Abstract 1074: Cellular uptake and metabolism of MT1-MMP-activated taxane prodrugs

ICT3205 is a targeted cytotoxic agent, comprised of an MT1-MMP-specific peptide and a paclitaxel warhead. Paclitaxel, originally approved in 1992, is one of the most commonly used chemotherapies for various cancer types, but is often characterized by its dose-limiting toxicity and low aqueous solubility. Tumor-targeted prodrugs are a promising strategy for the selective delivery of taxanes to prostate tumors, especially given the results of STAMPEDE trial1. Previous work has shown that ICT3205 is selectively metabolized in tumor tissue over the normal tissue, and that this is specifically mediated by MT1-MMP2. In vivo studies have demonstrated that when administered at an equimolar dose to paclitaxel, ICT3205 has a superior anticancer effect, with an absence of systemic toxicity. In this study we aim to further investigate the cellular uptake and metabolism of ICT3205 and other taxane analogues in MT1-MMP +ve (HT1080) and MT1-MMP -ve (MCF-7) cells in vitro. The compound will be also studied in the PC3 prostate cancer cell line, since it has been demonstrated before that there is a good correlation between MT1-MMP protein and mRNA expression. ICT3205 and analogues have been synthesized, and purified by semi-preparative HPLC. We report the tumor-specific metabolism of ICT3205 in prostate tumors ex vivo, and we are currently studying its cellular uptake and metabolism in MT1-MMP +ve and MT1-MMP -ve cancer cell-lines using HPLC, mass spectrometry and immunofluorescent microscopy. Moreover, ex vivo metabolism studies are performed on the analogues, while they will be also assessed for their metabolism and cellular uptake. These data will provide a better understanding of the mechanism of uptake and metabolism of this type of peptide prodrugs, and will provide the basis for the future synthesis and optimization of these prodrugs.

1.James ND et al. Addition of docetaxel, zoledronic acid, or both to first-line long-term hormone therapy in prostate cancer (STAMPEDE): survival results from an adaptive, multiarm, multistage, platform randomized controlled trial. Lancet. 2016;387(10024):1163-772.Loadman PM et al. Improved delivery of paclitaxel to prostate tumors: a membrane-type matrix metalloproteinase (MT-MMP)-targeted approach. Cancer Res. 2016;76:3

Citation Format: Athina Polykandritou, Alexandra Serre, Hannah Spencer, Goreti R. Morais, Amanda Race, Steven Shnyder, Paul Loadman, Robert A. Falconer. Cellular uptake and metabolism of MT1-MMP-activated taxane prodrugs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1074.

Abstract 4926: Preclinical intratumoral pharmacokinetics (PK) of capecitabine (Cap) given +/- eribulin (Eri)

Background: Eri & Cap are active as single agents in metastatic breast cancer, but the combination appears particularly active & well tolerated clinically. We explored the hypothesis that normalisation of tumor vasculature by Eri seen in preclinical models may enhance delivery of Cap to the tumor when given in combination.

Methods: Mice bearing MDA-MD-231 xenografts were treated with Cap 540mg/kg p.o. day 1 alone or following Eri 1mg/kg i.v. on day -8 then sacrificed on day 1 at 15min, 30min, 1h, 2h, 4h, 6h or 24h after Cap (n=3/ time point). Concentrations of Cap & its metabolites (5'-deoxy-5-fluorocytidine, 5DFCR; 5-Fluoro-5'-deoxyuridine, 5DFUR; 5-Fluorouracil, 5FU; 5-Fluorouridine, 5FUrd; & 5-Fluoro-2'-deoxyuridine, 5FdUrd) in plasma, tumor, skin & muscle were analysed by LC-MS/MS. Half the tumor was reserved to study Cap distribution using matrix-assisted laser desorption/ionization mass spectrometry imaging with haem imaged as a surrogate marker for tumour vasculature.

