Biomedical subjects

Patrick Hunt

Publications and source records attributed to Patrick Hunt.

5 recordsLinked to original sources

PubMed2006

Soft tissue graft interference fit fixation: observations on graft insertion site healing and tunnel remodeling 2 years after ACL reconstruction in sheep.

Using soft tissue grafts for anterior cruciate ligament (ACL) reconstruction, insertion site healing plays a crucial role in the long-term fate of the graft. It has been shown in an experimental animal study that using a soft tissue graft and anatomic graft fixation, a direct ligamentous insertion alike the native ACL developed 24 weeks postoperatively. Yet there are no reports on the long-term insertion site healing of anatomically fixed soft tissue grafts. The objective of this study was to evaluate graft insertion site healing, the intra-tunnel fate of the graft and its osseous replacement 2 years after ACL reconstruction in sheep. The left ACLs of six sheep were replaced by an autologous flexor tendon split graft and anatomically fixed with biodegradable poly-(D, L-lactide) interference screws. Animals received polychromic sequential labeling at different points in time to determine bone apposition per period. For evaluation of the insertion site healing and intra-tunnel changes, MRI scans were taken in vivo. Following sacrifice, radiographic imaging, conventional histology and fluorescence microscopy was undertaken. Most of the specimens showed a wide direct ligamentous insertion. It showed patterns alike the direct ligament insertion seen in intact ACLs. The intra-tunnel part of the graft had completely lost its tendon-like structure and in two cases, it was separated from the graft insertion by a thick bony layer. The biodegradable interference screw was fully degraded in all specimens. Ossification of the former drill tunnels was intense, showing only partial-length tunnel remnants in one femoral and three tibial specimens. As the graft heals to the joint surface and the aperture site is closed with soft tissue, mechanical stress of the intra-tunnel part of the graft is eliminated and the bone tunnel is protected from synovial fluid, resulting in osseous bridging of the tunnel aperture site, accelerated intra-tunnel graft resorption and its osseous replacement.

Animals↗

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↗

PubMed2005

The impact of radiofrequency shrinkage on the mechanical and histologic properties of the elongated anterior cruciate ligament in a sheep model.

PURPOSE: Shrinkage of the elongated anterior cruciate ligament (ACL) and its grafts with radiofrequency (RF) energy has become increasingly popular as an alternative to ACL reconstruction in the field of knee surgery. Although there have been a few clinical studies on the outcome and complications of RF shrinkage of the elongated ACL, there is a substantial lack of in vivo basic science studies to evaluate the mechanical and histologic changes of such treated tissue. Therefore, it was the aim of this study to simulate an ACL elongation in an animal model, treat this pathology with RF shrinkage, and analyze the mechanical and histologic changes at 6 months after initial treatment. TYPE OF STUDY: Experimental in vivo animal study. METHODS: A chronic elongation of the ACL was simulated in 16 mature female merino sheep. In group A, no treatment was applied; in group B, RF shrinkage was used. For biomechanical testing anteroposterior (AP) laxity was measured at time zero and 24 weeks. A load-to-failure test was also performed at 24 weeks. For histologic analysis, cell number and crimp pattern were measured by conventional histologic examination and the vascular status by immunohistochemical histologic examination. RESULTS: The initial reduction of AP laxity after RF shrinkage could not be maintained at 24 weeks. A significant reduction in ultimate load was found at 24 weeks in the RF-treated group B compared with the untreated group A. At 24 weeks, an intensive process of tendon remodeling was ongoing in the RF-treated group that differed substantially from the untreated elongated ACLs and the intact ACL. CONCLUSIONS: The treatment of an elongated ACL with RF energy resulted in a significant impairment of its ultimate load and induced a process of intensive remodeling that was not completed at 24 weeks. Therefore, strong caution is warranted during the time of rehabilitation, considering the impaired ligamentous structure. CLINICAL RELEVANCE: This study provides insights into the consequences of RF shrinkage of the ACL that will guide the clinician in the appropriate rehabilitation of patients and informs of possible complications associated with this procedure.

Animals↗

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↗