Neuromuscular Ultrasound of a Common Fibular Nerve Intraneural Ganglion Cyst With Selective Involvement of the Deep Fibular Fascicles.

While ultrasound assessment of cross-sectional area and echogenicity has gained popularity as a biomarker for various neuropathies, there is a scarcity of data regarding fascicle count and density in neuropathies or even healthy controls. The aim of this study was to determine whether fascicles within select lower limb nerves (common fibular, superficial fibular, and sural nerves) can be counted in healthy individuals using ultrahigh-frequency ultrasound (UHFUS). Twenty healthy volunteers underwent sonographic examination of the common fibular, superficial fibular, and sural nerves on each lower limb using UHFUS with a 48 MHz linear transducer. Fascicle counts and density in each examined nerve were determined by a single rater. The mean fascicle number for each of the measured nerves included the following: common fibular nerve 9.85 (SD 2.29), superficial fibular nerve 5.35 (SD 1.59), and sural nerve 6.73 (SD 1.91). Multivariate linear regression analysis revealed a significant association between cross-sectional area and fascicle count for all three nerves. In addition, there was a significant association seen in the common fibular nerve between fascicle density and height, weight, and body mass index. Age and sex did not predict fascicle count or density (all p > .13). UHFUS enabled the identification and counting of fascicles and fascicle density in the common fibular, superficial fibular, and sural nerves. Knowledge about normal values and normal peripheral nerve architecture is needed in order to further understand and identify pathological changes that may occur within each nerve in different disease states.

To the Editor, Clinical Anatomy:The basis for the articular (unified) theory for the for-mation of intraneural ganglion cysts is a capsular disrup-tion through which joint (cyst) fluid egresses into thearticular branch and then a parent nerve (Spinner et al.,2003). Trauma has been associated with intraneural gan-glion cysts. A recent meta-analysis revealed trauma beingassociated with intraneural ganglion cysts in our group (Figs. 2A–2E) showed both a neuroma in conti-12% ofcases (Desy and Spinner, 2014). Our group has describedthe pathoanatomy by which direct and indirect traumamay give rise to the most common form, fibular (pero-neal), and its rarer corollary, tibial intraneural ganglioncysts, both derived from the superior tibiofibularjoint (STFJ) (Lalezari et al., 2012; Spinner et al.,2012a,b; Cesmebasi et al., 2014). In direct trauma, therewould be a force generated near the proximal leg/kneeregion that would affect the STFJ (Ogden, 1972, 1974;Sekiya and Kuhn, 2003); in indirect trauma, forces wouldbe translated from the ankle region (such as in anklesprains or fracture) via the interosseous membrane to theproximal leg (Cesmebasi et al., 2014). A direct cause–effect relationship between traumatic injury and intraneu-ral ganglion cyst formation has yet to be definitivelyestablished.A 20-year-old man tripped off a curb and fell on his leftknee. He sustained a multi-ligamentous knee injury as aresult from a knee dislocation. He presented to an emer-gency room with exquisite pain and foot drop from a com-mon fibular nerve (CFN) palsy and was discharged afternegative plain radiographs were obtained. Several days later,he noted increasing pain and was found to have elevated legcompartment pressures for which he underwent four com-partment fasciotomies. MRI performed 7 days after the initialinjury revealed a posterolateral corner injury involving dis-ruption of the fibular collateral and posterior cruciate liga-ments, posterolateral capsule, and the musculotendinousjunction of the popliteus, lateral meniscus, and medial patel-lofemoral ligament. There was edema and thickening of theCFN extending from the fibular neck to a point just distal tothe sciatic nerve bifurcation (Figs. 1A–1C). He was referredto colleagues at our institution for definitive care of themulti-ligament injury and the CFN injury. Repeat MRI 3months after the injury confirmed the previous findingsreferable to the ligamentous injury. The CFN was markedlyenlarged in the popliteal fossa. There was anterior and lat-eral compartment musculature atrophy consistent withdenervation. Electromyography (EMG) confirmed a com-plete common fibular neuropathy. He underwent stagedreconstruction over the course of 9 months: (1) explora-tion and nerve grafting of the left CFN with 2 cable grafts(9 cm in length) using the superficial fibular nerve; (2)high tibial wedge osteotomy with allograft bone graft; and(3) multi-ligament knee reconstruction. At last follow-up,15 months post nerve grafting, he had no return of neuro-logic function but had regained a stable knee. It was rec-ommended he undergo tendon transfer for persistent footdrop. Retrospective reinterpretation of the second MRI bynuity involving the CFN as well as an unrecognized com-plex fibular intraneural cyst, which could be traced alongits articular branch to the anterior portion of the STFJ. Afracture line was noted at the STFJ extending to the originof the intraneural cyst from the joint. The cyst was notpresent on the initial MRI.Direct blunt force trauma to the knee has long beenknown to result in severe injuries to the knee causing pos-terolateral corner, multi-ligamentous knee, and CFN inju-ries. They have also been associated with instability of theSTFJ (Fallon et al., 1994; Kapur et al., 2009; Jabara et al.,2014). The resultant stretch tends to affect a long seg-ment of the CFN. Stretch injuries associated with kneedislocations are known to have poor recovery after nervesurgery (Fallon et al., 1994; Seidel et al., 2008). In ourpatient, we believe that the knee dislocation caused theimmediate clinical appearance of the foot drop involvingthe CFN. This stretch injury resulted in a lengthy neuromain continuity of the CFN. The effect of the stretch injury onthe articular branch and/or the bony injury to the STFJresulted in a capsular injury (without instability) and theegress of joint fluid (Fallon et al., 1994; Spinner et al.,2003, 2012a,b; Lalezari et al., 2012). Unfortunately, the2nd MRI was done of the knee rather than the CFN andSTFJ and did not provide full visualization of the proximalleg. In this case, despite the limitations, serial MR imagingdemonstrates a temporal relationship following kneetrauma and documents the evolution of an intraneuralganglion cyst.

