Introduction. Geometric variations of the hip joint can give rise to repeated abnormal contact between the femur and acetabular rim, resulting in cartilage and labrum damage. Population-based geometric parameterisation can facilitate the flexible and automated in silico generation of a range of clinically relevant hip geometries, allowing the position and size of cams to be defined precisely in three dimensions. This is advantageous compared to alpha angles, which are unreliable for stratifying populations by cam type. Alpha angles provide an indication of cam size in a single two-dimensional view, and high alpha angles have been observed in asymptomatic individuals. Parametric geometries can be developed into finite element models to assess the potential effects of morphological variations in bone on soft tissue strains. The aim of this study was to demonstrate the capabilities of our parameterisation research tool by assessing impingement severity resulting from a range of parametrically varied femoral and acetabular geometries. Methods. Custom made MATLAB (MathWorks) and Python codes. [1]. were used to generate bone surfaces, which were developed into finite element models in Abaqus (SIMULIA). Parametric femoral surfaces were defined by a spherical proximal head and ellipse sections through the neck/cam region. This method produced surfaces that were well fitted to bone geometry segmented from CT scans of cam patients and capable of producing trends in results similar to those found using segmented models. A simplified spherical geometry, including the labrum and acetabular cartilage, represented the acetabulum. Femoral parameters were adjusted to define relevant variations in cam size and position. Two radii (small and large cams) and two positions (anterior and superior cams) were defined resulting in four models. Alpha angles of these parametric femurs were measured in an anterior-posterior view and a cross-table lateral view using ImageJ (NIH). A further model was developed using a femur with a medium cam size and position, and the level of acetabular coverage and labrum length were varied. Bones were modelled as rigid bodies and soft tissues were modelled as transversely isotropic linearly elastic materials. With the acetabulum fully constrained in all cases, the femurs were constrained in translation and rotated to simulate flexion followed by internal rotation to cause impingement against the labrum. Results and Discussion. Models generated using the parametric approach showed that potential for tissue damage, indicated through local strain, was not predicted by measured alpha angle, but resulted from cam extent and position as defined by the ellipses. When variations were made to the acetabular rim, an increase in bone coverage had the greatest effect on impingement severity, indicated by strain in the cartilage labral-junction. An increase in labral length increased labral displacement, but had less effect on cartilage-labral strain. Patient specific models currently require full image segmentation, but there is potential to further develop these parametric methods to assess likely impingement severity based on a series of measures of the neck and acetabulum when three-dimensional imaging of patients is available

Introduction:. Cam type femoroacetabular impingement (FAI) may lead to osteoarthritis (OA)[1]. In 2D studies, an alpha angle greater than 55° was considered abnormal however limitations of 2D alpha angle measurement have led to the development of 3D methods [2–4]. Failure to completely address the bony impingement lesions during surgery has been the most common reason for unsuccessful hip arthroscopy surgery [5]. Robotic technology has facilitated more accurate surgery in comparison to the conventional means. In this study we aim to assess the potential application of robotic technology in dealing with this technically challenging procedure of cam sculpting surgery. Methods:. CT scans of three patients' hips with severe cam deformity (A, B and C models) were obtained and used to construct 3D dry bone models. A 3D surgical plan was made in custom written software. Each 3D plan was imported into the Acrobot Sculptor robot and bone resection was carried out. In total, 42 femoral models were sculpted (14/subset), thirty of which were performed by a single operator and the remaining 12 femurs were resected by two other operators. CT of the pre/post resected specimens was segmented and a 3D alpha angle and head neck ratios were measured [3–4] and compared using Mann-Whitney U test. Coefficient of variation (CV) was used to determine the degree of variation between the mean and maximum observed alpha angles for inter and intra observer repeatability. Results:. The maximal alpha angle in cam A, B and C (90.8°, 91.3° and 87.1°). There was significant reduction (p < 0.001) in maximum alpha angles post-operatively within all three models when compared to original model (Figure 1). The HNRs for cam A, B and C prior to surgery were found to be 3.2, 3.4 and 3.1 respectively that were reduced to a mean of 3.0 ± 0.1, 3.1 ± 0.1 and 3.1 ± 0.0, following resection surgery. The results of the intra and inter-observer repeatability study found good reproducibility (CV<10%) of the maximum and mean alpha angles between the 12 resected femurs. Discussion:. In this study we evaluated the use of robotic system to perform cam correction surgery by evaluating the 3D morphology of head/neck prior to and post surgery. With existing surgical options there is a potential for under or over-resection of the cam lesion, which runs the risk of the need for further surgery or rarely neck fracture and dislocation. Based on the calculated alpha angles and HNRs we have proved that we have successfully performed the surgery by avoiding under and over resection respectively. Amore accurate bony resection performed here may minimize the complications due to over and under resection and hence will decrease the burden on the health service

Arthroscopic hip procedures have increased dramatically over the last decade as equipment and techniques have improved. Patients who require hip arthroscopy for femoroacetabular impingement on occasion require surgery on the contralateral hip. Previous studies have found that younger age of presentation and lower Charlson comorbidity index have higher risk for requiring surgery on the contralateral hip but have not found correlation to anatomic variables. The purpose of this study is to evaluate the factors that predispose a patient to requiring subsequent hip arthroscopy on the contralateral hip.

This is an IRB-approved, single surgeon retrospective cohort study from an academic, tertiary referral centre. A chart review was conducted on 310 primary hip arthroscopy procedures from 2009-2020. We identified 62 cases that went on to have a hip arthroscopy on the contralateral side. The bilateral hip arthroscopy cohort was compared to unilateral cohort for sex, age, BMI, pre-op alpha angle and centre edge angle measured on AP pelvis XRay, femoral torsion, traction time, skin to skin time, Tonnis grade, intra-op labral or chondral defect. A p-value <0.05 was deemed significant.

Of the 62 patients that required contralateral hip arthroscopy, the average age was 32.7 compared with 37.8 in the unilateral cohort (p = 0.01) and BMI was lower in the bilateral cohort (26.2) compared to the unilateral cohort (27.6) (p=0.04). The average alpha angle was 76.3⁰ in the bilateral compared to 66⁰ in the unilateral cohort (p = 0.01). Skin to skin time was longer in cases in which a contralateral surgery was performed (106.3 mins vs 86.4 mins) (p=0.01). Interestingly, 50 male patients required contralateral hip arthroscopy compared to 12 female patients (p=0.01). No other variables were statistically significant.

