Trabecular bone is a multiscale hierarchical composite material that is known to display time-dependant properties. However, most biomechanical models treat this material as time independent. Time-dependant properties, such as creep and relaxation, are thought to play an important role in many clinically relevant orthopaedic issues: implant loosening, vertebral collapse, and non-traumatic fractures. In this study compressive multiple-load-creep-unload-recovery (MLCUR) tests were applied to human trabecular bone specimens. 15 female femoral heads were harvested, with full ethical approval and patient consent, at the time of total hip replacement. Central cores were extracted and cut parallel under constant irrigation. Specimens were embedded in end caps using surgical cement, an epoxy tube was secured around the end caps and filled with phosphate buffered saline (PBS) to ensure the specimens remained hydrated throughout. Embedded samples were scanned by microCT (SkyScan 1172, Bruker) at a resolution of 17µm to determine microarchitecture. Bone volume fraction (BVF) was used to represent microarchitecture. Specimens had an effective length of 16.37mm (±1.90SD) with diameter of 8.08mm (±0.05SD), and BVF of 19.22% (±5.61SD). The compressive MLCUR tests were conducted at 5 strain levels, 2000µε, 4000µε, 6000µε, 8000µε and 10000µε. At each strain level, the load required to maintain each strain was held for 200s (creep) then unloaded to 1N for 600s (recovery). The instantaneous, creep, unloading and recovered strains can be easily obtained from the strain-time curves. Stress-strain plots revealed the Young's modulus. Data was modelled using line of best fit with appropriate curve fitting. R2 values were used to indicate association. Mechanical testing demonstrated the expected time independent relationship between BVF and stiffness: higher stiffness was found for specimen with higher BVF and this was consistent for all strain levels. Creep strain was found to depend on instantaneous strain and BVF. At low levels of instantaneous strain, there was a greater amount of creep strain in low BVF samples (R2 = 0.524). This relationship was no longer apparent at higher strain levels (R2 = 0.058). Residual strain also depended on the applied instantaneous strain and BVF: at low levels of strain, residual strain was similar with all BVF (R2 = 0.108) and at high levels of strain, residual strain was greater in low BVF samples (R2 = 0.319). The amount of instantaneous strain applied to each sample is constant, variations in stiffness result in different applied loads. In low BVF bone, the stiffness is also low, therefore the stress required to reach designed strain is also lower: yet, there is more creep and less recovery. We have demonstrated that even at loads below recognised yield levels, time-dependence affects the mechanical response and residual strain is present. In cases of low BVF, deflection due to creep, and increased irrecoverable strain could have clinically relevant consequences, such as implant loosening and vertebral collapse. The role of time-dependant properties of bone is seldom considered. This data could be developed into a constitutive model allowing these time-dependant behaviours to be incorporated in finite element modelling, leading to better predictions of implant loosening, especially for lower quality bone

Aim

The aim of this study was to compare the cost-effectiveness of intramedullary nail fixation and ‘locking’ plate fixation in the treatment of extra-articular fractures of the distal tibia.

End caps are intended to prevent nail migration (push-out) in elastic stable intramedullary nailing. The aim of this study was to investigate the force at failure with and without end caps, and whether different insertion angles of nails and end caps would alter that force at failure. Simulated oblique fractures of the diaphysis were created in 15 artificial paediatric femurs. Titanium Elastic Nails with end caps were inserted at angles of 45°, 55° and 65° in five specimens for each angle to create three study groups. Biomechanical testing was performed with axial compression until failure. An identical fracture was created in four small adult cadaveric femurs harvested from two donors (both female, aged 81 and 85 years, height 149 cm and 156 cm, respectively). All femurs were tested without and subsequently with end caps inserted at 45°. In the artificial femurs, maximum force was not significantly different between the three groups (p = 0.613). Push-out force was significantly higher in the cadaveric specimens with the use of end caps by an up to sixfold load increase (830 N, standard deviation (SD) 280 vs 150 N, SD 120, respectively; p = 0.007). These results indicate that the nail and end cap insertion angle can be varied within 20° without altering construct stability and that the risk of elastic stable intramedullary nailing push–out can be effectively reduced by the use of end caps. Cite this article: Bone Joint J 2015;97-B:558–63

Conventional methods of treating ankle fractures in the elderly are associated with high rates of complication. We describe the results of treating these injuries in 48 frail elderly patients with a long calcaneotalotibial nail.

The mean age of the group was 82 years (61 to 96) and 41 (85%) were women. All were frail, with multiple medical comorbidities and their mean American Society of Anaesthesiologists score was 3 (3 to 4). None could walk independently before their operation. All the fractures were displaced and unstable; the majority (94%, 45 of 48) were low-energy injuries and 40% (19 of 48) were open.

