Periprosthetic femoral fractures--incidence, classification problems and the proposal of a modified classification scheme.

INTRODUCTION: The increasing incidence of periprosthetic fractures correlates directly with the year-after-year increasing frequency of primary joint replacement surgery. The most common fracture localisation is the femur. The undisputed leader in frequency is the fracture that occurs around a total hip arthroplasty. Unfortunately, no general epidemiologic data exist dealing with exact fracture incidence numbers. Furthermore, existing classifications are lacking important information like time point of fracture occurrence, type of the implanted prosthesis and implantation technique (cemented vs. cementless). Additionally, information about mechanical quality of the bone structure and the fracture type are also missing in part. METHODS: We scanned the literature for adequate and widely used classifications in the field of hip and knee arthroplasty. In a next step we analyzed those classification systems in order to find out to what extent they are able to describe the specific aspects of the fracture event. Therefore we compared the existing classifications and presented their most relevant emphasis. Furthermore, we looked at our own patient population to evaluate incidence of fracture occurrence over time and percentage of loosened components. RESULTS: The existing classification systems address themselves specifically to the task of describing fracture localization and to some extent fracture type, or combine these two in order to calculate the possibility of loosening of the implanted prosthesis. Some of the important criteria like mechanical quality of the bone stock, primary implantation technique or time point of the prosthesis loosening (prior to or because of the fracture) remain ignored. The incidence of periprosthetic femur fractures at our department increased approximately 2.5 fold over the past two decades. The risk of suffering from a periprosthetic fracture was substantially higher after THA than after TKA. We observed a loose femoral component of the THA in about 45 % of the cases. Finally, we postulate the application of a modified classification for periprosthetic fractures as an alternative to the already published ones; not only for the femur, but also universally for all joints with an arthroplasty. CONCLUSION: The classification that is introduced in this study allows, in our opinion, a differentiated reflection of the given post-traumatic pathologic changes and enables the description of the fracture itself according to a generally accepted fracture classification scheme.

Do meta-analyses reveal time-dependent differences between the clinical outcomes achieved by microfracture and autologous chondrocyte implantation in the treatment of cartilage defects of the knee?

PURPOSE: To test the hypothesis that autologous chondrocyte implantation (ACI) has a better treatment effect than microfracture (MF), and increasing superiority over the years, when performed under similar patient-specific and defect-specific conditions. METHODS: We scanned four electronic databases for controlled clinical trials or controlled prospective observational studies. We conducted random-effects meta-analyses of equivalent data using standardized mean differences as the outcome measure of choice at 1, 2, and 5-year follow-up. We assessed heterogeneity with the I (2) index and publication bias with funnel plots and Kendall's tests. RESULTS: Our literature search revealed six study populations (nine papers) which satisfied our eligibility criteria. Overall, 399 patients aged between 16 and 60 years with 1-10 cm(2) chondral defects were available. The MF and the ACI study groups were well matched regarding patient baseline characteristics. For all papers, microfracture was performed according to Steadman, whereas three generations of ACI were applied. When all were combined, non-significant superiority of ACI over MF was revealed; surprisingly, this superiority decreased over the years. However, our meta-analyses combining solely second and third-generation ACI revealed significant standardized differences, becoming smaller over the years, but always representing a large effect. Nevertheless, our approximate estimate of the difference between the treatment effects provoked by second and third-generation ACI and by MF is not indicative of clinically relevant superiority of ACI over MF at 5-year follow-up. CONCLUSIONS: Both series of meta-analyses (combining either all ACI modifications or solely the second and third generations of ACI) suggest that the treatment effects resulting from ACI and MF converge over the years.

Growth potential of different zones of the growth plate-an experimental study in rabbits.