In conclusion, this study does re-enforce existing literature by stating that younger patients are more likely to require contralateral hip arthroscopy. This may be due to the fact that these patients require increased range of motion from the hip joint to perform activities such as sports where as older patients may not need the same amount of range of motion to perform their activities. Significantly higher alpha angles were noted in patients requiring contralateral hip arthroscopy, which has not been shown in previous literature. This helps to explain that larger CAM deformities will likely require contralateral hip arthroscopy because these patients likely impinge more during simple activities of daily living. Contralateral hip arthroscopy is also more common in male patients who typically have a larger CAM deformity. In summary, this study will help to risk stratify patients who will likely require contralateral hip arthroscopy and should be a discussion point during pre-operative counseling. That offering early subsequent or simultaneous hip arthroscopy in young male patients with large CAMs should be offered when symptoms are mild.

Introduction

Femoro-acetabular impingement (FAI) is a common source of impaired motion of the hip, often attributed to the presence of an aspherical femoral head. However, other types of femoral deformity, including posterior slip, retroversion, and neck enlargement, can also limit hip motion. This study was performed to establish whether the “cam” impinging femur has a single deformity of the head/neck junction or multiple abnormalities.

Surgical management of cam-type femoroacetabular impingement (FAI) aims to preserve the native hip, restore joint function, and delay the onset of osteoarthritis. However, it is unclear how surgery affects joint mechanics and hip joint stability. The aim was to examine the contributions of each surgical stage (i.e., intact cam hip, capsulotomy, cam resection, capsular repair) towards hip joint centre of rotation and microinstability. Twelve fresh, frozen cadaveric hips (n = 12 males, age = 44 ± 9 years, BMI = 23 ± 3 kg/m2) were skeletonized to the capsule and included in this study. All hips indicated cam morphology on CT data (axial α = 63 ± 6°, radial α = 74 ± 4°) and were mounted onto a six-DOF industrial robot (TX90, Stäubli). The robot positioned each hip in four sagittal angles: 1) Extension, 2) Neutral 0°, 3) Flexion 30°, and 4) Flexion 90°, and performed internal and external hip rotations until a 5-Nm torque was reached in each direction, while recording the hip joint centre's neutral path of translation. After the (i) intact hip was tested, each hip underwent a series of surgical stages and was retested after each stage: (ii) T-capsulotomy (incised lateral iliofemoral capsular ligament), (iii) cam resection (removed morphology), and (iv) capsular repair (sutured portal incisions). Eccentricity of the hip joint centre was quantified by the microinstability index (MI = difference in rotational foci / femoral head radius). Repeated measures ANOVA and post-hoc paired t-tests compared the within-subject differences in hip joint centre and microinstability index, between the testing stages (CI = 95%, SPSS v.24, IBM). At the Extension and Neutral positions, the hip joint centre rotated concentrically after each surgical stage. At Flexion 30°, the hip joint centre shifted inferolaterally during external rotation after capsulotomy (p = 0.009), while at Flexion 90°, the hip joint centre further shifted inferolaterally during external rotation (p = 0.005) and slightly medially during internal rotation after cam resection, compared to the intact stages. Consequently, microinstability increased after the capsulotomy at Flexion 30° (MI = +0.05, p = 0.003) and substantially after cam resection at Flexion 90° (MI = +0.07, p = 0.007). Capsular repair was able to slightly restrain the rotational centre and decrease microinstability at the Flexion 30° and 90° positions (MI = −0.03 and −0.04, respectively). Hip microinstability occurred at higher amplitudes of flexion, with the cam resection providing more intracapsular volume and further lateralizing the hip joint during external rotation. Removing the cam deformity and impingement with the chondrolabral junction also medialized the hip during internal rotation, which can restore more favourable joint loading mechanics and stability. These findings support the pathomechanics of cam FAI and suggest that iatrogenic microinstability may be due to excessive motions, prior to post-operative restoration of static (capsular) and dynamic (muscle) stability. In efforts to limit microinstability, proper nonsurgical management and rehabilitation are essential, while activities that involve larger amplitudes of hip flexion and external rotation should be avoided immediately after surgery

Introduction. In the evaluation of patients with pre-arthritic hip disorders, making the correct diagnosis and identifying the underlying bone pathology is of upmost importance to achieve optimal patient outcomes. 3-dimensional imaging adds information for proper preoperative planning. CT scans have become the gold standard for this, but with the associated risk of radiation exposure to this generally younger patient cohort. Purpose. To determine if 3D-MR reconstructions of the hip can be used to accurately demonstrate femoral and acetabular morphology in the setting of femoroacetabular impingement (FAI) and development dysplasia of the hip (DDH) that is comparable to CT imaging. Materials and Methods. We performed a retrospective review of 14 consecutive patients with a diagnosis of FAI or DDH that underwent both CT and MRI scans of the same hip with 3D reconstructions. 2 fellowship trained musculoskeletal radiologists reviewed all scans, and a fellowship trained hip preservation surgeon separately reviewed scans for relevant surgical parameters. All were blinded to the patients' clinical history. The 3D reconstructions were evaluated by radiologists for the presence of a CAM lesion and acetabular retroversion, while the hip preservation surgeon also evaluated CAM extent using a clock face convention of a right hip, location of femoral head blood supply, and morphological anterior inferior iliac spine (AIIS) variant. The findings on the 3D CT reconstructions were considered the reference standard. Results. Of 14 patients, there were 9 females and 5 males with a mean age 32 (range 15–42). There was no difference in the ability of MRI to detect the presence of a CAM lesion (100% agreement between 3D-MR and 3D-CT, p=1), AIIS morphology (p=1, mode=type 1 variant), or acetabular retroversion (85.7%, p=0.5). 3D-MR had a sensitivity and specificity of 100 in detecting a CAM lesion relative to 3D-CT. Four CT studies were inadequate to adequately evaluate for presence of a CAM. Five CT studies were inadequate to evaluate for location of the femoral head vessels, while MRI was able to determine location in those patients. In the 10 remaining patients for presence of CAM, and nine patients for femoral head vessel location, there was no statistically significant difference between 3D-MR and 3D-CT in determining the location of CAM lesion on a clock face (p=0.8, mean MRI = 12:54, mean CT: 12:51, SD = 66 mins MR, 81 mins CT) or in determining vessel location (p=0.4, MR mean 11:23, CT mean 11:36, SD 33 mins for both). Conclusion. 3D MRI reconstructions are as accurate as 3D CT reconstructions in evaluating osseous morphology of the hip, and may be superior to CT in determining other certain clinically relevant hip parameters. 3D-MR was equally useful in determining the presence and extent of a CAM lesion, acetabular retroversion, and AIIS morphologic variant, and more useful than 3D CT in determining location of the femoral head vessels. In evaluating FAI or hip dysplasia, a 3D-MR study is sufficient to evaluate both soft tissue and osseous anatomy, sparing the need for a 3D CT scan and its associated radiation exposure and cost

