Aims. Research on hip biomechanics has analyzed femoroacetabular contact pressures and forces in distinct hip conditions, with different procedures, and used diverse loading and testing conditions. The aim of this scoping review was to identify and summarize the available evidence in the literature for hip contact pressures and force in cadaver and in vivo studies, and how joint loading, labral status, and femoral and acetabular morphology can affect these biomechanical parameters. Methods. We used the PRISMA extension for scoping reviews for this literature search in three databases. After screening, 16 studies were included for the final analysis. Results. The studies assessed different hip conditions like labrum status, the biomechanical effect of the cam, femoral version, acetabular coverage, and the effect of rim trimming. The testing and loading conditions were also quite diverse, and this disparity limits direct comparisons between the different researches. With normal anatomy the mean contact pressures ranged from 1.54 to 4.4 MPa, and the average peak contact pressures ranged from 2 to 9.3 MPa. Labral tear or resection showed an increase in contact pressures that diminished after repair or reconstruction of the labrum. Complete cam resection also decreased the contact pressure, and acetabular rim resection of 6 mm increased the contact pressure at the acetabular base. Conclusion. To date there is no standardized methodology to access hip contact biomechanics in hip arthroscopy, or with the preservation of the periarticular soft-tissues. A tendency towards improved biomechanics (lower contact pressures) was seen with labral repair and reconstruction techniques as well as with cam correction. Cite this article: Bone Joint Res 2023;12(12):712–721

Aims. The aim of this study was to compare the biomechanical models of two frequently used techniques for reconstructing severe acetabular defects with pelvic discontinuity in revision total hip arthroplasty (THA) – the Trabecular Metal Acetabular Revision System (TMARS) and custom triflange acetabular components (CTACs) – using virtual modelling. Methods. Pre- and postoperative CT scans from ten patients who underwent revision with the TMARS for a Paprosky IIIB acetabular defect with pelvic discontinuity were retrospectively collated. Computer models of a CTAC implant were designed from the preoperative CT scans of these patients. Computer models of the TMARS reconstruction were segmented from postoperative CT scans using a semi-automated method. The amount of bone removed, the implant-bone apposition that was achieved, and the restoration of the centre of rotation of the hip were compared between all the actual TMARS and the virtual CTAC implants. Results. The median amount of bone removed for TMARS reconstructions was significantly greater than for CTAC implants (9.07 cm. 3. (interquartile range (IQR) 5.86 to 21.42) vs 1.16 cm. 3. (IQR 0.42 to 3.53) (p = 0.004). There was no significant difference between the median overall implant-bone apposition between TMARS reconstructions and CTAC implants (54.8 cm. 2. (IQR 28.2 to 82.3) vs 56.6 cm. 2. (IQR 40.6 to 69.7) (p = 0.683). However, there was significantly more implant-bone apposition within the residual acetabulum (45.2 cm. 2. (IQR 28.2 to 72.4) vs 25.5 cm. 2. (IQR 12.8 to 44.1) (p = 0.001) and conversely significantly less apposition with the outer cortex of the pelvis for TMARS implants compared with CTAC reconstructions (0 cm. 2. (IQR 0 to 13.1) vs 23.2 cm. 2. (IQR 16.4 to 30.6) (p = 0.009). The mean centre of rotation of the hip of TMARS reconstructions differed by a mean of 11.1 mm (3 to 28) compared with CTAC implants. Conclusion. In using TMARS, more bone is removed, thus achieving more implant-bone apposition within the residual acetabular bone. In CTAC implants, the amount of bone removed is minimal, while the implant-bone apposition is more evenly distributed between the residual acetabulum and the outer cortex of the pelvis. The differences suggest that these implants used to treat pelvic discontinuity might achieve short- and long-term stability through different biomechanical mechanisms. Cite this article: Bone Joint J 2024;106-B(5 Supple B):74–81

Objectives. Legg–Calvé–Perthes’ disease (LCP) is an idiopathic osteonecrosis of the femoral head that is most common in children between four and eight years old. The factors that lead to the onset of LCP are still unclear; however, it is believed that interruption of the blood supply to the developing epiphysis is an important factor in the development of the condition. Methods. Finite element analysis modelling of the blood supply to the juvenile epiphysis was investigated to understand under which circumstances the blood vessels supplying the femoral epiphysis could become obstructed. The identification of these conditions is likely to be important in understanding the biomechanics of LCP. Results. The results support the hypothesis that vascular obstruction to the epiphysis may arise when there is delayed ossification and when articular cartilage has reduced stiffness under compression. Conclusion. The findings support the theory of vascular occlusion as being important in the pathophysiology of Perthes disease. Cite this article: M. Pinheiro, C. A. Dobson, D. Perry, M. J. Fagan. New insights into the biomechanics of Legg-Calvé-Perthes’ disease: The Role of Epiphyseal Skeletal Immaturity in Vascular Obstruction. Bone Joint Res 2018;7:148–156. DOI: 10.1302/2046-3758.72.BJR-2017-0191.R1

