Purpose: To describe a strategy for coronal alignment using a computed tomography (CT) based custom total knee arthroplasty (TKA) system, and to evaluate the agreement between the planned and postoperative Hip–Knee–Ankle (HKA) angle, Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA).Methods: From a consecutive series of 918 primary TKAs, 266 (29%) knees received CT‐based posterior‐stabilized cemented custom TKA. In addition to a preoperative CT‐scan, pre‐ and post‐operative radiographs of weight‐bearing long leg, anterior–posterior and lateral views of the knee were obtained, on which the FMA, TMA and HKA angles were measured. CT‐based three‐dimensional (3D) models enabled to correct for cases with bony wear by referring to the non‐worn areas and to estimate the native pre‐arthritic angles. The alignment technique aimed to preserve or restore constitutional alignment (CA) within predetermined limits, by defining a ‘target zone’ based on three criteria: 1) a ± 3° (range 87°–93°) primary tolerance for the femoral and tibial resections; 2) a ± 2° secondary tolerance for component obliquity, extending the bounds for FMA and TMA (range 85°–95°); 3) a planned HKA angle range of 175°–183°. Agreement between preoperative, planned and postoperative measurements of FMA, TMA and HKA angle were calculated using intra‐class correlation coefficients (ICC).Results: Preoperative radiograph and CT‐scan measurements revealed that, respectively, 73 (28%) and 103 (40%) knees were in the ‘target zone’, whereas postoperative radiographs revealed that 217 (84%) TKAs were in the ‘target zone’. Deviation from the planned angles were − 0.5° ± 1.8° for FMA, − 0.5° ± 1.8° for TMA, and − 1.1° ± 2.1° for HKA angle. Finally, the agreement between the planned and achieved targets, indicated by ICC, were good for FMA (0.701), fair for TMA (0.462) and fair for HKA angle (0.472).Conclusion: Using this strategy for coronal alignment, 84% of custom TKAs were within the ‘target zone’ for FMA, TMA and HKA angles. These findings support the concepts of emerging personalized medicine technologies, and emphasise the importance of accurate strategies for preoperative planning, which are key to achieving satisfactory ‘personalised alignment’ that can further be improved by customisation of implant components.Level of evidence: IV.

Purpose: To adapt the current D. Dejour trochlear dysplasia classification (v2.0) to only rely on quantitative magnetic resonance imaging (MRI) measurements (v3.0) to maximize objectivity and repeatability.Methods: A consecutive series of adult knee MRIs were divided into objective patellar instability (OPI, n = 127) or controls (n = 103; isolated meniscal tears) and postprocessed with multiplanar reconstruction (MPR) to standardize the sagittal plane and ensure true lateral views. Thresholds for sulcus angle, lateral trochlear inclination (LTI) and central bump were established using regression tree models to distinguish OPI from controls. The sensitivity and specificity of sulcus angle and LTI combinations to diagnose OPI were then evaluated, and the combination yielding the highest sensitivity was selected as basis for trochlear dysplasia classification. Finally, sulcus angle and LTI measurability and presence of a central bump >5 mm were used to grade dysplasia as low, moderate or high.Results: The regression tree models produced thresholds of ≥157° for sulcus angle and <14° for LTI to distinguish OPI from controls. ‘Sulcus angle ≥157° OR LTI < 14°’ yielded the highest sensitivity (87%) to diagnose OPI. The quantitative MRI classification was sulcus angle <157° AND LTI ≥ 14° for Type 0 (No dysplasia); (sulcus angle ≥ 157° OR LTI < 14°) AND central bump <5 mm for Type 1 (Low‐grade dysplasia); (sulcus angle OR LTI are ‘unmeasurable’) AND central bump <5 mm for Type 2 (Moderate‐grade dysplasia); (sulcus angle ≥ 157° OR ‘unmeasurable’ OR LTI < 14° OR ‘unmeasurable’) AND central bump ≥5 mm for Type 3 (High‐grade dysplasia).Conclusion: This MRI classification depends exclusively on quantitative measurements, has excellent interobserver agreement, and yields high sensitivity to diagnose OPI. The MRI imaging protocol with MPR mode and standardized measurements could be quickly adopted and correctly applied by clinicians worldwide in any type of institution to determine the ideal treatment plan.Level of Evidence: Level III.

