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Background: The purpose of this study was to compare muscle forces and hip contact forces (HCFs) during squatting in patients with cam-type femoroacetabular impingement (cam-FAI) before and after hip corrective surgery and with healthy control participants.Methods: Ten symptomatic male patients with cam-FAI performed deep squatting preoperatively and at 2 years postoperatively. Patients were matched by age and body mass index to 10 male control participants. Full-body kinematics and kinetics were computed, and muscle forces and HCFs were estimated using a musculoskeletal model and static optimization. Normalized squat cycle (%SC) trials were compared using statistical nonparametric mapping (SnPM).Results: Postoperatively, patients with cam-FAI squatted down with higher anterior pelvic tilt, higher hip flexion, and greater hip extension moments than preoperatively. Preoperative patients demonstrated lower anterior pelvic tilt and lower hip flexion compared with the participants in the control group. Postoperative patients showed increased semimembranosus force compared with their preoperative values. Preoperative forces were lower than the control group for the adductor magnus, the psoas major, and the semimembranosus; however, the preoperative patients showed greater inferior gluteus maximus forces than the patients in the control group, whereas the postoperative patients did not differ from the control patients. Higher posterior, superior, and resultant HCF magnitudes were identified postoperatively in comparison with the preoperative values. Preoperative posterior HCF was lower than in the control group, whereas the postoperative posterior HCF did not differ from those in the control group.Conclusions: Higher postoperative anterior pelvic tilt was associated with an indication of return to closer to normal pelvic motion, which resembled data from the control group. Lower preoperative anterior pelvic tilt was associated with muscle force imbalance, indicated by decreased semimembranosus and increased gluteus maximus forces. The overall increased postoperative muscle forces were associated with improved pelvic mobility and increased HCFs that were comparable with the control-group standards.Clinical Relevance: Muscle forces and HCFs may be indicative of postoperative joint health restoration and alleviated symptoms. [ABSTRACT FROM AUTHOR]

Background: Surgical management of cam femoroacetabular impingement (FAI) aims to preserve the native hip and restore joint function, although it is unclear how the capsulotomy, cam deformity, and capsular repair influence joint mechanics to balance functional mobility. Purpose: To examine the contributions of the capsule and cam deformity to hip joint mechanics. Using in vitro, cadaveric methods, we examined the individual effects of the surgical capsulotomy, cam resection, and capsular repair on passive range of motion and resistance of applied torque. Study Design: Descriptive laboratory study. Methods: Twelve cadaveric hips with cam deformities were skeletonized to the capsule and mounted onto a robotic testing platform. The robot positioned each intact hip in multiple testing positions: (1) extension, (2) neutral 0°, (3) flexion 30°, (4) flexion 90°, (5) flexion-adduction and internal rotation (FADIR), and (6) flexion-abduction and external rotation. Then the robot performed applicable internal and external rotations, recording the neutral path of motion until a 5-N·m of torque was reached in each rotational direction. Each hip then underwent a series of surgical stages (T-capsulotomy, cam resection, capsular repair) and was retested to reach 5 N·m of internal and external torque again after each stage. During the capsulotomy and cam resection stages, the initial intact hip's recorded path of motion was replayed to measure changes in resisted torque. Results: Regarding changes in motion, external rotation increased substantially after capsulotomies, but internal rotation only further increased at flexion 90° (change +32%, P = .001, d = 0.58) and FADIR (change +33%, P < .001, d = 0.51) after cam resections. Capsular repair provided marginal restraint for internal rotation but restrained the external rotation compared with the capsulotomy stage. Regarding changes in torque, both internal and external torque resistance decreased after capsulotomy. Compared with the capsulotomy stage, cam resection further reduced internal torque resistance during flexion 90° (change −45%, P < .001, d = 0.98) and FADIR (change −37%, P = .003, d = 1.0), where the cam deformity accounted for 21% of the intact hip's torsional resistance in flexion 90° and 27% in FADIR. Conclusion: Although the capsule played a predominant role in joint constraint, the cam deformity provided 21% to 27% of the intact hip's resistance to torsional load in flexion and internal rotation. Resecting the cam deformity would remove this loading on the chondrolabral junction. Clinical Relevance: These findings are the first to quantify the contribution of the cam deformity to resisting hip joint torsional loads and thus quantify the reduced loading on the chondrolabral complex that can be achieved after cam resection. [ABSTRACT FROM AUTHOR]

