Imperial College London

ProfessorAndrewAmis

Faculty of EngineeringDepartment of Mechanical Engineering

Professor
 
 
 
//

Contact

 

+44 (0)7722 225 409a.amis

 
 
//

Assistant

 

Ms Fabienne Laperche +44 (0)20 7594 7033

 
//

Location

 

713City and Guilds BuildingSouth Kensington Campus

//

Summary

 

Publications

Publication Type
Year
to

470 results found

Shatrov J, Bonacic Bartolin P, Holthof SR, Ball S, Williams A, Amis AAet al., 2024, A Comparative Biomechanical Study of Alternative Medial Collateral Ligament Reconstruction Techniques., Am J Sports Med

BACKGROUND: There is little evidence of the biomechanical performance of medial collateral ligament (MCL) reconstructions for restoring stability to the MCL-deficient knee regarding valgus, external rotation (ER), and anteromedial rotatory instability (AMRI). HYPOTHESIS: A short isometric reconstruction will better restore stability than a longer superficial MCL (sMCL) reconstruction, and an additional deep MCL (dMCL) graft will better control ER and AMRI than single-strand reconstructions. STUDY DESIGN: Controlled laboratory study. METHODS: Nine cadaveric human knees were tested in a kinematics rig that allowed tibial loading while the knee was flexed-extended 0° to 100°. Optical markers were placed on the femur and tibia and displacements were measured using a stereo camera system. The knee was tested intact, and then after MCL (sMCL + dMCL) transection, and loaded in anterior tibial translation (ATT), ER, varus-valgus, and combined ATT + ER (AMRI loading). Five different isometric MCL reconstructions were tested: isolated long sMCL, a short construct, each with and without dMCL addition, and isolated dMCL reconstruction, using an 8 mm-wide synthetic graft. RESULTS: MCL deficiency caused an increase in ER of 4° at 0° of flexion (P = .271) up to 14° at 100° of flexion (P = .002), and valgus laxity increased by 5° to 8° between 0° and 100° of flexion (P < .024 at 0°-90°). ATT did not increase significantly in isolated MCL deficiency (P > .999). All 5 reconstructions restored native stability across the arc of flexion apart from the isolated long sMCL, which demonstrated residual ER instability (P≤ .047 vs other reconstructions). CONCLUSION: All tested techniques apart from the isolated long sMCL graft are satisfactory in the context of restoring the valgus, ER, and AMRI stability to the MCL-deficient knee in a cadaveric model. CLINICAL RELEVANCE: Contemporary MCL reconstruction techniques fail to control ER an

Journal article

Stoddart J, Garner A, Tuncer M, Amis A, Cobb J, van Arkel RJet al., 2024, Load transfer in bone after partial, multi-compartmental, and total knee arthroplasty, Frontiers in Bioengineering and Biotechnology, Vol: 12, ISSN: 2296-4185

Introduction: Arthroplasty-associated bone loss remains a clinical problem: stiff metallic implants disrupt load transfer to bone and hence its remodeling stimulus. The aim of this research was to analyze how load transfer to bone is affected by different forms of knee arthroplasty: isolated partial knee arthroplasty (PKA), compartmental arthroplasty (CPKA, two or more PKAs in the same knee) and total knee arthroplasty (TKA). Methods: An experimentally validated subject-specific finite element model was analyzed native, and with medial unicondylar, lateral unicondylar, patellofemoral, biunicondylar, medial bicompartmental, lateral bicompartmental, tricompartmental and total knee arthroplasty. Three load cases were simulated for each: gait, stair ascent and sit-to-stand. Strain shielding and overstraining were calculated from the differences between the native and implanted states. Results: For gait, the TKA femoral component led to mean strain shielding (30%) more than three times higher than PKA (4% to 7%) and CPKA (5% to 8%). Overstraining was predicted in the proximal tibia (TKA 21%, PKA/CPKA 0 to 6%). The variance in the distribution for TKA was an order of magnitude greater than for PKA/CPKA indicating less physiological load transfer. Only the TKA-implanted femur was sensitive to load case: for stair ascent and gait, almost the entire distal femur was strain-shielded, whereas during sit-to-stand the posterior femoral condyles were overstrained. Discussion: TKA requires more bone resection than PKA and CPKA. These finite element analyses suggest that a longer-term benefit for bone is probable as partial and multicompartmental knee procedures lead to more natural load transfer compared to TKA. High-flexion activity following TKA may be protective of posterior condyle bone resorption, which may help explain why bone loss affects some patients more than others. The male and female intact bone models are included as supplementary material.

Journal article

Borque KA, Han S, Dunbar NJ, Lanfermeijer ND, Sij EW, Gold JE, Ismaily SK, Amis AA, Laughlin MS, Kraeutler MJ, Williams A, Lowe WR, Noble Pet al., 2024, Single-Strand "Short Isometric Construct" Medial Collateral Ligament Reconstruction Restores Valgus and Rotational Stability While Isolated Deep MCL and Superficial MCL Reconstruction Do Not., Am J Sports Med, Vol: 52, Pages: 968-976

BACKGROUND: Historical MCL (medial collateral ligament) reconstruction (MCLR) techniques have focused on the superficial MCL (sMCL) to restore valgus stability while frequently ignoring the importance of the deep MCL (dMCL) in controlling tibial external rotation. The recent recognition of the medial ligament complex importance has multiple studies revisiting medial anatomy and questioning contemporary MCLR techniques. PURPOSE: To assess whether (1) an isolated sMCL reconstruction (sMCLR), (2) an isolated dMCL reconstruction (dMCLR), or (3) a novel single-strand short isometric construct (SIC) would restore translational and rotational stability to a knee with a dMCL and sMCL injury. STUDY DESIGN: Controlled laboratory study. METHODS: Biomechanical testing was performed on 14 fresh-frozen cadaveric knee specimens using a custom multiaxial knee activity simulator. The specimens were divided into 2 groups. The first group was tested in 4 states: intact, after sectioning the sMCL and dMCL, isolated sMCLR, and isolated dMCLR. The second group was tested in 3 states: intact, after sectioning the sMCL and dMCL, and after single-strand SIC reconstruction (SICR). In each state, 4 loading conditions were applied at 0°, 20°, 40°, 60°, and 90° of knee flexion: 8-N·m valgus torque, 5-N·m external rotation torque, 90-N anterior drawer, and combined 90-N anterior drawer plus 5-N·m tibial external rotation torque. Anterior translation, valgus rotation, and external rotation of the knee were measured for each state and loading condition using an optical motion capture system. RESULTS: sMCL and dMCL transection resulted in increased laxity for all loading conditions at all flexion angles. Isolated dMCLR restored external rotation stability to intact levels throughout all degrees of flexion, yet valgus stability was restored only at 0° of flexion. Isolated sMCLR restored valgus and external rotation stability at 0°, 20°, and 40°

