Hip arthroscopy rates continue to increase. As a result, there is growing interest in capsular management techniques. Without careful preservation and surgical techniques, failure of the repair result in capsular deficiency, contributing to iatrogenic instability and persistent post-operative pain. In this setting, capsular reconstruction may be indicated, however there is a paucity of objective evidence comparing surgical techniques to identify the optimal method. Therefore, the objective of this study was to evaluate the biomechanical effect of capsulectomy and two different capsular reconstruction techniques (iliotibial band [ITB] autograft and Achilles tendon allograft) on hip joint kinematics in both rotation and abduction/adduction. Eight paired fresh-frozen hemi-pelvises were dissected of all overlying soft tissue, with the exception of the hip joint capsule. The femur was potted and attached to a load cell connected to a joint-motion simulator, while the pelvis was secured to a custom-designed fixture allowing adjustment of the flexion-extension arc. Optotrak markers were rigidly attached to the femur and pelvis to track motion of the femoral head with respect to the acetabulum. Pairs were divided into ITB or Achilles capsular reconstruction. After specimen preparation, three conditions were tested: (1) intact, (2) after capsulectomy, and (3) capsular reconstruction (ITB or Achilles). All conditions were tested in 0°, 45°, and 90° of flexion. Internal rotation (IR) and external rotation (ER) as well abduction (ABD) and adduction (ADD) moments of 3 N·m were applied to the femur via the load cell at each position. Rotational range of motion and joint kinematics were recorded. When a rotational force was applied the total magnitude of internal/external rotation was significantly affected by the condition of the capsule, independent of the type of reconstruction that was performed (p=0.001). The internal/external rotation increased significantly by approximately 8° following the capsulectomy (p<0.001) and this was not resolved by either of the reconstructions; there remained a significant difference between the intact and reconstruction conditions (p=0.035). The total anterior/posterior translation was significantly affected by the condition of the capsule (p=0.034). There was a significant increase from 6.7 (6.0) mm when the capsule was intact to 9.0 (6.7) mm following the capsulectomy (p=0.002). Both of the reconstructions (8.6 [5.6] mm) reduced the anterior/posterior translation closer to the intact state. There was no difference between the two reconstructions. When an abduction/adduction force was applied there was a significant increase in the medial-lateral translation between the intact and capsulectomy states (p=0.047). Across all three flexion angles the integrity of the native hip capsule played a significant role in rotational stability, where capsulectomy significantly increased rotational ROM. Hip capsule reconstruction did not restore rotational stability and also increased rotational ROM compared to the intact state a statistically significant amount. However, hip capsule reconstruction restored coronal and sagittal plane stability to approach that of the native hip. There was no difference in stability between ITB and Achilles reconstructions across all testing conditions

Femoroacetabular impingement (FAI) – enlarged, aspherical femoral head deformity (cam-type) or retroversion/overcoverage of the acetabulum (pincer-type) – is a leading cause for early hip osteoarthritis. Although anteverting/reverse periacetabular osteotomy (PAO) to address FAI aims to preserve the native hip and restore joint function, it is still unclear how it affects joint mobility and stability. This in vitro cadaveric study examined the effects of surgical anteverting PAO on range of motion and capsular mechanics in hips with acetabular retroversion. Twelve cadaveric hips (n = 12, m:f = 9:3; age = 41 ± 9 years; BMI = 23 ± 4 kg/m2) were included in this study. Each hip was CT imaged and indicated acetabular retroversion (i.e., crossover sign, posterior wall sign, ischial wall sign, retroversion index > 20%, axial plane acetabular version < 15°); and showed no other abnormalities on CT data. Each hip was denuded to the bone-and-capsule and mounted onto a 6-DOF robot tester (TX90, Stäubli), equipped with a universal force-torque sensor (Omega85, ATI). The robot positioned each hip in five sagittal angles: Extension, Neutral 0°, Flexion 30°, Flexion 60°, Flexion 90°; and performed hip internal-external rotations and abduction-adduction motions to 5 Nm in each position. After the intact stage was tested, each hip underwent an anteverting PAO, anteverting the acetabulum and securing the fragment with long bone screws. The capsular ligaments were preserved during the surgery and each hip was retested postoperatively in the robot. Postoperative CT imaging confirmed that the acetabular fragment was properly positioned with adequate version and head coverage. Paired sample t-tests compared the differences in range of motion before and after PAO (CI = 95%; SPSS v.24, IBM). Preoperatively, the intact hips with acetabular retroversion demonstrated constrained internal-external rotations and abduction-adduction motions. The PAO reoriented the acetabular fragment and medialized the hip joint centre, which tightened the iliofemoral ligament and slackenend the pubofemoral ligament. Postoperatively, internal rotation increased in the deep hip flexion positions of Flexion 60° (∆IR = +7°, p = 0.001) and Flexion 90° (∆IR = +8°, p = 0.001); while also demonstrating marginal decreases in external rotation in all positions. In addition, adduction increased in the deep flexion positions of Flexion 60° (∆ADD = +11°, p = 0.002) and Flexion 90° (∆ADD = +12°, p = 0.001); but also showed marginal increases in abduction in all positions. The anteverting PAO restored anterosuperior acetabular clearance and increased internal rotation (28–33%) and adduction motions (29–31%) in deep hip flexion. Restricted movements and positive impingement tests typically experienced in these positions with acetabular retroversion are associated with clinical symptoms of FAI (i.e., FADIR). However, PAO altered capsular tensions by further tightening the anterolateral hip capsule which resulted in a limited external rotation and a stiffer and tighter hip. Capsular tightness may still be secondary to acetabular retroversion, thus capsular management may be warranted for larger corrections or rotational osteotomies. In efforts to optimize surgical management and clinical outcomes, anteverting PAO is a viable option to address FAI due to acetabular retroversion or overcoverage

