Aims

There are two techniques widely used to determine the rotational alignment of the components in total knee arthroplasty (TKA); gap balancing (GB) and measured resection (MR). Which technique is the best remains controversial. We aimed to investigate this in a systematic review and meta-analysis.

Aims. The aims of this study were to determine the effect of osteophyte excision on deformity correction and soft tissue gap balance in varus knees undergoing computer-assisted total knee arthroplasty (TKA). Methods. A total of 492 consecutive, cemented, cruciate-substituting TKAs performed for varus osteoarthritis were studied. After exposure and excision of both cruciates and menisci, it was noted from operative records the corrective interventions performed in each case. Knees in which no releases after the initial exposure, those which had only osteophyte excision, and those in which further interventions were performed were identified. From recorded navigation data, coronal and sagittal limb alignment, knee flexion range, and medial and lateral gap distances in maximum knee extension and 90° knee flexion with maximal varus and valgus stresses, were established, initially after exposure and excision of both cruciate ligaments, and then also at trialling. Knees were defined as ‘aligned’ if the hip-knee-ankle axis was between 177° and 180°, (0° to 3° varus) and ‘balanced’ if medial and lateral gaps in extension and at 90° flexion were within 2 mm of each other. Results. Of 50 knees (10%) with no soft tissue releases (other than cruciate ligaments), 90% were aligned, 81% were balanced, and 73% were aligned and balanced. In 288 knees (59%) only osteophyte excision was performed by subperiosteally releasing the deep medial collateral ligament. Of these, 98% were aligned, 80% were balanced, and 79% were aligned and balanced. In 154 knees (31%), additional procedures were performed (reduction osteotomy, posterior capsular release, and semimembranosus release). Of these, 89% were aligned, 68% were balanced, and 66% were aligned and balanced. The superficial medial collateral ligament was not released in any case. Conclusion. Two-thirds of all knees could be aligned and balanced with release of the cruciate ligaments alone and excision of osteophytes. Excision of osteophytes can be a useful step towards achieving deformity correction and gap balance without having to resort to soft tissue release in varus knees while maintaining classical coronal and sagittal alignment of components. Cite this article: Bone Joint J 2020;102-B(6 Supple A):49–58

Aims

The aim of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft-tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilized (PS) total knee arthroplasty (TKA).

Aims

The primary aim was to assess whether robotic total knee arthroplasty (rTKA) had a greater early knee-specific outcome when compared to manual TKA (mTKA). Secondary aims were to assess whether rTKA was associated with improved expectation fulfilment, health-related quality of life (HRQoL), and patient satisfaction when compared to mTKA.

Total hip and knee arthroplasty (THA, TKA) are largely successful procedures; however, both have variable outcomes, resulting in some patients being dissatisfied with the outcome. Surgeons are turning to technologies such as robotic-assisted surgery in an attempt to improve outcomes. Robust studies are needed to find out if these innovations are really benefitting patients. The Robotic Arthroplasty Clinical and Cost Effectiveness Randomised Controlled Trials (RACER) trials are multicentre, patient-blinded randomized controlled trials. The patients have primary osteoarthritis of the hip or knee. The operation is Mako-assisted THA or TKA and the control groups have operations using conventional instruments. The primary clinical outcome is the Forgotten Joint Score at 12 months, and there is a built-in analysis of cost-effectiveness. Secondary outcomes include early pain, the alignment of the components, and medium- to long-term outcomes. This annotation outlines the need to assess these technologies and discusses the design and challenges when conducting such trials, including surgical workflows, isolating the effect of the operation, blinding, and assessing the learning curve. Finally, the future of robotic surgery is discussed, including the need to contemporaneously introduce and evaluate such technologies.

Cite this article: Bone Joint J 2024;106-B(2):114–120.