Journal article

Adam NC, Smith CR, Herzog W, Amis AA, Arampatzis A, Taylor WRet al., 2023, In Vivo Strain Patterns in the Achilles Tendon During Dynamic Activities: A Comprehensive Survey of the Literature, SPORTS MEDICINE-OPEN, Vol: 9, ISSN: 2199-1170

Journal article

Willinger L, Athwal KK, Holthof S, Imhoff AB, Williams A, Amis AAet al., 2023, Anterolateral rotational instability Anterior cruciate ligament, anterolateral complex or lateral meniscus?, ARTHROSKOPIE, ISSN: 0933-7946

Journal article

Bartolo MK, Newman S, Dandridge O, Provaggi E, Accardi MA, Dini D, Amis Aet al., 2023, Ovine knee kinematics and contact pressures of a novel fibre matrix-reinforced hydrogel total meniscus replacement, Orthopaedic Proceedings, Vol: 105-B, Pages: 14-14

Journal article

Willinger L, Athwal KK, Holthof S, Imhoff AB, Williams A, Amis AAet al., 2023, Role of the anterior cruciate ligament, anterolateral complex, and lateral meniscus posterior root in anterolateral rotatory knee instability: a biomechanical study, American Journal of Sports Medicine, Vol: 51, Pages: 1136-1145, ISSN: 0363-5465

BACKGROUND: Injuries to the anterior cruciate ligament (ACL), Kaplan fibers (KFs), anterolateral capsule/ligament (C/ALL), and lateral meniscus posterior root (LMPR) have been separately linked to anterolateral instability. PURPOSE: To investigate the contributions of the ACL, KFs, C/ALL, and LMPR to knee stability and to measure instabilities resulting from their injury. STUDY DESIGN: Controlled laboratory study. METHODS: Ten fresh-frozen human knees were tested robotically to determine restraints of knee laxity at 0° to 90° of flexion. An 88-N anterior-posterior force (anterior and posterior tibial translation), 5-N·m internal-external rotation, and 8-N·m valgus-varus torque were imposed and intact kinematics recorded. The kinematics were replayed after sequentially cutting the structures (order varied) to calculate their contributions to stability. Another 10 knees were tested in a kinematics rig with optical tracking to measure instabilities after sequentially cutting the structures across 0° to 100° of flexion. One- and 2-way repeated-measures analyses of variance with Bonferroni correction were used to find significance (P < .05) for the robotic and kinematics tests. RESULTS: The ACL was the primary restraint for anterior tibial translation; other structures were insignificant (<10% contribution). The KFs and C/ALL resisted internal rotation, reaching 44% ± 23% (mean ± SD; P < .01) and 14% ± 13% (P < .05) at 90°. The LMPR resisted valgus but not internal rotation. Anterior tibial translation increased after ACL transection (P < .001) and after cutting the lateral structures from 70° to 100° (P < .05). Pivot-shift loading increased anterolateral rotational instability after ACL transection from 0° to 40° (P < .05) and further after cutting the lateral structures from 0° to 100° (P < .01). CONCLUSION: The anterolateral complex acts as a functional unit to provi

Journal article

Borque KA, Ball S, Sij E, Amis AA, Laughlin MS, Jones M, Williams Aet al., 2023, A "Short Isometric Construct" Reconstruction Technique for the Medial Collateral Ligament of the Knee, ARTHROSCOPY TECHNIQUES, Vol: 12, Pages: E167-E171, ISSN: 2212-6287

Journal article

Miyaji N, Holthof SR, Ball SV, Williams A, Amis AAet al., 2022, Medial collateral ligament reconstruction for anteromedial instability of the knee: a biomechanical study in vitro., American Journal of Sports Medicine, Vol: 50, Pages: 1823-1831, ISSN: 0363-5465

BACKGROUND: Although a medial collateral ligament (MCL) injury is associated with anteromedial rotatory instability (AMRI) and often with an anterior cruciate ligament (ACL) injury, there has been little work to develop anteromedial (AM) reconstruction to address this laxity. PURPOSE: To measure the ability of a novel "anatomic" AM reconstruction technique to restore native knee laxity for isolated AM insufficiency and combined AM plus posteromedial insufficiency. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 12 cadaveric knees were mounted in a kinematic testing rig that allowed the tibia to be loaded while the knee flexed-extended 0° to 100° with 88-N anteroposterior translation, 5-N·m internal rotation-external rotation (ER), 8-N·m valgus, and combined anterior translation plus ER to simulate AMRI. Joint motion was measured using optical trackers with the knee intact, after superficial MCL (sMCL) and deep MCL (dMCL) transection, and after AM reconstruction of the sMCL and dMCL with semitendinosus autografts. The posteromedial capsule (PMC)/posterior oblique ligament (POL) was then transected to induce a grade 3 medial injury, and kinematic measurements were repeated afterward and again after removing the grafts. Laxity changes were examined using repeated-measures analysis of variance and post-testing. RESULTS: sMCL and dMCL deficiency increased valgus, ER, and AMRI laxities. These laxities did not differ from native values after AM reconstruction. Additional PMC/POL deficiency did not increase these laxities significantly but did increase internal rotation laxity near knee extension; this was not controlled by AM reconstruction. CONCLUSION: AM reconstruction eliminated AMRI after transection of the dMCL and sMCL, and also eliminated AMRI after additional PMC/POL transection. CLINICAL RELEVANCE: Many MCL injuries occur in combination with ACL injuries, causing AMRI. These injuries may rupture the AM capsule and dMC

