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Biomedical subjects

A A Amis

Publications and source records attributed to A A Amis.

At least 19 recordsLinked to original sources
PubMed2006

The consequences of meniscectomy.

The menisci of the knee have an important role in load-bearing and shock absorption within the joint. They may also function as secondary stabilisers, have a proprioceptive role, and aid the lubrication and nutrition of the articular cartilage. Complete or partial loss of a meniscus can have damaging effects on a knee, leading to serious long-term sequelae. This paper reviews the consequences of meniscectomy and summarises the body of evidence in the literature regarding those factors most relevant to long-term outcome.

Biomechanical Phenomena↗
PubMed2005

Effects of lateral retinacular release on the lateral stability of the patella.

The objective of this cadaveric study was to evaluate quantitatively the effects of lateral retinacular release on the lateral stability of the patella. A materials testing machine was used to displace the patella of seven cadaveric specimens 10 mm laterally while measuring the required force, with 175 N quadriceps tension. The patella was connected via a ball-bearing patellar mounting 10 mm deep to the anterior surface to allow rotations. Patellar force--displacement behaviour was tested from 0 degrees to 60 degrees knee flexion. At 0 degrees , 10 degrees and 20 degrees flexion the mean force required to displace the patella 10 mm laterally was reduced significantly due to lateral retinacular release, by 16-19%. The average force required to displace the patella was also reduced for larger flexion angles, although this was not statistically significant. These findings suggest that lateral retinacular release may not be appropriate in treatment of patellar lateral instability.

Aged↗
PubMed2005

Anatomy of the posterior cruciate ligament and the meniscofemoral ligaments.

This paper describes the anatomy of the posterior cruciate ligament (PCL) and the meniscofemoral ligaments (MFLs). The fibres of the PCL may be split into two functional bundles; the anterolateral bundle (ALB) and the posteromedial bundle (PMB), relating to their femoral attachments. The tibial attachment is relatively compact, with the ALB anterior to the PLB. These bundles are not isometric: the ALB is tightest in the mid-arc of knee flexion, the PMB is tight at both extension and deep flexion. At least one MFL is present in 93% of knees. On the femur, the anterior MFL attaches distal to the PCL, close to the articular cartilage; the posterior MFL attaches proximal to the PCL. They both attach distally to the posterior horn of the lateral meniscus. Their slanting orientation allows the MFLs to resist tibial posterior drawer.

Femur↗
PubMed2005

The porcine forelimb as a model for human flexor tendon surgery.

Technical skills have been shown to transfer very well from bench models to practical use. The central two rays of 30 forelimbs of pigs were dissected and anatomical observations were made. The rays contained deep and superficial flexor tendons enclosed in a fibro-osseous tunnel and these were present in all 60 specimens. The fibrous part of the tunnel had specific constant condensations in annular and oblique directions which were present in all 60 rays. The anatomy of the porcine forelimb digital flexor tendon system is sufficiently similar to the human system to be used as a model for surgeons wishing to master the technical aspects of zone II flexor tendon repair. This paper proposes the porcine forelimb as a bench model for zone II flexor tendon repair.

Animals↗
PubMed2005

The effects of articular, retinacular, or muscular deficiencies on patellofemoral joint stability: a biomechanical study in vitro.

Normal function of the patellofemoral joint is maintained by a complex interaction between soft tissues and articular surfaces. No quantitative data have been found on the relative contributions of these structures to patellar stability. Eight knees were studied using a materials testing machine to displace the patella 10 mm laterally and medially and measure the force required. Patellar stability was tested from 0 degrees to 90 degrees knee flexion with the quadriceps tensed to 175 N. Four conditions were examined: intact, vastus medialis obliquus relaxed, flat lateral condyle, and ruptured medial retinaculae. Abnormal trochlear geometry reduced the lateral stability by 70% at 30 degrees flexion, while relaxation of vastus medialis obliquus caused a 30% reduction. Ruptured medial retinaculae had the largest effect at 0 degrees flexion with 49% reduction. There was no effect on medial stability. There is a complex interaction between these structures, with their contributions to loss of lateral patellar stability varying with knee flexion.

Aged↗
PubMed2005

Tensile strength of the medial patellofemoral ligament before and after repair or reconstruction.

