Transthecal Arthroscopy of the Palmar Distal Interphalangeal Joint in the Horse: A Cadaver Study.

OBJECTIVE: To describe a transthecal approach to the palmar pouch of the distal interphalangeal joint (DIPJ) in horses and compare it with the conventional blind arthroscopic technique. STUDY DESIGN: Ex vivo study. SAMPLE POPULATION: Cadaver forelimbs (n = 26 pairs) from mature horses. METHODS: One limb from each pair was randomly assigned to each arthroscopic approach (conventional or transthecal). The conventional arthroscopic approach was performed as previously described and the transthecal approach was performed through sharp dissection of the distal reflection of the digital flexor tendon sheath (DFTS). The proportion (0-100%) of the navicular bone, palmar aspect of the condyles of the 2nd phalanx, collateral sesamoidean ligaments, and palmar synovial pouches of the DIPJ visualized by each approach was estimated. Limbs were dissected and iatrogenic damage of relevant structures was assessed. Nondirectional Mann-Whitney U-test was used to compare groups. Significance was set at P < .05. RESULTS: The transthecal approach provided greater visualization of the navicular bone (P < .001), palmar aspect of the 2nd phalanx (P < .001), and palmar synovial pouches of the DIPJ (P < .001) than the conventional approach. There were no significant differences in iatrogenic damage between approaches. CONCLUSION: The transthecal approach provides improved visualization of the palmar aspect of the DIPJ compared to the conventional blind approach and may be useful in nonseptic conditions of the DIPJ. However, because of the creation of communication with the DFTS, use of the transthecal approach for suspected synovial sepsis of the DIPJ may be contraindicated.

The effect of varying echo time using T2-weighted FSE sequences on the magic angle effect in the collateral ligaments of the distal interphalangeal joint in horses.

Eight skeletally mature equine cadaver distal forelimbs were imaged using T2-weighted fast spin echo (FSE) sequences in a 1.0 T horizontal bore magnet. Each limb was parallel to the main magnetic field and with 16° angulation of the limb relative to the main magnetic field, which places one of the collateral ligaments of the distal interphalangeal joint at or near the magic angle. Each limb was imaged using an echo time (TE) of 80, 100, 120, and 140 ms. Reversal of the magic angle effect was achieved at echo time of 140 ms. However, given the alterations in tissue contrast and subjective decrease in the signal-to-noise ratio at this TE, it may be preferable to use a shorter TE for clinical imaging. A T2-weighted FSE sequence with an echo time of 120 ms maintained image quality while subjectively minimizing the magic angle effect. A sequence with long TE can be used to aid in the differentiation of pathologic change from artifactual increases in signal intensity in collateral ligaments of the equine distal interphalangeal joint, but could decrease the sensitivity for small or low contrast lesions. Multiple factors should be considered when selecting the TE for a T2-weighted FSE sequence that will be utilized in a musculoskeletal protocol including evaluation of equine feet.

How many joints does the 5th toe have? A review of 606 patients of 655 foot radiographs.

BACKGROUND: It is a common understanding that the fifth toe has three bones with two interphalangeal joints. However, our experience shows that a significant number have only two phalanges with one interphalangeal joint. METHODS: We identified 676 patients listed as having had a foot radiograph, during an eight week period, of which 606 radiographs were available for the assessment. The radiographs were then assessed counting the number of phalanges in the fifth toe. RESULTS: The patients consisted of 344 females and 262 males. Bilateral radiographs had been performed in 49 patients. 362 radiographs (55.3%) were found to have 3 phalanges in their 5th toe, with 291 (44.4%) having only two phalanges. CONCLUSIONS: We have demonstrated the presence of two phalanges is a common anatomical variant. This finding has clinical implications with regard to the treatment of deformities of the fifth toe and the type of internal fixation device used.

Intra-articular ossicle in interphalangeal joint of the great toe and clinical implication.

Failure of closed reduction for an interphalangeal joint dislocation of the great toe resulted from an intra-articular ossicle interposed between the articular cartilages of the phalanges. The knowledge concerning the intra-articular ossicle is unclear. A study was thus carried out on 100 fresh great toes to document the appearance, number, size, and location of the intra-articular ossicle found in the interphalangeal joint of the great toe. Roentgenographic studies of the joint revealed 86% of bony mass representing either the sesamoid bone or the intra-articular ossicle. Anatomical studies revealed no sesamoid bone in the flexor hallucis longus tendon. There was 88% of intra-articular ossicle on the dorsal surface of the plantar capsule of the interphalangeal joint. A medial surgical approach to reduce the irreducible dislocation is thus suggested as easier and safer than other approaches.

