Dorsal Capsulodesis for Scapholunate Instability: A Masterclass

Fellows, welcome to the operating theater. Today, we're addressing a common yet often challenging wrist pathology: scapholunate instability. Specifically, we'll be performing a dorsal capsulodesis, a cornerstone procedure for restoring stability to the scaphoid and lunate. This isn't just about fixing a ligament; it's about understanding the intricate kinematics of the carpus and preventing the cascade of degenerative changes that can lead to a devastating SLAC wrist.

Understanding Scapholunate Instability: The Foundation

Before we make our incision, let's review the fundamental principles of scapholunate dissociation (SLD). This is more than just a torn ligament; it's the rupture of the critical anatomic linkage between the scaphoid and lunate, leading to progressive dysfunction, with or without carpal malalignment.

The sequence of ligamentous failure in SLD is crucial to grasp. It typically initiates volarly, where the volar scapholunate ligament, being the weaker of the two, tears first. This is subsequently followed by the more robust dorsal scapholunate ligament. Early, subtle injuries, often termed "predynamic" or "dynamic" instability, may not show classical radiographic signs but are critical to diagnose and treat to prevent progression.

The Progressive Nature of SLD

Remember Mayfield's progressive perilunar destabilization? SLD often presents as an initial stage in this spectrum, ranging from mild sprains to complete perilunar dislocations. In many cases, only partial tears or sprains occur, which may only be evident arthroscopically.

Once the primary scapholunate ligaments are compromised, the secondary stabilizers of the scaphoid begin to bear increased load. These include the scaphotrapezial-trapezoid (STT) ligament, the scaphocapitate (SC) ligament, and the radioscaphocapitate (RSC) ligament. Their eventual failure, often after repeated wrist loading, leads to overt carpal malalignment and static instability. Initially, the scaphoid might still be reducible, but over time, it becomes permanently flexed and pronated. If this altered motion persists, cartilage degeneration ensues, culminating in the dreaded scapholunate advanced collapse (SLAC) wrist. Once arthrosis is present, ligament reconstruction is no longer a viable option, underscoring the importance of early intervention.

Essential Surgical Anatomy

Let's focus on the anatomical structures critical to this procedure.

• Scapholunate Ligaments: These are divided into three fibrous structures:
  • Dorsal Ligament: This is the thickest (2-3 mm) and shortest (2-5 mm) component, and biomechanically, it is the strongest and most resistant to failure under load. Its integrity is paramount.
  • Volar Ligament: Thinner and weaker, often the first to tear.
  • Thin Proximal Membrane: Less biomechanically significant.
    

    
    
    

FIG 1 • A. The elements that maintain the scaphoid in its normal position, highlighting the scapholunate ligaments.

• Secondary Stabilizers: The scaphoid's position and its relationship with the lunate and distal carpal row are maintained by the scapholunate ligaments and these secondary stabilizers (STT, SC, and RSC ligaments). They prevent excessive scaphoid flexion.
  

  
  
  

FIG 1 • B. Volar view of secondary stabilizers, including the scaphotrapezial-trapezoid (STT), scaphocapitate (SC), and radioscaphocapitate (RSC) ligaments.

• Dynamic Stabilizers: Don't forget the flexor carpi radialis (FCR) tendon. It's closely related to the scapholunate joint and acts as a crucial dynamic stabilizer, preventing excessive scaphoid flexion and pronation during grip.
  

  
  
  

FIG 1 • C. The dynamic stabilizer of the scaphoid, the FCR tendon.

• Neurovascular Structures:

  • Superficial Radial Nerve: This sensory nerve runs subcutaneously on the dorsoradial aspect of the wrist. We must identify, mobilize, and protect its branches, particularly during the initial skin and subcutaneous dissection, to prevent painful neuromas or dysesthesias.
  • Posterior Interosseous Nerve (PIN): This is the terminal motor branch of the radial nerve. It provides sensory innervation to the dorsal wrist capsule. A neurectomy of the PIN is often performed during dorsal wrist approaches to provide long-term pain relief, as it does not innervate any critical motor function in this region.
  • Dorsal Carpal Arch: This vascular arcade lies just beneath the extensor retinaculum and must be identified and preserved or meticulously ligated if necessary during capsular flap creation to maintain flap viability.

