In absence of available quantitative measures, the assessment of fracture healing based on clinical examination and X-rays remains a subjective matter. Lacking reliable information on the state of healing, rehabilitation is hardly individualized and mostly follows non evidence-based protocols building on common guidelines and personal experience. Measurement of fracture stiffness has been demonstrated as a valid outcome measure for the maturity of the repair tissue but so far has not found its way to clinical application outside the research space. However, with the recent technological advancements and trends towards digital health care, this seems about to change with new generations of instrumented implants – often unfortunately termed “smart implants” – being developed as medical devices.

The AO Fracture Monitor is a novel, active, implantable sensor system designed to provide an objective measure for the assessment of fracture healing progression (1). It consists of an implantable sensor that is attached to conventional locking plates and continuously measures implant load during physiological weight bearing. Data is recorded and processed in real-time on the implant, from where it is wirelessly transmitted to a cloud application via the patient's smartphone. Thus, the system allows for timely, remote and X-ray free provision of feedback upon the mechanical competence of the repair tissue to support therapeutic decision making and individualized aftercare.

The device has been developed according to medical device standards and underwent extensive verification and validation, including an in-vivo study in an ovine tibial osteotomy model, that confirmed the device's capability to depict the course of fracture healing as well as its long-term technical performance. Currently a multi-center clinical investigation is underway to demonstrate clinical safety of the novel implant system. Rendering the progression of bone fracture healing assessable, the AO Fracture Monitor carries potential to enhance today's postoperative care of fracture patients.

Local antimicrobial therapy is an integral aspect of treating orthopaedic device related infection (ODRI), which is conventionally administered via polymethylmethacrylate (PMMA) bone cement. PMMA, however, is limited by a suboptimal antibiotic release profile and a lack of biodegradability.

In this study, we compare the efficacy of PMMA versus an antibioticloaded hydrogel in a single- stage revision for chronic methicillin-resistant Staphylococcus aureus (MRSA) ODRI in

sheep. Antibiofilm activity of the antibiotic combination (gentamicin and vancomycin) was determined in vitro. Swiss alpine sheep underwent a single-stage revision of a tibial intramedullary nail with MRSA infection. Local gentamicin and vancomycin therapy was delivered via hydrogel or PMMA (n = 5 per group), in conjunction with systemic antibiotic therapy. In vivo observations included: local antibiotic tissue concentration, renal and liver function tests, and quantitative microbiology on tissues and hardware post-mortem.

There was a nonsignificant reduction in biofilm with an increasing antibiotic concentration in vitro (p = 0.12), confirming the antibiotic tolerance of the MRSA biofilm. In the in vivo study, four out of five sheep from each treatment group were culture negative. Antibiotic delivery via hydrogel resulted in 10–100 times greater local concentrations for the first 2–3 days compared with PMMA and were comparable thereafter. Systemic concentrations of gentamicin were minimal or undetectable in both groups, while renal and liver function tests were within normal limits.

This study shows that a single-stage revision with hydrogel or PMMA is equally effective, although the hydrogel offers certain practical benefits over PMMA, which make it an attractive proposition for clinical use.

Aim

The treatment of chronic orthopedic device-related infection (ODRI) often requires multiple surgeries and prolonged antibiotic therapy. In a two-stage exchange procedure, the treatment protocol includes device removal and placement of an antibiotic-loaded bone cement spacer to achieve high local antibiotic concentrations. At the second stage, further surgery is required to remove the spacer and replace it with the definitive device. We have recently developed a thermo-responsive hyaluronan hydrogel (THH) that may be loaded with antibiotics and used as delivery system. Since the material is bio-resorbable, it does not require surgical removal and may therefore be suitable for use as treatment strategy in a single-stage exchange.

This aim of this study was to evaluate gentamicin sulphate (Genta)-loaded THH (THH-Genta) for treating a chronic Staphylococcus aureus ODRI in sheep using a single-stage procedure.

Injury to the syndesmosis occurs in 10–13% of all operative ankle fractures and there is evidence that both incomplete treatment and malreduction of the syndesmosis can lead to poor clinical outcomes. Much attention has been given to post–operative malreduction documented by computer tomography (CT), however, there is limited data about the intact positioning and relative motion of the native syndesmosis. The aim of this study is to elucidate more detailed information on the position of the fibula in the syndesmosis during simulated weight–bearing in intact state, with sequential ligament sectioning and following two reconstructive techniques.