Aims

Conflicting clinical results are reported for the ATTUNE Total Knee Arthroplasty (TKA). This randomized controlled trial (RCT) evaluated five-year follow-up results comparing cemented ATTUNE and PFC-Sigma cruciate retaining TKAs, analyzing component migration as measured by radiostereometric analysis (RSA), clinical outcomes, patient-reported outcome measures (PROMs), and radiological outcomes.

Aims

The aim of this study was to compare the migration of the femoral component, five years postoperatively, between patients with a highly cross-linked polyethylene (HXLPE) insert and those with a conventional polyethylene (PE) insert in an uncemented Triathlon fixed insert cruciate-retaining total knee arthroplasty (TKA). Secondary aims included clinical outcomes and patient-reported outcome measures (PROMs). We have previously reported the migration and outcome of the tibial components in these patients.

Orthopaedic surgeons are currently faced with an overwhelming number of choices surrounding total knee arthroplasty (TKA), not only with the latest technologies and prostheses, but also fundamental decisions on alignment philosophies. From ‘mechanical’ to ‘adjusted mechanical’ to ‘restricted kinematic’ to ‘unrestricted kinematic’ — and how constitutional alignment relates to these — there is potential for ambiguity when thinking about and discussing such concepts. This annotation summarizes the various alignment strategies currently employed in TKA. It provides a clear framework and consistent language that will assist surgeons to compare confidently and contrast the concepts, while also discussing the latest opinions about alignment in TKA. Finally, it provides suggestions for applying consistent nomenclature to future research, especially as we explore the implications of 3D alignment patterns on patient outcomes.

Cite this article: Bone Joint J 2023;105-B(2):102–108.

Aims

The primary aim of this study was to compare the migration of the femoral and tibial components of the cementless rotating platform Attune and Low Contact Stress (LCS) total knee arthroplasty (TKA) designs, two years postoperatively, using radiostereometric analysis (RSA) in order to assess the risk of the development of aseptic loosening. A secondary aim was to compare clinical and patient-reported outcome measures (PROMs) between the designs.

Aims

The aim was to assess whether robotic-assisted total knee arthroplasty (rTKA) had greater knee-specific outcomes, improved fulfilment of expectations, health-related quality of life (HRQoL), and patient satisfaction when compared with manual TKA (mTKA).

Literature surrounding artificial intelligence (AI)-related applications for hip and knee arthroplasty has proliferated. However, meaningful advances that fundamentally transform the practice and delivery of joint arthroplasty are yet to be realized, despite the broad range of applications as we continue to search for meaningful and appropriate use of AI. AI literature in hip and knee arthroplasty between 2018 and 2021 regarding image-based analyses, value-based care, remote patient monitoring, and augmented reality was reviewed. Concerns surrounding meaningful use and appropriate methodological approaches of AI in joint arthroplasty research are summarized. Of the 233 AI-related orthopaedics articles published, 178 (76%) constituted original research, while the rest consisted of editorials or reviews. A total of 52% of original AI-related research concerns hip and knee arthroplasty (n = 92), and a narrative review is described. Three studies were externally validated. Pitfalls surrounding present-day research include conflating vernacular (“AI/machine learning”), repackaging limited registry data, prematurely releasing internally validated prediction models, appraising model architecture instead of inputted data, withholding code, and evaluating studies using antiquated regression-based guidelines. While AI has been applied to a variety of hip and knee arthroplasty applications with limited clinical impact, the future remains promising if the question is meaningful, the methodology is rigorous and transparent, the data are rich, and the model is externally validated. Simple checkpoints for meaningful AI adoption include ensuring applications focus on: administrative support over clinical evaluation and management; necessity of the advanced model; and the novelty of the question being answered.

Cite this article: Bone Joint J 2022;104-B(12):1292–1303.

Aims

Intraoperative pressure sensors allow surgeons to quantify soft-tissue balance during total knee arthroplasty (TKA). The aim of this study was to determine whether using sensors to achieve soft-tissue balance was more effective than manual balancing in improving outcomes in TKA.

