Baxter Nerve - Journal of Ultrasound in Medicine

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1 3209jum_Layout 1 8/20/13 11:44 AM Page 1643 ORIGINAL RESEARCH Sonographic Visualization of the First Branch of the Lateral Plantar Nerve (Baxter Nerve) Technique and Validation Using Perineural Injections in a Cadaveric Model James C. Presley, MD, Eugene Maida, MB, ChB, Wojciech Pawlina, MD, Naveen Murthy, MD, Daniel B. Ryssman, MD, Jay Smith, MD Videos online at ObjectivesThe primary purpose of this investigation was to document the ability of high-resolution sonography to accurately identify the first branch of the lateral plantar nerve (FBLPN) using sonographically guided perineural injections in an unembalmed cadaveric model. MethodsA single experienced operator completed sonographically guided perineural FBLPN injections in 12 unembalmed cadaveric specimens (6 right and 6 left) obtained from 10 donors (5 male and 5 female) aged 47 to 95 years (mean, 71 years) with an average body mass index of 24.2 kg/m2 (range, 17.231.6 kg/m2). All injections were completed using 22-gauge, 38-mm stainless steel needles to deliver 1 mL of 50% diluted colored latex adjacent to the FBLPN in the abductor hallucis-quadratus plantae (AH- QP) interval. Six injections were completed using a cart-based ultrasound (US) machine and a 175-MHz transducer, and 6 were completed using a portable US machine and a 123-MHz transducer. Nerve conspicuity was graded on a 4-point scale (1, poor; 4, Received December 10, 2012, from the Depart- excellent). After a minimum of 24 hours, study coinvestigators dissected each speci- ments of Physical Medicine and Rehabilitation men to assess injectate placement. (J.C.P., J.S.), Anatomy (W.P., J.S.), Radiology ResultsAll 12 injections accurately placed latex onto the FBLPN within the AH-QP (N.M., J.S.), and Orthopedics (D.B.R.), Mayo Clinic College of Medicine, and Mayo Clinic interval, with 11 of 12 (91%) resulting in complete nerve coverage. Proximal latex over- Sports Medicine Center (E.M., J.S.), Rochester, flow to the lateral plantar nerve occurred in 82% of cases (10 of 12). The average dis- Minnesota USA. Revision requested January 14, tance between the plantar fascia and injected latex was 1.2 cm (range, 1.01.75 cm). 2013. Revised manuscript accepted for publication No vascular injury was seen in any specimen. The average nerve conspicuities were 3.7 February 19, 2013. (range, 34) using the cart-based US machine and 1.8 (range, 14) using the portable This project was funded by Mayo Clinic US machine. institutional funds. Address correspondence to Jay Smith, MD, ConclusionsSonographic visualization of the FBLPN in the AH-QP interval is feasi- Department of Physical Medicine and Rehabili- ble and should be considered for diagnostic and therapeutic purposes in patients pre- tation, Mayo Clinic College of Medicine, 200 First senting with chronic or atypical heel pain syndromes. Further clinical experience should St SW, 14th Floor, Rochester, MN 55905 USA. refine the role of FBLPN sonography and explore the utility of sonographically guided E-mail: [email protected] diagnostic and therapeutic FBLPN perineural injections. Key WordsBaxter nerve; first branch of the lateral plantar nerve; perineural injections Abbreviations ADM, abductor digiti minimi; AH, abductor hallucis; FBLPN, first branch of the lateral plantar nerve; FDB, flexor digitorum brevis; LPN, lateral plantar nerve; MCN, medial calcaneal nerve; MPN, medial plantar nerve; QP, quadratus plantae; TN, tibial nerve; US, ultrasound P lantar heel pain is one of the most common clinical condi- tions presenting to foot and ankle specialists, with an esti- mated lifetime prevalence of 10% among people in the United States.1 The differential diagnosis of plantar heel pain is broad and includes plantar fasciitis, plantar fascia rupture, calcaneal doi:10.7863/ultra.32.9.1643 stress fracture, and fat pad disorders such as fat pad atrophy.2 2013 by the American Institute of Ultrasound in Medicine | J Ultrasound Med 2013; 32:16431652 | 0278-4297 |

