Risk for hip fracture before and after total knee replacement in Sweden

We studied the risk for hip fracture before and after total knee replacement (TKR) in the entire population in Sweden. Women and men had a low risk for hip fracture before TKR but an increased risk the first year after TKR.

PURPOSE

It is known that osteoarthritis is associated with high bone mass. We therefore studied the risk of hip fracture before and after total knee replacement (TKR), risk of different hip fracture types, and risk subdivided in genders and age groups.

METHODS

We followed the total Swedish population born between 1902 and 1952 (n = 4,258,934) during the period 1987-2002 and identified all patients with TKR due to primary OA (n = 39,291), and all patients with hip fracture (n = 195,860) in the Swedish National Inpatient Register. The risk time analyses were based on Poisson regression models.

RESULTS

The hazard ratio (HR) for hip fracture the last year before TKR was 0.86 (95% CI 0.74 to 1.00) and the first year after 1.26 (95% CI 1.11 to 1.42) compared to individuals without TKR. The HR for femoral neck fracture 0-10 years after TKR was 0.95 (95% CI 0.89 to 1.01) and for trochanteric fracture was 1.13 (95% CI 1.06 to 1.21). The HR for hip fracture in the age group 50-74 was 1.28 (95% CI 1.14 to 1.43) and in the age group 75-90 years was 0.99 (95% CI 0.94 to 1.04) 0-10 years after TKR, compared to individuals without TKR.

CONCLUSION

Individuals had a low risk for hip fracture before TKR but an increased risk the first year after TKR. The risk in individuals below age 75 years and for trochanteric fractures was increased after TKR. Possible explanations include changed knee kinematics after a TKR, physical activity level, fall risk, and other unknown factors.

Evaluation of in vivo wear of vitamin E-diffused highly crosslinked polyethylene at five years

Aims

The primary aim of this study was to compare the wear properties of vitamin E-diffused, highly crosslinked polyethylene (VEPE) and one formulation of moderately crosslinked and mechanically annealed ultra-high molecular weight polyethylene (ModXLPE) in patients five years after primary total hip arthroplasty (THA). The secondary aim was to assess the clinical results of patients treated with VEPE by evaluating patient-reported outcome measures (PROMs), radiological evidence of fixation, and the incidence of mechanical failure.

Patients and Methods

A total of 208 patients (221 THAs) from four international centres were recruited into a prospective study involving radiostereometric analysis (RSA) and the assessment of clinical outcomes. A total of 193 hips (87%) were reviewed at the five-year follow-up. Of these, 136 (70%) received VEPE (vs ModXLPE) liners and 68 (35%) received ceramic (vs metal) femoral heads. PROMs and radiographs were collected preoperatively and at one, two, and five years postoperatively. In addition, RSA images were collected to measure PE wear postoperatively and at one, two, and five years after surgery.

Results

We observed similar bedding in one year postoperatively and wear two years postoperatively between the two types of liner. However, there was significantly more penetration of the femoral head in the ModXLPE cohort compared with the VEPE cohort five years postoperatively (p < 0.001). The only variables independently predictive of increased wear were ModXLPE (vs VEPE) liner type (β = 0.22, p = 0.010) and metal (vs ceramic) femoral head (β = 0.21, p = 0.013). There was no association between increased wear and the development of radiolucency (p = 0.866) or PROMs. No patient had evidence of osteolysis.

Conclusion

Five years postoperatively, patients with VEPE (vs ModXLPE) and ceramic (vs metal) femoral heads had decreased wear. The rates of wear for both liners were very low and have not led to any osteolysis or implant failure due to aseptic loosening.

Low risk for hip fracture and high risk for hip arthroplasty due to osteoarthritis among Swedish farmers

We aimed to study the risk of hip fracture and risk of hip arthroplasty among farmers in Sweden. Our results indicate that farming, representing an occupation with high physical activity, in men is associated with a lower risk of hip fracture but an increased risk of hip arthroplasty.

INTRODUCTION

The risks of hip fracture and hip arthroplasty are influenced by factors including socioeconomic status, education, urbanization, latitude of residence, and physical activity. Farming is an occupation encompassing rural living and high level of physical activity. Therefore, we aimed to study the risk of hip fracture and risk of hip arthroplasty among farmers in Sweden.

METHODS

We studied the risk of hip fracture, and hip arthroplasty due to primary osteoarthritis, in all men and women aged 35 years or more in Sweden between 1987 and 2002. Documented occupations were available in 3.5 million individuals, of whom 97,136 were farmers. The effects of age, sex, income, education, location of residence, and occupation on risk of hip fracture or hip arthroplasty were examined using a modification of Poisson regression.

RESULTS

A total of 4027 farmers and 93,109 individuals with other occupations sustained a hip fracture, while 5349 farmers and 63,473 others underwent a hip arthroplasty. Risk of hip fracture was higher with greater age, lower income, lower education, higher latitude, and urban area for all men and women. Compared to all other occupations, male farmers had a 20% lower age-adjusted risk of hip fracture (hazard ratio (HR) 0.80, 95%CI 0.77-0.84), an effect that was not seen in female farmers (HR 0.96, 95% CI 0.91-1.01). Both male and female farmers had a higher age-adjusted risk for hip arthroplasty.

CONCLUSIONS

Our results indicate that farming, representing an occupation with high physical activity, in men is associated with a lower risk of hip fracture but an increased risk of hip arthroplasty.

Promising early results for trabecular metal acetabular components used at revision total hip arthroplasty

Aims

The aim of this study was to compare the incidence of aseptic loosening after the use of a cemented acetabular component and a Trabecular Metal (TM) acetabular component (Zimmer Inc., Warsaw, Indiana) at acetabular revision with bone impaction grafting.

Patients and Methods

A total of 42 patients were included in the study. Patients were randomised to receive an all- polyethylene cemented acetabular component (n = 19) or a TM component (n = 23). Radiostereometric analysis and conventional radiographic examinations were performed regularly up to two years post-operatively or until further revision.

Results

The proximal migration was significantly higher in the cemented group. At two years, the median proximal migration was 1.45 mm and 0.25 mm in the cemented and TM groups, respectively (p = 0.02). One cemented component was revised due to dislocation. There were no revisions in the TM group.

Conclusion

Lower proximal migration in the TM group suggests that this design might be associated with a lower risk of aseptic loosening in the long term compared with an all polyethylene cemented component. Longer follow-up is required to confirm the clinical advantages of using this component at acetabular revision. Cite this article: Bone Joint J 2017;99-B:880–6.

Cement-in-cement revision of the femoral stem

Aims

Compared with primary total hip arthroplasty (THA), revision surgery can be challenging. The cement-in-cement femoral revision technique involves removing a femoral component from a well-fixed femoral cement mantle and cementing a new stem into the original mantle. This technique is widely used and when carried out for the correct indications, is fast, relatively inexpensive and carries a reduced short-term risk for the patient compared with the alternative of removing well-fixed cement. We report the outcomes of this procedure when two commonly used femoral stems are used.

Patients and Methods

We identified 1179 cement-in-cement stem revisions involving an Exeter or a Lubinus stem reported to the Swedish Hip Arthroplasty Register (SHAR) between January 1999 and December 2015. Kaplan-Meier survival analysis was performed.

Results

Survivorship is reported up to six years and was better in the Exeter group (91% standard deviation (sd) 2.8% versus 85% sd 5.0%) (p = 0.02). There was, however, no significant difference in the survival of the stem and risk of re-revision for any reason (p = 0.58) and for aseptic loosening (p = 0.97), between revisions in which the Exeter stem (94% sd 2.2%; 98% sd 1.6%) was used compared with those in which the Lubinus stem (95% sd 3.2%; 98% sd 2.2%) was used. The database did not allow identification of whether a further revision was indicated for loosening of the acetabular or femoral component or both.