Background: Cam-type femoroacetabular impingement (FAI) is a causative factor for hip pain and early hip osteoarthritis. Although cam FAI can alter hip joint biomechanics, it is unclear what role muscle forces play and how they affect the hip joint loading. Purpose/Hypothesis: The purpose was to examine the muscle contributions and hip contact forces in individuals with symptomatic cam FAI during level walking. Patients with symptomatic cam FAI would demonstrate different muscle and hip contact forces during gait. Study Design: Controlled laboratory study. Methods: Eighteen patients with symptomatic cam FAI were matched for age and body mass index with 18 control participants. Each participant’s walking kinematics and kinetics were recorded throughout a gait cycle (ipsilateral foot-strike to ipsilateral foot-off) by use of a motion capture system and force plates. Muscle and hip contact forces were subsequently computed by use of a musculoskeletal modeling program and static optimization methods. Results: The FAI group walked slower and with shorter steps, demonstrating reduced joint motions and moments during contralateral foot-strike, compared with the control group. The FAI group showed reduced psoas major (median, 1.1 newtons per bodyweight [N/BW]; interquartile range [IQR], 1.0-1.5 N/BW) and iliacus forces (median, 1.2 N/BW; IQR, 1.0-1.6 N/BW), during contralateral foot-strike, compared with the control group (median, 1.6 N/BW; IQR, 1.3-1.6 N/BW, P = .004; and median, 1.5 N/BW; IQR, 1.3-1.6 N/BW, P = .03, respectively), which resulted in lower hip contact forces in the anterior (P = .026), superior (P = .02), and medial directions (P = .038). The 3 vectors produced a resultant peak force at the anterosuperior aspect of the acetabulum for both groups, with the FAI group demonstrating a substantially lower magnitude. Conclusion: FAI participants altered their walking kinematics and kinetics, especially during contralateral foot-strike, as a protective mechanism, which resulted in reduced psoas major and iliacus muscle force and anterosuperior hip contact force estimations. Clinical Relevance: Limited hip mobility not only is attributed to bone-on-bone impingement, caused by cam morphology, but could be attributed to musculature as well. Not only would the psoas major and iliacus be able to protect the hip joint during flexion-extension, athletic conditioning could further strengthen core muscles for improved hip mobility and pelvic balance. [ABSTRACT FROM AUTHOR]

Background: The hip joint capsule passively restrains extreme range of motion, protecting the native hip against impingement, dislocation, and edge-loading. We hypothesized that following total hip arthroplasty (THA), the reduced femoral head size impairs this protective biomechanical function.Methods: In cadavers, THA was performed through the acetabular medial wall, preserving the entire capsule, and avoiding the targeting of a particular surgical approach. Eight hips were examined. Capsular function was measured by rotating the hip in 5 positions. Three head sizes (28, 32, and 36 mm) with 3 neck lengths (anatomical 0, +5, and +10 mm) were compared.Results: Internal and external rotation range of motion increased following THA, indicating late engagement of the capsule and reduced biomechanical function (p < 0.05). Internal rotation was affected more than external. Increasing neck length reduced this hypermobility, while too much lengthening caused nonphysiological restriction of external rotation. Larger head sizes only slightly reduced hypermobility.Conclusions: Following THA, the capsular ligaments were unable to wrap around the reduced-diameter femoral head to restrain extreme range of motion. The posterior capsule was the most affected, indicating that native posterior capsule preservation is not advantageous, at least in the short term. Insufficient neck length could cause capsular dysfunction even if native ligament anatomy is preserved, while increased neck length could overtighten the anterior capsule.Clinical Relevance: Increased understanding of soft-tissue balancing following THA could help to prevent instability and improve early function. This study illustrates how head size and neck length influence the biomechanical function of the hip capsule in the early postoperative period. