ECU Subsheath Reconstruction: An Intraoperative Masterclass for Ulnar Wrist Stability

Welcome, fellows, to the operating theater. Today, we're addressing a common yet often challenging condition: Extensor Carpi Ulnaris (ECU) subluxation. This procedure demands meticulous attention to detail, a profound understanding of wrist anatomy, and precise surgical technique to restore stability and function. We're going to walk through this step-by-step, as if you're scrubbed in right next to me.

Understanding the Pathoanatomy of ECU Subluxation

Before we make an incision, let's review the critical anatomy. The Extensor Carpi Ulnaris (ECU) tendon is a crucial dynamic stabilizer of the distal radioulnar joint (DRUJ) and a powerful ulnar deviator and wrist extensor. Its stability at the wrist is paramount.

The Sixth Dorsal Compartment and its Subsheath

The ECU tendon resides within the sixth dorsal compartment, a unique fibro-osseous tunnel along the dorsum of the distal ulna. This compartment is distinct from the other extensor compartments. The key structure here is the ECU subsheath, which is a separate, robust fibro-osseous structure. It originates from the radial wall of the ulnar osseous groove and arcs tightly over the ECU tendon, attaching to the ulnar wall. This subsheath ensheathes approximately 1.5 to 2.0 cm of the distal ulna, maintaining the tendon securely within its groove.

When this subsheath is torn or attenuated, its competence is lost, allowing the ECU tendon to subluxate or even dislocate out of the ulnar groove. Clinically, this manifests as a painful click, often exacerbated by resisted supination, ulnar deviation, and palmar flexion. This phenomenon is frequently observed in athletes involved in racket sports, baseball, and golf, often stemming from a traumatic injury involving active ECU contraction combined with forced supination, palmar flexion, and ulnar deviation.

Layers of the Dorsal Extensor Retinaculum

Let's look at the broader picture of the extensor retinaculum, which has two primary layers:

• The Supratendinous Retinaculum: This superficial layer originates approximately 2 to 3 cm proximal to the radiocarpal joint and inserts distinctly at the carpometacarpal joints. Its most radial attachment forms the radial septum for the first extensor compartment. It courses medially, overlying the ulna. Critically, while it provides a block to subluxation for compartments one through five, it does not prevent subluxation of the ECU tendon.
• The Infratendinous Retinaculum: This deeper layer runs from the radiocarpal to the carpometacarpal joints, found deep to the fourth and fifth extensor compartments on the radius. The ECU's own separate fibro-osseous subsheath is, in fact, considered a duplication of this infratendinous retinaculum.
  

  
  
  

FIG 1 • Axial representation of dorsal extensor compartments. The ECU tendon has a separate compartment along the dorsum of the ulna. The supratendinous retinaculum courses ulnarward over the sixth compartment and does not communicate with the separate ECU fibro-osseous subsheath in any significant way.

ECU Subsheath and TFCC Relationship

The ECU subsheath is not an isolated structure; it contributes significantly to the dorsal portion of the triangular fibrocartilage complex (TFCC). Therefore, disruption of the ECU subsheath can lead to not only ECU instability but also static instability of the DRUJ, which can progress to pain, dysfunction, and ultimately degenerative changes in the joint. The dislocation of the ECU tendon effectively removes a dynamic stabilizer of the DRUJ, further compromising wrist mechanics.

Natural History and Clinical Presentation

Patients often present in the subacute phase after an acute injury, complaining of persistent ulnar wrist pain aggravated by pronation and supination. They frequently describe a "click" or "snap" sensation. Chronic subluxation can lead to painful snapping and even progressive ECU tendinopathy. Some patients, however, may experience minor, non-progressive symptoms that improve with conservative care. Our goal with surgery is to address those with persistent, clinically significant symptoms.

Preoperative Planning and Patient Assessment

Before we even consider the knife, a thorough preoperative assessment is non-negotiable.

Patient History and Physical Examination

We must conduct a complete physical examination of the ulnar-sided wrist to rule out confounding conditions and identify associated pathologies.

