Introduction
In horses, the DFTS (vaginae synoviales tendinum digitorum manus1) is a multilayered membrane that encapsulates the superficial and deep digital flexor tendons on the palmar or plantar aspect of the distal portion of the limbs, allowing the tendons to glide freely along the metacarpo− or metatarsophalangeal (fetlock) region. The DFTS is 14 to 20 cm in length, originates on the palmar or plantar aspect of the metacarpus or metatarsus, and inserts on the palmar or plantar aspect of the second phalanx.1
Effusion of the DFTS is common in all types of horses regardless of their primary use.2 Inflammation in the ligamentous tissues may result in effusion of the DFTS.2 In horses for which lameness, injuries, or infection have been localized to this structure, synoviocentesis of the DFTS may be performed for wound evaluation, fluid analysis, local or targeted administration of medication, and regional anesthesia.3 In most horses with an injured, inflamed, or infected DFTS, effusion of the structure is marked. However, not all injuries to the DFTS result in distention, which can make synoviocentesis more challenging.4 Identification of a synoviocentesis approach that successfully yields sufficient synovial fluid for analysis, even in cases without DFTS distention, with a minimal number of attempts is desirable to decrease both the risk of injury to the practitioner and trauma to the horse.
There are 4 described techniques for synoviocentesis of the DFTS in horses, namely the proximolateral pouch approach, axial sesamoidean approach, basilar sesamoidean approach, and distal approach. The proximolateral pouch is accessed proximal to the palmar or plantar annular ligament and palmar or plantar to the lateral branch of the suspensory ligament.4 The axial sesamoidean approach uses a needle directed axially to the midbody of the lateral proximal sesamoid bone to penetrate the palmar or plantar annular ligament.3,4 The basilar sesamoidean approach involves needle insertion on the lateral aspect of the fetlock region between the palmar or plantar annular ligament and proximal digital annular ligament at the level of the base of the proximal sesamoid bones, superficial to the deep digital flexor tendon.3 The distal approach involves insertion of a needle on the lateral aspect of the distal portion of the proximal interphalangeal joint and on the palmar or plantar aspect of the deep digital flexor tendon, between the proximal digital annular ligament and the distal digital annular ligament.2,3
Previous evaluations of synoviocentesis approaches to the DFTS have been performed in both cadaveric limbs5 and standing, sedated horses.3,4 Hassel et al4 reported that the axial sesamoidean approach was more reliable than the conventional proximolateral pouch approach in cadaveric limbs without tendon sheath effusion, as determined by both the number of attempts and time required to obtain a synovial fluid sample. A more recent study3 compared the basilar sesamoidean and axial sesamoidean approaches in standing, sedated horses without DFTS effusion and found the basilar sesamoidean approach was superior, by being both faster and requiring fewer attempts, for collection of a synovial fluid sample. To date, the distal approach to the DFTS, although described in textbooks6,7 and used in practice, has not been systematically evaluated in live horses.
The objective of the study reported here was to evaluate synoviocentesis of the forelimb DFTS of horses by use of a basilar sesamoidean or distal approach. We hypothesized that the distal approach would yield an equivalent amount of synovial fluid but require significantly fewer attempts, compared with the basilar sesamoidean approach.
Materials and Methods
Horses and group allotment
Twenty-one healthy adult horses were recruited from the university teaching herd. Distal portions of the forelimbs were assessed for any abnormalities of the DFTS prior to synoviocentesis. Any horses with forelimb lameness attributed to the DFTS or related structures or with palpable digital flexor tendon abnormalities, including heat, signs of pain, or effusion, were excluded from the study. Of the 21 horses assessed, all were included in the study. There were 7 Quarter Horses, 5 Thoroughbreds, 3 Standardbreds, 2 Tennessee Walking Horses, 2 mixed-breed horses, 1 Arabian, and 1 warmblood. There were 17 mares, 2 geldings, and 2 stallions; the median age was 11 years (range, 3 to 27 years). All procedures were approved by the University of Illinois’ Institutional Animal Care and Use Committee (protocol No. 18232).
