Between 1972 and 1990, we performed 168 primary low-friction arthroplasties in 125 patients with acetabular protrusion. Twelve hips were lost to follow-up within eight years and eight which became infected were excluded from the final study. Of the 148 hips remaining, 62 with a mild protrusion were classified as group 1, 54 with moderate or severe protrusion as group 2 and, after 1985, 32 with moderate and severe protrusion which required bone grafts as group 3. The mean follow-up was 18.3 years (3 to 24) for group 1, 17.4 years (8 to 22) for group 2 and ten years (8 to 13) for group 3. There were 31 revisions of the cup, 12 in group 1 and 19 in group 2. According to the Kaplan-Meier analysis the overall rates at 20 years were 21 ± 10.79% in group 1 and 37 ± 11.90% in group 2. There have been 43 radiological loosenings: 22 in group 1, 21 in group 2 and none so far in group 3, at ten years. The overall loosening rates at 20 years were 42 ± 14.76% in group 1 and 49 ± 19.50% in group 2. The grafts were well incorporated in all group-3 hips, and the bone structure appeared normal after one year. The distance between the centre of the head of the femoral prosthesis and the approximate true centre of the femoral head was less in group 3 than in groups 1 and 2 (p < 0.01). According to the Cox proportional-hazards regression this was the single most important factor in loosening of the cup (odds ratio 1.11; 95% CI 1.05 to 1.18/mm). Better results were obtained in moderate and severe protrusions reconstructed with bone grafting than in hips with mild protrusion which were not grafted

Introduction and Aims: We undertook this study to detemine the results of acetabular fixation using the Duraloc 300 uncemented acetabular component combined with impaction bone grafting in patients with acetabular protrusion. Method: Thirty consecutive total hip replacements using a Duraloc 300 cup in patients with acetabular protrusion requiring impaction bone grafting were reviewed at an average of 5.2 years. Pre-operative x-rays were analysed for degree of protrusion. Post-operative x-rays were analysed for cup placement and interface gaps. Follow-up films were analysed for graft incorporation, lucent lines, osteolysis, wear and migration. Kaplan-Meier survivorship analysis was performed. Results: All components were found to be stable with no evidence of loosening or migration. All but two cases showed trabeculated bone with an average minimum thickness of 7mm of bone medial to the cup in zone 2. Mean rate of wear was 0.10mm per year. No cases of pelvic osteolysis were seen. Conclusion: The Duraloc 300 cup provides excellent fixation in patients with acetabular protrusion and impaction bone grafting. The graft has been found to incorporate and remodel. We are therefore optimistic that the durability of fixation should equal that of primary hip surgery without protrusion

Introduction Controversy exists regarding the value of lumbar plain x-ray imaging for patients with low back pain with or without radicular pain (. 1. ,. 2. ,. 3. ). Methods Plain film x-ray and CT imaging from thirty (30; 19M:11F) consecutive patients (aged 20–68 years; mean 42 years) presenting to a public hospital’s spinal pain clinic with low back pain +/− radicular pain, without a history suggesting ‘red flag’ pathology, was examined and measured to determine the incidence of retrolisthesis of L5 on S1 and any associated disc bulge/protrusion. Results Sixteen of the thirty patients (53%) had retrolisthesis of L5 on S1 ranging from 2–9 mm; these patients had either intervertebral disc bulging or protrusion on CT examination ranging from 3–7 mm into the spinal canal. Fourteen patients (47%) without retrolisthesis (control group) did not show any retrolisthesis and the CT did not show any bulge/protrusion. On categorizing x-ray and CT pathology as being present or not, the well positioned ie. true lateral plain x-ray film revealed a sensitivity and specificity of 100% ([95% Conf. Int. = [89%–100%]) for bulge/protrusion in this preliminary study. On taking into account the numerical values of x-ray and CT, a significant correlation (p< 0.001) was found. Discussion In this preliminary study, carefully positioned lateral lumbosacral x-ray films showing L5 on S1 retrolisthesis are highly suggestive of intervertebral disc bulge/protrusion, providing valuable guidance for consideration of lumbosacral CT of MRI examination that is likely to be contributory regarding such pathology

