Ulnar impaction syndrome : A case series and imaging approach

Ulnar-sided wrist pain can be attributed to many pathological processes whether traumatic, inflammatory or degenerative in nature. The patient with an acute traumatic incident can usually easily be identified from the history but others may present with non-specific complaints of intermittent wrist pain or swelling, sometimes aggravated by certain actions, or stiffness. Often the only positive finding may be a degree of tenderness or joint swelling. This clinical scenario may create a diagnostic and therapeutic dilemma. We report a series of four patients with histories ranging from intermittent ulnar-sided wrist pain and swelling to persistent pain on the ulnar side of the wrist, and discuss the impaction syndromes with the emphasis on imaging of the condition. Case reports


Introduction
Ulnar-sided wrist pain can be attributed to many pathological processes whether traumatic, inflammatory or degenerative in nature.The patient with an acute traumatic incident can usually easily be identified from the history but others may present with non-specific complaints of intermittent wrist pain or swelling, sometimes aggravated by certain actions, or stiffness.Often the only positive finding may be a degree of tenderness or joint swelling.This clinical scenario may create a diagnostic and therapeutic dilemma.We report a series of four patients with histories ranging from intermittent ulnar-sided wrist pain and swelling to persistent pain on the ulnar side of the wrist, and discuss the impaction syndromes with the emphasis on imaging of the condition.

Case 2
A 42-year-old female presented with pain in the right wrist and intermittent ulnar-sided swelling.Plain film radiographs confirmed a neutral ulnar variance.The MRI demonstrated subtle sclerosis of the ulna and proximal pole of the lunate (Figure 2a), especially at the volar aspect, with minimal punctate high signal on the PDFS coronal study in keeping with early cystic changes (Figure 2b).The MRI findings were in keeping with subtle signs of chronic ulnar lunate impaction.

Case 3
A 34-year-old female with a history of sports training presented with ulnar-sided right wrist pain.Neutral ulnar variance was noted on plain film and MRI.Radial perforation of the triangular fibrocartilage complex (TFCC) with leakage of contrast into the distal radio-ulnar space was noted on T1-weighted coronal fat suppressed image (Figure 3a).There were also impaction changes and sclerosis involving the ulna and proximal pole of the lunate which could be attributed to her sporting activity (Figure 3b).

Figure 2b. Coronal proton density fat suppressed tSE sequence demonstrating punctate high signal in the proximal lunate in keeping with cystic change (arrow)
A diagnosis of ulnar impaction syndrome was made on imaging.

Case 4
A 47-year-old male presented with history of left wrist pain.The plain film radiographs demonstrated a mildly positive ulnar variance and an old styloid fracture with evidence of previous surgery (Figure 4a).Moderate oedema was noted in the distal styloid, the proximal ulnar pole of the lunate as well as the styloid fracture fragment (Figure 4b).A diagnosis of ulnar impaction syndrome was made.

