Abstract
Background As numerous repairs, reconstructions, and replacements have been used following scapholunate interosseous ligament (SLIL) injury, there is a need to define the structural requirements for any reconstruction or replacement.
Methods Research has been conducted on the force needed to keep the scaphoid and lunate reduced following simulated injury, the failure force of the native SLIL and various replacements, the stiffness of the SLIL and replacements, and the torsional resistance of the scaphoid relative to the lunate.
Results Forces on the order of 50 N are needed to keep the scaphoid and lunate reduced during simple wrist motions in the chronically injured wrist. Even greater forces (up to 110 N) are needed to keep the bones reduced during strenuous activities, such as pushups. The failure force of the entire SLIL has been reported to be as high as 350 N and the failure force of just the dorsal component of the SLIL to be 270 N.
Conclusions The design requirements for a reconstruction or repair may vary depending upon the demands of the patient. In a high demand patient, a reconstruction needs to support the above-mentioned forces during cyclic loading (50 N), when performing strenuous activities (110 N), or during a fall (at least 350 N). Any artificial replacement must undergo careful biocompatibility testing.
Keywords: scapholunate interosseous ligament, design requirements
Numerous autografts, allografts, and artificial materials have been used for reconstructing the scapholunate interosseous ligament (SLIL). 1 Each of these methods seeks to reduce or eliminate the carpal changes that occur with SLIL disruption. Many new methods and materials, due to the limited success of previous reconstructions, continue to be proposed.
Disruption of the SLIL, often accompanied by tears of other secondary stabilizing ligaments, causes angular changes to the scaphoid and lunate. Typically, the scaphoid flexes and ulnarly deviates and the lunate extends and radially deviates during both wrist flexion–extension and radioulnar deviation. 2 3 4 Gapping between the scaphoid and lunate, 2 3 4 as well as scaphoid dorsal translation with wrist extension, 2 3 4 may occur. The gapping between the scaphoid and lunate is manifested by the scaphoid moving radially and lunate moving ulnarly. 5
SLIL reconstructions aim to reduce or prevent these angular and translational changes to prevent long-term degenerative changes to the distal radius and carpal bones. Some reports on new reconstructive methods have focused on reducing the gap between the scaphoid and lunate, while others have tried to reduce the gap and restore the normal angular alignment of the scaphoid and lunate. To develop or evaluate new SLIL reconstruction methods, one needs to address the design requirements to correct all of the kinematic changes that occur with SLIL dissociation.
The purpose of this review is to provide data on the required biomechanical design requirements for SLIL reconstructions. These include the forces needed to keep the dissociated scaphoid and lunate together, the tensile and torsional properties of the native SLIL and several reported replacements, and the role of the dorsal and volar components of the SLIL.
Summary of Forces Required to Reduce the Scaphoid and Lunate following SLIL Disruption
The force in the SLIL during active wrist motions and simulated pushup positions was reported in three studies from our research group 6 7 8 using an inline force transducer assembly ( Fig. 1 ). To measure the force in the SLIL, the force transducer was attached to the scaphoid via a post and cable assembly. The ulnar end of the cable was anchored to the lunate and passed radially through the scaphoid. The radial end of the cable was secured to a turnbuckle that allowed pre-tensioning of the cable that caused a nominal (7.5 N) compressive force on a donut shaped force transducer with the wrist in a neutral position and the SLIL intact. A compression spring, with a stiffness of 90 N/mm, was used to simulate the stiffness of the SLIL as reported by Johnston et al. 9 To ensure that the cable between the scaphoid and lunate measured the force normally transmitted through the SLIL, all portions of the SLIL were sectioned. A limitation to this study is that a single cable was used to represent the dorsal, volar, and proximal components of the SLIL.
Fig. 1.
A force transducer was attached to the scaphoid to measure the tensile force between the scaphoid and lunate. Preloading of the cable was achieved by compression of the spring and adjusted by a turnbuckle. The thumb was removed and a radial styloidectomy performed to allow unimpeded motion of the scaphoid post. ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris. Image courtesy: Dimitris et al. 6
In the first study by Dimitris et al, 6 six cadaver wrists were repetitively moved using a wrist joint motion simulator through four physiological wrist motions, consisting of two flexion-extension and two dart throw motions. From a group of 31 fresh-frozen cadaver wrists, 10 specimens that were either Geissler grade 1 or 2, as determined by arthroscopic examination, were selected for testing. The results from four specimens were excluded due to incomplete SLIL sectioning or scaphoid post loosening during testing. During the four wrist motions, SLIL force measurements were taken after the SLIL was acutely sectioned. The average maximum SLIL force ( Table 1 ) during any of the cyclic motions was 20 N. The maximal force during any of the motions in any of the wrists was 26 N. The average maximum SLIL forces were significantly greater at maximum wrist extension ( p = 0.003) than at maximum wrist flexion for both the wrist flexion/extension and the dart thrower's motions ( Fig. 2 ). These results suggest that, following acute SLIL injury or after SLIL reconstruction, it may be best to avoid forceful wrist extension.
