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Corresponding author: Frederick W. Werner, MME, Department of Orthopedic Surgery, SUNY Upstate Medical University, 750 E Adams Street, Syracuse, NY 13210.
This study evaluated the biomechanics of Geissler IV (G4) wrists in cadavers and compared them with intact specimens after multiple ligament sectioning to create scapholunate instability. It also evaluated carpal motion changes after sectioning of the lunotriquetral interosseous ligament (LTIL).
Methods
Eight cadaver wrists determined to be G4 arthroscopically were tested using a wrist joint motion simulator. The LTIL was then sectioned, and carpal motion was recorded again. Carpal motions were compared with 37 normal wrists after sectioning of the scapholunate interosseous ligament and other ligaments to create a G4 wrist.
Results
Carpal motion of the 37 normal wrists after ligamentous sectioning was similar to motion of the 8 specimens noted to be G4. These wrists did not demonstrate subluxation of the scaphoid that may occur after ligament sectioning. After sectioning of the LTIL, there were significant changes in lunate and triquetral motion.
Conclusions
These findings support the hypothesis that sectioning multiple ligaments in normal wrists to create scapholunate instability causes average motion comparable to that seen in G4 wrists. Ligamentous sectioning can cause a range of scaphoid instability. Lunotriquetral interosseous ligament sectioning in native G4 wrists caused greater changes in triquetral than scaphoid range of motion.
Clinical relevance
Patients with arthroscopically determined G4 lesions have an incompetent SLIL and scapholunate instability but do not necessarily have scapholunate dissociation and subluxation. Cadaver studies that evaluate instability by sectioning specific intact wrist ligaments are similar to the G4 specimens and thus are a good approximation of naturally occurring wrist instability. The functionality of secondary stabilizers not seen arthroscopically may explain the differences in motion. Geissler IV wrists and ligament-sectioned wrists are points on the spectrum of carpal instability, which is determined by the extent of damage to multiple ligamentous structures.
These cadaver models create instability by taking an intact wrist and converting it to a Geissler grade IV (G4) wrist by sharp transection of the SLIL and/or its secondary stabilizers.
We undertook the current study to assess whether this testing protocol resulted in motion similar to that measured in cadaver specimens found to have a chronic Geissler IV lesion arthroscopically before experimentation.
The primary purpose of this study was to compare the range of motion (ROM) of the scaphoid, lunate, and triquetrum in G4 cadaver wrists (native G4) with wrists identified as intact that later underwent transection of the SLIL and various secondary stabilizers. A second purpose was to determine secondary changes to the scaphoid, lunate, and triquetrum ROM after sectioning of the LTIL in native G4 wrists.
Materials and Methods
Three primary kinematic comparisons of 8 G4 wrists were made with a group of 37 previously tested intact wrists before and after sectioning the SLIL and other wrist ligaments. The sample size of 8 wrists was based on a previous sample size calculation for similar wrist kinematic testing.
The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor Into the radiocarpal joint on scaphoid and lunate kinematics.
The first comparison was performed to determine whether the native G4 wrists had significantly different carpal kinematics from the 37 wrists with intact wrist ligaments. The second comparison was to determine whether the native G4 wrists had carpal motion equivalent to that of the 37 wrists after the ligaments were acutely sectioned. The third comparison was between the native G4 wrists and a subset of 8 of the 37 wrists in which only the SLIL was sectioned. The fourth comparison of this study was to evaluate carpal kinematics in wrists identified as G4 arthroscopically before and after LTIL sectioning.
Eight fresh-frozen cadaver upper extremities (average age, 83 years; 3 females) were selected from 32 wrists after they were determined to be G4 wrists by arthroscopic evaluation performed by a board-certified hand surgeon or a hand fellow experienced in wrist arthroscopy. Inclusion criteria were G4 wrists with no radiocarpal or midcarpal arthritic changes and no previous identifiable trauma or other visible ligamentous defects except at the SLIL.
We obtained radiographs of each specimen. One specimen had a scapholunate gap of 4 mm and a dorsal intercalated segment instability deformity and was included because it had been identified arthroscopically as a G4 wrist. No other specimens had plain radiographic evidence of carpal instability.
Electromagnetic motion sensors (Polhemus Fastrak sensors, Colchester, VT) used to track the motion of the scaphoid, lunate, and triquetrum were attached to each bone (Fig. 1), as previously described.
Figure 1Preparation of the limbs. A, B Fluoroscopy was used to guide unicortical placement of K-wires into the scaphoid, lunate, and triquetrum. These K-wires then were overdrilled with a drill bit. Both the K-wire and the drill bit were removed. A carbon fiber rod was fixed to the bone with expanding polyurethane adhesive. C A Plexiglas platform was then attached to each carbon rod and sensors were secured to each platform.
and moved through 7 motions (Table 1) by hydraulic force activation of 5 wrist tendons (Figure 2). The peak tendon forces were approximately 30 to 50 N during wrist flexion-extension.