The occurrence of impingement can lead to instability, accelerated wear, and unexplained pain after THA. While implant and bony impingement were widely investigated, importance of soft tissue impingement was unclear. In the THA through posterior approach, it is known that posterior soft tissue repair can decrease the risk of dislocation. However, it is not known whether anterior soft tissue impingement by anterior hip capsule will influence hip ROM. The purpose of this study is to quantitatively measure the effect of anterior capsule resection on hip ROM in vivo during posterior approach THA using hip navigation system. From June 2011, 26 hips (25 patients) that underwent primary THA using Stryker CT-based hip navigation system were the subjects. All were female osteoarthritis patients and the average age at the operation was 59 (47–76) years. Intraoperatively, acetabular cup and femoral stem placement were performed through posterior approach under the navigation system. After reduction of the joint, we measured hip ROM using the same navigation system. We measured them before and after the resection of anterior hip capsule and compared the difference. After the resection of anterior hip capsule, the average increases of ROM were 0.7±3.5 degrees for flexion, 2.3±2.3 degrees for extension, 1.1±2.3 degrees for abduction and 2.1±2.9 degrees for external rotation at flexion 0 degree compared with ROM before the resection. However, it significantly increased 7.5±5.1 degrees for internal rotation at flexion 90 degree (range; −3–20, paired t-test p<0.001) and 6.1±5.5 degrees for internal rotation at flexion 45 degree (range; −4–18, p<0.001). In this study, we used navigation system for assessment of soft tissue impingement. We found that during posterior approach THA, resection of anterior hip capsule brought about significant increase of ROM, especially in the direction of flexion with internal rotation. We also found that this procedure did not change ROM of flexion, extension, abduction and external rotation. These results indicated that, during THA through posterior approach, resection of anterior hip capsule could reduce the risk of posterior instability without increasing the risk of anterior instability

Introduction. Dual Mobility (DM) implants have gained popularity for the treatment and prevention of hip dislocation, with increased stability provided by a large diameter mobile liner. However, distal regions of the liner can impinge on soft-tissues like hip capsule and iliopsoas, leading to anterior hip pain. Additionally, soft-tissue impingement may trap the mobile liner, leading to excessive loading of the liner rim, from engagement with the femoral stem, and subsequent intra-prosthetic dislocation. The hypothesis of this study was that reducing the liner profile below the equator (contoured design) can mitigate soft-tissue impingement without compromising inner-head pull-out resistance and overall hip joint stability (Fig. 1). Methods. The interaction of conventional and contoured liners with anterior soft-tissues was evaluated in 10 cadaveric hips (5 specimens; 2 male, 3 female; age 65 ± 10 yrs; liner diameter 42–48mm) via visual observation and fluoroscopic imaging. A metal wire was sutured to the deep fibers of the iliopsoas tendon/muscle, and metal wires were embedded in the mobile liners for fluoroscopic visualization (Fig. 2). All soft-tissue except the anterior hip capsule and iliopsoas was removed, and a rope was attached to the iliopsoas to apply tension along its natural orientation. Resistance to inner-head pull-out was evaluated via Finite Element Analysis (FEA) by simulating a full cycle of insertion of the inner head into the mobile liner and subsequent pullout. The femoral head, acetabular shell, and stem were modeled as rigid, while the mobile liner was modeled as plastically deformable. Hip joint stability was evaluated by dynamic simulations in for two dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal hip rotation; (B) Posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction. A 44 mm diameter conventional and a 44 mm contoured liner were evaluated during these tests. Results. The cadaver experiments showed that distal portion of conventional liners impinge on anterior hip capsule and iliopsoas at low flexion angles (<30°). Additionally, when the hip moved from flexion into extension, the liner motion was blocked between posterior neck engagement, and anterior soft-tissue impingement. In all hips, the soft-tissue impingement / tenting was significantly reduced with contoured liners (Fig. 7). The change in tenting could be visualized as change in distance between the iliopsoas wire, and the contoured/conventional liners on sequential fluoroscopic images. The maximum reduction in iliopsoas tenting for a given specimen ranged from 1.8 mm to 5.5 mm. Additionally, the contoured and conventional liners had identical inner-head pull-out resistance (901N vs. 909N), jump distance (9.4 mm mode-A, 11.7 mm mode-B) and impingement-free range of motion (47° mode-A, 29° mode-B). Conclusion. This study showed that distal portions of conventional DM liners can impinge against iliopsoas and hip capsule in low flexion leading to functional impediment of liner motion. Additionally, reducing the liner profile below the equator led to significant reduction in soft-tissue impingement/tenting without affecting mechanical performance. Thus, a contoured dual mobility liner design may reduce the risk of anterior hip pain and intra-prosthetic dislocation resulting from soft-tissue impingement and liner entrapment. To view tables/figures, please contact authors directly

