AJR 2003; 181:195-198
© American Roentgen Ray Society
MR Imaging of Ulnocarpal Impaction After Fracture of the Distal Radius
Marc Steinborn1,
Matthias Schürmann2,
Axel Staebler1,
Ingrid Wizgall2,
Christoph Pellengahr3,
Andreas Heuck1 and
Maximilian Reiser1
1 Department of Clinical Radiology, Ludwig Maximilians University, Klinikum
Grosshadern, Marchioninistr. 15, D-81377 Munich, Germany.
2 Department of Surgery, Ludwig Maximilians University, Klinikum Grosshadern,
D-81377 Munich, Germany.
3 Department of Orthopedic Surgery, Ludwig Maximilians University, Klinikum
Grosshadern, D-81377 Munich, Germany.
Received July 12, 2002;
accepted after revision December 6, 2002.
Address correspondence to M. Steinborn.
Abstract
OBJECTIVE. The purpose of our study was to evaluate the incidence of
ulnocarpal impaction after distal radius fracture using MR imaging and to
correlate imaging findings with those of radiography and clinical
findings.
CONCLUSION. Ulnocarpal impaction is a common finding after distal
radius fracture. MR imaging can detect characteristic bone marrow changes of
the lunate early after the trauma. A significant correlation exists between MR
imaging findings and the extent of posttraumatic ulnar variance and pain
levels.
Introduction
Ulnocarpal impaction syndrome has been recognized as a common clinical
finding in patients with chronic ulnar-sided wrist pain and functional
restriction of the ulnocarpal joint
[1]. Posttraumatic shortening
of the distal radius after a distal radius fracture that leads to a positive
ulnar variance is one of the major causes of ulnocarpal impaction syndrome.
Although changes on radiography may be characteristic in advanced cases,
findings on radiography are often negative or subtle in the early course of
the disease [1,
2].
MR imaging has become the modality of choice for the evaluation of chronic
wrist pain. However, only a few studies have investigated the value of MR
imaging in patients with suspected ulnocarpal impaction syndrome
[3,
4]. The purpose of this study
was twofold: to evaluate the incidence of characteristic findings of
ulnocarpal impaction on MR imaging in patients with distal radius fractures
and to correlate the MR imaging findings with those of radiography and
clinical findings.
Subjects and Methods
Seventy-two patients (42 women, 30 men; age range, 18–84 years; mean,
50 years) with radiographically proven distal radius fractures were included
in the study. The local ethics committee approved this study, and all patients
gave written consent for participation. All fractures were classified
according to the classification system of the Orthopaedic Trauma Association
Committee for Coding and Classification
[5]. Depending on the fracture
type, nonoperative or operative treatment was performed.
All MR images and radiographs were evaluated on a consensus basis by two
reviewers who specialized in musculoskeletal radiology. In all 72 patients,
the ulnar variance was calculated on standard radiographs taken immediately
after the trauma and 8 weeks later. In patients with MR imaging findings
suggesting ulnocarpal impaction, additional radiographs, taken after 16 weeks,
were evaluated retrospectively for radiographic signs of ulnocarpal
impaction.
All 72 patients underwent MR imaging 8 and 16 weeks after the trauma. MR
imaging was performed on a 1.5-T whole-body system (Vision, Siemens, Erlangen,
Germany) using a 3-inch (8-cm) circular wraparound coil. The imaging protocol
consisted of a coronal short tau inversion recovery (STIR) sequence (TR/TE,
3912/60; inversion time, 150 msec; acquisition time, 4 min 18 sec),
T1-weighted spin-echo sequences (TR/TE, 500/20; acquisition time, 4 min 51
sec) in the coronal and axial planes, and a T2-weighted turbo spin-echo
sequence (TR/TE, 3500/96; acquisition time, 4 min 6 sec) in the axial plane.