Experimental design
Each horse had 1 forelimb randomly assigned by a coin flip to undergo the basilar sesamoidean approach; the contralateral forelimb was assigned to undergo the distal approach. The order of horses for procedure allocation was randomly assigned with a random number generator.a
Synoviocentesis was performed under standard physical restraint, whereby each horse was fitted with a halter, lead rope, and nose twitch and standing sedation was achieved (IV administration of detomidine hydrochloride at a dose of 0.01 to 0.02 mg/kg with or without butorphanol tartrate at a dose of 0.1 mg/kg). All horses received 4.4 mg of phenylbutazone/kg IV as an analgesic and anti-inflammatory medication prior to the procedure. The hair on the palmar aspect of the distal portion of both forelimbs was clipped. The sites for synoviocentesis were aseptically prepared with chlorhexidine scrub applied for a period of 10 minutes and rinsed with 70% alcohol solution. With the exception of the actions of an assistant who flexed and held each forelimb during synoviocentesis, sterile techniques were observed, including the use of fresh sterile gloves for each procedure.
Synoviocentesis
A 20-gauge, 1.5-inch-long hypodermic needle was inserted into the DFTS of each forelimb with the basilar sesamoidean or distal approach, as assigned. The needle was redirected as needed to obtain a sample of synovial fluid. The number of attempts at needle placement or redirection prior to fluid collection was recorded. Successful synoviocentesis was deemed as the presence of synovial fluid in the hub of the needle. A maximum of 5 attempts (needle placements or redirections) was allowed; if no fluid was collected after 5 attempts, the approach for that limb was classified as a failure. A 6-mL syringe was used to aspirate synovial fluid, and the total fluid volume was noted. A stopwatch was used to record the interval from first skin puncture to appearance of synovial fluid in the hub of the needle. All synoviocenteses were performed by a single investigator (KMS-M).
The basilar sesamoidean approach—For synoviocentesis of the DFTS via the basilar sesamoidean approach, the fetlock region was held in a flexed position by an assistant (Figures 1 and 2). The needle was inserted on the lateral aspect of the distal portion of the fetlock region between the palmar annular ligament and the proximal digital annular ligament at the level of the base of the proximal sesamoid bones, superficial to the deep digital flexor tendon.3
Representative photograph of the distal portion of a horse's left forelimb illustrating needle insertion for synoviocentesis of the DFTS by means of the basilar sesamoidean approach. The metacarpo− or metatarsophalangeal (fetlock) region is held in a flexed position by an assistant. The needle is inserted on the lateral aspect of the distal portion of the fetlock region between the palmar annular ligament and the proximal digital annular ligament at the level of the base of the proximal sesamoid bones, superficial to the deep digital flexor tendon.
Citation: American Journal of Veterinary Research 82, 3; 10.2460/ajvr.82.3.225
Illustration of the 3-D anatomic structures of the distal portion of a horse's forelimb outlining needle insertion (arrow) for synoviocentesis of the DFTS by means of the basilar sesamoidean approach.
Citation: American Journal of Veterinary Research 82, 3; 10.2460/ajvr.82.3.225
The distal approach—For synoviocentesis of the DFTS via the distal approach, the fetlock region was held in a flexed position by an assistant (Figures 3 and 4). The needle was inserted on the palmarolateral aspect of the distal portion of the proximal interphalangeal joint and on the palmar aspect of the deep digital flexor tendon, between the proximal digital annular ligament and the distal digital annular ligament.2,3,7
Representative photograph of the distal portion of a horse's left forelimb illustrating needle insertion for synoviocentesis of the DFTS by means of the distal approach. The fetlock region is held in a flexed position by an assistant. The needle is inserted on the palmarolateral aspect of the distal portion of the proximal interphalangeal joint, on the palmar aspect of the deep digital flexor tendon, and between the proximal digital annular ligament and the distal digital annular ligament.
Citation: American Journal of Veterinary Research 82, 3; 10.2460/ajvr.82.3.225
Illustration of the 3-D anatomic structures of the distal portion of a horse's forelimb outlining needle insertion (arrow) for synoviocentesis of the DFTS by means of the distal approach.
