Scapholunate Instability: A Masterclass in Dorsal Ligament-Splitting Capsulotomy and Brunelli Tenodesis

Welcome, fellows, to another session in the operating theater. Today, we're tackling a challenging yet rewarding pathology: scapholunate dissociation (SLD). This is a symptomatic wrist dysfunction stemming from a partial or total rupture of the scapholunate ligamentous complex, often accompanied by carpal malalignment. Our goal is to restore stability using a modified Brunelli tenodesis technique, a robust soft tissue reconstruction.

Understanding Scapholunate Instability: A Foundation for Surgical Success

Before we even make an incision, a thorough understanding of the anatomy and biomechanics is paramount. The scapholunate interosseous ligament complex, the primary stabilizer we're addressing, comprises three critical structures: the palmar scapholunate ligament, the dorsal scapholunate ligament, and the proximal fibrocartilaginous membrane.

FIG 1 • Schematic representation of the periscaphoid ligaments seen from a dorsoulnar perspective. Both the lunate and the distal row have been drawn away from the scaphoid to better expose the ligaments.

The proximal membrane, fellows, connects the adjacent convex borders of the scaphoid and lunate, effectively separating the radiocarpal and midcarpal joint spaces. It's important to recognize that while this membrane can be perforated in older individuals, that alone doesn't necessarily cause instability.

SLD can manifest as an isolated injury, or it can be associated with distal radius fractures or displaced scaphoid fractures. Most commonly, it's the result of a traumatic hyperextension and ulnar deviation injury to the wrist. However, remember that chronic inflammatory arthropathies, such as rheumatoid arthritis or chondrocalcinosis, can also lead to SLD.

Let's delve deeper into the specific ligaments:
* The dorsal scapholunate ligament consists of dense, slightly oblique connective fibers. It's the strongest component, boasting an average yield strength of 260 Newtons (N). This is our primary target for stabilization.
* The palmar scapholunate ligament has longer, more obliquely oriented fibers, allowing for substantial rotation of the scaphoid relative to the lunate. It's weaker, with a yield strength of about 118 N.
* The proximal membrane, as we discussed, is the weakest, at 63 N.

Under normal physiological load, the scaphoid is inherently unstable due to its oblique alignment relative to axial forces. The degree of instability is influenced by:
* The strength of the dorsal and palmar scapholunate ligaments.
* The geometry of the radioscaphoid joint – a deeper scaphoid fossa offers greater stability.
* The stabilizing efficacy of the secondary periscaphoid ligaments: the dorsal scaphotriquetral (STq), palmar scaphocapitate (SC), and lateral scapho-trapezial-trapezoidal (STT) ligaments.

Pathogenesis of Scapholunate Dissociation: The Cascade of Instability

When the wrist is axially loaded, the proximal carpal bones don't react uniformly. The scaphoid tends to rotate into flexion and pronation, while the triquetrum is pulled into extension by the dorsally subluxing hamate.

FIG 2 • A. Under axial load ( blue arrows ) the scaphoid tends to rotate into flexion ( red arrows ) while the triquetrum tends to extend.

If all the primary ligaments – palmar and dorsal scapholunate, and lunotriquetral (LTq) – are intact, these opposing moments counteract each other, generating increasing torques that enhance coaptation and stability of the proximal carpal row.

FIG 2 • B. If both the scapholunate and lunotriquetral ligaments are intact, the two opposite moments counteract each other and a stable equilibrium is reached, allowing force to be transmitted across the proximal row.

However, if the scapholunate ligaments are completely torn, the scaphoid loses its constraint and collapses into an abnormally flexed and pronated posture – what we call "rotatory subluxation of the scaphoid." Concurrently, the lunate and triquetrum translate ulnarly and rotate abnormally into extension, leading to a dorsal intercalated segment instability (DISI) pattern.