The field of view ranged from 10 to 12 cm. The matrix size measured 256
x 200 for the STIR and T2-weighted sequences and 512 x 336 for the
T1-weighted sequence. The slice thickness was 3 mm with a 1-mm intersection
gap. MR images were evaluated for bone marrow abnormalities in the lunate, the
triquetrum, and the distal portion of the ulna. In all patients, the course of
bone marrow changes was assessed by comparing the 8- and 16-week examinations.
On the basis of the MR imaging findings, the diagnosis of ulnocarpal impaction
was made when MR imaging showed a characteristic bone marrow edema at the
proximal ulnar-sided pole of the lunate on the 16-week examination. To rule
out a trauma-related bone contusion, the bone marrow edema of the lunate had
to either increase or remain unchanged compared with that in the 8-week
examination. In addition, each MR image was evaluated for triangular
fibrocartilage complex lesions. A complete tear of the triangular
fibrocartilage was diagnosed when discontinuity or fragmentation was seen on
coronal images.
A detailed clinical examination was performed by an orthopedic surgeon 16
weeks after the trauma, and a combined clinical and radiologic score according
to the grading of Castaing [6]
was calculated. This score combines subjective (perfect to very bad) and
objective (extension, flexion, abduction, adduction, pronation, and
supination) assessments of wrist function with radiographic findings
(dorsal—radial tilt, arthrosis, and ulnar variance) resulting in values
ranging from 0 (perfect outcome) to 27 (very bad outcome). The extent of
overall pain in the resting position and during wrist motion was evaluated
separately by a visual analogue scale using a patient questionnaire with
responses ranging from 0 (no pain) to 10 (maximal pain).
The results of radiographic and clinical examinations were correlated with
the MR imaging findings. A statistical comparison was performed with a
two-tailed unpaired Student's t test with a p value of less
than 0.05 indicating significance.
Results
According to the Orthopaedic Trauma Association Committee for Coding and
Classification, 37 (51%) of the 72 patients had extraarticular fractures, 14
patients (19%) had partially intraarticular fractures, and 21 patients (29%)
had complete intraarticular fractures. Twenty-nine patients (40%) were treated
nonoperatively, 43 patients (60%) had operative treatment (K-wire fixation
[n = 12], external fixator [n = 14], external fixator and
K-wire fixation [n = 6], and internal plate fixation [n =
11]). All external fixations were removed at the time of MR imaging. In
patients with internal plate fixations, the metal artifacts were restricted to
the region of the distal radius and did not affect the area of the ulnocarpal
joint (Figs. 1A,
1B).
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Fig. 1A. —44-year-old man with distal radius fracture and posttraumatic
edema of lunate. Coronal STIR image obtained 8 weeks after trauma shows focal
bone marrow edema of proximal ulnar- and radial-sided lunate
(arrows). Metal artifacts are caused by internal plate fixation of
distal radius.
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Fig. 1B. —44-year-old man with distal radius fracture and posttraumatic
edema of lunate. Coronal STIR image obtained 8 weeks after A shows that
focal bone marrow edema of lunate is no longer detectable. Minor diffuse
increase of bone marrow signal is most likely related to reactive changes in
bone metabolism.
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Eight weeks after sustaining the radius fractures, 25 patients showed focal
bone marrow edema of the lunate on MR imaging. On the 16-week examination, the
bone marrow edema had completely resolved in 12 patients (Figs.
1A,
1B). In five patients, the bone
marrow edema was unchanged (Figs.
2A,
2B), and in eight patients an
increase of bone marrow abnormalities of the lunate was seen (Figs.
3A and
3B), resulting in 13 (18%) of
72 patients with positive findings of ulnocarpal impaction on MR imaging. In
all 13 patients with positive findings, the bone marrow edema involved the
proximal ulnar-sided pole of the lunate.
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Fig. 2A. —54-year-old man with early development of ulnocarpal
impaction. Coronal STIR image obtained 8 weeks after distal radius fracture
shows focal bone marrow edema at proximal ulnar-sided pole of lunate
(arrow).
