Aims. The aim of the study was to investigate whether the primary stability of press-fit acetabular components can be improved by altering the impaction procedure. Methods. Three impaction procedures were used to implant acetabular components into human cadaveric acetabula using a powered impaction device. An impaction frequency of 1 Hz until complete component seating served as reference. Overimpaction was simulated by adding ten strokes after complete component seating. High-frequency implantation was performed at 6 Hz. The lever-out moment of the acetabular components was used as measure for primary stability. Permanent bone deformation was assessed by comparison of double micro-CT (µCT) measurements before and after impaction. Acetabular component deformation and impaction forces were recorded, and the extent of bone-implant contact was determined from 3D laser scans. Results. Overimpaction reduced primary acetabular component stability (p = 0.038) but did not significantly increase strain release after implantation (p = 0.117) or plastic deformations (p = 0.193). Higher press-fits were associated with larger polar gaps for the 1 Hz reference impaction (p = 0.002, R. 2. = 0.77), with a similar trend for overimpaction (p = 0.082, R. 2. = 0.31). High-frequency impaction did not significantly increase primary stability (p = 0.170) at lower impaction forces (p = 0.001); it was associated with smaller plastic deformations (p = 0.035, R. 2. = 0.34) and a trend for increased acetabular component relaxation between strokes (p = 0.112). Higher press-fit was not related to larger polar gaps for the 6 Hz impaction (p = 0.346). Conclusion. Overimpaction of press-fit acetabular components should be prevented since additional strokes can be associated with increased bone damage and reduced primary stability as shown in this study. High-frequency impaction at 6 Hz was shown to be beneficial compared with 1 Hz impaction. This benefit has to be confirmed in clinical studies. Cite this article: Bone Joint J 2023;105-B(3):261–268

Aims. The aim of this prospective cohort study was to evaluate the early migration of the TriFit cementless proximally coated tapered femoral stem using radiostereometric analysis (RSA). Methods. A total of 21 patients (eight men and 13 women) undergoing primary total hip arthroplasty (THA) for osteoarthritis of the hip were recruited in this study and followed up for two years. Two patients were lost to follow-up. All patients received a TriFit stem and Trinity Cup with a vitamin E-infused highly cross-linked ultra-high molecular weight polyethylene liner. Radiographs for RSA were taken postoperatively and then at three, 12, and 24 months. Oxford Hip Score (OHS), EuroQol five-dimension questionnaire (EQ-5D), and adverse events were reported. Results. At two years, the mean subsidence of the head and tip for the TriFit stem was 0.38 mm (SD 0.32) and 0.52 mm (SD 0.36), respectively. The total migration of the head and tip was 0.55 mm (SD 0.32) and 0.71 mm (SD 0.38), respectively. There were no statistically significant differences between the three to 12 months' migration (p = 0.105) and 12 to 24 months' migration (p = 0.694). The OHS and EQ-5D showed significant improvements at two years. Conclusion. The results of this study suggest that the TriFit femoral stem achieves initial stability and is likely to be stable in the mid and long term. A long-term outcome study is required to assess late mechanisms of failure and the effects of bone mineral density (BMD) related changes. Cite this article: Bone Joint J 2021;103-B(4):644–649

Aims. The aim of this study was to determine the stability of a new short femoral stem compared with a conventional femoral stem in patients undergoing cementless total hip arthroplasty (THA), in a prospective randomized controlled trial using radiostereometric analysis (RSA). Patients and Methods. A total of 53 patients were randomized to receive cementless THA with either a short femoral stem (MiniHip, 26 patients, mean age: 52 years, nine male) or a conventional length femoral stem (MetaFix, 23 patients, mean age: 53 years, 11 male). All patients received the same cementless acetabular component. Two-year follow-up was available on 38 patients. Stability was assessed through migration and dynamically inducible micromotion. Radiographs for RSA were taken postoperatively and at three, six, 12, 18, and 24 months. Results. At two years, there was significantly less subsidence (inferior migration) of the short femoral stem (head, 0.26 mm, 95% confidence interval (CI) 0.08 to 0.43, . sd. 0.38; tip, 0.11 mm, 95% CI -0.08 to 0.31, . sd. 0.42) compared with the conventional stem (head, 0.62 mm, 95% CI 0.34 to 0.90, . sd. 0.56, p = 0.02; tip, 0.43 mm, 95% CI 0.21 to 0.65, . sd. 0.44, p = 0.03). There was no significant difference in dynamically inducible micromotion, rate of complications or functional outcome. Conclusion. This study demonstrates that the short femoral stem has a stable and predictable migration. However, longer-term survival analysis still needs to be determined. Cite this article: Bone Joint J 2018;100-B:1148–56

