Geometric Analysis of the Proximal Medullary Cavity of the Femur in the German Shepherd Dog

Forty-one cadaver femora of German Shepherd dogs were prepared for implantation of a cementless total hip prosthesis by reaming of the proximal medullary cavity with standard orthopaedic instruments. Silicone paste imprints of the cavity were taken and measured with a 3 D laser reflection system. Data were processed statistically according to a geometric model with these parameters: distal diameter Ø dist , medio-frontal radius r, laterofrontal angle α, medio-frontal angle β, helix angle γ and increment eccentricity δ e . Correlations between body mass and Ø disv body mass and r, body mass and β were moderately significant (p <0.05, p <0.06, p <0.05 resp.). Other correlations between body mass and parameters were not significant. Simple weighing of a German Shepherd is not a useful predictor of the internal dimensions of the proximal femur.

The distribution of the most important parameter Ø dist was compared with the range of Ø dist sizes of the iso-elastic veterinary hip prosthesis (IVHP). This comparison showed that the test sample of 41 bones could be fitted with four IVHP sizes. However, 25 femora out of 41 do not fit into the available r values of the IVHP assortment. Less than adequate proximal canal fill will be the result if an IVHP is implanted, unless substantial reaming is done proximomedially.

It was shown that measurements on radiographs of intact dog cadaver femora do not yield equivalent results to the imprints. Moreover, comparison of the internal dimensions of the medullary cavity of the human femur showed that a press-fit human prosthesis cannot be geometrically proportional to the IVHP.

Dimensions of reamed cavities of forty-one cadaver femora of German Shepherd dogs were measured with a system of silicone imprinting and 3D laser reflectometry. Data were processed statistically according to a geometric model with seven parameters. Correlations between parameters and body mass were moderately significant for three parameters and not significant for the others. Distributions of the geometric parameters were calculated and implications with respect to prosthesis design are discussed. A comparison with geometric parameters obtained from radiographs was made and the significance of the differences is discussed. Finally, a comparison with the geometric parameters of the medullary cavity of the human femur is made.

Fatigue behavior of porous biomaterials manufactured using selective laser melting

Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4).

Aberrant pelvis and hip kinematics impair hip loading before and after total hip replacement

Musculoskeletal loading is an important factor affecting the development of osteoarthritis, bone remodelling and primary fixation of total hip replacement (THR). In this study, we analyzed the relation between muscular force, gait kinematics and kinetics and hip loading in 20 patients before and six weeks after THR. Hip contact forces were calculated from gait analysis data using musculoskeletal modelling, inverse dynamics and static optimization. We found aberrant pelvis and hip kinematics and kinetics before and six weeks after surgery, confirming previous findings in literature. Furthermore, we found a decrease in the total contact force and its vertical component. These changes result in a decrease of the associated inclination angles of the total hip contact force in the sagittal and transverse planes, changing the orientation towards more vertical implant loading after THR. These changes in hip loading were related to observed gait kinematics and kinetics. Most importantly, excessive pelvic obliquity and associated hip adduction related to impaired implant loading. We concluded, therefore, that physical therapy in the early post-operative phase should primarily focus on stretching of anterior and medial structures and strengthening of hip flexors and abductors to achieve normalization of the hip and pelvis kinematics and consequently normalize hip loading.

Subject-specific hip geometry and hip joint centre location affects calculated contact forces at the hip during gait

Hip loading affects the development of hip osteoarthritis, bone remodelling and osseointegration of implants. In this study, we analyzed the effect of subject-specific modelling of hip geometry and hip joint centre (HJC) location on the quantification of hip joint moments, muscle moments and hip contact forces during gait, using musculoskeletal modelling, inverse dynamic analysis and static optimization. For 10 subjects, hip joint moments, muscle moments and hip loading in terms of magnitude and orientation were quantified using three different model types, each including a different amount of subject-specific detail: (1) a generic scaled musculoskeletal model, (2) a generic scaled musculoskeletal model with subject-specific hip geometry (femoral anteversion, neck-length and neck-shaft angle) and (3) a generic scaled musculoskeletal model with subject-specific hip geometry including HJC location. Subject-specific geometry and HJC location were derived from CT. Significant differences were found between the three model types in HJC location, hip flexion-extension moment and inclination angle of the total contact force in the frontal plane. No model agreement was found between the three model types for the calculation of contact forces in terms of magnitude and orientations, and muscle moments. Therefore, we suggest that personalized models with individualized hip joint geometry and HJC location should be used for the quantification of hip loading. For biomechanical analyses aiming to understand modified hip joint loading, and planning hip surgery in patients with osteoarthritis, the amount of subject-specific detail, related to bone geometry and joint centre location in the musculoskeletal models used, needs to be considered.

