DIAGNOSTIC IMAGING

How to Perform a Transrectal Ultrasound Examination of the Lumbosacral and Sacroiliac

Erik H.J. Bergman, DVM, Diplomate ECAR, Associate Member LA-ECVDI*; Sarah M. Puchalski, DVM, Diplomate ACVR; and Jean-Marie Denoix, DVM, PhD, Agre´ge´, Associate Member LA-ECVDI

Authors’ addresses: Lingehoeve Veldstraat 3 Lienden 4033 AK, The Netherlands (Bergman); Uni- versity of California, Davis, One Shields Avenue, School of Veterinary Medicine, Davis, CA 95616 (Puchalski); E´ cole Nationale Ve´te´rinaire d’Alfort, 7 Avenue du Ge´ne´ral de Gaulle, 94700 Maisons- Alfort, France (Denoix); e-mail: [email protected]. *Corresponding and presenting author. © 2013 AAEP.

1. Introduction have allowed for identification of these structures 5 There is increasing interest in pathology of the and the inter-transverse joints. These authors urge lumbosacral and sacroiliac joints giving rise to stiff- caution in the interpretation of lesions identified on ness and/or lameness and decreased performance radiography in the absence of other diagnostic im- in equine sports medicine.1–3 Pain arising from aging and clinical examination. Nuclear scintigra- these regions can be problematic alone or in con- phy is an important component of work-up for junction with lameness arising from other sites sacroiliac region pain, but limitations exist. Sev- 9,10 (thoracolumbar spine, hind limbs, or forelimbs).4 eral reports exist detailing the and tech- Localization of pain to this region is critically impor- nique findings in normal horses11,12 and findings in tant through clinical assessment, diagnostic anes- lame horses.13 Patient motion, camera positioning, thesia, and imaging. and muscle asymmetry can cause errors in interpre- In general, diagnostic imaging of the axial skele- tation. In normal horses, the appearance of the ton and is difficult to perform and to interpret. sacroiliac region varies with age but is generally Radiography is infrequently performed. To obtain symmetric. In horses with sacroiliac problems, it is good-quality diagnostic radiographs, general anes- more difficult to distinguish the tubera sacrale from thesia, a high-output radiographic generator, and the sacroiliac than in normal horses, and, in special techniques must be performed.5,6 Variation horses with lameness, there is more asymmetry in the size and shape of the sacroiliac joints and detected.12,13 sacral wings and caudal sacral osteophytes are com- Techniques for percutaneous and transrectal ul- mon7,8; special techniques for taking radiographs trasound examination have been described, and

