Incisional negative pressure wound therapy after hemiarthroplasty for femoral neck fractures - reduction of wound complications.

The aim of the study was to evaluate the use of incisional negative pressure wound therapy (iNPWT) in wound healing after femoral neck fracture (FNF) treated with hip hemiarthroplasty (HA) and its influence on postoperative seromas, wound secretion, as well as time and material consumption for dressing changes. The study is a prospective randomised evaluation of iNPWT in patients with large surgical wounds after FNF. Patients were randomised either to be treated by iNPWT (group A) or a standard wound dressing (group B). Follow-up included ultrasound measurements of seroma volumes on postoperative days 5 and 10, duration of wound secretion, and time and material spent for wound dressing changes. For comparison of the means, we used the t-test for independent samples, P > 0·05 was considered significant. There were 21 patients randomised in this study. Group A (11 patients, 81·6 ± 5·2 years of age) developed a seroma of 0·257 ± 0·75 cm(3) after 5 days and had a secretion of 0·9 ± 1·0 days, and the total time for dressing changes was 14·8 ± 3·9 minutes, whereas group B (ten patients, 82·6 ± 8·6 years of age) developed a seroma of 3·995 ± 5·01 cm(3) after 5 days and had a secretion of 4·3 ± 2·45 days, and the total time for dressing changes was 42·9 ± 11·0 minutes. All mentioned differences were significant. iNPWT has been used on many different types of traumatic and non-traumatic wounds. This prospective, randomised study has demonstrated decreased development of postoperative seromas, reduction of total wound secretion days and reduction of needed time for dressing changes.

Negative pressure wound therapy for seroma prevention and surgical incision treatment in spinal fracture care.

To evaluate the clinical use and economic aspects of negative pressure wound therapy (NPWT) after dorsal stabilisation of spinal fractures. This study is a prospective randomised evaluation of NPWT in patients with large surgical wounds after surgical stabilisation of spinal fractures by internal fixation. Patients were randomised to either standard wound dressing treatment (group A) or NPWT (group B). The wound area was examined by ultrasound to measure seroma volumes in both groups on the 5th and 10th day after surgery. Furthermore, data on economic aspects such as nursing time for wound care and material used for wound dressing were evaluated. A total of 20 patients (10 in each group) were enrolled. Throughout the whole study, mean seroma volume was significantly higher in group A than that in group B (day 5: 1·9 ml versus 0 ml; P = 0·0007; day 10: 1·6 ml versus 0·5 ml; P <0·024). Furthermore, patients of group A required more wound care time (group A: 31 ± 10 minutes; group B 13·8 ± 6 minutes; P = 0·0005) and more number of compresses (total number; group A 35 ± 15; group B 11 ± 3; P = 0·0376). NPWT reduced the development of postoperative seroma, reduced nursing time and reduced material required for wound care.

Value of incisional negative pressure wound therapy in orthopaedic surgery.

Soft tissue and wound treatment after orthopaedic interventions (especially after trauma) is still an enormously challenging situation for every surgeon. Since development of negative pressure wound therapy (NPWT), new indications have been consistently added to the original field of application. Recently, NPWT has been applied directly over high-risk closed surgical incisions. Review of the literature indicates that this therapy has shown positive effects on incisions after total ankle replacement or calcaneal fractures, preventing haematoma and wound dehiscence. In those cases reduced swelling, decreased pain and healing time of the wound were seen. Additionally, NPWT applied on incisions after acetabular fractures showed a decreased rate of infection and wound healing problems compared with published infection rates. Even after total hip arthroplasty, incisional NPWT reduced incidence of postoperative seroma and improved wound healing. In patients with tibial plateau, pilon or calcaneus fractures requiring surgical stabilisation after blunt trauma, reduced risk of developing acute and chronic wound dehiscence and infection was observed when using incisional NPWT. To conclude, incisional NPWT can help to reduce risk of delayed wound healing and infection after severe trauma and orthopaedic interventions.