Despite clinical efforts to treat growth disturbances only little is known about the growth potential of the different zones of the growth plate. The aim of this study was to investigate the growth potential of different zones of the growth plate. A total of 20 New Zealand White rabbits were used for this experiment. The right and left ulna of each animal were used resulting in a total of 40 ulnae. Animals were assigned into five groups. In groups I and II resection of the metaphyseal (n = 12) or the epiphyseal (n = 6) segment of the growth plate was performed. In group III resection of the growth plate and re-implantation was performed (n = 6). In group IV the growth plate was resected and re-implanted after a 180° rotation (n = 6). Animals in group V served as controls. Histologic and radiologic examinations were performed to evaluate the growth process at 1, 2, 4, and 12 weeks following surgery. In group I, III, and IV temporary growth disturbance which was compensated within a short time was observed. Resection of the epiphyseal part resulted in growth arrest of the distal ulna in combination with normal growth of the radius which led to and valgus deformity of the limb. The results of this study indicate the importance of the reserve zone for the functioning of the growth plate.

Obesity-related juvenile form of cartilage lesions: a new affliction in the knees of morbidly obese children and adolescents.

OBJECTIVES: Overweight and obesity are afflictions that lead to an increased risk of health problems including joint problems. The aim of the study was to assess the condition of articular cartilage in obese adolescent patients suffering from knee pain. METHODS: MRI of 24 knees of 20 morbidly obese patients, mean age 14.2 years, was performed in an open 1.0 Tesla MR system, where the cartilage, the quality and structure of the menisci, and the presence or absence of surrounding changes was examined. RESULTS: In all patients a cartilage lesion in at least one region of the knee could be detected. Retropatellar cartilage lesions have been found in 19 knees. Ten cartilage lesions grade I, and four lesions grade II have been described in the lateral compartment of the knee, whereas the medial compartment showed in eight cases a grade I, in 13 cases a grade II and in two cases a grade III cartilage lesion. Meniscal changes were assessed in most patients. CONCLUSION: Morbidly obese children and adolescents show major abnormalities in the articular cartilage of the knee. Whether obesity alone is the causal factor for the development of the pattern of these changes, remains to be seen. KEY POINTS: • Morbidly obese children and adolescents often suffer from knee pain • Prospective study showed cartilage and meniscal lesions in morbidly obese adolescents • MRI is an adequate tool for assessing cartilage lesions even in morbidly obese patients • It is unclear whether cartilage abnormalities are mainly due to mechanical overload.

The effect of drilling and screw fixation of the growth plate--an experimental study in rabbits.

Injury of the growth plate is a specific problem in traumatology and can cause limb deformity and length discrepancy as a result of growth arrest. The purpose of this study was to evaluate alterations of the growth plate after artificially created injuries. A total of 14 New Zealand White rabbits were used for this experiment. The right and left ulna of each animal was used resulting in a total of 28 ulnae. In six animals drill holes were driven into the growth plate either from the distal/epiphyseal side or from the proximal/metaphyseal side of the physis. In six animals a fracture of the distal ulna corresponding to a Salter-Harris fracture type IV was created. This fracture was fixed by screws from either the epiphyseal or the metaphyseal side. Two animals served as controls. Histologic and radiologic examinations were performed to evaluate the growth process at 1, 2, 4, and 12 weeks following surgery. Drilling or fixation of the growth plate from the metaphyseal side resulted in temporary growth disturbance which was compensated within a short time. In contrast fixation from the epiphyseal side caused severe growth disturbances. Based on our findings K-wires or screws should be inserted from the metaphyseal side and be placed in the center of the growth plate.

Physeal injuries of the proximal humerus: long-term results in seventy two patients.

PURPOSE: The aim of this study was to evaluate our treatment methods of proximal humeral physeal injuries retrospectively and elucidate the relationship between the trauma mechanism, the radiographic injury pattern, the consequent therapy and the functional outcome, and to further deduct and verify prognostic criteria. METHODS: At our Department of Trauma Surgery, 303 children and adolescent patients with fractures of the proximal humeral epiphysis were treated from 1992 to 2009. 72 cases were diagnosed as physeal fractures according to the Salter-Harris classification and were included in our study. RESULTS: 15 physeal fractures of the proximal humerus were reconstructed anatomically by open or closed reduction and produced 93.3% excellent results. 57 physeal fractures were treated in a conservative way and produced 94.7% excellent results. CONCLUSION: We state that epiphyseal injuries should to be treated depending on the age of the patient. This is the only way to decrease the rate of posttraumatic epiphysiodesis with consequent problems, including limb-length discrepancy and/or angular deformities.