Aims

Neither a surgeon’s intraoperative impression nor the parameters of computer navigation have been shown to be predictive of the outcomes following total knee arthroplasty (TKA). The aim of this study was to determine whether a surgeon, with robotic assistance, can predict the outcome as assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) for pain (KPS), one year postoperatively, and establish what factors correlate with poor KOOS scores in a well-aligned and balanced TKA.

Aims

Alternative alignment concepts, including kinematic and restricted kinematic, have been introduced to help improve clinical outcomes following total knee arthroplasty (TKA). The purpose of this study was to evaluate the clinical results, along with patient satisfaction, following TKA using the concept of restricted kinematic alignment.

Aims

Total knee arthroplasty (TKA) using functional alignment aims to implant the components with minimal compromise of the soft-tissue envelope by restoring the plane and obliquity of the non-arthritic joint. The objective of this study was to determine the effect of TKA with functional alignment on mediolateral soft-tissue balance as assessed using intraoperative sensor-guided technology.

Aims

A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA).

Aims

This study aimed to evaluate the association between the sagittal alignment of the femoral component in total knee arthroplasty (TKA) and new Knee Society Score (2011KSS), under the hypothesis that outliers such as the excessive extended or flexed femoral component were related to worse clinical outcomes.

Aims

The primary aim of this study was to compare the postoperative systemic inflammatory response in conventional jig-based total knee arthroplasty (conventional TKA) versus robotic-arm assisted total knee arthroplasty (robotic TKA). Secondary aims were to compare the macroscopic soft tissue injury, femoral and tibial bone trauma, localized thermal response, and the accuracy of component positioning between the two treatment groups.

Aims

To compare patients undergoing total knee arthroplasty (TKA) with ≤ 80° range of movement (ROM) operated with a 2 mm increase in the flexion gap with matched non-stiff patients with at least 100° of preoperative ROM and balanced flexion and extension gaps.

Aims

Aseptic loosening of the tibial component is a frequent cause of failure in primary total knee arthroplasty (TKA). Management options include an isolated tibial revision or full component revision. A full component revision is frequently selected by surgeons unfamiliar with the existing implant or who simply wish to “start again”. This option adds morbidity compared with an isolated tibial revision. While isolated tibial revision has a lower morbidity, it is technically more challenging due to difficulties with exposure and maintaining prosthetic stability. This study was designed to compare these two reconstructive options.

Aims

The objectives of this study were to assess the effect of anterior cruciate ligament (ACL) resection on flexion-extension gaps, mediolateral soft tissue laxity, maximum knee extension, and limb alignment during primary total knee arthroplasty (TKA).

Aims

The results of kinematic total knee arthroplasty (KTKA) have been reported in terms of limb and component alignment parameters but not in terms of gap laxities and differentials. In kinematic alignment (KA), balance should reflect the asymmetrical balance of the normal knee, not the classic rectangular flexion and extension gaps sought with gap-balanced mechanical axis total knee arthroplasty (MATKA). This paper aims to address the following questions: 1) what factors determine coronal joint congruence as measured on standing radiographs?; 2) is flexion gap asymmetry produced with KA?; 3) does lateral flexion gap laxity affect outcomes?; 4) is lateral flexion gap laxity associated with lateral extension gap laxity?; and 5) can consistent ligament balance be produced without releases?

Aims

It is unknown whether kinematic alignment (KA) objectively improves knee balance in total knee arthroplasty (TKA), despite this being the biomechanical rationale for its use. This study aimed to determine whether restoring the constitutional alignment using a restrictive KA protocol resulted in better quantitative knee balance than mechanical alignment (MA).

Aims

There is little literature about total knee arthroplasty (TKA) after distal femoral osteotomy (DFO). Consequently, the purpose of this study was to analyze the outcomes of TKA after DFO, with particular emphasis on: survivorship free from aseptic loosening, revision, or any re-operation; complications; radiological results; and clinical outcome.

Aims

The aim of this study was to determine whether closed suction drain (CSD) use influences recovery of quadriceps strength and to examine the effects of drain use on secondary outcomes: quadriceps activation, intra-articular effusion, bioelectrical measure of swelling, range of movement (ROM), pain, and wound healing complications.

