The short stem: promises and pitfalls.

Conventional uncemented femoral implants provide dependable long-term fixation in patients with a wide range of functional requirements. Yet challenges associated with proximal-distal femoral dimensional mismatch, preservation of bone stock, and minimally invasive approaches have led to exploration into alternative implant designs. Short stem designs focusing on a stable metaphyseal fit have emerged to address these issues in total hip replacement (THR). Uncemented metaphyseal-engaging short stem implants are stable and are associated with proximal bone remodeling closer to the metaphysis when compared with conventional stems and they also have comparable clinical performances. Short stem metaphyseal-engaging implants can meet the goals of a successful THR, including tolerating a high level of patient function, as well as durable fixation.

Fixed and mobile bearing total knee arthroplasty--influence on wear generation, corresponding wear areas, knee kinematics and particle composition.

BACKGROUND: Several studies in literature are dealing with a direct comparison between fixed and mobile bearing knee replacements, but to our knowledge there is no published data comparing the wear behaviour of the two design principles based on the same femur and superior gliding surface geometry. The objective of our study was to investigate a fixed and mobile bearing knee design with identical femoral articulation in regard to wear, tibio-femoral kinematics and particle size distribution. METHODS: In vitro wear simulation according to ISO 14243-1 has been performed with the Columbus knee system (Aesculap, Tuttlingen) in the configurations fixed and mobile bearing for five million cycles on a customized four station knee wear simulator. The tests were running under force control and the tibio-femoral kinematics were assessed. A particle analysis has been undergone after each inspection interval when the lubricant was replaced. FINDINGS: Due to the additional wear in the tibial articulation of the mobile bearing design the mean gravimetric wear rates are not statistically different between the two groups. Apart of that there is a substantial reduction in the amount of wear per area unit for the mobile versus the fixed bearing gliding surfaces. Both groups show comparable tibio-femoral kinematics and a similar wear debris morphology. INTERPRETATION: Our investigation of a fixed and mobile bearing knee design with identical femoral articulation demonstrates that there are no significant differences in wear rate, resulting kinematics and polyethylene particle release. Therefore it can be recommended that surgeons decision for one or the other design principle should be based on the individual patient profile.

Computer assisted knee replacement.

Accurate alignment of knee implants is essential for the success of total knee replacement. Although mechanical alignment guides have been designed to improve alignment accuracy, there are several fundamental limitations of this technology that will inhibit additional improvements. Various computer assisted techniques have been developed to examine the potential to install knee implants more accurately and consistently than can be done with mechanical guides. For example, computer integrated instrumentation incorporates highly accurate measurement devices to locate joint centers, track surgical tools, and align prosthetic components. Image guided knee replacement provides a three-dimensional preoperative plan that guides the placement of the cutting blocks and prosthetic components. Robot assisted knee replacement allows one to machine bones accurately without the use of standard cutting blocks. The rationale for the development of computer assisted knee replacement systems is presented, the operation of several different systems is described, the advantages and disadvantages of different approaches are discussed, and areas for future research are suggested.

Posterior tilting of the tibial component decreases femoral rollback in posterior-substituting knee replacement: a computer simulation study.

Posterior tilting of the tibial component is thought to increase the range of motion in posterior cruciate-retaining total knee replacement, but its effect on implant motion in posterior cruciate-substituting total knee replacement is unknown. This issue has become of interest recently because manufacturers have introduced instrumentation that produces a posteriorly tilted tibial cut for both implant types. The purpose of this study was to investigate how motion of posterior cruciate-substituting total knee replacement is affected when the tibial component is installed with posterior tilt. Sagittal plane implant motions were predicted from prosthesis geometry with use of a computer simulation in which the femoral condyles were assumed to sit in the bottoms of the tibial condylar wells when the knee was in extension. Rollback of the femoral component was produced by a cam-spine mechanism at higher angles of flexion. The simulations revealed that even small degrees of posterior tilt reduced rollback by limiting the interaction between the cam and spine. Tilting the component posteriorly by 5 degrees caused the cam to contact the spine at a knee flexion angle that was 18 degrees higher than with the untilted component. The results suggest that posterior tilting of the tibial component in posterior cruciate-substituting knee replacement may not produce the same beneficial effects that have been reported for the tilting of tibial components in posterior cruciate-retaining knee replacement.

