[Biomechanical evaluation of stability of the volar capsular ligament complex]

To investigate the effect of the volar capsular ligament complex on stability of the wrist joint and to provide basic biomechanical theoretical criteria for clinic application of the external fixator.

Nine upper limbs specimens (left 6, right 3) were taken from fresh adult cadavers to make wrist joint-bone capsular ligament complex specimens. Firstly, soft tissues of forearms and hands were resected and capsular membranes and ligaments were reserved to make the bone-articular ligament complex (normal specimen). Secondly, the volar capsular ligament complex was cut off from radial malleolus to ulnar malleolus (impaired specimen). Thirdly, the impaired volar capsular ligament complex was uninterruptedly sutured by the use of 4# suture silk (repaired specimen). To simulate clinical operation with external fixator, the biomechanical test was done according to the sequence (normal, impaired, repaired, repaired and fixed, impaired and fixed). Statistical significance was analyzed through selected loads at the three different shifts (1.5, 2.0, 2.5 cm).

According to the sequence (normal, impaired, repaired, repaired and fixed, impaired and fixed), when the shift was 1.5 cm, the different respective loads were (60.74 +/- 20.60), (35.23 +/- 13.88), (44.36 +/- 20.78), (168.40 +/- 29.21) and (139.00 +/- 33.18) N, respectively. When the shift was 2.0 cm, the different loads were (138.46 +/- 12.93), (87.17 +/- 24.22), (97.52 +/- 23.29), (289.00 +/- 54.29) and (257.98 +/- 55.74) N, respectively. When the shift was 2.5 cm, the different loads were (312.87 +/- 37.15), (198.16 +/- 37.14), (225.66 +/- 30.96), (543.15 +/- 74.33) and (450.35 +/- 29.38) N, respectively. There was no statistically significant difference between the impaired and repaired specimens (P > 0.05). Similarly, there was statistically significant difference among the rest specimens (P < 0.05). The same statistical results were obtained when the two different shifts were compared. There was statistically significant difference at the three different shifts for the same specimen (P < 0.05).

Volar capsular ligament complex is an important anatomic structure to keep stability of the wrist joint. The carpal instability arises out of the injured complex. Repairing the injured complex only can not immediately restore stability of the wrist joint. The external fixator can effectively help to diminish the relative shift of the impaired capsular ligament complex, to reduce the load of the repaired complex and to protect the complex accordingly. The device plays an important role in maintaining stability of the wrist joint.