Aims

Between 15% and 20% of patients remain dissatisfied following total knee arthroplasty (TKA). The SAIPH knee system (MatOrtho, Surrey, United Kingdom) is a medial ball and socket TKA that has been designed to replicate native knee kinematics in order to maximize the range of movement, stability, and function. This system is being progressively introduced in a stepwise fashion, with this study reporting the mid-term clinical and radiological outcomes.

Aims

The objectives of this study were to compare postoperative pain, analgesia requirements, inpatient functional rehabilitation, time to hospital discharge, and complications in patients undergoing conventional jig-based unicompartmental knee arthroplasty (UKA) versus robotic-arm assisted UKA.

At least four ways have been described to determine femoral component rotation, and three ways to determine tibial component rotation in total knee replacement (TKR). Each method has its advocates and each has an influence on knee kinematics and the ultimate short and long term success of TKR. Of the four femoral component methods, the author prefers rotating the femoral component in flexion to that amount that establishes a stable symmetrical flexion gap. This judgement is made after the soft tissues of the knee have been balanced in extension.

Of the three tibial component methods, the author prefers rotating the tibial component into congruency with the established femoral component rotation with the knee is in extension. This yields a rotationally congruent articulation during weight-bearing and should minimise the torsional forces being transferred through a conforming tibial insert, which could lead to wear to the underside of the tibial polyethylene. Rotating platform components will compensate for any mal-rotation, but can still lead to pain if excessive tibial insert rotation causes soft-tissue impingement.

Cite this article: Bone Joint J 2013;95-B, Supple A:140–3.

Previous studies of failure mechanisms leading to revision total knee replacement (TKR) performed between 1986 and 2000 determined that many failed early, with a disproportionate amount accounted for by infection and implant-associated factors including wear, loosening and instability. Since then, efforts have been made to improve implant performance and instruct surgeons in best practice. Recently our centre participated in a multi-centre evaluation of 844 revision TKRs from 2010 to 2011. The purpose was to report a detailed analysis of failure mechanisms over time and to see if failure modes have changed over the past 10 to 15 years. Aseptic loosening was the predominant mechanism of failure (31.2%), followed by instability (18.7%), infection (16.2%), polyethylene wear (10.0%), arthrofibrosis (6.9%) and malalignment (6.6%). The mean time to failure was 5.9 years (ten days to 31 years), 35.3% of all revisions occurred at less than two years, and 60.2% in the first five years. With improvements in implant and polyethylene manufacture, polyethylene wear is no longer a leading cause of failure. Early mechanisms of failure are primarily technical errors. In addition to improving implant longevity, industry and surgeons must work together to decrease these technical errors. All reports on failure of TKR contain patients with unexplained pain who not infrequently have unmet expectations. Surgeons must work to achieve realistic patient expectations pre-operatively, and therefore, improve patient satisfaction post-operatively.

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):101–4.

Total knee replacement (TKR) smart tibial trials have load-bearing sensors which will show quantitative compartment pressure values and femoral-tibial tracking patterns. Without smart trials, surgeons rely on feel and visual estimation of imbalance to determine if the knee is optimally balanced. Corrective soft-tissue releases are performed with minimal feedback as to what and how much should be released. The smart tibial trials demonstrate graphically where and how much imbalance is present, so that incremental releases can be performed. The smart tibial trials now also incorporate accelerometers which demonstrate the axial alignment. This now allows the surgeon the option to perform a slight recut of the tibia or femur to provide soft-tissue balance without performing soft-tissue releases. Using a smart tibial trial to assist with soft-tissue releases or bone re-cuts, improved patient outcomes have been demonstrated at one year in a multicentre study of 135 patients (135 knees).

Cite this article: Bone Joint J 2014;96-B(11 Suppl A):78–83.

Collateral ligament release is advocated in total knee arthroplasty (TKA) to deal with significant coronal plane deformities, but is also associated with significant disadvantages.