INTRODUCTION. Stimulation of angiogenesis via the delivery of growth factors (GFs) like vascular endothelial growth factor (VEGF) is a promising strategy for the treatment of avascular necrosis (AVN). Tyraminated poly-vinyl-alcohol hydrogels (PVA-Tyr), which have the ability to covalently incorporate GFs, were proposed as a platform for the controlled delivery of therapeutic levels VEGF to the necrotic areas[1]. Nevertheless, PVA hydrophilicity and bioinertness limits its integration with the host tissues. The aim of this study was to investigated the effectiveness of incorporating gelatin, an FDA-approved, non-immunogeneic biomaterial with biological recognition sites, as a strategy to facilitate blood vessels invasion of PVA-Tyr hydrogels and to restore the vascular supply to necrotic tissues. METHODS. Progressively higher gelatin concentrations (0.01–5wt%) were incorporated in the PVA-Tyr network. Hydrogel physico-chemical properties and endothelial cell attachment were evaluated. Afterwards, the capability of the released VEGF and gelatin to promote vascularization was evaluated via chorioallantoic membrane (CAM) assay. VEGF-loaded PVA-Tyr hydrogels with or without gelatin (n=7) were implanted in a subcutaneous mouse model for 3 weeks. Vascularization (CD31+ cells) and cell infiltration (H&E) were evaluated. Finally, AVN was induced in 6 weeks old male piglets as previously described [2]. A transphyseal hole (3mm) was drilled and PVA-Tyr hydrogels with 1% gelatin were delivered in the defects. Piglets were euthanized after 4 weeks and microCT analysis was performed. RESULTS. The incorporation of 1% gelatin significantly enhanced cell attachment without compromising hydrogels physical properties, degradation time, VEGF retention and release. Thus, this gelatin concentration was selected for further analysis. Additionally, the covalent incorporation of VEGF or gelatin to the PVA-Tyr network does not hamper their bioactivity, as both still promoted neo-angiogenesis in a CAM assay. Following subcutaneous implantation, the presence of gelatin did not increase the cellular infiltration in the PVA-Tyr hydrogels. Nevertheless, higher vascular infiltration was observed in the groups where either gelatin or VEGF were included. Additionally, preliminary microCT results indicated that the delivery of PVA-Tyr hydrogels containing 1% gelatin in an AVN model was effective in preventing the necrosis-associated resorption of the bone. DISCUSSION & CONCLUSIONS. These results indicated that the presence of either gelatin or VEGF was sufficient to promote vascular infiltration. Additionally, preliminary results suggested the suitability of the developed hydrogels to treat AVN

Few epidemiological studies from Asian countries have addressed this issue and reported that FAI is less prevalent in Asian population. The purpose of this study was to determine the prevalence of radiographic hip abnormalities associated with FAI in asymptomatic Korean volunteers. The authors hypothesized that the prevalence of FAI in Korean population would not be less than that in western population. Two hundred asymptomatic volunteers with no prior hip surgery or childhood hip problems underwent three-view plain radiography (pelvis anteroposterior (AP) view, Sugioka view, and 45° Dunn view) of both hips. Cam lesions were defined as the presence of the following signs on each views: pistol-grip deformity, osseous bump at the femoral head-neck junction, flattening of the femoral head-neck offset, or alpha angle >50°. Pincer lesions were determined by radiographic signs, including crossover sign, posterior wall deficient sign, or lateral center-edge (CE) angle >40°. Only positive cases agreed by both observers were defined as true FAI-related deformities. There were 146 male and 254 female hips, with a mean age of 34.7 years. On pelvis AP view, the prevalence of pistol grip deformity, bump, flattening, and alpha angle >50° was 1.3% (male 3.4%, female 0%), 0.8% (male 2.1%, female 0%), 0.8% (male 2.1%, female 0%), and 1.0% (male 2.7%, female 0%), respectively. On Sugioka view, the prevalence of bump, flattening, and alpha angle >50° was 9.8% (male 14.4%, female 7.1%), 13.5% (male 20.5%, female 9.4%), and 14.0% (male 26.7%, female 6.7%), respectively. On 45° Dunn view, the prevalence of bump, flattening, and alpha angle >50° was 8.0% (male 14.4%, female 4.3%), 17.5% (male 27.4%, female 11.8%), and 27.5% (male 44.5%, female 17.7%), respectively. The prevalence of cam lesion which was identified on at least one radiograph was 42.5% (male 62.3%, female 31.1%). The prevalence of cam lesion which was identified on ≥2 radiographs was 19.3% (male 30.8%, female 12.6%). The prevalence of cam type FAI (at least one cam lesion) was 2.0% (male 5.5%, female 0%) on pelvis AP view, 25.8% (male 37.0%, female 19.3%) on Sugioka view, and 35.8% (male 55.5%, female 24.4%) on 45° Dunn view. On pelvis AP view, the prevalence of crossover sign, posterior wall sign, and CE angle >40° was 20.0% (male 23.3%, female 18.1%), 20.8% (male 22.6%, female 19.7%), and 2.0% (male 2.7%, female 1.6%), respectively. The prevalence of pincer type of FAI (at least one pincer lesion) was 23.0% (male 27.4%, female 20.5%). In asymptomatic Korean volunteers, the prevalence of cam type FAI was low on AP pelvis radiographs, whereas the prevalence of cam type FAI on Sugioka and 45° Dunn view was found to be comparable to that previously reported in Western populations. The prevalence of pincer type FAI in asymptomatic Korean volunteers was also comparable that in Western populations and was similar in both gender. Considering the high prevalence of FAI morphologic features on plain radiographs in asymptomatic Korean populations, it is also important to determine whether FAI is a cause of hip pain when considering surgery in Asian patients