The overall mortality at six months was 35%. Of the surviving patients, 90% returned to their pre-injury level of function. The mean pre- and post-operative Olerud and Molander questionnaire scores were 62 and 57 respectively. Complications included superficial infection (4%, two of 48); deep infection (2%, one of 48); a broken or loose distal locking screw (6%, three of 48); valgus malunion (4%, two of 48); and one below-knee amputation following an unsuccessful vascular operation. There were no cases of nonunion, nail breakage or peri-prosthetic fracture.

A calcaneotalotibial nail is an excellent device for treating an unstable fracture of the ankle in the frail elderly patient. It allows the patient to mobilise immediately and minimises the risk of bone or wound problems. A long nail which crosses the isthmus of the tibia avoids the risk of peri-prosthetic fracture associated with shorter devices.

Cite this article: Bone Joint J 2014; 96-B:817–22.

This review is aimed at clinicians appraising preclinical trauma studies and researchers investigating compromised bone healing or novel treatments for fractures. It categorises the clinical scenarios of poor healing of fractures and attempts to match them with the appropriate animal models in the literature.

We performed an extensive literature search of animal models of long bone fracture repair/nonunion and grouped the resulting studies according to the clinical scenario they were attempting to reflect; we then scrutinised them for their reliability and accuracy in reproducing that clinical scenario.

Models for normal fracture repair (primary and secondary), delayed union, nonunion (atrophic and hypertrophic), segmental defects and fractures at risk of impaired healing were identified. Their accuracy in reflecting the clinical scenario ranged greatly and the reliability of reproducing the scenario ranged from 100% to 40%.

It is vital to know the limitations and success of each model when considering its application.

Impaction allograft is an established method of securing initial stability of an implant in arthroplasty. Subsequent bone integration can be prolonged, and the volume of allograft may not be maintained. Intermittent administration of parathyroid hormone has an anabolic effect on bone and may therefore improve integration of an implant.

Using a canine implant model we tested the hypothesis that administration of parathyroid hormone may improve osseointegration of implants surrounded by bone graft. In 20 dogs a cylindrical porous-coated titanium alloy implant was inserted into normal cancellous bone in the proximal humerus and surrounded by a circumferential gap of 2.5 mm. Morsellised allograft was impacted around the implant. Half of the animals were given daily injections of human parathyroid hormone (1–34) 5 μg/kg for four weeks and half received control injections. The two groups were compared by mechanical testing and histomorphometry. We observed a significant increase in new bone formation within the bone graft in the parathyroid hormone group. There were no significant differences in the volume of allograft, bone-implant contact or in the mechanical parameters.

These findings suggest that parathyroid hormone improves new bone formation in impacted morsellised allograft around an implant and retains the graft volume without significant resorption. Fixation of the implant was neither improved nor compromised at the final follow-up of four weeks.

This case highlights the close association between osteo-fibrous dysplasia (OFD) and adamantinoma, drawing attention to the role for more radical treatment options when treating OFD. We discuss the advancements in joint-sparing endoprostheses using bicortical fixation. Finally we describe a unique biomedical design allowing for manufacture of an end cap to allow amputation through a custom made joint-sparing proximal tibial replacement as opposed to an above knee amputation. A 37 year old presented 7 years ago having sustained a pathological fracture of her tibia. Subsequent biopsy revealed OFD, curettage with bone graft was performed. She later developed recurrence, two percutaneous biopsies confirmed OFD. 6 years following her initial diagnosis she was referred to RNOH with further recurrence, a biopsy at this stage revealed a de-differentiated adamantinoma. A joint-sparing proximal tibial replacement was performed and adjuvant chemotherapy administered, she remained well for one year. Recurrence was noted at the distal bone-prosthesis interface, histology revealed a high grade dedifferentiated osteosarcoma, limb preservation was not deemed possible and an amputation was performed through the prosthesis. The proximal tibial device was uncoupled leaving a residual 7 cms insitu, a small custom made end cap was attached to the remaining prosthesis and a myocutaneous flap fashioned over it, this ultimately enabled the patient to mobilise well with a below–knee orthotic device. This case highlights the need for more radical surgery when treating cases of OFD and the relationship between OFD and adamantinoma. It also introduces a joint-sparing proximal tibial device for use in proximal tibial tumours that do not invade the proximal tibial metaphysis. The biomechanical design solution has given us the unique option of preserving the knee joint allowing the patient a below knee amputation whereas previously an above knee amputation would have been performed thereby significantly reducing her functional outcome

