To review the results of the treatment of pilon fracture with percutaneous internal fixation and extrarticular ring fixation in neutralization, twenty-two fractures in twenty-one patients were included in the study. The mean follow-up time was 5.3 years. Five fractures were classified Ruedi-Algower type I, six were Ruedi-Algower type II and eleven Ruedi-Algower type III. Six were open fractures (3 Gustilo type III) and there were 19 associated fibular fractures (five were internally fIxed). Thirteen fractures (60%) were associated with metaphysealdiaphyseal dissociation (MDD). The majority of fractures were high energy (18 out of 22). General health outcome was assessed with the use of the SF-36 and functional outcome was evaluated with AOFAS score and Bone’s criteria.

The average AOFAS score for the study population was 79.4. The AOFAS scores decreased as the severity of the fracture increases and these differences were statistically significant between the Ruedi-Algower types I and III. The pilon fractures population scored lower in all SF-36 categories but mental health and energy and vitality when compared to an age matched population but statistically significant differences were only found in the categories of physical function and limitation due to health problems. 65% achieved excellent or good results according to Bone’s criteria. No significant differences were found in the union times in the MDD group (253 days) when compared to the fractures with no MDD (224 days), but this can be due to the high incidence of autograft in the MDD group (7 out of 13). All patients achieved full weight bearing at 6 weeks. Fourteen patients had superficial pin site infections (one needed screw removal) that settled with oral antibiotics. There was one case of non-union and two varus heels.

Conclusion: Good results are achieved treating pilon fractures with minimal internal fixation and the Sheffield ring fixator in neutralization but quality of life and functional scores significantly worsen in the most severe Ruedi-Algower type III fractures.

To review the results of limb lengthening and deformity correction in fibular hemimelia, fifty-five patients with fibular hemimelia underwent limb reconstruction at Sheffield Children’s Hospital. According to Achter-man and Kalamchi classification, twenty-six were classified as Type IA, six as Type IB and twenty-three as Type II fibular hemimelia. All patients had at least some shortening of ipsilateral femur but forty-nine had sig-nificant femoral deficiency. Lengthening of tibia and in significant cases femur was done using De Bastiani or Vilarrubias or Ilizarov methods. Ankle valgus and heel valgus were corrected through osteotomies either in the supramalleolar region or heel. Equinus was corrected by lengthening of tendoachelis with posterior soft tissue release and in severe cases using Ilizarov technique.

The average length gained was 4.2 cm (range 1 to 8) and the mean percentage of length increase was 15.82 (range 4.2 to 32.4). Mean bone healing index was 54.23 days/cm. Significant complications included knee subluxation, transient common paroneal nerve palsy, and recurrence of equinus and valgus deformity of foot. Overall alignment and ambulation improved in all patients. Knee stiffness due to cruciate deficient subluxations needed prolonged rehabilitation. Presence of 3-ray foot gives a better functional result and cosmetic acceptance by patients. The Ilizarov frame has the advantage to cross joints and lengthen at the metaphysis.

Limb reconstruction in fibular hemimelia using limb lengthening and deformity correction techniques improve functional status of involved lower limb.

We report a series of sixty corrections in fifty-five adult patients performed from 1989 to 2001 for complex deformities of the foot and ankle, using circular external fixation, with a mean follow up of 4.4 years. We studied the aetiology, pathophysiology of injury, clinical and radiological evaluation, and the method and outcome of treatment. The patients mean age was 37 years (range 16–65). 37 male. 18 females. 44 deformities were sequel of severe lower limb trauma; the others were due to neurological, congenital and iatrogenic causes. 38 patients had associated proximal pathology including non-union, malunion, shortening and deformities. This required simultaneous correction. In most patients, conventional surgery had failed to achieve correction and many of them were considered for amputation. The aim of surgery was correction of deformity in forty-two occasions and correction of deformity with ankle fusion in eighteen occasions.

For each patient, specific treatment goals were delineated that were realistically achievable. Initial complete correction was achieved in fifty-two patients; there was recurrence of the deformity in fourteen. Forty patients needed corrective osteotomies (16 ankles, 24 tibia and fibula). The results were classified as excellent in six patients, good in thirty-five patients, fair in eight patients, poor in six patients, five of whom had a below-knee amputation. Complications were minor and all resolved with appropriate therapy.