Aims. The hip’s capsular ligaments passively restrain extreme range of movement (ROM) by wrapping around the native femoral head/neck. We determined the effect of hip resurfacing arthroplasty (HRA), dual-mobility total hip arthroplasty (DM-THA), conventional THA, and surgical approach on ligament function. Materials and Methods. Eight paired cadaveric hip joints were skeletonized but retained the hip capsule. Capsular ROM restraint during controlled internal rotation (IR) and external rotation (ER) was measured before and after HRA, DM-THA, and conventional THA, with a posterior (right hips) and anterior capsulotomy (left hips). Results. Hip resurfacing provided a near-native ROM with between 5° to 17° increase in IR/ER ROM compared with the native hip for the different positions tested, which was a 9% to 33% increase. DM-THA generated a 9° to 61° (18% to 121%) increase in ROM. Conventional THA generated a 52° to 100° (94% to 199%) increase in ROM. Thus, for conventional THA, the capsule function that exerts a limit on ROM is lost. It is restored to some extent by DM-THA, and almost fully restored by hip resurfacing. In positions of low flexion/extension, the posterior capsulotomy provided more normal function than the anterior, possibly because the capsule was shortened during posterior repair. However, in deep flexion positions, the anterior capsulotomy functioned better. Conclusion. Native head-size and capsular repair preserves capsular function after arthroplasty. The anterior and posterior approach differentially affect postoperative biomechanical function of the capsular ligaments. Cite this article: Bone Joint J 2019;101-B:426–434

Aims. It has been well documented in the arthroplasty literature that lumbar degenerative disc disease (DDD) contributes to abnormal spinopelvic motion. However, the relationship between the severity or pattern of hip osteoarthritis (OA) as measured on an anteroposterior (AP) pelvic view and spinopelvic biomechanics has not been well investigated. Therefore, the aim of the study is to examine the association between the severity and pattern of hip OA and spinopelvic motion. Methods. A retrospective chart review was conducted to identify patients undergoing primary total hip arthroplasty (THA). Plain AP pelvic radiographs were reviewed to document the morphological characteristic of osteoarthritic hips. Lateral spine-pelvis-hip sitting and standing plain radiographs were used to measure sacral slope (SS) and pelvic femoral angle (PFA) in each position. Lumbar disc spaces were measured to determine the presence of DDD. The difference between sitting and standing SS and PFA were calculated to quantify spinopelvic motion (ΔSS) and hip motion (ΔPFA), respectively. Univariate analysis and Pearson correlation were used to identify morphological hip characteristics associated with changes in spinopelvic motion. Results. In total, 139 patients were included. Increased spinopelvic motion was observed in patients with loss of femoral head contour, cam deformity, and acetabular bone loss (all p < 0.05). Loss of hip motion was observed in patients with loss of femoral head contour, cam deformity, and acetabular bone loss (all p < 0.001). A decreased joint space was associated with a decreased ΔPFA (p = 0.040). The presence of disc space narrowing, disc space narrowing > two levels, and disc narrowing involving the L5–S1 segment were associated with decreased spinopelvic motion (all p < 0.05). Conclusion. Preoperative hip OA as assessed on an AP pelvic radiograph predicts spinopelvic motion. These data suggest that specific hip osteoarthritic morphological characteristics listed above alter spinopelvic motion to a greater extent than others. Cite this article: Bone Joint J 2023;105-B(5):496–503

The advent of modular porous metal augments has ushered in a new form of treatment for acetabular bone loss. The function of an augment can be seen as reducing the size of a defect or reconstituting the anterosuperior/posteroinferior columns and/or allowing supplementary fixation. Depending on the function of the augment, the surgeon can decide on the sequence of introduction of the hemispherical shell, before or after the augment. Augments should always, however, be used with cement to form a unit with the acetabular component. Given their versatility, augments also allow the use of a hemispherical shell in a position that restores the centre of rotation and biomechanics of the hip. Progressive shedding or the appearance of metal debris is a particular finding with augments and, with other radiological signs of failure, should be recognized on serial radiographs. Mid- to long-term outcomes in studies reporting the use of augments with hemispherical shells in revision total hip arthroplasty have shown rates of survival of > 90%. However, a higher risk of failure has been reported when augments have been used for patients with chronic pelvic discontinuity. Cite this article: Bone Joint J 2024;106-B(4):312–318

