Residency · Residency · Orthopedic Surgery

Distal Radius Malunion and Distal Radioulnar Joint Instability

Overview

The distal radioulnar joint (DRUJ) is a critical component of forearm rotation. DRUJ instability and distal radius malunion frequently coexist and must be evaluated together. Understanding ulnar variance, TFCC anatomy, and the biomechanical consequences of malunion is essential for treatment planning.

DRUJ Anatomy

Osseous Anatomy

The sigmoid notch of the radius articulates with the ulnar head. The DRUJ is inherently incongruent, with only 20% of the ulnar head articulating with the sigmoid notch at any given position. Stability therefore depends heavily on soft tissue constraints.

Triangular Fibrocartilage Complex (TFCC)

The articular disc (TFC proper) is a fibrocartilaginous disc extending from the sigmoid notch to the ulnar styloid base. The dorsal and palmar radioulnar ligaments are the primary stabilizers of the DRUJ. Their deep fibers (ligamentum subcruentum) insert on the fovea of the ulnar head and are the most important for stability, while the superficial fibers insert on the ulnar styloid. Additional components include the meniscus homologue (ulnar extension of the disc), the ECU subsheath (stabilizing the ECU tendon over the ulnar head), and the ulnolunate and ulnotriquetral ligaments (providing ulnocarpal stability).

Palmer Classification of TFCC Tears

Class 1 (Traumatic) tears include: 1A, a central perforation in the avascular zone that will not heal; 1B, an ulnar avulsion with or without ulnar styloid fracture, which is the most important to repair; 1C, a distal avulsion involving ulnolunate/ulnotriquetral ligament disruption; and 1D, a radial avulsion from the sigmoid notch. Class 2 (Degenerative) tears represent ulnocarpal abutment syndrome and progress through stages 2A-2E, from TFCC wear to lunate and ulnar head chondromalacia.

<image>Anatomy of the TFCC complex showing the articular disc, radioulnar ligaments, and foveal insertion</image>

Ulnar Variance

Definition and Measurement

Ulnar variance describes the relative length of the ulna compared to the radius at the DRUJ. Neutral variance indicates the ulnar head is level with the lunate fossa of the radius. Positive variance means the ulna is longer (increasing ulnocarpal loading), and negative variance means the ulna is shorter (decreasing ulnocarpal loading). Measurement is taken on a PA wrist radiograph with the shoulder abducted 90 degrees and elbow flexed 90 degrees, using the method of perpendiculars.

Clinical Significance

Positive ulnar variance increases load transmission through the ulnocarpal joint (normally approximately 20% of axial load, increasing to over 40% with even 2.5 mm of positive variance). It is associated with ulnocarpal abutment syndrome, TFCC degeneration, and lunotriquetral ligament tears. Distal radius fracture malunion with dorsal angulation increases ulnar variance due to relative radial shortening.

DRUJ Instability

Evaluation

Clinical tests include the ballottement test (piano key test), performed by stabilizing the radius and translating the ulna dorsally and palmarly while comparing to the contralateral side (some physiologic laxity is normal). Testing should occur in neutral, full pronation, and full supination. The fovea sign is point tenderness at the fovea (between the ulnar styloid and FCU tendon), indicating foveal TFCC detachment.

Imaging includes CT scan with bilateral comparison in neutral, pronation, and supination to assess subluxation of the ulnar head relative to the sigmoid notch. MRI or MR arthrography evaluates TFCC tears, specifically foveal detachment. Wrist arthroscopy is the gold standard for TFCC assessment, using the "trampoline test" and "hook test" for foveal detachment.

Treatment of TFCC Tears

1A (central tears) are treated with arthroscopic debridement because there is no healing capacity in the avascular central zone. 1B (ulnar-sided tears) are repaired arthroscopically or with open technique. Peripheral tears with an intact foveal attachment undergo arthroscopic outside-in or inside-out repair. Foveal detachments require transosseous foveal repair (bone tunnel or suture anchor technique), which is critical for restoring DRUJ stability. 1C and 1D tears are repaired or reconstructed as indicated by instability. Class 2 (degenerative) lesions are treated with ulnar shortening osteotomy or wafer procedure for symptomatic ulnocarpal abutment.

<image>Arthroscopic view of a peripheral TFCC tear (Palmer 1B) with probe demonstrating detachment</image>

Distal Radius Malunion

Parameters of Normal Distal Radius Anatomy

Normal anatomy includes radial inclination of 22-23 degrees, radial height of 11-12 mm, volar tilt of 11-12 degrees (range 0-22), and neutral ulnar variance (0 mm, range -2 to +2 mm).

