Introduction: There is a recent trend of using a raft of small diameter 3.5 mm cortical screws instead of the large diameter 6.5mm screws in depressed tibial plateau fractures. Our aim was to compare the biomechanical properties of these two constructs in the normal and osteoporotic synthetic bone model.

Methods: 20 rigid polyurethane foam blocks with a density simulating osteoporotic bone and normal bone were obtained. A Schatzker type 3 fracture was created in each block. The fracture fragments were then elevated and supported using 2, 6.5mm cancellous screws or 4, 3.5mm cortical screws.

The fractures were loaded using a Lloyd’s machine and a load displacement curve was plotted.

Results: Osteoporotic model. The mean force needed to produce a depression of 5mm was 700.8N with the 4-screw construct and 512.4N with the 2 screw construct (p=0.007).

Non-osteoporotic model. The mean force requires to produce the same depression was 1878.2N with the 2-screw construct and 1938.2N with the 4 screw construct (p=0.42).

An increased fragmentation of the synthetic bone fragments was noticed with the 2-screw construct but not with the 4-screw construct.

Conclusion: A raft of 4, 3.5 mm cortical screws is biomechanically stronger than two, 6.5mm cancellous screws in resisting axial compression in osteoporotic bone.

The aim of this study was to determine whether there is a difference in the functional outcome between fixed and mobile bearings in total knee arthroplasty.

120 patients were randomized (computer generated) to receive either a fixed or mobile bearing P.F.C. Sigma total knee replacement. 96 patients were needed to detect a 20° difference in range of motion (ROM) with a significance level of 0.05 and a test power of 0.97. Oxford knee score (OKS) and ROM were assessed independently before and one year after surgery.

Mean ROM and Oxford knee score before and at one year after surgery for both groups are shown as preliminary results for 70 patients (follow-up expected to be completed by March 2006):

There is no statistically significant difference in the mean ROM at one year and in change in ROM between the two groups (p=0.53 and p=0.21 respectively). The findings were similar for Oxford Knee Score at one year and change in Oxford Knee Score (p=0.45 and p=0.82). There was no early aseptic loosening in either group.

The one year results suggest that there is no significant difference in functional outcome measured as ROM and Oxford Knee Score between the two types of bearing. Further follow-up will be carried out to detect any differences in the long term outcome.

Aim: We have carried out a prospective study to compare duplex ultrasonography and transcutaneous oxygen tension as predictors of wound healing after knee arthroplasty.

Methods and Materials: 53 patients were included in the study. All underwent pre-operative duplex scans of their lower limbs. In addition, transcutaneous oxygen tension measurements were made adjacent to the proposed incision pre-operatively and on days 1, 3 and 7 post knee arthroplasty. Wound healing was assessed using the ASEPSIS wound score.

Results: 4 wounds had evidence of delayed wound healing. Duplex ultrasonography was a poor predictor of such problems; however there was a significant correlation between pre-operative transcutaneous oxygen tension and post-operative wound scores.

Conclusion: Pre-operative transcutaneous oxygen tension measurement is a better predictor of wound healing after knee replacement surgery than duplex ultrasonograph, and may be a useful adjunct to the investigation of patients at risk of wound problems post knee arthroplasty.

Introduction and aims: There is a recent trend of using a raft of small diameter 3.5 mm cortical screws instead of the large diameter 6.5mm screws in depressed tibial plateau fractures (Schatzker type 3). Our aim was to compare the biomechanical properties of these two constructs in the normal and osteoporotic sawbone model.

Methods: 10 sawbone (solid rigid polyurethane foam) blocks with a density simulating that of an osteoporotic bone and 10 blocks of a density simulating normal bone were obtained. A Schatzker type 3 fracture was created in each block. The fracture fragments were then elevated and supported using 2, 6.5mm cancellous screws in 10 blocks and 4, 3.5mm cortical screws in the remaining.

The models were loaded to failure using a Lloyd’s machine. A displacement (depression) of 5mm was taken to be the point of failure. A load displacement curve was plotted using Nexygen software and the force needed to cause a depression of 5mm was calculated in each block. Mann Whitney U test was used for statistical analysis.

Results: Osteoporotic model

The mean force needed to produce a depression of 5mm was 700.8N with the 4-screw construct and 512.4N with the 2 screw construct. This difference was statistically significant (p=0.007).

