Introduction. Lumbar spondylolysis is a fatigue fracture of the pars interarticularis and correlates with Spina Bifida Oculta (SBO) in 67%. Hpothesis. Load is normally transferred across the arch in axial rotation. Bifid arch results in increased strain across the isthmus of the loaded inferior articular process. Aim of investigation. Finite element (FE) analysis of altered load transfer in combined axial rotation and anteroposterior shear in SBO potentially predisposing to fatigue fracture of the pars interarticularis. Methods. FE models of natural and SBO (L5-S1) including ligaments were axially load to 1kN and an axial rotation of 3° applied. Bilateral stresses and strains on intact and SBO lateral inferior lines of the L5 isthmus were assessed and compared. Results. Under 1000N axial load: Maximum von Mises stress observed on left and right lateral inferior lines of L5 isthmus were 0.13 and 0.24 MPa, with maximum equivalent strain values of 1.56 and 2.91 (strain, for natural spine and SBO, respectively. Combined with 3° axial rotation (rotation of spinal processes toward right lateral side): Left lateral L5 isthmus stresses increased to 0.49 and 0.77 MPa for natural spine and SBO, respectively. Right lateral L5 isthmus values increased to 0.67 and 0.95 MPa for natural spine and SBO, respectively. The percentage increase in SBO strains compared to the natural spine on the L5 isthmus were +57.9 and +40.2%. Conclusion. Significant load transfer occurs through the vertebral arch in axial rotation. In SBO this load transfer is lost and mechanical demand on the isthmus is significantly increased. Strain increases across the L5 isthmus in axial rotation by +40.2% to +57.9% compared to normal and may predispose to fatigue fracture

Aims: To evaluate the function of cement restrictors beyond the femoral isthmus. Introduction: Pressurisation of cement is key to achieving good cement-bone interdigitation in Total Hip Replacement. During insertion of the femoral stem, pressures of up to 1000kPa may be generated. To maintain pressurisation the medullary canal must be sealed distally using a cement restrictor. As a secondary effect, cement restrictors also prevent excess injection of cement into the medullary canal. To fulfil these functions the cement restrictor must remain stable in the femoral canal. Methods: Five different cement restrictors were evaluated, namely the Exeter Cement Plug (Stryker, UK), Biostop (De Puy, UK), Hardinge (De Puy, UK), Rex CementStop (A-One-Medical, Netherlands) and a preinjected cement plug (Surgical Simplex, Stryker, UK). The restrictor was deployed in a sawbone that had been rasped to produce a distal flare. Low viscosity bone cement (Surgical Simplex, Stryker, UK) was injected and pressurised using a custom made cement ram connected to a 10bar pressurised air supply. An electronically controlled pressure valve increased the pressure in the cement. Pressure in the cement was measured using a pressure transducer. A linear variable displacement transducer was used to measure movement of the cement restrictor. Leakage of cement around the restrictor was also recorded. Activation of the pressure valve and recording of measurements was controlled by a customised computer package. Results: The Rex CementStop withstood the greatest pressures (mean 565.8kPa). This was a significantly greater pressure than any of the other cement restrictors (p= 0.027). Pre-injected cement plugs were able to resist the next highest pressures (mean 350.4kPa). They did not displace but leaked cement and were technically difficult to deliver in the distal femur. Cement restrictors that function well above the isthmus were ineffective (Biostop mean 118.7kPa) or could not be deployed below the isthmus (Exeter). The Hardinge cement restrictor recorded a mean 162.3kPa. Discussion: It is important for a surgeon to consider where the cement restrictor will sit in the femur during pre-operative templating in Total Hip Replacement. When the cement restrictor is going to be deployed beyond the femoral isthmus, an alternate method of cement restriction may need to be used. Universal sized plugs (e.g. Hardinge) function poorly in this situation. Press-fit plugs such as Biostop and Exeter have been previously shown to allow the generation of high pressures in bone cement when sited above the femoral isthmus or in stove pipe femurs. However their function is severely compromised when inserted past the femoral isthmus. Pre-injected cement plugs are variable in efficacy. The expandable Rex CementStop was simple to use and reliably occluded the femur, allowing the highest pressures to be generated

Introduction: Cement pressurisation is key to achieving good cement-bone interdigitation in THR. To obtain adequate pressurisation the medullary canal must be sealed distally using a cement restrictor. The cement restrictor must remain stable in the femoral canal. Methods: Five different cement restrictors were evaluated, namely the Exeter Cement Plug, Biostop G, Hardinge, Rex CementStop and a preinjected cement plug. The restrictor was deployed in a sawbone that had been reamed to produce a distal flare, based on radiographic measurements. Low viscosity bone cement pressurised using a cement ram connected to a 10bar air supply. An electronic pressure valve increased the pressure in the cement. Cement pressure and cement restrictor displacement were continuously measured. The pressure valve and recording of measurements was controlled by a customised computer package. Results: The Rex CementStop withstood the greatest pressures (mean 565.8kPa). This was a significantly greater pressure than any of the other cement restrictors (p< 0.001). Pre-injected cement plugs were able to resist the next highest pressures (mean 350.4kPa). They did not displace but leaked cement and were technically difficult to deliver in the distal femur. Cement restrictors that function well above the isthmus were ineffective (Biostop mean 118.7kPa) or could not be deployed below the isthmus (Exeter). The Hardinge recorded a mean 162.3kPa. Discussion: During pre-operative templating it is important to consider where the cement restrictor will sit in the femur. When the cement restrictor is going to be deployed beyond the femoral isthmus, an alternate method of cement restriction may need to be used. Universal sized plugs (e.g. Hardinge) function poorly in this situation. Press-fit plugs such as Biostop and Exeter are severely compromised when inserted past the femoral isthmus. Pre-injected cement plugs are variable in efficacy. The expandable Rex CementStop reliably occluded the femur, allowing the highest pressures to be generated