We describe steps to avoid release of the collateral (superficial medial and lateral collateral) ligaments during TKA in severely deformed knees, while correcting deformity and balancing the knee.

Cite this article: Bone Joint J 2016;98-B(1 Suppl A):101–4.

Instability is a common indication for early revision after both primary and revision total knee arthroplasty (TKA), accounting for up to 20% in the literature. The number of TKAs performed annually continues to climb exponentially, thus having an effective algorithm for treatment is essential. This relies on a thorough pre- and intra-operative assessment of the patient. The underlying cause of the instability must be identified initially and subsequently, the surgeon must be able to balance the flexion and extension gaps and be comfortable using a variety of constrained implants.

This review describes the assessment of the unstable TKA, and the authors’ preferred form of treatment for these difficult cases where the source of instability is often multifactorial.

Cite this article: Bone Joint J 2016;98-B(1 Suppl A):116–19.

The treatment of bone loss in revision total knee arthroplasty has evolved over the past decade. While the management of small to moderate sized defects has demonstrated good results with a variety of traditional techniques (cement and screws, small metal augments, impaction bone grafting or modular stems), the treatment of severe defects continues to be problematic. The use of a structural allograft has declined in recent years due to an increased failure rate with long-term follow-up and with the introduction of highly porous metal augments that emphasise biological metaphyseal fixation. Recently published mid-term results on the use of tantalum cones in patients with severe bone loss has reaffirmed the success of this treatment strategy.

Cite this article: Bone Joint J 2016;98-B(1 Suppl A):120–4.

Obtaining a balanced flexion gap with correct femoral component rotation is one of the prerequisites for a successful outcome after total knee replacement (TKR). Different techniques for achieving this have been described. In this study we prospectively compared gap-balancing versus measured resection in terms of reliability and accuracy for femoral component rotation in 96 primary TKRs performed in 96 patients using the Journey system. In 48 patients (18 men and 30 women) with a mean age of 65 years (45 to 85) a tensor device was used to determine rotation. In the second group of 48 patients (14 men and 34 women) with a mean age of 64 years (41 to 86), an ‘adapted’ measured resection technique was used, taking into account the native rotational geometry of the femur as measured on a pre-operative CT scan.

Both groups systematically reproduced a similar external rotation of the femoral component relative to the surgical transepicondylar axis: 2.4° (sd 2.5) in the gap-balancing group and 1.7° (sd 2.1) in the measured resection group (p = 0.134). Both gap-balancing and adapted measured resection techniques proved equally reliable and accurate in determining femoral component rotation after TKR. There was a tendency towards more external rotation in the gap-balancing group, but this difference was not statistically significant (p = 0.134). The number of outliers for our ‘adapted’ measured resection technique was much lower than reported in the literature.

We retrospectively reviewed the records of 1150 computer-assisted total knee replacements and analysed the clinical and radiological outcomes of 45 knees that had arthritis with a pre-operative recurvatum deformity. The mean pre-operative hyperextension deformity of 11° (6° to 15°), as measured by navigation at the start of the operation, improved to a mean flexion deformity of 3.1° (0° to 7°) post-operatively. A total of 41 knees (91%) were managed using inserts ≤ 12.5 mm thick, and none had mediolateral laxity > 2 mm from a mechanical axis of 0° at the end of the surgery. At a mean follow-up of 26.4 months (13 to 48) there was significant improvement in the mean Knee Society, Oxford knee and Western Ontario and McMaster Universities Osteoarthritis Index scores compared with the pre-operative values. The mean knee flexion improved from 105° (80° to 125°) pre-operatively to 131° (120° to 145°), and none of the limbs had recurrent recurvatum.

These early results show that total knee replacement using computer navigation and an algorithmic approach for arthritic knees with a recurvatum deformity can give excellent radiological and functional outcomes without recurrent deformity.

