In 2021, Vigdorchik et al. published a large multicentre study validating their simple Hip-Spine Classification for determining patient-specific acetabular component positioning in total hip arthroplasty (THA). The purpose of our study was to apply this Hip-Spine Classification to a sample of Australian patients undergoing THA surgery to determine the local acetabular component positioning requirements. Additionally, we propose a modified algorithm for adjusting cup anteversion requirements. 790 patients who underwent THA surgery between January 2021 and June 2022 were assessed for anterior pelvic plane tilt (APPt) and sacral slope (SS) in standing and relaxed seated positions and categorized according to their spinal stiffness and flatback deformity. Spinal stiffness was measured using pelvic mobility (PM); the ΔSS between standing and relaxed seated. Flatback deformity was defined by APPt <-13° in standing. As in Vigdorchik et al., PM of <10° was considered a stiff spine. For our algorithm, PM of <20° indicated the need for increased cup anteversion. Using this approach, patient-specific cup anteversion is increased by 1° for every degree the patient's PM is <20°. According to the Vigdorchik simple Hip-Spine classification groups, we found: 73% Group 1A, 19% Group 1B, 5% Group 2A, and 3% Group 2B. Therefore, under this classification, 27% of Australian THA patients would have an elevated risk of dislocation due to spinal deformity and/or stiffness. Under our modified definition, 52% patients would require increased cup anteversion to address spinal stiffness. The Hip-Spine Classification is a simple algorithm that has been shown to indicate to surgeons when adjustments to acetabular cup anteversion are required to account for spinal stiffness or flatback deformity. We investigated this algorithm in an Australian population of patients undergoing THA and propose a modified approach: increasing cup anteversion by 1° for every degree the patient's PM is <20°

Introduction. Lumbar spine fusion in patients undergoing THA (total hip arthroplasty) is a known risk factor for hip dislocation with some studies showing a 400% increased incidence compared to the overall THA population. Reduced spine flexibility can effectively narrow the cup anteversion safe zone while alterations in pelvic tilt can alter the center of the anteversion safe zone. The use of precision cup alignment technology combined with patient-specific cup alignment goals based on preoperative assessment has been suggested as a method of addressing this problem. The current study assess the dislocation rate of THA patients with stiff or fused lumbar spines treated using surgical navigation with patient-specific cup orientation goals. Methods. Seventy-five THA were performed in 54 patients with a diagnosis of lumbar fusion, lumbar disc replacement, and scoliosis with Cobb angles greater than 40 degrees were treated by the senior author (SM) as part of a prospective, non-randomized study of surgical navigation in total hip arthroplasty. All patients were treated using a smart mechanical navigation tool for cup alignment (HipXpert System, Surgical Planning Associates, Inc., Boston, MA). Cup orientation goals were set on a patient-specific basis using supine pelvic tilt as measured using CT. Patients with increased pelvic tilt had a goal for increased cup anteversion and patients with decreased pelvic tilt had a goal for decreased cup anteversion (relative to the anterior pelvic plane coordinate system). Each patient's more recent outpatient records were assessed for history of dislocation, instability, mechanical symptoms, decreased range of motion or progressive pain. Additionally, last clinic radiographs were reviewed to confirm lumbar pathology in the form of spinal surgical hardware. Results. Seventy-five total hip arthroplasties with stiff lumbar spine were reviewed with and average follow up of 6.04 years. The average number of levels of lumbar fusion was 2.3 levels. Since the most recent follow up on all patients in this cohort no hip dislocations had occurred. Discussion and Conclusion. Fusion or stiffness of the lumbar spine is a known risk factor for instability following elective THA. The current study demonstrates that patient-specific planning of cup placement taking abnormal pelvic tilt into consideration combined with the use of accurate intra-operative cup alignment technology can be used to address this problem

Musculoskeletal modeling techniques simulate reverse total shoulder arthroplasty (RTSA) shoulders and how implant placement affects muscle moment arms. Yet, studies have not taken into account how muscle-length changes affect force-generating capacity postoperatively. We develop a patient-specific model for RTSA patients to predict muscle activation. Patient-specific muscle parameters were estimated using an optimization scheme calibrating the model to isometric arm abduction data at 0°, 45°, and 90°. We compared predicted muscle activation to experimental electromyography recordings. A twelve-degree of freedom model with experimental measurements created patient-specific data estimating muscle parameters corresponding to strength. Optimization minimized the difference between measured and estimated joint moments and muscle activations, yielding parameters corresponding to subjects' strength that can predict muscle activation and lengths. Model calibration was performed on RTSA patients' arm abduction data. Predicted muscle activation ranged between 3% and 70% of maximum. The maximum joint moment produced was 10 Nm. The model replicated measured moments accurately (R. 2. > 0.99). The optimized muscle parameters produced feasible muscle moments and activations for dynamic arm abduction when using data from isometric force trials. A normalized correlation was found between predicted and experimental muscle activation for dynamic abduction (r > 0.9); the moment generation to lift the arm was tracked (R. 2. = 0.99). Statement of Clinical Significance: We developed a framework to predict patient-specific muscle parameters. Combined with patient-specific models incorporating joint configurations, kinematics, and bone anatomy, they can predict muscle activation in novel tasks and, e.g., predict how RTSA implant and surgical decisions may affect muscle function