INTRODUCTION. Clinical studies have shown that the knee tends to experience laterally higher AP motion (posterior directed) than medially (Asano at al., 2001; Dennis et al., 2005; Hill et al., 2000; Moro Oka et al., 2007). Traditional posterior stabilized (PS) total knee arthroplasty (TKA) designs allow deep flexion stability and femoral rollback once cam/spine engagement occurs, however mechanical stability provided by tibial bearing conformity during early to mid-flexion is highly variable. In this study a computer knee model is used to compare AP kinematics in PS TKA designs while evaluating multiple sagittal tibia bearing conformities. We hypothesized that highly conforming designs would be necessary to promote AP stability prior to cam/spine engagement. METHOD. A specimen specific computer model consisting of the femur, tibia and fibula, as well as the contribution of the ligaments and capsule was virtually implanted with TKA designs of the appropriate size at 5° tibia slope with the posterior cruciate ligament sacrificed. A single PS femoral component was evaluated with five PS tibia bearing designs with variable sagittal conformity ratios ranging from 1.05:1 to 2.2:1 (conformity ratio = tibia bearing sagittal radius / femur sagittal condylar radius). Designs were fully conforming frontally, with cam/spine engagement beyond 90° flexion. In all designs, lateral conformity ratios were increased relative to medial conformity ratios to facilitate lateral femoral rollback. Resultant AP kinematic predictions were obtained for femoral Low Points (LP) during 1) envelope of motion during internal external (IE) laxity evaluation and 2) knee bend functional activity. RESULTS. Designs with increased conformity resulted in improved AP stability in early to mid-flexion. In the envelope of laxity evaluations (Figure 1), the Medial LP laxity was similar for the 1.05:1 and 1.15:1 designs (approximately 2–3mm from extension to flexion), but then increased for the 1.35:1, 1.55:1, and 2.20:1 designs. Lateral LP laxity was more similar in all designs, however the designs with lower medial conformity ratio tended to have a greater Lateral LP laxity. During the Knee Bend activity (Figure 2), minimal (<1mm) Medial LP AP motion occurred from extension to cam/spine engagement in both the 1.05:1 and 1.15:1 designs, and greater AP motion occurred in the remaining designs. DISCUSSION. This study demonstrates that similar knee kinematics in PS TKA can be achieved over a small range of sagittal conformities, when designs approach 1:1 conformity. More conforming medial geometries can lead to greater lateral LP motion, suggesting greater medial conformity is necessary to replicate normal knee kinematics. Further work could evaluate impact of other factors such as tibia slope, further refinement in conformity, and additional specimen sizes. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

The debate regarding the superiority of retaining (CR) or substituting (PS) for the PCL in total knee arthroplasty (TKA) has continued for a generation, without a clear consensus as to which is superior. That debate continues today. Many studies on this subject have been published, including recent meta-analyses, which demonstrate similar outcomes between CR and PS TKA. Pain scores and functional outcomes appear quite similar between the groups. One outcome measure that appears superior in PS knees, although by a small margin, is in final range of motion, with higher final flexion observed in PS knees. Another study demonstrated superior extensor mechanism efficiency in PS designs compared to CR. The primary explanation for improved motion is the rollback induced by the cam and post mechanism of the PS knee. By insuring rollback of the femur on the tibia, the chance of impingement between the back of the femur and polyethylene is diminished. This cam and post induced rollback has been shown to be more consistent with native knee kinematics compared to the CR knee, which can be subject to “paradoxical motion”, the forward sliding of the femur on the tibia during knee flexion. The clear downsides of the PS knee include an increased rate of patellar clunk and crepitus, intercondylar femur fracture, post failure, and bone loss due to the box cut. The gaps must be carefully balanced to prevent a loose flexion gap which can allow the cam to “jump the post”. With improved implant design and materials, each of these complications has been reduced, but surgeons need to recognise these possibilities to reduce the incidence and identify them when they occur. Improvements in the trochlear geometry have significantly reduced the patellofemoral complications, a significant historical problem for patients with PS devices. Indications for using a PS knee include patients with a prior patellectomy, patients with PCL deficiency, or those with a higher risk of late PCL rupture such as patients with poor neuromuscular control or rheumatoid arthritis, although there are reports successful use of CR TKA in rheumatoid arthritis

Purpose. Femoroacetabular impingement (FAI) may contribute to the development of early onset hip osteoarthritis (OA). A cam lesion (or pistol grip deformity) of the proximal femur reduces head-neck offset resulting in cam type FAI. The alpha angle is a radiographic measurement recommended for diagnosis of cam type FAI. The purpose of this study was to determine if patients that develop end stage hip OA prior to 55 years of age have radiographic evidence of cam type FAI. Method. The anteroposterior (AP) pelvis and lateral hip radiographs of 244 patients (261 hips) who presented to our institution for hip arthroplasty or hip fracture fixation between 2006 and 2008 were retrospectively reviewed. Three cohorts were compared: 1) patients with end stage hip OA < 55 years old (N=76); 2) patients with end stage hip OA > 55 years old (N=84); 3) hip fracture patients > 65 years old without radiographic evidence of hip arthritis were used as controls (N=101). Patients with inflammatory arthritis, avascular necrosis and post-traumatic hip OA were excluded. Alpha angles were measured on the AP pelvis and lateral radiographs by three coauthors using ImageJ 1.43 software (National Institutes of Health, USA). For patients with end stage hip OA, AP alpha angles were measured on both the hip with OA and the contralateral hip. Lateral alpha angles were measured only on the hip with OA. For patients with hip fracture, AP alpha angles were measured on the non-fractured hip and lateral alpha angles were measured on the fractured hip. A one-way ANOVA with post hoc Tukeys HSD test was used to compare the AP and lateral alpha angles for the three cohorts. Results. The intraclass correlation coefficient (ICC) for the three coauthors measuring AP and lateral alpha angles was 0.85 and 0.86 respectively, indicating excellent inter-rater agreement. Patients < 55 years old with end stage hip OA had the largest AP and lateral alpha angles (82.711.6 degrees AP and 63.918.5 degrees lateral). These angles were significantly larger (p<0.01 for both comparisons) than patients > 55 years old with end stage hip OA (71.717.8 degrees AP and 55.518.0 degrees lateral) and hip fracture patients without hip OA (52.710.9 degrees AP and 44.411.4 degrees lateral). Comparing AP alpha angles of the contralateral hips, the mean AP alpha angle for patients < 55 years old with hip OA (70.813.2 degrees) was significantly larger (p=0.04) than patients > 55 years old with hip OA (64.516.2 degrees) which in turn was significantly larger (p<0.01) than the hip fracture patients (52.710.9 degrees). Conclusion. Patients < 55 years old with hip OA had the largest mean AP and lateral alpha angles, significantly larger than patients > 55 years old with hip OA and hip fracture patients without hip OA. Thus young patients with end stage hip OA do have radiographic evidence of cam type FAI. Furthermore, this case-controlled study suggests that cam type FAI may contribute to the development of early onset hip OA