• Palpation and Inspection: Tenderness localized to the distal ulna and its groove, over the sixth dorsal compartment, is highly indicative of an acute sheath rupture or tendinopathy. Tenderness directly at the joint line may suggest an associated TFCC tear, which we must investigate further.
• Range of Motion (ROM): An inflamed ECU tendon typically causes pain with full passive radial wrist flexion. While overall wrist motion is often full in chronic cases, acute injuries can limit motion.
• Stability Testing: This is critical.
  • If the ECU tendon frankly dislocates with passive supination, palmar flexion, and ulnar deviation, we're dealing with gross instability.
  • If active ECU contraction is required to elicit dislocation, some inherent stability remains, though it's clearly insufficient.
  • The presence of pain with subluxation is a critical finding that guides our decision toward surgical intervention.
• Resisted Finger Abduction: Pain over the wrist and ECU tendon during this maneuver can signify an inflammatory ECU condition.

Imaging and Diagnostic Studies

• Radiographs: Routine AP, lateral, and oblique views are essential to rule out bony pathology. Pronated grip views can provide additional information regarding ulnar variance or other pathologies contributing to ulnar-sided pain.
• MRI: This is our most sensitive and specific imaging modality for detecting ECU subluxation.
  

  
  
  

FIG 3 • A. This MRI scan shows a “perched” ECU tendon, out of the dorsal ulnar groove. Notice the increased signal in the tendon substance.
To maximize sensitivity, MRI studies should ideally be performed with both wrists positioned in pronation, neutral, and supination, allowing for side-by-side comparison with the asymptomatic wrist and dynamic assessment of the ECU's position relative to the ulnar osseous groove. While the actual subsheath tear may or may not be directly visualized, inflammation and partial interstitial tendon disruption are often evident.

Differential Diagnosis

We must meticulously rule out other causes of ulnar-sided wrist pain:

• ECU Tenosynovitis: Fullness and pain with palpation, often with a painful snap or click, but without frank subluxation.
• TFCC Injury: Tenderness over the TFCC, pain with axial loading and rotation of the ulnar-deviated wrist (TFCC compression test), and DRUJ instability compared to the contralateral wrist.
• Lunotriquetral Ligament Injury: Tenderness over the dorsal lunotriquetral articulation, pain/crepitance with ulnar deviation. Provocative maneuvers like the ballottement test or ulnar snuff box test have good sensitivity but poor specificity.
• Ulnocarpal Impaction Syndrome: More common in ulna-positive variance. Similar physical findings to TFCC injury, with pain on forced ulnar deviation and increased pain with rotation through the loaded ulnocarpal articulation. Tenderness along the ulnar border of the triquetrum and distal ulna.
• Ulnar Styloid Nonunion: Uncommon, usually associated with widely displaced styloid fractures. Can lead to TFCC dysfunction and DRUJ instability due to its intimate relationship with the TFCC attachment.
• DRUJ Arthrosis: Pain, swelling, stiffness, exacerbated by forearm rotation, especially with manual compression of the DRUJ.

Nonoperative Management

In the acute setting (less than 3 weeks since injury), nonoperative treatment is often attempted. This involves immobilizing the patient in an above-elbow cast with the wrist in neutral to slight pronation, neutral to slight radial deviation, and neutral to slight extension. After 4 to 5 weeks, the cast is removed, and therapy is initiated with a custom-fabricated sugartong splint (forearm in slight pronation) and a progressive active and active-assisted ROM protocol. Three weeks later, a forearm-based splint is provided, and the patient slowly progresses back to activities. Unprotected, full activity is typically allowed 3 to 4 months after the initiation of treatment.

However, the literature is not entirely in agreement on the efficacy of nonoperative treatment for true subluxation. In our experience, and supported by case reports of surgical treatment for acute traumatic subluxation, if the intraoperative findings show significant separation of the subsheath edges (e.g., 7 mm or more), nonoperative treatment often leads to persistent symptoms and clinical ECU subluxation.