Significance. In ideal shared decision making (SDM), evidence-based treatment options, their likelihood of success, and the probability of adverse events is discussed with the patient. However, current SDM is fundamentally flawed because evidence for patient-specific treatment effectiveness and patient-specific adverse event risks is lacking. Observational outcome registries are better than randomized clinical trials for determining patient prognostic factors for outcomes and adverse events. No orthopaedic SDM clinical tools exist to predict patient-specific outcomes. Hypothesis: A patient-specific shared decision making tool can predict clinically significant outcomes and adverse events for total knee replacement (TKR) surgery. Methods. A web–based prospective observational outcome registry collects patient reported outcomes (PROs) for TKR surgery. The data set for TKR surgery includes: (1) European quality of life (EQ-5D); (2) Oxford Knee Score (OKS); (3) Lower Extremity Activity Scale (LEAS); and (4) Pain Likert Scale (PLS). A TKR outcome calculator predicts patient-specific functional outcome with a regression model using patient-specific pre-operative Oxford Knee Scores, diagnosis, co-morbidities, and demographics. Patient-specific joint infection relative risk is calculated using diagnosis, co-morbidities, and demographics. Functional outcomes are presented as minimum clinically important differences (MCIDs). MCID=σ. Δ. /2. Results. The MCID for the EQ-5D Health State Score (HSS) is 0.094 (0.000–1.000). The MCID for the EQ-5D Visual Analog Scale (VAS) is 9.1 (0–100). The MCID for the OKS is 4.45 (0–48). The MCID for the LEAS is 1.6 (1–18). The MCID for the PLS is 1.4 (0–10). Examples. (1) A 55-year-old white male with post-traumatic arthritis (ICD-9 716.16, BMI = 28.7, non-diabetic, recently quit smoking) has a pre-operative Oxford Knee Score of 10. His predicted outcome is 6.3 MCIDs and his relative risk of infection is 6.1 (4.4%) (Figure 1). He is expected to have an excellent outcome. His risk of infection can be reduced by using antibiotic-laden cement. Depending on the patient's preferences, he is an excellent candidate for a total knee replacement. (2) A 60-year-old white male with osteoarthritis (ICD-9 715.16, BMI = 25.0, non-diabetic, non-smoker) has a pre-operative Oxford Knee Score of 45. He has full thickness cartilage loss on his medial femoral condyle by MRI only. His predicted outcome is 0.67 MCIDs and his relative risk of infection is 1.9 (1.4%) (Figure 2). He is expected to have a poor outcome even though his risk of infection is low. Although he has full thickness cartilage loss on MRI, his pre-operative Oxford Knee Score of 45 demonstrates that he is very functional and has minimal opportunity for improving his knee function with a total knee replacement. He is a poor candidate for TKR surgery. Conclusions. The patient-specific SDM tool for TKR surgery can distinguish between excellent and poor surgical candidates when both patients meet radiographic criteria for surgery. The pre-operative Oxford Knee Score assesses knee function and/or disability. Patients with relatively high OKSs are less likely to achieve clinically significant improvements after total knee replacement surgery

Background. Accurate placement of the glenoid component in total shoulder arthroplasty (TSA) is critical to optimize implant longevity. Commercially available patient-specific instrumentation systems can improve implant placement, but may involve considerable expense and production delays of up to six weeks. The purpose of this study was to develop a novel technique for in-house production of 3D-printed, patient-specific glenoid guides, and compare the accuracy of glenoid guidepin placement between the patient-specific guide and a standard guide using a cadaveric model. Methods. Twenty cadaveric shoulder specimens were randomized to receive glenoid guidepin placement via standard TSA guide (Wright Medical, Memphis, TN) or patient-specific guide. Three-dimensional scapular models were reconstructed from CT scans with Mimics 20.0 imaging software (Materialise NV, Leuven, Belgium). A pre-surgical plan was created for all specimens for the central glenoid guidepin of 0º version and inclination angles. Central pin entry and exit points were also calculated. Patient-specific guides were constructed to achieve the planned pin trajectory in Rhino3D software (Robert McNeel & Associates, Seattle, WA). Guides were 3D-printed on a Form2 printer with Formlabs Dental SG Resin (Formlabs, Somerville, MA). Glenoid labrum and cartilage were removed with preservation of other soft tissues in all specimens to mimic intraoperative TSA conditions. A fellowship-trained, board-eligible orthopaedic surgeon placed a 2.5 mm diameter titanium guidepin into each glenoid using the assigned guide for each specimen. After pin placement, repeat CT scans were performed, and a blinded measurer used superimposed 3D scapular reconstructions to calculate deviation from the pre-surgical plan in version and inclination angles, dot product angle, and guide pin entry and exit points. Student's t tests were performed to detect differences between pin placements for the two groups. Results. Cadaver age, sex, and BMI did not differ between groups (p>0.05 for all). Average production cost and time for the patient-specific guides were $29.95 and 4 hours and 40 minutes per guide, respectively. Guidepin version deviation did not differ between the patient-specific and standard guides (1.59º ± 1.60º versus 2.88 º ± 2.11º, respectively, p=0.141). Guidepin inclination deviation was significantly lower in the patient-specific group (1.54º ± 1.58º versus 6.42º ± 5.03º, p=0.009), similarly the dot product angle was lower in the patient-specific compared to standard guide group (2.35º ± 1.66º versus 7.48º ± 4.76º, p=0.005). Glenoid entry site exhibited less deviation for the patient-specific compared to standard guide (0.75mm ± 0.54mm versus 2.05mm ± 1.19mm, p=0.006). Glenoid exit site also was closer to the target for the patient- specific compared to standard group (1.75mm ± 0.99mm versus 4.75mm ± 2.97mm, p=0.010). Conclusion. We present a novel technique for in-house production of 3D-printed, patient-specific glenoid guides for TSA glenoid pin placement. These patient-specific guides improved pin placement accuracy based on 3D-CT measurements compared to standard TSA guides in a cadaveric model. Our patient-specific glenoid guides can be produced on-demand, in-house, inexpensively, and with significantly reduced time compared to commercially available guides. Future studies are required to validate these findings in clinical applications and determine the potential impact on implant longevity