2 3209jum_Layout 1 8/20/13 11:44 AM Page 1644 Presley et alSonography of the First Branch of the Lateral Plantar Nerve Although uncommon, chronic heel pain may also arise Neuropathy affecting the FBPLN is an uncommon from focal neuropathies secondary to trauma or entrap- but well-documented cause of chronic heel pain.2,3,812 The ment. More specifically, entrapment of the first branch diagnosis of FBLPN neuropathy can be challenging, as of the lateral plantar nerve (FBLPN), also known as the patients may present with generalized heel pain symptoms Baxter nerve, has been implicated in up to 20% of chronic often overlapping with more common clinical entities such heel pain cases.2,3 as plantar fasciitis. A sharp, radiating pain along the course The FBLPN is a small (2 mm) mixed motor and of the FBLPN, a focal Tinel sign, and maximal tenderness sensory nerve typically arising from the lateral plantar nerve at the point of nerve entrapment suggest FBLPN involve- (LPN) just distal to its origin from the tibial nerve (TN; ment, although the sensitivity and specificity of these clin- Figure 1).46 It provides motor innervation to the quadra- ical symptoms and signs have not been established.3,12,13 tus plantae (QP), flexor digitorum brevis (FDB), and Consequently, clinicians may use ancillary diagnostic test- abductor digiti minimi (ADM) muscles and sensory inner- ing to confirm clinically suspected FBLPN neuropa- vation to the calcaneal periosteum and long plantar liga- thy.2,3,10,12 Although plain radiographs can identify plantar ment.4 The FBLPN traverses the medial and plantar calcaneal spurs, they are unable to directly visualize nerve aspects of the heel region, where it may be injured or entrapment, and many patients with calcaneal spurs are entrapped at two well-described locations (Figure 2). asymptomatic.14 Magnetic resonance imaging provides More proximally, the FBPLN may be entrapped between excellent soft tissue detail of the TN and its branches, but the deep, taut fascia of the abductor hallucis (AH) muscle the sensitivity of magnetic resonance imaging to detect and the medial aspect of the QP, where the nerve changes FBLPN neuropathy remains indeterminate. In addition, course from vertical to horizontal as it travels toward the up to 6% of asymptomatic individuals have ADM atrophy lateral foot. Distally, the nerve may be entrapped at the and/or fatty infiltration, reducing the specificity of this anterior aspect of the medial calcaneal tuberosity as it magnetic resonance imaging finding in the context of sus- passes laterally, bordered by the FDB plantarly and the QP pected FBPLN entrapment.10,11,15 Finally, electrodiag- dorsally.79 Chronic inflammation of the plantar fascia or nostic testing has been inconsistently useful in the FDB from plantar fasciitis or plantar calcaneal spurs can diagnosis of FBLPN entrapment.10,1618 produce conditions favoring FBLPN nerve entrapment at this location.9 Figure 2. Cross-sectional coronal anatomic drawing at the anterior cal- caneus showing two potential entrapment sites for the FBLPN (Baxter nerve). Proximally, the nerve may be entrapped between the AH and QP muscles (Site 1), while distal entrapment may occur between the FDB Figure 1. Anatomic drawing of the medial ankle showing the branching muscle and the QP (Site 2). The proximal entrapment site was visualized pattern of the TN in the tarsal tunnel region. The AH has been partially as part of the current investigation, whereas the distal FBLPN was unable removed to show the vertical course of the FBLPN (Baxter nerve) to be visualized sonographically. Note the position of a typical plantar between the AH (removed) and QP muscles. SPHN indicates saphe- calcaneal spur in the dorsal aspect of the FDB (asterisk). Left is lateral; nous nerve. Reproduced with permission from the Mayo Clinic. and right, medial. PT indicates peroneal tendons. Reproduced with per- mission from the Mayo Clinic. 1644 J Ultrasound Med 2013; 32:16431652

3 3209jum_Layout 1 8/20/13 11:44 AM Page 1645 Presley et alSonography of the First Branch of the Lateral Plantar Nerve Due to the limitations of the history, physical exami- Anatomic Dissection nation, and diagnostic testing to identify FBLPN neuropa- The authors completed a detailed medial ankle dissection thy, clinicians may consider the use of diagnostic injections in an unembalmed cadaveric specimen to gain familiarity to confirm or refute suspected FBLPN neuropathy. In addi- with the regional anatomy and provide a template for tion, therapeutic corticosteroid injections have been used attempted sonographic identification of the FBLPN as part of comprehensive nonsurgical treatment programs (Figure 3). As expected based on prior anatomic descrip- that also include activity modification, physical therapy, tions, the FBLPN arose from the LPN just distal to the anti-inflammatory medications, and orthoses.12,13,19,20 TN bifurcation, was approximately 2 mm in maximal High-resolution sonography provides submillimeter diameter, and demonstrated a relatively vertical course resolution and theoretically should be able to image the as it passed caudally within the plane between the AH and FBLPN.21 Nonetheless, no prior investigation has formally QP (ie, AH-QP interval).49 The nerve then assumed a attempted to identify the FBLPN