Patellofemoral replacement: the third compartment.

Isolated patellofemoral arthritis is a common condition and there are varying opinions on the most effective treatments. Non-operative and operative treatments have failed to demonstrate effective long-term treatment for those in an advanced stage of the condition. Newer designs and increased technology in patellofemoral replacement (PFR) have produced more consistent outcomes. This has led to a renewed enthusiasm for this procedure. Newer PFR prostheses have addressed the patellar maltracking issues plaguing some of the older designs. Short-term results with contemporary prostheses and new technology are described here.

Relationship between bone ingrowth, mineral apposition rate, and osteoblast activity.

To better understand skeletal attachment of porous coated total hip and knee implants over time, this study investigated the dynamics of osteoblast populations at the interface of porous coated implants in a weight-bearing ovine model. The relationship between cancellous bone ingrowth, mineral apposition rate (MAR), and osteoblast activity indicators such as osteoblast area, relative osteoblast number, osteoid width, and osteoid area (O.Ar.) were investigated. The data demonstrated that the percent O.Ar. was a marginally significant predictor of bone ingrowth and MAR over time, suggesting that the amount of osteoid present influenced bone ingrowth and MAR in the porous coated implants. The data also demonstrated that all osteoblast activity indicators were significantly greater in the porous coated region compared to the host bone region, while controlling for in situ time (p < 0.05). This may have been due to the trauma of implantation or the influence of the implant load on the bone tissue promoting a regional acceleratory phenomenon. The localized response suggests that specific therapies may be developed to affect the physiology of osteoblasts at the interface of implants, which may allow for improve skeletal attachment of biomaterials and clinical outcomes of cementless joint replacements.

Ten- to 14-year clinical followup of the cementless Natural Knee system.

Of 300 consecutive knees (238 patients) that had undergone arthroplasty with the cementless Natural Knee prosthesis from 1985 to 1989, 176 knees (141 patients) were available for followup at an average of 12 +/- 1 years after the operation. Knee function was improved significantly. Modified Hospital for Special Surgery knee scores improved from 59.1 +/- 13.2 points preoperatively to 97.8 +/- 4.7 points at last followup. At last followup, knee range of motion averaged 0 degrees +/- 2 degrees to 120 degrees +/- 10 degrees. Implant survival was 93.4% (including infection and simple polyethylene exchanges) and 95.1% (excluding infection and simple polyethylene exchanges) at 10 years when applying the Kaplan-Meier survival analysis, using loose components, revision, or both as failure criteria. Besides the three revisions for infection, only two femoral and one tibial component required revision. The patellar component survivorship at 10 years was 95.1%. All patellar revisions were attributed to edge wear. Subsequent operative and design changes, including patellar component medialization and countersinking, have decreased the incidence of patellar revision. The long-term results of this cementless knee system compare favorably with those of cemented systems. The Natural Knee design has provided excellent and predictable long-term clinical results in the current series of active patients.

The contribution of cortical and cancellous bone to dual-energy X-ray absorptiometry measurements in the female proximal femur.

Dual-energy X-ray absorptiometry (DXA) is the most common method for determining bone mineral density (BMD) in the proximal femur. However, there remain questions concerning the contribution of cortical and cancellous bone to this technology in the proximal femur. The purpose of this investigation was to identify structural and compositional characteristics of human bone in the proximal femur that significantly influence DXA BMD measurements. Twenty-four femora were obtained at autopsy from Caucasian females ranging in age from 17 to 92 years (mean +/- SD, 61 +/- 25 years). DXA scans were performed on each specimen with a Hologic QDR-2000 densitometer. Direct measurements were determined from proximal femoral sections for cancellous bone (volume fraction, ash fraction, cancellous cross-sectional area and percent cancellous cross-sectional area), cortical bone (thickness, ash fraction, porosity, cortical cross-sectional area and percent cortical cross-sectional area) and anteroposterior thickness. These parameters were compared with the associated DXA measurements by means of simple and multiple regressions. Cancellous volume fraction was the best predictor of variability of DXA measurements for both the neck and trochanter, with an R2 of 0.87 and 0.76, respectively (p < 0.0001). There was only a minor influence of cortical factors such as thickness (neck and trochanter R2 = 0.51 and 0.42, respectively, p < 0.001) and trochanteric cross-sectional area (R2 = 0.21, p < 0.05). Although the accuracy for determining specific components of the proximal femur was low, the DXA BMD measurement was a strong predictor of cancellous bone factors, but not cortical bone factors that have been shown to change significantly with age.

Cementless primary total hip arthroplasty with a tapered, proximally porous-coated titanium prosthesis: a 4- to 8-year retrospective review.