Fourteen paired, fresh–frozen human cadaveric limbs were mounted in a weight–bearing simulation jig. CT scans were obtained under simulated foot–flat loading (75 N) and in single–legged stance (700 N), in five foot positions: neutral, 15° external rotation, 15° internal rotation, 20° dorsiflexion, and 20° plantarflexion. The elements of the syndesmosis and the deltoid ligament were sequentially sectioned. One limb of each pair was then reconstructed via one of two methods: Achilles autograft and peroneus longus ligamentoplasty. The specimens were rescanned in all 5 foot positions following each ligament resection and reconstruction. Measurements of fibular diastasis, rotation and anterior–posterior translation were performed on the axial cuts of the CT scans, 1 cm proximal to the roof of the plafond.

Multiple measurements were made to define the position of the fibula in the incisura. Clinically relevant deformity patterns were produced. The deformity at the incisura was consistent with clinical injury, and the degree of displacement in all ligament states was dependent on the foot position. The most destructive state resulted in the most deformity at the syndesmosis. Differences between the intact and reconstructed states were found with all measurements, especially when the foot was in external rotation and dorsiflexion. There was no significant difference with direct comparison of the reconstructions.

This study has detailed the motion of the fibula in the incisura and its variation with foot position. Neither reconstruction was clearly superior and both techniques had difficulty in the externally rotated and dorsiflexed foot positions. This study design can serve as a model for future ex–vivo testing of reconstructive techniques.

Introduction

Optimal orthopaedic implant placement is a major contributing factor to the long term success of all common joint arthroplasty procedures. Devices such as 3D printed bespoke guides and orthopaedic robots are extensively described in the literature and have been shown to enhance prosthesis placement accuracy. These technologies have significant drawbacks such as logistical and temporal inefficiency, high cost, cumbersome nature and difficult theatre integration. A radically new disruptive technology for the rapid intraoperative production of patient specific instrumentation that obviates all disadvantages of current technologies is presented.

One of the most challenging complications in orthopedic trauma surgery is the development of infection. Improved infection prophylaxis could be achieved by providing local delivery of antibiotics directly to the tissue-implant interface. Especially implant-associated bone infections caused by antibiotic-resistant pathogens pose significant clinical challenges to treating physicians. Prophylactic strategies that act against resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), are urgently required.

The objective of this experimental study was to determine the efficacy of a biodegradable Polymer-Lipid Encapsulation MatriX (PLEX) loaded with the antibiotic doxycycline as a local prophylactic strategy against implant-associated osteomyelitis in a humeral non-fracture rabbit model.

Activity of the PLEX-doxycycline-coating was tested against both a doxycycline susceptible (doxyS) methicillin-susceptible S. aureus (MSSA) as well as a doxycycline-resistant (doxyR) MRSA. In a rabbit intramedullary (IM) nail-related infection model, twelve rabbits received an inoculum of a doxyS MSSA direct into the medullary cavity of the humerus. After inoculation, animals received either a PLEX-doxycycline-coated nail, or an uncoated nail. The animals were observed for four weeks. Upon euthanasia, quantitative bacteriology was performed to determine bacterial load in tissues and biofilm formation on the implant. A second study was performed with sixteen rabbits receiving a DoxyR MRSA inoculum, again in coated and uncoated groups.

In vitro elution studies revealed that 25% of the doxycycline was released from the PLEX-coated implants within the first day, followed by a 3% release per day up to day 28. Quantitative bacteriology revealed the presence of osteomyelitis in all animals receiving an uncoated nail in both the MSSA and the DoxyR MRSA studies (figure). All rabbits receiving a PLEX-doxycycline-coated nail were culture negative in the doxyS MSSA-group and the surrounding bone displayed a normal physiological appearance in both histological sections and radiographs. In the doxyR MRSA inoculated rabbits, a statistically significant reduction in the number of culture-positive samples was observed for the PLEX-doxycycline-coated group when compared to the animals that had received an uncoated nail, although the reduction in bacterial burden did not reach statistical significance.

