Determination of the in situ forces in the human posterior cruciate ligament using robotic technology. A cadaveric study

We examined the in situ forces in the posterior cruciate ligament as well as the force distribution between its anterolateral and posteromedial bundles. Using a robotic manipulator in conjunction with a universal force-moment sensor system, we applied posterior tibial loads from 22 to 110 N to the joint at 0 degrees to 90 degrees of knee flexion. The magnitude of the in situ force in the posterior cruciate ligament and its bundles was significantly affected by knee flexion angle and posterior tibial loading. In situ forces in the posterior cruciate ligament ranged from 6.1 +/- 6.0 N under a 22-N posterior tibial load at 0 degree of knee flexion to 112.3 +/- 28.5 N under a 110-N load at 90 degrees. The force in the posteromedial bundle reached a maximum of 67.9 +/- 31.5 N at 90 degrees of knee flexion, and the force in the anterolateral bundle reached a maximum of 47.8 +/- 23.0 N at 60 degrees of knee flexion under a 110-N load. No significant differences existed between the in situ forces in the two bundles at any knee flexion angle. This study provides insight into the knee flexion angle at which each bundle of the posterior cruciate ligament experiences the highest in situ forces under posterior tibial loading. This information can help guide us in more accurate graft placement, fixation, and tensioning, and serve as an assessment of graft performance.

Engineering the healing of the rabbit medial collateral ligament

A biological approach to improve healing of the medial collateral ligament (MCL) was investigated by exploring the use of therapeutic growth factors based on in vitro and in vivo experiments. The in vitro cell culture studies involved screening a variety of growth factors to select those that exhibit the most positive effects on cell proliferation and extracellular matrix synthesis. The selected growth factors were applied in vivo to a rabbit model where the MCL was ruptured. Biomechanical and histological evaluations are performed to determine whether the selected growth factors can enhance the properties of the healed MCL, whether these improvements are dose dependent, and whether combinations of growth factors can enhance MCL healing to a greater extent than individual growth factors. In vitro studies showed that epidermal growth factor (EGF) and platelet derived growth factor-BB (PDGF-BB) have the greatest effect on ligament fibroblast proliferation, whereas transforming growth factor-beta 1 (TGF-beta 1) superiorly promotes extracellular matrix synthesis. These growth factors were then applied in vivo at different dosages, in isolation and in combination, and the ligaments were evaluated six weeks post-operatively. Tensile testing of the femur-MCL-tibia complexes (FMTCs) revealed that the specimens treated with a high dose of PDGF-BB have ultimate load, ultimate elongation and energy absorbed to failure values that are significantly greater than those from the other groups. The high dose of PDGF-BB was more effective than the low dose, indicating a dose dependency. The addition of TGF-beta 1 to PDGF-BB did not lead to any further increases in the structural properties of the FMTC. These encouraging results suggest that PDGF-BB may be a potential growth factor to enhance the quality of the healing ligament.

Quantitative anthropometry of the subatlantal cervical longitudinal ligaments

STUDY DESIGN

The quantitative anthropometry of the cervical longitudinal ligaments was determined in 20 human cadaveric subatlantal cervical spines at the limits of flexion and extension.

OBJECTIVES

To provide measurements of cervical anterior and posterior longitudinal ligament lengths, widths, and cross-sectional areas at segmental levels.

SUMMARY OF BACKGROUND DATA

Although mathematical models of the cervical spine require specific data to predict kinematics, the anthropometry of the cervical spine has not been examined in detail. The dimensional changes of ligaments in physiologic motion are not well characterized.

METHODS

Segmental lengths and widths of the cervical longitudinal ligaments were measured in sagittal plane flexion and extension, using a three-dimensional electromagnetic digitizer. The cross-sectional areas of the ligaments at resting length were measured with a laser micrometer system. Comparisons between anterior and posterior location and among segmental levels were made. Several ligaments were examined histologically to determine the insertion sites and, thus, to define the segmental length.

RESULTS

The anterior longitudinal ligaments were shorter in flexion than in extension. In extension, they were longer than the posterior longitudinal ligaments in flexion. The resting isolated ligaments were longer than the longest in situ lengths at several vertebral levels. The anterior longitudinal ligaments were wider at the disc than at the body. The cross-sectional area at C2-C3 was smaller than at subaxial levels. The longitudinal ligaments were observed to insert along the entire underlying vertebral body.