Ankle laxity: stress investigation under MRI control.

OBJECTIVE: The purpose of this study was to examine the advantages of MRI-guided ankle stress examinations in the detection of chronic ankle instability. SUBJECTS AND METHODS: An MRI-compatible stress device was developed and tested for MRI safety. Bilateral MRI stress examinations were performed on 50 volunteers with and without clinically evident subjective instability of the ankle joints (72 subjective stable ankle joints in 37 subjects, 28 ankles in 15 subjects with chronic ankle instability). Both the inversion test and the anterior drawer test were performed under axial, coronal, 45° paraxial, and sagittal T2-weighted fast spin-echo image control. MR images were assessed for talar tilt, subtalar tilt, anterior talus translation, anterior calcaneus translation, medial talocalcaneal translation, and the diameters of the lateral ankle ligaments (anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament). RESULTS: The MRI stress device was found suitable and safe for use in the MRI environment. The talocrural and subtalar joints could be assessed simultaneously. Significant differences between groups A and B (p≤0.05) were found in talar tilt, subtalar tilt, anterior talus translation, anterior calcaneus translation, medial talocalcaneal translation, and decrease in diameters of calcaneofibular and posterior talofibular ligaments. Also found were sex differences in talar tilt, subtalar tilt, anterior talus translation, and diameters of the anterior talofibular, calcaneofibular, and posterior talofibular ligaments. Significant relations were found between talar tilt and anterior talus translation, subtalar tilt and anterior calcaneus translation, subtalar tilt and medial talocalcaneal translation, and between anterior calcaneus translation and medial talocalcaneal translation in groups A and B. CONCLUSION: Stress examination under MRI control has advantages in the assessment of mechanical ankle instability. Additional diagnostic and clinically relevant information is obtained through direct imaging of the ligaments and assessment of additional parameters of ankle laxity (subtalar tilt, anterior calcaneus translation, medial talocalcaneal translation). The main advantages are objective imaging and measurement of abnormal looseness of the lower ankle joint and its direct simultaneous comparison with the upper ankle joint.

A 5-mm femoral defect in female but not in male rats leads to a reproducible atrophic non-union.

INTRODUCTION: The objectives of this study were to (1) establish a reproducible atrophic non-union model in rats by creation of a segmental femoral bone defect that allows, (2) in-depth characterization of impaired healing, and (3) contrast its healing patterns to the normal course. Hypothesis was that a 5-mm bone defect in male rats would deviate from uneventful healing patterns and result in an atrophic non-union. MATERIALS AND METHODS: A femoral osteotomy was performed in two groups of 12-week-old male rats (1 vs. 5 mm gap) stabilized with an external fixator. Bone healing in these models was evaluated by radiology, biomechanics, and histology at 6 or 8 weeks. The evaluation of the 5-mm group revealed in some cases a delayed rather than a non-union, and therefore, a group of female counterparts was included. RESULTS: The creation of a 5-mm defect in female rats resulted in a reproducible atrophic non-union characterized by sealing of the medullary canal, lack of cartilage formation, and negligible mechanical properties of the callus. In both gap size models, the male subjects showed advanced healing compared to females. DISCUSSION AND CONCLUSION: This study showed that even under uneventful healing conditions in terms of age and bone defect size, there is a sex-specific advanced healing in male compared to female subjects. Contrary to our initial hypothesis, only the creation of a 5-mm segmental femoral defect in female rats led to a reproducible atrophic non-union. It has been shown that an atrophic non-union exhibits different healing patterns compared to uneventful healing. A total lack of endochondral bone formation, soft tissue prolapse into the defect, and bony closure of the medullary cavity have been shown to occur in the non-union model.

Development of a signal-inducing bone cement for magnetic resonance imaging.

