Dynamic Wrist Radiographs in Patients with and without a Ganglion Cyst

Abstract

Objectives  The purpose of this study was to find out if carpal instability played a role in the etiology of ganglion cysts.

Materials and Methods  Dynamic wrist radiographs of 33 patients with and without a ganglion cyst of the wrist were compared. The control group consisted of patients who had dynamic radiographs of both wrists after a traumatic event in one wrist. Measurements were performed on the contralateral uninjured side. Radiological parameters that may indicate carpal instability included: width of the scapholunate gap, scapholunate, radiolunate, and lunocapitate angles, and ulnar translocation.

Results  No statistically significant difference was found between the two groups except for lunocapitate angle which was higher in wrists with ganglion cysts. However, mean lunocapitate angle was still within the normal range.

Conclusions  It could be concluded that in this study we did not see a difference between scapholunate gap and radiocarpal angles with the presence or absence of a ganglion cyst.

A ganglion cyst is a benign soft tissue tumor with a high incidence and prevalence and should therefore immediately be identified by every hand surgeon. Sixty to seventy percent of the ganglion cysts of the wrist are visualized at the dorsal aspect of the wrist and communicate with the joint by means of a pedicle. Thirteen to twenty percent of the cysts are located palmarly and another 10% originates from a flexor sheath. ¹

Although ganglion cysts constitute the most common tumor type of the hand and wrist region, still little is known about the pathomechanism of the ganglion cyst formation. According to one theory, a ganglion cyst results from a herniation of the synovial tissue of the joint capsule. The cyst fluid arises from the joint and is pumped into the cyst via a one-way valve mechanism. The weakness of this assumption is the absence of synovial lining of the cyst wall. In addition, the cyst fluid also has a different composition than intra-articular synovial fluid. ^{1 2}

The capsular rent theory is based on the assumption that injuries to the wrist joint lead to damage resulting in leakage of synovial fluid in the periarticular tissue. Watson et al, suggested in a study of 1989 that a ganglion cyst was caused by an underlying ligament injury around the scaphoid. ³ However, the hypothesis that ligament pathology would be the cause of the formation of a ganglion cyst remains controversial.

A third theory speculates that an extra-articular degenerative process (mucoid degeneration) would be the cause of both the formation of the cyst and its direct connection to the joint. ^{1 2}

A fourth theory states that persistent irritation of the joint would incite the mesenchymal cells to secrete mucin. Small accumulations of mucin form the cyst around which a pseudocapsule develops without synovial alignment. ¹

Different classification systems exist to describe the patterns of carpal instability. The most frequently used is the Mayo classification. ⁴

1. Carpal instability dissociative involves the disruption of an intercarpal ligament within a carpal row. This can result in dorsal-intercalated segment instability (DISI), volar-intercalated segment instability (VISI), or axial carpal instability.

2. Carpal instability nondissociative is a result of ligamentous disruption leading to instability between rows (radiocarpal or midcarpal).

3. Carpal instability combined, is a combination of the above-mentioned instabilities and is a result of ligamentous disruption both within and between rows. The most often quoted example of this is the perilunate dislocation.

4. Carpal injury adaptive are extracarpal instabilities which include secondary changes in the carpus which result from a nonunion or malunion of the distal radius.

The aim of the study was to find out if carpal instability may play a role in the etiology of ganglion cysts of the wrist as has been hypothesized by the capsular rent theory. Therefore, radiological parameters that may indicate carpal instability or misalignment were measured on dynamic radiographs of wrists with and without ganglions.

Materials and Methods

A retrospective analysis was performed by searching in a database of patients in whom dynamic radiographs of both wrists were made between 2012 and 2017. Thirty-three patients with a ganglion cyst of the wrist were included (24 dorsal ganglions cysts and 9 palmar ganglion cysts). There was no significant difference in the tested radiological parameters between dorsal and volar ganglions. In the electronic patients' files was searched for information that showed that the ganglions originated from the wrist. This was provided by ultrasound and/or surgery in 24 patients and by magnetic resonance imaging (MRI) in one. In eight patients the diagnosis of ganglion was made by clinical examination.

The control group consisted of 33 patients, selected from the same database, who underwent dynamic radiographs of both wrists after a traumatic event in one wrist. Radiological measurements were performed on the contralateral uninjured side. There was no history of trauma of the wrists that were used as controls.