INTRODUCTION. Interest in tissue-preserving or minimally invasive total hip arthroplasty (THA) is increasing with focus toward decreased hospital stay, enhanced rehabilitation, and quicker recovery for patients. Two tissue-preserving techniques, the anterior and superior approaches to THA, have excellent clinical results, but little is known about their relative impact on soft tissue. The purpose of this study was to evaluate the type and extent of tissue damage after THA with each approach, focusing on abductors, short external rotators, and the hip capsule. METHODS. Total hip arthroplasty was performed on bilateral hips of eleven fresh-frozen cadavers (22 hips). They were randomized to anterior THA performed on one side and superior THA performed on the other, in the senior authors' standard technique. Two independent examiners graded the location and extent of tissue injury by performing postsurgical dissections. Muscle bellies, tendons, and capsular attachments were graded as intact, split, damaged (insignificant, minimal, moderate, or extensive damage), or detached based on direct visual inspection of each structure. Tissue injury was analyzed with either a chi-squared (≥5 qualifying structures) or Fisher's exact test (<5 qualifying structures). P values <0.05 were significant. RESULTS. The abductor muscles or tendons were intact or insignificantly damaged in 63.6% of anterior approach specimens compared with 84.1% of the superior specimens (p= 0.03). Specifically, the gluteus minimus tendon had moderate or extensive damage in 63.6% of anterior specimens compared with none of the superior specimens (p <0.01). Short external rotators (SERs) group, defined as both the muscle and tendon of the piriformis, conjoint, obturator externus, and quadratus, were intact or insignificantly damaged in 63.6% of anterior approach specimens compared with 80.5% of the SER group of superior specimens (p = 0.02). The femoral attachments of the anterior, posterior, and superior capsules were extensively damaged or detached in 90.9%, 81.8%, and 100% of anterior approach specimens respectively compared with 0%, 9.1% and 9.1% of superior approach specimens respectively (all p <0.01). CONCLUSION. In a cadaveric study examining superior and anterior approaches to THA, the superior approach demonstrated significantly less soft-tissue destruction than the anterior approach, specifically to the gluteus minimus tendon, short external rotators, and the hip capsule

Introduction. Current methodologies for designing and validating existing THA systems can be expensive and time-consuming. A validated mathematical model provides an alternative solution with immediate predictions of contact mechanics and an understanding of potential adverse effects. The objective of this study is to demonstrate the value of a validated forward solution mathematical model of the hip that can offer kinematic results similar to fluoroscopy and forces similar to telemetric implants. Methods. This model is a forward solution dynamic model of the hip that incorporates the muscles at the hip, the hip capsule, and the ability to modify implant position, orientation, and surgical technique. Muscle forces are simulated to drive the motion, and a unique contact detection algorithm allows for virtual implantation of components in any orientation. Patient-specific data was input into the model for a telemetric subject and for a fluoroscopic subject. Results. For both stance and swing phase, the model predicted similar patterns and magnitudes compared to telemetry (forces) and fluoroscopy (kinematics). During stance phase, the model predicts 2.5 xBW of maximum hip force while telemetry predicts 2.3 xBW, yielding 8.7% error (Figure 1a). During swing phase, the model predicts 1.1 xBW maximum hip force, similar to telemetry (Figure 1b). During stance phase, the model predicts 1.3mm of hip separation (sliding) compared to 1.6mm for fluoroscopy, yielding 18.8% error (Figure 1c). During swing phase, the model predicts 1.9mm of separation compared to 1.7mm for fluoroscopy, yielding 11.8% error (Figure 1d). The model was also used to assess component placement, version, and optimal positioning compared to live surgery, producing very promising results. Conclusion. The model has proven accurate in predicting kinematics and forces. Therefore, forward solution mathematical modeling can be used to efficiently evaluate new component designs, positioning and technique differences, patient-specific scenarios, and any specific contribution towards THA outcomes that cannot be controlled in vivo. For any figures or tables, please contact the authors directly

Purpose. While changes in lower limb alignment and pelvic inclination after total hip arthroplasty (THA) using certain surgical approaches have been studied, the effect of preserving the joint capsule is still unclear. We retrospectively investigated changes in lower limb alignment, length and pelvic inclination before and after surgery, and the risk of postoperative dislocation in patients who underwent capsule preserving THA using the anterolateral-supine (ALS) approach. Methods. Between July 2016 and March 2018, 112 hips (non-capsule preservation group: 42 hips, and capsule preservation group: 70 hips) from patients with hip osteoarthritis who underwent THA were included in this study. Patients who underwent spinal fusion and total knee arthroplasty on the same side as that of the THA were excluded. Using computed tomography, we measured lower limb elongation, external rotation of the knee, and femoral neck/stem anteversion before operation and three to five days after operation. We examined the pelvic inclination using vertical/transverse ratio of the pelvic cavity measured by X-ray of the anteroposterior pelvic region in the standing position before and six to 12 months after operation. All operations were performed using the ALS approach and taper wedge stem. Results. No dislocation was found in both groups. Lower limb elongation was 14.5±6.3 (mean±SD) mm in the non-capsule preservation group and 9.4±8.8 mm in the capsule preservation group. A significant reduction was found in the capsule preservation group (p<0.05). Changes in knee external rotation was 7.2±10.5 degrees in the non-capsule preservation group and 3.5±10.3 degrees in the capsule preservation group. A trend toward decreased knee external rotation in the capsule preservation group (p=0.07) was observed. There was no difference in femoral neck/stem anteversion and vertical/transverse ratio of the pelvic cavity between both groups. Discussion. Patients in the capsule preservation group tended to have reduced external rotation of lower limb, which might prevent postoperative anterior dislocation due to preservation of anterior structures. The capsule preservation group had significantly reduced lower limb elongation, suggesting that preservation of the hip joint capsule ligament contributes to joint stability. There was no significant difference in the pelvic inclination between both groups. Long-term changes will be assessed by regular follow up after operation