CONCLUSIONS

The quantitative anthropometry of the cervical longitudinal ligaments is important in the development of accurate mathematical models of the cervical spine. The in situ ligaments may not be under tension in the physiologic range of motion.

A dynamic analysis of glenohumeral motion after simulated capsulolabral injury. A cadaver model

We used a dynamic shoulder-testing apparatus and nine fresh-frozen, entire upper extremities from cadavera to evaluate the effects of varying degrees of capsulolabral injury on the kinematics of the glenohumeral joint during abduction in the scapular plane and external rotation. Joint kinematics were recorded with use of a six-degrees-of-freedom magnetic tracking device before and after the creation of each capsulolabral lesion in a progressive manner. Dislocation did not occur after simulation of a large Bankart lesion or even after sectioning of the anterior aspect of the joint capsule. However, division of the entire joint capsule (that is, both the anterior aspect and the posterior aspect) resulted in a significant increase (p < 0.05) in posterior translation during abduction in the scapular plane, and two of the nine shoulders dislocated posteriorly. External rotation of the abducted extremity produced no increase in anterior or posterior translation.

The efficacy of adenovirus-mediated gene therapy of ovarian cancer is enhanced by using the cytomegalovirus promoter

The cytomegalovirus(CMV) promoter is considered one of the strongest positive regulators. In this study toxicity, cell killing efficacy and bystander effect of Rous Sarcoma Virus(RSV) driven herpes simplex thymidine kinase(TK) gene therapy was compared with CMV driven TK gene therapy in three ovarian cancer cell lines with different growth patterns using a 3-(4,5-dimethylthiazol)-2,5-diphenyl tetra-zolium bromide (MTT) based assay. ADV/CMV-TK was shown to be 2 to 10 times more effective in tumor cell killing than ADV/RSV-TK. The difference in cell killing efficacy between ADV/CMV-TK and ADV/RSV-TK was dependent on the individual cell line. A CMV promoter dependent eight to ten fold improvement in cell killing efficacy was observed in the relatively slow growing SKOV3 cell line which is not easily transducible, while only a 2 to 4 fold difference was observed in the easily transducible OV-CA-2774 and OV-CA-1225 cell lines. ADV/CMV-TK also showed a stronger bystander effect than ADV/RSV-TK in all three ovarian cancer cell lines. Our data demonstrated that the efficacy of adenovirus-mediated gene therapy of ovarian cancer can be enhanced by using the CMV promoter without increasing toxicity.

The effects of proximal load on the excursion of autogenous flexor tendon grafts

To determine the relationship between the intrinsic properties of tendon and tendon excursion in 2 types of autogenous tendon grafts, hindpaw intrasynovial and extrasynovial tendons were transferred to the lateral and medial forepaws of adult mongrel dogs (16 experimental and 16 control tendons). After each digit was marked with radiopaque markers, it was placed in a specialized jig, and weights of 25 g, 100 g, or 200 g were applied to the flexor tendons. Specialized radiographs were obtained with the digit in flexion and extension. Tendon excursion and joint rotation were calculated. There were no statistically significant differences between experimental groups for tendon excursion or for joint angular rotation (p > .05). For intrasynovial tendon grafts, the angular rotation per millimeter tendon excursion was 10.9 degrees +/- 2.4 degrees/mm, 9.4 degrees +/- 1.2 degrees/mm, and 9.0 degrees +/- 1.4 degrees/mm with 25-g, 100-g, and 200-g loads, respectively. Comparisons between experimental groups revealed that a statistically significant difference could not be determined (p > .05). With varying proximal loads, both intrasynovial and extrasynovial grafts showed similar amounts of tendon excursion. Variations in proximal load did not significantly influence the amount of excursion within the range of loads tested. Based on these data, it appears that the difference in repair potential for these 2 types of tendon grafts is not related to a differential in the amount of tendon graft excursion following transfer to the synovial space.