Bone loss in the proximal tibia and distal femur is frequently encountered in revision knee replacement surgery. The various options for dealing with this depend on the extent of any bone loss. We present our results with the use of cementless metaphyseal metal sleeves in 103 patients (104 knees) with a mean follow-up of 43 months (30 to 65). At final follow-up, sleeves in 102 knees had good osseointegration. Two tibial sleeves were revised for loosening, possibly due to infection.

The average pre-operative Oxford Knee Score was 23 (11 to 36) and this improved to 32 (15 to 46) post-operatively. These early results encourage us to continue with the technique and monitor the outcomes in the long term.

Cite this article: Bone Joint J 2013;95-B:1640–4.

The outcome of total knee replacement (TKR) using components designed to increase the range of flexion is not fully understood. The short- to mid-term risk of aseptic revision in high flexion TKR was evaluated. The endpoint of the study was aseptic revision and the following variables were investigated: implant design (high flexion vs non-high flexion), the thickness of the tibial insert (≤ 14 mm vs > 14 mm), cruciate ligament (posterior stabilised (PS) vs cruciate retaining), mobility (fixed vs rotating), and the manufacturer (Zimmer, Smith & Nephew and DePuy). Covariates included patient, implant, surgeon and hospital factors. Marginal Cox proportional hazard models were used.

In a cohort of 64 000 TKRs, high flexion components were used in 8035 (12.5%). The high flexion knees with tibial liners of thickness > 14 mm had a density of revision of 1.45/100 years of observation, compared with 0.37/100 in non-high flexion TKR with liners ≤ 14 mm thick. Relative to a standard fixed PS TKR, the NexGen (Zimmer, Warsaw, Indiana) Gender Specific Female high flexion fixed PS TKR had an increased risk of revision (hazard ratio (HR) 2.27 (95% confidence interval (CI) 1.48 to 3.50)), an effect that was magnified when a thicker tibial insert was used (HR 8.10 (95% CI 4.41 to 14.89)).

Surgeons should be cautious when choosing high flexion TKRs, particularly when thicker tibial liners might be required.

Cite this article: Bone Joint J 2014;96-B:217–23.

Smart trials are total knee tibial trial liners with load bearing and alignment sensors that will graphically show quantitative compartment load-bearing forces and component track patterns. These values will demonstrate asymmetrical ligament balancing and misalignments with the medial retinaculum temporarily closed. Currently surgeons use feel and visual estimation of imbalance to assess soft-tissue balancing and tracking with the medial retinaculum open, which results in lower medial compartment loads and a wider anteroposterior tibial tracking pattern. The sensor trial will aid the total knee replacement surgeon in performing soft-tissue balancing by providing quantitative visual feedback of changes in forces while performing the releases incrementally. Initial experience using a smart tibial trial is presented.

The success of total knee replacement (TKR) depends on optimal soft-tissue balancing, among many other factors. The objective of this study is to correlate post-operative anteroposterior (AP) translation of a posterior cruciate ligament-retaining TKR with clinical outcome at two years. In total 100 patients were divided into three groups based on their AP translation as measured by the KT-1000 arthrometer. Group 1 patients had AP translation < 5 mm, Group 2 had AP translation from 5 mm to 10 mm, and Group 3 had AP translation >  10 mm. Outcome assessment included range of movement of the knee, the presence of flexion contractures, hyperextension, knee mechanical axes and functional outcome using the Knee Society score, Oxford knee score and the Short-Form 36 questionnaire.

At two years, patients in Group 2 reported significantly better Oxford knee scores than the other groups (p = 0.045). A positive correlation between range of movement and AP translation was noted, with patients in group 3 having the greatest range of movement (mean flexion: 117.9° (106° to 130°)) (p < 0.001). However, significantly more patients in Group 3 developed hyperextension > 10° (p = 0.01).

In this study, the best outcome for cruciate-ligament retaining TKR was achieved in patients with an AP translation of 5 mm to 10 mm.

