Destruction of joint homografts. An experimental study

Cartilage immunoprivilege depends on donor source and lesion location

The ability to repair damaged cartilage is a major goal of musculoskeletal tissue engineering. Allogeneic (same species, different individual) or xenogeneic (different species) sources can provide an attractive source of chondrocytes for cartilage tissue engineering, since autologous (same individual) cells are scarce. Immune rejection of non-autologous hyaline articular cartilage has seldom been considered due to the popular notion of "cartilage immunoprivilege". The objective of this study was to determine the suitability of allogeneic and xenogeneic engineered neocartilage tissue for cartilage repair. To address this, scaffold-free tissue engineered articular cartilage of syngeneic (same genetic background), allogeneic, and xenogeneic origin were implanted into two different locations of the rabbit knee (n=3 per group/location). Xenogeneic engineered cartilage and control xenogeneic chondral explants provoked profound innate inflammatory and adaptive cellular responses, regardless of transplant location. Cytological quantification of immune cells showed that, while allogeneic neocartilage elicited an immune response in the patella, negligible responses were observed when implanted into the trochlea; instead the responses were comparable to microfracture-treated empty defect controls. Allogeneic neocartilage survived within the trochlea implant site and demonstrated graft integration into the underlying bone. In conclusion, the knee joint cartilage does not represent an immune privileged site, strongly rejecting xenogeneic but not allogeneic chondrocytes in a location-dependent fashion. This difference in location-dependent survival of allogeneic tissue may be associated with proximity to the synovium.

STATEMENT OF SIGNIFICANCE

Through a series of in vivo studies this research demonstrates that articular cartilage is not fully immunoprivileged. In addition, we now show that anatomical location of the defect, even within the same joint compartment, strongly influences the degree of the resultant immune response. This is one of the first investigations to show that (1) immune tolerance to allogeneic tissue engineered cartilage and (2) subsequent implant survival are dependent on the implant location and proximity to the synovium.

Effect of tissue culture storage on the in vivo survival of canine osteochondral allografts

In vitro studies in our laboratory have shown that the biomechanical and biochemical characteristics of osteochondral grafts can be preserved for as long as 28 days under tissue culture conditions. This study represents an attempt to extend these results to an in vivo model. In adult mongrel dogs, either an autograft, a fresh allograft, or a stored allograft was placed in a standardized defect on the weight-bearing surface of the medial femoral condyle. The stored grafts were kept at 4 degrees C in tissue culture medium for 14 days prior to implantation. The animals were killed at 12 weeks. Cartilage from the contralateral knee served as a control. The modulus and permeability of the cartilage were assessed with confined compression creep tests. The collagen and glycosaminoglycan contents were measured, and the cartilage was analyzed histologically with hematoxylin and eosin and safranin O stains. Grossly, the cartilage appeared viable at harvest. The histologic results were similar in the treatment groups, with the same spectrum of mild degenerative changes being noted in each group. The glycosaminoglycan content was significantly less in the autograft group than in its control group and than in the fresh allograft group. The glycosaminoglycan content did not differ significantly between fresh and stored allografts. The collagen content, modulus, and permeability did not differ either between experimental and control groups or between graft types. Our results support the conclusion that osteochondral allografts can be stored for as many as 14 days without significantly affecting the results of the procedure.

The immunology of bone and cartilage transplantation

Bone tissue was one of the earliest human transplanted tissues, yet little is known about its transplant biology. For many years, bone and cartilage tissues were though to be immunoprivileged tissues because of the absence of acute rejection phenomenon. Advances in the understanding of transplant immunology of vascularized tissue grafts (kidney, heart, liver, etc) have led to a renewed interest in the immunobiology of bone and cartilage allograft transplantation. Since prosthetic materials used in orthopedic reconstructive surgery have a limited lifespan, there is great interest in the transplantation of bone and cartilage tissue. The first half of the article discusses transplant terminology, basic principles of immunology, and experimental studies on the immunogenicity of bone and cartilage tissue. The second half of the article discusses how allotransplanted bone and cartilage behaves in human transplants, storage and preservation techniques, and future directions in bone and cartilage transplantation.

Digital distraction lengthening followed by free vascularized epiphyseal joint transfer

This is the first report of combined digital distraction lengthening followed by free vascularized metatarsophalangeal joint transfer. This restored mobility, stability, length, and growth potential in the ring finger of the mutilated hand in a child.

Long-term follow-up of free vascularized joint transfers to the hand in children

Toe-to-hand vascularized joint transfers in four children were reviewed 6 to 8 years after operation (average, 6.6 years). Two children had vascularized metatarsophalangeal (MTP) joints. Both children have near normal active range of motion. The transferred epiphyses have provided a major contribution to digital growth. The other two children had second toe proximal interphalangeal (PIP) joints transferred to damaged hand joints. Active PIP joint extension has been disappointing, and the overall growth contribution of the transferred epiphysis has been small. We conclude that MTP to metacarpophalangeal vascularized joint transfer can provide painless, functional, stable motion, with near normal growth potential, and the usefulness of toe PIP to hand PIP joint transfer is limited by the inability to achieve good active extension and limited growth potential.

Free vascularized small joint transfer to the hand

Free vascularized digital joint transfers should provide joint stability, painless functional range of motion (ROM), tolerance of normal stresses without degeneration, and growth potential in children. In our department since 1977, seven transfers have been carried out in seven patients, including four children aged 4 to 11 years and three adults aged 19 to 46 years. Donor sites were the metatarsophalangeal joint of the second toe (four cases), the proximal interphalangeal (PIP) joint of the second toe (two cases), and the PIP joint of a useless amputated small finger (one case). Recipient sites were digital PIP and metacarpophalangeal (MP) joints (three cases each) and the MP joint of a thumb (one case). Six of the seven procedures were successful. There was retention of normal joint space and stable, painless functional ROM, while epiphyseal centers in the children remained open and showed normal growth. Follow-up ranged from 2 to 4.7 years, averaging 3.5 years. Some adherence of an associated extensor tendon has been observed. The feet have been asymptomatic. When digital joint replacement is required because of local causes of destruction, free toe joint transfer should certainly be considered in children and in young adults.