Computed tomography evaluation of shoulder prosthesis retroversion.

Computed tomography (CT) allows calculation of anatomic and prosthetic humeral head retroversion. The purpose of this study was to demonstrate how the retroversion angle measured by CT scan varied with changes in arm position in the CT scan reference system. A trigonometric analysis shows that the measured retroversion angle decreases when the arm is in extension and increases when it is in flexion, compared with the true retroversion angle determined perioperatively. For the same degree of flexion, or extension, the error of measurement is greater when the initial true retroversion is low. A shoulder prosthesis with 20 degrees of true head retroversion was radiologically scanned with different degrees of flexion, extension, and abduction. The results validate the theoretical analysis. Trigonometric formulas are proposed to correct the retroversion angle measured by CT scan.

Histopathology of a well-functioning hydroxyapatite-coated femoral prosthesis after 52 months.

A fully hydroxyapatite-coated femoral implant was retrieved during autopsy. This component, provided with a bipolar femoral head, had been inserted for a displaced fracture of the femoral neck 52 months before. Osseointegration of the implant was evident, without any formation of fibrous tissue :39.9% of the perimeter of the prosthesis at the level of its proximal third was interfaced with bone (62.8% at the mid-third and 65.2% at the distal third). Remodeling of bone had ensued. Deposition of bone was most prominent in the calcar zone, along the medial and lateral aspects and around the tip. Proximally, cortical porosity was found to be increased by 73%, whereas medullary bone porosity was increased by a factor of 2. Cell-mediated resorption of the coating was systematically present in these bone remodeling areas. The average thickness of the coating was respectively 10.8, 50.2 and 151.2 microns in the proximal, mid- and distal thirds of the implant. Formation of new bone was often coupled with resorption. No debris from the coating was found in the joint tissues or in the articulating surface of the polyethylene insert. These overall histopathological features support mechanical stability of the implant and active remodelling of bone along with focal removal of HA coating associated with osteoclastic activity. No side effects from coating degradation could be demonstrated.

Use of an intramedullary hip-screw compared with a compression hip-screw with a plate for intertrochanteric femoral fractures. A prospective, randomized study of one hundred patients.

One hundred elderly patients who had an intertrochanteric femoral fracture were randomized to treatment with a compression hip-screw with a plate (fifty patients) or a new intramedullary device, the intramedullary hip-screw (fifty patients). All patients were followed prospectively for one year or until death. A detailed assessment of the functional status and the plain radiographs of the hip was performed one, three, six, and twelve months postoperatively. The two treatment groups were strictly comparable. The operative time needed to insert the intramedullary hip-screw was significantly greater than that needed to insert the compression hip-screw with the plate (p = 0.02), but use of the intramedullary hip-screw was associated with less estimated intraoperative blood loss (p = 0.011). The prevalence of perioperative complications, such as bronchopneumonia, cardiac failure, and urinary tract infection, was comparable in the two treatment groups. There were one intraoperative fracture of the femoral shaft and two intraoperative fractures of the greater trochanter in the group managed with the intramedullary hip-screw. One patient had pulling-out of the compression hip-screw on the seventh postoperative day. Four patients had a trochanteric wound hematoma, without infection, after insertion of an intramedullary hip-screw. All but one of the fractures healed. The one non-union, which was in a patient who had a compression hip-screw, was treated with a hemiarthroplasty. The mortality rate was similar in the two treatment groups. The patients who had an intramedullary hip-screw had, on the average, significantly better mobility at one (p < 0.0001) and three months (p = 0.0013) postoperatively. This difference was no longer seen at six and twelve months, although the patients who had an intramedullary hip-screw still had significantly better walking ability outside the home at those time-periods (p = 0.05). The compression hip-screw was removed from two patients because of pain in the mid-portion of the thigh, which had begun after consolidation of the fracture. Fourteen patients who had an intramedullary hip-screw had cortical hypertrophy at the level of the tip of the nail at twelve months postoperatively. Cortical hypertrophy was significantly related to the use of two interlocking screws (p = 0.02). Six of these patients also had pain in the mid-portion of the thigh, and the nail had been locked with two screws in five of them. Three of the six patients had the hardware removed because of the pain, and the symptoms resolved. A seventh patient had pain without cortical hypertrophy. The intramedullary hip-screw device was associated with significantly less sliding of the lag-screw and subsequent shortening of the limb in the region of the thigh (p = 0.012 and 0.019, respectively); these differences were more pronounced when the unstable fractures in the two treatment groups were compared (p < 0.001).

Two-year outcome of hydroxyapatite-coated prostheses. Two femoral prostheses retrieved at autopsy.

We performed a histological study of the bone-implant interface on 2 human femurs implanted with a hydroxyapatite-coated self-locking stem for 2 years. Extensive bone formation with no intervening fibrous tissue was noted around the entire circumference of the 2 prostheses. The newly-formed bone had 2 morphotypes: an alveolar disposition with a continuous contact between bone and hydroxyapatite, and a digitiform one where distinct bony trabeculae were in contact with the ceramic coating or with the bone marrow. Partial or even total resorption of the hydroxyapatite coating was clearly identified, these areas showing bone in contact with the metal.

Stress fracture of the hip. An unusual complication of total knee arthroplasty.

Stress fracture of the hip is a rare complication of total knee arthroplasty (TKA). Only eight cases seem to have been reported in the literature. A ninth case is reported in the present study. A 76-year-old obese woman was treated by right TKA for osteoarthrosis with cementing of the tibial component because of insufficient primary fixation. One year after TKA, she complained of tenderness above the right adductor tendons. There was no history of trauma. One month later, bone scintigrams and roentgenograms demonstrated a stress fracture of the femoral neck. Conservative management was successful. Etiologic factors such as rheumatoid arthritis, osteoporosis, steroid medication, or changes in static or dynamic forces of the hip secondary to knee arthroplasty could not be demonstrated in this patient. The increase in activity after TKA may be a factor in the incidence of these stress fractures of the hip. Radionuclear-type bone scan is helpful in diagnosis. The foci of increased isotope uptake are not always seen at the site of the stress fracture and only later visualized by roentgenograms.

Bonding of hydroxyapatite-coated femoral prostheses. Histopathology of specimens from four cases.

We examined specimens of hydroxyapatite-coated femoral prostheses from four patients who had died within nine months of implantation for fractured neck of femur. Histology showed newly formed immature bone overlying the hydroxyapatite coating with new trabeculae bridging to the endosteal bone layer. In the diaphysis, where there had been contact between the hydroxyapatite and the cortex, there was dense, firmly anchored bone with an haversian architecture. In other places the newly formed bone had a trabecular structure, containing bone marrow tissue with normal cellularity. It appeared that biological osseointegration had taken place.