Comparative effects of monopolar radiofrequency energy and conservative management of mechanical properties of elongated lateral collateral ligament in rabbits: an experimental study

The Effects of Irreversible Electroporation on the Achilles Tendon: An Experimental Study in a Rabbit Model

Background

To evaluate the potential effects of irreversible electroporation ablation on the Achilles tendon in a rabbit model and to compare the histopathological and biomechanical changes between specimens following electroporation ablation and radiofrequency ablation.

Methods

A total of 140 six-month-old male New Zealand rabbits were used. The animals were randomly divided into two groups, 70 in the radiofrequency ablation group and 70 in the electroporation group. In situ ablations were applied directly to the Achilles tendons of rabbits using typical electroporation (1800 V/cm, 90 pulses) and radiofrequency ablation (power control mode) protocols. Histopathological and biomechanical evaluations were performed to examine the effects of electroporation ablation and radiofrequency ablation over time.

Results

Both electroporation and radiofrequency ablation produced complete cell ablation in the target region. Thermal damage resulted in tendon rupture 3 days post radiofrequency ablation. In contrast, electroporation-ablated Achilles tendons preserved their biomechanical properties and showed no detectable rupture at this time point. The electroporation-ablated tendons exhibited signs of recovery, including tenoblast regeneration and angiogenesis within 2 weeks, and the restoration of their integral structure was evident within 12 weeks.

Conclusions

When applying electroporation to ablate solid tumors, major advantage could be that collateral damage to adjacent tendons or ligaments is minimized due to the unique ability of electroporation ablation to target the cell membrane. This advantage could have a significant impact on the field of tumor ablation near vital tendons or ligaments.

Small hook thread (Quill) and soft felt internal splint to increase the primary repair strength of lacerated rabbit Achilles tendons: biomechanical analysis and considerations for hand surgery

BACKGROUND

For the prevention of re-rupture during early healing phase, the primary repair strength of repaired lacerated tendons in hand surgery should be maximal and the reconstructed diameter minimal. Two new repair methods (small hook thread and internal splint) were assessed for strength and reconstructed diameter characteristics.

METHODS

Achilles tendons of 43 female New Zealand White rabbits were sectioned 2 cm above the calcaneus. Specimens were divided into 7 groups and repaired as follows: Kirchmayr method 2-strand with 4.0 polypropylene thread; Becker method 4-strand; 6-strand; internal splint; Kirchmayr method small hook 2-strand; Becker method small hook 4-strand, non-modified tendon. Load until failure, load until gap formation, gap length, cross-sectional area and failure stress were determined.

FINDINGS

The small hook 2-strand suture had 1.3 fold higher loads until failure compared to a conventional 2-strand suture, P<0.05. The internal splint had a similar load until failure (22 N (SD 6)) as the conventional 2-strand suture (23 N (SD 4)); around half the load until failure of the conventional 4-strand suture (38 N (SD 9)). Load until gap formation correlated positively with load until failure (y=0.65+3.6; r(2)=0.72). The running suture increased the cross-sectional area at the repair site by a factor of 1.3.

INTERPRETATION

Using a small hook thread instead of a 4.0 polypropylene thread significantly increases the primary repair strength with the same number of strands. Internal splints may be an alternative to conventional 2-strand sutures for bridging large gaps.

The effect of postoperative immobilization on the healing of radiofrequency heat probe modified tissue: assessment of tissue length, stiffness, and morphology

The effect of postoperative immobilization on the length, stiffness, and structure of connective tissue after radiofrequency probe shrinkage was examined in a rabbit patellar tendon model. Tendon lengths were measured before, immediately following, and 2, 4, and 8 weeks following heat application, with the contralateral tendon as a control. The animals were randomly assigned to three groups. In Group I, the controls, the animals were allowed free caged activity for 8 weeks. In Groups II and III, the experimental limb was immobilized at 15 degrees of knee flexion for 2 and 4 weeks, respectively, after which the animals were allowed 6 and 4 weeks of free caged activity. Changes in tendon length, stiffness, and cross-sectional area were compared using repeated measures ANOVA and differences between groups examined using Tukey's post-hoc analysis. Patellar tendon lengths were increased in all 3 groups at 8 weeks (P< .001). Tissue elongation was less extensive in group III compared to group I at 8 weeks (P< .001), while tissue cross-sectional area was decreased in both groups II and III compared to group I at 8 weeks (P< .001). All groups demonstrated decreases in tensile strength when compared to controls (P< .001). These findings suggest that postoperative immobilization is important following thermal shrinkage of connective tissue, as early activity can lead to stretching of the heat-modified tissue.

Mechanical changes induced by thermal stimulation in collagenous tissue

Radiofrequency thermal stimulation is used as a therapeutic procedure for joint laxity, but its thermal effects are still controversial. Although collagen shrinkage may be expected, this conclusion is empirical and not universally accepted. The purpose of this study was to investigate the mechanical response of collagen to thermal stimulation. A longitudinal cut was made in rabbit Achilles tendons previously marked with monofilament sutures. The distance between the sutures was measured before the cut, just after it was made, and after 8 weeks. The results did not show any shrinkage or significant change in tendon resistance to traction 8 weeks after thermal stimulation; however, comparison with the opposite, normal tendon revealed a statistically significant increase in tendon stiffness.