Surgical Indications and Classification

Surgical reconstruction of the ECU subsheath should be considered in patients with clinically significant symptoms related to painful subluxation of the ECU tendon, particularly if the injury is more than 3 weeks old and conservative measures have failed. Treatment must always be individualized based on the patient's needs and expectations.

The guiding principles for surgical repair depend on the specific osteofibrous sheath lesion. Inoue and Tamura classified three distinct patterns of injury, which dictate our surgical strategy:

• Type A Lesion: The fibro-osseous sheath is disrupted from the ulnar wall, and the tendon may lie beneath the disrupted sheath.
  • Recommended Treatment: If acute and adequate tissue is present, a direct repair may be attempted. If non-reconstructible, a sheath reconstruction with a retinacular free graft or retinacular sling is employed.
• Type B Lesion: The fibro-osseous sheath is disrupted from the radial wall, and the tendon may rest on top of the sheath, preventing healing.
  • Recommended Treatment: A sheath reconstruction with a retinacular free graft or retinacular sling is suggested.
• Type C Lesion: The fibro-osseous sheath is stripped from the periosteum but remains in continuity, forming a false pouch.
  • Recommended Treatment: Imbrication of the false pouch, reinforced with suture anchors or drill holes.

In cases of inflammatory arthropathy causing secondary volar dislocation of the ECU tendon, surgical stabilization of the ulnar wrist and DRUJ may be considered even in the absence of pain, to forestall progression of deformity.

Intraoperative Masterclass: Step-by-Step Execution

Alright, fellows, let's get scrubbed in.

Patient Positioning

The patient is positioned supine on the operating table. The injured extremity is extended on an armboard in the usual manner. Initially, we'll perform the procedure with the arm extended and pronated. If, during the procedure, we need to place the wrist in a neutral or supinated position to assess stability or facilitate reconstruction, we will flex the elbow to maintain comfort and access.

Preoperative Planning Review

At this point, we've thoroughly reviewed all preoperative information: the patient's history, physical examination findings, and imaging studies. We've synthesized this into our operative plan. For instance, if MRI indicated a concomitant TFCC injury or significant dorsal synovitis, we would have planned for a preliminary wrist arthroscopy or a tenosynovectomy. We've also considered the depth of the ulnar osseous groove; if it's shallow, we may need to plan for groove deepening. Finally, we've assessed the potential paucity of local soft tissue for reconstruction and considered alternative graft choices, such as the palmaris longus or flexor carpi ulnaris tendons, which we would have prepped for harvest.

Surgical Approach: Incision and Initial Dissection

1. Incision Planning: We'll choose a precise incision that allows optimal exposure for our predetermined method of reconstruction, whether it's a direct repair, a retinacular sling, or graft augmentation.

2. Brunner Zigzag Incision: We'll make a Brunner zigzag incision directly over the sixth extensor compartment. This curvilinear incision begins approximately 1 to 2 cm distal to the ulnocarpal joint and is carried proximally for about 5 cm. The zigzag pattern helps to prevent scar contracture across joint lines.

3. Skin and Subcutaneous Dissection: Using a #15 blade, we carefully incise the skin. Then, with Metzenbaum scissors, we continue our dissection through the subcutaneous tissues.

   Surgical Warning: Dorsal Cutaneous Branch of the Ulnar Nerve
   As we dissect distally and ulnarly, be extremely vigilant for the dorsal cutaneous branch of the ulnar nerve. This sensory nerve typically emerges from beneath the flexor carpi ulnaris tendon about 5-7 cm proximal to the pisiform, then courses dorsally and radially to supply sensation to the dorsum of the ulnar hand and digits. It is highly susceptible to injury during ulnar wrist approaches. Use fine blunt dissection, such as with a mosquito hemostat or small Metzenbaum scissors, to identify and meticulously protect this nerve in the distal incision. Retract it gently out of the field, usually ulnarly, with a vessel loop or small rubber elastic.

4. Exposure of Extensor Retinaculum: Once the subcutaneous fat is cleared, we will visualize the glistening, fibrous sheath of the dorsal extensor retinaculum.

