The carpal bones of the wrist make 2 rows of bones, the proximal and distal carpal row. Ulnar Sided Midcarpal instability (MCI) is related to lack of ligament support between the proximal carpal row and the midcarpal joint (between the 2 rows of bones). While MCI most frequently presents as a palmar (volar) subluxation, it can also manifest as dorsal or extrinsic instability, depending on the specific intrinsic or extrinsic ligaments compromised.
|
How to Treat TFCC: Symptoms & Causes |
Injury to the ligaments in the midcarpal joint causes a loss of the coupled motion of the carpal rows. Specifically, this means that the proximal carpal row has an abrupt change from flexion to extension at end range for ulnar deviation instead of smooth coupled motion in the radial to ulnar deviation range. This abrupt change in position of the carpal bones is responsible for the classic, often painful, audible "clunk."
Patients presenting with MCI frequently report no history of acute trauma. When a specific etiology is present, it is most commonly secondary to a malunited distal radius fracture that has altered carpal alignment. Clinically, MCI presents as a visible volar sag on the ulnar side of the wrist. Symptoms include painful clicking or snapping at end-range ulnar deviation—particularly when the forearm is pronated and the carpal rows abruptly re-couple—along with localized tenderness over the triquetrohamate and capitolunate intervals, and reduced grip strength.
The clinical test commonly used for assessment for suspected midcarpal laxity is the Midcarpal Shift Test (also referred to as the pivot shift or catch-up clunk test). This maneuver reproduces the loss of smooth carpal translation. To perform the test:
A positive test is indicated by a painful, often audible clunk as the proximal row suddenly snaps into extension, reproducing the patient’s familiar symptoms.
While a static lateral radiograph in neutral alignment may occasionally demonstrate altered carpal angles, standard X-rays often appear normal. Dynamic fluoroscopy remains the gold standard for imaging MCI. It allows the clinician to visualize the real-time kinematics of the carpal bones, capturing the classic "jump" of the proximal row from flexion to extension as the wrist moves into ulnar deviation.
Conservative management is the primary line of defense, typically beginning with a 3-to-6-week trial of an orthosis for 3-6 weeks. A good option for this diagnosis is a pisiform or ulnar carpal boosting orthosis to realign the carpal bones despite ligament instability. When properly fitted, the orthosis should immediately reduce localized pain and significantly diminish or eliminate the mechanical clunking.
Targeted solutions for carpal support include the 3pp® Carpal Lift™ and the 3pp® Wrist™ POP Splint, both engineered to restore structural alignment to the ulnar carpus.
The 3pp Carpal Lift targets ulnar-sided pain and popping by utilizing a targeted foam pad beneath the ulnar carpus. Combined with adjustable straps, it delivers a dynamic, upward lift to the triquetrum and pisiform without placing direct, painful pressure on the ulnar head.
The 3pp Wrist POP Splint (Point of Pressure) utilizes a counter-force design. By applying adjustable compression over the distal ulna paired with a corrective counter-pressure point under the distal radius, it restores stable midcarpal alignment to successfully manage chronic instability.
Managing ulnar-sided midcarpal instability requires a precise understanding of carpal kinematics and targeted stabilization. Because MCI stems from ligamentous laxity rather than an acute tear, conservative treatment focused on realigning the carpus is highly effective. Utilizing a specialized ulnar carpal boosting orthosis allows clinicians to counteract volar sag, eliminate the painful "catch-up clunk," and restore functional wrist mechanics for immediate symptomatic relief.