The tensile strength of the medial patellofemoral ligament (MPFL), and of surgical procedures which reconstitute it, are unknown. Ten fresh cadaver knees were prepared by isolating the patella, leaving only the MPFL as its attachment to the medial femoral condyle. The MPFL was either repaired by using a Kessler suture or reconstructed using either bone anchors or one of two tendon grafting techniques. The tensile strength and the displacement to peak force of the MPFL were then measured using an Instron materials-testing machine. The MPFL was found to have a mean tensile strength of 208 N (SD 90) at 26 mm (SD 7) of displacement. The strengths of the other techniques were: sutures alone, 37 N (SD 27); bone anchors plus sutures, 142 N (SD 39); blind-tunnel tendon graft, 126 N (SD 21); and through-tunnel tendon graft, 195 N (SD 66). The last was not significantly weaker than the MPFL itself.

Aged↗
PubMed2004

Patellar resection during total knee arthroplasty: effect on bone strain and fracture risk.

Patellae in small knees, or after severe patellar erosion, may be vulnerable to fracture after resection during arthroplasty. The patellar remnant may be thin, while the polyethylene component has a standard thickness. Anterior patellar bone strain was measured in cadaver knees loaded via the quadriceps, from 0 to 90 degrees flexion, with the patella intact, and after resections to 16, 13 and 11 mm thick and replacement by an 8-mm-thick polyethylene component. Strain increased significantly with knee flexion with constant 500 N quadriceps tension. Resection caused significant changes from intact values in knee flexion and extension and no significant effect at 30 degrees flexion. In flexion, bending caused the anterior surface to become more convex, with high tensile bone strains. In extension, resection caused negative anterior strains, representing bending in the opposite direction, with large tensile strains on the cut posterior surface. For normal activities, such as rising from a chair (1.8 kN quadriceps tension) the patella appears safe against fracture with a minimal resection to 16 mm thick. An eroded patella resected to 11 mm thickness may be at risk of fracture with that loading.

Arthroplasty, Replacement, Knee↗
PubMed2004

The posteromedial corner revisited. An anatomical description of the passive restraining structures of the medial aspect of the human knee.

We have reviewed the literature on the anatomy of the posteromedial peripheral ligamentous structures of the knee and found differing descriptions. Our aim was to clarify the differing descriptions with a simplified interpretation of the anatomy and its contribution to the stability of the knee. We dissected 20 fresh-frozen cadaver knees and the anatomy was recorded using video and still digital photography. The anatomy was described by dividing the medial collateral ligament (MCL) complex into thirds, from anterior to posterior and into superficial and deep layers. The main passive restraining structures of the posteromedial aspect of the knee were found to be superficial MCL (parallel, longitudinal fibres), the deep MCL and the posteromedial capsule (PMC). In the posterior third, the superficial and deep layers blend. Although there are oblique fibres (capsular condensations) running posterodistally from femur to tibia, no discrete ligament was seen. In extension, the PMC appears to be an important functional unit in restraining tibial internal rotation and valgus. Our aim was to clarify and possibly simplify the anatomy of the posteromedial structures. The information would serve as the basis for future biomechanical studies to investigate the contribution of the posteromedial structures to joint stability.

Aged↗
PubMed2003

Biomechanics of the PCL and related structures: posterolateral, posteromedial and meniscofemoral ligaments.

This paper reviews and updates our knowledge of the anatomy and biomechanics of the posterior cruciate ligament, and of the posterolateral, posteromedial and meniscofemoral ligaments of the knee. The posterior cruciate ligament is shown to have two functional fibre bundles that are tight at different angles of knee flexion. It is the primary restraint to tibial posterior draw at all angles of knee flexion apart from near full extension. In contrast, the posterolateral and posteromedial structures are shown to tighten as the knee extends, and to be well-aligned to resist tibial posterior draw. These structures also act as primary restraints against other tibial displacements. Tibial internal rotation is restrained by the medial and posteromedial structures, while tibial external rotation is restrained by the lateral and posterolateral structures. They are also the primary restraints against tibial abduction-adduction rotations. The meniscofemoral ligaments are shown, for the first time, to contribute significantly to resisting tibial posterior draw, and to have a strength of approximately 300 N. Taken together, this evidence shows how the posterolateral and posteromedial structures are responsible for posterior knee stability near extension, and this, along with the action of the meniscofemoral ligaments, may explain why an isolated rupture of the posterior cruciate ligament does not often lead to knee instability

Biomechanical Phenomena↗
PubMed2003

An anatomical study of meniscal allograft sizing.