Comparison of third toe joint cartilage thickness to that of the finger proximal interphalangeal (PIP) joint to determine suitability for transplantation in PIP joint reconstruction.

PURPOSE: To compare the cartilage thickness of the third toe joints to the finger proximal interphalangeal (PIP) joints to assess the appropriateness of using third toe osteochondral grafts for finger PIP joint reconstruction. METHODS: A laser scanner was used to construct 3-dimensional computer models of 6 matched cadaver right third toe PIP joints, condyles of the third toe middle phalanx, and finger PIP joints with and without cartilage. Cartilage distribution patterns were computed and analyzed for each surface. The cartilage thickness of both sides of the third toe PIP joint and the third toe middle phalanx condyles were compared to the PIP joint of the fingers. A total of 18 third toe and 48 finger joint surfaces were analyzed. RESULTS: For the third toe middle phalanx condyles, the mean thickness was 0.20 ± 0.09 mm with a maximum of 0.52 ± 0.18 mm, and a coefficient of variation (CV%; a measure of uniformity of cartilage distribution) of 62. For the third toe proximal phalanx condyles, the mean cartilage thickness was 0.26 ± 0.10 mm with a maximum thickness of 0.56 ± 0.14 mm and a CV% of 44. The mean thickness, maximum thickness, and CV% of the finger proximal phalanx condyles was 0.43 ± 0.11 mm, 0.79 ± 0.16 mm, and 31, respectively. For the third toe middle phalanx base, the mean thickness was 0.28 ± 0.06 mm with a maximum of 0.47 ± 0.09 mm and a CV% of 34, compared to the finger middle phalanx base mean of 0.40 ± 0.12 mm with a maximum of 0.67 ± 0.14 mm and a CV% of 27. CONCLUSIONS: There were significant differences in cartilage thickness between the third toe and the fingers in this study. However, fewer differences were observed with the third toe middle phalanx base cartilage thickness than with the third toe condyles in comparison to the fingers.

Standing low-field magnetic resonance imaging appearance of normal collateral ligaments of the equine distal interphalangeal joint.

High- and low-field magnetic resonance (MR) imaging systems are available for clinical diagnosis of collateral desmopathy of the equine distal interphalangeal joint (DIJ). Knowledge of the normal appearance, size, shape,and signal variation of these ligaments on high- and low-field MR images is essential when assessing desmopathy detected by MR imaging. However, there are no descriptions of the normal features of DIJ collateral ligaments on images obtained with a standing low-field MR system. Low-field MR imaging characteristics of normal collateral ligaments of the DIJ of cadaver feet were corroborated with high-field MR imaging and histologic examination to exclude desmopathy. The size and shape of the collateral ligaments of the DIJ was similar among limbs; however, the signal pattern of the ligaments varied depending on the segment of the ligament being assessed and the MR sequence used. In limbs positioned within the magnet as recommended for clinical MR imaging, collateral ligaments of the DIJ have heterogeneous signal pattern with a peripheral region of increased signal intensity at the level of the middle phalanx that can be confused with a desmopathy.The MR imaging characteristics of normal collateral ligaments of the DIJ are related to their anatomy and fiber configuration. The results of this study support the presence of magic angle effect within the axial margin of the CL of the DIJ at the level of fiber divergence within the proximal to mid-portion of the ligament.

Structural comparison of the finger proximal interphalangeal joint surfaces and those of the third toe: suitability for joint reconstruction.

PURPOSE: This study compared the degree of surface structural similarity between finger proximal interphalangeal joints and third toe articular surfaces to assess the appropriateness of using partial toe articular osteochondral grafts for finger joint reconstruction. METHODS: Computer models were generated from 4 paired cadaver hands and feet and compared the radius of curvature of toe and finger articular surfaces. The angle created by the palmar divergence of adjacent condyles of the same phalanx was also compared and described as the angular difference. The distal articular surfaces of the third toe proximal and middle phalanx were compared to distal articular surfaces of all 4 finger proximal phalanges. The radius of curvature was also compared between the third toe middle phalanx base and those of all 4 fingers. RESULTS: The toe middle phalanx medial and lateral condyles were 66% and 60% the size of the respective finger condyles. The mean angular difference between adjacent condyles of the toe middle phalanx compared to the finger was 20°. The toe proximal phalanx medial and lateral condyles were 75% and 70% the size of the respective finger condyles, with a mean angular difference between adjacent condyles of 6°. The toe middle phalanx medial base was closer in size to that of the finger (95% to 178%) compared to the toe middle phalanx lateral base (205% to 254%). CONCLUSIONS: This study revealed that the third toe proximal phalanx distal articular surface more closely matched the geometric characteristics of the finger proximal phalanx distal articular surface than did the toe middle phalanx distal articular surface. The medial base of the toe middle phalanx more closely approximated the size of the finger middle phalanx base than did the lateral toe middle phalanx base. CLINICAL RELEVANCE: Quantitative data have been provided to help guide third toe osteochondral donor site selection when reconstructing traumatic finger proximal interphalangeal joint defects. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