In general TKA can be divided into two distinct groups: cruciate retaining and cruciate substituting. The cam and post of the latter system is in fact a mechanical substitution of the intricate posterior cruciate ligament. In our previous work we and many other investigators have focused on the movement of the femoral component relative to the tibial tray. Little information is available about the relative movement between the cam part of the femoral component and the post of the tibial insert. In this study we determine the distance and the changes in distance between the cam of the femoral component and the tibial post during extension, flexion at 90° and full flexion. The secondary purpose is to analyse possible differences between FBPS and MBPS TKA. Methods. 12 subjects' knees were imaged using fluoroscopy from extension over 90° to maximum kneeling flexion. The images were digitized. The 3-dimensional (3D) position and orientation of the implant components were determined using model-based shape-matching techniques, manual matching, and image-space optimization routines. The implant surface model was projected onto the geometry-corrected image, and its 3D pose was iteratively adjusted to match its silhouette with the silhouette of the subject's TKA components. The results of this shapematching process have standard errors of approximately 0.5° to 1.0° for rotations and 0.5 mm to 1.0 mm for translations in the sagittal plane. Joint kinematics were determined from the 3D pose of each TKA component using the 3-1-2 Cardan angle convention. This process resulted in a distance map of the femoral and tibial surfaces, from which the minimum separations were determined for the purpose of this study between cam and post (fig1.). Separation distances between the tibial polyethylene (PE) insert's post and the femoral prosthesis component have been calculated in three steps. First, the surface models of all three components as well as their position and orientation were extracted from the data files produced by the fluoroscopic kinematic analysis. Next, a set of 12 points were located on the post of each tibial insert (fig2.). Finally, for each point, the distance to the femoral component was quantified. For each step in this process, custom MATLAB. (r). (The MathWorks(tm) Inc., Natick, MA, USA) programs were used. For each of the 12 points on the post, a line was constructed through the point and parallel to the outward-facing local surface normal of the post. The resulting set of lines was then intersected with the femoral component model. Intersection points where lines ran “out of” the femoral component, detected by a positive dot product of the femoral component surface normal with the post surface normal (used to define the line), were discarded. Finally, the distances between the 12 points on the post and the intersection points on each line were calculated. For each line, the smallest distance was retained as a measure of the separation between insert and femoral component. Where a line did not intersect the femoral component, the corresponding separation distance was set to infinity. In each position, distances are measured at 6 pairs of points. Two indices of asymmetry are analysed: . The absolute difference between both measurements within a pair. Perfect symmetry is present when this absolute difference equals zero. The proportion of pairs where one of both measurements equals infinity. Indeed, this situation refers to the presence of ‘extreme’ asymmetry. A linear model for repeated measures is used to analyse the absolute differences as a function of the between-subjects factor condition (mobile bearing or fixed bearing) and the within-subject factors position (4 levels) and pair (6 levels). More specifically, a direct likelihood approach is adopted using a compound symmetric covariance matrix. Results. There is a significant difference in absolute difference between the fixed and mobile bearing condition (p=0.046). On average, the absolute difference is higher in the fixed bearing condition, 1.75 (95%CI: 1.39;2.11) vs 1.20 (95%CI:0.78;1.62). (fig2.). Conclusion. The separation distances between post and cam show less asymmetry in the Rotating platform TKA, meaning less or no contact between the post and cam surfaces which are possible sources of wear

