Biomedical subjects

Frank N Unterhauser

Publications and source records attributed to Frank N Unterhauser.

6 recordsLinked to original sources

PubMed2005

Development of a perforated biodegradable interference screw.

PURPOSE: The objective was to develop a perforated biodegradable interference screw to allow for enhanced osseous implant integration without impairing screw stability during insertion. TYPE OF STUDY: Mechanical testing, followed by animal study. METHODS: At first, manual perforation of 8 x 23-mm biodegradable poly-(L-co-D,L-lactide) interference screws was performed, using 3 different perforation patterns (clockwise spiral, counter-clockwise spiral, and parallel perforation), followed by torsional tests. Next, parallel perforated screws (n = 6) and unperforated control screws (n = 6) were applied to the proximal tibia of 12 sheep. The sheep were put down after 24 weeks and the screw site was examined histologically. Subsequently, molding of a parallel perforated screw followed by torsional tests was undertaken. RESULTS: The parallel perforated screw presented a torsional strength insignificantly different from the unperforated control screw and well beyond the reported maximum manual insertion torques of biodegradable interference screws in young human bone. When compared with the regular unperforated interference screw, the molded perforated screw exhibited a torsional strength of 91%, indicating a secure surgical application. In contrast to the unperforated screw, histologic evaluations revealed clear bone ingrowth into the perforations including the core of the perforated interference screw. CONCLUSIONS: Perforated, "cage-like" interference screws may be promising for the acceleration of osseous implant integration into the bone with a very low risk of screw breakage during insertion. CLINICAL RELEVANCE: To ameliorate osseous implant integration and possibly enhance ossification of former implant site in anterior cruciate ligament surgery.

Absorbable Implants↗

PubMed2004

Alpha-smooth muscle actin containing contractile fibroblastic cells in human knee arthrofibrosis tissue. Winner of the AGA-DonJoy Award 2003.

INTRODUCTION: Primary arthrofibrosis is of major concern after joint trauma or knee ligament surgery. The underlying mechanism in detail remains unclear. Highly differentiated fibroblastic cells, so-called myofibroblasts, express the actin isoform alpha-smooth muscle actin (ASMA) and have been found to play a major role in tissue contraction during wound healing and organ fibrosis. We therefore studied the expression of myofibroblasts in human primary knee arthrofibrosis tissue. MATERIALS AND METHODS: Tissue samples were taken from the infrapatellar fat pad and intercondylar region of nine patients who underwent revision surgery due to arthrofibrosis after anterior cruciate ligament (ACL) reconstruction (study group). Control tissue was taken from five patients who underwent primary ACL reconstruction (control group I) and from eight patients, who underwent second-look arthroscopy after primary ACL reconstruction (control group II). ASMA containing fibroblasts were immunostained with a monoclonal antibody. Histomorphometry was performed for total cell amount, ASMA containing fibroblasts, and vessel cross-sections. RESULTS: The arthrofibrosis group showed a tenfold higher amount of ASMA containing myofibroblasts (23.4% vs. 2.3%) than in control group I. There was a significantly higher total cell count and lower vessel density than in control group I. Control group II showed an upregulation of myofibroblasts almost five times that in control group I; nevertheless there was no evidence of scar formation or tissue fibrosis. CONCLUSIONS: Myofibroblasts are responsible for scar tissue contraction during wound healing. In arthrofibrosis tissue fibroblast contraction may be involved in tissue fibrosis and contraction with consecutive loss of motion. We found that myofibroblasts are upregulated in arthrofibrosis tissue. ACL reconstruction itself caused an up regulation of myofibroblast content. Nevertheless these patients did not show any clinical or histological signs of arthrofibrosis. Thus it is reasonable to assume that the ratio of myofibroblasts and total cell amount in connective tissue are responsible for the onset of arthrofibrosis. Address the expression of this highly differentiated cell type may therefore present a target for future therapeutic interventions.

Actins↗

PubMed2004

A model of soft-tissue graft anterior cruciate ligament reconstruction in sheep.

INTRODUCTION: Since there is to our knowledge no clinically valid and reproducible animal model of soft-tissue anterior cruciate ligament (ACL) reconstruction currently available, we developed one in sheep, in terms of graft suitability, postsurgical recovery, and knee stability. MATERIALS AND METHODS: To find a suitable graft, anatomical dissections of the hind limbs of 7 sheep were performed. After a pilot study in 3 sheep, we reconstructed the ACL with an ipsilateral, longitudinally split, superficial digital flexor tendon autograft and anatomic graft fixation in 42 sheep (study 1) and with a full, superficial digital flexor tendon autograft and extracortical graft fixation in 48 sheep (study 2). Follow-up examinations ranged from 6 to 104 weeks (study 1) and 3 to 24 weeks (study 2). RESULTS: All animals tolerated the graft harvest well and returned to physiological movement after about 4 weeks. Only 1 out of 93 ACL reconstructions failed. At final follow-up, the anteroposterior (AP) drawer displacement in both studies had almost regained the value of the intact contralateral knee. Maximum load-to-failure improved over time in both studies but was significantly lower at all time points compared with the intact ACL and the graft tissues. Tensile stress was significantly lower at final follow-up in both studies compared with the intact ACL and graft tissues. It attained 43.3% of the intact ACL and 58.3% of the graft tissue in study 1 and 28.9% and 22.8% in study 2, respectively. CONCLUSION: The flexor tendon is suitable, and sheep appear to be an appropriate animal model for soft-tissue graft ACL reconstruction. They tolerate the graft harvest well and quickly return to full weight-bearing and physiological movement. Their knees become stable without showing signs of macroscopically evident osteoarthritis.