Objectives: Short leg casts are routine applications in orthopaedic practice. The aim of the study was to investigate the course of the common fibular nerve and its branches (deep and superficial fibular nerves) around the fibular neck in order to describe a convenient method for applying the lower extremity casts with low risk of fibular nerve entrapment. Methods: Fifty lower extremities of 26 cadavers were examined. The point where common fibular nerve itself or its branches (deep and superficial fibular nerves) crossed over the fibular neck were dissected. The points where the nerve or its branches have risk of compression between the fibula and the cast were investigated in relation to fibular length. Results: The average fibular length was 356.9±26.4 mm. The common fibular nerve did not pass over the fibular neck in any specimen, instead, its branches crossed over it. The average distance from the tip of the fibular head to deep fibular nerve and superficial fibular nerve were 42.9±6.5 mm and 52±6.3 mm, respectively. The mean ratio of fibular length to these distances were 8.5±1.2 and 7.0±0.8, respectively. Conclusion: As short knee casts is a frequent application in clinical practice, it is important to determine a safe upper border for the casts to protect common fibular nerve or its branches. We recommend that the upper border of short leg casts should not exceed the upper 1/7th of the fibular length of the patient in order to avoid fibular nerve palsy.

Letter to the editor

Traction injuries of the common fibular (peroneal) nerve frequently result in significant morbidity due to tibialis anterior muscle paralysis and the associated loss of ankle dorsiflexion. Because current treatment options are often unsuccessful or unsatisfactory, other treatment approaches need to be explored. In this investigation, the anatomical feasibility of an alternative option, consisting of nerve transfer of motor branches from the tibial nerve to the deep fibular nerve, was studied. In ten cadaveric limbs, the branching pattern, length, and diameter of motor branches of the tibial nerve in the proximal leg were characterized; nerve transfer of each of these motor branches was then simulated to the proximal deep fibular nerve. A consistent, reproducible pattern of tibial nerve innervation was seen with minor variability. Branches to the flexor hallucis longus and flexor digitorum longus muscles were determined to be adequate, based on their branch point, branch pattern, and length, for direct nerve transfer in all specimens. Other branches, including those to the tibialis posterior, popliteus, gastrocnemius, and soleus muscles were not consistently adequate for direct nerve transfer for injuries extending to the bifurcation of the common fibular nerve or distal to it. For neuromas of the common fibular nerve that do not extend as far distally, branches to the soleus and lateral head of the gastrocnemius may be adequate for direct transfer if the intramuscular portions of these nerves are dissected. This study confirms the anatomical feasibility of direct nerve transfer using nerves to toe-flexor muscles as a treatment option to restore ankle dorsiflexion in cases of common fibular nerve injury.

Sciatic nerve divides into tibial nerve and common peroneal nerve at the level of superior angle of popliteal fossa and variations in its branching pattern are common. The most common nerve entrapment syndrome in the lower limbs is common peroneal nerve entrapment at fibular head. Invariably it can also be trapped in gluteal region due to split piriformis muscle which compresses sciatic nerve as whole or its division such as common peroneal nerve. In this case report, we describe a case of high division of sciatic nerve along with duplicated piriformis associated with a communicating branch between inferior gluteal nerve and common peroneal nerve. Such an anatomical variation of common peroneal nerve with the communicating nerve is discussed with its embryological basis.