1. A study of fifty-nine patients with protrusion of the acetabulum showed that they fell into three age groups: those in their teens, those aged thirty-five to fifty years, and those presenting from fifty-one years onwards. 2. The juvenile age group was investigated clinically and biochemically but no causative metabolic factor was found. 3. The familial incidence was confirmed by radiological and biochemical surveys of several families. 4. The results of treatment show that when conservative treatment is insufficient a total hip replacement gives the best result from operation

Purpose of the study: We have tried to produce a new acetabular ring in order to obtain an early stability of cemented cup for acetabular protrusion in R.A. In this presentation, we intend to introduce this new support ring and report these results. Materials and methods: The new support ring with double-hook we produced was made of pure titanium, and has eight screw holes in medial side and two screw holes in superolateral side. Size variation of this ring comprises 40mm, 42mm, 46mm, 48mm and 50mm in inner diameter. Width of the hook is 10.05mm and its thickness is 1.19mm. Hook length is 33.5mm. After the remaining bone defect is packed with morselizd and mushed allograft bone, proper support ring with double hook is selected. Straight portions of double hook are bent in order to fit to acetabular shape after bone grafts. If good fitting is achieved, this support ring was fixed to the acetabulum with three to five screws. Total hip arthroplasty with this support ring was performed in ten patients with eleven hips. Three cases were in male and seven in female. The age at surgery ranged from 46 to 73 years old with an average of 59.8 years. Results: Setting angle of support ring ranged from 40 to 50 degrees with an average of 43.7 degrees. Follow-up period was from one year to three years with an average of two years one month. No loosening was encountered and no migration of support ring and cup was visualized on radiological findings. JOA(Japanese Orthopaedic Association) hip score which was adopted for clinical evaluation was 31.3+/−10.2 before surgery and 70.1+/−8.5 after surgery. Discussion: Various types of reinforcement ring have been used with or without bone grafts for acetabular protrusion. I had prefered Ganz ring among them. Bending a hook of Ganz ring, however, is not easy as its hook portion is slightly thick. Accordingly, setting angle of the ring is often apt to be acute as it must be fitted to acetablualr shape. In superior cortical defect of the acetabulum, hook length is often insufficient because a hip center of the ring is in high position. Therefore, it is sometimes impossible to hook acetabular notch. We produced a new support ring with double-hook in order to solve these problems. As the hook was thinner in the new ring than in Ganz ring, it was easier to bend the hook. As the hook of of the new ring was longer than that of Ganz ring, it was possible to hook acetabular notch in spite of high hip center. Setting angle of the new rings was less than 50 degrees. Radiological findings and clinical results were good though follow-up period was short