Discussion
The wrist joint has a unique and complex structure comprising bony structures of the distal radius and ulna, covered with cartilage at the articular surfaces, and the interpositioned ligaments for stability.The relevant joints involved are the distal radio-ulnar, radiocarpal, ulnocarpal and intercarpal joints.All components need to be in a specific relationship to the other structures for normal functioning.One of these important relationships is that between the distal radius and ulna.The relative length of the ulna in relation to the radius at the distal radio-ulnar articular surface is termed ulnar variance -also known as the radio-ulnar index.
1 Imaging for ulnar variance is done on radiographs with the forearm in the neutral rotation.This is best achieved by placing the upper arm on the X-ray table with the elbow at 90°.The palm should face the cassette.Neutral ulnar variance refers to an equal level of the distal ulna and radius at the articulation site with lunate.The radial styloid process would extend more inferiorly beyond this level by 9-12 mm.In the case where the ulna extends more distally beyond the radius, it is termed positive ulna variance (ulna plus variance) or when projecting more proximally, negative ulna variance (ulna minus variance). 2n addition to the relationship of the bony elements, the soft tissue structures are equally important and responsible for normal function.Most notable is the triangular fibrocartilage complex (TFCC).This structure is located between the distal ulna and the proximal carpal row with a medial attachment on the fovea of the ulna and a lateral attachment to the lunate fossa of the radius.The components of the TFCC are the triangular fibrocartilage, radio-ulnar ligament, ulnocarpal ligament, extensor carpi ulnaris tendon sheath and meniscal homologue.It acts as a cushion for the axial forces between the ulna and carpal bones and lends stability to the distal radio-ulnar joint. 2 The axial load from the forearm is transferred through the wrist to the carpal bones from which approximately 20% is transferred through the ulnar side. 3By increasing the ulna length by 25 mm, the axial load is increased from 20% to 41.9%, and decreasing the ulna length by 25 mm decreases the load to 4.8%. 4,5An increased load transmission across the ulnar side of the wrist can predispose to degenerative conditions including ulnocarpal impaction syndrome. 3Ulna variance therefore plays a major role in the mechanical stress transmitted through the wrist.
Chronic degenerative ulnar-sided wrist pathology may be due to overuse with abnormal stress on the ulnar side of the wrist, abnormal joint configuration or a combination of both.The sequelae are an impaction syndrome of the wrist.
There are five impaction syndromes producing ulnarsided wrist pain: The above impaction syndromes are all degenerative conditions with differences in pathological processes.Ulnar impaction syndrome is caused by excessive load bearing across the ulnar side of the wrist 3 presenting typically with symptoms of ulnar-sided wrist pain, decreased range of motion and joint swelling.The pain is mechanical in nature -exacerbated by exercise and relieved by rest.Some activities, e.g.][8][9][10] The disease process, however, develops over time and patients may have radiological features while being asymptomatic. 1 sequence of pathological features of ulnar impaction syndrome occurs depending on the degree and duration of chronic impaction between the ulnar head, the interpositioned TFCC and the ulnar carpus.The pathological radiological features include: fraying (patient described in case 1) or tearing (patient described in case 3) of the TFCC, chondromalacia of the ulnar head, lunate or triquetral bone, instability or tear of the lunotriquetral ligament, and a late and advanced feature is osteoarthritis of the distal radio-ulnar joint and ulnocarpal joint. 1,6,11,12,13lnar impaction syndrome is associated with positive ulna variance but may occur with neutral or negative variance. 1,6,8,14Only one patient described in our series had a mildly positive ulnar variance.All other patients had a neutral variance.Other conditions creating positive ulnar variance include previous distal radius fracture or surgery with foreshortening or premature distal radius physeal arrest. 1,6,8Pronated grip radiography was described by Tomaino to demonstrate increased variance and the subsequent impaction. 8,14he Palmer classification describes the mechanism and degree of injury in the event of TFCC injuries.A distinction was made between class I (traumatic) and class II (degenerative) injuries.Class I traumatic lesions usually cause a sharp disruption of the TFCC. 4 Class II lesions focus on degenerative ulnar impaction syndrome -specifically on the horizontal part of the TFCC, ulnar head, ulnar carpus and lunotriquetral ligament. 3,15arious imaging modalities are available for evaluating ulnar wrist pathology, each with its own advantages and limitations.The initial imaging usually entails radiographyanterior-posterior views, lateral views and oblique views with or without pronation and supination and occasionally with carpal tunnel views. 8ossible associated X-ray findings of ulnar impaction syndrome include positive ulnar variance, distal radius changes including previous distal radius fracture with malunion, radial head resection or early physeal closure.Other secondary degenerative changes can include subchondral sclerosis (described in all patients in our case series) and also cystic changes of the distal ulna and ulnar poles of the triquetrum and lunate (as described in patient in the patient in case 2). 1,6,11,13hese radiological changes may be subtle in both the early and late stages of the condition.In such cases, when there is a high clinical index of suspicion of ulnar impaction syndrome, further imaging including MRI should be considered for detection of occult disease. 1,6,12epending on the suspected pathology, other modalities including ultrasound, CT, 99Technetium bone scans, MRI, MR arthrography or conventional arthrography may be used.
