Load Sharing Among Collateral Ligaments, Articular Surfaces, and the Tibial Post in Constrained Condylar Knee Arthroplasty.

The normal knee joint maintains stable motion during activities of daily living. After total knee arthroplasty (TKA), stability is achieved by the conformity of the bearing surfaces of the implant components, ligaments, and constraint structures incorporated in the implant design. The large, rectangular tibial post in constrained condylar knee (CCK) arthroplasty, often used in revision surgery, provides added stability, but increases susceptibility to polyethylene wear as it contacts the intercondylar box on the femoral component. We examined coronal plane stability to understand the relative contributions of the mechanisms that act to stabilize the CCK knee under varus-valgus loading, namely, load distribution between the medial and lateral condyles, contact of the tibial post with the femoral intercondylar box, and elongation of the collateral ligaments. A robot testing system was used to determine the joint stability in human cadaveric knees as described by the moment versus angular rotation behavior under varus-valgus moments at 0 deg, 30 deg, and 90 deg of flexion. The angular rotation of the CCK knee in response to the physiological moments was limited to ≤1.5 deg. The primary stabilizing mechanism was the redistribution of the contact force on the bearing surfaces. Contact between the tibial post and the femoral box provided a secondary stabilizing mechanism after lift-off of a condyle had occurred. Collateral ligaments provide limited stability because little ligament elongation occurred under such small angular rotations. Compressive loads applied across the knee joint, such as would occur with the application of muscle forces, enhanced the ability of the bearing surfaces to provide resisting internal varus-valgus moment and, thus, reduced the exposure of the tibial post to the external varus-valgus loads. Our results suggest that the CCK stability can be refined by considering both the geometry of the bearing surfaces and the contacting geometry between the tibial post and femoral box.

Asymmetric varus and valgus stability of the anatomic cadaver knee and the load sharing between collateral ligaments and bearing surfaces.

Knee joint stability is important in maintaining normal joint motion during activities of daily living. Joint instability not only disrupts normal motion but also plays a crucial role in the initiation and progression of osteoarthritis. Our goal was to examine knee joint coronal plane stability under varus or valgus loading and to understand the relative contributions of the mechanisms that act to stabilize the knee in response to varus-valgus moments, namely, load distribution between the medial and lateral condyles and the ligaments. A robot testing system was used to determine joint stability in human cadaveric knees as described by the moment versus angular rotation behavior under varus and valgus loads at extension and at 30 deg and 90 deg of flexion. The anatomic knee joint was more stable in response to valgus than varus moments, and stability decreased with flexion angle. The primary mechanism for providing varus-valgus stability was the redistribution of the contact force on the articular surfaces from both condyles to a single condyle. Stretching of the collateral ligaments provided a secondary stabilizing mechanism after the lift-off of a condyle occurred. Compressive loads applied across the knee joint, such as would occur with the application of muscle forces, enhanced the ability of the articular surface to provide varus-valgus moment, and thus, helped stabilize the joint in the coronal plane. Coupled internal/external rotations and anteroposterior and medial-lateral translations were variable and in the case of the rotations were often as large as the varus-valgus rotations created by the applied moment.

A validation model for measurement of acetabular component position.

There is no agreement on a standard approach to evaluating acetabular cup orientation, ideal target orientation, or a standardized measurement method for cup orientation in total hip arthroplasty. The purpose of this study was to investigate a simple method for validating measurements of acetabular orientation obtained using computer navigation and computed tomography scans. This study validated the imageless navigation system to be accurate with a precision of 1 degrees and a bias of 0.02 degrees for inclination and a precision of 1.3 degrees and a bias of 0 degrees for anteversion measurements. From this study, we propose that acetabular cup alignment is accurately assessed using computer navigation. We suggest acetabular orientation be reported in the radiographic plane (coronal plane), which incorporates pelvic tilt and therefore is more functional definition of cup position.

Range of motion and function are similar in patients undergoing TKA with posterior stabilised and high-flexion inserts.

It is debatable whether high-flexion (HF) total knee arthroplasty (TKA) designs will improve postoperative flexion and function or will diminish the need for manipulation under anaesthesia (MUA). We retrospectively analysed range of motion (ROM), flexion, Knee Society Score (KSS), and rate of MUA in a consecutive group of patients who underwent TKA with a conventional posterior stabilised (PS) insert or an HF insert using identical surgical technique, implant design, and postoperative care. Fifty TKAs with a standard PS insert were matched for patient's age, gender, preoperative ROM, and KSS with 50 TKA performed with an HF insert. The patient's ROM and KSS were evaluated at six weeks, four months, and one year postoperatively. The outcome variables (flexion, ROM, KSS, and manipulation rate) in both groups were compared using the generalised estimating equations method. A second analysis of patients with preoperative flexion ≥120° was performed. The ROM, flexion, and patient-reported KSS was similar in both groups at each time period. The rate of MUA was also similar. Patients with a preoperative ROM of at least 120° showed similar results. Our study found that one year after surgery, patients who underwent TKA with a PS or an HF insert achieved similar flexion, ROM, and function.

