Radioscaphoid Pressures and Carpal Kinematics After Wrist Ligament Sectioning

Abstract

Background

Scapholunate dissociation is usually the result of failure of multiple wrist ligaments. With continued use other structures attenuate, which results in change in position of the carpal bones. It is presumed that load characteristics in the wrist joint change with changes in carpal bone position. This is thought to result in localized pressure overload and arthritic change.

Questions/Purposes

The purpose of this study was to evaluate radioscaphoid joint pressures and carpal kinematics after sectioning specific wrist ligaments. Our hypotheses are that there would be increased scaphoid flexion and ulnar deviation, increased lunate extension and radial deviation, increased contact pressure in the radioscaphoid fossa, and increased tendon forces.

Materials and Methods

Eight cadaver wrists were instrumented with an electromagnetic motion tracking device and a pressure sensor was inserted into the radioscaphoid joint. Using a wrist joint motion simulator, motion and pressure data were obtained in the moving wrist in the intact state and after sectioning the dorsal radiocarpal, dorsal intercarpal, and scapholunate interosseous ligaments.

Results

After ligament sectioning there was increased scaphoid flexion, scaphoid ulnar deviation, lunate extension, and lunate radial deviation resulting in carpal instability. There was also an increase in pressure in the radioscaphoid fossa. Several specimens showed evidence of scaphoid subluxation.

Conclusion/Clinical Significance

It is our conclusion that this combination of ligament sectioning produces scapholunate instability and increased pressures in the radioscaphoid fossa in the laboratory setting. We believe that if left untreated in the clinical setting, scapholunate advanced collapse could result.

Injury to the scapholunate interosseous ligament may lead to symptoms of pain and instability. As the injury progresses, other ligaments may become attenuated or torn affecting carpal kinematics. ¹ Eventually, static deformities in the positions of the carpal bones occur. At the end stage, arthritic changes occur between the scaphoid and radius but spare the lunate radius articulation. ²

Changes in carpal motion following in vitro sectioning of the scapholunate interosseous ligament (SLIL), dorsal radiocarpal ligament (DRC), and the dorsal intercarpal ligament (DIC) have been shown to occur by Short et al ³ and by Pérez et al. ⁴ Huddleston et al have suggested that isolated sectioning of the SLIL does not alter the contact pressures on the radius. ⁵ As suggested by Figueroa et al, ligamentous sectioning can cause a spectrum of scaphoid instability, with some arms having gross instability. ⁶ It seems important to look further into this problem to see how sectioning of multiple scapholunate stabilizers affects carpal kinematics and contact pressures in the wrist, which may, in turn, lead to degenerative arthritis.

The purpose of this study was to biomechanically examine carpal bone motion changes, contact pressure changes, and tendon force changes with in vitro sectioning of the primary ligamentous stabilizers of the scaphoid and lunate. Our hypotheses are that there would be increased scaphoid flexion and ulnar deviation, increased lunate extension and radial deviation, increased contact pressure in the radioscaphoid fossa, and increased tendon forces.

Materials and Methods

Eight fresh frozen right upper extremities (average age 70, three females, five males) were selected from a large group of cadaver specimens. The right upper extremity was used because the testing apparatus only allows right arms. Prior to inclusion in the study, each specimen from the larger group of arms was radiographed in the anteroposterior (AP) and lateral planes to rule out bony deformity. Each specimen was then arthroscoped in both the radiocarpal and midcarpal joint. Specimens that had no visual evidence of intrinsic or extrinsic ligament pathology were then considered Geissler 0 specimens. The first eight that met these criteria were included in the study group. In this group of eight specimens four wrists had degenerative tears of the Triangular Fibrocartilage Complex (TFCC). The sample size of eight was selected based on earlier ligament sectioning studies. ⁷