Conclusion: Circular external fixation offer a versatile and effective method of treatment of a variety of complex foot and ankle deformities; however, the surgeon should be familiar with both, their application and subsequent management. If foot and leg deformities coexist consider simultaneous correction. Corrective osteotomies may lead to less recurrence than soft tissue correction alone. Fusion should be considered where muscular imbalance or severe degenerative changes exists. In some cases with severe pathology; the only other option may be amputation.

To review the results of reconstruction of pseudoar-throsis and/or significant varus with retroversion of proximal femur in congenital longitudinal lower limb deficiencies, twenty-three of ninety-five patients with lower limb deficiencies underwent proximal femoral reconstruction at the Sheffield Children’s Hospital. All twenty-three underwent valgus derotation osteotomies to correct coxa vara and retroversion of femur. Seven patients also had pseudoarthrosis of the neck of femur. Three of these were treated with valgus derotation osteotomy and cancellous bone grafting, two with fibular strut grafts, one King’s procedure and one with excision of fibrous tissue and valgus derotation osteotomy. A variety of internal fixation devices and external fixator were used.

Seventeen of the twenty-three patients had valgus osteotomies repeated more than once (average 2.3) for recurrence of varus deformity. Average initial neck-shaft angle was 72 degrees, which improved to an average of 115 degrees after reconstruction.

All seven patients with pseudoarthroses underwent multiple procedures (average 3.3) to achieve union. Cancellous bone grafting was repeated twice in two patients to achieve union but all three with cancellous bone grafting underwent repeat osteotomies to correct residual varus. Two patients achieved union after fibu-lar strut grafting. One patient, who underwent excision of pseudoarthrosis, achieved union but had to undergo further valgus osteotomy. No particular advantage of any one-fixation device over the others was noted in achieving correction.

Early axis correction using valgus derotation oste-otomy is important in limb reconstruction when there is significant coxa vara and retroversion, although recurrence may require repeated osteotomies. Pseudoarthro-ses needed more aggressive surgery to achieve union.

Introduction: Circular fixators are widely utilised in orthopaedic surgery. Their biomechanical characteristics have been studied in some detail and it is known that the widest wire crossing angles yield maximum stability. Unfortunately, due to anatomical constraints, mechanically optimum wire crossing angles are seldom achievable, especially in the tibial diaphysis. Narrowed crossing angles are usually accepted thereby compromising sagittal plane bending stability. With a hybrid circular fixator, narrowed crossing angles exacerbate the problem of fracture site shear. It is hypothesised that by minimising slippage at the wire-bone interface by using threaded wires, stability can be maintained even with narrowed crossing angles. The aim of this study is to examine the effect of threaded wires on fracture site shear with a hybrid fixator.

Method: Bone-fixator models were created from nylon rods and the Orthofix Ring Fixator. Constructs with wire crossing angles of 70, 60, 45 and 30 degrees were loaded axially and in four point bending. Each construct was tested four times; the first test was not analysed. The whole fixator was then rebuilt and all tests repeated. Fracture motion (compression, angulation & shear) was measured using a strain gauge intersegmentary motion device and stiffness calculated by linear regression. Smooth & threaded wires were compared by univariate analysis of variance, which makes allowance for variation between individual frames.

Results: Axial stiffness was comparable to previous studies (85–96N/mm) with no difference between wire types. Threaded wires produced a 29% reduction in shear during axial compression (p=0.02). In four-point-bending, angulation stiffness (in the half-pin plane) was directly related to crossing angle and at all angles threaded wires were associated with a significant improvement. The table shows the effect of wire type on shear (in mm) measured in the plane of the half-pins for a 10Nm bending moment. Shear becomes appreciably higher with narrow crossing angles (almost 2mm) but this is effectively controlled by threaded wires.

Discussion: Of all the factors influencing fracture healing, the mechanical environment is one over which the surgeon has most control. It is generally accepted that excessive shear inhibits fracture healing. This study has shown that by using threaded wires in a circular frame, crossing angles can be narrowed without compromising stability. in particular they control undesirable shear motion seen with hybrid frames and narrow crossing angles. The principle is equally applicable to all-wire frames as they invariably are constructed with compromised crossing angles leading to reduced sagittal plane stability.

