Finite element modeling of the cement-bone interface beneath the tibial tray of a total knee arthroplasty: Study of the stress shielding effect (modellazione agli elementi finiti dell'interfaccia cemento-osso sotto il piatto tibiale di protesi totale di ginocchio: Analisi dello stress shielding)

The goal of this thesis was the study of the cement-bone interface in the tibial component of a cemented total knee prosthesis. One of the things you can see in specimens after in vivo service is that resorption of bone occurs in the interdigitated region between bone and cement. A stress shielding effect was investigated as a cause to explain bone resorption. Stress shielding occurs when bone is loaded less than physiological and therefore it starts remodeling according to the new loading conditions. µCT images were used to obtain 3D models of the bone and cement structure and a Finite Element Analysis was used to simulate different kind of loads. Resorption was also simulated by performing erosion operations in the interdigitated bone region. Finally, 4 models were simulated: bone (trabecular), bone with cement, and two models of bone with cement after progressive erosions of the bone. Compression, tension and shear test were simulated for each model in displacement-control until 2% of strain. The results show how the principal strain and Von Mises stress decrease after adding the cement on the structure and after the erosion operations. These results show that a stress shielding effect does occur and rises after resorption starts.

Percutaneous cement augmentation for the treatment of depression fractures of the tibial plateau

The management of insufficiency fractures of the tibial plateau in osteoporotic patients can be very challenging, since it is difficult to achieve a stable fixation, an essential condition for the patients' early mobilization. We present a minimally invasive technique for the treatment of proximal tibial plateau fractures, "tibiaplasty", using percutaneous polymethylmethacrylate augmentation. Five osteoporotic patients (7 fractures) with a non-traumatic insufficiency tibial plateau fracture were treated with this technique at the authors' institution from 2006 to 2008. The patients' median age was 79 (range 62-88) years. The intervention was performed percutaneously under general or spinal anesthesia; after the intervention, immediate full weight bearing was allowed. The technique was feasible in all patients and no complications related to the intervention were observed. All patients reported a relevant reduction in pain, were able to mobilize with full weight bearing and would undergo the operation again. No secondary loss of reduction or progression of arthrosis was observed in radiological controls; no revision surgery was required. Our initial results indicate that tibiaplasty is a good treatment option for the management of insufficiency in tibial plateau fractures in osteoporotic patients. The technique is minimally invasive, safe and allows immediate mobilization without restrictions. In our group of patients, we found excellent early to mid-term results.

Stereologic analysis of tibial-plateau cartilage and femoral cancellous bone in guinea pigs with spontaneous osteoarthritis

Two strains of guinea pig develop spontaneous osteoarthritis of the knee. Although the disease evolves at different rates in the two strains, it is not known whether these differences are reflected in the structure of the cartilage and cancellous bone.

Stabilization of Juxta-Physeal Distal Tibial and Fibular Fractures in a Juvenile Tiger Using a Hybrid Circular-Linear External Fixator

OBJECTIVE: To report stabilization of closed, comminuted distal metaphyseal transverse fractures of the left tibia and fibula in a tiger using a hybrid circular-linear external skeletal fixator. STUDY DESIGN: Clinical report. ANIMAL: Juvenile tiger (15 months, 90 kg). METHODS: From imaging studies, the tiger had comminuted distal metaphyseal transverse fractures of the left tibia and fibula, with mild caudolateral displacement and moderate compression. Multiple fissures extended from the fractures through the distal metaphyses, extending toward, but not involving the distal tibial and fibular physes. A hybrid circular-linear external skeletal fixator was applied by closed reduction, to stabilize the fractures. RESULTS: The fractures healed and the fixator was removed 5 weeks after stabilization. Limb length and alignment were similar to the normal contralateral limb at hospital discharge, 8 weeks after surgery. Two weeks later, the tiger had fractures of the right tibia and fibula and was euthanatized. Necropsy confirmed pathologic fractures ascribed to copper deficiency. CONCLUSION: Closed application of the hybrid construct provided sufficient stability to allow this 90 kg tiger's juxta-articular fractures to heal with minimal complications and without disrupting growth from the adjacent physes.

