Aims. Anterior cruciate ligament (ACL) rupture commonly leads to post-traumatic osteoarthritis, regardless of surgical reconstruction. This study uses standing MRI to investigate changes in contact area, contact centroid location, and tibiofemoral alignment between ACL-injured knees and healthy controls, to examine the effect of ACL reconstruction on these parameters. Methods. An upright, open MRI was used to directly measure tibiofemoral contact area, centroid location, and alignment in 18 individuals with unilateral ACL rupture within the last five years. Eight participants had been treated nonoperatively and ten had ACL reconstruction performed within one year of injury. All participants were high-functioning and had returned to sport or recreational activities. Healthy contralateral knees served as controls. Participants were imaged in a standing posture with knees fully extended. Results. Participants’ mean age was 28.4 years (SD 7.3), the mean time since injury was 2.7 years (SD 1.6), and the mean International Knee Documentation Subjective Knee Form score was 84.4 (SD 13.5). ACL injury was associated with a 10% increase (p = 0.001) in contact area, controlling for compartment, sex, posture, age, body mass, and time since injury. ACL injury was associated with a 5.2% more posteriorly translated medial centroid (p = 0.001), equivalent to a 2.6 mm posterior translation on a representative tibia with mean posteroanterior width of 49.4 mm. Relative to the femur, the tibiae of ACL ruptured knees were 2.3 mm more anteriorly translated (p = 0.003) and 2.6° less externally rotated (p = 0.010) than healthy controls. ACL reconstruction was not associated with an improvement in any measure. Conclusion. ACL rupture was associated with an increased contact area, posteriorly translated medial centroid, anterior tibial translation, and reduced tibial external rotation in full extension. These changes were present 2.7 years post-injury regardless of ACL reconstruction status. Cite this article: Bone Joint J 2021;103-B(9):1505–1513

Aims

Obtaining solid implant fixation is crucial in revision total knee arthroplasty (rTKA) to avoid aseptic loosening, a major reason for re-revision. This study aims to validate a novel grading system that quantifies implant fixation across three anatomical zones (epiphysis, metaphysis, diaphysis).

Aims. The objective of this study is to assess the use of ultrasound (US) as a radiation-free imaging modality to reconstruct 3D anatomy of the knee for use in preoperative templating in knee arthroplasty. Methods. Using an US system, which is fitted with an electromagnetic (EM) tracker that is integrated into the US probe, allows 3D tracking of the probe, femur, and tibia. The raw US radiofrequency (RF) signals are acquired and, using real-time signal processing, bone boundaries are extracted. Bone boundaries and the tracking information are fused in a 3D point cloud for the femur and tibia. Using a statistical shaping model, the patient-specific surface is reconstructed by optimizing bone geometry to match the point clouds. An accuracy analysis was conducted for 17 cadavers by comparing the 3D US models with those created using CT. US scans from 15 users were compared in order to examine the effect of operator variability on the output. Results. The results revealed that the US bone models were accurate compared with the CT models (root mean squared error (RM)S: femur, 1.07 mm (SD 0.15); tibia, 1.02 mm (SD 0.13). Additionally, femoral landmarking proved to be accurate (transepicondylar axis: 1.07° (SD 0.65°); posterior condylar axis: 0.73° (SD 0.41°); distal condylar axis: 0.96° (SD 0.89°); medial anteroposterior (AP): 1.22 mm (SD 0.69); lateral AP: 1.21 mm (SD 1.02)). Tibial landmarking errors were slightly higher (posterior slope axis: 1.92° (SD 1.31°); and tubercle axis: 1.91° (SD 1.24°)). For implant sizing, 90% of the femora and 60% of the tibiae were sized correctly, while the remainder were only one size different from the required implant size. No difference was observed between moderate and skilled users. Conclusion. The 3D US bone models were proven to be closely matched compared with CT and suitable for preoperative planning. The 3D US is radiation-free and offers numerous clinical opportunities for bone visualization rapidly during clinic visits, to enable preoperative planning with implant sizing. There is potential to extend its application to 3D dynamic ligament balancing, and intraoperative registration for use with robots and navigation systems. Cite this article: Bone Joint J 2021;103-B(6 Supple A):81–86