Fine-wire fixator systems have been used successfully for the treatment of fractures, malunions and for limb lengthening for many years. There has been much research investigating the biomechanical properties of these systems but this has been almost entirely centred on the mechanical properties of the fixator as a whole. Our knowledge of the interactions occurring at the interface between wire and bone remains sparse. To this end we devised an experimental model to analyse the distribution of pressure in cancellous bone surrounding a tensioned wire under loading conditions. The Sawbones cancellous bone material (type 1522-11) was cut into 65x30x40 mm blocks. A 2 mm olive wire was inserted into each block, parallel to the surface and along the 65 mm dimension. The distance from the wire to the surface was variable, from 0.5mm to 5mm in a 0.5mm increment. The wire was mounted on a 150 mm ring and tensioned to 1200 N against a load cell. The ring was rigidly mounted on a material testing machine and a second bone block was incorporated into the testing machine crosshead with a universal joint. Three grades of pressure-sensitive films (Low, Superlow and Ultralow) were sandwiched in turn between the testing block and cross head. The force applied was 175 N for 5 s. The developed film was scanned into a computer and a Matlab program was developed to analyse the pressure image. The results show three phases of pressure distribution. Very close to the wire there is a polar distribution of pressure that is, the pressure is concentrated towards the entry and exit points of the wire. At a depth of 1.5mm away from the wire the pressure becomes evenly distributed along the path of the wire in a beam-loading manner. At a distance of greater than 4mm from the wire there is even distribution of pressure throughout the bone. The peak pressures (6–8 MPa) were found closest to the wire. Most of the pressure measured was less than 1 MPa, which is less than the yield strength of cancellous bone (2–7 MPa, Li and Aspden, 1997). In contrast a similar analysis using threaded half pins under the same conditions showed far higher peak pressures (20 MPa), which were present deeper in the bone specimen. The pressure was concentrated toward the pin entry site and was not well distributed throughout the pin-bone interface. These results allow us to explain why ring fixators are superior to half pin fixators when used in metaphyseal bone.

Introduction: The Sheffield Ring Fixator (SRF) uses wires in the metaphysis and screws in the diaphysis for bone stabilisation. It has four 2mm wires tensioned to 1400N in two parallel groups to stabilise the ring in the metaphysis. For maximum stability, these parallel wires should cross at 60 degrees or greater and the position of the crossing should be in the centre of the bone. Fixation stability and clinical outcome may well depend on the accuracy of surgical application.

Aims: To review the consistency with which the SRF frames were applied by a single surgeon.

Materials and Methods: The fixators of 39 patients aged between 6 and 75 years of age (11.5 years mean age in children and 38.7 years mean age in adults) were examined. 7 patients had proximal and distal metaphyseal wires making a total of 46 recording sites. The angle of the wires was calculated using the number of holes between the wire clamps since each hole subtends an arc of 7.5 degrees. The crossing angles were divided into two groups with crossing angles of greater than 60 degrees and less than 60 degrees. The position of the crossing of the wires was determined by creating a cross section of the metaphyseal rings, reducing the size of the ring to 100mm and transposing a cross section of the tibia of the correct size and at the correct level. Scaling down the distances measured between the inner ring and the patient limb, the position of the cross section and consequently of the wire crossing was determined. Using contour lines the tibia was divided into four zones. Zone 1 was central tibia and zone 4 was the tibial cortex. All crossing within zone 1 and 2 were considered satisfactory, and zone 3 and 4 poor.

Results: 67.5% of patients had crossing angles greater than 60 degrees and 32.5 % had crossing angles of less than 60 degrees. 85% of the rings had zone 1 or 2 crossing positions. 6.5% of the rings had subcortical crossing positions and 8.5% of the rings had cortical crossing positions. 8.5% of rings had crossing angles of less than 60 degrees as well as wire crossing positions in zone 3 and 4.