Aims. Precise implant positioning, tailored to individual spinopelvic biomechanics and phenotype, is paramount for stability in total hip arthroplasty (THA). Despite a few studies on instability prediction, there is a notable gap in research utilizing artificial intelligence (AI). The objective of our pilot study was to evaluate the feasibility of developing an AI algorithm tailored to individual spinopelvic mechanics and patient phenotype for predicting impingement. Methods. This international, multicentre prospective cohort study across two centres encompassed 157 adults undergoing primary robotic arm-assisted THA. Impingement during specific flexion and extension stances was identified using the virtual range of motion (ROM) tool of the robotic software. The primary AI model, the Light Gradient-Boosting Machine (LGBM), used tabular data to predict impingement presence, direction (flexion or extension), and type. A secondary model integrating tabular data with plain anteroposterior pelvis radiographs was evaluated to assess for any potential enhancement in prediction accuracy. Results. We identified nine predictors from an analysis of baseline spinopelvic characteristics and surgical planning parameters. Using fivefold cross-validation, the LGBM achieved 70.2% impingement prediction accuracy. With impingement data, the LGBM estimated direction with 85% accuracy, while the support vector machine (SVM) determined impingement type with 72.9% accuracy. After integrating imaging data with a multilayer perceptron (tabular) and a convolutional neural network (radiograph), the LGBM’s prediction was 68.1%. Both combined and LGBM-only had similar impingement direction prediction rates (around 84.5%). Conclusion. This study is a pioneering effort in leveraging AI for impingement prediction in THA, utilizing a comprehensive, real-world clinical dataset. Our machine-learning algorithm demonstrated promising accuracy in predicting impingement, its type, and direction. While the addition of imaging data to our deep-learning algorithm did not boost accuracy, the potential for refined annotations, such as landmark markings, offers avenues for future enhancement. Prior to clinical integration, external validation and larger-scale testing of this algorithm are essential. Cite this article: Bone Jt Open 2024;5(8):671–680

Objectives. Malalignment of the tibial component could influence the long-term survival of a total knee arthroplasty (TKA). The object of this study was to investigate the biomechanical effect of varus and valgus malalignment on the tibial component under stance-phase gait cycle loading conditions. Methods. Validated finite element models for varus and valgus malalignment by 3° and 5° were developed to evaluate the effect of malalignment on the tibial component in TKA. Maximum contact stress and contact area on a polyethylene insert, maximum contact stress on patellar button and the collateral ligament force were investigated. Results. There was greater total contact stress in the varus alignment than in the valgus, with more marked difference on the medial side. An increase in ligament force was clearly demonstrated, especially in the valgus alignment and force exerted on the medial collateral ligament also increased. Conclusion. These results highlight the importance of accurate surgical reconstruction of the coronal tibial alignment of the knee joint. Varus and valgus alignments will influence wear and ligament stability, respectively in TKA. Cite this article: D-S. Suh, K-T. Kang, J. Son, O-R. Kwon, C. Baek, Y-G. Koh. Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis. Bone Joint Res 2017;6:623–630. DOI: 10.1302/2046-3758.611.BJR-2016-0088.R2

Objectives. Posterior condylar offset (PCO) and posterior tibial slope (PTS) are critical factors in total knee arthroplasty (TKA). A computational simulation was performed to evaluate the biomechanical effect of PCO and PTS on cruciate retaining TKA. Methods. We generated a subject-specific computational model followed by the development of ± 1 mm, ± 2 mm and ± 3 mm PCO models in the posterior direction, and -3°, 0°, 3° and 6° PTS models with each of the PCO models. Using a validated finite element (FE) model, we investigated the influence of the changes in PCO and PTS on the contact stress in the patellar button and the forces on the posterior cruciate ligament (PCL), patellar tendon and quadriceps muscles under the deep knee-bend loading conditions. Results. Contact stress on the patellar button increased and decreased as PCO translated to the anterior and posterior directions, respectively. In addition, contact stress on the patellar button decreased as PTS increased. These trends were consistent in the FE models with altered PCO. Higher quadriceps muscle and patellar tendon force are required as PCO translated in the anterior direction with an equivalent flexion angle. However, as PTS increased, quadriceps muscle and patellar tendon force reduced in each PCO condition. The forces exerted on the PCL increased as PCO translated to the posterior direction and decreased as PTS increased. Conclusion. The change in PCO alternatively provided positive and negative biomechanical effects, but it led to a reduction in a negative biomechanical effect as PTS increased. Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, J-S. Lee, S. K. Kwon. A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty. Bone Joint Res 2018;7:69–78. DOI: 10.1302/2046-3758.71.BJR-2017-0143.R1

There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision. A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability. Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity

Aims

The objectives of this study were to assess the effect of anterior cruciate ligament (ACL) resection on flexion-extension gaps, mediolateral soft tissue laxity, maximum knee extension, and limb alignment during primary total knee arthroplasty (TKA).