Table 1. Average measured tensile forces (N) across the scapholunate joint during different wrist motions with an acutely sectioned SLIL compared with those with a preexisting SLIL tear.
| SLIL force measured by Dimitris et al, with an acutely sectioned SLIL. Standard deviation in parentheses | SLIL force measured in Yi et al's study with a preexisting SLIL tear. Standard deviation in parentheses | |||||
|---|---|---|---|---|---|---|
| At maximum flexion | At maximum extension | Maximum during all of cycle | At maximum flexion | At maximum extension | Maximum during all of cycle | |
| Large flexion–extension | 4.3 (0.6) | 17.5 (5.8) | 20.0 (3.3) | 30.4 (13.6) | 48.2 (11.6) | 48.5 (11.7) |
| Small dart throw | 4.3 (1.6) | 17.1 (5.1) | 17.3 (5.1) | 28.2 (12.7) | 42.8 (9.3) | 43.2 (9.2) |
| Large dart throw | 4.1 (1.7) | 17.0 (5.2) | 18.5 (4.1) | 24.4 (11.4) | 43.2 (11.4) | 43.9 (11.5) |
| Large dart throw with ulnar offset | 22.7 (11.1) | 43.7 (11.0) | 43.9 (11.0) | |||
Abbreviation: SLIL, scapholunate interosseous ligament.
Source: Reproduced from Yi et al. 8
For the flexion–extension motion, force in extension > force in flexion ( p = 0.048).
For the large dart throw motion with ulnar offset, force in extension > force in flexion ( p = 0.04).
For the flexion–extension motion and the small and large dart throw motions, at all parameters (max flexion, max extension, max over entire cycle), the force was greater with a pre-existing tear compared with the force with an acutely sectioned SLIL at p < 0.02.
Fig. 2.
Scapholunate interosseous ligament (SLIL) force during the large dart throw motion for six arms after acute sectioning of all components of the SLIL is plotted as a function of time. The flexion–extension component of the motion is also plotted to indicate when SLIL loading occurs. Image courtesy: Dimitris et al. 6
To determine the magnitude of the force required to maintain reduction in a preexisting scapholunate dissociation, a second study was performed by Yi et al. 8 Here, 15 Geissler grade 4 wrists were tested. They were selected from a pool of 52 fresh-frozen cadaver wrists. The results from seven wrists were excluded due to fracture of the scaphoid or loosening of the scaphoid or lunate posts during testing. Of the remaining eight wrists, five had only a preexisting SLIL tear and three had both a preexisting SLIL and a lunotriquetral interosseous (LTIL) tear. The force in the SLIL was measured in the same manner as done in Dimitris et al's study. However, before testing, the scaphoid and lunate were reduced using joysticks in the scaphoid and lunate to reduce the lateral scapholunate angle and bone reduction forceps were clamped across the scaphoid and lunate to reduce the scapholunate gap. Kirschner wires (K-wires) were inserted to maintain reduction before freezing the wrist. With the wrist frozen, the force transducer assembly was attached. After each wrist was placed in the wrist simulator and the force assembly pretensioned to 7.5 N, the K-wires and bone reduction clamp were removed. Each wrist was moved through a large flexion–extension and three dart thrower's motions. As observed in the study by Dimitris' et al, the measured SLIL force was greater in wrist extension than in wrist flexion ( p < 0.05; Fig. 3 ). Since there were three similar wrist motions performed in both Dimitris et al's and Yi et al's studies, the force to maintain reduction in the scaphoid and lunate in wrists with a preexisting tear could be compared with the force following acutely sectioning the SLIL. During these three motions, the measured force to maintain reduction in a preexisting SLIL tear was significantly greater ( p < 0.05) than the force to maintain reduction in wrists with an acutely sectioned SLIL ( Table 1 ). Analysis of the combined data of Yi et al and Dimitris et al revealed that the force to maintain reduction in the scaphoid and lunate was significantly less during a dart throw motion than during a pure flexion–extension motion ( p < 0.05). Lastly, the study by Yi et al showed that the reduction force was less in those wrists with both a preexisting SLIL and LTIL tear than those with only a SLIL tear ( p < 0.05; Tables 1 and 2 ). Yi et al's results demonstrate that during simple unresisted wrist motions, forces on the order of 50 N can occur in a SLIL replacement being used to maintain reduction in the scaphoid and lunate.
