Introduction

Aseptic loosening of the acetabular cup in total hip replacement (THR) remains a major problem. Current diagnostic imaging techniques are ineffective at detecting early loosening, especially for the acetabular component. The aim of this preliminary study was to assess the viability of using a vibration analysis technique to accurately detect acetabular component loosening.

Stable, anatomical fixation of acetabular fractures gives the best chance of a good outcome. We performed a biomechanical study to compare fracture stability and construct stiffness of three methods of fixation of posterior wall acetabular fractures.

Two-dimensional motion analysis was used to measure fracture fragment displacement and the construct stiffness for each fixation method was calculated from the force / displacement data.

Following 2 cyclic loading protocols of 6000 cycles, to a maximum 1.5kN, the mean fracture displacement was 0.154mm for the rim plate model, 0.326mm for the buttress plate and 0.254mm for the spring plate model. Mean maximum displacement was significantly less for the rim plate fixation than the buttress plate (p=0.015) and spring plate fixation (p=0.02).

The rim plate was the stiffest construct 10962N/mm (SD 3351.8), followed by the spring plate model 5637N/mm (SD 832.6) and the buttress plate model 4882N/mm (SD 387.3).

Where possible a rim plate with inter-fragmentary lag screws should be used for isolated posterior wall fracture fixation as this is the most stable and stiffest construct. However, when this method is not possible, spring plate fixation is a safe and superior alternative to a posterior buttress plate method.

Posterior lumber interbody fusion (PLIF) has the theoretical advantage of optimising foraminal decompression, improving sagittal alignment and providing a more consistent fusion mass in adult patients with isthmic spondylolisthesis (IS) compared to posterolateral fusion (PLF). Previous studies with only short-term follow-up have not shown a difference between fusion techniques.

An observational cohort study was performed of a single surgeon's patients treating IS over a ten year period (52 patients), using either PLF (21 pts) or PLIF (31pts). Preoperative and 12-month data were collected prospectively, and long-term follow-up was by mailed questionnaire. Preoperative patient characteristics between the two groups were not significantly different. Average follow-up was 7 years, 10 months, and 81% of questionnaires were returned. Outcome measures were Roland Morris Disability Questionnaire (RMDQ), Low Back Outcome Score (LBOS), SF-12v2 and SF-6D R2. The SF-6D R2 is a “whole of health” measure.

PLIF provided better short- and long-term results than PLF. The PLIF group had significantly better LBOS scores in the long term, and non-significantly better RMDQ scores in the long term. As measured by RMDQ Minimum Clinically Important Difference (MCID) short term set at 4, RMDQ MCID set at 8, the LBOS MCID set at 7.5 points and by SF-12v2 physical component score (PCS), PLIF patients performed better than PLF patients. When analysing single level fusions alone, the difference is more pronounced, with PCS, mental component scores and SF-6D R2 all being significantly better in the PLIF group rather than the PLF group.

This paper strongly supports the use of PLIF to obtain equivalent or superior clinical outcomes when compared to PLF for spinal fusion for lumbar isthmic spondylolisthesis. The results of this study are the first to report to such long-term follow-up comparing these two procedures.

Finger arthroplasty lacks the success seen with hip and knee joint replacements. The Van Straten Leuwen Poeschmann Metal (LPM) prosthesis was intended for the proximal interphalangeal (PIP) joints. However revision rates of 30% after 19 months were reported alongside massive osteolysis. Three failed LPM titanium niobium (TiNb) coated cobalt chrome (CoCr) components were obtained- two distal and one proximal.

All three components were analysed using an environmental scanning electron microscope (ESEM). This gave the chemical composition of the surface to determine if the TiNb surface coating was still intact. The distal components were analysed using a ZYGO non-contact profilometer (1nm resolution) with the proximal component unable to be analysed due to its shape. ZYGO analysis gave the roughness average (Ra) of the surface and determined the presence of scratches, pitting and other damage.