• Osteology & Landmarks:

  • Lister's Tubercle: A key palpable landmark on the dorsal aspect of the distal radius, serving as a guide for our incision and for locating the third dorsal compartment.
  • Radial Styloid: Another palpable bony prominence, marking the radial extent of the wrist.
  • Scaphoid: The boat-shaped carpal bone, highly susceptible to instability. We'll be creating a trough in its dorsal aspect, distal to its axis of rotation (scaphoid neck).
  • Lunate: The moon-shaped carpal bone, whose relationship with the scaphoid is central to this instability. We aim to fix it in a neutral position.
  • Capitate: The largest carpal bone, acting as a stable anchor for our scaphoid-capitate K-wire.

• Muscular & Tendinous Intervals:

  • Extensor Retinaculum: This fibrous band overlies the extensor tendons. We'll incise the retinaculum over the fourth dorsal extensor compartment.
  • Extensor Digitorum Communis (EDC): Retracted ulnarly.
  • Extensor Pollicis Longus (EPL) and Extensor Carpi Radialis Brevis (ECRB): Retracted radially. This interval exposes the dorsal capsule.

Preoperative Planning and Patient Positioning

Thorough preoperative planning is paramount for a successful outcome.

Diagnostic Review

We've meticulously reviewed all preoperative radiographs and diagnostic studies. Crucially, arthroscopy remains the gold standard for diagnosing and staging SLD, allowing us to accurately grade the instability using the Geissler classification (Table 1). This also provides invaluable information on cartilage status and concomitant carpal injuries.

Table 1: Arthroscopic (Geissler) Grading of Interosseous Ligament Tears
| Grade | Description |
| :---- | :---------- |
| 1 | Attenuation or hemorrhage of interosseous ligament from radiocarpal joint. No incongruency of carpal alignment in midcarpal space. |
| 2 | Attenuation or hemorrhage of interosseous ligament from radiocarpal joint. Incongruency or stepoff from midcarpal space. Slight gap (less than width of 1-mm probe) between carpal bones. |
| 3 | Incongruency or stepoff from both radiocarpal and midcarpal spaces. 1-mm probe able to pass through gap between carpal bones. |
| 4 | Incongruency or stepoff from both radiocarpal and midcarpal spaces. Gross instability with manipulation noted. 2.7-mm probe able to pass through gap between carpal bones. |

Our patient today presents with a dynamic SLD, a Geissler Grade 3, fulfilling our criteria for capsulodesis: complete disruption of both palmar and dorsal scapholunate components, a repairable dorsal ligament with good healing potential, intact secondary stabilizers, and no evidence of cartilage degeneration. This procedure is contraindicated in cases of static SLD or established arthrosis.

Radiographs, while not always definitive in early stages, provide crucial information.
* PA View: We look for a scapholunate gap >3mm or wider than the contralateral side, and the cortical "ring" sign.
* AP View (Clenched-fist): This view accentuates the scapholunate gap by applying axial load.

Patient Positioning and Setup

Our patient is already under general anesthesia and positioned supine on the operating table.

1. Lower Extremity Comfort: The hips and knees are flexed at 30 degrees to ensure low back comfort during what can be a lengthy procedure.
2. Arm Preparation: The affected arm is carefully placed on a specialized hand table. We ensure the arm is in pronation, presenting the dorsal aspect of the wrist directly to the surgical field. This allows optimal exposure and ergonomic access for the surgical team.
3. Tourniquet Application: A pneumatic tourniquet has been applied to the upper arm and inflated to 250 mmHg after exsanguination with an Esmarch bandage. This provides a bloodless field, crucial for identifying delicate neurovascular structures and meticulously dissecting the dorsal capsule.
4. Fluoroscopy Setup: The C-arm is positioned to allow for immediate and easy access for intraoperative fluoroscopic imaging in both PA and lateral projections without repositioning the patient or the arm. This is critical for confirming carpal alignment during reduction and K-wire placement.

Intraoperative Execution: The Blatt Capsulodesis Masterclass

Alright, fellows, let's scrub in. We're now operating on the patient. Pay close attention to every detail; precision here is key to long-term stability.

1. Incision and Initial Dissection

First, let's identify our key bony landmarks: Lister's tubercle and the radial styloid. You can feel Lister's tubercle as a small dorsal prominence on the distal radius, usually a centimeter or so ulnar to the midline.

• Skin Incision: We'll make an oblique skin incision, approximately 4-5 cm in length. This incision starts from a point about 1 cm distal and ulnar to Lister's tubercle and extends distally and radially to a point approximately 1 cm distal to the radial styloid. This oblique orientation provides excellent exposure while minimizing tension on the skin edges and respecting Langer's lines for a more cosmetic scar.
  

  
  
  

TECH FIG 1 • The planned oblique incision site, extending from distal-ulnar to Lister's tubercle to distal-radial to the radial styloid.

