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Abstract Background Investigation of polyethylene liner movement in total hip arthroplasty requires bead-marking for radiographic visibility of the liner. However, occlusion of markers poses a challenge for marker registration in radiographs. Methods The polyethylene of a dual mobility acetabular system was marked with twelve 1-mm tantalum markers (four groups of three markers) using a custom-made drill guide. Liner motion in a phantom and a patient was investigated with dynamic radiostereometry analysis (dRSA) at 1-year follow-up and static radiostereometry analysis (sRSA) postoperatively and at 1- and 2-year follow-up. A combined marker configuration (CMC) model was calculated from the registered positions of the liner markers and the femoral head in several images. Furthermore, the CMC model and the theoretic marker positions from computer-assisted models of the drill guide were combined in a hybrid model. Results The CMC model included eleven markers in the phantom and nine markers in the patient, which was sufficient for dRSA. Liner movement in the phantom followed liner contact with the femoral neck, while liner movement in the patient was independent. The hybrid model was necessary to determine liner orientation in sRSA recordings, which clearly changed from postoperative to 1- and 2-year follow-up even though the patient was positioned similarly. Conclusion Polyethylene liner motion in dual mobility hip prosthesis can be assessed with CMC models in dRSA recordings. In sRSA, the liner position between follow-ups is unpredictable and analysis requires inclusion of all markers in the model, accomplished with a hybrid marker model. Trial registration ClinicalTrials.gov [ NCT02301182 ], 25 October 2015.

Background and purpose: Dual mobility (DM) articulation total hip arthroplasty (THA) is used increasingly to reduce dislocation risk. We investigated cup fixation, polyethylene (PE) wear, serum chromium and cobalt ions, and their correlation to physical activity in patients with DM cups at 6-year follow-up. Patients and methods: In a patient-blinded RCT, 60 patients with hip osteoarthritis at a median age of 74 years (70–82) were randomly allocated to cemented (n = 30) or cementless hydroxyapatite-coated (n = 30) fixation of Avantage DM THA with a highly-crosslinked vitamin-E PE liner. Cup migration and PE wear were measured with radiostereometric analysis (RSA), chromium and cobalt ions were measured in serum, and physical activity was measured with accelerometers. Results: At 6-year follow-up, proximal cup migration was similar: 0.14 mm (95% CI 0.01–0.28) for cemented cups and 0.21 mm (0.02–0.39) for cementless cups. The PE wear rate from 1- to 6-year follow-up was also similar: 0.06 mm/year (0.04–0.09) for cemented cups and 0.07 mm/year (0.04–0.11) for cementless cups. Serum metal ion levels were undetectable or very low. Physical activity was mainly low intensity and did not correlate to PE wear rate or cup migration. Conclusion: Cemented and cementless DM cups with highly crosslinked vitamin-E infused liners have similar cup migration and PE wear when used for primary THA surgery.

Background and purpose: BoneMaster (BM) is a thin electrochemically applied hydroxyapatite (HA) implant coating marketed with expectations of improved osseointegration properties but less polyethylene (PE) wear. We compared the midterm cup migration and PE wear of cementless porous-coated hemispherical cups with and without BM. Patients and methods: In this patient-blinded, randomized controlled trial, 53 patients with a mean age of 64 years (55–75) received total hip arthroplasty with a porous-coated (P) or porous and BoneMaster (PBM) coated Exceed cup and ArCom E1 infused PE. Patients were followed with RSA, Hip Osteoarthritis Outcome Score (HOOS), and Euro-Qol-5-3L (EQ-5D) at 3 and 6 months, and 1-, 2-, and 5-year follow-up. Results: At 5-year follow-up, total translation and maximum total point motion was 0.28 mm (95% CI 0.08; 0.47) and 0.52 mm (CI 0.12; 0.93) higher in the PBM group than in the P group. PE wear was comparable between PBM and P cups, and 2D wear rate from 1-year follow-up to last follow-up was 0.03 mm (CI 0.02–0.03). The 5-year anterior translation was 0.05 mm (CI –0.10 to 0.21) in the normal BMD group and 0.40 mm (CI 0.22–0.57) in the osteopenia group. Interpretation: At 5-year follow-up, Exceed cups in the PBM group migrated more than in the P group but the PE wear rate was low and similar. This study does not indicate any advantage of additional BoneMaster coating compared with porous coating alone on cementless hemispherical cups with regards to migration, polyethylene wear, and clinical outcomes.

Background and purpose: Dual-mobility hip arthroplasty utilizes a freely rotating polyethylene acetabular liner to protect against dislocation. As liner motion has not been confirmed in vivo, we undertook this using dynamic radiostereometry (RSA). Patients and methods: 6 patients with Anatomical Dual Mobility acetabular components were included. Markers were implanted in the liners using a drill guide. Static RSA recordings and patient-reported outcome measures were obtained postoperatively and at 1-year follow-up. Dynamic RSA recordings were obtained at 1-year follow-up during passive hip movement: abduction/external rotation, adduction/internal rotation (modified FABER–FADIR), to end-range and at 45° hip flexion. Liner and neck movements were described as anteversion, inclination, and rotation. Results: Liner movement during modified FABER–FADIR was detected in 12 of 16 patients. Median (range) absolute liner movements were: anteversion 10° (5–20), inclination 6° (2–12), and rotation 11° (5–48) relative to the cup. Median absolute change in the resulting liner/neck angle (small articulation) was 28° (12–46) and in liner/cup angle (larger articulation) was 6° (4–21). Static RSA showed changes in median liner anteversion from 7° (−12 to 23) postoperatively to 10° (−3 to 16) at 1-year follow-up and inclination from 42° (35–66) postoperatively to 59° (46–80) at 1-year follow-up. Liner/neck contact was associated with high initial liner anteversion (p = 0.01). Interpretation: The polyethylene liner moves over time. 1 year after surgery the liner can move with or without liner/neck contact. The majority of movement is in the smaller articulation between head and liner.