In the light of the increasing popularity of femoral resurfacing implants, there has been growing concern regarding femoral neck fracture. This paper presents a detailed investigation of femoral neck anatomy, the knowledge of which is essential to optimise the surgical outcome of hip resurfacing as well as short hip stem implantation. Three-dimensional lower limb models were reconstructed from the CT-scan data by using the Mimics (Materialise NV, Leuven, Belgium). We included the CT data for 22 females and nine males with average age of 60.7 years [standard deviation: 16.4]. A local coordinate system based on anatomical landmarks was defined and the measurements were made on the unaffected side of the models. First, the centre of the femoral head was identified by fitting an optimal sphere to the femoral head surface. Then, two reference points, one each on the superior and the inferior surface of the base of femoral neck were marked to define the neck resection line, to which an initial temporary neck axis was set perpendicular. Cross-sectional contours of the cancellous/cortical border were defined along the initial neck axis. For each cross-sectional contour, a least-square fitted ellipse was determined. The line that connects the centre of the ellipse at the base of the femoral neck and the centre of the femoral head was defined as the new neck axis. The above process was repeated to reduce variances in the estimation of the initial neck axis. The neck isthmus was identified according to the axial distributions of the cross-sectional ellipse parameters. The short axis of the ellipse decreased monotonically since it was calculated from the center of the femoral head to the neck resection level (base of neck), whereas the long axis changed with the local minima. The cross section at which the long axis of the fitted ellipse had the local minima was determined as the neck isthmus. The following measurements were made on the proximal part of the femur. The neck axis length measured from the center of the femoral head to the lateral endosteal border of the proximal femur was 67.3 mm [6.4]. The length between the center of the femoral head and the neck isthmus was 22.5 mm [2.7]. The diameter of the ellipse long axis at the neck isthmus was 27.6 mm [3.5] and was 23.6 mm [3.3] for the short axis. The center of the neck isthmus did not align with the neck axis. The deviation of the isthmus from the neck axis which we defined as the isthmus offset was 0.7 mm [0.4]. If an alternative neck axis was defined between the center of the femoral head and the center of the neck isthmus, there would be a certain degree of angular shift with respect to the original neck axis. An angular shift of 1.8 degrees between the two axes can be expected for a 0.7-mm isthmus offset. In the worst case, an angular shift of 4.59 degrees was estimated for a subject with the largest isthmus offset of 1.93 mm. Further investigations would be necessary to determine the axis configuration that represents the clinically relevant centre of the femoral neck. In order to reduce the deviations in the three-dimensional determination of the femoral neck axis, the reference anatomical landmarks and methods of evaluation should be carefully selected

Background. Spondylolysis (SL) of the lower lumbar spine is frequently associated with spina bifida occulta (SBO). There has not been any study that has demonstrated biomechanical or genetic predispositions to explain the coexistence of these two pathologies. Purpose. To test the hypothesis that fatigue failure limits will be exceeded in the case of a bifid arch, but not in the intact case, when the segment is subjected to complex loading corresponding to normal sporting activities. Methods. Finite element models of natural and SBO (L4-S1) including ligaments were loaded axially to 1kN and were combined with axial rotation of 3°. Bilateral stresses, alternating stresses and shear fatigue failure on intact and SBO L5 isthmus were assessed and compared. Results. Under 1kN axial load, the von Mises stresses observed in SBO and in the intact cases were very similar (differences < 5MPa) having a maximum at the ventral end of the isthmus that decreases monotonically to the dorsal end. However, under 1kN axial load and rotation, the maximum von Mises stresses observed in the ipsilateral L5 isthmus in the SBO case (31MPa) was much higher than the intact case (24.2MPa) indicating a lack of load sharing across the vertebral arch in SBO. When assessing the equivalent alternating shear stress amplitude, this was found to be 22.6 MPa for the SBO case and 13.6 MPa for the intact case. From this it is estimated that shear fatigue failure will occur in less than 70,000 cycles, under repetitive axial load & rotation conditions in the SBO case, while for the intact case, fatigue failure will occur only after more than 10 million cycles. Conclusion. SBO predisposes SL by generating increased stresses across the inferior isthmus of the inferior articular process, specifically in combined axial rotation and anteroposterior shear

Introduction. Surgical reconstruction of deformed Charcot feet carries high risk of non-union, metalwork failure and deformity recurrence. The primary aim of this study was to identify the factors contributing to these complications following hindfoot Charcot reconstructions. Methods. We retrospectively analysed patients who underwent hindfoot Charcot reconstruction with an intramedullary nail between 2007 and 2019 in our unit. Patient demographics, co-morbidities, weightbearing status and post-operative complications were noted. Metalwork breakage, non-union, deformity recurrence, concurrent midfoot reconstruction and the measurements related to intramedullary nail were also recorded. Results. There were 70 patients with mean follow up of 50±26 months. Seventy-two percent were fully weightbearing at 1 year post-operatively. The overall union rate was 83%. Age, BMI, HbA1c and peripheral vascular disease did not affect union. The ratio of nail diameter and isthmus was greater in the united compared to the non-united group (0.90±0.06 and 0.86±0.09, respectively; p = 0.03). Supplemental compression devices were used for 33% of those in the united compared to 8% in the non-united group (p = 0.04). All patients in the non-union group did not have a miss-a-nail screw. Metalwork failure was seen in 13 patients(19%). There was a significantly greater distal screw metalwork failure in those with supplementary bridging of tibia to midfoot (23% vs. 3%; p = 0.001). An intact medial malleolus was found more frequently in those with intact metalwork (77% vs. 54%, respectively; p = 0.02) and those with union (76% vs. 50%; p = 0.02). Broken metalwork occurred more frequently in patients with non-unions (69% vs. 8%; p < 0.001) and deformity recurrence (69% vs. 9%; p < 0.001). Conclusion. Satisfactory clinical and radiographic outcomes occur in over 80% of patients. Union after hindfoot reconstruction occurs more frequently with an isthmic fit of the intramedullary nail, supplementary compression and miss-a-nail screws. An intact medial malleolus is protective against non-union and metalwork failure. Broken metalwork is linked to deformity recurrence and non-union