Consequences of Malunion

Loss of volar tilt (dorsal angulation) shifts load to the dorsal rim, increases DRUJ incongruity, and limits forearm rotation. Every 10 degrees of dorsal angulation creates approximately 2 mm of relative ulnar positive variance. Loss of radial inclination and height alters carpal mechanics, creates ulnar positive variance, and decreases grip strength. Loss of articular surface reduction with an intra-articular step-off greater than 2 mm is associated with post-traumatic arthritis and DRUJ incongruity.

Clinical Presentation

Patients present with wrist pain, decreased grip strength, loss of forearm rotation (especially supination), DRUJ pain and instability, and midcarpal instability (dorsal malunion alters carpal alignment).

Corrective Osteotomy

Indications include symptomatic malunion with correctable deformity in a young or active patient where preoperative assessment confirms the deformity correlates with symptoms. Preoperative planning involves comparison radiographs of the contralateral wrist, CT scan for 3D assessment, and increasingly, 3D-printed models and patient-specific cutting guides.

The technique involves an opening wedge osteotomy through the malunion site to restore volar tilt, radial inclination, and radial height. Structural bone graft (iliac crest autograft or distal radius allograft) fills the opening wedge, and a fixed-angle volar locking plate provides fixation. DRUJ stability and ulnar variance are assessed after correction.

Adjunct procedures include ulnar shortening osteotomy if persistent positive ulnar variance remains after radius correction, and DRUJ stabilization if instability persists after bony correction.

Salvage Procedures for DRUJ Pathology

Ulnar Shortening Osteotomy

Ulnar shortening osteotomy is indicated for ulnocarpal abutment syndrome and positive ulnar variance. An oblique or transverse osteotomy of the ulnar diaphysis is fixed with compression plating, with shortening typically of 2-4 mm based on ulnar variance. Complications include nonunion (5-10%), hardware irritation, and need for plate removal.

Darrach Procedure (Distal Ulna Resection)

The Darrach procedure involves resection of the distal ulna (ulnar head). Once commonly performed, it is now largely reserved for low-demand or elderly patients and those with rheumatoid arthritis. Complications include ulnar stump instability, painful convergence of the radius and ulna with grip, and weakness.

Sauve-Kapandji Procedure

This procedure combines arthrodesis of the DRUJ with creation of a proximal ulnar pseudarthrosis. It preserves the ulnar head as a buttress for the carpus, with forearm rotation occurring through the pseudarthrosis segment. It is better suited for younger patients than the Darrach procedure. The primary complication is instability of the proximal ulnar stump.

Hemiresection-Interposition Arthroplasty (Bowers)

This technique involves resection of the ulnar seat (articular surface) with soft tissue interposition, preserving the ulnar styloid and TFCC insertion. It represents an intermediate option between Darrach and Sauve-Kapandji.

Ulnar Head Replacement

Prosthetic replacement of the ulnar head is indicated for failed salvage procedures and post-traumatic DRUJ arthritis in higher-demand patients. It maintains ulnocarpal support and DRUJ kinematics.

<image>Corrective osteotomy of distal radius malunion with opening wedge technique and bone graft</image>

Clinical Pearls

DRUJ laxity should always be compared to the contralateral wrist because there is wide normal variation in baseline laxity. The fovea sign is highly sensitive and specific for foveal TFCC detachment, and a positive finding should prompt further workup with MRI arthrogram or arthroscopy. Distal radius fractures with ulnar styloid base fractures (greater than 2 mm displacement) should raise suspicion for deep TFCC foveal detachment. After distal radius ORIF, the DRUJ must always be assessed intraoperatively because instability may require TFCC repair or ulnar styloid fixation. Corrective osteotomy for distal radius malunion has reliable outcomes in appropriately selected patients but must address both the radius deformity and any secondary DRUJ pathology. In the rheumatoid wrist, the Darrach procedure combined with extensor tendon reconstruction is a workhorse; in non-rheumatoid patients, Sauve-Kapandji or ulnar head replacement may preserve better function.

References

• Palmer AK. Triangular fibrocartilage complex lesions: a classification. J Hand Surg Am. 1989;14(4):594-606.
• Tay SC, et al. The "ulnar fovea sign" for defining ulnar wrist pain: an analysis of sensitivity and specificity. J Hand Surg Am. 2007;32(4):438-444.
• Fernandez DL. Correction of post-traumatic wrist deformity in adults by osteotomy, bone grafting, and internal fixation. JBJS Am. 1982;64(8):1164-1178.
• Adams BD. Distal radioulnar joint instability. In: Green's Operative Hand Surgery. 7th ed.
• Sauve L, Kapandji M. Nouvelle technique de traitement chirurgical des luxations recidivantes isolees de l'extremite inferieure du cubitus. J Chir. 1936;47:589-594.

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