FIG 2 • C. If the scapholunate ligaments fail and the secondary stabilizers do not succeed in maintaining the scaphoid aligned, a diastasis appears between the scaphoid and lunate ( red arrow ). This gap is formed as the consequence of the capitate edging into that space ( blue arrow ), forcing the proximal scaphoid to subluxate over the dorsal edge of the distal radius. In such circumstances, the lunate follows the triquetrum into further extension (dorsal intercalated segment instability) and ulnar translation.

Natural History and Progression: The SLAC Wrist

Partial scapholunate injuries, often termed "predynamic instability," may not be immediately symptomatic or radiologically evident. If left untreated, however, these can progress to a complete disruption, leading to symptomatic dysfunction. Initially, this might be "dynamic instability," where a gap is visible only under stress.

FIG 3 • A. PA radiographic view demonstrating a scapholunate gap and a foreshortened scaphoid with the classic ring sign indicating static scapholunate dissociation.

Over time, the secondary stabilizers (STT and SC ligaments) stretch, becoming inefficient. This results in permanent malalignment, or "static instability." The abnormal joint contact between the radius and scaphoid can cause cartilage deterioration of the scaphoid's proximal pole and reactive osteophyte formation at the radial styloid. This, fellows, is scapholunate advanced collapse (SLAC), stage 1.

FIG 3 • B. Coronal MRI showing the remnants of the disrupted proximal membrane hanging into the scapholunate gap, which is filled with fluid.

The lunate becomes fixed in DISI, and the scaphoid adopts a flexed, collapsed position, with its proximal pole subluxing dorsoradially over the edge of the radioscaphoid fossa.

FIG 3 • C. Sagittal MRI showing the abnormal dorsal subluxation of the proximal scaphoid over the edge of the radius.

Untreated, SLAC stage 1 progresses to stage 2 (cartilage loss involving the entire scaphoid fossa). As the lunate remains in DISI, the dorsally subluxing capitate may also develop cartilage deterioration, progressing from radial to ulnar, eventually involving the entire capitolunate joint – this is SLAC stage 3.

Patient History and Physical Findings

Two main clinical scenarios lead to an SLD diagnosis:
1. Violent trauma: A fall from height or motorcycle accident, often with obvious carpal derangement.
2. Insidious onset: Patients may not recall specific trauma but present with symptoms. This requires a high index of suspicion.

Key findings include:
* Scapholunate point tenderness: Sharp pain elicited by pressing this area suggests localized synovitis, though occult ganglia can mimic this.
* Resisted finger extension test: Low specificity but excellent sensitivity. Sharp pain at the scapholunate area indicates dorsal subluxation of the scaphoid.
* Scaphoid shift test (Watson's test): If the scapholunate ligaments are completely torn, the proximal pole may sublux dorsally out of the radius, causing pain. Be aware of its low specificity; hyperlaxity, occult ganglia, or radioscaphoid arthritis can produce similar symptoms.

Staging of Scapholunate Dissociation (Modified from Garcia-Elias et al.):
* Stage 1: Partial rupture, normal dorsal scapholunate ligament. Diagnosed often by arthroscopy.
* Stage 2: Complete SL ligament injury, dorsal ligament reparable. Normal wrist alignment.
* Stage 3: Complete SL ligament injury, dorsal ligament non-reparable, normally aligned scaphoid.
* Stage 4: Complete SL ligament injury, non-reparable, reducible rotary subluxation of scaphoid. Radioscaphoid angle > 45 degrees. Lunate may be ulnarly translated and in DISI.
* Stage 5: Complete SL ligament injury with irreducible malalignment, but normal cartilage.
* Stage 6: Complete SL ligament injury with irreducible malalignment and cartilage degeneration (SLAC wrist).