Images obtained from both the ZYGO and the ESEM indicated that the surfaces of all components were heavily worn. On the articulating surfaces of both distal components unidirectional scratching was dominant, while the non-articulating surface showed multidirectional scratching. The presence of unidirectional scratching suggested two-body wear, whilst the multidirectional scratching on the non-articulating surface of the distal component suggested that trapped debris may have caused three-body wear.

The ESEM chemical analysis showed that in some regions on the distal component the TiNb coating had been removed completely and in other areas it had been scratched or penetrated. On the proximal component the TiNb coating had been almost completely removed from the articulating surfaces and was only present in small amounts on the non-articulating surfaces. There was little evidence of bone attachment to the titanium coating which was intended to help provide fixation.

ESEM images showed the coating had been removed in some sections where there was minimal scratching, suggesting this scratching did not impact significantly in the coating removal. Therefore here the main cause of coating removal may have been corrosion, although scratching may have also have played a part.

The osteolysis reported clinically may have been linked to the wear debris from the failed coating.

Restoration of bone stock is the single greatest challenge facing the revision hip surgeon today. This has been dealt with by means of impaction grafting with morsellised allograft from donor femoral heads.

Alternatives to allograft have been sought. This study investigates the use of a porous biphasic ceramic in impaction grafting of the femur.

Impaction grafting of the femur was performed in four groups of sheep. Group one received pure allograft, group two 50% allograft and 50% BoneSave, group three 50% allograft and 50% BoneSave 2 and group four 10% allograft and 90% BoneSave as the graft material.

Function was assessed by measuring peak vertical reaction forces. Changes in bone mineral density were measured by DEXA scanning. Loosening and subsidence were assessed radiographically and by examination of explanted specimens.

All outcome measures showed no statistically significant difference between the four groups after eighteen months of full function.

Conclusion: When used as allograft expanders, Bone-Save and similar porous biphasic ceramics perform as well as pure allograft in impaction grafting of the femur.

Aim: To compare the biomechanical properties of paired flexible steel and titanium nails in simulated transverse fractures of synthetic composite bones.

Methods: Steel and titanium nails (3mm diameter) were individually used in pairs of divergent configuration to study torsion, cantilever bending (anteroposterior and lateral), and axial loading properties of adolescent synthetic composite tibiae model (10mm diameter). Properties of the intact bone, simulated fresh fracture with nails and simulated healing fracture with nails were studied. Instron 4303 universal testing machine was used to study axial loading. Applying fibreglass layers around the fracture with epoxy resin simulated fracture healing with callus formation.

Results: Steel and titanium nails maintained good alignment of fracture fragments. Both the nails demonstrated very poor stability of fresh fractures in torsion loading. Steel nail/bone construct was 57% stronger than Titanium nail/bone construct under similar testing conditions during fracture healing (p< 0.05) but still < 50% stiffness of intact bone. In bending tests, both types of nails showed < 10% of the stiffness of intact bone in fresh fractures (p< 0.05). Mediolateral stiffness was better than anteroposterior stiffness. In fracture healing, the bending stiffness of both types of nail/bone constructs was > 50% that of intact bone. Axial stiffness of both nails was more than bending or torsion stiffness implying that fracture fragments play a significant role in the stability of the fracture.

Although both types of nail/bone constructs demonstrated similar stiffness results in fresh and healing fractures, steel nails performance was statistically better than Titanium nails in all loading tests (p< 0.05).

Conclusion: Fractures fixed with either type of flexible nails should be supplemented with splints or plaster for a short duration until callus formation. Flexible nails should be used with caution in comminuted fractures, over weight patients since they may not provide adequate stability or allow early mobilization. Additional research with cadaver bones may provide further insight into the performance of the flexible nails.