Meniscus-to-femoral condyle congruity is essential for the development of circumferential hoop stresses and thus function of the meniscus. When meniscal allograft transplantation is performed using bony anchorage of the insertional ligaments, accurate graft-to-host size matching is therefore essential. The standard method currently employed for size matching of meniscal allografts is to rely on plain radiographs of the host's knee, from which expected meniscal dimensions are measured. This study aimed to examine the correlation between tibial plateau dimensions and meniscal dimensions. We studied 44 donor tibial plateaus with medial and lateral meniscal allografts attached intact. Meniscal and tibial plateau dimensions were measured. Linear regression analysis was used to calculate expected meniscal dimensions from each specimen's plateau dimensions. Using specific medial and lateral tibial plateau width and length measurements, meniscal dimensions could be predicted with a mean error of only 5.0+/-6.4%. When predicting meniscal dimensions from only total bony plateau width, the mean error observed was 6.2+/-8.0%. The difference between the two methods was not statistically significant. The results suggest that meniscal dimensions can be predicted accurately from tibial plateau measurements, with only small mean errors. However, potential size mismatches should be carefully borne in mind by surgeons using meniscal allografts.

Anthropometry↗
PubMed2003

Quantitative measurement of patellofemoral joint stability: force-displacement behavior of the human patella in vitro.

Patellofemoral joint instability is a common clinical problem. However, little quantitative data are available describing the stability characteristics of this joint. We measured the stability of the patella against both lateral and medial displacements across a range of knee flexion angles while the quadriceps were loaded physiologically. For eight fresh-frozen knee specimens a materials testing machine was used to displace the patella 10 mm laterally and 10 mm medially while measuring the required force, with 175 N quadriceps tension. The patella was connected via a ball-bearing patellar mounting 10 mm deep to the anterior surface to allow natural tilt and other rotations. Patellar force-displacement behavior was tested at flexion angles of 0 degrees, 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. Significant differences were found between the lateral and medial restraining forces at 10 mm displacement. For lateral displacement, the restraining force was least at 20 degrees of knee flexion (74 N at 10 mm displacement), rising to 125 N at 0 degrees and 90 degrees of knee flexion. The restraining force increased progressively with knee flexion for medial patellar displacement, from 147 N at 0 degrees to 238 N at 90 degrees. With quadriceps tension, the patella was more resistant to medial than lateral displacement. Our finding that lateral patellar displacement occurred at the lowest restraining force when the knee was flexed 20 degrees agrees with clinical experience of patellar instability.

Aged↗
PubMed2003

The effect of screw length and position on fixation of four-stranded hamstring grafts for anterior cruciate ligament reconstruction.

The aim of this study was to examine interference screw fixation of four strand hamstring grafts for anterior cruciate ligament reconstruction in vitro. Bovine tibiae and cannon tendons were used. Screws were introduced from 'outside-in'. The tendons were loaded cyclically to 150 N to simulate walking and 450 N to simulate jogging. Slippage of the tendon from the anchorage was recorded after 100, 300 and 1000 cycles. Cortico-cancellous and cancellous only fixations were compared using a 7-mm screw in an 8-mm tunnel with a 7-mm graft. The effect of screw length was studied by comparing 8 x 25 and 8 x 45 mm screws. Graft slippage with cancellous only fixation was significantly greater than with cortico-cancellous screw fixation (P 0.105), the longer screws gave more consistent behaviour. We concluded that the screw should be placed so that its head engages the cortex, while increasing screw length within cancellous bone did not significantly improve graft fixation. Cyclical load testing reflects the repetitive forces imposed in the early post-operative period following hamstring anterior cruciate ligament reconstruction and is important for the evaluation of graft fixations.

Animals↗
PubMed2003

Anatomy and biomechanics of the medial patellofemoral ligament.

The medial patellofemoral ligament (MPFL) is a band of retinacular tissue connecting the femoral medial epicondyle to the medial edge of the patella. The MPFL is approximately 55 mm long, and its width has been reported to range from 3 to 30 mm. The MPFL is overlaid by the distal part of vastus medialis obliquus to a variable extent, and fibres of MPFL merge into the deep aspect of the muscle. Despite the MPFL being very thin, it had a mean tensile strength of 208 N, and has been reported to be the primary passive restraint to patellar lateral displacement. Lateral patellar displacement tests in vitro showed that the patella subluxed most easily at 20 degrees knee flexion. The contribution of the MPFL to resisting patellar lateral subluxation was greatest in the extended knee. This finding was linked to the retinaculae being tightest in full knee extension, and slackening with flexion.

Biomechanical Phenomena↗
PubMed2003

A technique for the measurement of patellar tracking during weight-bearing activities using ultrasound.

