Effects of Superior Check Desmotomy on Flexor Tendon and Suspensory Ligament Strain in Equine Cadaver Limbs

OBJECTIVE: To measure the effects of transection of the accessory ligament of the superficial digital flexor (SDF) muscle (superior check desmotomy) on flexor tendon and suspensory ligament (SL) strain in vitro. STUDY DESIGN: In vitro experimental biomechanical investigation. ANIMALS USED: Ten equine cadaver forelimbs. METHODS: The effects of superior check desmotomy were determined using equine cadaver forelimbs secured in a servocontrolled hydraulic testing machine. Strain sensors were used to measure strain on the superficial and deep digital flexor tendons and SL, and a goniometer was used to measure joint angles when the limb was loaded at 890 N and 3,115 N before desmotomy, and at 3,115 N after desmotomy. RESULTS: Superior check desmotomy was associated with significantly increased strains on the SDF tendon and SL, and significant alterations in the angles of the metacarpophalangeal and carpal joints. CONCLUSIONS: The superior check ligament has an important role in maintaining joint angles and load distribution in the forelimb. Lengthening of the SDF musculotendinous unit after superior check desmotomy may be associated with increased strain on the SL. CLINICAL RELEVANCE: Transection of the accessory ligament of the SDF muscle may predispose horses to SL desmitis postoperatively.     

Superficial digital flexor tendonitis in Thoroughbred race horses: outcome following non-surgical treatment and superior check desmotomy

Objective This study documents the results of non-surgical treatment and treatment by superior check desmotomy in Thoroughbred racehorses with superficial digital flexor (SDF) tendonitis. Design A prospective study was made of 124 thoroughbred racehorses with unilateral or bilateral SDF tendonitis. Procedure The flexor tendons were assessed by physical and ultrasonographic examination before treatment, and the lesions detected in affected tendons were characterised according to lesion type, length and cross-sectional area. Ninety three horses were managed non-surgically and 31 by superior check desmotomy. Recurrent or new injuries were defined as injuries affecting a previously injured superficial digital flexor tendon, the contralateral SDF tendon, or the suspensory ligament (interosseous muscle) in either forelimb. Results No statistically significant difference was found in ultrasonographic lesion severity between treatment groups. Horses managed by superior check desmotomy were 1.3 times more likely to complete five or more races than horses managed non-surgically (95% confidence limits 0.93–1.82). Horses treated surgically were 1.2 times more likely to develop recurrent or new injuries after returning to training than horses managed non-surgically (95% CL 0.95–1.55). Horses under-going superior check desmotomy were 5.5 times more likely to develop suspensory desmitis than horses treated non-surgically (95% CL 1.13–26.4). There was no difference in the time to recurrent or new injury between treatment groups. Conclusion There was no statistically significant difference between treatment groups in the proportions of horses able to complete five or more races after an episode of superficial digital flexor tendonitis. Superior check desmotomy did not appear to offer an advantage over non-surgical treatment in preventing recurrent or new injuries in Thoroughbred racehorses. Horses undergoing superior check desmotomy appeared to be at greater risk of developing suspensery ligament injuries than horses managed non-surgically.     

Desmotomy of the accessory ligament of the deep digital flexor tendon for treatment of chronic deep digital flexor tendinopathy in three Quarter Horses

Effective treatments for horses diagnosed with severe deep digital flexor (DDF) tendinopathy are limited. In this study, three Quarter Horses diagnosed with severe bilateral DDF tendinopathy underwent bilateral desmotomy of the accessory ligament of the DDF tendon after failing to respond to conservative therapy. Lameness markedly improved in all three horses. Given that severe DDF tendinopathy is typically associated with persistent or recurrent lameness, desmotomy of the accessory ligament of the DDF tendon might be a treatment option to alleviate lameness in horses with DDF tendinopathy. This treatment option appears promising; however, a larger number of cases is necessary to support the results in these three horses.     

