David K. DeBoer

The use of vancomycin and tobramycin in acrylic bone cement: biomechanical effects and elution kinetics for use in joint arthroplasty.

We examined the effects of vancomycin on the compressive strength and fatigue life of bone cement and the pharmacokinetics and antimicrobial activity against methicillin-resistant Staphylococcus aureus of vancomycin eluted from bone cement, both alone and in combination with tobramycin. Two cements, Palacos and Simplex, were tested. Three antibiotic preparations were tested: lyophilized vancomycin (vancomycin-L), vancomycin powder (vancomycin-P), and tobramycin powder (Lilly, Indianapolis, IN). Although antibiotics did not significantly affect compressive strength, the fatigue life of bone cement was significantly decreased with vancomycin. Thus, fatigue testing revealed effects on cement strength not apparent by compression testing. Vancomycin-P had a substantially less detrimental effect on fatigue strength than vancomycin-L. Vancomycin-P elutes less efficiently than tobramycin. Although relatively little vancomycin-P eluted from bone cement, it retained biologic activity.

Revision total hip arthroplasty for pelvic discontinuity

BACKGROUND Revision of a failed total hip arthroplasty with massive acetabular bone loss and pelvic discontinuity is a reconstructive challenge. This report presents the mid-term to long-term results of revision total hip arthroplasty with a custom-made porous-coated triflange acetabular prosthesis in a consecutive series of patients with pelvic discontinuity. METHODS Twenty-eight consecutive patients (thirty hips) with a failed total hip arthroplasty and pelvic discontinuity underwent revision total hip arthroplasty. The prosthesis was custom-manufactured on the basis of a three-dimensional model of the hemipelvis created with computed tomography. Initial stability of the implant was provided with screw fixation. Two patients did not return for follow-up after three months, and eight died and were followed for less than seven years, leaving twenty hips in eighteen patients followed for a mean of ten years. Harris hip scores and sequential radiographs were used to evaluate the clinical and radiographic results. RESULTS Definite healing of the pelvic discontinuity was indicated by the presence of bridging callus in eighteen of the twenty hips. There were no broken screws and no cases of implant migration, even when the discontinuity persisted. Small nonprogressive radiolucent lines were observed in six hips. Complications included one partial sciatic nerve palsy that resolved completely and one case of loose ischial screws in a radiographically stable implant in the same patient. Five patients had one or more dislocations postoperatively. The mean Harris hip score improved from 41 points preoperatively to 80 points at the time of the latest follow-up. Eleven of the eighteen patients required ambulatory aids postoperatively. No component was revised. CONCLUSIONS Performance of a revision total hip arthroplasty with a custom triflange acetabular prosthesis to treat massive acetabular bone loss and pelvic discontinuity can provide a durable solution with good clinical results. LEVEL OF EVIDENCE Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.

Primary Total Hip Arthroplasty with Use of the Modular S-ROM Prosthesis. Four to Seven-Year Clinical and Radiographic Results*

BACKGROUND A multicenter retrospective study was conducted to determine the clinical and radiographic results of primary total hip arthroplasty with insertion of the S-ROM modular femoral stem without cement in a series of patients who had been followed for four to seven years. Four centers participated in the study, with one contributing surgeon at each center. METHODS Two hundred and eight consecutive patients who had a total hip arthroplasty with implantation of the S-ROM femoral prosthesis at one of the four centers during the study period were identified. Twenty-nine patients were lost to follow-up or had incomplete radiographic data, and twenty patients died from causes unrelated to the index arthroplasty. The remaining 159 patients formed the basis of this study. Sixteen of these patients had a bilateral procedure, resulting in 175 hips with complete clinical and radiographic data. The average age of the patients at the time of the index operation was fifty-nine years (range, twenty-two to ninety-three years). The duration of clinical follow-up averaged 5.3 years (range, four to 7.8 years), and the duration of radiographic follow-up averaged 4.9 years (range, four to 7.3 years). RESULTS One patient (0.6 percent) had a failed femoral component, which was evidenced by progressive subsidence and lack of bone ingrowth. In addition, two patients (1 percent) had a revision of the acetabular component. The average Harris hip score increased from 35 points (range, 10 to 76 points) preoperatively to 91 points (range, 52 to 100 points) at the most recent follow-up examination. The radiographic evaluation revealed that 172 hips (98 percent) had stable bone ingrowth, two hips (1 percent) had stable fibrous ingrowth, and one hip (0.6 percent) had unstable fibrous ingrowth. Periprosthetic osteolytic lesions were noted in twelve hips (7 percent). The lesions were observed in the femur in eight hips, in the acetabulum in two hips, and in both the femur and the acetabulum in two hips. All femoral osteolytic lesions were localized within the greater trochanter or the proximal-medial portion of the femoral neck. No osteolytic lesions were evident distal to the stem-sleeve junction. CONCLUSIONS Use of the modular S-ROM femoral prosthesis yielded excellent intermediate-term outcomes with respect to standard radiographic and clinical criteria. The issue regarding the theoretical increase in the rate of osteolysis due to metal debris generated at the modular femoral stem-sleeve junction was specifically addressed. We found that the rate of osteolysis in this series was not notably higher than that in other series reported in the orthopaedic literature. Although many possible factors may influence the rate of osteolysis in total hip arthroplasty, this finding suggests that the potential increase in osteolysis theoretically associated with this modular femoral implant was not observed at intermediate-term follow-up. Although longer follow-up is warranted so that the potential for osteolysis can be evaluated fully, no osteolytic lesions were evident distal to the stem-sleeve interface at the time of intermediate-term follow-up. This finding suggests that there is a circumferential seal at the modular junction of the stem that prevents the distal egress of wear debris.