No difference in anterior tibial translation with and without posterior cruciate ligament in less invasive total knee replacement

The relative advantages of cruciate retaining or cruciate resecting total knee replacement are still controversial. If the posterior cruciate ligament (PCL) is preserved, it should be properly balanced. In a previous study, it was demonstrated that increasing the flexion gap leads to an anterior translation of the tibia relative to the femur. Based on these results, we hypothesized that cutting the PCL increases the flexion gap and lessens anterior tibial translation.

Treatment of tibial fractures with plates using minimally invasive percutaneous osteosynthesis in dogs and cats

OBJECTIVES: The aim of the here described case series was to develop and evaluate the minimally invasive percutaneous osteosynthesis for the plate fixation of tibial fractures in dogs and cats. METHODS: Six dogs and four cats with shaft fractures of the tibia were treated using minimally invasive percutaneous osteosynthesis. Follow-up radiographs four to six weeks after fracture fixation were evaluated for fracture healing. For the long-term follow-up (minimum 2.4 years), owners were contacted by phone to complete a questionnaire. RESULTS: All fractures healed without the need for a second procedure. Follow-up radiographs obtained after four to six weeks in seven cases showed advanced bony healing with callus formation and filling of the fracture gaps with calcified tissue in all seven. All the patients had a good to excellent long-term result with full limb function. The time needed for regaining full limb use was two to three months. CLINICAL SIGNIFICANCE: Minimally invasive percutaneous osteosynthesis seems to be a useful technique for the treatment of tibial shaft fractures in dogs and cats.

Cerebral correlates of muscle tone fluctuations in restless legs syndrome: A pilot study with combined functional magnetic resonance imaging and anterior tibial muscle electromyography

BACKGROUND: The pathology of restless legs syndrome (RLS) is still not understood. To investigate the pathomechanism of the disorder further we recorded a surface electromyogram (EMG) of the anterior tibial muscle during functional magnetic resonance imaging (fMRI) in patients with idiopathic RLS. METHODS: Seven subjects with moderate to severe RLS were investigated in the present pilot study. Patients were lying supine in the scanner for over 50min and were instructed not to move voluntarily. Sensory leg discomfort (SLD) was evaluated on a 10-point Likert scale. For brain image analysis, an algorithm for the calculation of tonic EMG values was developed. RESULTS: We found a negative correlation of tonic EMG and SLD (p <0.01). This finding provides evidence for the clinical experience that RLS-related subjective leg discomfort increases during muscle relaxation at rest. In the fMRI analysis, the tonic EMG was associated with activation in motor and somatosensory pathways and also in some regions that are not primarily related to motor or somatosensory functions. CONCLUSIONS: By using a newly developed algorithm for the investigation of muscle tone-related changes in cerebral activity, we identified structures that are potentially involved in RLS pathology. Our method, with some modification, may also be suitable for the investigation of phasic muscle activity that occurs during periodic leg movements.

[Chronic anterior tibial syndrome]

In two young athletic men we made the diagnosis of chronic tibialis anterior syndrome. Pain during strenuous exercise was localized in the anterolateral aspect of both calves. After stopping exercise the complaints disappeared within 15-20 minutes and not in 2-3 minutes as it would be typical for patients with atherosclerotic peripheral arterial occlusive disease. Diagnosis is based on patient history, normal clinical examination (systolic ankle pressure determined by Doppler-Sonography, electronic segmental oscillography) and increased intramuscular pressure at rest (> 10 mmHg) and after exercise (42 and 35 mmHg). Bilateral fasciotomy was performed in both patients. They are free of pain after 3 respectively 6 months postoperatively.