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Fig. 2B. —54-year-old man with early development of ulnocarpal
impaction. Coronal STIR image obtained 8 weeks after A shows that focal
bone marrow edema at proximal ulnar-sided pole of lunate is still clearly
detectable (solid arrow). Note complete rupture of radial attachment
of triangular fibrocartilage (open arrow).
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Fig. 3A. —61-year-old woman with distal radius fracture and increasing
ulnocarpal impaction. STIR image obtained 8 weeks after trauma shows linear
subchondral bone marrow edema along proximal surface of lunate (solid
arrow) and along distalmost ulnar head (open arrow). Note
suspicion of triangular fibrocartilage rupture.
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Fig. 3B. —61-year-old woman with distal radius fracture and increasing
ulnocarpal impaction. On STIR image obtained 16 weeks after A, bone
marrow edema of lunate has distinctively increased (solid arrow).
Torn triangular fibrocartilage can be seen with fluid extending into distal
radioulnar joint (open arrow).
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Bone marrow changes of the ulnar head (n = 21) and triquetrum
(n = 36) were common findings on the 8-week MR imaging. After 16
weeks, however, only three patients showed persisting edematous changes in the
triquetrum (n = 1) or ulnar head (n = 2). All three patients
had associated bone marrow changes of the lunate consistent with ulnocarpal
impaction.
Half of the 72 patients had triangular fibrocartilage lesions on MR
imaging. In reference to ulnocarpal impaction, the number of triangular
fibrocartilage lesions was not substantially different between the positive
(7/13) and negative patient groups (29/59).
There was no significant difference in the average positive ulnar variances
between patients with and without ulnocarpal impaction measured initially
after the trauma. The radiographs taken 8 weeks later, however, showed a
significantly higher positive ulnar variance in the patients with positive
findings on MR imaging compared with the group with negative findings
(Table 1). Three patients with
MR imaging findings of ulnocarpal impaction after 16 weeks had neutral ulnar
variances on the 8-week radiograph.
Comparing the results of the Castaing
[6] scores, we found no
statistically significant difference between patients with and without
ulnocarpal impaction. When comparing the postoperative pain levels in resting
position and under wrist motion, however, we found that the scores of the
visual analogue scale taken 16 weeks after the trauma differed significantly
between patients with and without findings of ulnocarpal impaction on MR
imaging (Table 1). There was no
difference in the scores of the visual analogue scale between patients with
operative (resting position, mean ± SD, 0.44 ± 1.18; wrist
motion, mean, 2.52 ± 1.95) and nonoperative treatment (resting
position, mean, 0.45 ± 1.23; wrist motion, mean, 2.28 ± 1.74).
The additional radiographs obtained after 16 weeks in the 13 patients with
positive MR imaging findings showed radiographic changes suggesting ulnocarpal
impaction in only five patients (38%) (Fig.
3C). In one patient, sclerosis along the subcortical margin of the
proximal lunate was already seen on the initial posttraumatic radiograph,
whereas in the remaining four patients, sclerosis (n = 3),
demineralization (n = 2), and cyst formation (n = 1) had
recently developed.
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Fig. 3C. —61-year-old woman with distal radius fracture and increasing
ulnocarpal impaction. Posteroanterior radiograph obtained 16 weeks after
trauma shows complete fracture healing with posttraumatic shortening of distal
radius. As result of ulnocarpal impaction, subchondral demineralization can be
seen in proximal portion of lunate (arrow).
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Discussion
Ulnocarpal impaction syndrome is a condition of chronic wrist pain that is
caused by impaction of the distal ulna against the proximal lunate and
triquetrum. Palmer and Werner
[7] examined the transmission
of mechanical forces in the wrist joint as they relate to ulnar variance and
the condition of the triangular fibrocartilage complex. According to this
study, 80% of the mechanical force is transmitted across the radius and 20%,
across the ulna in a normal joint with neutral ulnar variance. A change of the
ulnar variance of only 1 mm can change the mechanical load on the ulnocarpal
joint by more than 25%. The increased mechanical load on the triangular
fibrocartilage complex and the underlying proximal ulnar-sided pole of the
lunate leads to triangular fibrocartilage complex lesions and chondromalacia
of the lunate bone and distal ulnar head
[8,
9]. In advanced stages,
osteoarthritis of the distal radioulnar and ulnocarpal joints appears.