Conclusion

The cement-in-cement technique for revision of the femoral component gave promising results using both designs of stem, six years post-operatively. Cite this article: Bone Joint J 2017;99-B(4 Supple B):27–32.

Risk of early mortality after cemented compared with cementless total hip arthroplasty

Aims

It has been suggested that cemented fixation of total hip arthroplasty (THA) is associated with an increased peri-operative mortality compared with cementless THA. Our aim was to investigate this through a nationwide matched cohort study adjusting for age, comorbidity, and socioeconomic background.

Patients and Methods

A total of 178 784 patients with osteoarthritis who underwent either cemented or cementless THA from the Swedish Hip Arthroplasty Register were matched with 862 294 controls from the general population. Information about the causes of death, comorbidities, and socioeconomic background was obtained. Mortality within the first 90 days after the operation was the primary outcome measure.

Results

Patients who underwent cemented THA had an increased risk of death during the first 14 days compared with the controls (hazard ratio (HR) 1.3, confidence interval (CI) 1.11 to 1.44), corresponding to an absolute increase in risk of five deaths per 10 000 observations. No such early increase of risk was seen in those who underwent cementless THA. Between days 15 and 29 the risk of mortality was decreased for those with cemented THA (HR 0.7, CI 0.62 to 0.87). Between days 30 and 90 all patients undergoing THA, irrespective of the mode of fixation, had a lower risk of death than controls. Patients selected for cementless fixation were younger, healthier and had a higher level of education and income than those selected for cemented THA. A supplementary analysis of 16 556 hybrid THAs indicated that cementation of the femoral component was associated with a slight increase in mortality up to 15 days, whereas no such increase in mortality was seen in those with a cemented acetabular component combined with a cementless femoral component.

Conclusion

This nationwide matched cohort study indicates that patients receiving cemented THA have a minimally increased relative risk of early mortality that is reversed from day 15 and thereafter. The absolute increase in risk is very small. Our findings lend support to the idea that cementation of the femoral component is more dangerous than cementation of the acetabular component. Cite this article: Bone Joint J 2017;99-B:37–43.

Association between hospital procedure volume and risk of revision after total hip arthroplasty: a population-based study within the Nordic Arthroplasty Register Association database

OBJECTIVE

Outcome after total hip arthroplasty (THA) depends on several factors related to the patient, the surgeon and the implant. It has been suggested that the annual number of procedures per hospital affects the prognosis. We aimed to examine if hospital procedure volume was associated with the risk of revision after primary THA in the Nordic countries from 1995 to 2011.

DESIGN

The Nordic Arthroplasty Register Association database provided information about primary THA, revision and annual hospital volume. Hospitals were divided into five volume groups (1-50, 51-100, 101-200, 201-300, >300). The outcome of interest was risk of revision 1, 2, 5, 10 and 15 years after primary THA. Multivariable regression was used to assess the relative risk (RR) of revision.

RESULTS

417,687 THAs were included. For the 263,176 cemented THAs no differences were seen 1 year after primary procedure. At 2, 5, 10 and 15 years the four largest hospital volume groups had a reduced risk of revision compared to group 1-50. After 10 years RR was for volume group 51-100 0.79 (CI 0.65-0.95), group 101-200 0.76 (CI 0.61-0.95), group 201-300 0.74 (CI 0.57-0.96) and group >300 0.57 (CI 0.46-0.71). For the uncemented THAs an association between hospital volume and risk of revision were only present for hospitals producing 201-300 THAs per year, beginning at years 2 through 5 and in all subsequent time intervals to 15 years.

CONCLUSION

Hospital procedure volume was associated with a long term risk of revision after primary cemented THA. Hospitals operating 50 procedures or less per year had an increased risk of revision after 2, 5, 10 and 15 years follow up.

Association between fixation technique and revision risk in total hip arthroplasty patients younger than 55 years of age. Results from the Nordic Arthroplasty Register Association

OBJECTIVES

To evaluate implant survival following primary total hip replacement (THR) in younger patients. To describe the diversity in use of cup-stem implant combinations.

DESIGN

29,558 primary THRs osteoarthritis (OA) patients younger than 55 years of age performed from 1995 through 2011 were identified using the Nordic Arthroplasty Registry Association database. We estimated adjusted relative risk (aRR) of revision with 95% confidence interval (CI) using Cox regression.

RESULTS

In general, no difference was observed between uncemented and cemented implants in terms of risk of any revision. Hybrid implants were associated with higher risk of any revision (aRR = 1.3, CI: 1.1-1.5). Uncemented implants led to a reduced risk of revision due to aseptic loosening (aRR = 0.5, CI: 0.5-0.6), whereas the risk was similar for hybrid and cemented implants. Compared with cemented implants, both uncemented and hybrid implants led to elevated risk of revision due to other causes, as well as elevated risk of revision due to any reason within 2 years. 183 different uncemented cup-stem implant combinations were registered in Denmark, of these, 172 were used in less than 100 operations which is similar to Norway, Sweden and Finland.

CONCLUSIONS

Uncemented implants perform better in relation to long-term risk of aseptic loosening, whereas both uncemented and hybrid rather than cemented implants in patients younger than 55 years had more short-term revisions because problems due to dislocation, periprosthetic fracture and infection has not yet been completely solved. The vast majority of cup-stem combinations were used in very few operations.

Patient-reported outcome is influenced by surgical approach in total hip replacement

The effects of surgical approach in total hip replacement on health-related quality of life and long-term pain and satisfaction are unknown. From the Swedish Hip Arthroplasty Register, we extracted data on all patients that had received a total hip replacement for osteoarthritis through either the posterior or the direct lateral approach, with complete pre- and one-year post-operative Patient Reported Outcome Measures (PROMs). A total of 42 233 patients met the inclusion criteria and of these 4962 also had complete six-year PROM data. The posterior approach resulted in an increased mean satisfaction score of 15 (sd 19) vs 18 (sd 22) (p <  0.001) compared with the direct lateral approach. The mean pain score was 13 (sd 17) vs 15 (sd 19) (p < 0.001) and the proportion of patients with no or minimal pain was 78% vs 74% (p < 0.001) favouring the posterior approach. The patients in the posterior approach group reported a superior mean EQ-5D index of 0.79 (sd 0.23) vs 0.77 (sd 0.24) (p < 0.001) and mean EQ score of 76 (sd 20) vs 75 (sd 20) (p < 0.001). All observed differences between the groups persisted after six years follow-up. Although PROMs after THR in general are very good regardless of surgical approach, the results indicate that some patients operated by the direct lateral approach report an inferior outcome compared with the posterior approach. The large number of procedures and the seemingly sustained differences make it likely these findings are clinically relevant.

Cite this article: Bone Joint J 2014;96-B:590–6.

The influence of comorbidity scores on re-operations following primary total hip replacement: comparison and validation of three comorbidity measures

While an increasing amount of arthroplasty articles report comorbidity measures, none have been validated for outcomes. In this study, we compared commonly used International Classification of Diseases-based comorbidity measures with re-operation rates after total hip replacement (THR). Scores used included the Charlson, the Royal College of Surgeons Charlson, and the Elixhauser comorbidity score. We identified a nationwide cohort of 134 423 THRs from the Swedish Hip Arthroplasty Register. Re-operations were registered post-operatively for up to 12 years. The hazard ratio was estimated by Cox's proportional hazards regression, and we used C-statistics to assess each measure's ability to predict re-operation. Confounding variables were age, gender, type of implant fixation, hospital category, hospital implant volume and year of surgery. In the first two years only the Elixhauser score showed any significant relationship with increased risk of re-operation, with increased scores for both one to two and three or more comorbidities. However, the predictive C-statistic in this period for the Elixhauser score was poor (0.52). None of the measures proved to be of any value between two and 12 years. They might be of value in large cohort or registry studies, but not for the individual patient.