Results: We found no differences in the plasma, skin, muscle or tumor PK profiles of Cape & its metabolites with the addition of Eri (Table 1). In both treatment arms intratumoral concentrations of 5DFUR, 5FU, 5FUrd & 5FdUrd appeared higher in tumors while those of Cape & 5DFCR appeared higher in normal healthy tissues. To mitigate the variability in tumor Cape concentrations between animals, we also expressed the results as the ratio of drug concentration in tumour:healthy tissue but again found no apparent effect of Eri on intratumoral drug concentrations. Analyses of drug distribution are on-going & will be presented.

Conclusion: No clear effect of Eri on intratumoral concentrations of Cape or its metabolites was seen. We are exploring potential differences in tumour drug distribution.

Citation Format: Maria Jove Casulleras, Jade Spencer, Paul Loadman, Malcolm Clench, Steve Shnyder, Patricia Cooper, Cristina Russo, Amanda Race, Ramon Salazar, Chris Twelves. Preclinical intratumoral pharmacokinetics (PK) of capecitabine (Cap) given +/- eribulin (Eri) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4926.

Abstract 4205: Intracellular pharmacokinetics of 5FU and palbociclib: Uptake and efflux in disaggregated cells and 3D models

Introduction:

Pre-clinical drug development does not routinely assess drug penetration beyond use of the human intestinal Caco-2 cell line as an in vitro model of the intestinal barrier to evaluate potential drug absorption. Detailed in vivo tumour pharmacokinetic (PK) studies are unusual. However, the ability of a drug to reach its target plays a key role in drug efficacy.

Here we present a methodology to study drug PK in disaggregated cells and in a 3D cell culture model (spheroids) using 5FU and palbociclib. The comparison of these 2 drugs is of interest taking into account their different mechanisms and chemical properties, logP 0.58 and 2.12 respectively. Knowledge of cellular uptake and efflux in disaggregated cells and 3D models together with intracellular binding characteristics is vital to optimise a better drug delivery.

Experimental procedures:

MCF-7 and DLD-1 cells were used for cellular and spheroid experiments. Spheroid growth was optimized to produce a spheroid of 300-400µm diameter at day 4. Drug uptake: 1x106 cells or 30 spheroids/time point were exposed to 10µM 5FU or 0.1µM of palbociclib for different time durations. For 5FU, drug uptake at 100µM was also monitored to detect 5FU metabolites. Drug efflux: 1x106 cells were exposed first to 100µM 5FU or 0.1µM of palbociclib for 60min then, drug media removed, substituted by fresh media and sample over a 4h period. Drug concentration inside cells and in the fresh media was measured. Drug concentrations were measured using HPLC-Tandem Mass Spectrometry. Each experiment was carried out in triplicate.

Results:

5FU achieves intracellular steady state within 5-10min in cells and spheroids with equal concentrations inside and outside the cell/spheroids. Intracellular metabolites of 5FU were only seen with 100µM treatment and had a similar PK characteristics to 5FU. 5FU drug efflux experiments showed that efflux occurred rapidly within 5min achieving a new equilibrium with 30% of 5FU remaining inside the cells. 5FUrd was also detected extracellularly after 1h in the fresh media, showing that cells have both 5FU and metabolite efflux. In contrast, palbociclib cellular uptake had an initial intracellular drug concentration peak at 5-10min which then plateaued. Interestingly, total intracellular concentrations of palbociclib were over 30 times higher compared to the external media drug at steady state. Spheroid and efflux experiments of palbociclib are on-going and will be presented.

Conclusions:

Our results suggest that both drugs penetrate quickly in cancer cells. Palbociclib intracellular concentrations were 30 times higher than the external media suggesting excessive intracellular binding while 5FU achieve equal concentrations between the inside and outside of the cell. These data and methodology may be useful to allow generation of mathematical models to improve drug delivery design.