Acute compartment syndrome in children: a case series in 24 patients and review of the literature.

Trauma-associated acute compartment syndrome (ACS) of the extremities is a well-known complication in adults. There are only a handful of articles that describe the symptoms, the diagnostic procedure and treatment of ACS in children. The aim of this study was to analyse the diagnostic procedures in children compared to adolescents with ACS to obtain evidence for the diagnosis, treatment and outcome of children with ACS. Twenty-four children and adolescents with ACS have been treated at the Department of Trauma Surgery of the Medical University of Vienna, Austria. Two age-related groups were investigated to compare the diagnostic and therapeutic algorithm: group A comprising children aged 2-14 years (n = 12) and group B comprising adolescents aged 15-18 years (n = 12). Patient characteristics, diagnosis and therapy-associated data, complications and clinical outcome were analysed. In both groups we found fractures in most of our patients (n = 19) followed by contusion of the soft tissues (n = 3). In group A most of our patients were injured as pedestrians in car accidents (n = 5) followed by low-energy blunt trauma (n = 3). The most common region of injury and traumatic ACS was the lower leg (n = 7) followed by the feet (n = 3). For fracture stabilisation most of the patients (n = 6) received an external fixator. The mean time from admission to the fasciotomy was 27.9 hours. In four patients a compartment pressure measurement was performed with pressure levels from 30 to 75 mmHg. A histological examination of soft tissue was performed in five patients. From fasciotomy to definitive wound closure 2.4 operations were necessary. The mean hospital stay was 18.9 days. In group B most of our patients had a motorcycle accident (n = 5). The most common region for traumatic ACS in this group was also the lower leg (n = 9). In most of the patients (n = 6) intramedullary nails could be implanted. The mean time from admission to the fasciotomy was 27.1 hours. In six patients a compartment pressure measurement was performed with pressures from 25 to 90 mmHg. In five patients a histological examination was performed. From fasciotomy to definitive wound closure 2.3 operations were necessary. The mean hospital stay was 18.4 days. Secondary fasciotomy closure was performed in all cases. A split-skin graft was only necessary in three patients (13%). We avoided primary closure in the same setting when the fasciotomy was performed. Thus, we found no difference between the two groups in the diagnostic procedures, the indication for fasciotomy, the number of operations needed from fasciotomy to definitive wound closure, time of hospitalisation and clinical outcome. The rate of permanent complications was 4.2% (one patient from group A), which means that nearly all patients experienced full recovery after fasciotomy. ACS represents a surgical emergency and the indication should be determined early even in doubtful cases to avoid complications.

Surgery for pathological proximal femoral fractures, excluding femoral head and neck fractures: resection vs. stabilisation.

Pathological femoral head and neck fractures are commonly treated by arthroplasty. Treatment options for the trochanteric region or below are not clearly defined. The purpose of this retrospective, comparative, double-centre study was to analyse survival and influences on outcome according to the surgical technique used to treat pathological proximal femoral fractures, excluding fractures of the femoral head and neck. Fifty-nine patients with 64 fractures were operated up on between 1998 and 2004 in two tertiary referral centres and divided into two groups. One group (S, n = 33) consisted of patients who underwent intramedullary nailing alone, and the other group (R, n = 31) consisted of patients treated by metastatic tissue resection and reconstruction by means of different implants. Median survival was 12.6 months with no difference between groups. Surgical complications were higher in the R group (n = 7) vs. the S group (n = 3), with no statistically significant difference. Patients with surgery-related complications had a higher survival rate (p = 0.049), as did patients with mechanical implant failure (p = 0.01). Survival scoring systems did not correlate with actual survival. Resection of metastases in patients with pathological fractures of the proximal femur, excluding femoral head and neck fractures, has no influence on survival. Patients with long postoperative survival prognosis are at risk of implant-related complications.