using ultrasound (US). more horizontal oblique orientation as it coursed laterally Therefore, the purpose of this study was 2-fold: (1) to toward the ADM, bordered dorsally by the QP and on its attempt to identify the FBLPN in 12 unembalmed cadav- plantar surface by the FDB. As the nerve continued later- eric specimens using high-frequency linear transducers; ally toward the ADM, it passed beyond the lateral margin and (2) to perform sonographically guided FBLPN per- of the QP, where it was bordered dorsally by the plantar ineural latex injections at the level of the AH-QP interval. calcaneal surface and the long plantar ligament. One or Given recent technological advances in high-resolution more small arteries and accompanying veins arising from sonography, we hypothesized that the FBLPN could be the tibial or lateral plantar vessels accompanied the FBLPN identified in all 12 unembalmed cadaveric specimens as along its course and were typically located adjacent to its confirmed by sonographically guided perineural latex anterior (ie, distal) surface. Based on the dissection and injections with subsequent dissection.22 previously published anatomic descriptions, the authors Diagnostically, the results of this investigation would postulated that the FBLPN could be located by using the support a potential role for high-resolution sonography to easily identified landmarks of the TN, LPN, and AH-QP directly visualize the FBLPN at the AH-QP interval and interval. for performing precise sonographically guided diagnostic injections. Therapeutically, sonographically guided FBLPN perineural injections or ablative procedures could facilitate functional improvement in patients with confirmed neu- Figure 3. Anatomic dissection of the tarsal tunnel region showing the ropathic heel pain syndromes arising from the FBLPN. course of the FBLPN (Baxter nerve; compare with Figure 1). The AH muscle has been cut at the level of the calcaneus and reflected distally Materials and Methods (to the left) to expose the QP muscle. The FBLPN arises from the pos- terior aspect of the LPN and courses in a vertical direction within the AH- QP interval. It then turns laterally to innervate the ADM muscle. Left is General distal; and right, proximal. Asterisks in this and other images indicate the The authors completed a literature review and anatomic dis- plantar fascia sectioned from the calcaneus and retracted distally, expos- section to gain familiarity with the neurologic anatomy ing the FDB arising from its deep surface. within the tarsal tunnel region. After developing a technique to potentially identify the FBPLN, the senior author (J.S.) attempted to sonographically localize the FBLPN in 12 unembalmed cadaveric specimens and confirm its localiza- tion via sonographically guided perineural latex injections. Six procedures were completed using a cart-based US machine, and 6 injections were completed using a portable US machine. Study coinvestigators dissected each specimen at a minimum of 24 hours after injection to assess the accu- racy of sonographic FBLPN localization by determining the proximity of the injected latex to the anatomically identified FBLPN. All components of this investigation were com- pleted in the Mayo Clinic Procedural Skills Laboratory. The Mayo Clinics Bio-Specimens Subcommittee of the Institu- tional Review Board approved the project. J Ultrasound Med 2013; 32:16431652 1645

4 3209jum_Layout 1 8/20/13 11:44 AM Page 1646 Presley et alSonography of the First Branch of the Lateral Plantar Nerve Anatomic Specimens Figure 4. Initial visualization of the TN (TIB NRV) in the proximal tarsal tun- Twelve unembalmed cadaveric ankle-foot specimens were nel region. A, The anterior aspect of the transducer is placed on the medial malleolus, and its posterior aspect is directed posteriorly-inferiorly. B, Rela- used for the investigation. All specimens were fully thawed tionship of the transducer (box) to the underlying anatomy. C, Correlative at room temperature immediately before use and were free short-axis sonographic view of the TN (white arrows) lying deep to the flexor from signs of surgery, trauma, or major deformity about the retinaculum (yellow arrows) and superficial to the flexor hallucis longus ten- ankle-foot region. Age, sex, body mass index, and side (left, don (FHL). Bottom is deep/lateral; left, distal (DIST); right, proximal; and top, superficial/medial. DIV indicates division; and TAL, medial talus. right, or both) were recorded for each donor. Specimens were obtained on the basis of availability and therefore were A not necessarily paired (ie, left and right foot-ankle from the same donor). However, specimens were chosen to