Revision of the failed femoral component can be challenging. Multiple reconstructive options are available and the procedure is technically difficult and thus meticulous pre-operative planning is required. The Paprosky Femoral Classification is useful as it helps the surgeon determine what bone stock is available for fixation and hence, which type of femoral reconstruction is most appropriate. Type 1 Defect: This is essentially a normal femur and reconstruction can proceed as the surgeon would with a primary femur. Type 2 Defect: The metaphysis is damaged but still supportive and hence a stem that gains primary fixation in the metaphysis can be used. Type 3 Defect: The metaphysis is damaged and non-supportive and hence a stem that gains primary fixation in the diaphysis is required. Broken down into types “A” and “B” based on the amount of intact isthmus available for distal fixation. Type 3A Defect: >4 cm of intact femoral isthmus is present. Can be managed with a fully porous coated stem, so long as the diameter is <18 mm and torsional remodeling is not present. Type 3B Defect: There is < 4 cm of intact femoral isthmus and based on lower rates of osseointegration if a fully porous coated stem is used, a modular titanium tapered stem is recommended. Type 4 Defect: The most challenging to manage as there is no isthmus available for distal fixation. Can be managed with proximal femoral replacement if uncontained and impaction grafting if contained. We have also successfully used modular titanium tapered stems that appear to gain “3-point fixation” in this type of defect

Background. The purpose of this study was to investigate the morphology characteristic of proximal femur of Chinese people. 170 healthy Southern Chinese hips being measured using 3D computer tomographic, in order to improve prosthesis design and preoperation plan of total hip arthroplasty. Methods. This study measured proximal femoral geometry in 85 healthy Southern Chinese, included 39 women (78 hips) and 46 men (92 hips) (mean age: 33.9 y, mean height: 164.7 cm, mean weight 59.9 kg). Medullary canal morphology measurements, include: the position of isthmus, medial-lateral(ML) and anteroposterior(AP) medullary canal diameter of isthmus and 20 mm, 10 mm, 0 mm, −20 mm, −160 mm, −200 mm upon less trochanter(LT) (medullary canal height, MCH), canal flare index(CFI), aspect ratio(ML/AP), epiphysis-shaft angel (ES angel) (a posterior bow in the metapysis in lateral view). Exterior morphology measurements include: femoral head offset, ML and UD diameter, femoral head position(FHP) from LT, height of the femoral head center from the tip of the great trochanter(GT)(FHCH), femoral neck and head anteversion angle, femoral neck-shaft angle, neck length, neck width, intertrochanteric length (Fig 1, Fig 2). And then we use student's t–test to compare means, linear regression and correlation to analysis these data's relationship, p value <0.05 indicated a significant effect. Results. Males had a larger diameter of medullary canal than females (Fig3). The isthmus position is 117.69±11.95 VS 111.14±13.01 mm (male VS female) (p=0.070) below less trochanter, and it's ML diameter is 9.57±1.52 VS 8.88±1.80 mm (p=0.151), AP diameter is 11.85±2.68 VS 10.53±2.49 mm (p=0.073). The mean medullary canal aspect ratio is 1.38±0.20, 1.30±0.12, 1.15±0.13, 1.03±0.09, 0.84±0.11, 0.87±.011 and 1.04±0.17 respectively at 20 mm, 10 mm, 0 mm, −20 mm, isthmus, −160 mm, −200 mm upon less trochanter. The medullary canal diameter were positively correlated to MCH (R=0.793, p=0.000 VS R=0.790, p=0.000) (ML VS AP). The ES angle is 156.78±4.29 VS 157.90±4.90 degree (p=0.395) (male VS female). The femoral head offset is 39.14±3.87 VS 35.86±3.68 mm (p=0.003), femoral neck, head and comprehensive anteversion angle is 18.34±8.07 VS 17.9±10.64 degree (p=0.872), −2.61±6.47 VS −2.36±5.55 degree (p=0.881) and 15.73±7.26 VS 15.54±8.54 degree (p=0.934). FHP is 51.67±7.82 VS 45.37±5.59 mm (p=0.001), FHCH is −6.77±5.58 VS −6.13±4.87 mm (p=0.665), femoral head diameter is (ML: 43.94±2.62 VS 39.25±2.66 mm (p=0.000), UD: 45.16±1.96 VS 41.26±2.23 mm (p=0.000)). Femoral neck-shaft is 130.10±4.57 VS 130.83±6.40 degree (p=0.652), femoral neck length and width is 21.84±4.87 VS 20.69±3.41 mm (p=0.322) and 34.75±2.26 VS 31.80±2.63 mm (p=0.000), femoral intertrochanteric length is 68.11±4.72 VS 61.27±5.04 mm (p=0.000), most of these dimensions were positively correlated to height. Conclusion. Males had a larger medullary canal than females, the long diameter of medullary canal is transverse at proximal femoral, and it gradually become longitudinal when move to isthmus then become transverse again below isthmus, this may offer valuable revelation for our anti-rotation design and better distal fixation. The medullary canal diameter were positively correlated to MCH. 71% (121 hips) femoral heads had a retroversion angle compare to femoral neck. The femoral head rotation center is below the tip of the GT rather than on the same level that may suggested a shorter neck implants for Southern Chinese patients

