Background. Digital planning of implants in regard to position and size is done preoperatively in most cases. Intraoperative it can only be made by navigation systems. With the development of the VIPS-method (Virtual Implant Planning System) as an application for mobile C-arms, it is possible to do an intraoperative virtual planning of the screws near the joint in treatment of distal radius fractures by plating. Screw misplacement is a well known complication in the operative treatment of these fractures. The aim of this prospective randomised trial was to gain first clinical experiences and to compare VIPS with the conventional technique. The study hypothesis was that there will be less screw misplacement in the VIPS group. Methods. We included 40 patients with distal radius fractures type A3, C1 and C2 according to the AO-classification. In a pilot study the first 10 Patients were treated by the VIPS method to gain experience with VIPS in a clinical set-up. The results of the pilot-study are not part of this analysis. Then 15 Patients were web-based randomised into two groups. After diaphysial fixation of a 2.4 mm Variable Angle Two-Column Volar Distal Radius Plate and fracture reduction matching of a three-dimensional virtual plate to the two-dimensional image of the plate in the fluoroscopy shots in two plains was performed automatically in the VIPS group. The variable angle locking screws were planed in means of direction and length. Drilling was done by the use of the Universal Variable Angle Locking Drill Guide that was modified by laser marks at the rim of the cone to transfer the virtual planning. The drill guide enables drilling in a cone of 30°. In the control group the same implant was used in a conventional technique that means screw placement by the surgeon without digital planning. After implant placement an intraoperative three-dimensional scan was performed to check the position and length of the screws near the joint. OR- and fluoroscopy-time was documented. In addition the changes of misplaced screws were engaged. Results. In the VIPS group six A3-fractures, one C1-fracture and eight C2-fractures were included. In the control group six A3-fractures and nine C2-fractures were included. The intraoperative fluoroscopy time was 2.53 min (SD 1.44, range 1.27–7.14) in the VIPS group and 2.26 min (SD 0.51, range 1.55–3.39) in the control group (p=0.40). The OR-time was 53.33 min (SD 34.49, range 34–171) in the VIPS group and 42.27 min (SD 8.76, range 20–58) in the control group (p=0.23). In the VIPS group we changed three screws (two were too long, one was borderline near the joint) and two screws in the control group (one was too long, one was borderline near the joint) (p=0.24). Conclusions. The Virtual Implant Planning System is a reliable method that can be integrated easily in the workflow in treatment of distal radius fractures. There is a tendency that the virtual implant planning needs additional time, but there are no significant differences between the two groups. Further development is necessary to make the VIPS method beneficial

Contemporary indications for unicompartmental knee replacement (UKR) include bone on bone radiographic changes in the medial compartment with relatively preserved lateral and patellofemoral compartments. The role of MRI in identifying candidates for UKR is commonplace. The aim of this study was to assess the relationship between radiographic and MRI pre-operative grade and outcome following UKR.

A retrospective analysis of medial UKR patients from 2017 to 2021. Inclusion criteria were medial UKR for osteoarthritis with pre-operative and post-operative Oxford Knee Scores (OKS), pre-operative radiographs and MRI.

89 patients were included. Whilst all patients had grade 4 ICRS scores on MRI, 36/89 patients had grade 3 KL radiographic scores in the medial compartment, 50/89 had grade 4 KL scores on the medial compartment. Grade 3 KL with grade 4 IRCS medial compartment patients had a mean OKS change of 17.22 (Sd 9.190) meanwhile Grade 4 KL had a mean change of 17.54 (SD 9.001), with no statistical difference in the OKS change score following UKR between these two groups (p=0.873). Medial bone oedema was present in all but one patient. Whilst lateral compartment MRI ICRS scores ranged from 1 to 4 there was no association with MRI score of the lateral compartment and subsequent change in oxford score (P value 0.458). Patellofemoral Compartment (PFC) MRI ICRS ranged from 0 to 4. There was no association between PFC ICRS score and subsequent change in oxford knee score (P value .276)

Radiographs may under report severity of some medial sided knee osteoarthritis. We conclude that in patients with grade 3 KL score that would normally not be considered for UKR, pre-operative MRI might identify grade 4 ICRS scores and this subset of patients have equivalent outcomes to patients with radiographic Grade 4 KL medial compartment osteoarthritis.