PURPOSE: To develop a signal-inducing bone cement for musculoskeletal procedures in magnetic resonance imaging (MRI). MATERIALS AND METHODS: Acrylic resins were mixed with contrast agents (CAs) and water. We determined the ideal concentration of the components and assessed feasibility in cadaveric bones in an open high-field MR scanner. The contrast-to-noise ratio (CNR) in air and bone was evaluated and mechanical tests were achieved. We determined the amount of water that was not incorporated and measured the amount of CA released with photometric analysis. The cement was analyzed microscopically. RESULTS: Preparation and application of the CA-water-cement compound was feasible and its differentiation in MRI was clear. The maximal CNR(air) had a value of 157.5 (SD 18.3) in an interventional fast T1W turbo-spin echo (TSE) sequence. The compressive strength decreased with the amount of water added. Although nearly 50% of the water added was not incorporated in the cement, the CNR was sufficient for cement detection. The threshold for systemic toxicity of delivered CA was not reached and the microscopic analysis showed water bubbles in the cement. CONCLUSION: A signal-inducing bone cement is feasible for the use in MRI.

A comparison of three scores to screen for delirium on the surgical ward.

BACKGROUND: Postoperative delirium is associated with adverse outcome. The aim of this study was to find a valid and easy-to-use tool to screen for postoperative delirium on the surgical ward. METHODS: Data were collected from 88 patients who underwent elective surgery. Delirium screening was performed daily until the sixth postoperative day using the Confusion Assessment Method (CAM), the Nursing Delirium Screening Scale (Nu-DESC), and the Delirium Detection Score (DDS), and the DSM-IV criteria as the gold standard. RESULTS: Seventeen of 88 patients (19%) developed delirium on at least one of the postoperative days according to the gold standard. The DDS scored positive for 40 (45%) patients, the CAM for 15 (17%), and the Nu-DESC for 28 (32%) patients. Sensitivity and specificity were 0.71 and 0.87 for the DDS, 0.75 and 1.00 for the CAM, and 0.98 and 0.92 for the Nu-DESC. The interrater reliability was 0.83 for the Nu-DESC, 0.77 for the DDS, and 1.00 for the CAM. CONCLUSIONS: All scores showed high specificity but differed in their sensitivity. The Nu-DESC proved to be the most sensitive test for screening for a postoperative delirium on the surgical ward followed by the CAM and DDS when compared to the gold standard.

Passive navigation principle for orthopedic interventions with MR fluoroscopy.

INTRODUCTION: Of late, computer-assisted surgery has become a novel challenge for orthopedic surgeons. However, for orthopedic interventions magnetic resonance (MR) fluoroscopy is in its early stages of development. The authors have developed an innovative passive navigation concept, which is potentially applicable for many magnetic resonance image (MRI)-guided musculoskeletal interventions. With this method, no switching between different planes is required, since the cross-sectional modality of the MRI is used as a new navigation approach. MATERIALS AND METHODS: This method was mainly evaluated in retrograde drilling of artificial osteochondral lesions of the talus as an example of difficult navigation in drill placement due to poor visualization with X-ray and complex anatomy. To accomplish this objective, a passive navigation device was constructed and evaluated in nine cadaveric ankle joint specimens. Feasibility and accuracy of navigated drillings were evaluated. RESULTS: The interactive high-field MR fluoroscopy and the passive aiming device allow precise drilling of osteochondral lesions of the talus, despite the complex anatomy of the ankle. Drillings could be performed with an accuracy of 1.6 mm. The drilling guide was safe and easy to handle. CONCLUSION: The MR-assisted retrograde drilling of osteochondral lesions may enable precise and safe treatment without radiation exposure. This passive navigation technique for MR fluoroscopy is potentially applicable for many orthopedic interventions and may present an alternative to other navigation methods. Especially, the treatment of pediatric and adolescent patients may benefit from the typical MRI properties.

Osteochondral lesions of the talus: retrograde drilling with high-field-strength MR guidance.