Patient-reported outcomes in the Swedish Hip Arthroplasty Register: results of a nationwide prospective observational study

We present the development and results of a nationwide, prospective, observational follow-up programme including patient-reported outcome measures (PROMs) for the Swedish Hip Arthroplasty Register. The programme started in 2002 and has gradually expanded to include all units performing total hip replacement in Sweden. The self-administered PROMs protocol comprises the EQ-5D instrument, the Charnley class categorisation and visual analogue scales for pain and satisfaction. These current analyses include 34 960 total hip replacements with complete pre- and one-year post-operative questionnaires. Patients eligible for total hip replacement generally report low health-related quality of life and suffer from pain. One year post-operatively the mean EQ-5D index increased to above the level of an age- and gender-matched population, with a considerable reduction of pain (p < 0.001). Females, younger patients and those with Charnley category C reported a lower EQ-5D index pre-operatively than males, older patients and Charnley category A or B, respectively (all p < 0.001). In a multivariable regression analysis Charnley category C, male gender and higher age were associated with less improvement in health-related quality of life (p < 0.001). Nationwide implementation of a PROMs programme requires a structured organisation and effective data capture. Patients' response rates to the Registry are good. The continuous collection of PROMs permits local and national improvement work and allows for further health-economic evaluation.

Improvements in hip- and pelvic motion for patients with osseointegrated trans-femoral prostheses

This study describes the changes in hip and pelvic kinematics in 19 trans-femoral amputees, who were treated with an osseointegrated trans-femoral prosthesis. Patients were studied with 3-dimensional gait analysis, walking with socket prosthesis within two days before the osseointergration procedure. The post-operative gait analysis was carried out at the 2 year follow-up visit. Fifty-seven; age-, side- and gender-matched healthy subjects served as controls. Post-operative data showed that patients who had an osseointegrated transfemoral prosthesis increased their hip extension by 7.3° (p=0.007), changing from -2.6° (range -13.4° to 10.7°) to -9.9° (range -29.4° to 5°). Moreover, the pre-operative anterior pelvic tilt was reduced by 4.0° (p=0.016), changing from 21.7° (range 11.9-34.8°) to 17.7° (range 5.5-25.7°). Values for hip extension and pelvic tilt changed toward those of controls. These results confirm that patients treated with osseointegrated trans-femoral prosthesis encounter significant changes of their kinematic pattern in terms of hip extension and anterior pelvic tilt. Even though the changes were moderate they may, in the long-term have a positive influence on low-back biomechanics and could contribute to reducing the risk of further problems with low back pain.

Outcome after primary and secondary replacement for subcapital fracture of the hip in 10 264 patients

Between 1999 and 2005, 10 264 patients who had undergone total hip replacement (THR) for subcapital fracture of the hip were compared with 76 520 in whom THR had been performed for other reasons. All the cases were identified through the Swedish Hip Arthroplasty Register. The THRs performed as primary treatment for fracture were also compared with those done after failure of internal fixation.

After seven years the rate of revision was higher in THR after fracture (4.4% vs 2.9%). Dislocation and periprosthetic fracture were the most common causes of revision. The risk was higher in men than in women. The type of femoral component and the surgical approach influenced the risk. After correction for gender, type of component and the surgical approach the revision rates were similar in the primary and secondary fracture THR groups.

Total hip replacement is therefore a safe method for both the primary and secondary management of fracture of the hip.

Cemented versus hydroxyapatite fixation of the femoral component of the Freeman-Samuelson total knee replacement

We have carried out a radiostereometric study of 50 patients (54 knees) with osteoarthritis of the knee who were randomly allocated to receive a cemented or a hydroxyapatite-coated femoral component for total knee replacement. The patients were also stratified to receive one of three types of articulating surface (standard, rotating platform, Freeman-Samuelson (FS)1000) all based on the Freeman-Samuelson design. The tibial components were cemented in all cases. Radiostereometry was performed post-operatively and at 3, 12 and 24 months. The analysis was restricted to rotation of the femoral component over time.

After two years, rotation of the femoral components in the transverse, longitudinal and sagittal planes did not differ between the cemented and the hydroxyapatite-coated implants (p = 0.2 to 0.9).

In total knee replacements with a rotating platform, the femoral component tended to tilt more posteriorly than in the other two designs, regardless of the choice of fixation (cemented or hydroxyapatite-coated, p = 0.04). The standard version of the femoral component, whether cemented or hydroxyapatite-coated, rotated more into valgus than was observed with the rotating-platform and FS1000 designs (p = 0.005). The increased constraint provided by the FS1000 component did not appear to have any adverse effect on fixation of the femoral component.

Influence of joint area design on tibial component migration: comparison among a fixed symmetrical, asymmetrical, and moveable bearing

Fifty-four knees (50 patients) were allocated to three different tibial polyethylene inserts (standard/rotating platform/FS1000) in the Freeman-Samuelson (Finsbury Orthopaedics Ltd, Surrey, United Kingdom) total knee arthroplasty. The FS1000 design has a spherical medial and a roller-in-trough configuration laterally. Radiostereometric examinations were done postoperatively and after 3, 12, and 24 months. The median migration of the metal-backing and the Hospital for Special Surgery scores did not differ between the three groups. At 2 years, the median external/ internal displacements for the rotating platforms were 2.8 degrees and 0.2 degrees, respectively (rotating platforms versus standard inserts/rotating platforms versus FS1000: P < .0005). Longitudinal rotations above the detection limits for radiostereometry were observed in some of the fixed implants (standard and FS1000 designs), indicating conditions for backside wear.

Shoulder kinematics in 25 patients with impingement and 12 controls

We used dynamic radiostereometry to study the three-dimensional kinematics of the shoulder joint during active abduction. Twenty-five patients experiencing shoulder symptoms (Neer Stage 2) for more than 18 months, without total rotator cuff tears, participated. Eight men and four women without shoulder symptoms constituted controls. The rotation of the humeral head relative to a fixed scapula and the absolute rotation of the humerus (caused by humeral, scapular, and trunk motion) were measured. The rotations were calculated in the order of abduction/adduction (anteroposterior axis), internal/external rotation (longitudinal axis), and flexion/extension (transverse axis). The absolute abduction of the humerus in our patients did not differ from controls, nor did the abduction in the glenohumeral joint. During abduction, the humeral centre displaced medially, proximally, and anteriorly. In the patient group, slightly more (1-1.5 mm) proximal translation was observed. Presence of impingement syndrome was associated with increased proximal translation of the humeral head center, which occurred in the early phase of the arc of motion.

LEVEL OF EVIDENCE

Diagnostic Level I. See Guidelines for Authors for a complete description of Levels of Evidence.

Is increased segmental motion early after lumbar discectomy related to poor clinical outcome 5 years later?

The purpose of the study was to compare segmental motion in the early postoperative phase after lumbar discectomy to the outcome 5 years postoperatively. The study population had radiologically verified symptomatic L4-L5 or L5-S1 lumbar disc herniation and was referred with an indication for lumbar discectomy. Radiostereometry was performed in the supine and standing positions. The L4-L5 and L5-S1 segments were analysed separately. L4-L5 segments adjacent to the operated L5-S1 segment constituted a reference segment for the operated L4-L5 and vice versa. Twenty-one patients were available for the follow-up at 5 years. Outcome was classified as functionally good or poor. Repeated or planned repeat surgery at the same level during follow-up was considered as poor outcome. The L4-L5 segments in the poor group showed different direction of sagittal rotation (anterior versus posterior) of L4 on L5 compared with the good group (p<0.01). On the L5-S1 segment, patients with poor outcome displayed an increased anterior translation of about 1 mm (p<0.01) compared with the reference segments. Our study suggests that increased inducible vertebral displacement in the early postoperative phase after discectomy is associated with a poor clinical outcome.