The purpose of this study was to investigate whether a gender-specific high-flexion posterior-stabilised (PS) total knee replacement (TKR) would offer advantages over a high-flex PS TKR regarding range of movement (ROM), ‘feel’ of the knee, pain and satisfaction, as well as during activity. A total of 24 female patients with bilateral osteoarthritis entered this prospective, blind randomised trial in which they received a high-flex PS TKR in one knee and a gender-specific high-flexion PS TKR in the other knee. At follow-up, patients were assessed clinically measuring ROM, and questioned about pain, satisfaction and daily ‘feel’ of each knee. Patients underwent gait analysis pre-operatively and at one year, which yielded kinematic, kinetic and temporospatial parameters indicative of knee function during gait. At final follow-up we found no statistically significant differences in ROM (p = 0.82). The median pain score was 0 (0 to 8) in both groups (p = 0.95). The median satisfaction score was 9 (4 to 10) in the high-flex group and 8 (0 to 10) in the gender-specific group (p = 0.98). The median ‘feel’ score was 9 (3 to 10) in the high-flex group and 8 (0 to 10) in the gender-specific group (p = 0.66). Gait analysis showed no statistically significant differences between the two prosthetic designs in any kinematic, kinetic or temporospatial parameters.

Both designs produced good clinical results with significant improvements in several gait parameters without evidence of any advantage in the gender-specific design.

Achieving deep flexion after total knee replacement remains a challenge. In this study we compared the soft-tissue tension and tibiofemoral force in a mobile-bearing posterior cruciate ligament-sacrificing total knee replacement, using equal flexion and extension gaps, and with the gaps increased by 2 mm each. The tests were conducted during passive movement in five cadaver knees, and measurements of strain were made simultaneously in the collateral ligaments. The tibiofemoral force was measured using a customised mini-force plate in the tibial tray. Measurements of collateral ligament strain were not very sensitive to changes in the gap ratio, but tibiofemoral force measurements were. Tibiofemoral force was decreased by a mean of 40% (sd 10.7) after 90° of knee flexion when the flexion gap was increased by 2 mm. Increasing the extension gap by 2 mm affected the force only in full extension. Because increasing the range of flexion after total knee replacement beyond 110° is a widely-held goal, small increases in the flexion gap warrant further investigation.

The requirement for release of collateral ligaments to achieve a stable, balanced total knee replacement has been reported to arise in about 50% to 100% of procedures. This wide range reflects a lack of standardised quantitative indicators to determine the necessity for a release. Using recent advances in computerised navigation, we describe two navigational predictors which provide quantitative measures that can be used to identify the need for release. The first was the ability to restore the mechanical axis before any bone resection was performed and the second was the discrepancy in the measured medial and lateral joint spaces after the tibial osteotomy, but before any femoral resection.

These predictors showed a significant association with the need for collateral ligament release (p < 0.001). The first predictor using the knee stress test in extension showed a sensitivity of 100% and a specificity of 98% and the second, the difference between medial and lateral gaps in millimetres, a sensitivity of 83% and a specificity of 95%. The use of the two navigational predictors meant that only ten of the 93 patients required collateral ligament release to achieve a stable, neutral knee.

The appearance of the ‘grand-piano sign’ on the anterior resected surface of the femur has been considered to be a marker for correct femoral rotational alignment during total knee replacement. Our study was undertaken to assess quantitatively the morphological patterns on the resected surface after anterior femoral resection with various angles of external rotation, using a computer-simulation technique. A total of 50 right distal femora with varus osteoarthritis in 50 Korean patients were scanned using computerised tomography. Computer image software was used to simulate the anterior femoral cut, which was applied at an external rotation of 0°, 3° and 6° relative to the posterior condylar axis, and parallel to the surgical and clinical epicondylar axes in each case. The morphological patterns on the resected surface were quantified and classified as the ‘grand-piano sign’, ‘the boot sign’ and the ‘butterfly sign’. The surgeon can use the analogy of these quantified sign patterns to ensure that a correct rotational alignment has been obtained intra-operatively.