Hip impingement causes clinical problems for both the native hip, where labral or chondral damage can cause severe pain, and in the replaced hip, where subluxation can cause squeaking/metallosis through edge loading, or can cause dislocation. There is much research into bony/prosthetic hard impingements showing that anatomical variation/component mal-positioning can increase the risk of impingement. However, there is a lack of basic science describing the role of the hip capsule and its intertwined ligaments in restraining range of motion, ROM, and so it is unclear if careful preservation/repair of the capsular ligaments would offer clinical benefits to young adults, or could also help prevent edge loading in addition to reducing the postoperative dislocation rate in older adults. This in-vitro study quantifies the ROM where the capsule passively stabilises the hip and compares this to hip kinematics during daily activities at risk for hip subluxation. Ten cadaveric left hips were skeletonised preserving the joint capsule and mounted in a testing rig that allowed application of loads, torques and rotations in all six-degrees of freedom (Figure 1). At 27 positions encompassing a complete hip ROM, the passive rotation resistance of each hip was recorded. The gradient of the torque-rotation profiles was used to quantify where the capsule is taut/slack and after resecting the capsule, where labral impingement occur. The ROM measurements were compared against hip kinematics from daily activities. The capsule tightly restrains the hip in full flexion/extension with large slack regions in mid-flexion. Whilst ligament recruitment varies throughout hip ROM, the magnitude of restraint provided is constant (0.82 ± 0.31 Nm/degree). This restraint acts to prevent or reduce loading of the labrum in the native hip (Figure 2). The measured passive rotational stability envelope is less than clinical ROM measurements indicating the capsule does provide restraint to the joint within a relevant ROM. Activities such as pivoting, stooping, shoe tying and rolling over in bed all would recruit the capsular ligaments in a stabilising role. The fine-tuned anatomy of the hip capsule provides a consistent contribution to hip rotational restraint within a functionally relevant ROM for normal activities protecting the hip against impingement. Capsulotomy should be kept to a minimum and routinely repaired in the native hip to maintain natural hip mechanics. Restoring its native function following hip replacement surgery may provide a method to prevent subluxation and edge loading in the replaced hip

Introduction. The large diameter mobile polyethylene liner of the dual mobility implant provides increased resistance to hip dislocation. However, a problem specific to the dual mobility system is intra-prosthetic dislocation (IPD), secondary to loss of the retentive rim, causing the inner head to dissociate from the polyethylene liner. We hypothesized that impingement of the polyethylene liner with the surrounding soft-tissue inhibits liner motion, thereby facilitating load transfer from the femoral neck to the liner and leading to loss of retentive rim over time. This mechanism of soft-tissue impingement with the liner was evaluated via cadaver experiments, and retrievals were used to assess polyethylene rim damage. Methods. Total hip arthroplasty was performed on 10 cadaver hips using 3D printed dual mobility components. A metal wire was sutured to the posterior surface (underside) of the iliopsoas, and metal wires were embedded into grooves on the outer surface of the liner and inner head to identify these structures under fluoroscopy. Tension was applied to the iliopsoas to move the femur from maximum hyperextension to 90° of flexion for the purpose of visualizing the iliopsoas and capsule interaction with the mobile liner. The interaction of the mobile liner with the iliopsoas was studied using fluoroscopy and direct visual observation. Fifteen retrieved dual mobility liners were assessed for rim edge and rim chamfer damage. Rim edge damage was defined as any evidence of contact, and rim chamfer damage was classified into six categories: impact ribs on the chamfer surface, loss of machining marks, scratching or pitting, rim deformation causing a raised lip, a rounded rim edge, or embedded metal debris. Results. Manipulation of the cadaver specimens through full range of motion showed liner impingement with the iliopsoas tendon in low flexion angles, which impeded liner motion. At high flexion angles (beyond 30°), the iliopsoas tendon moved away from the liner and impingement was not observed. The fluoroscopy tests using the embedded metal wires confirmed what was observed during manual manipulation of the specimen. When observing the hip during maximum hyperextension, 0°, 15°, and 30° of flexion, there was obvious tenting of the iliopsoas. All retrieved components showed damage on the rim and the chamfer surface. The most common damage seen was scratching/ pitting. There was no association between presence of damage and time in vivo controlling for age and Body Mass Index (p≥0.255). Discussion. The cadaver studies showed that the mobile liner motion could be impeded by impingement with the iliopsoas tendon and hip capsule. Visual and fluoroscopic observation showed impingement of iliopsoas and hip capsule with the distal portion of the mobile liner, particularly during low flexion angles. All retrieved liners showed damage despite their limited time in vivo and despite being retrieved for reasons other than IPD. This suggests that soft-tissue impingement may inhibit liner motion routinely in vivo, resulting in load transfer from the femoral neck on to the rim of the liner. This may be an important mechanism for IPD

Background. In vivo fluoroscopic studies have proven that femoral head sliding and separation from within the acetabular cup during gait frequently occur for subjects implanted with a total hip arthroplasty. It is hypothesized that these atypical kinematic patterns are due to component malalignments that yield uncharacteristically higher forces on the hip joint that are not present in the native hip. This in vivo joint instability can lead to edge loading, increased stresses, and premature wear on the acetabular component. Objective. The objective of this study was to use forward solution mathematical modeling to theoretically analyze the causes and effects of hip joint instability and edge loading during both swing and stance phase of gait. Methods. The model used for this study simulates the quadriceps muscles, hamstring muscles, gluteus muscles, iliopsoas group, tensor fasciae latae, and an adductor muscle group. Other soft tissues include the patellar ligament and the ischiofemoral, iliofemoral, and pubofemoral hip capsular ligaments. The model was previously validated using telemetric implants and fluoroscopic results from existing implant designs. The model was used to simulate theoretical surgeries where various surgical alignments were implemented and to determine the hip joint stability. Parameters of interest in this study are joint instability and femoral head sliding within the acetabular cup, along with contact area, contact forces, contact stresses, and ligament tension. Results. During swing phase, it was determined that femoral head pistoning is caused by hip capsule laxity resulting from improperly positioned components and reduced joint tension. At the point of maximum velocity of the foot (approximately halfway through), the momentum of the lower leg becomes too great for a lax capsule to properly constrain the hip, leading to the femoral component pistoning outwards. This pistoning motion, leading to separation, is coupled with a decrease in contact area and an impulse-like spike in contact stress (Figure 1). During stance phase, it was determined that femoral head sliding within the acetabular cup is caused by the proprioceptive notion that the human hip wants to rotate about its native, anatomical center. Thus, component shifting yields abnormal forces and torques on the joint, leading to the femoral component sliding within the cup. This phenomenon of sliding yields acetabular edge-loading on the supero-lateral aspect of the cup (Figure 2). It is also clear that joint sliding yields a decreased contact area, in this case over half of the stable contact area, corresponding to a predicted increase in contact stress, in this case over double (Figure 2). Discussion. From our current analysis, the causes and effects of hip joint instability are clearly demonstrated. The increased stress that accompanies the pistoning/impulse loading scenarios during swing phase and the supero-lateral edge-loading scenarios during stance phase provide clear explanations for premature component wear on the cup, and thus the importance of proper alignment of the THA components is essential for a maximum THA lifetime. For any figures or tables, please contact authors directly

