Roger H. Emerson

Comparison of a static with a mobile spacer in total knee infection.

Patients with infections of a total knee arthroplasty were stratified by medical status. Twenty-six knees in 26 patients treated with a static antibiotic-impregnated polymethylmethacrylate block spacer before 1995 were compared with 22 knees in 22 patients treated after 1995 with a mobile articulating spacer. Both groups were treated with 6 weeks of parenteral antibiotics and had reimplantation within 6 to 12 weeks after placement of the spacer. Followup for the patients who had block spacers was an average 7.5 years (range, 2.8–12.7 years), and followup for the patients with a mobile spacer was an average of 3.8 years (range, 2.6–6.4 years). Results showed that the patients with the mobile spacers had significantly better average range of motion at followup compared with patients who had block spacers (107.8° compared with 93.7°). The reinfection rate was the same between the two groups at 36 months, 7.6% (two of 26) for the patients with block spacers and 9% (two of 22) for the patients with mobile spacers. Extended followup available for the patients who had block spacers revealed a late reinfection rate of 23% (six of 26) with a new organism. There was no difference in the reinfection rate, with new or old organisms, in healthy hosts compared with patients with as many as two medical problems.

Unicompartmental Knee Arthroplasty with the Oxford Prosthesis in Patients with Medial Compartment Arthritis

BACKGROUND The mobile-bearing feature of the Oxford unicompartmental knee replacement has the potential to optimize polyethylene wear, thereby leading to longer-term function of the implant. The function of the bearing requires intact soft tissues, with the ligaments being balanced throughout the range of motion intraoperatively through bone resection only. Final limb alignment is determined by the restored soft-tissue tension. The purposes of this study were to determine the limb alignment achieved in the absence of ligament release and to investigate the interplay of failure mode, survivorship, and limb alignment. METHODS Fifty-five knees in fifty-one patients with medial compartment osteoarthritis had a unicompartmental replacement with an Oxford prosthesis. Evaluation included Knee Society clinical scores, radiographic evaluation, survivorship analysis, and modes of failure. The average duration of clinical follow-up was 11.8 years. Only two patients (three knees) were lost to follow-up. RESULTS The mean postoperative Knee Society knee score and function score at the latest follow-up evaluation were 75 and 90 points, respectively. The overall alignment of the knee was restored to neutral, averaging 5.6 degrees of valgus alignment. Forty-seven of the fifty-five knees had the mechanical axis crossing the central 50% of the tibial plateau. Seven knees had revision surgery, and six of them required conversion to a total knee prosthesis. The main reason for revision was the progression of arthritis in the lateral compartment, which occurred in four knees at an average of 10.2 years postoperatively. These four knees had not been overcorrected into excessive valgus at the time of the original surgery, and we found no correlation, with the numbers studied, between alignment and bearing size. Survivorship analysis showed that the rate of survival at ten years was 85% with failure for any reason as the end point, 90% with progression of lateral compartment arthritis as the end point, and 96.3% with component loosening as the end point. CONCLUSIONS With this unicompartmental knee arthroplasty, the mechanical limb alignment resulting from balancing the knee ligaments, accomplished without releasing them, was consistently through the center of the knee. Progression of arthritis in the lateral compartment was the most common reason for late failure in this series and was not related to the initial postoperative alignment.

Extensor mechanism reconstruction with an allograft after total knee arthroplasty.

The authors report on a series of 15 knees in which an extensor mechanism allograft was used to treat a rupture of the patellar tendon associated with a total knee arthroplasty. Nine of the knees have greater than two-year follow-up evaluation (average, 4.1 years; range, 2.3-7 years). Postoperatively, the average flexion was 106 degrees. All but three patients achieved full passive extension. Six of the nine knees had no extensor lag. The average post-operative clinical score for the follow-up group was 78 points. Graft complications include one early graft rupture, one early quadriceps junction failure, and one patellar component loosening. One graft fractured after revision of a metal-backed patella.

Cortical strut allografts in the reconstruction of the femur in revision total hip arthroplasty. A basic science and clinical study.

