The connective-tissue envelope in revascularisation of patellar tendon grafts

Dorsal Skinfold Chamber Preparation in Mice: Studying Angiogenesis by Intravital Microscopy

Intravital microscopy represents an internationally accepted and sophisticated experimental method to study angiogenesis, microcirculation, and many other parameters in a wide variety of neoplastic and nonneoplastic tissues. Since 1924, when the first transparent chamber model in animals was introduced, many other chamber models have been described in the literature for studying angiogenesis and microcirculation. Because angiogenesis is an active and dynamic process, one of the major strengths of chamber models is the possibility of monitoring angiogenesis in vivo continuously for up to several weeks with high spatial and temporal resolution. In addition, after the termination of experiments, tissue samples can be excised easily and further examined by various ex vivo methods such as histology, immunohistochemistry, and molecular biology. This chapter describes the protocol for the surgical preparation of a dorsal skinfold chamber in mice as well as the method to implant tumors in this chamber for further investigations of angiogenesis and other microcirculatory parameters. However, the application of the dorsal skinfold chamber model is not limited to the investigation of neoplastic tissues. To this end, the investigation of angiogenesis and other microcirculatory parameters of nonneoplastic tissues such as tendons, osteochondral grafts, or pancreatic islets has been an object of interest.

Graft bending angle is correlated with femoral intraosseous graft signal intensity in anterior cruciate ligament reconstruction using the outside-in technique

BACKGROUND

The purposes of this study were as follows: 1) to determine the correlation between the bending angle of the anterior cruciate ligament (ACL) graft at the femoral tunnel and the magnetic resonance imaging (MRI) signal intensity of the ACL graft and 2) to analyze the difference in the MRI signal intensity of the reconstructed ACL graft in different areas of the graft after single-bundle hamstring autograft ACL (SB ACL) reconstruction using an outside-in (OI) technique with bone-sparing retro-reaming.

METHODS

Thirty-eight patients who underwent SB ACL reconstruction with the hamstring tendon autograft using the OI technique were enrolled in this study. All patients were assessed using three-dimensional computed tomography (CT) to evaluate femoral tunnel factors, including tunnel placement, tunnel length, tunnel diameter, and femoral tunnel bending angle. At a mean of 6.3±0.8months after surgery, 3.0-T MRI was used to evaluate the graft signal intensity using signal/noise quotient for high-signal-intensity lesions.

RESULTS

Among various femoral tunnel factors, only the femoral tunnel bending angle in the coronal plane was significantly (p=0.003) correlated with the signal/noise quotient of the femoral intraosseous graft. The femoral intraosseous graft had significantly (p=0.009) higher signal intensity than the other graft zone. Five cases (13.2%) showed high-signal-intensity zones around the femoral tunnel but not around the tibial tunnel.

CONCLUSION

After ACL reconstruction using the OI technique, the graft bending angle was found to be significantly correlated with the femoral intraosseous graft signal intensity, indicating that increased signal intensity by acute graft bending might be related to the maturation of the graft.

LEVEL OF EVIDENCE

This was a retrospective comparative study with Level III evidence.

Evaluation with contrast-enhanced magnetic resonance imaging of the anterior cruciate ligament graft during its healing process: a two-year prospective study

OBJECTIVE

The aim of this study was to evaluate, with contrast-enhanced-magnetic resonance imaging (MRI), the changing imaging appearance of an anterior cruciate ligament (ACL) graft during the revascularization phase by quantitatively assessing the morphological and signal intensity changes taking place at its cross-sectional surface over time.

MATERIALS AND METHODS

Fifty patients underwent contrast-enhanced-MRI on the third postoperative day and at a mean of 6, 12, and 24 months time interval after surgery. Proton-density images were obtained to evaluate morphological and signal intensity characteristics. Oblique-axial T1-weighted images obtained before and after intravenous gadolinium administration were used for quantitative analysis. Enhancement index (EI: signal-to-noise quotient(after gadolinium)÷signal-to-noise quotient(before gadolinium)) and cross-sectional area (CSA) were calculated for two regions of interest: the transplanted graft and its surrounding hypervascular tissue, and at three distinct graft sites (intra-articular, intraosseous tibial tunnel, and intraosseous juxta screw sites). Comparisons of EI and CSA at every site and time interval were performed using analysis of variance.

RESULTS

A variable MRI appearance of the graft during the different time intervals was attributed to the varying amount of the hypervascular tissue gradually surrounding the graft. Graft EI and peripheral tissue CSA progress in a parallel, time- and site-related pattern along the graft course. The initial heterogeneity with intermediate signal intensity at the intra-articular graft site reflected intense revascularization. A slower revascularization progress was noticed at the other two intraosseously enclosed sites.