Introduction. Since 1981, we have used various types of the total hip prosthesis for the reconstruction of the acetabular protrusion in rheumatoid arthritis. The cemented Charnley prosthesis was used during the initial 8 years, and we experienced loosening of the cemented acetabular socket in some cases. The bipolar femoral head prosthesis, which started to be used from 1984, was one of the cementless prosthesis. And it showed high frequency of proximal migration of outerhead. The threaded socket also showed frequent loosening. To overcome these problems, we started to utilize a new method from 1988. This method included packing morselized bone grafts into the acetabulum and fix them using a porous coated socket and screws. This study describes the results of cementless total hip arthroplasty (THA) for the acetabular protrusion in rheumatoid arthritiswith this method. Materials and methods. Sixty -one cementless THAs with use of porous coated acetabular socket were performed in 50 patients who had sever protruded acetabulum due to rheumatoid arthritis. The average follow –up period was 9 years and 5 months (range, 5 to 13 years). A Mallory/ Head prosthesis with porous coated socket was used in 43 hips and other types in 18 hips. In all operated hips, autogenous morselized bones were grafted on the thin acetabullar wall. Results. The clinical improvement in pain was the most apparent. X-ray findings of the grafted bone in the acetabulum showed a homogenous pattern in most cases (90. 2%) at 6 months after the operation. A radiolucent zone at a non-weight-bearing area between the grafted bone and socket was seen in 20 hips (32. 7%) for 3 years after the operation, and it gradually disappeared and changed to a sclerotic zone. Collapse and /or absorption of the grafted bone were noted in 3 hips of the patients with sever osteoporosis and high disease activity. Discussion. There are several technical key points to succeed THA in patients with rheumatoid arthritis. The first is the selection of the acetabular socket. The second is the method of bone grafting, and the third is the size and the shape of grafted bones. We have used various types of prosthesis for the protruded acetabulum so far, and it was considered that the bipolar and threaded types are not acceptable because of their high frequency of proximal migration and loosening. The mass and /or block bone should not be used, because they are liable to fall into collapse. It is safely recommended to use slice or morselized bones to lead the grafts to early survival and remodelling caused by tight and close contacts. Conclusion. THA with the use of morselized bone grafting into the acetabulum and a fixation with a porous coated socket-and screws is a simple and useful procedure for treating protruded acetabulum in rheumatoid arthritis

1. The technique of correction of mandibular protrusion and retrusion by osteotomies through the rami of the mandible is described and illustrated. 2. The best age for the operation, and the factors that might favour or prevent relapse, are discussed. 3. Illustrative cases are described

Aims. Mechanical impingement of the iliopsoas (IP) tendon accounts for 2% to 6% of persistent postoperative pain after total hip arthroplasty (THA). The most common initiator is anterior acetabular component protrusion, where the anterior margin is not covered by anterior acetabular wall. A CT scan can be used to identify and measure this overhang; however, no threshold exists for determining symptomatic anterior IP impingement due to overhang. A case-control study was conducted in which CT scan measurements were used to define a threshold that differentiates patients with IP impingement from asymptomatic patients after THA. Methods. We analyzed the CT scans of 622 patients (758 THAs) between May 2011 and May 2020. From this population, we identified 136 patients with symptoms suggestive of IP impingement. Among them, six were subsequently excluded: three because the diagnosis was refuted intraoperatively, and three because they had another obvious cause of impingement, leaving 130 hips (130 patients) in the study (impingement) group. They were matched to a control group of 138 asymptomatic hips (138 patients) after THA. The anterior acetabular component overhang was measured on an axial CT slice based on anatomical landmarks (orthogonal to the pelvic axis). Results. The impingement group had a median overhang of 8 mm (interquartile range (IQR) 5 to 11) versus 0 mm (IQR 0 to 4) for the control group (p < 0.001). Using receiver operating characteristic curves, an overhang threshold of 4 mm was best correlated with a diagnosis of impingement (sensitivity 79%, specificity 85%; positive predictive value 75%, negative predictive value 85%). Conclusion. Pain after THA related to IP impingement can be reasonably linked to acetabular overhang if it exceeds 4 mm on a CT scan. Below this threshold, it seems logical to look for another cause of IP irritation or another reason for the pain after THA before concluding that impingement is present. Cite this article: Bone Joint J 2024;106-B(3 Supple A):97–103

