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The Bone & Joint Journal
Vol. 105-B, Issue 12 | Pages 1271 - 1278
1 Dec 2023
Rehman Y Korsvold AM Lerdal A Aamodt A

Aims. This study compared patient-reported outcomes of three total knee arthroplasty (TKA) designs from one manufacturer: one cruciate-retaining (CR) design, and two cruciate-sacrificing designs, anterior-stabilized (AS) and posterior-stabilized (PS). Methods. Patients scheduled for primary TKA were included in a single-centre, prospective, three-armed, blinded randomized trial (n = 216; 72 per group). After intraoperative confirmation of posterior cruciate ligament (PCL) integrity, patients were randomly allocated to receive a CR, AS, or PS design from the same TKA system. Insertion of an AS or PS design required PCL resection. The primary outcome was the mean score of all five subscales of the Knee injury and Osteoarthritis Outcome Score (KOOS) at two-year follow-up. Secondary outcomes included all KOOS subscales, Oxford Knee Score, EuroQol five-dimension health questionnaire, EuroQol visual analogue scale, range of motion (ROM), and willingness to undergo the operation again. Patient satisfaction was also assessed. Results. Patients reported similar levels of pain, function, satisfaction, and general health regardless of the prosthetic design they received. Mean maximal flexion (129° (95% confidence interval (CI) 127° to 131°) was greater in the PS group than in the CR (120° (95% CI 121° to 124°)) and AS groups (122° (95% CI 120° to 124°)). Conclusion. Despite differences in design and constraint, CR, AS, and PS designs from a single TKA system resulted in no differences in patient-reported outcomes at two-year follow-up. PS patients had statistically better ROM, but the clinical significance of this finding is unclear. Cite this article: Bone Joint J 2023;105-B(12):1271–1278


The Bone & Joint Journal
Vol. 106-B, Issue 7 | Pages 728 - 734
1 Jul 2024
Poppelaars MA van der Water L Koenraadt-van Oost I Boele van Hensbroek P van Bergen CJA

Aims. Paediatric fractures are highly prevalent and are most often treated with plaster. The application and removal of plaster is often an anxiety-inducing experience for children. Decreasing the anxiety level may improve the patientssatisfaction and the quality of healthcare. Virtual reality (VR) has proven to effectively distract children and reduce their anxiety in other clinical settings, and it seems to have a similar effect during plaster treatment. This study aims to further investigate the effect of VR on the anxiety level of children with fractures who undergo plaster removal or replacement in the plaster room. Methods. A randomized controlled trial was conducted. A total of 255 patients were included, aged five to 17 years, who needed plaster treatment for a fracture of the upper or lower limb. Randomization was stratified for age (five to 11 and 12 to 17 years). The intervention group was distracted with VR goggles and headphones during the plaster treatment, whereas the control group received standard care. As the primary outcome, the post-procedural level of anxiety was measured with the Child Fear Scale (CFS). Secondary outcomes included the children’s anxiety reduction (difference between CFS after and CFS before plaster procedure), numerical rating scale (NRS) pain, NRS satisfaction of the children and accompanying parents/guardians, and the children’s heart rates during the procedure. An independent-samples t-test and Mann-Whitney U test (depending on the data distribution) were used to analyze the data. Results. The post-procedural CFS was significantly lower (p < 0.001) in the intervention group (proportion of children with no anxiety = 78.6%) than in the control group (56.8%). The anxiety reduction, NRS pain and satisfaction scores, and heart rates showed no significant differences between the control group and the intervention group. Subanalyses showed an increased effect of VR on anxiety levels in young patients, females, upper limb fractures, and those who had had previous plaster treatment. Conclusion. VR effectively reduces the anxiety levels of children in the plaster room, especially in young girls. No statistically significant effects were seen regarding pain, heart rate, or satisfaction scores. Cite this article: Bone Joint J 2024;106-B(7):728–734


The Bone & Joint Journal
Vol. 106-B, Issue 10 | Pages 1059 - 1066
1 Oct 2024
Konishi T Hamai S Tsushima H Kawahara S Akasaki Y Yamate S Ayukawa S Nakashima Y

Aims

The Coronal Plane Alignment of the Knee (CPAK) classification has been developed to predict individual variations in inherent knee alignment. The impact of preoperative and postoperative CPAK classification phenotype on the postoperative clinical outcomes of total knee arthroplasty (TKA) remains elusive. This study aimed to examine the effect of postoperative CPAK classification phenotypes (I to IX), and their pre- to postoperative changes on patient-reported outcome measures (PROMs).