Objectives. External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF). Methods. A fracture gap model was created to simulate comminuted mid-shaft tibia fractures using synthetic composite bones. Fifteen constructs were stabilised with ET-LCP, ESS-LCP or UEF (five constructs each). The constructs were loaded under both axial and torsional directions to determine construct stiffness. Results. The mean axial stiffness was very similar for UEF (528 N/mm) and ESS-LCP (525 N/mm), while it was slightly lower for ET-LCP (469 N/mm). One-way analysis of variance (ANOVA) testing in all three groups demonstrated no significant difference (F(2,12) = 2.057, p = 0.171). There was a significant difference in mean torsional stiffness between the UEF (0.512 Nm/degree), the ESS-LCP (0.686 Nm/degree) and the ET-LCP (0.639 Nm/degree), as determined by one-way ANOVA (F(2,12) = 6.204, p = 0.014). A Tukey post hoc test revealed that the torsional stiffness of the ESS-LCP was statistically higher than that of the UEF by 0.174 Nm/degree (p = 0.013). No catastrophic failures were observed. Conclusion. Using the LCP as an external fixator may provide a viable and attractive alternative to the traditional UEF as its lower profile makes it more acceptable to patients, while not compromising on axial and torsional stiffness. Cite this article: B. F. H. Ang, J. Y. Chen, A. K. S. Yew, S. K. Chua, S. M. Chou, S. L. Chia, J. S. B. Koh, T. S. Howe. Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness. Bone Joint Res 2017;6:216–223. DOI: 10.1302/2046-3758.64.2000470

A consecutive series of 150 patients with clavicular fractures is presented. In 81% detailed information regarding the mechanism of the injury was available and, of these, 94% had fractured their clavicle from a direct blow on the shoulder; only 6% had fallen on the outstretched hand. This finding, at variance with commonly held views regarding the mechanism of this injury, was further investigated by biomechanical analysis of the forces involved in clavicular fractures. The biomechanical model supported the clinical findings

Aims

The aim of this study was to compare any differences in the primary outcome (biphasic flexion knee moment during gait) of robotic arm-assisted bi-unicompartmental knee arthroplasty (bi-UKA) with conventional mechanically aligned total knee arthroplasty (TKA) at one year post-surgery.

Objectives. Malrotation of the femoral component can result in post-operative complications in total knee arthroplasty (TKA), including patellar maltracking. Therefore, we used computational simulation to investigate the influence of femoral malrotation on contact stresses on the polyethylene (PE) insert and on the patellar button as well as on the forces on the collateral ligaments. Materials and Methods. Validated finite element (FE) models, for internal and external malrotations from 0° to 10° with regard to the neutral position, were developed to evaluate the effect of malrotation on the femoral component in TKA. Femoral malrotation in TKA on the knee joint was simulated in walking stance-phase gait and squat loading conditions. Results. Contact stress on the medial side of the PE insert increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. There was an opposite trend in the lateral side of the PE insert case. Contact stress on the patellar button increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. In particular, contact stress on the patellar button increased by 98% with internal malrotation of 10° in the squat loading condition. The force on the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) increased with internal and external femoral malrotations, respectively. Conclusions. These findings provide support for orthopaedic surgeons to determine a more accurate femoral component alignment in order to reduce post-operative PE problems. Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, C. Baek, S. H. Jung, K. K. Park. Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation. Bone Joint Res 2016;5:552–559. DOI: 10.1302/2046-3758.511.BJR-2016-0107.R1