INTRODUCTION. Posterior stabilized (PS) total knee arthroplasty (TKA) provides posterior stability with the use of a cam-post mechanism which performs the function of the posterior cruciate ligament. The tibial post engages with the femoral cam, prevents the femur from sliding anteriorly and provides the posterior femoral rollback necessary for achieving deep flexion of the knee. However, these designs do not substitute the resection of the anterior cruciate ligament. In order to overcome this deficit, other TKA designs have been recently introduced to provide dual support, with the help of dual cam-post engagement mechanism. Various studies conducted on the PS TKA have suggested that the cam-post mechanism does not engage as designed, resulting in tibial post wear and increased stresses resulting in backside wear of the polyethylene insert component. Also, the in vivo data pertaining to the actual cam-post engagement mechanism in bi-cruciate stabilized knees is still very limited. Therefore, the objective of this study was to determine the cam-post mechanism interaction under in vivo, weight bearing conditions for subjects implanted with either a Rotating Platform (RP) Posterior Stabilized (PS) TKA or a bi-cruciate stabilizing TKA (BCS). METHODS. In-vivo, weight-bearing, 3D knee kinematics were determined for eight subjects (9 knees) having a RP-PS TKA (DePuy Inc.) and eight subjects (10 knees) having BCS TKA (Smith&Nephew Inc.), while performing a deep knee bend. 3D kinematics was recreated from the fluoroscopic images using a previously published 3D-to-2D registration technique (Figure 1). Images from full extension to maximum flexion were analyzed at 10° intervals. Once the 3D kinematics of all implant components was recreated, the cam-post mechanism was scrutinized. The distance between the interacting surfaces was monitored throughout the flexion and the predicted contact map was calculated. The instances, when the minimum distance between the cam and post surfaces dropped to zero was considered to indicate the engagement of the mechanism. This analysis was carried out for both the, anterior and posterior cam-post engagement sites. RESULTS. The average range-of-motion achieved by the subjects implanted with the RP-PS TKA was 105.9° (SD=13.2°), and subjects with the BCS TKA achieved, on average 126.5° (SD=4.5°) of maximum flexion. During the deep knee bend activity all knees experienced a posterior femoral rollback (PFR) of both condyles. Anterior Contact (BCS TKA). Seven of the 10 knees analyzed had the femoral component engaged with the anterior aspect of the tibial post at full extension (Figure 2). However, the contact between them was lost in very early flexion (average: 4.9°; maximum: 9.9°). The contact was always located centrally on the anterior aspect of the tibial post. Posterior Contact. The cam-post engaged at 34° for the BCS and at 97° for RP-PS TKA. In the BCS knees, the contact initially occurred on the medial aspect of the tibial post and then gradually moved centrally and superiorly with increasing flexion, while for the RP-PS TKA it was located centrally on the post at all times (Figure 3). Also, there were two subjects in the BCS group who had engagement during mid-flexion (50–90°), but, lost contact with the post between 100–110°, before regaining contact in deeper flexion. One subject in the RP-PS group did not experience cam/post engagement (the minimum distance was 2.2mm at 86° of flexion, which was the maximum for this subject). This could be because the maximum flexion for this patient was less than the average cam-post engagement angle for the RP-PS group subjects. DISCUSSION. The anterior cam-post interaction in the BCS group was found to be present in a majority of subjects. However, there were three subjects who did not have any contact with the anterior aspect of the tibial post. This can be explained from the fact that the contact point (at full extension) on the medial and lateral side for these three patients was more anterior than any of the other seven subjects analyzed in this study. On the posterior side, contact was established by all subjects analyzed in the BCS group and 8/9 subjects analyzed in the RP-PS group. Also, for the BCS group the initial contact with the tibial post was achieved on the medial aspect, before the contact area tended to move centrally and superiorly with increasing flexion. This could be due to the large amount of lateral PFR combined with lesser amounts of medial PFR (femoral component rotating externally) experienced by the subjects. Therefore, the posterior surface of the tibial post was not parallel to the femoral cam surface. Interestingly, in the RP-PS group, the contact between the cam and post was located centrally on the post at all times when engaged. This is probably due to the mobility of the polyethylene, characteristic for the analyzed TKA design. The polyethylene insert rotated axially in accord with the rotating femur. Therefore the posterior surface of the mobile bearing post was able to remain parallel to the surface of the femoral cam. This phenomenon in the BCS group (Fixed bearing TKA) may increase the chances of edge loading on the polyethylene, resulting in wear patterns on the post

Introduction. Total-knee-arthroplasty (TKA) is a well-established method to restore the joint function of the human knee. Different types of TKA designs are clinically available which can be divided in two main groups, the posterior-cruciate- ligament (PCL) sacrificing and retaining group. However, pre-operatively it is often difficult to plan for one or the other. Therefore, the research question was: Is it possible to develop a TKA bearing design which works for both the cruciate sacrificing and retaining technique? A medial-congruent (MC) bearing design was developed, characterized by a high medial sagittal conformity and lower lateral sagittal conformity, which can be used for both cruciate ligament states. This study compares the laxity and kinematics of this MC design to a contemporary PS design for the cruciate sacrificing technique and to a contemporary CR design for the cruciate retaining technique. Methods. Four specimen-specific computer models of the human knee, consisting of a femur, tibia and fibula bone as well as the contribution of the ligaments and capsule, were virtually implanted with three TKA designs in four constellations: 1) MC without PCL, 2) MC with PCL, 3) contemporary PS without PCL and 4) contemporary CR with PCL following the design specific surgical technique and tibia slopes. Laxity tests in internal-external rotation (moment ± 4 Nm) were performed with the implanted models for a weight bearing case (500N compression). In addition, a high demanding activity (lunge) was simulated. The resulting averaged laxities and kinematics were analysed and compared to each other. Results. When sacrificing the PCL, MC showed lower medial laxity throughout flexion and higher lateral laxity above 60° flexion compared to the PS design. When retaining the PCL, the MC resulted in lower medial laxity throughout flexion, lower lateral laxity in extension and similar lateral laxity in flexion compared to the CR design. When sacrificing the PCL in the lunge activity, the MC design had a more posterior position throughout flexion on both condyles until deep flexion when the engagement of the cam/spine occurred for the PS design and posterior motion of the medial condyle during mid-flexion as opposed to anterior motion for the PS design. When retaining the PCL in the lunge-activity, the MC design had a more posterior position throughout the activity, and similar medial and lateral condyle motion throughout flexion compared to the CR design. Conclusion. When sacrificing the PCL, MC behaved similar to a contemporary PS design with more medial stability, more lateral laxity in deep flexion, and a posterior position during a lunge activity that did not depend on a cam/spine mechanism. When retaining the PCL, MC behaved similar to a contemporary CR design with more medial stability, similar lateral laxity in deep flexion, and a posterior position during a lunge activity demonstrating that the increased medial conformity did not cause a kinematic conflict with the retained PCL. These findings illustrate the concept that the MC design can be used for both the PCL sacrificing and retaining technique