Aims. The introduction of a novel design of total knee arthroplasty (TKA) must achieve outcomes at least as good as existing designs. A novel design of TKA with a reducing radius of the femoral component and a modified cam-post articulation has been released and requires assessment of the fixation to bone. Radiostereometric analysis (RSA) of the components within the first two postoperative years has been shown to be predictive of medium- to long-term fixation. The aim of this study was to assess the stability of the tibial component of this system during this period of time using RSA. Patients and Methods. A cohort of 30 patients underwent primary, cemented TKA using the novel posterior stabilized fixed-bearing (ATTUNE) design. There was an even distribution of men and women (15:15). The mean age of the patients was 64 years (sd 8) at the time of surgery; their mean body mass index (BMI) was 35.4 kg/m2 (sd 7.9). RSA was used to assess the stability of the tibial component at 6, 12, and 24 months compared with a six-week baseline examination. Patient-reported outcome measures were also assessed. Results. The mean maximum total point motion (MTPM) of the tibial component between 12 and 24 months postoperatively was 0.08 mm (sd 0.08), which is well below the published threshold of 0.2 mm (p < 0.001). Patient-reported outcome measures consistently improved. Conclusion. The tibial component of this novel design of TKA showed stability between assessment 12 and 24 months postoperatively, suggesting an acceptably low risk of medium- to long-term failure due to aseptic loosening

Aims. Instability of the hip is the most common mode of failure after reconstruction with a proximal femoral arthroplasty (PFA) using an endoprosthesis after excision of a tumour. Small studies report improved stability with capsular repair of the hip and other techniques, but these have not been investigated in a large series of patients. The aim of this study was to evaluate variables associated with the patient and the operation that affect post-operative stability. We hypothesised an association between capsular repair and stability. Patients and Methods. In a retrospective cohort study, we identified 527 adult patients who were treated with a PFA for tumours. Our data included demographics, the pathological diagnosis, the amount of resection of the abductor muscles, the techniques of reconstruction and the characteristics of the implant. We used regression analysis to compare patients with and without post-operative instability. Results. A total of 20 patients out of 527 (4%) had instability which presented at a mean of 35 days (3 to 131) post-operatively. Capsular repair was not associated with a reduced rate of instability. Bivariate analysis showed that a posterolateral surgical approach (odds ratio (OR) 0.11, 95% confidence interval (CI) 0.02 to 0.86) and the type of implant (p = 0.046) had a significant association with reduced instability; age > 60 years predicted instability (OR 3.17, 95% CI 1.00 to 9.98). Multivariate analysis showed age > 60 years (OR 5.09, 95% CI 1.23 to 21.07), female gender (OR 1.73, 95% CI 1.04 to 2.89), a malignant primary bone tumour (OR 2.04, 95% CI 1.06 to 3.95), and benign condition (OR 5.56, 95% CI 1.35 to 22.90), but not metastatic disease or soft-tissue tumours, predicted instability, while a posterolateral approach (OR 0.09, 95% CI 0.01 to 0.53) was protective against instability. No instability occurred when a synthetic graft was used in 70 patients. Conclusion. Stability of the hip after PFA is influenced by variables associated with the patient, the pathology, the surgical technique and the implant. We did not find an association between capsular repair and improved stability. Extension of the tumour often dictates surgical technique; however, our results indicate that PFA using a posterolateral approach with a hemiarthroplasty and synthetic augment for soft-tissue repair confers the lowest risk of instability. Patients who are elderly, female, or with a primary benign or malignant bone tumour should be counselled about an increased risk of instability. Cite this article: Bone Joint J 2017;99-B:531–7