In cases of suspected ulnar impaction syndrome, to evaluate for a TFCC injury, the examiner is in fact limited to CT and MRI with or without arthrography or conventional arthrography.Ultrasound, which is known to provide valuable information regarding the soft tissue of the wrist, can detect the TFCC, but the internal structure of the TFCC cannot be accurately demonstrated for final diagnosis and the technique is highly operator-dependent. 8he procedure of choice, until recently, to evaluate the TFCC has been arthrography. 2It was considered to be the 'gold standard' to diagnose TFCC perforations with tripleinjection arthrography. 8A relatively high rate of falsenegative findings have however been reported by several authors related to arthrography of the wrist. 8he current general belief is that MRI approaches arthrography in accuracy for diagnosing pathology of the TFCC. 2 MRI has largely supplanted arthrography during the past several years 8 and the reference standard method for detection of TFCC lesions is now considered to be direct MR arthrography. 3ast improvements of the magnetic quality and surface coils have been made over the last years especially with advances such as the 3T magnetic field to achieve higher resolution images. 8High resolution is essential for the evaluation of normal and abnormal features of the wrist. 8rogressive features of ulnar impaction syndrome can be seen on MRI indicating the degree and extent of the disease process.MR imaging and MR arthrography may be necessary to demonstrate the integrity of the TFCC and lunotriquetral ligaments in patients with radiographic evidence of ulnar impaction syndrome. 1,6,12,13The joint cartilage of the ulnar head and ulnar carpus is characterised by fibrillation in the early stages of ulnar impaction syndrome.Further disease progression leads to bone hyperaemia and later to sclerosis.MRI distinguishes this progression with low signal intensity on T1-weighted images and high signal on T2-weighted images demonstrating bone hyperaemia (bone oedema).When sclerosis sets in, T1-and T2-weighted images display low signal intensity. 1The normal TFC complex can be seen on coronal T1-weighted images as a low signal intensity biconcave band.TFC complex tears can be seen on T2-weighted images with regions of fragmentation or irregularity of the cartilage with high signal in the areas of interruption. 2irect MR arthrography is useful for assessing the TFCC.Limitations of this technique are the technical difficulty, time, invasiveness and high cost. 8On non-gadolinium sequences, the presence of fluid in the distal radio-ulnar joint suggests synovitis and on post-gadolinium sequences, the presence of contrast material in the distal radio-ulnar joint (DRUJ) usually indicates a TFCC tear. 8 study by Zanetti et al., however, demonstrated leakage of contrast into the DRUJ of 46% of asymptomatic wrists of patients undergoing bilateral arthrograms of the wrist when presenting with unilateral wrist pain. 16This serves to emphasise that the diagnosis should never be based on an isolated finding but a combination of various radiological signs (bone oedema, sclerosis) and clinical assessment.
With indirect MR arthrography, Schweitzer et al. suggested excellent imaging accuracy for the diagnosis of TFCC tears. 17owever, Haims et al. showed that indirect MR did not significantly improve the ability to evaluate the central TFCC disc when compared to non-enhanced MRI. 18As a result, its usefulness for the evaluation of TFCC lesions is controversial. 8All our cases were assessed by routine MRI without arthrogram or intravenous gadolinium.Only the patient described in case 3 had an MRI with arthrogram.
Another modality for diagnosis is multidetector computed tomography (MDCT) which is playing an increasingly important role in osseous wrist pathology. 8Modern MDCT has significantly higher spatial resolution than MRI.For the detection of TFC and intrinsic ligament lesions, MDCT arthrography yielded comparable results compared to direct MR arthrography. 19MDCT provides superior osseous detail, especially with fracture evaluation. 8When combined with arthrography, MDCT can provide clear images of the ligamentous structures with detailed bony anatomy of the wrist. 8MDCT is also more exact in the diagnosis and localisation of tears and perforations of the TFCC when compared to conventional arthrography. 8The capability of MDCT arthrography in evaluation of soft tissue abnormalities is however limited and often needs to be combined with other modalities such as ultrasound and MRI. 8 Moser et al. demonstrated in a recent report that for the detection of TFCC tears, lunotriquetral tears and cartilage abnormalities, MDCT arthrography was more accurate than MRI and MR arthrography. 20When MR arthrography is contraindicated or MRI is unavailable, MDCT should be considered, as it is a powerful diagnostic tool to diagnose wrist pathology. 3

Conclusion
Patients with ulnar-sided wrist pain may often present a diagnostic dilemma for clinicians The symptoms may be intermittent and rather minimal, even in the late stages of the disease.X-ray findings can also vary from prominent to a few non-specific findings.It is, however, very important to maintain a high index of suspicion of the condition as it is a progressive condition which, if left untreated or partially treated by means of a wrong diagnosis, can result in significant morbidity to the patient.Advanced imaging modalities such as MRI with arthrography and MDCT with arthrography are excellent in assisting clinicians with making an accurate diagnosis, as was proven in our four patients presented here.