Management and outcome of interprosthetic femoral fractures.

INTRODUCTION: Interprosthetic femoral fractures following ipsilateral hip and knee arthroplasty are a rare but serious complication in clinical practice. In most cases, adequate management of these injuries might constitute a challenging problem. However, the literature provides only few data regarding the treatment and outcome of interprosthetic femoral fractures, and there are only few classifications available, which might assist in finding an appropriate treatment concept. The purpose of this study was to analyse our experience in the management of interprosthetic femoral fractures following ipsilateral hip and knee joint replacement. MATERIALS AND METHODS: We reviewed the clinical and radiographic records of 23 patients (15 female and eight male, average age: 79.2 years) with an interprosthetic fracture after ipsilateral hip and knee joint replacement between 1992 and 2008. For the classification of interprosthetic femoral fractures, the fractures were divided into three types, depending on the fracture site and the adjacency to the prostheses. All patients underwent operative stabilisation, either by lateral plate fixation (n=19), by revision arthroplasty using a long stem (n=2) or by plate fixation and revision arthroplasty (n=2). RESULTS: Referring to the clinical outcome, 16 patients returned to their pre-injury activity level and were satisfied with their clinical outcome. In six patients, we saw a relevant decrease of hip or knee function and severe limitations in gait and activities of daily living. We had a mean Harris Hip Score (HHS) of 78.4 points, and a mean Knee injury and Osteoarthritis Outcome Score (KOOS) of 71.8 points. Relating to the radiographic outcome, successful fracture healing was achieved in 19 of 22 patients (86%) within 6 months. Failures of reduction and fixation were noted in four (18%) of 22 patients. CONCLUSION: We had a satisfactory outcome following individualised treatment of interprosthetic femoral fractures following ipsilateral hip and knee joint replacement. Compared to the rare data in current literature, we had promising functional result and high rate of bony fusion. Regarding the complexity and challenges in many of these cases, interprosthetic fractures require an adequate analysis of the fracture aetiology and a suitable transfer into the best possible treatment concept.

Management and outcome of periprosthetic fractures after total knee arthroplasty.

BACKGROUND: The incidence of periprosthetic fractures after total knee arthroplasty is continuously rising because of an increasing number of knee joint replacements and an enhanced survivorship of the elderly population after knee arthroplasty. The purpose of this study was to analyze the practicability and effectiveness of the various treatment methods for management of periprosthetic fractures after total knee arthroplasty, and to determine the clinical and radiographic long-term results of patients following surgical and nonoperative treatment of these injuries. METHODS: We reviewed the clinical and radiographic records of 41 patients (31 women and 10 men; average age, 78.6 years) with periprosthetic fractures after total knee arthroplasty between 1992 and 2008. Thirty-seven patients showed a periprosthetic fracture of the distal femur, and four patients had a periprosthetic proximal tibial fracture. Thirty-six patients underwent operative stabilization by plate fixation (n = 18), intramedullary nailing (n = 15) or revision arthroplasty (n = 3), and five patients were treated nonoperatively by long-term cast immobilization. RESULTS: Twenty-eight patients returned to their preinjury activity level and were satisfied with their clinical outcome. In 10 patients, we saw a relevant decrease of knee function and severe limitations in gait and activities of daily living. Three patients died related to surgery. Successful fracture healing within 6 months was achieved in 33 (87%) of 38 patients. Failures of reduction or fixation occurred in 8 (21%) of 38 patients. Reoperation due to technical failures was necessary in three patients. CONCLUSIONS: Compared with current data in literature, we had a satisfactory outcome in following individualized treatment of periprosthetic fractures after knee joint replacement. Referring to the wide field of treatment options and high rates of complications, periprosthetic femoral fractures around the knee commonly constitute a challenging problem for the treating surgeons and require an adequate analysis of fracture etiology and a corresponding transfer into an individual treatment concept.

Delayed Chylothorax Following Blunt Chest Trauma.