Citation: American Journal of Veterinary Research 82, 3; 10.2460/ajvr.82.3.225
Monitoring
Following the procedures, the horses were each returned to a stall and monitored for 24 hours for signs of discomfort or swelling or lameness of the forelimbs. The horses were then returned to their normal pasture housing, where they continued to be monitored according to the standard operating protocols for these teaching horses.
Statistical analysis
Analysis of the data was performed with freely available statistical software.b For each approach, the mean, median (interquartile [25th to 75th percentile] range), and range for the volume of synovial fluid aspirated, time from skin puncture to appearance of synovial fluid in the hub of the needle, and number of attempts to place a needle in the DFTS were calculated. Fluid volume and time to fluid collection were analyzed as continuous variables, whereas the number of attempts was evaluated as a categorical variable. A Shapiro-Wilk test showed that the data were not normally distributed. Thus, the data were analyzed with the nonparametric Wilcoxon signed rank test. A z test was performed to analyze significance between proportions. Significance was set at a value of P ≤ 0.05 for all analyses.
Results
Synovial fluid was successfully obtained from 16 of the 21 (76.2%) forelimbs with the basilar sesamoidean approach and from 20 of the 21 (95.2%) forelimbs with the distal technique (Table 1). The success rates were significantly (P = 0.039) different. For both techniques, more experience with either approach did not affect the volume of synovial fluid aspirated, time from skin puncture to appearance of synovial fluid in the hub of the needle, or number of attempts to obtain fluid samples.
Results of synoviocentesis of the DFTS via a basilar sesamoidean approach or distal approach in the forelimbs of 21 horses
| Approach | ||
|---|---|---|
| Variable | Basilar sesamoidean | Distal |
| Successful synoviocentesis (No. of limbs [%]) | 16 (76.2) | 20 (95.2) |
| Synovial fluid volume (mL) | ||
| Mean (SD) | 0.79 (0.91) | 0.97 (0.82) |
| Median (IQR) | 0.40 (0.1–1.0) | 0.70 (0.0–1.2) |
| Range | 0–3.40 | 0–3.01 |
| Time to synovial fluid aspiration (s) | ||
| Mean (SD) | 29.78 (23.80) | 25.42 (19.35) |
| Median (IQR) | 17.91 (10.94–51.92) | 18.48 (7.74–39.22) |
| Range | 5.16–70.26 | 5.26–63.53 |
| No. of attempts required to obtain synovial fluid | ||
| Mean (SD) | 2 (1.16) | 1.4 (0.68) |
| Median (IQR) | 2 (1–3) | 1 (1–2) |
| Range | 1–5 | 1–3 |
Both forelimbs of 21 horses were randomly assigned to undergo synoviocentesis of the DFTS by use of a basilar sesamoidean or distal approach (21 limbs/approach). Standing horses were manually restrained and sedated. For the basilar sesamoidean approach, the fetlock region was flexed and the needle was inserted on the lateral aspect of the distal portion of the fetlock region between the palmar annular ligament and the proximal digital annular ligament at the level of the base of the proximal sesamoid bones, superficial to the deep digital flexor tendon. For the distal approach, the fetlock region was flexed and the needle was inserted on the palmarolateral aspect of the distal portion of the proximal interphalangeal joint, on the palmar aspect of the deep digital flexor tendon, and between the proximal digital annular ligament and the distal digital annular ligament. Following insertion, the needle was redirected as needed to obtain a sample of synovial fluid. The number of attempts at needle placement or redirection prior to fluid collection was recorded. Successful synoviocentesis was deemed as the presence of synovial fluid in the hub of the needle. A maximum of 5 attempts (needle placement and redirections) was allowed; if no fluid was collected after 5 attempts, the approach for that limb was classified as a failure. The total synovial fluid volume collected was noted. A stopwatch was used to record the interval from first skin puncture to appearance of synovial fluid in the hub of the needle.
IQR = Interquartile (25th to 75th percentile) range.