Discussion: In a carefully controlled situation a surgeon’s surgical technique was consistent in 67.5% of the rings, with satisfactory crossing angles and wire crossing positions. Only 8.5 % of the rings had poor crossing angles and crossing positions. Inability to achieve ideals may be due to technical errors or anatomical variations. There were increased infection rates in patients with reduced crossing angles, however the position of the crossing had no apparent effect on infection rates and patient mobility. A further study would be required to separate the relative importance of these two factors on patient complications.

Purpose: The aim of this part retrospective and part prospective study was to establish the incidence of pinsite infections and assess evolution of changes in practice

Methods: Data was collected retrospectively and prospectively for pin site infections from the inception of limb reconstruction service viz. 1985 to January 2002. There were 812 patients, 1042 limb segments, and 9935 pins. The various external fixators used were limb reconstruction system (LRS) 549; Ilizarov 397; Sheffield ring fixator (SRF); Dynamic axial fixator (DAF) 35; LRS/Sequoia 8; LRS/Garche 7; and Pennig 5.

Results: The pin site infections were graded from 0 to 6 ( Saleh & Scott). There were no infections in 206 segments. The infection grade is shown below:

We changed our pin tract care practice from 1996. We had a significant decrease in pin tract infections since then (p< 0.0001). We also found that using Ilizarov wires had significantly less infections than with half pins used with monolateral fixators (p< 0.0001; linear trend, p= 0.0338). There were 48 patients that required hospital admissions for IV antibiotics. and of these 10 patients required debridement. There were no residual long lasting infections or chronic osteomyelitis.

Conclusion: Attention to detail in insertion of wires and half pins is crucial to avoid pin site infections. This audit supports the fact that external fixation is a safe method from the point of view of infection contrary to general belief.

Aim: To review the results of tibial lengthening and deformities correction in children using the Sheffield Ring Fixator.

Materials and methods: We have reviewed, retrospectively, 25 patients (average 12.2 years old) who underwent predominantly lengthening of the tibia using the Sheffield Ring fixator.

The average follow up was 25.7 months. For logistic regression analysis the patients were binary coded into two groups: those with a good outcome (BHI< 45 days/cm) and those with a poor outcome (BHI> 45 days/cm). Various factors which may influence the out come were then analysed.

Results: The most common indication for tibial lengthening in our series was for fibular hemimelia in 6 patients and achondroplasia in 4 and growth arrest secondary to trauma in 3. The mean lengthening of 48.1 mm (25–76). The mean accuracy of lengthening achieved was 85%.

11 patients had foot plate extension, and 5 had cross knee extension for unstable knee. 10 patients had bifocal osteotomy, and 8 patients had spontaneous SLR for femoral lengthening or correction.

The mean bone healing index was 49 days/cm (20–95). The mean maximum correction in any one plane was 150 (3–40), the site of the osteotomy was mainly metaphyseal at an average of 25% of the tibial length.

There were 5 grade II complications, 9 grades I complications and one type III complication. Thirteen patients had grade I pin site infection, three had grade II and 12 had no pin site problems.

A moderately strong relationship was identified between the BHI and a number of variables such as complications, maximum correction and pin site infection grade.

The analysis of the factors which may influence the BHI suggested a correlation between increasing angular correction and poor out come BHI.

Conclusion: In tibial lengthening in children there is a correlation between increasing angular correction and poor out come BHI

Aim: To review the outcome following growth plate arrest in distal femur and proximal tibia of different aetiology in adults.

Materials and methods: We have reviewed, retrospectively, eight adult patients with lower leg deformity in the distal femur and proximal tibia, as a sequelae of growth plate arrest of different aetiology. These patients underwent tibial and femoral, correction and lengthening. The total number was 8 patients, there were 6 male and 2 female, with an average age of 22.8 years (17–34.8) The average follow up was 32.9 months (7.9–51.4)

Results: Four patients had growth plate arrest following trauma (two patients were involved in road traffic accidents, one had Salter-Harris type V fracture of the proximal tibia and one had sport injury), two patients had iatrogenic growth plate arrest after internal fixation of tibial spine in one patient and after internal fixation of a popliteal muscle rupture in the other, one patient had Osgood Schlater disease, one patient had childhood osteomyelitis and one unknown pathology.

The average shortening was 34.8 mm (8–60), the average maximum deformity in any one plane was 19.8 degree (6–40).