Introduction. EOS® is a low dose imaging system which allows the acquisition of coupled AP and lateral high-definition images while the patient is in standing position. HipEos has been developped to perform pre-surgical planning including hip implants selection and virtual positioning in functional weight-bearing 3D. The software takes advantage of the real size 3D patient anatomical informations obtained from the EOS exam. The aim of this preliminary study on 30 consecutive THP patients was to analyze the data obtained from HipEos planning for acetabular and femoral parameters and to compare them with pre and post-operative measurements on standing EOS images. Material and methods. Full body images were used to detect spino-pelvic abnormalities (scoliosis, pelvic rotation) and lower limbs discrepancies. One surgeon performed all THP using the same type of cementless implants (anterior approach, lateral decubitus). The minimum delay for post-op EOS controls was 10 months. A simulation of HipEos planning was performed retrospectively in a blinded way by the same surgeon after the EOS controls. All measurements were realized by an independent observer. Comparisons were done between pre and post-op status and the “ideal planning” taking in account the parameters for the restitution of joint offset and femur and global limb lengths according to the size of the selected implants. Regarding cup anteversion, the data included the anatomical anteversion (with reference to the anterior pelvic plane APP) and functionnal anteversion (according to the horizontal transverse plane in standing position). Results. The difference between pre-op and post-op APP angles is not statistically significant (p = 0.85), likewise for the sacral slope (p = 0.3). Thus, there has been no change in the orientation of the pelvis after THP. Comparing the two hips on post-op EOS data shows that the difference in femoral offset is not statistically significant (p = 0.76). However, the femoral length is statistically different (p <0.05) (mean 4mm, 0–12mm). The difference for femoral offset between HipEOS planning and post-op EOS data is not statistically significant (p = 0.58). However, the mean difference is significant (p <0.05) for femur length (5mm), inclination (5°) and anteversion of the cup. The mean post-op anatomic anteversion measured in the APP is 27°, whereas it is 11° with HipEOS planning. The mean functional anteversion of the cup on standing post-op EOS data is 35° while planning it is 17°. Otherwise, differences in femoral anteversion are not significant. Conclusion. The planning tools currently available include only the local anatomy of the hip for THP adjustment. This software integrates weight-bearing position, which allows to consider the impact of spine deformities and length discrepancies. This preliminary study is only retrospective, but it highlights the potential interest this “global planning” particularly for the optimization of acetabular anteversion and length adjustment according to pelvic tilt. Planning using the standing lateral view is interesting not only for visualization of the sagittal curvature of the femur and the detection of potential difficulties, but also for the visual data provided on the sagittal orientation of the cup

Dysmorphic pelves are a known risk factor for malpositioned iliosacral screws. Improved understanding of pelvic morphology will minimise the risk of screw misplacement, neurovascular injuries and failed fixation. Existing classifications for sacral anatomy are complex and impractical for clinical use. We propose a CT-based classification using variations in pelvic anatomy to predict the availability of transosseous corridors across the sacrum. The classification aims to refine surgical planning which may reduce the risk of surgical complications.

The authors postulated 4 types of pelves. The “superior most point of the sacroiliac joint” (sSIJ) typically corresponds with the mid-lower half of the L5 vertebral body. Hence, “the anterior cortex of L5” (L5_a) was divided to reference 3 distinct pelvic groups. A 4^th group is required to represent pelves with a lumbosacral transitional vertebra. The proposed classification:

Specific measures such as the width of the S1 and S2 axial and coronal corridors and the S1 lateral mass angles were used to differentiate between pelvic types.