Purpose: Pelvic discontinuity associated with bone loss is a complex challenge in acetabular revision surgery. Reconstruction with anti protrusion cages, Trabecular Metal (Zimmer, Warsaw, Indiana) cups and morselized bone (Cup-Cage) constructs is a relatively new technique used by the authors for the past 6 years. The purpose of the study was to examine the clinical outcome of these patients. Method: Thirty-two consecutive acetabular revision reconstructions in 30 patients with pelvic discontinuity and bone loss treated by cup cage technique between January 2003 and September 2007 were reviewed. Average clinical and radiological follow up was 38.5 ± 19 months (range 12 – 68, median 34.5). Failure was defined as component migration > 5mm. Results: In 29 (90.6%) patients there was no clinical or radiographic evidence indicative of loosening at latest follow up. Harris Hip Scores improved significantly (p< 0.001) from 46.6 ± 10.4 to 78.7 ± 10.4 at 2 year follow up. In 3 patients the construct migrated at 1 year post surgery. One construct was revised to anti protrusion cage with a structural graft while the other was revised to a large Trabecular Metal cup. The third patient is scheduled for revision. Complications included 2 dislocations, 1 infection and 1 partial peroneal nerve palsy. Two patients died due to unrelated reasons at 1 and 3 years post surgery, respectively. Conclusion: Treatment of pelvic discontinuity by Cup-Cage construct is a reliable option based on preliminary results which suggest restoration of the pelvic mechanical stability. However, patients should be followed closely in order to detect cup migration until satisfactory bony ingrowth into the cup takes place

To quantify bone-nail fit in response to varying nail placements by entry point translation in straight antegrade humeral nailing using three-dimensional (3D) computational analysis. CT scans of ten cadaveric humeri were processed in 3D Slicer to obtain 3D models of the cortical and cancellous bone. The bone was divided into individual slices each consisting of 2% humeral length (L) with the centroid of each slice determined. To represent straight antegrade humeral nail, a rod consisting of two cylinders with diameters of 9.5mm and 8.5mm and length of 0.22L mm and 0.44L mm respectively joined at one end was modelled. The humeral head apex (surgical entry point) was translated by 1mm in both anterior-posterior and medio-lateral directions to generate eight entry points. Total nail protrusion surface area, maximum nail protrusion distance into cortical shell and top, middle, bottom deviation between nail and intramedullary cavity centre were investigated. Statistical analysis between the apex and translated entry points was conducted using paired t-test. A posterior-lateral translation was considered as the optimal entry point with minimum protrusion in comparison to the anterior-medial translation experiencing twice the level of protrusion. Statistically significant differences in cortical protrusion were found in anterior-medial and posterior-lateral directions producing increased and decreased level of protrusion respectively compared to the apex. The bottom anterior-posterior deviation distance appeared to be a key predictor of cortical breach with the distal nail being more susceptible. Furthermore, nails with anterior translation generated higher anterior-posterior deviation (>4mm) compared to posterior translation (<3mm). Aside from slight posterolateral translation of the entry point from the apex, inclusion of a distal posterior-lateral bend into current straight nail design could improve nail fitting within the curved humeral bone, potentially improving distal working length within the flat and narrow medullary canal of the distal humeral shaft

Bone defects are frequently observed in anterior shoulder instability. Over the last decade, knowledge of the association of bone loss with increased failure rates of soft-tissue repair has shifted the surgical management of chronic shoulder instability. On the glenoid side, there is no controversy about the critical glenoid bone loss being 20%. However, poor outcomes have been described even with a subcritical glenoid bone defect as low as 13.5%. On the humeral side, the Hill-Sachs lesion should be evaluated concomitantly with the glenoid defect as the two sides of the same bipolar lesion which interact in the instability process, as described by the glenoid track concept. We advocate adding remplissage to every Bankart repair in patients with a Hill-Sachs lesion, regardless of the glenoid bone loss. When critical or subcritical glenoid bone loss occurs in active patients (> 15%) or bipolar off-track lesions, we should consider anterior glenoid bone reconstructions. The techniques have evolved significantly over the last two decades, moving from open procedures to arthroscopic, and from screw fixation to metal-free fixation. The new arthroscopic techniques of glenoid bone reconstruction procedures allow precise positioning of the graft, identification, and treatment of concomitant injuries with low morbidity and faster recovery. Given the problems associated with bone resorption and metal hardware protrusion, the new metal-free techniques for Latarjet or free bone block procedures seem a good solution to avoid these complications, although no long-term data are yet available. Cite this article: Bone Joint J 2024;106-B(10):1100–1110

