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Biomedical subjects

R P Grelsamer

Publications and source records attributed to R P Grelsamer.

At least 19 recordsLinked to original sources
PubMed2001

Applied biomechanics of the patella.

Although numerous prominent orthopaedists of the twentieth century considered the patella to be useless, even detrimental, it now is clear that the patella serves an important biomechanical function. It is a complex lever that magnifies the moment arm of the extensor mechanism. The patellofemoral contact area (the fulcrum of the lever) shifts along a proximodistal axis through the knee's arc of motion. As the knee flexes, the force within the patellar tendon diminishes relative to that of the quadriceps tendon. One's interpretation of patellar tracking is dependent on the choice of coordinates. When assessing tracking by way of anatomic coordinates, patellas are seen to be slightly lateralized at 0 degrees flexion and to follow similar paths down the trochlea. The tracking pattern is the result of an elaborate interplay between the quadriceps muscles, patellofemoral ligaments, the geometry of the trochlea, and the quadriceps angle. The articular cartilage of the patella is the thickest in the human body and does not follow the contour of the subchondral bone. Patellar cartilage is softer and more permeable than that of the trochlea. It is insensate. In size, nature, and number, the facets of the patellar articulation vary from person to person.

Biomechanical Phenomena↗
PubMed2000

Hamstrings and iliotibial band forces affect knee kinematics and contact pattern.

Many clinical studies have emphasized the role of the hamstrings and the iliotibial band on knee mechanics, although few biomechanical studies have investigated it. This study therefore examined two hypotheses: (a) with loading of the hamstrings, the tibia translates posteriorly and rotates externally and the tibial contact pattern shifts anteriorly; furthermore, the changes in tibial kinematics alter patellar kinematics and contact; and (b) loading the iliotibial band alters the kinematics and contact pattern of the tibiofemoral joint similarly to loading the hamstrings, and loading the iliotibial band laterally translates the patella and its contact location. Five cadaveric knee specimens were tested with a specially designed knee-joint testing machine in an open-chain configuration. At various flexion angles, the knees were tested always with a quadriceps force but with and without a hamstrings force and with and without an iliotibial band force. The results support the first hypothesis. Hence, the hamstrings may be important anterior and rotational stabilizers of the tibia, a role similar to that of the anterior cruciate ligament. The results also support the second hypothesis, although the iliotibial band force had a smaller effect on the tibia than did the hamstrings force. Both forces also changed patellar kinematics and contact, demonstrating that these structures should also be considered during the clinical management of patellar disorders.

Aged↗
PubMed1998

The biomechanics of the patellofemoral joint.

Physical therapy for patella malalignment differs from therapy for other knee conditions. In fact, accepted forms of knee therapy can be counterproductive when one is dealing with patella malalignment. This article reviews some of the biomechanical foundations of patella-specific therapy and addresses common controversies. We emphasize the concept of articular cartilage stress over that of joint reaction force. The rationale for strengthening the vastus medialis obliquus and for avoiding certain forms of open chain strengthening are discussed, and we outline some of the exciting work being done in our laboratory concerning patellofemoral tracking, contact area, and cartilage properties.

Biomechanical Phenomena↗
PubMed1998

Patellar stabilization: a quantitative evaluation of the vastus medialis obliquus muscle.

Twenty-one cadaveric knees were dissected to analyze the functional anatomy of the vastus medialis complex (VMC), which is composed of the vastus medialis obliquus (VMO) and the vastus medialis longus (VML) muscles. The physiologic cross-sectional area of the VMO for 20 of the knees was 29% of the total physiologic cross-sectional area for the VMC. These values differed in one knee with a dysplastic VMO. The quantitative description of the VMO provided by this study will facilitate future efforts to accurately model the physiologic function of the VMO in cadaveric investigations on patellofemoral mechanics. The effect of simulated pathologies and surgical reconstructions then may be determined with more certainty to improve patient management.

Adult↗
PubMed1997

Anatomy of the human patellofemoral joint articular cartilage: surface curvature analysis.