Aims: Periprosthetic osteolysis, generally ascribed to cup polyethylene debris is the most common reason for revision THR. We carried out a radiological – retrieval study in 63 patients undergoing revision THR in order to explore potential correlation between osteolysis and wear in the cup. Material and Methods: 43 intact polyethylene liners were retrieved following revision THR because aseptic loosening. Radiological osteolysis was assessed from the De Lee and Gruen zones. The linear wear depth in the cups was measured using the shadowgraph technique and the volumetric wear was assessed using the Hashimoto formula. Statistical analysis was performed using the SPSS® software package. Results: There was a statistically significant inverse correlation between Volumetric Wear Rate (VWR)-Total Femoral Osteolysis (TFO) (p=0.024), VWR -Total Osteolysis TO (p=0.003), Volumetric Wear (VW) – TFO (p=0.015), and a trend between VW – TO (p=0.087). This shows that increased levels of osteolysis appear to be associated with lower VWR. Conclusions: Overall these results demonstrate an overall inverse relationship between long term wear of the polyethylene and periprosthetic osteolysis in pre-revision patients. Restriction in the mobility-activity could be a reason for that.

Aims: The reliability of accurately determining wear in polyethylene cups using plain x-rays has been questioned by many authors. In order to explore the accuracy of wear assessment radiologically, we carried out a radiological-retrieval study in 63 patients undergoing revision THR.

Methods:We retrieved 45 intact polyethylene liners from patients after revision THR. The Linear Wear Depth (LWD) in the cups was assessed radiologically measuring the femoral head eccentricity on the plain non-weight bearing x-ray films. The LWD was assessed in the laboratory using the shadowgraph technique. Statistical analysis was performed using the SPSS® software package.

Results: Themean radiological eccentricity of the femoral head was 2.09±2.17 mm (ranging from 0 to 9.50) and the mean LWD 3.52±1.85 mm (ranging from 0.50 to 9.29). The results of Wilcoxon sign ranks test indicated that this 1.43mm-difference is statistically significant (p< 0.001). The measured wear on the plain x-rays was 40,6% less than the true linear wear measured on the retrieved cup.

Conclusions: It is obvious that the radiological eccentricity of the femoral head underestimates the Linear Wear Depth (“true wear”) quite substantially. That difference could be less if the x-rays had been taken weight bearing.

Aims: It is well established that implant characteristics influence the Volumetric Wear Rate (VWR) of the polyethylene cup at the Total Hip Replacement (THR). In order to explore these, a retrieval study in 63 patients having revision THR was carried out. Methods: 45 intact THR components were retrieved from patients after revision THR. The polyethylene VWR was assessed in the laboratory using the shadowgraph technique. Implant features such as femoral head size, stem/cup modularity and liner thickness were recorded. Statistical analysis to identify potential correlations with the VWR was performed. Results: 22 mm diameter femoral heads produced significantly lower VWR values than 28 mm (p=0.006) and 32 mm (p< 0.001), however, there was no significant difference between the 28mm and 32mm (p=0.375) heads. There was no statistically significant difference between the mean VWR in the metal-backed and the all-polyethylene cups with the first 25% higher than the second. However, the femoral stems with a modular head generated a VWR about 3.5 times higher than the solid monoblock femoral components (p< 0.001). Polyethylene thickness didn’t influence statistically significantly the VWR (p=0.135). Conclusions: Modular implants with large femoral head size significantly influence the polyethylene wear rate. However, in this study, the liner thickness did not influence the wear rate, although it is recognised that there is probably a critical thickness below which wear is accelerated.