Viscosupplementation in the hip: evaluation of hyaluronic acid formulations

This study compares three different hyaluronate formulations and evaluates functionality, time of satisfactory pain relief and also the delay in performing a total hip arthroplasty. One hundred and twenty patients (126 hips) received viscosupplementation with one of the three hyaluronate formulations. All patients were candidate for surgical treatment with a total hip arthroplasty. Three different products were consecutively used: Adant, Synocrom or Synvisc. Patients were assessed 6 weeks after each infiltration using Visual Analogue Scale and Harris Hip Score. The Harris Hip Score increased significantly in two of the three groups compared to baseline, but no statistical significant difference was noted between the groups. Viscosupplementation provides significant pain reduction in two of the three groups. There is no significant difference in duration of the effect of the first infiltration between the three groups. The positive effect was still ongoing at the end point of the study in 46 hips: 51% of the patients did not undergo total hip arthroplasty, 3 years after viscosupplementation.

Detection of the insertion end point of cementless hip prostheses using the comparison between successive frequency response functions

Vibration analysis is a non-destructive testing technique, which has a potential to assess the mechanical properties of the stem/femur system in total hip replacement (THR). Different methods based on vibration analysis have already been successfully used to determine bone mechanical properties, to monitor fracture healing, and to quantify the fixation of dental implants. This paper describes an in vitro study of the change in the frequency response function (FRF) of the hip stem/femur structure during implant insertion. At successive insertion stages, the FRF of the system was measured by impulse excitation on the prosthesis neck, in the range 0-5000 Hz. To quantify the difference between two successive FRF spectra, the Pearson's correlation coefficient and the cross correlation function were used. The stiffness of the implant/bone system varies during insertion, which results in a change in FRF, especially in the range of higher frequencies. If the FRF spectrum shifts to the right, then the stiffness of the implant/bone connection increases and, consequently, the stability of the implant increases as well. If the FRF does not change between two successive insertion stages, then the mechanical properties of the prosthesis-femur structure does not change; therefore, the stem-bone connection is stable and the insertion should stop to avoid intra-operative fractures. Based on the obtained results, a per-operative protocol based on FRF analysis can be designed to assess the stability of a cementless hip prosthesis, and to detect the insertion end point.

Core decompression for avascular necrosis of the femoral head

The results of core decompression as the sole treatment for Ficat stages 1, 2 and 3 avascular necrosis of 51 femoral heads in 39 patients were studied. The mean follow-up time was 24 months (6-47 months); 19 hips (38.8%) were good and 30 hips (61.2%) had failed (two hips were lost to follow-up). The good results as stated in the literature could not be obtained, but we believe core decompression can delay the need for total hip replacement in avascular necrosis of the femoral head.

Short stature of prenatal origin: craniofacial growth and dental maturation

Recently, children born small for gestational age (SGA) with a catch-up growth failure, have been selected for high dose growth hormone (GH) treatment. In order to gain greater insight concerning dentofacial growth and maturation of these patients, and to evaluate the possible effects of high does GH administration on facial structures, craniofacial growth and dental maturation were evaluated in short SGA persons. Seventy-seven cephalograms and orthopantomograms were available from 48 subjects, aged between 2 and 32 years. Craniofacial growth was assessed by calculating age- and gender-specific standard deviation scores (SDS) for eight linear and five angular measurements. Tooth formation was evaluated by means of a dental delay score (i.e. dental age minus chronological age). The SDS for craniofacial growth measurements for the lateral aspect showed a short anterior cranial base (-1.8 SDS), a small retropositioned mandible (< or = -1.7 SDS) and a small maxilla (-1.5 SDS); a high mandibular plane angle (+1.9 SDS) and a wide cranial base angle (+1 SDS). These findings result in a small retrognathic face with a relatively increased lower anterior face height (+1.7 SDS). In contrast to skeletal maturation, dental age was not delayed. The general growth retardation is, apparently, reflected to a differential extent within the craniofacial complex, while dental maturation appears to be a distinct process tightly linked to chronological age, and independent of general growth and bone age.

Conservative treatment of femoral shaft fractures in patients with total hip arthroplasty

Over a period of 20 years, 34 patients with a total hip arthroplasty were treated conservatively for a femoral shaft fracture. Thirty-five fractures were treated by traction followed by cast-brace or by cast-brace alone. Sound healing was obtained in 33 fractures. Problems were angular malalignment jeopardizing revision surgery in cases of loosening, long hospitalization, and a considerable complication rate. As a consequence, the authors no longer recommend conservative treatment as the first choice for these difficult fractures.