Journal article

Miyaji N, Holthof SR, Bastos RPS, Ball SV, Espregueira-Mendes J, Williams A, Amis AAet al., 2022, A triple-strand anatomic medial collateral ligament reconstruction restores knee stability more completely than a double-strand reconstruction: a biomechanical study in vitro., American Journal of Sports Medicine, Vol: 50, ISSN: 0363-5465

BACKGROUND: There are many descriptions of medial collateral ligament (MCL) reconstruction, but they may not reproduce the anatomic structures and there is little evidence of their biomechanical performance. PURPOSE: To investigate the ability of "anatomic" MCL reconstruction to restore native stability after grade III MCL plus posteromedial capsule/posterior oblique ligament injuries in vitro. STUDY DESIGN: Controlled laboratory study. METHODS: Twelve cadaveric knees were mounted in a kinematic testing rig to impose tibial displacing loads while the knee was flexed-extended: 88-N anteroposterior translation, 5-N·m internal-external rotation, 8-N·m valgus-varus, and combined anterior translation plus external rotation (anteromedial rotatory instability). Joint motion was measured via optical trackers with the knee intact; after superficial MCL (sMCL), deep MCL (dMCL), and posterior oblique ligament transection; and then after MCL double- and triple-strand reconstructions. Double strands reproduced the sMCL and posterior oblique ligament and triple-strands the sMCL, dMCL, and posterior oblique ligament. The sMCL was placed 5 mm posterior to the epicondyle in the double-strand technique and at the epicondyle in the triple-strand technique. Kinematic changes were examined by repeated measures 2-way analysis of variance with posttesting. RESULTS: Transection of the sMCL, dMCL, and posterior oblique ligament increased valgus rotation (5° mean) and external rotation (9° mean). The double-strand reconstruction controlled valgus in extension but allowed 5° excess valgus in flexion and did not restore external rotation (7° excess). The triple-strand reconstruction restored both external rotation and valgus throughout flexion. CONCLUSION: In a cadaveric model, a triple-strand reconstruction including a dMCL graft restored native external rotation, while a double-strand reconstruction without a dMCL graft did not. A reconstruction with t

Journal article

Dandridge O, Garner A, Amis A, Cobb J, van Arkel RJet al., 2022, Variation in the patellar tendon moment arm identified with an improved measurement framework, Journal of Orthopaedic Research, Vol: 40, Pages: 799-807, ISSN: 0736-0266

The mechanical advantage of the knee extensor mechanism depends heavily on the patellar tendon moment arm (PTMA). Understanding which factors contribute to its variation may help improve functional outcomes following arthroplasty. This study optimized PTMA measurement, allowing us to quantify the contribution of different variables. The PTMA was calculated about the instantaneous helical axis of tibiofemoral rotation from optical tracked kinematics. A fabricated knee model facilitated calculation optimization, comparing four data smoothing techniques (raw, Butterworth filtering, generalized cross-validated cubic spline-interpolation and combined filtering/interpolation). The PTMA was then measured for 24 fresh-frozen cadaveric knees, under physiologically based loading and extension rates. Combined filtering/interpolation enabled sub-mm PTMA calculation accuracy throughout the range of motion (root-mean-squared error 0.2 mm, max error 0.4 mm), whereas large errors were measured for raw, filtered-only and interpolated-only techniques at terminal flexion/extension. Before scaling, the mean PTMA was 46 mm; PTMA magnitude was consistently larger in males (mean differences: 5 to 10 mm, p < .05) and was strongly related to knee size: larger knees have a larger PTMA. However, while scaling eliminated sex differences in PTMA magnitude, the peak PTMA occurred closer to terminal extension in females (female 15°, male 29°, p = .01). Knee size accounted for two-thirds of the variation in PTMA magnitude, but not the flexion angle where peak PTMA occurred. This substantial variation in angle of peak PTMA has implications for the design of musculoskeletal models and morphotype-specific arthroplasty. The developed calculation framework is applicable both in vivo and vitro for accurate PTMA measurement.

Journal article

Marsland D, Morris AM, Gould AER, Calder JDF, Amis AAet al., 2022, Systematic review of tendon transfers in the foot and ankle using interference screw fixation: Outcomes and safety of early versus standard postoperative rehabilitation, Foot and Ankle Surgery, Vol: 28, Pages: 166-175, ISSN: 1268-7731

AIMS: To compare the outcomes of early and standard rehabilitation protocols following tendon transfers in the foot and ankle using interference screw fixation (ISF). METHODS: A systematic review was performed for relevant articles (1998 to 2020) reporting foot tendon transfer using ISF in adults. The primary outcome was early tendon failure. Secondary outcomes included function and complications. RESULTS: In total, 21 studies met the inclusion criteria, totalling 494 patients. Seven studies reported early rehabilitation protocols. The rate of early tendon failure was zero for each protocol and studies consistently reported a significant improvement in function. No differences were found comparing different rehabilitation protocols for tendon transfer for Achilles tendon pathology and foot drop. CONCLUSION: Both early and standard rehabilitation protocols are associated with high patient satisfaction and low complication rates, but currently there is a lack of evidence to support early loaded activities or motion. LEVEL OF EVIDENCE: IV Systematic review including case series.