A new fixation device, the femoral clamp, was developed in this study for the ultrasound measurement of patellar medio-lateral motion during sitting and squatting knee flexion/extension. Seventeen subjects, 6 males, 11 females, aged between 18 and 40 years were recruited for the test. Results showed that the patella moved medially then laterally from extension to flexion when sitting. Weight-bearing knee motion produced a more laterally tracked patella without the presence of the initial medial patellar translation. The tracking patterns of the patellae were similar regardless of knee movement direction. The patellar lateral position was greatly affected by the movement task (p < 0.0005), and was also influenced by gender for maximum medial position (p < 0.05). The reproducibility of the measurement was between 0.29 and 0.90 for the intra-rater and 0.34-0.75 for the inter-rater reliability. The accuracy of the ultrasound measurement was validated by interventional magnetic resonance (iMR) imaging of the patella and the mean error of the measurement was 1.4 +/- 3.2 mm. Although further research is needed to improve the accuracy and reliability of this method, it has demonstrated the feasibility of obtaining patellar tracking data during load-bearing activities.

Adult↗
PubMed2003

Mechanical factors in the initiation and propagation of tears of the rotator cuff. Quantification of strains of the supraspinatus tendon in vitro.

Differential strain has been proposed to be a causative factor in failure of the supraspinatus tendon. We quantified the strains on the joint and bursal sides of the supraspinatus tendon with increasing load (20 to 200 N) and during 120 degrees of glenohumeral abduction with a constant tensile load (20 to 100 N). We tested ten fresh frozen cadaver shoulders on a purpose-built rig. Differential variable reluctance extensometers allowed calculation of the strain. Static loading to 100 N or more increased strains on the joint side significantly more than on the bursal side. During glenohumeral abduction an increasing and significant difference in strain was measured between the joint and bursal sides of the supraspinatus tendon, which reached a maximum of 10.6% at abduction of 120 degrees. The joint side strain of 7.5% reached values which were previously reported to cause failure. Differential strain causes shearing between the layers of the supraspinatus tendon, which may contribute to the propagation of intratendinous defects that are initiated by high joint side strains.

Aged↗
PubMed2002

A biomechanical study of four different meniscal repair systems, comparing pull-out strengths and gapping under cyclic loading.

Most studies comparing the biomechanical properties of different meniscal repair systems have simply investigated load to failure. Meniscal tissue is highly anisotropic, and far weaker under tension in the radial direction. Radially oriented loading to failure may not therefore be the most physiologically relevant in vitro test for repair of circumferential tears, and determining gapping across repair sites under cyclical loading at lower loads may be of greater importance. Using bovine menisci, vertical circumferential incisions were repaired using a simple vertical 2-0 PDS suture, Meniscal Arrow, Meniscal Fastener or T-Fix. Repairs were tested by simple loading to failure in a materials testing machine, and by cyclic loading between 5 and 10 N for 25 cycles. Initial gapping across the repairs was measured using a digital micrometer, and the increase in gapping under cyclic loading measured using a Differential Voltage Reluctance Transducer. The mean loads to failure for each of the repair groups were: sutures 72.7 N, Arrows 34.2 N, Fasteners 40.8 N and T-Fix 49.1 N. The load to failure was significantly greater with sutures than with Arrows or Fasteners. The mean gapping across the repairs for each of the repair groups after 25 loading cycles were: sutures 3.29 mm, Arrows 2.18 mm, Fasteners 3.99 mm and T-Fix 3.47 mm. The mean gapping was significantly less with Arrows than with Sutures, Fasteners or T-Fix. These results confirm that meniscal repair by suturing gives the highest load to failure, but show that Arrows give superior hold under lower loads, with the least gapping across repairs under cyclic loading of the four methods tested.

Animals↗
PubMed2002

Standardisation of the description of patellofemoral motion and comparison between different techniques.

Patellofemoral motion is significant clinically, yet in the literature many different methods and terminologies are used, thus making comparison between studies difficult. We review and explain the different methods used for the description of patellofemoral joint motion, compare these methods by experimentation, and propose a standardised method. We found three main methods for describing patellar motion: motion of the patella about femoral body fixed axes, about patellar body fixed axes, and a combination of these. Description about femoral body fixed axes does not make sense clinically. Description about patellar body fixed axes is straightforward, yet the definition of these axes is prone to error due to the lack of anatomical landmarks. The combination method makes most sense clinically and uses more easily found anatomical landmarks. Patellar flexion varied by up to 26% when describing the motion about different axes. Tilt and shift were highly sensitive to the choices of coordinate systems and the axes of motion. The pattern of rotation was consistent between all methods; however, differences between the methods increased with patellar flexion. We propose the description of patello-femoral motion in terms of shift (along a femoral medial-lateral axis), tilt (about the patellar long axis), rotation (about a floating patellar anterior-posterior axis) and flexion (about the femoral medial-lateral axis).

Femur↗