We found no significant difference between the groups in the EMG intensity of vastus lateralis relative to biceps femoris, or vastus medialis relative to vastus lateralis, during the balance test or during the step up task (Mann Whitney U test all p>
0.05). We did not find any difference in the proprioceptive abilities of the two groups
The fractures were loaded using a Lloyd’s machine and a load displacement curve was plotted.
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.
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.
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.
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.
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.
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.
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.
Stable fractures of the ankle can be successfully treated non-operatively by a below-knee plaster cast. In some centres, patients with this injury are routinely administered low-molecular-weight heparin, to reduce the risk of deep-vein thrombosis (DVT). We have assessed the incidence of DVT in 100 patients in the absence of any thromboprophylaxis. A colour Doppler duplex ultrasound scan was done at the time of the removal of the cast. Five patients did develop DVT, though none had clinical signs suggestive of it. One case involved the femoral and another the popliteal vein. No patient developed pulmonary embolism. As the incidence of DVT after ankle fractures is low, we do not recommend routine thromboprophylaxis.
This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting. Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured. Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum. The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.
We reviewed 78 femoral and tibial nonunions treated between January 1992 and December 2003. Of these, we classified 41 in 40 patients as complex cases because of infection (22), bone loss (6) or failed previous surgery (13). The complex cases were all treated with Ilizarov frames. At a mean time of 14.1 months (4 to 38), 39 had healed successfully. Using the Association for the Study and Application of the Methods of Ilizarov scoring system we obtained 17 excellent, 14 good, four fair and six poor bone results. The functional results were excellent in 14 patients, good in 14, fair in two and poor in two. A total of six patients were lost to follow-up and two had amputations so were not evaluated for final functional assessment. All but two patients were very satisfied with the results. The average cost of treatment to the treating hospital was approximately £30 000 per patient. We suggest that early referral to a tertiary centre could reduce the morbidity and prolonged time off work for these patients. The results justify the expense, but the National Health Service needs to make financial provision for the reconstruction of this type of complex nonunion.
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.
We describe three cases of traumatic myositis ossificans in which fractures occurred through a mature, quiescent ossification mass. None of the fractures reactivated the original pathological process, no callus was formed and union did not occur. The nonunion became painless over a period of months. This unusual late complication of myositis ossificans seems to require only symptomatic treatment by temporary splintage and subsequent mobilisation. We could find no previous report of a similar case.