We investigated the effect of locally administered bisphosphonate on distraction osteogenesis in a rabbit model and evaluated its systemic effect. An osteotomy on the right tibia followed by distraction for four weeks was performed on 47 immature rabbits. They were divided into seven equal groups, with each group receiving a different treatment regime. Saline and three types of dosage of alendronate (low, 0.75 μg/kg; mid, 7.5 μg/kg and high 75 μg/kg) were given by systemic injection in four groups, and saline and two dosages (low and mild) were delivered by local injection to the distraction gap in the remaining three groups. The injections were performed five times weekly during the period of distraction. After nine weeks the animals were killed and image analysis and mechanical testing were performed on the distracted right tibiae and the left tibiae which served as a control group. The local low-dose alendronate group showed a mean increase in bone mineral density of 124.3 mg/cm. 3. over the local saline group (analysis of variance, p < 0.05) without any adverse effect on the left control tibiae. The findings indicate that the administration of local low-dose alendronate could be an effective pharmacological means of improving bone formation in distraction osteogenesis

Permanent growth arrest of the longer bone is an option in the treatment of minor leg-length discrepancies. The use of a tension band plating technique to produce a temporary epiphysiodesis is appealing as it avoids the need for accurate timing of the procedure in relation to remaining growth. We performed an animal study to establish if control of growth in a long bone is possible with tension band plating. Animals (pigs) were randomised to temporary epiphysiodesis on either the right or left tibia. Implants were removed after ten weeks. Both tibiae were examined using MRI at baseline, and after ten and 15 weeks. The median interphyseal distance was significantly shorter on the treated tibiae after both ten weeks (p = 0.04) and 15 weeks (p = 0.04). On T. 1. -weighted images the metaphyseal water content was significantly reduced after ten weeks on the treated side (p = 0.04) but returned to values comparable with the untreated side at 15 weeks (p = 0.14). Return of growth was observed in all animals after removal of implants. Temporary epiphysiodesis can be obtained using tension band plating. The technique is not yet in common clinical practice but might avoid the need for the accurate timing of epiphysiodesis. Cite this article: Bone Joint J 2013;95-B:855–60

The release of prostaglandins E and F from the tibiae of rabbits and the surrounding muscle in vitro after fracture and pinning, or pinning alone, has been compared to the release from unoperated tissues. The fractured tibiae released significantly more prostaglandins E and F than the control tibiae three to 14 days after operation. The pinned tibiae also released more of the two prostaglandins, although this was significant only after 14 days. Consequently it was only around the third day that the fractured tibiae released significantly more prostaglandin E than the tibiae which had been pinned, but not fractured. Similar results were obtained for the release from the muscles surrounding the tibiae. Prostaglandins are important mediators of inflammation as well as potent stimulators of bone resorption. Their increased formation in response to fracture and pinning may stimulate the vascular changes, bone resorption and the proliferation of osteogenic cells observed after trauma to bone

Aims. Double-level lengthening, bone transport, and bifocal compression-distraction are commonly undertaken using Ilizarov or other fixators. We performed double-level fixator-assisted nailing, mainly for the correction of deformity and lengthening in the same segment, using a straight intramedullary nail to reduce the time in a fixator. Patients and Methods. A total of 23 patients underwent this surgery, involving 27 segments (23 femora and four tibiae), over a period of ten years. The most common indication was polio in ten segments and rickets in eight; 20 nails were inserted retrograde and seven antegrade. A total of 15 lengthenings were performed in 11 femora and four tibiae, and 12 double-level corrections of deformity without lengthening were performed in the femur. The mean follow-up was 4.9 years (1.1 to 11.4). Four patients with polio had tibial lengthening with arthrodesis of the ankle. We compared the length of time in a fixator and the external fixation index (EFI) with a control group of 27 patients (27 segments) who had double-level procedures with external fixation. The groups were matched for the gain in length, age, and level of difficulty score. Results. The mean gain in length was statistically similar in the two groups: 3.9 cm (1.5 to 9.0) in the study group and 4.2 cm (3.4 to 5.0) in the control group (p = 0.350). The mean time in a fixator was significantly less in the study group compared with the control group: 8.6 weeks (2.0 to 22.8) versus 30.2 weeks (25.0 to 35.4; p < 0.001). The mean EFI was significantly lower in the study group compared with the control group: 17.7 days/cm (10.6 to 35.6) versus 73.4 days/cm (44.5 to 102.3; p < 0.001). The ASAMI (Association for the Study and Application of the Method of Ilizarov) bone score was excellent in 22, good in four, and fair in one. The ASAMI functional score was excellent in 20 and good in seven. There were no infections, superficial or deep. Conclusion. Double-level osteotomies or two procedures using a custom-made straight nail and external fixation can be used to correct deformities or to treat nonunion or malunion and may be combined with arthrodesis of the ankle with lengthening. It is a reasonably safe procedure that allows accurate and cost-effective treatment with a relatively short time in a fixator

