Biomedical subjects

Andrew A Freiberg

Publications and source records attributed to Andrew A Freiberg.

9 recordsLinked to original sources

PubMed2006

Knee biomechanics after UKA and its relation to the ACL--a robotic investigation.

Unicompartmental knee arthroplasty (UKA) has regained popularity in recent years. However, limited data exist on how UKA affects knee biomechanics. The role of the anterior cruciate ligament (ACL) after fixed bearing UKA remains controversial. In this study, a robotic testing system was used to apply a quadriceps/hamstrings load to cadaveric knee specimens in the intact state, after medial UKA, and after transection of the ACL in UKA. The load was applied to the knee from full extension to 120 degrees of flexion in 30 degrees increments. UKA generally did not affect anterior-posterior (AP) femoral position, but did cause external tibial rotation and variations in varus-valgus rotation compared to the intact knee. ACL transection after UKA shifted the femur posteriorly compared to the intact and UKA knees and increased internal tibial rotation compared to the UKA knee at low flexion. The AP motion of the articular contact position in the implant was increased after ACL transection. These data might help explain the mechanism of tibial component loosening and provide insight into further investigations of polyethylene wear in UKA. Based on the kinematic data, the ACL should be functional to provide patients the greatest opportunity for long-term success after medial UKA.

Aged↗

PubMed2006

Investigation of in vivo 6DOF total knee arthoplasty kinematics using a dual orthogonal fluoroscopic system.

Fluoroscopic techniques have been recently used to detect in vivo knee joint kinematics. This article presents a technique that uses two fluoroscopes to form a dual orthogonal fluoroscopic system for accurately measuring in vivo 6DOF total knee arthoplasty (TKA) kinematics. The system was rigorously validated and used to investigate in vivo kinematics of 12 patients after cruciate-retaining TKA. In a repeatability study, the pose of two different TKA components was reproduced with standard deviations (SD) of 0.17 mm and 0.57 degrees about all three axes. In an accuracy study, the reproduced component positions were compared to the known component positions. Position and rotation mean errors were all within 0.11 mm and 0.24 degrees, with SD within 0.11 mm and 0.48 degrees, respectively. The results of this study show that the matching process of the imaging system is able to accurately reproduce the spatial positions and orientations of both the femoral and tibial components. For CR TKA patients, a consistent anterior femoral translation was observed with flexion through 45 degrees of flexion, and thereafter, the femur translated posteriorly with further flexion. The medial-lateral translation was measured to be less than 2 mm throughout the entire flexion range. Internal tibial rotation steadily increased through maximum flexion by approximately 6 degrees. Varus rotation was also measured with flexion but had a mean magnitude less than 2.0 degrees. In conclusion, the dual orthogonal fluoroscopic system accurately detects TKA kinematics and is applicable towards other joints of the musculoskeletal system, including the wrist, elbow, shoulder, ankle, and spine.

Arthroplasty, Replacement, Knee↗

PubMed2006

Large diameter femoral heads on highly cross-linked polyethylene: minimum 3-year results.

Contemporary highly cross-linked polyethylenes have become the most widely used alternative bearing surfaces in total hip replacement and may be paired with large diameter femoral heads (> 32 mm) in patients considered to be at high risk for dislocation. We report on a prospective series of 42 patients (45 hips) who had total hip replacement using large diameter cobalt-chrome femoral heads articulating with a highly cross linked polyethylene after a minimum of 3 years followup (mean 3.3 years). At final followup, the final patient cohort showed excellent clinical results with no radiographic failures or episodes of loosening. There was no evidence of pelvic or femoral osteolysis. One patient sustained a dislocation due to a grossly malpositioned acetabular component necessitating early isolated acetabular revision. The average yearly steady state wear rate was -0.06 +/- 0.41 mm/year. The results of our short-term prospective series indicated total hip replacement with large femoral heads articulating with a highly cross linked polyethylene showed excellent wear characteristics and clinical results and could be considered in patients at increased risk for dislocation.

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PubMed2006

Knee arthrodesis.

Arthrodesis is one of the last options available to obtain a stable, painless knee in a patient with a damaged knee joint that is not amenable to reconstructive measures. Common indications for knee arthrodesis include failed total knee arthroplasty, periarticular tumor, posttraumatic arthritis, and chronic sepsis. The primary contraindications to knee fusion are bilateral involvement or an ipsilateral hip arthrodesis. A variety of techniques has been described, including external fixation, internal fixation by compression plates, intramedullary fixation through the knee with a modular nail, and antegrade nailing through the piriformis fossa. Allograft or autograft may be necessary to restore lost bone stock or to augment fusion. For the carefully selected patient with realistic expectations, knee arthrodesis may relieve pain and obviate the need for additional surgery or extensive postoperative rehabilitation.

Arthrodesis↗

PubMed2005

The effect of real-time aging on the oxidation and wear of highly cross-linked UHMWPE acetabular liners.