Three-hundred pelvic CT scans were classified into their respective types. Analysis of the specific measures mentioned above illustrated the significant difference between each pelvic type. Changes in the size of S1 and S2 axial corridors formed a pattern that was unique for each pelvic type. The intra- and inter-observer ratings were 0.97 and 0.95 respectively.

Distinct relationships between the sizes of S1 and S2 axial corridors informed our recommendations on trans-sacral or iliosacral fixation, number and orientation of screws for each pelvic type. This classification utilises variations in the posterior pelvic ring to offer a planning guide for the insertion of iliosacral screws.

Introduction

Osteomyelitis is a challenge in diagnosis and treatment. 18F-FDG PET-CT provides a non-invasive tool for diagnosing and localizing osteomyelitis with a sensitivity reaching 94% and specificity reaching 100%. We aimed to assess the agreement in identifying the geographic area of infected bone and planned resection on plain X-ray versus 18F-FDG PET-CT.

Introduction

Osteogenesis imperfect (OI) is a geno- and phenotypically heterogeneous group of congenital collagen disorders characterized by fragility and microfractures resulting in long bone deformities. OI can lead to progressive femoral coxa vara from bone and muscular imbalance and continuous microfracture about the proximal femur. If left untreated, patients develop Trendelenburg gait, leg length discrepancy, further stress fracture and acute fracture at the apex of the deformity, impingement and hip joint degeneration. In the OI patient, femoral coxa vara cannot be treated in isolation and consideration must be given to protecting the whole bone with the primary goal of verticalization and improved biomechanical stability to allow early loading, safe standing, re-orientation of the physis and avoidance of untreated sequelae. Implant constructs should therefore be designed to accommodate and protect the whole bone. The normal paediatric femoral neck shaft angle (FNSA) ranges from 135 to 145 degrees. In OI the progressive pathomechanical changes result in FNSA of significantly less than 120 degrees and decreased Hilgenreiner epiphyseal angles (HEA). Proximal femoral valgus osteotomy is considered the standard surgical treatment for coxa vara and multiple surgical techniques have been described, each with their associated complications. In this paper we present the novel technique of controlling femoral version and coronal alignment using a tubular plate and long bone protection with the use of teleoscoping rods.

The reverse total shoulder replacement (rTSR) has excellent clinical outcomes and prosthesis longevity, and thus, the indications have expanded to a younger age group. The use of a stemless humeral implant has been established in the anatomic TSR; and it is postulated to be safe to use in rTSR, whilst saving humeral bone stock for younger patients. The Lima stemless rTSR is a relatively new implant, with only one paper published on its outcomes.

This is a single-surgeon retrospective matched case control study to assess short term outcomes of primary stemless Lima SMR rTSR with 3D planning and Image Derived Instrumentation (IDI), in comparison to a matched case group with a primary stemmed Lima SMR rTSR with 3D planning and IDI.

Outcomes assessed: ROM, satisfaction score, PROMs, pain scores; and plain radiographs for loosening, loss of position, notching. Complications will be collated. Patients with at least 1 year of follow-up will be assessed.

With comparing the early radiographic and clinical outcomes of the stemless rTSR to a similar patient the standard rTSR, we can assess emerging trends or complications of this new device.

41 pairs of stemless and standard rTSRs have been matched, with 1- and 2-year follow up data. Data is currently being collated. Our hypothesis is that there is no clinical or radiographical difference between the Lima stemless rTSR and the traditional Lima stemmed rTSR.

Glenoid baseplate positioning for reverse total shoulder replacements (rTSR) is key for stability and longevity. 3D planning and image-derived instrumentation (IDI) are techniques for improving implant placement accuracy. This is a single-blinded randomised controlled trial comparing 3D planning with IDI jigs versus 3D planning with conventional instrumentation.