Fig. 3.
Scapholunate interosseous ligament (SLIL) loading measured during two cycles of a flexion–extension motion, a large dart throw motion and a dart throw motion with an ulnar shift in an illustrative wrist with a pre-existing scapholunate dissociation is plotted as a function of time. Greater forces are seen in wrist extension. Smaller forces are seen with the dart throw motions compared with a planar flexion-extension motion. Image courtesy: Yi et al. 8
Table 2. SLIL forces (N) with both a preexisting SLIL tear and a preexisting LTIL tear.
| At maximum flexion | At maximum extension | Maximum during all of cycle | |
|---|---|---|---|
| Large flexion–extension | 21.8 (2.9) | 21.4 (2.5) | 23.4 (2.1) |
| Small dart throw | 16.8 (5.5) | 19.8 (4.1) | 20.4 (3.4) |
| Large dart throw | 16.9 (4.9) | 20.1 (2.9) | 21.6 (0.9) |
| Large dart throw with ulnar offset | 15.6 (6.1) | 19.8 (2.9) | 20.3 (2.7) |
Abbreviations: LTIL, lunotriquetral interosseous ligament; SLIL, scapholunate interosseous ligament.
Source: Yi et al. 8
Note: Standard deviation is in parentheses.
Since at some stage of rehabilitation, some form of forceful wrist loading may occur, a third study by Scordino et al 7 was performed, specifically to compare two types of pushups. Frequently, a pushup is performed with the wrist in extension, but occasionally a pushup may be performed with the wrist in neutral (a knuckle pushup). Using the same force-measuring methods as for the previous two studies, six fresh-frozen cadaver wrists were loaded with the wrist in both simulated pushup positions. Three of the wrists were classified as Geissler 1 and three were Geissler 2. In this study, the SLIL load-measuring assembly was pretensioned to 9 N. Each wrist was axially loaded 10 times to a maximum load of 0.5 times its body weight ( Fig. 4 ). During loading, data were continuously acquired after the SLIL was sectioned, and then after the dorsal radiocarpal and dorsal intercarpal ligaments were also sectioned, and, finally, after the radioscaphocapitate ligament was also sectioned. The force required to maintain reduction of the scaphoid and lunate was significantly greater in extension than in flexion ( p < 0.05; Table 3 ). Because a nonlinear relationship between the applied force and the resultant force at the scapholunate articulation was observed, a second-order polynomial curve-fit between these variables was performed to estimate the force at the scapholunate articulation when greater axial forces might be applied such as during a strenuous pushup. With the wrist in extension and only the SLIL sectioned, a doubling of the experimentally applied axial force of 0.5 body weight would cause a predicted increase in the SLIL force from 44.5 to 110 N ( Fig. 5 ). As this greater force is ∼25 to 65% of the SLIL failure forces (discussed later), strenuous pushups should be avoided during early rehabilitation.
Fig. 4.
Dorsal view of a cadaver wrist positioned in a pushup position with the hand in extension. Dowels between the fingers restricted hand motion. Image courtesy: Scordino et al. 7
Table 3. SLIL force (N) upon application of maximum axial force during pushup in the extension position and in the neutral wrist position (knuckle pushup).
| Wrist position | SLIL cut | DRC/DIC also cut | RSC also cut |
|---|---|---|---|
| Neutral | 25.2 (13.5) | 28.1 (11.9) | 26.9 (12.9) |
| Extension | 44.5 (9.0) | 43.2 (9.4) | 39.5 (11.8) |
Abbreviations: DIC, dorsal intercarpal ligament; DRC, dorsal radiocarpal ligament; RSC, radioscaphocapitate ligament; SLIL, scapholunate interosseous ligament.
Source: Scordino et al. 7
Note: Standard deviation is in parentheses.
Fig. 5.
