How to Select Cases and Use Autologous Conditioned Serum to Treat Proximal Suspensory Desmitis

1. Introduction

The suspensory ligament (SL) can be divided into 3 regions subject to injury: the proximal region, the body, and the medial and lateral branches. In this presentation, only treatment of the proximal region is discussed.

Proximal suspensory desmitis (PSD) is a common injury of athletic horses causing pain and lameness. It can occur unilaterally or bilaterally and can affect the hind limbs, the fore limbs, or both.¹ Clinical signs displayed by horses with PSD have been well documented¹ and pain causing lameness can be localized to the proximal aspect of the suspensory ligament (PSL) by using a variety of local and regional anesthetic techniques.¹  The PSL and adjacent bone is usually imaged by using ultrasonography and radiography. Nuclear scintigraphic examination of horses affected with PSD can be helpful, but magnetic resonance imaging (MRI) is the most defining method by which the ligament and surrounding structures can be imaged.¹ 

Most horses lame because of acute PSD of the fore limb, respond favorably to stall confinement and controlled walking exercise for 3 months,^1,2 but for the 3-year-old Western performance horse, 3 months of confinement may end the horse’s show career, thereby significantly reducing the horse’s worth. The prognosis for return to soundness for horses lame because of PSD of one or both hind limbs is poor when affected horses are treated by confinement and incremental increase in exercise.^3,4

Besides stall rest, a myriad of adjunctive therapies have been recommended for horses lame because of PSD, including systemic and topical administration of an NSAID; periligamentous injection of a corticosteroid, hyaluronan, polysulfated glycosaminoglycans, extract of the pitcher plant^a, or a combination of these drugs; topical application of dimethyl sulfoxide (DMSO), with or without a corticosteroid or other drugs; extracorporeal shockwave therapy; and intralesional injection of 2% iodine in almond oil, extracellular matrix^b, mesenchymal stem cells, or platelet rich plasma.¹

Surgical treatments of horses for PSD include splitting the ligament, lateral palmar/plantar neurectomy, neurectomy of the deep branch of the lateral palmar or plantar nerve, ulnar or tibial neurectomy, fasciotomy of the fascia overlying the ligament, and combinations of these surgical treatments.¹

In this presentation, we describe periligamentous injection of autologous conditioned serum (ACS)^c for the treatment of horses lame because of PSD. Autologous conditioned serum is made by collecting the patient’s blood in a proprietary syringe containing glass beads soaked in chromium sulfate. The blood is incubated in the syringe for approximately 24 hours (18–26 h) and then centrifuged, filtered, and divided into dose-sized aliquots, which can be injected immediately or frozen for future use. The processing procedure is designed to specifically harvest anti-inflammatory cytokines,⁵ but anabolic cytokines and morphogenic proteins may be harvested, as well.⁶

Commercial veterinary systems are available for the horse for patient-side production of ACS.^c,d Autologous, conditioned serum has been used in the horse for several years to modulate synovitis and has become an accepted mode of equine joint therapy.^1,7-13 Autologous conditioned serum has also been investigated for modulation of the post-breeding inflammatory response in the mare’s uterus.¹⁴ Autologous, conditioned serum is used to treat humans for a variety of synovial and non-synovial orthopedic maladies,^15,16 and experimental studies using rats have demonstrated improved tendon healing after ACS therapy.^17,18

The purpose of this report is to describe how we select horses lame because of PSD for treatment with ACS using the irap^c system. Our criteria for selection of horses for this treatment are based on our experience in treating 271 horses lame because of PSD.

2. Materials and Methods

Case Selection

Horses in this study were those determined to be lame solely because of PSD and that were treated with ACS by one of the authors^e between September 2004 and September 2013. All horses included in this study were lame at the time of treatment, showed signs of pain during palpation of the PSL, and had the pain causing lameness localized to the PSL by performing various techniques of diagnostic analgesia using 2% mepivacaine hydrochloride (HCl). Only horses with a minimum follow-up time of 3 months, after the initiation of treatment were included in the study.

Fore Limb Blocks

Pain in the distal portion of the fore limb(s) was excluded as a cause of lameness by observing no improvement in lameness after administering a low four-point nerve block or after administering an abaxial sesamoid nerve block in combination with intrasynovial anesthesia of the fetlock joint and, occasionally, intrasynovial anesthesia of the digital flexor tendon sheath. Pain was isolated to the PSL by observing substantial improvement in lameness after desensitizing the PSL by anesthetizing the lateral palmar nerve at the level of the accessory carpal bone.

Hind Limb Blocks

Pain in the distal portion of the hind limb(s) was excluded as a cause of lameness by observing no improvement in lameness after administering a low four-point nerve block or after administering an abaxial sesamoid nerve block in combination with intrasynovial analgesia of the fetlock and, occasionally, intrasynovial analgesia of the digital flexor tendon sheath. Pain was isolated to the PSL by observing substantial improvement in lameness after desensitizing the PSL by anesthetizing the tibial nerve or by locally infiltrating the PSL with local anesthetic solution. For some horses, pain originating from the distal joints of the hock was excluded as a cause of lameness by observing little or no improvement in lameness after intrasynovial analgesia of the distal intertarsal and tarsometatarsal joints during lameness exam performed after the effects of local or regional analgesia had dissipated.

Imaging

The metacarpus (Mc III) or metatarsus (Mt III) of all horses were radiographically examined to exclude horses with substantial bone disease at the proximal aspect of Mc/Mt III, and all were examined sonographically in the palmar/plantar metacarpal/metatarsal region. Horses with a stress fracture of the proximal palmar/plantar Mc/Mt III were excluded from the study. Horses with substantial tissue disruption of the PSL or damage to other structures in the area such as the inferior check ligament were excluded. Horses that had enlargement of a PSL or edema of a PSL, as compared to the contralateral limb, were included (Fig. 1). For horses with bilateral PSD, assessment of enlargement and edema of the PSL was based on published guidelines.⁴

ACS Harvest and Processing

Whole blood harvested from each horse was incubated in the proprietary syringe in which it was collected and processed according to the manufacture’s guidelines. Some aliquots were used immediately after processing whereas others were stored in a -20°C freezer for future use. Frozen aliquots were thawed in a water bath immediately prior to use, and the ACS was filtered through a 0.2 µm disk filter^f prior to injection. [...]