Craniofacial growth in short children born small for gestational age: effect of growth hormone treatment

The effects of growth hormone (GH) therapy in children have yet to be completely catalogued. In the present study, the effect of high-dose GH treatment on craniofacial growth was evaluated once yearly in 21 pre-pubertal, non-GH-deficient children born small for gestational age. These children were randomly allocated to be either untreated or treated with GH at a daily subcutaneous dose of 0.2 or 0.3 IU/kg for 2 yrs. The group consisted of 12 girls and 9 boys with a mean age of 5.1 yr (range, 2 to 8 yr), bone age of 3.4 yr, and height SDS of -3.6. At the start of the study, all children showed an overall delay of craniofacial growth. This cohort of short children born small for gestational age showed a small SNB angle and a large ANB angle; all other angular measurements were within normal range. GH treatment accelerated growth in several craniofacial components, especially the posterior total facial height, the cranial base length, and the overall mandibular length. The increase of the mandibular length increased the SNB angle; no other angular measurements were affected. Age at start of treatment differently influenced the increase in posterior and total cranial base length, the increase in mandibular corpus length, and the position of the mandible in relation to the cranial base. Although GH treatment for 2 yrs led to a craniofacial growth acceleration, the position of the mandible in relation to the cranial base and the craniofacial size in lateral aspect were not normalized in the majority of the GH-treated children. No signs of disproportional growth were evidenced after 2 yrs of high-dose GH treatment. In conclusion, short pre-pubertal SGA children display an overall delay of linear craniofacial growth and a retrognathic mandible. High-dose GH treatment over 2 yrs leads to craniofacial catch-up growth, which is pronounced in regions where interstitial cartilage is involved and results in a less convex face in profile.

Progressive pseudorheumatoid arthritis of childhood (PPAC) and normal adult height

Two brothers and a sister presented with spondyloepiphyseal dysplasia and progressive arthropathy. Stiffness and restricted mobility of several large joints had been present since childhood. Their adult height was normal, and skeletal radiography showed mild platyspondyly, abnormal epiphyses and severe osteoarthrosis with extensive synovial osteochondromatosis. This autosomal recessive type of spondyloepiphyseal dysplasia tarda must be distinguished from other forms of spondyloepiphyseal dysplasia, rheumatoid arthritis in childhood and osteoarthrosis in adults.

New derivatives of kanamycin B obtained by modifications and substitutions in position 6". 1. Synthesis and microbiological evaluation

The clinical use of the potent, wide-spectrum aminoglycoside antibiotics is limited by oto- and nephrotoxicities. The latter is related to the binding of these polycationic drugs to negatively charged phospholipids and to the subsequent inhibition of lysosomal phospholipases. In order to explore the influence of a modification of the hydrophobic/hydrophilic balance at a specific site of an aminoglycoside, kanamycin B has been chemically modified in position 6" by substitution of the hydroxyl group with a halogen atom (or a pseudohalogen group), or an amino, an amido, a thioalkyl, or an alkoxy group, each series containing increasingly bulkier chains. Examination of the antibacterial activity of the synthesized compounds revealed a negative correlation between the size of the 6"-substituent and the antibacterial activity against kanamycin B sensitive Gram-positive and -negative organisms. Only derivatives with small substituents in position 6", namely chloro, bromo, azido, amino, methylcarbamido, acetamido, methylthio, methylsulfinyl, O-methyl, O-ethyl, and O-isopropyl, showed acceptable activity (geometric mean of minimum inhibitory concentrations for Gram-negative strains less than or equal to 2.5 mg/L; value for kanamycin B, 0.5 mg/L). In vitro toxicological evaluation of all derivatives and computer-aided conformational analysis of selected compounds inserted in a phosphatidylinositol monolayer are presented in the following paper in this issue.

A new system to produce intraoperatively custom femoral prosthesis from measurements taken during the surgical procedure

A system has been developed that allows the surgeon to match a prosthesis to any femoral cavity. The surgeon may choose how and where it will preferentially fit. The surgeon does not have to create a cavity to suit a premade prosthesis. The system is based on a novel technique for making a mold of the prepared femoral cavity. This is accurately and thoroughly measured using a laser. An implant is designed and manufactured while the operation is in progress using state-of-the-art computer and machining techniques. All important parameters such as neck length, offset, and anteversion are fully variable intraoperatively. To date, more than 800 consecutive procedures have been carried out. In a limited trial, no subjective difference was found with a cemented Charnley total hip arthroplasty at one year. It currently takes about 40 minutes to manufacture the implant and make it available in the operating room, and this time is being continually reduced. Using a femur first approach, operating time is not greatly extended. In the future, perhaps the operating time will not be extended at all. All data including cavity geometry are centrally recorded for analysis.