Femoroacetabular impingement is defined as abnormal abutment between the femoral head, or the femoral head-neck junction, and the acetabulum. It is now established that FAI is a major etiological factor in the development of osteoarthritis (OA) of the hip. FAI is increasingly recognized as a cause of hip pain in young active individuals. Clinical features of FAI include pain in the groin but this may also be felt in the gluteal region, trochanteric region, or in the thigh. Symptoms most commonly begin as an intermittent discomfort, often during or following periods of repetitive hip motion e.g. running, walking, progressing to more constant and intense pain. Stiffness is common, with reductions in the range of hip flexion, and internal rotation in particular. Patients may also complain of clicking, popping, or snapping sensations in the affected hip. Operative treatment of FAI is principally aimed at removing cam lesions and increasing femoral head-neck offset (osteochondroplasty), and treating associated soft tissue lesions such as labral tears. Acetabular recession with labral reattachment is increasingly used for pincers lesions but great care is needed to ensure that the overall coverage of the hip is not reduced. As proficiency with arthroscopic techniques has improved, arthroscopic osteochondroplasty and labral debridement/repair has become increasingly popular for the treatment for FAI, with promising functional results in a range of studies. 150 consecutive patients who underwent hip arthroscopy for CAM type FAI with minimum 1 year follow up were prospectively studied. Patient satisfaction, non-arthritic hip score, re-operations and conversion to arthroplasty were analysed. There were a total of 90 males and 60 females. The average age group was 32 years (27 to 46 years). All patients underwent osteoplasty of the CAM lesion and stabilisation/ repair of the labral tears. A comparison of pre procedure non arthritic hip scores with the scores at latest follow up (minimum 1 year, maximum 3 years) showed a significant improvement (56 vs 86; p <0.01). There were 2 re operations for unresolved symptoms and 1 conversion to arthroplasty for continued pain associated with significant loss of articular cartilage. Perineal numbness was noted in 9 patients all of which resolved. No other major complications were noted in this series. Hip impingement symptoms resolved in all cases and a good (20 %) to excellent (75%) outcome was reported. Arthroscopic management of CAM type FAI is associated with subjective and objective improvement in hip function at early follow up. Longer follow-up is necessary to analyse the ability of this procedure to arrest progression of degenerative hip disease

Introduction. Currently, knee and hip implants are evaluated experimentally using mechanical simulators or clinically using long-term follow-up. Unfortunately, it is not practical to mechanically evaluate all patient and surgical variables and predict the viability of implant success and/or performance. More recently, a validated mathematical model has been developed that can theoretically simulate new implant designs under in vivo conditions to predict joint forces kinematics and performance. Therefore, the objective of this study was to use a validated forward solution model (FSM) to evaluate new and existing implant designs, predicting mechanics of the hip and knee joints. Methods. The model simulates the four quadriceps muscles, the complete hamstring muscle group, all three gluteus muscles, iliopsoas group, tensor fasciae latae, and an adductor muscle group. Other soft tissues include the patellar ligament, MCL, LCL, PCL, ACL, multiple ligaments connecting the patella to the femur, and the primary hip capsular ligaments (ischiofemoral, iliofemoral, and pubofemoral). The model was previously validated using telemetric implants and fluoroscopic results and is now being used to analyze multiple implant geometries. Virtual implantation allows for various surgical alignments to determine the effect of surgical errors. Furthermore, the model can simulate resecting, weakening, or tightening of soft tissues based on surgical errors or technique modifications. Results. The model revealed PCL weakening leads to paradoxical anterior slide of both femoral condyles. This paradoxical slide reduces maximum flexion and increases knee forces as seen in TKA fluoroscopic studies. Cam/post kinematics in posterior-stabilized designs were also analyzed, revealing cam/post forces increasing linearly with flexion. While cam/post engagement should ideally occur superiorly on the post and move inferiorly throughout knee flexion, fluoroscopy documented implants contacting inferiorly and rolling superiorly with flexion. Thus, a theoretical new implant was simulated to overcome this problem such that TKA design would experience the desired motion, yielding inferior contact in later flexion when forces approach 1.0 × BW. At the hip, the model predicts maximum compressive hip forces of 1.5–2.5 xBW throughout stance phase of gait. The model determines how this force is distributed on the femoral head and acetabular cup throughout the entire activity, allowing wear patterns on implant components to be predicted. During stance phase, the model predicts posterior-to-anterior sliding of the femoral head, with larger magnitudes of motion occurring on the supero-lateral aspect of the cup. The model can predict femoral neck impingement on the acetabular cup and shows that excessive anteversion of the cup leads to the femoral component levering away from the acetabular cup, yielding up to 2.0 mm of hip separation. Conclusions. This study demonstrates the ability of an in-vivo data based forward solution model to evaluate the impact of variation upon implant forces, motion and performance. This will improve understanding of observations such as polyethylene wear, pain associated with excessive soft-tissue forces, subluxation and dislocation, among others. Ultimately, the model could become a theoretical simulator that could evaluate implants much quicker for longer time durations, be less costly and provide comparative analyses when compared to present day experimental simulators

Introduction. Mid-flexion stability is believed to be an important factor influencing successful clinical outcomes in total knee arthroplasty. The post of a posterior-stabilizing (PS) knee engages the cam in >60° of flexion, allowing for the possibility of paradoxical mid-flexion instability in less than 60° of flexion. Highly-conforming polyethylene insert designs were introduced as an alternative to PS knees. The cruciate-substituting (CS) knee was designed to provide anteroposterior stability throughout the full range of motion. Methods. As part of a prospective, randomized, five-year clinical trial, we performed quantitative stress x-rays on a total of 65 subjects in two groups (CS and PS) who were more than five years postoperative with a well-functioning total knee. Antero-posterior stability of the knee was evaluated using stress radiographs in the lateral position. A 15 kg force was applied anteriorly and posteriorly with the knee in 45° and 90° of flexion. Measurements of anterior and posterior displacement were made by tracing lines along the posterior margin of the tibial component and the posterior edge of the femoral component, which were parallel to the posterior tibial cortex. (Figures 1–4). Results. In both 45° and 90° of flexion, the PS group demonstrated significantly less total anterior/posterior displacement compared to the CS group, (45°: 7.33 mm vs 12.44 mm, p ≤ 0.0001, 90°: 3.54 mm vs. 9.74 mm, p ≤ 0.0001). (Figures 5,6) The only statistically significant outcomes score difference was seen with the KSS function score in the female subset, with the CS score lower (81.8) compared to the PS score (94.7). (Figure 7) All of the other scores, KSS pain/motion and KSS function scores, as well as the LEAS and FJS scores, were all similar statistically, as was the range of motion and the long axis x-ray alignment. Discussion & Conclusion. The post and cam posterior-stabilized knee has traditionally been thought to be the best choice for providing stability for knee replacement with PCL-insufficiency or sacrifice. However, this difference in stability as measured with stress xrays did not correlate with any detectible differences in any of the clinical outcomes measurements collected (Knee Society Score, Forgotten Joint Score, Lower Extremity Activity Scale) or in the range of motion or coronal alignment, with the exception of the female subgroup KSS function score. In summary, the CS knee demonstrates greater total antero-posterior laxity compared to the PS knee, as measured by stress radiographs, but there is not a strong correlation with clinical outcomes measurements. A greater number of subjects and/or a younger, higher demand population studied with this protocol might produce greater differences in the outcomes, especially in the FJS score. For any figures or tables, please contact the authors directly