Non-osteoporotic model

The mean force requires to produce the same depression was 1878.2N with the 2-screw construct and 1938.2N with the 4 screw construct. The difference was not statistically significant (p=0.42).

An increased fragmentation of the sawbone fragments was noticed with the 2-screw construct but not with the 4-screw construct.

Conclusion: A raft of 4, 3.5 mm cortical screws is biomechanically stronger than 2, 6.5mm cancellous screws in resisting axial compression in osteoporotic bone.

Femoral head deformity with flattening and lateral protrusion can occur secondary to epiphyseal dysplasia or avascular necrosis of any aetiology in childhood. This causes painful impingement of the lateral femoral head on the acetabular lip, a phenomenon known as hinge abduction. We aimed to review our experience of valgus extension osteotomy in the treatment of hinge abduction in children and young adults with avascular necrosis.

Twenty patients undergoing valgus osteotomy for hinge abduction performed by a single specialist were clinically and radiologically reviewed. The aetiology was Perthes disease in 16 patients and treatment of DDH in 4 patients. The indication for the procedure was pain and limited abduction. The mean follow-up was 4.5 years. Patients were assessed using modified Iowa hip scores at final follow-up. The procedure corrected some leg shortening and improved the abduction range of the affected hip. Overall 80 % of patients did well. The mean Iowa hip score in Perthes group was 84 at final follow-up.

Four patients preoperatively had cysts/ defects in their femoral head. These were seen to fill up during their postoperative follow-up. Poorer outcome was associated with preoperative hip stiffness and surgery before stabilisation of the avascular process.

Conclusion: Valgus osteotomy is an effective procedure for relieving hinge abduction with associated additional benefits including improvement of leg shortening and improvement in hip abduction. The procedure should be avoided in stiff hips.

Purpose: To compare the analgesia provided by pure subcutaneous infiltration (Gale technique) of lignocaine with that provided by infiltration of lignocaine into the carpal tunnel in addition to the subcutaneous tissue (Altissimi technique) for carpal tunnel decompression

Methods: 20 patients with bilateral carpal tunnel syndromes were chosen for the study. Patients were randomised to receive one local anaesthetic technique on one side and the other on the other side. The pain scores were recorded intraoperatively and 2 and 4 hours postoperatively.

Results: 5 patients experienced intra-operative pain with the Gale technique, while one did with the Altissimi technique (p=0.15 using Mann Whitney U test). Postoperative analgesia at 2 hours was significantly better with the Altissimi technique (p= 0.009). Patients with the Altissimi technique also required less number of analgesic tablets over 24 hours post surgery (p=0.01).

Conclusions: We found no statistically significant difference in the intra-operative pain scores with the two techniques. However, postoperative pain relief was much better with the Altissimi technique.

Purpose: To biomechanically compare the stability provided by 2, 6.5mm cancellous screws versus that provided by 4, 3.5mm cortical screws in depressed tibial plateau fractures

Methods: We obtained 20 sawbone(solid polyurethane foam) blocks of dimensions 9x6.5x3.5cm. 10 of these blocks had a density of normal cancellous bone (20pcf) and 10 represented osteoporotic bone (10pcf). We created a depressed fracture(Schatzker type 3) using a coring saw. Each fracture had 4 depressed fragments, which were elevated and supported using either 2,6.5mm cancellous screws or 4, 3.5mm cortical screws. The fractures were loaded axially using the Lloyds materials testing machine. A force displacement curve was plotted. A depression of 5mm was considered to be failure.

Results: Osteoporotic model|The mean force needed to produce a depression of 5mm was 700.8N with the 4-screw construct and 512.4N with the 2 screw construct. This difference was significantly significant (p=0.007). |Non-osteoporotic model|The mean force requires to produce the same depression was 1878.2N with the 2-screw construct and 1938.2N with the 4 screw construct. The difference was not statistically significant (p=0.42).

Conclusions: A raft of 4, 3.5 mm cortical screws was biomechanically stronger than 2, 6.5mm cancellous screws in resisting axial compression in the osteoporotic bone model. There was no significant difference in the 2 constructs in non-osteoporotic bone model.