Citation Format: Maria Jove, Paul Loadman, Jade Spencer, Lava Sulayman, Jo Wicks, Amanda Race, Chris Twelves. Intracellular pharmacokinetics of 5FU and palbociclib: Uptake and efflux in disaggregated cells and 3D models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4205. doi:10.1158/1538-7445.AM2017-4205

Measurement of red blood cell eicosapentaenoic acid (EPA) levels in a randomised trial of EPA in patients with colorectal cancer liver metastases

We investigated red blood cell (RBC) PUFA profiles, and the predictive value of RBC EPA content for tumour EPA exposure and clinical outcomes, in the EMT study, a randomised trial of EPA in patients awaiting colorectal cancer (CRC) liver metastasis surgery (Cockbain et al., 2014) [8]. There was a significant increase in RBC EPA in the EPA group (n=43; median intervention 30 days; mean absolute 1.26[±0.14]% increase; P<0.001), but not in the placebo arm (n=45). EPA incorporation varied widely in EPA users and was not explained by treatment duration or compliance. There was little evidence of 'contamination' in the placebo group. The EPA level predicted tumour EPA content (r=0.36; P=0.03). Participants with post-treatment EPA≥1.22% (n=49) had improved OS compared with EPA <1.22% (n=29; HR 0.42[95%CI 0.16-0.95]). RBC EPA content should be evaluated as a biomarker of tumour exposure and clinical outcomes in future EPA trials in CRC patients.

A phase I pharmacokinetic (PK) and pharmacodynamic (PD) study of the selective aurora kinase inhibitor GSK1070916A

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Background: GSK1070916A is a potent and selective inhibitor of Aurora B and C. This phase I study in collaboration with GlaxoSmithKline was part of the Cancer Research UK Clinical Development Programme. Methods: Patients (pts) with advanced/metastatic solid cancers for whom there was no standard therapy, with adequate performance status and organ function were eligible for GSK1070916A (1 hour i.v. infusion days 1 – 5, every 21 days). The primary objectives were to determine the safety profile, dose limiting toxicity (DLT) and maximum tolerated dose (MTD) of GSK1070916A. The starting dose was 5mg/m2/day, with initial single pt cohorts, followed by “3 + 3” cohorts and expansion at the MTD. DLTs included prolonged (> 5 days) or complicated grade 4 neutropenia; the MTD was the highest dose at which < 1 of 3 - 6 pts experienced DLT. Cycle 1 blood and healthy skin biopsies were obtained for PK and PD assays. The expanded cohort included 6 pts having pre- and post-treatment functional imaging studies (FDG PET-CT and MRI), and a further 6 having paired tumour biopsies for PD studies. Results: Nine single pt cohorts received up to 73mg/m2/day of GSK1070916A with no grade 3 or 4 related adverse events. At 102.2mg/m2/day, 1 pt had a DLT (febrile neutropenia) and 2 pts non-DLT grade 4 neutropenia; this dose was considered unacceptably toxic and 23 pts received a lower dose of 85mg/m2/day; 7/23 pts had prolonged/complicated grade 4 neutropenia, 5 of whom continued GSK1070916A with dose reduction +/- delay. There were no treatment related deaths. A pt with ovarian cancer (102.2mg/m2/day) had a RECIST PR; 19 pts had stable disease for < 223 days. GSK1070916A PK were linear with a strong correlation between exposure (AUC) and reduction in neutrophils (r2 0.91). At the 85 mg/m2 dose, mean day 1 t1/2 was 8.98 hours and Cl 9.2 l/h; AUCinf was 10% higher on day 5 than day 1. PD results in healthy skin (phosphoHistone-H3, Ki 67 and cleaved caspase-3) were inconsistent. Conclusions: The MTD of GSK1070916A as a 1 hour i.v. infusion on days 1 – 5, every 21 days is 85mg/m2/day, with predictable and manageable neutropenia as the DLT and evidence of clinical activity. Serum levels of cytokeratin-18, tumour PD and functional imaging data will be presented. Clinical trial information: NCT01118611.