Each wrist was moved through six cycles of six different wrist motions as well as held in a neutral position using a wrist joint motion simulator. ⁸ The motions were caused by a previously described, but modified, control algorithm ⁹ in which five wrist tendons were used to cause each desired motion. The five tendons were the extensor carpi ulnaris (ECU), extensor carpi radialis brevis (ECRB), extensor carpi radialis longus (ECRL), flexor carpi radialis (FCR), and flexor carpi ulnaris (FCU). The six desired cyclic wrist motions were a large flexion/extension motion (30 degrees of extension to 50 degrees of flexion and back), a dart motion (30 degrees extension and 10 degrees radial deviation to 30 degrees flexion and 10 degrees ulnar deviation and back), a dart offset motion (same as the dart motion but all radioulnar positioning offset 5 degrees ulnarly), a dart45 motion (15 degrees of extension and 15 degrees of radial deviation to 15 degrees of flexion and 15 degrees of ulnar deviation and back, but with all radioulnar positioning offset 5 degrees ulnarly), a radioulnar deviation motion (20 degrees of ulnar deviation to 10 degrees of radial deviation and back), and a circumduction motion (10 degrees of radial deviation to 30 degrees of flexion to 10 degrees of ulnar deviation to 30 degrees of extension to 10 degrees of radial deviation). The tendon forces were dynamically varied to cause each actual motion to match the desired motion. As described below, the motion of the wrist was measured using an electromagnetic sensor attached to the dorsum of the 3rd metacarpal. The wrist motion measurement, tendon force measurements, and the correction to the tendon forces were performed every 12.1 milliseconds (82.6 Hz).

Prior to placing the specimen in the wrist joint simulator, the DRC and DIC were outlined under direct visualization using a surgical marker. An incision was made in the radiocarpal joint sparing the DRC and DIC. ¹⁰ A Tekscan (S. Boston, MA) 6900 conductive ink sensor was placed in a tape package and inserted through the capsulotomy to cover the radioscaphoid fossa. The sensor was sutured to the radial and volar wrist capsule to secure it in position. The specimen was placed in the wrist joint simulator and intact data obtained. The DRC was sectioned from the radius, the DIC was sectioned at its radial attachment to the trapezium and scaphoid, and the entire dorsal, volar, and membranous portion of the SLIL were sectioned using a surgical scalpel. This was all done under direct visualization. After ligamentous sectioning data were again collected.

Electromagnetic motion sensors were attached to the scaphoid, lunate, capitate, 3rd metacarpal, and distal radius to measure carpal motion during each wrist motion ( Fig. 1 ). For each carpal bone, the sensor was mounted on a plastic platform that was attached to a composite rod inserted into the bone and secured with an expanding foam epoxy. The sensors for the 3rd metacarpal and distal radius were mounted on platforms screwed onto each bone. The data for the carpal sensors were recorded at 20.4 Hz and zeroed back to a neutral wrist position. The change in scaphoid flexion/extension, scaphoid radioulnar deviation, lunate flexion/extension, and lunate radioulnar deviation after ligament sectioning was determined at each increment of data collection during a cycle of wrist motion. The largest change in each carpal motion and when it occurred during a cycle of motion was tabulated. The flexion/extension and radioulnar deviation angular position of each bone at the time the change was largest was compared between the intact and ligament-sectioned states using a paired t -test. During the wrist flexion/extension motion, changes in scaphoid flexion and lunate extension were computed by determining the difference in their motion before and after ligamentous sectioning at each increment of motion.

Fig. 1.

Wrist joint motion simulator showing insertion of pressure sensor into radioscaphoid fossa and the three carpal motion sensors attached to each bone using a composite rod.

Pressure measurements were continuously recorded at the same sampling rate as tendon force data were recorded. During each cycle of wrist motion, the pressure data were recorded and the peak pressure over the fossa was noted. The peak pressure anytime during the cycle of motion and the peak area of contact anytime during the cycle of motion were determined with the wrist intact and following ligament sectioning. Changes in peak pressure and area of contact were compared using a paired t -test.

