Many surgical procedures have been described to reconstruct SL dissociation. Garcia-Elias et al. advice, how to stage SL dissociation and how to treat it adequately . At stage 2 (complete SL ligament injury with a repairable dorsal SL ligament), direct ligament repair and additional capsulodesis is recommended, if surgery is performed in early stages. At stage 3 (complete non-repairable SL ligament injury with a normally aligned scaphoid), ligament reconstruction should be performed, if no carpal malalignment is present. A bone-ligament-bone reconstruction could be one of the possible procedures [21,22,23]. Deciding whether a ligament is repairable or not is not always easy. Very often the quality of the ligament is critical for primary repair in non-recent injuries, but there is a pronounced donor-side morbidity with a more extensive reconstruction. Therefore, an additional stabilizer of the sutured SL ligament is desirable.
Many biomechanical studies have investigated different methods of SL ligament repair [13, 19, 24, 25]. The measurements were always carried out using fluoroscopy. The angles between scaphoid and lunate were then determined using a two-dimensional X-ray image. Static radiography alone may miss a dynamic SL dissociation [26, 27]. Intra- and interobserver reliability to recognize carpal instability is discouraging . The angles cannot be measured exactly and measurements are only approximative. Furthermore, in the lateral view, only the sagittal movement of the carpal bones is considered. As we all know, carpal bones follow a complex three-dimensional kinetic, and a two-dimensional image is insufficient to describe this intricate motion. Therefore, a more accurate method should be used for the representation of the movement of the carpal bones. Thus, we analyzed the movements using the 3D reconstructed computed tomography. Moreover, only a momentary situation is taken with the standard x-rays. The displacements at different wrist positions can hardly be detected due to the superimposition of the carpal bones with normal x-rays. That was the reason why we carried out the analysis of the carpal movement using 3D models, to obtain more precise measurements of the complex, three-dimensional movement.
Our results show that after dissecting the SL ligament, the scaphoid follows its natural movement into flexion, especially during wrist flexion, radial, and ulnar deviation. Simultaneously, the lunate follows a dorsal extension movement, again during flexion of the wrist, but particularly during fist closure. It's worth mentioning that these are relative motions to each other. We could demonstrate that the ligament reconstruction neutralizes this abnormal movement after a divided SL interval. During wrist flexion and radial deviation, the scaphoid itself undergoes radial inclination, while the lunate does not perform any particular movement in the coronary plane. This pathological deviation could also be corrected by bone-ligament reconstruction described above. When looking at the scaphoid and the lunate from the axial view, one will be able to recognize a pronation of the scaphoid and a slight supination of the lunate after an SL dissociation has been created. Again, this effect is not observed in all wrist positions.
On the other hand, we could show that the separation of the SL ligament and its secondary stabilizers result in a significant increase of the SL distance in all wrist positions. Interestingly, the SL distance increases more during fist closure, flexion, and radial deviation. With the radio-luno-triquetral reconstruction, the SL distance could be restored in its original position.
Comparing other techniques like Blatt capsulodesis , which create a tether form, the dorsal rim of the radius to the distal scaphoid in order to limit scaphoid flexion, our described bone-ligament transfer lead to a more anatomic reconstruction, since the dorsal SL-ligament is strengthened along its original anatomy. It can be assumed that the bone block heals well in the scaphoid under optimal conditions, thus creating a very stable bone-ligament interface.
The modified Brunelli technique as described by Talwalkar, Van den Abbeele, and Garcia-Elias [29,30,31], tries to correct the flexion of the scaphoid by routing the FCR tendon through te distal volar surface of the scaphoid and securing it to the dorsal pole of the lunate as well as looping it around the radiolunotriquetral ligament. This method addresses both distal and volar secondary stabilizing ligaments, as well as the SL-ligament, which is recommended in higher stage SL instability. Our described technique does not restore secondary stabilizers and is therefore not suitable for chronic and static SL instability. On the other hand, donor-side morbidity by the rather big approach described by the modified Brunelli technique is significantly more serious than our technique.
Other authors suggest a bone-ligament-bone reconstruction to restore SL instability [22, 23]. Donor-side morbidity is again much greater than in our described technique. In addition, the advantage over a free bone-ligament bone graft is that the bone block is still attached on one side with a better blood supply as well. The described technique may also be performed with a mini-open approach together with arthroscopic-assisted SL transfixation.
Limitations of our study include those inherent in cadaver-based studies. Cadaver specimens do not allow tissue healing to assess reconstruction durability accurately. The age of the deceased and their degenerative changes on the wrist may have an influence on the results, particularly since this injury must be treated surgically, principally in younger patients. Although we could show that the SL distance can be reconstructed very well with this technique, the evidence for anatomical carpal alignment is more difficult to realize. For certain wrist positions, this seems to be possible, but for others not at all. This is probably due to the fact that the bone ligament graft does not address the secondary stabilizers, which is not the aim of this technique.
In conclusion, this study showed a more detailed analysis of the pathological movement that occurs in the carpal structure after SL dissociation. Especially during wrist flexion, clenched fist, and radial deviation, an increased aberration of scaphoid and lunate from the native position is apparent. It can be assumed that the stress of the SL interval is greatest in these positions. We also demonstrated that the described radio-luno-triquetral bone-ligament transfer restores the pathological deviations in the corresponding wrist positions. In particular, the widened SL gap could be significantly reduced by the bone-ligament reconstruction.
Since the described surgical technique causes low donor-side morbidity, this surgical procedure can be considered in addition to the primary suture, if the quality of the SL ligament is doubtful. So far, we have little experience in the clinical use of this new bone-ligament transfer. It will have to be demonstrated, whether SL dissociation can be corrected in the long-term follow-up using this method. The biomechanical results are very promising.