Effects of presurgical and post-surgical irradiation on the healing process of Medpor in dogs

Acetabular fixation in total hip arthroplasty in the previously irradiated pelvis: a review of basic science and clinical outcomes

Radiation therapy is a common primary, adjuvant, or palliative treatment for many intrapelvic tumors, including primary gastrointestinal, genitourinary, and hematopoietic tumors, as well as metastatic disease to bone. Radiation has well documented microbiologic and clinical effects on bone ranging from radiation osteitis to early degenerative changes of the hip joint and avascular necrosis of the femoral head. Conventional total hip arthroplasty methods have demonstrated high rates of failure in this population, with historical data describing aseptic loosening rates as high as 44-52%, as radiation have been shown to preferentially diminish osteoblast and osteocyte number and function and limit capacity for both cement interdigitation and biologic bony ingrowth. A review of the clinical literature suggests that patients with prior pelvic irradiation are at higher risk for both septic and aseptic loosening of acetabular components, as well as lower postoperative Harris Hip Score (HHS) when compared to historical controls. With limited evidence, trabecular metal shells with multi-screw fixation and cemented polyethene liners, as well as cemented cup-cage constructs both appear to be durable acetabular fixation options, though the indications for each remains elusive. Further prospective data are needed to better characterize this difficult clinical problem.

Irradiation affects the structural, cellular and molecular components of jawbones

PURPOSE

Emerging evidence shows that changes in the bone and its microenvironment following radiotherapy are associated with either an inhibition or a state of low bone formation. Ionizing radiation is damaging to the jawbone as it increases the complication rate due to the development of hypovascular, hypocellular, and hypoxic tissue. This review summarizes and correlates the current knowledge on the effects of irradiation on the bone with an emphasis on jawbone, as these have been a less extensively studied area.

CONCLUSIONS

The stringent regulation of bone formation and bone resorption can be influenced by radiation, causing detrimental effects at structural, cellular, vascular, and molecular levels. It is also associated with a high risk of damage to surrounding healthy tissues and an increased risk of fracture. Technological advances and research on animal models as well as a few human bone tissue studies have provided novel insights into the ways in which bone can be affected by high, low and sublethal dose of radiation. The influence of radiation on bone metabolism, cellular properties, vascularity, collagen, and other factors like inflammation, reactive oxygen species are discussed.

Vitronectin promotes the vascularization of porous polyethylene biomaterials

Rapid implant vascularization is a prerequisite for successful biomaterial engraftment. Vitronectin (VN) is a matricellular glycoprotein well known for its capability to interact with growth factors, proteases, and protease inhibitors/receptors. Since such proteins are highly relevant for angiogenic processes, we hypothesized that VN contributes to the tissue integration of biomaterials. Employing different in vivo and ex vivo microscopy techniques, engraftment of porous polyethylene (PPE) implants was analyzed in the dorsal skinfold chamber model in wild-type (WT) and VN^-/- mice. Upon PPE implantation, vascularization of this biomaterial was severely compromised in animals lacking this matricellular protein. Proteome profiling revealed that VN deficiency does not cause major changes in angiogenic protein composition in the implants suggesting that VN promotes PPE vascularization via mechanisms modulating the activity of angiogenic factors rather than by directly enriching them in the implant. Consequently, surface coating with recombinant VN (embedded in Matrigel®) accelerated implant vascularization in WT mice by enhancing the maturation of a vascular network. Thus, VN contributes to the engraftment of PPE implants by promoting the vascularization of this biomaterial. Surface coating with VN might provide a promising strategy to improve the vascularization of PPE implants without affecting the host's integrity. STATEMENT OF SIGNIFICANCE: Porous polyethylene (PPE) is a biomaterial frequently used in reconstructive surgery. The proper vascularization of PPE implants is a fundamental prerequisite for its successful engraftment in host tissue. Although the overall biocompatibility of PPE is good, there are less favorable application sites for its use in tissue reconstruction mostly characterized by low blood supply. Employing advanced in vivo microscopy methods and proteomic analyses in genetically engineered mice, we here describe a previously unrecognized function of vitronectin (VN) that enables this abundantly present glycoprotein to particularly promote the vascularization of PPE biomaterial. These properties of VN specifically facilitate the formation of a dense vessel network within the implant which relies on modulating the activity of angiogenic mediators rather than on the enrichment of these factors in the implant. Consequently, surface coating with this matricellular protein effectively accelerated and intensified implant vascularization which might be beneficial for its implementation at unfavorable sites for implantation without affecting the host's integrity.