Using 'subcement' to simulate the long-term fatigue response of cemented femoral stems in a cadaver model: could a novel preclinical screening test have caught the Exeter matt problem?

Previously, cement was formulated with degraded fatigue properties (subcement) to simulate long-term fatigue in short-term cadaver tests. The present study determined the efficacy of subcement in a 'preclinical' test of a design change with known clinical consequences: the 'polished'-to-'matt' transition of the Exeter stem (revision rates for polished stems were twice those for matt stems). Contemporary stems were bead blasted to give Ra = 1 microm (matt finish). Matt and polished stems were compared in cadaver pairs under stair-climbing loads (three pairs of size 1; three pairs of size 3). Stem micromotion was monitored during loading. Post-test transverse sections were examined for cement damage. Cyclic retroversion decreased for polished stems but increased for matt stems (p < 0.0001). The implant size had a substantial effect; retroversion of (larger) size-3 stems was half that of size-1 stems, and polished size-3 stems subsided 2.5 times more than the others. Cement damage measures were similar and open through-cracks occurred around both stems of two pairs. Stem retroversion within the mantle resulted in stem-cement gaps of 50-150 microm. Combining information on cyclic motion, cracks, and gaps, it was concluded that this test 'predicted' higher revision rates for matt stems (it also implied that polished size-3 stems might be superior to size-1 stems).

Novel methods to study functional loading micromechanics at the stem-cement and cement-bone interface in cemented femoral hip replacements

We have developed a technique to directly observe the micromechanics of the stem-cement and cement-bone interfaces of cemented femoral stems under physiologically relevant loading conditions. Thick transverse sections of a stem-cement-femur construct were fixed to the base of a test frame. Ante- and retro-verting torques were applied to the femoral stem by screwing the stem (via a pair of through holes) to an axle, which was turned using a lever arm actuated by the test frame cross-head. The surface of each transverse section was serially digitally imaged during loading. The displacements of the stem, cement and bone were determined using digital image correlation. These data were then used to calculate the relative displacements across the interfaces. This method provides a path to more thorough understanding of load-transfer from femoral stem to femur.

Vacuum-mixing cement does not decrease overall porosity in cemented femoral stems

The role of vacuum mixing on the reduction of porosity and on the clinical performance of cemented total hip replacements remains uncertain. We have used paired femoral constructs prepared with either hand-mixed or vacuum-mixed cement in a cadaver model which simulated intra-operative conditions during cementing of the femoral component. After the cement had cured, the distribution of its porosity was determined, as was the strength of the cement-stem and cement-bone interfaces.

The overall fraction of the pore area was similar for both hand-mixed and vacuum-mixed cement (hand 6%; vacuum 5.7%; paired t-test, p = 0.187). The linear pore fractions at the interfaces were also similar for the two techniques. The pore number-density was much higher for the hand-mixed cement (paired t-test, p = 0.0013). The strength of the cement-stem interface was greater with the hand-mixed cement (paired t-test, p = 0.0005), while the strength of the cement-bone interface was not affected by the conditions of mixing (paired t-test, p = 0.275). The reduction in porosity with vacuum mixing did not affect the porosity of the mantle, but the distribution of the porosity can be affected by the technique of mixing used.

Vacuum-mixing cement does not decrease overall porosity in cemented femoral stems: an in vitro laboratory investigation

The role of vacuum mixing on the reduction of porosity and on the clinical performance of cemented total hip replacements remains uncertain. We have used paired femoral constructs prepared with either hand-mixed or vacuum-mixed cement in a cadaver model which simulated intra-operative conditions during cementing of the femoral component. After the cement had cured, the distribution of its porosity was determined, as was the strength of the cement-stem and cement-bone interfaces. The overall fraction of the pore area was similar for both hand-mixed and vacuum-mixed cement (hand 6%; vacuum 5.7%; paired t-test, p = 0.187). The linear pore fractions at the interfaces were also similar for the two techniques. The pore number-density was much higher for the hand-mixed cement (paired t-test, p = 0.0013). The strength of the cement-stem interface was greater with the hand-mixed cement (paired t-test, p = 0.0005), while the strength of the cement-bone interface was not affected by the conditions of mixing (paired t-test, p = 0.275). The reduction in porosity with vacuum mixing did not affect the porosity of the mantle, but the distribution of the porosity can be affected by the technique of mixing used.

