Difference in hip prosthesis femoral offset affects hip abductor strength and gait characteristics during obstacle crossing.

The purpose of this article is to determine if individuals with high rather than low femoral offset of a total hip arthroplasty achieve improved hip abductor muscle strength and thus improved their ability to step over an obstacle safely. These outcomes will help surgeons decide whether increasing the femoral offset helps a patient's physical function.

Morphologic differences of the distal femur between Caucasian and Japanese women.

PURPOSE: To compare the morphology of the distal femur between Caucasian and Japanese women. METHODS: 30 Caucasian women aged 41 to 84 (mean, 67) years and 70 Japanese women aged 54 to 86 (mean, 70) years who underwent total knee arthroplasty for osteoarthritis were randomly selected. Morphologic measurements of the distal femur were compared using lateral radiographs. Both race and height influenced the morphology. To adjust for the influence of height on morphology, each measurement was divided by the patient's height and the ratios were compared. RESULTS: Caucasian women were generally taller and heavier (p<0.001) and had higher body mass index (p=0.03) than the Japanese women. Each morphologic measurement of the distal femur was significantly longer in the Caucasian women. In both groups, anteroposterior width of the condyle correlated more with height than weight. In women of equal height, the anteroposterior and metaphyseal widths of the femur and the anterior and resected condyles were longer in Caucasian women, but the posterior condyle was longer in Japanese women. CONCLUSION: Both the size of the femur and the anterior and posterior condyles are significantly larger in Caucasian than Japanese women.

A biomechanical comparison between the single-axis and multi-axis total knee arthroplasty systems for the stand-to-sit movement.

BACKGROUND: Compared to the design of a traditional multi-axis total knee arthroplasty, the single-axis arthroplasty studied has a fixed flexion/extension center of rotation in the femoral component. The influence of this characteristic on functional daily activity, i.e., stand-to-sit, is not well understood. The purpose of this study was to investigate the effect of different arthroplasty designs on knee kinematic and lower limb muscular activation for the stand-to-sit movement. METHODS: Sixteen unilateral, posterior-stabilized knee arthroplasty participants (8 single-axis and 8 multi-axis) with excellent Knee Society scores performed 4 trials of the stand-to-sit test. Three-dimensional video analysis of whole body and joint kinematics and electromyography analysis of quadriceps and hamstrings were conducted. One-way ANOVAs were used for statistical analyses (alpha=0.05). FINDINGS: The multi-axis group showed some functional adaptations while sitting down. The single-axis group exhibited less arthroplasty limb quadriceps electromyography and hamstring co-activation electromyography than the multi-axis group. For the arthroplasty limb, single-axis demonstrated less abduction angular displacement and reached peak abduction earlier than the multi-axis arthroplasty limb. The estimated effect size for this study was 0.196. INTERPRETATION: The single-axis design requires less eccentric knee extensor muscle activation and exhibits greater medio-lateral stability than the multi-axis designs. Findings from this study could provide useful information to orthopedic knee surgeons and rehabilitative specialists.

Rotational constraint in posterior-stabilized total knee prostheses.

Rotational stresses from box-post impingement have been implicated in the loosening of posterior-stabilized total knee prostheses. A bench model was constructed to assess the forces generated by tibiofemoral rotation. Rotational torque under load was measured in two different posteriorstabilized total knee prostheses using an axial-torsion load cell at 0 degrees, 20 degrees, and 40 degrees flexion over 20 degrees internal and external rotation. The Sigma posterior-stabilized prosthesis generated little torque through 5 degrees internal and external rotation. An increase in torque then occurred because of box-post impingement, generating peak torques of 17 to 18 N-m at 12 degrees to 14 degrees rotation. The bench model produced the same deformation of the polyethylene post as seen on retrieved specimens. The Scorpio posterior-stabilized prosthesis had a relatively continuous rise in generated torque from tibiofemoral conformity. Box-post impingement did not occur resulting in 32% lower torque between 12 degrees and 14 degrees rotation. Peak rotational torques of 15 to 16 N-m were reached at 19 degrees to 20 degrees rotation. Tibiofemoral conformity is the primary source of rotational constraint. Box-post impingement can be a source of additional rotational constraint. Depending on specific design features, small changes in relative tibiofemoral component rotation can more than double the generated torque. Axial rotation of the knee in vivo can generate substantial torque. Relative tibiofemoral rotational position is an important factor influencing component function and fixation.

Loosening and osteolysis with the press-fit condylar posterior-cruciate-substituting total knee replacement.