Aims. The aim of this study was to describe the use of 3D-printed sacral endoprostheses to reconstruct the pelvic ring and re-establish spinopelvic stability after total en bloc sacrectomy (TES) and to review its outcome. Patients and Methods. We retrospectively reviewed 32 patients who underwent TES in our hospital between January 2015 and December 2017. We divided the patients into three groups on the basis of the method of reconstruction: an endoprosthesis group (n = 10); a combined reconstruction group (n = 14), who underwent non-endoprosthetic combined reconstruction, including anterior spinal column fixation; and a spinopelvic fixation (SPF) group (n = 8), who underwent only SPF. Spinopelvic stability, implant survival (IS), intraoperative haemorrhage rate, and perioperative complication rate in the endoprosthesis group were documented and compared with those of other two groups. Results. The mean overall follow-up was 22.1 months (9 to 44). In the endoprosthesis group, the mean intraoperative hemorrhage was 3530 ml (1600 to 8100). Perioperative complications occurred in two patients; both had problems with wound healing. After a mean follow-up of 17.7 months (12 to 38), 9/10 patients could walk without aids and 8/10 patients were not using analgesics. Imaging evidence of implant failure was found in three patients, all of whom had breakage of screws and/or rods. Only one of these, who had a local recurrence, underwent re-operation, at which solid bone-endoprosthetic osseointegration was found. The mean IS using re-operation as the endpoint was 32.5 months (95% confidence interval 23.2 to 41.8). Compared with the other two groups, the endoprosthesis group had significantly better spinopelvic stability and IS with no greater intraoperative haemorrhage or perioperative complications. Conclusion. The use of 3D-printed endoprostheses for reconstruction after TES provides reliable spinopelvic stability and IS by facilitating osseointegration at the bone-implant interfaces, with acceptable levels of haemorrhage and complications. Cite this article: Bone Joint J 2019;101-B:880–888

Aims. The stability of cementless acetabular components is an important factor for surgical planning in the treatment of patients with pelvic osteolysis after total hip arthroplasty (THA). However, the methods for determining the stability of the acetabular component from pre-operative radiographs remain controversial. Our aim was to develop a scoring system to help in the assessment of the stability of the acetabular component under these circumstances. Patients and Methods. The new scoring system is based on the mechanism of failure of these components and the location of the osteolytic lesion, according to the DeLee and Charnley classification. Each zone is evaluated and scored separately. The sum of the individual scores from the three zones is reported as a total score with a maximum of 10 points. The study involved 96 revision procedures which were undertaken for wear or osteolysis in 91 patients between July 2002 and December 2012. Pre-operative anteroposterior pelvic radiographs and Judet views were reviewed. The stability of the acetabular component was confirmed intra-operatively. Results. Intra-operatively, it was found that 64 components were well-fixed and 32 were loose. Mean total scores in the well-fixed and loose components were 2.9 (0 to 7) and 7.2 (1 to 10), respectively (p < 0.001). In hips with a low score (0 to 2), the component was only loose in one of 33 hips (3%). The incidence of loosening increased with increasing scores: in those with scores of 3 and 4, two of 19 components (10.5%) were loose; in hips with scores of 5 and 6, eight of 19 components (44.5%) were loose; in hips with scores of 7 or 8, 13 of 17 components (70.6%) were loose; and for hips with scores of 9 and 10, nine of nine components (100%) were loose. Receiver-operating-characteristic curve analysis demonstrated very good accuracy (area under the curve = 0.90, p < 0.001). The optimal cutoff point was a score of ≥ 5 with a sensitivity of 0.79, and a specificity of 0.87. Conclusion. There was a strong correlation between the scoring system and the probability of loosening of a cementless acetabular component. This scoring system provides a clinically useful tool for pre-operative planning, and the evaluation of the outcome of revision surgery for patients with loosening of a cementless acetabular component in the presence of osteolysis. Cite this article: Bone Joint J 2017;99-B:601–6

Aseptic loosening of the femoral component is an important indication for revision surgery in unicompartmental knee replacement (UKR). A new design of femoral component with an additional peg was introduced for the cemented Oxford UKR to increase its stability. The purpose of this study was to compare the primary stability of the two designs of component. Medial Oxford UKR was performed in 12 pairs of human cadaver knees. In each pair, one knee received the single peg and one received the twin peg design. Three dimensional micromotion and subsidence of the component in relation to the bone was measured under cyclical loading at flexion of 40° and 70° using an optical measuring system. Wilcoxon matched pairs signed-rank test was performed to detect differences between the two groups. . There was no significant difference in the relative micromotion (p = 0.791 and 0.380, respectively) and subsidence (p = 0.301 and 0.176, respectively) of the component between the two groups at both angles of flexion. Both designs of component offered good strength of fixation in this cadaver study. Cite this article: Bone Joint J 2014;96-B:896–901

Aims

Reverse total shoulder arthroplasty (rTSA) can be used in complex cases when the glenoid requires reconstruction. In this study, a baseplate with composite bone autograft and a central trabecular titanium peg was implanted, and its migration was assessed for two years postoperatively using radiostereometric analysis (RSA).