Calculated forelimb flexor tendon forces in horses with experimentally induced superficial digital flexor tendinitis and the effects of application of heel wedges

OBJECTIVE: To calculate forces in the flexor tendons and the influence of heel wedges in affected and contralateral (compensating) forelimbs of horses with experimentally induced unilateral tendinitis of the superficial digital flexor (SDF) tendon. ANIMALS: 5 Warmblood horses. Procedure-Ground reaction force and kinematic data were obtained during a previous study while horses were trotting before and after induction of tendinitis in 1 forelimb SDF and after application of 6 degrees heel wedges to both forehooves. Forces in the SDF, deep digital flexor (DDF), and the suspensory ligament (SL) and strain in the accessory ligament (AL) of the DDF were calculated, using an in vitro model of the distal region of the forelimb. RESULTS: After induction of tendinitis, trotting speed slowed, and forces decreased in most tendons. In the affected limb, SL force decreased more than SDF and DDF forces. In the compensating limb, SDF force increased, and the other forces decreased. After application of heel wedges, SDF force in both limbs increased but not significantly. Furthermore, there was a decrease in DDF force and AL strain. CONCLUSIONS AND CLINICAL RELEVANCE: The increase in SDF force in the compensating forelimb of horses with unilateral SDF tendinitis may explain the high secondary injury rate in this tendon. The lack of decrease of SDF force in either limb after application of heel wedges suggests that heel wedges are not beneficial in horses with SDF tendinitis. Instead, heel wedges may exacerbate the existing lesion.     

Superior check ligament desmotomy for treatment of superficial digital flexor tendonitis in Thoroughbred and Standardbred horses

Summary Bilateral superior check ligament desmotomy was performed on 31 Thoroughbred and 17 Standardbred horses as the sole method of treatment for superficial digital flexor tendonitis. Horses resumed racing between 6 and 19 months after surgery. Horses that were able to compete in 5 or more races without injury to the tendon again were considered to have had a successful return to racing. Twenty-five Thoroughbreds were suitable for later study and 13 of these (52%) raced on 5 or more occasions. Fifteen Standardbreds were suitable for later study and 10 of these (66%) raced on 5 or more occasions. Within the racing industry it is generally thought that about 20 to 30% of horses with superficial digital flexor tendonitis can return to racing after a prolonged rest. The results of this study suggest that bilateral superior check ligament desmotomy may improve the prognosis for a horse returning to racing after injury to the superficial digital flexor tendon.     

Desmotomy of the accessory ligament of the superficial digital flexor tendon in the horse with use of a tenoscopic approach to the carpal sheath

Objective— To describe a tenoscopic approach to the carpal sheath for desmotomy of the accessory ligament of the superficial digital flexor tendon. Study Design— The surgical procedure was developed with use of normal forelimbs from equine cadavers and experimental horses. Animals or Sample Population— Twelve equine cadaveric forelimbs, 4 forelimbs from 2 horses anesthetized for terminal surgical laboratories, and 10 forelimbs from five experimental horses were used. Methods— The limbs were positioned lateral side up with the carpus slightly flexed. After distention of the carpal sheath, a portal was made approximately 2 cm proximal to the distal radial physis for arthroscope insertion. An instrument portal was made approximately 0.2 cm proximal to the distal radial physis. After flexion of the limb to 90°, the accessory ligament of the superficial digital flexor tendon was palpated and desmotomy was performed. Cadaveric limbs were dissected to confirm complete desmotomy. Experimental horses were monitored for short- (perioperative) and long- (4 weeks) term postoperative complications. Results— A tenoscopic approach to the carpal sheath provided adequate surgical access to the accessory ligament of the superficial digital flexor tendon for desmotomy. Most of the accessory ligament of the superficial digital flexor tendon could be easily seen within the sheath, except for the proximal 2 cm that could be readily palpated and subsequently transected. Important technical considerations were location of the arthroscope portal, adequate sheath distention, limb flexion to 90°, and desmotomy location. It was beneficial, but apparently not essential, to avoid the proximal perforating vessel. Postoperatively, some horses had swelling but were not lame and had normal range of motion of the carpus. Conclusions— Desmotomy of the accessory ligament of the superficial digital flexor tendon could be performed by using a lateral tenoscopic approach to the carpal sheath. Clinical Relevance— Desmotomy of the accessory ligament of the superficial digital flexor tendon by using a tenoscopic approach to the carpal sheath is an alternative technique to the medial incisional approach.     