The institutional review board approved the use of cadaveric specimens, and informed consent was obtained from all volunteers. The authors performed and assessed a magnetic resonance (MR)-assisted navigation method for minimally invasive retrograde drilling of talar osteochondral lesions. For this method, a single imaging plane is sufficient for navigation during intervention. To accomplish this objective, a passive MR navigation device was used to evaluate 16 cadaveric ankle joints. Use of this interactive MR-assisted navigation method in combination with a passive aiming device allowed precise and rapid retrograde drilling of talar osteochondral lesions.

Distraction osteogenesis enhances remodeling of remote bones of the skeleton: a pilot study.

Bone injuries have a systemic influence on the remodeling of bone. This effect has not been examined concerning its extent and duration. We measured the systemic effect of distraction osteogenesis on the remodeling of bones of the axial skeleton by means of the mineral apposition rate and bone formation rate in an animal experiment. Distraction osteogenesis was performed on the tibiae of 24 mature Yucatan minipigs. After a 4-day latency period, the tibiae were distracted 2 mm/day for 10 days. The ensuing consolidation phase lasted 10 days. Three fluorescent labeling substances were applied intravenously: calcein green at the second postoperative day, tetracycline 1 day after the end of the distraction phase, and xylene orange 2 days before sacrifice. We prepared ground sections from the ninth right ribs. The mineral apposition rate and bone formation rate were measured histomorphometrically on labeled osteons. The median mineral apposition rate during distraction was 2.39 microm/day (2.12-2.62 microm/day), which was higher than the rate during consolidation (median, 1.62 microm/day; 1.54-1.84 microm/day). The median bone formation rate confirmed this result and was 840.51 microm(2)/day (744.20-1148.26 microm(2)/day) during distraction and 384.25 microm(2)/day (330.84-467.71 microm(2)/day) during consolidation. Thus, a short period of distraction osteogenesis appears to have an anabolic effect on the mineral apposition rate of remote cortical bone.

Tibia fracture following removal of the ETN (Expert Tibia Nail): a case report.

We report on a patient who sustained a fracture of the tibial shaft during the removal of the newest type of an intramedullary nail (Expert Tibia Nail, Synthes. In this case report, we discuss the causes of this complication and possible ways to prevent this.

Mechanical induction of critically delayed bone healing in sheep: radiological and biomechanical results.

This study aimed to mechanically produce a standardized ovine model for a critically delayed bone union. A tibial osteotomy was stabilized with either a rigid (group I) or mechanically critical (group II) external fixator in sheep. Interfragmentary movements and ground reaction forces were monitored throughout the healing period of 9 weeks. After sacrifice at 6 weeks, 9 weeks and 6 months, radiographs were taken and the tibiae were examined mechanically. Interfragmentary movements were considerably larger in group II throughout the healing period. Unlike group I, the operated limb in group II did not return to full weight bearing during the treatment period. Radiographic and mechanical observations showed significantly inferior bone healing in group II at 6 and 9 weeks compared to group I. After 6 months, five sheep treated with the critical fixator showed radiological bridging of the osteotomy, but the biomechanical strength of the repair was still inferior to group I at 9 weeks. The remaining three animals had even developed a hypertrophic non-union. In this study, mechanical instability was employed to induce a critically delayed healing model in sheep. In some cases, this approach even led to the development of a hypertrophic non-union. The mechanical induction of critical bone healing using an external fixation device is a reasonable attempt to investigate the patho-physiological healing cascade without suffering from any biological intervention. Therefore, the presented ovine model provides the basis for a comparative evaluation of mechanisms controlling delayed and standard bone healing.

An easily reproducible and biomechanically standardized model to investigate bone healing in rats, using external fixation.