Imaging and Other Diagnostic Studies

• Posteroanterior (PA) radiographic view (neutral wrist):
  • Terry Thomas sign: Increased scapholunate joint space compared to the contralateral side suggests static SLD.
  • Ring sign: Foreshortened scaphoid with the scaphoid tuberosity projected as a ring over the distal two-thirds of the scaphoid, indicating rotatory subluxation. Not specific to SLD; can be seen in LTq dissociations.
• Lateral radiographic view:
  • Increased scapholunate angle (> 60 degrees) compared to the contralateral side. Crucially, the wrist must be in strict neutral alignment and prono-supination for this measurement to be significant.
• Stress views: Essential for detecting dynamic instability.
• Arthroscans (tomograms with dye injection): Very useful for assessing cartilage status, especially preoperatively.
• Magnetic Resonance Imaging (MRI): Provides valuable information on ligament integrity, bone vascularity, local synovitis, and other soft tissue status.
• Arthroscopy: The gold standard for diagnosis and assessing the degree of interosseous ligament injury. It's often the best tool for definitive preoperative planning.

Nonoperative Management

For acute, minimally dysfunctional SLD (Stage 1), a period of 3 to 5 weeks of wrist immobilization, anti-inflammatory medication, and subsequent physical rehabilitation may be effective. Re-education of the dynamic scaphoid stabilizing capability of the flexor carpi radialis (FCR) muscle can be helpful.

FIG 4 • The flexor carpi radialis (FCR ) tendon is in close relationship to the scaphoid tuberosity. Based on this, the scaphoid flexion tendency that appears when the bone is unstable can be effectively compensated by the dynamic action of the FCR muscle. Indeed, proprioception re-education of this muscle may be useful in stage 1 scapholunate dissociation.

The FCR utilizes the scaphoid tuberosity as a hinge, generating a dorsally directed vector that prevents scaphoid collapse into flexion. Optimizing its time response to wrist loading can potentially prevent progression of ligament disruption.

Surgical Management: Indications and Contraindications

Partial ligament injuries causing discomfort from remnant irritation may benefit from arthroscopic debridement. Electrothermal shrinkage of stretched ligaments has shown benefit in selected cases of dynamic instability, but careful fluid temperature control is mandatory to avoid thermal burns.

Today, we're performing a tendon reconstruction. This is recommended only for SLD stages 3 or 4 – meaning a complete, non-reparable scapholunate ligament injury causing carpal malalignment. For this to be successful, two critical conditions must be met:
1. The malalignment must be easily reducible. If we cannot reduce it with minimal force, no soft tissue reconstruction will achieve effective stability. Intra-articular fibrosis is the most common cause of irreducibility.
2. The periscaphoid cartilages must be completely normal. If there's any significant cartilage degeneration (SLAC stage 1 or higher), a tenodesis is unlikely to provide a lasting solution.

Contraindications:
* Irreducible malalignment: As discussed, if the carpal bones cannot be reduced, a tenodesis will fail.
* Significant cartilage degeneration: SLAC wrist stages 1 and above are contraindications.
* Heavy manual workers: These patients may require a more solid form of stabilization, such as a partial fusion, as a tenodesis is prone to deterioration under chronic high stress. Tendon reconstructions cannot fully restore the protective capsular proprioception, making them vulnerable to chronic overload.

Preoperative Planning: Leaving Nothing to Chance

Our planning for this case was meticulous.
* We obtained a complete set of plain radiographic views, including stress views, to assess both static and dynamic instability.
* Arthroscans were performed to precisely evaluate cartilage status across all carpal joints.
* A high-quality MRI provided valuable accessory information regarding bone vascularity, synovitis, and the overall status of other soft tissues.
* Ultimately, an arthroscopy was performed just prior to this definitive reconstruction. This allowed us to confirm the extent of the ligamentous injury, assess reducibility, and ensure the articular cartilage was pristine – confirming this patient is an ideal candidate for a Brunelli tenodesis.

Patient Positioning and Anesthesia

Let's ensure our patient is perfectly positioned.
* Anesthesia: An axillary block has been administered, supplemented with general anesthesia for patient comfort and muscle relaxation.
* Patient Position: The patient is in the supine position.
* Arm Preparation: The arm is exsanguinated with an Esmarch bandage and a tourniquet is inflated to 250 mmHg. The arm is then draped free, allowing full manipulation of the wrist. We'll use a hand table for stable support.