Pharmacological and biological evaluation of a series of substituted 1,4-naphthoquinone bioreductive drugs

The indolequinone compound EO9 has good pharmacodynamic properties in terms of bioreductive activation and selectivity for either NAD(P)H:quinone oxidoreductase-1 (NQO1)-rich aerobic or NQO1-deficient hypoxic cells. However, its pharmacokinetic properties are poor and this fact is believed to be a major reason for EO9's lack of clinical efficacy. The purpose of this study was to develop quinone-based bioreductive drugs that retained EO9's good properties, in terms of bioreductive activation, but have improved pharmacokinetic properties. Out of 11 naphthoquinone compounds evaluated, 2-aziridinyl-5-hydroxy-1,4-naphthoquinone (compound 2), 2,3-bis(aziridinyl)-5-hydroxy-1,4-naphthoquinone (compound 3), and 2-aziridinyl-6-hydroxymethyl-1,4-naphthoquinone (compound 11) were selected for further evaluation based on good substrate specificity for NQO1 and selectivity towards NQO1-rich cells in vitro. Compound 3 was of particular interest as it also demonstrated selectivity for NQO1-rich cells under hypoxic conditions. Compound 3 was not metabolised by murine whole blood in vitro (in contrast to compounds 2, 11 and EO9) and pharmacokinetic studies in non-tumour-bearing mice in vivo (at the maximum soluble dose of 60 mg kg(-1) administered intraperitoneally) demonstrated significant improvements in plasma half-life (16.2 min) and AUC values (22.5 microM h) compared to EO9 (T(1/2) = 1.8 min, AUC = 0.184 microM h). Compound 3 also demonstrated significant anti-tumour activity against H460 and HCT-116 human tumour xenografts in vivo, whereas EO9 was inactive against these tumours. In conclusion, compound 3 is a promising lead compound that may target both aerobic and hypoxic fractions of NQO1-rich tumours and further studies to elucidate its mechanism of action and improve solubility are warranted.

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

The influence of surface roughness on stem-cement gaps

We have compared the interface morphology at the stem-cement interface of standard Charnley stems with a satin finish (Ra = 0.75 microm) with identical stems which had been grit-blasted over their proximal third (Ra = 5.3 microm) to promote a proximal bond. The stems were cemented into cadaver femora using conventional contemporary cementing techniques. After transverse sectioning, we determined the percentage of the perimeter of the stem which had a gap at the interface. There were substantial gaps (mean 31.4 +/- 17.1%) at the stem-cement interface in the grit-blasted region. This fraction was significantly (paired t-test, p = 0.0054) higher than that found around the contralateral satin-finished stems (mean 7.7 +/- 11.7%). Although studies of isolated metal-cement interfaces have shown that the bond strength can increase with surface roughness it cannot be assumed that this effect will be observed under clinical conditions.

The influence of surface roughness on stem-cement gaps

We have compared the interface morphology at the stem-cement interface of standard Charnley stems with a satin finish (Ra = 0.75 μm) with identical stems which had been grit-blasted over their proximal third (Ra = 5.3 μm) to promote a proximal bond. The stems were cemented into cadaver femora using conventional contemporary cementing techniques. After transverse sectioning, we determined the percentage of the perimeter of the stem which had a gap at the interface.

There were substantial gaps (mean 31.4 ± 17.1%) at the stem-cement interface in the grit-blasted region. This fraction was significantly (paired t-test, p = 0.0054) higher than that found around the contralateral satin-finished stems (mean 7.7 ± 11.7%). Although studies of isolated metal-cement interfaces have shown that the bond strength can increase with surface roughness it cannot be assumed that this effect will be observed under clinical conditions.