Objective patellar instability has been correlated with dysplasia of the femoral trochlea. This in vitro study tested the hypothesis that trochleoplasty would increase patellar stability and normalise the kinematics of a knee with a dysplastic trochlea. Six fresh-frozen knees were loaded via the heads of the quadriceps. The patella was displaced 10 mm laterally and the displacing force was measured from 0° to 90° of flexion. Patellar tracking was measured from 0° to 130° of knee flexion using magnetic sensors. These tests were repeated after raising the central anterior trochlea to simulate dysplasia, and repeated again after performing a trochleoplasty on each specimen. The simulated dysplasia significantly reduced stability from that of the normal knee (p < 0.001). Trochleoplasty significantly increased the stability (p < 0.001), so that it did not then differ significantly from the normal knee (p = 0.244). There were small but statistically significant changes in patellar tracking (p< 0.001). This study has provided objective biomechanical data to support the use of trochleoplasty in the treatment of patellar instability associated with femoral trochlear dysplasia

Normal function of the patellofemoral joint is maintained by a complex interaction between soft tissues and articular surfaces. No quantitative data have been found on the relative contributions of these structures to patellar stability. Eight knees were studied using a materials testing machine to displace the patella 10 mm laterally and medially and measure the force required. Patellar stability was tested from 0° to 90° knee flexion with the quadriceps tensed to 175 N. Four conditions were examined: intact, vastus medialis obliquus relaxed, flat lateral condyle, and ruptured medial retinaculae. Abnormal trochlear geometry reduced the lateral stability by 70% at 30° flexion, while relaxation of vastus medialis obliquus caused a 30% reduction. Ruptured medial retinaculae had the largest effect at 0° flexion with 49% reduction. There was no effect on medial stability. There is a complex interaction between these structures, with their contributions to loss of lateral patellar stability varying with knee flexion

Valgus high tibial osteotomy for osteoarthritis of the medial compartment of the knee can be performed using medial opening- and lateral closing-wedge techniques. The latter have been thought to offer greater initial stability. We measured and compared the stability of opening- and closing-wedge osteotomies fixed by TomoFix plates using radiostereometry in a series of 42 patients in a prospective, randomised clinical trial. There were no differences between the opening- and closing-wedge groups in the time to regain knee function and full weight-bearing. Pain and knee function were significantly improved in both groups without any differences between them. All the osteotomies united within one year. Radiostereometry showed no clinically relevant movement of bone or differences between either group. Medial opening-wedge high tibial osteotomy secured by a TomoFix plate offers equal stability to a lateral closing-wedge technique. Both give excellent initial stability and provide significantly improved knee function and reduction in pain, although the opening-wedge technique was more likely to produce the intended correction

We measured the stability of fixation in femoral neck fractures treated with von Bahr screws, investigated the influence of impaction and correlated peroperative stability with the clinical results. Stability was measured at operation using a metal probe fitted with strain gauges. Its tip was anchored in the subchondral bone of the femoral head and its lateral end was fixed in the lateral femoral cortex. The shearing force produced by longitudinal compression applied to the foot of the operated leg was recorded. The results in 41 consecutive patients all followed for 30 months, showed that fractures with early loosening or nonunion had all had significantly poorer stability than the fractures that had healed. Impaction improved stability in only 23 out of the 41 fractures; in the others stability had deteriorated or was unchanged

