M.C. de Waal Malefijt

Stress Shielding After Total Knee Replacement May Cause Bone Resorption In The Distal Femur

Inadequate bone stock is often found in revision surgery of femoral components of total knee replacements. Our aim was to test the hypothesis that these remodelling patterns can be explained by stress shielding, and that prosthetic bonding characteristics affect maintenance of bone mass. We made a three-dimensional finite-element model of an average male femur with a cemented femoral knee component. This model was integrated with iterative remodelling procedures. Two extreme prosthetic bonding conditions were analysed and gradual changes in bone density were calculated. The long-term bone loss under the femoral knee component resembled clinical findings which confirms the hypothesis that stress shielding can cause distal femoral bone loss. Our study predicts, contrary to clinical findings, that an equilibrium situation is not reached after two years, but that bone resorption may continue. This hidden bone loss may be so drastic that large reconstructions are needed at the time of revision.

Oto-spondylo-megaepiphyseal dysplasia (OSMED): Clinical description of three patients homozygous for a missense mutation in the COL11A2 gene

We describe a syndrome of midface hypoplasia, non-progressive sensorineural deafness and epiphyseal dysplasia in 3 sibs born to consanguineous parents. Clinical and roentgenographic findings are compatible with a diagnosis of oto-spondylo-megaepiphyseal dysplasia (OSMED). Histologic study of cartilage shows severe osteoarthritis, which may necessitate joint replacements in early adulthood. Ultrastructurally, collagen fibrils are increased in diameter and show aggregation. These findings have not been reported previously and may be diagnostic of OSMED. The affected sibs are homozygous for a COL11A2 missense mutation. We compare the clinical findings in our patients with a group of patients who have a dominantly inherited, non-ocular form of Stickler syndrome due to a COL11A2 splice-site mutation. Both syndromes include midface hypoplasia, epiphyseal dysplasia, and deafness, more pronounced in OSMED. Since mutations affecting the collagen XI genes can obviously result in a spectrum of phenotypes, we performed a literature-search using POSSUM, OSSUM, and the LDDB to identify conditions that might also be caused by mutations in one of the collagen XI genes. A number of conditions matched the search terms in all databases. Of these, Marshall syndrome is very similar to OSMED. Considering these phenotypic similarities and the close association between the COL11A1 and COL11A2 gene products, we propose that Marshall syndrome may be caused by a mutation in COL11A1. We also identify a number of other conditions that could be caused by mutations in one of the collagen XI genes.

A clinical, radiological and biomechanical study of the TARA hip prosthesis

SummaryWe reviewed 60 patients with 72 TARA (total articular replacement arthroplasty) resurfacing hip prostheses. To analyse the behaviour of the femoral component a radiographic study was done and a two-dimensional finite element model was constructed. The stem of the femoral component plays a role in the load transfer mechanism. Stress shielding is seen in the proximal femur but depends on the interface conditions. When only the dome of the cup is assumed to be bonded to the bone, the stresses in the head increase dramatically and there is no more stress shielding. Five years after implantation radiographic signs of loosening of the femoral component were seen in 6.8% of the implants placed without notching in the femoral neck and in 28.6% of the components with notching (significant difference, P = 0.0005). Signs of loosening of the acetabular component were seen in 37.7% 5 years postoperatively. The cumulative survival rates of the femoral and acetabular components were 89.7% and 85.6% respectively 5 years after implantation. The overall clinical results are represented by an integration of the clinical results (Harris Hip Score System), the radiographic results and the survival analysis. This gave a success rate of only 72% 5 years after implantation.

Femoral neck shortening after internal fixation of a femoral neck fracture.

This study assesses femoral neck shortening and its effect on gait pattern and muscle strength in patients with femoral neck fractures treated with internal fixation. Seventy-six patients from a multicenter randomized controlled trial participated. Patient characteristics and Short Form 12 and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores were collected. Femoral neck shortening, gait parameters, and maximum isometric forces of the hip muscles were measured and differences between the fractured and contralateral leg were calculated. Variables of patients with little or no shortening, moderate shortening, and severe shortening were compared using univariate and multivariate analyses. Median femoral neck shortening was 1.1 cm. Subtle changes in gait pattern, reduced gait velocity, and reduced abductor muscle strength were observed. Age, weight, and Pauwels classification were risk factors for femoral neck shortening. Femoral neck shortening decreased gait velocity and seemed to impair gait symmetry and physical functioning. In conclusion, internal fixation of femoral neck fractures results in permanent physical limitations. The relatively young and healthy patients in our study seem capable of compensating. Attention should be paid to femoral neck shortening and proper correction with a heel lift, as inadequate correction may cause physical complaints and influence outcome.

Thigh-calf contact: does it affect the loading of the knee in the high-flexion range?

Recently, high-flexion knee implants have been developed to provide for a large range of motion (ROM>120 degrees ) after total knee arthroplasty (TKA). Since knee forces typically increase with larger flexion angles, it is commonly assumed that high-flexion knee implants are subjected to larger loads than conventional knee implants. However, most high-flexion studies do not consider thigh-calf contact which occurs during high-flexion activities such as squatting and kneeling. In this study, we hypothesized that thigh-calf contact reduces the knee forces during deep knee flexion as the tibio-femoral load shifts from occurring inside the knee towards the thigh-calf contact interface. Hence, the effect of thigh-calf contact on the knee loading was evaluated using a free body diagram and a finite element model and both the knee forces and polyethylene stresses were analyzed. Thigh-calf contact force characteristics from an earlier study were included and a squatting movement was simulated. In general, we found thigh-calf contact considerably reduced both the knee forces and polyethylene stresses during deep knee flexion. At maximal flexion (155 degrees ), the compressive knee force decreased from 4.89 to 2.90 times the bodyweight (BW) in case thigh-calf contact was included and the polyethylene contact stress at the tibial post decreased from 49.3 to 28.1MPa. Additionally, there was a clear correlation between a subjects thigh and calf circumference and the force reduction at maximal flexion due to thigh-calf contact (R=0.89). The findings presented in this study can be used to optimize the mechanical behavior of high-flexion total knee arthroplasty designs.