The offset dart-throw motion was similar to the large dart-throw motion except that all radioulnar deviation values were offset ulnarly by 5° to represent the dart thrower’s motion based on a study by Garg et al.18
Motion
Extreme Extension
Extreme Flexion
Extreme Radial Deviation
Extreme Ulnar Deviation
Small flexion-extension
30°
30°
0°
0°
Large flexion-extension
30°
50°
0°
0°
Radioulnar deviation
0°
0°
10°
20°
Small dart-throw motion
30°
30°
10°
10°
Large dart-throw motion
30°
50°
10°
10°
Offset dart-throw motion
30°
50°
5°
15°
Circumduction motion
30°
30°
10°
10°
∗ The offset dart-throw motion was similar to the large dart-throw motion except that all radioulnar deviation values were offset ulnarly by 5° to represent the dart thrower’s motion based on a study by Garg et al.
Figure 2Wrist simulator setup. The tendons were attached to hydraulic actuators to cause 7 different wrist motions. During each wrist motion, the kinematics of the scaphoid, lunate, and triquetrum were acquired.
During each wrist motion, the scaphoid, lunate, and triquetrum flexion-extension and radioulnar deviation ROMs were measured relative to an electromagnetic sensor attached to a composite rod screwed into the distal radius.
The carpal bone motion data from these 8 native G4 wrists were compared using an independent measures analysis of variance (ANOVA) to a set of 37 previously tested intact wrists (average age, 69 years; 18 females) that were arthroscopically determined to be normal with an intact SLIL. The 8 wrists in this study were tested using the same wrist simulator as these 37 wrists. The collected data were compared with the motion of these 37 wrists while intact (first comparison) and then with these wrists after a gap and scapholunate instability was created by sectioning various ligaments and moving the wrists through 1,000 cycles of motion to represent a naturally occurring G4 wrist as the result of repetitive motion (second comparison). In this independent-measures ANOVA, we used a Games-Howell post hoc test when the variances of the groups were different. If the variances were not different, as determined by a Levene check of the variance, we used a Tukey post hoc test. In 22 of the 37 intact wrists, the SLIL, radioscaphocapitate (RSC), and scaphotrapeziotrapezoid (STT) ligaments were sectioned.
was employed to compare the 37 intact wrists after ligament sectioning with the 8 native G4 wrists. Equivalency testing allows a determination of whether 2 groups are equivalent. It differs from superiority testing, which shows there is a significant difference between 2 or more groups by using a Student t test or an ANOVA.
Of the 37 intact wrists, 16 were visually determined to have scaphoid subluxation during wrist motion after ligament sectioning. In 7 of these, the SLIL, RSC, and STT ligaments had been sectioned. In the rest, the SLIL, DIC, and DRC ligaments had been sectioned. Of these 16 wrists, the 8 most recently tested were selected and compared (second comparison) with the native G4 wrists using a Student t test.
There was a subset of 8 of the 37 wrists in which the SLIL had been sectioned first. Data from this subset of 8 wrists were compared (third comparison) with data of the native G4 wrists using a Student t test.
The LTIL was then sectioned in the native G4 wrists. To ensure that the LTIL was completely sectioned, the DRC was either completely or partially sectioned. Carpal motion was again recorded. The cadaver testing ranged from 1 to 2 hours, during which the wrists were periodically moistened. The motions of native G4 wrists before and after LTIL sectioning were compared using a paired t test (fourth comparison).
Changes in scaphoid flexion-extension, scaphoid radioulnar deviation, lunate flexion-extension, and lunate radioulnar deviation ROMs were compared for each wrist motion.
Under direct dissection, we then assessed the integrity of the native G4 wrist carpal ligaments.
In the last 6 wrists, animated models of the scaphoid, lunate, and triquetrum were created based on kinematic data collected during the experiment (Fig. 3). The minimum distances (gap) between the articulating surfaces of the scaphoid, lunate, and triquetrum were computed during each motion. During a cycle of motion, the average minimum distance and average largest minimum distance were found. A 2-way repeated-measures ANOVA, including a Bonferroni correction for multiple comparisons, was used to determine whether there were differences in the gaps between the scaphoid and lunate, between the lunate and the triquetrum, and between the LTIL intact wrist and after sectioning.