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the change in hip distractive stability after a cam over-resection, labral tear, repair, labrectomy, or circumferential 6-mm or 10-mm labral reconstruction in a biomechanical model., Methods: Ten fresh-frozen matched pair human cadaveric hips were analyzed using a materials testing system to measure the force and distance required to disrupt the suction seal of the hip (1) with an intact capsule and labrum, (2) after a capsulectomy and labral repair, (3) after a capsulectomy, 5-mm cam over-resection and labral repair, (4) after a capsulectomy, 5-mm cam over-resection and labral tear, (5) after a capsulectomy, 5-mm cam over-resection and labrectomy, and (6) after a capsulectomy, 5-mm cam over-resection, and a 6- or 10-mm circumferential labral reconstruction with iliotibial band (5 hips each). Each specimen was retested at 0° flexion, 45° flexion, and 45° flexion and 15° internal rotation and analyzed using non-parametric statistical methods., Results: The Friedman test of differences was significant among structural conditions and hip positions (P = 0.001). In all positions, the resistive force that opposed the disruption of the suction seal in an intact hip was significantly greater compared to all other conditions. The resistive force for the capsulectomy, 5-mm cam over-resection and labrectomy condition was significantly less compared to almost all other conditions and hip positions. A qualitative suction seal was achieved in 20% of hip specimens with a 6-mm labral reconstruction while a seal was in achieved 60% of specimens with a 10-mm labral reconstruction., Conclusions: After a cam over-resection, a circumferential labral reconstruction improves the distractive stability of a labral deficient hip, comparable to a labral repair or tear in a biomechanical model., Clinical Relevance: Circumferential labral reconstruction may be a viable treatment option for patients with ongoing symptoms after hip arthroscopy with evidence of a cam over-resection and a deficient labrum., (Copyright © 2024. Published by Elsevier Inc.)

Background: Previous biomechanical studies have identified capsular closure, labral repair or reconstruction, and osteochondroplasty as important surgical interventions to improve hip stability., Purpose: To investigate the outcome metrics used to quantify hip stability and assess and measure the relative contributions of the labrum, capsule, and bone to hip stability through a quantitative analysis., Study Design: Systematic review and meta-analysis; Level of evidence, 4., Methods: PubMed and Embase databases were searched using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Included studies evaluated cadaveric hip biomechanics related to capsular, labral, and bony management during hip arthroscopy. Studies were assessed for distraction force and distance, fluid measures, and contact forces used to quantify the suction seal. Exclusion criteria included open surgery, arthroplasty, reorientation osteotomy, or traumatic dislocation., Results: A total of 33 biomechanical studies comprising 322 hips that evaluated 1 or more of the following were included: distraction force or distance (24 studies), fluid measures (10 studies), and contact forces (6 studies). Compared with a capsulotomy or capsulectomy, capsular repair or reconstruction demonstrated greater resistance to distraction (standardized mean difference [SMD], 1.13; 95% CI, 0.46-1.80; P = .0009). Compared with a labral tear, a labral repair or reconstruction demonstrated less resistance to distraction (SMD, -0.67; 95% CI, -1.25 to -0.09; P = .02). Compared with a labral debridement, repair or reconstruction demonstrated greater resistance to distraction (SMD, 1.74; 95% CI, 1.23 to 2.26; P < .00001). No quantitative analysis was feasible from studies evaluating the effect of osseous resection due to the heterogeneity in methodology and outcome metrics assessed., Conclusion: Most biomechanical evidence supports capsulotomy repair or reconstruction to improve hip distractive stability at the end of hip arthroscopic surgery. While the repair of a torn labrum does not improve distractive resistance, it is superior to labral debridement in most biomechanical studies., Competing Interests: The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Background: Knowing the mechanical properties of trabecular bone is critical for many branches of orthopaedic research. Trabecular bone is anisotropic and the principal trabecular direction is usually aligned with the load it transmits. It is therefore critical that the mechanical properties are measured as close as possible to this direction, which is often perpendicular to a curved articulating surface., Methods: This study presents a method to extract trabecular