As the number of patients who have undergone total hip arthroplasty rises, the number of patients who require surgery for a failed total hip arthroplasty is also increasing. It is estimated that 183,000 total hip replacements were performed in the United States in the year 2000 and that 31,000 of these (17%) were revision procedures. Reconstruction of the failed femoral component in revision total hip arthroplasty can be challenging from a technical perspective and in pre-operative planning. With multiple reconstructive options available, it is helpful to have a classification system which guides the surgeon in selecting the appropriate method of reconstruction. A classification of femoral deficiency has been developed and an algorithmic approach to femoral reconstruction is presented. Type I:. Minimal loss of metaphyseal cancellous bone with an intact diaphysis. Often seen when conversion of a cementless femoral component without biological ingrowth surface requires revision. Type II: Extensive loss of metaphyseal cancellous bone with an intact diaphysis. Often encountered after the removal of a cemented femoral component. Type IIIA: The metaphysis is severely damaged and non-supportive with more than 4cm of intact diaphyseal bone for distal fixation. This type of defect is commonly seen after removal of grossly loose femoral components inserted with first generation cementing techniques. Type IIIB: The metaphysis is severely damaged and non-supportive with less than 4cm of diaphyseal bone available for distal fixation. This type of defect is often seen following failure of a cemented femoral component that was inserted with a cement restrictor and cementless femoral components associated with significant distal osteolysis. Type IV: Extensive meta-diaphyseal damage in conjunction with a widened femoral canal. The isthmus is non-supportive. An extensively coated, diaphyseal filling component reliable achieves successful fixation in the majority of revision femurs. The surgical technique is straightforward and we continue to use this type of device in the majority of our revision total hip arthroplasties. However, in the severely damaged femur (Type IIIB and Type IV), other reconstructive options may provide improved results. Type IIIB:. Based on the poor results obtained with a cylindrical, extensively porous coated implant (with 4 of 8 reconstructions failing), our preference is a modular, cementless, tapered stem with flutes for obtaining rotational stability. Excellent results have been reported with this type of implant and by virtue of its tapered design, excellent initial axial stability can be obtained even in femurs with a very short isthmus. Subsidence has been reported as a potential problem with this type of implant and they can be difficult to insert. However, with the addition of modularity to many systems that employ this concept of fixation, improved stability can be obtained by impaction of the femoral component as far distally as needed while then building up the proximal segment to restore appropriate leg length. Type IV:. The isthmus is completely non-supportive and the femoral canal is widened. Cementless fixation cannot be reliably used in our experience, as it is difficult to obtain adequate initial implant stability that is required for osseointegration. Reconstruction can be performed with impaction grafting if the cortical tube of the proximal femur is intact. However, this technique can be technically difficult to perform, time consuming and costly given the amount of bone graft that is often required. Although implant subsidence and peri-prosthetic fractures (both intra-operatively and post-operatively) have been associated with this technique, it can provide an excellent solution for the difficult revision femur where cementless fixation cannot be utilised. Alternatively, an allograft-prosthesis composite can be utilised for younger patients in an attempt to reconstitute bone stock and a proximal femoral replacing endoprosthesis used for more elderly patients

Objective. To three-dimensionally reconstruct the proximal femur of DDH (Developmental dysplasia of the hip) and measure the related anatomic parameters, so that we could have a further understanding of the morphological variation of the proximal femur of DDH, which would help in the preoperative planning and prosthesis design specific for DDH. Methods. From Jan.2012 to Dec.2014, 38 patients (47 hips) of DDH were admitted and 30 volunteers (30 hips) were selected as controls. All hips from both groups were examined by CT scan and radiographs. The Crowe classification method was applied. The CT data were imported into Mimics 17.0. The three-dimensional models of the proximal femur were then reconstructed, and the following parameters were measured: neck-shaft angle, neck length, offset, height of the centre of femoral head, height of the isthmus, height of greater trochanter, the medullary canal diameter of isthmus(Di), the medullary canal diameter 10mm above the apex of the lesser trochanter(DT+10), the medullary canal diameter 20mm below the apex of the lesser trochanter(DT-20), and then DT+10/Di, DT-20/Di and DT+10/DT-20 were calculated. Results. There is no significant difference in neck-shaft angle between Crowe I-III DDH and the control group, while the neck-shaft angle is much smaller in Crowe IV DDH. The neck length of Crowe IV DDH is much smaller than those of Crowe I-III DDH. As for Di there is neither significant difference between Crowe I DDH and the control group, nor significant difference between CroweII-III and Crowe IV, but the difference is significant between the first two groups and the latter two groups. DT+10/DT-20 and the offset have no significant difference between the control group and DDH groups. DT-20, DT+10, DT+10/Di and DT-20/Di are much smaller in Crowe IV DDH than that in Crowe I-III and the control groups. Height of greater trochanter in Crowe IV is larger than those in Crowe I-III and the control group. Height of the centre of femoral head in Crowe IV DDH is smaller than those in Crowe I-III DDH and the control group. The height of the isthmus in Crowe IV is much smaller than those in Crowe I-III DDH and the control group. Conclusion. The neck-shaft angle in DDH groups is not larger than that in the control group, while in contrast, it's much smaller in Crowe IV DDH than that in the control group. Comparing to Crowe I-III DDH and the control group, Crowe IV DDH has a dramatic change in the intramedullary and extramedullary parameters. The isthmus and the great trochanter are higher and there is apparent narrowing of the medullary canal around the level of the lesser trochanter