Objectives. The goals of this study were: 1) to determine if high-fat diet (HFD) feeding in female mice would negatively impact biomechanical and histologic consequences on the Achilles tendon and quadriceps muscle; and 2) to investigate whether exercise and branched-chain amino acid (BCAA) supplementation would affect these parameters or attenuate any negative consequences resulting from HFD consumption. Methods. We examined the effects of 16 weeks of 60% HFD feeding, voluntary exercise (free choice wheel running) and BCAA administration in female C57BL/6 mice. The Achilles tendons and quadriceps muscles were removed at the end of the experiment and assessed histologically and biomechanically. Results. HFD feeding significantly decreased the Achilles tendon modulus without histological alterations. BCAA administration significantly decreased the stiffness of Achilles tendons in the exercised normal diet mice. Exercise partially ameliorated both the weight gain and glucose levels in the HFD-fed mice, led to a significant decrease in the maximum load of the Achilles tendon, and an increase in the average fibril diameter of the quadriceps femoris muscle. There were significant correlations between body weight and several biomechanical properties, demonstrating the importance of controlling obesity for maintaining healthy tendon properties. . Conclusions. In summary, this study showed a significant impact of obesity and body weight on tendon biomechanical properties with limited effects of exercise and BCAAs. Cite this article: Bone Joint Res 2013;2:186–92

The purpose of this study was to test the hypothesis that patella alta leads to a less favourable situation in terms of patellofemoral contact force, contact area and contact pressure than the normal patellar position, and thereby gives rise to anterior knee pain. A dynamic knee simulator system based on the Oxford rig and allowing six degrees of freedom was adapted in order to simulate and record the dynamic loads during a knee squat from 30° to 120° flexion under physiological conditions. Five different configurations were studied, with variable predetermined patellar heights. The patellofemoral contact force increased with increasing knee flexion until contact occurred between the quadriceps tendon and the femoral trochlea, inducing load sharing. Patella alta caused a delay of this contact until deeper flexion. As a consequence, the maximal patellofemoral contact force and contact pressure increased significantly with increasing patellar height (p < 0.01). Patella alta was associated with the highest maximal patellofemoral contact force and contact pressure. When averaged across all flexion angles, a normal patellar position was associated with the lowest contact pressures. Our results indicate that there is a biomechanical reason for anterior knee pain in patients with patella alta

This animal study compares different methods of performing an osteotomy, including using an Erbium-doped Yttrium Aluminum Garnet laser, histologically, radiologically and biomechanically. A total of 24 New Zealand rabbits were divided into four groups (Group I: multihole-drilling; Group II: Gigli saw; Group III: electrical saw blade and Group IV: laser). A proximal transverse diaphyseal osteotomy was performed on the right tibias of the rabbits after the application of a circular external fixator. The rabbits were killed six weeks after the procedure, the operated tibias were resected and radiographs taken. . The specimens were tested biomechanically using three-point bending forces, and four tibias from each group were examined histologically. Outcome parameters were the biomechanical stability of the tibias as assessed by the failure to load and radiographic and histological examination of the osteotomy site. . The osteotomies healed in all specimens both radiographically and histologically. The differences in the mean radiographic (p = 0.568) and histological (p = 0.71) scores, and in the mean failure loads (p = 0.180) were not statistically significant between the groups. . Different methods of performing an osteotomy give similar quality of union. The laser osteotomy, which is not widely used in orthopaedics is an alternative to the current methods. Cite this article: Bone Joint J 2015;97-B:1628–33

Objectives. Secondary fracture healing is strongly influenced by the stiffness of the bone-fixator system. Biomechanical tests are extensively used to investigate stiffness and strength of fixation devices. The stiffness values reported in the literature for locked plating, however, vary by three orders of magnitude. The aim of this study was to examine the influence that the method of restraint and load application has on the stiffness produced, the strain distribution within the bone, and the stresses in the implant for locking plate constructs. Methods. Synthetic composite bones were used to evaluate experimentally the influence of four different methods of loading and restraining specimens, all used in recent previous studies. Two plate types and three screw arrangements were also evaluated for each loading scenario. Computational models were also developed and validated using the experimental tests. Results. The method of loading was found to affect the gap stiffness strongly (by up to six times) but also the magnitude of the plate stress and the location and magnitude of strains at the bone-screw interface. Conclusions. This study demonstrates that the method of loading is responsible for much of the difference in reported stiffness values in the literature. It also shows that previous contradictory findings, such as the influence of working length and very large differences in failure loads, can be readily explained by the choice of loading condition. Cite this article: A. MacLeod, A. H. R. W. Simpson, P. Pankaj. Experimental and numerical investigation into the influence of loading conditions in biomechanical testing of locking plate fracture fixation devices. Bone Joint Res 2018;7:111–120. DOI: 10.1302/2046-3758.71.BJR-2017-0074.R2