The aim of this study was to report the pattern of severe open diaphyseal tibial fractures sustained by military personnel, and their orthopaedic–plastic surgical management.The United Kingdom Military Trauma Registry was searched for all such fractures sustained between 2006 and 2010. Data were gathered on demographics, injury, management and preliminary outcome, with 49 patients with 57 severe open tibial fractures identified for in-depth study. The median total number of orthopaedic and plastic surgical procedures per limb was three (2 to 8). Follow-up for 12 months was complete in 52 tibiae (91%), and half the fractures (n = 26) either had united or in the opinion of the treating surgeon were progressing towards union. The relationship between healing without further intervention was examined for multiple variables. Neither the New Injury Severity Score, the method of internal fixation, the requirement for vascularised soft-tissue cover nor the degree of bone loss was associated with poor bony healing. Infection occurred in 12 of 52 tibiae (23%) and was associated with poor bony healing (p = 0.008). This series characterises the complex orthopaedic–plastic surgical management of severe open tibial fractures sustained in combat and defines the importance of aggressive prevention of infection. Cite this article: Bone Joint J 2013;95-B:101–5

Corrective osteotomies are often planned and performed on the basis of normal anatomical proportions. We have evaluated the length and torsion of the segments of the lower limb in normal individuals, to analyse the differences between left and right sides, and to provide tolerance figures for both length and torsion. We used CT on 355 adult patients and measured length and torsion by the Ulm method. We excluded all patients with evidence of trauma, infection, tumour or any congenital disorder. The mean length of 511 femora was 46.3 ± 6.4 cm (±2. sd. ) and of 513 tibiae 36.9 ± 5.6 cm; the mean total length of 378 lower limbs was 83.2 ± 11.4 cm with a tibiofemoral ratio of 1 to 1.26 ± 0.1. The 99th percentile level for length difference in 178 paired femora was 1.2 cm, in 171 paired tibiae 1.0 cm and in 60 paired lower limbs 1.4 cm. In 505 femora the mean internal torsion was 24.1 ± 17.4°, and in 504 tibiae the mean external torsion was 34.9 ± 15.9°. For 352 lower limbs the mean external torsion was 9.8 ± 11.4°. The mean torsion angle of right and left femora in individuals did not differ significantly, but mean tibial torsion showed a significant difference between right (36.46° of external torsion) and left sides (33.07° of external torsion). For the whole legs torsion on the left was 7.5 ± 18.2° and 11.8 ± 18.8°, respectively (p < 0.001). There was a trend to greater internal torsion in femora in association with an increased external torsion in tibiae, but we found no correlation. The 99th percentile value for the difference in 172 paired femora was 13°; in 176 pairs of tibiae it was 14.3° and for 60 paired lower limbs 15.6°. These results will help to plan corrective osteotomies in the lower limbs, and we have re-evaluated the mathematical limits of differences in length and torsion

Osteomyelitis was induced in the tibiae of rabbits by injecting a suspension of Staphylococcus aureus and sodium tetradecylsulphate, a sclerosing agent. These rabbits were then divided into two groups: one group remained untreated and the other was fed a diet containing sodium salicylate. Two and four weeks after induction of osteomyelitis the tibiae taken from untreated rabbits with osteomyelitis and incubated in vitro released significantly more prostaglandin E and F than the control uninjected or uninfected tibiae. Tibiae taken from rabbits treated with sodium salicylate showed minimal radiographic changes and a significantly decreased release of prostaglandin E and F compared to the untreated rabbits. Prostaglandins are known to be potent bone resorbing agents and the results of this study suggest that they may also be involved in the destruction of bone which is characteristic of osteomyelitis. The treatment of rabbits with osteomyelitis using anti-inflammatory drugs, which block synthesis of prostaglandins, in addition to antibiotics, may prevent the destruction of bone and possible sequestration thereby decreasing the risk of chronic disease