Chylothorax is a very rare disease, and its diagnosis following blunt chest trauma is exceptional. Only a small number of cases have been reported in the literature. We report a case of a male patient involved in a car accident presenting a delayed chylothorax after blunt chest trauma with a bilateral serial rib fracture and fracture of the ninth thoracic vertebrae. The therapy includes thorax drainage, dietary modifications with total parenteral nutrition and, in severe cases, PEEP ventilation. Hematological monitoring is mandatory to detect metabolic abnormalities resulting from chyle loss. Surgical treatment is only required in cases of persistent or increasing intrathoracal chyle flow. Thoracoscopic ligation of the thoracic duct is then required.Severe consequences, such as cardiopulmonary abnormalities and metabolic, nutritional and immunologic disorders, can result from chylothorax. Our patient was treated successfully by chest drainage and parenteral nutrition.

Today's Role of External Fixation in Unstable and Complex Pelvic Fractures.

INTRODUCTION: The treatment of pelvic fractures has undergone a change over the past few years. As there seems to be a trend away from external towards internal fixation, the goal of this study was to investigate whether the use of an external fixator is still a standard procedure for the initial as well as - if necessary - for the definitive treatment of complex and unstable pelvic injuries. METHODS: During a period of five years at the Level I Trauma Center, an external fixator was applied in 28 (11%) out of 236 pelvic ring fracture cases. The common indications were open fractures, complex fractures and multiple injuries with hemodynamic instability. Hemorrhage control, fracture stabilization and infection prophylaxis in cases of open fracture were achieved by variable placement and fixation of Schanz screws. In some cases, the assembly of a hybrid combined with internal osteosynthesis was used to increase stability. RESULTS: Of the 28 patients, 20 survived, while eight (28.6%) died in the course of treatment due to fatal hemorrhage, craniocerebral trauma, multi-organ failure and sepsis. A satisfactory result (anatomical and functional outcome) was achieved in 16 of the 20 cases (80%). The remaining four (20%) suffered from serious complications, the majority of them caused by the initial type of injury. CONCLUSIONS: The use of the external fixator for the initial and in some cases for the definitive fixation of unstable and complex pelvic injuries with hemodynamic instability is still a successful treatment of multiply injured patients.

Physeal injuries of the distal tibia: long-term results in 376 patients.

The aim of this study was to evaluate our treatment of distal tibial physeal injuries retrospectively and explain the relationship between the trauma mechanism, the radiographic injury pattern, the subsequent therapy and the functional outcome, as well as to further deduce and verify prognostic criteria. At the Department of Trauma Surgery, Vienna Medical University, 419 children and adolescent patients with physeal injuries of the distal tibia were treated from 1993 to 2007, of these 376 were included in our study and evaluated retrospectively. Seventy-seven displaced physeal fractures of the distal tibia were reconstructed anatomically by open or closed reduction and produced 95% excellent results. A perfect anatomical reduction, if necessary by open means, should be achieved to prevent a bone bridge with subsequent epiphysiodesis and post-traumatic deformities due to growth inhibition and/or retardation.

Surgical treatment of metastatic fractures of the femur: a retrospective analysis of 142 patients.

BACKGROUND: Pathologic fractures of long bones are common complications of the metastatic disease; however, the influence of the primary tumor, the stage of metastatic disease, different surgical techniques, and the postoperative mobility on the postoperative survival has not been clearly defined. The aim of this retrospective study was to evaluate outcome after surgical treatment for pathologic femur fractures. PATIENTS AND METHODS: A consecutive series of 142 patients with metastatic fractures of femur were retrospectively studied. The operative treatment was based on intramedullary fixation (n = 94), gliding screws (n = 15), other extramedullary fixation devices (n = 7), and arthroplasty (n = 23). RESULTS: Seventeen percent and 6% of the patients survived 1 year and 2 years, respectively, postoperatively. Postoperative survival was higher in patients with pathologic femur fractures because of breast carcinoma than in patients with other primary tumors. The rate of complications for patients with intramedullary stabilization, gliding screw fixation, and endoprosthetic replacement was 3.2%, 20%, and 8.6%, respectively. CONCLUSION: Although many studies describe the endoprosthetic replacement as the safer method to treat pathologic femur fractures, our data showed that intramedullary stabilization and endoprosthetic replacement to be safe, and equivalent alternatives to treat complete pathologic fractures of the femur in patients with advanced metastatic disease.