All the patient underwent corrective surgery and lengthening, five patients had Sheffield Ring Fixator, two had Limb Reconstruction System and one had percutaneous osteotomy on Albizzia nail. The patients who underwent SRF and LRS stayed in the frame for an average 258 days (150–435)

The residual leg length discrepancy was 5.5 mm (0–12). There was three grade one complications, three grade two complications, and one patient had grade IV complication following compartment syndrome. Four patients had grade two pin site infection and three patients had grade one.

Conclusion: Growth plate arrest of the distal femur and proximal tibia can cause severe deformity and shortening of the lower limb in adult, and this deformity is amenable to correction in the end of growth using different techniques. We used Sheffield ring fixator in complex cases, to address both deformities and lengthening, while other techniques were used in less complex cases.

We present a series of 88 non-unions in which non-union, infection, bony alignment and length were addressed simultaneously, by using the Sheffield Ring Fixator.

The mean follow up was 50 months (range 6–110) after union, which was achieved in 90.5% of the patients. The mean deformity correction was 16.80 (range 60–320), and mean length gain was 12.5 mm (range 2–40 mm).

Smoking and infection had a statistical significant association with the time of healing, as healing of the non-union in over 18 months was more common in smoker and patients with infected non-union.

There was no statistical difference between the functional score (SF-36) between these patients and normal population, at a follow up of minimum 2 years, but that was significant between pre operative and less than one year follow up on one side, and more than 2 years follow up on the other.

Introduction and Aims: We report a series of 41 corrections in 36 adult patients performed for complex deformities of the foot and ankle using circular external fixation, with a mean follow-up of 4.4 years. The foot and ankle deformities were 18 hindfoot equines, two forefoot equines, six hindfoot and forefoot equines, eight equinovarus, two equinovalgus, one heel varus, four combination of these deformities. All patients had associated proximal pathology. These included seven shortening (six tibia, one femur), eight deformities (seven tibia, one femur), eight non-union (five infected non-union), (14) combination of these pathologies. All required simultaneous correction.

Method: We studied the aetiology, pathophysiology of injury, clinical and radiological evaluation, and the outcome of treatment. The patients’ mean age was 37 years (range 16–56). Thirty deformities were sequelae of severe lower limb trauma; the others were due to neurological, congenital and iatrogenic causes. In all patients, conventional surgical methods had failed to achieve correction and many of them were considered for amputation. We describe the operative strategy and technique.

Results: The aim of foot and ankle surgery was correction of deformity and contractures in 28 instances, correction of deformity and ankle fusion in 11 instances, and correction of deformity and ankle distraction in two instances. Thirty patients underwent bony corrective osteotomies, nine foot and ankle, 20 tibia and fibulae, one femur. For each patient, specific treatment goals were delineated that were realistically achievable. There were (78%) good to excellent results, (14%) fair result and (8%) poor results, which resulted in below knee amputation.

Conclusion: Circular external fixation offers a versatile and effective method of treatment of a variety of complex foot and ankle deformities. If foot and leg deformities coexist consider simultaneous correction. Fusion should be considered where muscular imbalance exists.

Objective: To compare the mechanical stability of fixation of bicondylar tibial plateau fractures using available internal and external fixation techniques.

Method: A bicondylar tibial plateau fracture was simulated on a uniform synthetic bone and tested with loading to failure. Following power calculations, seven tibias were used for each fixation method; five types of fixation were tested: 1) Dual plating. 2) Ring Fixator with inter-fragmentary screws. 3) Hybrid fixator (Ring-Bar) with interfragmentary screws. 4) Lateral plate and medial monolateral external fixator. 5) Lateral plate and medial interfragmentary screws. The specimens were tested in compression to failure. The vertical subsidence in either medial or lateral plateau was measured using an electrical transducer.

Results: In all cases the mode of failure was consistent with collapse occurring in the medial plateau. There was no significant difference in the ultimate strength between dual plating and the ring fixator [4218N, 4184N respectively; P=0.28, t test]. Failure was seen at lower loads with the other fixation systems (Table).

