Decellularised porcine superflexor tendon (pSFT) has been demonstrated to be a suitable scaffold for anterior cruciate ligament reconstruction[1]. While the role of collagen in tendons is well known, the mechanical role of glycosaminoglycans (GAGs) is less clear and may be altered by the decellularisation process.

To determine the effects of decellularisation on pSFT GAG content and mechanical function and to investigate the consequences of GAG loss in tensile and compressive loading.

pSFTs were decellularised following previous techniques [2]. For GAG removal, native pSFTs were treated with chondroitinase ABC (ChABC; 0.1U/mL, 72h). Cell and GAG removal was validated using histology and quantitative assays. Native, decellularised and ChABC treated groups (n=6) were biomechanically characterised. In tension, specimens underwent stress relaxation and strength testing using previous protocols [1]. Stress relaxation data was fitted to a modified Maxwell-Weichert model to determine time-dependent (E1 & E2) and time-independent moduli (E0). The toe and linear region moduli (Etoe, Elinear), in addition to tensile strength (UTS) and failure strain were determined from strength testing. In compression, specimens underwent confined loading conditions (ramp at 10 s-1 to 10% strain and hold). The aggregate modulus (HA) and zero-strain permeability (k0) were determined using previous techniques [3]. Data was analysed by one-way ANOVA with Tukey post-hoc test to determine significant differences between test groups (p<0.05).

Quantitative assays showed no GAG reduction post-decellularisation, but a significant reduction after ChABC treatment. HA was only significantly reduced in the ChABC group. k0 was significantly higher for the ChABC group compared to decellularised. E0 was significantly reduced in the decellularised group compared to native and ChABC groups, while E1 and E2 were not different between groups. Etoe, Elinear, UTS and failure strain were not different between groups.

Decellularisation does not affect GAG content or impair mechanical function in pSFT. GAG loss adversely affects pSFT compressive properties, revealing major mechanical contribution under compression, but no significant role under tension.

Patients with osteoarthritis (OA) of the knee commonly alter their movement to compensate for deficiencies. This study presents a new numerical procedure for classifying sit-to-walk (STW) movement strategies.

Ten control and twelve OA participants performed the STW task in a motion capture laboratory. A full body biomechanical model was used. Participants were instructed to sit in a comfortable self-selected position on a stool height adjusted to 100% of their knee height and then stand and pick up an object from a table in front of them. Three matrices were constructed defining the progression of the torso, feet and hands in the sagittal plane along with a fourth expressing the location of the hands relative to the knees. Hierarchical clustering (HC) was used to identify different strategies. Trials were also classified as to whether the left (L) and right (R) extremities used a matching strategy (bilateral) or not (asymmetrical). Fisher's exact test was used to compare this between groups.

Clustering of the torso matrix dichotomised the trials in two major clusters; subjects leaning forward (LF) or not. The feet and hands matrices revealed sliding the foot backward (FB) and moving an arm forward (AF) strategies respectively. Trials not belonging in the AF cluster were submitted to the last HC of the fourth matrix exposing three additional strategies, the arm pushing through chair (PC), arm pushing through knee (PK) and arm not used (NA). The control participants used the LF+FBR+PK combination most frequently whereas the OA participants used the AFR+PCL. OA patients used significantly more asymmetrical arm strategies, p=0.034.

The results demonstrated that control and OA participants favour different STW strategies. The OA patients asymmetrical arm behaviour possibly indicates compensating for weakness of the affected leg. These strategy definitions may be useful to assess post-operative outcomes and rehabilitation progress.

Extracorporeal irradiation and re-implantation of a bone segment is a technique employed in bone sarcoma surgery for limb salvage in the setting of reasonable bone stock. There is neither consensus nor rationale given for the dosage of irradiation used in previous studies, with values of up to 300Gy applied. We investigated the influence of extracorporeal irradiation on the elastic and viscoelastic properties of bone. Bone specimens were extracted from mature cattle and subdivided into thirteen groups; twelve groups exposed to increasing levels of irradiation and a control group. The specimens, once irradiated, underwent mechanical testing in saline at 37°C.

Mechanical properties were calculated by experimental means which included Young's Modulus, Storage Modulus and Loss Modulus. These were all obtained for comparison of the irradiated specimens to the control group.

There were non-significant negligible changes in all of the mechanical properties of bone that were assessed with increasing dosage of irradiation. Therefore, we conclude that the overall mechanical effect of high levels of extracorporeal irradiation (300Gy) is minute, and can be administered to reduce the risk of malignancy recurrence.

Summary Statement

Uptake of robotically-assisted orthopaedic surgery may be limited by a perceived steep learning curve. We quantified the technological learning curve and 5 surgeries were found to bring operating times to appropriate levels. Implant positioning was as planned from the outset.

This study aimed to overcome the subjective nature of routine assessment of knee laxity and develop a repeatable, objective method using a hand-held force application device (FAD).