Improved prophylaxis against infection in trauma and orthopedic implant surgery is clearly required today. In this study, we investigated a PLEX-doxycycline-coated IM nail in a humeral non-fracture rabbit model. The PLEX-doxycycline coating on titanium alloy implants provided complete protection against implant-associated MSSA osteomyelitis, and resulted in a significant reduction in the number of culture positive samples when challenged with a doxycycline-resistant MRSA.

Background:

Little is known about the forces carried by the Taylor Spatial Frame (TSF) hexapod fixator. Our aim was to measure the TSF resultant force and how this changed during the consolidation phase.

Summary

The two-step labeling protocol using Lysostaphin and bio-orthogonal click chemistry for staining bacteria is described. The click protocol is efficient in labeling staphylococci and is non-toxic. This protocol promises the efficient of infections that are difficult to assess by conventional imaging.

Summary Statement

Tibia plateau split fracture fixation with two cancellous screws is particularly suitable for non-osteoporotic bone, whereas four cortical lag screws provide a comparable compression in both non-osteoporotic and osteoporotic bone. Angle-stable locking plates maintain the preliminary compression applied by a reduction clamp.

Summary

Biomechanically, a 2° screw deviation from the nominal axis in the PFLCP leads to significantly earlier implant failure. Screw deviation relies on a technical error on insertion, but in our opinion cannot be controlled intraoperatively with the existing instrumentation devices.

The position of the pelvis has been shown to influence acetabular orientation. However there have been no studies quantifying that effect on the native acetabulum. Our aims were to investigate whether it is possible to quantify the relationship between pelvic tilt and acetabular orientation in native hips, and whether pelvic tilt affects acetabular cover of the femoral head.

Computerized tomography scans of 93 hips (36 normal, 31 dysplastic and 26 with acetabular retroversion) were analyzed. We used a CT technique that allows standardised three-dimensional (3D) analysis of acetabular inclination and anteversion and calculation of femoral head cover in relation to the anterior pelvic plane and at different degrees of forward and backward tilt. Acetabular anteversion, inclination and cover of the femoral head were measured at pelvic tilt angles ranging from −20° to 20° in relation to the anterior pelvic plane using 5° increments.

The effect of pelvic tilt on version was similar in the normal, dysplastic and retroverted groups, with a drop in anteversion ranging from 2.5° to 5° for every 5° of forward tilt. The effect on inclination was less marked and varied among the three groups. Pelvic tilt increased femoral head cover in both normal and dysplastic hips. The effect was less marked, and tended to be negligible at higher positive tilt angles, in the retroverted group.

This study has provided benchmark data on how pelvic tilt affects various acetabular parameters which in turn may be helpful in promoting greater understanding of acetabular abnormalities and how pelvic tilt affects the interpretation of pelvic radiographs.

We have investigated whether a system of four inertial measurement units (IMUs) attached to the segments of the lower limbs could provide useful information about the kinematics of limb segment movement in gait in a healthy population. Four IMUs were attached to participants over their clothes. Participants then walked at their self-selected speed for 10 metres along a corridor and back. IMUs were removed, data downloaded on to a computer and ranges of motion were calculated for thigh, calf and knee, in addition to stride duration. 128 participants were recruited aged 18–97. There was little variation in most angle parameters up to age of 80. The relationships between angle and age are non-linear. There was a slight increase in stride duration with age of about 0.1% per year. The study concentrated on active subjects, with no specific co-morbidities that might affect gait. Results obtained may represent what is achievable for any given age, and approximate to changes that occur due to primary ageing. We propose that, after the age 80, peak muscle power declines below a threshold, such that muscular activity required to move a limb approaches the peak power available, and that it is the decline in peak muscle power that ultimately limits gait in active older people. Walking ability is important in maintaining independence as people age. It would be more effective to encourage exercises to maintain normal gait at a much earlier age. Deviations from the normal range could be identified early, and appropriate intervention given.

Introduction: The diagnosis of acetabular retroversion has traditionally been established by the presence of a cross-over sign on a plain pelvic radiograph. This however can be greatly influenced by the radiograph’s quality and degree of pelvic tilt. The aim of this study was to look at the relationship between cross-over and true anatomical version as measured in relation to an anatomical reference plane. The secondary aim was to determine whether in true retroversion there was excess coverage of the femoral head anteriorly.