5. Incising the Extensor Retinaculum: Now, this is a critical step, fellows. We need to incise the extensor retinaculum on its far ulnar border, carefully separating it from the underlying sixth extensor compartment fibro-osseous sheath. This is not a haphazard cut. Conservation and a planned incision in the extensor retinaculum are absolutely critical, as we often rely on this tissue for sling reconstruction to stabilize the ECU tendon. We want to preserve a substantial, viable flap of retinaculum for later use.

6. Exposure of the ECU Subsheath: Following the careful incision and retraction of the superficial extensor retinaculum, we expose the separate fibro-osseous sheath of the ECU. At this point, we will inspect the integrity of this subsheath and note the position of the ECU tendon. We'll then gently pronate and supinate the forearm to dynamically assess the tendon's stability and confirm the subluxation. This is where we classify the lesion according to Inoue and Tamura (Type A, B, or C).

7. Tenosynovectomy (as indicated): If we observe any dorsal synovitis or tenosynovitis of the ECU tendon, we will perform a meticulous tenosynovectomy using fine rongeurs and curettes, ensuring complete débridement of inflamed tissue. This improves the gliding surface and reduces postoperative pain.

Retinacular Sling Reconstruction for Type A and B Lesions

For Type A and B lesions, where the native ECU subsheath is ruptured and deemed irreparable, a retinacular sling reconstruction is often the preferred method due to its simplicity and the ability to create a smooth gliding surface between the bone and the tendon. We have two primary approaches: the radially-based sling and the ulnarly-based sling.

Technique 1: Radially-Based Retinacular Sling Reconstruction

This technique involves creating a flap from the extensor retinaculum, based radially, and passing it deep to the ECU tendon.

1. Flap Creation: At the level of the ulnar groove, we carefully create a rectangular flap of tissue, approximately 2 to 3 cm wide, based on the septum separating the fifth and sixth extensor compartments. This flap is fashioned from the superficial extensor retinaculum.
   

   
   
   

TECH FIG 1 • Retinacular sling reconstruction of type A and B lesions. A. Creation of a radially based extensor retinaculum sling.

1. Sling Passage: Now, with the flap developed, we will pass this radially-based sling in an ulnar direction, volar (deep) to the ECU tendon. Use a small right-angle clamp or a tendon passer to gently guide the flap underneath the tendon. This is crucial for creating the new floor of the compartment.

2. Sling Creation and Securing: Once the flap is deep to the ECU tendon, we then fold it back radially over the tendon, creating the roof of the new compartment. We then secure this flap to the ulnar portion of the fifth compartment, or to the remaining proximal extensor retinaculum. This places the superficial surface of the retinaculum in direct contact with the ECU tendon, providing a smooth gliding surface.
   

   
   
   

> **Surgical Warning: Avoiding Tendon Constriction**
> When securing the sling, it is absolutely vital to **avoid constricting the ECU tendon**. The sling must be wide and loose enough to allow free gliding of the tendon, yet tight enough to prevent subluxation. Test the tendon's excursion throughout pronation and supination to ensure it glides smoothly without impingement. A sling that is too tight will lead to tenosynovitis, pain, and potentially tendon necrosis.

1. Retinaculum Repair: The portion of the extensor retinaculum not used for the sling is then repaired anatomically with absorbable sutures to reconstruct the superficial layer and prevent bulging.

Technique 2: Alternate Ulnarly-Based Retinacular Sling Reconstruction

This alternative technique utilizes an ulnarly-based flap, which may offer more length in some cases.

1. Flap Development: We develop an ulnarly-based, rectangular flap of supratendinous retinacular tissue, again about 2 to 3 cm wide. This flap can begin at Lister’s tubercle or even further radially, over the second extensor compartment, if greater length is required. The flap is based on the ulnar septum of the fifth extensor compartment.
   

   
   
   

TECH FIG 2 • Alternate retinacular sling reconstruction of type A and B lesions. A. The ulnarly based extensor retinaculum flap is harvested, then swung ulnarward, deep to the ECU tendon.