Medial and lateral osteoarthritis of the knee is related to variations of hip and pelvic anatomy

OBJECTIVE

We evaluated if increased risk of combined hip and lateral knee osteoarthritis (OA) could be attributed to anatomical reasons in the hip region resulting in increased abductor moment over the knee.

METHODS

We measured pelvic width, femoral offset, femoral neck length and angle in 29 women with lateral knee OA (13 unilateral, 16 bilateral) and 27 women with bilateral medial OA. Twenty-one of these patients with normal hips (lateral/medial OA of the knee=12/9) and 35 with associated hip OA (lateral/medial OA of the knee=17/18) were evaluated separately. Radiographic examinations in 14 women planned for hip prosthesis because of failures after hip fracture acted as controls.

RESULTS

Patients with lateral OA of the knee had wider pelvis than controls (13.7 mm increased distance between the medial borders of the acetabulum, P=0.001). Patients with medial OA had 11.4mm longer distance from the centre of the femoral head to the centre of the proximal part of the femoral shaft (P=0.005), corresponding to a higher offset. The pelvic and hip anatomy also differed between patients with medial and lateral OA of the knee. In the groups without hip OA, presence of lateral knee OA was associated with a wider pelvis (P=0.009), shorter femoral neck (P=0.02) and Head-Shaft distance (P=0.04). In the groups with OA of the hip associated lateral OA of the knee also implied increased Neck Shaft angle (coxa valga, P=0.008), but there was no difference in pelvic width (P=0.15). We found a shorter lever arm over the hip in lateral knee OA compared to medial knee OA (P=0.02), but not when compared to controls.

CONCLUSION

Our findings suggest that occurrence of medial or lateral OA has a biomechanical background originating from pelvis and hip anatomy.

The effect of standard lumbar discectomy on segmental motion: 5-year follow-up using radiostereometry

We measured the effects of lumbar discectomy on segmental motion over a period of 5 years. Twenty-four patients with lumbar disc herniation were treated by standard lumbar discectomy at the L4-L5 or L5-S1 level. Peroperatively, tantalum markers were inserted into L4, L5, and the sacrum. Radiostereometric analysis was performed at discharge from hospital and 5 years postoperatively. The treated level was compared with the corresponding untreated level. Thus, patients who had discectomy at the L4-L5 level served as controls for patients with L5-S1 lesions and vice versa. The relative rotation and translation in relation to the three cardinal axes were calculated. Inducible displacements over the two discs were calculated between the supine and standing positions. At the L4-L5 level, there were no differences in inducible displacements between the operated and control levels at discharge or 5 years postoperatively. At the L5-S1 level we found decreasing inducible movement in the sagittal plane over time for discectomy patients. The reason for decreasing mobility over time after discectomy at the L5-S1 but not at the L4-L5 level is unknown. Mechanical factors caused by the more vertical orientation of the L5-S1 disc in combination with degenerative changes could be one explanation.

Imaging knee position using MRI, RSA/CT and 3D digitisation

The purpose of this study was to compare 3 methods of imaging knee position. Three fresh cadaver knees were imaged at 6 flexion angles between 0 degrees and 120 degrees by MRI, a combination of RSA and CT and 3D digitisation (in two knees). Virtual models of all 42 positions were created using suitable computer software. Each virtual model was aligned to a newly defined anatomically based Cartesian coordinate system. The angular rotations around the 3 coordinate system axes were calculated directly from the aligned virtual models using rigid body kinematics and found to be equally accurate for the 3 methods. The 3 rotations in each knee could be depicted using anatomy-based diagrams for all 3 methods. We conclude that the 3 methods of data acquisition are equally and adequately accurate in vitro. MRI may be the most useful in vivo.

Bone cement with reduced proportion of monomer in total hip arthroplasty: preclinical evaluation and randomized study of 47 cases with 5 years' follow-up

Bone cement with reduced amount of monomer and low curing temperature may improve implant fixation due to reduced toxicity. We analyzed the mechanical, chemical and thermal properties of such a cement (Cemex Rx) using Palacos R as control. The in vivo performance of the 2 cements was also evaluated in a prospective randomized study of 47 hips, where either of the cement types was used to fixate Lubinus SP2 prostheses with the stem made of titanium alloy. Cemex Rx had a reduced tensile strength, probably because this cement was manually mixed, as recommended by the manufacturer. A standardized labor tory test showed lower curing temperature for Cemex, but measurements at 37 degrees and with prechilled Palacos R and Cemex Rx, as in clinical work, showed no difference. In the clinical study radiostereometric measurements of cup and stem migration showed similar values in the 2 groups up to 5 years after the operation. The cement mantle was stable in both groups, but the stems migrated similarly inside the cement mantle regardless of the type of cement used. Proximal wear was low (0.04-0.05 mm/year) and tended to be lower in the Cemex group (p = 0.02). Aluminum and vanadium levels in serum increased 5 years after the operation, but no difference was noted between the 2 groups. Collagen markers (PICP, ICTP) showed similar increases in bone turnover 6 weeks and 6 months after operation in both groups.

Inducible displacements of cemented tibial components during weight-bearing and knee extension observations during dynamic radiostereometry related to joint positions and 2 years history of migration in 16 TKR

The inducible displacements of the tibial component caused by active extension were studied in 16 knees 1 yr after an AMK total knee arthroplasty with either flat. concave or posterior-stabilised (PS) designs of the joint area. Continuous change of the position of the tibial component occurred with proceeding extension. Rocking, subsidence and lift-off at different localisations were observed. In 3 of 4 knees with flat inserts the tibial component tilted anteriorly from 45 degrees to 35 degrees of flexion. A similar anterior tilt was seen in 2 of 6 with concave inserts and 5 of 6 with the PS design, but the tilting started later, when the knee had 5-20 degrees more extension. From 45-15 degrees of flexion most components tilted into valgus. Three knees (1 concave with, 1 concave without PCL and 1 PS) showed a sudden tilt into varus direction followed by a rocking motion in the opposite direction. The other types of displacements studied showed a more uniform pattern. The inducible maximum translation (MTPM) at 20 degrees of extension tended to be associated with increased migration between 0 and 2 yr when measured with the same parameter (Spearman's rho = 0.54, P = 0.03). Increased medial displacement of the center of the proximal tibia at 25 degrees was associated with increased anterior tilt. This type of motion was most commonly seen with the concave design. Our observations demonstrate that the forces acting on the tibial component vary during active extension, which results in rocking movements. This will influence the migration and the patttern of wear, factors of importance for the clinical longevity of a total knee replacement (TKR).

Charnley cups retained during revision of the femoral component: repeated clinical and radiographic observations of 49 cups for 7-15 years

This article concerns 49 consecutive polyethylene cups retained in cemented first revisions of the femoral component and evaluated on several occasions 7-15 years after the index operation. At the last follow-up 5 cups were revised, 3 were radiographically loose, 1 was revised because of recurrent dislocation and 1 stable cup was revised because the surgeon wished to use a 28 mm head. Moreover, 1 unrevised cup was radiographically loose. This corresponded to a mechanical failure rate of 0.1 (5/49) and revision rate of 0.1 (4/49). 3 cups which were radiographically loose (100% radiolucency) had not been revised when the stem was exchanged. If these cups were excluded, the revision rate would have dropped to 0.02 (1/46) and the mechanical failure rate to 0.04 (2/46). This indicates the importance of careful preoperative radiographic evaluation on both AP and lateral views. Progression of radiolucent lines always occurred as an increase in extension from the periphery to the central region of the interface. In conclusion, Charnley cups with non-circumferential radiolucent lines and little, if any, wear can be retained without compromising the longevity of the implant. However, it should be stressed that this conclusion is based on a patient population in which four-fifths of the patients at the index operation were 65 years of age or older.