Revision of the failed femoral component of a total hip arthroplasty can be challenging. Multiple reconstructive options are available and the operation itself can be particularly difficult and thus meticulous preoperative planning is required to pick the right “tool” for the case at hand. The Paprosky Femoral Classification is useful as it helps the surgeon determine what bone stock is available for fixation and hence, which type of femoral reconstruction is most appropriate. Monoblock, fully porous coated diaphyseal engaging femoral components are the “work-horse” of femoral revision. This type of a stem is used in my practice for Type 1–3a femoral defects. These stems are not used, however, in the following situations: The canal diameter is greater than 18mm; There is less than 4cm available for distal fixation in the isthmus; There is proximal femoral remodeling into retroversion. While many surgeons often believe that revision femoral components need to be “long”, they really only need to be long enough to engage 4cm of intact femoral isthmus, which is oftentimes the shortest, “primary length” fully porous coated stem. Advantages of using a shorter revision stem include: Easier surgical technique as you avoid the femoral bow, with a lower risk of fracture and under-sizing; Preserves bone stock for future revisions if required; Easier to remove if required

The femur begins to bow anteriorly at the 200 mm level, but may bow earlier in smaller people. If the stem to be used is less than 200 mm, a straight stem can be used. If the stem is longer than 200 mm, it will perforate the anterior femoral cortex. I know this because I did this on a few occasions more than 20 years ago. To use a long straight stem, there are two techniques. One can either do a diaphyseal osteotomy or one can do a Wagner split (extended trochanteric osteotomy). Both of these will put the knee in some degree of hyperextension, probably insignificant in the elderly, but it may be of significance in the young. In very young people, therefore, it may be preferable to use a bowed stem to avoid this degree of recurvatum. There are two different concepts of loading. Diaphyseal osteotomy implies a proximal loading has been sought. The Wagner split ignores the proximal femur and seeks conical fixation in the diaphysis. There will be very little bone-bone contact between what remains of the attached femur and the detached anterior cortex so that it is important to ensure that the blood supply to the anterior cortex remains intact, preferably by using Wagner's technique, using a quarter-inch osteotome inserted through the vastus to crack the medial cortex. Current modularity is of two types. Distal modularity was attempted many years ago and was never successful. Proximal modularity, as for example, the S-ROM stem, implies various sizes of sleeves fit onto the stem to get a proximal canal fill. In mid-stem modularity, the distal stem wedges into the cone. It has to be driven into where it jams and this can be somewhat unpredictable. For this reason, the solid Wagner stem has been replaced by the mid-stem modular. Once the distal femur is solidly embedded, the proximal body is then selected for height and version. The proximal body is unsupported in the mid-stem modular and initially, few fractures were noted at the taper junction. Cold rolling, shot peening and taper strengthening seem to have solved these problems. There are a variety of types of osteotomy, which can be used for different deformities. With a mid-stem modular system, generally, all that needs to be done is a Wagner-type split and fixation is sought in the mid-diaphysis by conical reaming. No matter what stem is used, distal stability is necessary. This is achieved by flutes, which engage the endosteal cortex. The flutes alone must have sufficient rotational stability to overcome the service loads on the hip of 22 Nm. I divide revision into three categories. In type one, the isthmus is intact, i.e. the bone below the lesser trochanter so that a primary stem can be used. In type two, the isthmus is damaged, i.e. the bone below the lesser trochanter, so a long revision stem is required. In a type three, there is more than 70 mm of missing proximal femur. The Wagner stem may be able to handle this on its own, but most other stems are better supported with a structural allograft cemented to the stem. The reported long term results of mid-stem modular revision implants are good as in most, over 90% survivorship. The introduction of modularity appears to have overcome initial disadvantage of the Wagner stem, i.e. its unpredictability in terms of leg length