As many as 25% to 40% of unicompartmental knee replacement (UKR) revisions are performed for pain, a possible cause of which is proximal tibial strain. The aim of this study was to examine the effect of UKR implant design and material on cortical and cancellous proximal tibial strain in a synthetic bone model. Composite Sawbone tibiae were implanted with cemented UKR components of different designs, either all-polyethylene or metal-backed. The tibiae were subsequently loaded in 500 N increments to 2500 N, unloading between increments. Cortical surface strain was measured using a digital image correlation technique. Cancellous damage was measured using acoustic emission, an engineering technique that detects sonic waves (‘hits’) produced when damage occurs in material. Anteromedial cortical surface strain showed significant differences between implants at 1500 N and 2500 N in the proximal 10 mm only (p < 0.001), with relative strain shielding in metal-backed implants. Acoustic emission showed significant differences in cancellous bone damage between implants at all loads (p = 0.001). All-polyethylene implants displayed 16.6 times the total number of cumulative acoustic emission hits as controls. All-polyethylene implants also displayed more hits than controls at all loads (p < 0.001), more than metal-backed implants at loads ≥ 1500 N (p < 0.001), and greater acoustic emission activity on unloading than controls (p = 0.01), reflecting a lack of implant stiffness. All-polyethylene implants were associated with a significant increase in damage at the microscopic level compared with metal-backed implants, even at low loads. All-polyethylene implants should be used with caution in patients who are likely to impose large loads across their knee joint. . Cite this article: Bone Joint J 2013;95-B:1339–47

1. The probable greatest bending moment applied to a plated or nailed fracture of the tibia during restricted weight-bearing is estimated to be, in men, up to about 79 Newton metres (58 poundsforce feet). The maximum twisting moment is estimated to be about 29 Newton metres (22 poundsforce feet). 2. Twenty-two human tibiae were loaded in three-point bending and broke at bending moments of from 57·9 to 294 Newton metres (42·7 to 216 poundsforce feet) if they had not previously been drilled; tibiae which had holes made through both cortices with a c. 3-millimetre (⅛-inch) drill broke at from 32·4 to 144 Newton metres (23·8 to 106 poundsforce feet). Tibiae loaded in torsion broke at twisting moments of from 27·5 to 892 Newton metres (20·2 to 65·8 poundsforce feet) when not drilled, 23·6 to 77·5 Newton metres (l7·3 to 57·1 poundsforce feet) when drilled. 3. When bent so as to open the fracture site, the 14-centimetre Stamm was the strongest of all the single plates tested (reaching its elastic limit at a bending moment of 17·6 Newton metres (13 poundsforce feet) and 5 degrees total angulation at 22·6 Newton metres (16·6 poundsforce feet)), while the Venable was the weakest (elastic limit 4·9 Newton metres (3·6 poundsforce feet) and 5 degrees at 7·9 Newton metres (5·8 poundsforce feet)). A 13-millimetre Küntscher nail reached its elastic limit at 42·2 Newton metres (31·1 poundsforce feet) and 5 degrees total angulation at 49 Newton metres (36 poundsforce feet). 4. In torsion the 15-centimetre Hicks was the strongest ofthe plates (elastic limit 27·5 Newton metres (20·2 poundsforce feet) and 5 degrees rotation at 16·7 Newton metres (l2·3 poundsforce feet)). 5. Küntscher nails in bones provided no dependable strength in torsion. 6. In both bending and torsion, a preparation of one Venable plate on each of the two anterior surfaces was stronger than any single plate, and was as strong as the weaker drilled tibiae. 7. The three currently available metallic materials (stainless steel, cobalt-chrome and titanium) have static mechanical properties so similar that the choice between them can be made on other grounds. 8. The highest load applied to a screw during bending tests was about half that needed to pull a screw out of even a thin-walled tibia. 9. Screws beyond four for one plate are mechanically redundant at the moment of implantation but may be necessary as an insurance against subsequent deterioration in strength. 10. Countersinks in plates are a source of significant weakness, and should preferably be as shallow as possible. 11. An unoccupied screw hole in the centre of a plate is a source of serious weakness. 12. Only the strongest implants tested were strong enough to withstand the bending or twisting moments to be expected in restricted weight-bearing. In two-plate preparations a danger is introduced by the fact that these moments are similar to those required to Ireak a drilled tibia

