Ultrasound-guided Hydrodissection and Integrated Rehabilitation for Postsurgical Common Peroneal Nerve Entrapment

Summary

This article demonstrates ultrasound-guided hydrodissection and a structured, task-oriented rehabilitation program for postsurgical common peroneal nerve entrapment.

Abstract

Postoperative common peroneal nerve (CPN) entrapment is a common iatrogenic cause of foot drop, and an established rehabilitation protocol is currently lacking. This article provides a step-by-step visual demonstration of an integrated approach, combining ultrasound-guided hydrodissection with structured task-oriented rehabilitation. The protocol includes: (1) real-time ultrasound identification of CPN entrapment; (2) in-plane, multi-quadrant hydrodissection using a 5% dextrose, lidocaine, and mecobalamin injectate; and (3) a phased rehabilitation program initiated 24 h post procedure, comprising neural gliding, therapeutic ultrasound, neuromuscular electrical stimulation, and five task-oriented training modules. In the representative case, the leg-foot angle during maximal dorsiflexion effort demonstrated a 38° reduction (from 142° to 104°), and gait analysis showed restoration of heel-strike, push-off, and swing-phase foot clearance. Post-intervention EMG revealed reinnervation potentials in the tibialis anterior, peroneus longus, and extensor hallucis longus. This visually formatted, stepwise protocol demonstrates the feasibility of combining percutaneous nerve decompression with task-specific rehabilitation, offering a replicable framework for managing refractory postoperative CPN entrapment.

Introduction

Postoperative common peroneal nerve (CPN) dysfunction is a significant cause of morbidity. While direct intraoperative injury (e.g., from knee dislocation or fibular fracture) is a well-recognized etiology^1,2, a more insidious and frequently overlooked mechanism is delayed entrapment by postoperative fibrotic scar tissue². Unlike acute structural damage, this scarring forms progressively, creating a chronic compressive barrier around the nerve. This compression not only mechanically tethers the nerve, impeding axonal transport, but also critically compromises its microvascular blood supply, leading to ischemic injury that further exacerbates neural dysfunction². Consequently, patients develop foot drop, gait abnormalities, and sensory deficits^3,4, severely impairing mobility and quality of life.

Conventional management has largely relied on conservative measures and rehabilitative exercises aimed at preserving joint mobility, delaying muscular atrophy, and supporting neural recovery⁵. However, when the nerve is densely encased in scar tissue, this predominantly “downstream” functional approach often reaches a therapeutic plateau because it does not address the physical barrier posed by perineural scarring⁴. Conversely, open surgical neurolysis, while directly addressing the entrapment, is invasive, carries risks of bleeding and new scar formation, and is often viewed with caution—particularly in young, active individuals for whom functional restoration is paramount⁶. Thus, a minimally invasive technique that effectively releases the nerve from adhesions while avoiding the morbidity of open surgery is needed.

Ultrasound-guided percutaneous techniques have recently transformed the diagnosis and management of peripheral nerve disorders. Among these techniques, ultrasound-guided hydrodissection is a minimally invasive intervention that utilizes real-time sonography to position a needle at the nerve-adhesion interface. Hydrostatic pressure from injected fluid then mechanically separates adhesions to relieve compression, offering a visualizable, less traumatic, and repeatable alternative to surgery^7,8,9. While hydrodissection effectively addresses the mechanical component of entrapment, it does not, by itself, restore coordinated motor function or retrain the neuromotor pathways compromised by chronic compression. Neural recovery following decompression requires not only the removal of the physical barrier but also systematic neuromuscular re-education to translate restored neural continuity into functional movement. Therefore, coupling mechanical decompression with a structured, task-specific rehabilitation program is essential to achieve meaningful functional recovery.

This illustrative protocol visually demonstrates: (1) real-time identification of the CPN and perineural adhesions; (2) in-plane needle placement and multi-quadrant hydrodissection; and (3) a phased rehabilitation protocol that begins 24 h post procedure. By integrating these two complementary components—percutaneous decompression and targeted neuromotor retraining—this workflow addresses both the structural and functional dimensions of recovery, offering a comprehensive approach that is advantageous over either intervention alone. Each step is presented in a numbered, visually guided format to support replication by clinicians with basic musculoskeletal ultrasound experience.

Protocol

All procedures were performed in accordance with the ethical standards of the institutional research committee and with patient-informed consent. This protocol was approved by the Ethics Committee of Wenzhou TCM Hospital of Zhejiang Chinese Medical University (Approval Number: WZY2025-LW-068-02).