After completion of the study, the border of the radioscaphoid fossa was outlined on the sensor. Data within the outline were collected and correlated with the position within the fossa. Data outside of the border were excluded from analysis.

The tendon forces in the ECU, ECRB, ECRL, FCR, and FCU causing each motion were recorded at 82.6 Hz. The largest force in each tendon during each motion was determined during the 4th and 5th cycles of wrist motion with the wrist intact and following ligament sectioning, and compared using a paired t -test.

At the conclusion of the experiment the specimen was dissected to verify that all ligaments had been completely transected and the pressure sensor had not migrated from its original position in the radioscaphoid fossa.

Results

Download video file ^{(1.5MB, mp4)}

Video 1

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Video 2

Sectioning of the SLIL, DRC, and DIC caused scapholunate instability and dissociation in two of the eight arms. In these arms the scapholunate gap, based on direct visualization, was up to 4 to 5mm and the scaphoid would snap or clunk back into the radioscaphoid fossa as the wrist moved from extension into flexion (defined here as Grade 3 instability; see animation of an illustrative arm before ( Video 1 ) and after ligamentous sectioning ( Video 2 ). Video 1 is an animation of the scaphoid and lunate from a dorsal perspective, with the wrist ligaments intact, during a large wrist flexion/extension motion (30 degrees of extension to 50 degrees of flexion). Video 2 is an animation of the scaphoid and lunate from a dorsal perspective, after the wrist ligaments have been sectioned, during a large wrist flexion/extension motion (30 degrees of extension to 50 degrees of flexion). Four arms had gapping from 2.5 to 5 mm but without any snapping or clunking of the scaphoid (defined as Grade 2). The remaining two arms had only a 2-mm gap and no snapping or clunking of the scaphoid (defined as Grade 1).

There were significant increases in scaphoid flexion ( p  < 0.01), lunate extension ( p  < 0.017), scaphoid ulnar deviation ( p  < 0.015), and lunate radial deviation ( p  < 0.018) following ligament sectioning in all six wrist motions. The largest increases in scaphoid flexion (>8.6 degrees) and lunate extension (>10.3 degrees) occurred during the wrist flexion/extension and circumduction motions ( Table 1 ). The largest increase in scaphoid ulnar deviation (9.2 degrees) occurred during the circumduction motion. The largest increase in lunate radial deviation (6.4 degrees) occurred during the flexion/extension motion.

Table 1. Largest angular changes in scaphoid and lunate motion after SLIL, DRC, and DIC sectioning during a cycle of wrist motion (degrees) (average of eight arms).

Wrist motion	Increase in scaphoid flexion	Increase in lunate extension	Increase in scaphoid ulnar deviation	Increase in lunate radial deviation
Large flexion/extension motion	8.6	12.7	5.8	6.4
Radioulnar deviation motion	7.8	4.6	6.4	2.3
Dart throw motion	8.5	6.4	5.3	2.6
Offset dart throw motion	8.4	4.1	5.6	1.6
Dart motion at 45-degree orientation	6.7	2.3	5.1	1.5
Circumduction motion	10.5	10.3	9.2	5.4

Abbreviations: DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; SLIL, scapholunate interosseous ligament.

Arms with greater instability (Grades 2 and 3) appeared to have larger increases in lunate extension ( Fig. 2 ) but not in scaphoid flexion ( Fig. 3 ) than those with minimal instability (Grade 1) during the large wrist flexion/extension motion.

Fig. 2.

Increase in lunate extension angle (degrees) after ligament sectioning during one cycle of the large wrist flexion/extension motion. The x-axis is a time representation of the wrist motion from 10 degrees of flexion to 50 degrees of flexion to 10 degrees of flexion to 30 degrees of extension (extension is negative) and back to 10 degrees of flexion. Grade 1 data are the average of two arms, grade 2 the average of four arms, and grade 3 the average of two arms.

Fig. 3.

