In-vivo time-dependent articular cartilage contact behavior of the tibiofemoral joint.

OBJECTIVE: The purpose of this study was to investigate the in-vivo time-dependent contact behavior of tibiofemoral cartilage of human subjects during the first 300 s after applying a constant full body weight loading and determine whether there are differences in cartilage contact responses between the medial and lateral compartments. DESIGN: Six healthy knees were investigated in this study. Each knee joint was subjected to full body weight loading and the in-vivo positions of the knee were captured by two orthogonal fluoroscopes during the first 300 s after applying the load. Three-dimensional models of the knee were created from MR images and used to reproduce the in-vivo knee positions recorded by the fluoroscopes. The time-dependent contact behavior of the cartilage was represented using the peak cartilage contact deformation and the cartilage contact area as functions of time under the constant full body weight. RESULTS: Both medial and lateral compartments showed a rapid increase in contact deformation and contact area during the first 20s of loading. After 50s of loading, the peak contact deformation values were 10.5+/-0.8% (medial) and 12.6+/-3.4% (lateral), and the contact areas were 223.9+/-14.8 mm(2) (medial) and 123.0+/-22.8 mm(2) (lateral). Thereafter, the peak cartilage contact deformation and contact area remained relatively constant. The respective changing rates of cartilage contact deformation were 1.4+/-0.9%/s (medial) and 3.1+/-2.5%/s (lateral); and of contact areas were 40.6+/-20.8 mm(2)/s (medial) and 24.0+/-11.4 mm(2)/s (lateral), at the first second of loading. Beyond 50 s, both changing rates approached zero. CONCLUSIONS: The peak cartilage contact deformation increased rapidly within the first 20s of loading and remained relatively constant after approximately 50 s of loading. The time-dependent response of cartilage contact behavior under constant full body weight loading was significantly different in the medial and lateral tibiofemoral compartments, with greater peak cartilage contact deformation on the lateral side and greater contact area on the medial side. These data can provide insight into normal in-vivo cartilage function and provide guidelines for the improvement of ex-vivo cartilage experiments and the validation of computational models that simulate human knee joint contact.

In vivo cartilage contact deformation in the healthy human tibiofemoral joint.

OBJECTIVES: In vivo cartilage contact deformation is instrumental for understanding human joint function and degeneration. This study measured the total deformation of contacting articular cartilage in the human tibiofemoral joint during in vivo weight-bearing flexion. METHODS: Eleven healthy knees were magnetic resonance (MR) scanned and imaged with a dual fluoroscopic system while the subject performed a weight-bearing single-leg lunge. The tibia, femur and associated articulating cartilage were constructed from the MR images and combined with the dual fluoroscopic images to determine in vivo cartilage contact deformation from full extension to 120 degrees of flexion. RESULTS: In both compartments, minimum peak compartmental contact deformation occurred at 30 degrees of flexion (24 +/- 6% medial, 17 +/- 7% lateral) and maximum peak compartmental deformation occurred at 120 degrees of flexion (30 +/- 13% medial, 30 +/- 10% lateral) during the weight-bearing flexion from full extension to 120 degrees. Average medial contact areas and peak contact deformations were significantly greater than lateral compartment values (P < 0.05). In addition, cartilage thickness in regions of contact was on average 1.4- and 1.1-times thicker than the average thickness of the tibial and femoral cartilage surfaces, respectively (P < 0.05). CONCLUSIONS: These data may provide base-line knowledge for investigating the effects of various knee injuries on joint contact biomechanics and the aetiology of cartilage degeneration.

The effect of tibiofemoral joint kinematics on patellofemoral contact pressures under simulated muscle loads.