Conclusion: The Ring Fixator and dual plating demonstrated a greater strength and the most stable fixation, choice may depend on tissue viability and surgeon preference. Furthermore mobilisation of the patient may be undertaken earlier with more confidence using these two methods rather than less stable techniques.

Aims: To identify the distraction forces and contact pressures of the ankle joint at two different joint positions during articulated ankle distraction.

Material and Methods: Four amputated lower limbs were collected from patients undergoing amputation for vascular disease and frozen at -70° C. The ankle joint of the specimens were normal. Before use the limbs were thawed at room temperature for 24 hours. The skin and subcutaneous tissues were removed. A Sheffield ring fixator consisting of a proximal tibial ring and a foot plate connected through three threaded bars and hinges aligned with ankle axis was mounted on the limb. Force transducers were placed in the threaded bars between the tibial ring and the foot plate on the lateral, medial and posterior aspect of the ankle joint to measure the ankle distraction forces. Once the ankle distraction forces have been measured an anterior ankle arthrotomy was performed to permit the insertion of Fuji pressure sensitive film within the ankle joint. The limb-fixator construct was mounted in a loading machine and axially loaded on the tibia. The ankle joint was distracted at 2 mm intervals to a maximum of 20 mm. Pressure sensitive film was introduced in the ankle joint at each distraction interval and the tibia was axially loaded at 350, 700, 1050 and 1400N (half to two times body weight).

Results: The forces necessary to distract the ankle joint are almost double in the medial side than the lateral side. With 10° of plantarflexion the forces necessary to distract the lateral side increase by about 10%.

We found the center of pressure of the ankle joint to be situated in the antero-medial quadrant, close to the center of the ankle joint. Distraction of the ankle joint by 5 mm eliminated any contact pressures at the ankle joint when the tibia was loaded up to 700N (one time body weight). When the joint was distracted by 10 mm no contact pressures were found in the ankle when loaded up to 1400N (two times body weight)

Conclusions: With the ankle in the plantigrade position the forces necessary to distract the ankle joint are double in the medial side when compared to the lateral side. Plantarflexion increases the forces necessary to distract the lateral aspect of the ankle. This finding may have clinical implications when distracting ankle joints with equinus deformities as this can increase the risk of damaging the lateral ankle ligaments leading to ankle instability. In our opinion equinus deformities should be corrected before the start of ankle joint distraction.

The center of pressure of the ankle joint is situated in the antero-medial quadrant. Distraction of 5 mm will eliminate ankle contact pressure up to one times body weight whereas distraction of 10 mm will eliminate contact pressures up to two times body weight.

Introduction: Distraction osteogenesis has been used as a method of generating new bone in limb lengthening and deformity realignment; and is achieved in our unit though the use of the Sheffield Ring Fixator. The development of soft tissue tension creates an entirely different mechanical environment, and can often result in severe complications during treatment. Fixators must therefore be able to resist these forces. Furthermore, biomechanical modelling is very different from fracture and bone gap simulation.

The model developed in this study intended to look at linear distraction, i.e. lengthening.

Aims: To create a mechanical model that simulates the soft tissue effects during lengthening with an external fixator

To obtain a synthetic material with similar passive tensile properties to that measured in lengthened soft tissue

To measure the effect of tensioned synthetic soft tissue on osteotomy motion and multi-planar stiffness during cyclic loading.

Materials and Methods: A standard two 150mm ring frame was mounted on an acrylic rod, with a centrally placed osteotomy gap of 75mm. One ring was fixed with wires and the other with screws. An inter-fragmentary motion device was attached across the osteotomy, to measure axial, angular and shear deformation with both axial and off-axis loading.

Soft tissue tension was simulated with the use of neoprene rubber sheeting, attached to the nylon rod by Jubilee clips, with a gap anteriorly or medially. Extensive tensile testing was performed to determine the visco-elastic behaviour of the rubber, which showed it to be consistent and reliable. Tension of a similar magnitude to lengthened muscle (35–125N) was achieved, and could be accurately predicted for certain distraction lengths.

The stiffness of the frame was calculated from osteotomy motion with various distraction lengths both with the rubber attached and without.