Irradiation decreases the wear of ultra-high molecular weight polyethylene (UHMWPE) but generates residual free radicals, precursors to long-term oxidation. Melting or annealing is used in quenching free radicals. We hypothesized that irradiated and once-annealed UHMWPE would oxidize while irradiated and melted UHMWPE would not, and that the oxidation in the former would increase wear. Acetabular liners were real-time aged by immersion in an aqueous environment that closely mimicked the temperature and oxygen concentration of synovial fluid. After 95 weeks of real-time aging, once-annealed components were oxidized; the melted components were not. The wear rate of the real-time aged irradiated and once-annealed components was higher than the literature reported values of other contemporary highly cross-linked UHMWPEs. Single annealing after irradiation used with terminal gamma sterilization may adversely affect the long-term oxidative stability of UHMWPE components.

Acetabulum↗

PubMed2004

Surface analysis of early retrieved acetabular polyethylene liners: a comparison of conventional and highly crosslinked polyethylenes.

In vivo wear behavior of 16 highly cross-linked and 19 conventional polyethylene acetabular explants, at an average in vivo duration of 6 months were studied. Highly cross-linked groups showed machining marks from the original manufacturing process in some areas and extensive scratching and some polishing of the articulating surfaces. The conventional group showed greater loss of machining marks, scratching, and polishing. Representative samples were melted to allow recovery of plastic deformation and to show true removal of material caused by wear. Melt-recovery experiments consistently showed the disappearance of surface scratches and the restoration of the original machining marks in the highly cross-linked explants. In the conventional group, few of the scratches were eliminated and only limited restoration of the machining marks was apparent. These observations support the hypothesis that the early in vivo scratching of highly cross-linked polyethylene acetabular liners is primarily caused by plastic deformation.

Cross-Linking Reagents↗

PubMed2004

Function of the anterior cruciate ligament after unicompartmental knee arthroplasty: an in vitro robotic study.

The objective of this study was to investigate the role of the anterior cruciate ligament (ACL) in the anterior-posterior (AP) stability of the knee after unicompartmental knee arthroplasty (UKA). AP tibial loads were applied to human cadaveric knee specimens using a robotic testing system. After UKA, the knee exhibited tibial translations similar to that of the native knee, and the forces in the ACL were also similar to those seen in the native knee. The ACL-deficient knee after UKA exhibited significantly greater anterior tibial translations than the native knee and the knee after UKA with an intact ACL. These data suggest that medial UKA does not alter the anterior stability of the knee, but a functional ACL is necessary to ensure normal stability after UKA.

Aged↗

PubMed2004

The high hip center.

Revision of a failed acetabular component presents many challenges to the arthroplasty surgeon. The goal in most cases should be to reconstruct the acetabulum by positioning the hip center as close as possible to the anatomic hip center. However, severe acetabular bone stock deficiency and distorted acetabular anatomy often preclude placement of the acetabular component at the true anatomic hip center. In these cases, many options exist for reconstruction of the acetabulum, including placement of the cup superiorly at a high hip center. Although biomechanical studies have shown that superolateral placement of the hip center may lead to increased moments and forces across the hip (leading to potentially higher rates of loosening), superior only displacement of the hip center does not seem to adversely affect the forces about the hip. Proximal placement of the hip center facilitates contact between intact, viable host bone and the acetabular implant, thereby reducing the need for structural bone grafts, and increasing the chances for stable bony ingrowth. With proper patient selection and meticulous surgical technique, the high hip center can be a useful technique for reconstruction of the deficient acetabulum in the patient with a loose acetabular component after total hip arthroplasty.

Acetabulum↗

PubMed2003

Osteolysis of the pelvis: evaluation and treatment.

Osteolysis of the pelvis is a common and well-recognized complication associated with total hip arthroplasty. The diagnosis and treatment of osteolysis of the pelvis is a challenging and controversial problem. Osteolysis of the pelvis often is asymptomatic and does not present with symptoms until considerable bone loss and loosening of the acetabular socket occur. Radiographs are the most common way to detect and monitor osteolysis around an implant. However, lesions viewed radiographically usually are underestimations of the lesions found intraoperatively. Moreover, some advocate computed tomography scanning to evaluate these lesions. The indications for treatment of osteolysis with cemented acetabular components are defined more clearly than with a cementless component. If the cemented or cementless acetabular component is loose, then revision is necessary. However, it is less clear when to intervene surgically with a well-fixed cup with osteolysis. Many early reports advocated the removal of a well-fixed socket during revision surgery for osteolysis and polyethylene wear. However, the removal of a well-fixed socket has the potential for significant damage and loss of the surrounding bone resulting in loss of integrity of a column or pelvic discontinuity, which may compromise placing another acetabular component. Recently, a new treatment strategy of retaining a well-fixed socket, exchanging the liner, and grafting lesions has proven successful. Without the removal of the acetabular shell, different techniques are needed to graft the osteolytic lesions. Osteolysis is a difficult problem; however, with radiographic surveillance to monitor patients for lesions, proper indications, and good surgical techniques, the treatment of osteolysis of the pelvis can result in a well-functioning total hip arthroplasty.

Algorithms↗