Eligible patients were enrolled and had 3D pre-operative planning. They were randomised to either IDI or conventional instrumentation; then underwent their rTSR. 6 weeks post operatively, a CT scan was performed and blinded assessors measured the accuracy of glenoid baseplate position relative to the pre-operative plan.

47 patients were included: 24 with IDI and 23 with conventional instrumentation. The IDI group were more likely to have a guidewire placement within 2mm of the preoperative plan in the superior/inferior plane when compared to the conventional group (p=0.01). The IDI group had a smaller degree of error when the native glenoid retroversion was >10° (p=0.047) when compared to the conventional group. All other parameters (inclination, anterior/posterior plane, glenoids with retroversion <10°) showed no significant difference between the two groups.

Both IDI and conventional methods for rTSA placement are very accurate. However, IDI is more accurate for complex glenoid morphology and placement in the superior-inferior plane. Clinically, these two parameters are important and may prevent long term complications of scapular notching or glenoid baseplate loosening.

Image-derived instrumentation (IDI) is significantly more accurate in glenoid component placement in the superior/inferior plane compared to conventional instrumentation when using 3D pre-operative planning. Additionally, in complex glenoid morphologies where the native retroversion is >10°, IDI has improved accuracy in glenoid placement compared to conventional instrumentation. IDI is an accurate method for glenoid guidewire and component placement in rTSA.

Introduction

Acetabular dysplasia, also known as developmental dysplasia of the hip, has been shown to contribute to the onset of osteoarthritis. Surgical correction involves repositioning the acetabulum in order to improve coverage of the femoral head. However, ideal placement of the acetabular fragment can often be difficult due to inadequate visualization. Therefore, there has been an increased need for pre-operative planning and navigation modalities for this procedure.

Introduction

Conventional hip radiographs allow surgeons, during preoperative planning, to make important decisions. Size and location of implants are routinely measured by overlaying schematics of the implanted components onto preoperative radiographs. Most currently available planning tools are in two-dimensions (2D), using X-ray images and 2D templates of the implants. Determination of the ideal component size requires two radiographic views of the femur: the anterior-posterior (AP) and the lateral direction. The surgeon uses this information to determine component sizes. Even though this approach has been used for many years leading to very good results, this manual process potentially carries multiple shortcomings. The biggest issue with the AP X-ray image is the fact that it is 2D in nature while the measurement's objective is to obtain three-dimensional (3D) parameters.

The keys to revision total knee arthroplasty start with understanding the nature of the problem. Revision TKR is a major undertaking and should be focused on problem solving. Know the problem and remember pain is not a diagnosis. Review history of the problem and think of the possibilities: infection, loosening, instability, stiffness, malalignment, and poor kinematics.

Ensure an adequate workup including an adequate history, exam and imaging including radiographs, MRI for soft tissue issues, and CT scans to assess rotational alignment. Labs should include CBC, ESR, C-reactive protein, and an aspiration including cell count and culture.

Synthesise a working diagnosis and formulate a provisional plan to include what is to be revised, how will you get there remembering old incisions, and how will get the parts out? Think about equipment: what tools do you need and implant specific tools.

Finally, once everything is out, think about what you have left (soft tissue defects and bone defects) to “rebuild”? This involves pondering constraint for soft tissue defects, stems for mechanical stability, cones, augments, bone graft for osseous defects and fixation.

Introduction

Traditionally, conventional radiographs of the hip are used to assist surgeons during the preoperative planning process, and these processes generally involve two-dimensional X-ray images with implant templates. Unfortunately, while this technique has been used for many years, it is very manual and can lead to inaccurate fits, such as “good” fits in the frontal view but misalignment in the sagittal view. In order to overcome such shortcomings, it is necessary to fully describe the morphology of the femur in three dimensions, therefore allowing the surgeon to successfully view and fit the components from all possible angles.