Articular cartilage surfaces of 49 human patellae and 24 distal femora were characterized by identifying distinctive features with surface curvature analysis. Paired specimens from the same donor generally exhibited natural symmetry, so only results from nonpaired specimens were considered (39 patellae and 19 femora). In 23 of 39 patellae, proximal median and lateral transverse ridges extended to form an oblique ridge resembling a skewed lambda (lambda). Most of the unpaired patellae (37 of 39) exhibited only a single lateral transverse ridge, and most (32 of 39) had an odd facet. All but one patella exhibited a concave depression in the lateral and medial facets and a sellar area in the proximal region. All distal femoral surfaces exhibited a sellar trochlea. The concavity of the trochlea was greatest in the posterior aspect, near the intercondylar notch.

Adolescent↗
PubMed1997

Osteochondritis dissecans of the distal femur and patella.

Osteochondritis dissecans (OCD) is a pathologic process characterized by a partial or total separation of a fragment of bone with overlying articular cartilage. OCD may affect any joint, but the knee joint is affected most commonly. This article reviews several potential causes of OCD and classification systems for OCD. Diagnosis and treatment strategies are discussed.

Diagnostic Imaging↗
PubMed1996

Unicompartmental knee arthroplasty surgery. 10-year minimum follow-up period.

Sixty knees in 54 patients were followed a minimum of 10 years after unicompartmental knee arthroplasty surgery. Follow-up periods ranged from 10 to 18 years (average, 12 years). In all cases, a Marmor prosthesis was used. Two patients required arthroplasty surgery after the 10-year mark. Seven knees required revision prior to 10 years, and the 10- to 12-year survivorship for the entire cohort was 93%. Slight undercorrection of varus alignment and adequate polyethylene thickness of the tibial component appear to be important contributors to a successful outcome.

Adult↗
PubMed1995

Cemented revision of failed total hip arthroplasty. Survivorship analysis.

A review of 107 total hip arthroplasties performed with acrylic cement in 89 patients at Columbia-Presbyterian Medical Center by 1 surgeon from 1971 to 1990 revealed a clinical survivorship of 97% at 5 years and 76% at 10 years. The average followup was 7.7 years. Analysis of radiographs revealed a 94% success rate at 5 years and 62% at 10 years. A transtrochanteric approach was used in 99% of procedures. The 13 definite failures (12.1%) included 8 rerevisions (7.5%) and 5 failures (4.6%) pending revision. Modified Merle d'Aubigné and Postel postoperative scores increased significantly from preoperative values (pain, 2.8-5.3 points; movement, 3.2-5.2 points; function, 2.6-5.4 points). Bone grafting was required in 33% of procedures and did not affect survivorship: 24% of procedures required acetabular bone grafts; 4% femoral bone grafts; and 5% acetabular and femoral grafts. In 46% of hips, removal of the original well-fixed femoral cement and plug was deliberately incomplete. Stems of standard length were used for these partially rechannelized femurs because the old distal cement column served as a plug for the canal. Old osseointegrated polymethylmethacrylate was left behind to bond with the new cement column. Cement fracture, complete demarcation, and young age were negatively correlated with survivorship.

Bone Cements↗
PubMed1994

Computer simulation of glenohumeral and patellofemoral subluxation. Estimating pathological articular contact.

Analytic stereophotogrammetry and an interactive computer graphics program were used to obtain first order assessments of joint contact patterns in patellofemoral and glenohumeral joints, simulating normal and abnormal articulations. Precise (90 microns accuracy) computer graphic representations of the humeral head, glenoid, patella, and femoral articular surfaces were obtained from cadaver knees and shoulders. These surface representations were then manipulated into an articulated position, and joint contact areas computed by a proximity criterion. Pathologic states were then simulated, and contact recomputed. Simulated glenohumeral subluxations dramatically reduced contact area, and focused it eccentrically on the glenoid rim. Simulated size mismatch of humeral heads to glenoids reduced contact area, producing a pattern of peripheral contact on the glenoid if the humeral head had a larger radius of curvature, and central contact on the glenoid if the humeral head had a smaller radius of curvature. At 30 degrees knee flexion, the patellofemoral joint demonstrated a broad distribution of contact along the distal aspect of the patella and proximal aspect of the trochlea. Simulated lateral tilt (5 degrees) and translation (5 mm) of the patella resulted in shift of the predominant contact area laterally, along with a drastic decrease in the contact area. These results have implications for prosthetic sizing and biomechanical modeling of the glenohumeral and patellofemoral joints, and in selecting models for more rigorous empiric studies of joint contact. Furthermore, this technique allows a first order assessment of the effects of specific surgical reconstructions on articular mechanics.

Computer Graphics↗