Measured scapholunate interosseous ligament (SLIL) force (N) in an illustrative wrist plotted as a function of the force applied to the distal radius and ulna. A polynomial curve fit was created using the data up to ½ times body weight applied force. It was then extrapolated to one times body weight. Image courtesy: Scordino et al. 7
Relative Importance of the Dorsal and Volar Components of the SLIL
As noted by Waters et al, 10 many SLIL repairs have focused on primarily repairing the dorsal component of the SLIL. 11 12 13 Similarly, many reconstructions have recreated the dorsal component or some sort of central tethering of the scaphoid and lunate. 1 14 15 16 17 18 19 20 21 This is based partially on anatomical studies that have shown the dorsal component of the SLIL to be 2 to 5 mm thick and the volar SLIL to be only 1 mm thick, 22 23 24 and from the work by Berger et al 23 who reported that the failure force of the dorsal component is 260 N, the volar component is 118 N, and the proximal component is 63 N. In Berger el al's study, there were four specimens in each of these three groups. Two biomechanical studies have shown the failure force of the volar SLIL to be comparable to or greater than the dorsal SLIL. Nikolopoulos et al 25 did not find a significant difference in the failure force between the two (dorsal SLIL, 83 N; volar SLIL 86 N; with each group having 8 specimens). Logan et al 26 found the failure force of the volar SLIL (125 N) to be greater than that of the dorsal (62 N) in a single specimen. Another difference among these studies includes the way the bones were secured to the testing machine. Berger et al potted the bones after passing K-wires though each bone. Nikolopoulos et al trimmed each bone and pinched them with pneumatic grips. Logan et al transfixed each bone with heavy gauge wire. It appears that Nikolopoulos et al divided the bones so that half of the proximal ligament was included in the dorsal SLIL and half with the volar SLIL. Different rates of loading were used by the different investigators. Berger et al tested at 5 mm/sec and Nikolopoulos et al tested at 5mm/min. In this comparison, Logan et al used a testing rate of 100 mm/min. Using two additional specimens, Logan et al showed that greater force was required to cause failure of the volar SLIL at higher testing rates. This may explain why Berger et al's failure forces are larger than in the other studies. Since injury to the SLIL may occur during a fall when the SLIL is rapidly loaded, the failure results by Berger et al and others who used a faster testing rate may be more appropriate to use as a design requirement for an SLIL reconstruction or replacement.
Waters et al 10 biomechanically studied the relative roles of the dorsal and volar portions of the SLIL in stabilizing the scaphoid and lunate. They tested 16 fresh frozen cadaver wrists in a wrist joint motion simulator with 8 wrists having the dorsal SLIL sectioned first and the other 8 having the volar SLIL sectioned first. The motion of the scaphoid and lunate was measured with all wrists intact, after the initial sectioning and then after full ligamentous sectioning during three wrist motions (flexion-extension, radioulnar deviation and dart thrower's motion). They found that sectioning the dorsal SLIL alone accounted for a greater increase in scaphoid flexion and lunate extension than first sectioning the volar SLIL ( Table 4 ) alone. However, they found the volar SLIL also provides some stability suggesting that there may be some value in implementing a volar SLIL repair or reconstruction.
Table 4. Percent increase in carpal motion with SLIL hemisectioning (volar or dorsal) completed compared with complete SLIL sectioning during 3 wrist motions.
| Flexion–extension | Radioulnar deviation | Dart throw | ||||
|---|---|---|---|---|---|---|
| Dorsal SLIL sectioned first | Volar SLIL sectioned first | Dorsal SLIL sectioned first | Volar SLIL sectioned first | Dorsal SLIL sectioned first | Volar SLIL sectioned first | |
| Increase in scaphoid flexion | 37 | 7 | 72 | 6 | 68 | 14 |
| Increase in lunate extension | 55 | 27 | 57 | 28 | 58 | 22 |
| Increase in scaphoid ulnar deviation | 53 | 0 | 77 | 12 | 32 | 7 |
Abbreviation: SLIL, scapholunate interosseous ligament.
Source: Waters et al. 10
Note: All comparisons between dorsal sectioned first to volar sectioned first were significant ( p < 0.05) except during the dart throw motion for changes in scaphoid ulnar deviation.
