Biomedical subjects
Publications and source records attributed to Stephen J Incavo.
Simultaneous femoral deformity correction combined with total knee arthroplasty can be a complex procedure, which can be simplified with this described technique. A femoral component that allows access to the intramedullary canal is necessary to be able to use this technique.
Component malrotation may result in unsuccessful total knee arthroplasty. We asked whether revision improves function in patients with malrotated total knee arthroplasty components. We retrospectively reviewed 22 revision total knee arthroplasties performed for femoral and/or tibial component malrotation. Revision surgery was performed within 2 years of the primary arthroplasty in 81% of the cases (18 of 22) with the remainder within 5 years. Although all patients had pain, 32% of patients had associated instability and 36% of patients had poor range of motion. Average Knee Society Scores improved from 42 preoperatively to 77 postoperatively. Average Oxford Knee Scores improved from 38 preoperatively to 29 postoperatively. Although clinical and functional improvement was observed, these results are inferior to those for primary knee arthroplasty, and they emphasize the need for proper component rotational positioning during primary total knee arthroplasty. Internal component malrotation leads not only to patellofemoral problems, but also to difficulty in gap balancing and femoral component sizing, which may in turn lead to either poor range of motion or symptoms of knee instability.
Proximal ingrowth of femoral components in total hip arthroplasty (THA) is desirable because it minimizes proximal stress shielding associated with distal ingrowth stems and maximizes bone stock. This is a retrospective evaluation of initial results of revision THA using a proximally hydroxyapatite-coated femoral stem nominally designed for primary use. Patients requiring femoral stem revision were included if they had sufficient femoral bone stock to support a proximally fixed prosthesis (n = 33). This represents 53% of the femoral revisions performed during the period of the study. The average follow-up was 5 years (range 48-88 months). The mean Harris hip and Oxford hip scores were 86.5 and 25.2, respectively. Radiographically, 100% of the stems demonstrated bone ingrowth fixation. These results are superior to previous reports of primary cementless stems for revision THA. The use of a cementless nonmodular implant provides a viable option in some patients undergoing revision THA.
Simultaneous bilateral total hip arthroplasty (THA) is an increasingly common procedure. Although use of a cementless stem can eliminate cement complications, some surgeons limit application of cementless THA because of concerns about early implant loosening. In this article, we report on 30 cementless THA cases (15 patients) followed up for a minimum of 2 years (range, 26-50 months). Despite 73% of femoral bone being type B or type C, all stems showed stable bone ingrowth fixation and no evidence of subsidence. Polyethylene wear rates (left, 0.154 mm/y; right, 0.114 mm/y) did not differ significantly. The excellent clinical results obtained with simultaneous bilateral cementless THA are comparable with those obtained with unilateral THA.
A retrospective review of 81 sequential primary total hip arthroplasties using a cementless, high-offset femoral stem was performed. Follow-up was 24 to 60 months. The average age at the time of surgery was 54 years. The femoral bone types were: 36% Dorr A, 51% Dorr B, and 13% Dorr C. The mean postoperative Harris Hip Score was 95. The mean postoperative Oxford score was 17. Eighty-five percent had no clinical leg-length difference. All stems were radiographically stable. The stem features of hydroxyapatite coating on a rough circumferential titanium arc-deposit proximal surface in conjunction with distal flutes seem to provide immediate stability, making this implant clinically versatile. Potential benefits of increased offset include improved joint stability and avoidance of leg lengthening.
Generally, 2 different methods are used to select femoral size. These can be termed "size-matched resection" and "flexion-space balancing." The purpose of this paper is to compare these 2 methods during 50 sequential total knee arthroplasty surgeries. The flexion-space-balancing method led to a smaller size selection than the size-matched-resection method in 28 (56%) knees. In the remaining 22 knees, the measurement methods led to the selection of the same size femoral component. The difference in measurement methods was significant (P<.05). The preoperative varus knees were more sensitive to the differences in measurement methods than the valgus knees (P<.05). A flexion space that is too small may adversely affect the clinical outcome of knee arthroplasty.
Some surgeons warn against kneeling after total knee arthroplasty (TKA), because limited clinical data exist. We describe the tibiofemoral contact position of TKA components during kneeling in vivo. Ten posterior-substituting (PS) and 10 cruciate-retaining (CR) designs were examined using a radiographic image-matching technique. Movement from standing to kneeling at 90 degrees produced different responses. CR knees translated anteriorly (medial, 4 +/- 4 mm; lateral, 2 +/- 6 mm). PS knees underwent little posterior translation (medial, 0.2 +/- 3 mm; lateral, 1 +/- 4 mm). Movement from 90 degrees to maximum flexion produced femoral posterior translation (CR medial, 5 +/- 4 mm; CR lateral, 5 +/- 4 mm; PS medial, 6 +/- 4 mm; PS lateral, 6 +/- 3 mm). The relationship between tibiofemoral contact position and flexion angle was more variable for CR (r2=.38) than for PS (r2=.64). Knee kinematics was similar to other deep-flexion weight-bearing activities.