Desmotomy of the Accessory Ligament of the Superficial Digital Flexor Muscle in Equine Cadaver Limbs

Effects of longitudinal compression before and after transection of the accessory ligament of the superficial digital flexor (SDF) muscle were measured in eight equine cadaver forelimbs. When compression was increased from 890 N to 3115 N, the metacarpophalangeal (MCP) and carpal joints hyperextended 20 degrees and 4 degrees, respectively, and strain in the SDF and deep digital flexor tendons was increased 3.5% and 1.4%, respectively. The accessory ligament did not elongate. Immediately after transection of the accessory ligament at 3115 N load, a 2.8 mm gap formed between the transected ends of the accessory ligament, and the muscle belly of the SDF elongated and moved distad. The MCP joint hyperextended 15.8% further and strain of the SDF tendon increased 11.2% further. These results show that the accessory ligament transferred load in the SDF musculotendinous unit away from the muscle belly and that desmotomy altered this function. Decrease in the MCP joint angle indicated that the accessory ligament contributed to the support of the MCP joint under load. Increase in SDF strain after desmotomy was probably influenced by the change in the moment about the MCP joint and increased length of the SDF musculotendinous unit.     

Ultrasound-Guided Transection of the Accessory Ligament of the Deep Digital Flexor Muscle (Distal Check Ligament Desmotomy) in Horses

Transection of the accessory ligament of the deep digital flexor muscle (distal check ligament desmotomy) was completed in 44 horses using an ultrasound-guided technique. The technique used real-time ultrasound with a 7.5 MHz transducer to observe the dissection and isolation of the check ligament through a 1 to 1.5 cm incision and to check for complete transection of the check ligament. The technique was effective in correcting flexural deformity of the distal inter-phalangeal joint and the metacarpophalangeal joint in all but three horses. Check ligament desmotomy at a young age (median, 6 months) resulted in more horses with normal foot conformation than when surgery was completed at an older age (median, 12 months). Age at surgery had no effect on subsequent appearance of the surgical site. Based on the authors experience this technique reduced immediate postoperative wound morbidity.     

Long-term effects of desmotomy of the accessory ligament of the deep digital flexor muscle in standardbreds: 23 cases (1979-1989).

Desmotomy of the accessory ligament of the deep digital flexor muscle (inferior check desmotomy) permitted Standardbred foals affected with flexural deformities to reach their full athletic potential. Long-term effects of inferior check desmotomy were examined in 23 Standardbreds over a 10-year period. Six of 11 foals that were treated surgically either raced 6 times and obtained a race record or were training sound (if yearlings). All 12 horses with flexural deformity that did not receive an inferior check desmotomy had an unfavorable outcome (no race record). Foals that had surgery performed at a younger age apparently had a better chance of racing or training sound because no foals treated surgically after 8 months of age had a favorable outcome and only 1 foal that was older than 5 months at the time of surgery had a favorable outcome. In 5 foals that had surgery with an unsuccessful outcome, 3 were greater than or equal to 1 year old at the time of surgery and were lame when training was started on the limb(s) with the desmotomy.     

Determination of passive mechanical properties of the superficial and deep digital flexor muscle-ligament-tendon complexes in the forelimbs of horses

OBJECTIVE: To determine the relative contributions of the muscles, tendons, and accessory ligaments to the passive force-length properties of the superficial (SDF) and deep digital flexor (DDF) myotendinous complexes. SAMPLE POPULATION: 8 cadaveric forelimbs from 6 adult Thoroughbreds. PROCEDURE: In vitro, limb configurations during slack position and myotendinous lengths during subsequent axial loading of forelimbs were recorded before and after transection of accessory ligaments. Expressions were derived to describe the force-length behavior of each muscle, tendon, and accessory ligament-tendon unit; linear stiffness was computed for these components. The elastic modulus was established for the SDF and DDF tendons. RESULTS; Linear stiffness was 2.80 +/- 0.38 kN/cm for the SDF muscle, 3.47 +/- 0.66 kN/cm for the DDF muscle, 2.73 +/- 0.18 kN/cm for the SDF tendon, 3.22 +/- 0.20 kN/cm for the DDF tendon, 6.46 +/- 0.85 kN/cm for the SDF accessory ligament, 1.93 +/- 0.11 kN/cm for the SDF accessory ligament-tendon unit, and 2.47 +/- 0.11 kN/cm for the DDF accessory ligament-tendon unit. The elastic modulus for the SDF and DDF tendons was 920 +/- 77 and 843 +/- 56 MPa, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Both the muscle-tendon and ligament-tendon portions of SDF and DDF myotendinous complexes had important roles in supporting the forelimb of horses. Although muscle tension can be enhanced by elbow joint flexion and active contraction, the accessory ligaments transmitted more force to the distal tendons than did the muscles under the conditions tested.     

