Porosity-graded hydroxyapatite ceramics to replace natural bone.

Porous hydroxyapatite HA bodies were prepared with an aim to simulate bone tissue morphology. By varying the characteristics of starting HA powders and the impregnation strategy of cellulosic sponges with rheologically optimized slurries, a wide range of physico-chemical and mechanical properties of the porous ceramics can be obtained. The samples were characterized microstructurally, by density and porosimetry and by mechanical strength. Cylindrical specimens exhibiting a porosity gradient showed a promising behaviour after implantation in rabbits' femur: newly formed bone grew in tight contact with the ceramic in a very short time, no modified cells are induced and bone tissue fills even the inner pores.

Tibial plateau fracture after arthroscopic anterior cruciate ligament reconstruction.

Complications have been described with each technique for reconstruction of the anterior cruciate ligament (ACL) in the knee, both open and arthroscopically assisted. The authors describe a case of tibial plateau fracture occurring 7 months after an ACL reconstruction using the half tunnel technique. The fracture occurred at the tibial fixation site and required open reduction with internal fixation. To our knowledge, only 2 cases of proximal tibial fracture after patellar tendon autograft ACL reconstruction have been previously reported. The authors hypothesize that patellar tendon harvesting with bone blocks and transosseous tibial tunnel can produce a "stress riser" effect and somehow act synergistically to create decreased strength at the level of proximal tibial metaphysis.

Light and scan electron microscopic analysis of cyclops syndrome: etiopathogenic hypothesis and technical solutions.

The loss of range of motion after anterior cruciate ligament (ACL) reconstruction is one of the most common and most challenging complications of this kind of surgery. Recently, an intercondylar notch fibrous proliferation, called cyclops syndrome because of its arthroscopic appearance, has been identified as one of the specific causes of loss of extension. The incidence of cyclops syndrome is 2%-4% [17, 18], but there is still no understanding of its etiology. We speculate on the etiology and suggest some technical solutions to reduce this complication. In 180 patients submitted to arthroscopic ACL reconstruction with patellar tendon, we observed in 4 cases a fibrous nodule adherent to the neoligament that caused a loss of extension between 12 degrees and 17 degrees. In all cases, arthroscopic removal of this nodule solved completely the loss of articular motion. The nodules were subjected to light and scanning electron microscope evaluation. We observed numerous, newly formed vessels in all 4 nodules. These vessels were made up of hyperplastic and hypertrophic cells and were surrounded by bundles of disorganized fibrous tissue. No inflammatory cells or bone or cartilaginous tissue was observed. We hypothesize a microtraumatic genesis for cyclops syndrome. Repeated microtraumas expose the graft collagen fibers, which can lead to productive inflammatory process and thence to the formation of the cyclops nodule. We suggest some technical solutions to avoid graft impingement with the notch and with the tibial bone tunnel.

Bone-ligament interaction in patellar tendon reconstruction of the ACL.

The bone-ligament junction is one of the most complex biological tissues. Its key function is distribution of mechanical loads applied to the ligament in such a way as to diminish the concentration of stresses or shearing at the interface. This paper reports an experimental assessment of the extent to which a nearly normal junction is formed following reconstruction of the anterior cruciate ligament (ACL) with patellar tendon in 20 New Zealand white rabbits sacrificed after 2-38 weeks. A histological comparison was also made with cadaver ACLs. After 5 weeks the new ligament was still separate from the tunnel wall, inflammation was no longer present, and there was no junction tissue. A thin fibrocartilage layer was observed between the bone and the ligament after 12 weeks and was thicker 6 weeks later. After 28 weeks, there was a substantial layer of fibrocartilage. The new junction was virtually "physiological" by the 38th week, with all four layers present. Many fibrocartilaginous cells were also visible between the collagen fibres. The bone-ligament insertion was almost normal. These findings indicate that tendon reconstruction results in the formation of a structure very similar to a physiological junction, and thus ensures better load distribution over a greater ligament insertion area.

The bone-ligament junction: a comparison between biological and artificial ACL reconstruction.

The physiological bone-ligament junction is composed of four zones: ligament, fibrocartilage, calcified fibrocartilage and bone. It plays a very important part in the distribution of mechanical loads applied to ligaments so as to diminish stress concentration or shearing at the interface. This paper examines types of bone and neoligament insertion after anterior cruciate ligament (ACL) reconstruction with a Dacron prothesis, the Leeds-Keio scaffold ligament (LK), patellar tendon with LAD augmentation (PT+LAD) and bone patellar tendon bone alone (PT). The anterior cruciate reconstructions were implanted in 16 sheep via double-isometric bone tunnels without postoperative knee immobilization. Histological examination of the new insertions (using haematoxylin-eosin, Giemsa, Masson, and Mallory stains) was performed following animal sacrifice after 2, 3, 6 and 9 months. A layer of fibrocartilage between the bone and the ligament was observed with PT, followed by a nearly normal insertion after 6 months. With PT, followed by PT+LAD, the augmentation was surrounded by fibrous tissue (also noted inside the LAD). The PT insertion was virtually physiological after 3-6 months. With the LK scaffold, fibrous tissue was noted in and around the scaffold, even after 6 and 9 months. With the Dacron prosthesis, fibrous tissue around the ligament was unaccompanied by ingrowth into the prosthesis. Nerve endings (pacinian corpuscles) were only present in the PT. These findings show that even after 9 months artificial ligaments are separated from bone by fibrous tissue and devoid of the histological and biomechanical features of a physiological junction.(ABSTRACT TRUNCATED AT 250 WORDS)