Increase in scaphoid flexion angle (degrees) after ligament sectioning during one cycle of the large wrist flexion/extension motion. The x-axis is a time representation of the wrist motion from 10 degrees of flexion to 50 degrees of flexion to 10 degrees of flexion to 30 degrees of extension (extension is negative) and back to 10 degrees of flexion. Grade 1 data are the average of two arms, grade 2 the average of four arms, and grade 3 the average of two arms.

Based on all eight arms, the peak pressure in the radioscaphoid (RS) fossa had a non-significant trend to increase after ligament sectioning ( Table 2 ). However, as noted above, two arms became grossly unstable following ligament sectioning. In these two arms, the scaphoid was noticed to slide up the dorsal rim of the radioscaphoid fossa as the wrist moved into extension and no longer contacted the pressure sensor. With removal of these two arms, there was a significant increase in the peak pressure in the RS fossa ( p  = 0.001) during the large flexion/extension motion ( Fig. 4 , Fig. 5 ).

Table 2. Peak pressure (MPa) measured in RS fossa before and after SLIL, DRC, and DIC sectioning (peak pressure during anytime during a cycle of motion).

	Average based on eight arms		With removal of two grossly unstable arms which reduced contact with the pressure sensor during part of the motion, thus average based on the remaining six arms
Wrist motion	Intact wrist	After ligament sectioning	Intact	After ligament sectioning
Neutral position	1.9	2.4	1.6	2.0
Large flexion/extension motion	5.7	7.2	5.3	8.0
Radioulnar deviation motion	3.4	3.4	2.7	3.5
Dart throw motion	3.5	4.1	3.1	4.3
Offset dart throw motion	3.3	3.5	3.0	3.6
Dart motion at 45-degree orientation	2.8	2.8	2.4	3.0
Circumduction motion	4.6	5.0	4.1	5.4

Abbreviations: DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; RS, radioscaphoid; SLIL, scapholunate interosseous ligament.

Fig. 4.

Peak pressure on radioscaphoid fossa during the large flexion/extension motion in an illustrative arm. The x-axis is a time representation of the wrist motion from 10 degrees of flexion to 50 degrees of flexion to 10 degrees of flexion to 30 degrees of extension (extension is negative) and back to 10 degrees of flexion.

Fig. 5.

Pressure in the radioscaphoid fossa was acquired continuously during the wrist flexion/extension motion. Shown here for one wrist is the pressure in the intact wrist (left) and following ligamentous sectioning (right) at 10 degrees of wrist flexion as the wrist is coming out of flexion. A larger peak pressure is seen after ligamentous sectioning. The centroid of pressure is shown in each picture as a white and gray diamond and in this one wrist moves dorsally and radially following ligamentous sectioning. However, only the dorsal movement was found to be significant ( p  < 0.05).

In the neutral wrist position, based on all eight arms, after ligament sectioning, the centroid of pressure moved dorsally 1.6 mm (SD 2.0 mm); however, this was not significant ( p  = 0.058). With removal of the two arms in which the scaphoid no longer contacted the pressure sensor during wrist motion, there was a significant increase in the dorsal movement of the centroid of contact (1.7 mm, SD of 1.4 mm; p  = 0.03). This change is for the six arms without any snapping or clunking of the scaphoid back into the fossa.

During the wrist flexion/extension motion after ligamentous sectioning, as the wrist was flexing from 7 degrees of flexion to 34 degrees of flexion, the centroid of pressure moved dorsally significantly ( p  < 0.05), an average of 1.4 mm during this 27 degrees of wrist motion (SD 0.3 mm; average maximum of 1.8 mm). During the same flexion/extension motion after ligamentous sectioning, as the wrist was moving from 19 degrees of flexion to 6 degrees of flexion, the centroid of pressure again moved dorsally significantly ( p  < 0.05), an average of 1.8 mm during this 13 degrees of motion (SD 0.4 mm; average maximum of 2.2 mm). Between these portions of the flexion/extension motion, the centroid of pressure returned to its path observed with the wrist intact. There was no significant change in the radioulnar location of the centroid of pressure during the flexion/extension motion ( p  > 0.12). These changes were also based on the six arms that did not have any snapping or clunking of the scaphoid.