Local inflammatory response and vector spread after direct intraprostatic injection of a recombinant adenovirus containing the herpes simplex virus thymidine kinase gene and ganciclovir therapy in mice

We have evaluated the safety and potential toxicity of an adenoviral vector containing the herpes simplex virus thymidine kinase gene (adenovirus/Rous sarcoma virus thymidine kinase in a preclinical model for prostate cancer. Clinical grade vector prepared for human trials was injected directly into the dorsolateral prostate of C57Bl/6 mice in a volume of 5 microL at doses of 2.5 x 10(6), 2.5 x 10(7), or 2.5 x 10(8). The mice received intraperitoneal injections of either ganciclovir or saline twice daily for 6 days, beginning 12 hours after vector injection. Representative tissues and fluids were collected for evaluation the day after the final dose. Microscopic pathologic evaluation revealed inflammatory infiltration without necrosis within the dorsolateral and ventral prostate, but no necrosis or leukocyte infiltration was observed in sample tissues from lung, liver, large intestine, bladder, seminal vesicle, testis, or epididymis. DNA was extracted from the above tissues as well as pelvic lymph nodes, blood, seminal fluid, urine, and sperm and analyzed by polymerase chain reaction for the presence of vector sequences. The vector was readily detected in the dorsolateral prostate, the site of injection. The amount of vector detected was reduced in some samples from ganciclovir-treated animals. At the highest dose, vector spread was observed in the ventral prostate, seminal vesicle, testis, pelvic lymph nodes, gut, and liver. Spread to the testis was observed in only one animal. Vector DNA was not detected in urine, seminal fluid, or sperm but was detected in the blood of one animal. This adenoviral vector, therefore, appears to have minimal spread to sites distant from the site of injection and no detectable pathological sequelae within this dose range in this preclinical model for prostate cancer, which may be generalizable to other solid tumors.

Improvement of gene therapy for ovarian cancer by using acyclovir instead of ganciclovir in adenovirus mediated thymidine kinase gene therapy

Adenovirus(ADV) mediated thymidine kinase(TK) gene therapy followed by ganciclovir(GCV) administration is widely used in different types of cancer. ACV shares the same mechanism of selective cell killing in ADV/TK positive cells as GCV and can be used at 4.5 times higher doses in patients without significant side effects. An increased dose of TK substrate is associated with improved bystander effect and more efficient cell killing. Toxicity and cell killing efficacy were assessed using a 3-(4,5-dimethylthiazol)-2,5-diphenyl tetrazolium bromide(MTT) based assay in three ovarian cancer cell lines with different proliferation patterns. At the same concentration, equal or higher cell killing efficacy and bystander effect were observed using ACV rather than GCV. 2.5 and 5 times (25 micrograms/ml and 50 micrograms/ml) higher concentrations of ACV always resulted in more effective cell killing than GCV (10 micrograms/ml, P < 0.01). Our data indicate that replacing GCV with ACV in the ADV-TK gene therapy may increase the treatment effect without increasing toxicity.

The effects of multiple-strand suture methods on the strength and excursion of repaired intrasynovial flexor tendons: a biomechanical study in dogs

This study was designed to determine the effects of in vivo multistrand, multigrasp suture techniques on the strength and gliding of repaired intrasynovial tendons when controlled passive motion rehabilitation was used. Twenty-four adult mongrel dogs were divided into 4 groups and their medial and lateral forepaw flexor tendons were transsected and sutured by either the Savage, the Tajima, the Kessler, or the recently developed 8-strand suture method. The tendon excursion, joint rotation, and tensile properties of the repaired tendons were evaluated biomechanically at 3 and 6 weeks after surgery. It was found that neither time nor suture method significantly effected proximal and distal interphalangeal joint rotation or tendon excursion when the 4 techniques were compared to each other. Normalized load value (experimental/control) was significantly affected by both the suture method and the amount of time after surgery, however. The Savage and 8-strand repair methods had significantly greater strength than did the Tajima method at each time interval (p < .05 for each comparison). In addition, the 8-strand method had significantly greater normalized load values than did the Savage method at each time interval (p < .05 for each comparison). Normalized stiffness (experimental/control) for the 8-strand repair method was significantly greater than that for the Tajima and Savage methods at 3 and 6 weeks after surgery (p < .05). In addition, the normalized stiffness values for the 6-week groups was significantly greater than those for the 3-week groups (p < .05). It was concluded that the method of tendon suture was a significant variable insofar as the regaining of tendon strength was concerned and that the newer low-profile 8-strand repair method significantly expands the safety zone for the application of increased in vivo load during the early stages of rehabilitation.