Intraneural ganglion cyst of the common peroneal nerve causing foot drop in a 12-year old child

Slimmer’s paralysis refers to a common fibular nerve palsy caused by significant and rapid weight loss. This condition usually results from entrapment of the common fibular nerve due to loss of the fat pad surrounding the fibular head. Several etiologies of common fibular nerve palsy have been proposed, including trauma, surgical complications, improperly fitted casts or braces, tumors and cysts, metabolic syndromes, and positional factors. We present 5 cases of slimmer’s paralysis in patients who had lost 32–57 kg in approximately 1 year. In 2 cases, MR neurogram of the knee demonstrated abnormalities of the common fibular nerve at the fibular head. Two patients underwent a common fibular nerve decompression at the fibular head and attained improved gait and sensorimotor function. Weight loss, diabetes mellitus, and immobilization may have contributed to slimmer’s paralysis in 1 case. Awareness of slimmer’s paralysis in patients who have lost a significant amount of weight in a short period of time is imperative to detect and treat a fibular nerve neuropathy that may ensue.

An historical perspective on ulnar intraneural ganglion cysts and their joint origins.

The aims of this research were: (1) to minimize injury to the common fibular nerve by a detailed anatomical study of the nerve and its branches and (2) clinically to establish a protocol for preoperative and postoperative assessment of patients undergoing surgery on the proximal third of the leg. Thus the incidence of fibular nerve palsy would definitely be negligible. The first part of the research consisted of an anatomical study of the common fibular nerve and its branches, paying particular attention to the motor nerve branches innervating different muscles of the leg. Dissections were done on 20 unselected lower limbs of cadavers, of unknown gender, age and dominant side, to study the anatomy of the common fibular nerve and its branches and the neighboring structures, such as the tibia, the fibula and the muscles of the leg. It was found that 76.7% of all motor nerve branches were located in the proximal third of the leg, 19.5% in the middle third and 3.8% in the distal third. The free courses of the motor nerve branches were 48.5% in the proximal third, 44.4% in the middle third and 7.1% in the distal third. Within a distance of 6 cm from the fibular head we found 51.1% of the motor nerve branches and from 6 to 11 cm there were only 25.5%. Hence there were danger zones of high and low risk for injury to the common fibular nerve and its branches. Results obtained are evaluated and discussed with regard to safer surgical approaches and insertion of Steinmann pins in the proximal third of the leg.

Peroneal nerve ganglion cyst.R M Spillane, G J Whitman and F S ChewAudio Available | Share

To the editor: During the course of a routine cadaveric dissection of the wrist, an intraneural ganglion cyst was incidentally identified at a unique site. The posterior interosseous nerve (PIN) and artery were identified with loupe magnification in the floor of the 4th extensor compartment overlying the distal interosseous membrane. Just distal to the point of arborization at the level of the radiocarpal joint, an intraneural ganglion cyst was noted within one of the branches of the PIN (Figure 1A). This branch, along with the grossly visible cyst, was carefully dissected through the dorsal wrist capsule. The intraneural cyst originated from the scapholunate joint and extended through a fenestration in the scapholunate ligament (Fig. 1B–D). It propagated proximally for approximately 2 cm. A pseudocyst with adjacent nerve fascicles was confirmed histologically, and was traced to the level of the joint in serial sections (Fig. 2). Pathology findings. A: The longitudinal histological sections from formalin-fixed paraffin-embedded tissue stained with hematoxylin and eosin (H&E). The fibrocollagenous tissue forming the ligament is to the right of the figure, and the joint is not seen here. The wall of the cystic structure is composed of dense fibrocollagenous tissue, and no epithelial lining (20×). An internal fibrocollagenous septa is also present. B: Inset from A. Small peripheral nerve fascicles were identified adjacent to the pseudocyst wall, showing mild myxoid change (200×). C: Nerve fascicles were highlighted by the S-100 immunostain (200×, polyclonal, Dako). D: Neurofilament staining did not demonstrate any nerve fibers in the pseudocyst wall (200×, clone 2F11; Dako). [Color figure can be viewed at wileyonlinelibrary.com] Operative findings. A: At the level of the wrist, an intraneural ganglion cyst (arrow) can be seen within one of the two terminal branches of the posterior interosseous nerve (PIN) [blue background]. B: The intraneural cyst (arrow) specimen and the scaphoid and lunate bones were removed. C: Disarticulation has been performed. The cyst (probe) and its origin to the scapholunate ligament are seen. S, scaphoid; L, lunate. D: A defect in the scapholunate ligament (probe) near the articular branch of the PIN is present. S, scaphoid; L, lunate. [Color figure can be viewed at wileyonlinelibrary.com] This rare anatomic finding has broad clinical implications. A posterior interosseous intraneural ganglion cyst has not been reported at the wrist (Desy et al., 2017). The PIN intraneural cyst described herein communicated with the scapholunate joint by an articular branch. The scapholunate joint/ligament is the most common site for extraneural ganglion cysts at the wrist. Extraneural cysts in this location arise from non-neural pedicles; some have thought that they can cause occult dorsal wrist pain because of the consistent proximity of the ganglion cyst and the PIN (Dellon and Seif, 1978; Steinberg and Kleinman, 1999). Our group has put forth a unifying articular theory to explain the formation and propagation of intraneural and extraneural ganglion cysts (Spinner et al., 2009). Mounting anatomic and clinical evidence supports this theory (Spinner et al., 2011). Intraneural and extraneural ganglion cysts form from synovial surfaces. Intraneural cysts originate from a synovial joint, egress through a capsular rent and dissect along an articular branch typically extending to the parent nerve; extraneural cysts would egress separate from the nerve. Both may present with findings of neuropathy, the former by intrinsic, and the latter by extrinsic compression. The shape and dimensions of these cysts would obey basic principles of fluid dynamics such as the path of least resistance and pressure fluxes. A posterior interosseous intraneural cyst has been described in one case in the elbow region (Hashizume et al., 1995); despite its not being described as having a joint connection by the original authors, our group's reinterpretation of the published imaging supported an elbow joint connection (Wang et al., 2009). This is the third known example of a joint-related intraneural ganglion cyst found in a cadaver (Spinner and Wang, 2016); the others being a deep ulnar nerve cyst connecting to a carpal bone and a tibial nerve cyst connecting to the knee joint. This specimen extends (and further unifies) our understanding of the pathogenesis of intraneural and extraneural ganglion cysts at the wrist and elsewhere.