A study was made of the mechanics of blood-bearing in a series of patients treated with a cast-brace for fracture of the distal femur. Knee hinges incorporating strain-gauges, a simple force-plate on the floor and a standardised weight-bearing test were used to record axial loads through the cast-brace itself and through the fracture during the phases of healing. The cast-brace carried loads of only 10 to 20 per cent of body weight and functioned mainly as an antibuckling hinged tube. Patterns of weight-bearing recovery showed that the fracture itself limited loads to safe levels. A measure of the recovery of strength at the fracture was determined and termed the "fracture load index". Graphs obtained in this way demonstrated four biomechanical phases of bony union which correlated well with the stages of clinical healing. The clinical application of these results have led to improvements in the design of braces and the use of a cylinder cast-brace for fractures of the distal half of the femoral shaft and of a new type of brace with a hinge at the hip attached to the thigh cast for fractures of the proximal shaft. A simple clinical test is described by which it is possible to monitor the healing of fractures in cast-braces

This paper presents a prospective trial carried out using the Monk "soft top" endoprosthesis in 33 patients. Two years after operation 70 per cent of the remaining patients had pain. A biomechanical and histopathological analysis of the endoprosthesis and the surrounding tissue, obtained from a further two patients at the time of revision, is presented. It is concluded that the prosthesis has inherent design faults which result in excessive wear of the polyethylene component. The wear debris produced stimulates a prolific fibrous tissue reaction which is associated with progressive clinical deterioration

Aims

The aim of this study was to compare the peak pull-out force (PPF) of pedicle-lengthening screws (PLS) and traditional pedicle screws (TPS) using instant and cyclic fatigue testing.

Objectives. Initial stability of tibial trays is crucial for long-term success of total knee arthroplasty (TKA) in both primary and revision settings. Rotating platform (RP) designs reduce torque transfer at the tibiofemoral interface. We asked if this reduced torque transfer in RP designs resulted in subsequently reduced micromotion at the cemented fixation interface between the prosthesis component and the adjacent bone. Methods. Composite tibias were implanted with fixed and RP primary and revision tibial trays and biomechanically tested under up to 2.5 kN of axial compression and 10° of external femoral component rotation. Relative micromotion between the implanted tibial tray and the neighbouring bone was quantified using high-precision digital image correlation techniques. Results. Rotational malalignment between femoral and tibial components generated 40% less overall tibial tray micromotion in RP designs than in standard fixed bearing tibial trays. RP trays reduced micromotion by up to 172 µm in axial compression and 84 µm in rotational malalignment models. Conclusions. Reduced torque transfer at the tibiofemoral interface in RP tibial trays reduces relative component micromotion and may aid long-term stability in cases of revision TKA or poor bone quality. Cite this article: Mr S. R. Small. Micromotion at the tibial plateau in primary and revision total knee arthroplasty: fixed versus rotating platform designs. Bone Joint Res 2016;5:122–129. DOI: 10.1302/2046-3758.54.2000481

We evaluated the biomechanical properties of two different methods of fixation for unstable fractures of the proximal humerus. Biomechanical testing of the two groups, locking plate alone (LP), and locking plate with a fibular strut graft (LPSG), was performed using seven pairs of human cadaveric humeri. Cyclical loads between 10 N and 80 N at 5 Hz were applied for 1 000 000 cycles. Immediately after cycling, an increasing axial load was applied at a rate of displacement of 5 mm/min. The displacement of the construct, maximum failure load, stiffness and mode of failure were compared. The displacement was significantly less in the LPSG group than in the LP group (p = 0.031). All maximum failure loads and measures of stiffness in the LPSG group were significantly higher than those in the LP group (p = 0.024 and p = 0.035, respectively). In the LP group, varus collapse and plate bending were seen. In the LPSG group, the humeral head cut out and the fibular strut grafts fractured. No broken plates or screws were seen in either group. We conclude that strut graft augmentation significantly increases both the maximum failure load and the initial stiffness of this construct compared with a locking plate alone

We performed a biomechanical study to compare the augmentation of isolated fractured vertebral bodies using two different bone tamps. Compression fractures were created in 21 vertebral bodies harvested from red deer after determining their initial strength and stiffness, which was then assessed after standardised bipedicular vertebral augmentation using a balloon or an expandable polymer bone tamp. The median strength and stiffness of the balloon bone tamp group was 6.71 kN (. sd. 2.71) and 1.885 kN/mm (. sd. 0.340), respectively, versus 7.36 kN (. sd. 3.43) and 1.882 kN/mm (. sd. 0.868) in the polymer bone tamp group. The strength and stiffness tended to be greater in the polymer bone tamp group than in the balloon bone tamp group, but this difference was not statistically significant (strength p > 0.8, and stiffness p = 0.4)

Repeated trauma to the radial head may be one of the causative factors in the genesis of osteochondritis dissecans of the capitellum. We measured the force, contact area and pressure across the radiocapitellar articulation of the elbow before and after radial shortening osteotomy in five fresh-frozen cadaver upper limbs with loads of 45, 90 and 135 N, respectively. Measurements were made on pressure-sensitive film placed in the radiocapitellar articulation with the forearm in the supinated, neutral and pronated positions before and after radial shortening. Radial shortening significantly reduced the mean force and contact area across the radiocapitellar articulation in all positions of the forearm.