The advent of Elastic Stable Intramedullary Nailing has revolutionised the conservative treatment of long human bone fractures in children (Metaizeau, 1988; Metaizeau et al., 2004). Unfortunately, failures still occur due to excessive bending and fatigue (Linhart et al., 1999; Lascombes et al., 2006), bone refracture or nail failure (Bråten et al., 1993; Weinberg et al., 2003). Ideally, during surgery, nail insertion into the diaphyseal medullary canal should not interrupt or injure cartilage growth; nails should provide an improved rigidity and fracture stabilisation. This study aims at comparing deflections and stiffnesses of nail-bone assemblies: standard cylindrically-shaped nails (MI) vs. new cylindrical nails (MII) with a flattened face across the entire length allowing more inertia and a curved tip allowing better penetration into the cancellous bone of the metaphysis (Figure 1). MII exhibits a section with two parameters: a diameter C providing nail stiffness and a height C' providing practical dimension when both nails are crossed at the isthmus of the diaphysis: C/C' is set to 1.25 for all MII nails. A CT scan of a patient aged 22 years was used to segment a 3D model of a 471mm-long right femur model. The medullary canal diameters at the isthmus are 10.8mm and 11.4mm in the ML and AP direction, respectively. Titanium-made CAD models of MI (Ø=4mm) and MII (flat face: Ø=5mm) were pre-curved to maintain their flat face and carefully placed and positioned according to surgeon's instructions. Both nails were inserted via lateral holes in the distal femur with their extremities either bumping against the cortex or lying in the trabecular bone. Transverse and comminuted fractures were simulated (Figure 1). For each assembly, a Finite Element (FE) tetrahedral mesh was generated (∼100181 nodes and 424398 elements). Grey-scale levels were used to assign heterogeneous material properties to the bone (E=6850 ρ. 1.49. (Morgan et al., 2003)). Two modes of loading were considered: 4-point bending (varus and recurvatum: F. max. =6000N) and internal torsion (M. max. =70kNmm). This led to the simulation of 15 FE models, including a reference intact femur. Results show that in valgus, for the transverse (comminuted) fracture, the mean displacement of the assembly decreased by around 50%: from 15.24mm (27.49mm) to 8.15mm (13.85mm) for MI and MII, respectively, compared to 3.59mm for the intact bone. The assembly stiffness increased by 87% and 99% for transverse and comminuted fracture, respectively (Table 1). Similar trends were found in recurvatum with higher increases in assembly stiffness of 170% and 143% for transverse and comminuted fracture, respectively (Table 1). In torsion, for the transverse (comminuted) fracture, the measured angle of rotation decreased from: 0.43rad (0.66rad) to 0.22rad (0.43rad) for MI and MII, respectively, compared to 0.09rad for the intact bone. This corresponded to an increase of 95% and 55% in assembly stiffness for transverse and comminuted fracture, respectively. In conclusion, using the 5mm-diameter new nails (MII) for the same intramedullar space, during either bending or torsion, assemblies were always stiffer than when using standard cylindrical nails

Background. Cement restrictors are used for maintaining good filling and pressurization of bone cement during hip and knee arthroplasties. The limitations of certain cement restrictors include the inability to accommodate for large medullary canals particularly in revision procedures. We describe a technique using SurgicelTM (Johnson & Johnson) and SPONGOSTAN™ (Johnson & Johnson) (Fig 1) to form a cement restrictor that can accommodate for large canal diameters and provide excellent pressurisation. Technique. The technique involves the application of SPONGOSTAN™ (Johnson & Johnson) foam onto a SurgicelTM (Johnson & Johnson) mesh which is then rolled onto the SPONGOSTAN™ foam forming a uniform cylindrical structure Figs 2,3. The diameter of the restrictor can be adjusted according to the desired femoral canal diameter through increasing the thickness of the SPONGOSTAN™ (Johnson & Johnson) foam. The restrictor is then inserted into the desired position in the medullary canal where it expands uniformly creating an effective restrictor and bone plug Fig 4. Bone cement is then applied and pressurisation commenced prior to the insertion of the implant Fig5. SPONGOSTAN™ is an absorbable haemostatic sponge intended for haemostatic use by applying to a bleeding surface. It consists of a sterile, water-insoluble, malleable, porcine gelatin absorbable sponge. Surgicel ™ is an absorbable hemostatic agent composed of oxidized regenerated cellulose. It is a sterile, absorbable knitted fabric that is flexible and adheres readily to bleeding surfaces. Both products are routinely used for their haemostatic properties in various surgical disciplines. Discussion. The use of intramedullary plugs in cemented total joint arthroplasty is essential in order to achieve good filling and pressurization in hip and knee arthoplasties, traditionally, a small piece of bone or a cement restrictor may be used to plug the shaft. Distal plugs seal the femoral canal, improve fixation and prevent bone cement from leaking during delivery and pressurization. Plugging the intramedullary canal during total hip arthroplasty increases penetration of cement into cancellous bone proximal to the intramedullary plug. Numerous plug designs and materials are available ranging from non-resorbable to resorbable. Regardless of design, all restrictors should avoid intramedullary cement leakage and plug migration during cement and stem insertion to ensure adequate intramedullary pressures. In some instances the diameter of the femoral canal is too wide to accommodate a conventional cement restrictor particularly when crossing the femoral isthmus and even more so in revision procedures requiring the implantation of long stemmed cemented components. The use of the Surgicel-Spongostan haemostatic restrictor overcomes some of the limitations of a standard cement restrictors. These include the ability to bypass a narrow femoral isthmus, accommodate large femoral canals, particularly in revision procedures, and the flexibility of adjusting the restrictor to the desired diameter of the medullary canal and in effect providing a bespoke cement restrictor. This technique was used successfully in over 300 revision hip and knee procedures with no adverse effects and excellent outcomes