Elastic stable intramedullary nailing (ESIN) is generally acknowledged to be the treatment of choice for displaced diaphyseal femoral fractures in children over the age of three years, although complication rates of up to 50% are described. Pre-bending the nails is recommended, but there are no published data to support this. Using synthetic bones and a standardised simulated fracture, we performed biomechanical testing to determine the influence on the stability of the fracture of pre-bending the nails before implantation. Standard ESIN was performed on 24 synthetic femoral models with a spiral fracture. In eight cases the nails were inserted without any pre-bending, in a further eight cases they were pre-bent to 30° and in the last group of eight cases they were pre-bent to 60°. Mechanical testing revealed that pre-bending to 60° produced a significant increase in the stiffness or stability of the fracture. Pre-bending to 60° showed a significant positive influence on the stiffness compared with unbent nails. Pre-bending to 30° improved stiffness only slightly. These findings validate the recommendations for pre-bending, but the degree of pre-bend should exceed 30°. Adopting higher degrees of pre-bending should improve stability in spiral fractures and reduce the complications of varus deformity and shortening

Aims. Vitamin E-diffused, highly crosslinked polyethylene (VEPE) and porous titanium-coated (PTC) shells were introduced in total hip arthroplasty (THA) to reduce the risk of aseptic loosening. The purpose of this study was: 1) to compare the wear properties of VEPE to moderately crosslinked polyethylene; 2) to assess the stability of PTC shells; and 3) to report their clinical outcomes at seven years. Patients and Methods. A total of 89 patients were enrolled into a prospective study. All patients received a PTC shell and were randomized to receive a VEPE liner (n = 44) or a moderately crosslinked polyethylene (ModXLPE) liner (n = 45). Radiostereometric analysis (RSA) was used to measure polyethylene wear and component migration. Differences in wear were assessed while adjusting for body mass index, activity level, acetabular inclination, anteversion, and head size. Plain radiographs were assessed for radiolucency and patient-reported outcome measures (PROMs) were administered at each follow-up. Results. In total, 73 patients (82%) completed the seven-year visit. Mean seven-year linear proximal penetration was -0.07 mm (. sd. 0.16) and 0.00 mm (. sd. 0.22) for the VEPE and ModXLPE cohorts, respectively (p = 0.116). PROMs (p = 0.310 to 0.807) and radiolucency incidence (p = 0.330) were not different between the polyethylene cohorts. The mean proximal shell migration rate was 0.04 mm per year (. sd. 0.09). At seven years, patients with radiolucency (34%) demonstrated greater migration (mean difference: 0.6 mm (. sd. 0.2); p < 0.001). PROMs were lower for patients with radiolucency and greater proximal migration (p = 0.009 to p = 0.045). No implants were revised for aseptic loosening. Conclusion. This is the first randomized controlled trial to report seven-year RSA results for VEPE. All wear rates were below the previously reported osteolysis threshold (0.1 mm per year). PTC shells demonstrated acceptable primary stability through seven years, as indicated by low migration and lack of aseptic loosening. However, patients with acetabular radiolucency were associated with higher shell migration and lower PROM scores. Cite this article: Bone Joint J 2019;101-B:760–767

1. Practical experience has shown that subcapital fractures of the femur unite freely if reduction is stable and fixation is secure. 2. Stable reduction is obtained when the muscular and gravitational forces tending to redisplace the fracture are opposed by equal and opposite counterforces, and inherent stability is believed to depend upon the integrity of the flared cortical buttress at the postero-inferior junction of the femoral neck and head. 3. In the stable subcapital fracture a state of equilibrium is reached when the forward and upward thrust of the fixation appliance in the femoral head is opposed by the counterthrust of the closely applied and cleanly broken fragments at the postero-inferior aspect of the fracture. When the postero-inferior cortical buttress is comminuted, inherent stability is lost, lateral rotation deformity recurs and the fixation device is avulsed from the cancellous bone of the head. 4. Stability may be restored by reduction in the "valgus" position, by various forms of osteotomy, by refashioning the fracture fragments or by a postero-inferiorly positioned bone graft. Theoretically, stability may also be obtained by a double lever system of fixation in which an obliquely placed fixation device or bone graft is combined with a horizontally disposed wire, pin, nail or screw crossing it anteriorly. Multilever fixation by three or more threaded wires or pins inserted at different angles and lying in contact at their point of crossing may likewise provide stability. 5. Fixation by two crossed screws has been chosen for clinical trial in 100 displaced subcapital fractures. Imperfect positioning of the screws in seven patients has been followed by early breakdown of reduction and non-union, but satisfactory positioning has been associated with radiological union in fifty patients who have been observed for twelve months or more. 6. Ultimate breakdown in some of these fractures is certain to follow avascular necrosis, and this complication has already been seen in a few patients treated by cross screw fixation more than two years ago. It is also expected that non-union will occur in some of those patients still under observation for less than a year. Even so, these preliminary findings indicate a percentage of union far greater than that obtained by previous methods of treatment, and, although statistically inadequate, they are presented in support of the belief that it should no longer be considered impossible to achieve the same percentage of union in subcapital fractures of the femur as we are accustomed to expect in the treatment of fractures elsewhere. It is not implied, however, that this ideal will be reached merely by the adoption of some form of double or multilever fixation, and much will continue to depend upon the quality of the radiographic services, the precision of reduction and the perfection of operative technique. 7. Every advance in our understanding of what is meant by "perfection of operative technique" lends increasing support to the ultimate truth of Watson-Jones's (1941) dictum: "A perfect result may be expected from a technically perfect operation; an imperfect result is due to imperfect technique." But the simple and foolproof method of fixation which will end the search for technical perfection in the treatment of the displaced subcapital fracture has yet to be evolved, and many questions remain to be answered about this injury. Nevertheless, it is clear that the surgeon should now be prepared to attribute early mechanical failure in the treatment of femoral neck fractures to his own shortcomings, and the temptation to blame capital ischaemia for every disaster should be resisted