Distal interphalangeal articular cartilage assessment using low-field magnetic resonance imaging.

The suitability of low-field magnetic resonance (MR) imaging for assessment of articular cartilage has been questioned, based on insufficient image quality. The purposes of this study were to describe the MR anatomy of the normal distal interphalangeal (DIP) cartilage, and to evaluate the sensitivity and accuracy of low-field MR imaging for identification of cartilage erosions that were created ex vivo. Imaging sequences included sagittal and dorsal multiple-oblique T1-weighted gradient-recalled echo (GRE) and sagittal dual echo sequences. In the thickest regions, normal cartilage appeared as a trilaminar structure on high-resolution T1-weighted GRE sequences. All 8 mm large full-thickness erosions were correctly identified (100% sensitivity and accuracy) using T1-weighted GRE sequences. Sensitivity and accuracy ranged from 80% to 100% and 10% to 80%, respectively, for detecting focal full-thickness erosions and from 35% to 80% and 35% to 60%, respectively, for detecting partial thickness erosions, using T1-weighted GRE sequences. Superficial irregularities were not diagnosed using any sequence. Overall, fewer cartilage alterations were detected with sagittal dual echo sequences than with sagittal T1-weighted GRE sequences. The dorsal multiple-oblique plane was useful to detect linear dorsopalmar erosions. A combination of T1-weighted GRE sequences in two planes has potential for identification of severe DIP cartilage erosion in anesthetized horses using low-field MR imaging.

Magic angle effect in normal collateral ligaments of the distal interphalangeal joint in horses imaged with a high-field magnetic resonance imaging system.

Distal forelimb specimens of eight skeletally mature horses were imaged using proton density turbo spin echo, T1-weighted spoiled gradient echo, T2*-weighted gradient echo, short tau inversion recovery and T2-weighted fast spin echo sequences with the limb parallel to the main magnetic field, and with angulation of the limb relative to the main magnetic field. The magic angle effect can be identified in the collateral ligaments of the distal interphalangeal joint when imaged in a high-field magnetic resonance (MR) imaging system with a horizontally oriented main magnetic field. This effect has previously been described in the collateral ligaments of the distal interphalangeal joint in a low-field system with a vertically oriented main magnetic field. The curvature of the ligaments places the fibers at the magic angle in both horizontally and vertically orientated main magnetic fields. This effect can be identified on short time of echo sequences and impacts the signal pattern of the ligaments at the level of the middle phalanx with the limb in a neutral position and with angulation of the limb. Magic angle effect should be considered as a possible cause of an asymmetrical signal pattern, depending on the positioning of the limb and the sequences used for imaging, when evaluating the collateral ligaments of the distal interphalangeal joint on images acquired with a high-field MR imaging system that has a horizontally oriented main magnetic field.

Magnetic resonance imaging findings of desmopathy of the collateral ligaments of the equine distal interphalangeal joint.

We report the use of a low-field magnetic resonance (MR) imaging system for the detection of desmopathy of the collateral ligament of the distal interphalangeal joint and the long-term outcome. Twenty horses were studied and their medical records and MR images were reviewed retrospectively. Long-term follow-up information was obtained by telephonic questionnaires of owners, trainers, or referring veterinarians. Desmopathy of the medial collateral ligament (80%) and enthesopathy of the affected collateral ligament (80%) were common MR imaging features. Treatment consisted of stall rest followed by a rehabilitation period. Additional treatments included shoeing, extracorporeal shock wave therapy, application of a half limb or foot cast, and medication of the distal interphalangeal joint. Twelve (60%) horses returned to their previous level of exercise and maintained their previous level, whereas eight horses had a poor outcome. Low-field MR imaging in the standing patient can be used to detect collateral ligament desmopathy of the distal interphalangeal joint without a need for general anesthesia.

Magnetic resonance imaging of distal sesamoidean ligament injury.