1. Ultrasound-guided hydrodissection for CPN entrapment

NOTE: In this demonstration, a single session was performed. Repeat intervention, if considered, should be based on persistent functional deficits or sonographic evidence of residual entrapment, with the frequency and total number individualized; evidence-based criteria remain to be established.

1. Preparation of materials and equipment
   1. Prepare an ultrasound device equipped with a high-frequency linear array transducer (e.g., 10–15 MHz) and color Doppler capability.
   2. Adjust the initial ultrasound settings: set the depth to 3–4 cm to encompass the target area; adjust the gain to clearly distinguish the hyperechoic nerve fascicles from the hypoechoic muscle background.
   3. Prepare a 22 G or 25 G, 50–80 mm needle (a blunt-tip nerve block needle) and a 10 mL syringe.
   4. Under aseptic conditions, draw up 1 mL of 50% dextrose, 1 mL of 2% lidocaine, 1 mL of mecobalamin (500 µg/mL), and 7 mL of 0.9% sodium chloride into the syringe to prepare a 10 mL solution.
      NOTE: The final dextrose concentration is 5%.
   5. Prepare other sterile items: ultrasound gel, skin disinfectants (e.g., povidone-iodine), a sterile ultrasound probe cover, sterile gloves, and sterile gauze.
2. Instruct the patient to lie prone with the ipsilateral leg exposed. Have the operator stand on the ipsilateral side of the patient, facing the ultrasound screen. Place a small pillow under the ipsilateral ankle to maintain the knee in full extension and the ankle in neutral. Palpate and mark the popliteal crease, fibular head, and lateral femoral condyle before probe placement.
3. Nerve identification and entrapment site localization
   1. Apply a generous amount of coupling gel to the skin over the popliteal fossa. Hold the linear transducer with a firm, stable grip, orienting it transversely (perpendicular to the long axis of the limb). Place the transducer transversely over the popliteal fossa, aligning it with the popliteal crease. Identify the popliteal vessels, then locate the sciatic nerve just lateral to these vessels.
   2. Slide the probe distally (toward the foot) while maintaining transverse orientation to trace the sciatic nerve to its bifurcation into the tibial and common peroneal nerves. Maintain consistent light pressure to avoid compressing the underlying structures.
      NOTE: The bifurcation site presents a characteristic "double-bundle" appearance where two oval, hyperechoic structures separate. The laterally located bundle is the CPN (Figure 1).
   3. Continue sliding the probe distally to the level just inferior to the fibular head to identify where the CPN typically bifurcates into the superficial and deep peroneal nerves.
   4. Carefully scan along the course of the identified nerve by slowly translating the transducer proximally to distally while maintaining a transverse plane. Look for signs of entrapment, including focal nerve swelling, regional hypoechogenicity, and loss of clear demarcation from the surrounding scar tissue. Rotate the transducer into a longitudinal plane if needed to assess the nerve course and confirm the level of maximal compression. For a standardized approach to sonographic evaluation of the knee, refer to a previous report¹⁰.
4. Sterile field establishment and needle path planning
   1. Perform standard skin disinfection of the procedural area using povidone-iodine or chlorhexidine in concentric circles from the center outward. Apply sterile drapes to establish a sterile field, leaving only the targeted skin entry site exposed.
   2. Cover the ultrasound transducer with a sterile probe cover, ensuring no air bubbles remain between the cover and the transducer’s face. Apply sterile gel to the probe surface.
   3. Under real-time ultrasound guidance, center the target nerve on the screen. Activate color Doppler mode and sweep the transducer to identify and mark the location of any adjacent vessels (e.g., popliteal artery, superior lateral genicular artery) to avoid vascular injury from the needle.
   4. Plan a safe, in-plane needle trajectory. Using the transducer as a reference, determine the skin entry point such that the needle path avoids neurovascular structures. A lateral approach (entering from the lateral aspect of the leg, with the needle directed medially toward the nerve) is typically preferred for the CPN at the fibular neck, while a medial approach may be used for the bifurcation site. Mark the planned entry point with a sterile marker.
   5. Prior to skin puncture, perform a final real-time assessment by gently rocking the transducer proximally and distally to confirm that the chosen trajectory remains clear of vessels and aligns with the long axis of the nerve. If the nerve is obscured by overlying scar tissue or if the planned trajectory cannot be maintained within the imaging plane, adjust the skin entry point or approach angle accordingly before proceeding.
5. Needle insertion and real-time guidance
   1. Hold the needle with the dominant hand using a pencil grip to allow fine control. Hold the transducer with the non-dominant hand, maintaining steady, light pressure. Use the hypothenar aspect or the ulnar border of the non-dominant hand to gently stabilize the skin adjacent to the planned entry site, thereby reducing tissue mobility during needle insertion.