Introduction

Obtaining accurate anatomical landmarks may lead to a better morphologic understanding, but this is challenging due to the variation of bony geometries. A manual approach, non-ideal for surgeons or engineers, requires a CT or MRI scan, and landmarks must be chosen based on the 3D representation of the scanned data. Ideally, anatomical landmarking is achieved using either a statistical shape model or template matching. Statistical modeling approaches require multitude of training data to capture population variation. Prediction of anatomical landmarks through template matching techniques has also been extensively investigated. These techniques are based on the minimization or maximization of an objective or cost function. As is the nature of non-rigid algorithms, these techniques can fail in the local maxima if the template and new bone models have noise or outliers. Therefore, a combination of rigid and non-rigid registration techniques is needed, in order to obtain accurate anatomical landmarks and improve the prediction process.

Background

Accurate acetabular cup positioning is considered to be essential to prevent postoperative dislocation and improve the long-term outcome of total hip arthroplasty (THA). Recently various devices such as navigation systems and patient-specific guides have been used to ensure the accuracy of acetabular cup positioning.

Pre-operative planning in revision total knee replacement is important to simplify the surgery for the implant representative, operating room personnel and the surgeon.

Revision knee arthroplasty is performed for many different reasons and of variable complexity. Many implant options can be considered including cemented and cementless primary and stemmed revision tibial and femoral components, with posterior cruciate retention or resection, and either with no constraint, varus/valgus constraint, or with rotating hinge bearings. One may also need femoral and tibial spacers, metaphyseal augments, or bulk allograft. It is important to pre-operatively determine which of these implants you may need. If you schedule a revision total knee and ask the implant representative to “bring everything you've got, just in case,” they will have to bring a truck full of instruments and implants.

The first step of pre-operative planning is to determine how much implant constraint will be needed. Survivorship of revision total knees with modern varus/valgus constrained or rotating hinge implants are not that unacceptable. Ideally to enhance longevity, the least constraint needed should be used. This requires determination of the status of the ligaments. Varus and valgus stress is applied to the knee in near full extension, mid-flexion, and ninety degrees of flexion. If instability of the knee is noted, then radiographs are reviewed to determine if component malposition or malalignment is the reason for the collateral ligament laxity. If radiographs don't show a reason, then have additional constraint available in case the knee can't be balanced with proper component position and ligament balancing. In cases other than simple revisions, the posterior cruciate ligament is usually inadequate or needs to be resected to balance the knee. Substitution for the posterior cruciate ligament is usually needed for most revisions

The second step of pre-operative planning is to review radiographs to determine the amount and location of any bone loss. Osteolysis induced bone loss is usually worse than seen on plain radiographs. If unsure, a CT scan can be of help. The presence of significant bone loss contraindicates the use of primary components and mandates the need for stemmed implants. Larger defects may warrant having metallic augments or bulk graft present. Most revision knee implants can be conservatively metaphyseal cemented with diaphyseal engaging press-fit stems.

The third step of pre-operative planning is to be familiar with what implants are present. Occasionally, one may not need to revise components that are stable and well aligned. Having compatible components available may simplify the surgery

Excellent pre-operative planning will minimise the need to bring in an excessive number of instruments and implants. It will help assure that the patient has a stable revision knee and simplify the surgery for all participants

Two critical steps in achieving optimal results and minimizing complications (dislocation, lengthening, and intraoperative fracture) are careful preoperative planning and more recently, the option of intraoperative imaging in order to optimise accurate and reproducible total hip replacement. The important issues to ascertain are relative limb length, offset and center of rotation. It is important to start the case knowing the patient's perception of their limb length. Patient perception is equally important, if not more important, than the radiographic assessment. On the acetabular side, the teardrop should be identified and the amount of reaming necessary to place the inferior margin of the acetabular component adjacent to the tear drop should be noted. Superiorly the amount of exposed metal that is expected to be seen during surgery should be measured in millimeters. Once the key issues of limb length, offset, center of rotation, and acetabular component position relative to the native acetabulum have been confirmed along with the expected sizing of the acetabular and femoral components, it is critical that the operative plan is reproduced at the time of surgery and this can best be consistently performed with the use of intraoperative imaging. Advances in digital imaging now make efficient, cost-effective assessment of hip replacement possible. Embedded software allows accurate confirmation of the preoperative plan intraoperatively when correction of potential errors is easily possible. Such technology is now mature after years of clinical use and studies have confirmed its success in avoiding outliers and achieving optimal results.