Altered patellofemoral joint contact pressures are thought to contribute to patellofemoral joint symptoms. However, little is known about the relationship between tibiofemoral joint kinematics and patellofemoral joint contact pressures. The objective of this paper was to investigate the effect of tibiofemoral joint kinematics on patellofemoral joint pressures using an established in vitro robotic testing experimental setup. Eight cadaveric knee specimens were tested at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under an isolated quadriceps load of 400 N and a combined quadriceps/hamstrings load of 400 N/200 N. Tibiofemoral joint kinematics were measured by the robot and contact pressures by a TekScan pressure sensor. The isolated quadriceps loading caused anterior translation and internal rotation of the tibia up to 60 degrees of flexion and posterior translation and external rotation of the tibia beyond 60 degrees. The co-contraction of the hamstring muscles caused a posterior translation and external rotation of the tibia relative to the motion of the tibia under the quadriceps load. Correspondingly, the contact pressures were elevated significantly at all flexion angles. For example, at 60 degrees of flexion, the hamstrings co-contraction increased the posterior tibial translation by approximately 2.8 mm and external tibial rotation by approximately 3.6 degrees. The peak contact pressure increased from 1.4+/-0.8 to 1.7+/-1.0 MPa, a 15% increase. The elevated contact pressures after hamstrings co-contraction indicates an intrinsic relation between the tibiofemoral joint kinematics and the patellofemoral joint biomechanics. An increase in posterior tibial translation and external rotation is accompanied by an increase in contact pressure in the patellofemoral joint. These results imply that excessive strength conditioning with the hamstring muscles might not be beneficial to the patellofemoral joint. Knee pathology that causes an increase in tibial posterior translation and external rotation might contribute to degeneration of the patellofemoral joint. These results suggest that conservative treatment of posterior cruciate ligament injury should be reconsidered.

Effect of the posterior cruciate ligament on posterior stability of the knee in high flexion.

Most biomechanical studies of the knee have focused on knee flexion angles between 0 degrees and 120 degrees. The posterior cruciate ligament (PCL) has been shown to constrain posterior laxity of the knee in this range of flexion. However, little is known about PCL function in higher flexion angles (greater than 120 degrees ). This in vitro study examined knee kinematics before and after cutting the PCL at high flexion under a posterior tibial load and various muscle loads. The results demonstrated that although the PCL plays an important role in constraining posterior tibial translation at low flexion angles, the PCL had little effect in constraining tibial translation at 150 degrees of flexion under the applied loads.

Results of biceps tenotomy for treatment of pathology of the long head of the biceps brachii.

Historically, the surgical treatment of bicipital pathology has been a variety of tenodesis techniques. The purpose of this study is to report the results of simple biceps tenotomy for the treatment of bicipital pathology. Thirty shoulders in 30 consecutive patients who had a simple arthroscopic biceps tendon release were reviewed. Data was collected according to the method of the American Shoulder and Elbow Surgeons (ASES) shoulder evaluation form. Outcome was assessed with the rating system of the ASES. The mean ASES shoulder score was 81.8. There was a significant reduction in pain and improvement in function after the procedure. The complication rate was 13.3%. Bicipital pathology is a significant cause of morbidity around the shoulder. The results of this study demonstrate that functional outcome as measured by the ASES scoring system can be very good with an arthroscopic biceps tendon release for the treatment of biceps tendon pathology.

Relationships between throwing mechanics and shoulder distraction in professional baseball pitchers.

The extreme forces and torques and the high speeds and excessive ranges of motion of baseball pitching place tremendous stress on the soft tissues of the throwing shoulder. Little is known about the relationship between pitching mechanics and shoulder joint stress, especially in professional athletes. The purpose of this study was to quantify joint loads and kinematic parameters of pitching mechanics at the major league level and to study their relationships. Three-dimensional, high-speed video data were collected on 40 professional pitchers during the 1998 Cactus League spring training. A clinically significant distraction force was calculated at the shoulder joint, which reached an average peak value of 947 +/- 162 N (108% +/- 16% body weight). Descriptive statistics and a multiple linear regression analysis were used to relate shoulder distraction to kinematic and kinetic parameters of pitching mechanics. This study was undertaken not only to investigate the peak forces and torques on the shoulder, but also to identify potential areas of intervention that might prevent throwing injuries. Knowledge of joint ranges of motion, angular velocities, and joint-reaction forces can provide a scientific basis for improved preventive and rehabilitative protocols for baseball pitchers.

Arthroscopic reduction and internal fixation of tibial plateau fractures in skiing.