A consecutive series of 100 primary total hip arthroplasties were performed at a single institution on 87 patients using a cementless collared titanium press-fit stem. Of patients, 87% received a hemispheric porous-coated cup, and 13% received a nonmodular titanium fibermesh press-fit cup. Ten hips were excluded from the longer-term evaluation: 6 were lost to follow-up, and 4 patients were deceased. Ninety hips, with an average follow-up of 81 +/- 12 months, were retrospectively reviewed. The average postoperative hip score was 94, compared with an average preoperative hip score of 42. No postoperative infections were observed, but there were 2 cases of postoperative dislocation (2%) and 1 case of thigh pain (1%) at last follow-up. There were 2 revisions, both for cup failures. There were no femoral component loosenings or revisions. There was no evidence of stem subsidence or instability. These midterm results are encouraging with this stem design.

Possible explanation for the white band artifact seen in clinically retrieved polyethylene tibial components.

Studies have focused attention on the appearance of a subsurface white band in clinically retrieved polyethylene components and the possible contribution of this phenomenon to early polyethylene delamination. Unconsolidated polyethylene particles and oxidation have been suggested as possible reasons for the appearance of the white band. Calcium stearate and other additives used in processing ultra-high molecular weight polyethylene may also contribute to formation of the white band. A quantitative investigation was conducted on 11 retrieved tibial components that exhibited a subsurface white band to determine whether the amount of calcium stearate particles and additives were greater in the white band region when compared with the mid-portion of the same section of polyethylene. Calcium stearate particles and other additives were quantified using backscattered electron imaging with correlated elemental analysis. The particles were identified based on morphology and elemental patterns similar to reference calcium stearate particles and known additives. Significantly more (p < 0. 0001) calcium stearate particles and additives were present in the white band region (4578 +/- 418 particles/mm(2); mean +/- standard error) than the mid-portion region (1250 +/- 147 particles/mm(2)) of the sectioned tibial inserts. The percent area occupied by calcium stearate particles and additives was five times higher (p < 0.0001) within the white band region (0.81 +/- 0.10%) than the mid-portion region (0.16 +/- 0.03%). The increased presence of calcium stearate and other additives in the white band region suggests that they may play a role in the formation of the white band. In future investigations it may be important to consider how calcium stearate and other additives in polyethylene resins affect white band formation and the possible contribution to crazing, early delamination, and osteolysis in total joint replacement.

Posterior stabilization in total knee arthroplasty with use of an ultracongruent polyethylene insert.

Fifty-three primary and 47 revision posterior cruciate ligament (PCL)-substituting total knee arthroplasties (TKAs) using a highly conforming (ultracongruent) polyethylene insert were retrospectively reviewed over a 48- to 106-month (mean, 60+/-11 months) follow-up period. These 100 knees were age and sex matched with another 100 TKAs performed using a PCL-sparing design. The ultracongruent design has an anterior buildup of 12.5 mm and a more conforming articular surface to match better the radius of the femoral component. In primary and revision TKAs, the average Hospital for Special Surgery knee score (P = .3) and range of motion (P = .43) were similar between the PCL-sparing and ultracongruent groups. In primary and revision TKAs, there were no revisions resulting from instability for patients receiving an ultracongruent insert versus 5 knees in the PCL-sparing control group secondary to subsequent postoperative anteroposterior instability and PCL insufficiency.

Elemental and morphological identification of third-body particulate and calcium stearate inclusions in polyethylene components.

Third-body particulate such as human bone chips, hydroxyapatite, and bone cement are considered contributing factors in accelerated wear in total joint replacement. Particulate wear debris is now considered the major contributing factor in aseptic loosening of total joint replacements. The ability to distinguish between different third-body particulate is necessary to better understand wear mechanisms when conducting implant retrieval analysis. The objective of this investigation is to demonstrate that backscattered electron imaging with correlated energy dispersive X-ray analysis can accurately identify third-body particulate in retrieved polyethylene components. It is important that this technique can also distinguish between third-body particulate and normal inclusions in the polyethylene such as calcium stearate, based on the distinct morphology and elemental composition of each material. Therefore, the ability to distinguish third-body particulate from calcium stearate inclusions is essential in gaining a better understanding of the contributing factors associated with coating separation and accelerated wear observed in clinically retrieved polyethylene components.

High tibial osteotomy with a calibrated osteotomy guide, rigid internal fixation, and early motion. Long-term follow-up.