Eighteen clinicians (physiotherapists, consultants, trainees) volunteered to measure the coronal angular deviation of the right knee of a healthy volunteer using a validated non-invasive infrared measuring system. Effort was taken to ensure the knee flexion angle (∼2°) and hand positions were constant during testing. Three varus and valgus stress tests were conducted, in which maximum angular deviation was determined and subsequently averaged, in the following order of conditions: manual stress without the FAD up to a perceived end-point (before); with the FAD to apply a moment of 18 Nm; and again without the FAD (after). A repeated measures ANOVA was used to analyse the results.

All three groups of clinicians produced measurements of valgus laxity with consistent mean values and standard deviations (<1°) for each condition. For varus mean values were consistent but standard deviations were larger.

Valgus deviations varied significantly between conditions (p < 0.01), with deviations achieved using the FAD greater than both before (p < 0.01) and after (p < 0.05) indicating that the perceived endpoints were less than that achieved at 18 Nm. However varus perceived endpoints were no different to that achieved at 18 Nm, suggesting that clinicians usually apply a greater valgus moment than varus. Furthermore, the non-significant increase in valgus deviation between before and after (p = 0.123) is suggestive of a training trend, especially for trainees.

Our standardised knee laxity assessment may have a role in improving the balancing techniques of TKA and the diagnosis of collateral ligament injuries. Also, by quantifying the technique of senior clinicians, and with use of the FAD, the perceptive skills of more junior trainees may be enhanced.

Knee alignment is a fundamental measurement in the assessment, monitoring and surgical management of patients with OA. In spite of extensive research into the consequences of malalignment, there is a lack of data regarding the potential variation between supine and standing (functional) conditions. The purpose of this study was to explore this relationship in asymptomatic, osteoarthritic and prosthetic knees. Our hypothesis was that the change in alignment of these three groups would be different.

Infrared position capture was used to assess knee alignment for 30 asymptomatic controls and 31 patients with OA, before and after TKA. Coronal and sagittal mechanical femorotibial (MFT) angles in extension (negative values varus/hyperextension) were measured supine and in bi-pedal stance and changes analysed using a paired t-test. To quantify this change in 3D, vector plots of ankle centre displacement relative to the knee centre were produced.

Alignment in both planes changed significantly from supine to standing for all three groups, most frequently towards relative varus and extension. In the coronal plane, the mean±SD(°) of the supine/standing MFT angles was 0.1±2.5/−1.1±3.7 for asymptomatic (p=0.001), −2.5±5.7/−3.6±6.0 for osteoarthritic (p=0.009) and −0.7±1.4/ −2.5±2.0 for prosthetic knees (p<0.001). In the sagittal plane, the mean±SD(°) of the supine/standing MFT angles was −1.7±3.3/−5.5±4.9 for asymptomatic (p<0.001), 7.7±7.1/1.8±7.7 for osteoarthritic (p<0.001) and 6.8±5.1/1.4±7.6 for prosthetic knees (p<0.001). The vector plots showed that the trend of relative varus and extension in stance was similar in overall magnitude and direction between the groups.

The similarities between each group did not support our hypothesis. The consistent kinematic pattern for different knee types suggests that soft tissue restraints rather than underlying joint deformity may be more influential in dynamic control of alignment from lying to standing. This potential change should be considered when positioning TKA components on supine limbs as post-operative functional alignment may be different.

Assessment of coronal knee laxity via manual stress testing is commonly performed during joint examination. While it is generally accepted that the knee should be flexed slightly to assess its collateral restraints, the importance of the exact degree of flexion at time of testing has not been documented. The aim of this study therefore was to assess the effect of differing degrees of knee flexion on the magnitude of coronal deflection observed during collateral stress testing.

Using non-invasive infrared technology, the real-time coronal and sagittal mechanical femorotibial (MFT) angles of three asymptomatic volunteers were measured. A single examiner, blinded to the real-time display of coronal but not sagittal alignment, held the knee in maximum extension and performed manual varus and valgus stress manoeuvres to a perceived end-point. This sequence was repeated at 5° increments up to 30° of flexion. This provided unstressed, varus and valgus coronal alignment measurements as well as overall envelope of laxity (valgus angle – varus angle) which were subsequently regressed against knee flexion.

Regression analysis indicated that all regression coefficients were significantly different to zero (p < 0.001). With increasing knee flexion, valgus MFT angles became more valgus and varus MFT angles became more. The overall laxity of the knee in the coronal plane increased approximately fourfold with 30° of knee flexion.

The results demonstrated that small changes in knee flexion could result in significant changes in coronal knee laxity, an observation which has important clinical relevance and applications. For example the assessment of medial collateral ligament (MCL) injuries can be based on the perceived amount of joint opening with no reference made to knee flexion at time of assessment. Therefore, close attention should be paid to the flexion angle of the knee during stress testing in order to achieve a reliable and reproducible assessment.