Polished, tapered stems are now widely used for cemented total hip replacement and many such designs have been introduced. However, a change in stem geometry may have a profound influence on stability. Stems with a wide, rectangular proximal section may be more stable than those which are narrower proximally. We examined the influence of proximal geometry on stability by comparing the two-year migration of the Exeter stem with a more recent design, the CPS-Plus, which has a wider shoulder and a more rectangular cross-section. The hypothesis was that these design features would increase rotational stability. Both stems subsided approximately 1 mm relative to the femur during the first two years after implantation. The Exeter stem was found to rotate into valgus (mean 0.2°, . sd. 0.42°) and internally rotate (mean 1.28°, . sd. 0.99°). The CPS-Plus showed no significant valgus rotation (mean 0.2°, . sd. 0.42°) or internal rotation (mean −0.03°, . sd. 0.75°). A wider, more rectangular cross-section improves rotational stability and may have a better long-term outcome

Aims

The aims of this study were to compare clinically relevant measurements of hip dysplasia on radiographs taken in the supine and standing position, and to compare Hip2Norm software and Picture Archiving and Communication System (PACS)-derived digital radiological measurements.

The osseo-integration of an uncemented acetabular component depends on its initial stability. This is usually provided by under-reaming of the acetabulum. We have assessed the fixation of 52 mm porous-coated hemispherical prostheses inserted into cadaveric acetabula under-reamed by 1, 2, 3 and 4 mm. We tested the torsional stability of fixation, after preloading with 686 N in compression, by measuring the torque required to produce 1 degree and 2 degrees of rotation. Under-reaming by 2 mm and 3 mm gave significantly better fixation than 1 mm (p less than 0.01, p less than 0.02). Insertion after under-reaming of 4 mm caused some fractures. To obtain maximum interference fit and optimal implant stability, we recommend the use of an implant 2 mm or 3 mm larger than the last reamer

The radiolucent lines and the stability of the components of 66 knee arthroplasties were assessed by six orthopaedic surgeons on conventional anteroposterior and lateral radiographs and on fluoroscopic views which had been taken on the same day. The examiners were blinded as to the patients and clinical results. The interpretation of the radiographs was repeated after five months. On fluoroscopically-assisted radiographs four of the six examiners identified significantly more radiolucent lines for the femoral component (p < 0.05) and one significantly more for the tibial implant. Five examiners rated more femoral components as radiologically loose on fluoroscopically-assisted radiographs (p = 0.0008 to 0.0154), but none did so for the tibial components. The mean intra- and interobserver kappa values were higher for fluoroscopically-assisted radiographs for both components. We have shown that fluoroscopically-assisted radiographs allow more reproducible, and therefore reliable, detection of radiolucent lines in total knee arthroplasty. Assessment of the stability of the components is significantly influenced by the radiological technique used. Conventional radiographs are not adequate for evaluation of the stability of total knee arthroplasty and should be replaced by fluoroscopically-assisted films