Repeated total hip arthroplasties cause a loss of bone stock that will produce diminished component support, and can compromise implant function. There is, therefore, a compelling argument to return bone stock to the femur at the time of revision arthroplasty. Cortical strut allografts serve this purpose. They unite consistently and reliably, by 8.4 months on average. The overall rate of strut union is 96.6%. The sequence of healing events starts with round-off, followed by partial bridging and complete bridging. The repair process includes remodeling of the host femur, as well as the graft. Although there is variable resorption of some grafts, usually where not opposed to the host bone, there is also extension of others from host callus build-up such that, on average, there is no significant measurable loss of graft length or width. Most of the allograft struts, 78%, maintained a radiodense appearance. Clinical results of femoral revision with strut allografting have shown satisfactory end results compared with historic controls, with an average Harris score of 79.6 and a 2.7% subsidence rate. Of particular note is that the subsidence rate and clinical scores did not vary with the state of the preoperative femur, as has been shown repeatedly in the past. The canine model shows that the strut allografts are biologically active. Through mobilization of mesenchymal tissue, they are transformed into vascularized calluslike structures while maintaining good strength, and then further remodel to lamellar bone.

Comparison of a mobile with a fixed-bearing unicompartmental knee implant.

Two well-matched groups of patients with unicompartmental knee arthroplasties were compared. The first 51 knees were treated with a fixed-bearing knee implant and the second 50 knees were treated with a mobile meniscal-bearing implant. Followup was 7.7 years for the patients with fixed-bearing implants and 6.8 years for patients with mobile-bearing implants. Both groups functioned well clinically. Radiographic analysis with 3-foot standing views taken preoperatively showed both groups had an average varus alignment of −2°. Postoperatively patients with fixed-bearing implants had an average +2.6° alignment and the patients with mobile-bearing implants had +5.5° alignment, which was significantly different. Survivorship analysis based on component loosening and revision showed a 99% survival for the meniscal-bearing implant and 93% survival for the fixed-bearing implant at 11 years. However, the fixed-bearing knee implants failed significantly more often because of tibial component failure, in six of eight knees, at an average of 6.3 years. The mobile-bearing implants showed a trend to fail because of arthritic degeneration in the lateral compartment, at an average of 10 years, although not statistically significant. The mobile-bearing implants had no tibial component failures. These differences may be attributable to implant design or surgical technique.

Reconstruction of patellar tendon rupture after total knee arthroplasty with an extensor mechanism allograft.

Although patellar tendon rupture after total knee arthroplasty (TKA) is a rare complication, the consistently poor outcome of conventional tendon repair has convinced some to abandon such reconstruction in favor of a prospective protocol using an allograft distal extensor mechanism. The graft consists of a quadriceps tendon, a patella with a cemented prosthesis, a patellar tendon, and a tibial tubercle. Since December 1985, 13 knees in 12 patients were reconstructed using this method. Ten knees were followed for six to 51 months; five of these knees were followed for more than 24 months. Knee extension power and improved function were ultimately attained in all cases, although minimal extensor lags were present in three cases. Preoperative motion returned in all but one knee. Healing of the allograft to the host tissue was attained primarily at all of the tibial junctions. Two graft complications occurred, both in the first three months after surgery: one quadriceps junction treated by resuture failed at the one-month mark, and the other graft had to be revised for extensor weakness from rupture of the graft at the patella-patellar tendon junction, which was attributed to surgical damage to the tendon. After completion of healing to the host and rehabilitation of the knee joint, no grafts in the series failed during the course of normal daily activities. One patient fractured the allograft patella in a severe fall. The long-term durability of this construct needs to be studied further.

Effect of circumferential plasma-spray porous coating on the rate of femoral Osteolysis after total hip arthroplasty