• Subcutaneous Dissection and Nerve Protection: Now, with a fine scalpel (e.g., #15 blade), we carefully incise the skin. Immediately, we encounter the subcutaneous fat. This is where we must be extremely vigilant. Using blunt dissection with fine Metzenbaum scissors, we gently elevate the subcutaneous tissue and fat as a single flap, both radially and ulnarly. Our primary concern here is identifying and protecting the branches of the superficial radial nerve. These sensory branches are highly variable but typically run along the dorsoradial aspect of the wrist. We must mobilize and retract them with the subcutaneous tissue, ensuring they are never put under excessive tension or directly incised.
  > SURGICAL WARNING: Injury to the superficial radial nerve can lead to chronic, debilitating neuropathic pain or a painful neuroma. Always identify and protect these branches. Use careful, deliberate dissection.

• Vessel Management: As we deepen our dissection, we'll encounter superficial veins. These are meticulously coagulated with bipolar cautery or ligated with fine absorbable sutures (e.g., 4-0 Vicryl). We also divide and coagulate any communicating vessels that run from the superficial layers to the deeper dorsal carpal arch. A bloodless field is crucial for clear visualization of the deeper structures.

2. Exposure of the Dorsal Capsule and Extensor Compartments

Next, we identify the extensor retinaculum. This is a thick, fibrous band that holds the extensor tendons in place.

• Retinacular Incision: We'll make a longitudinal incision directly over the fourth dorsal extensor compartment. This compartment typically houses the extensor digitorum communis (EDC) tendons. The incision should be just ulnar to Lister's tubercle.

• Retinacular Flaps: Once incised, we carefully raise the extensor retinaculum as two flaps: a radially-based flap and an ulnarly-based flap. This frees the extensor tendons from the second to fourth compartments, allowing us to retract them effectively. We'll preserve these flaps for later repair.

• Tendon Retraction: Now, using blunt retractors (e.g., Senn retractors or small army-navy retractors), we carefully retract the tendons:

  • The extensor digitorum communis (EDC) tendons are retracted ulnarly.
  • The extensor pollicis longus (EPL) and extensor carpi radialis brevis (ECRB) tendons are retracted radially.
    This maneuver exposes the underlying dorsal capsule of the wrist joint.

• Posterior Interosseous Nerve (PIN) Neurectomy (Optional but Recommended): At this point, fellows, it's an excellent opportunity to perform a neurectomy of the posterior interosseous nerve. This provides a valuable adjunct for long-term pain relief. We identify the PIN as it emerges from the interosseous membrane, typically running along the floor of the fourth dorsal compartment. It's often found on the dorsal aspect of the distal radius, just proximal to the joint line. We resect a 1-2 cm segment of the nerve, ensuring no tension on the cut ends.
  > SURGICAL PEARL: Performing a PIN neurectomy can significantly reduce chronic dorsal wrist pain post-operatively without functional deficit, as it primarily supplies sensory innervation to the dorsal capsule.

3. Creation of the Dorsal Capsular Flap

Now we focus on the dorsal capsule itself, which will form the basis of our capsulodesis.

• Flap Design: We need to create a robust, rectangular capsular flap. The dimensions are critical: approximately 25 mm long and 10 mm wide.
• Proximal Incision: We make a transverse capsular incision just proximal to the vascular dorsal carpal arch. This arch typically runs transversely across the dorsal aspect of the carpus. By staying proximal to it, we ensure the blood supply to our flap is preserved.
• Flap Elevation: Using a small periosteal elevator and careful sharp dissection with a #15 blade, we elevate the tissue in a distal-to-proximal direction. The key is to keep the flap thick and full-thickness, incorporating all layers of the dorsal capsule. We meticulously dissect it off the underlying carpal bones (scaphoid, lunate, capitate).

Additional Intraoperative Imaging & Surgical Steps

REFERENCES

1. Berger RA. Ligament anatomy. In Cooney WP, Linsheid RL, Dobyns JH, eds. The Wrist: Diagnosis and Operative Treatment. St. Louis: Mosby, 1998:73–105.

2. Blatt G. Capsulodesis in reconstructive hand surgery. Hand Clin 1987;3:81–102.

3. Deshmukh SC, Givissis P, Belloso D, et al. Blatt’s capsulodesis for chronic scapholunate dissociation. J Hand Surg Br 1999;24B: 215–220.

4. Garcia-Elias M, Geissler WB. Carpal instability. In Green DP, Hotchkiss RN, Pederson WC, et al, eds. Green’s Operative Hand Surgery, 5th ed. Philadelphia: Elsevier, 2005:535–604.