Results: Tension in the soft tissues summates with the force applied in loading, with the effect of increasing the axial stiffness of the fixator by up to 70N, with a directly proportional relationship. It also acts as a restraint for shear and angulatory motion. In anterior and lateral loading positions however, the angulation stiffness remains low; this is thought to be due to the unequal distribution of soft tissues around the bony column, as seen in vivo. The stiffness of the frame is lowered by increasing the distance between rings; this effect can be counteracted by soft tissue tension in axial stiffness, but less so for angular and shear.

Conclusions: We conclude that osteotomy stability is dependent on soft tissue tension, and the magnitude of tension greatly alters the stiffness characteristics of the external fixator. This study highlights the important role of soft tissue tension in biomechanical modelling and clinical limb lengthening, and has exciting ramifications for future orthopaedic models.

Introduction and Aims: To review the existing classifications in characterising the pathologic morphology of congenital lower limb deficiencies (CLLLD) and their usefulness in planning limb reconstruction.

Method: Ninety-five patients undergoing limb reconstruction were classified using existing classifications. Predominantly femoral deficiencies were classified using Aitken, Amstutz, Hamanishi, Gillespie and Torode, Fixsen and Lloyd-Roberts, Kalamchi, and Pappas systems and fibular deficiencies were classified using Coventry and Johnston, Achterman and Kalamchi, and Birch systems.

Results: All patients with predominant deficiency of one segment (femoral or fibular) also had associated shortening of the other segment in the same limb. Acetabular dysplasia, knee instability due to cruciate insufficiency and lateral femoral condylar hypoplasia were found in both femoral and fibular deficiencies. None of the existing classification systems were able to represent the complete pathologic morphology in any given patient. Due consideration of alignment, joint stability and length discrepancy of affected limb as a whole at the planning stage of reconstruction could not be ascertained using these classification systems. Instead, it was useful to characterise the morphology of the involved limb using the following method:

Acetabulum: Dysplastic/Non-dysplastic

Conclusion: Existing classifications do not represent the complete morphology of the entire involved lower limb in CLLLD and therefore a systematic method of characterising the morphology of the lower limb is more useful in planning limb reconstruction.

Background: The stability of fracture fixation is influenced by the type of fixation, densitometric and geometric structure of the bone. DXA measures the integral mass of trabecular and cortical bone mineral but cannot discriminate between the structurally and mechanically separate constitutes. Distribution and organisation of bone mass (the geometric structure) has the final determination of the mechanical properties of bone. Pq CT scan is able to measure densitometric and geometric parameters of bone structure. However, there are no reports in the literature on the relationship between these measurements and the strength of fracture fixation. Our aim is to study the correlation between geometric and densitometric measurements of Pq CT scan, with the strength of fixation of bicondylar tibial plateau fractures and to assess the role of both trabecular and cancellous bone in that strength.

Method: Eight Fresh frozen human cadaveric tibias were collected from subjects without a medical history of skeletal pathology. The proximal 10% of the tibia was scanned in a peripheral quantitative computer tomography scanner 1mm thick transverse slides, the cancellous and cortical bone mineral density of the proximal tibia were measured. The geometrical parameters: cortical area, trabecular area, bone strength index (BSI) and the Stress strain index (SSI) as non invasive indicators of the mechanical strength of the bone, were also calculated. A bicondylar tibial plateau fracture was simulated, stabilised, and then tested. All tibias were fixed with Dual buttress plating using a standard AO technique. Cyclic axial compression tests were performed. Inter-fragmentary shear displacements were measured using four extensometers. Failure was defined as over 3mm displacement.

Results: Except for the cortical density, there was a strong correlation between failure load and geometric and densitometric parameters. The trabecular density was the best predictor of fixation strength of tibial plateau fracture.

Discussion: Trabecular density is a more reliable parameter to measure than the cortical density. Therefore, the fixation strength of tibial plateau fracture is dominantly influenced by the mechanical properties of cancelous bone. Cortical bone has a secondary role.

These results highlight the importance of fixation techniques that rely on cancellous bone anchoring such as tensioned fine wire fixation in tibial plateau fractures.

Objectives: To develop a non-invasive method to assess the wire tension quantitatively which can be used in clinic.