INTRODUCTION. To test whether there are differences in postoperative mechanical and component alignment, and in functional results, between conventional, navigated and patient-specific total knee arthroplasties in a low-volume centre?. MATERIAL AND METHODS. Retrospective cohort study of 391 patients who received conventional, navigated or patient- specific primary cemented TKA in a low-volume hospital. RESULTS. The risk of mechanical alignment outliers was 89% lower in the navigated group compared to the conventional TKA group. There was a 63% lower risk of femoral component malalignment and a 66% lower risk of tibial component malalignment in the navigated group. No significant reduction in the risk of malalignment was seen in the patient-specific group. Total WOMAC and Oxford scores were no different between the three techniques. The patient-specific group reported better WOMAC pain scores. PSI TKA was 33% more expensive than conventional TKA and 28% more expensive than Navigated TKA. DISCUSSION. Navigated TKA improved alignment, but neither navigated nor patient-specific TKA improved functional outcomes. Patient-specific TKA was more expensive, with little additional benefit. Clinical relevance: The routine use of patient-specific instrumentation in low-volume centers is not supported by the currently available data

Introduction. Current modeling techniques have been used to model the Reverse Total Shoulder Arthroplasty (RTSA) to account for the geometric changes implemented after RTSA [2,3]. Though these models have provided insight into the effects of geometric changes from RTSA these is still a limitation of understanding muscle function after RTSA on a patient-specific basis. The goal of this study sought to overcome this limitation by developing an approach to calibrate patient-specific muscle strength for an RTSA subject. Methods. The approach was performed for both isometric 0° abduction and dynamic abduction. A 12 degree of freedom (DOF) model developed in our previous work was used in conjunction with our clinical data to create a set of patient-specific data (3 dimensional kinematics, muscle activations (), muscle moment arms, joint moments, muscle length, muscle velocity, tendon slack length (), optimal fiber length, peak isometric force)) that was used in a novel optimization scheme to estimate muscle parameters that correspond to the patient's muscle strength[4]. The optimization varied to minimize the difference between measured (“in vivo”) and predicted joint moments and measured (“in vivo”) and predicted muscle activations (). The predicted joint moments were constructed as a summation of muscle moments. The nested optimization was implemented within matlab (Mathworks). The optimization yields a set of muscle parameters that correspond to the subject's muscle strength. The abduction activity was optimized [4,5]. To validate the model we predicted dynamic joint moment and activation for the abduction activity (Figure 1). Results. The muscle activation for the lateral deltoid had a normalized correlation of value of .91(Figure 1 left). The maximum joint moment produced was 18 newton-meters. The joint moments were reproduced to an value of 1 (Figure 1 Right). Muscle parameters were calculated for both isometric and dynamic abduction. The muscle parameters produced provided a feasible solution to reproduce the muscle activation and joint moments seen “in vivo” (Figure 1). Discussion. Current modeling techniques of the upper extremity focus primarily on geometric changes and their effects on shoulder muscle moment arms. In efforts to create patient-specific models we have developed a framework to predict subject-specific strength characteristics. In order to fully understand muscle function we need muscle parameters that correspond to the subject's strength. This effort in conjunction with patient-specific models that incorporate the patient's joint configurations, kinematics and bone anatomy provide a framework to gain insight into muscle tensioning effects after RTSA. This framework describes the relationship between muscle lengthening and muscle performance (recruitment and force generation). With this framework improvements can be made to the surgical implementation and design of RTSA to improve surgical outcomes. Significance. This abstract is the first of its kind to use patient-specific fluoroscopy kinematics, muscle activation and joint moments to create a framework to predict a patients muscle function (activation, force) for RTSA groups. This now allows us to understand how differences in implant design and surgical technique affect each muscle's ability to generate force and function. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

BACKGROUND. The aim of Patient-specific instrumentation surgery is to improve accuracy and limit the range of surgical variability. The main purpose of this study is to summarize and compare the radiographic outcomes of TKA performed using Patient-specific instrumentation compared with conventional techniques. PURPOSES. In this study, we compared varus/valgus of the individual prosthesis components, rotation of femoral components and posterior slope of tibial components of 40 TKAs performed using a patient-specific technique with values from a matched control group of patients who were operated on by conventional intramedullary alignment technique. METHODS. We retrospectively evaluated 55 primary TKAs performed for osteoarthritis: conventional instrumentation using the PFC Sigma (n = 15) patient-specific instrumentation using GMK MyKnee© (n = 40). Varus/valgus of the individual prosthesis components, rotation of femoral components and posterior slope of tibial components were measured from CT images taken post operation, whether there were more outliers with one of the two methods. The fraction of outliers (> 3°) was determined. RESULTS. There was excellent reliability with low standard deviations for the determination of femoral component rotation and varus/valgus of the tibial components. There were significantly more outliers in the conventional (26.7%) group than in the patient-specific instrument group (10.0%). Outliers in Varus/valgus of femoral components were comparable between groups (7.5% in the patient-specific instrument group and 6.7% in the conventional instrument group). Other parameters such as posterior slope of tibial components did not differ in terms of outliers. CONCLUSIONS. In this study, Patient-specific instrument was effective in significantly reducing outliers of rotational femoral component and varus/valgus of the tibial components alignment during TKA. Therefore, additional studies are needed to determine whether patient-specific instrumentation improves clinical function or patient satisfaction

