The clinician firmly stabilizes the distal radius with one hand and grasps the head of the ulna between the thumb and the index finger of the other hand.
The ulnar head is depressed in an anterior direction (as in depressing a key on a piano).
What is a positive piano key sign?
The piano key sign is positive for a triangular fibrocartilage complex (TFCC) tear or triquetral instability if there is excessive movement in an anterior (palmar) direction or if upon release of the ulna, the bone springs back into its high posterior (dorsal) position.
There may also be discomfort reported during piano key test.
Sensitivity & Specificity
A descriptive study by LaStayo and Howell2 found that the Sensitivity & Specificity of Piano Key sign is:
Distal Radioulnar Joint DRUJ:
The distal radioulnar joint (DRUJ) plays an important role in wrist and forearm function.
The DRUJ is a uniaxial pivot joint that joins the distal radius and ulna and an articular disk.
The articular disk, known as the TFCC, assists in binding the distal radius and is the main stabilizer of the DRUJ.
At its distal end, the radius widens to form a broad concave articular surface.
The articular surface has an ulnar inclination in the frontal plane, which averages 23 degrees, and a anterior (palmar) inclination in the sagittal plane, which averages 11 degrees.
The distal end of the ulna expands slightly laterally into a rounded head and medially into an ulnar styloid process. The rounded head of the ulnar head contacts both the ulnar notch of the radius laterally and the TFCC distally.
The ulnar styloid process is approximately one-half inch shorter than the radial styloid process, resulting in more ulnar deviation than radial deviation being available.
The articular capsule, which attaches to the articular margins of the radius and ulna and to the disk enclosing the inferior radioulnar joint, is lax.
Anterior (palmar) and posterior (dorsal) radioulnar ligaments strengthen the capsule anteriorly and posteriorly.
Forearm supination tightens the anterior capsule and pronation tightens the posterior part, adding to the overall stability of the wrist.
The DRUJ functions to transmit the loads from the hand to the forearm.
Triangular Fibrocartilage Complex TFCC:
The TFCC essentially comprises a fibrocartilage disk interposed between the medial proximal row and the distal ulna within the medial aspect of the wrist.
The primary function of the TFCC is to enhance joint congruity and to cushion against compressive forces.
Indeed the TFCC transmits about 20 percent of the axial load from the hand to the forearm.
The broad base of the disk is attached to the medial edge of the ulnar notch of the radius, and its apex is attached to the lateral aspect of the base of the ulnar styloid process. The disk’s anterior and posterior borders are thickened.
A number of ligaments originate from the TFCC and provide support to it. These include:
The ulnolunate ligament.
The ulnar collateral and the radioulnar ligaments.
Other structures that lend support to the TFCC include the following:
The ulnocarpal ligaments.
The sheath of the extensor carpi ulnaris (ECU) tendon, which is the only wrist tendon that broadly connects to the TFCC.
Both the superior and the inferior articular surfaces of the TFCC are smooth and concave. The disk separates the distal ulna from direct contact with the carpals but allows gliding between the carpals, disk, and ulna during forearm pronation and supination.
The TFCC is innervated by branches of the posterior interosseous, ulnar, and posterior (dorsal) sensory ulnar nerves.
Skirven T: Clinical examination of the wrist. J Hand Ther 9:96–107, 1996.
LaStayo P, Howell J: Clinical provocative tests used in evaluating wrist pain: A descriptive study. J Hand Ther 8:10–17, 1995. PMID: 7742888
Ward LD, Ambrose CG, Masson MV, et al: The role of the distal radioulnar ligaments, interosseous membrane, and joint capsule, in distal radioulnar joint stability. J Hand Surg Am 25:341–351, 2000.
Palmer AK, Werner FW: The triangular fibrocartilage complex of the wrist – anatomy and function. J Hand Surg Am 6:153–162, 1981.