bone cores perpendicular to a curved articulating surface of the distal femur. Cutting guides were generated from computed tomography scans of 12 human distal femora and a series of cutting tools were used to release cylindrical bone cores from the femora. The bone cores were then measured to identify the angle between the bone core axis and the principal trabecular axis., Findings: The method yielded an 83% success rate in core extraction over 10 core locations per distal femur specimen. In the condyles, 97% of extracted cores were aligned with the principal trabecular direction., Interpretation: This method is a reliable way of extracting trabecular bone specimens perpendicular to a curved articular surface and could be useful across the field of orthopaedic research., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose: To evaluate the impact of capsular management on joint constraint and femoral head translations during simulated activities of daily living (ADL)., Methods: Using 6 (n = 6) cadaveric hip specimens, the effect of capsulotomies and repair was then evaluated during simulated ADL. Joint forces and rotational kinematics associated with gait and sitting, adopted from telemeterized implant studies, were applied to the hip using a 6-degrees of freedom (DOF) joint motion simulator. Testing occurred after creation of portals, interportal capsulotomy (IPC), IPC repair, T-capsulotomy (T-Cap), partial T-Cap repair, and full T-Cap repair. The anterior-posterior (AP), medial-lateral (ML), and axial compression DOFs were operated in force control, whereas flexion-extension, adduction-abduction, and internal-external rotation were manipulated in displacement control. Resulting femoral head translations and joint reaction torques were recorded and evaluated. Subsequently, the mean-centered range of femoral head displacements and peak signed joint restraint torques were calculated and compared., Results: During simulated gait and sitting, the mean range of AP femoral head displacements with respect to intact exceeded 1% of the femoral head diameter after creating portals, T-Caps, and partial T-Cap repair (Wilcoxon signed rank P < .05); the mean ranges of ML displacements did not. Deviations in femoral head kinematics varied by capsule stage but were never very large. No consistent trends with respect to alterations in peak joint restrain torques were observed., Conclusions: In this cadaveric biomechanical study, capsulotomy and repair minimally affected resultant femoral head translation and joint torques during simulated ADLs., Clinical Relevance: The tested ADLs appear safe to perform after surgery, regardless of capsular status, because adverse kinematics were not observed. However, further study is required to determine the importance of capsular repair beyond time-zero biomechanics and the resultant effect on patient-reported outcomes., (Copyright © 2023 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.)

Background: Hip dysplasia is characterized by insufficient acetabular coverage around the femoral head, which leads to instability, pain, and injury. Periacetabular osteotomy (PAO) aims to restore acetabular coverage and function, but its effects on capsular mechanics and joint stability are still unclear. The purpose of this study was to examine the effects of PAO on capsular mechanics and joint range of motion in dysplastic hips., Methods: Twelve cadaveric dysplastic hips (denuded to bone and capsule) were mounted onto a robotic tester and tested in multiple positions: (1) full extension, (2) neutral 0°, (3) flexion of 30°, (4) flexion of 60°, and (5) flexion of 90°. In each position, the hips underwent internal and external rotation, abduction, and adduction using 5 Nm of torque. Each hip then underwent PAO to reorient the acetabular fragment, preserving the capsular ligaments, and was retested., Results: The PAO reduced internal rotation in flexion of 90° (∆IR = -5°; p = 0.003), and increased external rotation in flexion of 60° (∆ER = +7°; p = 0.001) and flexion of 90° (∆ER = +11°; p = 0.001). The PAO also reduced abduction in extension (∆ABD = -10°; p = 0.002), neutral 0° (∆ABD = -7°; p = 0.001), and flexion of 30° (∆ABD = -8°; p = 0.001), but increased adduction in neutral 0° (∆ADD = +9°; p = 0.001), flexion of 30° (∆ADD = +11°; p = 0.002), and flexion of 60° (∆ADD = +11°; p = 0.003)., Conclusions: PAO caused reductions in hip abduction and internal rotation but greater increases in hip adduction and external rotation. The osseous acetabular structure and capsule both play a role in the balance between joint mobility and stability after PAO., Competing Interests: Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/G919)., (Copyright © 2022 by The Journal of Bone and Joint Surgery, Incorporated.)