Animals↗

PubMed2004

The influence of locally applied platelet-derived growth factor-BB on free tendon graft remodeling after anterior cruciate ligament reconstruction.

BACKGROUND: Ligaments and tendons do not gain mechanical properties of the native tissue after injury or grafting. PURPOSE: To determine the influence of platelet-derived growth factor on tendon graft remodeling. STUDY DESIGN: Laboratory animal study. METHODS: Forty-eight sheep underwent anterior cruciate ligament reconstruction and were sacrificed after 3, 6, 12, and 24 weeks. In 6 animals at each time point, platelet-derived growth factor was locally delivered via coated sutures. After mechanical testing, tissue samples were taken for histologic, immunohistochemical, and electron microscopy evaluations. RESULTS: With platelet-derived growth factor treatment, cross-sectional area was significantly lower at 3 and 12 weeks. Load to failure was significantly higher at 6 weeks. Tensile stress was significantly higher at 3 and 12 weeks. Crimp length was significantly higher at 3 and 6 weeks. Vascular density was significantly higher at 6 weeks. Electron microscopy showed a significantly higher collagen fibril amount at 12 weeks. Differences in these parameters at other time points were not significant. CONCLUSIONS: There were alterations in several but not all time points. The local application of platelet-derived growth factor alters the tissue's mechanical properties during free tendon graft remodeling after anterior cruciate ligament reconstruction. Growth factors present a promising tool toward the complete mechanical restitution of a healing ligament substitute.

Animals↗

PubMed2003

Endoligamentous revascularization of an anterior cruciate ligament graft.

After replacement of the anterior cruciate ligament with a free tendon graft, the substitute initially is avascular and without a synovial surface. To ensure long-term survival, the graft must become revascularized. Despite numerous studies on the topic, there still is discussion regarding revascularization. The goal of the current study was to investigate the endoligamentous microcapillary revascularization of the free tendon graft after anterior cruciate ligament replacement with time. Thirty-six mature sheep had an anterior cruciate ligament reconstruction with an ipsilateral flexor tendon split graft. Midsubstance tissue samples were immunostained for von Willebrand factor (Factor VIII) at 6, 9, 12, 24, 52, and 104 weeks to detect the endothelial cells of capillaries. Cross sections of vessels were determined in three zones (subsynovial, intermediate, and center of the graft) and were evaluated by means of histomorphometry using a digital imaging analysis system. The observations showed that capillary vessels, which originate from the synovial envelope, invaded the avascular graft tissue from the surface toward the center zone. The highest level of vascular density was found after 6 weeks, reaching the vascular status of the native anterior cruciate ligament after 24 weeks. These findings are in contrast to the findings of previous studies in animals. The current study showed, for the first time, the kinetics of an endoligamentous revascularization of a free tendon graft at the capillary level. In the current model, the process of revascularization terminated earlier than previously described.

Animals↗

PubMed2002

Alpha-smooth muscle actin is expressed by fibroblastic cells of the ovine anterior cruciate ligament and its free tendon graft during remodeling.

Contractile fibroblastic cells expressing the alpha-smooth muscle actin isoform, so-called myofibroblasts, have been identified to play a possible role during the healing of the medial collateral ligament by means of restoring the tissues in situ strain via extracellular matrix contraction. Recently, these cells have also been identified to be a normal part of the human anterior cruciate ligament. It has been hypothesized that myofibroblasts play a role in the wrinkling of the extracellular matrix. The goal of the present study was to identify myofibroblasts in the intact ovine anterior cruciate ligament and a free autologous tendon graft during remodeling after anterior cruciate ligament reconstruction. In 36 mature merino sheep the anterior cruciate ligament was replaced with an ipsilateral Achilles tendon split graft. Midsubstance tissue samples were immunostained for alpha-smooth muscle actin at 6, 9, 12, 24, 52, and 104 weeks. Myofibroblasts were identified in the intact ovine anterior cruciate ligament as well as in the Achilles tendon graft prior to implantation. During remodeling the first myofibroblasts were found at six weeks within newly formed fiber bundles. At 24, 52, and 104 weeks myofibroblast distribution and cell density were similar to those of the intact ovine anterior cruciate ligament. These findings indicate that alpha-smooth muscle actin containing fibroblastic cells are a regular part of the intact as well as the remodeled anterior cruciate ligament. There is evidence that myofibroblasts may be involved in maintaining tissue homeostasis in the mature ligament e.g., by means of crimp formation. The presence of these cells during the early remodeling may further indicate that alpha-smooth muscle actin containing fibroblastic cells are involved in the earliest stages of fiber bundle formation. The role and function of this special cell type for the anterior cruciate ligament needs to be further clarified.

Achilles Tendon↗