Distal sesamoidean ligament injury is a recognized cause of lameness but diagnosis using ultrasonography is sometimes difficult. Herein, we describe the normal appearance of the distal sesamoidean ligaments on magnetic resonance (MR) images and the changes that occur when the ligaments are injured. The appearance of the distal sesamoidean ligaments on MR images from 66 control horses and 58 horses with distal sesamoidean desmitis were described and the cross-sectional area and signal intensity of the ligaments measured. In control horses, the ligaments had a characteristic appearance and strong left-right symmetry, and the lateral oblique sesamoidean ligament was larger and had higher signal intensity than the medial ligament. Cross-sectional area and signal intensity were significantly greater in injured straight sesamoidean ligaments compared with the controls. Signal intensity increased significantly with oblique sesamoidean desmitis compared with the controls. Lesions of the distal sesamoidean ligaments were considered the sole cause of lameness in only 2 of 58 horses. Eighty percent of lesions in the distal sesamoidean ligaments were not detected using ultrasonography.

Is a magic angle effect observed in the collateral ligaments of the distal interphalangeal joint or the oblique sesamoidean ligaments during standing magnetic resonance imaging?

Collagen fibers oriented at 55 degrees to the static magnetic field (B0) are characterized by an artifactual increase in signal intensity due to the magic angle effect. We hypothesized that there would be increased signal intensity in the collateral ligaments of the distal interphalangeal joint and oblique sesamoidean ligaments when these ligaments were at angles approaching 55 degrees to a horizontal B0 during standing magnetic resonance (MR) imaging. MR imaging was performed on four cadaver forelimbs in a 0.27 T standing system. Transverse and dorsal images were obtained using various sequences, with limbs angled at 0 degrees, 4 degrees, 8 degrees, and 12 degrees to the vertical. Images were analyzed and the angle of each ligament to B0 determined. Mean signal intensity in the ligament and cortex of the adjacent phalanx was measured and ratios calculated. With subjective interpretation, there was increased signal intensity in the collateral ligaments of the distal interphalangeal joint and oblique sesamoidean ligaments over ranges of angles of 60-78 degrees and 57-69 degrees, respectively, to B0. In fast spin echo (FSE) sequences, with a long echo time (72ms), the effect was less pronounced. FSE sequences can help determine the significance of increased signal intensity within tissues. In spite of limited positions of a limb during standing MR imaging compared with horses under general anesthesia, deviation from a vertical posture sufficient to cause a magic angle effect can still occur in both ligaments tested. Conformation may contribute to the occurrence of the magic angle effect during standing MR imaging. Effort should be made to position horses squarely and to minimize leaning during image acquisition.

Asymmetric signal intensity in normal collateral ligaments of the distal interphalangeal joint in horses with a low-field MRI system due to the magic angle effect.

Increased signal intensity in one of the collateral ligaments of the distal interphalangeal (DIP) joint of sound horses in images acquired using a low-field magnet with vertical orientation of the magnetic field was investigated as a possible manifestation of the magic angle effect. Three isolated equine digits were imaged using the following pulse sequences: (1) spin echo TI, (2) turbo spin echo proton density and T2, and (3) 3D gradient echo T1, in different positions by mildly changing the orientation of the long axis of the digit, in the dorsal plane, relative to the magnetic field. The signal intensity in a ligament was significantly increased when the ligament orientation relative to the magnetic field was 55 +/- 10 degrees. The signal intensity was markedly increased in pulse sequences with short echo time (TE) 5.0, 4.9, and 3.9 times increased, respectively, for 3D gradient echo T1, spin echo T1, and turbo spin echo proton density) and to a lesser extent with pulse sequences with a longer TE (1.8 times increased for turbo spin echo T2). These changes are characteristic of the magic angle effect. Because of the anatomic orientation of the collateral ligaments of the DIP joint, a slight deviation of the long axis of the digit in the dorsal plane, from the ideal horizontal position, will induce an increased signal intensity that can be confused with desmitis. Careful positioning of the foot in magnetic resonance imaging systems where B0 is perpendicular to the long axis of the digit is critical to prevent the occurrence of the magic angle effect.

Intraarterial contrast-enhanced computed tomography of the equine distal extremity.