Modern musculoskeletal modeling techniques have been used to simulate shoulders with reverse total shoulder arthroplasty and study how geometric changes resulting from implant placement affect shoulder muscle moment arms. These studies do not, however, take into account how changes in muscle length will affect the force generating capacity of muscles in their post-operative state. The goal of this study was to develop and calibrate a patient-specific shoulder model for subjects with RTSA in order to predict muscle activation during dynamic activities. Patient-specific muscle parameters were estimated using a nested optimization scheme calibrating the model to isometric arm abduction data at 0°, 45° and 90°. The model was validated by comparing predicted muscle activation for dynamic abduction to experimental electromyography recordings. A twelve-degree of freedom model was used with experimental measurements to create a set of patient-specific data (three-dimensional kinematics, muscle activations, muscle moment arms, joint moments, muscle lengths, muscle velocities, tendon slack lengths, optimal fiber lengths and peak isometric forces) estimating muscle parameters corresponding to each patient's measured strength. The optimization varied muscle parameters to minimize the difference between measured and estimated joint moments and muscle activations for isometric abduction trials. This optimization yields a set of patient-specific muscle parameters corresponding to the subject's own muscle strength that can be used to predict muscle activation and muscle lengths for a range of dynamic activities. The model calibration/optimization procedure was performed on arm abduction data for a subject with reverse total shoulder arthroplasty. Muscle activation predicted by the model ranged between 3% and 90% of maximum. The maximum joint moment produced was 20 Nm. The model replicated measured joint moments accurately (R2 > 0.99). The optimized muscle parameter set produced feasible muscle moments and muscle activations for dynamic arm abduction, when calibrated using data from isometric force trials. Current modeling techniques for the upper extremity focus primarily on geometric changes and their effects on shoulder muscle moment arms. In an effort to create patient-specific models, we have developed a framework to predict subject-specific muscle parameters. These estimated muscle parameters, in combination with patient-specific models that incorporate the patient's joint configurations, kinematics and bone anatomy, provide a framework to predict dynamic muscle activation in novel tasks and, for example, predict how joint center changes with reverse total shoulder arthroplasty may affect muscle function

Current modeling techniques have been used to model the Reverse Total Shoulder Arthroplasty (RTSA) to account for the geometric changes implemented after RTSA. Though these models have provided insight into the effects of geometric changes from RTSA these is still a limitation of understanding muscle function after RTSA on a patient-specific basis. The goal of this study sought to overcome this limitation by developing an approach to calibrate patient-specific muscle strength for an RTSA subject. The approach was performed for both isometric 0° abduction and dynamic abduction. A 12 degree of freedom (DOF) model developed in our previous work was used in conjunction with our clinical data to create a set of patient-specific data (3 dimensional kinematics, muscle activations, muscle moment arms, joint moments, muscle length, muscle velocity, tendon slack length, optimal fiber length, peak isometric force)) that was used in a novel optimization scheme to estimate muscle parameters that correspond to the patient's muscle strength[4]. The optimization varied to minimize the difference between measured(“in vivo”) and predicted joint moments and measured (“in vivo”) and predicted muscle activations. The predicted joint moments were constructed as a summation of muscle moments. The nested optimization was implemented within matlab (Mathworks). The optimization yields a set of muscle parameters that correspond to the subject's muscle strength. The abduction activity was optimized. The maximum activation for the muscles within the model ranged between .03–2.4 (Figure 1). The maximum joint moment produced was 11 newton-meters. The joint moments were reproduced to an value of 1. Muscle parameters were calculated for both isometric and dynamic abduction (Figure 2). The muscle parameters produced provided a feasible solution to reproduce the joint moments seen “in vivo” (Figure 3). Current modeling techniques of the upper extremity focus primarily on geometry. In efforts to create patient-specific models we have developed a framework to predict subject-specific strength characteristics. In order to fully understand muscle function we need muscle parameters that correspond to the subject's strength. This effort in conjunction with patient-specific models that incorporate the patient's joint configurations, kinematics and bone anatomy hopes to provide a framework to gain insight into muscle tensioning effects after RTSA. With this framework improvements can be made to the surgical implementation and design of RTSA to improve surgical outcomes

Introduction. Unicompartmental Knee Replacement Arthroplasty (UKA) is a treatment option for early knee OA that appears under-utilised, partly because of a lack of clear guidance on how to best restore lasting knee function using such devices. Computational tools can help consider inherent uncertainty in patient anatomy, implant positioning and loading when predicting the performance of any implant. In the present research an approach for creating patient-specific finite element models (FEM) incorporating joint and muscle loads was developed to assess the response of the underlying bone to UKA implantation. Methods. As a basis for future uncertainty modelling of UKA performance, the geometriesof 173 lower limbs weregenerated from clinical CT scans. These were segmented (ScanIP, Simpleware Ltd, UK) to reconstruct the 3D surfaces of the femur, tibia, patella and fibula. The appropriate UKA prosthesis (DePuy, U.S.) size was automatically selected according to tibial plateau size and virtually positioned (Figure 1). Boolean operations and mesh generation were accomplished with ScanIP. A patient-specific musculoskeletal model was generated in open-source software OpenSim (Delp et al. 2007) based on the Gait2392 model. The model was scaled to a specific size and muscle insertion points were modified to corresponding points on lower limb of patient. Hip joint load, muscle forces and lower limb posture during gait cycle were calculated from the musculoskeletal model. The FE meshes of lower limb bones were transformed to the corresponding posture at each time point of a gait cycle and FE analyses were performed (Ansys, Inc. U.S) to evaluate the strain distribution on the tibial plateau in the implanted condition. Results. With the tibial component positioned above, along or below the joint line, the lower limb alignment was more varus, remained unaltered or more valgus respectively (Figure 2). With the tibial component positioned 3mm above the joint line, the peak strain in the underlying bone was 670 µstrain on medial (UKA) side and 6780 µstrain on the intact side. With the tibial component positioned 3mm below the joint line, the peak strain was 3010 µstrain on the medial side and 5330 µstrain on the intact side. Here, the strains on the medial side increased by 2640 µstrain whilst they were reduced by 1450 µstrain on the intact side compared to the unimplanted case. Conclusion. The present research has delivered a framework which can be exploited in future uncertainty modelling of UKA performance predictions. The patient-specific model incorporates loading, anatomical and material property variability, and can be applied to evaluate the performance of UKA prostheses for metrics such as stress/strain/micromotions in larger patient populations. For figures/tables, please contact authors directly.