While hip arthroscopy utilization continues to increase, capsular management remains a controversial topic. Therefore the purpose of this research was to investigate the biomechanical effect of capsulotomy and capsular repair techniques on hip joint kinematics in varying combinations of sagittal and coronal joint positions. Eight fresh-frozen hemipelvises (4 left, 6 male) were dissected of all overlying soft tissue, with the exception of the hip joint capsule. The femur was potted and attached to a load cell, while the pelvis was secured to a custom-designed fixture allowing static alteration of the flexion/extension arc. Optotrak markers were rigidly attached to the femur and pelvis to track motion of the femoral head with respect to the acetabulum. Following specimen preparation, seven conditions were tested: i) intact, ii) after portal placement (anterolateral and mid-anterior), iii) interportal capsulotomy (IPC) [35 mm in length], iv) IPC repair, v)T-capsulotomy [15 mm longitudinal incision], vi) partial T-repair (vertical limb), vii) full T-repair. All conditions were tested in 15° of extension (−15˚), 0°, 30°, 60° and 90° of flexion. Additionally, all flexion angles were tested in neutral, as well as maximum abduction and adduction, resulting in 15 testing positions. 3Nm internal and external rotation moments were manually applied to the femur via the load cell at each position. Rotational range of motion and joint kinematics were recorded. IPC and T-capsulotomies increased rotational ROM and mediolateral (ML) joint translation in several different joint configurations, most notably from 0–30˚ in neutral abduction/adduction. Complete capsular repair restored near native joint kinematics, with no significant differences between any complete capsular repair groups and the intact state, regardless of joint position. An unrepaired IPC resulted in increased rotational ROM, but no other adverse translational kinematics. However, an unrepaired or partially repaired T-capsulotomy resulted in increased rotational ROM and ML translation. The results of this study show that complete capsular repair following interportal or T-capsulotomy adequately restores rotational ROM and joint translation to near intact levels. Where feasible, complete capsular closure should be performed, especially following T-capsulotomy. However, further clinical evaluation is required to determine if adverse kinematics of an unrepaired capsule are associated with patient reported outcomes

Recently, a special type of surface pitting found on metal implants was proposed to arise from “inflammatory cell-induced” corrosion (ICI, Figure 1) (1, 2). The actual mechanism of this was unknown, but similar features were suggested to be artefacts of electrocautery damage from revision surgery (3). Under lab conditions and without the influence of any cells, we aimed to reproduce the same surface pits and structures with electrocautery. Methods. A polished cobalt-chromium disk (40 mm diameter, 8 mm thick) was marked into 8 sections for various testing conditions (Figure 2a). A stainless steel Bovie tip with a unipolar electrocautery machine (SYSTEM 5000, ConMed, USA) was used at typical surgical coagulation conditions: (70 volt, 120 watts, 562 KHz frequency). We mimicked three types of surgical techniques with the electrocautery: “Dotting” was repeated, on and off, direct surface contact; “Dragging” was constant, direct surface contact; “Hovering” was pausing several millimeters above the surface. We also examined the interplay of these practices on diamond-tip-induced scratches and either dry or wet (normal saline) conditions. High magnification images (Keyence VHX-2000E) were taken after the disk was cleaned with laboratory soap, light mechanical scrubbing, and formalin soak. Results. Coagulation mode generated electrical sparks when dotting/dragging and electrical arcs when hovering. These left seared marks that persisted even after cleaning (Figure 2b). At higher magnification, the surface features were comparable in size and shape to those attributed to ICI (1, 2). Areas wet with saline (Figure 3a) showed an abundance of ringed pits with raised edges that closely resembled those observed in Figure 1. Furthermore we obtained images similar to the phenomenon of “cellular tracks” (Figure 3b) (1). Premade scratches did not influence the pit arrangement but scratches made by the Bovie tip produced the characteristic scratch-associated ICI features as observed on implant retrievals in the past (Figure 3c) (4). Discussion. In the absence of cells, pitting equivalent to proposed ICI features was successfully replicated using an electrocautery in coagulation mode. Previously (4), we found a high incidence but small surface area of these features on the majority of retrievals, predominantly located in a focal area of the superior aspect of the femoral ball next to the junction of the stem. There were fewer on the inferior aspect which is consistent with electocautery damage when dissecting the hip capsule. The effect of this damage on retained parts is unknown, but electrocautery damage around areas of implant fractures has been reported (3). Conclusion. The striking similarities of the recreated pit structures imaged here suggest that the noted features of “inflammatory cell induced corrosion” were artefacts of the electrocautery during revision surgery. Future implant retrieval analysis should acknowledge these structures are not related to any particular mode of failure but should check for them around implant fracture sites