Fracture repair occurs by two broad mechanisms: direct healing, and indirect healing with callus formation. The effects of bisphosphonates on fracture repair have been assessed only in models of indirect fracture healing. A rodent model of rigid compression plate fixation of a standardised tibial osteotomy was used. Ten skeletally mature Sprague–Dawley rats received daily subcutaneous injections of 1 µg/kg ibandronate (IBAN) and ten control rats received saline (control). Three weeks later a tibial osteotomy was rigidly fixed with compression plating. Six weeks later the animals were killed. Fracture repair was assessed with mechanical testing, radiographs and histology. The mean stress at failure in a four-point bending test was significantly lower in the IBAN group compared with controls (8.69 Nmm. -2. (. sd. 7.63) vs 24.65 Nmm. -2. (. sd. 6.15); p = 0.017). On contact radiographs of the extricated tibiae the mean bone density assessment at the osteotomy site was lower in the IBAN group than in controls (3.7 mmAl (. sd. 0.75) vs 4.6 mmAl (. sd. 0.57); p = 0.01). In addition, histological analysis revealed progression to fracture union in the controls but impaired fracture healing in the IBAN group, with predominantly cartilage-like and undifferentiated mesenchymal tissue (p = 0.007). . Bisphosphonate treatment in a therapeutic dose, as used for risk reduction in fragility fractures, had an inhibitory effect on direct fracture healing. We propose that bisphosphonate therapy not be commenced until after the fracture has united if the fracture has been rigidly fixed and is undergoing direct osteonal healing. Cite this article: Bone Joint J 2013;95-B:1263–8

We aimed to obtain anthropometric data on Korean knees and to compare these with data on commonly available total knee arthroplasties (TKAs). The dimensions of the femora and tibiae of 1168 knees were measured intra-operatively. The femoral components were found to show a tendency toward mediolateral (ML) under-coverage in small femurs and ML overhang in the large femurs. The ML under-coverage was most prominent for the small prostheses. The ML/anteroposterior (ML/AP) ratio of Korean tibiae was greater than that of tibial components. This study shows that, for different reasons, current TKAs do not provide a reasonable fit for small or large Korean knees, and that the ‘gender-specific’ and ‘stature-specific’ components help for large Korean femurs but offer less satisfactory fits for small femurs. Specific modifications of prostheses are needed for Asian knees

A silver-containing hydroxyapatite (Ag-HA) coating has been developed using thermal spraying technology. We evaluated the osteoconductivity of this coating on titanium (Ti) implants in rat tibiae in relation to bacterial infection in joint replacement. At 12 weeks, the mean affinity indices of bone formation of a Ti, an HA, a 3%Ag-HA and a 50%Ag-HA coating were 97.3%, 84.9%, 81.0% and 40.5%, respectively. The mean affinity indices of bone contact of these four coatings were 18.8%, 83.7%, 77.2% and 40.5%, respectively. The indices of bone formation and bone contact around the implant of the 3%Ag-HA coating were similar to those of the HA coating, and no significant differences were found between them (bone formation, p = 0.99; bone contact, p = 0.957). However, inhibition of bone formation was observed with the 50%Ag-HA coating. These results indicate that the 3%Ag-HA coating has low toxicity and good osteoconductivity, and that the effect of silver toxicity on osteoconductivity depends on the dose

We report the results of using a combination of fixator-assisted nailing with lengthening over an intramedullary nail in patients with tibial deformity and shortening. Between 1997 and 2007, 13 tibiae in nine patients with a mean age of 25.4 years (17 to 34) were treated with a unilateral external fixator for acute correction of deformity, followed by lengthening over an intramedullary nail with a circular external fixator applied at the same operating session. At the end of the distraction period locking screws were inserted through the intramedullary nail and the external fixator was removed. The mean amount of lengthening was 5.9 cm (2 to 8). The mean time of external fixation was 90 days (38 to 265). The mean external fixation index was 15.8 days/cm (8.9 to 33.1) and the mean bone healing index was 38 days/cm (30 to 60). One patient developed an equinus deformity which responded to stretching and bracing. Another developed a drop foot due to a compartment syndrome, which was treated by fasciotomy. It recovered in three months. Two patients required bone grafting for poor callus formation. We conclude that the combination of fixator-assisted nailing with lengthening over an intramedullary nail can reduce the overall external fixation time and prevent fractures and deformity of the regenerated bone