In addition to a positive ulnar variance, characteristic radiographic
findings in ulnocarpal impaction are sclerosis, demineralization, and cyst
formation in the distal ulna and in the proximal portion of the ulnar-sided
lunate [10]. These changes,
however, most often represent a chronic long-standing process, so findings on
radiographs are often negative at the beginning of the disease
[3]. Arthrography and
arthroscopy are sensitive but invasive procedures for the detection and
grading of cartilage and triangular fibrocartilage lesions in patients with
ulnocarpal impaction. In the early course of the disease, however, the
triangular fibrocartilage can still be intact. This finding might explain why
only six of our 13 patients with characteristic findings of ulnocarpal
impaction on MR imaging had triangular fibrocartilage tears that corresponded
with the frequency of triangular fibrocartilage lesions seen in the group with
negative findings on MR imaging.
A bone marrow edema of the proximal ulnar-sided pole of the lunate has been
described as a specific finding of ulnocarpal impaction on MR imaging
[3,
4]. Bone marrow edema can even
be seen in patients without cartilaginous degeneration revealed at
arthroscopy, indicating that it is also a sensitive sign of ulnocarpal
impaction [3]. On the basis of
these findings, our aim was to investigate the incidence and course of
ulnocarpal impaction in patients with distal radius fractures using MR
imaging; this study has not been done previously. A major problem for the
interpretation of MR images obtained early after a distal radius fracture is
the extensive bone and soft-tissue changes that are directly related to the
trauma. To differentiate trauma-related bone marrow changes from the typical
findings occurring in ulnocarpal impaction, we performed MR imaging after 8
and 16 weeks and compared the extent of bone marrow edema shown by the two
examinations. Whereas all fracture-related edema showed a distinct decrease
over the 8-week interval, patients with suspected ulnocarpal impaction showed
unchanged or even increased extent of bone marrow edema in the lunate bone.
Comparing MR imaging findings with the radiographic measurements of ulnar
variance, we found significantly higher values for ulnar variance on 8-week
follow-up radiographs in the group with positive MR imaging findings. Our
observation that the extent of the ulnar variance on the initial posttraumatic
radiographs did not differ significantly between the patients with positive
and negative findings on MR imaging suggests that insufficient fracture
reduction leading to persisting positive ulnar variance is the major cause for
the early development of ulnocarpal impaction. However, the fact that three of
our patients with positive findings on MR imaging had a neutral ulnar variance
on the 8-week radiograph also shows that the absence of a positive ulnar
variance on a standard radiograph does not exclude the diagnosis of ulnocarpal
impaction [11].
Although our study shows that ulnocarpal impaction seems to be a common
finding after distal radius fracture, the imaging findings must be related to
clinical results. Whereas the values of the combined functional and radiologic
score according to Castaing [6]
did not differ statistically between the positive and negative patient groups,
patients with MR findings suggesting ulnocarpal impaction had significantly
higher posttraumatic pain levels. The fact that pain levels were not related
to the extent of the initial trauma or the kind of treatment might suggest
that early ulnocarpal impaction syndrome can be responsible for persisting
posttraumatic pain in patients with distal radius fractures.
There are two limitations of our study. The more significant is the lack of
surgical confirmation. In all patients, the diagnosis of ulnocarpal impaction
was primarily based on characteristic MR imaging findings. Because we did not
perform further follow-up examinations, we also do not know how many patients
with early signs of ulnocarpal impaction on MR imaging will develop the full
clinical picture of the ulnocarpal impaction syndrome.
In conclusion, our study shows that MR imaging signs of ulnocarpal
impaction are a common finding after a distal radius fracture. We found a
significant correlation between the development of ulnocarpal impaction on MR
imaging, persisting positive ulnar variance, and elevated posttraumatic pain
levels.
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Abstract
Introduction