Introduction. The primary purpose of Total Hip Arthroplasty (THA), aside from pain relief, is to restore hip biomechanics such that the patient experiences no discernible functional deficit, while also providing an environment conducive to implant longevity. Key factors in determining a successful THA include achieving the desired pre-operative femoral offset and leg length, as well as the restoration of range of motion (ROM). Minor leg length discrepancies (LLDs), less than a centimetre, are common after THA and usually well tolerated. However, in some patients, even these small discrepancies are a source of dissatisfaction. More significant discrepancies can be a risk factor for more serious concerns such as nerve injury, abnormal gait and chronic pain. The level of the femoral neck osteotomy is a critical step in reproducing a planned femoral stem position. Frequently the femoral osteotomy is too high and can lead to an increase in leg length and varus stem positioning. If the desired implant positions are identified from preoperative 3D templating, a planned femoral osteotomy can be used as a reference to recreate the correct leg length and offset. The aim of this study was assess the accuracy of a 3D printed patient-specific guide for delivering a pre-planned femoral neck osteotomy. Methodology. A consecutive series of 33 patients, from two surgeons at a single institution, were sent for Trinity OPS pre-operative planning (Optimized Ortho, Australia). Trinity OPS is a pre-operative, dynamic, patient-specific modelling system for acetabular and femoral implant positioning. The system requires a pre-operative CT scan which allows patient specific implant sizing as well as positioning. Once the preoperative implant positioning plan was confirmed by the surgeon, a patient-specific guide was designed and printed to enable the planned level of femoral neck osteotomy to be achieved, Fig 1. All patients received a Trinity cementless acetabular component (Corin, UK) and a cementless TriFit TS femoral component (Corin, UK) through a posterior approach. The achieved level of osteotomy was confirmed postoperatively by doing a 3D/2D registration, in the Mimics X-ray Module (Materialise, Belgium), of the planned 3D resected femur to the postoperative AP radiograph, Fig 2. The image was then scaled and the difference between the planned and achieved level of osteotomy was measured (imatri Medical, South Africa), Fig 2. Results. The mean absolute difference between the planned and achieved osteotomy level was 0.7mm (range 0.1mm − 6.6mm). Only 1 patient had a difference of more than 3mm, Fig 3. Of the 33 patients, 28 had a difference of less than 1mm. Conclusions. The results from this initial series of 33 patients suggest that a 3D printed patient-specific guide can be a simple and accurate way of intraoperatively reproducing a planned femoral neck osteotomy, though there was one significant outlier. Whether the 3D planning, patient-specific guide and accurate femoral osteotomy can then be used to achieve precise leg length and offset recreation is the subject of an on-going evaluation

Introduction:. Despite over 95% long-term survivorship of TKA, 14–39% of patients express dissatisfaction due to anterior knee pain, mid-flexion instability, reduction in range of flexion, and incomplete return of function. Changing demographics with higher expectations are leading to renewed interest in patient-specific designs with the goal of restoring of normal kinematics. Improved imaging and image-processing technology coupled with rapid prototyping allow manufacturing of patient-specific cutting guides with individualized femoral and tibial components with articulating surfaces that maximize bony coverage and more closely approximate the natural anatomy. We hypothesized that restoring the articular surface and maintaining medial and lateral condylar offset of the implanted knee to that of the joint before implantation would restore normal knee kinematics. To test this hypothesis we recorded kinematics of patient-specific prostheses implanted using patient-specific cutting guides. Methods:. Preoperative CT scans were obtained from nine matched pairs of human cadaveric knees. One of each pair was randomly assigned to one of two groups: one group implanted with a standard off-the-shelf posterior cruciate-retaining design using standard cutting guides based on intramedullary alignment; the contralateral knee implanted with patient-specific implants using patient-specific cutting guides, both manufactured from the preoperative CT scans. Each knee was tested preoperatively as an intact, normal knee, by mounting the knee on a dynamic, quadriceps-driven, closed-kinetic-chain Oxford knee rig (OKR), simulating a deep knee bend from 0° to 120° flexion. Following implantation with either the standard or patient-specific implant, knees were mounted on the OKR and retested. Femoral rollback, tibiofemoral rotation, tibial adduction, patellofemoral tilt and shift were recorded using an active infrared tracking system. Results:. To reduce the effect of variability, change in each kinematic measure was quantified as the absolute difference between the normal kinematic measure and the same measure after implantation (10° flexion increments). The cumulative difference from normal kinematics was calculated by summing the area beneath the curve (Fig 2). Cumulative differences in kinematics from normal were statistically lower for the patient-specific group compared to the standard group for all measures except patellar shift (Fig 2, paired t-test). Discussion:. Knee kinematics with the patient-specific design more closely approximated normal femoral rollback and tibial adduction than knees with the standard design. Femoral rollback is significantly closer qualitatively and quantitatively to normal in specimens implanted with patient-specific designs (Figs 1). The tibia rotated internally with flexion; however, the patient-specific group more closely approximated normal rotation. The patient-specific group more closely approximated normal tibial adduction suggesting ligament balance was better restored. Due to substantial differences in articular morphology among genders, races and patients, it is impossible to provide multiple sized implants to address the full range of inter-patient variability. Patient-specific designs that remove this variation, restore normal articular geometry, and maintain alignment are more likely to result in normal kinematics. Our results support the hypothesis that knees with patient-specific implants generate kinematics more closely resembling normal knee kinematics than standard knee designs. Clinical outcome studies are necessary to determine if our results translate into better outcomes