Journal article

Dandridge O, Garner A, Jeffers JRT, Amis AA, Cobb JP, van Arkel RJet al., 2021, Validity of repeated-measures analyses of in vitro arthroplasty kinematics and kinetics, Journal of Biomechanics, Vol: 129, Pages: 1-5, ISSN: 0021-9290

In vitro models of arthroplasty enable pre-clinical testing and inform clinical decision making. Repeated-measures comparisons maximise resource efficiency, but their validity without testing order randomisation is not known. This study aimed to identify if there were any large testing order effects for cadaveric models of knee and hip arthroplasty. First, the effect of testing order on total knee arthroplasty (TKA) biomechanics was assessed. Extension moments for TKAs (N=3) implanted into the native knee (TKA-only) were compared to a dataset of TKAs (N=24) tested after different combinations of partial knee arthroplasty (TKA-last). The effect of repeatedly testing the same knee five times over 36 hours on patellofemoral and tibiofemoral kinematics was also quantified. Second, the effect of testing order on capsular ligament function after total hip arthroplasty (THA) was assessed. Randomisation was removed from a previously published dataset to create increasing and decreasing head size groups, which were compared with t-tests.All three TKA-only extension moments fell within the 95% CI of the TKA-last knees across the full range of knee flexion/extension. Repeated testing resulted in root-mean-squared kinematics errors within 1 mm, 1°, or < 5 % of total range of motion. Following THA, smaller head-size resulted in greater laxity in both the increasing (p=0.01) and decreasing (p<0.001) groups. Testing order did not have large effects on either knee or hip arthroplasty biomechanics measured with in vitro cadaveric models.

Journal article

Garner A, Dandridge O, Amis A, Cobb J, van Arkel RJet al., 2021, Bi-unicondylar arthroplasty: a biomechanics and clinical outcomes study, Bone & Joint Research, Vol: 10, Pages: 723-733, ISSN: 2046-3758

Aims Bi-Unicondylar Arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL) preserving alternative to Total Knee Arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA. Methods Bi-UKA subjects (N = 22) were measured on an instrumented treadmill, using standard gait metrics, at top walking speeds. Age, sex and BMI-matched healthy (N = 24) and primary TKA (N = 22) subjects formed control groups. TKA subjects with pre-operative patellofemoral or tricompartmental arthritis or ACL dysfunction were excluded. The Oxford Knee Score (OKS) and EuroQol-5D (EQ-5D) were compared. Bi-UKA then TKA were performed on eight fresh frozen cadaveric knees, to investigate knee extensor efficiency under controlled laboratory conditions, using a repeated measures study design. Results Bi-UKA walked 20% faster than TKA (Bi-UKA 6.70.9km/h, TKA 5.60.7km/h p<0.001), exhibiting nearer-normal vertical Ground Reaction Forces in maximum weight-acceptance and mid-stance, with longer step and stride lengths compared to TKA (p<0.05). Bi-UKAsubjects reported higher OKS (p=0.004) and EQ-5D (p<0.001). In vitro, Bi-UKA generated the same extensor moment as native knees at low flexion angles, whilst reduced extensor moment was measured following TKA (p<0.003). Conversely, at higher flexion angles, the extensor moment of TKA was normal. Over the full range, the extensor mechanism was more efficient following Bi-UKA than TKA (p<0.05). Conclusion Bi-UKA had more normal gait characteristics and improved patient reported outcomes, compared to matched TKA subjects. This can, in part, be explained by differences in extensor efficiency.

Journal article

Garner A, Dandridge O, Amis A, Cobb J, van Arkel Ret al., 2021, Partial and combined partial knee arthroplasty: greater anterior-posterior stability than posterior-cruciate retaining total knee arthroplasty, The Journal of Arthroplasty, Vol: 36, Pages: 3765-3772.e4, ISSN: 0883-5403

BackgroundLittle is known regarding anterior-posterior stability after anterior cruciate ligament–preserving partial (PKA) and combined partial knee arthroplasty (CPKA) compared to standard posterior cruciate–retaining total knee arthroplasty (TKA).MethodsThe anterior-posterior tibial translation of twenty-four cadaveric knees was measured, with optical tracking, while under 90N drawer with the knee flexed 0-90°. Knees were tested before and after PKA, CPKA (medial and lateral bicompartmental and bi-unicondylar), and then posterior cruciate–retaining TKA. The anterior-posterior tibial translations of the arthroplasty states, at each flexion angle, were compared to the native knee and each other with repeated measures analyses of variance and post-hoc t-tests.ResultsUnicompartmental and bicompartmental arthroplasty states had similar laxities to the native knee and to each other, with ≤1-mm differences throughout the flexion range (P ≥ .199). Bi-unicondylar arthroplasty resulted in 6- to 8-mm increase of anterior tibial translation at high flexion angles compared to the native knee (P ≤ .023 at 80-90°). Meanwhile, TKA exhibited increased laxity across all flexion angles, with increased anterior tibial translation of up to 18 ± 6 mm (P < .001) and increased posterior translation of up to 4 ± 2 mm (P < .001).ConclusionsIn a cadaveric study, anterior-posterior tibial translation did not differ from native laxity after PKA and CPKA. Posterior cruciate ligament–preserving TKA demonstrated increased laxity, particularly in anterior tibial translation.

Journal article

Amis A, Bartolo MK, Accardi M, Williams A, Newman S, Provaggi E, Dini D, Athwal Ket al., 2021, Strength of interference screw fixation of meniscus prosthesis matches native meniscus attachments, Knee Surgery Sports Traumatology Arthroscopy, Vol: 30, ISSN: 0942-2056