Shoulder hemiarthroplasty in rheumatoid arthritis. 19 cases reexamined after 1-17 years.

We reexamined 19 shoulder hemiarthroplasties in patients with rheumatoid arthritis after a mean of 8 (1-17) years. For the evaluation, we used the Constant and Murley score and routine radiographs. At the follow-up examination, 12 of the 19 shoulders showed little, if any, pain. In 7 shoulders the pain was moderate and no patient had severe pain. The range of motion was not improved. In 7/18 shoulders proximal subluxation of the head of the humeral prosthesis and in 9/15 shoulders, progression of the glenoid erosion were seen. The increase in glenoid erosion and the postoperative pain were not correlated. Hemiarthroplasty of the shoulder effectively relieves the pain in rheumatoid patients and this seems long-lasting.

The kinematic total knee arthroplasty. A 10 - to 15-year follow-up and survival analysis.

Abstract In 86 patients 102 consecutive cemented Kinematic total knee arthroplasties were reviewed 10–15 years after surgery to determine the clinical and radiographic results and to assess the survival rate. The average age of the 65 female and 21 male patients at the time of surgery was 63 years. Forty-six knees were affected by rheumatoid arthritis (RA), 46 by osteoarthritis (OA), 7 by haemophilic arthropathy and 3 by osteonecrosis. One patient ¶(1 knee) was lost to follow-up, and 31 patients (38 knees) died. Eleven knees had been revised for deep infection (4), wear (4), malposition (2) or persistent pain (1). Fifty-two knees were examined at an average follow-up period of 12 years. The mean Knee Society Score of 89 points was the same for RA and AO knees. Also, 92% of the knees caused no pain or only occasional mild pain. There were no cases of aseptic loosening of any component. Progressive radiolucent lines were not seen on the follow-up radiographs (43 knees, mean follow-up 12 years) The 10- and 14-year survival rates with revision as the endpoint were 90% (confidence interval, CI: 81%–95%) and 82% (CI: 67%–92%), respectively. In the worst case scenario, with knees lost to follow-up and knees with moderate pain considered as failures, the 10- and 14-year survival rates were 80% (CI: 69%–88%) and 62% (CI: 46%–77%), respectively. The Kinematic total knee arthroplasty yields equally good long-term results in patients with RA and those with OA. Deep infection and wear were the main reasons for revision.

Bone grafting in cemented knee replacement - 45 primary and secondary cases followed for 2-5 years

From 1989 through 1993, we treated 36 knees in 30 patients by bone grafting (31 tibial and 14 femoral grafts) and a cemented total knee prosthesis. We used 23 morsellized and 22 solid bone grafts. After a mean follow-up period of 3 years, the mean clinical (IKS) knee score was 90. Radiographic signs of incorporation of the tibial bone graft were noted in 28 cases. Of the 8 solid femoral bone grafts, we observed twice a disintegration of the graft.

A mechanical comparison of high-flexion and conventional total knee arthroplasty.

The question addressed in this study was whether high-flexion total knee arthroplasty (TKA) designs improve the mechanical behaviour of TKAs in high flexion and whether they maintain the mechanical performance of conventional TKAs at normal flexion angles. A finite element study was performed in which the mechanical behaviour of the conventional Sigma RP and the new high-flexion Sigma RP-F were compared, during a dynamic simulation of a high-flexion squatting activity. Forces, stresses, and contact positions were calculated during different stages of the simulations. In general, higher stresses were found with larger flexion angles for both designs. Mechanical parameters were similar in normal flexion. In high flexion, lower stress and deformation values were found for the high-flexion Sigma RP-F, except for the contact stress at the post of the insert. This study confirms that a high-flexion design can improve mechanical behaviour at high-flexion without changing the performance in normal flexion. Hence, although a high-flexion TKA may show a similar or better performance in comparison with a conventional TKA, high-flexion activities still cause an increase in the implant stress levels. Therefore, the patients demand for large flexion angles may reduce the longevity of TKA implants.

Total knee arthroplasty in patients with inherited dwarfism--a report of five knee replacements in two patients with Morquio's disease type A and one with spondylo-epiphyseal dysplasia.

In Morquio’s disease and in hereditary spondylo-epiphyseal dysplasia of longer duration, malalignment, instability and unfavourable anatomy are generally the main surgical problems, but as these patients nowadays do not have a reduced life expectancy, it is worthwhile giving them a functional replacement for their severely deformed and painful knees. We report three patients with inherited dwarfism, in whom a replacement of the knee was performed.Abstract In Morquio’s disease and in hereditary spondylo-epiphyseal dysplasia of longer duration, malalignment, instability and unfavourable anatomy are generally the main surgical problems, but as these patients nowadays do not have a reduced life expectancy, it is worthwhile giving them a functional replacement for their severely deformed and painful knees. We report three patients with inherited dwarfism, in whom a replacement of the knee was performed.