Combined anteversion technique for total hip arthroplasty.

UNLABELLED: Combined cup and stem anteversion in THA based on femoral anteversion has been suggested as a method to compensate for abnormal femoral anteversion. We investigated the combined anteversion technique using computer navigation. In 47 THAs, the surgeon first estimated the femoral broach anteversion and validated the position by computer navigation. The broach was then measured with navigation. The navigation screen was blocked while the surgeon estimated the anteversion of the broach. This provided two estimates of stem anteversion. The navigated stem anteversion was validated by postoperative CT scans. All cups were implanted using navigation alone. We determined precision (the reproducibility) and bias (how close the average test number is to the true value) of the stem position. Comparing the surgeon estimate to navigation anteversion, the precision of the surgeon was 16.8 degrees and bias was 0.2 degrees ; comparing the navigation of the stem to postoperative CT anteversion, the precision was 4.8 degrees and bias was 0.2 degrees , meaning navigation is accurate. Combined anteversion by postoperative CT scan was 37.6 degrees +/- 7 degrees (standard deviation) (range, 19 degrees -50 degrees ). The combined anteversion with computer navigation was within the safe zone of 25 degrees to 50 degrees for 45 of 47 (96%) hips. Femoral stem anteversion had a wide variability. LEVEL OF EVIDENCE: Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Imaging and navigation measurement of acetabular component position in THA.

There are six different definitions of acetabular position based on observed inclination and anteversion made in either the (1) anterior pelvic plane or (2) coronal planes and based on whether each of the observations made in one of these two planes is (1) anatomic, (2) operative, or (3) radiographic. Anteroposterior pelvic tilt is the angle between the anterior pelvic plane and the coronal plane of the body. The coronal plane is a functional plane and the anterior pelvic plane is an anatomic pelvic plane. A cup may be in the "safe zone" by one definition but may be out of the "safe zone" by another definition. We reviewed published studies, analyzed the difference in varying definitions, evaluated the influence of the anterior pelvic tilt, and provided methods to convert from one definition to another. We recommend all inclination and anteversion measurements be converted to the radiographic inclination and anteversion based on the coronal plane, which is equivalent to the inclination and anteversion on the anteroposterior pelvic radiograph.

Impingement as a mechanism of dissociation of a metasul metal-on-metal liner.

This case report is of a patient with disassociation of the acetabular cup liner caused by impingement. The cup inclination (39 degrees) and anteversion (24 degrees) were good as measured by computer navigation. Impingement occurred because the head-neck ratio was 2.0, and the hip length and offset were short by one head length. Successful revision without intraoperative impingement was accomplished with one size head larger (32 mm; head-neck ratio, 2.3) and one size longer to correct hip length and offset.

Impingement with total hip replacement.

Impingement is a cause of poor outcomes of prosthetic hip arthroplasty; it can lead to instability, accelerated wear, and unexplained pain. Impingement is influenced by prosthetic design, component position, biomechanical factors, and patient variables. Evidence linking impingement to dislocation and accelerated wear comes from implant retrieval studies. Operative principles that maximize an impingement-free range of motion include correct combined acetabular and femoral anteversion and an optimal head-neck ratio. Operative techniques for preventing impingement include medialization of the cup to avoid component impingement and restoration of hip offset and length to avoid osseous impingement.

Pathological variations in mummified feet between two near-distance/long-time populations in Ancient Egypt.

BACKGROUND: In ancient populations, a significant quantity of foot pathology was related either to the type of footwear they used or the underlying terrain they walked on. Our study was carried out to analyze these parameters with the foot pathologies the mummies presented. METHODS: Between 2006 and 2012, more than 650 individuals were recovered from the Sharuna and Qarara necropolis (Middle Egypt) dating from the VIth Dynasty of the first Ptolemaic Period to the second Coptic Period. From among them, a total of 73 mummified feet (41 from Sharuna and 32 from Qarara) were studied. We took into account the differences existing between both sites in location (15 km apart) and in time (2500 years apart). RESULTS: Almost all feet from Sharuna were wrapped and impregnated with a preservative substance (anthropological mummification), while the mummification process in Qarara was quite natural. Pathologies were found in 36 of the 73 ft (20 from Sharuna and 16 from Qarara). The differences in foot pathologies between the two sites were analysed. CONCLUSIONS: The foot pathologies we found in both necropolises have led us to hypothesise that the majority of the diachronic differences could be related more to progressive changes in the type of the terrain brought out through droughts, than the changes in footwear habits.