BACKGROUND: We studied the results of sixty-four valgus-producing high tibial osteotomies performed with the use of a calibrated osteotomy cutting guide and rigid internal fixation, and followed by early motion, in fifty-six patients who had medial unicompartmental osteoarthritis and varus malalignment. Long-term studies have demonstrated that a high tibial osteotomy performed with staple fixation and followed by immobilization in a cast has an expected survival rate of approximately 85 percent at five years and 60 percent at ten years (in studies of ninety-five knees and 213 knees, respectively). To the best of our knowledge, there are no long-term reports on high tibial osteotomies performed with a calibrated osteotomy cutting guide and rigid internal fixation and followed by early motion. METHODS: The indications for high tibial osteotomy were medial unicompartmental osteoarthritis and varus malalignment. A lateral closing-wedge osteotomy was performed. The patients were reexamined to obtain a knee score, to make lateral radiographs of both knees, and to make a full-length anteroposterior radiograph (showing the entire lower extremity, including the hip and ankle) of the involved knee with the patient standing. RESULTS: Twenty-one knees were treated with a subsequent total knee arthroplasty at an average of sixty-five months after the high tibial osteotomy. The remaining forty-three knees had a good or excellent clinical result, with an average knee score of 94 points at an average of 8.5 years after the osteotomy. Survivorship analysis showed an expected rate of survival, with conversion to a total knee arthroplasty as the end point, of 85 percent at five years and 53 percent at ten years. No patient had patella baja postoperatively. There were six complications: four superficial wound infections, one superficial-vein thrombosis, and one delayed union (union occurred at five months). CONCLUSIONS: High tibial osteotomy has been criticized because of a high rate of complications, a loss of effectiveness with time, and the difficulty of conversion to a total knee arthroplasty secondary to patella baja. In our series, in which an osteotomy was performed with a calibrated osteotomy cutting guide and rigid internal fixation and was followed by early motion, the rate of complications was low and approximately two-thirds of the knees had a good or excellent clinical result at an average of 8.5 years. Conversion to a total knee arthroplasty was accomplished without difficulty in the patients who had this procedure. We highly recommend high tibial osteotomy with a calibrated osteotomy cutting guide, rigid internal fixation, and early motion for patients who wish to continue an active lifestyle.

Porous-coated metal-backed patellar components in total knee replacement. A postmortem retrieval analysis.

The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45+/-36 months (range, one to eighty-four months). Analysis of the high-resolution contact radiographs revealed that a mean of 86+/-12 per cent (range, 61 to 100 per cent) of the porous coating was in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13+/-9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.

Dissolution of particulate hydroxyapatite in a macrophage organelle model.

It is controversial as to whether debris from hydroxyapatite (HA)-coated implants jeopardizes the long-term success of total joint replacements. It has been hypothesized that liberated HA particles are engulfed by macrophages and through normal cellular digestion prevent osteolysis and third-body wear. HA particulates, however, have been observed at the interface and on polyethylene articulating surfaces. There is limited data demonstrating the ability of HA to dissolve at the acidity levels associated with macrophage organelle digestion. The objective of this study was to determine if particulate HA could dissolve at the pH levels found in macrophage organelles. Characterized HA particles were placed into buffered solutions corresponding to phagosomal organelle pH levels: cytoplasmic (pH 7), phagosomal (pH 6), and lysosomal (pH 5). Flasks were under continuous agitation in a shaker chamber at 37 degrees C. Calcium and phosphate ions were measured beyond the maximum life span of an activated macrophage. The data showed that calcium ions rose within the first 24 h and then remained constant throughout the experiment for all pH groups. Phosphate ion concentration showed a similar pattern at the lysosomal pH but remained undetected at the other organelle pH levels. The saturation point was highest at the lysosomal pH level and lowest at the cytoplasmic pH level. The results of this experiment leave the potential for HA particles to dissolve following macrophage digestion. However, caution must be exercised when interpreting the macrophage organelle digestion hypothesis; the size of the HA particle, the length of time required to completely dissolve the particle, and potential cellular toxicity all are factors that have yet to be determined before this hypothesis can be validated.

Analysis of particles in acetabular components from patients with osteolysis.

Acetabular polyethylene components were quantitatively analyzed for the presence of third body particles from 38 consecutively retrieved components. Backscattered electron imaging and correlated energy dispersive x-ray analysis were used for the assessments. Retrievals were divided into 4 groups based on methods of fixation and metal alloy types: 8 hydroxyapatite coated, 6 cobalt chrome porous coated, 17 titanium porous coated, and 7 cemented implants were evaluated. The backscattered electron imaging data showed that the components from the hydroxyapatite coated implants had larger particles than did the components from the cemented group. The hydroxyapatite group had 51 +/- 52 particles per mm2. The cobalt chrome alloy group had 10 +/- 9 particles per mm2, and the titanium alloy group had 9 +/- 16 particles per mm2. The cemented group had 5 +/- 4 particles per mm2. The difference between the cement group and the hydroxyapatite group was statistically significant. The elemental analysis showed that 70% of the particles in the hydroxyapatite group had calcium and phosphorus elements. Third body particles likely contribute to particulate generation. The results suggest that the hydroxyapatite coated components have the potential for producing greater amounts of particulate debris. Continued analysis of retrieved components for the presence of the third body particles is required.

Progression of human bone ingrowth into porous-coated implants. Rate of bone ingrowth in humans.

We report the measured progression of human cancellous bone ingrowth into load-bearing porous-coated titanium implants over 5 time periods (0, 3, 6, 9, and 12 months). There was a statistically significant progression of bone ingrowth into the implants over a 9-month period, but the 9- and 12-month data were not different. Investigators are advised to analyze time "0" implants in order to distinguish mechanical impaction of bone from the biological process of bone ingrowth.