Plate fixation of odontoid fractures without C1-C2 arthrodesis: practice of a novel surgical technique for stabilization of odontoid fractures, including the opportunity to extend the fixation to C3.

OBJECTIVE: Surgical treatment of odontoid fractures that do not allow interfragmentary fracture compression involves either posterior atlantoaxial arthrodesis or additional anterior stabilization using a plate construct. The purpose of this study was to determine the clinical and radiographic outcome after anterior plate fixation of odontoid fractures that were not suitable for anterior screw fixation. METHODS: We reviewed the clinical and radiographic records of 9 patients with an average age of 54 years at the time of surgery who had undergone anterior plate fixation of an odontoid fracture. Indications for using a plate construct were odontoid fractures with anterior oblique fracture lines, fractures with comminution or major displacement, and pathological fractures. RESULTS: Eight patients returned to their preinjury activity level and were satisfied with their treatment. One patient reported chronic pain symptoms and a notable decrease in cervical spine motion. Using the Smiley-Webster Scale to quantify their clinical outcome, we achieved an overall outcome score of 1.6. Bony fusion was achieved in all patients. Reduction or fixation failed in 2 patients. Reoperation for technical failures was not necessary in any of the patients. CONCLUSION: We had promising results using anterior plate fixation for surgical treatment of odontoid fractures that did not allow interfragmentary fracture compression. Because this method avoids the rigid fixation of the atlantoaxial joint in contrast to techniques of posterior cervical arthrodesis, it seems to be a practical option for the management of fracture types that require additional stabilization of the odontoid.

VEGF serum concentrations in patients with long bone fractures: a comparison between impaired and normal fracture healing.

Vascular endothelial growth factor (VEGF) plays an important role in the bone repair process as a potent mediator of angiogenesis and it influences directly osteoblast differentiation. Inhibiting VEGF suppresses angiogenesis and callus mineralization in animals. However, no data exist so far on systemic expression of VEGF with regard to delayed or failed fracture healing in humans. One hundred fourteen patients with long bone fractures were included in the study. Serum samples were collected over a period of 6 months following a standardized time schedule. VEGF serum concentrations were measured. Patients were assigned to one of two groups according to their course of fracture healing. The first group contained 103 patients with physiological fracture healing. Eleven patients with delayed or nonunions formed the second group of the study. In addition, 33 healthy volunteers served as controls. An increase of VEGF serum concentration within the first 2 weeks after fracture in both groups with a following decrease within 6 months after trauma was observed. Serum VEGF concentrations in patients with impaired fracture healing were higher compared to the patients with physiological healing during the entire observation period. However, statistically significant differences were not observed at any time point between both groups. VEGF concentrations in both groups were significantly higher than those in controls. The present results show significantly elevated serum concentrations of VEGF in patients after fracture of long bones especially at the initial healing phase, indicating the importance of VEGF in the process of fracture healing in humans.

Surgical treatment of pathological fractures of the shaft of the humerus.

BACKGROUND: This report deals with the advantages and disadvantages associated with the most commonly used methods of stabilization after a pathologic fracture of the humerus shaft. PATIENTS: A total of 39 patients with 41 metastatic lesions and pathologic fractures of the humerus, treated surgically between 1992 and 2007, were retrospectively analyzed. RESULTS: The rate of local complications was 14.6% (6 of 41). Radial nerve injury was the only local complication and was exclusively observed in patients who underwent open reduction and plate fixation. The overall rate of osteosynthesis failure was 12.2% (5 of 41). Two failures were observed in 21 patients with open reductions and plate fixations, compared with three failures in 20 procedures involving closed reductions and intramedullary stabilization. The 1- and 2-year survival rates were 0.35 and 0.2 in ORIF and 0.07 and 0 in patients with IM fixation retrospectively. CONCLUSION: Intramedullary stabilization is a reliable method for fixation of pathologic fractures of the humerus diaphysis for patients in the advanced stage of metastatic disease. ORIF are preferable to IM fixations for the treatment of metaphyseal fractures and for those patients with a solitary metastasis in the humerus or those with a better prognosis.

