacarpophalangeal region after transcutaneous periosteal stripping at the distal medial aspect of McIII in both limbs. Some slight periosteal reaction can be seen medially at the level of the physis, but smaller than at the time of surgery. Good correction was achieved.