The Discovery Of LC Complexes And Their Clinical Implications In Bone And Soft Tissue Tumors Around The Knee

Objectives:Bidirectional dissemination of bone and soft tissue tumors from the articular cavity to the metaphysis or even diaphysis is a typical clinical phenomenon in knee joint.The various lesion range caused by tumor dissemination will affect the appropriate surgical strategies.Generally,the mature articular cartilage is regarded as a barrier between intraosseous and intraarticular compartments in tumor spread,meanwhile,the growth plate is considered to be a barrier for transphyseal tumor extension in pediatric patients.However,such bidirectional tumor disseminations still occur in some situations.Due to the limited understanding of the anatomical structure of the knee joint,the tumor cells may conceal in undiscovered specific region of subchondral bone or epiphysis to escape from the surgical curettage or resection,resulting in tumor recurrence.Based on the above background,our group discovered a new-identified vasculature-canal structure called LC complex in the distal femur and proximal tibia of both adults and children using radiographical,anatomical and histological methodologies.This study aims to investigate the anatomical characteristics and clinical significance of adult and pediatric LC complex,and therefore enriches the anatomical and clinical basis for more effective treatment of bone and soft tissue tumors around the knee.Methods:(1)Two hundred knees(from 124 adults)were scanned under 1-mm-thick computed tomography(CT)and the reconstructed sagittal and coronal,and three-dimensional images were obtained.The occurrence and number of the foramen of the tibial intercondylar eminence(FTIE)and intercondylar fossa foramen(IFF)were recorded,so was their maximum diameters measured.On 50 reconstructed three-dimensional CT images which clearly showed the IFF and FTIE,a nine-zone model was established for the location analysis.(2)Based on magnetic resonance imaging(MRI),we measured the related parameters to determine the location information of adult LC complex on 100 images clearly showing FTIE and 100 images clearly showing IFF(from 142 adults).(3)The anatomical characteristics of the intraosseous segment of the LC complex were observed by dissecting 60 normal adult knee specimens.Each component of the adult femoral and tibial LC complex was stained by hematoxylin and eosin(HE)to observe its histological characteristics.(4)Twenty-eight pediatric knee joints(from 28 children)were scanned under 1-mm-thick MRI.The radiographic characteristics and parameters of pediatric LC complex were observed and measured,respectively.(5)The anatomical characteristics of the intraosseous segment of pediatric LC complex were observed by dissecting 10 normal intact knee specimens of children.The components of the pediatric femoral and tibial LC complex were sent for HE and immunofluorescence staining to observe the histological structural characteristics.(6)The radiographical,anatomical and pathological features of the LC complex were analyzed in 55 cases of adult knee joints with LC complex involved by tumor.(7)In 82 patients with primary giant cell tumor of bone(GCTB)in tibia or femur,we investigate whether the tumor involvement in subchondral LC complex(including FTIE or IFF)is a risk factor to facilitate the GCTB recurrence after curettage.(8)We analyze the typical clinical manifestations of femoral and tibial LC complexes in 38 pediatric patients with osteosarcoma.Meanwhile,the discrepancy in transphyseal osteosarcoma extension between different physeal regions was evaluated.Results:(1)The LC complex is composed of an epiphyseal and metaphyseal canal which encloses a blood vessel,FTIE or IFF,and foramen-covered synovium.In children with open physis,pediatric LC complexes originate from the intraarticular region,traverse the whole epiphysis and growth plate,and reach the metaphyseal region.In adults,there are usually 2-4 LC complexes in the femur,and the tibial LC complex usually locates behind the intercondylar eminence.(2)The FTIE and IFF were observed with 100%occurrence in 200 1-mm-thick CTs,and the average diameter of FTIE was 1.28±0.16 mm(200 foramina),while the average diameter of the IFF was 1.21±0.13 mm(588 foramina).(3)On 1-mm-thick MRI of 142 adult knee joints,both FTIE and IFF showed relatively fixed locations on anteroposterior and mediolateral lines.