Verrucous carcinoma of the tibia arising after chronic osteomyelitis: a case report.

Verrucous carcinoma is an uncommon complication of chronic osteomyelitis. The incidence of fistular carcinomas is reported to be between 0.21% and 3.36%. We present a case of verrucous carcinoma of the tibia arising after 58 years of chronic osteomyelitis. The primary presenting symptoms were acute pain, foul-smelling pus discharge and increasing lesion size. We used modern diagnostic investigations (biopsy, computed tomography, angiography, immunoscintigraphy, magnetic resonance tomography) to visualize the extent of the malignant lesion. No metastases were detected. Knee exarticulation was successful in treating the tumor and chronic infection in this case.

Alterations in CD44 isoforms and HAS expression in human articular chondrocytes during the de- and re-differentiation processes.

The purpose of this study was to investigate the expression of different CD44 and hyaluronan synthase isoforms in cartilage, their alterations during the chondrocyte dedifferentiation process in monolayer culture and during the redifferentiation process on 3D scaffolds. Chondrocytes isolated from human articular cartilage were cultured as a monolayer for up to 36 days and were seeded on two different 3D scaffolds (HYAFF 11 and Bio-Gide). Expression levels of CD44s, CD44-lt, CD44-st, HAS1, HAS2, HAS3 and UDPGD were determined by real-time RT-PCR at different time points. At the protein level CD44 and CD90 were analyzed by flow cytometry. HAS2 was found to be the predominantly expressed hyaluronan synthase in chondrocytes and was not subjected to any regulation during the dedifferentiation process. CD44s, CD44-lt, CD44-st and UDPGD, however, were upregulated immediately after cell isolation. In addition, a high cell density was found to significantly increase CD44-st and CD44-lt expression. Redifferentiation on 3D scaffolds reversed the increase of the CD44 expression. Our data point out that CD44 expression does not correlate with matrix assembly in chondrocytes and that CD44 has a regulatory function in chondrocytes, not necessarily on differentiation, but probably on proliferation.

Biomechanical comparison of modified Kessler and running suture repair in 3 different animal tendons and in human flexor tendons.

PURPOSE: To establish the animal flexor tendon that best mimics the biomechanical performance of human flexor tendons. We investigated the biomechanical behavior of core and running sutures in 3 different animal flexor tendons and in human flexor tendons. Additionally, we attempted to help standardize future flexor tendon studies. To that purpose, nearly all variables occurring in the test setup have been highlighted. METHODS: The species selected were pig, calf, sheep, and human. Two groups were formed. In the first group we tested 3-0 core sutures (Ticron; Tyco Healthcare, Vienna, Austria), and in the second group we tested 5-0 running sutures (Ethilon; Ethicon, Vienna, Austria). In each group, 10 tendons of each specimen were tested, which yielded a total of 80 tendons. In each group, the repaired tendons were subjected to 3,000 linear load cycles at a load of 15 N. At the end of this procedure, final gap values were recorded. In the next step, ultimate load-to-failure data were obtained from each specimen. RESULTS: Core sutures behaved similarly in the human, sheep, and pig tendons with respect to ultimate loads. With respect to gap formation, core sutures behaved similarly in the human, sheep, and calf tendons. Deep running sutures behaved similarly in the human, sheep, and pig tendons in terms of ultimate load to failure. CONCLUSIONS: In this study, sheep tendons were found to best mimic the biomechanical behavior of human tendons. Calf tendons seem to be unsuitable. There is a strong need for consistency in biomechanical test setups.