Myofibroblasts in the accessory ligament (distal check ligament) and the deep digital flexor tendon of foals

OBJECTIVE: To demonstrate myofibroblasts in the accessory ligament of the deep digital flexor tendon (ie, distal check ligament) and deep digital flexor tendon of clinically normal foals. SAMPLE POPULATION: Tissue specimens from 25 foals that were necropsied for reasons unrelated to this study and unrelated to musculoskeletal disease. PROCEDURE: The distal check ligament and deep digital flexor tendon of both forelimbs were examined histologically. Myofibroblasts were identified by immunohistochemical staining specific for alpha-smooth muscle actin (alpha-SMA). RESULTS: Most of the cells in the distal check ligament and deep digital flexor tendon of all foals stained positive for alpha-SMA. CONCLUSION AND CLINICAL RELEVANCE: Myofibroblasts made up most of the cells in the distal check ligament and deep digital flexor tendon of clinically normal foals. These cells have contractile ability and therefore, may play a role in flexure contracture of these tendons. The ability of tetracycline to chelate calcium or decrease the expression of the contractile protein alpha-smooth muscle actin could inhibit the myofibroblasts' ability to contract, thus providing a rationale for tetracycline administration as a treatment of distal interphalangeal joint flexor deformity in foals.     

An in vivo equine forelimb model for short-term recording of peak isometric force in the superficial and deep digital flexor muscles

OBJECTIVE: To develop and test an experimental model for in vivo short-term recording of peak isometric forces of the digital flexor muscles in the forelimb of adult horses. STUDY DESIGN: In vivo experimental study. SAMPLE POPULATION: Four healthy, anesthetized, adult Thoroughbred horses (3 to 7 years old; 527 +/- 87 kg) METHODS: In dorsal recumbency, ulnar and median nerves were exposed and instrumented with insulated bipolar cuff stimulation electrodes for later connection to an electrical stimulator. In left lateral recumbency, a biplanar fixator was applied to the right humerus and a custom-made, rigid, aluminum frame connected to it, to allow loading of muscles distal to the fixator. Threaded transfixation pins through the radial and metacarpal condyles were clamped to the rigid frame so that the humerus, radius, ulna, and metacarpus were fixed in position. Each digital flexor muscle insertion tendon was transected just above the metacarpophalangeal joint, extracted from the carpal canal, and secured in a metal clamp positioned at the distal myotendinous (MT) junction. Distally, the clamp was connected in series to a load cell and a pneumatic actuator to record force and to maintain muscle length during nerve stimulation. A linear potentiometer was connected in parallel to the actuator to record MT junction position. Initial trials were conducted to identify median and ulnar nerve stimulation variables to achieve maximal muscle contraction. Isometric contractions were performed at different muscle lengths and peak forces registered during 3 seconds of supramaximal dual (ulnar and median) nerve stimulation. RESULTS: A stimulation voltage of 2.5 to 5.0 V at 50 Hz usually produced maximal force for both the superficial digital flexor (SDF) and deep digital flexor (DDF) muscles. Single ulnar and median nerve stimulation elicited force development not only in the DDF muscle but also in the SDF muscle. At voltages higher than 1 V, normalized force was greatest with combined median and ulnar nerve stimulation for both the DDF and SDF muscles; however, normalized force was greater for median nerve stimulation than ulnar nerve stimulation in the DDF muscle, and the opposite relationship was observed for the SDF muscle. Final recording of dual supramaximal nerve stimulation of SDF and DDF muscles resulted in peak isometric forces of 716 +/- 192 N and 1,577 +/- 203 N, respectively. CONCLUSIONS: The instrumentation technique and experimental protocol enabled recording of peak isometric forces in the SDF and DDF muscles of anesthetized adult horses. CLINICAL RELEVANCE: Studies using this model will improve knowledge of SDF and DDF muscle mechanics with insight to functional implications of the complex architecture of these muscles. Knowledge of the dynamic performance of the SDF and DDF muscles would also be useful for the development of new treatment strategies for flexor deformities and tendon injuries in horses.     