INTRODUCTION: As the number of patients who have undergone total hip arthroplasty rises, the number of patients who require surgery for a failed total hip arthroplasty is also increasing. It is estimated that 183,000 total hip replacements were performed in the United States in the year 2000 and that 31,000 of these (17%) were revision procedures. Reconstruction of the failed femoral component in revision total hip arthroplasty can be challenging from both a technical perspective and in pre-operative planning. With multiple reconstructive options available, it is helpful to have a classification system which guides the surgeon in selecting the appropriate method of reconstruction. DISCUSSION: An extensively coated, diaphyseal filling component reliably achieves successful fixation in the majority of revision femurs. The surgical technique is straightforward and we continue to use this type of device in the majority of our revision total hip arthroplasties. However, in the severely damaged femur (Type IIIB and Type IV), other reconstructive options may provide improved results. Based on our results, the following reconstructive algorithm is recommended for femoral reconstruction in revision total hip arthroplasty: TYPE I: In a Type I femur, there is minimal loss of cancellous bone with an intact diaphysis. Cemented or cementless fixation can be utilised. If cemented fixation is selected, great care must be taken in removing the neo-cortex often encountered to allow for appropriate cement intrusion into the remaining cancellous bone. TYPE II: In a Type II femur, there is extensive loss of the metaphyseal cancellous bone and thus fixation with cement is unreliable. In this cohort of patients, successful fixation was achieved using a diaphyseal fitting, extensively porous coated implant in 26 of 29 cases (90%) However, as the metaphysis is supportive, a cementless implant that achieves primary fixation in the metaphysis can be utilized. TYPE III A: In a Type IIIA femur, the metaphysis is non-supportive and an extensively coated stem of adequate length is utilised to ensure that more than 4 cm of scratch fit is obtained in the diaphysis. TYPE III B: Based on the poor results obtained with a cylindrical, extensively porous coated implant, our present preference is a modular, cementless, tapered stem with flutes for obtaining rotational stability. Excellent results have been reported with this type of implant and by virtue of its tapered design, excellent initial axial stability can be obtained even in femurs with a very short isthmus. Subsidence has been reported as a potential problem with this type of implant and they can be difficult to insert. However, with the addition of modularity to many systems that employ this concept of fixation, improved stability can be obtained by impacting the femoral component as far distally as needed while then building up the proximal segment to restore appropriate leg length. TYPE IV: In a Type IV femur, the isthmus is completely non-supportive and the femoral canal is widened. Cementless fixation cannot be reliably used in our experience, as it is difficult to obtain adequate initial implant stability that is required for osseointegration. Reconstruction can be performed with impaction grafting if the cortical tube of the proximal femur is intact. However, this technique can be technically difficult to perform, time consuming and costly given the amount of bone graft that is often required. Although implant subsidence and peri-prosthetic fractures have been associated with this technique, it can provide an excellent solution for the difficult revision femur where cementless fixation cannot be utilised. Alternatively, an allograft-prosthesis composite can be utilised for younger patients in an attempt to reconstitute bone stock and a proximal femoral replacing endoprosthesis used for more elderly patients

Summary Statement. We used three-dimensional software to assess different anatomic variables in the femur. The canal of Femur twisted slightly below the lesser trochanter in cases with a larger angle of anteversion. Introduction. Accurate positioning of the joint prosthesis is essential for successful total hip arthroplasty (THA). To aid in tailoring of the prosthesis, we used three-dimensional software to assess different anatomic variables in the femur. Patients & Methods. We used CT imaging data of the unaffected normal side of the 25 patients (22 females, age range 30 to 81 years) who underwent THA in 2012 in our hospital. The femur was reconstructed from CT data and measured using three-dimensional modeling software (Mimics 16.0 Materialise, Leuven, Belgium). We measured ellipse fitting to the medullary canal in the axial plane of the femur at 20-mm intervals. The angle between the major axis of those ellipses and the axis of the femoral neck was measured and expressed as the canal rotation. The distance between the lesser trochanter and the center of the femoral head was measured along the Z axis. Results. The major axes of the ellipses direct to medial, front and medial side in the level of epiphysis, above isthmus and distal portion respectively in all cases. The maximum rotated level was above isthmus. The rotation angle in the proximal portion ranged from 36 to 84 degrees (mean, 60.6 degrees, SD ± 12.1). The rotation angle of the distal portion ranged from 71 to 95 degrees (mean, 86.1 degrees, SD ± 6.1). Discussion/Conclusion. The torsion of the canal varied more widely between individuals in the proximal portion than did the distal portion. In addition, the torsion of the proximal aspect, although more variable, was on average smaller when the angle of anteversion was large. Because the canal twisted slightly below the lesser trochanter in cases with a larger angle of anteversion, it is suggested that attention to the degree of anteversion of a flat prosthesis stem is warranted

Objective. The purpose of this study was to compare the proximal femoral morphology between normal Chinese and Caucasian populations by 3D analysis derived from CT data. Materials and Methods. 141 anonymous Chinese femoral CT scans (71 male and 70 female) with mean age of 60.1years (range 20–93) and 508 anonymous Caucasian left femoral CT scans (with mean age of 64.8years (range 20–93). The CT scans were segmented and converted to virtual bones using custom CT analytical software. (SOMA™ V.4.0) Femoral Head Offset (FHO) and Femoral Head Position (FHP) were measured from head center to proximal canal central axis and to calcar or 20mm above Lesser Trochanter (LT) respectively. The Femoral neck Anteversion (FA) and Caput-Collum-Diaphyseal (CCD) angles were also measured. The Medial Lateral Widths(MLW. n. ) of femoral canal were measured at 0, -10, LT, -30, -40, -60, -70 and -100mm levels from calcar. Anterior Posterior Widths (APW. n. ) were measured at 0, -60 and -100mm levels. The Flare Index (FI) was derived from the ratio of widths at 0 and -60mmor FI=W. 0. /W. −60. All measurements were performed in the same settings for both populations. The comparison was analyzed by Student T test. P<0.05 was considered significant. Results. The average FHO and FHP of Chinese were 38.4mm and 25.2mm and were both shorter than 42.1mm and 29.7mm of Caucasian's, P=2.3E-15 and P=1.7E-10. (Figure 1) CCD angle was 130.3° comparing to 127.7° of Caucasian P=1.5E-05. Chinese FA angle was 15.6° and Caucasian's was 14.7°, P=0.31. The average MLW. 1-8. were 43.1, 34.6, 28.5, 23.8, 20.6, 17, 16.2 and 14.4mm for Chinese and 43.7, 35.0, 28.7, 24.0, 20.6, 16.7, 15.7 and 13.5mm for Caucasian. P=9.4E-02, .32, .47, .50, .93, .20, .02 and 1.7E-05 respectively. (Figure 2) The average APW. 1-3. were 35.9, 15.5 and 13.7mm for Chinese and 43.7, 15.2 and 12.5mm for Caucasian. P=4E-62, 0.11 and 7.4E-10. (Figure 3) The total medial/lateral and medial/center FI were 2.5 and 2.8 for Chinese, 2.6 and 2.9 for Caucasian. P=.004 and 4.5E-06. The total anterior/posterior and anterior/center FI were 2.3 and 2.6 for Chinese, 2.9 and 2.5 for Caucasian. P=5.3E-61 and 8.5E-04. Conclusion and Discussion. Chinese had significantly lower FHO, FHP, APW. calcar. , FI. medial, M-L. and FI. A-P. ; significantly higher CCD angle and MLW. isthmus. , APW. isthmus. and FI. anterior. than that of Caucasian population. There were no significant differences in FA and MLW from 10mm above to 50mm bellow LT. The average reduction of 3.7mm in FHO and 4.5mm in FHP for Chinese suggests a necessary adjustment of femoral implant neck length designed for Caucasian population. Due to the findings of the similarity in MLW and dissimilarity in APW, the study suggested the M-L fitting stem will fit well for both populations