Intramedullary nailing is acknowledged as a safe and effective mode of treatment for many tibial fractures. Implant removal is frequently indicated either as an elective procedure following union or because of problems such as infection or delayed fracture union. It is therefore essential that intramedullary rod removal should be reasonably straightforward and atraumatic. We describe three cases in which bony growth into the implant has made rod removal either difficult or impossible. We include photographs of two removed implants with clearly visible areas of osseo-integration with bony growth into the cannulation through the interlocking holes as well as radiographs demonstrating the same phenomenon. The average time between insertion and removal was 16 months. In all cases an end cap had been used such that insertion of the extraction device was straightforward but for two patients nail removal was extremely difficult due to bone ingrowth and in the third patient the nail had to be left in-situ. All three implants were made of titanium and the patients were all active young males. The authors have never encountered this problem with steel rods and speculate that the osteointegrative property of titanium is the major causative factor. We suggest that unremoved intramedullary rods represent a major risk in fracture management and that close monitoring of these implants should be undertaken

This paper describes the preliminary results of a proximal tibial endoprosthesis which spares the knee joint and enables retention of the natural articulation by replacing part of the tibial metaphysis and diaphysis. In eight patients who had a primary malignant bone tumour of the proximal tibia, the distal stem, which had a hydroxyapatite-coated collar to improve fixation, was cemented into the medullary canal. The proximal end had hydroxyapatite-coated extracortical plates which were secured to the remaining proximal tibial metaphysis using cortical screws. The mean age of the patients at operation was 28.9 years (8 to 43) and the mean follow-up was for 35 months (4 to 48). The mean Musculoskeletal Tumour Society score was 79% (57% to 90%), the mean Oxford Knee score was 40 points of 48 (36 to 46) and the mean knee flexion was 112° (100° to 120°). In one patient, revision to a below-knee amputation through the prosthesis was required because of recurrence of the tumour. Another patient sustained a periprosthetic fracture which healed with a painful malunion. This was revised to a further endoprosthesis which replaced the knee.

In the remaining six patients the prosthesis allowed preservation of the knee joint with good function and no early evidence of loosening. Further follow-up is required to assess the longevity of these prostheses.

We report a case which highlights the progression of osteofibrous dysplasia to adamantinoma and questions whether intralesional curettage is the appropriate treatment. The role of a joint-sparing massive endoprosthesis using cortical fixation is demonstrated and we describe a unique biomedical design which resulted in the manufacture of an end cap to allow amputation through a custom-made proximal tibial replacement, rather than an above-knee amputation following recurrence

An understanding of the remodelling of tendon is crucial for the development of scientific methods of treatment and rehabilitation. This study tested the hypothesis that tendon adapts structurally in response to changes in functional loading. A novel model allowed manipulation of the mechanical environment of the patellar tendon in the presence of normal joint movement via the application of an adjustable external fixator mechanism between the patella and the tibia in sheep, while avoiding exposure of the patellar tendon itself. Stress shielding caused a significant reduction in the structural and material properties of stiffness (79%), ultimate load (69%), energy absorbed (61%), elastic modulus (76%) and ultimate stress (72%) of the tendon compared with controls. Compared with the material properties the structural properties exhibited better recovery after re-stressing with stiffness 97%, ultimate load 92%, energy absorbed 96%, elastic modulus 79% and ultimate stress 80%. The cross-sectional area of the re-stressed tendons was significantly greater than that of stress-shielded tendons.

The remodelling phenomena exhibited in this study are consistent with a putative feedback mechanism under strain control. This study provides a basis from which to explore the interactions of tendon remodelling and mechanical environment.

Introduction and Aims: A retrospective review of the medical records and radiographs of patients treated with operative fixation of two-part proximal humerus fractures was undertaken to compare the results of different modes of fixation. Comparison was made between ORIF with a blade plate, percutaneous Kirschner wire fixation, and intramedullary nail fixation utilising a Polarus nail. Method: Thirty-six patients were treated with intramedullary fixation, 11 with blade plate fixation and 10 with percutaneous fixation, utilising Kirschner wires. Union rates were 34/36 (94%) for the Polarus nail, 9/10 (90%) for K-wire fixation and 9/11 (82%) for blade plate fixation. Time to union averaged 12.4 weeks for the Polarus nail, 11 weeks for K-wire fixation and 21 weeks for blade plate fixation. Average active shoulder range of motion in forward flexion/abduction were 125/118 degrees for intramedullary nail, 132/132 degrees for the blade plate and 112/111 degrees for patients treated with K-wire fixation. Results: The major discrepancy in comparison of the different modes of fixation was in the complication rate. Ten complications occurred in the group treated with intramedullary fixation. These included one non-union, one painless fibrous non-union and back out of the proximal interlocking screw in eight patients, five of which required screw removal. Seven of 11 patients treated with blade plate fixation experienced complications, including two non-unions, two malunions, two with functionally limiting heterotopic ossification, one arthrofibrosis and one with persistent pain. The complications associated with percutaneous Kirschner wire fixation included one non-union, two malunions, four developed functionally limiting heterotopic ossification, five incidences of early pin removal secondary to pin migration, one arthrofibrosis requiring surgical intervention and one infection requiring surgical irrigation and debridement. Conclusion: Results comparable in all groups. Fewer complications seen with intramedullary fixation. Majority of complications with Polarus nail related to backing out of proximal interlocking screw. Modification of implant to include end cap, which locks the proximal screw seems to eliminate complication. Results indicate that intramedullary nail fixation is superior to blade plate fixation or pecutaneous Kirschner wire fixation for two-part proximal humerus fractures

