【Abstract】 Objective To investigate the effect of the volar capsular l igament complex on stabil ity of the wrist jointand to provide basic biomechanical theoretical criteria for cl inic appl ication of the external fixator. Methods Nine upperl imbs specimens (left 6, right 3) were taken from fresh adult cadavers to make wrist joint-bone capsular l igament complex specimens. Firstly, soft tissues of forearms and hands were resected and capsular membranes and l igaments were reserved to make the bone-articular l igament complex (normal specimen). Secondly, the volar capsular l igament complex was cut off from radial malleolus to ulnar malleolus (impaired specimen). Thirdly, the impaired volar capsular l igament complex was interruptedly sutured by the use of 4# suture silk (repaired specimen). To simulate cl inical 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). Results 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 gt; 0.05). Similarly, there was statistically significant difference among the rest specimens (P lt; 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 lt; 0.05). Conclusion Volar capsular l igament complex is an important anatomic structure to keep stabil ity of the wrist joint. The carpal instabil ity arises out of the injured complex. Repairing the injured complex only can not immediately restore stabil ity of the wrist joint. The external fixator can effectively help to diminish the relative shift of the impaired capsular l igament complex, to reduce the load of the repaired complex and to protect the complex accordingly. The device plays an important role in maintaining stabil ity of the wrist joint.
To evaluate the changes in stabil ity of the wrist after experimental traumatic triangular fibrocartilage complex (TFCC) lesions, and to provide basic theoretical criteria for cl inical treatment. Methods Fourteen adult cadaver upper extremities specimens were included. Two of 14 specimens were tested in pre-experiment. The specimens were tested in a INSTRON 8874 biomechanics measuring instrument. First a dorsal arthrotomy (ART) was performed, and second test was with 1 of 4 different experimental lesions according to Palmer’s classification of traumatic TFCC lesions (n=3). 1A: central perforation; 1B: ulnar avulsion with or without fracture of processus styloideus ulnae; 1C: distal avulsion with l igament injury; 1D: radial avulsion. Forced internal∕external rotation torque were recorded in the interval — 60° to 60° of flexion. Results The average torque of the dorsal ART was (0.713 ± 0.121) Nm, and the 1B-1 lesion (ulnar avulsion without ulnar styloid fracture) was (0.709 ± 0.134) Nm, the 1B-2 lesion (ulnar avulsion with ulnar styloid fracture) was (0.409 ± 0.113) Nm. The difference between the 1B-1 lesion and the dorsal ART was not significant but the difference between the 1B-2 lesion and the dorsal ART was significant (P lt; 0.05). The average torque of the 1C lesion in about 45° of wrist extention and flexion were (0.878 ± 0.184) Nm and (0.988 ± 0.197) Nm, and the dorsal ART were (1.510 ± 0.173) Nm and (1.540 ± 0.093) Nm. The difference between the two groups was significant (P lt; 0.05). The 1A lesion and 1D lesion did not alter significantly wrist stabil ity. Conclusion The 1B-2 lesion and 1C lesion alter significantly the stabil ity of the wrist.
To provide the scientific theoretical basis for cl inical practice by comparing biomechanicalcharacteristics of single compressed plate with intramedullary pin, locking intramedullary nail and simple arm externalfixator with simple internal fixation devices. Methods Eighteen wet humeral bone specimens of adult cadaver were madecompl icated fracture models of humeral shaft and divided into 3 groups according to fixation methods. Fracture was fixed by single compressed plate with intramedullary pin in plate group, by locking intramedullary nail in intramedullary nail group and by external fixator with simple internal fixation devices in external fixator group. The intensity and rigidity of compl icated fracture models of humeral shaft was measured in compress test and torsion test. Results In compress test, the maximum load in plate group (6 162.09 ± 521.06) N and in intramedullary nail group (6 738.32 ± 525.89) N was significantly larger than that in external fixator group (2 753.57 ± 185.59) N (P lt; 0.05); but there was no significant difference between plate group and intramedullary nail group (P gt; 0.05). Under 600 N physiological compress load, the rigidity was (171.69 ± 6.49) N/mm in plate group, (333.04 ± 36.85) N/mm in intramedullary nail group and (132.59 ± 2.93) N/mm in external fixator group; showing no significant difference between plate group and external fixator group (P gt; 0.05), and showing significant difference between intramedullary nail group and plate, external fixator groups (P lt; 0.05). In torsion test, the maximum torque in plate group (38.24 ± 7.08) Nm was significantly larger than those in intramedullary nail group (17.12 ± 5.73) Nm and external fixator group (20.26 ± 6.42) Nm (P lt; 0.05), but there was no significant difference between intramedullary nail group and external fixator group (P gt; 0.05). Under 0.80 Nm physiological torque, the rigidity was (16.36 ± 2.07) Ncm/° in plate group and (18.79 ± 2.62) Ncm/° in external fixator group, which was significantly larger than that in intramedullary nail group (11.45 ± 0.22) Ncm/° (P lt; 0.05); but there was no significant difference between plate group and external fixator group (P gt; 0.05). Conclusion Those fracture models fixed by single compressed plate with intramedullary pin have better compress and torsion intensity, they also have better torsion rigidity but less compress rigidity. Those fracture models fixed by locking intramedullary nail have better compress intensity but less torsion intensity, they also have better compress rigidity but less torsion rigidity. Those fracture models fixed by external fixator with simple internal fixation device have less compress and torsion intensity, they also have less compress rigidity but better torsion rigidity.