A pilot study at Washington University demonstrated that intraoperative imaging was able to eliminate outliers for acetabular inclination and anteversion. In addition, the ability to achieve accurate reproduction of femoral offset and limb length within 5mm was three times better with intraoperative imaging (P < 0.001).

Revision total knee arthroplasty (TKA) can pose significant challenges. Successful reconstruction requires a systematic approach with the ultimate goal being a well fixed and balanced knee prosthesis. Careful preoperative planning is necessary for safe exposure, component removal, and appropriate management of bone loss during revision knee surgery.

Prior to surgery, the cause of failure must be understood. Revision TKA without a clear diagnosis has been shown to lead to predictable poor results. A careful history and physical examination for both intrinsic and extrinsic causes of knee pain need to be performed. An ESR and C-reactive protein should be obtained in every patient with a painful TKA and in cases of serologic abnormalities, a joint aspiration performed.

The integrity of the collateral ligaments and the degree of anticipated bone loss at the time of revision needs to be established. In cases of severe collateral ligament deficiency, the need for constrained or hinged knee implants should be anticipated. Plain radiographs are needed to evaluate present component position, loosening, and osteolysis. Oblique radiographs and advanced imaging (i.e. CT or MRI) have been shown to more accurately quantify the severity of lysis compared to standard radiographs. This careful assessment can help prepare for the need of special implants, stems, wedges, or augments.

Finally, patient risk stratification and medical co-management can help minimise complications following revision TKA. Optimization of potentially modifiable risk factors such as glycemic control, BMI, and preoperative hemoglobin can reduce perioperative morbidity and complications.

Preoperative planning is a crucial step for total hip arthroplasty (THA), and 2D X-ray images are commonly used. The planning aims to provide the correct implant size, restore functional biomechanical conditions and avoid early complication such as dislocation, leg length discrepancy or abductors insufficiency. Limitations of 2D planning, besides the low accuracy in sizing, concerns the inability of planning the anteversion of both acetabular and femoral component on axial plane. Also, the verification of the planning intraoperatively is wholly left to qualitative measurements and the surgeon's experience. The need for having a more accurate and functional preoperative planning has been addressed using 3D models. The MyHip Planner (MHP) (Medacta International, Castel San Pietro, Switzerland), is a preoperative planning software which through artificial intelligent algorithm converts the CT scans into a 3D model that perfectly match the patient's anatomy. Then, automatic positioning of the implants is performed following the personal settings of the surgeon which will check and validate the planning, a personalized simulation of six daily activities to detect impingement of implants and bones. The MyHip Verifier (MHV) intraoperatively verifies the execution of the planning in terms of leg length and offset using two fluoroscopic images. Also, the size and cup angles can be calculated. The purpose of the present study was to validate the accuracy of the MHP [Fig 1] and MHV [Fig 2].