Effect of combined axial compressive and anterior tibial loads on in situ forces in the anterior cruciate ligament: a porcine study

This study investigated the impact of a combination of axial compressive and anterior-posterior tibial loads on the in situ forces in the anterior cruciate ligament. An axial compressive load is believed to contribute to increased stability of the knee joint; however, its effect on in situ forces in the anterior cruciate ligament has not been clearly defined, to our knowledge. It was hypothesized that the application of an axial compressive load, when combined with an anterior tibial load, would result in larger in situ forces in the anterior cruciate ligament than those caused by an isolated anterior tibial load. With use of a porcine knee model, the results confirmed this hypothesis; the addition of a 200 N axial compressive load to a 100 N anterior tibial load increased knee stability by reducing anterior-posterior tibial translation and internal-external tibial rotation and also caused a significant increase in in situ forces in the anterior cruciate ligament (p < 0.05). Specifically, there was a 34% increase in the in situ force at 30 degrees of flexion, a 68% increase at 60 degrees of flexion, and an 84% increase at 90 degrees of flexion compared with those for an isolated anterior tibial load of 100 N. Additionally, there was a statistically significant increase of the in situ forces in the anterior cruciate ligament at 60 and 90 degrees as compared with those at 30 degrees. These results suggest that axial compressive loads on the knee may play a role in injury of the anterior cruciate ligament when the knee is flexed.

The Marshall R. Urist Young Investigator Award. Autogenous flexor tendon grafts. Biologic mechanisms for incorporation

To examine the hypothesis that different types of dense regular connective tissue may have different repair mechanisms within the synovial space, intrasynovial and extrasynovial autogenous donor flexor tendon grafts were placed within the synovial sheaths of the medial and lateral forepaw digits of dogs. Histologic, ultrastructural, biochemical, and biomechanical analyses were done between 10 days and 6 weeks after tendon grafting. Intrasynovial tendon grafts remained viable when transferred to the synovial space and appeared to heal through an intrinsic process with preservation of the gliding surface and improved functional characteristics. Extrasynovial tendon grafts functioned as a scaffolding for the early ingrowth of new vessels and cells. Early cellular necrosis consistently was followed by the ingrowth of fibrovascular adhesions from the periphery. The formation of dense peripheral adhesions, obliterating the gliding surface of the tendon, led to diminished tendon excursion and proximal interphalangeal joint rotation.

Combination therapy with suicide and cytokine genes for hepatic metastases of lung cancer

Metastases of lung cancer are a major cause of treatment failure. To evaluate the therapeutic efficacy of gene therapy in metastatic lung cancer, we used adenoviral (ADV) mediated transfer of the herpes simplex virus thymidine kinase (HSV-tk) gene and the cytokine gene interleukin-2 (IL-2) to treat a murine model of metastatic lung cancer in the liver. Hepatic metastases were established by intrahepatic implantation of LL2 cells in syngeneic recipient mice. One week after tumor implantation, various replication defective ADV vectors were injected intratumorally. Treatment with a vector expressing the HSV-tk followed by ganciclovir administration with ADV.tk resulted in significant regression of tumor (p<0.01) as well as prolongation of survival (p<0.001). While a vector expressing mouse IL-2 ADV.IL-2 alone was ineffective, combination therapy with HSV-tk resulted in further tumor regression and improvement of animal survival (p<0.05). These results demonstrate that suicide and cytokine genes can be utilized in combination to treat metastatic lung cancer in vivo.

Functional evaluation of the ligaments at the acromioclavicular joint during anteroposterior and superoinferior translation

We examined the anatomy and measured the in situ force in ligaments at the acromioclavicular joint using a universal force-moment sensor. The in situ force in the coracoacromial, conoid, trapezoid, superior acromioclavicular capsular, and inferior acromioclavicular capsular ligaments of 10 fresh-frozen cadaveric shoulders was determined for a load of 70 N applied to the clavicle in anteroposterior and superoinferior directions. The lengths of the conoid and trapezoid ligaments were found to be 15.1 +/- 4.1 and 11.5 +/- 2.2 mm, respectively; the widths of the conoid and trapezoid ligaments were 10.7 +/- 1.5 and 11.0 +/- 2.8 mm, respectively. The in situ force of the trapezoid (42.9 +/- 15.4 N) was significantly greater than that for the other ligaments during posterior displacement. Otherwise, no statistically significant differences could be found between any of the in situ forces in each ligament during all other motions examined. During anterior displacement, the inferior acromioclavicular capsular ligament appeared to be the major restraint. The trapezoid ligament was the primary restraint during posterior displacement and provided 55.8% +/- 20.0% of the resisting force. Our results suggest that the coracoclavicular and other acromioclavicular joint capsular ligaments should be considered for reconstruction to restore normal joint function, especially in the anterior, posterior, and superior directions.