Abstract We have established a new small animal model to investigate the process of bone regeneration. A total of 42 male Sprague-Dawley rats received an osteotomy of the left femur, stabilized with a custom-made external fixator. The fixation method was chosen to create an easily reproducible, biomechanically well-defined model with minimized interference of the implant with the healing zone. At 14 or 56 days post-operation, the animals were sacrificed and examined biomechanically, histologically and radiologically. Radiologically, the femurs of all animals were anatomically positioned directly post-operation and remained in that position throughout the examination period. At 14 days post-operation, a typical periosteal callus formation could be observed both histologically and radiologically. At 56 days post-operation, the osteotomy was almost completely bridged by periosteal callus and the biomechanical competence of the bones was fully restored. Relative to the intact contralateral femur, the torsional stiffness median was 130.3% (interquartile range 118.9-157.7%) and the maximum torsional failure moment median was 135.6% (interquartile range 69.5-208.7%). As this model provides standardized conditions, it is suitable for a wide range of investigations and is particularly valuable for investigations of locally applied therapies, such as osteoconductive materials or osteoinductive factors.

Instability prolongs the chondral phase during bone healing in sheep.

In this sheep study, we investigated the influence of fixation stability on the temporal and spatial distribution of tissues in the fracture callus. As the initial mechanical conditions have been cited as being especially important for the healing outcome, it was hypothesized that differences in the path of healing would be seen as early as the initial phase of healing. Sixty-four sheep underwent a mid-shaft tibial osteotomy that was treated with either a rigid or a semi-rigid external fixator. Animals were sacrificed at 2, 3, 6 and 9 weeks postoperatively and the fracture calluses were analyzed using radiological, biomechanical and histological techniques. Statistical comparison between the groups was performed using the Mann-Whitney U test for unpaired non-parametric data. In the callus of the tibia treated with semi-rigid fixation, remnants of the fracture haematoma remained present for longer, although new periosteal bone formation during early healing was similar in both groups. The mechanical competence of the healing callus at 6 weeks was inferior compared to tibiae treated with rigid fixation. Semi-rigid fixation resulted in a larger cartilage component of the callus, which persisted longer. Remodeling processes were initiated earlier in the rigid group, while new bone formation continued throughout the entire investigated period in the semi-rigid group. In this study, evidence is provided that less rigid fixation increased the time required for healing. The process of intramembranous ossification appeared during the initial stages of healing to be independent of mechanical stability. However, the delay in healing was related to a prolonged chondral phase.

CYR61 (CCN1) protein expression during fracture healing in an ovine tibial model and its relation to the mechanical fixation stability.

The formation of new blood vessels is a prerequisite for bone healing. CYR61 (CCN1), an extracellular matrix-associated signaling protein, is a potent stimulator of angiogenesis and mesenchymal stem cell expansion and differentiation. A recent study showed that CYR61 is expressed during fracture healing and suggested that CYR61 plays a significant role in cartilage and bone formation. The hypothesis of the present study was that decreased fixation stability, which leads to a delay in healing, would lead to reduced CYR61 protein expression in fracture callus. The aim of the study was to quantitatively analyze CYR61 protein expression, vascularization, and tissue differentiation in the osteotomy gap and relate to the mechanical fixation stability during the course of healing. A mid-shaft osteotomy of the tibia was performed in two groups of sheep and stabilized with either a rigid or semirigid external fixator, each allowing different amounts of interfragmentary movement. The sheep were sacrificed at 2, 3, 6, and 9 weeks postoperatively. The tibiae were tested biomechanically and histological sections from the callus were analyzed immunohistochemically with regard to CYR61 protein expression and vascularization. Expression of CYR61 protein was upregulated at the early phase of fracture healing (2 weeks), decreasing over the healing time. Decreased fixation stability was associated with a reduced upregulation of the CYR61 protein expression and a reduced vascularization at 2 weeks leading to a slower healing. The maximum cartilage callus fraction in both groups was reached at 3 weeks. However, the semirigid fixator group showed a significantly lower CYR61 immunoreactivity in cartilage than the rigid fixator group at this time point. The fraction of cartilage in the semirigid fixator group was not replaced by bone as quickly as in the rigid fixator group leading to an inferior histological and mechanical callus quality at 6 weeks and therefore to a slower healing. The results supply further evidence that CYR61 may serve as an important regulator of bone healing.