The aims of this study were to assess the efficacy of a newly designed radiological technique (the radial groove view) for the detection of protrusion of screws in the groove for the extensor pollicis longus tendon (EPL) during plating of distal radial fractures. We also aimed to determine the optimum position of the forearm to obtain this view. We initially analysed the anatomy of the EPL groove by performing three-dimensional CT on 51 normal forearms. The mean horizontal angle of the groove was 17.8° (14° to 23°). We found that the ideal position of the fluoroscopic beam to obtain this view was 20° in the horizontal plane and 5° in the sagittal plane. We then intra-operatively assessed the use of the radial groove view for detecting protrusion of screws in the EPL groove in 93 fractures that were treated by volar plating. A total of 13 protruding screws were detected. They were changed to shorter screws and these patients underwent CT scans of the wrist immediately post-operatively. There remained one screw that was protruding. These findings suggest that the use of the radial groove view intra-operatively is a good method of assessing the possible protrusion of screws into the groove of EPL when plating a fracture of the distal radius. Cite this article: Bone Joint J 2013;95-B:1372–6

Introduction and Objective. Pectus carinatum is a common congenital anterior chest wall deformity, characterized by outward protrusion of sternum and ribcage resulted from rib cartilage overgrowth. The protrusion may be symmetrical or asymmetrical. Pectus carinatum association with mitral valve diseases, Marfan's syndrome, and scoliosis enforces that poor connective tissue development as possible etiological factor. Despite the coexistence of pectus carinatum and scoliosis has attracted the attention of some researchers, the association between pectus carinatum and the other spinal deformities has not been studied comprehensively. The frequency of spinal deformity in patients with pectus carinatum and the mutual relationships of their subtypes are needed to be studied to determine the epidemiological character of the combined deformity and to plan patient evaluation and management. Our study aimed to investigate the association, define the incidence and evaluate the characteristics between different types of spinal deformities and Pectus carinatum. Materials and Methods. Radiological and physical examinations were performed for 117 pectus carinatum patients in Marmara university hospital/Turkey in the years between 2006 and 2013. The incidence of spinal deformity was calculated. Spinal deformities were classified as scoliosis, kyphosis, kyphoscoliosis, and spinal asymmetry, whereas pectus carinatum were subdivided into symmetric and asymmetric subgroups. The relationship between spinal deformities and the symmetrical-asymmetric subtype of pectus excavatum was statistically analyzed, Pearson chi-square test was used to compare the association of qualitative data. The significance level was accepted as p <0.05. Lastly, the angular values of the deformities of scoliosis and kyphosis patients were measured using the Cobb method. In this way, the magnitude of the deformity was given as a numerical value. Results. Spinal deformity was detected in 23 (17 symmetrical PE and 6 asymmetrical PE) of 117 pectus excavatum patients. Scoliosis and kyphosis were seen equally in symmetrical pectus carinatum, whereas scoliosis was seen in 33.3% and kyphosis in 50% in asymmetric pectus carinatum patients, respectively. However, there were no statistically significant differences in the distribution of scoliosis and kyphosis in patients with symmetrical and asymmetrical PE. Idiopathic scoliosis constituted the most common scoliosis group. Congenital kyphosis was not found in any kyphosis patient. The average Cobb angle of scoliosis patients was 32°, and the mean T2-T12 kyphosis angle of these patients was 55.5°, while the average kyphosis angle of those with kyphosis deformity was 71°. Conclusions. Patients with Pectus carinatum have a higher incidence of spinal deformities than the normal population. Such high concomitant incidence should be taken under consideration in evaluating and treating patients presenting with either deformity