The effects of age on rabbit MCL fibroblast matrix synthesis in response to TGF-beta 1 or EGF

In this study, we examined the effects of age on collagen and total protein synthesis by ligament fibroblasts in response to growth factors. Three different doses of transforming growth factor-beta 1 (TGF-beta 1) or epidermal growth factor (EGF) were individually added to in vitro fibroblast cultures from the medial collateral ligament (MCL) of skeletally immature (age 3 months), mature (age 12 months) and senescent (age 48-51 months) rabbits. Analysis of the effects of age revealed that fibroblasts from senescent rabbits produced significantly less collagen in response to TGF-beta 1 or EGF stimulation when compared to fibroblasts from immature rabbits. Furthermore, increased age was found to result in significant reductions in the baseline levels of collagen synthesis but not total protein synthesis. Additionally, collagen and total protein synthesis by MCL fibroblasts were significantly affected by the TFG-beta 1 dose, but not by the EGF dose. When fibroblasts were normalized to their own controls, the increase in collagen and total protein synthesis due to TGF-beta 1 and EGF for the senescent group were found to be greater than those for the skeletally immature rabbits at all doses. This demonstrates that MCL fibroblasts from senescent rabbits are responsive to growth factors.

Adenoviral-mediated herpes simplex virus thymidine kinase gene transfer: regression of hepatic metastasis of pancreatic tumors

Pancreatic cancer is the fifth leading cause of cancer death in the United States. Most patients have obvious metastases or locally advanced disease at the time of presentation. Surgical resection does not significantly change the clinical outcome. Combination chemotherapy induces a partial response but overall survival remains low. The aim of this study was to evaluate the feasibility of adenovirus-mediated suicide gene transduction as a therapeutic approach for pancreatic cancer. A cell line was established from a murine pancreatic ductal adenocarcinoma and intrahepatic tumors were generated by inoculation of pancreatic cancer cells into the left lateral liver lobe. Transduction efficiency was characterized in vitro and in vivo. Intrahepatic tumors were treated by intratumoral adenovirus injection in combination with intraperitoneal administration of ganciclovir. Adenovirus-mediated herpes simplex virus (HSV)-thymidine kinase (tk) gene expression followed by ganciclovir treatment was highly efficient in inhibiting pancreatic cancer cell proliferation in vitro. The proliferation of nontransduced cells was significantly reduced in the presence of HSV-tk expressing cells. Intrahepatic inoculation of pancreatic cancer cells leads to successful formation of solid adenocarcinomas in syngeneic recipients. Ad.RSV-tk injection of the tumor followed by intraperitoneal ganciclovir application caused highly significant tumor volume reduction and necrosis. These results indicate that transduction of the HSV-tk gene followed by ganciclovir is highly efficient for growth inhibition of hepatic metastases of pancreatic carcinoma.

Viral vector-mediated gene therapy for hemophilia B

Over the past five years, significant advances have been made in the development of novel viral vector systems for the treatment of hemophilia B by somatic gene therapy. At present, both a sustained but partial or a complete but transient correction of the hemophilia B phenotype have been observed in a clinically relevant animal model. Present efforts are being directed toward the development of safe, effective and persistent methods of virally-mediated gene transfer to achieve the complete restoration of normal hemostasis in individuals with hemophilia B.

