Aims Pelvic tilt (PT) can significantly change the functional orientation of the acetabular component and may differ markedly between patients undergoing total hip arthroplasty (THA). Patients with stiff spines who have little change in PT are considered at high risk for instability following THA. Femoral component position also contributes to the limits of impingement-free range of motion (ROM), but has been less studied. Little is known about the impact of combined anteversion on risk of impingement with changing pelvic position. Methods We used a virtual hip ROM (vROM) tool to investigate whether there is an ideal functional combined anteversion for reduced risk of hip impingement. We collected PT information from functional lateral radiographs (standing and sitting) and a supine CT scan, which was then input into the vROM tool. We developed a novel vROM scoring system, considering both seated flexion and standing extension manoeuvres, to quantify whether hips had limited ROM and then correlated the vROM score to component position. Results The vast majority of THA planned with standing combined anteversion between 30° to 50° and sitting combined anteversion between 45° to 65° had a vROM score > 99%, while the majority of vROM scores less than 99% were outside of this zone. The range of PT in supine, standing, and sitting positions varied widely between patients. Patients who had little change in PT from standing to sitting positions had decreased hip vROM. Conclusion It has been shown previously that an individual’s unique spinopelvic alignment influences functional cup anteversion. But functional combined anteversion, which also considers stem position, should be used to identify an ideal THA position for impingement-free ROM. We found a functional combined anteversion zone for THA that may be used moving forward to place total hip components. Cite this article: Bone Jt Open 2021;2(10):834–841.

Soft tissue balancing while crucial for a successful total knee arthroplasty (TKA) is incompletely defined and the subject of broad recommendations. We analyzed 69 unilateral computer-assisted surgery posterior stabilized (PS) TKA subjects who postoperatively scored ≥36 out of a possible 40 points on the satisfaction section of the American Knee Society score (2011). We examined a range of postoperative coronal plane laxity parameters and the correlation between preoperative and postoperative laxity. Total postoperative coronal laxity arcs at maximum extension and 20 degrees of flexion varied between 2 and 12 and 3 and 13 degrees, respectively. Depending on the position of measurement, medial laxity was between 0.5 and 9.5 degrees and lateral laxity between 1 and 12 degrees. The change in laxity between maximum extension and 90 degrees of flexion demonstrated a range of 7 degrees medially and 12 degrees laterally. The total coronal arc of movement did not affect functional outcomes. A moderate correlation of 0.452 and 0.424 was seen between initial and postoperative total coronal laxity arcs in maximum extension and 20 degrees of flexion, respectively. The individual variability for each measured parameter within our cohort demonstrates TKA satisfaction is not as simple as producing a narrow range of coronal laxity parameters and that as with many body systems considerable variation is still consistent with excellent function. Our findings help to define acceptable balance parameters for PS TKA. It does not appear necessary to closely match postoperative laxity to that present preoperatively.

Soft tissue balancing, while accepted as crucial to total knee arthroplasty (TKA) outcomes, is incompletely defined as the subject of broad recommendations. We analyzed 120 computer-assisted, posterior stabilized TKA undertaken for osteoarthritis. Coronal plane laxity was measured, in the 91 varus and 29 valgus knees, prior to any bone resection or soft tissue release, and again after implant insertion. Soft tissue laxity parameters were correlated to the American Knee Society Score (2011) at a minimum follow-up of 12 months with a focus on patient function and satisfaction. Thirteen specific laxity parameters showed a significant correlation to satisfaction, one parameter correlated to function, and another to both functional and satisfaction outcomes. Most correlations were weak, the strongest related to postoperative decreases in coronal plane laxity. Greater preoperative varus but not valgus deformity was associated with higher satisfaction scores. Additionally, 30 patients who reported 40 of 40 satisfaction and that their TKA knee felt normal at all times did not have soft tissue balancing parameters distinguishing them from other subjects. Patient satisfaction and function outcomes demonstrated limited correlation to coronal plane soft tissue parameters. It appears that optimizing TKA satisfaction and function is not as simple as producing a narrow range of coronal laxity parameters. The ongoing debate around optimal coronal plane alignment and its subsequent effect on coronal plane soft tissues may not be as independently important as currently argued. Soft tissue balance may need to be considered as a more complex global envelope.

Reuse of Gulf of Mexico platforms is common practice if the facility is also destined for the Gulf of Mexico. However, reuse of a Gulf of Mexico platform in the North Sea is uncommon. An existing Gulf of Mexico platform installed in 1990 in 303 ft water depth was evaluated for reuse in the North Sea. While the water depth was similar at both sites, regulatory and environmental conditions differed. This paper summarizes the evaluation process which covered feasibility level analyses of in-place storm, in-place fatigue, in-place damage, lifting, transport strength and transport fatigue. The evaluation also included in-depth consideration of material properties and weld procedures. A cost and schedule comparison between reuse of the Gulf of Mexico platform and fabrication of a new platform showed that the reuse option provided a lower cost and shorter schedule compared to fabrication of a new platform. While not all Gulf of Mexico platforms can be used in the North Sea, this paper points out that the newer generation Gulf of Mexico platform designs can exhibit the necessary design features and level of safety that is required for North Sea operations. Introduction Platform reuse, which is common in the Gulf of Mexico and also other areas of the world, has been a viable field development scenario for many years. For example, the first OTC conference in 1969 included a paper1 which described the successful decommissioning, removal, and re-installation of a 165 foot water depth Gulf of Mexico platform point-to-point in 1966. More recently, the larger amount of new North Sea fields considered economically marginal, coupled with declining production from existing fields, has led to platform reuse being considered as an alternative decommissioning field development scenario Amoco UK is considering the development of several fields in the UK North Sea with one scenario including subsea completions fed to a gas compression platform. Amoco has developed cost estimates for several options including a newbuild platform, a retrofit on an existing platform, and a reused platform. This paper discusses preliminary technical work performed to determine the feasibility of reusing a modem (1990's vintage) Gulf of Mexico platform to the North Sea. Consideration was given to elements involved with the development of a Safety Case, however, only preliminary discussions have been held with UK verification agents. A cost estimate was developed for reusing a specific existing platform and is compared with the costs of a new-build platform. Platform Configuration Figure I shows a comparison between the original existing platform for Gulf of Mexico (GOM) operations and the proposed upgraded platform for North Sea (NS) operations. The original GOM configuration was a four leg configuration and was originally installed in 1990. The platform follows the Amoco TAMPA2 (tender assisted minimum platform arrangement) design standard. The platform has 57 ½ inch diameter legs containing 54 inch diameter piles driven to approximately 345 feet penetration. The pile were not grouted to the legs in its original GOM location. The platform is vertically X-braced with 20 to 24 inch diameter braces. Horizontal bracing consists of 20 inch diameter X-bracing at each major elevation; however, exterior face horizontal framing exists only at the first elevation below the waterline and at the mudline (other elevations have horizontal framing for lifting purposes).

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