Nicolaas Jacobus Joseph Verdonschot

Rotational malalignment after intramedullary nailing of femoral fractures.

Objectives: Intramedullary nailing has been accepted as the treatment of choice for femoral shaft fractures. The aim of our study was to determine the incidence and implications of rotational malalignment after intramedullary nailing using computed tomography measurements. Design: Cohort study. Setting: Patients who postoperatively visited the orthopaedic outpatient and radiology clinics. Patients: Seventy-six patients, 59 men and 17 women, with a mean age of 28.4 years (15–88). Intervention: Patients treated on a fracture table with an antegrade reamed AO nail (n = 46) or Grosse Kempf nail (n = 30) for a unilateral femoral shaft fracture between 1988 and 1998 were included in the study. Main Outcome Measurements: Patients filled out a questionnaire concerning pain, daily activities, and sport. Oxford, Western Ontario and McMaster University osteoarthritis index, and Harris Hip and Knee Society scores were obtained. Physical exams and computed tomography measurements were established. Results: Twenty-one patients (28%) were found to have a rotational malalignment of 15° or more. There was no significant difference in rotational deformity with either the AO or Grosse Kempf nail. The incidence of malrotation was independent of the fracture level. Patients with a torsional deformity had difficulties with more demanding activities like running, sports, and climbing stairs. Patients with an external rotational malalignment (n = 12) have more functional problems than patients with an internal rotational malalignment (n = 9). Clinically determined rotation differences are not accurate (±20°) compared with the established computed tomography measurements. Conclusions: Rotational malalignment after intramedullary nailing for femoral fractures is found in 28% of the patients in this study. These patients have difficulties with more demanding activities, especially when they have an external torsional deformity.

Acetabular revision with impacted morsellised cancellous bone grafting and a cemented cup. A 15- to 20-year follow-up.

This study presents the clinical and radiological results of 62 consecutive acetabular revisions in 58 patients, at a mean of 16.5 years follow-up (15 to 20). The Kaplan-Meier survivorship for the cup with end-point revisions for any reason, was 79% at 15 years (95% confidence interval (CI); 67 to 91). Excluding two revisions for septic loosening at three and six years, and one revision of a well-fixed cup after 12 years in the course of a femoral revision, the survivorship was 84% at 15 years (95% CI; 73 to 95). At review there were no additional cases of loosening, although seven acetabular reconstructions showed radiolucent lines in one or two zones. Acetabular revision using impacted large morsellised bone chips (0.7 cm to 1.0 cm) and a cemented cup, is a reliable technique of reconstruction, when assessed at more than 15 years.

The effects of cement-stem debonding in THA on the long-term failure probability of cement

The damage accumulation failure scenario is one of the most prominent ones of cemented THA reconstruction, and involves the accumulation of mechanical damage in materials and interfaces due to repetitive dynamic loading eventually resulting in gross loosening. This study addresses this scenario by combining finite element techniques with the theory of continuum damage mechanics, to analyze the damage accumulation process in the cement mantle. It was investigated how damage accumulation was affected by stem-cement debonding, and what the effects of a layer with poor bone quality around the cement mantle were. For the unbonded stem, it was determined if clinical migration rates can be explained by failure of the cement mantle, and whether cement failure promotes the formation of a pathway for debris at the stem-cement interface. It was found that stem-cement debonding not only elevated the initial stress levels with a factor of about two to three as demonstrated in earlier studies, but remained to have an impact on the failure process of the cement mantle. Stem-cement debonding accelerated the failure process by a factor of four, and promoted the formation of a pathway for debris at the stem-cement interface, particularly when the bone support to the cement mantle was reduced. The amount of subsidence was only substantial when the damaged cement mantle was surrounded by a layer of bone with reduced stiffness. This study supports the hypothesis that the survival of cemented THA is enhanced by a firm and lasting bond between the stem and the cement mantle, although this may be difficult to realize clinically.

Hip-joint and abductor-muscle forces adequately represent in vivo loading of a cemented total hip reconstruction.