Complications after total knee arthroplasty (TKR) such as malalignment, instability, subluxation, excessive wear, and loosening have been attributed to poor soft-tissue balance. Traditional approaches for soft-tissue balance involve static measurements in full extension and at 90° flexion. A trial prosthesis instrumented with force transducers was used to measure soft-tissue balance through the entire range of flexion.

The trial prosthesis was instrumented with four force transducers, one at each corner of the tibial tray, and was implanted in four cadaver knees and four patients intra-operatively. Tibial forces were recorded during passive knee flexion after the tibial and femoral bone cuts were made and again after soft-tissue balance was achieved using standard techniques.

In all eight knees measurable imbalance was initially recorded. The differences in forces were a mean of 18 N (range, 6 to 72) mediolateral and a mean of 26 N (range, 13 to 108) anteroposterior. After a routine procedure of soft-tissue balancing, the mean imbalance between the transducers was reduced by 62 % to 87 % (p < 0.05). However, even the knees that appeared perfectly balanced at 0° and 90° flexion, some imbalance occurred [mean 22 N (range, 2 to 34)] at flexion angles other than 0° and 90°.

Soft-tissue balance in TKR remains a complex concept. Even after accurate static balancing was achieved in extension and 90° flexion, dynamic measurements revealed discrepancies in mid flexion, which may explain the wide variation in knee kinematics reported after TKR and in the reported incidences of mid-flexion knee instability. Computer-aided surgical navigation systems can increase the precision and accuracy of component alignment. However, these systems cannot directly address soft-tissue balance and knee tightness. An instrumented tibial prosthesis could be a useful adjunct to enhance the value of these navigation tools.

The knee is a complex joint that is difficult to model accurately. Although significant advances have been made in mathematical modeling, these have yet to be validated successfully in vivo. Direct measurement of knee forces should lead to a better understanding of the stresses seen in total knee arthroplasty. An instrumented knee prosthesis was developed to measure forces in vivo after total knee arthroplasty.

An instrumented tibial prosthesis was implanted in an 80-year-old male weighing 66 kg. The prosthesis measured forces at the four corners of the tibial tray. The patient walked approximately 1.6million steps per year before surgery (ankle accelerometer measurements). Knee forces were measured postoperatively during passive and active knee flexion, rehabilitation, rising from a chair, standing, walking, and climbing stairs.

The patient was walking with the help of a walker by postoperative day 3. Peak tibial forces were 1.2 times body weight (BW). By the sixth postoperative day the tibial forces during gait were 1.7 times BW. At six weeks the peak tibial forces during walking had risen to 2.4time BW. Stair climbing increased from 1.9 times BW on day 6 to 3.3 times BW at six weeks.

This represents the first direct in vivo measurement of tibial forces. In vivo tibiofemoral force data will be used to develop better biomechanical knee models and in vitro wear tests and will be used to evaluate the effect of improvements in implant design and bearing surfaces, rehabilitation protocols, and orthotics. This should lead to refining surgical techniques and to enhancing prosthetic designs that will improve function, quality of life, and longevity of total knee arthroplasty. This information is vital given the current trend in the increase of older population groups that are at higher risk for chronic musculoskeletal disorders.

Purpose: There is little information in the literature regarding outcomes of unicompartmental knee arthroplasty (UKA) in patients receiving worker’s compensation (WC). The purpose of the present study is to compare the outcomes of UKA in patients receiving WC compared to patients without WC.

Methods: Nineteen patients with a WC claim treated by UKA for medial compartment arthritis were compared to twenty patients who underwent similar procedure but had no WC claim. Average follow up period was 37 months (range 30–60 months). Outcomes were evaluated using Knee Society Score (KSS) data. T test was used for statistical analysis. Comparisons were also made with respect to conversion in to total knee arthroplasty (TKA).

Results: WC patients improved from a mean preoperative KSS of 47.4 (range 30–70) to 76.9 (range 55–99), while non-WC patients improved from 43.3 (range 35–63) to 90.7 (range 74–100). The difference in improvement between the two groups was statistically significant (p=0.004). Furthermore, the postoperative KSS in the non-WC patients was significantly higher than that of the WC group (p=0.007). There was no significant difference between the incidences of conversion to TKA between the two groups.

Conclusions: These findings suggest that patients with WC claims have poorer outcomes after UKA in comparison to non-WC patients.