Background: Fine-wire external fixators are widely used in the fixation of fractures and limb reconstruction. A requirement of stable fixation is that the wires maintain their tension. Recent lab tests have shown that substantial reduction in wire tension occurred during the simulated operative procedures. Clinical experience also indicated that wire site discomfort might be related to loss in wire tension. It would be very helpful if the wire tension could be assessed quantitatively by a non-invasive method.

Methods: An apparatus based on a LVDT (Linear Variable Differential Transformer) was developed to apply a constant transverse force to a wire and measure its deflection with respect to another parallel wire. An unstable oblique fracture was created in a Sawbones tibia and stabilized by a Sheffield Ring Fixator. The deflection of the testing wire was measured in four tests: (1) Two parallel wires fixation, tensioned reference wire, variable clamp to bone distance; (2) Two parallel wires fixation, loose reference wire, 80mm clamp-bone distance. (3) Two groups of parallel wires fixation with 70° crossing angle, tensioned reference wire, 80mm clamp-bone distance; (4) Two groups of parallel wires fixation with 70° crossing angle, tensioned reference wire, 80mm clamp-bone distance, osteotomy site fixed with a lag screw to simulate a stable fracture or a healing fracture. Fracture stiffness in the above conditions was derived from previous work. Stepwise multiple variable regression analyses were performed to determine the relationship between wire deflection and wire tension, clamp-bone distance, number of wires, reference wire tension, and fracture stiffness.

Results: The reference wire tension and fracture stiffness was excluded from the regression equation, indicating that they did not affect the wire deflection. The regression equation containing only the testing wire tension had an adjusted R-square value of 0.521, while the equation containing the testing wire tension and clamp-bone distance had the R-square values of 0.854. The addition of the number of wires to the regression equation resulted in a slight increase of the R-square value (0.862).

Conclusion: The wire deflection and the clamp-bone distance are the two most important factors that affect wire deflection. The measurement of wire deflection has the potential to predict wire tension and the effect of clamp-bone distance must be considered. Further work is required to refine the apparatus for clinical use.

Introduction and Aims: A previous study showed the inhibitory effect of 30% metaphyseal lengthening on tibial growth (Lee 1993). This study was to investigate the effect of 30% diaphyseal lengthening of tibia on tibial growth plate and growth.

Method: 32 immature rabbits were equally divided into two groups: lengthening and sham. A bilateral external fixator was applied to the tibia and a mid-diaphyseal osteotomy performed. The lengthening group had their tibia distracted on the fifth day after the surgery at a rate of 0.4 mm twice daily until the achievement of 30% lengthening. In each group, half were sacrificed at the end of lengthening and another half after an additional five weeks. Standard radiographs were used to measure the lengths of the tibiae from the most proximal part of the intercondylar eminence to the most distal part of the medial malleollus. The actual length gained was measured by subtracting the pre-operative distance from the lengthened distance using the central points of two middle wires in the tibia as reference points. Specimens from the proximal and distal tibia were sectioned longitudinally in the midcoronal plane and the mean growth plate thickness was calculated from several measurements taken at the middle third of both medial and lateral halves of the section.

Results: In the sham group, the thickness of the growth plates continued to increase with skeletal development showing an increase in total tibial length compared with the contra-lateral control. In contrast, the lengthening group showed no increase in total tibial length compared to the contra-lateral control, suggesting that the stimulation due to the osteotomy may be matched by an inhibitory effect of 30% lengthening.

Conclusion: Thirty percent diaphyseal lengthening of tibia did not change the longitudinal growth of the tibia.

Biomechanical studies involving all-wire and hybrid types of circular frame have shown that oblique tibial fractures remain unstable when they are loaded. We have assessed a range of techniques for enhancing the fixation of these fractures. Eight models were constructed using Sawbones tibiae and standard Sheffield ring fixators, to which six additional fixation techniques were applied sequentially.

The major component of displacement was shear along the obliquity of the fracture. This was the most sensitive to any change in the method of fixation. All additional fixation systems were found to reduce shear movement significantly, the most effective being push-pull wires and arched wires with a three-hole bend. Less effective systems included an additional half pin and arched wires with a shallower arc. Angled pins were more effective at reducing shear than transverse pins.

The choice of additional fixation should be made after consideration of both the amount of stability required and the practicalities of applying the method to a particular fracture.