Using finite element analyses, we investigated which muscle groups acting around the hip-joint most prominently affected the load distributions in cemented total hip reconstructions with a bonded and debonded femoral stem. The purpose was to determine which muscle groups should be included in pre-clinical tests, predicting bone adaptation and mechanical failure of cemented reconstructions, ensuring an adequate representation of in vivo loading of the reconstruction. Loads were applied as occurring during heel-strike, mid-stance and push-off phases of gait. The stress/strain distributions within the reconstruction, produced by the hip-joint contact force, were compared to ones produced after sequentially including the abductors, the iliotibial tract and the adductors and vastii. Inclusion of the abductors had the most pronounced effect. They neutralized lateral bending of the reconstruction at heel-strike and increased medial bending at mid-stance and push-off. Bone strains and stem stresses were changed accordingly. Peak tensile cement stresses were reduced during all gait phases by amounts up to 50% around a bonded stem and 11% around a debonded one. Additional inclusion of the iliotibial tract, the adductors and the vastii produced relatively small effects during all gait phases. Their most prominent effect was a slight reduction of bone strains at the level of the stem tip during heel-strike. These results suggest that a loading configuration including the hip-joint contact force and the abductor forces can adequately reproduce in vivo loading of cemented total hip reconstructions in pre-clinical tests.

Frictional heating of total hip implants. Part 1: measurements in patients.

Hip implants heat up due to friction during long lasting, high loading activities like walking. Thermal damage in the surrounding soft and hard tissues and deteriorated lubrication of synovial fluid could contribute to implant loosening. The goal of this study was to determine the implant temperatures in vivo under varying conditions. Temperatures and contact forces in the joints were measured in seven joints of five patients using instrumented prostheses with alumina ceramic heads and telemetry data transmission. The peak temperature in implants with polyethylene cups rose up to 43.1 degrees C after an hour of walking but varied considerably individually. Even higher temperatures at the joints are probable for patients with higher body weight or while jogging. The peak temperature was lower with a ceramic cup, showing the influence of friction in the joint. During cycling the peak temperatures were lower than during walking, proving the effect of force magnitudes on the produced heat. However, no positive correlation was found between force magnitude and maximum temperature during walking. Other individual parameters than just the joint force influence the implant temperatures. Based on the obtained data and the available literature about thermal damage of biological tissues a detrimental effect of friction induced heat on the stability of hip implants cannot be excluded. Because the potential risk for an individual patient cannot be foreseen, the use and improvement of low friction implant materials is important.

Finite element and experimental models of cemented hip joint reconstructions can produce similar bone and cement strains in pre-clinical tests

Finite element (FE) models could be used for pre-clinical testing of cemented hip replacement implants against the damage accumulation failure scenario. To accurately predict mechanical failure, the models should accurately predict stresses and strains. This should be the case for various implants. In the current study, two FE models of composite hip reconstructions with two different implants were validated relative to experimental bone and cement strains. The objective was an overall agreement within 10% between experimental and FE strains. Two stem types with different clinical results were analyzed: the Lubinus SPII and the Mueller Curved with loosening rates of 4% and 16% after 10 yr, respectively (Prognosis of total hip replacement. 63rd Annual Meeting of the American Academy of orthopaedic surgeons, Atlanta, USA). For both implant types, six stems were implanted in composite femurs. All specimens were subjected to bending. The Mueller Curved specimens were additionally subjected to torsion. Bone strains were recorded at 10 locations on the cortex and cement strains at three locations within the cement mantle. An FE model was built for both stem types and the experiments were simulated. Bone and cement strains were calculated at the experimental gauge locations. Most FE bone strains corresponded to the mean experimental strains within two standard deviations; most FE cement strains within one standard deviation. Linear regression between the FE and mean experimental strains produced slopes between 0.82 and 1.03, and R(2) values above 0.98. Particularly for the Mueller Curved, agreement improved considerably when FE strains were compared to the strains from the experimental specimen used to build the FE model. The objective of overall agreement within 10% was achieved, indicating that both FE models were successfully validated. This prerequisite for accurately predicting long-term failure has been satisfied.