BACKGROUND: Aseptic loosening and osteolysis are rarely associated with cemented posterior-cruciate-substituting total knee replacements. Consequently, there is a paucity of information on this topic. METHODS: After a mean follow-up interval of fifty-six months (range, thirty-seven to eighty-nine months), sixteen (2.9%) of 557 posterior-cruciate-substituting primary total knee replacements were revised by a single surgeon because of loosening and osteolysis. Clinical, radiographic, and retrieval analyses were conducted to determine the mechanism of loosening and to identify associated risk factors. RESULTS: All sixteen knees (fifteen patients) were rated as good or excellent at one year after the primary replacement, with mean clinical and functional Knee Society scores of 95 and 86 points, respectively. Nine of the fifteen patients who had a revision because of loosening and osteolysis had had a total knee arthroplasty on the contralateral side compared with only 18% of the patients who did not have a revision (p = 0.026). No evidence of transmission of substantial anteroposterior stresses from the posterior-cruciate-substituting mechanism was found. All twelve retrieved knee implants, however, had damage to the lateral and medial side walls of the polyethylene posterior-cruciate-substituting post. Damage to the inferior surface of the polyethylene inserts had a rotational pattern, with the axis of rotation in the medial compartment. Surface damage in a rotational pattern was also present on the superior and inferior surfaces of the titanium tibial base-plates. CONCLUSIONS: In the knees in our study, rotational forces were generated by impingement of the side walls of the intercondylar box on the polyethylene post. Such box-post impingement can occur throughout the range of motion. Rotational stresses are transmitted to the modular interfaces and to the metal-cement interfaces, resulting in loosening and osteolysis. A reduction in rotational constraint would be desirable. Patients with bilateral total knee replacement may be at increased risk for this type of loosening.

Posterior cruciate function following total knee arthroplasty. A biomechanical study.

The strain developed in the posterior cruciate ligament (PCL) of eight fresh cadaveric knees was measured before and after total knee arthroplasty using a loading technique that simulated stair ascent and descent. Each knee was instrumented with a Hall Effect strain gauge (Micro-Strain, Burlington, VT) in the PCL, a load cell in the quadriceps tendon, an electrogoniometer, and an array of linear displacement transducers to measure femoral rollback. Testing was undertaken with each knee in its normal state with the anterior cruciate cut and with a cruciate-retaining prosthesis, a cruciate-excising prosthesis, and a cruciate-substituting prosthesis. Normal PCL strain levels were produced in only 37% of the trials following implantation of the cruciate-retaining knee arthroplasties. With a cruciate-retaining prosthesis, femoral rollback decreased by an average of 36% and was associated with a 15% loss in extensor efficiency. In the procedures performed with excision of the PCL, rollback decreased by 70% and extensor efficiency by 19%. Cruciate substitution resulted in a 12% loss in rollback and an 11% decrease in extensor efficiency. The strain developed within the PCL during knee flexion was found to be extremely sensitive to the thickness of the polymeric tibial insert. In the majority of cases, it was not possible to restore normal ligament loading with flexion while simultaneously maintaining acceptable varus/valgus stability of the knee joint. Using a range of contemporary knee arthroplasties, the authors were unable to consistently reproduce normal function of the PCL.

The effect of continuous epidural analgesia on postoperative pain, rehabilitation, and duration of hospitalization in total knee arthroplasty.

Efficacies of three alternate methods of postoperative analgesia were studied in 156 patients who had total knee arthroplasty (TKA). Forty-two of these patients received parenteral meperidine hydrochloride or morphine (Group 1), 58 patients received periodic epidural injections of morphine (Group 2), and 56 patients received continuous epidural infusions of bupivacaine hydrochloride and Duramorph (Group 3). The postoperative course of all patients was documented in terms of the incidence and severity of pain, range of joint motion, duration of hospitalization, and occurrence of complications. Although epidural analgesia increased the cost and duration of the operation, good-to-excellent pain relief was attained in 86% (Group 2) and 88% (Group 3) of cases with epidural analgesia compared with 61% of patients (Group 1) receiving conventional analgesia. Moreover, 67% of patients in Group 1 experienced frequent episodes of moderate-to-severe postoperative pain in contrast to 40% of patients in Group 2 and only 10% of patients in Group 3. As a result of diminished pain, greater joint motion was obtained within the first 72 hours in Groups 2 and 3. They also had shorter hospitalization (9.6 days versus 11.2 days for Group 1 and 10.8 days for Group 2). However, the use of epidural analgesia did not reduce the incidence of complications, including nausea. Continuous infusion of epidural bupivacaine and Duramorph provided good-to-excellent control of postoperative pain after TKA. However, better analgesics are needed to reduce the high incidence of side effects associated with various treatment methods.

The effect of femoral component position on patellar tracking after total knee arthroplasty.

In a laboratory study, seven fresh anatomic knee specimens were evaluated to define the three-dimensional motions of the patella before and after total knee arthroplasty (TKA) with the AMK knee. The patella was displaced medially by an average of 4 mm and tilted medially by an average of 4 degrees after standard TKA. Medial translation or internal rotation of the femoral component further displaced and tilted the patella medially, but lateral translation or external rotation of the femoral component produced less predictable changes in patellar tracking. The patterns of patellar tracking after external rotation of the femoral component came closer to reproducing those of the intact knee than any other femoral component position. The high lateral ridge on the femoral component effectively prevents patellar dislocation but may produce abnormally high stresses on the patellar implant, especially if the implant is medially displaced or internally rotated. This could lead to accelerated wear or loosening of the patellar component.