Introduction. Rottinger published a description of an anterior muscle sparing approach to the hip. It utilizes the same muscle interval as the classic WatsonJones approach between the gluteus medius laterally and tensor fascia lata medially. However, this technique has the disadvantage of needing asplit table and a sterile bag to mobilize the operative leg as extension, adduction and external rotation are the key points for femoral preparation. This study describes our experience for an equivalent of the Watson Jones approach with a simplified technique for the femoral preparation. Material and Methods. Incision starts 1cm distal and 3cm posterior to the ASIS and continues distally for about 8–10 cm along the straightline joining the lateral edge of the patella. It can be extended proximally or distally if necessary. The surgeon is placed posteriorly and the assistant anteriorly. The hip is dislocated with extension and external rotation to osteotomize the femoral neck. During the preparation of the acetabulum the femur is pushed posteriorly with internal rotation. Steinman pins are placed around the acetabulum to improve visualization for reaming and implanting theacetabular components. The femur is then exposed in a simplified way. The operated limb remains on the table. It is adducted above the contralateral limb and rotated outward to allow the femoral metaphysis to protrude. The foot is placed on the edge of the table beside the assistant, the knee is maintained with 45° flexion. The hip capsule is released postero-laterally to improve the femur exposure using Hohman retractors without cutting the short external rotator muscles. Femoral preparation is performed in this position. Once the appropriate implant is selected, the desired head trials are placed. The hip is reduced and the length and stability can be checked with the leg free. In case of isolated cup revision, the femoral head can be conserved. In case of femoral revision, a femorotomy can be easily performed due to the possibility of extended and stable exposure of the femur. Table 1 summarizes the main data of the series. Results. Mean operative duration was 57mn for primary THP (SD 10mn) and 124mn for revisions (SD 28mn). Table 2 summarizes the main complications according to the time line after the first implantation. High BMI patients and exposure of the acetabulum were never a problem; moreover this technique is very attractive for isolated cup revisions. Complications were mainly focused on femoral preparation due to a suboptimal use of the retractors for the exposure (4/13 fracture cases). Poor bone quality (old patients) was responsible for the 9 additional fractures. False route were observed in 4 curved femurs. 3 nerve compressions were due to excessive pressure on the knee by the assistant. Using short stems facilitates femoral exposure and reduces operative time. Conclusions. Hip approaches have been modified throughout the years in attempts to improve patient outcomes. This simplified technique did not induceunusual morbidity or mechanical problems. The benefit in terms of operative time and complications is significant in comparison with our previous experience using a fracture table. To view tables/figures, please contact authors directly

We perform the direct approach using a standard radiolucent operative table with extender at the foot, and the assistance of fluoroscopy. The patient is positioned supine with the pubic symphysis aligned at the table break. The anterior superior iliac spine (ASIS) and center of the knee are marked, and a line drawn between. The incision commences proximally from two finger breadths distal and two finger breadths lateral to the ASIS, and extends distally 8–10 cm. Using fluoroscopy, the anterior aspect femoral neck is located. The incision is placed over the lateral aspect of the greater trochanter, which avoids the lateral femoral cutaneous nerve. The tensor fascia lata is identified, which has a distinctive purple hue, and dissected free from the intermuscular septum lateral to the sartorius and the rectus muscles. The deep, investing aponeurosis of the tensor fascia lata is split using a tonsil. Just below lie the lateral circumflex vessels, two veins and one artery, which must be either ligated or cauterised. A retractor is placed superior to the femoral neck over top of the superior hip capsule. A blunt, cobra-type retractor is then placed along the inferior femoral neck, deep to the rectus muscle and the rectus tendon. A sharp retractor is then used to peel the rectus off from the anterior capsule and placed over the anterior rim of the acetabulum. An anterior capsulectomy is performed. A saw blade is positioned for femoral neck resection and confirmed with fluoroscopy. After resection, acetabular retractors are placed, the socket is reamed, the cup is placed, and position confirmed with fluoroscopy. Turning to the femoral side, the surgeon palpates underneath and around the tensor, around the lateral aspect of the femur, proximal to the gluteus maximus tendon, and places a bone hook around the proximal femur. Femoral preparation and stem insertion require maneuvering the table and adjusting the patient position. The table is “jack-knifed” by lowering the foot of the table to approximately 45 degrees and placing the bed into approximately 15 degrees of Trendelenburg. The contralateral well leg is placed on the padded Mayo stand. A table-mounted femur elevator is attached to the bed, requiring a change in surgical gloves, and attached to the traction hook around the proximal femur. Gentle retraction is placed on the femur to tension the capsule. As the capsule is released the femur will begin to come up/out of the wound and into view. With increasing gentle retraction via the table-mounted hook, the femur is elevated. Simultaneously, the operative limb is externally rotated and adducted underneath the non-operative leg in a lazy “figure of 4” position by the assistant. The use of a “broach-only” stem design is preferred as direct straight reaming of the femur is difficult in most cases. Fluoroscopic images are obtained to confirm femoral implant positioning, offset, neck and leg length. A standardised rapid recovery hospitalization and rehabilitation protocol is used in all cases