Is it safe to assist proximal humeral nailing to residents? An analysis of 1134 cases.

INTRODUCTION: Intramedullary nailing is a common procedure for the treatment of proximal humeral fractures. In practical resident training this standardized operation plays an important role in the introduction to osteosynthesis. Our aim was to investigate whether assisting this operation to residents influences the surgical complication rate both in-house and on re-admission. METHODS: All 1134 patients who received a proximal humeral Targon PH nail (Aesculap) for proximal humeral fractures were included between 2000 and 2013. Several age groups (≤60 years, 61-70 years, 71-80 years, 80-90 years, and over 90 years) were analyzed separately. Complications including screw/nail protrusion, displacement, infection, humeral head necrosis, nonunion, stiffness, hematoma, impingement, screw loosening, implant failure, dislocation were recorded. 803 (70.7%) of the patients were female. Mean patient age was 71.7 years (standard deviation: 14.0 years). For detection of significantly different complication frequencies between operations performed by residents or attending physicians, we used the χ2 test in cases with all expected values greater than five, otherwise we used the two-sided Fisher's exact test. RESULTS: Supervised residents performed 204 operations. Overall complication rate was 12.6% (95% CI: 10.7-14.5%). The complication rate of the attending operations was 13.2% while it was 9.8% for resident operations. The difference was not significant. No statistically significant relation between age group and complication rate was found. In all patients older than 80 years the complication rate was higher when operated by residents compared to those operated by consultants, whereas in younger patients it was lower. Whereas the difference was not significant in patients younger than 60 and older than 80, we found significantly less complications in the group of patients between 61 and 80 years of age. On the other hand patients between 81 and 90 years displayed a 1.46 fold higher risk after training operations. No significant differences in the frequency of the different complications were found. CONCLUSION: We conclude that proximal humeral nailing is an operation suitable for teaching purposes. However, patients between 81 and 90 years of age seem to be at an increased risk for complications if operated by a resident.

Initial vascularization and tissue differentiation are influenced by fixation stability.

Fracture healing requires a certain degree of mechanical stability and an adequate blood supply. The hypothesis of the present study was that increased interfragmentary shear leads to a reduced initial vascularization and prolonged healing. The aim of the study was to quantitatively analyze the histological appearance of vascularization and tissue differentiation with regard to fracture stability during the course of healing. A mid-shaft osteotomy of the tibia was performed in two groups of sheep and stabilized with either a rigid or semirigid external fixator, differing in bending stiffness. Interfragmentary movements and ground reaction forces were evaluated in vivo during a 9-week period. The sheep were sacrificed at 2, 3, 6, and 9 weeks postoperatively. The tibiae were tested biomechanically and histological sections from the callus were prepared for analysis of tissue differentiation and vascularization. Larger interfragmentary shear movements in the semirigid fixator group were associated with a reduced initial blood supply. At 6 weeks the semirigid fixator group showed a significantly lower percentage of mineralized bone and a higher amount of fibrous tissue leading to a significantly lower stiffness of the callus than the rigid fixator group. This initial delay in healing was compensated for in the later stages with the production of greater volumes of callus tissue so that both groups showed the same callus stiffness at 9 weeks. However, the rigid fixator group showed signs of the beginning of callus remodeling at the latest time points suggesting a faster bone healing. The results indicate the important role of the initial mechanical stability specifically in the vascularization of an osteosynthesis. Further studies should illustrate the precise role of mechanical conditions on the regulation of angiogenesis during early bone healing.

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.

Tendon healing in a bone tunnel. Part II: Histologic analysis after biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep.