Intramedullary tibial nailing was performed in ten paired cadavers and the insertion of a medial-to-lateral proximal oblique locking screw was simulated in each specimen. Anatomical dissection was undertaken to determine the relationship of the common peroneal nerve to the cross-screw. The common peroneal nerve was contacted directly in four tibiae and the cross-screw was a mean of 2.6 mm (1.0 to 10.7) away from the nerve in the remaining 16. Iatrogenic injury to the common peroneal nerve by medial-to-lateral proximal oblique locking screws is therefore a significant risk during tibial nailing

Clinical experience of impaction bone grafting for revision knee arthroplasty is limited, with initial stability of the tibial tray emerging as a major concern. The length of the stem and its diameter have been altered to improve stability. Our aim was to investigate the effect of the type of stem, support of the rim and graft impaction on early stability of the tray. We developed a system for impaction grafting of trays which we used with morsellised bone in artificial tibiae. Trays with short, long thick or long thin stems were implanted, with or without support of the rim. They were cyclically loaded while measuring relative movement. Long-stemmed trays migrated 4.5 times less than short-stemmed trays, regardless of diameter. Those with support migrated 2.8 times less than those without. The migration of short-stemmed trays correlated inversely with the density of the impacted groups. That of impaction-grafted tibial trays was in the range reported for uncemented primary trays. Movements of short-stemmed trays without cortical support were largest and sensitive to the degree of compaction of the graft. If support of the rim was sufficient or a long stem was used, impacted morsellised bone graft achieved adequate initial stability

Congenital pseudarthrosis of the tibia is an uncommon manifestation of neurofibromatosis type 1 (NF1), but one that remains difficult to treat due to anabolic deficiency and catabolic excess. Bone grafting and more recently recombinant human bone morphogenetic proteins (rhBMPs) have been identified as pro-anabolic stimuli with the potential to improve the outcome after surgery. As an additional pharmaceutical intervention, we describe the combined use of rhBMP-2 and the bisphosphonate zoledronic acid in a mouse model of NF1-deficient fracture repair. Fractures were generated in the distal tibiae of neurofibromatosis type 1-deficient (Nf1. +/−. ) mice and control mice. Fractures were open and featured periosteal stripping. All mice received 10 μg rhBMP-2 delivered in a carboxymethylcellulose carrier around the fracture as an anabolic stimulus. Bisphosphonate-treated mice also received five doses of 0.02 mg/kg zoledronic acid given by intraperitoneal injection. When only rhBMP but no zoledronic acid was used to promote repair, 75% of fractures in Nf1. +/−. mice remained ununited at three weeks compared with 7% of controls (p < 0.001). Systemic post-operative administration of zoledronic acid halved the rate of ununited fractures to 37.5% (p < 0.07). These data support the concept that preventing bone loss in combination with anabolic stimulation may improve the outcome following surgical treatment for children with congenital pseudarthoris of the tibia and NF1

We investigated the fracture-free survival of long bones stabilised by a telescopic intramedullary rod (TIMR) in patients with osteogenesis imperfecta with respect to the remodelling status of fracture or osteotomy sites and TIMR regions, in order to identify risk factors for fracture. A total of 44 femora and 28 tibiae in 25 patients with a mean age of 5.0 years (1.9 to 10.5) at presentation were studied. There were six patients with Sillence type I, five with type III, 13 with type IV and one with type V osteogenesis imperfecta. All received bisphosphonate treatment at the same stage during the mean follow-up of 7.3 years (0.5 to 18.1). The fracture-free survival was estimated at 6.2 years (95% confidence interval 5.1 to 7.3) by Kaplan-Meier analysis. More than half the fracture or osteotomy sites remained in a less-remodelled state at the latest follow-up or time of fracture. Of the 33 fractures, 29 (87.9%) occurred in long bones containing a less-remodelled site, and these fractures were located at this site. The relative fracture risk at the rod tip was significantly greater than in any other TIMR region (p < 0.001), and this was higher in bone segments having a less-remodelled site. This study shows a persistent fracture risk in TIMR-stabilised long bones, especially at less-remodelled fracture or osteotomy sites and at the rod tip