Background: Patellar tendinopathy is a common condition affecting the posterior region of the proximal patellar tendon, but the reason for this typical location remains unclear. Hypothesis: The posterior region of the proximal patellar tendon is subjected to greater tendinous forces than is the corresponding anterior region. Study Design: Descriptive laboratory study. Method: An optic fiber technique was used to detect forces in both the anterior and the posterior regions of the proximal patellar tendon in 7 healthy persons. The optic fiber force sensor works on the principle of the amplitude modulation of transmitted light when the optic fiber is geometrically altered owing to the forces acting on it. Longitudinal strain in the tendon or ligament produces a negative transverse strain, thus causing a force that effectively squeezes the optic fiber. Measurements were recorded during the following exercises: closed kinetic chain quadriceps contraction (eccentric and concentric), open kinetic chain quadriceps contraction (eccentric and concentric), a step exercise, and a jump exercise. Results: During all the exercises, the peak differential signal output in the posterior location of the proximal patellar tendon was greater than in the corresponding anterior location. The greatest differential signal output was found in the jump and squat exercises. Conclusion: The posterior region of the proximal patellar tendon is subjected to greater tendinous forces than is the corresponding anterior region. This finding supports the tensile-overload theory of patellar tendinopathy. Clinical Relevance: Jump activities and deep squat exercises expose the patellar tendon to very large tendinous forces.

As wireless motion sensors become more compact and robust, new opportunities emerge to develop wearable measurement technologies for in-field sports analysis. This paper presents a nonlinear complimentary filter for tracking 3-D hip joint angles during cycling using inertial and magnetic measurement systems (IMMSs). The filter utilizes a novel method of dynamic acceleration compensation in the sensor frame based on the assumption of pendulum motion of the thigh around the hip joint center. A dynamic calibration is proposed in which the center of rotation of the thigh IMMS can be estimated during a functional hip movement in standing. Validation results from a gold-standard optical system showed that the filter IMMS tracking is drift-free with mean absolute errors of less than 3° for all IMMS axes combined at low, medium, and high pedaling speeds. Hip angles were also validated using the Vicon biomechanical model for standing and sitting calibration poses as well as true and normalized soft-tissue-artefact (STA). The best mean absolute errors for the sagittal, frontal, and coronal planes were 0.8°, 6.7°, and 2.2°, respectively. Variability due to calibrations and STA ranged from 1.4° to 8.1°. This demonstrates the high accuracies possible for IMMS tracking using algorithms designed for specific sports despite larger errors due to modeling.

In reverse shoulder arthroplasties (RSA), osseous in-growth is promoted if glenoid micromotion does not exceed 150 μm. The purpose of this study was to determine whether the configuration of central fixation for RSA glenoid baseplates reduces implant micromotion or changes scapula bone stresses. Using finite element analysis, glenoid baseplate fixation was tested in a cohort of 3 male and 2 female patients who were to undergo RSA. Computer models were created for 3 different RSA glenoid baseplate and 84 glenosphere designs, a central threaded peg (1 variant, D-TP), a central unthreaded peg (2 variants, I- 85 P(15) and I-P(25)), and a central peg with a screw (2 variants, A-PS and I-PS). A compressive and shear force of 756 N was distributed across the glenosphere with the scapula anchored. Displacement was within 20-130 μm at the glenosphere baseplate-bone interface for all baseplates. The glenospheres with unthreaded pegs had intermediate displacement values (I-P(15): median, 89 μm; range, 32-112 μm; and I-P(25): median, 93 μm; range, 31-109 μm). The von Mises stresses were 1.8-7.0 MPa within cortical bone and 0.6-1.6 MPa within trabecular bone. Cortical bone stresses were similar with unthreaded pegs (I-P(15): median, 4.2 MPa; range, 1.8-6.0 MPa; and I-P(25): median, 4.2 MPa; range, 1.8-6.1 MPa), whereas mean trabecular stresses were similar for all configurations. All configurations yielded adequate stability, with micromotions being below 150 μm. The unthreaded pegged designs provided a valid alternative to the stable threaded pegged convex baseplates in terms of micromotions and bone stresses.