Surgical treatment options for Femoroacetabular impingement (FAI) includes both surgical dislocation and hip arthroscopy techniques. The primary aim of this study was to evaluate and compare the survivorship of arthroscopies (scope) and surgical dislocations (SD) at minimum 5-year follow-up. The secondary aim was to describe differences in functional outcomes between the 2 groups. This was a retrospective, single surgeon, consecutive, case-series from a large tertiary care centre. We evaluated all surgeries that were performed between 2005 and 2011. Our institutional database was queried for any patient undergoing surgery for FAI (pincer (n=23), cam (n=306), or mixed (n=103) types). Patients with childhood pathologies i.e. Legg Calve Perthes and slipped capital femoral epiphysis were excluded. This resulted in 221 hips (169 males, 52 females) who underwent either SD (94, 42.5%) or scope (127, 57.5%). A manual chart review was completed to identify patients who sustained a complication, underwent revision surgery or progressed to a total hip arthroplasty (THA). In addition, we reviewed prospectively collected patient reported outcome measure (PROMs) using (SF12, HOOS, and UCLA). Survivorship outcome was described for the whole cohort and compared between the 2 surgical groups. PROMs between groups were compared using The Mann-Whitney U test and the survival between groups was assessed using the Kaplan-Meier Analysis and the Log-Rank Mantel Cox test. All analyses were performed in SPSS (IBM, v. 26.0). The cohort included 110 SDs and 320 arthroscopies. The mean age of the whole cohort was 34±10; patients in the SD group (32±9) were younger compared to the arthroscopy group (39±10) (p<0.0001). There were 16 post-operative complications (similar between groups) and 77 re-operations (more common in the SD group (n=49) due to symptomatic metal work (n=34)). The overall 10-year survival was 91±3%. Survivorship was superior in the arthroscopy group at both 5- (96% (95%CI: 93 – 100)) and 8- years 94% (95%CI: 90 – 99%) compared to the SD Group (5-yr: 90% (95%CI: 83 – 98); 8-yr: 84% (95%CI:75 – 93)) (p=0.003) (Figure 1). On average HOOS improved from 54±19 to 68±22 and WOMAC from 65±22 to 75±22. The improvement in PROMs were similar between the 2 groups. We report very good long-term joint preservation for the treatment of FAI, which is similar to those reported in hip dysplasia. In addition, we report satisfactory improvement in function following such treatment. The differences reported in joint survival likely reflect selection biases from the treating surgeon; more complex cases and those associated with more complex anatomy were more likely to have been offered a SD in order to address the pathology with greater ease and hence the inferior joint preservation identified in this group. For any figures or tables, please contact the authors directly

Stair stepping motion is important in daily living, similar to gait. In this study, we did a Kinematic Analysis of total knee arthroplasty during stair-stepping. A total of 20 patients implanted with Bi-Surface 5PS were assessed. The Bi-Surface knee is a posterior-cruciate substitute prosthesis with a unique ball-and-socket joint in the mid-posterior portion of the femoral and tibial components. This joint functions as a posterior stabilizing cam mechanism and as a load-bearing surface in flexion. Patients were examined during stair-stepping motion using a 2-dimensional to 3-dimensional registration technique. The kinematic pattern in step up was a medial pivot, in which the level of anteroposterior translation was very small. In step down, the kinematic pattern was neither pivot shift nor rollback. From minimum to maximum flexion, anterior femoral translation occurred slightly. However, it became clear in this study that the joint's stability during stair-stepping was affected by the design of the femorotibial joint rather than Post/Cam engagement

A unique, laterally stabilized design concept (3D Knee-DJO Surgical, Inc) for total knee arthroplasty (TKA) without traditional post and cam construct was developed to allow surgeons to resurface the arthritic knee while choosing to maintain or sacrifice the posterior cruciate ligament (PCL). Reported complications with current ‘post and cam’ designs of PCL-substituting TKRs include higher polyethylene wear associated with cam-post impingement, increased bone interface shear stresses, and more distal femoral bone resection making revisions more complex and problematic. The effectiveness of this laterally stabilized TKA design has been extensively studied biomechanically using both in-vitro and in-vivo methods. It was hypothesized that for this total knee arthroplasty design; the mid-term clinical, radiographic and functional results would be the same for patients having two different surgical techniques in which the posterior cruciate ligament was either completely retained or completely resected. This study reports on eight year clinical results as well as in-vivo fluoroscopic results and retrieval data. Reported are 159 patients with 116 knees done by a surgeon who preserved the PCL with a bone block technique and 43 knees by a second surgeon who completely resected the PCL. Clinical results did not statistically differ between the two groups and found Knee Society Scores of 96 for Pain and 91 for Function. Average ROM was measured at 124 degrees. Comparative fluoroscopic imaging analysis of in-vivo dynamic flexion activities of thirty-three (20 PCL-preserved and 13 PCL resected) knees was performed demonstrating stable performance and only small (non-significant) mechanical differences. Analysis of two unrelated groups of tibial polyethylene inserts, the first retrieved from patients after 1–4 years in-vivo function (n = 14) and the second after in-vitro knee wear simulation (n = 4) showed low wear rates with no delamination. There was only one failure for mechanical loosening in the cruciate resected group and radiolucent lines of greater than 2 mm were only seen in 4% with none being progressive. Kaplan-Meier Survivorship, using mechanical loosening as the end point, was 99.2% at an average of 8.8 years. In summary, this laterally stabilized TKR design offers a very good alternative to standard ‘post and cam’ PCL sacrificing TKRs while still giving surgeons the ability to maintain the PCL if desired