We examined the effect of the Gamma nail on strain distribution in the proximal femur, using ten cadaver femora instrumented with six unidirectional strain gauges along the medial and lateral cortices. The femora were loaded to 1800 N and strains were determined with or without distal interlocking screws before and after experimentally created two-part and four-part fractures. Motion of the sliding screw and the nail was also determined. Strain patterns and screw motion were compared with previously obtained values for a sliding hip screw device (SHS). The Gamma nail was shown to transmit decreasing load to the calcar with decreasing fracture stability, such that virtually no strain on the bone was seen in four-part fractures with the posteromedial fragment removed; increasing compression was noted, however, at the proximal lateral cortex. Conversely, the SHS showed increased calcar compression with decreasing fracture stability. The insertion of distal interlocking screws did not change the pattern of proximal femoral strain. The Gamma nail imparts non-physiological strains to the proximal femur, probably because of its inherent stiffness. These strains may alter bone remodelling and interfere with healing. Distal interlocking screws may not be necessary for stable intertrochanteric fractures.

The aim of this study was to examine the loading of the other joints of the lower limb in patients with unilateral osteoarthritis (OA) of the knee. We recruited 20 patients with no other symptoms or deformity in the lower limbs from a consecutive cohort of patients awaiting knee replacement. Gait analysis and electromyographic recordings were performed to determine moments at both knees and hips, and contraction patterns in the medial and lateral quadriceps and hamstrings bilaterally. The speed of gait was reduced in the group with OA compared with the controls, but there were only minor differences in stance times between the limbs. Patients with OA of the knee had significant increases in adduction moment impulse at both knees and the contralateral hip (adjusted p-values: affected knee: p < 0.01, unaffected knee p = 0.048, contralateral hip p = 0.03), and significantly increased muscular co-contraction bilaterally compared with controls (all comparisons for co-contraction, p < 0.01).

The other major weight-bearing joints are at risk from abnormal biomechanics in patients with unilateral OA of the knee.

Cite this article: Bone Joint J 2013;95-B:348–53.

The use of prolonged halo stabilisation in a child is increasingly indicated for trauma and congenital instability of the cervical spine, but complications of pin fixation in this age group are frequent. We have analysed four aspects of the mechanics of the halo pin: the forces applied by each of six surgeons was shown to vary widely, penetration of the inner table occurred relatively easily, friction at the pin-halo interface influenced forces, and the skull thickness measured by CT scan varied from 1.1 mm to 4.3 mm in children under six years of age. We recommend CT scanning of the skull before elective halo application in young children to ascertain the safest pin sites.

The effects of advancement of the tibial tuberosity by inserting bony wedges was studied on cadaveric specimens of the knee. The geometry, the contact areas and the forces acting on the patellofemoral joint were investigated, and the forces acting on the tibiofemoral compartment were calculated. A 1 cm advancement was found to be optimal in reducing the high patellofemoral joint forces occurring at 90 degrees and 110 degrees of flexion, whilst causing least reduction of the contact areas; the stresses on the joint were reduced significantly. Advancement by 2 cm and by 3 cm drastically reduced the congruity and the size of the contact area. It was also shown that 2 cm and 3 cm advancement caused an increase in forces at the patellofemoral joint and also in the tibiofemoral joint in a direction tangential to the articular surfaces.

Objectives

Cadaveric models of the shoulder evaluate discrete motion segments using the glenohumeral joint in isolation over a defined trajectory. The aim of this study was to design, manufacture and validate a robotic system to accurately create three-dimensional movement of the upper body and capture it using high-speed motion cameras.

We compared the bulking and tensile strength of the Pennington modified Kessler, Cruciate and the Savage repairs in an ex vivo model. A total of 60 porcine tendons were randomised to three groups, half repaired using a core suture alone and the remainder employing a core and peripheral technique. The tendons were distracted to failure. The force required to produce a 3 mm gap, the ultimate strength, the mode of failure and bulking for each repair were assessed. We found that there was a significant increase in strength without an increase in bulk as the number of strands increased. The Cruciate repair was significantly more likely to fail by suture pullout than the Pennington modified Kessler or Savage repairs. We advise the use of the Savage repair, especially in the thumb, and a Cruciate when a Savage is not possible. The Pennington modified Kessler repair should be reserved for multiple tendon injuries.