Fragility fractures of the ankle occur mainly in elderly osteoporotic women. They are inherently unstable and difficult to manage. There is a high incidence of complications with both non-operative and operative treatment.

We treated 12 such fractures by closed reduction and stabilisation using a retrograde calcaneotalotibial expandable nail. The mean age of patients was 84 years (75 to 95). All were women and were able to walk fully weight-bearing after surgery. There were no wound complications. One patient died from a myocardial infarction 24 days after surgery. The 11 other patients were followed up for a mean of 67 weeks (39 to 104).

All the fractures maintained satisfactory alignment and healed without delay. Six patients refused removal of the nail after union of the fracture. The functional rating using the scale of Olerud and Molander gave a mean score at follow-up of 61, compared with a pre-injury value of 70.

This chamber is designed for use with conscious or unconscious patients requiring treatment with oxygen under high pressure. It can be pressurised to a maximum of 45 pounds per square inch above ambient (60 pounds per square inch absolute). The unit consists of two parts, the pressure chamber and the control console, connected together by flexible hose. The chamber can be operated up to a distance of 100 feet from the control console and both parts are mobile. The chamber consists of two concentrically mounted transparent cylinders, closed at the ends by domed metal caps. One end cap is detachable and can be removed, complete with the bed. The bed will accommodate a patient 6 feet 6 inches tall. The fully transparent chamber allows a complete view of the patient during treatment. A communication system is provided between the patient and operators. A loud speaker and microphone are built into the door of the chamber and two external pick-up points are situated on the console and the fixed end cap of the chamber. Two-way or three-way conversation is possible and the patient can be temporarily isolated from the system if required. Oxygen and electrical services must be coupled to the console. The chamber will operate directly from oxygen cylinders charged to a maximum of 1,800 pounds per square inch or from any piped supply with a minimum pressure of 75 pounds per square inch absolute. A self-contained 12-volt direct current battery supplies the necessary electrical power. A charging unit is incorporated in the control console and this is normally connected to an alternating current supply to keep the battery fully charged. If initially the battery is fully charged the unit can be operated in a continuous pressurisation-depressurisation cycle for at least twenty-four hours without further charging. Pressurisation and depressurisation are achieved by means of a motorised valve on the outlet of the pressure chamber. During pressurisation a variable speed motor applies a gradually increasing load to a helical spring. This in turn loads the outlet valve. By this means smooth pressure changes are obtained and the motor speed can be used to control the rate of pressure change. Operating the pressure chamber is simple. After the patient has been placed in the chamber and the door sealed by screw-down knobs, pressurisation is started by turning a selector switch on the control console. The required working pressure can be preset or the pressure can be held at any point between ambient and the top working pressure of 45 pounds per square inch above ambient. Pressurisation stops automatically when the preset level is reached or at 45 pounds per square inch. The rate of pressurisation is selected on the console and can be varied up to a maximum of approximately 8 pounds per square inch per minute. In the same manner, depressurisation can be controlled at any rate up to 8 pounds per square inch per minute down to ambient pressure, or held at any intermediate pressure according to the wishes of the operator. Coloured lights on the control panel indicate whether the chamber is ready for use, in the pressurisation or depressurisation state, holding a steady pressure or holding at the chosen maximum pressure. This pressure chamber is run as an open circuit. A continuous ventilating flow of oxygen passes through the chamber to wash out carbon dioxide and water vapour. In the event of an emergency affecting the patient, fast depressurisation controls are provided on both the chamber and the console. An electrically operated dumping valve can be triggered from the control console or the same valve operated manually from the end of the chamber. A pressure drop of one pound per square inch per second is obtained when this valve is used, and it is possible to reduce from maximum pressure and remove the patient from the chamber in approximately one minute. If a total power failure should occur, a manually operated, slow depressurisation valve can be opened on the control console. A number of sealed electrical plugs are provided in the door of the chamber. With suitable apparatus these allow electro-physiological monitoring of the patient throughout the course of the treatment