A comparative study of 'isometric' points for anterior cruciate ligament graft attachment

Anterior cruciate ligament (ACL) reconstruction depends critically on isometric graft placement. Unfortunately, different supposedly isometric points have been published, and no prior work has compared them to find out which are really isometric. The purpose of this study was to compare the isometry of previously published 'isometric' points for ACL reconstruction. The isometric points and knee loadings of previous studies were reproduced accurately in 12 fresh cadaveric knees. The length changes were measured through 140 degrees knee flexion, using an intra-articular suture attached to a displacement transducer. Six points had less than 1 mm length change and were located proximally in the natural ACL attachment at the posterior end of Blumensaat's line. The other seven points had length change patterns that would cause ACL graft tightening or slackening with knee flexion if they were used as the sites of bone tunnels for graft placement. This study confirms the existence of an isometric zone close to the posterior end of Blumensaat's line under several loading conditions. Other graft attachment points are less suitable for ACL reconstruction.

Effect of loading rate and hydration on the mechanical properties of the disc

STUDY DESIGN

The mechanical response of bovine intervertebral discs to axial compression at different loading rates and hydration levels was quantified.

OBJECTIVES

To quantify the effects of hydration and loading rate on the mechanical response of the intervertebral disc to compressive axial load.

SUMMARY OF BACKGROUND DATA

The disc is known to be viscoelastic, but there are few experimental data showing the effect of loading rate and hydration on its response to compression.

METHODS

Hydration level reduced by creep-loading from a fully hydrated starting point. Four groups were tested: Group A: fully hydrated (n = 5), six loading rates, from 0.3 kPa/sec to 30 MPa/sec; Group B: after 30 minutes of creep (n = 4); and Group C: after 2 hours of creep (n = 4) under a static load of 1 MPa, loading rates 3 MPa/sec, 30 kPa/sec, and 0.3 kPa/sec; Group D: at 5-minute intervals, during an 8-hour period of creep (n = 3) under a static load of 1 MPa, loading rate 3 MPa/sec. Data normalized by disc area and height: nominal stress, strain, and modulus calculated.

RESULTS

Group A: Modulus increased with load and rate of loading, with significant differences among the lower three loading rates. The highest three loading rates were significantly different from the lower rates, but not from each other. Group B: At the two higher loading rates, modulus was greater than in group A. At the lowest loading rate the modulus was similar to that in Group A. Group C: At the highest loading rate, the modulus was less than that of Groups A and B. At the lower two loading rates, the modulus was similar to that in Group A. Group D: The modulus increased in the first 30 minutes and decreased in the interval from 60 to 480 minutes.

CONCLUSIONS

Intervertebral disc compressive mechanical properties are significantly dependent on loading rate and hydration.

PCL reconstruction. In vitro biomechanical comparison of 'isometric' versus single and double-bundled 'anatomic' grafts

We compared the ability of three different posterior cruciate ligament (PCL) reconstructions to restore normal anteroposterior laxity to the knee from 0 to 130 degrees of knee flexion. Cadaver knees were tested intact, after PCL rupture or after bone-patellar tendon-bone grafting. Grafts were performed isometrically or with a single bundle representing the anatomical anterior PCL fibre bulk (aPC) or with a double bundle that added the posterior PCL fibre bulk (pPC). The grafts were tensioned to restore normal knee laxity at 60 degrees of flexion, except for the pPC which was tensioned at 130 degrees. The isometric graft led to overconstraint as the knee extended resulting in high graft tension in extension and excess laxity in flexion. The aPC graft matched normal laxity from 0 to 60 degrees of flexion but was lax from 90 to 130 degrees of flexion. Only the double-bundled graft could restore normal knee laxity across the full range of flexion.