Patients who are Jehovah's witnesses do not accept blood transfusions. Thus, total hip arthroplasty can be challenging in this group of patients due to the potential for blood loss. Multiple strategies have been developed in order to prevent blood loss. A 76-year-old female, Jehovah's witness medicated with a platelet antiaggregant, presented to the emergency department after a fall from standing height. Clinically, she had pain mobilizing the right lower limb and radiological examination revealed an acetabular fracture with femoral head protrusion and ipsilateral isquiopubic fracture. Skeletal traction was applied to the femur during three weeks and no weight bearing was maintained during the following weeks. Posteriorly, there was an evolution to hip osteoarthritis with necrosis of the femoral head. The patient was submitted to surgery six months after the initial trauma, for a total hip arthroplasty. The surgery was performed with hypotensive anaesthesia, careful surgical technique and meticulous haemostasis and there was no need for blood transfusion. Posteriorly, there was a positive clinical evolution with progressive improvement on function and deambulation. Total hip arthroplasty may be safely carried out with good clinical outcomes in Jehovah's witnesses, without the need for blood transfusion, if proper perioperative precautions are taken, as has already been shown in previous studies

Cartilage degeneration and loss are key events in the initiation and progression of osteoarthritis (OA). Changes to chondrocyte volume and morphology (in the form of cytoplasmic processes) and thus cell phenotype are implicated, as they lead to the production of a mechanically-weakened extracellular matrix. The chondrocyte cytoskeleton is intimately linked to cell volume and morphology and hence we have investigated alterations to levels and distribution of chondrocyte F-actin that occur during early OA. The femoral heads (FH) from hip joints (N=16) were obtained with ethical permission and patient consent following femoral neck fracture. Cartilage was assessed as grade 0 (non-degenerate) and grade 1 (superficial fibrillation) using OARSI criteria. In situ chondrocyte volume and F-actin distribution were assessed using the fluorescent indicators (5-chloromethyl fluorescein diacetate (CMFDA)) and phalloidin, and imaged and quantified by confocal microscopy, Imaris. TM. and ImageJ software. There were no differences between the volume or total F-actin levels of in situ chondrocytes within the superficial zone of grade 0 (n=164 cells) compared to grade 1 (n=145) cartilage (P>0.05). However, a more detailed analysis of phalloidin labelling was performed, which demonstrated significant increases in both intense punctuate (IP) or intense areas (IA) (P<0.0001; P=0.0175 respectively). A preliminary analysis of IP and IA F-actin labelling suggested that while the former did not appear to be associated with changes to chondrocyte morphology, most of the cytoplasmic processes were associated with the presence of IA at the starting point of the protrusion. These results demonstrate marked changes to F-actin distribution in chondrocytes in the very early stages of cartilage degeneration as occurs in OA. These subtle changes are probably an early indication of a change to the chondrocyte phenotype and thus worthy of further study as they may lead to deleterious alterations to matrix metabolism and ultimately cartilage weakening

The purpose of this study is to evaluate risk factors for distal construct failure (DCF) in posterior spinal instrumented fusion (PSIF) in adolescent idiopathic scoliosis (AIS). We observed an increased rate of DCF when the pedicle screw in the lowest instrumented vertebra (LIV) was not parallel to the superior endplate of the LIV, however this has not been well studied in the literature. We hypothesise a more inferiorly angled LIV screw predisposes to failure and aim to find the critical angle that predisposes to failure. A retrospective cohort study was performed on all patients who underwent PSIF for AIS at the Starship Hospital spine unit from 2010 to 2020. On a lateral radiograph, the angle between the superior endplate of the LIV was measured against its pedicle screw trajectory. Data on demographics, Cobb angle, Lenke classification, instrumentation density, rod protrusion from the most inferior screw, implants and reasons for revision were collected. Of 256 patients, 10.9% (28) required at least one revision. The rate of DCF was 4.6% of all cases (12 of 260) and 25.7% of revisions were due to DCF. The mean trajectory angle of DCF patients compared to all others was 13.3° (95%CI 9.2° to 17.4°) vs 7.6° (7° to 8.2°), p=0.0002. The critical angle established is 11°, p=0.0076. Lenke 5 and C curves, lower preoperative Cobb angle, titanium only rod constructs and one surgeon had higher failure rates than their counterparts. 9.6% of rods protruding less than 3mm from its distal screw disengaged. We conclude excessive inferior trajectory of the LIV screw increases the rate of DCF and a screw trajectory greater than 11° predisposes to failure. This is one factor that can be controlled by the surgeon intraoperatively and by avoiding malposition of the LIV screw, a quarter of revisions can potentially be eliminated

