No abstract

We studied the course of spontaneous healing of Achilles tendons in a sheep model after transection and partial resection of the tendon by means of histological and biomechanical analyses. In 18 sheep used for another animal study the operated knee had to be excluded from weight-bearing; therefore the Achilles tendons were transected and for 1.5 cm partially resected in the middle substance of the tendon. For evaluation these spontaneously healed tendons (n = 18) were compared with the contralateral noninvolved tendons (n = 18). Specimens were analyzed 3, 6, and 12 months postoperatively by means of histology, polarized light, angiography, and mechanically analyzing the specific tensile strength and absolute tensile strength. We found that in all animals the resected tendon healed spontaneously. All animals exhibited a normal gait pattern at least 6 weeks postoperatively. Histologically, the tendinous area of healing demonstrated after 3 months a fibrous collagenous tissue with a loose fiber orientation. The cross-sectional area had at 3 months increased to maximum but decreased later. Concomitantly the fiber orientation improved with time and 12 months after transection the specimens showed a nearly normal histological structure of the healed tendon. Biomechanically the specimens exhibited a rather low specific rupture force after 3 months (28.8% of normal tendons) and 6 months (30.2%) but increased after 12 months (56.7%). In regard to the resulting total rupture force the decrease in the spontaneously healed tendons was less (75.6% after 3 months, 56.1% after 6 months, 81.18% after 12 months), because the cross-sectional area of the healing tendon had significantly (P < 0.05) increased to maximum after 3 and 6 months. Sheep Achilles tendons thus healed spontaneously without any immobilization. The initial healing mechanism is thickening of the scar tissue with improvement of the fiber orientation towards a tendonlike structure within 1 year. Parallel to this, the specific rupture force increased and the thickness of the newly tendonlike area decreased.

Our aim was to examine the potential of autologous perichondral tissue to form a meniscal replacement. In 18 mature sheep we performed a complete medial meniscectomy. The animals were then divided into two groups: 12 had a meniscal replacement using strips of autologous perichondral tissue explanted from the lower rib (group G) and six (group C) served as a control group without a meniscal replacement. In all animals restriction from weight-bearing was achieved by means of transection and partial resection of tendo Achillis. Six animals (four from group G and two from group C) were each killed at 3, 6 and 12 months. The grafts and the underlying articular cartilage were removed and studied by gross macroscopic examination, light microscopy, SEM, polarised light examination, and by biomechanical tests. In all the transplanted animals a new perichondral meniscus developed. After three months the transplants resembled normal menisci in size and thickness, while in the control animals only small rims of spontaneously grown tissue were seen. Microscopically, the perichondral menisci showed a normal orientation of collagen fibres and normal cellular characteristics, but in the central region, areas of calcification disturbed the regular tissue differentiation. Healing tissue in control animals lacked the normal fibre orientation and cellularity. SEM of perichondral menisci showed surface characteristics similar to those of normal sheep menisci without fissures and lacerations; the control specimens had these defects. The femoral and tibial cartilage in contact with the new menisci had normal surface characteristics apart from one animal with slight surface irregularities. Control animals showed superficial lesions after three months which increased at six to 12 months postoperatively. Microangiography of the newly grown tissue demonstrated a less intense vascularisation after three months when compared with normal menisci. The failure stress and tensile modulus of perichondral menisci were significantly lower than those of normal contralateral menisci, and spontaneously regenerated tissue in meniscectomised animals had even lower values. There were no significant differences in values between newly grown perichondral menisci and spontaneously grown tissue.

Our aim was to examine the potential of autologous perichondral tissue to form a meniscal replacement. In 18 mature sheep we performed a complete medial meniscectomy. The animals were then divided into two groups: 12 had a meniscal replacement using strips of autologous perichondral tissue explanted from the lower rib (group G) and six (group C) served as a control group without a meniscal replacement. In all animals restriction from weight-bearing was achieved by means of transection and partial resection of tendo Achillis. Six animals (four from group G and two from group C) were each killed at 3, 6 and 12 months. The grafts and the underlying articular cartilage were removed and studied by gross macroscopic examination, light microscopy, SEM, polarised light examination, and by biomechanical tests.In all the transplanted animals a new perichondral meniscus developed. After three months the transplants resembled normal menisci in size and thickness, while in the control animals only small rims of spontaneously grown tissue were seen. Microscopically, the perichondral menisci showed a normal orientation of collagen fibres and normal cellular characteristics, but in the central region, areas of calcification disturbed the regular tissue differentiation. Healing tissue in control animals lacked the normal fibre orientation and cellularity. SEM of perichondral menisci showed surface characteristics similar to those of normal sheep menisci without fissures and lacerations; the control specimens had these defects. The femoral and tibial cartilage in contact with the new menisci had normal surface characteristics apart from one animal with slight surface irregularities. Control animals showed superficial lesions after three months which increased at six to 12 months postoperatively. Microangiography of the newly grown tissue demonstrated a less intense vascularisation after three months when compared with normal menisci.The failure stress and tensile modulus of perichondral menisci were significantly lower than those of normal contralateral menisci, and spontaneously regenerated tissue in meniscectomised animals had even lower values. There were no significant differences in values between newly grown perichondral menisci and spontaneously grown tissue. [Br] 1998;80-B:918-23. J Bone Joint Surg

In a cadaveric biostatic model the pressure distribution at the weightbearing ankle has been investigated under different joint positions and stages of artificial lateral ligament dissection mimicking a supination trauma. The location of the transduced contact area, the size of these areas and amount of pressure were evaluated after application of axial load. The results showed that the location, size of contact area and the maximum transduced pressure were depending on the joint position and stage of ligament dissection. Interestingly the peak pressure was located at the medial talar rim even without lateral ligament dissection. The transduced pressure areas were located at that locations were osteochondral lesions are mostly observed. In regard to these results the etiology and pathogenesis of osteochondritis dissecans tali is discussed. It is thought that supination traumas as well as other biomechanical factors such as overweight and lax ankle ligaments have an important influence on the development of osteochondritis dissecans at least at the medial rim of the talus.