The median volume of synovial fluid aspirated with the basilar sesamoidean approach was 0.4 mL, compared with 0.7 mL when the distal approach was used; this difference was not significant (P = 0.912). The median time from skin puncture to appearance of synovial fluid in the hub of the needle for the basilar sesamoidean and distal approaches was 17.91 and 18.48 seconds, respectively; these times were not significantly (P = 0.161) different. The median number of attempts to obtain fluid from the DFTS with the basilar sesamoidean technique was 2, compared with 1 when the distal approach was used; this difference between approaches was significant (P = 0.031).
Discussion
Equine veterinarians frequently encounter clinical problems involving flexor tendons, which may have a traumatic, inflammatory, or infectious origin, in both ambulatory and hospital settings. Synoviocentesis of the DFTS is not only an essential diagnostic technique, but also a primary treatment for pathological processes involving this structure.3,4
In horses, collection of a synovial fluid sample from a distended DFTS is relatively straightforward; however, not all pathological changes in this structure result in its distention. For clinical problems that do not induce distention of the DFTS, a reliable technique that allows collection of a sufficient volume of synovial fluid for diagnostic testing with the least number of attempts is highly desirable. Further, needle insertion into synovial structures can result in synovial infection even when sterile techniques are applied, although this sequela is uncommon.8,9 With every additional insertion attempt, the probability for infection increases.9 Thus, it is advantageous to choose a synoviocentesis technique that has a high likelihood of successful fluid collection on the first attempt to minimize tissue trauma and the potential for infection. The results of the present study indicated that in healthy adult horses without palpable DFTS abnormalities, the distal approach for synoviocentesis of the DFTS required significantly fewer attempts to achieve successful collection of a synovial fluid sample, compared with the basilar sesamoidean approach. The number of attempts required with the basilar sesamoidean approach was similar to that reported previously3 (accounting for differences in the definition of an attempt between studies), which suggested that the advantages of the distal approach were real and not solely reliant on our investigator's familiarity with that procedure relative to the basilar sesamoidean approach.
Although the volume of synovial fluid aspirated and time from skin puncture to appearance of synovial fluid in the hub of the needle did not differ between the 2 approaches, the success rate of 95.2% for the distal approach was significantly greater than the success rate of 76.2% for the basilar sesamoidean approach. This finding provided support for the usefulness of the distal approach for synoviocentesis of nondistended DFTSs in horses.
Because of the complex anatomic features of the distal portion of the forelimbs of horses, successful synoviocentesis of a noneffusive DFTS via the basilar sesamoidean approach can be challenging. This approach requires palpation of multiple structures, and only a small area is available for needle access. In contrast, the correct location for needle insertion with the distal approach is easily palpable with a comparatively greater area available for needle insertion. The higher success rate and reduced number of attempts needed for synovial fluid collection via the distal approach may be related to the ease of identifying relevant anatomic landmarks.
The main limitation of the present study was that it included horses that had no DFTS abnormalities. Synoviocentesis of the DFTS is most commonly performed on horses because of tendon sheath effusion or other tendon sheath problems. Wright and McMahon10 reported marked distention of the DFTS in each of 20 horses with tenosynovitis associated with longitudinal tears of the digital flexor tendons. Thus, the clinical relevance of the findings of the present study would be enhanced by performing a similar study involving horses with pathological changes of the DFTS.
Results of the present study indicated that the distal approach for synoviocentesis of the DFTS in horses appears to be efficient and effective and may minimize tissue trauma by requiring fewer attempts for collection of synovial fluid than would other approaches. The distal approach should be considered a useful alternative technique for practitioners who perform synoviocentesis of the DFTS in horses in clinical settings.
Acknowledgments
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript.
The authors declare that there were no conflicts of interest.
Abbreviations
| DFTS | Digital flexor tendon sheath |
Footnotes
Excel, version 16.32, Microsoft Corp, Redmond, Wash.
R: A language and environment for statistical computing, version 3.5.3, R Foundation for Statistical Computing, Vienna, Austria.
References
- 1. ↑
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- 3. ↑
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- 4. ↑
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