A technique for regional delivery of contrast medium to the foot of the horse to increase the diagnostic utility of computed tomography (CT) for the characterization of soft tissue structures within the hoof capsule was developed. An intraarterial catheter was placed under ultrasound guidance into the medial palmar artery at the level of the carpus to facilitate a steady-state infusion of iodinated contrast medium. Two 5 mm collimated contiguous acquisition CT scans were performed in 10 horses without lameness or radiographic evidence of distal sesamoid bone degeneration. CT examination was performed before and during regional arterial infusion of iodinated contrast medium administered at a rate of 2 ml/s. Cross-sectional area and mean pre- and post-contrast attenuation of the deep digital flexor tendon and the collateral ligaments of the distal interphalangeal joint were quantified from CT images. Soft tissue anatomy of the foot was also qualitatively characterized from pre- and postcontrast images. Catheterization was successful and without complication in all horses. The evaluated tendons and ligaments were clearly visible and had a small (8-20 Hounsfield Unit) but significant (P < 0.05, paired t-test) increase in attenuation during the steady-state infusion of contrast medium. This study should enhance the diagnostic potential of CT by providing baseline quantitative data for comparison with horses affected with soft tissue injuries in the distal extremity causing lameness that is alleviated with a palmar digital nerve block.

The effect of gallop training on hoof angle in thoroughbred racehorses.

REASONS FOR PERFORMING STUDY: The economic impact of soundness problems in racehorses is very high and low hoof angle at the toe has been associated with a lack of soundness. However, it is not clear what environmental and management factors might contribute to a low hoof angle. OBJECTIVES: To investigate the hypothesis that the hooves of racehorses become flatter when in gallop training, as well as to determine factors contributing to this trend. METHODS: Weekly hoof measurements were taken with a hoof gauge from 45 Thoroughbred racehorses; 4 Thoroughbred show horses kept in consistent conditions and shod by the same farrier as some of the racehorses; and 6 unshod free-ranging horses. A further 15 horses were measured twice in one day to determine the repeatability of the method. RESULTS: Repeatability coefficients were 0.31 degrees for the left hoof and 0.37 degrees for the right. Racehorses in training showed a significant decrease in hoof angle over time while free ranging horses and show horses did not. Free-ranging horses had a significantly lower angle in winter (wet) compared with summer (dry) in both left (P = 0.040) and right (P = 0.017). Show horses had no significant change in hoof angle. Racehorses that had a period of rest during the experiment (n = 11) showed a decrease in hoof angle during training and an increase over their rest period for both hooves (P = 0.005 for the left hoof, P = 0.0009 for the right). CONCLUSIONS: Training for fast exercise in Thoroughbred racehorses is associated with a reduction in hoof angle and wet pasture conditions may also be associated with a reduced hoof angle in free-ranging horses. POTENTIAL RELEVANCE: Gallop exercise has a potentially large effect on hoof angle and therefore, a change in angle should be expected to occur in racehorses starting fast exercise work. Hence management of horses with abnormally low hoof angles may require an adaptation to their training regime in order to minimise this effect.

Gross anatomy of the interphalangeal joint of the great toe: implications for excision of plantar capsular accessory ossicles.

Bony or cartilaginous ossicles occur at the plantar aspect of the interphalangeal joint of the great toe. The variation in pattern, prevalence, and anatomic relationships of these structures is not clearly established in the literature, especially in a Caucasian population. Without this knowledge, pathology at this joint may be underestimated and surgical approaches may be poorly planned particularly as radiographs underestimate the incidence of ossicles at this joint. The aims of this study were to determine the incidence and pattern of ossicles at this joint and to establish their anatomic relationships to aid planning the approach for their excision. The interphalangeal joint of the left hallux was dissected in 40 British Caucasian cadavers and the pattern of nodules and their anatomic relationships were established. In 27.5% of subjects, there was no identifiable ossicle and, in these specimens, the tendon of flexor hallucis longus was adherent to the joint capsule. In the remaining specimens (72.5%), a bursa separated the tendon of flexor hallucis longus from the plantar joint capsule and nodules were found embedded within the joint capsule. More than half (52.5%) of the specimens had a single nodule located centrally within the plantar capsule and the remaining 20% had two nodules lying within the capsule. This study shows that a large proportion of the population have either one or two bony or cartilaginous ossicles at this joint. It has also shown that, when present, these structures do not lie within the tendon of flexor hallucis longus and may be most safely excised from a medial approach.

Form and function of the equine digit.

The list of possible diagnoses derived from matching anatomic structures or tissues to pathologic processes is inevitably broad in nature. Understanding and observation of distal limb function, conformation, and balance is the basis of identifying where the greatest abnormal stresses within the distal limb are likely to occur. This is key to focusing the diagnostic process and, in some instances, to treating the horse when a definitive diagnosis cannot be achieved.