Excision of the proximal femur for tumour with prosthetic reconstruction using a bipolar femoral head places a considerable load on the unreplaced acetabulum. . We retrospectively reviewed the changes which occur around the affected hip joint by evaluating the post-operative radiographs of 65 consecutive patients who underwent proximal prosthetic arthroplasty of the femur, and in whom an acetabular component had not been used. There were 37 men and 28 women with a mean age of 57.3 years (17 to 93). Radiological assessment included the extent of degenerative change in the acetabulum, heterotopic ossification, and protrusio acetabuli. . The mean follow-up was 9.1 years (2 to 11.8). Degenerative changes in the acetabulum were seen in three patients (4.6%), Brooker grade 1 or 2 heterotopic ossification in 17 (26%) and protrusion of the prosthetic head in nine (13.8%). . A total of eight patients (12.3%) needed a revision. Five were revised to the same type of prosthesis and three (4.6%) were converted to a total hip arthroplasty. . We conclude that radiological evidence of degenerative change, heterotopic ossification and protrusion occur in a few patients who undergo prosthetic arthroplasty of the proximal femur for tumour. The limited extent of these changes and the lack of associated symptoms do not justify the routine arthroplasty of the acetabulum in these patients. . Cite this article: Bone Joint J 2015;97-B:1704–9

Intramedullary nailing is the standard fixation method for displaced diaphyseal fractures of the tibia in adults. Anecdotal clinical evidence indicates that current nail designs do not fit optimally for Asian patients. This study aimed to develop a method to quantitatively assess the fitting of two nail designs for Asian tibiae. We used 3D models of two different tibial nail designs (ETN (Expert Tibia Nail) and ETN-Proximal-Bend, Synthes), and 20 CT-based 3D cortex models of Japanese cadaver tibiae. The nail models were positioned inside the medullary cavity of the intact bone models. The anatomical fitting between nail and bone was assessed by the extent of the nail protrusion from the medullary cavity into the cortical bone, which in a real bone would lead to axial malalignments of the main fragments. The fitting was quantified in terms of the total surface area, and the maximal distance of nail protrusion. In all 20 bone models, the total area of the nail protruding from the medullary cavity was smaller for the ETN-Proximal-Bend (average 540 mm2) compared to the ETN (average 1044 mm2). Also, the maximal distance of the nail protruding from the medullary cavity was smaller for the ETN-Proximal-Bend (average 1.2 mm) compared to the ETN (average 2.7 mm). The differences were statistically significant (p < 0.05) for both the total surface area and the maximal distance measurements. For all bone models, the nail protrusion occurred on the posterior side in the middle third of the tibia. For 12 bones the protrusion was slightly lateral to the centre of the shaft, for seven bones it was centred, and for one bone it was medial to the shaft. The ETN-Proximal-Bend shows a statistical significantly better intramedullary fit with less cortical protrusion than the original ETN. The expected clinical implications of an improved anatomical nail fit are fewer complications with malreduction and malalignments, a lower likelihood for fracture extension and/or new fracture creation during the nail insertion as well as an easier handling for the nail insertion. By utilising computer graphical methods we were able to conduct a quantitative fit assessment between implanted nail and bone geometry in 3D. In addition to the application in implant design, the developed method could potentially be suitable for pre-operative planning enabling the surgeon to choose the most appropriate nail design