Structural Properties of the SLIL and Various Replacements
Berger et al's study on the constraint and material properties of the SLIL is a classic and frequently quoted. 23 As noted above, they found the dorsal SLIL had a larger failure force than the volar or proximal components ( Table 5 ). In general, the failure force of the dorsal SLIL ranged from 62 N as measured by Logan et al 26 to Pang et al's 270 N. 27 The failure force of the volar SLIL ranged from 86 N as measured by Nikolopoulos et al 25 to 125 N determined by Logan et al. 26 Others have quantified the tensile failure force of the entire SLIL ( Table 6 ) and found that it ranged from 170 N 28 to 357 N. 9 Again larger failure forces seem to be associated with faster testing rates. As shown by Rajan and Day, 29 other studies have found failure forces on the same order of magnitude.
Table 5. Structural properties of SLIL components (N). Standard deviation in parentheses if available.
| Failure force of SLIL components ( N ) | Failure loading rate | Stiffness of dorsal SLIL (N/mm) | |||
|---|---|---|---|---|---|
| Dorsal SLIL | Volar SLIL | Proximal SLIL | – | ||
| Berger et al 23 | 260 (118) | 118 (21) | 63 (32) | 5 mm/sec | – |
| Nikolopoulos et al 25 | 83 | 86 | – | 5 mm/min | – |
| Logan et al 26 | 62 | 125 | – | 100 mm/min | – |
| Hofstede et al 32 | 141 (20) | – | – | 6.4 mm/min | 61 (6) |
| Cuénod et al 31 | 93 (33) | – | – | 10 mm/min | 97 (43) |
| Pang et al 27 | 270 (91) | – | – | 10 mm/min | 240 (65) |
Abbreviation: SLIL, scapholunate interosseous ligament.
Table 6. Structural properties of the entire SLIL. Standard deviation in parentheses.
| Failure force ( N ) | Failure loading rate | Stiffness (slower loading rate) (N/mm) | Stiffness (faster loading of 100 mm/min) (N/mm) | |
|---|---|---|---|---|
| Johnston et al 9 | 357 (110) | 100 mm/min | 66 (29) | 95 (44) |
| Svoboda et al 33 | 260 (73) | 0.1 mm/sec | 150 (46) | – |
| Harvey et al 28 | 170 (97) | 10 mm/min | 81 (60) | – |
Abbreviation: SLIL, scapholunate interosseous ligament.
The linear stiffness of the entire SLIL was found to range from 66 to 150 N/mm ( Table 6 ). Johnston et al 9 showed that the stiffness increases with faster loading. Although a computation of the linear stiffness makes for an easy comparison of structures, it's important to note that most soft tissues exhibit nonlinear behavior. 30
Anatomical replacements for the entire SLIL or the dorsal SLIL have been studied by several authors. 28 31 32 33 The failure forces ranged from 44 to 188N and the stiffness from 34 to 169 N/mm ( Table 7 ), which are in the range of the native SLIL properties. The properties of these replacements are also sensitive to the loading rate.
Table 7. Structural properties of the alternative materials that could be used for a reconstruction of the SLIL.
| Material | Failure force (N) | Stiffness (N/mm) | |
|---|---|---|---|
| Svoboda et al 33 | Dorsal tarsometatarsal ligament between the lateral cuneiform and the third metatarsal | 154 (38) | 108 (20) |
| Harvey et al 28 | “Dorsal periosteum ligament” | 44 (24) | 34 (31) |
| Harvey et al 28 | “Third metacarpal-capitate ligament” | 172 (61) | 78 (21) |
| Harvey et al 28 | “Second metacarpal-trapezoid ligament” | 188 (145) | 96 (51) |
| Hofstede et al 32 | Third dorsal tarsometatarsal ligament | 143 (42) | 67 (17) |
| Hofstede et al 32 | Dorsal calcaneocuboid ligament | 149 (41) | 55 (14) |
| Cuénod et al 31 | Capitate-to-trapezoid ligament | 93 (35) | 109 (63) |
| Cuénod et al 31 | Trapezoid-to-second metacarpal | 147 (66) | 169 (87) |
Abbreviation: SLIL, scapholunate interosseous ligament.
Note: Standard deviation set in parentheses.
All of these properties have focused on the tensile behavior of the SLIL or possible replacements. Berger et al examined other important aspects of the SLIL. 23 These include the rotation of the scaphoid relative to the lunate after a 45.2 N-cm (0.45 N-m) torque was applied in each direction and the amount of dorsal or volar translation of the scaphoid relative to the lunate after a 17.8 N force was applied in each direction. They found that in the intact SLIL, the scaphoid could extend 17.2 (5.1) degrees and flex 17.5 (4.0) degrees relative to the lunate upon application of the given torque. The scaphoid could dorsally translate 1.8 (1.4) mm relative to the lunate and volarly translate 2.4 (1.4) mm relative to the lunate upon application of the dorsal or volar load. Testing of isolated components of the SLIL showed that the dorsal SLIL provided more restraint to translation than the volar SLIL. Both components had roles in preventing rotation between the scaphoid and lunate.