Both groups were comparable with respect to age, sex, and side of the wrist (left/right) ( Table 1 ).

Table 1. Characteristics of patients with and without ganglion.

	Study group		Control group
Number of patients	33		33
Mean age (y)	34		33
Sex	M: 8	F: 25	M: 15	F: 18
Side	L: 16	R: 17	L: 17	R: 16

Abbreviations: M, male; F, female; L, left; R, right.

Radiological measurements that may indicate carpal instability were determined on the digital radiographs with tools available in the picture archiving and communication system. Measurements for distances were automatically rounded after the decimal point.

The width of the scapholunate gap was determined on standard posteroanterior (PA) radiographs of the wrist according to Pliefke et al. ⁵ The distance was measured from midpoint ulnar facet of the scaphoid to midpoint radial facet of the lunate ( Fig. 1 ). This was also determined on PA clenched fist views and PA views of the wrist in ulnar deviation. A gap of more than 2.9 mm was considered as abnormal. ⁵

Fig. 1.

Measurement of the width of the scapholunate gap.

Angles were determined on lateral wrist radiographs. The scapholunate angle is measured between a line along the axis of the scaphoid and a line perpendicular to the axis of the lunate. The scaphoid line is drawn tangential to the scaphoid along the palmar aspects of the distal and proximal poles and the lunate line is drawn perpendicular to a line connecting the palmar and dorsal points of the lunate ( Fig. 2 ). Normal values are ranging between 30 and 60 degrees. ⁶

Fig. 2.

Determination of the scapholunate angle (between lines b and c). ( a ) Line connecting the palmar and dorsal points of the lunate, ( b ) line tangential to the scaphoid connecting the palmar proximal and distal edge of the scaphoid, ( c ) line perpendicular to line a.

The radiolunate angle is measured between a line along the axis of the radius and a line perpendicular to the line connecting the palmar and dorsal points of the lunate ( Fig. 3 ). Normal values are ranging between −15 and 15 degrees. ⁷

Fig. 3.

Measurement of the radiolunate angle (between lines b and c). ( a ) Line connecting the palmar and dorsal pints of the lunate, ( b ) line perpendicular to line a, ( c ) line along the axis of the radius.

The lunocapitate angle is between a line drawn, along the longitudinal axis of the capitate and a line perpendicular to a line connecting the palmar and dorsal points of the lunate ( Fig. 4 ). The angle is considered negative when the axis of the capitate is dorsal to the axis of the lunate and positive when the axis of the capitate is more palmarly than the axis of the lunate. Normal values are ranging between −15 and 15 degrees. ⁸ Others consider a lunocapitate angle of more than 30 degrees as abnormal. ⁶

Fig. 4.

Measurement of the lunocapitate angle (between lines b and c). ( a ) Line connecting the palmar and dorsal points of the lunate, ( b ) line perpendicular to line a, ( c ) longitudinal axis through the capitates.

At last a possible ulnar translocation was identified on standard wrist PA views. This is the distance between the center of the capitate head and the longitudinal axis of ulna divided by the length of the third metacarpal ( Fig. 5 ). A normal ratio is more than 0.3. ⁹

Fig. 5.

Determination of ulnar translocation (c/b). ( a ) Longitudinal axis of the ulna, ( b ) length of the third metacarpal, ( c ) length of line perpendicular to line a, and the center of the capitate head.

Statistical Analysis

A power analysis was performed for scapholunate distance. This parameter was considered to be the primary end point. The desired power (1 −  β ) of this study was set at 80% and 0.05 was chosen as the desired significance level ( α ). Pliefke et al found an average radiographic scapholunate distance in patients with an arthroscopically proven scapholunate dissociation of 2.9 ± 0.9 mm compared with 2.2 ± 0.4 mm in patients with normal arthroscopic findings. These values were implemented to calculate the sample size. The power analysis was performed using the G * Power 3.1.9.2 program. Each group had to contain at least 17 patients to achieve an 80% power with a total sample size of at least 34 patients.

IBM SPSS Statistics 25 was used for statistical analysis.

Null hypothesis stated that there is no difference in the measurements in the study population with ganglion cysts compared with the control group with a significance level α of 0.05. If the p -value of the statistical test is less than 0.05, the null hypothesis is rejected and there is a statistically significant difference.

The choice of the statistical test was based on whether the values were numerical, ordinal, or nominal as well as their normality.

