A new technique has been used to repair severed digital flexor tendons in horses. Dr Roger Smith and the team working at the Royal Veterinary College in London have used implants made of the bioabsorbable material poly-L-lactic acid (PLLA) to repair lacerated tendons in four horses.
Skin wounds extending into the flexor tendons are a serious injury in the horse. Regardless of the treatment used, it is difficult to predict the response and the prospects for a return to work. Various methods have been used to repair severed tendons, often involving a variety of suture materials or implants. The long time taken for tendons to heal presents problems. Materials which are not absorbed, such as polyester and carbon-fibre, can be used, but they are often associated with sinus formation and persistent lameness. Dr Smith and his team believe that the scar tissue may tear away from the non-absorbable implant and contribute to the persistent lameness.
The absorbable suture materials that are currently available are absorbed too quickly for use in tendon repair. Poly-L-lactic acid, however, lasts longer, and so was used to treat the horses in this study.
All four horses had completely severed at least one of the flexor tendons of the hind leg. The most severely injured had completely severed the superficial and deep flexor tendons and the lateral branch of the suspensory ligament. In all cases the laceration resulted in a substantial defect such that the ends of the tendon could not be apposed.
The wounds were cleaned under general anaesthesia. When all the damaged tissue had been cut away there was a gap of from 2 to 10 cm between the cut ends of the tendon. The surgeons used a 25cm long 9 mm wide braided implant of poly-L-lactic acid (PLLA) to bridge the gap between the severed ends of the tendon. Two separate implants were used in the horse with the two severed tendons. In each horse the skin and subcutaneous tissue was sutured routinely. A cast was applied which extended from the foot to the hock with the fetlock in a neutral position.
About six weeks after the operation the cast was changed and an ultrasound examination was carried out. Dr Smith found that the PLLA was well incorporated into the scar tissue by that time.
About six months after surgery two of the horses were mildly lame at the trot. They were sound and working after 12 months. The other two horses remained lame.
In two of the horses, ultrasound examination showed that the implant had pulled out of the distal stump. Despite this, it appeared to have been able to act as a scaffold for the formation of scar tissue. No complications were noticed with the implant, although they persisted for several years.
Substantial fibrous tissue was deposited around the implant in 3 of the 4 cases. One horse which had been injured within the digital sheath showed no such fibrous tissue formation. "The lack of fibrous tissue around the implant within the fetlock canal was due partly to the forces generated on the implant by the surrounding structures and partly due to its position within the sheath." said Dr Smith.
"The PLLA implants were well tolerated by the tissues in these horses" he said. "They may help to maintain the alignment of the tendon stumps and act as a scaffold for the formation of scar tissue."
"This implant is an improvement over what we have used before. However, it persists for longer than we would have ideally wished. Even so, it does not give the problems seen with other non- absorbable implants - probably because it has lost its strength and therefore complies to the repair tissue better. We are working towards finding the ideal implant for tendon lacerations in horses. This is one of the steps on the road!"
"We will need to do more work to determine whether PLLA implants are superior to other methods of treating tendon lacerations - such as casting alone, or using other implants or tendon grafting."
for more details see:
Use of a bioabsorbable implant for the repair of severed digital flexor tendons in four horses. E Eliashar, M C Schramme, J Schumacher, RKW Smith, Y Ikada. Veterinary Record (2001) 148, 506-509