Femoral component revisions with extensively coated stems have shown promising clinical results, although concerns over stress shielding still exist. We retrospectively reviewed 59 patients undergoing femoral component revision with an extensively hydroxyapatite (HA)-coated stem. The average length of follow-up was 3.3 years (range, 2-5 years). The average preoperative Harris Hip Score was 43 points, which improved to 86 points at the latest follow-up (P < .01). The overall mechanical failure rate was 2%. No evidence of stress shielding was seen in 78% of patients. The clinical results of this series using an extensively HA-coated stem are similar to those using an extensively porous-coated stem. Long-term follow-up is required to determine if an extensively HA-coated implant will be superior to an extensively porous-coated implant with regard to stress shielding.
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Femoral revision is difficult when the femoral canal exceeds 20 mm in diameter. For this subset of patients, we used a technique of cementing cortical allograft sleeves to a proximal ingrowth stem. The diameter of the allograft sleeves are matched to the diameter of the host femur. The stem-allograft construct provides initial stability with the opportunity for proximal bone ingrowth.
The orientation of the femur, tibia, and patella are important considerations in total knee arthroplasty. Our goal was to describe the relationships between the femoral epicondylar (FE) axis, posterior femoral (PF) axis, posterior tibial (PT) axis, patellar (PAT) axis, and patellar ligament (PL). A secondary goal was to determine where the short axis of the tibial tray intersects the patellar ligament as a function of tibial component rotation. Thirty normal magnetic resonance imaging (MRI) scans were analyzed. Strong relationships were found between the FE and PAT axes (2 degrees +/- 3 degrees, r(2) = 0.73), and between the FE and PF axes (6 degrees +/- 2 degrees, r(2) = 0.77). When the tibial baseplate was aligned along the PT axis, 30% of the cases were in an ideal position. When the FE axis was used, 73% were ideal.
We report the 2-year results for a prospective randomized trial comparing highly cross-linked with standard polyethylene in total hip replacements. In our study, 46 hips were available for radiographic analysis at 2- and 3-year follow-up. Femoral bearings were 28-mm cobalt chrome with the polyethylene insert randomly selected at the time of implantation to be highly cross-linked polyethylene (Crossfire; Stryker Howmedica Osteonics, Allendale, NJ) or standard polyethylene (N(2)/Vac, Stryker Howmedica Osteonics). Polyethylene wear rates were measured based on anterior-posterior (AP) and lateral pelvis radiographs at 6 weeks and at yearly intervals using a validated computer-assisted edge-detection method. Wear rates between the 2 groups were compared using the nonparametric Mann-Whitney test at the 95% level. A significant reduction in 2- and 3-dimensional linear wear rates (42% and 50%) was found in the highly cross-linked group (P =.001 and P =.005).
A laboratory-based study was performed to describe the tibial axis and patellar position relative to the femoral epicondylar (FE) axis during squatting. During the squat, the angle between the tibial and FE axes averaged 90.5 degrees, and 66% of internal rotation of the tibia occurred before 15 degrees flexion. In the mid-sagittal plane of the femur, the patella followed a circular arc, and mediolateral patellar shift averaged 4.3 mm. These findings can be used as the basis for development of new total knee arthroplasty components that recreate normal patellofemoral kinematics, and may provide important guidelines for alignment of the tibial and femoral components. The perpendicular relationship between the tibial and the FE axes may be useful in locating the FE axis intraoperatively. The reduced mediolateral shift of the patella suggests that alignment of the femoral component with the FE axis will aid patellar tracking about a circular arc with small deviations in the medial-lateral direction.
Minimizing aseptic loosening of cemented femoral stems in total hip arthroplasty remains a goal. Recent investigation suggests that improved cement intrusion may result from elevated pressures shown to occur during stem placement into higher viscosity late stage polymethylmethacrylate cement when compared with low viscosity early stage cement. The hypothesis tested is that placement of a femoral stem in late stage cement can increase cement-bone contact as compared with placement in early stage cement. The variable tested in this experiment was cement viscosity. Radiographic analysis was done on nine paired femurs from cadavers that had placement of a cemented femoral stem with either early or late stage polymethylmethacrylate. Radiographs were assessed quantitatively by measuring the extent of radiolucency observed at the cement-bone interface. Specimens that had late stage cement had significantly less radiolucency in the middle zone region, corresponding to combined Gruen Zones 2 and 6. Similar trends were observed in the proximal and distal zone regions of the stem. Elevated stem insertion pressure associated with late stage cement can minimize void space between the cement and trabecular bone. These findings suggest that the surgeon should consider femoral stem placement later in the cement cure cycle, generating higher intramedullary pressure, and leading to improved cement intrusion into the surrounding bone.
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