NOTES

AAEP PROCEEDINGS ր Vol. 59 ր 2013 229 DIAGNOSTIC IMAGING their use is increasingly common.2,14–19 Ultra- sound is very useful for the evaluation of the joint margins and lumbosacral .14 Similar to the radiographic anatomy of the region, variability exists in the appearance of the tubera sacrale, dorsal sacroiliac , thoracolumbar fasciae, and the .3,19 Artifacts of acquisition and interpretation can occur with im- proper technique in the ultrasound examination, and knowledge of reference images and the regional anatomy is paramount in accurate interpretation of diagnostic imaging studies of this region. All diag- nostic imaging techniques should also be interpreted in light of the anamnesis and the static and dynamic clinical examination. The purpose of this “How-to” presentation is to provide a review of the technique for transrectal ultrasound with reference images and ultrasound images of examples of pathology of the lumbosacral junction, lumbosacral intertransverse joints, and sacroiliac joints. This presentation will review im- aging findings in 231 horses presenting to Linge- hoeve Diergeneeskunde, Equine Referral Hospital, The Netherlands, for evaluation of stiffness or poor performance in 2012. Fig. 1. Schematic drawing by Denoix of the ventral aspect of the 2. Materials and Methods lumbosacral region illustrates the stepwise procedure of trans- The diagnostic imaging picture archiving and com- rectal evaluation of the lumbosacral and sacroiliac joints. Red munications system (PACS) of Lingehoeve Dierge- lines indicate probe orientation. A, Sixth ; neeskunde was searched for all horses undergoing B, ; C, sciatic nerve; a, L6 ; b, S1 nerve transrectal ultrasound during 2012. Age and breed root; 1, lumbosacral intervertebral joint; 2, L5–6 intervertebral data were collected. All horses had a complete joint; 3, lumbosacral intervertebral foramen; 4, lumbosacral in- tertransverse joint; 5, S1–2 intervertebral foramen; 6, sacroiliac clinical evaluation for poor performance. After an- joint; 7, direction of imaging the psoas minor tendon. amnesis and static and dynamic examination, a per- cutaneous examination of the lumbar spine and a transrectal examination of the sacroiliac and lum- bosacral junction were performed. Transrectal ultrasound examination was per- the lumbosacral (LS) disc, the ventral longitudinal formed with the use of the technique described by , and, occasionally, the dorsal longitudinal Denoix.20 and illustrated in Fig. 1. A 5- to 10-MHz ligament, can be identified (Fig. 2). At this loca- micro-convex intra-operative ultrasound probe was tion, scan the entire disc by moving the probe left used per rectum. All horses were sedated with an and right, maintaining a paramedian orientation of ␣-2 agonist and restrained in stocks. The rectum the probe. was cleaned, and copious lubricant was introduced into the rectum. A stand-off pad was not used. Step 2: Intervertebral Disc and Vertebral Bodies of Anti-spasmodic agents were used infrequently (nine L5–6 and L4–5 horses). The ultrasound images are oriented so From the LS disc, move the ultrasound probe in that ventral is to the bottom of the image display a cranial direction while maintaining the median screen, and, when appropriate, cranial is to the left. plane orientation. As the probe is moved forward, maintain visualization of the ventral vertebral Technique margin. The L5–6 disc is just dorsal and is usually caudal to the aortic bifurcation. The probe is Step 1: Lumbosacral Disc moved cranially to identify the L4–5 disc space dor- Transrectally, the and its bifurcation (nor- sal to the aorta. mally at the level of the fifth lumbar vertebra) can be palpated. Place the ultrasound probe in a me- Step 3: Lumbosacral Intervertebral Foramen dian plane, caudal to the aorta and vena cava (bi- Identify the LS disc space. Move the probe in a furcation normally at the level of L5). The L6 and lateral direction, maintaining a paramedian imag- S1 vertebrae can be recognized by the well-defined ing plane. As the probe is moved laterally, look hyperechoic shadowing ventral margins, meeting for a smoothly demarcated defect in the bone surface at approximately a 140° to 150° angle. At this site, that represents the intervertebral foramen. Once

230 2013 ր Vol. 59 ր AAEP PROCEEDINGS DIAGNOSTIC IMAGING

Fig. 2. These images depict the desired ultrasound image and probe position for evaluation of the lumbosacral joint, including the LS disc, in a median plane (A1 and A2) and a transverse plane (B1 and B2). This represents Step 1 of the examination. Stars mark the ; X marks the ventral longitudinal ligament.

the defect is identified, look for the L6 nerve root tified, the imaging plane will be oblique to the nerve, that can be identified as a bundle of long, parallel, and probe manipulation is needed to orient the ul- hyperechoic fibers. When the foramen is first iden- trasound probe parallel to the nerve root to char-

Fig. 3. This image depicts a paramedian plane of the lumbosacral intertransverse joint and the associated probe position along the ventral aspect of the sacrum. This represents Step 4 of the examination. Arrow demarcates the joint space.

AAEP PROCEEDINGS ր Vol. 59 ր 2013 231 DIAGNOSTIC IMAGING

Fig. 4. These images depict longitudinal sections through three different sacroiliac joints (A) and the associated probe position (A1 and A2). Star marks the ventral sacroiliac ligament. This represents Step 6 of the examination. Arrow marks the joint space.