Materials and Methods: Radiographs of 33 patients (64 hips) being investigated for symptoms of femoro-acetabular impingement were analysed. The presence of a cross-over sign was documented and the extent of cross-over was measured by noting the point on the rim where the cross-over occurs. CT scans of the same hips were analysed to determine anatomical version, and to calculate total, anterior and posterior coverage of the femoral head. This was done in relation to the anterior pelvic plane after correcting for pelvic tilt.

Results: The sensitivity, specificity and positive and negative predictive values for the cross-over sign were 92%, 55%, 59% and 91% respectively. The cross-over distance was correlated with 3D version (p=0.01). There was no significant difference in total cover of the femoral head between the anteverted and retroverted subgroups (71% vs. 72% respectively; p=0.55). Anterior cover was higher in the retroverted subgroup (35% vs. 32%; p = 0.0001), and posterior cover was significantly lower in this subgroup (37% vs. 39%; p = 0.002).

Discussion: Although the cross-over sign was sensitive enough to identify 92% of the retroverted cases, its specificity was low with just under half of the anteverted cases being labelled as retroverted. The findings for femoral head cover suggest that retroversion is characterised by posterior deficiency and increased cover anteriorly.

INTRODUCTION: Periprosthetic bone remodeling after uncemented hip replacement has always been a matter of research and debate. DEXA analysis of BMD was studied by previous groups but not the cross sectional cortical volume. We report a validated CT based algorithm for accurate measurement of cortical volume in these group of patients.

METHODS: Twenty two patients (34 hips) who have undergone Uncemented Furlong total hip replacement agreed to undergo CT scan of their hips for our study. The mean age was 74.6 yrs. The mean follow up was 5.4 yrs. 12 patients had bilateral replacement.

Using software adapted for the specific purpose, femoral cortical volume was measured at three different levels at a fixed distance from the lower border of the lesser trochanter on both sides: 6mm distal to the tip of the prosthesis (z), At the top of the cylindrical portion(x) Midway between x and z (y).

Accuracy and precision of the of the method was also assessed.

RESULTS: The mean cortical volume in the proximal cylindrical portion (x), midpoint(y) and the portion of bone distal to the prosthesis (z) were 458 mm3, 466 mm3, 504 mm3 respectively. The corresponding cortical volumes in the contralateral native femur in unilateral hip replacements were 530 mm3(x), 511 mm3(y), 522 mm3 (z) giving a ratios of 0.86(x), 0.91(y) and 0.97(z). The mean cortical volumes on the left side of bilateral hips were 490 mm3(x), 499 mm3(y) and 528 mm3 (z). The mean cortical volumes on the right side were 456 mm3(x), 463 mm3 (y) and 516 mm3 (z).

No significant trend was noted with change of volume of bone with time.

In the three cases who had cemented hips on their other side, the cemented hips exhibited substantially more stress shielding than their cementless controls (ratios of 0.82, 0.74 and 0.85).

A high correlation between the test and standard measurements was noted. The interobserver agreement between two observers was also good.

DISCUSSION & CONCLUSION: In a fully coated uncemented femoral component, with documented long term results, it is to be expected that load will be shed steadily along the length of the prosthesis. In this study we have confirmed this supposition, with volumetric data, by showing that an almost normal bone just below the tip of the stem (97% volume) reduces to a bone volume of 91% by the middle of the stem and then 86% by the shoulder of the prosthesis. This decrease in the volume of cortical bone effectively normal at the tip of the prosthesis while not optimal appears to stabilize early with no trend of continued reduction over a decade. The effect of cementation on stress shielding was only examined incidentally in this study but appears to contribute to more marked bone loss.