   2. Under continuous ultrasound visualization, slowly advance the needle along the planned trajectory using short, controlled, stepwise movements. Keep the needle parallel to the transducer axis to maintain the entire shaft within the imaging plane.
   3. Ensure the entire needle shaft, especially the tip, remains within the ultrasound imaging plane at all times. Use subtle wrist adjustments to redirect the needle if it deviates from the plane. If the needle tip becomes obscured or deviates from the imaging plane, pause advancement, perform a subtle wrist rotation to re-align the needle with the transducer axis, and reacquire the tip before proceeding.
   4. Precisely guide the needle tip to the target location: the interface between the hyperechoic nerve epineurium and the adjacent hypoechoic entrapping tissue.
      NOTE: The tip should be positioned immediately adjacent to the nerve, not within it.
   5. Confirm the final needle tip position is adjacent to, but not within, the nerve substance by rotating the transducer slightly proximally and distally to visualize the tip in multiple planes.
      CAUTION: Avoid intraneural injection. If the patient reports paresthesia or sharp pain during needle advancement, withdraw the needle slightly and redirect.
6. Hydrodissection execution
   1. Under continuous, real-time ultrasound guidance, slowly inject 0.5–1.0 mL of the prepared solution. Use steady, gentle finger pressure on the syringe plunger. Observe the real-time formation and expansion of an anechoic fluid pocket at the needle tip. If the fluid pocket expands asymmetrically or extends away from the nerve-epineurium interface rather than separating the nerve from adhesions, pause injection, reassess the needle tip position, and gently redirect the tip toward the target interface before resuming.
      NOTE: Successful initial hydrodissection is indicated by the real-time formation and expansion of an anechoic fluid pocket at the needle tip, beginning to separate the hyperechoic border of the nerve from the adherent tissue (Figure 2).
   2. Always aspirate before injection to confirm the absence of blood and avoid intravascular placement.
      CAUTION: Immediately stop injection if sudden, significant resistance is encountered or if the patient reports severe or radiating pain. In such cases, withdraw the needle slightly and reassess the tip position.
   3. To achieve circumferential nerve release, slightly withdraw the needle by 1–2 mm and reorient the tip angle. To reposition the needle tip to a new quadrant, partially withdraw the needle until the tip is just outside the epineurial-adhesion interface (approximately 1–2 mm proximal to the initial injection site). Using subtle wrist supination or pronation to change the trajectory angle while maintaining the needle within the imaging plane, advance the tip toward the desired quadrant (e.g., anterior, posterior, medial, or lateral) under continuous visualization. Inject an additional 0.5–1.0 mL aliquot at this new location.
   4. Repeat the needle repositioning and injection process described in step 1.6.3 for 2–4 cycles to cover different quadrants around the nerve (e.g., anterior, posterior, medial, lateral); this range is based on the authors' procedural experience rather than a validated therapeutic standard. The total injectate volume typically ranges from 3 to 6 mL.
      NOTE: If significant resistance is met during initial injection due to dense scar tissue, slightly withdraw the needle to create a superficial "pilot" fluid pocket in a more accessible tissue plane. This establishes a hydraulic working space to facilitate subsequent needle advancement and deeper dissection.
   5. To follow this protocol, continue quadrantal injection until ultrasound imaging demonstrates fluid-mediated separation of >>50% of the nerve's circumference from the surrounding adhesive tissue. Rotate the transducer slightly to visualize the nerve in both transverse and longitudinal planes to confirm circumferential release.
      NOTE: This fluid-mediated separation criterion is based on the authors' procedural experience and is intended as a practical intraprocedural guide rather than an evidence-based therapeutic endpoint.
7. Postprocedure management
   1. Upon completion, gently withdraw the needle while applying gentle counterpressure with the non-dominant hand to stabilize the tissues. Apply brief, light pressure to the insertion site with sterile gauze for 30–60 s to achieve hemostasis.
   2. Perform a final ultrasound sweep of the treated area. Scan the nerve from proximal to distal in both transverse and longitudinal planes. Confirm the extent of nerve separation and rule out immediate procedure-related complications, such as active bleeding or hematoma formation.

2. Posthydrodissection rehabilitation protocol

NOTE: The second-phase rehabilitation commences 24 h after the hydrodissection procedure. Its core objective is to utilize the restored neural pathway to achieve functional remodeling.