Flat vs. concave tibial joint surface in total knee arthroplasty: randomized evaluation of 39 cases using radiostereometry

40 patients with non-inflammatory arthrosis and minor preoperative deformity (< or =5 degrees ) were operated on with an AMK type (DePuy, Johnson & Johnson) total knee arthroplasty (TKA). The posterior cruciate ligament was retained. The patients were divided into those with a flat (terminology of the manufacturer: standard) or a concave (terminology of the manufacturer: constrained) polyethylene insert (20 in each group). Radiostereometric (RSA) examinations were done postoperatively and after 3,12 and 24 months. The median absolute rotations of the tibial inserts varied between 0.12 and 0.24 (range 0.00-1.54) degrees, with no differences between the 2 groups. The median maximum total-point motions (flat/concave = 0.41/0.42 mm), the maximum subsidence or lift-off did not differ. The Hospital for Special Surgery knee score and the patients' opinion about the operation, based on their preoperative expectations, showed little, if any, differences. At 2 years, 10 of 20 patients with flat and 13 of 19 with concave inserts regarded their knee function as normal or almost so.

Kinematics after tear in the anterior cruciate ligament: dynamic bilateral radiostereometric studies in 11 patients

We studied the kinematics of both knees using radiostereometry in 11 patients with unilateral injury of the anterior cruciate ligament and normal contralateral knee. Continuous radiostereometric exposures at a speed of 24 exposures a second were performed, when the patients ascended an 8 cm high platform. The tibial center was more dorsally displaced and the tibia more externally rotated on the injured side. This increasing external tibial rotation was associated with increased anterior displacement of the lateral femoral condyle. The latter also displayed less anterior-posterior translations during continuous extension. The anterior-posterior translation of the medial condyle was about the same as on the uninjured side. Changes in the kinematics of the knee joint due to rupture of the anterior cruciate ligament can result in an abnormal joint load, which may increase the risk of damage to the cartilage and the menisci.

Flat vs. concave tibial joint surface in total knee arthroplasty: randomized evaluation of 39 cases using radiostereometry

40 patients with non-inflammatory arthrosis and minor preoperative deformity (< or =5 degrees ) were operated on with an AMK type (DePuy, Johnson & Johnson) total knee arthroplasty (TKA). The posterior cruciate ligament was retained. The patients were divided into those with a flat (terminology of the manufacturer: standard) or a concave (terminology of the manufacturer: constrained) polyethylene insert (20 in each group). Radiostereometric (RSA) examinations were done postoperatively and after 3,12 and 24 months. The median absolute rotations of the tibial inserts varied between 0.12 and 0.24 (range 0.00-1.54) degrees, with no differences between the 2 groups. The median maximum total-point motions (flat/concave = 0.41/0.42 mm), the maximum subsidence or lift-off did not differ. The Hospital for Special Surgery knee score and the patients' opinion about the operation, based on their preoperative expectations, showed little, if any, differences. At 2 years, 10 of 20 patients with flat and 13 of 19 with concave inserts regarded their knee function as normal or almost so.

The influence of fracture etiology and type on fracture healing: a review of 104 consecutive tibial shaft fractures

This study was conducted to determine retrospectively the factors which influence fracture healing and risk for nonunion in patients with tibial shaft fractures. One hundred consecutive patients with 104 tibial shaft fractures and a mean age of 40 (14-85) years were reviewed. Fractures were classified according to the AO classification system. There were 22 open fractures and 52 comminuted fractures. Thirty-eight fractures were caused by high-energy trauma. Fracture pattern, soft-tissue condition, level of energy of the trauma, malalignment, and treatment methods were identified. The influence of these factors on the time of hospital stay and sick-leave, delayed union, and nonunion were calculated. Normal healing occurred in 61 fractures with a mean healing time of 17 weeks, delayed union in 27 with a mean of 35 weeks, and nonunion in 16 with a mean of 69 weeks. The relative risk of developing nonunion in open fractures was 8.2 (CI = 2.9-10.5) and 2.9 (CI = 1.2-3.2) in fractures exposed to high-energy trauma. This study showed that the soft-tissue condition and level of trauma energy are good predictors for the development of complications. Considering these risk factors at an early stage in the planning of treatment might reduce the risk of nonunion. ergy level of the trauma, fracture comminution, initial fracture displacement, treatment method, contamination, and associated injuries will influence fracture healing. Conservative treatment has in general been recommended for undisplaced closed or grade I open fractures caused by low-energy trauma [15, 18, 21]. However, conservative treatment of a tibial shaft fracture means immobilization of the lower leg for a long period of time, especially if healing is delayed. Thus, it is important to consider the risk of healing complications when planning the appropriate treatment method in the early stage after the injury. The purpose of this study was to analyze complications such as delayed union and nonunion and to identify factors which affect the healing of tibial shaft fractures.

Deformation across the zone of callotasis during loading. radiostereometric analysis in a patient with achondroplasia

The present study demonstrates that high-resolution radiostereometric analysis (RSA) can be used to assess global longitudinal compressive deformation across the callotasis zone during loading. In an achondroplastic patient operated with bifocal lengthening of the tibia by use of the Ilizarov external fixator, the axial compressive intersegmental strain in the proximal lengthening zone under a load of 71% of body weight was 7.7 mm. The proximal lengthening zone was 51.0 mm, and accordingly the overall linear strain across the callotasis was 15.1%. This large strain value found in distraction osteogenesis 6 weeks after end of distraction is not consistent with classical theory of the magnitude of micromotion needed for adequate stimulation of bone formation in fracture healing. The increased axial displacement did not stimulate bone healing and delayed union was observed. This one single observation does not allow for any conclusions to be drawn about the relationship of strain to fracture healing, but further and refined use of the RSA method will certainly improve our understanding of the role of axial strains in distraction osteogenesis.

Does metal backing improve fixation of tibial component in unicondylar knee arthroplasty? A randomized radiostereometric analysis

In a prospective, randomized study, patients with medial gonarthrosis stage I to III according to Ahlbäck were allocated to a unicondylar knee arthroplasty (Miller-Galante, Zimmer, Inc., Warsaw, IN) with an all-polyethylene tibial component or metal-backed tibial component of the same design. The purpose of the study was to evaluate if metal backing enhanced tibial component fixation. A total of 45 knees (42 patients; 23 metal-backed components and 22 all-polyethylene components) were examined. We used radiostereometric analysis to measure micromotion of the tibial component over a period of 2 years after surgery. Hospital for Special Surgery score was used for clinical evaluation. We found no statistically significant differences in clinical results or migration of the tibial component over a 2-year follow-up period. These findings do not support better fixation of metal-backed tibial components. Because of these findings, we advocate all-polyethylene tibial components in unicondylar knee arthroplasties because of optimal biomechanical strength at a given height of tibial component, avoiding potential problems of modularity and minimizing the amount of interfaces, at a lower cost.

Low effectiveness of prescribed partial weight bearing. Continuous recording of vertical loads using a new pressure-sensitive insole

To enable objective measurements of weight bearing in hip replacement patients a portable instrument set-up with an on-line registering pressure-sensitive insole was developed. Six men and 9 women, median age 58 (48-67) years, who had been operated on with a cementless or hybrid hip arthroplasty were studied. All patients were independent and functional. A physiotherapist instructed the patients to use crutches in order to support 30% of their body weight. The patients then walked a standardized distance with crutches over five different types of terrain: level, uphill, downhill, upstairs and downstairs. The trial was repeated once. In both men and women most of the steps taken resulted in a load of >30% of body weight. None of the patients managed to comply with the directive, even though five of them thought they did. The type of terrain had no significant influence on the pattern of load. Our findings indicate that the effectiveness of prescribing limited weight bearing is questionable.