acterize this structure as it passes through the L6 nerve root. The operator must maintain aware- foramen. ness of their orientation and location relative to the described landmarks in order to insure accurate Step 4: Lumbosacral Intervertebral Intertransverse identification of these structures. Joints From the LS intervertebral foramen, continue to Step 6: move in a lateral direction to cross the LS inter- From the S1 nerve root, move the entire probe in a transverse joint. The joint is identified as a small lateral direction, maintaining a paramedian probe defect in the bone surface (Fig. 3). Center the sur- orientation. The ventral surface of the sacral wing face defect (joint space) in the ultrasound image and has a convex contour, allowing it to be identified. move the probe in a medial to lateral direction while As the probe is moved along the convexity of the maintaining a paramedian probe orientation. This sacrum, a large artery, the caudal gluteal artery, allows for evaluation of the joint margins. will be identified. Immediately dorsal to the caudal gluteal artery, the convex surface of the sacral wing Step 5: S1–2 Intervertebral Foramen will form a junction with another hyperechoic shad- Return to the L6 nerve root at the LS intervertebral owing but flat bone surface. This junction repre- foramen (see Step 3). Move the entire probe in a sents the sacroiliac joint. The caudal gluteal artery caudal direction, maintaining the same probe orien- is used as an acoustic window for evaluation of the tation to identify the S1–2 intervertebral foramen sacroiliac joint margins. Additionally, the ventral and the S1 nerve root. The imaging characteristics sacroiliac ligament can be identified, providing an are similar to the LS intervertebral foramen and the additional landmark for the sacroiliac joint. The

232 2013 ր Vol. 59 ր AAEP PROCEEDINGS DIAGNOSTIC IMAGING

Fig. 5. These composite images depict three different grades of alterations in echogenicity and homogenicity in the lumbosacral disc. Median plane images are displayed along the top and transverse images along the bottom. A1 and A2, Mild change in echogenicity and homogenicity; B1 and B2, moderate; C1 and C2, severe.

ventral sacroiliac ligament long is oblique to the structure can be tracked by means of ultrasound to paramedian imaging plane and perpendicular to the its attachment on the ilium. joint margin; therefore, probe manipulation is re- quired to optimize images of this ligament. Step 8 Make longitudinal images of the caudomedial Repeat for the contralateral side. Using the same margin of the sacroiliac joint including the ventral imaging landmarks identify the contralateral in- sacroiliac ligament (Fig. 4). tervertebral forminae, lumbosacral intertransverse joint, sacroiliac joint, and ventral sacroiliac liga- Optional: Step 7: Psoas Minor Tendon ment. The psoas minor tendon and its insertion on Move the entire probe in a lateral and ventral direc- the ilium can also be visualized at this site. tion along the ventral concavity of the ilium. The Ultrasound images were reviewed on a dedicated psoas minor tendon is encountered and can be workstation with DICOM viewing software (eFilm, identified by the typical imaging characteristics of Merge Healthcare), including digital calipers. One a tendon (long, parallel hyperechoic fibers). This author reviewed the images of the lumbosacral disc,

AAEP PROCEEDINGS ր Vol. 59 ր 2013 233 DIAGNOSTIC IMAGING

Fig. 6. These composite images depict three different grades demonstrating alterations in the lumbosacral joint vertebral margins. Images are made in a median plane. Alteration in margination is demarcated by the arrowheads. A, Focal, mild change; B, regional, moderate change; C, severe change along the majority of the visible margin of L6.