PurposeMeniscal surgery is one of the most common orthopaedic surgical interventions. Total meniscus replacements have been proposed as a solution for patients with irreparable meniscal injuries. Reliable fixation is crucial for the success and functionality of such implants. The aim of this study was to characterise an interference screw fixation system developed for a novel fibre-matrix-reinforced synthetic total meniscus replacement in an ovine cadaveric model.MethodsTextile straps were tested in tension to failure (n = 15) and in cyclic tension (70–220 N) for 1000 cycles (n = 5). The textile strap-interference screw fixation system was tested in 4.5 mm-diameter single anterior and double posterior tunnels in North of England Mule ovine tibias aged > 2 years using titanium alloy (Ti6Al4Va) and polyether-ether-ketone (PEEK) screws (n ≥ 5). Straps were preconditioned, dynamically loaded for 1000 cycles in tension (70–220 N), the fixation slippage under cyclic loading was measured, and then pulled to failure.ResultsStrap stiffness was at least 12 times that recorded for human meniscal roots. Strap creep strain at the maximum load (220 N) was 0.005 following 1000 cycles. For all tunnels, pull-out failure resulted from textile strap slippage or bone fracture rather than strap rupture, which demonstrated that the textile strap was comparatively stronger than the interference screw fixation system. Pull-out load (anterior 544 ± 119 N; posterior 889 ± 157 N) was comparable to human meniscal root strength. Fixation slippage was within the acceptable range for anterior cruciate ligament graft reconstruction (anterior 1.9 ± 0.7 mm; posterior 1.9 ± 0.5 mm).ConclusionThese findings show that the textile attachment-interference screw fixation system provides reliable fixation for a novel ovine meniscus implant, supporting

Journal article

Alkoheji M, El-Daou H, Lee J, Carlos A, Di Mascio L, Amis AAet al., 2021, Acromioclavicular joint reconstruction implants have differing ability to restore horizontal and vertical plane stability, Knee Surgery Sports Traumatology Arthroscopy, Vol: 29, Pages: 3902-3909, ISSN: 0942-2056

PurposePersistent acromioclavicular joint (ACJ) instability following high grade injuries causes significant symptoms. The importance of horizontal plane stability is increasingly recognised. There is little evidence of the ability of current implant methods to restore native ACJ stability in the vertical and horizontal planes. The purpose of this work was to measure the ability of three implant reconstructions to restore native ACJ stability.MethodsThree groups of nine fresh-frozen shoulders each were mounted into a robotic testing system. The scapula was stationary and the robot displaced the clavicle to measure native anterior, posterior, superior and inferior (A, P, S, I) stability at 50 N force. The ACJ capsule, conoid and trapezoid ligaments were transected and the ACJ was reconstructed using one of three commercially available systems. Two systems (tape loop + screw and tape loop + button) wrapped a tape around the clavicle and coracoid, the third system (sutures + buttons) passed directly through tunnels in the clavicle and coracoid. The stabilities were remeasured. The data for A, P, S, I stability and ranges of A–P and S–I stability were analyzed by ANOVA and repeated-measures Student t tests with Bonferroni correction, to contrast each reconstruction stability versus the native ACJ data for that set of nine specimens, and examined contrasts among the reconstructions.ResultsAll three reconstructions restored the range of A–P stability to that of the native ACJ. However, the coracoid loop devices shifted the clavicle anteriorly. For S–I stability, only the sutures + buttons reconstruction did not differ significantly from native ligament restraint.ConclusionsOnly the sutures + buttons reconstruction, that passed directly through tunnels in the clavicle and coracoid, restored all stability measures (A, P, S, I) to the native values, while the tape implants wrapped a

Journal article

Amis A, Athwal K, Willinger L, Wang D, Williams Aet al., 2021, Knee joint line obliquity causes tibiofemoral subluxation that alters contact areas and meniscal loading, American Journal of Sports Medicine, Vol: 49, Pages: 2351-2360, ISSN: 0363-5465

Background:Little scientific evidence is available regarding the effect of knee joint line obliquity (JLO) before and after coronal realignment osteotomy.Hypotheses:Higher JLO would lead to abnormal relative position of the femur on the tibia, a shift of the joint contact areas, and elevated joint contact pressures.Study Design:Descriptive laboratory study.Methods:10 fresh-frozen human cadaveric knees (age, 59 ± 5 years) were axially loaded to 1500 N in a materials testing machine with the joint line tilted 0°, 4°, 8°, and 12° varus (“downhill” medially) and valgus, at 0° and 20° of knee flexion. The mechanical compression axis was aligned to the center of the tibial plateau. Contact pressure and contact area were recorded by pressure sensors inserted between the tibia and femur below the menisci. Changes in relative femoral and tibial position in the coronal plane were obtained by an optical tracking system.Results:Both medial and lateral JLO caused significant tibiofemoral subluxation and pressure distribution changes. Medial (varus) JLO caused the femur to subluxate medially down the coronal slope of the tibial plateau, and vice versa for lateral (valgus) downslopes (P < .01), giving a 6-mm range of subluxation. The areas of peak pressure moved 12 mm and 8 mm across the medial and lateral condyles, onto the downhill meniscus and the “uphill” tibial spine. Changes in JLO had only small effects on maximum contact pressures.Conclusion:A 4° change of JLO during load bearing caused significant mediolateral tibiofemoral subluxation. The femur slid down the slope of the tibial plateau to abut the tibial eminence and also to rest on the downhill meniscus. This caused large movements of the tibiofemoral contact pressures across each compartment.Clinical Relevance:These results provide important information for understanding the consequences of creating coronal JLO and for clinical practice in terms of osteotomy

Journal article

Willinger L, Athwal KK, Williams A, Amis AAet al., 2021, An anterior cruciate ligament In vitro rupture model based on clinical imaging, American Journal of Sports Medicine, Vol: 49, Pages: 2387-2395, ISSN: 0363-5465