Bilateral pathological hip fractures in a patient with a bipulmonary transplant: a case report.

The use of immunosuppressive agents to prevent tissue rejection may predispose patients to osteoporosis and fractures. We report a case of bilateral pathological hip fractures in a woman with osteoporosis who had undergone a bipulmonary transplant. To reduce the risk of pathological fractures, patients are given prophylaxes for osteoporosis prior to organ transplantation, but they remain at increased risk of fractures. They should be informed that this side-effect may occur after transplantation.

A comparison of surgeon estimation and computed tomographic measurement of femoral component anteversion in cementless total hip arthroplasty.

BACKGROUND: The intraoperative estimation of the anteversion of the femoral component of a total hip arthroplasty is generally made by the surgeon's visual assessment of the stem position relative to the condylar plane of the femur. Although the generally accepted range of intended anteversion is between 10 degrees and 20 degrees, we suspected that achieving this range of anteversion consistently during cementless implantation of the femoral component was more difficult than previously thought. METHODS: We prospectively evaluated the accuracy of femoral component anteversion in 109 consecutive total hip arthroplasties (ninety-nine patients), in which we implanted the femoral component without cement. In all hips, we measured femoral stem anteversion postoperatively with three-dimensional computed tomography reconstruction of the femur, using both the distal femoral epicondyles and the posterior femoral condyles to determine the femoral diaphyseal plane. The bias and precision of the measurements were calculated. RESULTS: The surgeon's estimate of femoral stem anteversion was a mean (and standard deviation) of 9.6 degrees +/- 7.2 degrees (range, -8 degrees to 28 degrees). The anteversion of the stem measured by computed tomography was a mean of 10.2 degrees +/- 7.5 degrees (range, -8.6 degrees to 27.1 degrees) (p = 0.324). The correlation coefficient between the surgeon's estimate and the computed tomographic measurement was 0.688; the intraclass coefficient was 0.801. Anteversion measured by computed tomography found that forty-nine stems (45%) were between 10 degrees and 20 degrees of anteversion; forty-three stems (39%) were between 0 degree and 9 degrees of femoral anteversion; eight stems (7%) were in anteversion of >20 degrees; and nine stems (8%) were in retroversion. CONCLUSIONS: The surgeon's estimation of the anteversion of the cementless femoral stem has poor precision and is often not within the intended range of 10 degrees to 20 degrees of anteversion. The implications of this finding increase the importance of achieving a safe range of motion by evaluating the combined anteversion of the stem and the cup.

The science of minimally invasive total hip arthroplasty.

Minimally invasive hip surgery has stimulated a new process in hip arthroplasty. There is consensus among surgeons about the benefits of anesthesia, pain management, and rapid recovery protocols. The benefits of the surgical technique for small incision surgery remain controversial. Some patients influence this controversy because they prefer minimally invasive hip surgery: they associate less body violation and better cosmesis with smaller incisions. Small incision surgery is associated with a learning curve and requires specialized instruments for favorable outcomes. Despite being a more difficult operation to perform, in skilled hands it is a safe procedure that does not increase complication rates as shown by recent prospective, randomized studies. Correct component positioning has been achieved consistently with these procedures and short-term results of small incision surgery are the same as with long incisions. New anesthesia and pain management techniques have led to remarkable early functional results, making same-day surgery possible. With improved instrumentation such as computer navigation, minimally invasive total hip arthroplasty will become more prevalent.

Precision and bias of imageless computer navigation and surgeon estimates for acetabular component position.

Computer navigation has the potential to permit accurate placement of components. We first hypothesized acetabular inclination and anteversion using navigation would be within 5 degrees of postoperative computed tomography scans, then secondly, computer precision would be better than that of surgeons. In the first phase, we obtained postoperative CT scans in 30 hips to ascertain the computer navigation values for inclination and anteversion of the cup. In the second phase, in 99 patients with 101 hips, we determined the surgeon's precision by comparing surgeons' blind estimates for trial cup position with computer navigation values. The navigation precision for inclination was 4.4 degrees with a bias of 0.03 degrees and for anteversion was 4.1 degrees with a bias of 0.73 degrees. The experienced surgeons' precision was 11.5 degrees for inclination and 12.3 degrees for anteversion, whereas the less experienced surgeons' precision was 13.1 degrees for inclination and 13.9 degrees for anteversion. The data supported the first hypothesis as computer navigation had a bias for inclination and anteversion of less than 1 degrees with precision less than 5 degrees. The precision of computer navigation was better than that of surgeons. This imageless computer navigation system allows more accurate acetabular component placement.