Background/Purpose. Patient-specific design (PSD) total knee arthroplasty (TKA) implants are marketed to restore neutral mechanical axis alignment (MAA) and provide better anatomic fit compared to standard off-the-shelf (OTS) TKA designs. The purpose of this study was to compare the Knee-Society scores, radiographic outcomes, and complications of PSD and OTS implants. Methods. IRB approved prospective study comparing PSD and OTS by a single surgeon. Implant design change in PSD occurred during the study leading to PSD-1 and PSD-2 subgroups. Demographic, radiographic data including MAA, coronal-tibial angle (CTA), femoro-tibial angle (FTA), tibial-slope (TS) and patella-tilt (PT), and complications were analyzed. Minimum follow-up was 2 year or until revision, and patients completed Knee-Society scores preoperatively, and postoperatively at 3-, 6-, 12-, 24 weeks and final follow up. Results. 136 patients (154 knees), average age (62.7 ± 8.4 years) and follow up (3.1 ± 1.5 years). PSD-1 (77 knees), PSD-2 (36 knees), and OTS (41 knees). PSD-2 had significantly higher early Knee-Society function scores compared to PSD-1 and OTS up to 6 months. All groups had excellent knee society scores after 6 months. PSD-2 had significantly shorter hospital stay (p<0.001), and less hemoglobin drop (p = 0.031) compared to PSD-1 and OTS. No significant difference in MAA (p=0.349) or final ROM (p=0.629). There was approximately 1 degree difference between the groups in the CTA, FTA, TS and PT. Failures requiring revision were 24% (18/75) PSD-1, 0% PSD-2, and 3% (1/35) OTS. Most common modes-of- failure were tibial subsidence (56%) and polyethylene locking mechanism failure (22%) in PSD-1. Conclusion. PSD-2 had better early Knee-Society function scores, shorter hospital stay, lower hemoglobin drop, and no failures compared to PSD-1 and OTS. There was an unexpected high failure rate in the early patient-specific design TKA that was not seen after the manufacturer changed the design

Introduction. The Intellijoint HIP system is a mini-optical navigation system designed to intraoperatively assist with cup orientation, leg length and offset in total hip replacement (THR). As with any imageless navigation system, acquiring the pelvic reference frame intraoperatively requires assumptions. The system does however have the ability to define the native acetabular orientation intra-operatively by registering 3-points along the bony rim. In conjunction with a pre-operative CT scan, the authors hypothesised that this native acetabular plane could be used as an intraoperative reference to achieve a planned patient-specific cup orientation. Method. Thirty-eight THR patients received preoperative OPS. TM. dynamic planning (Optimized Ortho, Sydney). On the pre-operative 3D model of each patient's acetabulum, a 3-point plane was defined by selecting recognisable features on the bony rim. The difference in inclination and anteversion angles between this native 3-point reference plane and the desired optimal orientation was pre-operatively calculated, and reported to the surgeon as “adjustment angles”. Intraoperatively, the surgeon tried to register the same 3-points on the bony rim. Knowing the intraoperative native acetabular orientation, the surgeon applied the pre-calculated adjustment angles to achieve the planned patient specific cup orientation. All patients received a post-operative CT scan at one-week and the deviation between planned and achieved cup orientation was measured. Additionally, the cup orientation that would have been achieved if the standard Intellijoint pelvic acquisition was performed was retrospectively determined. Results. The absolute mean inclination deviation from plan of the 3-point rim method was 5.6° (0.0° to 16.7°). The absolute mean anteversion deviation from plan of the 3-point rim method was 2.7° (0.1° to 9.5°). This constituted 90% within 10° of the desired patient-specific target. All anteversion measurements were within 10°, with 90% within 5°. The retrospective analysis on what would have been achieved if the standard pelvic acquisition was used, showed that the absolute mean inclination deviation from plan would have been 4.0° (0.0° to 14.2°) and the absolute mean anteversion deviation would have been 6.7° (0.1° to 24.1°). Only 74% of cups would have been within 10° of the desired target. Conclusions. Using the native acetabular orientation as a reference plane for delivering a patient-specific cup orientation showed promising preliminary results. Errors in inclination were significantly larger than anteversion. More points on the rim could reduce this error

Introduction. Surgical techniques for implant alignment in total knee arthroplasty (TKA) is a expanding field as manufacturers introduce patient-specific cutting blocks derived from 3D reconstructions of pre-operative imaging, commonly MRI or CT. The patient-specific OtisMed system uses a detailed MRI scan of the knee for 3D reconstruction to estimate the kinematic axis, dictating the cutting planes in the custom-fit cutting blocks machined for each patient. The resulting planned alignment can vary greatly from a neutral mechanical axis. The purpose of this study was to evaluate the early fixation of components in subjects randomized to receive shape match derived kinematic alignment or conventional alignment using computer navigation. A subset of subjects were evaluated with gait analysis. Methods. Fifty-one patients were randomized to receive a cruciate retaining cemented total knees (Triathlon, Stryker) using computer navigation aiming for neutral mechanical axis (standard of care) or patient-specific cutting blocks (OtisMed custom-fit blocks, Stryker). Pre-operatively, all subjects had MRI scans for cutting block construction to maintain blinding. RSA exams and health outcome questionnaires were performed post-operatively at 6 week, 3, 6, and 12 month follow-ups. A subset (9 subjects) of the patient-specific group underwent gait analysis (Optotrak TM 3020, AMTI force platforms) one-year post-TKA, capturing three dimensional (3D) knee joint angles and kinematics. Principal component analysis (PCA) was applied to the 3D gait angles and moments of the patient-specific group, a case-matched control group, and 60 previously collected asymptomatic subjects. Results. Five MRI scans for surgical planning were not useable due to motion artifacts, with 2 successfully rescanned. Ligament releases were performed in 62% of navigation cases and 32% of patient-specific cases. One patient-specific case was revised for failure of the cruciate ligament, resulting in a polyethylene liner exchange for a thicker, cruciate substituting insert. Implant migration at 1 year was 0.40±0.25 mm for the patient-specific group and 0.37±0.20 mm for the navigation group (maximum total point motions; t-test P=0.65). EQ-5D scores, Oxford Knee scores, satisfaction, pain, and range of motion were not different between groups at any follow-up to 1 year, including the polyethylene liner exchange case. The gait analysis showed that there were no statistical differences between groups. PCA captured a lower early stance phase flexion moment magnitude in the patient-specific group than the computer navigated recipients, bringing patterns further away from asymptomatic characteristics (flexion moment PC2, P=0.02). Conclusions. Implant migration was not different between groups at 1 year despite differences in implant alignment methods. Subject function and satisfaction were also not different between groups, despite significantly fewer ligament releases in the patient-specific group. However, gait analysis of a subgroup has not shown an improvement towards restoring asymptotic gait. It should be acknowledged that the production of patient-specific cutting blocks may not be possible for all patients due to the MRI scanning requirements. Continued evaluation with RSA to 2 years will be performed to monitor these subjects over the longer term