INTRODUCTION Assessing femoral head coverage is a crucial element in acetabular surgery for hip dysplasia. CT has proven to be more accurate, practical and informative than plain radiography at analysing hip geometry. Klaue et al first used a computer-assisted model to indirectly derive representations of femoral head coverage. Jansen et al then described a CT-based method for measuring centre edge angle of Wiberg at 10 rotational increments. Haddad et al used that method to look at dysplastic hips pre- and post-acetabular osteotomy. We present a novel CT-based method that automatically gives an image of the head with the covered area precisely represented. We used this technique to accurately measure femoral head coverage (FHC) in normal hips and in a prospective study of patients with hip dysplasia undergoing peri-acetabular osteotomy. The impact of surgery on acetabular anteversion and inclination was also assessed.

METHODS Using a custom software programme, anatomical landmarks for 25 normal and 26 dysplastic hips were acquired on the 3D reconstructed CT image and used to define the frame of reference. Points were then assigned on the femoral head surface and the superior half of the acetabular rim after aligning the pelvis in the anterior pelvic plane. The programme then automatically produced an image representing the femoral head and its covered part along with the calculated femoral head coverage. To do so, the software represents the femoral head by a best-fit sphere, and the sphere and the acetabular contour are then projected onto a plane in order to calculate the load bearing fraction and area.

RESULTS In the normal hips FHC averaged 73% (SD 4), whereas anteversion and inclination averaged 16° (SD 7°) and 44° (SD 4°) respectively. In the dysplastic group the mean FHC was 50% (SD 6), with a mean anteversion of 19° (SD 10°) and mean inclination of 53° (SD 5°). Peri-acetabular osteotomy has been performed on 16 hips so far, and the FHC for those averaged 66% (SD 5), a mean improvement of 32%. The respective anteversion and inclination post-operatively were 18° (SD 12°) and 40° (SD 8°).

DISCUSSION This is the first study to our knowledge that has used a reliable and practical measurement technique to give an indication of the percent coverage of the femoral head by the acetabulum in normal hips. When this is applied to assessing coverage in surgery to address hip dysplasia it gives a clearer understanding of where the corrected hip stands in relation to a normal hip, and this should allow for better determination of the likely outcome of this type of surgery. The versatility of the method gives it significant attraction for acetabular surgeons and makes it useful not only for studying dysplastic hips but also other hip problems such as acetabular retroversion.

Wear and loosening are the major causes for long tem failure in Total Hip Replacement (THR). Accurate three dimensional wear analysis of radiographs has its own limitations. We report the results of our clinical study of three dimensional volumetric wear measurements using our custom low radiation risk CT based algorithm and special software

Twenty four patients (32 hips) agreed to take part in our study. The male: female ratio was 1:4. The mean age was 75 years and the mean follow up was 5.4 years. All patients had 28 mm diameter ceramic heads. Of the 32 hips, 17 hips had polyethylene inserts and 15 hips had ceramic inserts. The maximum follow up for the polyethylene and ceramic groups were 12 years and 5.5 years respectively. All the patients were scanned using Somatom Sensation 4 scanner. Using custom software, 3D reconstruction of the components was done and landmark acquisition done on the femoral head, acetabular metal component and the insert. From these landmarks, a dedicated program was used to calculate the centre of the femoral head in relation to the centre of the acetabular component in all three axes and an indirect measurement of wear obtained. Using the axes measurements graphical 3D models of migration of the femoral head component into the acetabular liner were created and volume of wear measured using special software. Accuracy of the method was assessed by measuring the radius of the femoral head since all patients had 28mm diameter heads implanted in them. Assessment of precision of method was done by calculating the level of agreement between two independent observers.

In the polyethylene group, there was no significant (< 1mm) wear in x and y axis with time. However there was significant evidence of wear in relation to time in the z axis (max wear = −2.5 mm). In the ceramic group with relatively shorter follow up, there was no evidence of significant wear in all three axes. The mean volume measured in the polyethylene group was 685 mm3 (max = 1629 mm3, min = 132mm3 ). The mean volume measured in the ceramic group was 350mm3 (max = 1045 mm3, min = 139mm3 ). The mean radius of the femoral head measured in both groups was 14.02mm (range =13.8 to 14.4 mm). Accuracy was limited by artifacts particularly in bilateral hip arthroplasties and further in the ceramic group because of the restricted access to the ceramic head for placement of markers. Measurements obtained by two independent observers showed a strong correlation (0.99, p value = 0.001) for the polyethylene group. In the ceramic group the correlation (0.69, p value=0.0126) was not as strong as the polyethylene group.