intertransverse joint, and sacroiliac joint, retrospec- mal if proliferation was identified. Descriptive sta- tively (H.J.B.). To grade the following structures, tistics were calculated. a subset of reference images were identified and graded as normal, mild, moderate, or severe by two 3. Results authors (H.J.B. and S.M.P.). On the basis of the Two hundred thirty-one horses were identified. subset of reference images, the grading of the re- The breed distribution included 199 Warmblood maining images was performed. The LS disc echo- horses and 32 other breeds. The mean age was 8.8 genicity and homogeneity were considered together, years (standard deviation ϭ 3.7). The median age and the disc was graded (normal, mild, moderate, severe). The LS disc grading was mild if the disc has localized regions of increased echogenicity or changes from homogenous to mildly heterogeneous, moderate if there was increased echogenicity and the disc appeared heterogeneous, and severe if the disc was hyperechoic and heterogeneous (Fig. 5). The vertebral margins at the LS intervertebral space were characterized for changes in shape and margination (normal, mild, moderate, severe). They were considered mildly abnormal if there was focal irregularity or shape change, moderate if the irregular margination involved most but not all of the vertebral border, and severe if the margin was irregular and there was shape change indicating bone modeling (Fig. 6). The intervertebral space was measured from the caudoventral margin of L6 to the cranioventral margin of S1. The degree of ventral bulging of the LS disc was measured in the fashion described by Nagy et al3 (Fig. 7). The left and right sacroiliac joints were considered sepa- rately. Bone proliferation as identified by in- creased size and irregular margination at the joint margin was characterized for the ilium and the sa- Fig. 7. This median plane image of the lumbosacral joint dem- onstrates the measurements. Measurement A (1.8 cm) was crum (normal, mild, moderate, and severe) (Fig. 8 made from the caudoventral margin of L6 to the cranioventral and Fig. 9). The ventral sacroiliac ligament was margin of S1. Measurement B (0.3 cm) was made by drawing a noted as normal or abnormal if it was thickened and line perpendicular to measurement A to the ventral margin of the heterogeneous). The lumbosacral intertransverse intervertebral disc. Stars mark the ventral longitudinal liga- joints were also characterized as normal or abnor- ment.

234 2013 ր Vol. 59 ր AAEP PROCEEDINGS DIAGNOSTIC IMAGING

Fig. 8. These composite images depict three different grades of sacral margin proliferation. The images are made in a paramedian plane. S indicates sacrum; I, ilium; joint space is demarcated by the open arrow. Arrowheads identify bone proliferation that is mild in A, moderate in B, and severe in C on the sacrum at the level of the sacroiliac joint.

was 8, with a range of 3 to 22 years. In 227 horses, Images of 228 lumbosacral disc spaces were re- poor performance was attributed at least in part to viewed. There was sacralization of the LS space abnormalities of the lumbosacral or sacroiliac joints. in three horses (ϳ1%). Three horses were excluded Four horses were asymptomatic, and transrectal ul- because diagnostic images were not saved to the trasound was performed as a part of pre-purchase PACS. Because of data presented previously by examination. Nagy and Dyson, normal and mild were considered

Fig. 9. These composite images depict three different grades of ilium margin proliferation. The images are made in a paramedian plane. S indicates sacrum; I, ilium; joint space is demarcated by the open arrow. Arrowheads identify bone proliferation that is mild in A, moderate in B, and severe in C on the ilium at the level of the sacroiliac joint.

AAEP PROCEEDINGS ր Vol. 59 ր 2013 235 DIAGNOSTIC IMAGING

Table 1. Lumbosacral Disc Table 3. Lumbosacral Disc Space Measurements

Echogenicity Number (n ϭ 225) Percentage LS Disc Measurement A Measurement B

Normal 120 Mean (SD) 15.4 mm (2.5) 1.7 mm (0.95) 186 82 Mild 66 Median (range) 15 (8–22) 2 (0–3) Moderate 35 16 Severe 4 2