The number of joint revision surgeries is rising, and the complexity of the cases is increasing. In 58% of the revision cases, the acetabular component has to be revised. For these indications, literature decision schemes [Paprosky 2005] point at custom pre-shaped implants. Any standard device would prove either unfeasible during surgery or inadequate in the short term. Studies show that custom-made triflanged implants can be a durable solution with good clinical results. However, the number of cases reported is few confirming that the device is not in widespread use. Case Report. A patient, female 50 yrs old, diagnosed having a pseudotumor after Resurfacing Arthroplasty for osteo-arthritis of the left hip joint. The revision also failed after 1 y and she developed a pelvic discontinuity. X-ray and Ct scans were taken and sent to a specialized implant manufacturer [Mobelife, Leuven, Belgium]. The novel process of patient-specific implant design comprises three highly automated steps. In the first step, advanced 3D image processing presented the bony structures and implant components. Analysis showed that anterior column was missing, while the posterior column was degraded and fractured. The acetabular defect was diagnosed being Paprosky 3B. The former acetabular component migrated in posterolateral direction resulting in luxation of the joint. The reconstruction proposal showed the missing bone stock and anatomical joint location. In the second step, a triflanged custom acetabular metal backing implant was proposed. The bone defect (35ml) is filled with a patient-specific porous structure which is rigidly connected to a solid patient-specific plate. The proposed implant shape is determined taking into account surgical window and surrounding soft tissues. Cup orientation is anatomically analyzed for inclination and anteversion. A cemented liner fixation was preferred (Biomet Advantage 48mm). Screw positions and lengths are pre-operatively planned depending on bone quality, and transferred into surgery using jig guiding technology (Materialise NV, Leuven, Belgium). In the third step, the implant design was evaluated in a fully patient-specific manner in dedicated engineering (FEA) software. Using the novel automated CT-based methodology, patient-specific bone quality and thickness, as well as individualised muscle attachments and muscle and joint forces were included in the evaluation. Implants and jig were produced with Additive Manufacturing techniques under ISO 13485 certification, using respectively Selective Laser Melting (SLM) techniques [Kruth 2005] in medical grade Ti6Al4V material, and the Selective Laser Sintering technique using medical grade epoxy monomer. The parts were cleaned ultrasonically, and quality control was performed by optical scanning [Atos2 scanning device, GOM Intl. AG, Wilden, Switzerland]. Sterilization is performed in the hospital. CONCLUSION. A unique combination of advanced 3D planning, patient-specific designed and evaluated implants and drill guides is presented. This paper illustrates, by means of a clinical case, the novel tools and devices that are able to turn reconstruction of complex acetabular deficiencies into a reliable procedure

Introduction. Total knee arthroplasty is the standard treatment for advanced knee osteoarthritis. Patient-specific instrument (PSI)has been reported by several authors using different techniques produced by implant companies. The implant manufacturers produce PSI exclusively for their own knee implants and for easy straightforward cases. However, the PSI has become very expensive and unusable as a universal or an open platform. In addition, planning the implant is done by technicians and not by surgeons and needs long waiting time before surgery (6 weeks). Methods. We proposed a new technique which is a device and method for preparing a knee joint in a patient undergoing TKA surgery of any knee implant (prosthesis). The device is patient specific, based on a method comprised of image-based 3D preoperative planning (CT, MRI or computed X-ray) to design the templates (PSI) that are used to perform the knee surgery by converting them to physical templates using computer-aided manufacturing such as computer numerical control (CNC) or additive-manufacturing technologies. The device and method are used for preparing a knee joint in a universal and open-platform fashion for any currently available knee implant. Results. All patient-specific implants and any knee implant could be produced. The technique was applied on NExGen implant (Zimmer)on 21 patients, PFC implant (Depuy, J & J) on 5 patients, Scorpio NRG implant (Stryker) on 24 patients and SLK Evo implant (Implant International) on 81 patients. The >15 degrees varus gave a mean of 10.44 degrees in 56.67% of cases and the <15 degrees varus gave a mean of 24.04 degrees in 43.33% of cases. The total varus of 5–30 degrees gave a mean of 16.33 degrees in 90.9% of cases and the total valgus of 20–40 gave a mean of 25 degrees in 9.1% of cases. The fixed flexion deformity of < 20 degrees gave a mean of 9.4 degrees in 75.3% of cases while the fixed flexion deformity of >20 gave a mean of 31.87 degrees in 24.7% of cases. Discussion. The system is based on CT images, generic data of implant sizes, average bone geometry and standard TKA parameters for bone cutting, mechanical axis and rotation (e.g., zero-degree coronal cut, adjustable posterior slope, femoral flexion, epicondylar axis, no notching or overhang, etc.). The method of planning and completing virtual surgery of TKA includes several steps based on 3D reconstruction and segmentation of computed tomography (CT) or MRI scan data. The universal device and method are suitable to be used for any commercially and currently available knee implant. They are used for all on-shelf implants and all patient-specific instruments. The device is specifically designed for TKA and the planning is based on the 3D files of a universal TKA prosthesis. There are four standard sizes of the universal TKA prosthesis which were built depending on the average bone geometry. These 4 sizes are 55, 60, 65 and 70 mm. These sizes are consistent with the six most common implants available today: NexGen Zimmer, PFC Depuy, Sigma Knee, Triathlon Stryker, Vanguard Biomet, and Smith & Nephew Proflex. However, for extreme cases, one size above or below the maximum and minimum range can be used. The device has 2 parts: a femoral part and a tibial part, both of which are independent of any commercially available knee implant