BACKGROUND: Biomechanical studies on anterior cruciate ligament (ACL) injuries and reconstructions are based on ACL transection instead of realistic injury trauma. PURPOSE: To replicate an ACL injury in vitro and compare the laxity that occurs with that after an isolated ACL transection injury before and after ACL reconstruction. STUDY DESIGN: Controlled laboratory study. METHODS: Nine paired knees were ACL injured or ACL transected. For ACL injury, knees were mounted in a rig that imposed tibial anterior translation at 1000 mm/min to rupture the ACL at 22.5° of flexion, 5° of internal rotation, and 710 N of joint compressive force, replicating data published on clinical bone bruise locations. In contralateral knees, the ACL was transected arthroscopically at midsubstance. Both groups had ACL reconstruction with bone-patellar tendon-bone graft. Native, ACL-deficient, and reconstructed knee laxities were measured in a kinematics rig from 0° to 100° of flexion with optical tracking: anterior tibial translation (ATT), internal rotation (IR), anterolateral (ATT + IR), and pivot shift (IR + valgus). RESULTS: The ACL ruptured at 26 ± 5 mm of ATT and 1550 ± 620 N of force (mean ± SD) with an audible spring-back tibiofemoral impact with 5o of valgus. ACL injury and transection increased ATT (P < .001). ACL injury caused greater ATT than ACL transection by 1.4 mm (range, 0.4-2.2 mm; P = .033). IR increased significantly in ACL-injured knees between 0° and 30° of flexion and in ACL transection knees from 0° to 20° of flexion. ATT during the ATT + IR maneuver was increased by ACL injury between 0° and 80° and after ACL transection between 0° and 60°. Residual laxity persisted after ACL reconstruction from 0° to 40° after ACL injury and from 0° to 20° in the ACL transection knees. ACL deficiency increased ATT and IR in the pivot-shift test (P < .001). The ATT in the pivot-shift increased

Journal article

Lee J, El-Daou H, Alkoheji M, Carlos A, Di Mascio L, Amis Aet al., 2021, Ligamentous and capsular restraints to anterior posterior and superior inferior laxity of the acromioclavicular joint - a biomechanical study, Journal of Shoulder and Elbow Surgery, Vol: 30, Pages: 1251-1256, ISSN: 1058-2746

BACKGROUND: Approximately 9% of shoulder girdle injuries involve the acromioclavicular joint (ACJ). There is no clear gold standard or consensus on surgical management of these injuries, in part perpetuated by our incomplete understanding of native ACJ biomechanics. We have therefore conducted a biomechanical study to assess the stabilizing structures of the ACJ in superior-inferior (SI) and anterior-posterior (AP) translation. METHODS: Twenty fresh frozen cadaver specimens were prepared and mounted to a robotic arm. The intact native joint was tested in SI and AP translations under 50N displacing force. Each specimen was re-tested after sectioning of its stabilizing structures in the following order; investing fascia, ACJ capsular ligaments, trapezoid ligament, and conoid ligament. Their contributions to resisting ACJ displacements were calculated. RESULTS: In the intact native ACJ, mean anterior displacement of the clavicle was 7.9 +/- 4.3mm, mean posterior displacement was 7.2 +/- 2.6mm, mean superior displacement 5.8 +/- 3.0mm, and mean inferior displacement 3.6 +/- 2.6mm. The conoid ligament was the primary stabilizer of superior displacement (45.6%). The ACJ capsular ligament was the primary stabilizer of inferior displacement (33.8%). The capsular ligament and conoid ligament contributed equally to anterior stability, with 23% and 25.2% respectively. The capsular ligament was the primary contributor to posterior stability (38.4%). CONCLUSION: The conoid ligament is the primary stabilizer of superior displacement of the clavicle at the ACJ and contributes significantly to AP stability. Consideration should be given to reconstruction of the ACJ capsular ligament for complete AP stability in high grade and horizontally unstable ACJ injuries.

Journal article

Bartolo MK, Accardi MA, Dini D, Amis Aet al., 2021, A machine-learning approach for measuring articular cartilage damage in the knee, International Society for Technology in Arthroplasty (ISTA) Meeting, New Early-Career Webinar Series (NEWS), Publisher: Bone & Joint, Pages: 11-11

Conference paper

Garner A, Dandridge O, Amis A, Cobb J, van Arkel Ret al., 2021, The extensor efficiency of unicompartmental, bicompartmental and total knee arthroplasty, Bone and Joint Research, Vol: 10, Pages: 1-9, ISSN: 2046-3758

Aims: Unicompartmental (UKA) and bicompartmental (BCA) knee arthroplasty have been associated with improved functional outcomes compared to Total Knee Arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function. Methods: Extensor function was measured for sixteen cadaveric knees and then re-tested following the different arthroplasties. Eight knees underwent medial UKA then BCA, then posterior-cruciate retaining TKA, and eight underwent the lateral equivalents then TKA. Extensorefficiency was calculated for ranges of knee flexion associated with common 46activities of daily living. Data were analyzed with repeated measures analysis of variance (=0.05). Results: Compared to native, there were no reductions in either extension moment or efficiency following UKA. Conversion to BCA resulted in a small decrease in extension moment between 70-90° flexion(p<0.05), but when examined in the context of daily activity ranges of flexion, extensor efficiency was largely unaffected. Following TKA, large decreases in extension moment were measured at low knee flexion angles(p<0.05), resulting in 12-43% reductions in extensor efficiency for the daily activity ranges. Conclusion: This cadaveric study found that TKA resulted in inferior extensor function compared to UKA and BCA. This may, in part, help explain the reported differences in 58function and satisfaction differences between partial and total knee arthroplasty.

Journal article

Ball S, Stephen JM, El-Daou H, Williams A, Amis AAet al., 2020, The medial ligaments and the ACL restrain anteromedial laxity of the knee, Knee Surgery Sports Traumatology Arthroscopy, Vol: 28, Pages: 3700-3708, ISSN: 0942-2056

PurposeThe purpose of this study was to determine the contribution of each of the ACL and medial ligament structures in resisting anteromedial rotatory instability (AMRI) loads applied in vitro.MethodsTwelve knees were tested using a robotic system. It imposed loads simulating clinical laxity tests at 0° to 90° flexion: ±90 N anterior–posterior force, ±8 Nm varus–valgus moment, and ±5 Nm internal–external rotation, and the tibial displacements were measured in the intact knee. The ACL and individual medial structures—retinaculum, superficial and deep medial collateral ligament (sMCL and dMCL), and posteromedial capsule with oblique ligament (POL + PMC)—were sectioned sequentially. The tibial displacements were reapplied after each cut and the reduced loads required allowed the contribution of each structure to be calculated.ResultsFor anterior translation, the ACL was the primary restraint, resisting 63–77% of the drawer force across 0° to 90°, the sMCL contributing 4–7%. For posterior translation, the POL + PMC contributed 10% of the restraint in extension; other structures were not significant. For valgus load, the sMCL was the primary restraint (40–54%) across 0° to 90°, the dMCL 12%, and POL + PMC 16% in extension. For external rotation, the dMCL resisted 23–13% across 0° to 90°, the sMCL 13–22%, and the ACL 6–9%.ConclusionThe dMCL is the largest medial restraint to tibial external rotation in extension. Therefore, following a combined ACL + MCL injury, AMRI may persist if there is inadequate healing of both the sMCL and dMCL, and MCL deficiency increases the risk of ACL graft failure.