Pang et al 27 also examined the cyclic torsional and tensile properties of the native SLIL and the failure force and stiffness of the dorsal SLIL ( Table 5 ). They suggest that their failure force and stiffness values are higher than other reported values due to their testing setup that allowed off-axis translations and rotations. Pang et al looked at the torsional stiffness for a positive and negative 0.45 N-m torque between the scaphoid and lunate and observed a large neutral rotational zone of nearly 30 degrees when there was little noticeable resisting torque. The total peak-to-peak rotation in flexion–extension was 47 degrees, which is larger than that found by Berger et al for the same applied torques. When Pang et al looked at the stiffness of the dorsal SLIL, they found a 0.4 mm displacement occurred after a 50 N tensile force was applied. Their results show the nonlinear tensile behavior of the dorsal SLIL and how its computed linear stiffness is dependent upon which region of the loading curve is used.
In a subsequent study, Pang et al 34 looked for a relationship between these tensile and torsional properties of the native SLIL and how the scaphoid and lunate moved during wrist radioulnar deviation. In this study, it appears that they looked at the entire SLIL. For a given amount of wrist ulnar deviation, they found that the amount of scaphoid and lunate ulnar deviation decreased as the torsional laxity of the SLIL increased. They also found that the ratio of lunate flexion–extension to radioulnar deviation increased with increasing SLIL torsional rotation. These findings suggest there is a relationship between how the scaphoid and lunate move, at least in the native, normal wrist and how much laxity there is in the SLIL.
Different biological and artificial materials are available for replacement of the SLIL. Any material needs to provide comparable stiffness and failure force as in the intact SLIL. As noted above, there are a variety of soft tissue grafts that can be harvested as autografts or allografts. One benefit of an autograft is the reduced risk of soft tissue rejection. However, a perfect match of the failure force or the stiffness has yet to be found. An allograft may provide a better structural match but is more likely to be rejected. A benefit of artificial materials is that they can be modified to have different structural properties and fabricated in different sizes and shapes. Some are designed to allow for soft tissue ingrowth. Much work is needed to determine the biocompatibility of any new material as well as its resistance to fatigue and abrasion. A good resource are the standards developed by the ASTM (The American Society for Testing and Materials). These standards look at the response of the implant material to the human environment as well as how the implant may affect the body. For example, F1983, Standard Practice for Assessment of Selected Tissue Effects of Absorbable Biomaterials for Implant Applications, 35 provides a guideline for screening tests to look at the soft tissue response to materials that are designed to be absorbed into the body within 3 years.
Discussion
A SLIL injury can have long-term consequences that may require surgical intervention. When reconstruction is needed, factors such as the strength and location of the repair may be important, but, depending upon the amount of joint disruption, different types of repairs must be considered.
Several important points should be considered in the selection of a reconstruction.
Reconstruction methods should be able to support a minimum cyclic force of 50 N for simple unresisted wrist motions, especially in the case of chronic injuries. During healing, the reconstruction method may need to support forces greater than 100 N.
The dorsal and volar components of the SLIL each have important roles in stabilizing the scaphoid and lunate and reconstruction of both components may be warranted. Reconstruction of just the dorsal SLIL may not be sufficient, depending upon which components of the SLIL have been injured.
Although there is much variability in the force to failure of the SLIL, a review of the existing literature suggests that an allograft or artificial replacement needs a failure force of at least 300 N.
With even greater variability in the stiffness of the SLIL reported by some researchers, an allograft or artificial replacement might need an overall stiffness of 100 N/mm. This corresponds to a 0.5 mm gap between the scaphoid and lunate when a 50 N force is applied during simple unresisted wrist motions.
Reconstruction techniques need to restrict rotation of the scaphoid relative to the lunate. A 0.45 N-m torque should not cause more than 20 degrees in each direction.
Rehabilitation of a patient following SLIL reconstruction should avoid forceful wrist extension and should encourage a dart thrower's motion.
Funding Statement
Funding The study was supported by Department of Orthopedic Surgery, State University of New York, Upstate Medical University.
Footnotes
Conflict of Interest None declared.
References
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