PCL reconstruction

We compared the ability of three different posterior cruciate ligament (PCL) reconstructions to restore normal anteroposterior laxity to the knee from 0 to 130° of knee flexion.

Cadaver knees were tested intact, after PCL rupture or after bone-patellar tendon-bone grafting. Grafts were performed isometrically or with a single bundle representing the anatomical anterior PCL fibre bulk (aPC) or with a double bundle that added the posterior PCL fibre bulk (pPC). The grafts were tensioned to restore normal knee laxity at 60° of flexion, except for the pPC which was tensioned at 130°.

The isometric graft led to overconstraint as the knee extended resulting in high graft tension in extension and excess laxity in flexion. The aPC graft matched normal laxity from 0 to 60° of flexion but was lax from 90 to 130° of flexion. Only the double-bundled graft could restore normal knee laxity across the full range of flexion.

Cross-sectional area measurement of soft tissue. A new casting method

A new replica moulding technique for determining cross-sectional area has been developed. The accuracy of this technique has been investigated. Comparisons have been made with the area micrometer and the laser micrometer to establish the relative accuracy of each technique. The replica technique systematically underestimated the cross-sectional area by 6.2%. However, when this shrinkage artefact was corrected for, the residual error was +/- 1.8%. Relative to the corrected replica method, it was calculated that the area micrometer underestimated cross-sectional area by 16.2 +/- 6.9% (SD) and that the assumption of a convex cross-section would have caused the laser micrometer to overestimate cross-sectional area by an average of 2.3 +/- 1.5% (SD) for tendon, 4.7 +/- 2.5% for 'round' ligament specimens and 19.1 +/- 6.4% for cruciate ligament bundles with obvious concavities in their cross-sections. The moulding method was thought to be particularly useful for soft tissue specimens with irregular cross-sections.

Loading of the two bundles of the posterior cruciate ligament: an analysis of bundle function in a-P drawer

The purpose of this study was to clarify the role of the posterior cruciate ligament (PCL) in posterior drawer and to test the hypothesis that the anterolateral (aPC) and the posteromedial (pPC) bundles have different functions over the range of flexion. Selective cutting was utilised to determine percentage contributions to resisting posterior drawer. At lower flexion angles the primary restraint to posterior drawer was not the PCL but combined secondary structures. The percentage contribution of the combined secondary structures dropped below 50% at 30, 20 and 15 degrees of flexion for 2, 4 and 6 mm displacement respectively. In the midrange of flexion (40-120 degrees) the aPC was the primary restraint as it resisted between 50 and 75% of posterior drawer force. Towards full flexion the contribution of the aPC reduced, while the contribution of the pPC approximately doubled from extension to full flexion. This resulted in equal contributions from the aPC and pPC at full flexion for 2 and 4 mm displacement. For 6 mm displacement the percentage contribution of the pPC rose from 23% at extension to 57% of the total restraint at 130 degrees of flexion when it exceeded the 36% contribution of the aPC, although not significantly (p = 0.053).

The mechanical properties of the two bundles of the human posterior cruciate ligament

Successful reconstruction of ligaments requires knowledge of the properties of the intact ligament. This study examined the strength of the human posterior cruciate ligament (PCL), treating it as two separate fibre bundles. It was hypothesized (i) that the mechanical and material properties of the anterolateral (aPC) and the posteromedial (pPC) bundles of the PCL were significantly different and (ii) that previous studies have underestimated the strength of the whole PCL. The properties of the two bundles were measured in 10 donors (53-98 yr). The mechanical and material properties of the two bundles were found to be significantly different, the aPC was six times as strong as the pPC. The aPC had a mean strength of 1.6 kN. Allowing for age effects this study suggests that the strength of the PCL in young active people is 4 kN, which is higher than that suggested by previous studies. Because of the difference in the strengths of the two bundles, we conclude that the aPC is primarily responsible for the stabilising effect of the PCL. We therefore recommend that PCL reconstructions should be centered on the middle of the aPC bundle.