This study has produced a method for three dimensional estimation of wear that can be obtained from low dose CT scans with better accuracy and repeatability (< 0.5 mm) even than to ex vivo studies particularly in polyethylene bearings(wear rate 0.14mm/yr). Noise reduction with appropriate artefact reduction software may further improve the accuracy of this simple and repeatable method.

Various frames of reference are routinely used for hip and knee arthroplasty. We hypothesised that the linea aspera is a constant anatomical feature which can be used as a frame of reference.

Twenty cadaveric femora were CT scanned with high resolution 1mm slices. Robin 3D software was used to manipulate the CT data. Three points were identified on the posterior aspect of the lesser trochanter, medial and lateral femoral condyles to position the femora in similar positions based on the posterior femoral plane (PFP). Centres of the femoral head and neck were derived by surface markers placed on the head and around the neck respectively. Joining the 2 centres gave head neck axis (HNA). The most prominent point on the linea aspera was identified at a level midway along the length of the femur. At that level the centre of the canal was derived by placing surface markers. Joining the most prominent point on the linea aspera to the centre of the canal identified our plane, linea aspera – centre plane (LCP). Angle measurements were made between PFP to HNA, PFP to LCP and LCP to HNA.

PFP to HNA is the traditional method for measuring anteversion angle which in our series had a mean of 13°, SD of 5 (range 5–24). PFP to LCP gave very similar results with mean 101°, SD 6 (range 92–112). However it was noted that there is weak correlation between PFP to HNA angle and PFP to LCP angle for each femur. LCP to HNA measurements were more variable with mean 89°, SD 8 (range 76–108).

From these data we conclude that the proximal half of the femur has more variable torsion compared to the distal half. This study shows that the linea aspera should not be used as a frame of reference for hip nor knee arthroplasties. However, further studies are needed to evaluate the linea aspera in-vivo where it is expected to be more prominent and easier to identify.

Periprosthetic bone remodeling after uncemented hip replacement has always been a matter of research and debate. DEXA analysis of bone density was studied by previous groups but not the cross sectional cortical volume. We report a validated CT based algorithm for accurate measurement of cortical volume in these group of patients.

Twenty two patients who have undergone Uncemented Furlong total hip replacement agreed to undergo CT scan of their hips for our study. The mean age was 74.6 yrs. The mean follow up was 5.4 yrs. Using software adapted for the specific purpose, femoral cortical volume was measured at three different levels at a fixed distance from the lower border of the lesser trochanter on both sides:

6mm distal to the tip of the prosthesis (z),

Accuracy of the method was assessed by measuring the volume of artificial cavities created on a polyurethane pelvis. Assessment of precision of method was done by calculating the level of agreement between two observers.

The mean cortical volume in the proximal cylindrical portion (x), midpoint(y) and the portion of bone distal to the prosthesis (z) were 458 mm3, 466 mm3, 504 mm3 respectively. The corresponding cortical volumes in the contralateral native femur in unilateral hip replacements were 530 mm3(x), 511 mm3(y), 522 mm3 (z) giving a ratios of 0.86(x), 0.91(y) and 0.97(z). The mean cortical volumes on the left side of bilateral hips were 490 mm3(x), 499 mm3(y) and 528 mm3 (z). The mean cortical volumes on the right side were 456 mm3(x), 463 mm3 (y) and 516 mm3 (z). No significant trend was noted with change of volume of bone with time. In the three cases who had cemented hips on their other side, the cemented hips exhibited substantially more stress shielding than their cementless controls (ratios of 0.82, 0.74 and 0.85). A high correlation between the test and standard measurements was noted. The interobserver agreement between two observers was also good.

In a fully coated uncemented femoral component, with documented long term results, it is to be expected that load will be shed steadily along the length of the prosthesis. In this study we have confirmed this supposition, with volumetric data, by showing that an almost normal bone just below the tip of the stem (97% volume) reduces to a bone volume of 91% by the middle of the stem and then 86% by the shoulder of the prosthesis. This decrease in the volume of cortical bone effectively normal at the tip of the prosthesis while not optimal appears to stabilize early with no trend of continued reduction over a decade. The effect of cementation on stress shielding was only examined incidentally in this study but appears to contribute to more marked bone loss.