without clinical signs of lumbosacral disease dem- onstrated that there can be variability in the echo- together for the lumbosacral disc space descriptive genicity and margination at this site, but marked characteristics. The results for ultrasound findings change was not present.3 Although it is impossible of the lumbosacral disc and vertebral margins are to make a direct comparison of the two studies, it presented in Table 1 and Table 2, respectively. is likely that horses in this population with moder- Measurements of the lumbosacral disc space and ate or severe ultrasound changes have clinically sig- LS disc bulging are presented in Table 3. Abnor- nificant imaging findings. Moderate to severe malities of the lumbosacral intertransverse joints changes at the lumbosacral junction are identified in were infrequent, with 38 of 462 (8%) identified. clinically abnormal horses. It must be underlined Sacroiliac joint abnormalities were separated into that subclinical manifestations with incidence on joint margin abnormalities on the ilium and on the the horse behavior, locomotion, or performance do sacrum; the results are presented in Table 4. Left exist. and right were considered separately, and, of the Anomalous anatomy was rare in this population. ϭ total abnormal sacroiliac joints (n 173), abnormal- Historic literature has discussed variability in the ities of the left were identified in 71 and abnormal- anatomic configuration of the pelvis and lumbosa- ities of the right were identified in 102. The ventral cral region,5 and sacralization of the lumbar verte- sacroiliac ligament was characterized as abnormal bra has been reported previously.2,5 Ultrasound (thickened and heterogeneous) in 113 of 461 (24%) evaluation is limited to the ventral aspect of the joints. Similar to the intertransverse joints, when osseous structures, and the identification of anoma- considering moderate and severe abnormalities of lies is dependent on the anomaly causing overall the sacroiliac joints, abnormalities of higher severity shape change of the vertebra or loss of the interver- were more frequently identified on the right 71 of tebral disc space, visible from the ventral surface. 113 than the 42 of 113. Lumbosacral intertransverse joint pathology was also very uncommon in this population. Ultra- 4. Discussion sound evaluation of these joints is limited to the The objective of this report was to provide a review ventral joint margin. Postmortem evaluation of of the procedure for transrectal ultrasound evalua- Thoroughbred racehorses showed that the entire tion technique of the lumbosacral and sacroiliac population had degenerative changes of the inter- joints and to provide reference images from a popu- transverse joints.21 The low incidence of inter- lation of horses with clinical signs of lumbosacral transverse joint pathology relative to this previous and/or sacroiliac dysfunction. For each of the ana- report may be caused by the differences in patient tomic sites evaluated, this population of horses had population or possibly the limitations of transrectal variability in the severity of the abnormal findings. ultrasound as compared with ex vivo postmortem It remains difficult to determine the clinical sig- evaluation. Lumbosacral intertransverse joint pa- nificance of alterations in echogenicity and margin- thology has been observed with a higher prevalence ation at the lumbosacral joint. In this group of in racing Standardbred trotters. horses, there was variability in the echogenicity The sacroiliac joint abnormalities of the majority of the LS disc and the margination of the endplates of horses in this study showed normal or mild of L6 and S1, but the majority of horses were cate- changes. Nevertheless, slightly greater than one gorized as normal or mildly abnormal. A moderate proportion of horses were described as moderate to severely abnormal. Previous reports detailing the ultrasound evaluation of this region in horses Table 4. Sacroiliac Joint Margin Bone Proliferation Number Percentage

Sacrum (n ϭ 462) Normal 187 289 63 Table 2. Lumbosacral Disc Space Vertebral Margins Mild 102 Vertebral Margin Number (n ϭ 225) Percentage Moderate 120 26 Severe 53 11 Normal 146 Ilium (n ϭ 462) Normal 136 207 92 311 67 Mild 61 Mild 175 Moderate 12 5 Moderate 119 26 Severe 6 3 Severe 32 7