The peak area of joint contact in the RS fossa appeared to decrease after ligament sectioning. It was significantly less ( p  < 0.04) during the neutral, radioulnar deviation, dart45, and circumduction motions when based on all eight arms ( Table 3 ). However, in two arms the scaphoid was on the dorsal rim and therefore off the sensor, which could reduce the area of measurement contact. Looking at the remaining six arms, when contact did occur, the area of contact was significantly reduced during the neutral and radioulnar deviation motions ( p  < 0.03).

Table 3. Peak area of joint contact (mm ² ) measured in the RS fossa before and after SLIL, DRC, and DIC sectioning (the peak area is during anytime during a cycle of motion) .

	Average based on eight arms		With removal of two grossly unstable arms which reduced contact with the pressure sensor during part of the motion, thus average based on the remaining six arms
Wrist motion	Intact wrist	After ligament sectioning	Intact	After ligament sectioning
Neutral position	54.0	39.3	51.1	36.6
Large flexion/extension motion	90.3	68.8	86.0	69.4
Radioulnar deviation motion	72.4	47.0	63.7	43.0
Dart throw motion	80.8	56.7	76.3	55.4
Offset dart throw motion	70.0	54.8	61.6	51.9
Dart motion at 45-degree orientation	75.0	48.0	67.7	48.1
Circumduction motion	82.5	59.5	77.2	60.5

Abbreviations: DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; RS, radioscaphoid; SLIL, scapholunate interosseous ligament.

The peak tendon forces, anytime during the 4th and 5th cycles of wrist motion, were frequently significantly greater following ligament sectioning ( Table 4 ). Specifically, after ligament sectioning, the peak ECU tendon force was significantly greater ( p  < 0.045) during the flexion/extension, dart, dart offset, and circumduction motions; the peak ECRB tendon force was greater during the flexion/extension motion ( p =0.024); the peak ECRL tendon force was greater ( p  < 0.046) during the flexion/extension, dart offset, and circumduction motions; and the peak FCU tendon force was significantly less ( p  < 0.048) during the radioulnar deviation motion. Of interest, extensor tendon forces were significantly greater ( p  < 0.023) with the wrist going from flexion to extension than from extension to flexion during the flexion/extension motion.

Table 4. Peak extensor tendon forces anytime during the 4th and 5th cycles of wrist motion (N) before and after ligament sectioning (cut) (average of eight arms).

Wrist Motion	Intact	Cut	Intact	Cut	Intact	Cut	Intact	Cut	Intact	Cut
	ECU	ECU	ECRB	ECRB	ECRL	ECRL	FCR	FCR	FCU	FCU
FE50	65.5	89.0	61.9	75.8	56.2	82.2	69.0	69.5	38.4	39.6
Dart	37.0	47.3	43.8	45.0	52.4	59.3	40.1	38.5	46.8	46.5
Dart offset	40.4	56.4	39.4	44.1	43.3	55.9	31.5	33.6	49.7	48.7
Dart45	28.5	36.4	33.4	31.3	44.2	52.9	34.1	32.7	45.9	44.1
Circumduction	62.6	78.2	50.1	57.3	43.6	56.1	65.6	55.8	27.6	27.3
RU15	46.0	48.6	27.5	28.9	50.8	53.3	38.1	33.0	27.2	24.6

Abbreviations: Dart45, Dart motion at 45-degree orientation; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris; FCR, flexor carpi radialis; FCU, flexor carpi ulnaris; FE50, Large flexion/extension motion; RU15, Radioulnar deviation motion.