The use of intramedullary column screws in the treatment of acetabular fractures is becoming more widely utilized. The development of percutaneous methods to insert these screws under image intensifier guidance is one of the main reasons for their increased use. Few groups are navigating insertion of these screws. The available screws are cannulated 6.5–8 mm screws. Most surgeons prefer using 3.2 mm guide wires to reduce deflection. With a shank diameter of 4.5 mm, 3.2 mm cannulation significantly weakens the screws. We postulated that both columns, specially the posterior column can accommodate larger screw diameters which will increase the stability of fixation allowing earlier full weight bearing. The currently used screws were designed for fixation of femoral neck fractures. As percutaneous fixation of acetabular fractures is a growing area of interest, this warrants designing suitable screws with larger diameters.

Eight CT scans of the adult pelvis –performed for non fracture related indications-, were studied (7 females, 1 male). We found that the anatomical cross-section of the columns is irregular but approximately triangular. The method we used to determine the largest diameter of a screw to fit each column was fitting cylinders in the columns. Robin’s 3D software was used to segment acetabula and convert the CT data into polygon mesh (stereolithography STL format) bone surfaces at an appropriate Hounsfield value. The resulting STL files were imported in Robin’s Cloud software, where polygon mesh cylinders of 10 mm diameter were fitted in each column. These cylinders were then manipulated to achieve best fit and their diameters were gradually increased to the biggest diameter which still fitted in the column.

The mean diameters of the fitted cylinders were 10.8 mm (range: 10–13mm) and 15.2 mm (range 14–16.5mm) for the anterior and posterior columns respectively.

To our knowledge, this is the first investigation to study the cross sectional dimensions of the anterior and posterior columns of the acetabulum. Our small sample shows that both columns can safely accommodate larger screws than those currently used. We plan to investigate this further using cadavers.

Periacetabular osteolysis is now considered one of the major long term complications following uncemented total hip replacement. Radiographs are inaccurate and lack sensitivity in detecting lesions even with multiple views. Very few clinical studies have shown the use of CTscan for measuring these lesions. We report our clinical experience with CT based algorithm for measuring it.

Twenty two patients (32 hips) who have undergone Uncemented Furlong total hip replacement agreed to undergo CT scan of their hips for our study. The mean follow up was 5.4 yrs. Of the 34 hips,17 were polyethylene bearings and 15 were ceramic bearings. Nine patients had bilateral replacement in this group. Using custom reconstruction software, 3D models were created and volume measurements made after identifying the lesions in the slices and painting them using appropriate tools available in the software.

Accuracy of the method was assessed by measuring the volume of artificial cavities created on polyurethane pelvis with and without the components. In our control experiments, a high correlation between the test and standard measurements was noted in the cavities above the component, while medial to the acetabular component in bilateral cases it was difficult to be accurate, with cavities less than 10mm in diameter being hard to detect reliably.

In our clinical group of 32 hips, degenerative cysts were noted in 13, secondary rheumatoid cysts in 2 and wear cysts were noted in 2, the largest having a maximum dimension of 10mm. All the degenerative cysts were in the peripheral zone and both the wear cysts were seen in the central zone communicating with the screw holes. These cysts were identified by the characteristic absence of sclerosis surrounding the cyst and obvious communication with screw holes. Both the wear cysts were found with polyethylene bearings at a minimum of 5yrs follow up.

The mean volume of the degenerative cysts was 799 mm3 (71–3500) and the mean volume of the wear cysts was 567 mm3 (550–585)

The low dose CT method we describe and the results we report show that cavities can be measured reliably, above or below the acetabular component. On the medial side, in bilateral cases in particular, although location is possible, volumetric analysis of anything less than 10mm in diameter is not.

Regarding surveillance strategy for wear cysts, we have established that in this series the incidence is 14%, with one at 5 yrs and another noted at 12 yrs, with 10mm in maximum dimension. The absence of any wear cysts at all in the ceramic group, albeit after a shorter follow up of only 5 years is encouraging.

Based on these figures, with these implants, we would recommend that there is no need to undertake surveillance more frequently than every 10 years.