Concave versus posterior-stabilized tibial joint surface in total knee arthroplasty: randomized evaluation of 47 knees

Forty-seven knees in 43 patients with severe deformities randomly received AMK total knee arthroplasty with concave (C, n = 25) or posterior-stabilized (PS, n = 22) polyethylene insert and with resection of the posterior cruciate ligament. Radiostereometric examinations were done postoperatively and after 3, 12, and 24 months. Two patients (1 C, 1 PS) underwent revision surgery. At the 2-year follow-up, the median absolute rotations of the tibial inserts ranged from 0.13 degrees to 0.26 degrees (C vs PS; P =.1-.7). The maximum total point motion was almost identical in the 2 groups (C, 0.38; PS, 0.39; P =.9). Maximum subsidence, lift-off, and Hospital for Special Surgery scores did not differ (P =.1-.6). Recipients of 20 of 24 knees with concave design and 14 of 19 knees with posterior-stabilized design reported that their knee could be regarded as normal or almost normal. Variations of the configuration of the polyethylene insert did not alter the outcome in the short term.

Impaction technique and graft treatment in revisions of the femoral component: laboratory studies and clinical validation

The micromotions of femoral stems cemented into impacted bone-graft were studied in 23 femora from adult sows. The model was validated against 2 patient groups. Conventional impaction technique and a new impaction technique using polished and rotating impactors were studied in the preclinical model and in 14 and 10 patients with type II defects. The specimens were loaded in an MTS (Minneapolis Testing System) machine for 72,000 cycles at 250N to 3,250N. The bone-graft was rinsed in tepid water, and most of the bone marrow and fat were removed. Radiostereometric measurements revealed small subsidence of the stems cemented into the specimens and the patients 6 weeks after the operation without any difference (median values, -0.06 to -0.16 mm). Further studies of specimens operated with nontreated bone-graft showed that extraction of fat increased the stability. Our findings suggest that the early postoperative implant stability after impaction grafting of the femur mainly is an effect of surgical technique and graft treatment. The new impaction technique, with which we hoped to obtain a more reproducible procedure and less risk for perioperative fracture, resulted in stability equal to that obtained with the conventional technique.

In vivo kinematics of total knee arthroplasty: flat compared with concave tibial joint surface

This study evaluated the influence of the geometric configuration of the tibial joint area on the kinematics of the knee. Twenty-two patients with noninflammatory arthritis and minor preoperative deformity were studied. They each received an AMK total knee replacement with retention of the posterior cruciate ligament. Eleven patients without any knee abnormalities were used as controls. The patients were stratified to either the flat (terminology of the manufacturer: standard) or concave (terminology of the manufacturer: constrained) polyethylene insert (n = 11 in each group). Knee kinematics were assessed 1 year after the operation by having the patient ascend a platform corresponding to an extension of the knee from 50 to 70 degrees of flexion. During this motion, two film-exchangers simultaneously exposed six to 13 pairs of serial stereoradiographs. The concave geometric configuration of the tibial insert resulted paradoxically in increased anterior-posterior translations compared with the flat insert but no significant change of rotations and translations in the other directions. Compared with normal knees, the most obvious abnormality was increased anterior-posterior translations (p < 0.004). At 50 degrees of flexion, the implants with the flat tibial polyethylene insert had displaced 2 times and the concave ones had displaced 2.5 times more posteriorly than the normal knees (p < or = 0.001). Less internal tibial rotation was also recorded in the flexed positions for both types of inserts compared with the normal knees (p < 0.02). Four knees in four patients, who reported symptoms of instability and abnormal knee function, showed significantly increased proximal displacement of the center of the tibial plateau in the flexed position. The findings suggest that current prosthetic designs and surgical technique do not restore normal knee kinematics and indicate that design improvements should rely on in vivo kinematic studies.

Tibial component fixation in porous- and hydroxyapatite-coated total knee arthroplasty: a radiostereo metric evaluation of migration and inducible displacement after 5 years

A total of 51 knees (45 patients) with osteoarthrosis were stratified in a randomized study to receive a hydroxyapatite-coated Freeman-Samuelson (FS HA) or a porous-coated Miller-Galante II (MG II) uncemented total knee arthroplasty. Repeated clinical, radiographic, and radiostereometric analysis (RSA) evaluations of the tibial components were done for 5 years. The clinical outcome was equal at the 5-year follow-up (mean Hospital for Special Surgery score, 93). Standard radiographs displayed more zones around the tibial stem in the MG II group. RSA revealed that the FS HA components migrated less (smaller maximum total point motion and maximum subsidence) after 5 years and showed less inducible displacements at the 1-year follow-up. The stability of the implants obtained is equal to or better than cemented implants after 5 years. Key words: knee prosthesis, cementless, hydroxyapatite, radiostereometry, inducible displacement.

Cemented first-time revisions of the femoral component: prospective 7 to 13 years' follow-up using second-generation and third-generation technique

In a prospective, consecutive study of first-time cemented femoral revisions, 109 hips were evaluated for a minimum of 7 years. There were 87 Charnley (18 standard, 69 long), 21 Spectron (3 standard, 18 long), and 1 Brunswick long-stem arthroplasties. There was an increased risk for rerevision in younger patients (P = .0001) and with use of standard stems (P = .002). Factors of importance for development of mechanical failure were younger age (P = .0001), presence of more pronounced bone defects (P < .005), use of standard stems (P < .0005), and presence of radiolucencies on the postoperative radiographs (Gruen zones 4 and 6) (P < .01). Our results confirm that cemented femoral revisions are a durable option in elderly patients, when improved cementing techniques and long-stem prostheses are used.

Hydroxyapatite and tricalcium phosphate-coated cups with and without screw fixation: a randomized study of 64 hips

Sixty-two patients (64 hips) were provided with porous press-fit cups (Trilogy), plasma-sprayed with a coating consisting of 70% hydroxyapatite and 30% tricalcium phosphate. The patients were randomized to a cup with cluster holes for adjunctive screw fixation (n = 30) or to a cup without holes (n = 34). Radiostereometry was used to study migration and wear. Up to 2 years median translations and rotations <0.2 mm and <0.2 degrees were recorded in the 2 groups, without any difference. The median annual proximal wear (0.11 and 0.12 mm) was within the expected range despite the use of a ceramic coating, and it did not differ between the 2 designs. Radiolucent lines were frequently seen postoperatively but diminished during the follow-up without any sign of migration into the gaps. At 2 years, the median Harris scores were 99 points (range, 51-100 points) in the group with and 98 points (range, 69-100 points) in the group without screws. The results indicate that early fixation can be achieved for ceramic-coated press-fit cups without using additional screw fixation.

In vivo kinematics of total knee arthroplasty. Concave versus posterior-stabilised tibial joint surface

We studied the kinetics of the knee in 20 patients (22 knees) 12 months after total knee arthroplasty (TKA), by using three-dimensional radiostereometry and film-exchanger techniques. Eleven knees had a concave (constrained) tibial implant and 11 a posterior-stabilised prosthesis. Eleven normal knees served as a control group. In the posterior-stabilised knees there was less proximal and posterior displacement of the centre of the tibial plateau during extension from 45 degrees to 15 degrees, with a decrease in the anterior translation of the femoral condyles of 4 mm at 45 degrees. There was less internal tibial rotation and increased distal positioning of the centre of the tibial plateau with both designs when compared with the normal knees, and in both the centre of the plateau was displaced posteriorly by more than 1 cm. Increased AP translation has been recorded in all prosthetic designs so far studied by radiostereometry. The use of a posterior-stabilised design of tibial insert could reduce this translation but not to that of the normal knee.