Components of the plasminogen activation system promote engraftment of porous polyethylene biomaterial via common and distinct effects

Rapid fibrovascularization is a prerequisite for successful biomaterial engraftment. In addition to their well-known roles in fibrinolysis, urokinase-type plasminogen activator (uPA) and tissue plasminogen activator (tPA) or their inhibitor plasminogen activator inhibitor-1 (PAI-1) have recently been implicated as individual mediators in non-fibrinolytic processes, including cell adhesion, migration, and proliferation. Since these events are critical for fibrovascularization of biomaterial, we hypothesized that the components of the plasminogen activation system contribute to biomaterial engraftment. Employing in vivo and ex vivo microscopy techniques, vessel and collagen network formation within porous polyethylene (PPE) implants engrafted into dorsal skinfold chambers were found to be significantly impaired in uPA-, tPA-, or PAI-1-deficient mice. Consequently, the force required for mechanical disintegration of the implants out of the host tissue was significantly lower in the mutant mice than in wild-type controls. Conversely, surface coating with recombinant uPA, tPA, non-catalytic uPA, or PAI-1, but not with non-catalytic tPA, accelerated implant vascularization in wild-type mice. Thus, uPA, tPA, and PAI-1 contribute to the fibrovascularization of PPE implants through common and distinct effects. As clinical perspective, surface coating with recombinant uPA, tPA, or PAI-1 might provide a novel strategy for accelerating the vascularization of this biomaterial.

Radiation effects on bone healing and reconstruction: interpretation of the literature

OBJECTIVE

Reconstructing irradiated mandibles with biomaterials is still a challenge but little investigated. We collected data that could help us understand studies in the field of regeneration with biomaterials and irradiated bone.

STUDY DESIGN

Systematic review of the literature.

RESULTS

Delay and duration of radiation delivery and total equivalent dose are the most variable parameters in the various studies, resulting in confusion when interpreting the literature. Most reproducible experiments show that radiation reduces osteogenic cell numbers, alters cytokine capacity, and delays and damages bone remodeling. Interindividual variations and how such changes become irreversible lesions are still uncertain. In the case of regeneration using biomaterials, most studies have addressed the question of reconstruction in previously irradiated bone. The results show that osseointegration is often possible, although the failure rate is higher. The sooner the implantation takes place after the end of the radiation, the higher the likelihood of failure. Few studies have focused on primary reconstruction followed by early irradiation, and most of the currently available engineering models would be altered by radiation. Good outcomes have been obtained with bone morphogenetic protein and with total bone marrow transplanation.

CONCLUSION

This review points out the difficulties in achieving reproducible experiments and interpreting literature in this underinvestigated field.

The use of temporal polyethylene implant after temporalis myofascial flap transposition: clinical and radiographic results from its use in 21 patients

PURPOSE

The use of temporalis myofascial flap (TMF) as a pedicled flap in craniofacial reconstructive surgery is well established. The transposition of temporalis muscle results in a large hollowing of the temporal fossa that leaves the patient with a cosmetic impairment. Reconstruction of this donor site deformity is desirable. One of the established reconstructive techniques is the use of a prefabricated porous high-density polyethylene (HDPE) temporal implant. In order to evaluate results from its use, we retrospectively reviewed a series of 21 consecutive patients.

MATERIALS AND METHODS

From October 1999 to October 2004, 21 patients (7 men and 14 women) aged 32 to 85 years (mean, 65) had their surgical defects reconstructed with the use of a TMF. The majority of patients (15 of 21) had squamous cell carcinoma of the maxilla or the maxillary sinus. In 17 patients, the reconstructive procedure was performed simultaneously with the oncological resection, whereas in 4, a secondary reconstruction was performed. In 1 patient, bilateral TMFs were used to cover a total maxillectomy defect. Standard surgical approach was used in all patients during TMF elevation. The temporal defect was reconstructed with the use of a prefabricated sterile HDPE implant (Medpor; Porex Surgical Inc, College Park, GA). Fixation of the implant to the recipient infratemporal fossa was performed with black silk sutures (in 2 patients) or titanium miniscrews (in 19 patients). The manufacturer's instructions for the placement of the implant were followed in all cases. One of the 21 operated patients preoperatively received radiotherapy (RT). Of the remaining 20 patients, 5 underwent postoperative RT.

RESULTS

Eighteen patients are alive and free from disease. One died during the perioperative period from myocardial infarction and 2 more from locoregional recurrence of their disease, 18 and 27 months postoperatively. In all 21 patients, the placement of the Medpor temporal implant was successful and no immediate or perioperative complications resulting from its use were encountered, giving an overall success implantation rate of 100%. Follow-up ranged from 9 to 70 months (mean, 39). The condition of the implant was evaluated with computed tomography in 18 of the 21 patients as part of the standard postoperative assessment. Radiographic results of the recipient site did not reveal any abnormalities. In 7 patients, the contour of the HDPE implant could be manually palpated, and in 3, it could be seen to protrude subcutaneously. Esthetic results were judged satisfactory from all patients. The hemicoronal skin flap healed uneventfully in all patients and did not cause a visible scar even to bald male patients.

CONCLUSIONS

The reconstruction of the temporal defect after TMF transposition with the use of a Medpor temporal implant is an easy and safe method. The implant does not seem to cause any tissue reaction, and long-term functional and esthetic results are excellent. When properly used and the relevant manufacturers' instructions are carefully followed, the success rate of the method is extremely high.