The December 2015 Children’s orthopaedics Roundup360 looks at: Paediatric femoral fractures: a single incision nailing?; Lateral condylar fractures: open or percutaneous?; Forearm refracture: the risks; Tibial spine fractures; The child’s knee in MRI; The mechanics of SUFE; Idiopathic clubfoot
There has been an evolution recently in the management of unstable
fractures of the ankle with a trend towards direct fixation of a
posterior malleolar fragment. Within these fractures, Haraguchi
type 2 fractures extend medially and often cannot be fixed using
a standard posterolateral approach. Our aim was to describe the
posteromedial approach to address these fractures and to assess
its efficacy and safety. We performed a review of 15 patients with a Haraguchi type 2
posterior malleolar fracture which was fixed using a posteromedial
approach. Five patients underwent initial temporary spanning external
fixation. The outcome was assessed at a median follow-up of 29 months (interquartile
range (IQR) 17 to 36) using the Olerud and Molander score and radiographs were
assessed for the quality of the reduction.Aims
Patients and Methods
Adolescent idiopathic scoliosis (AIS) is a complex
3D deformity of the spine. Its prevalence is between 2% and 3% in the
general population, with almost 10% of patients requiring some form
of treatment and up to 0.1% undergoing surgery. The cosmetic aspect
of the deformity is the biggest concern to the patient and is often
accompanied by psychosocial distress. In addition, severe curves
can cause cardiopulmonary distress. With proven benefits from surgery,
the aims of treatment are to improve the cosmetic and functional
outcomes. Obtaining correction in the coronal plane is not the only
important endpoint anymore. With better understanding of spinal
biomechanics and the long-term effects of multiplanar imbalance,
we now know that sagittal balance is equally, if not more, important.
Better correction of deformities has also been facilitated by an
improvement in the design of implants and a better understanding
of metallurgy. Understanding the unique character of each deformity
is important. In addition, using the most appropriate implant and
applying all the principles of correction in a bespoke manner is important
to achieve optimum correction. In this article, we review the current concepts in AIS surgery. Cite this article:
The best method of treating unstable pelvic fractures that involve
the obturator ring is still a matter for debate. This study compared
three methods of treatment: nonoperative, isolated posterior fixation
and combined anteroposterior stabilization. The study used data from the German Pelvic Trauma Registry and
compared patients undergoing conservative management (n = 2394),
surgical treatment (n = 1345) and transpubic surgery, including
posterior stabilization (n = 730) with isolated posterior osteosynthesis
(n = 405) in non-complex Type B and C fractures that only involved the
obturator ring anteriorly. Calculated odds ratios were adjusted
for potential confounders. Outcome criteria were intraoperative
and general short-term complications, the incidence of nerve injuries,
and mortality.Aims
Patients and Methods
Unicompartmental knee arthroplasty (UKA) is a demanding procedure, with tibial component subsidence or pain from high tibial strain being potential causes of revision. The optimal position in terms of load transfer has not been documented for lateral UKA. Our aim was to determine the effect of tibial component position on proximal tibial strain. A total of 16 composite tibias were implanted with an Oxford Domed Lateral Partial Knee implant using cutting guides to define tibial slope and resection depth. Four implant positions were assessed: standard (5° posterior slope); 10° posterior slope; 5° reverse tibial slope; and 4 mm increased tibial resection. Using an electrodynamic axial-torsional materials testing machine (Instron 5565), a compressive load of 1.5 kN was applied at 60 N/s on a meniscal bearing via a matching femoral component. Tibial strain beneath the implant was measured using a calibrated Digital Image Correlation system.Objectives
Methods
Corticosteroids are prescribed for the treatment of many medical conditions and their adverse effects on bone, including steroid-associated osteoporosis and osteonecrosis, are well documented. Core decompression is performed to treat osteonecrosis, but the results are variable. As steroids may affect bone turnover, this study was designed to investigate bone healing within a bone tunnel after core decompression in an experimental model of steroid-associated osteonecrosis. A total of five 28-week-old New Zealand rabbits were used to establish a model of steroid-induced osteonecrosis and another five rabbits served as controls. Two weeks after the induction of osteonecrosis, core decompression was performed by creating a bone tunnel 3 mm in diameter in both distal femora of each rabbit in both the experimental osteonecrosis and control groups. An In the osteonecrosis group all measurements of bone healing and maturation were lower compared with the control group. Impaired osteogenesis and remodelling within the bone tunnel was demonstrated in the steroid-induced osteonecrosis, accompanied by inferior mechanical properties of the bone. We have confirmed impaired bone healing in a model of bone defects in rabbits with pulsed administration of corticosteroids. This finding may be important in the development of strategies for treatment to improve the prognosis of fracture healing or the repair of bone defects in patients receiving steroid treatment.