Managing bone loss with augmentation.

Augmentation blocks are effective ways of treating the problem of bone loss on the distal and posterior femur. They allow accurate and durable reestablishment of the distal and posterior joint line in revision total knee replacements. They are particularly appropriate in revisions being carried out in elderly, osteopenic patients with severe deformities or instabilities. Revision instrumentation can and should philosophically and mechanically remind one of and be consistent with primary total knee instrumentation.

Maintenance of proximal bone mass with an uncemented femoral stem analysis with dual-energy x-ray absorptiometry.

Bone ingrowth into uncemented femoral implants with proximal porous coatings has been designed to avoid proximal stress shielding and preserve femoral strength. Dual-energy x-ray absorptiometry allows repeated quantitative analysis of anteroposterior scans of the proximal femur. By use of dual-energy x-ray absorptiometry and qualitative radiographic changes, 31 total hip arthroplasties with an individually designed, proximally porous-coated prosthesis were evaluated after surgery and at intervals up to 2 years. All implants appeared to achieve successful bone ingrowth and subsequent remodeling. At the most proximal level around the neck osteotomy, the postoperative loss of bone density at 6 months was -14.5%, which persisted at 24 months with -11.6%. At the level of the distal portion of the porous coating in the lower metaphysis, the density change was -8.7%, but bone had remodeled at 24 months with a change in density of only -1.0% compared with the immediate postoperative scan. With a design that results in reliable proximal ingrowth, this study predicts that after an initial decline in bone density, a positive bone remodeling response occurs that could lead to long-term stable fixation of the femoral implant.

Role of growth hormone status in the outcome of total knee replacement.

The objective was to assess whether the aging related, variable decline in growth hormone influences total knee replacement outcome. In this prospective cohort study, consecutive patients who underwent unilateral total knee replacement and who met criteria were enrolled from the practice of 1 orthopaedic surgeon at a university hospital. Participants were evaluated 1 month before and 3 months after total knee replacement. Evaluators were not involved in patient care. The primary outcome measure was the Medical Outcome Study 36-item Short Form Health Survey Physical Functioning Scale score 3 months after total knee replacement. In a multiple regression analysis performed to assess the influence of growth hormone status, controlling for social support, body mass index, gender, previous reconstruction, mental health, motivation, and baseline physical functioning, only mental health contributed significantly to outcome. Mental health accounted for 18% of outcome variance. Growth hormone levels did not predict functional status after total knee replacement. Psychological status contributes significantly to total knee replacement physical functional outcome.

Outcome of hip and knee arthroplasty in persons aged 80 years and older.

Recent studies have established the cost effectiveness and safety of total joint arthroplasties. As the population ages, it is important to determine whether these procedures are equally beneficial in the elderly. The short term safety and efficacy of total hip and knee arthroplasties in subjects 80 years of age and older was evaluated. Between 1988 and 1993, preoperative and postoperative physical and functional information was collected on 99 consecutive elective hip and knee arthroplasties in subjects 80 years of age or older. These data were compared with those derived from a younger otherwise matched control group. Data collected included subject demographics and characteristics, information concerning the acute and postacute hospital stay, comorbid conditions, postoperative complications, discharge disposition, Hospital for Special Surgery knee and Harris hip scores, pain scores, and functional capacity. The average age of the subjects was 83 years; osteoarthritis was the most common diagnosis; and the average followup was 25 months. Complication rates and length of stay in acute care facilities were not significantly different than for the control group. Mean preoperative Hospital for Special Surgery knee and Harris hip scores were 58 and 60, respectively, with postoperative scores of 77 and 88, respectively. Pain dramatically improved with 98% of total knee arthroplasty and 100% of total hip arthroplasty subjects reporting mild or no pain at followup. Preoperatively, none of the knee or hip subjects could walk unlimited distances. Postoperatively 51% of the total knee arthroplasty and 54% of the total hip arthroplasty subjects could walk more than five blocks; 71% of the total knee arthroplasty and 86% of the total hip arthroplasty subjects walked with a cane or no assistive device. The most dramatic postoperative functional gains were seen in the most disabled subjects. Total charges of care for patients 80 years of age and older was slightly greater than for a younger group. It was established that total joint arthroplasty can be performed safely in patients 80 years of age and older, promising excellent pain relief and improved functional outcome.