Arthroscopic reduction and internal fixation of tibial plateau fractures can facilitate restoration of articular congruity while permitting rigid fracture stabilization. Twenty-five patients who underwent arthroscpoic reduction and internal fixation of a tibial plateau fracture were reviewed. The average age of the patients was 45. At a mean followup of 24 months, 76% of patients rated their result as excellent and 16% as good. Eighty-four percent returned to full sporting activity. There were no episodes of nonunion, failure of fixation, wound infection, deep venous thrombosis, compartment syndrome, or arthrofibrosis. Preoperative fracture depression averaged 7.7 mm (range, 1-18 mm). Fracture depression at final followup averaged 0.8 mm (range, 0-5 mm). Sixty-four percent of patients had associated intraarticular injury diagnosed and treated at the time of arthroscopy. Arthroscopic reduction and internal fixation provides an accurate assessment of, and allows definitive treatment for, intraarticular injuries associated with tibial plateau fractures. The technique allows less soft tissue stripping than with traditional arthrotomy, better visualization of the articular surface, early return to physical activities, and obviates the need for meniscal detachment and repair.

Commonly used rat strains.

It is critical that genetically defined animals be used in immunological studies so that data can be adequately compared both within and between strains to examine the genetic effects on the phenomena being studied. This appendix lists some of the most commonly used rat strains and their immunogenetic properties.

Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis.

Surgical dislocation of the hip is rarely undertaken. The potential danger to the vascularity of the femoral head has been emphasised, but there is little information as to how this danger can be avoided. We describe a technique for operative dislocation of the hip, based on detailed anatomical studies of the blood supply. It combines aspects of approaches which have been reported previously and consists of an anterior dislocation through a posterior approach with a 'trochanteric flip' osteotomy. The external rotator muscles are not divided and the medial femoral circumflex artery is protected by the intact obturator externus. We report our experience using this approach in 213 hips over a period of seven years and include 19 patients who underwent simultaneous intertrochanteric osteotomy. The perfusion of the femoral head was verified intraoperatively and, to date, none has subsequently developed avascular necrosis. There is little morbidity associated with the technique and it allows the treatment of a variety of conditions, which may not respond well to other methods including arthroscopy. Surgical dislocation gives new insight into the pathogenesis of some hip disorders and the possibility of preserving the hip with techniques such as transplantation of cartilage.

The management of severe acetabular bone loss using structural allograft and acetabular reinforcement devices.

The cases of 37 acetabular reconstructions in 35 patients with major structural pelvic bone loss were reviewed. At an average follow-up of 7.1 years, patients rated their results as excellent in 12 cases (32.4%), good in 22 (59.5%), fair in 2 (5.4%), and poor in 1 (2.7%). Thirty-four cases (91.9%) were classified as a clinical success. Thirty-six allografts (97.3%) had radiographic evidence of full incorporation. Of the unrevised hips, 1 (2.7%) was classified as definitely loose, 2 (5.4%) as probably loose, and 4 (10.8%) as possibly loose. One revision of an acetabular component was required because of late sepsis. This is the first reported series on the use of acetabular reinforcement devices with solid bulk allograft covering more than 50% of the socket. The allograft is protected in the early postoperative period, superior migration of the cup is virtually eliminated as a complication, and the incidence of aseptic loosening is greatly diminished.

Lateral insufficiency fractures of the femur caused by osteopenia and varus angulation: a complication of total hip arthroplasty.

Lateral femoral insufficiency fractures in total hip arthroplasty occur due to osteopenia and varus positioning of the femoral component, the femur itself, or both. The presentation of these fractures can be unclear but usually involves the insidious onset of unexplained thigh or groin pain. The patients are likely to have significant comorbidities as well. Characteristic radiographic findings may be present, depending on when the patient presents. The insufficiency fractures generally occur at the level of the femoral stem tip on the lateral cortex of the femur. If left untreated, pain and loss of function continue. Eventually an insufficiency fracture can progress to a displaced periprosthetic fracture. Nonsurgical treatment is not successful. Recommended treatment involves revision to a long-stem femoral component. The risk of postoperative complications is significant.

Cytogenetic localization of the growth and reproduction complex (Grc) in the rat and in the mouse and its position in relation to RT1.EC and other loci in the rat MHC.