In vivo kinematics of total knee arthroplasty

We studied the kinetics of the knee in 20 patients (22 knees) 12 months after total knee arthroplasty (TKA), by using three-dimensional radiostereometry and film-exchanger techniques. Eleven knees had a concave (constrained) tibial implant and 11 a posterior-stabilised prosthesis. Eleven normal knees served as a control group.

In the posterior-stabilised knees there was less proximal and posterior displacement of the centre of the tibial plateau during extension from 45° to 15°, with a decrease in the anterior translation of the femoral condyles of 4 mm at 45°. There was less internal tibial rotation and increased distal positioning of the centre of the tibial plateau with both designs when compared with the normal knees, and in both the centre of the plateau was displaced posteriorly by more than 1 cm.

Increased AP translation has been recorded in all prosthetic designs so far studied by radiostereometry. The use of a posterior-stabilised design of tibial insert could reduce this translation but not to that of the normal knee.

Outcome scores in degenerative cervical disc surgery

Forty-six consecutive patients with neck pain and arm radiculopathy were treated with anterior cervical discectomy and fusion. All patients had neurological symptoms corresponding to a herniated disc and/or spondylosis at one or two cervical levels, verified by magnetic resonance imaging. The patients were stabilized with an anterior graft and randomized to either fixation with a CSLP plate or no internal fixation. Preoperatively and 2 years postoperatively the patients filled in a questionnaire that included a modified Million Index, a modified Oswestry Index and the Zung Depression Scale. They were also asked to register their pain in the arm and in the neck on a vertical visual analogue scale (VAS). At the 2-year follow-up, an unbiased observer graded the patients' clinical outcome using Odom's criteria. A test-retest procedure was carried out to examine the questionnaire reproducibility. In the group that was operated at one level, there was no significant improvement in any of the scores. Nevertheless, 81% of the patients were satisfied with the outcome of the surgery. All scores improved in the group operated at two levels. The pain in the neck and arm, as measured on a VAS, decreased in both groups. The improvement in arm pain was significantly more pronounced in patients operated with a plate at two levels compared to those who were operated without a plate. At the 2-year follow-up, patients with an excellent or good result according to Odom's criteria had a lower Million Index (P < 0.0005), Oswestry Index (P < 0.0005), and Zung (P = 0.024) score, than the group classified as fair or poor. There was a significant correlation (P < 0.0001 for all scores) between the test and retest results. We conclude that the modified Million Index and Oswestry Index are clinically useful tools in the evaluation of outcome after degenerative cervical disc surgery. The clinical benefits of plate fixation were minimal. The outcome after surgery, measured with the Oswestry Index, Million Index and VAS for arm and neck pain, seems to correlate well with the classification of outcome by Odom.

Increased migration of the SHP prosthesis: radiostereometric comparison with the Lubinus SP2 design in 40 cases

40 patients with primary arthrosis were randomized to receive either a cemented SHP (Scientific Hip Prosthesis) or Lubinus SP2 prosthesis. At 2 years radiostereometric measurements showed increased proximal migration (0.4/0.2 mm; p = 0.02) and more proximal wear (0.3/0.1 mm, p = 0.01) of the SHP socket. The SHP stem also subsided (-O.6/-0.1 mm, p<0.001) and rotated more into retroversion (2.6/0.3 degrees ) than did the SP2 design. This subsidence mainly occurred inside the cement mantle in 17 of 18 cases (13 SHP, 4 SP2), where this type of motion could be measured. The changes in bone mineral density evaluated with DEXA and the clinical results did not differ between the 2 groups. The subsidence of the SHP stem is the most pronounced so far recorded with radiostereometry in stems without a completely polished surface. This subsidence and the rotational instability imply a substantial risk of abrasive wear and increased stresses in the cement mantle.

Determination of inter-spinous process distance in the lumbar spine. Evaluation of reference population to facilitate detection of severe trauma

Fracture of a spinal segment with minimal or no compression of the vertebral body can be highly unstable. Screening for such an injury in the lumbar spine is often obstructed in a multi-injured patient, because of difficulty in obtaining adequate sagittal radiographs. The position of the spinous processes in relation to each other is the key for proper evaluation of the status of the posterior stabilising structures. The amount of separation or axial rotation of the posterior part of the vertebra that can occur before failure of the posterior structures has not been unambiguously defined. Despite this, it can be assumed that severe separation of the spinous processes indicates a more or less pronounced loss of mechanical support. An analysis of how the posterior spinous processes relate to each other on an anteroposterior (AP) radiograph could obviate this problem. A new, simple and reproducible radiographic tool is presented for screening of an eventual rupture of posterior structures of the lumbar spine. This method is based on measurements of the variation in interspinal process distance between adjacent levels in lumbar spine in a normal population. Two hundred normal AP radiographs of non-injured thoracolumbar spine were studied. The interspinal process distance was measured as the distance between the cranial ends of the adjacent projections of spinous processes on AP radiographs. The mean values and 99% confidence limits for changes in the interspinal process distances between adjacent spinal levels were determined and analysed in relation to age, gender and spinal segment level. An upper limit of a normal difference in distance between the spinous processes at two adjacent levels was determined to be 7-10 mm, depending on age and location in the lumbar spine. A difference in interspinal process distance exceeding 7 mm between two adjacent lumbar levels should alert a surgeon to severe and unstable injury.

Porous cups with and without hydroxylapatite-tricalcium phosphate coating: 23 matched pairs evaluated with radiostereometry

Migration, wear, and presence of radiolucencies were studied in 23 matched pairs of patients operated with porous-coated acetabular cups with additional screw fixation. All implants had the same type of titanium fiber mesh. In each pair, one of the cups was plasma-sprayed with a coating consisting of 70% hydroxylapatite (HA) and 30% tricalcium phosphate (TCP). Radiostereometric analysis up to 2 years after the operation revealed smaller rotations around the horizontal axis in cups with HA/TCP coating. The migration of the cup center was not significantly influenced. Evaluation of femoral head penetration in 12 of the matched pairs did not reveal any significant difference. Immediately after operation, implants with HA/TCP coating had more central radiolucencies, which, despite minimal migration, disappeared during the follow-up. The clinical results did not differ between the 2 groups. The findings of less tilting and diminishing radiolucencies in the cups with HA/TCP coating suggest a more complete ingrowth of bone and a better sealing of the interface.

Poor outcome of the PCA and Harris-Galante hip prostheses. Randomized study of 171 arthroplasties with 9-year follow-up

155 patients (171 hips) with a mean age of 50 years (24-64) were randomized to uncemented PCA (84 hips) or Harris-Galante type I (87 hips) total hip arthroplasty. Clinical and radiographic evaluations were done regularly. The improvements in the Harris hip and pain scores did not differ. Osteolysis developed in 5 PCA and 17 Harris-Galante hips. 13 hips in the PCA and 16 in the Harris-Galante (HG) group were revised because of mechanical failures and 1 hip (HG) because of infection after a mean follow-up of 9 years. Decreased 10-year survival rate, based on revision as end-point, was noted for the PCA (85%), compared with the Harris-Galante cup (99%). The corresponding survival rate of the PCA stem (96%) was higher than that observed for the Harris-Galante design (86%). When radiographic failures were included, the survival rates of the 4 different components dropped to between 73% and 94%. These findings indicate that further revisions will be necessary and continuous radiographic follow-up is indicated to enable revision before severe bone destruction has occurred. Although the PCA and the Harris-Galante designs differed as regards the survival of the individual components, the overall clinical and radiographic survival rates of these cementless total hip arthroplasties were poor.