Unsatisfactory results with a ceramic total hip prosthesis.

We reviewed the results of forty-two total hip replacements that had been done with the self-locking Autophor ceramic total hip prosthesis in thirty-four patients. The patients ranged in age from twenty-five to sixty-seven years (average, forty-eight years). The diagnoses were avascular necrosis (eight patients), degenerative arthritis (nineteen patients), ankylosing spondylitis (one patient), post-traumatic arthritis (two patients), and rheumatoid arthritis (four patients). Seven procedures were revisions: five, of a loose cemented total hip prosthesis and two, of a loose noncemented endoprosthesis. No revision was done for infection. The length of follow-up ranged from twenty-seven to sixty-six months (average, fifty-one months). The patients were evaluated by physical examination, serial radiographs, and questionnaires. The hips were rated with the modified Harris hip score. At the time of follow-up, eleven of the twenty-seven patients who had had a primary hip replacement complained of at least moderate pain that limited activities; however, only three patients had to have a revision. The femoral components had a notable tendency to subside more than five millimeters, and in fifteen hips there was radiographic evidence of progressive loosening. Our experience with the self-locking Autophor ceramic total hip prosthesis has been disappointing. We no longer use it.

The use of banked autologous blood in patients undergoing surgery for spinal deformity.

The cases of fifty-two patients who underwent sixty elective spinal fusions for spinal deformity were studied to evaluate the efficacy of the use of banked autologous blood to replace operative loss of blood. The patients ranged in age from ten to forty-nine years. Each patient began to take 325 milligrams of ferrous sulphate, three times a day, as soon as surgery was scheduled, and was evaluated weekly at the Shepeard Community Blood Bank. If a patient's hemoglobin level was more than eleven milligrams per 100 milliliters, either a whole unit of blood or a half-unit was drawn at each visit. An average of 3.3 units of blood (range, 1.5 to 6.0 units) was obtained and was stored for as long as forty-two days. Either citrate phosphate dextrose with adenine (CPDA-1) or adenine, dextrose, and mannitol (ADSOL) was used as a preservative. In 85 per cent of the procedures only autologous blood was required for transfusion. This method proved to be simple, safe, and very well accepted.

Relationship between habitual physical activity and serum lipoprotein levels in white male adolescents.

It is currently thought that increased physical activity can have a positive influence on high-density lipoprotein cholesterol (HDL-C) levels in adults. However, only a limited amount of research has been directed at studying the influence of physical activity on HDL-C in adolescents. This study correlated the reported levels of physical activity, exercise capacity, physical measurements, and 48-hr dietary intake of 50 white male adolescents with their levels of HDL-C, ratio of total serum cholesterol (T.Chol) to HDL-C, and ratio of low-density lipoprotein (LDL-C) to HDL-C. Using multiple regression, age (r = -0.42) was the strongest predictor of HDL-C, followed in order by TV watched/night (r = -0.42) and height (r = -0.31) (R2 = 0.28). Age (r = 0.38) was the strongest predictor of the T.Chol/HDL-C ratio, followed by days jogged/week (r = -0.32), TV watched/night (r = 0.29), and systolic blood pressure (r = 0.30) (R2 = 0.30). The days jogged per week (r = -0.32) was the best predictor of the LDL-C/HDL-C ratio, followed in order by hours spent reading/day (r = 0.27) and systolic blood pressure (r = 0.23) (R2 = 0.23). Maximum exercise capacity was not related to these lipoprotein components. These findings suggest that the level of habitual physical activity in white male adolescents may be associated with the level of HDL-C in relation to T.Chol and LDL-C.

The effect of physical conditioning on serum lipids and lipoproteins in white male adolescents.

This study was designed to measure the effect of physical conditioning on the serum lipid and lipoprotein levels of white male adolescents. Fifty white males, ages 11-17 yr, underwent pre-test evaluations including physical measurements, physical activity levels, nutritional intake, physical working capacity, and fasting serum lipid and lipoprotein levels. Each subject was randomly assigned to a physical conditioning group or to a control group. There were no statistically significant differences in pre-test measurements. The physical conditioning group participated in an 8-wk progressive aerobic exercise program 30 min/d for 4 d each wk. The pre-test measurements were then repeated for both groups. Based on Student's t-test, the physical conditioning group had a significantly higher physical working capacity on the post-test than the control group. An analysis of covariance test showed no differences between the groups in the post-test serum lipid and lipoprotein levels. The results suggested that although the exercise program was strenuous enough to increase significantly the physical working capacity of the exercise group, it did not alter their serum lipid and lipoprotein levels during the 8-wk period.