Because of the contradictory body of evidence related to the
potential benefits of helical blades in trochanteric fracture fixation,
we studied the effect of bone compaction resulting from the insertion
of a proximal femoral nail anti-rotation (PFNA). We developed a subject-specific computational model of a trochanteric
fracture (31-A2 in the AO classification) with lack of medial support
and varied the bone density to account for variability in bone properties
among hip fracture patients.Objectives
Methods
Focal femoral inlay resurfacing has been developed
for the treatment of full-thickness chondral defects of the knee. This
technique involves implanting a defect-sized metallic or ceramic
cap that is anchored to the subchondral bone through a screw or
pin. The use of these experimental caps has been advocated in middle-aged
patients who have failed non-operative methods or biological repair
techniques and are deemed unsuitable for conventional arthroplasty
because of their age. This paper outlines the implant design, surgical
technique and biomechanical principles underlying their use. Outcomes
following implantation in both animal and human studies are also reviewed. Cite this article:
Favourable results for collarless polished tapered stems have been reported, and cement creep due to taper slip may be a contributing factor. However, the ideal cement thickness around polished stems remains unknown. We investigated the influence of cement thickness on stem subsidence and cement creep. We cemented six collarless polished tapered (CPT) stems (two stems each of small, medium and large sizes) into composite femurs that had been reamed with a large CPT rasp to achieve various thicknesses of the cement mantle. Two or three tantalum balls were implanted in the proximal cement in each femur. A cyclic loading test was then performed for each stem. The migration of the balls was measured three-dimensionally, using a micro-computed tomography (CT) scanner, before and after loading. A digital displacement gauge was positioned at the stem shoulder, and stem subsidence was measured continuously by the gauge. Final stem subsidence was measured at the balls at the end of each stem.Objectives
Methods
It is becoming increasingly common for a patient
to have ipsilateral hip and knee replacements. The inter-prosthetic (IP)
distance, the distance between the tips of hip and knee prostheses,
has been thought to be associated with an increased risk of IP fracture.
Small gap distances are generally assumed to act as stress risers,
although there is no real biomechanical evidence to support this. The purpose of this study was to evaluate the influence of IP
distance, cortical thickness and bone mineral density on the likelihood
of an IP femoral fracture. A total of 18 human femur specimens were randomised into three
groups by bone density and cortical thickness. For each group, a
defined IP distance of 35 mm, 80 mm or 160 mm was created by choosing
the appropriate lengths of component. The maximum fracture strength
was determined using a four-point bending test. The fracture force of all three groups was similar (p = 0.498).
There was a highly significant correlation between the cortical
area and the fracture strength (r = 0.804, p <
0.001), whereas
bone density showed no influence. This study suggests that the IP distance has little influence
on fracture strength in IP femoral fractures: the thickness of the
cortex seems to be the decisive factor. Cite this article:
Aseptic loosening of the acetabular component continues to be the most common indication for revision of total hip replacements in younger patients. Early in the evolution of the cemented hip, arthroplasty surgeons switched from removal to retention of the acetabular subchondral bone plate, theorising that unfavourable mechanical forces were the cause of loosening at the bone-cement interface. It is now known that the cause of aseptic loosening is probably biological rather than mechanical and removing the subchondral bone plate may enhance biological fixation of cement to bone. With this in mind, perhaps it is time to revive removal of the subchondral bone as a standard part of acetabular preparation.
The aim of the current study was to analyse the effects of posterior cruciate ligament (PCL) deficiency on forces of the posterolateral corner structure and on tibiofemoral (TF) and patellofemoral (PF) contact force under dynamic-loading conditions. A subject-specific knee model was validated using a passive flexion experiment, electromyography data, muscle activation, and previous experimental studies. The simulation was performed on the musculoskeletal models with and without PCL deficiency using a novel force-dependent kinematics method under gait- and squat-loading conditions, followed by probabilistic analysis for material uncertain to be considered.Objectives
Methods
An ongoing prospective study to investigate failing metal-on-metal
hip prostheses was commenced at our centre in 2008. We report on
the results of the analysis of the first consecutive 126 failed
mated total hip prostheses from a single manufacturer. Analysis was carried out using highly accurate coordinate measuring
to calculate volumetric and linear rates of the articular bearing
surfaces and also the surfaces of the taper junctions. The relationship
between taper wear rates and a number of variables, including bearing
diameter and orientation of the acetabular component, was investigated.Objectives
Methods
The bony shoulder stability ratio (BSSR) allows for quantification of the bony stabilisers Four polyethylene balls (radii: 19.1 mm to 38.1 mm) were used to mould four fitting sockets in four different depths (3.2 mm to 19.1mm). The SR was measured in biomechanical congruent and incongruent experimental series. The experimental SR of a congruent system was compared with the calculated SR based on the BSSR approach. Differences in SR between congruent and incongruent experimental conditions were quantified. Finally, the experimental SR was compared with either calculated SR based on the socket concavity or plastic ball radius.Objectives
Methods
The December 2012 Spine Roundup360 looks at: the Japanese neck disability index; adjacent segment degeneration; sacroiliac loads determined by limb length discrepancy; whether epidural steroids improve outcome in lumbar disc herniation; spondylodiscitis in infancy; total pedicle screws; and iliac crest autograft complications.