CONCLUSION

During the healing process the amount of revascularization tissue influences the MR imaging characteristics of the graft according to the examined site and the time interval after surgery. By 2 years postoperatively, revascularization completion coincides with the homogeneously low signal intensity of the graft, closely resembling native ACL.

Revascularization process of the bone--patellar tendon--bone autograft evaluated by contrast-enhanced magnetic resonance imaging 6 and 12 months after anterior cruciate ligament reconstruction

BACKGROUND

Contrast-enhanced magnetic resonance imaging (MRI) studies conducted on animal models have shown that the observed signal intensity changes are related to the degree of graft vascularity and its biomechanical properties.

PURPOSE

To evaluate by contrast-enhanced MRI the revascularization process at 3 distinct sites discerned in relation to the surrounding microenvironment along the course of bone-patellar tendon-bone (BPTB) autograft in uncomplicated human anterior cruciate ligament (ACL)-reconstructed knees.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Thirty-two male patients were assessed with a 3-dimensional fast field echo/short tau inversion recovery (FFE/STIR) MRI sequence at the third postoperative day and at time intervals of 6 and 12 months after surgery. Signal-to-noise quotient (SNQ) was calculated for 3 specific graft sites (intra-articular site, intraosseous tibial tunnel site, and intraosseous juxta screw site) before and after gadolinium administration. Comparisons of the enhancement index (EI: SNQ(after)/SNQ(before) gadolinium) were performed independently for each graft site and time interval.

RESULTS

Three days postoperatively, insufficient vascularization was noticed at the 3 sites. Six and 12 months after surgery, the enhancement index was significantly increased in all 3 sites (P < .001). The intra-articular site, 6 months postoperatively, achieved satisfactory contrast medium uptake (enhancement index >1), with significantly higher enhancement index values compared with the other 2 sites (P < .001). Twelve months after surgery, only the intraosseously enclosed sites displayed an increase of the enhancement index, although nonsignificant (P = .09 and P = .07, respectively).

CONCLUSION

Revascularization of the graft occurs gradually along its length, with the intra-articular site being the first and the faster part to complete this phase, while both the intraosseous sites are still in progress throughout the first postoperative year. Revascularization is an important link at the intrinsic healing chain of the ACL graft. The surrounding microenvironment does seem to play a significant role in this process, and the differences in its composition along the graft course are reflected at the revascularization progress of the corresponding sites.

Emerging ideas: soft tissue applications of radiostereometric analysis

BACKGROUND

Currently, the movement that occurs at the site of soft tissue repair cannot be measured accurately in vivo. Radiostereometric analysis (RSA) is the gold standard for measuring movement between two skeletal segments in vivo but its application to studying soft tissue migration has been limited by the unknown stability of tantalum beads in tendons and ligaments and their ability to define rigid bodies in these structures.

HYPOTHESIS

RSA can be used to accurately measure movement between two tendon segments or between a bony and a tendon segment in vivo.

METHODS OF STUDY

The stability of tantalum beads and the ability to use such beads to define rigid bodies in some soft tissues will be investigated in animal models of tendon repair. Several tantalum bead insertion techniques will be tested using in vivo RSA measurements of bead movement followed by morphologic studies of the repaired tendon and soft tissue reaction to the tantalum beads.

SIGNIFICANCE

RSA performed on tantalum beads encapsulated in muscles and tendons could be a powerful new tool to study the in vivo motion at the site of soft tissue repairs, for instance, the tendon gap formation. If RSA could be used to evaluate the efficiency of different tendon repair techniques in vivo, enhanced rehabilitation protocols could be developed and complications associated with prolonged protection or failure of repair could be reduced.

Ligamentization of tendon grafts treated with an endogenous preparation rich in growth factors: gross morphology and histology

PURPOSE

To investigate whether the application of a particular platelet-rich plasma preparation rich in growth factors (PRGF) during anterior cruciate ligament (ACL) surgery gives a potential advantage for better tendon graft ligamentization.

METHODS

This study included 37 volunteers who underwent either conventional (control group, n = 15) or PRGF-assisted (n = 22) ACL reconstruction with an autogenous hamstring and required second-look arthroscopy to remove hardware or loose bodies, treat meniscal tears or plica syndrome, or resect cyclops lesions at 6 to 24 months after ACL surgery. The gross morphologies of the grafts were evaluated on second-look arthroscopy by use of the full arthroscopic score (0 to 4 points) to evaluate graft thickness and apparent tension (0 to 2 points) plus synovial coverage (0 to 2 points). At the same time, biopsy specimens were harvested uniformly from the grafted tendons. In these specimens the histologic transformation of the tendon graft to ACL-like tissue was evaluated by use of the Ligament Tissue Maturity Index, and a score to assess the progression of new connective tissue enveloping the graft was created by use of 3 criteria previously used to characterize changes during ligament healing: cellularity, vascularity, and collagen properties.