1. Neural gliding (neurodynamic mobilization)
   CONTRAINDICATIONS: Perform this maneuver only in the absence of acute nerve inflammation, suspected nerve rupture, local malignancy, or severe instability (e.g., acute fracture).
   PRECAUTIONS: Exercise caution in patients with severe peripheral neuropathy or following recent nerve repair.
   CAUTION: Immediately discontinue the maneuver if it reproduces or exacerbates the patient's radicular or sharp, lancinating neurogenic pain.
   1. Position the patient supine with the affected lower extremity facing the operator. The contralateral leg remains relaxed, and the distal thigh is supported on a stable surface. The knee is flexed to 20–30°, and the ankle is maintained in a neutral position.
   2. Perform the technique as follows:
      1. Tensioning: Stabilize the patient's foot. Slowly perform passive ankle dorsiflexion with inversion until a mild neural stretch sensation (not pain) is felt.
      2. Gliding: While maintaining the ankle position, rhythmically flex the knee to 60–70° and then return it to 20–30°. This constitutes one cycle.
      3. Dosage: Perform 10–15 cycles. Briefly return the ankle to the neutral position between cycles.
2. Physical modalities
   1. Apply therapeutic ultrasound after hydrodissection to enhance local microvascular perfusion and reduce perineural edema, potentially extending the mechanical decompression effect by limiting early re-adhesion and supporting neural microenvironment recovery.
      1. Apply ultrasound coupling gel evenly over the skin of the treatment area, covering the CPN course from the popliteal fossa to the inferior border of the fibular neck.
      2. Set the ultrasound transducer to a frequency of 1 MHz, an intensity of 0.5–0.8 W/cm², and operate in pulsed mode with a 20–25% duty cycle (e.g., a 1:4 pulse ratio).
         CAUTION: Avoid using continuous mode over superficial nerves to prevent thermal injury.
      3. Move the soundhead in slow, continuous circular movements over the area at a speed of approximately 4 cm/s for 8 min.
   2. Neuromuscular electrical stimulation (NMES)
      1. Place two treatment electrodes (approximately 5 × 5 cm each) longitudinally over the belly of the tibialis anterior muscle. Place the reference electrode on the dorsum of the foot.
      2. Set the stimulator to deliver a biphasic square waveform at 20–25 Hz, with a pulse width of 200–250 µs, and an on:off ratio of 1:3 to 1:5. Increase the amplitude to elicit a moderate-to-strong, painless dorsiflexion contraction. Stimulate for 15–20 min.
         NOTE: This protocol aims to maintain muscle mass and excitability during reinnervation.
         Among the rehabilitation components, task-oriented training represents the core evidence-supported intervention.
3. Task-oriented training
   1. Heel-toe gait training
      1. Instruct the patient to walk from one end of a path to the other.
      2. Verbally cue the patient to focus on two key elements: making initial ground contact with the heel and generating a forceful push-off from the forefoot during toe-off.
      3. Monitor and cue the patient to maintain an upright trunk posture and forward gaze throughout the walk.
      4. Progression criteria: Increase difficulty when the patient can complete three consecutive walks with the correct pattern. Progress by increasing speed, walking on a low-pile carpet, or walking along a curved path.
   2. Lateral ball-kicking with toe control
      1. Place a soft soccer ball (size 4 or 5) on the floor next to the affected foot. Instruct the patient to stand while bearing most of their weight on the unaffected leg.
      2. Have the patient use the medial border of the affected foot to gently tap the ball sideways, focusing on controlled ankle inversion.
      3. Have the patient use the lateral border of the same foot to tap the ball back, focusing on controlled ankle plantarflexion.
      4. Progression Criteria: Progress by increasing the force/distance of the tap, using a smaller or partially deflated ball, or performing the activity while the patient stands on a foam pad with the unaffected leg.
   3. Level-ground obstacle crossing
      1. Place a series of low-density foam blocks (e.g., 5 cm, 10 cm, and 15 cm in height) in a line on the ground, spaced about one step apart.
      2. Instruct the patient to approach the first obstacle and step over it using the affected leg as the swing leg.
      3. Cue the patient to focus on lifting the swing leg with adequate hip and knee flexion to clear the obstacle without touching it.
      4. Emphasize a controlled landing on the affected leg, followed by a stable stance before proceeding to the next obstacle.
      5. Progression criteria: Progress by increasing obstacle height, decreasing the width of the base of support during landing, or having the patient step over obstacles placed in a zigzag pattern.
   4. Single-leg standing
      1. Instruct the patient to stand on the affected leg. For safety, position them near a stable surface (e.g., a countertop). Allow the patient to use light fingertip support on the surface for balance.
      2. Instruct the patient to maintain the single-leg stance with the knee slightly flexed. The goal for each repetition is to hold the position for up to 30 s.
      3. Progression criteria: Progress by gradually reducing fingertip support to no support, having the patient close their eyes, or performing the stance on an unstable surface (e.g., a foam balance pad).
   5. Stair walking
      1. Have the patient practice on a standard-height step (approximately 15 cm). Ensure a handrail is available.
      2. For ascent, instruct the patient to lead with the affected leg, focusing on the concentric control required to lift the body weight.
      3. For descent, instruct the patient to lower the body with the affected leg, focusing on the eccentric control to achieve a slow, steady movement.
      4. Progression criteria: Progress by gradually reducing handrail use, increasing the number of steps consecutively negotiated, carrying a light object, or practicing on stairs of varying heights.
         ​NOTE: Table 1 summarizes the posthydrodissection rehabilitation protocol.