236 2013 ր Vol. 59 ր AAEP PROCEEDINGS DIAGNOSTIC IMAGING third of horses in this group with clinical signs had 2. Denoix JM. Diagnosis of Sacroiliac Lesions in Horses. Essen, moderate to severe sacroiliac changes. Ultrasound Germany: Equitana XVI-Tagung; 2005. 3. Nagy A, Dyson S, et al. Ultrasonographic findings in the evaluation of the joint margins allows for the iden- lumbosacral joint of 43 horses with no clinical signs of back tification of periarticular proliferative new bone pain or hindlimb lameness. Vet Radiol Ultrasound 2010;51: (osteophytes), as expected in this or any other joint 533–539. with joint disease. Variability in the appearance 4. Dyson S, Murray R. Pain associated with the sacroiliac joint of the sacroiliac joint is expected in normal popula- region: a clinical study of 74 horses. Equine Vet J 2003;35: 240–245. tions; however, many publications agree that abnor- 5. Gorgas D, Kircher P, et al. Radiographic technique and malities of increasing severity are increasingly anatomy of the equine sacroiliac region. Vet Radiol Ultra- likely to be clinically significant.6,10,12,18,20 Scinti- sound 2007;48:501–506. graphic abnormalities are often identified in horses 6. Gorgas D, Luder P, et al. Scintigraphic and radiographic appearance of the sacroiliac region in horses with gait abnor- with hind limb lameness; however, care should be malities or poor performance. Vet Radiol Ultrasound 2009; taken in the interpretation of these findings because 50:208–214. overlap exists between horses with sacroiliac dis- 7. Dalin G, Jeffcott LB. Sacroiliac joint of the horse, 1: gross ease confirmed by diagnostic anesthesia and horses morphology. Anat Histol Embryol 1986;15:80–94. 4,12,13 8. Dalin G, Jeffcott LB. Sacroiliac joint of the horse, 2: mor- with other causes of hind limb lameness. phometric features. Anat Histol Embryol 1986;15:97–107. It is likely that a similar corollary exists for ultra- 9. Erichsen C, Berger M, et al. The scintigraphic anatomy of sound evaluation of the same region, whereby over- the equine sacroiliac joint. Vet Radiol Ultrasound 2002;43: lap exists between clinically significant and 287–292. clinically silent pathologic change. However, sac- 10. Erichsen C, Eksell P, et al. Scintigraphy of the sacroiliac joint region in asymptomatic riding horses: scintigraphic roiliac pathologic change has been a common finding appearance and evaluation of method. Vet Radiol Ultrasound in postmortem studies, which may indicate that this 2003;44:699–706. truly represents a common pathology.7,8,21 By con- 11. Feige K, Schwarzwald C, et al. Esophageal obstruction in trast, it is also important to recall that ultrasound of horses: a retrospective study of 34 cases. Can Vet J 2000; 41:207–210. the caudomedial margin of the sacroiliac joint may 12. Dyson S, Murray R, et al. The sacroiliac joints: evaluation represent a small window relative to overall size of using nuclear scintigraphy, part 2: lame horses. Equine Vet J the joint and associated soft tissue structures. 2003;35:233–239. In summary, transrectal ultrasound of the sacro- 13. Dyson S, Murray R, et al. The sacroiliac joints: evaluation iliac and lumbosacral joints is a key component the using nuclear scintigraphy, part 1: the normal horse. Equine Vet J 2003;35:226–232. evaluation of horses with lumbosacral and sacroiliac 14. Denoix JM. Spinal biomechanics and functional anatomy: stiffness or poor performance. The technique re- back problems. Vet Clin North Am Equine Pract 1999;15:27– quires a knowledge of the anatomy, the ability to 60. perform ultrasound, good equipment, and knowl- 15. Tomlinson JE, Sage AM, et al. Detailed ultrasonographic mapping of the pelvis in clinically normal horses and ponies. edge surrounding the identification and interpre- Am J Vet Res 2001;62:1768–1775. tation of abnormalities. Transrectal ultrasound 16. Tomlinson JE, Sage AM, et al. Ultrasonographic abnormal- should be used in conjunction with anamnesis, com- ities detected in the sacroiliac area in twenty cases of upper plete clinical examination, and percutaneous ultra- hindlimb lameness. Equine Vet J 2003;35:48–54. sound evaluation of the lumbar facet joints. This 17. Kersten AA, Edinger J. Ultrasonographic examination of the equine sacroiliac region. Equine Vet J 2004;36:602–608. technique can be used to guide diagnostic and treat- 18. Denoix JM, Coudry V. Diagnosis and Treatment of Lumbo- ment decisions. Although it is a potentially useful sacral and Sacroiliac Pain in Horses. Essen, Germany: XVI technique for prepurchase examination evaluation, Tagung uber Pferdekrankheiten; 2005. caution should be exercised in image interpretation 19. Engeli E, Yeager AE, et al. Ultrasonographic technique and normal anatomic features of the sacroiliac region in horses. until a broader body of knowledge exists. Vet Radiol Ultrasound 2006;47:391–403. 20. Denoix JM, Audigie F, et al. Review of Diagnosis and Treat- ment of Lumbosacral Pain in Sport and Race Horses, in References Proceedings. Am Assoc Equine Pract 2005;51:366–373. 1. Jeffcott LB, Dalin G, et al. Sacroiliac lesions as a cause of 21. Haussler KK, Stover SM, et al. Pathologic changes in the chronic poor performance in competitive horses. Equine Vet J lumbosacral vertebrae and pelvis in Thoroughbred race- 1985;17:111–118. horses. Am J Vet Res 1999;60:143–153.

AAEP PROCEEDINGS ր Vol. 59 ր 2013 237