Unstable bicondylar tibial plateau fractures: a clinical investigation

OBJECTIVE: To evaluate fracture patterns in bicondylar tibial plateau fractures and their impact on treatment strategy. DESIGN: Prospective data analysis with documentation of initial injury and treatment strategy, computed tomography scans, conventional x-rays, long-term evaluation of radiographs, and functional assessments. SETTING: Level 1 regional trauma center. PATIENTS: Prospective data acquisition of 14 consecutive patients (10 male and 4 female) with a bicondylar tibial plateau fracture (AO Type C). INTERVENTION: Application of a stepwise reconstruction strategy of the tibial plateau starting with the reposition and fixation of the posteromedial split fragment using a 3.5 buttress plate, followed by reposition and grafting of the lateral compartment and lateral fixation with a 3.5 plate in 90 degree to the medial fixation device. MAIN OUTCOME MEASUREMENTS: All patients were evaluated with full-length standing film, standardized x-rays, Lysholm score for functional assessment, and patient's self-appraisal. RESULTS: Most of the complex bicondylar fractures follow a regular pattern in that the medial compartment is split in a mediolateral direction with a posteromedial main fragment, combined with various amounts of multifragmental lateral compartment depression. The technique introduced allows for accurate and stable reduction and fixation of this fracture type. The final Lysholm knee score showed an average of 83.5 points (range: 64.5-92). CONCLUSIONS: Complex bicondylar tibial plateau fractures follow a regular pattern, which is not represented in existing 2-dimensional fracture classifications. A 2-incision technique starting with the reduction of the posteromedial edge results in accurate fracture reduction with low complication rates and excellent knee function.

Shell brace for stage II posterior tibial tendon insufficiency

BACKGROUND: The nonoperative treatment of posterior tibial tendon insufficiency (PTTI) can lead to unsatisfactory functional results. Short-term results are available but the impact on the evolution of the deformity is not known. To address these problems, a new brace for the flexible Stage II deformity was developed, and midterm followup was obtained. MATERIALS AND METHOD: In a prospective case series, eighteen patients (mean age 64.2 years; range, 31 to 82; four male, 14 female) with flexible Stage II PTTI were fitted with the new custom-molded foot orthosis. At latest followup of a mean of 61.4 (range, 20 to 87) months, functional results were assessed with the AOFAS ankle hindfoot score and clinical or radiographic progression was recorded. RESULTS: The score improved significantly from a mean of 56 points (range, 20 to 64) to a mean of 82 points (range, 64 to 100, p < 0.001). Three patients (3/18, 16%) had a clinical progression to a fixed deformity (Stage III) and a radiographic increase of their deformity. All the other patients were satisfied with the brace's comfort and noted an improvement in their mobility. Complications were seen in three patients (3/18, 16%), and consisted of the development of calluses. CONCLUSION: The "shell brace" is a valuable option for nonoperative treatment of the flexible Stage II PTTI. Hindfoot flexibility was conserved throughout the observation period in all but three patients. Functional outcome and patient acceptance was above average. Problems were few, and closely associated with a progression to a fixed, Stage III deformity.

Accelerated hypertrophic chondrocyte kinetics in GDF-7 deficient murine tibial growth plates

The Growth/Differentiation Factors (GDFs) are a subgroup of the Bone Morphogenetic Proteins (BMPs) well known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling molecules, GDF-5, have recently been shown to exhibit a decreased rate of endochondral bone growth in the proximal tibia due to a significantly longer hypertrophic phase duration. GDF-7 is a related family member, which exhibits a high degree of sequence identity with GDF-5. The purpose of the present study was to determine whether GDF-7 deficiency also alters the endochondral bone growth rate in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5-week-old female GDF-7 -/- mice and wild type control littermates were examined. GDF-7 deficiency resulted in a statistically significant increase in growth rate (+26%; p = 0.0084) and rate of cell loss at the chondrosseous junction (+25%; p = 0.0217). Cells from GDF-7 deficient mice also exhibited a significantly shorter hypertrophic phase duration compared to wild type controls (-27%; p = 0.0326). These data demonstrate that, in the absence of GDF-7, the rate of endochondral bone growth is affected through the modulation of hypertrophic phase duration in growth plate chondrocytes. These findings further support a growing body of evidence implicating the GDFs in the formation, maturation, and maintenance of healthy cartilage.

Tibial or hip BMD predict clinical fracture risk equally well: results from a prospective study in 700 elderly Swiss women

In a randomly selected cohort of Swiss community-dwelling elderly women prospectively followed up for 2.8 +/- 0.6 years, clinical fractures were assessed twice yearly. Bone mineral density (BMD) measured at tibial diaphysis (T-DIA) and tibial epiphysis (T-EPI) using dual-energy X-ray absorptiometry (DXA) was shown to be a valid alternative to lumbar spine or hip BMD in predicting fractures.