Background: In order to reduce the development of hip osteoarthritis related to cam-type femoroacetabular impingement syndrome (FAIS), corrective surgery has evolved to become a safe and effective treatment. Although corrective surgery produces high level of patient satisfaction, it is still unclear how it affects muscle and hip contact forces during level walking., Research Question: The purpose was to compare the muscle force contributions and hip contact forces in patients before and after surgical correction for cam FAIS with healthy control (CTRL) individuals during level walking., Methods: Eleven male patients with symptomatic cam-type morphology, who underwent hip osteochondroplasty, had their level walking recorded pre- and at 2-year postoperatively. The patients were sex-, age-, BMI-matched to 11 CTRL individuals. Sagittal and frontal hip kinematics and kinetics were computed and, subsequently, muscle and hip contact forces were estimated using musculoskeletal modelling and static optimization., Results: Patient-reported outcomes improved postoperatively. The pre- and postoperative FAIS walked slower and with shorter steps than the CTRL. Postoperative biceps femoris (CTRL: 0.35 ± 0.13 N/BW; pre-op: 0.28 ± 0.11 N/BW; post-op: 0.20 ± 0.07 N/BW) and semimembranosus forces (CTRL: 0.77 ± 0.24 N/BW; pre-op: 0.66 ± 0.24 N/BW; post-op: 0.41 ± 0.14 N/BW) were lower at ipsilateral foot-strike. Postoperative rectus femoris force (CTRL: 1.73 ± 0.35 N/BW; pre-op: 1.44 ± 0.24 N/BW; post-op: 1.18 ± 0.23 N/BW) was lower than the other two groups, and the pre- and postoperative FAIS had lower iliacus (CTRL: 1.17 ± 0.18 N/BW; pre-op: 0.93 ± 0.16 N/BW; post-op: 0.94 ± 0.21 N/BW) and psoas (CTRL: 1.55 ± 0.24 N/BW; pre-op: 1.14 ± 0.38 N/BW; post-op: 1.10 ± 0.46 N/BW) muscle forces at contralateral foot-strike compared with the CTRL. Pre- and postoperative FAIS demonstrated lower peak hip contact loading resultant than the CTRL., Significance: The altered gait parameters observed in the preoperative FAIS was not restored after surgery, and was still away from the CTRL. It is possible that the reduced dynamic muscle forces of the biceps femoris, semimembranosus and rectus femoris postoperatively were associated with the protected mechanism that involved the iliopsoas preoperatively. This is an indication that the gait adaptations affected by the FAIS do not restore to normal after surgical correction at the 2-years follow-up., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The use of robotic systems combined with force sensing is emerging as the gold standard for in vitro biomechanical joint testing, due to the advantage of controlling all six degrees of freedom independently of one another. This paper describes a novel robotic platform and the experimental protocol used for hip joint testing. An experimental protocol implemented optical tracking and registration techniques in order to define the position of the hip joint centre of rotation (COR) in the coordinate system of the robot's end effector. The COR coordinates defined the origin of the task-related coordinate system used to control the robot, with a hybrid force/position law to simulate standard clinical tests. The axes of this frame were defined using the International Society of Biomechanics (ISB) anatomical coordinate system. Experiments were carried out on two cadaveric hip joint specimens using the robotic testing platform and a mechanical testing rig previously developed and described by our group. Simulated internal-external and adduction/abduction laxity tests were carried out with both systems and the resulting peak range of motion (ROM) was measured. Similarities and differences were observed in these experiments, which were used to highlight some of the limitations of conventional systems and the corresponding advantages of robotics, further emphasising their added value in vitro testing., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Background: As there is a high prevalence of patients with cam deformities and no ongoing hip dysfunction, understanding the biomechanical factors predicting the onset of symptoms and degenerative changes is critical. One such variable is how the spinopelvic parameters may influence hip and pelvic sagittal mobility. Hypothesis/Purpose: Pelvic incidence may predict sagittal hip and pelvic motions during walking and squatting. The purpose was to determine which anatomic characteristics were associated with symptoms and how they influenced functional hip and pelvic ranges of motion (ROMs) during walking and squatting., Study Design: Controlled laboratory study., Methods: Fifty-seven participants underwent computed tomography and were designated either symptomatic (n = 19, cam deformity with pain), asymptomatic (n = 19, cam deformity with no pain), or control (n = 19, no cam deformity or pain). Multiple femoral (cam deformity, neck angle, torsion), acetabular (version, coverage), and spinopelvic (pelvic tilt, sacral slope, pelvic incidence) parameters were measured from each participant's imaging data, and sagittal hip and pelvic ROMs during walking and squatting were recorded using a motion capture system., Results: Symptomatic participants had large cam deformities, smaller femoral neck-shaft angles, and larger pelvic incidence angles compared with the asymptomatic and control participants. Discriminant function analyses confirmed that radial 1:30 alpha angle (λ 1 = 0.386), femoral neck-shaft angle (λ 2 = 0.262), and pelvic incidence (λ 3 = 0.213) ( P < .001) were the best anatomic parameters to classify participants with their groups. Entering these 3 parameters into a hierarchical linear regression, significant regressions were achieved for hip ROM only when pelvic incidence was included for walking ( R 2 = 0.20, P = .01) and squatting ( R 2 = 0.14, P = .04). A higher pelvic incidence decreased walking hip ROM ( r = -0.402, P = .004). Although symptomatic participants indicated a trend of reduced squatting hip and pelvic ROMs, there were no significant regressions with the anatomic parameters., Conclusion: A cam deformity alone may not indicate early clinical signs or decreased ROM. Not only was pelvic incidence a significant parameter to classify the participants, but it was also an important parameter to predict functional ROM. Symptomatic patients with a higher pelvic incidence may experience limited sagittal hip mobility., Clinical Relevance: Patients with symptomatic femoroacetabular impingement showed a higher pelvic incidence and, combined with a cam deformity and varus neck, can perhaps alter the musculature of their iliopsoas, contributing to a reduced sagittal ROM. With an early and accurate clinical diagnosis, athletes could benefit from a muscle training strategy to protect their hips.