(4)The histological characteristics of adult femoral and tibial LC complexes were as follows:the walls of the FTIE and IFF mainly contained bone tissue,and the soft tissue covering the foramen was synovium.Bone lamellae and bone marrow cells were observed in the walls of the epiphyseal and metaphyseal canals,while small blood vessels were found within these canals.The vasculatures in adult femoral LC complex were shown as either small arteries or small veins,however,only small veins were found in adult tibial LC complex.(5)FTIE and IFF were observed in all 28 1-mm-thick MRIs showing pediatric knees,and their location information were similar to those in adults,which were located in the tibial intercondylar region or femoral intercondylar fossa,however,the pediatric LC complexes showed wider located range on anteroposterior line than adult LC complexes.(6)The pediatric LC complex can be divided into three types:femoral LC complex,anterior tibial LC complex,and posterior tibial LC complex.In addition,both the pediatric femoral LC complex and tibial LC complex show the "transphyseal phenomenon" that traverse through the whole epiphyseal and physeal region.(7)Osseous tissue,cartilaginous tissue and bone marrow cells were observed in the metaphyseal canals of pediatric LC complex with the histological features similar to the adjacent epiphyses.The canal enclosed blood vessel and peripheral connective tissue.The soft tissue covering the foramen was synovium.(8)The vasculature-canal in the pediatric LC complex completely interrupts the continuity of the growth plate,and there are no typical reserve,proliferative or hypertrophic zones in transphyseal segment of pediatric LC complex.(9)The pediatric anterior tibial LC complex contains the branch of the middle genicular artery,and the pediatric posterior tibial LC complex contains the tributary of the middle genicular vein.Meanwhile,there are both branches of the middle genicular artery and tributaries of the middle genicular vein in the pediatric femoral LC complex.(10)Tumor cells may conceal in LC canals to facilitate tumor recurrence when the tumor invades the femoral or tibial LC complex at the level of the subchondral bone.(11)Compared with the articular cartilage of medial condyle and lateral condyle,the femoral and tibial LC complexes show relatively weak resistance to tumor,which may facilitate the bidirectional tumor dissemination via the"bone-LC complex-articular cavity" model.(12)An retrospective analysis of the recurrence of 82 patients with primary GCTB in the tibia or femur showed that the tumor involvement of the subchondral LC complex is a risk factor for GCTB recurrence after curettage.(13)Based on the discrepancy between LC complex and articular cartilage when defending tumor invasion,the femoral and tibial LC complex may be conductive to the tumor extension to the articular cavity.(14)In both radiographical and pathological observations,osteosarcoma may transgress the growth plate via pediatric LC complex without damaging the peripheral physeal cartilage.Osteosarcoma confined to the metaphyseal region may also invade the pediatric LC complex.(15)Compared to bilateral condylar physes,more osteosarcomas transgressed the open growth plates through intercondylar regions in which ITC was located,showing a statistically significant.Conclusion:(1)The existence of femoral and tibial LC complex in adults and children was determined by radiographical,anatomical and histological methods.(2)There are both similarities and differences between pediatric LC complex and adult LC complex in radiography,anatomy and histology.Specifically,the pediatric LC complexes showed wider located range on sagittal direction than adult LC complexes on articular facet.The transphyseal segment of pediatric LC complex can completely break the continuity of growth plate,and the peripheral physeal chondrocytes are entirely interrupted.(3)The intraosseous LC canals may be the potential space for tumor concealment,which interfere with the complete intraoperative removal of tumor.(4)The FTIE and IFF may be "breakpoints" on articular facet,and therefore facilitate the tumor extension to articular cavity via LC complex.(5)Transphyseal osteosarcoma extension can occur via pediatric femoral or tibial LC complex,which can be regarded as a channel for tumor dissemination from the metaphysis to the epiphysis.(6)The discovery and clinical significance of LC complex in this study provides novel anatomical and clinical evidence for the diagnosis and surgical treatment of knee tumors in adults and children,and further large-scale clinical study will be beneficial to the prognosis of knee tumors.