Aims: Although there have been theoretical expectations of increased polyethylene wear rate with the time a THR is in situ, wear rate is reported to slow down. We performed this study aiming to identify the relationship between wear rate and time of service for the prosthesis. Material and Methods: 45 intact polyethylene liners were retrieved from patients undergoing revision THR. The LWD was measured in the laboratory using the shadowgraph technique. Dividing LWD with time the prosthesis was in place allowed assessment of the Linear Wear Rate (LWR). A correlation between LWR and time of service was explored. Statistical analysis was performed using the SPSS® software package. Results: Linear Wear Rate (LWR) was not stable with time. There was a significant inverse correlation (p< 0.001) between the time that the prosthesis was in place and LWR. This relationship was stronger for the first 6 years of the THR service (p=0.005), while LWR does not change significantly after the 6th year of prosthesis implantation (p=0.060). Conclusions: The LWR is higher in the beginning either as result of the initial higher creep or because of initial lower conformity of the femoral head within the acetabular cup. As conformity increases, the LWR reduces to a more stable value.

Tibial fractures represent a heterogeneous group of fractures that are difficult to treat and vary widely in their time to union. Judging when it is safe to remove an external fixator or plaster cast requires clinical and radiological assessments both of which are subjective. Any errors in determining when a fracture has healed can lead to a prolonged treatment time or to refracture. Many methods have been employed to attempt to define clinical union in an objective manner including ultrasound, DEXA scanning, vibration analysis, and fracture stiffness measurements. Stiffness measurements are however time consuming to perform, of debatable clinical significance, and applicable only to fractures treated with external fixators. It has been previously observed^1,2 that weight bearing increases with time post-fracture. It has also been suggested³ that the ability of a patient to weight bear on the fractured limb is controlled by a biofeedback mechanism of biological self-control of fracture site strain that will be related to the stiffness of the fracture. We hypothesised that weight-bearing will be closely related to fracture healing and could be used as an alternative measure of healing where other objective measures of healing are not available or are impracticable.

A group of ten patients with tibial fractures treated by external fixation were studied. Using a Kistler force plate set into the floor, ground reaction forces for both lower limbs (fractured and non-fractured) were measured during normal walking at three weekly intervals. Concurrent fracture stiffness measurements were made using the Orthofix Orthometer.

In 8 patients who made good recoveries, the fixator was removed between 15–20 weeks post injury when the fracture stiffness had reached a minimum of 15 Nm/deg. Weight-bearing through the injured leg was seen to approach 90% of that through the uninjured leg in the 3 weeks prior to fixator removal. Two patients with delayed union achieved weight bearing of less than 40% of normal between 15–20 weeks. They also demonstrated low values of fracture stiffness (< 5 Nm/deg.) and subsequently required operative intervention to achieve union.

In this small study of 10 patients, weight bearing appears to correlate well with clinical union. It is quicker and easier to assess than stiffness and potentially has relevance to other fixation methods. We are continuing these measurements on conservatively treated, intra-medullary nailed, and externally fixed tibial fractures.

We measured fracture stiffness in 212 patients with tibial fractures treated by external fixation. In the first 117 patients (group 1) the decision to remove the fixator and allow independent weight-bearing was made on clinical grounds. In the other 95 patients (group 2) the frames were removed when the fracture stiffness had reached 15 Nm/degree. In group 1 there were eight refractures and in group 2 there was none (p = 0.02, Fisher's exact test). The time to independent weight-bearing was longer in group 1 (median 24 weeks) than in group 2 (21.7 weeks, p = 0.02). The greater precision of our objective measurement was associated with a reduction in refracture rate and in the time taken to achieve independent weight-bearing. We consider that a stiffness of 15 Nm/degree in the sagittal plane provides a useful definition of union of tibial fractures.

Diaphyseal fractures of the tibia in 80 patients were treated by external skeletal fixation using a unilateral frame, either in a fixed mode or in a mode which allowed the application of a small amount of predominantly axial micromovement. Patients were allocated to each regime by random selection. Fracture healing was assessed clinically, radiologically and by measurement of the mechanical stiffness of the fracture. Both clinical and mechanical healing were enhanced in the group subjected to micromovement, compared to those treated with frames in a fixed mode possessing an overall stiffness similar to that of others in common clinical use. The differences in healing time were statistically significant and independently related to the treatment method. There was no difference in complication rates between treatment groups.