Background: It is still unclear why many individuals with bilateral cam deformities demonstrate only unilateral symptoms of femoroacetabular impingement, thus symptoms may be attributed to additional anatomical parameters. The purpose was to examine patients with bilateral cam deformities, with unilateral symptoms, and compare anatomical hip joint parameters between their affected (symptomatic) hip and their contralateral, unaffected (asymptomatic) hip., Methods: Twenty participants (n=20) with unilateral symptoms, but bilateral cam deformities, underwent CT imaging to measure their affected and unaffected hip's: axial and radial alpha angles, femoral head-neck offset, femoral neck-shaft angle, medial proximal femoral angle, femoral torsion, acetabular version, center-edge angle; and a physical examination (hip flexion, straight-leg raise, internal rotation, external rotation) to ascertain clinical signs., Findings: The affected hips demonstrated limited motions during physical examination, compared with unaffected hips (effect size=0.550 to 0.955). The affected hips had significantly lower femoral neck-shaft angles (mean 125° (SD 3)) and lower medial proximal femoral angles (mean 79° (SD 4)), compared with the unaffected hips (mean 127° (SD 3), P=0.001, effect size=0.922; and mean 81° (SD 4), P=0.011, effect size=0.632; respectively). There were no differences in cam deformity parameters (axial and radial alpha angles, femoral head-neck offset), femoral torsion, acetabular version, and center-edge angle, between affected and unaffected hips., Interpretation: A decreased femoral neck-shaft angle or medial proximal femoral angle can be implemented as a diagnostic predictor, to determine which hip may be at a greater risk of developing early symptoms., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The purpose was to investigate the validity of Harrington's and Davis's hip joint center (HJC) regression equations on a population affected by a hip deformity, (i.e., femoroacetabular impingement). Sixty-seven participants (21 healthy controls, 46 with a cam-type deformity) underwent pelvic CT imaging. Relevant bony landmarks and geometric HJCs were digitized from the images, and skin thickness was measured for the anterior and posterior superior iliac spines. Non-parametric statistical and Bland-Altman tests analyzed differences between the predicted HJC (from regression equations) and the actual HJC (from CT images). The error from Davis's model (25.0 ± 6.7 mm) was larger than Harrington's (12.3 ± 5.9 mm, p<0.001). There were no differences between groups, thus, studies on femoroacetabular impingement can implement conventional regression models. Measured skin thickness was 9.7 ± 7.0mm and 19.6 ± 10.9 mm for the anterior and posterior bony landmarks, respectively, and correlated with body mass index. Skin thickness estimates can be considered to reduce the systematic error introduced by surface markers. New adult-specific regression equations were developed from the CT dataset, with the hypothesis that they could provide better estimates when tuned to a larger adult-specific dataset. The linear models were validated on external datasets and using leave-one-out cross-validation techniques; Prediction errors were comparable to those of Harrington's model, despite the adult-specific population and the larger sample size, thus, prediction accuracy obtained from these parameters could not be improved., (Copyright © 2015 Elsevier B.V. All rights reserved.)