Results

Functional recovery
Following the integrated protocol, the leg-foot angle during maximal voluntary dorsiflexion improved from 142° pre-intervention to 104° post-intervention, representing a 38° reduction (measured in seated position; Figure 3). This functional gain was accompanied by normalization of gait biomechanics. Pre-treatment gait analysis showed characteristic impairments of common peroneal nerve (CPN) palsy, including forefoot strike at initial contact (

Discussion

This article demonstrates an integrated approach that combines ultrasound-guided hydrodissection with structured rehabilitation for the management of refractory common peroneal nerve (CPN) entrapment. The observed functional recovery illustrates a potential synergy: precise structural intervention creates the necessary physical conditions, which neuromotor retraining may then exploit to restore function.

The successful execution of the procedure depends on several key, visually guided ste...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
50% Glucose Injection	China Otsuka Pharmaceutical Co., Ltd.	25G95J1	Component of injectate (1 mL, 5% final concentration)
Adhesive Dressing	Zhende Medical Co., Ltd.	N2206070111-2	Cover needle insertion site post-procedure
Balance Pad	Zhangjiagang Aonfit Trading Co., Ltd.	ATZJ383	Progression tool for single-leg standing training
Blunt-Tip Nerve Block Needle (22 G or 25 G, 50–80 mm)	Zhejiang Kindly Medical Devices Co., Ltd.	C20251117	For in-plane ultrasound-guided hydrodissection
Foam Blocks	Zhangjiagang Aonfit Trading Co., Ltd.	ATY0520	Obstacles for level-ground crossing training
Iodophor Disinfectant	Shandong Xiaoboshi Disinfection Technology Co., Ltd.	20250902K	Skin disinfection before needle insertion
Lidocaine Injection	Hunan Kelun Pharmaceutical Co., Ltd.	R24101103	Component of injectate
Mecobalamin Injection	Eisai China Inc.	230658	Neurotrophic support in injectate (1 mL)
Medical Underpad	Zhende Medical Supplies Co., Ltd.	20250911C	Protect patient positioning surface
Neuromuscular Electrical Stimulation Device	Beijing Yaoyangkangda Medical Equipment Co., Ltd.	KT-90B	Must deliver biphasic square wave.
Sodium Chloride Injection (0.9%)	China Otsuka Pharmaceutical Co., Ltd.	25I89B4	Diluent for injectate
Soft Soccer Ball	Peak (China) Co., Ltd.	YQ03207	Target for lateral ball-kicking training
Sterile Gauze	Henan Yadu Industrial Co., Ltd.	2509CA3138	Apply pressure to puncture site
Sterile Latex Gloves	Beijing Ruijing Latex Products Co., Ltd.	2025072425	Maintain aseptic technique
Sterile Probe Cover	Zhejiang Chun'an County Renhe Medical Products Industry and Trade Co., Ltd.	A1440EP	Sterile cover for ultrasound probe
Sterile Syringe (10 mL)	Zhejiang Longde Pharmaceutical Co., Ltd.	202601076	Prepare total injectate volume (10 mL)
Therapeutic Ultrasound Device	Shanghai Xibei Huachao Intelligent Medical Technology Co., Ltd.	Sonosail 2	With 1 MHz transducer head for pulsed application.
Ultrasound Gel	Hangzhou Kaipule Medical Equipment Co., Ltd.	KL-250	Acoustic coupling for ultrasound imaging
Ultrasound System	Fujifilm SonoSite Co., Ltd.	SII	With color Doppler function. Use high-frequency linear array transducer (10–15 MHz).