The Surgical Approach: Dorsal Exposure

Now, fellows, let's begin our approach.

1. Skin Incision:
* We'll make an 8-cm dorsal zigzag, lazy S, or longitudinal incision centered precisely over Lister's tubercle. I prefer a lazy S incision here, as it provides excellent exposure while minimizing scar contracture.
* Take your time with the skin incision. Use a #15 blade, making a clean, confident cut.
* Deepen the incision through the subcutaneous tissue.

2. Nerve Protection:
* Immediately, identify and protect the dorsal sensory branches of the radial nerve radially and the dorsal sensory branches of the ulnar nerve ulnarly. These are extremely vulnerable in this area.
> SURGICAL WARNING: Always be vigilant for the dorsal sensory nerves. Retract them gently using fine hooks or vessel loops. Damage to these nerves can lead to painful neuromas or significant sensory deficits.

3. Extensor Retinaculum Division:
* Now, we'll expose the extensor retinaculum. Our first step is to divide the retinaculum longitudinally along the third extensor compartment. This compartment houses the extensor pollicis longus (EPL) tendon.
* Carefully elevate the retinaculum, exposing the EPL.
* Retract the extensor pollicis longus tendon radially. This gives us access to the underlying dorsal capsule.
* Next, we'll section the retinacular septa between compartments II and V. This means dividing the septa separating the extensor carpi radialis longus and brevis (compartment II) from the extensor digiti minimi and extensor carpi ulnaris (compartment V).
* This maneuver creates two retinacular flaps – one radial, one ulnar – which we can then retract.
> SURGICAL WARNING: These septa often contain intraseptal vertical vessels. Ensure meticulous hemostasis using bipolar cautery to prevent excessive bleeding and hematoma formation.

Dorsal Ligament-Splitting Capsulotomy (Berger et al. Modification)

With the retinaculum retracted, we now have excellent exposure of the dorsal wrist capsule. This capsulotomy technique is designed to create a robust, radially-based capsular flap for later repair and augmentation.

1. First Incision:
* Using a #15 blade, make the first incision along the dorsal rim of the radius, extending distally to the center of the lunate fossa. This incision opens the radiocarpal joint capsule.

TECH FIG 1 • A. A radially based capsular flap is created by incising the dorsal capsule along the fibers of both the dorsal radiotriquetral ligament and the dorsal intercarpal ligament.

2. Second Incision:
* From the distal end of our first incision, continue the cut following the fibers of the dorsal radiotriquetral (DRT) ligament to its distal insertion onto the dorsal ridge of the triquetrum.
> SURGICAL PEARL: It is crucial to leave enough dorsal RTq ligament attached to the triquetrum. This remnant will be vital later to facilitate proper tensioning of our tendon reconstruction. Do not strip it completely.

3. Third Incision:
* Now, make the third incision. Start at the scapho-trapezial-trapezoid (STT) joint and progress medially along the dorsal intercarpal (DIC) ligament to its insertion onto the dorsum of the triquetrum.
* By connecting these three incisions, we have now defined our radially based capsular flap.
* Carefully elevate this flap by sectioning its connections to the dorsal edge of the scaphoid, lunate, and triquetrum. Use a small periosteal elevator or a Freer elevator for this, staying subperiosteal to maintain the integrity of the flap.

TECH FIG 1 • B. Once the capsular flap is retracted radially, the scapholunate injury can be inspected ( arrow ) and a final therapeutic decision can be made. A B

4. Inspection and Decision:
* With the capsular flap retracted radially, we now have a direct view of the scapholunate interval. This is your opportunity to meticulously inspect the injury (as indicated by the arrow in the figure). Confirm the extent of the ligamentous tear and the condition of the articular cartilage. This is our final confirmation before proceeding with the tenodesis.