RESULTS

The overall arthroscopic evaluation of PRGF-treated grafts showed an excellent rating in 57.1% of the knees (score of 4) and a fair rating in 42.9% (score of 2 or 3). In contrast, evaluation of untreated grafts showed an excellent rating in 33.3% of the knees, a fair rating in 46.7%, and a poor rating in 20% (score of 0 or 1). Overall, arthroscopic evaluations were not statistically different between PRGF and control groups (P = .051). PRGF treatment influenced the histologic characteristics of the tendon graft, resulting in tissue that was more mature than in controls (P = .024). Histologically evident newly formed connective tissue enveloping the graft was present in 77.3% of PRGF-treated grafts and 40% of controls. The appearance of the connective tissue envelope changed with increasing time from surgery. On the basis of the histologic findings, we suggest that the remodeling of PRGF-treated grafts involves the formation of synovial-like tissue enveloping the graft. This tissue is eventually integrated in the remodeled tendon graft, conferring a similar appearance to the normal ACL.

CONCLUSIONS

The use of PRGF influenced the histologic characteristics of tendon grafts, resulting in more remodeling compared with untreated grafts. We have shown temporal histologic changes during the 6- to 24-month postoperative period of graft maturation, with newly formed connective tissue enveloping most grafts treated with PRGF.

LEVEL OF EVIDENCE

Level III, case-control study.

The dorsal skinfold chamber: studying angiogenesis by intravital microscopy

Intravital microscopy represents an internationally accepted and sophisticated experimental method to study angiogenesis, microcirculation, and many other parameters in a wide variety of neoplastic and nonneoplastic tissues. Since 1924, when the first transparent chamber model in animals was introduced, many other chamber models have been described in the literature for studying angiogenesis and microcirculation. Because angiogenesis is an active and dynamic process, one of the major strengths of chamber models is the possibility of monitoring angiogenesis in vivo continuously for up to several weeks with high spatial and temporal resolution. In addition, after the termination of experiments, tissue samples can be excised easily and further examined by various in vitro methods, such as histology, immunohistochemistry, and molecular biology. This chapter describes the protocol for the surgical preparation of a dorsal skinfold chamber in mice as well as the method to implant tumors in this chamber for further investigations of angiogenesis and other microcirculatory parameters. However, the application of the dorsal skinfold chamber model is not limited to the investigation of neoplastic tissues. To this end, the investigation of angiogenesis and other microcirculatory parameters of nonneoplastic tissues such as tendons, osteochondral grafts, or pancreatic islets have been objects of interest.

Biomaterials and scaffolds for ligament tissue engineering

Tissue engineering has achieved much progress in an attempt to improve and recover impaired functions of tissues and organs. Although many studies have been done, progress for tissue-engineered anterior cruciate ligaments (ACLs) has been slow due to their complex structures and mechanical properties. In this review, the ACL anatomical structure, progresses achieved, material selection, structure design, and future direction have been discussed, while the challenges and requirements from materials and scaffolds are highlighted. There is a considerably huge amount work that needs to be carried out; as such, future direction in ligament tissue engineering is proposed in hope that this review will give information on future ligament tissue engineering.

The avascular talus: revascularization in an animal model

Avascular necrosis of bone such as the talus can lead to collapse and loss of function. To avoid this, early revascularization has been proposed as an important event. Revascularization can occur either by vessel growth directly through the bony surface, or by vessel growth into the periosteum or ligaments with secondary reconnection to the bone. The ability to attract new vessels (angiogenesis) of the bony surface and the connective tissue was compared in an animal model. A talus isograft (all cortical surface, periosteum, and ligaments remaining; n = 11) or a sector of a femoral head isograft (cancellous surface, no connective tissue; n = 12) of adult mice was implanted into dorsal skinfold chambers of mice of the same strain. The implants were observed by intravital microscopy every 12 hours. First indicators of angiogenesis were hemorrhages around the implants (tali: 11 of 11, 72 +/- 12 hours; femoral heads: 6 of 12, 84 +/- 24 hours). Next, a sudden redness of the transplant indicated marrow hemorrhage (tali: 9 of 11 after 84 +/- 36 hours; femoral heads: 10 of 12 after 96 +/- 36 hours). Histology showed clear growth of capillaries into the cancellous surface of the femoral heads and possible growth of capillaries into the ligament stumps (tali). However, there was widespread necrosis of the marrow cells indicating failure of recirculation. A cancellous bony surface as well as the soft tissues attached to the bone provided a stimulus to rapid revascularization of the grafts. This model was able to evaluate differing rates of early partial revascularization for various bone surfaces, which may have implications for studying treatment options for certain fracture dislocations (e.g., in the talus).