ensure an equal number of left and right ankle specimens. Equipment Two different machine-probe combinations were used to allow findings to be generalized to various clinical prac- tices. Six procedures were completed using a cart-based iU22 US machine and a 175-MHz linear array transducer (Philips Healthcare, Bothell, WA), whereas 6 procedures were completed using a Philips CX50 portable US machine with a 123-MHz linear array transducer. All B procedures were performed with 22-gauge, 38-mm stain- less steel needles. FBLPN Identification and Injection Procedure For the purpose of this investigation, the authors attempted to localize and inject around the FBLPN at the more proximal site of potential entrapment, within the AH-QP interval (Figure 2, Site 1). The preliminary inves- tigation suggested that the nerve could be localized in this region; conversely, direct identification of the FBLPN more distally at the FDB-QP interval (Figure 2, Site 2), was not feasible due to the combination of small nerve size, deep location, complex anatomy, and presence of the thick heel pad. The transducer was placed in an anatomic trans- verse plane posterior to the medial malleolus to localize the C TN in the short axis (Figure 4). Following image opti- mization, the transducer was moved caudad to identify the division of the TN into the medial plantar nerve (MPN), LPN, and medial calcaneal nerve (MCN; Figure 5 and Video 1). Thereafter, the LPN was centered and its poste- rior margin scrutinized as the transducer was moved fur- ther caudad. In the majority of cases (88%), the FBLPN originates from the LPN and should appear as a 1- to 2- mm-maximal-diameter fascicle arising from the LPNs pos- terior border (Figures 6 and 7 and Video 2).7 Once identified, the FBLPN was followed further caudad to ensure that it entered the AH-QP interval, thus confirming its sonographic identity (Figure 8 and Video 3). In approx- imately 12% of individuals, the FBLPN has a more proxi- mal origin from the TN.7 In such cases, the LPN cannot 1646 J Ultrasound Med 2013; 32:16431652

5 3209jum_Layout 1 8/20/13 11:44 AM Page 1647 Presley et alSonography of the First Branch of the Lateral Plantar Nerve Figure 5. Following TN localization as shown in Figure 4, the transducer A is moved caudad to visualize the TN division, at which point the TN splits into the MPN, LPN, and MCN. A and B, Transducer position (box) and underlying anatomy, respectively (compare with Figure 4, A and B). C E, Correlative short-axis sonographic views of the TN division (TIB NRV DIV) obtained sequentially in a cephalad-caudad direction. In C, the MPN (yellow arrows) and LPN (green arrows) have just originated from the TN. Branches of the MCN are not distinguishable from the LPN at this point. In D, slightly caudad to C, the MCN becomes more conspic- uous as it begins its courses in a posterior direction toward the subcu- taneous tissues (white arrow). In E, two MCN branches (white arrows) are distinguishable from the LPN. These MCN branches should not be confused with the FBLPN, as they traverse obliquely in a posterior and superficial direction, as opposed to the FBLPN, which would course in a more vertical direction and pass deep toward the AH-QP interval. Bot- tom is deep/lateral; left, distal (DIST); right, proximal; and top, superfi- cial/medial. FHL indicates flexor hallucis longus tendon; and TAL, medial talus. See also Video 1. B C D E J Ultrasound Med 2013; 32:16431652 1647

6 3209jum_Layout 1 8/20/13 11:44 AM Page 1648 Presley et alSonography of the First Branch of the Lateral Plantar Nerve be used to identify the FBLPN. Thus, if no vertically ori- Figure 6. AC, Transducer position (A, box) and underlying anatomy (B) ented branch was identified arising from the posterior to sonographically visualize the origin of the FBLPN from the posterior mar- gin of the LPN. Note the orientation of the transducer in A and B to obtain a aspect of the LPN and entering the AH-QP interval, the short-axis (SAX) view of the vertically oriented FBLPN. In C, the FBLPN LPN was traced proximally to the TN, and the TN was appears as a hypoechoic, monofascicular structure approximately 1 mm in traced proximally to identify the first/most proximal pos- diameter (green arrows) and lying adjacent and posterior to the LPN. Two teriorly directed branch. This branch represented the branches of the MCN continue to course in a posterior and superficial direc- tion. At this point, the superior fibers of the QP are just visible deep to the MCN and could be followed distally to its characteristic LPN and FBLPN and superficial to the calcaneus (the bony acoustic margin subcutaneous location along the medial heel. The TN