Dorsal subluxation of the proximal interphalangeal joint in the pelvic limb of three horses

In horses, dorsal subluxation of the proximal interphalangeal joint in the pelvic limb, which realigned when weight was applied to the limb, improved following surgery. Improvement was observed, if not immediately, at least within two weeks after treatment. The severity and duration of the condition appear to be important considerations in predicting the time necessary for resolution of the condition following surgery. Treatment consisted of surgical resection of a small segment of the medial head of the deep digital flexor tendon in the pelvic limb. The section removed was positioned distal to the tarsus, at the level prior to the tendon joining the main portion of the deep digital flexor tendon. Previously, a surgical treatment was described in which a portion of the accessory ligament (distal check ligament) of the deep digital flexor muscle was resected. Because the medial head is much stronger than the accessory ligament, resection of the tendon of the medial head provides more release of tension to allow stretching of the deep digital flexor muscle tendon.     

Acquired flexural deformity of the distalinterphalangeal joint in horses: Treatment by desmotomy of the accessory ligament of the deep digital flexor tendon: A retrospective study

Hospital records of 29 horses treated by desmotomy ofthe accessory ligament of the deep digital flexor tendon for correction of acquired flexural deformity of the distal interphalangeal joint in one or both forelimbs were reviewed and evaluated retrospectively. Information on correction of the deformity, cosmetic appearance of the surgery site, and current use of the horses was obtained by interviews with the owners.At the time of surgery, 27 horses were less than one year old and two horses were more than one year old. Eleven months to five years after surgery, 26 horses had normal appearance of the hoof and limb, and 26 horses had acceptable cosmetic appearance of the surgery site due to no or minimal scarring. At the time of interview, all but two of the 11 horses more than three years old were in full training.It is concluded that desmotomy of the accessory ligament of the deep digital flexor tendon is an effective and cosmetically acceptable treatment for acquired flexural deformity of the distal interphalangeal joint in the horse.     

Surgical Anatomy for Desmotomy of the Accessory Ligament of the Superficial Digital Flexor Tendon (Proximal Check Ligament) in Horses

Dissections were performed to study the surgical anatomy for desmotomy of the accessory ligament of the superficial digital flexor tendon (proximal check ligament [PCL]). The surgical approach was initiated by incising the skin cranial to the cephalic vein and caudal to the distal radius. A palpable foramen in the antebrachial fascia that transmits a branch of the cephalic vein was used to advance deeper dissection. After the antebrachial fascia was incised, the fan-shaped PCL was exposed by retracting the en-sheathed tendon of the flexor carpi radialis muscle caudally. Desmotomy was performed gradually to avoid severing branches of the palmar carpal rete that pervade the ligament. Complete transection was evidenced by visualization of the membranous roof of the carpal canal distally, the muscle belly of the radial head of the deep digital flexor centrally, and loose areolar connective tissue along the caudal radius proximally. The vessels of the palmar carpal rete were visible coursing between the severed edges of the PCL. This report highlights relevant anatomic landmarks to facilitate an accurate desmotomy.     