Compression syndromes of the common fibular nerve and its branches frequently occur primarily as well as secondarily to trauma and surgery. A keen knowledge of the course and the relationship of the deep fibular nerve to adjacent anatomical structures in the proximal leg is mandatory. Previous literature often lacks detailed information on the course of the deep fibular nerve and is based on a limited number of observations. The aim of this study was to investigate the common fibular nerve and its branching pattern with special regard to the relationship between the deep fibular nerve and the anterior intermuscular septum of the leg. Variations in the course of the fibular nerve were demonstrated. The fibular compartments of the leg (n = 111) were dissected in 57 embalmed cadavers and included: 1) investigation of the number of muscular branches; 2) entering passages to the respective compartments of the leg; and 3) the relationship between the fibularis longus muscle and the deep fibular nerve. The most proximal muscular branch of the deep fibular nerve directly "pierced" the anterior intermuscular septum of the leg. Narrow passages within the fibular compartment and, in consequence, areas of possible higher incidence of nerve compression were suggested at the level of the intermuscular septa of the leg, between the two distinct portions of the fibularis longus muscle and the crossing of the supplying vessels. There were hardly ever statistically significant differences between the two sides or male and female gender. According to our results, the anterior intermuscular septum of the leg may be regarded as an important landmark for the surgeon when dissecting the muscular branches of the deep fibular nerve. The variable branching pattern of the deep fibular nerve within the fibular compartment of the leg should be taken into account.

Common fibular nerve palsy due to fabella compression: An illustrative case report

Background and Objectives: The common fibular nerve (CFN) has anatomical variance between individuals as it transitions from the posterior thigh to the anterior leg. The nerve’s course around the fibular neck is of particular interest, where it becomes vulnerable to injury at the lateral knee. Therefore, we sought to compare factors that may predict distal CFN variability, such as height, age, sex, fibular length, and proximal sciatic variations, which individually or cumulatively play a role in predicting clinically significant locations where the CFN commonly transitions among certain populations. Methods: In this cadaveric study, twenty anatomically-fixed specimens were analyzed, ten males and ten females. Data gathered included age, sex, height, CFN transition point measured from the proximal head of the fibular to the point 90 degrees off the midline of the fibula where the CFN courses around the fibular neck, fibular length, and proximal sciatic nerve variations characterized based on the Beaton and Anson classification system. Factors were compared and statistical values were generated. Results: There was a statistically significant difference between CFN transition points compared to fibular lengths, heights, and between sexes. Sciatic nerve (SN) bifurcation levels and exits were bilaterally identical on all cadavers. All SN exits were Beaton and Anson type 1 (undivided nerve below and undivided piriformis), and bifurcation levels were 20% high, 25% middle, and 55% low. Conclusions: This study highlights the importance of considering a person’s height, fibular length, and sex when addressing injuries involving the CFN at the lateral leg.