Functional outcome and patient satisfaction in total knee patients over the age of 75.

Seventy-four patients, age 75 or older, who had undergone 98 primary total knee arthroplasties were evaluated in a retrospective cohort study, with validated questionnaires that assessed self-reported pain, physical function, mental health, and satisfaction. Average follow-up period was 34 months (range, 12-67 months). Overall, 90.8% reported improvement, 88.8% were satisfied with the results of surgery, and 91.8% felt they had made the right decision. Dissatisfaction with the results correlated with poorer mental health scores, decreased physical function, and increased bodily pain scores (P < .05). Satisfaction was correlated with better pain scores on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and SF-36 (P < .05) but not with Hospital for Special Surgery scores (P = .328). Poor surgical results leading to revision surgery (5%) were associated with preoperative deformity greater than 20 degrees. Based on this patient-assessed outcome analysis, total knee arthroplasty is a worthwhile and beneficial procedure in the elderly.

Prognostic factors for functional outcome of total knee replacement: a prospective study.

BACKGROUND: The objective was to investigate whether baseline physical functioning, medical, psychosocial, or demographic variables predict functional outcome in patients undergoing total knee replacement. METHODS: A prospective cohort study was performed between December 1991 and August 1993. Consecutive, unilateral tricompartmental total knee replacement patients aged > or = 55 yr with osteoarthritis, who met criteria, were enrolled and evaluated one month before and 3 months after total knee replacement. The primary outcome measure was the Medical Outcome Study 36 Item Short Form Health Survey (known as the SF36) Physical Functioning Scale score. The outcome evaluator was not involved in patient care. RESULTS: A hierarchical multiple regression analysis was performed to calculate the contribution of baseline variables to TKR outcome. Of the 27% of outcome variance explained by the model, demographic variables accounted for 4%, psychosocial variables (motivation, role functioning-emotional, and social functioning) for 19% (p = .013), medical variables (previous reconstruction, comorbidity, body mass index, bodily pain) for 2%, and baseline physical function for 2%. CONCLUSIONS: Psychosocial variables are significantly related to total knee replacement functional outcome. Assessment of baseline psychological and social functioning may identify a subset of patients at risk for worse outcome. Specific interventions for these patients should be developed and evaluated as components of patient management prior to and after the procedure.

CKS knee prosthesis: biomechanics and clinical results in 42 cases.

From 1991 to 1993 a total of 42 CKS prostheses were implanted for the following reasons: osteoarthrosis (34 cases), rheumatoid arthritis (7 cases) tibial necrosis (1 case). At follow-up obtained after 17 to 41 months the results were: excellent or good: 41; the only poor result was probably related to excessive tension of the posterior cruciate ligament. 94% of the patients reported complete regression of pain, 85% was capable of going up and down stairs without support. Mean joint flexion was 105 degrees. Radiologically the anatomical axis of the knee had a mean valgus of anatomical axis of the knee had a mean valgus of 6 degrees. The prosthetic components were always cemented. The posterior cruciate ligament was removed in 7 knees, so that the prosthesis with "posterior stability" was used. The patella was never prosthetized. One patient complained of peri-patellar pain two months after surgery which then regressed completely.