Bridging massive acetabular defects with the triflange cup: 2- to 9-year results.

An unresolved issue in total hip arthroplasty is acetabular reconstruction when there is bone loss that results in pelvic discontinuity, that involves radiation-compromised bone stock, or that is significant enough to exceed the limits of jumbo hemispherical cups. Achieving pain relief and initial and long-term implant stability on host bone are the major goals of this type of reconstruction. Seventy-eight hips in 76 patients in whom a large acetabular defect was bridged using a custom-designed, flanged component were reviewed retrospectively. The preoperative deficiency was classified as a combined deficiency in 39 hips and as a pelvic discontinuity in the other 39 hips. Six patients died before a minimum 2 years followup. With five patients considered lost to followup, there were 67 hips in 65 patients with an average followup of 53 months (range, 24–107 months). No Triflange Cup has been removed. Harris hip scores improved from a preoperative mean of 33.3 points to a postoperative mean of 82.1 points. Radiographically there are two patients with incompletely healed discontinuities but both are asymptomatic. Reoperation for recurrent dislocation occurred in six patients (7.8%). The Triflange Cup offers an alternative method of repair that reliably provides pain relief, initial implant stability, potential long-term implant stability, and pelvic stability in cases of discontinuity.

Salvage procedures for failed total knee arthroplasty

Revision total knee arthroplasty for aseptic loosening or following infection can pose formidable challenges to the reconstructive surgeon. In some cases, the patient will undergo a series of operations, each resulting in ever-increasing bone loss. In extreme circumstances, the end result may be amputation, arthrodesis, or permanent resection arthroplasty. Isiklar et al.1, in a study of amputation following total knee arthroplasty, found that patients had undergone an average of six operative procedures prior to having an amputation. In a review of patients who had a reinfection following reimplantation for an infection at the site of a total knee arthroplasty, Hanssen et al.2 found that patients had undergone an average of thirteen operative procedures. Although amputation or permanent resection arthroplasty results in a poor outcome that can be avoided in most patients, situations in which these options should be considered include life-threatening infection, persistent infection, irreparable soft-tissue deficiency, severe bone loss, and the wishes of the patient following multiple failed attempts at reconstruction. Resection arthroplasty may be best tolerated by patients who are willing to accept loss of ambulation, such as those who are already disabled because of multiple joint involvement. The prevalence of amputation following total knee arthroplasty has ranged from 0.02% to 0.18%, but it has been reported to be 6% in patients with a chronic infection at the site of a total knee arthroplasty1,3-5. The outcome of amputation or resection arthroplasty following total knee arthroplasty is predictably poor, with a low likelihood of ambulation. Isiklar et al.1 reported on a series of nine above-the-knee amputations in eight patients. The mean interval between the first total knee arthroplasty and the amputation was 9.7 years. Eight of the nine amputations were performed for infection with severe bone loss, and one …

Assessment of a Medial Pivot Total Knee Arthroplasty Design in a Cadaveric Knee Extension Test Model

A total knee has been designed to mimic less-compliant medial and more-compliant lateral behavior. In vivo testing compared open-kinematic chain behaviors of cadaver knees in their normal state and after implantation of the knee prosthesis. Specimens limbs were computed tomography scanned, and infrared arrays on tibia and femur were registered to bone markers. Motion of the joint and quadriceps force were reported from 90° flexion to full extension. Less medial and more lateral anterior-posterior motion was seen in both the intact and the implanted knees. Tibiofemoral rotation and translation were similar in direction but were reduced in magnitude for the prosthetic knees. Quadriceps force, defined as that applied force required to extend the knee, required after implantation was variable between specimens but not statistically different from the intact condition. The prosthesis tested exhibits kinematic behavior similar to that in their normal state, with no difference in quadriceps force required for extension.

Advantages of milling versus broaching the proximal femur.

Femoral canal preparation in cementless total hip arthroplasty requires either broaching or milling of the proximal femur to create an osseous envelope for component implantation. The purpose of this article is to discuss the merits of milling the proximal femur for implant placement in primary or revision total hip arthroplasty.

The spinal nail: a new implant for short-segment anterior instrumentation of the thoracolumbar spine.

The biomechanics of a new spinal implant were evaluated and its dependence on an anterior strut graft was determined. Six fresh-frozen adult porcine spines were used. An L3 corpectomy was created. The spinal nail was inserted intraosseously into the middle column of the L2-L4 vertebral bodies in a trough. Implant drill holes were made for proximal and distal locking bolts in L2 and L4. A locking plate bridged the L2 and L4 trough and anchored the exposed ends of the locking bolts. Testing was performed in axial compression, torsion, and flexion. The axial and torsional stability of the spine instrumented with the spinal nail are similar to results with other devices when used with anterior strut grafting. The axial and flexural stiffnesses of the instrumented spine are independent of strut grafting. This study suggests that this device may be useful for reconstruction of the anterior spine because of instability.