Model formulation and determination of in vitro parameters of a noninvasive method to calculate flexor tendon forces in the equine forelimb

OBJECTIVE: To describe a method to calculate flexor tendon forces on the basis of inverse dynamic analysis and an in vitro model of the equine forelimb and to quantify parameters for the model. SAMPLE POPULATION: 38 forelimbs of 23 horses that each had an estimated body mass of > or = 500 kg. PROCEDURE: Longitudinal limb sections were used to determine the lines of action of the tendons. Additionally, limb and tendon loading experiments were performed to determine mechanical properties of the flexor tendons. RESULTS: The study quantified the parameters for a pulley model to describe the lines of action. Furthermore, relationships between force and strain of the flexor tendons and between fetlock joint angle and suspensory ligament strain were determined, and the ultimate strength of the tendons was measured. CONCLUSION AND CLINICAL RELEVANCE: The model enables noninvasive determination of forces in the suspensory ligament, superficial digital flexor tendon, and distal part of the deep digital flexor (DDF) tendon. In addition, it provides a noninvasive measure of loading of the accessory ligament of the DDF tendon for within-subject comparisons. However, before application, the method should be validated. The model could become an important tool for use in research of the cause, prevention, and treatment of tendon injuries in horses.     

Proximal Digital Annular Ligament Desmotomy in Horses: A Cadaveric Study

Proximal digital annular ligament (PDAL) desmitis occurs in horses for which PDAL desmotomy is the only reported treatment. The presented work aims to develop a technique for safely performing PDAL desmotomy in horses. Twenty hind limbs and 13 forelimbs, harvested from horses dead or euthanized for reasons unrelated to any structure in the pastern region, were used. All horses were free of disease at the level of their PDAL. Proximal digital annular ligament desmotomy was performed using a minimally invasive approach to the digital flexor tendon sheath between the palmar (plantar) annular ligament and the PDAL, using a medial or a lateral access. Limbs were immediately dissected after the procedure to assess the completeness of the PDAL desmotomy and any possible damage to surrounding structures. The PDAL was successfully transected in all limbs except one. Damage to the surrounding tissue included transection of the palmar digital nerve (n = 1), longitudinal tear of the superficial digital flexor tendon (n = 3), and transection of the ligament of the ergot (n = 21). A medial approach was found to be safer than a lateral approach. In conclusion, PDAL desmotomy can be performed in a safe, repeatable, and technically easy way. This is, to our knowledge, the first report of a standardized technique for performing a PDAL desmotomy in the horse.     

Ultrasound appearance of the palmar metacarpal soft tissues of the horse

Using real-time ultrasound imaging, the normal anatomy of the soft tissues of the palmar aspect of the equine forelimb was examined. Sections of frozen specimens were prepared which correlated well with the ultrasound images. The superficial and deep digital flexor tendons, tendon sheaths, inferior check ligament (accessory ligament of the deep digital flexor tendon), suspensory ligament, contours of the apices of the proximal sesamoids and the intersesamoidean ligament, were identified.     

Intralesional injection of insulin-like growth factor-I for treatment of superficial digital flexor tendonitis in Thoroughbred racehorses: 40 cases (2000-2004)

OBJECTIVE-To evaluate outcome after intralesional injection of insulin-like growth factor-I (IGF-I) for treatment of superficial digital flexor (SDF) tendonitis in Thoroughbred racehorses. DESIGN-Retrospective case series. ANIMALS-40 Thoroughbred racehorses. PROCEDURES-Medical records of racehorses with SDF tendonitis treated within 13 weeks after injury by intralesional injection of IGF-I (25 or 50 μg every other day for 4 or 5 treatments) were reviewed. Outcome was determined via analysis of race records, owner follow-up, and examination. RESULTS-Mean age of the horses was 3.1 years (range, 2 to 7 years), and time from injury to treatment ranged from 8 to 90 days. Mean ± SD approximate lesion length on admission was 15.6 ± 6.0 cm, and mean percentage cross-sectional area of the tendon affected was 26 ± 18%. Twenty-six of the 40 horses underwent desmotomy of the accessory ligament of the SDF tendon. Echolucency was reduced in 23 of 26 horses by the end of the treatment period. Twenty-one of 34 (62%) horses for which race data were available raced at least once after treatment, including 10 (30%) horses that raced between 1 and 4 times and 11 horses (32%) that raced ≥ 5 times. Thirteen of 28 (46%) horses had a recurrence of tendonitis or developed tendonitis elsewhere. CONCLUSIONS AND CLINICAL RELEVANCE-Results suggested that in Thoroughbred racehorses with SDF tendonitis, intralesional injection of IGF-I led to a decrease in ultrasonographic lesion severity, but treated horses had only a moderate prognosis for return to racing.