Introduction. Dual Mobility (DM) implants have gained popularity for the treatment and prevention of hip dislocation, with increased stability provided by a large diameter mobile insert. However, distal regions of the insert may impinge on soft tissues like the iliopsoas, leading to groin pain. Additionally, soft-tissue impingement may trap the mobile insert, leading to excessive loading of the insert rim from engagement with the femoral neck and subsequent intra-prosthetic dislocation. To address this, an Anatomically Contoured Dual Mobility (ACDM) insert with a soft-tissue friendly distal geometry was developed (Fig.1). Previously, the ACDM insert was shown to maintain the femoroacetabular contact area and joint stability of a conventional DM insert [Duffy et al. BJJ 2013, 95-B:34, p298; Zumbrunn et al. BJJ 2013, 95-B:34, p605]. The goal of this study was to utilize cadaver specimens to verify whether the ACDM insert could reduce soft-tissue impingement relative to a conventional DM insert. Methods. Fluoroscopic imaging was used to evaluate soft-tissue interaction with ACDM and conventional DM inserts in four cadaver hips (Fig. 2). A metal wire was sutured to the deep fibers of the iliopsoas muscle/tendon, and metal wires were embedded in the inner head and the mobile insert for fluoroscopic visualization. All soft tissue except the anterior hip capsule and iliopsoas were removed, and a rope was attached to the iliopsoas to apply tension along its native orientation. A femoral stem and a DM acetabular shell were implanted sothe ACDM or conventional DM inserts, together with the inner heads, could be inserted. Fluoroscopic images of the hip joint were taken at maximum hyperextension, 0°, 15° and 30° hip flexion with the insert positioned in neutral and anteverted orientations (Fig. 2). Neutral orientation corresponded to the insert axis parallel to the femoral neck, while anteverted orientation corresponded to a flexed insert that contacted the femoral neck posteriorly. Results. In all hips, fluoroscopic images revealed iliopsoas tenting with the conventional DM insert, and impingement of the iliopsoas occurred at low hip flexion angles (hyperextension, 0°, 15°) with the insert in neutral and anteverted orientations (Fig. 2 and 3). Further, at certain low flexion positions during dynamic motion, the movement of the conventional DM insert was blocked due to trapping of the insert by the anterior soft tissue and the femoral stem (Fig. 2B). At flexion angles above 30°, the iliopsoas moved away from the mobile insert and no impingement was seen. In all hips, the soft-tissue impingement and insert trapping was significantly reduced with the ACDM insert (Fig. 2 and 3). The reduction in impingement occurred with the insert in both neutral and anteverted orientations, although it was more evident for the latter. Conclusion. This study showed that conventional DM inserts impinge against the iliopsoas in low flexion, and their motion can be blocked by soft-tissue impingement. The Anatomically Contoured Dual Mobility (ACDM) insert significantly reduced this undesirable soft-tissue impingement. Thus, the ACDM insert may reduce the risk of groin pain and intra-prosthetic dislocation resulting from soft-tissue impingement and entrapment of the mobile insert

The Superior Hip Approach allows for safe reconstruction of the hip while maximizing preservation of the surrounding soft tissues. The procedure involves an incision in the hip joint capsule posterior to the gluteus medius and minimus and anterior to the short external rotators. The technique involves preparation of the femur in-situ through the superior femoral neck and then excision of the femoral head, which avoids the attendant soft tissue dissection or injury associated with dislocation of the native hip. After component implantation, the capsule is closed anatomically. Two separate studies have demonstrated that over a 90-day period, patients whose hips were replaced using this technique consumed the least amount of cost of any patients treated by hip arthroplasty in the Commonwealth of Massachusetts. One study assessed all hips replaced in patients insured by Medicare over a four-year period. In this study, patients treated by the Superior Hip Approach were less costly by an average of more than $7,000 over 90 days. A second study assessed all hips replaced in patients insured by a large private insurer. This study showed again that patients treated by the Superior Hip Approach were the lowest cost patients. Notable, the cost on average was $23,500 less per procedure compared to the most well-known medical care organization in the state or roughly half the cost. Lower cost was due to both lower inpatient cost and reduced utilization of post-acute care resources. Since reduced resource utilization is a direct measure of accelerated recovery, these economic data combine with clinical outcomes and anatomical studies that document that the Superior Hip Approach is a reliable technique for achieving optimal results following THA

Purpose. Rectus femoris avulsion (RFA) injuries in paediatric patients are currently managed conservatively. However, the proximal attachment of the rectus femoris muscle lies in a critical zone in the hip joint with attachments to the anterior hip capsule and anterior inferior iliac spine. Violent avulsions therefore could cause damage to the adjacent acetabular labrum and articular cartilage initiating a process leading to early degenerative changes in the hip. To date, the association between rectus avulsions and labral tears has not been studied. Method. The complete medical records of patients who were presented to McMaster University Medical Center with rectus femoris avulsions between 1983 and 2008 who were between the ages of 2 and 18 were identified. Patients were included if they had documented plain radiographs and magnetic resonance arthrography images of their hip. MRIs were reviewed by an independent musculoskeletal radiologist blinded from the history of the patients. Results. 16 patients were identified in the database with rectus femoris avulsions diagnosed on plain radiograph and 7 were included in the study with documented MRIs. The average age of patients was 13 (Range 7–16). All injuries occurred during sports activity with 43% occurred during running, 29% with kicking during soccer and during skating acceleration while playing hockey. One patient had a concurrent sartorius avulsion. All patients with rectus femoris avulsions had labral tears identified on MRI in the zone adjacent to rectus insertion. All patients were treated conservatively. Clinical records suggested 72% of patients were still limping and 86% were experiencing residual pain at last follow-up. Conclusion. Patients with rectus femoris avulsions may be at risk for concurrent traumatic labral tears. These patients should be assessed for labral pathology including a clinical examination and MRI arthrography. Level of Evidence: Level IV