along the lower half of the image). Bottom is deep/lateral; left, distal (DIST); was then scanned inferiorly to identify the second/more right, proximal (PROX); and top, superficial/medial. See also Video 2. distal posteriorly directed branch. This branch typically A represents the FBLPN, although some individuals may have multiple MCN branches.23 Therefore, it was imperative to follow each branch to determine its final destination. Branches ending subcutaneously repre- sented MCN branches, whereas the more vertically ori- ented branch passing deeper and into the AH-QP interval represented the FBLPN. After identifying the FBLPN, the nerve was scanned in the short axis while the transducer was moved caudad into the AH-QP interval. The AH was identified by its superfi- cial location, while the QP was deeply located adjacent to B the medial-plantar calcaneus and easily moved with pas- sive lesser toe dorsiflexion (due to its attachment to the flexor digitorum longus; Figure 8 and Video 3). Once the FBLPN was localized at the AH-QP interval, a sono- graphically guided perineural injection was completed with a 22-gauge, 38-mm needle and 1 mL of 50% diluted col- ored latex. The initial injection was performed using an in- plane anterior-to-posterior approach but was deemed unnecessarily challenging due to the proximity of the ante- riorly located vessels and the curved contour of the medial arch. Therefore, the subsequent 11 injections were com- pleted using an in-plane posterior-to-anterior approach (Figure 9 and Video 4). Before each injection, the senior author graded nerve conspicuity using a 4-point ordinal scale (1, poor; 2, fair; 3, good; 4, excellent), reflecting the C ease of nerve visualization and confidence in perineural needle placement. Assessment After a minimum of 24 hours, study coinvestigators dis- sected each specimen to identify the injectate location rel- ative to the anatomically defined position of the FBLPN. The TN and accompanying vasculature were identified proximal to the tarsal tunnel, and through meticulous dis- section, all distal branches were exposed. During dissec- tion, the AH and plantar fascia-FDB were carefully reflected to reveal the full course of the FBLPN across the medial-plantar foot. The diameter of the FBLPN at the AH-QP was recorded and injection accuracy was graded as 1648 J Ultrasound Med 2013; 32:16431652

7 3209jum_Layout 1 8/20/13 11:44 AM Page 1649 Presley et alSonography of the First Branch of the Lateral Plantar Nerve follows: (1) accurate, latex partially or completely sur- Figure 8. AC, Transducer position (A, box) and underlying anatomy rounding the FBLPN; and (2) inaccurate, no latex in (B) to sonographically visualize the FBLPN in its short axis (SAX) at the level of the AH-QP interval. Note that in B, the AH has been sectioned at contact with the FBLPN. Coinvestigators also recorded the calcaneus and retracted distally. In C, once again, the FBLPN the extent of craniocaudal latex flow along the FBLPN appears as a small, monofascicular structure, in this case located (millimeters), the presence and location of any overflow between the AH and QP (green arrows). This deep location will distin- to adjacent regions of potential clinical importance guish it from branches of the MCN (not shown), which lie more superfi- cially. The conspicuity of the nerve can be increased through passive (absent/present), the closest distance between the injected motion of the QP, achieved by lesser toe flexion-extension. Bottom is latex and the plantar fascia (millimeters), and the presence deep/lateral; left, distal (DIST); right, proximal (PROX); and top, superfi- of any vascular injury or latex infiltration (absent/present). cial/medial. See also Video 3. A Statistics Descriptive statistics were used to report the distribution of latex following sonographically guided deep plantar fascia latex injections in the 12 unembalmed cadaveric speci- mens. Donor age, sex, and body mass index were summa- rized with the use of descriptive statistics. Results A total of 6 right and 6 left ankle-foot specimens were injected from 10 donors (5 male and 5 female) aged 47 to 95 years (mean, 71 years) with an average body mass index of 24.2 kg/m2 (range, 17.231.6 kg/m2). The conspicuity B of the FBLPN with the cart-based US machine ranged from 3 to 4 with an average of 3.7, whereas conspicuity using the portable US machine ranged from 1 to 4 with an Figure 7. Short-axis sonographic view of the MPN, LPN, and FBLPN (green arrows) in a different specimen obtained using transducer posi- tioning in shown in Figure 6, A and B. In this specimen, a wider field of view is used to show the relative positions of the three nerves. The FBLPN has just originated from the posterior aspect of the LPN. The nerves lie deep to the AH, but the image is taken just cranial to the origin of the QP (not shown). In this view, all three nerves are well seen in their short axes and lie adjacent to the medial-plantar calcaneal surface (the bony acoustic margin along the lower half of the image), with the exception of the MPN, which lies on the flexor hallucis longus tendon (FHL). Bottom is deep/lateral; left, distal; right, proximal; and top, superficial/medial. C J Ultrasound Med 2013; 32:16431652 1649