Introduction and Aims: Titanium foam implants simulate the trabecular structure of bone to maximise porous space for bone ingrowth. Plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Chemical deposition is an attractive alternative that produces consistent coats on porous surfaces.

Method: Titanium foam cylinders (5mm diameter by 25mm length) were implanted bilaterally in 40 rabbit femurs. Twenty implants were coated with 20 microns of hydroxyapatite (T-HA) by electrochemical deposition while 20 implants had no hydroxyapatite coat (T). Osseointegration was measured at six and 12 weeks by automated computerised histomorphometry of scanning electron microscopy images of sections taken through the implant at two levels: diaphyseal and metaphyseal. Bone ingrowth was quantified in the pores and was also measured up to 1mm beyond the surface of the implant to determine the pattern of bone growth.

Results: For the T-HA surface, bone ingrowth increased from 35.0 ±8.5 % at six weeks to 41.5 ± 7.4 % at 12 weeks (p < 0.05). For the T surface, bone growth was 14.1 ± 8.8% at six weeks and 11.4 ± 4.2 % at 12 weeks. At both time points mean bone ingrowth was significantly different between hydroxyapatite-coated and non-hydroxyapatite-coated implants, (p< 0.01). No significant differences were noted between the diaphyseal and metaphyseal bone response.

Conclusion: For the T-HA surface, bone ingrowth increased from 35.0 ±8.5 % at six weeks to 41.5 ± 7.4 % at 12 weeks (p < 0.05). For the T surface, bone growth was 14.1 ± 8.8% at six weeks and 11.4 ± 4.2 % at 12 weeks. At both time points mean bone ingrowth was significantly different between hydroxyapatite-coated and non-hydroxyapatite-coated implants, (p< 0.01). No significant differences were noted between the diaphyseal and metaphyseal bone response.

Introduction and Aims: A significant proportion of patients currently undergoing total knee arthroplasty have uni-compartmental disease. Unicondylar knee replacement (UKA) offers the benefits of less bone resection and better soft tissue retention. However, knee kinematic changes after UKA have not been established.

Method: A significant proportion of patients currently undergoing total knee arthroplasty have uni-compartmental disease. Unicondylar knee replacement (UKA) offers the benefits of less bone resection and better soft tissue retention. However, knee kinematic changes after UKA have not been established.

Results: In the normal knee, knee flexion was accompanied by femoral rollback and tibial internal rotation. Similar patterns of rollback and rotation were seen after UKA. Surprisingly, resecting the ACL did not affect rollback or tibial rotation. However, tibial rotation was significantly different and was more variable after TKA. This suggests that loss of the ACL may not be the major cause of abnormal kinematics after TKA.

Conclusion: Abnormal kinematics have been previously reported after TKA. However, UKA appeared to maintain normal kinematics. This study reported kinematic advantages to UKA, in addition to less bone resection and better recovery.

Introduction and Aims: Complications after total knee arthroplasty (TKA) have been attributed to soft-tissue imbalance. The current approach to soft-tissue balance is static measurements in extension and 90 degrees flexion. Dynamic balancing during the entire range of flexion may be more valuable.

Method: Complications after total knee arthroplasty (TKA) have been attributed to soft-tissue imbalance. The current approach to soft-tissue balance is static measurements in extension and 90 degrees flexion. Dynamic balancing during the entire range of flexion may be more valuable.

Results: All knees (in vitro and in vivo) initially recorded imbalance in the tibial forces: mean 18N (6–72) in the mediolateral and 26N (13–108) in the anteroposterior direction. After soft-tissue balancing, the mean imbalance reduced by 87%. Even when knees appeared well balanced at zero and 90-degree flexion, there was imbalance [mean 22N (2–34)] at flexion angles between zero and 90 degrees. The 2mm thicker insert increased forces by a mean of 89% (22–180%).

Conclusion: Soft-tissue balance in TKA remains a complex concept. The routine instruments used for soft-tissue balance only detect mediolateral imbalance. Even when accurate static balancing was achieved, dynamic measurements revealed imbalance in mid-flexion. These results explain some of the variability in knee kinematics after TKA and the incidence of mid-flexion instability.

This study measured polyethylene wear and correlated it with design features such as tibiofemoral conformity and contact areas.

