A 53-year-old male patient presented with severe chronic ulnar-sided pain, which intensified after overuse and repetitive motions of the hand. No recent traumatic incident was reported. On physical examination, the pain was elicited mostly upon pronation and grip.
MR imaging (MRI) of the wrist reveals non-union of the ulnar styloid (US) process tip with flattening, deformation and hypertrophy, as demonstrated on coronal T1-weighted image (Fig. 1). Coronal STIR image (Fig. 2) further depicts secondary remodeling at the ulnar side of the non-union (yellow outline), along with tenosynovitis of the extensor carpi ulnaris (ECU) tendon (blue arrows). Coronal STIR image at a more volar level than in Fig. 2 (Fig. 3), shows ulnotriquetral ligament thickening and increased signal (a, outline) along with effusion at its attachment at the triquetrum (b, arrow). There is also increased signal intensity of the capsule at the ulnar side of the joint. Notice that the triangular fibrocartilage discus (TFC) remains intact in all images.
Ulnar-sided wrist pain creates diagnostic dilemmas for both the radiologist and the clinician, due to the intricacy of wrist anatomy and biomechanics [1,2]. Multitudinal conditions have been associated with ulnar wrist pain. Ulnar impaction syndrome represents a common source of such pain. Less frequent impaction syndromes include: Ulnar impingement syndrome, ulnar styloid impaction syndrome (USIS), hamatolunate impingement syndrome and combined ulnar-US impaction syndrome [3]. USIS is a distinctive cause of ulnar-sided wrist pain, generated by impaction between an elongated, deviated or non-united US process and the triquetral bone [1]. Clinical significance lies in that potential forceful trauma can regularly induce a dorsal triquetral fracture, resulting in intermittent/recurrent wrist pain and motion limitation [4]. Symptomatic non-union can occur when the non-united fragment acts as an irritative loose body or induces carpal abutment [3]. Consequent ECU tenosynovitis is attributable to tendon irritation by the non-union. Hauck et al. classified US non-union into two types: In type I, only the styloid tip is affected, while the triangular fibrocartilage complex (TFCC) and distal radioulnar joint (DRUJ) remain stable. In type II, non-union involves the US base, inducing DRUJ subluxation due to avulsion of the TFC ulnar attachment [5]. USIS diagnosis is based on radiographic evidence of positive ulnar variance or US non-union, and positive findings on Ruby’s provocative test [4].
Among imaging methods, MR is optimal for early detection of TFCC and bone-marrow abnormalities, helping visualise occult disease and systematise the differential diagnosis [2,4]. MRI at 3-Tesla can identify, in advance, injuries at the TFC ulnar and/or distal attachment [6], as in our patient (ulnotriquetral ligament injury). MR arthrography can aid in further evaluating peripheral TFCC injury [7]. The key imaging finding in the differentiation from the more familiar ulnar impaction syndrome is that USIS pathology involves the US process and proximal triquetrum, rather than the ulnar head and proximal lunatum [2].
First-line treatment encompasses activity modifications, nonsteroidal anti-inflammatory drugs (NSAIDs) and steroid injections. In terms of operative-decompressive therapy, the Wafer procedure is most effective in type I non-union, preserving the TFC insertion by maintaining the two most proximal millimeters of the US. In type II, the non-union can be treated by internal fixation/excision of the fragment. Complications, though rare, include injury of the dorsal cutaneous ulnar nerve branches, US process fracture, postoperative ECU tendinitis, and incomplete relief [8,9]. Our patient responded well to NSAIDs and no surgical repair was required.
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Ulnar styloid impaction syndrome secondary to US non-union, type I
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An MRI examination of the patient’s wrist reveals:
Overall, this MRI examination indicates bone and soft tissue abnormalities caused by repeated impingement between the ulnar styloid and the triquetrum, consistent with Ulnar Styloid Impaction Syndrome (USIS).
Taking into account the patient’s age, chronic recurrent ulnar-sided wrist pain, MRI findings of impingement between the ulnar styloid and the triquetrum, and local TFCC injury, the most likely diagnosis is:
Ulnar Styloid Impaction Syndrome (USIS).
Currently, the patient’s symptoms have improved with conservative treatment (NSAIDs, avoiding overuse, etc.), and surgery is not necessary at this time.
1. Treatment Strategies
2. Rehabilitation/Exercise Prescription Recommendations
Rehabilitation training should follow the FITT-VP principle (Frequency, Intensity, Time, Type, Volume, Progression):
Throughout the rehabilitation process, closely monitor the wrist’s response. If persistent pain or swelling occurs, reduce training volume or pause the exercises, and seek medical evaluation promptly.
Precautions:
Disclaimer: This report is for reference only and does not replace face-to-face diagnosis or professional medical advice. The final determination of any treatment plan should consider the patient’s individual condition and be made by a specialist physician.
Ulnar styloid impaction syndrome secondary to US non-union, type I