The segment of rat chromosome 20 (RNO20p12) that contains the classical loci of the major histocompatibility complex (MHC; RT1.A-RT1.E) also contains genes affecting growth, reproduction and susceptibility to chemical carcinogens (the Grc) and multiple genes encoding class I MHC antigens (the EC region). The relative positions of the MHC, Grc, and EC region have not been demonstrated explicitly, although they have been postulated from genetic mapping studies. The present study was undertaken to map these regions cytogenetically by several different approaches using cosmids specific for the Rps 18, Hspa1 and Bat1 genes. The order was shown to be: centromere-Rps 18-Hspa1-Bat1-EC-Grc.

Biological effects of genes in the Grc and EC region of the rat major histocompatibility complex.

PROBLEM: To study the mechanism of action of major histocompatibility complex (MHC)-linked genes affecting reproduction, growth, and susceptibility to chemical carcinogens. METHOD OF STUDY: Tumors derived from rat embryonic fibroblasts were transfected with cosmids from the Grc and its linked regions, the unrelated A region, and a nonMHC region, or with genes from the Grc, Grc-linked, and nonMHC regions, to determine whether they could suppress tumor growth as determined by in vitro (soft agar) and in vivo assays. RESULTS: Tumor fibroblasts transfected with cosmids from the Grc or from the EC region decreased tumor growth in both the in vitro and in vivo assays. Transfection with individual genes from the Grc had no effect on tumor growth in either assay. CONCLUSIONS: The effects of the Grc on reproduction, growth, and tumorigenesis are mediated by extended genetic effects, i.e., by the conformation of the DNA in this region. Similar effects were seen following transfection with cosmids from the Grc-linked EC region, and this finding strengthens the hypothesis that the conformation of the DNA in this general region is critical for its function. A similar effect has been described for the locus control region (LCR) in the beta-globin gene family in the human.

Acetabular reconstruction in developmental dysplasia of the hip: results of the acetabular reinforcement ring with hook.

This study examined the clinical results and technical challenges associated with acetabular reconstruction in developmental dysplasia of the hip using the acetabular reinforcement ring with hook. We reviewed 33 consecutive reconstructions performed by a single surgeon. At an average follow-up of 6.7 years, the mean Merle-d'Aubigne score had increased from 7 to 16. Two revisions were performed for aseptic loosening. Of the unrevised hips, 1 was classified as definitely loose and 1 as possibly loose. These results compare favorably with others in the literature. The acetabular reinforcement ring may prevent graft resorption and cup migration, major causes of socket failure in reconstruction of the deficient acetabulum.

Mechanisms of action of major-histocompatibility-complex-linked genes affecting reproduction.

PROBLEM: To provide insight into the mechanisms of action of the major-histocompatibility-complex (MHC)-linked genes affecting reproduction. METHOD OF STUDY: The data were obtained using a variety of cellular and molecular techniques in experimental animals and from population genetic studies in humans. RESULTS: In the mouse, the preimplantation embryonic development (Ped) locus, whose functional gene is Q9, regulates fast and slow cleavage of the early embryo. There is also evidence for a growth and reproduction complex (Grc)-like region from serologic, molecular, and cytogenetic studies. In the human, the human leukocyte antigen (HLA)-G gene has been associated with an increased rate of embryonic cleavage in those embryos that express the HLA-G antigen. Sharing of HLA antigens in couples has been associated with recurrent spontaneous abortions, gestational trophoblastic tumors, and unexplained infertility. Detailed mapping studies showed that the genes responsible are not the HLA genes themselves, but genes closely linked to the HLA-DR-DQ-B genes. The HLA region genes can interact epistatically with the C3 allele of transferrin to increase the incidence of fetal loss. In the rat, the Grc region, which is closely linked to the MHC, has been associated with embryonic loss, growth defects, and susceptibility to chemical carcinogens. The Grc can interact epistatically with the tail anomaly lethal (Tal) gene or the hood restriction (Hre) gene to enhance these effects. CONCLUSIONS: There are two basic mechanisms for the effects of MHC-linked genes on reproduction and development: individual gene effects (Ped [Q9], HLA-G) and extended genetic effects (MHC-linked genes in the rat [Grc] and in the human). The nature of these genetic effects, particularly the MHC-linked effects, can also provide some insight into the different theories of human origins: These effects are most consistent with the monogenic theory.