Two femoral component designs were tested in a knee wear simulator. The femoral condyles of design A were flat-on-flat in the coronal plane, while those of design B were curved-on-curved. These femoral components were tested with two inserts. Insert PLI had a posterior lip, while insert C had a more curved sagital geometry, to improve stability in the anteroposterior direction. All components were tested for up to five million cycles in bovine serum lubricant. Triaxial forces were monitored to ensure that loading conditions were similar in all combinations tested. Gravimetric wear measurements were made at 500 000 cycle intervals. Contact stresses were measured using pressure sensitive film and dynamic finite element analysis.

Contact stresses were 22% higher for inserts tested with design A compared to design B. Sliding distance, sliding velocity, and patterns of crossing motion were found to be comparable between the two femoral designs. Inserts tested with design A wore significantly more (mean 10.9 mg/million cycles) than design B (mean 5.71 mg/million cycles, p < 0.001). No appreciable differences were found between wear rates of insert PLI and insert C.

Component design can have a significant impact on polyethylene wear rate. Careful control of kinematic and loading conditions allowed for comparison between specific design features. Increase in tibio-femoral contact area led to reduction of contact stresses, which was reflected in the reduced wear rate.

The purpose of this study was to determine if routine x-ray exposure produced any chemical oxidation of Ultra High Molecular Weight Polyethylene (UHMWPE), used for joint arthroplasty.

Three different polyethylene polymers were obtained from Biomet, Depuys and Howmedica. These samples had undergone sterilisation and packaging methods. Rectangular shapes of polymer were cut according to the standards specified by the ASTM (American Society For Testing and Materials). Eight samples of each polymer were obtained and divided randomly in to test and control subgroups. The test samples were exposed to ten x-rays with the standard dose used for the hip joint.

Polyethylene oxidation was measured using Fourier transform infrared spectroscopy. This technique can assess the incorporation of oxygen within the carbonyl region. Radiated and non-irradiated samples were compared in each polymer group.

Oxidation from the Fourier transform infrared spectroscopy was quantified by calculating the area under a signature absorption peak for UHMWPE (methylene band at 1370 cm-1) and an oxidation absorption peak (carbonyl band at 1720 cm-1). The ratio of the area of the oxidation peak to the area of the signature peak yields the carbonyl content, or oxidation, relative to the amount of polyethylene. There was no significant difference in oxidation after exposure to x-rays between test and control UHMWPE samples.

Although numerous studies have looked in to the effects of high dose radiation exposure on polyethylene, effects of routine x-rays have not been studied before. It is common practice to follow-up patients with joint replacements over a long period with xrays at each visit. Present study examined the effects of routine x-rays on oxidation of polyethylene. However there was no detectable oxidation after exposure to x-rays. This study paves way for further research in this direction.

It has been recently suggested that hyponatraemia may be a cause of significant iatrogenic harm in orthopaedic patients. In an attempt to test this theory, this observational study was done to establish the incidence of post-operative hyponatraemia following hip fracture and evaluate its correlation with outcome.

An observational study was carried out on 213 consecutive hip fracture patients. 201 patients completed the requirements of the study (Male-45, Female-156). Mean age was 80 years. Serum sodium concentrations were recorded during the first week of admission. Hyponatraemia defined as significant (Na < 130mmol/L) was identified in 9% at admission and 18% during first week of stay. Incidence of severe hyponatraemia was 3%. There were no acute complications of hyponatraemia in these patients. 78% of hyponatraemia patients had received 5% Dextrose infusion during the postoperative period as their main intravenous fluid. All hyponatraemic patients had their sodium levels restored to normal during their stay.

Long term outcome measures used were mortality, change in residential status, walking ability and use of walking aids at 4 months following fracture. There was 20% mortality at 4 months in the hyponatraemic group and it was 30% in the normal serum sodium group. However this difference was not statistically significant. Hyponatraemia did not significantly influence deterioration in residential status (p< 0. 05), walking independence (p< 0. 05) or increase of walking aids (p< 0. 05).

In hip fracture patients, hyponatraemia whilst common was not associated with a poor outcome and at the same time we did not find any evidence of lapse in the recognition and treatment of hyponatraemia in a general orthopaedic ward. However emphasis should be made to junior medical staff to avoid iatrogenic hyponatraemia by following a proper postoperative fluid regime.