1. Sling Passage: We then swing this tissue ulnarward, passing it deep (volar) to the ECU tendon.

2. Sling Creation and Securing: The tissue is then brought back over the tendon to create the sling. We will insert small suture anchors (e.g., 1.8 mm or 2.0 mm bioabsorbable anchors) on both the radial and ulnar margins of the ulnar groove.

   • Drilling: Use a small drill bit (e.g., 1.5 mm) with a drill guide to create pilot holes for the anchors. Ensure the drill angle is appropriate to engage good bone stock.
   • Anchor Placement: Carefully insert the suture anchors, ensuring they are fully seated.
   • Suture Fixation: Use the sutures from these anchors to stabilize the retinacular flap, securing it to itself and to the ulna. This places the deep surface of the retinaculum in contact with the ECU tendon.

   Surgical Warning: Anchor Placement and Tendon Irritation
   Ensure that the suture anchors are placed flush with the bone surface and that the sutures are tied securely without leaving any prominent knots that could irritate the ECU tendon. Also, verify that the sling is not too tight, allowing free tendon excursion.

3. Retinaculum Repair: The remaining retinaculum is repaired in an

Additional Intraoperative Imaging & Surgical Steps

REFERENCES

References 1. Allende C, Le Viet D. Extensor Carpi Ulnaris Problems At The Wrist: Classification, Surgical Treatment And Results. J Hand Surg Br 2005;30:3:265–272.

1. Burkhart S, Wood M, Linscheid Rl. Posttraumatic Recurrent Subluxation Of The Extensor Carpi Ulnaris Tendon. J Hand Surg Am 1982; 7:1:1–3.

2. Chun S, Palmer A. Chronic Ulnar Wrist Pain Secondary To Partial Rupture Of The Extensor Carpi Ulnaris Tendon. J Hand Surg Am 1987; 12:1032–1035.

3. Eckhardt W, Palmer A. Recurrent Dislocation Of Extensor Carpi Ulnaris Tendon. J Hand Surg Am 1981;6:629–631.

4. Inoue G, Tamura Y. Recurrent Dislocation Of The Extensor Carpi Ulnaris Tendon. Br J Sports Med 1998;32:172–177.

5. Inoue G, Tamura Y. Surgical Treatment For Recurrent Dislocation Of The Extensor Carpi Ulnaris Tendon. J Hand Surg Br 2001;26:556–559.

6. Rowland S. Acute Traumatic Subluxation Of The Extensor Carpi Ulnaris Tendon At The Wrist. J Hand Surg Am 1986;11:809–811.

7. Pratt R, Hoy Ga. Extensor Carpi Ulnaris Subluxation Or Dislocation? Ultrasound Measurement Of Tendon Excursion And Normal Values. Hand Surg 2004;9:137–143.

8. Spinner M, Kaplan E. Extensor Carpi Ulnaris: Its Relationship To The Stability Of The Distal Radio-Ulnar Joint. Clin Orthop Relat Res 1970;68:124–129.

9. Taleisnik J, Gelberman R, Miller Bw, Et Al. The Extensor Retinaculum Of The Wrist. J Hand Surg Am 1984:9:495–501.

10. The sutures are removed 2 weeks after surgery, and an above elbow cast is applied with the forearm and wrist positioned in the manner described.

11. This cast is removed 2 weeks later, and therapy is initiated with use of a fabricated sugartong splint and progressive range of motion as described in Nonoperative Management.

OUTCOMES
- No large conclusive studies on which to base outcomes have yet been published.

• A few case reports and smaller series have reported good results following surgical treatment for ECU subluxation. 1–4,6,7,9

Our experience mirrors these reports. COMPLICATIONS
- The uncommon nature of ECU subluxation, the uniformly acceptable surgical outcomes, and the lack of large surgical case series result in a sparse list of postoperative complications. Trends with which to define “routine” postsurgical complications are simply not present.

• Complications that have been reported in the literature include the following:

• Complex regional pain syndrome 1

• Decreased wrist motion

• Decreased grip strength