The Morphological And Bio-mechanic Study Of Resection Arthroplasty Of Talus With Or Without Tendon Ball Interposition In Rabbits

Objectives: carpal bone excision and tendon ball interposition is a treatment for carpal bone necrosis, arthritis and old scaphoid fracture, which is always required for tendon ball interposition to prevent carpal collapse after carpal bone excision. But recent clinical trials revealed that the tendon balls packed into the carpal joint can't resist the pressure from the carpals, carpal collapse usually occurred, and cause disastrous complication. So the biomechanical property of the tendon balls after interposition is correlated to the effect of the operation tightly. But little research was carried out in this area. In our experiment, we build an animal model by rabbit's talus excision and achilles's tendon ball interposition, and given a 32-week follow-up to expect the fate of tendon ball's histological and biomechanical property after carpal bone excision and tendon ball's interposition in human being.Methods: 28 rabbits of either sex, aged 4 to 6 months, were recruited, and divided into 7 groups (4 rabbits per group), the rabbit's talus was excised and implanted with achilles's tendon ball. the procedure was described briefly as below: made a longitudinal middle incision in the ankle joint of the rabbit, opened the joint, exposed and excised the talus completely by a sharp scalpel, after that, made a longitudinal posterior-lateral incision in the hind leg, and harvested half of the Achilles'tendon and sutured into a tendon ball, full it in the cavity of the ankle joint. After 2﹑ 4﹑ 6﹑ 8﹑ 16﹑ 24﹑ 32 weeks postoperatively, the rabbits were sacrificed by air injection intravenously and the implanted tendon balls were harvested, the diameters of tendon balls, stress degree and histological character of the tendon balls were evaluated independently.Result: the tendon balls were necrotized immediately after 2-4 weeks, revascularized and infiltrated by inflammatory cells and fibroblast cells in following weeks, and replaced completely by granulation tissues in 16 weeks, after that, the granulation tissues were scared. Biomechanically, the tendon ball's stress character was calculated as Green's modulus, which was in inverse proportion to the tissue's hardness, after interposition, the tendon balls Green's modulus were increase with the time and reached the maximum in 16 weeks which were 40% compared with 2 weeks postoperatively, and then reduced gradually, in 32 weeks, the Green's modulus of tendon balls were achieved the degree of 2 weeks postoperatively.Conclusions: By our observation, the histological changes of the tendon balls after operation were the same as other's reports: the tendon balls were necrotized, disintegrated, inflammatory infiltrated, and replaced by granulation tissue. The tendon balls implanted into the joint of which diameter was from 0.53 to 0.6 cm, and necrotized completely in 16 weeks post-operatively, and hyaline degenerated eventually, In the mean time, the inflammatory cells and neo-vessels were infiltrated from the synovium, and in 24 weeks, the tendon balls can be replaced completely by the granulation tissue, then the granulation tissue became scar and became much stiffer.But, there is no any sign of calcification or ossification in our experiments, even in 32 weeks post-operatively.The biomechanical property of the tendon balls were correlated tightly to their histological changes, when the tendon balls replaced by the granulation tissue, the tendon balls'hardness decreased, and the deformity increased under 200N constant stress. In 16 weeks, the tendon balls were replaced by the granulation tissue totally, the hardness of tendon balls reached the minimum point, about 40% of the hardness in 2 weeks, then with the granulation tissue becoming scar, the hardness of the tendon balls'increase, and in 32 weeks, it can reach the level of hardness in 2 weeks.When implanted into the carpals in the early time, the tendon balls will prevent carpal collapse efficiently, but with the tendon's granulation, tendon balls became much softer and not qualified for the joint support, carpal collapse will occur, when the tendon's granulation complete and scared, the hardness of tendon balls will be revived, and its will spend 32 weeks. So, the tendon balls should be large enough to fill the carpal cavity efficiently, and the tendon balls with a bone core or growth factor could have more promising effect.