Journal article

Athwal KK, Willinger L, Shinohara S, Ball S, Williams A, Amis AAet al., 2020, The bone attachments of the medial collateral and posterior oblique ligaments are defined anatomically and radiographically, Knee Surgery Sports Traumatology Arthroscopy, Vol: 28, Pages: 3709-3719, ISSN: 0942-2056

PurposeTo define the bony attachments of the medial ligaments relative to anatomical and radiographic bony landmarks, providing information for medial collateral ligament (MCL) surgery.MethodThe femoral and tibial attachments of the superficial MCL (sMCL), deep MCL (dMCL) and posterior oblique ligament (POL), plus the medial epicondyle (ME) were defined by radiopaque staples in 22 knees. These were measured radiographically and optically; the precision was calculated and data normalised to the sizes of the condyles. Femoral locations were referenced to the ME and to Blumensaat’s line and the posterior cortex.ResultsThe femoral sMCL attachment enveloped the ME, centred 1 mm proximal to it, at 37 ± 2 mm (normalised at 53 ± 2%) posterior to the most-anterior condyle border. The femoral dMCL attachment was 6 mm (8%) distal and 5 mm (7%) posterior to the ME. The femoral POL attachment was 4 mm (5%) proximal and 11 mm (15%) posterior to the ME. The tibial sMCL attachment spread from 42 to 71 mm (81–137% of A-P plateau width) below the tibial plateau. The dMCL fanned out anterodistally to a wide tibial attachment 8 mm below the plateau and between 17 and 39 mm (33–76%) A-P. The POL attached 5 mm below the plateau, posterior to the dMCL. The 95% CI intra-observer was ± 0.6 mm, inter-observer ± 1.3 mm for digitisation. The inter-observer ICC for radiographs was 0.922.ConclusionThe bone attachments of the medial knee ligaments are located in relation to knee dimensions and osseous landmarks. These data facilitate repairs and reconstructions that can restore physiological laxity and stability patterns across the arc of knee flexion.

Journal article

Williams A, Becker R, Amis A, 2020, The medial collateral ligament: the neglected ligament, Knee Surgery, Sports Traumatology, Arthroscopy, Vol: 28, Pages: 3698-3699, ISSN: 0942-2056

Journal article

Willinger L, Shinohara S, Athwal KK, Ball S, Williams A, Amis AAet al., 2020, Length-change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery, Arthroskopie, Vol: 33, Pages: 288-294, ISSN: 0933-7946

PurposeThe purpose of this study was to define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads.Material and methodsTen cadaveric knees were mounted in a kinematics rig with loaded quadriceps and hamstrings muscles. Length change patterns of the anterior and posterior fibres of the sMCL, dMCL and POL were recorded from 0 to 100° flexion. Length changes were recorded while a 90 N anterior load and a 5 Nm internal and external rotational torque were applied. Length changes were normalized to lengths at 0° flexion.ResultsThe anterior sMCL tightened as the knee was flexed (p < 0.01), and further tensioned under tibial external rotation (p < 0.001). Conversely, the posterior sMCL slackened with flexion (p < 0.001), while internal rotation tightened these fibers between 10 and 100° (p < 0.05). Tibial external rotation significantly lengthened the anterior dMCL fibres by 10% compared to the unloaded condition throughout flexion (p < 0.001). Release of the sMCL caused the dMCL fibres to become taut and increased valgus rotation (p < 0.01). The lengths of the anterior and posterior POL fibres decreased continuously with knee flexion (p < 0.001). Tibial internal rotation significantly increased the length of the POL (p < 0.001).ConclusionThe structures of the medial ligament complex reacted differently to knee flexion and applied loads. Structures attaching proximal and posterior to the medial epicondyle were taut in extension, whereas the anterior sMCL tensioned during flexion. The anterior dMCL was extensively strained by tibial external rotation and after sMCL release.

Journal article

Amis A, Willinger L, Shinohara S, Athwal K, Ball S, Williams Aet al., 2020, Length change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery, Knee Surgery Sports Traumatology Arthroscopy, Vol: 28, Pages: 3720-3732, ISSN: 0942-2056

PurposeTo define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads, and to relate these findings to their functions in knee stability and to surgical repair or reconstruction.MethodsTen cadaveric knees were mounted in a kinematics rig with loaded quadriceps, ITB, and hamstrings. Length changes of the anterior and posterior fibres of the sMCL, dMCL, and POL were recorded from 0° to 100° flexion by use of a linear displacement transducer and normalised to lengths at 0° flexion. Measurements were repeated with no external load, 90 N anterior draw force, and 5 Nm internal and 5 Nm external rotation torque applied.ResultsThe anterior sMCL lengthened with flexion (p < 0.01) and further lengthened by external rotation (p < 0.001). The posterior sMCL slackened with flexion (p < 0.001), but was lengthened by internal rotation (p < 0.05). External rotation lengthened the anterior dMCL fibres by 10% throughout flexion (p < 0.001). sMCL release allowed the dMCL to become taut with valgus rotation (p < 0.001). The anterior and posterior POL fibres slackened with flexion (p < 0.001), but were elongated by internal rotation (p < 0.001).ConclusionThe structures of the medial ligament complex react differently to knee flexion and applied loads. Structures attaching posterior to the medial epicondyle are taut in extension, whereas the anterior sMCL, attaching anterior to the epicondyle, is tensioned during flexion. The anterior dMCL is elongated by external rotation. These data offer the basis for MCL repair and reconstruction techniques regarding graft positioning and tensioning.