Femoral components in total hip replacements fail in well-known ways. There is vertical sink, posterior rotation and pivot, either distal or mid-stem. In order to sink, the stem moves into valgus and then slides down the inside of the calcar. It does not cut through the calcar. To prevent sink and pivot, a canal filling stem is required. Canal fill prevents the stem from moving into valgus and, therefore, it will not sink. Two centimeters with complete canal fill is adequate in a primary stem. A long stem will give longer canal fill in a revision. Sharp distal flutes will prevent rotation. The distal end of the stem should be polished. One is looking for a distal stability, not distal fixation. If the isthmus is intact, a primary stem can be used. If the isthmus is damaged, a long stem is necessary. If the calcar is intact, a primary neck is adequate. If the calcar is missing down to the level of the lesser trochanter, a calcar replacement neck is required. If there is more than 70 millimeters of completely missing proximal femur, a structural allograft is required. If the proximal femur is damaged, the ability to place a sleeve or collar to seek the best bone available independently of the stem version is very helpful. No matter how poor the proximal bone quality is, it can be supplemented by cerclage wires. The implant will sink only if the cerclage wires break. The advantage of proximal fixation is that loading the proximal femur speeds recovery. The huge disadvantage of distal fixation is removal of the implant should it become necessary. My long term results for the S-ROM stem used in revision are now out over 20 years. There were 119 primary stems with a minimum follow up of 5 years with no revisions for aseptic loosening. There were 262 long stems used. Nine (3.7%) underwent aseptic loosening. Most of these were due to technical errors due to my inexperience in the learning process of revision surgery. Four were dependent on strut-grafts and should have been treated with structural allografts. There were seven cases with structural allografts. Three were revised. Again, these were largely from problems arising from inexperience. I believe proximal modularity with distal stability allows the vast majority of revision cases to be treated with proximal fixation

The shape of the femoral canal is variable, infact more variable than most contemporary designs of femoral components would suggest or accommodate. Clinical and experimental studies of total hip replacement have demonstrated the need for a close geometric fit between the femoral component and the supporting bone for a durable implant fixation. In order to provide a basis for design and selection of femoral components in future, we undertook an anthropometric study of proximal femoral geometry on Indian specimens. 74 cadaveric femorae were studied to analyze the difference in the endosteal and periosteal geometry between Indian and Western population. Standard extra-cortical and endosteal dimensions were determined by direct measurements of radiographs. To enable comparison standard horizontal and vertical axis were established using the geometric center of lesser trochanter and the bisecting axis of the medullary canal at the level of the isthmus. Statistically significant differences were found for the following measurements: Femoral head offset, Width at lesser trochanter, Width at lesser trochanter-20mm, Proximal border of isthmus, Neck shaft angle

Canal Flare Index, defined as the ratio of the intracortical width of the femur at a point 20mm proximal to the lesser trochanter and at the canal isthmus by Noble et al,; is considered to express the proximal femoral geometory, but it is usually measured by a plain A-P X-ray. Then it is thought the index is influenced by rotational position of the femur, so we made 3-D femoral model based on CAT scans and measured the canal flare index three dimensionally. Then the effect of observation from rotated direction was evaluated. CAT scans of 49 femurs (18 male, 31 female) were obtained from the pelvis to the feet. The average age was 60.4 years old ranging from 25 to 82. Forty nine femurs contained 22 osteoarthritis of hip joint, 12 trauma, 9 knee arthritis, 3 avascular necrosis of femoral head, 3 normal candetes. From those data, 3-D models of normal side were individually made for measuring the parameters. 3-D models were made using CAD software. We measured the canal flare index at which the femur posterior condyles were parallel to the plane, reproducing the situation to take A-P X-ray. After that, those 3-D models were rotated and investigated the difference of the value to study the effect of femur position. The canal flare index was between 2.8 and 6.6 with the average value at 4.65. The stovepipe (canal flare index< 3), the normal range (3~canal flare index< 4.7), the champagne flute (4.7~canal flare index), included 2%(1 femur), 61.2%(30 femurs), 36.7%(18 femurs), respectively. About the effect of rotation, we found the value of canal flare index was more sensitive to proximal femur rotation than the canal isthmus. The results of the canal flare index at the plane parallel to the posterior condyle line varied widely compared with the results at the position considering the anteversion. So it was suggested that the canal flare index at the patella front position does not represent the canal characteristics. It should be argued in 3-D space