Abstract Purpose Dynamic radiostereometric analysis (dRSA) enables precise non‐invasive three‐dimensional motion‐tracking of bones for assessment of joint kinematics. Hereby, the biomechanical effects of arthroscopic osteochondroplasty of the hip (ACH) can be evaluated in patients with femoroacetabular impingement (FAI). The aim was to investigate the pre‐ and postoperative range of motion (ROM) and the CT bone volume removed (BV) after ACH. We hypothesize increase in ROM 1 year after surgery. Methods Thirteen patients (6 female) with symptomatic FAI were included prospectively. The patient’s hips were CT‐scanned and CT‐bone models were created. Preoperative dRSA recordings were acquired during passive flexion to 90°, adduction, and internal rotation (FADIR). ACH was performed, CT and dRSA were repeated 3 months and 1 year postoperatively. Hip joint kinematics before, and 3 months and 1 year after ACH were compared pairwise. The bone volume removal was quantified and compared to change in ROM. Results Mean hip internal rotation, adduction and flexion were all unchanged after ACH at 1‐year follow‐up (p > 0.84). HAGOS scores revealed improvement of quality of life (QOL) from 32 to 60 (p = 0.02). The BV was between 406 and 1783 mm3 and did not correlate to post‐operative ROM. Conclusions ACH surgery in FAI patients had no impact of ROM at 1‐year follow‐up. QOL improved significantly. This indicates that the positive clinical effects reported after ACH might be a result of reduced labral stress and cartilage pressure during end‐range motion rather than increased ROM. Level of evidence Therapeutic prospective cohort study, level II.

Background and purpose — BoneMaster (BM) is an electrochemically deposited hydroxyapatite (HA) implant-coating, which is evenly distributed, thin, and quickly resorbed. It is designed to stimulate osseointegration and early implant stability and alleviate longer-term HA-induced third-body polyethylene wear. This study evaluates early cup migration and functional outcomes of cementless porous-coated hemispherical cups with or without BM. Patients and methods — In a patient-blinded, randomized, controlled trial 53 patients at mean 64 years (55–75) with coxarthritis were operated with an Exceed cup (Zimmer Biomet) and Bi-Metric stem (Zimmer Biomet) with porous and BM coating (PBM) or with porous coating alone (P). Follow-ups were performed postoperatively and at 3, 6, 12, and 24 months. Effect measures were cup migration measured with RSA and PROMs. Results — At 6-month follow-up, proximal cup migration in the PBM group (0.09 mm, 95% CI 0.02–0.20) was higher than in the P group (0.25 mm, CI 0.15–0.35). At 1- and 2-year follow-up, cup migration in all 6 degrees of freedom was similar between groups (p > 0.2). From before surgery to 2-year follow-up, Oxford Hip Score (OHS) increased by 17 points (CI 14–20). Hip disability and Osteoarthritis Outcome Score (HOOS) increased in all sub-scores, but was more pronounced for PBM cups compared with P cups in the Symptoms sub-score (p = 0.04). Interpretation — Contrary to expectations, PBM cups had higher early migration than P cups. At 2-year follow-up, migration was similar between groups. There seems to be no early benefit of BM coating on acetabular cups.

Background: Vertical jump highs are used to quantify performance in the lower extremities. The aim of this study was to validate a wearable inertial measurement unit (IMU) for purpose of estimating countermovement jump height using the following methods: numerical double integration (NDI), takeoff velocity (TOV) and flight-time (FT). Methods: Fifteen students each performed three jumps in two different sessions, four weeks apart. Jump-heights calculated from motion capture and force plate were used as gold standard for global IMU position and center of mass (CoM) displacement, respectively. Results: The NDI method showed higher estimates for global position (1.39 cm, p = 0.025), and for CoM displacement (4.20 cm, p

Abstract Background Dynamic RSA (dRSA) enables non-invasive 3D motion-tracking of bones and may be used to evaluate in-vivo hip joint kinematics including hip pathomechanics such as femoroacetabular impingement (FAI) and the biomechanical effects of arthroscopic cheilectomy and -rim trimming (ACH). The study aim was to evaluate the kinematic changes in the hip joint after ACH. Methods Seven non-FAI affected human cadaveric hips were CT-scanned and CT-bone models were created. dRSA recordings of the hip joints were acquired at five frames/s during passive flexion, adduction to stop, and internal rotation to stop (FADIR). ACH was performed and dRSA was repeated. dRSA images were analyzed using model-based RSA. Hip joint kinematics before and after ACH were compared pairwise. The volume of removed bone was quantified and compared to the postoperative range of motion (ROM). Results Mean hip internal rotation increased from 19.1 to 21.9° (p = 0.04, Δ2.8°, SD 2.7) after ACH surgery. Mean adduction of 3.9° before and 2.7° after ACH surgery was unchanged (p = 0.48, Δ-1.2°; SD 4.3). Mean flexion angles during dRSA tests were 82.4° before and 80.8° after ACH surgery, which were similar (p = 0.18, Δ-1.6°, SD = 2.7). No correlation between volume of removed bone and ROM was observed. Conclusions A small increase in internal rotation, but not in adduction, was observed after arthroscopic cheilectomy and -rim trimming in cadaver hips. The hip flexion angle of the FADIR test was reproducible. dRSA kinematic analysis is a new and clinically applicable method with good potential to evaluate hip joint kinematics and to test FAI pathomechanics and other surgical corrections of the hip.