Journal article

Amis A, Joseph M, Carmont M, Stephen J, Tailor Het al., 2020, Total knee arthroplasty reduces knee extension torque in-vitro and patellofemoral arthroplasty does not, Journal of Biomechanics, Vol: 104, Pages: 1-6, ISSN: 0021-9290

Patients often have difficulty recovering knee extension strength post total knee arthroplasty (TKA), and that may reflect alteration of the mechanics including geometry and rollback kinematics, so the purpose of this work was to explore this by comparing the knee extension torque (KET) of the native knee, TKA and patellofemoral arthroplasty (PFA) in response to quadriceps tension. Eight fresh-frozen knees were mounted in a knee extension rig with quadriceps loading and tibial extension torque measurement. Each knee was subject to four conditions: native knee, PFA, cruciate-retaining (CR) and posterior-stabilized (PS) TKA. The KET was measured from 120° to 0° knee flexion. Data were analyzed using one-way ANOVA and post-hoc paired t-tests. The native KET was lowest in terminal extension and 70–100° flexion, and maximal at 20–30° flexion. PFA produced the greatest KET (p < 0.008) compared with native, CR- and PS-TKA, at 30–40° flexion. CR- and PS-TKA had lower KET across 0–50° flexion (p < 0.001 across 0–30°), falling to 25% of the native knee KET or the PFA at full extension. PFA had the highest KET in early flexion possibly due to increased trochlear offset and/or preservation of the cruciate mechanism, so PFA may be more beneficial during the functional range of motion. The claimed benefits of PS- over CR-TKA in deep flexion were not detected. Both CR- and PS-TKAs led to lower KET than the native and PFA knee states across 0–50° flexion. This mechanical effect may help to explain clinical findings of knee extension weakness post-TKA.

Journal article

Athwal KK, Willinger L, Manning W, Deehan D, Amis AAet al., 2020, A constrained-condylar fixed-bearing total knee arthroplasty is stabilised by the medial soft tissues, Knee Surgery Sports Traumatology Arthroscopy, Vol: 29, Pages: 659-667, ISSN: 0942-2056

PurposeRevision constrained-condylar total knee arthroplasty (CCK-TKA) is often used to provide additional mechanical constraint after failure of a primary TKA. However, it is unknown how much this translates to a reliance on soft-tissue support. The aim of this study was therefore to compare the laxity of a native knee to the CCK-TKA implanted state and quantify how medial soft-tissues stabilise the knee following CCK-TKA.MethodsTen intact cadaveric knees were tested in a robotic system at 0°, 30°, 60° and 90° flexion with ± 90 N anterior–posterior force, ± 8 Nm varus-valgus and ± 5 Nm internal–external torques. A fixed-bearing CCK-TKA was implanted and the laxity tests were repeated with the soft tissues intact and after sequential cutting. The deep and superficial medial collateral ligaments (dMCL, sMCL) and posteromedial capsule (PMC) were sequentially transected and the percentage contributions of each structure to restraining the applied loads were calculated.ResultsImplanting a CCK-TKA did not alter anterior–posterior laxity from that of the original native knee, but it significantly decreased internal–external and varus-valgus rotational laxity (p < 0.05). Post CCK-TKA, the sMCL restrained 34% of the tibial displacing load in anterior drawer, 16% in internal rotation, 17% in external rotation and 53% in valgus, across the flexion angles tested. The dMCL restrained 11% of the valgus rotation moment.ConclusionsWith a fully-competent sMCL in-vitro, a fixed-bearing CCK-TKA knee provided more rotational constraint than the native knee. The robotic test data showed that both the soft-tissues and the semi-constrained implant restrained rotational knee laxity. Therefore, in clinical practice, a fixed-bearing CCK-TKA knee could be indicated for use in a knee with lax, less-competent medial soft tissues.

Journal article

Athwal KK, Lord BR, Milner PE, Gutteridge A, Williams A, Amis AAet al., 2020, Redesigning metal interference screws can improve ease of insertion while maintaining fixation of soft-tissue anterior cruciate ligament reconstruction grafts, Arthroscopy and Sports Medicine Rehabilitation, Vol: 2, Pages: e137-e144, ISSN: 2666-061X

Purpose: To compare the fixation strength and loads on insertion of a titanium alloy interference screw with a modified tip against a conventional titanium interference screw. Methods: Slippage of bovine digital extensor tendons (as substitutes for human tendon grafts) under cyclic loading and interference fixation strength under a pullout test were recorded in 10 cadaveric knees, with 2 tunnels drilled in each femur and tibia to provide pair-wise comparisons between the modified-tip screw (MS) and conventional screw (CS). To analyze screw insertion, 10 surgeons blindly inserted pairs of the MS and CS into bone-substitute blocks (with polyester shoelaces as graft substitutes), with insertion loads measured using a force/torque sensor. Results: No differences were found between the MS and CS either in graft slippage from the femur (P = .661) or tibia (P = .950) or in ultimate load to failure from the femur (P = .952) or tibia (P = .126). On insertion, the MS required less axial force application (78 ± 38 N, P = .001) and fewer attempted turns (2 ± 1, P < .001) to engage with the bone tunnel than the CS (99 ± 43 N and 4 ± 4, respectively). In 90% of the paired insertion tests, the screw identified by the surgeon as being easier to initially insert was the MS. Conclusions: The MS was found to be easier to engage with the bone tunnel and initially insert than the CS while still achieving similar immediate postsurgical fixation strength. Clinical Relevance: The study shows that screw designs can be improved to ease insertion into a bone tunnel, which should reduce any likelihood of ligament reconstruction graft damage.

Journal article

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-html.jsp Request URI: /respub/WEB-INF/jsp/search-html.jsp Query String: respub-action=search.html&id=00000148&limit=30&person=true