Figure 3Carpal bone dissection. The carpal bones were carefully dissected from the soft tissues, taking care to preserve the sensor attachments and articular cartilage. Using a stylus, the articular surfaces of the scaphoid, lunate, and triquetrum were digitized in 6 of the 8 arms to aid in determining the minimum distance between the articulating surfaces. The entire surface of each bone was also digitized to generate 3-dimensional models of each bone. The articular portions of each bone are shown: A The scaphoid, with its surface that articulates with the lunate; B the lunate, with its surface that articulates with the scaphoid; C the lunate, with its surface that articulates with the triquetrum; and D the triquetrum, with its surface that articulates with the lunate.
The carpal motion of the 37 intact specimens after multiple ligamentous sectioning was similar to that of the 8 specimens noted arthroscopically to have native G4 instability (Table 2). The native G4 wrists tested in this experiment showed significant differences in the ROM compared with the 37 intact specimens. Specifically, significant differences in carpal motion between native G4 wrists and the 37 intact wrists (before ligamentous sectioning; first comparison) were found in 7 instances (Table 3). In these same 7 instances, there were significant differences in carpal motion between the previously tested 37 intact wrists before and after ligament sectioning (Table 3).
Table 2Range of Carpal Flexion-Extension (Degrees) During 4 Wrist Motions
During these comparisons of carpal motion, there was no significant difference between the native G4 wrists and intact wrists after ligamentous sectioning (P > .05) (Table 3; second comparison). Based on equivalency testing, these motions were found to be equivalent in 3 comparisons. For these 3 comparisons, a power analysis to show equivalence had 80% power with 95% confidence.
The native G4 wrists tested in this experiment did not demonstrate the gross instability of scaphoid and lunate subluxation that can occur after SLIL and secondary ligament sectioning (second data comparison). These native G4 wrists had significantly less scaphoid flexion-extension ROM than the subset of 8 of the 37 multiple ligament sectioned wrists that had subluxation of the scaphoid. In the native G4 wrists, during the small flexion-extension motion, the scaphoid flexion-extension motion was decreased by 7.7° (P < .05) relative to the ROM in the grossly unstable wrists. Similarly, during the small dart thrower’s wrist motion, this motion decreased by 8.7° (P < .05), and during the circumduction wrist motion, it decreased by 8.4° (P < .05).
In the comparison between the native G4 and the 8 intact wrists in which the SLIL had been sectioned before any of the other ligaments (third comparison of data), the range of carpal motion (scaphoid flexion-extension, scaphoid radioulnar deviation, lunate flexion-extension, and lunate radioulnar deviation) was not significantly different (P > .05).
There were no significant changes in scaphoid ROM after sectioning of the LTIL (fourth comparison). There were numerous changes in lunate and triquetral motion (Table 4, Table 5).
Table 4Carpal Motion Before and After LTIL Sectioning in Native G4 Wrists for Selected Motions
For the 7 wrist motions no significant differences were found between the gaps (average minimum or largest minimum) (Table 6) between the scaphoid and lunate, and between the lunate and the triquetrum (P > .05). Nor were there significant differences between gaps that occurred before and after the LTIL was sectioned (P > .05). Carpal bone animations (Videos 1, 2, available on the Journal’s Web site at www.jhandsurg.org) after LTIL sectioning showed that the lunate and triquetrum translated relative to each other in the sagittal plane. The triquetrum moved volarly relative to the lunate.
Table 6Average Minimum Distance and Largest Minimum Distance Between Proximal Row Carpal Bones During a Cycle of Wrist Motion in 8 Native G4 Wrists
Native G4 Wrists
Average Minimum Distance Over a Cycle of Motion, mm
Largest Minimum Distance Over a Cycle of Motion, mm
In these 8 native G4 wrists, the DRC and DIC were initially present in all wrists. In 2 wrists, 5% to 10% of the DRC remained intact after we sectioned the LTIL. In 2 different wrists, 10% of the DIC was sectioned when we sectioned the LTIL. The RSC, short and long radiolunate (RL), and STT were present in all wrists, except in one wrist in which only 50% of the STT was present. Attenuation (stretching) of the RSC was seen in 2 wrists, of the short and long RL in one wrist, and of the STT in 2 wrists.
The LTIL was completely sectioned in 5 wrists. In the other wrists, less than 10% of the ligament remained. The lunotriquetral joint could be manually separated 6 mm upon visual examination at the conclusion of the experiment. Examination of the dorsal SLIL showed that it was completely disrupted in 2 wrists, partially present in 4, and 100% present in 2. In all cases in which it was partially or completely present, gapping of up to 4 mm was possible at the dorsal SLIL at the conclusion of the experiment. Examination of the volar SLIL showed that it was completely disrupted in one wrist, partially present in 2, and 100% present in 5. In all cases in which it was partially or completely present, there was separation up to 5 mm. Gapping of up to 4 or 5 mm between the scaphoid and lunate supports the arthroscopic finding that these were G4 wrists.