The acetabular labrum is a soft-tissue structure
which lines the acetabular rim of the hip joint. Its role in hip
joint biomechanics and joint health has been of particular interest
over the past decade. In normal hip joint biomechanics, the labrum
is crucial in retaining a layer of pressurised intra-articular fluid
for joint lubrication and load support/distribution. Its seal around
the femoral head is further regarded as a contributing to hip stability through
its suction effect. The labrum itself is also important in increasing
contact area thereby reducing contact stress. Given the labrum’s
role in normal hip joint biomechanics, surgical techniques for managing
labral damage are continuously evolving as our understanding of
its anatomy and function continue to progress. The current paper
aims to review the anatomy and biomechanical function of the labrum
and how they are affected by differing surgical techniques. Take home message: The acetabular labrum plays a critical role
in hip function and maintaining and restoring its function during
surgical intervention remain an essential goal. Cite this article:
Surgeons have commonly used modular femoral heads and stems from
different manufacturers, although this is not recommended by orthopaedic
companies due to the different manufacturing processes. We compared the rate of corrosion and rate of wear at the trunnion/head
taper junction in two groups of retrieved hips; those with mixed
manufacturers (MM) and those from the same manufacturer (SM). We identified 151 retrieved hips with large-diameter cobalt-chromium
heads; 51 of two designs that had been paired with stems from different
manufacturers (MM) and 100 of seven designs paired with stems from
the same manufacturer (SM). We determined the severity of corrosion
with the Goldberg corrosion score and the volume of material loss
at the head/stem junction. We used multivariable statistical analysis
to determine if there was a significant difference between the two
groups. Aims
Materials and Methods
This article presents a unified clinical theory
that links established facts about the physiology of bone and homeostasis,
with those involved in the healing of fractures and the development
of nonunion. The key to this theory is the concept that the tissue
that forms in and around a fracture should be considered a specific
functional entity. This ‘bone-healing unit’ produces a physiological
response to its biological and mechanical environment, which leads
to the normal healing of bone. This tissue responds to mechanical
forces and functions according to Wolff’s law, Perren’s strain theory
and Frost’s concept of the “mechanostat”. In response to the local
mechanical environment, the bone-healing unit normally changes with
time, producing different tissues that can tolerate various levels
of strain. The normal result is the formation of bone that bridges
the fracture – healing by callus. Nonunion occurs when the bone-healing
unit fails either due to mechanical or biological problems or a
combination of both. In clinical practice, the majority of nonunions
are due to mechanical problems with instability, resulting in too
much strain at the fracture site. In most nonunions, there is an
intact bone-healing unit. We suggest that this maintains its biological
potential to heal, but fails to function due to the mechanical conditions.
The theory predicts the healing pattern of multifragmentary fractures
and the observed morphological characteristics of different nonunions.
It suggests that the majority of nonunions will heal if the correct
mechanical environment is produced by surgery, without the need
for biological adjuncts such as autologous bone graft. Cite this article:
The cortical strains on the femoral neck and proximal femur were measured before and after implantation of a resurfacing femoral component in 13 femurs from human cadavers. These were loaded into a hip simulator for single-leg stance and stair-climbing. After resurfacing, the mean tensile strain increased by 15% (95% confidence interval (CI) 6 to 24, p = 0.003) on the lateral femoral neck and the mean compressive strain increased by 11% (95% CI 5 to 17, p = 0.002) on the medial femoral neck during stimulation of single-leg stance. On the proximal femur the deformation pattern remained similar to that of the unoperated femurs. The small increase of strains in the neck area alone would probably not be sufficient to cause fracture of the neck However, with patient-related and surgical factors these strain changes may contribute to the risk of early periprosthetic fracture.