Hepatic insulin gene expression as treatment for type 1 diabetes mellitus in rats

Type 1 diabetes mellitus is caused by a lack of insulin that results from the autoimmune destruction of the pancreatic beta-cells. Severe diabetes, if not controlled by periodic insulin injections, can lead to ketoacidosis and death. We have previously shown that sustained low level production of insulin in the liver of diabetic rats prevented their death from complications of diabetes. To test the hypothesis that there is a window of serum insulin concentrations that can prevent ketoacidosis without significant risk of hypoglycemia secondary to hyperinsulinemia, rats were infused with various doses of a recombinant retrovirus encoding an engineered rat preproinsulin-1 gene. The gene was engineered to allow processing into mature insulin by the protease furin. At the lower doses tested, fatal ketoacidosis was prevented, but the rats exhibited nonfasting hyperglycemia. At intermediate doses, which resulted in serum insulin concentrations of 1.6 mg/ml, the rats achieved near-normoglycemia and no serum ketones. These rats did not exhibit hypoglycemia even during a 24-h fast. At high virus doses, the animals achieved nonfasting normoglycemia but exhibited hypoglycemia during the fast. In conclusion, we have defined a therapeutic window of hepatic insulin expression that provides protection against ketoacidosis without significant risk of hypoglycemia. This window of sustained hepatic insulin expression might permit its development into a novel treatment modality for the prevention of ketoacidosis in patients with severe insulin-dependent diabetes mellitus.

The role of interleukin-2 in combination adenovirus gene therapy for head and neck cancer

Interleukin-2 (IL-2) gene therapy alone and in combination with the herpes thymidine kinase gene (tk) was used to evaluate immunological responses and antitumor effects in head and neck cancer. Established floor of mouth squamous cell carcinomas in C3H/HeJ mice were directly injected with recombinant adenoviral vectors carrying both therapeutic and control genes. One week after adenoviral gene transfer, only the animals treated with combination IL-2+tk or tk alone demonstrated significant tumor regression. Residual tumors were harvested for microscopic evaluation and immunohistochemistry staining, which revealed a predominance of CD8+ lymphocytes in the tumor beds of the animals treated with IL-2. To evaluate the systemic immune effects of IL-2, animals treated with single or combination gene therapy received a second site challenge with parental tumor cells or a heterologous but syngeneic sarcoma cell line. Mice treated with combination IL-2 and tk demonstrated a protective systemic immunity specific to the parental tumor cell line, whereas no systemic immune response was evident in mice receiving IL-2 alone. In a separate experiment, a range of concentrations of the adenovirus IL-2 vector were used to treat established tumors. Even with the maximal single-dose adenovirus concentration, IL-2 alone was ineffective as a single therapy. These results support the use of adenovirus-mediated gene transfer of IL-2 as an effective immunotherapy when used adjuvantly with the tk "suicide gene".

Biomechanics of knee ligament healing, repair and reconstruction

Injuries of the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) are common, accounting for 90% of all knee ligament injuries in young and active individuals. During the last decade, our research center has focused on MCL healing and ACL reconstruction. We have found that the MCL heals without intervention after an isolated injury, and that primary repair offers no apparent advantage. After a combined injury of the ACL and MCL, the ACL requires reconstruction, whereas primary repair again contributes little or nothing toward MCL healing. Midsubstance ACL injuries have limited healing ability. Hence, the treatment of choice for a torn ACL in a young, active patient is generally reconstruction with an autograft or allograft. However, the appropriate replacement graft and reconstruction technique to use are still debated. Current research efforts have been placed on investigating the magnitude and direction of in situ forces in the human ACL. We use a six-component universal force moment sensor combined with a six-degree-of-freedom (DOF) robotic manipulator to learn as well as to reproduce the six-DOF motion of the knee before and after ACL injury. This way, the in situ force in the ACL under an anterior posterior tibial load of 110 N was obtained. This methodology should make it possible to obtain the needed data to aid in better understanding of ACL reconstruction and possible development of improved clinical management.

Tensile properties of canine intrasynovial and extrasynovial flexor tendon autografts

This study compared the biomechanical properties of intrasynovial and extrasynovial flexor tendon autografts in an adult canine model. Flexor digitorum profundus (FDP) tissue from the fifth toe of the hindpaw was harvested and transplanted as an intrasynovial graft to the second toe of the left forepaw of each animal. Peroneus longus tendon from the lateral compartment of the hind leg served as the source for the extrasynovial graft that was transplanted to the fifth toe of each dog's left forepaw. The second and fifth FDP tendons of the right forepaw constituted the respective contralateral controls. Postoperatively, each animal underwent a regimen of daily controlled passive mobilization. Three and 6 weeks after grafting, 6 animals were euthanized and their grafts evaluated for gliding function and tensile properties. Results reveal significantly greater angular rotation of the proximal interphalangeal joint in the digits that received intrasynovial grafts relative to those that received transplanted extrasynovial tendon at both 3 and 6 weeks postoperatively. The linear stiffness of the tendons receiving extrasynovial graft significantly exceeded that of the intrasynovial group. These findings correlated with histologic data that postoperative adhesions existed in the specimens with an extrasynovial graft. In addition, the extrasynovial tendon graft complex exhibited significantly higher ultimate loads than intrasynovial tendon graft complex at 6 weeks.