8 3209jum_Layout 1 8/20/13 11:44 AM Page 1650 Presley et alSonography of the First Branch of the Lateral Plantar Nerve average of 1.8. Despite the differences in qualitative In all 12 specimens, the FBLPN originated from the FBLPN visualization, all 12 sonographically guided injec- LPN and was approximately 2 mm in maximal diameter, tions placed some latex onto the FBLPN. In 11 of 12 consistent with our sonographic observations and previ- (91%), latex completely surrounded the FBLPN, whereas ously published anatomic data.46 Latex consistently in 1 specimen, the majority of the latex was located poste- tracked cranial and caudal along the nerves long axis, rior to the FBLPN (Figure 10). The latter specimen was despite needle placement using a short-axis view of the the first one injected for the study and, as previously nerve (Figure 9). The average craniocaudal nerve cover- described, was injected using an anterior-to-posterior age was 2.4 cm (range, 1.04.5 cm) and preferentially approach. This approach was subsequently abandoned tracked cranial toward the LPN rather than caudal toward due to the technical difficulties in avoiding the anteriorly the QP-FDB interval (ie, site of potential distal FBLPN located vessels and effectively tracking the needle along the entrapment). In fact, no specimen exhibited caudal/distal firm, convex medial surface of the heel region. flow into the QP-FDB interval. Consistent with these observations, the most common region of potentially clin- Figure 9. A, Setup for FBLPN perineural injection in the AH-QP interval ically important overflow was the LPN, with 10 of 12 using an in-plane, posterior-to-anterior approach in a cadaveric speci- FBLPN injections (82%) producing latex contact with the men. B, Correlative short-axis (SAX) image of the FBLPN (green arrows) LPN. A small amount of latex contacted the MCN in 2 at the AH-QP interval, showing a sonographically guided perineural of 12 specimens (17%), and the MPN in 1 of 12 (8%). No FBLPN injection using a 22-gauge, 38-mm needle (yellow arrows). The latex contacted or infiltrated the plantar fascia in any peripheral margins of the nerve show increased conspicuity due to the surrounding anechoic latex injectate (asterisk). The bony acoustic mar- specimen, and the average distance between the injected gin of the medial-plantar calcaneus appears at the bottom of the image. latex and plantar fascia was 1.2 cm (range, 1.01.75 cm). Bottom is deep/lateral; left, distal (DIST); right, proximal (PROX); and top, No evidence of vascular injury or vascular latex infiltration superficial/medial. See also Video 4. was seen in any specimen. A Discussion Neuropathy of the FBLPN is an uncommon but poten- tially important cause of chronic heel pain occurring in iso- lation or combination with more common causes of plantar heel pain such as plantar fasciitis.2 Due to the cur- Figure 10. Anatomic dissection showing yellow latex surrounding the FBLPN as it courses vertically between the QP and AH muscles. The AH has been cut and retracted distally. Note the cranial spread of latex along the FBLPN, coursing toward the nerves origin from the LPN. Bottom is plantar; left, distal; right, proximal; and top, cranial. Asterisks indicate plantar fascia. B 1650 J Ultrasound Med 2013; 32:16431652

9 3209jum_Layout 1 8/20/13 11:44 AM Page 1651 Presley et alSonography of the First Branch of the Lateral Plantar Nerve rent challenges in the diagnosis and management of The current investigation used both cart-based and FBLPN neuropathy, it is important to identify methods portable US machines to improve the generalization of our that can be used to more precisely diagnose or treat this results but not to directly compare the conspicuity ratings condition. This study is the first to document the ability of of the two machines. Nonetheless, the differences in nerve high-resolution sonography to identify the FBLPN in the conspicuity were obvious, and it was clearly easier to visu- AH-QP interval using easily identifiable landmarks. In our alize the FBLPN with the cart-based machine using a 175- cadaveric model, we