The dataset consisted of 13 patients who underwent primary uncemented THA. Each patient had a preoperative CT scan, intraoperative fluoroscopy, and postoperative CT scan after the surgery. The CT protocol used was low radiation (0,2 mm slicing for the pelvis, 0,5 mm for knees and ankles). The patients have been preoperatively planned used the MPH, and the accuracy of the components size prediction has been evaluated by comparing the preoperative planned values with the surgical reports. The MVH calculated the leg length and offset in terms of the difference between the preoperative and postoperative position of the femur concerning the pelvis. The accuracy of the measurements has been evaluated using postoperative CT scans. The MPH was able to predict the implanted size in 83% of the patient for the femoral stem and 96% for the acetabular component. The accuracy of the MVH in measuring the leg length was under 2 mm (1,6 ± 0,7 mm) while the offset was 2,5±1,6 mm. The cup angles were 5±1,1deg and 2,3±1,3deg for the anteversion and inclination, respectively. The average cup anteversion was 28,3°, mean cup inclination was 42,6°; femoral offset and leg length was restored in 96,5% of patients within a range of ±3 mm concerning the preoperative position. The results demonstrated the reliability of the MPH in predicting the implant size, and the accuracy of the MVH to verify the execution of the plan intraoperatively. The two software can be used in the clinical routine to improve the clinical outcome in THA. Limitations of this study are represented mainly by the small cohort of patients involved.

For any figures or tables, please contact the authors directly.

Introduction: Acetabular component positioning, offset, combined anteversion, leg length, and soft tissue envelope around the hip plays an important role in hip function and durability. In this paper we will focus on acetabular positioning of the cup.

Technique: The axis of the pelvis is identified intra-operatively as a line drawn from the highest point of the iliac crest to the middle of the greater trochanter. Prior to reaming the acetabulum, an undersized trial acetabular component is placed parallel and inside the transverse ligament, inside the anterior column and projecting posterior to the axis of the pelvis. This direction is marked and the subsequent reaming and final component placement is performed in the same direction. The lateral opening is judged based on 45-degree angle from the tear drop to the lateral margin of the acetabulum on anteroposterior pelvic radiographs. The final anteversion of the cup is adjusted based on increase or decrease of lumbar lordosis and combined anteversion.

Methods: Anteroposterior pelvic radiographs of 100 consecutive patients undergoing posterior THR between September 2010 and March 2011 with this method were evaluated for cup inclination angle and anteversion using EBRA software.

Results: There were no malalignment or dislocation. The mean cup inclination angle and anteversion were 41 ± 5.1 degrees (range 37.1 – 48.4) and 22.1 ± 4.8 degrees (range 16.6 – 29.3), respectively.

Conclusion: This is a reproducible method of cup positioning and with proper femoral component position, restores leg length, offset, combined anteversion, and balances soft tissue around the hip. These factors affect the incidence of dislocation, infection, reduced wear, and durability.

Two critical steps in achieving optimal results and minimizing complications (dislocation, lengthening, and intra-operative fracture) are careful pre-operative planning and more recently, the option of intra-operative imaging in order to optimise accurate and reproducible total hip replacement. The important issues to ascertain are relative limb length, offset and center of rotation. It is important to start the case knowing the patient's perception of their limb length. Patient perception is equally important, if not more important, than the radiographic assessment. On the acetabular side, the teardrop should be identified and the amount of reaming necessary to place the inferior margin of the acetabular component adjacent to the tear drop should be noted. Superiorly the amount of exposed metal that is expected to be seen during surgery should be measured in millimeters. Once the key issues of limb length, offset, center of rotation, and acetabular component position relative to the native acetabulum have been confirmed along with the expected sizing of the acetabular and femoral components, it is critical that the operative plan is reproduced at the time of surgery and this can best be consistently performed with the use of intra-operative imaging. Advances in digital imaging now make efficient, cost-effective assessment of hip replacement possible. Embedded software allows accurate confirmation of the pre-operative plan intra-operatively when correction of potential errors is easily possible. Such technology is now mature after years of clinical use and studies have confirmed its success in avoiding outliers and achieving optimal results.

A pilot study at Washington University demonstrated that intra-operative imaging was able to eliminate outliers for acetabular inclination and anteversion. In addition, the ability to achieve accurate reproduction of femoral offset and limb length within 5mm was three times better with intra-operative imaging (P <0.001).