Economic data, clinical outcome studies, and anatomical studies continue to support the Superior Hip Approach as a preferred approach for improved safety, maximal tissue preservation, rapid recovery, and minimised cost. Clinical studies show exceedingly low rates of all major complications including femur fracture, dislocation, and nerve injury. Economic data from Q1 2013 to Q2 2016 demonstrate that CMS-insured patients treated by the Superior Hip Approach have the lowest cost of all patients treated in Massachusetts by an average of more than $7,000 over 90 days. The data show that the patients treated by the Superior Hip Approach have lower cost than any other surgical technique. Matched-pair bioskills dissections demonstrate far better preservation of the hip joint capsule and short external rotators than the anterior approach. Design principles include: Preservation of the abductors; Preservation of the posterior capsule and short external rotators; Preparation of the femur in situ prior to femoral neck osteotomy; Excision of the femoral head, thereby avoiding surgical dislocation of the hip; In-line access to the femoral shaft axis; Ability to perform a trial reduction; Independence from intra-operative imaging; Independence from a traction table; Applicable to at least 99% of THA procedures. Conclusion. In contrast to the results of the Superior Approach, the anterior approach continues to show difficulties with wound problems, infection, intra- and post-operative fracture, and failure of femoral component osseointegration and even dislocation. Evidence continues to demonstrate that the Superior Hip Approach has advantages over all other surgical approaches to the hip

Goals for total hip arthroplasty include acceleration of recovery, optimisation of component placement, minimisation of peri-operative complications, and maximal preservation of surrounding soft tissues. Achieving these goals when combined with appropriate implant design and manufacture can lead to decades of excellent hip function. With the exception of relatively rapid recovery, which can also be achieved with virtually all modern surgical exposures, the anterior hip approach fails to reliably achieve these goals. Problems with the anterior exposure for total hip arthroplasty are becoming increasingly recognised. Complications with equal or higher incidences than alternative exposures include: 1.) Early wound complications, 2.) Infection, 3.) Intra-operative and post-operative femur fracture, 4.) Greater trochanteric fracture, 5.) Dislocation, 6.) Femoral component loosening, 7.) Poor component placement, 8.) Poor soft tissue balance, 9.) Incisions with poor aesthetics and associated superficial hypaesthesia and dysaesthesia. These complications may be in part due to: 1.) The anterior and posterior soft tissue releases often necessary to complete the exposure, 2.) Poor ability to anatomically repair the hip joint capsule, 3.) Reduced choices of femoral components with restriction generally to those with less robust fixation, 4.) The poorly extensile nature of the interval, 5.) The need to place the incision in the region of the flexion crease, 6.) The limited ability to assess soft tissue balance and impingement-free range of motion at the time of surgery, 7.) The undue reliance on unvalidated, inaccurate imaging techniques to assess component placement. While experienced surgeons can achieve excellent results with the anterior (or virtually any other) exposure for total hip arthroplasty, the anterior exposure is by no means close to being a first among equals

Introduction. Bony deformities in the hip that cause femoroacetabular impingement (FAI) can be resected in order to delay the onset of osteoarthritis and improve hip range of motion. However, achieving accurate osteoplasty arthroscopically is challenging because the narrow hip joint capsule limits field of view. Recently, image-based navigation using a preoperative plan has been shown to improve the accuracy of femoral bone surfaces following arthroscopic osteoplasty for FAI. The current standard for intraoperative monitoring, 3D x-ray fluoroscopy, is accurate at the initial registration step to within 0.8±0.5mm but involves radiation. Intraoperative 3D ultrasound (US) is a promising radiation-free alternative for providing real-time visual feedback during FAI osteoplasty. The objective was to determine if intraoperative 3D US of the femoral head/neck region can be registered to a CT-based preoperative plan with comparable accuracy to fluoroscopic navigation in order to visualise progress during arthroscopic FAI osteoplasty. Methods. The experiment used a plastic femur model that had a cam deformity on the femoral head/neck. Thirty metal fiducial markers were placed on the US-accessible anterior and lateral surfaces of the femur. A CT image was acquired and reconstructed, then used to develop a preoperative plan for resection of the cam deformity. Twenty-two sets of 3D US data were then gathered from the phantom using a clinical ultrasound machine and 3D transducer while the phantom was submerged in water. US surfaces from the anterior/lateral regions of the femur were extracted using a recently proposed image processing algorithm. Fiducials in the US volume were manually registered to corresponding CT fiducials to provide a reference standard registration. The reference standard fiducial registration error (FRE) was measured as the average distance between corresponding fiducials. After fiducial-based registration, each US surface was randomly misaligned and re-registered using a coherent point-drift algorithm. The resulting surface registration error (SRE) was measured using average distance between US and CT surfaces. Finally, a plastic model of the preoperative cam deformity resection plan was 3D-printed to represent the postoperative femur. Five US scans were acquired of the postoperative model near the femoral head/neck. Each US scan was initialised for 20 trials using three reference points, and then registered using coherent point drift. Surgical outcome accuracy was reported using final surface registration error (fSRE). Results. The reference standard FRE was 0.41±0.19mm. The distance between surfaces following misalignment and re-registration for all 2200 automated registration trials was similarly small (SRE = 0.31±0.04mm) and well below the required clinical limit. Lastly, the postoperative model was accurately registered to corresponding US scans (fSRE = 0.58±0.07mm). Qualitative visualisation showed good surface matching following US to CT registration. Conclusion. Initial registration between intraoperative 3D US and preoperative CT is critical for accurate visualisation of surgical progress during FAI osteoplasty. Given spatial initialisation, the achievable registration accuracy of 3D US to CT is 0.31±0.04mm (SRE) which is well within the fluoroscopy standard, 0.8±0.5mm. The results suggest strong potential for ultrasound to guide computer-assisted arthroscopic FAI osteoplasty