Discussion
The kinematic results from the G4 wrists were not significantly different from the intact specimens after ligamentous sectioning. This suggests that a cadaver model that uses intact wrists with sectioning of the SLIL and/or secondary stabilizers is comparable to that of a naturally occurring G4 wrist. None of the native G4 wrists demonstrated active clunking or subluxation of the scaphoid. However, after multiple ligament sectioning, 16 in the intact group demonstrated active clunking during ROM testing.
evaluated the SLIL and other stabilizers of the scaphoid and lunate. Dorsal subluxation of the scaphoid observed by Perez et al occurred only after ligaments were sectioned in a certain order. Data on dorsal subluxation measured by Perez et al were similar to measurements of the specimens that had subluxation or a clunking scaphoid in our data.
The secondary stabilizers in our G4 specimens may have been less attenuated compared with the multiple ligament sectioned specimens. Visual examination of the secondary stabilizers indicated that there was some attenuation of the STT in 2 wrists, of the short and long RL in one wrist, and of the RSC in 2 wrists. The DRC, which was initially intact, was sectioned by necessity while we sectioned the LTIL. Some of the G4 wrists had an SLIL that was present. Because there was a gap arthroscopically, the authors concluded that the SLIL was incompetent.
These data suggest that not all specimens with a G4 lesion have dorsal intercalated segment instability. It may be that the specimens we studied had attritional tears or laxity of the SLIL that is classified as G4 by arthroscopy. The data showed that there were changes in the ROM of the carpal bones after ligament sectioning or in G4 wrists. Although the changes in motion may seem small, they occurred in all 3 planes of motion and translational changes occurred. This resulted in altered kinematics of the carpal bones. We theorize that the native G4 wrists evaluated in this study represent a stage of carpal instability. This stage is one point on a continuum of instability depending on the ligaments damaged and the order in which they are damaged.
The authors conclude that various combinations of ligament injury produce different changes in carpal kinematics. The G4 wrists tested represent the stage of SLIL incompetence with partial deficiencies of other stabilizers. Each ligament or combination of ligamentous deficiency represents a stage along the spectrum of scapholunate instability. Our data suggest that the SLIL ligament is the most important. No significant instability is produced until that structure is weakened. Cutting more ligaments after the SLIL is damaged results in greater instability, but damage to the SLIL alone does not produce gross instability.
Cadaver dissections of the native G4 wrists in this experiment showed that the SLIL varied from complete disruption in one wrist to marked attenuation in another. In all wrists, 3 to 5 mm gapping of the bones could be demonstrated at final dissection, and all wrists demonstrated a drive-through sign during arthroscopy. Other researchers also found variable degrees of SLIL injuries.
The kinematics of the instability depend on an incompetent SLIL and varying deficiencies of the secondary restraints.
Evaluation of the animations revealed that only one specimen had a scapholunate gap during wrist motion. In the other 7 specimens, there was no gap but altered motion of the carpal bones. Those specimens had at least a 4 mm gap at arthroscopy. We believe that these G4 wrists represent instability of the scapholunate joint compared with an initially intact wrist after the SLIL had been sectioned.
Cutting the LTIL did not cause significant changes in the ROM of the scaphoid. Lunotriquetral interosseous ligament transection changed the ROM of the triquetrum. This fits with the known function of the LTIL, which causes the triquetrum to follow the lunate during wrist ROM.
Limitations of this study are that it was performed on cadaver wrists, and medical histories were unavailable. However, comparisons of carpal motion between this series of fresh cadavers as well as the previous 37 wrists were performed using the same methodology and can thus be compared with each other. Incomplete sectioning (up to 10%) of the DRC or DIC during LTIL sectioning may have affected the results. Complete sectioning would only have increased the angular changes that were detected and reinforced the findings. Also, the average age of 83 years may have caused different kinematics compared with those in the group of 37 wrists (average age, 69 years). Similarly, given the age of the specimens, our observation that the DIC and DRC were intact before LTIL sectioning may only reflect that they were structurally intact with uncertain functional competence. They may have had more attritional tears, because of the average age of 83 years, which may behave differently from acute injuries.
These findings support our hypothesis that sectioning multiple ligaments in normal wrists to create scapholunate instability causes average carpal motion comparable to that seen in native G4 wrists with arthroscopically demonstrated native tears. Ligamentous sectioning can cause a spectrum of levels of scaphoid instability, some with gross instability of the scaphoid. The G4 specimens in this experiment are probably a stage on the continuum. The results suggest that sectioning the LTIL in G4 wrists alters carpal kinematics. In addition, a G4 wrist may represent attritional tears of aging without clinical symptoms.
Acknowledgment
This study was funded in part by the Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, NY.
The effect of sectioning the dorsal radiocarpal ligament and insertion of a pressure sensor Into the radiocarpal joint on scaphoid and lunate kinematics.
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