BACKGROUND Osteolysis of the femur has been a serious problem associated with some designs of total hip-replacement implants; it frequently leads to failure of the femoral component. We evaluated the effect of a circumferential plasma-spray porous coating on the rate of osteolysis in a study that included two groups of hips, each of which received an implant with the same design except for the extent of the porous coating. Our goal was to determine the possible role of circumferential porous coating in protecting the bone-implant interface from osteolysis. METHODS A series of consecutive primary total hip replacements performed with insertion of the Mallory-Head implant without cement was divided into two study groups. The first 126 hips (Group 1) were treated with a femoral stem that had a noncircumferential plasma-spray porous titanium coating. The next ninety hips (Group 2) were treated with a circumferentially coated stem of the same design. The average duration of radiographic follow-up was 7.8 years in Group 1 and 7.5 years in Group 2. RESULTS The average rate of polyethylene wear was similar for the two groups (0.187 millimeter per year in Group 1 and 0.189 millimeter per year in Group 2). The prevalence of osteolysis in Group 1 (40 percent; fifty of 126 hips) was significantly higher than that in Group 2 (10 percent; nine of ninety hips) (p < 0.001). Osteolysis remote from the joint space (distal to zones 1 and 7) was found in 11 percent (fourteen) of the hips in Group 1 but in none of those in Group 2 (p = 0.0004). The average total area of osteolysis in Group 1 (5.0 square centimeters) was significantly larger than that in Group 2 (2.9 square centimeters) (p < 0.05). CONCLUSIONS A circumferential plasma-spray titanium porous coating on the femoral component of a total hip-replacement prosthesis inserted without cement appears to provide an effective barrier preventing wear debris from gaining access to the endosteal surface of the femur and the greater trochanter. This finding supports the hypothesis of the so-called effective joint space, which predicts that wear debris from the joint bearing can migrate, driven by intracapsular pressures, to all areas to which joint fluid has access and thus can result in osteolysis. The reduction of the prevalence of osteolysis and the elimination of osteolysis from the zones remote from the joint space by the use of a circumferential plasma-spray porous coating indicates that the femur was effectively sealed off from the joint space. We believe that the durability and longevity of the femoral component should be enhanced by the use of such a coating.

Metal-on-metal total hip arthroplasty with large heads may prevent early dislocation.

Postoperative dislocation is one of the major causes of morbidity and failure of total hip arthroplasty. We reviewed 327 patients (377 hips) retrospectively with varying diagnoses and indications but all of whom received large-diameter metal-on-metal prostheses. Two surgical approaches were used: the anterolateral abductor splitting (342 procedures) and a mini-incision poste rior approach (35 procedures). Average age at time of surgery was 55.9 years and average followup was 4.0 months. There were 346 (91.8%) primary procedures, 15 (4.0%) conversion procedures, and 16 (4.2%) revisions or reimplantations. The most common preoperative diagnoses included osteoarthritis (250 hips; 66.3%) and avascular necrosis (46 hips; 12.2%). There were 62 (16.4%) patients with high-risk diagnoses for dislocation. The status in terms of postoperative dislocation was known for all patients. During the short followup period, there were no dislocations. Use of large-diameter femoral heads and metal-on-metal articulations decreases the risk of dislocations, making their use a viable choice for primary and revision procedures. Level of Evidence: Therapeutic study, Level IV-1 (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Clinical and Radiographic Outcome of a Cementless, Titanium, Plasma Spray-coated Total Hip Arthroplasty Femoral Component Justification for Continuance of Use

Between 1984 and 1986, 177 nonconsecutive, primary total hip arthroplasties were performed in 150 patients using the Mallory-Head Porous femoral component (Biomet, Warsaw, IN) inserted without cement. Average time to follow-up evaluation for the entire population (including all early revisions) was 76 months (6.3 years). There were 10 revisions (6%) with an average time to revision of 50 months (4.2 years). Two revisions were for component undersizing; three revisions were for aseptic loosening; four revisions were for acetabular component failure and one revision was due to a femoral fracture secondary to trauma. At the most recent follow-up visit, the average Harris hip score for all hips increased from 41.5 before surgery to 86.8 (P < .001). Radiographic assessments yielded an average Engh fixation score of 20.7. The Kaplan-Meier survival estimate for the average time to follow-up evaluation was 0.98. Based on our patient selection criteria and excellent intermediate clinical and radiographic results, the initial design strategies of the Mallory-Head Porous femoral prosthesis have been confirmed.

Proximal femoral allografts in revision total hip arthroplasty.

Patients with total hip arthroplasty (THA) and aseptic loosening associated with severe bone deficiency were treated with freeze-dried bone allografts of the proximal one-third of the femur. Twenty-two of the first 25 patients were available for review with an average follow-up period of 28 months. Significant functional improvement was obtained in 16 patients (73%). The following complications occurred with allograft revisions: dislocation, wound hematoma, joint instability, nonunion, implant failure, and acetabular loosening. Nine patients required additional surgical procedures. There have been no infections or rapid lysis indicative of an allograft rejection phenomenon. The 73% success at the two-year postoperative interval of incorporation of freeze-dried allografts for salvage situations has been encouraging. However, the long-term durability of these grafts is not known and will require further follow-up study.