PURPOSE: Tendon-to-bone healing of soft-tissue grafts has been described to progress by the development of a fibrous interzone that undergoes a maturation process leading to the development of an indirect type of ligament insertion. Previous studies used extra-articular models or fixation far away from the joint line; thus, no data are available investigating tendon-to-bone healing of a soft-tissue graft fixed anatomically. Therefore, we studied the tendon-to-bone healing of the anatomic soft-tissue graft interference fit fixation in a model of anterior cruciate ligament (ACL) reconstruction in sheep. TYPE OF STUDY: Animal study. METHODS: Thirty-five mature sheep underwent ACL reconstruction with an autologous Achilles tendon split graft. Grafts were directly fixed with biodegradable poly-(D,L-lactide) interference screws. Animals were euthanized after 6, 9, 12, 24, and 52 weeks and histologic evaluations were performed. Undecalcified specimens were evaluated under normal and polarized light. Additionally, animals received a polychrome sequential labeling (tetracycline, xylenol orange, and calcein green) to determine bone growth per time under fluorescent light. RESULTS: Intratunnel histologic findings at 6 weeks showed a tendon-bone junction with only a partial fibrous interzone between the graft tissue and the surrounding bone. A mature intratunnel tendon-bone junction with a zone of fibrocartilage was found at 9 to 12 weeks. At the tunnel entrance site a wide regular ligamentous insertion site was seen in all specimens after 24 weeks. This insertion showed regular patterns such as the direct type of insertion of a normal ligament with a dense basophilic transition zone consisting of mineralized cartilage. CONCLUSIONS: A fibrous interzone between the graft tissue and the bone tunnel was only partially developed, which is in contrast to all previous studies in which nonanatomic fixation was used. Thus, it is reasonable to assume that the tendon-to-bone healing in the present study may progress partially by direct-contact healing without the development of a fibrous interzone. To our knowledge, this is the first report describing the development of a direct type of ligament insertion after ACL replacement with a soft-tissue graft. This is in contrast to previous studies reporting the development of an indirect type of insertion when using nonanatomic fixation far away from the joint line. Thus, histologic data strongly indicate that anatomic interference fit fixation is beneficial for tendon-to-bone incorporation by leading to the development of a direct type of ligament insertion.

A signal-inducing bone cement for magnetic resonance imaging-guided spinal surgery based on hydroxyapatite and polymethylmethacrylate.

The aim of this study was to develop a signal-inducing bone cement for magnetic resonance imaging (MRI)-guided cementoplasty of the spine. This MRI cement would allow precise and controlled injection of cement into pathologic lesions of the bone. We mixed conventional polymethylmethacrylate bone cement (PMMA; 5 ml methylmethacrylate and 12 g polymethylmethacrylate) with hydroxyapatite (HA) bone substitute (2-4 ml) and a gadolinium-based contrast agent (CA; 0-60 µl). The contrast-to-noise ratio (CNR) of different CA doses was measured in an open 1.0-Tesla scanner for fast T1W Turbo-Spin-Echo (TSE) and T1W TSE pulse sequences to determine the highest signal. We simulated MRI-guided cementoplasty in cadaveric spines. Compressive strength of the cements was tested. The highest CNR was (1) 87.3 (SD 2.9) in fast T1W TSE for cements with 4 µl CA/ml HA (4 ml) and (2) 60.8 (SD 2.4) in T1W TSE for cements with 1 µl CA/ml HA (4 ml). MRI-guided cementoplasty in cadaveric spine was feasible. Compressive strength decreased with increasing amounts of HA from 46.7 MPa (2 ml HA) to 28.0 MPa (4 ml HA). An MRI-compatible cement based on PMMA, HA, and CA is feasible and clearly visible on MRI images. MRI-guided spinal cementoplasty using this cement would permit direct visualization of the cement, the pathologic process, and the anatomical surroundings.