Discussion

The purpose of this study was to biomechanically examine carpal bone motion changes, contact pressure changes, and tendon force changes with in vitro sectioning of the important ligamentous stabilizers of the scaphoid and lunate. Our results support our hypotheses that there would be increased scaphoid flexion and ulnar deviation, increased lunate extension and radial deviation, increased contact pressure in the radioscaphoid fossa, and increased tendon forces.

Following acute carpal ligament injury, increased motion of the scaphoid and lunate was seen especially with the large flexion and extension wrist motion arcs as well as circumduction motion arcs. Increased scapholunate (SL) widening was visually noted in all the wrists, with two having Grade 1 instability (2mm SL gapping), four having Grade 2 instability (2.5 to 5mm SL gapping but no scaphoid clunking into the radioscaphoid fossa), and two having Grade 3 instability (4 to 5mm SL gapping, with the scaphoid clunking back into the radioscaphoid fossa during motion). The variation in gapping among the eight wrists may be dependent upon the bony anatomy of the distal radius and proximal scaphoid, as shown in a study by Werner et al. ¹¹ In that study, radioscaphoid and scaphoid curvatures were found to be larger in those wrists without gross instability following ligamentous sectioning. Wrists with a deeper radioscaphoid fossa and greater volar tilt were also found to be more stable. In the current study these curvatures were not determined, but we propose that these bony and other anatomical differences in the wrists may have had an influence in the observed variations in stability following ligamentous sectioning. Additionally, there were increased radioscaphoid fossa pressures after ligamentous sectioning with most of the increase in pressures seen as the wrist was coming out of terminal flexion.

The observed increased SL gapping following ligamentous sectioning would suggest the scaphoid centroid of pressure should be more radial than in the intact wrist. However, there was not a significant radial shift of the centroid of pressure in the radioscaphoid fossa since this calculation was based on the six wrists in which the scaphoid stayed on the pressure sensor during wrist motion. These six wrists were those which did not have any snapping or clunking of the scaphoid during wrist motion and had less gapping than those defined as having Grade 3 instability. If the two wrists which demonstrated snapping or clunking of the scaphoid (and unfortunately moved off the pressure sensor) could have been included, perhaps a significant radial movement of the pressure centroid would have been observed. The limitations of this study include that it is a cadaver study looking only at time zero which does not consider the effects of any soft tissue healing or repetitive joint loading. Additionally, the insertion of the pressure sensor could have disrupted secondary stabilizers and altered either the carpal motions or pressures. ¹² Also, this study examined only six wrist motions and the pressure sensor did not cover the dorsal rim of the radius.

The observed carpal motion changes are consistent with findings published by Short et al and Pérez et al. ^{3 4} Short et al found that sectioning of the SLIL after first sectioning the DIC and DRC caused significant increase in scaphoid flexion and lunate extension in a similar experimental model. Pérez et al also found that sectioning of the SLIL, DIC, and DRC caused increased lunate extension. Huddleston et al suggested that isolated sectioning of the SLIL may not be sufficient to alter the contact pressures of the wrist. ⁵ However, as noted by Pérez et al, isolated sectioning of only the SLIL did not, in their experimental model, cause significantly increased lunate extension, which may explain why Huddleston et al did not find increased contact pressures with only SLIL sectioning. In our study we sectioned not only the SLIL, but also the DIC and DRC.

This study is unique in that it simultaneously measures scaphoid, lunate, and third metacarpal motion and pressure distribution in the radiocarpal joint while the wrist is being moved by application of forces on the wrist tendons. The study shows that sectioning the ligaments under study alters the position of the scaphoid and lunate during wrist motion. This change in carpal bone position results in an increase in pressure in the radioscaphoid fossa. These findings support the hypothesis that damage to the studied ligaments may eventually overload the radial side of the wrist. This can be seen clinically in scapholunate collapse. Surgical correction of the abnormal carpal motion may correct the increased pressure abnormalities.

Funding Statement

Funding Funded by the Department of Orthopedic Surgery, State University of New York, Upstate Medical University.