Objectives. How to position a unicompartmental knee replacement (UKR) remains a matter of debate. We suggest an original technique based on the intra-operative anatomic and dynamic analysis of the operated knee by a navigation system, with a patient-specific reconstruction by the UKR. The goal of the current study was to assess the feasibility of the new technique and its potential pitfalls. Methods. 100 patients were consecutively operated on by implantation of a UKR with help of a well validated, non-image based navigation system, by one single surgeon. There were 41 men and 59 women, with a mean age of 68 years (range, 51 to 82 years). After data registration, the navigation system provided the dynamic measurement of the coronal tibio-femoral mechanical angle in full extension. The reducibility of the deformation was assessed by a manually applied torque in the valgus direction. The patient-specific analysis was based on the following hypotheses: 1) The normal medial laxity in full extension is 2° (after previous studies), 2) there was no abnormal medial laxity (which may be routinely accepted for varus knees) and 3) the total reducibility is the sum of the patient's own medial laxity and of the bone and cartilage loss. We assumed that the optimal correction may be calculated by the angle of maximal reducibility, less 2° to respect the normal medial laxity. The bone resections were performed accordingly to this calculated goal. No ligamentous balance or retension was performed. The fine tuning of the remaining laxity was performed by adapting the height of polyethylene component with a 1 mm step. The final measurements (coronal tibio-femoral angle in full extension and medial laxity in full extension) were performed with the navigation system after the final components fixation. The implantation had to fulfill these two parameters: optimal correction as defined previously, and a 2 ± 1° of medial laxity. Results. Before UKR, the mean coronal tibio-femoral angle in full extension was 3.9°± 2.4° without stress, and 0.7°+2.3° with valgus stress. The mean medial laxity in full extension before UKR was 3.2°+1.3°. After UKR, the mean coronal tibio-femoral angle in full extension was 2.6°+2.9°. The mean medial laxity in full extension after UKR was 1.9°+0.8°. The complete goal was obtained for 74% of the case. The optimal correction of the coronal tibio-femoral angle in full extension alone was achieved for 78% of the cases. 94% of the cases had an optimal medial laxity in full extension. Conclusion. The patient-specific UKR reconstruction according to the criteria defined was possible and its accuracy was good. The accuracy of a navigation system and the modularity of the prosthesis components seem to be significant prerequisites. The adaptation of the UKR to the patient may be easier, and the ligamentous physiology may be better restored because of the absence of any soft-tissue release. The final functional result may be improved

Objective:. Patient-specific or “custom” total knee replacements have been designed to fit the arthritic knee in primary total knee arthroplasty (TKA) better than “off-the-shelf” implants. Using computer technology, patient-specific cutting-blocks and custom-made implants are created to more accurately fit the contour of the knee and reproduce the anatomic J-curve with the hope of providing a better functional outcome. Purpose:. This retrospective, matched-pair study evaluates manipulation under anesthesia (MUA) rates in cemented patient-specific cruciate-retaining (PSCR) TKA compared to that in both cemented posterior-stabilized (PS) and non-cemented cruciate-retaining rotating-platform (NC CR RP) TKA. Materials and Methods:. From 2010 through November of 2012, 21 PSCR TKAs were performed in 19 patients. Using medical records from our patient database, these patients were matched for age, side, deformity, diagnosis, Charnley Class, and preoperative range of motion (ROM) with 42 PS TKAs performed during the same time period by the same surgeon using the same intra- and post-operative protocols. Additionally, 11 NC CR RP TKA were performed and evaluated based on the same criteria. Pre- and postoperative radiographs were performed using criteria as described by The Knee Society. Results:. Preoperatively the custom CR RP TKA cohort had a larger average ROM compared to the PS TKA cohort (P-value = 0.006). Postoperatively, however, the custom CR RP TKA cohort overall was found to have a significantly decreased average ROM compared to both the PS and NC CR RP TKA cohorts (2.0°–110.6° P-value = 0.0002 and 2.4°–117.3° P-value = 0.0003, respectively). 6 of the 21 (28.6%) PSCR TKAs performed underwent MUA to improve postoperative ROM. One manipulation was unsuccessful and the patient is scheduled for revision for arthrofibrosis. No patients in either the matched PS group or the CR RP group underwent postoperative MUA. Clinical and radiographic analysis including pre-operative ROM, deformity, side, Charnley Class, posterior tibial slope angle, epicondylar axis and posterior condylar offsets provided no insight into the reason for this higher MUA rate in the PSCR knees. Conclusion:. MUA rates in the patient-specific TKA group were significantly higher than that in the matched PS and NC CR RP groups. No correlations were found to clearly indicate the cause of the higher MUA rate among the PSCR knees. Early manipulation is recommended for stiffness with these custom devices. Level of Evidence: Level III, Retrospective comparative study. Keywords: Patient-specific total knee, Manipulation, TKA