Treatment of Angular Limb Deformities in Foals

Presently the approach to the treatment of angular limb deformities (ALD) is changing. While several years ago early recognition and early treatment was the aim, the recent trend goes more toward a selective approach. Immature foals with incomplete ossification of the precursor cartilage, best identified in the carpal and tarsal region are treated as early as possible with splints to facilitate ossification under even axial loads. Foals suffering from metaphyseal asymmetric growth but normal ossification are frequently observed for several months to allow to correct by themselves. In severe cases, meaning foals with deformities of greater than 12°, early treatment is proposed as well. Foals suffering from varus deformities of the metacarpophalangeal/metatarsophalangeal region should be treated before 1 month of age. The reason for this is the early closure of the physis at the approximate age of 3 months and in severe cases the development of an opposing valgus deformity within the proximal phalanx. Treatment techniques include growth acceleration, temporary unilateral growth retardation, and a combination thereof. The positive effect of hemicircumferential periosteal transection and stripping (HCPTS) was recently questioned, but in the mean time the pathway of the corrective mechanisms could be established with the help of molecular biology techniques. As a matter of fact, the experiments conducted to disprove the effect of HCPTS helped to clear up the mechanism. In a few words: the surgical insult near the shorter metaphyseal region upregulates Indian Hedge Hog (Ihh), which reach the physis via afferent blood vessels where they upregulate parathyroid hormones (PTH) and they accelerate the physeal growth locally. With the pathway cleared up, this technique regains part of its former popularity. Growth retardation can be achieved by several surgical techniques, which temporarily bridge the physis on the longer side of the bone until the shorter side has caught up. This type of management is proposed as state of the art in opposing valgus deformities of the proximal phalanx. Once the limb is straight the implants are removed. In bilateral deformities the implants in one limb may have to be removed before the other one. By waiting until the second limb is straight as well, the faster correcting one may have already overcorrected. Recently, radial extracorporal shock wave therapy has been introduced with apparently good results, to achieve a temporary growth retardation in a noninvasive manner. Once the physis is closed, angular limb deformities cannot be corrected any more through growth modulation. The only possible way is one type of corrective osteotomy or ostectomy.