Mechanical characteristics of impacted morsellised bone grafts used in revision of total hip arthroplasty

The use of impacted, morsellised bone grafts has become popular in revision total hip arthroplasty (THA). The initial stability of the reconstruction and the effectiveness of any subsequent process of revitalisation and incorporation will depend on the mechanical integrity of the graft. Our aim in this study was to document the time-dependent mechanical properties of the morsellised graft. This information is useful in clinical application of the graft, in studies of migration of the implant and in the design of the joint. We used 16 specimens of impacted, morsellised cancellous bone from the sternum of goats to assess the mechanical properties by confined compression creep tests. Consideration of the graft material as a porous, permeable solid, filled with fluid, allowed determination of the compressive modulus of the matrix, and its permeability to fluid flow. In all specimens the compression tests showed large, irreversible deformations, caused by flow-independent creep behaviour as a result of rolling and sliding of the bone chips. The mean permeability was 8.82 *10(-12) m4/Ns (SD 43%), and the compressive modulus was 38.7 MPa (SD 34%). No correlation was found between the apparent density and the permeability or between the apparent density and the compressive modulus. The irreversible deformations in the graft could be captured by a creep law, for which the parameters were quantified. We conclude that in clinical use the graft is bound to be subject to permanent deformation after operation. The permeability of the material is relatively high compared with, for example, human cartilage. The confined compression modulus is relatively low compared with cancellous bone of the same apparent density. Designs of prostheses used in revision surgery must accommodate the viscoelastic and permanent deformations in the graft without causing loosening at the interface.

How to quantify knee function after total knee arthroplasty

Total knee arthroplasty (TKA) is being undertaken in a younger population than before and as a result the functional demands on the knee are likely to be increasing. As a consequence, it is important to define quantitative functional knee tests that can monitor any increase. A valuable functional knee test has to be able to distinguish small differences (selectivity) and has to be independent of pain (content validity). In this study, patient-based questionnaires (WOMAC and Knee Society score) and performance-based tests (sit-to-stand movement, maximal isometric contraction and timed-up-and-go) were used to assess which of these tests are selective and valid to measure knee function. Tests were considered to be selective if they could discriminate between knee patients and healthy control subjects, and to have functional content validity if they were relatively independent of pain. Twenty-eight patients were measured 16 months after surgery and compared to a healthy control group of 31 subjects. The sit-to-stand movement and timed-up-and-go test were both selective and functionally content valid. The timed-up-and-go test can be used for a quick initial assessment of global function and the sit-to-stand movement as a more biomechanical instrument identifying how the knee function of the patient is affected.

Acrylic cement creeps but does not allow much subsidence of femoral stems

It has been suggested that the endurance of cemented femoral reconstructions in total hip arthroplasty is affected by the creep of acrylic cement, but it is not known to what extent cement creeps under loading conditions in vivo, or how this affects load transfer. We have simulated the long-term creep properties of acrylic cement in finite-element models of femoral stem constructs and analysed their effects. We investigated whether subsidence rates measured in vivo could be explained by creep of acrylic cement, and if polished, unbonded, stems accommodated creep better than bonded stems. Our findings showed that polished prostheses subsided only about 50 microm as a result of cement creep. The long-term prosthetic subsidence rates caused by creep of acrylic cement are therefore very small and do not explain the excessive migration rates which have sometimes been reported. Cement creep did, however, relax cement stresses and create a more favourable stress distribution at the interfaces. These trends were found around both the bonded and unbonded stems. Our results did not confirm that polished, unbonded, stems accommodated creep better than bonded stems in terms of cement and interface stress patterns.

Acetabular revision with impacted morsellised cancellous bone grafting and a cemented acetabular component: A 20- TO 25-YEAR FOLLOW-UP

We present an update of the clinical and radiological results of 62 consecutive acetabular revisions using impacted morsellised cancellous bone grafts and a cemented acetabular component in 58 patients, at a mean follow-up of 22.2 years (20 to 25). The Kaplan-Meier survivorship for the acetabular component with revision for any reason as the endpoint was 75% at 20 years (95% confidence interval (CI) 62 to 88) when 16 hips were at risk. Excluding two revisions for septic loosening at three and six years, the survivorship at 20 years was 79% (95% CI 67 to 93). With further exclusions of one revision of a well-fixed acetabular component after 12 years during a femoral revision and two after 17 years for wear of the acetabular component, the survivorship for aseptic loosening was 87% at 20 years (95% CI 76 to 97). At the final review 14 of the 16 surviving hips had radiographs available. There was one additional case of radiological loosening and four acetabular reconstructions showed progressive radiolucent lines in one or two zones. Acetabular revision using impacted large morsellised bone chips (0.5 cm to 1 cm in diameter) and a cemented acetabular component remains a reliable technique for reconstruction, even when assessed at more than 20 years after surgery.