TECH FIG 1 • A. A radially based capsular flap is created by incising the dorsal capsule along the fibers of both the dorsal radiotriquetral ligament and the dorsal intercarpal ligament. B. Once the capsular flap is retracted radially, the scapholunate injury can be inspected ( arrow ) and a final therapeutic decision can be made. A B
* At this stage, we can manually reduce the scaphoid and lunate. Apply gentle pressure to the distal pole of the scaphoid to bring it out of flexion and pronation, and extend the lunate. Confirm the reducibility. If irreducible, we would abort this procedure and consider other options like a partial fusion.

Palmar Scaphotrapezoid Plus Dorsal Radioscaphoid Tenodesis (Brunelli and Brunelli Modification)

This technique uses a strip of the FCR tendon to reconstruct the scapholunate linkage. This is a crucial step, fellows, requiring precision.

1. FCR Tendon Harvest:
* We need a strip of the FCR tendon. Make small, transverse palmar incisions along the course of the FCR tendon, starting at the level of the distal pole of the scaphoid and extending proximally.
* Isolate the FCR tendon. We will harvest a strip approximately 10-12 cm in length and about one-third to one-half the width of the main tendon. Leave the distal insertion of the FCR intact at the base of the second metacarpal.
* Carefully incise the tendon longitudinally with a #15 blade and then detach it proximally. Ensure the strip remains attached distally.
* Pass the harvested FCR strip dorsally through the interosseous membrane or a subcutaneous tunnel to bring it into the dorsal wrist wound.

• Self-generated image description: A schematic showing the FCR tendon being harvested as a distally-based strip, then routed dorsally to the wrist joint.

2. Scaphoid Reduction and K-wire Fixation:
* Now, we must meticulously reduce the scaphoid and lunate. Use a combination of direct pressure on the distal scaphoid pole to derotate and flex it, while extending the lunate.
* Once the scaphoid and lunate are in their anatomically correct, reduced position, provisionally fix them with two 1.2 mm K-wires. One K-wire should pass from the scaphoid into the lunate, and the other from the scaphoid into the capitate to maintain the scaphoid's alignment relative to the distal carpal row.
> SURGICAL PEARL: Confirm the reduction and K-wire placement with intraoperative fluoroscopy in both PA and lateral views. Ensure the scapholunate gap is closed and the scapholunate angle is restored to approximately 40-50 degrees. This is non-negotiable for a successful outcome.

3. Creating Bone Tunnels in the Scaphoid:
* We will now prepare the scaphoid for the FCR graft. Using a 2.5 mm drill bit, create two parallel bone tunnels through the waist of the scaphoid, from dorsal to palmar. These tunnels should be positioned to mimic the course of the native dorsal and palmar scapholunate ligaments.
* Use a K-wire to guide the drill, ensuring careful placement to avoid damaging the articular cartilage or neurovascular structures.

• Self-generated image description: A schematic showing two parallel drill tunnels created in the waist of the scaphoid, from dorsal to palmar aspect.

4. Passing the FCR Graft through the Scaphoid:
* Using a curved suture passer or a tendon passer, carefully thread the harvested FCR tendon strip through the two scaphoid tunnels, from dorsal to palmar.
* Bring both ends of the FCR strip out on the palmar side of the scaphoid.

• Self-generated image description: A schematic showing the FCR tendon strip passed through the two bone tunnels in the scaphoid, with both ends emerging on the palmar side.

5. Preparing the Lunate and Radius for Graft Fixation:
* Now, we need to secure the FCR graft to the lunate and radius to provide dorsal stability.
* On the dorsal aspect of the lunate, create a trough or a single drill hole using a 2.0 mm drill bit. This will be an attachment point for one limb of the FCR graft.
* Similarly, on the dorsal aspect of the distal radius, just radial to Lister's tubercle, create another trough or drill hole for the other limb. This addresses the "Dorsal Radioscaphoid" component of the Brunelli technique.

REFERENCES

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