were able to accurately identify the MHz probe versus the portable machine using a 123-MHz location of the FBLPN in all 12 specimens, as evidenced probe. Irrespective of the machine used, all injections placed by accurately placed sonographically guided perineural latex onto the FBLPN at the AH-QP interval. Using the latex injections. Consequently, sonographic identification CX50 portable machine, 5 of 6 nerves were graded as poor of the FBLPN in this region appears to be feasible and can or fair. In such cases, the senior author used the previously be considered for diagnostic and therapeutic purposes described landmarks to localize the presumed position of when evaluating and managing patients with chronic heel the FBLPN. This approach required identifying the LPN pain syndromes. and then moving the transducer posteriorly and then cau- Several aspects of this investigation warrant further dal to visualize the AH-QP interval. At the fascial plane discussion. First, although all 12 injections placed latex between the AH and QP, a slight separation could be seen onto the FBLPN, the first injection placed the majority of between the two muscles (accentuated by passively moving the latex posterior to the nerve. This injection was per- the QP via dorsiflexing-plantarflexing the lesser toes; Video formed using an anterior-to-posterior approach, which 3), indicating the course of the FBLPN. This area was was subsequently abandoned as previously discussed. chosen as the injection site. The accuracy of this technique This particular case was performed using the portable US in the setting of poor nerve visualization suggests that inject- machine with a nerve conspicuity grade of 4 (ie, excel- ing the AH-QP interval posterior to the LPN can be con- lent). Although we cannot definitely determine the rea- sidered in cases of poor FBLPN conspicuity. son for the paucity of perineural flow in this case, it is our This study had several limitations that should be con- belief that the anterior-to-posterior approach was sub- sidered when interpreting the results. First, clinicians stantially contributory and would recommend a posterior- should use caution when extrapolating our cadaveric to-anterior approach for perineural FBLPN injection. Not results to clinical patients. Although our initial clinical only was the posterior-to-anterior approach easier, but it experience in visualizing the FBLPN using the techniques also allowed us to avoid the anteriorly located vessels adja- described herein has thus far been successful, formal cent to the FBLPN. Second, cranial overflow to the LPN investigation documenting FBLPN conspicuity in clini- occurred in the majority of cases (10 of 12 [82%]; see cal patients is warranted. Second, at the time of this study, Figure 10). The extent of craniocaudal flow along the the primary investigator had 8 years of experience in diag- FBLPNs long axis was initially surprising given the small nostic and interventional musculoskeletal sonography. injectate volume (1.0 mL) and short-axis view of the nerve Although we feel confident that our techniques can be used during the injection. However, our dissections clearly by most experienced sonologists and sonographers, we rec- revealed the presence of a fascial plane or channel through ognize that visualization of this small nerve may be chal- which the FBLPN coursed, consistent with previous lenging for less experienced practitioners. Third, although anatomic studies describing independent channels for the we believe that the FBLPN can be visualized in most tarsal tunnel nerves.23 The clinical importance of LPN patients, the ability of sonography to detect abnormalities overflow remains indeterminate but could be problematic of this nerve in the AH-QP remains undefined. Further if pain generators in the LPN territory distal to the FBLPN clinical experience in this regard is warranted. Conversely, are included in the differential diagnosis. In such cases, we feel confident that clinicians can use sonographically placing the injection in a more caudal location within the guided FBLPN injections for diagnostic and therapeutic AH-QP interval or using smaller injectate volumes (eg, purposes when clinically indicated for the management of 0.5 mL) may improve diagnostic specificity.24 Third, in patients with chronic heel pain syndromes. Finally, we no case did the injectate spread into the plantar fascia were unable to visualize the FBLPN at its potential site of region, suggesting that the FBLPN perineural injection distal entrapment: the FDB-QP interval (Figure 2, Site 2). technique described herein provides differential diagnos- Consequently, the role of sonography in the diagnosis and tic value with respect to the FBLPN versus the plantar fas- treatment of suspected FBLPN disorders in the FDB-QP cia proper. interval requires further investigation. J Ultrasound Med 2013; 32:16431652 1651