Medial collateral knee ligament healing. Combined medial collateral and anterior cruciate ligament injuries studied in rabbits

We examined the histological appearance and biochemical properties of the healing medial collateral ligament (MCL) of a rabbit knee after combined MCL and anterior cruciate ligament (ACL) injury treated with ACL reconstruction and with or without MCL repair. By so doing, we hoped to understand better our previous bomechanical observations (Ohno et al. 1995) and possibly learn where to focus future investigation into improving the quality of the healing MCL. Ligaments were examined at 6 and 12 weeks of healing. We found healing of all ligaments with hypercellularity and fibroblast elongation along the axis of loading, as expected. Unexpected, however, was the finding of multiple osteophytes in both the repaired and nonrepaired specimens at the medial borders of the joint and at the MCL insertions. These were felt to affect possibly the biomechanics of the MCL by causing stress risers at the point where they undermine the ligament. Biochemically, we demonstrated a correlation between collagen content and hydroxypyridinium crosslinks and modulus of elasticity. While this implies that the modulus is dependent on collagen content and hydroxypyridinium crosslink density, modulus is also probably dependent on other factors such as collagen organization, type and internal structure. Overall, the detailed characterization and correlation between the histological, biochemical, and biomechanical properties of the healing MCL in the severe knee injury model provide insight into the functional behavior of the healing MCL.

The effect of anterior cruciate ligament graft fixation site at the tibia on knee stability: evaluation using a robotic testing system

Despite its current popularity and relative success, endoscopic reconstruction of the anterior cruciate ligament (ACL) using a bone-patellar tendon-bone (BPTB) graft has not yet been perfected. Using a recently developed robotic/UFS testing system, we assessed the overall stability of porcine knees following ACL reconstruction with different sites of tibial graft fixation--proximal, central, and distal. Testing of the intact knee was performed first to determine the normal anterior-posterior (A-P) displacements and in situ forces of the ACL under 110 N of anterior tibial loading of 30 degrees, 60 degrees, and 90 degrees of knee flexion. The knee was then reconstructed with a BPTB autograft, and the distal end of the graft was fixed sequentially at three different locations in each specimen--proximal, central, distal. A-P testing was repeated for each fixation site, and the resulting knee kinematics and the in situ forces of the grafts were compared to the intact case. The site of tibial fixation was demonstrated to have a significant effect on the resulting anterior displacement and internal rotation of the tibia as well as the in situ forces of the graft. Proximal fixation produced the most stable knee (A-P displacements reduced to 120% of intact at 30 degrees and 170% at 90 degrees), becoming significantly less stable with more distal fixation. These results suggest that proximal graft fixation may provide the most acute stability of the reconstructed knee.

Neurotoxicity of intracerebral injection of a replication-defective adenoviral vector in a semipermissive species (cotton rat)

The neurotoxicity of an adenoviral vector (Adv.RSVtk) carrying the gene for herpes simplex virus thymidine kinase (HSVtk) was tested in the cotton rat, a semipermissive host. Adv.RSVtk was injected intracerebrally in cotton rats at a dose of 5.0 x 10(6) or 7.5 x 10(7) p.f.u. No signs of illness were observed. Histological inspection at 12 and 28 days after injection showed inflammation of the ependyma and choroid plexus and at the injection site. No demyelination, viral inclusions, cerebral edema, necrosis, cavities or vascular necrosis were seen in the brains. There was no significant difference between animals injected with 5.0 x 10(6) or 7.5 x 10(7) p.f.u., nor was there a difference between animals analyzed at 12 or 28 days after vector injection. This inflammation was similar in animals that had been preimmunized with wild-type virus and in animals that had been treated with ganciclovir. No histopathology, was observed in the lungs of the animals and no replication-competent virus was detected. These experiments indicate that Adv.RSVtk has limited neurotoxicity which would not prohibit its use in a limited phase I clinical trial in humans that have malignant tumors of the central nervous system.