Three-dimensional knee kinematics and stability in patients with a posterior cruciate ligament tear

The three-dimensional kinematics of the knee were studied from 5 months to 15 years after unilateral posterior cruciate ligament tears occurred in eight patients. All but two patients had signs of additional ligament injuries. Repeated radiostereometric examinations were conducted when the patients ascended a platform (step-up test) and during an instrumented anterior-posterior drawer test with the knee at 30 degrees of flexion. No changes in knee kinematics were observed during the step-up test, whereas increased anterior-posterior laxity (3.8-11.3 mm) was recorded for all patients. Four of the patients had an increased side-to-side difference (more than 2 mm) in anterior as well as posterior laxity. A rupture of the posterior cruciate ligament can be diagnosed at 30 degrees of knee flexion, but an increase in anterior laxity can erroneously be interpreted as an injury of the anterior cruciate ligament. The unaffected kinematics of the knee suggest that factors such as joint load and congruity and muscle activity can compensate for the absent posterior cruciate ligament during static examinations.

Cytokine levels in synovial fluid from hips with well-functioning or loose prostheses

We analysed synovial fluid from 88 hips, 38 with osteoarthritis and 12 with well-functioning and 38 with loose hip prostheses. The levels of TNF-alpha, IL-1beta (71 hips) and IL-6 (45 hips) were measured using the ELISA technique. Joints with well-functioning or loose prostheses had significantly increased levels of TNF-alpha compared with those with osteoarthritis. Hips with aseptic loosening also had higher levels of IL-1beta but not of IL-6 compared with those without an implant. The levels of TNF-alpha and IL-1beta did not differ between hips with stable and loose prostheses. Higher levels of TNF-alpha were found in hips with bone resorption of type II and type III (Gustilo-Pasternak) compared with those with type-I loosening. The level of cytokines in joint fluid was not influenced by the time in situ of the implants or the age, gender or area of the osteolysis as measured on conventional radiographs. Our findings support the theory that macrophages in the joint capsule increase the production of TNF-alpha at an early phase probably because of particle load and in the absence of clinical loosening. Since TNF-alpha has an important role in the osteolytic process, the interfaces should be protected from penetration of joint fluid.

Subsidence of a non-polished stem in revisions of the hip using impaction allograft

We revised 24 consecutive hips with loosening of the femoral stem using impaction allograft and a cemented stem with an unpolished proximal surface. Repeated radiostereometric examinations for up to two years showed a slow rate of subsidence with a mean of 0.32 mm (−2.0 to +0.31). Fifteen cases followed for a further year showed the same mean subsidence after three years, indicating stabilisation. A tendency to retroversion of the stems was noted between the operation and the last follow-up. Retroversion was also recorded when displacement of the stem was studied in ten of the patients after two years. Repeated determination of bone mineral density showed an initial loss after six months, followed by recovery to the postoperative level at two years. Defects in the cement mantle and malalignment of the stem were often noted on postoperative radiographs, but did not correlate with the degrees of migration or displacement. After one year, increasing frequency of trabecular remodelling or resorption of the graft was observed in the greater trochanter and distal to the tip of the stem. Cortical repair was noted distally and medially (Gruen regions 3, 5 and 6). Migration of the stems was the lowest reported to date, which we attribute to the improved grafting technique and to the hardness of the graft.

Hydroxyapatite coating versus cemented fixation of the tibial component in total knee arthroplasty: prospective randomized comparison of hydroxyapatite-coated and cemented tibial components with 5-year follow-up using radiostereometry

Fifty-three consecutive patients (57 knees; mean age, 69 years) entered a prospective randomized study to compare the fixation of hydroxyapatite (HA)-coated (29 knees) with cemented (28 knees) tibial components in the Tricon II total knee arthroplasty. The quality of the fixation during 5 years postoperatively was evaluated with radiostereometric analysis (RSA). Three HA-coated implants were revised: 2 owing to infection, and 1 owing to early delamination of the coating and clinical loosening. Eight patients (9 knees) died, 1 patient sustained a stroke, and 1 patient refused investigations after 1 year. In the 40 patients (19 HA-coated, 21 cemented) remaining at 5 years, the magnitude of the micromotion between the HA-coated and cemented groups did not differ. The HA-coated implants displayed most of the migration within the initial 3 months then stabilized, whereas the cemented implants showed an initially lower, but over time continuously increasing migration. Between 1 and 2 years, 4 of 24 HA-coated and 10 of 23 cemented implants migrated >0.2 mm and were categorized unstable, which has been shown to have a prognostic value as regards future aseptic loosening. Progressive radiolucent lines developed in 2 cemented knees, which both were categorized unstable. If HA-coated implants can sustain the forces that threaten the fixation in the early period after implantation, a strong and enduring fixation may be obtained.

Cytokine levels in synovial fluid from hips with well-functioning or loose prostheses

We analysed synovial fluid from 88 hips, 38 with osteoarthritis and 12 with well-functioning and 38 with loose hip prostheses. The levels of TNF-α, IL-1ß (71 hips) and IL-6 (45 hips) were measured using the ELISA technique. Joints with well-functioning or loose prostheses had significantly increased levels of TNF-α compared with those with osteoarthritis. Hips with aseptic loosening also had higher levels of IL-1ß but not of IL-6 compared with those without an implant. The levels of TNF-α and IL-1ß did not differ between hips with stable and loose prostheses.

Higher levels of TNF-α were found in hips with bone resorption of type II and type III (Gustilo-Pasternak) compared with those with type-I loosening.

The level of cytokines in joint fluid was not influenced by the time in situ of the implants or the age, gender or area of the osteolysis as measured on conventional radiographs.

Our findings support the theory that macrophages in the joint capsule increase the production of TNF-α at an early phase probably because of particle load and in the absence of clinical loosening. Since TNF-α has an important role in the osteolytic process, the interfaces should be protected from penetration of joint fluid.

Subsidence of a non-polished stem in revisions of the hip using impaction allograft. Evaluation with radiostereometry and dual-energy X-ray absorptiometry

We revised 24 consecutive hips with loosening of the femoral stem using impaction allograft and a cemented stem with an unpolished proximal surface. Repeated radiostereometric examinations for up to two years showed a slow rate of subsidence with a mean of 0.32 mm (-2.0 to +0.31). Fifteen cases followed for a further year showed the same mean subsidence after three years, indicating stabilisation. A tendency to retroversion of the stems was noted between the operation and the last follow-up. Retroversion was also recorded when displacement of the stem was studied in ten of the patients after two years. Repeated determination of bone mineral density showed an initial loss after six months, followed by recovery to the postoperative level at two years. Defects in the cement mantle and malalignment of the stem were often noted on postoperative radiographs, but did not correlate with the degrees of migration or displacement. After one year, increasing frequency of trabecular remodelling or resorption of the graft was observed in the greater trochanter and distal to the tip of the stem. Cortical repair was noted distally and medially (Gruen regions 3, 5 and 6). Migration of the stems was the lowest reported to date, which we attribute to the improved grafting technique and to the hardness of the graft.

Ceramic coating improves tibial component fixation in total knee arthroplasty

Forty uncemented total knee arthroplasties (36 patients) were randomly allocated to a Miller-Galante II prosthesis with or without hydroxyapatite/tricalcium phosphate (HA/TCP) coating on the titanium fiber mesh on the undersurface of the tibial component. The patients were followed for 2 years with repeated radiostereometric examinations. After 2 years, the HA/TCP tibial components displayed smaller anterior-posterior tilt and less subsidence. The mean value of maximal total point motion was small: 0.5 mm in both groups. At 24 months, there were more radiolucent lines under the tibial tray and around the stem in the uncoated group, but the clinical results did not differ. HA/TCP coating on the undersurface of the tibial component improved the stability and seemed to improve the quality of the interface between the tibial component and the bone.