10 3209jum_Layout 1 8/20/13 11:44 AM Page 1652 Presley et alSonography of the First Branch of the Lateral Plantar Nerve In conclusion, sonographic visualization of the 16. Patel AT, Gaines K, Malamut R, Park TA, Toro DR, Holland N; American FBLPN in the AH-QP interval is feasible and should Association of Neuromuscular and Electrodiagnostic Medicine. be considered for diagnostic and therapeutic purposes in Usefulness of electrodiagnostic techniques in the evaluation of suspected patients presenting with chronic or atypical heel pain syn- tarsal tunnel syndrome: an evidence-based review. Muscle Nerve 2005; dromes. Further clinical experience should refine the role 32:236240. of FBLPN sonography and explore the utility of sono- 17. Colak T, Bama B, Gnener A, Ozbek A, Budak F. Comparison of nerve graphically guided diagnostic and therapeutic FBLPN conduction velocities of lower extremities between runners and controls. perineural injections, as well as ablative procedures in J Sci Med Sport 2005; 8:403410. appropriate patients. 18. Oztuna V, Ozge A, Eskandari MM, Colak M, Golpinar A, Kuyurtar F. Nerve entrapment in painful heel syndrome. Foot Ankle Int2002; 23:208 References 211. 19. Schon LC, Gruber F, Pfefer GB. Plantar heel pain. In: Porter DA, Schon 1. Rompe JD, Furia J, Weil L, Maffulli N. Shock wave therapy for chronic LC (eds). Baxters the Foot and Ankle in Sport. Philadelphia, PA: Elsevier plantar fasciopathy. Br Med Bull 2007; 8182:183208. Mosby; 2008:233236. 2. Alshami AM, Souvlis T, Coppieters MW. A review of plantar heel pain 20. McMillan AM, Landorf KB, Barrett JT, Menz HB, Bird AR. Diagnostic of neural origin: differential diagnosis and management. Man Ther 2008; imaging for chronic plantar heel pain: a systematic review and meta- 13:103111. analysis. J Foot Ankle Res 2009; 2:32. 3. Baxter DE, Pfeffer GB, Thigpen M. Chronic heel pain: treatment ration- 21. Martinoli C. Imaging of the peripheral nerves. Semin Musculoskelet Radiol ale. Orthop Clin North Am 1989; 20:563569. 2010; 14:461462. 4. Rondhuis JJ, Huson A. The first branch of the lateral plantar nerve and 22. Hobson-Webb LD, Padua L, Martinoli, C. Ultrasonography in the diag- heel pain. Acta Morphol Neerl Scand 1986; 24:269280. nosis of peripheral nerve disease. Expert Opin Med Diagn 2012; 6:457 5. Louisia S, Masquelet AC. The medial and inferior calcaneal nerves: an 471. anatomic study. Surg Radiol Anat 1999; 21:169173. 23. Sarrafian SK, Kelikian AS. Myology. In: Kelikian AS, Sarrafian SK (eds) 6. Arakawa T, Sekiya S, Kumaki K, Terashima T. Ramification pattern of Sarrafians Anatomy of the Foot and Ankle: Descriptive, Topographic, the deep branch of the lateral plantar nerve in the human foot. Ann Anat Functional. Philadelphia, PA: Lippincott Williams & Wilkins; 2011:257 2005; 187:287296. 269. 7. del Sol M, Olave E, Gabrielli C, Mandiola E, Prates JC. Innervation of the 24. Thallaj A, Marhofer P, Kettner SC, Al-Majed M, Al-Ahaideb A, Moriggl abductor digiti minimi muscle of the human foot: anatomical basis of B. High-resolution ultrasound accurately identifies the medial antebrachial the entrapment of the abductor digiti minimi nerve. Surg Radiol Anat cutaneous nerve at the midarm level: a clinical anatomic study. Reg Anesth 2002; 24:1822. Pain Med 2011; 36:499501. 8. Kenzora JE. The painful heel syndrome: an entrapment neuropathy. Bull Hosp Jt Dis Orthop Inst 1987; 47:178189. 9. Baxter DE, Thigpen CM. Heel pain: operative results. Foot Ankle 1984; 5:1625. 10. Jolly GP, Zgonis T, Hendrix CL. Neurogenic heel pain. Clin Podiatr Med Surg 2005; 22:101113, vii. 11. Farooki S, Theodorou DJ, Sokoloff RM, Theodorou SJ, Trudell DJ, Resnick D. MRI of the medial and lateral plantar nerves. J Comput Assist Tomogr 2001; 25:412416. 12. Baxter DE, Pfeffer GB. Treatment of chronic heel pain by surgical release of the first branch of the lateral plantar nerve. Clin Orthop Relat Res 1992; 279:229236. 13. Thomas JL, Christensen JC, Kravitz SR, et al. The diagnosis and treat- ment of heel pain: a clinical practice guidelinerevision 2010. J Foot Ankle Surg 2010; 49(suppl):S1S19. 14. Fuller EA. The windlass mechanism of the foot: a mechanical model to explain pathology. J Am Podiatr Med Assoc 2000; 90:3546. 15. Recht MP, Grooff P, Ilaslan H, Recht HS, Sferra J, Donley BG. Selective atrophy of the abductor digiti quinti: an MRI study. AJR Am J Roentgenol 2007; 189:W123W127. 1652 J Ultrasound Med 2013; 32:16431652

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