The anterior cruciate ligament was replaced in rabbits, using implants of carbon or polyester filaments with known mechanical properties. The biocompatibility of the implants was assessed in detail using light microscopy, and scanning and transmission electron microscopy. Mechanical tests were made of stability, in comparison with normal joints and controls after excision of the ligament. Some carbon fibre implants broke down in vivo, allowing instability; the fragments caused chronic inflammation. Intact carbon implants did not induce the formation of neoligaments; they were covered by tissue, but there was no ingrowth. Polyester did not degrade mechanically and supported early collagenous ingrowth within the implant, even in the mid-joint space. It was concluded that there was no justification for the use of carbon fibres as anterior cruciate replacements; polyester appeared to be suitable.

The off-loading characteristics of the cast-braces of 30 patients with fractures of the shaft of the femur have been investigated, during axial loading, using strain-gauge transducers. These were applied at the level of the fracture, where the cast was circumferentially split, and to the hinges of the brace at the knee. They measured the load transferred between the two portions of the thigh cast, and between the thigh cast as a whole and the below-knee cast; by subtraction from the total load on the limb, the skeletal force at the fracture level and at the knee could be calculated. In all patients there was an increase in the fracture load as union progressed which was thought to be due to physiological feedback mechanism from the fracture site. The load carried by the two portions of the thigh cast and by the thigh cast as a whole was proportionately high at first and stabilised at an average of 35 per cent of body weight.

In 65 mature Wistar rats a Kirschner wire was introduced into the medullary cavity of each femur. A closed transverse mid-shaft fracture of one femur was produced by a three-point bending technique. Subsequently the mechanical characteristics of the healing fracture, including the torque and angle of twist required to take the callus to its yield point and to ultimate failure, were compared with those for the opposite femur of each rat. Controls were killed in groups at two, three, four, five and seven weeks. Test animals were given bovine growth hormone in a daily dose of five milligrams before being killed in groups at two, three and four weeks. A significant increase in torque index was found in the two-week group of test animals but not in subsequent groups. No evidence was found that growth hormone given alone could produce an overall shortening of the healing time in fresh fractures.

Nine patients with nonunited humeral shaft fractures were treated by open reduction and internal fixation with an intramedullary fibular bone graft and a compression plate. Fixation of the screws was enhanced by passing them through the fibula as well as the two humeral cortices (quadricortical fixation). Eight of the nine fractures united at an average of 3.5 months. Tests on cadaver bones showed that quadricortical fixation was as strong as methylmethacrylate augmentation and significantly better than bicortical fixation.

Using 26 cadaver shoulders, we produced a standard defect in the supraspinatus tendon and performed one of three types of repair. Their strength was found by testing in tension the force required to produce a gap of 3 mm, then 6 mm, and finally total disruption of the repair. The use of a polyethylene patch to spread the forces over the lateral bone surface and of extra sutures to grasp the tendon end raised by 2.6 times the load at which a 3 mm gap in the repair occurred and by 1.7 times the load to failure.

A leading problem with cementless hip replacement is thigh pain, probably due to some degree of loosening. This is most pronounced during activities such as stair climbing or getting up from a chair. Our study compares the immediate fixation of three stems in widespread clinical use, using a cadaver test simulation in which the femur was horizontal, and cyclic forces acted vertically downward on the prosthetic head with gradual increments of load. We implanted and tested 18 pairs of femurs, making analyses between stem types by right to left comparisons. We found no statistically significant differences in loosening between cementless AML and PCA prostheses, but cemented stems withstood greater loads than uncemented stems by a factor of five or more.

To investigate the origin of fractures at the distal locking site of the Gamma nail, we loaded ten paired human cadaver femora fixed with a Gamma nail in torsion until they fractured. When an awl was hammered in to start the hole for distal locking a fissure appeared in the lateral cortex of all the femora, and the mean torsional load to create a fracture was reduced by 57.8% compared with that in a control group in which the distal locking hole had been started with a centre drill. When an additional drill hole was made, the mean failure load in torsion decreased by 35.7%. We strongly recommend that an awl should not be used at the distal locking site of the Gamma nail; we recommend the use of a centre drill. Additional drill holes should be avoided because they act as stress raisers.