Mann-Whitney U test was used to compare the values of scapholunate distance and ulnar translocation between the two groups.

The differences in scapholunate, radiolunate, and lunocapitate angles were analyzed with the unpaired t -test.

Results

Results of the radiological measurements are presented in Table 2 .

Table 2. Radiologic measurements in wrists with without a ganglion cyst.

	Study group	Control group	p -Value
Mean scapholunate distance in mm (range)	0.8 (0, 2)	0.6 (0, 2)	0.37
Mean scapholunate distance on clenched fist view in mm (range)	1.6 (0, 3)	1.7 (0, 3)	0.58
Mean scapholunate distance on ulnar deviated wrist in mm (range)	0.8 (0, 2)	0.7 (0, 2)	0.64
Mean scapholunate angle in degrees (range)	47.8 (34.3, 61.4)	50.3 (36.5, 63.5)	0.14
Mean radiolunate angle in degrees (range)	−3.9 (−26, 20.2)	−1.97 (−20.6, 10.6)	0.34
Mean lunocapitate angle in degrees (range)	−13.5 (−27.5, −0.70)	−8.1 (−22.1, 2.9)	0.01
Ulnar translocation Number of patients with a ratio <0.3	9	4	0.26

The only statistical difference between wrists with and without ganglion cyst was found in lunocapitate angle. Although, the mean lunocapitate angle in the study group was still within the normal range between −15 and 15 degrees, 12 patients had an angle of less than −15 degree in the group with a ganglion cyst versus six in the control group.

Discussion

Little is known about the pathogenesis of ganglion cysts in the wrist. The assumption that a ligamentous pathology is the cause of ganglion cyst formation remains controversial. ³ As already stated above, many theories are suggested to explain possible pathomechanisms of ganglion cyst formation, all of them with their limitations.

By our knowledge, no other studies were performed previously to determine radiologic signs of carpal instability or misalignment in wrists with and without a ganglion cyst. In the present study we could not find evidence that carpal instability plays a role in the etiology of ganglion cysts. The relevance is that a ganglion cyst may be considered as a benign disorder without underlying carpal instability.

One of the limitations of the study is that it was a radiological study and that measurements on dynamic radiographs may not have enough accuracy to identify carpal instability. Pliefke et al ⁵ compared dynamic radiographs of 102 patients with a fall on the outstretched hand to their arthroscopic findings. They found that a normal radiography had a sensitivity of 57.1% and a specificity of 98.3% to detect ligament tears. With dynamic radiographs, the sensitivity increased to 85.7% and the specificity to 95%. In the present study, scapholunate distance, scapholunate, and radiolunate angles were measured with the same methods as in the study by Pliefke et al.

Another limitation is that the exact origin of the ganglions was not known. Close evaluation with wrist MRIs of these patients could have provided a better means of assessing the origin of the ganglion.

Scapholunate dissociation is the most common type of carpal instability. ⁹ In case of an association between carpal instability and the occurrence of ganglion cysts of the wrist, it would most likely be a scapholunate instability. However, the values of the scapholunate distance (PA, PA clenched fist, and PA in an ulnar deviated wrist) and scapholunate angle in the group of patients with a ganglion cyst were comparable to those of a population without a cyst. The radiolunate angle is an objective parameter for a possible palmar or dorsal tilt of the lunate and therefore a DISI pattern. In the present study, mean values were normal. We can state that there was no increased prevalence of scapholunate instability in our study group compared with the control group.

As both scapholunate and radiolunate angles were comparable between the two groups and mean values were within the normal range, a VISI or lunotriquetral instability could also be excluded in wrists with ganglion cysts.

Patients with ganglions had a greater negative lunocapitate angle in the present study. According to some, normal values range between −15 and 15 degrees and an abnormal lunocapitate angle may indicate midcarpal misalignment. ⁸ In the present study, more patients in the group with ganglions had an abnormal lunocapitate angle, which may indicate that midcarpal misalignment could play a role. However, others considered a normal lunocapitate angle to range between 0 and 30 degrees ⁶ and in the present study all wrists had a lunocapitate angle less than 30 degrees.

In addition, there was no increased prevalence of radiocarpal nondissociative instability within the group of patients with a wrist cyst since no difference in the occurrence of ulnar translocation between the two groups was detected.

It can be concluded that the findings of the study could not find firm evidence that ganglions of the wrists are associated with radiographic parameters indicating carpal misalignment.