Methods

A questionnaire was administered to 340 patients (422 knees) who underwent primary TKA for osteoarthritis (OA) between September 2013 and June 2019. A total of 231 patients (284 knees) responded. The ­Knee Society Score 2011 (KSS 2011), Knee injury and Osteoarthritis Outcome Score-12 (KOOS-12), and Forgotten Joint Score-12 (FJS-12) were used to assess clinical outcomes. Using preoperative and postoperative anteroposterior full-leg radiographs, the arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) were calculated and classified based on the CPAK classification. To investigate the impact on PROMs, multivariable regression analyses using stepwise selection were conducted, considering factors such as age at surgery, time since surgery, BMI, sex, implant use, postoperative aHKA classification, JLO classification, and changes in aHKA and JLO classifications from preoperative to postoperative.


The Bone & Joint Journal
Vol. 101-B, Issue 8 | Pages 984 - 994
1 Aug 2019
Rua T Malhotra B Vijayanathan S Hunter L Peacock J Shearer J Goh V McCrone P Gidwani S

Aims. The aim of the Scaphoid Magnetic Resonance Imaging in Trauma (SMaRT) trial was to evaluate the clinical and cost implications of using immediate MRI in the acute management of patients with a suspected fracture of the scaphoid with negative radiographs. Patients and Methods. Patients who presented to the emergency department (ED) with a suspected fracture of the scaphoid and negative radiographs were randomized to a control group, who did not undergo further imaging in the ED, or an intervention group, who had an MRI of the wrist as an additional test during the initial ED attendance. Most participants were male (52% control, 61% intervention), with a mean age of 36.2 years (18 to 73) in the control group and 38.2 years (20 to 71) in the intervention group. The primary outcome was total cost impact at three months post-recruitment. Secondary outcomes included total costs at six months, the assessment of clinical findings, diagnostic accuracy, and the participants’ self-reported level of satisfaction. Differences in cost were estimated using generalized linear models with gamma errors. Results. The mean cost up to three months post-recruitment per participant was £542.40 (. sd. £855.20, n = 65) for the control group and £368.40 (. sd. £338.60, n = 67) for the intervention group, leading to an estimated cost difference of £174 (95% confidence interval (CI) -£30 to £378; p = 0.094). The cost difference per participant increased to £266 (95% CI £3.30 to £528; p = 0.047) at six months. Overall, 6.2% of participants (4/65, control group) and 10.4% of participants (7/67, intervention group) had sustained a fracture of the scaphoid (p = 0.37). In addition, 7.7% of participants (5/65, control group) and 22.4% of participants (15/67, intervention group) had other fractures diagnosed (p = 0.019). The use of MRI was associated with higher diagnostic accuracy both in the diagnosis of a fracture of the scaphoid (100.0% vs 93.8%) and of any other fracture (98.5% vs 84.6%). Conclusion. The use of immediate MRI in the management of participants with a suspected fracture of the scaphoid and negative radiographs led to cost savings while improving the pathway’s diagnostic accuracy and patient satisfaction. Cite this article: Bone Joint J 2019;101-B:984–994


The Bone & Joint Journal
Vol. 106-B, Issue 11 | Pages 1231 - 1239
1 Nov 2024
Tzanetis P Fluit R de Souza K Robertson S Koopman B Verdonschot N

Aims

The surgical target for optimal implant positioning in robotic-assisted total knee arthroplasty remains the subject of ongoing discussion. One of the proposed targets is to recreate the knee’s functional behaviour as per its pre-diseased state. The aim of this study was to optimize implant positioning, starting from mechanical alignment (MA), toward restoring the pre-diseased status, including ligament strain and kinematic patterns, in a patient population.

Methods

We used an active appearance model-based approach to segment the preoperative CT of 21 osteoarthritic patients, which identified the osteophyte-free surfaces and estimated cartilage from the segmented bones; these geometries were used to construct patient-specific musculoskeletal models of the pre-diseased knee. Subsequently, implantations were simulated using the MA method, and a previously developed optimization technique was employed to find the optimal implant position that minimized the root mean square deviation between pre-diseased and postoperative ligament strains and kinematics.


The Bone & Joint Journal
Vol. 105-B, Issue 5 | Pages 471 - 473
1 May 2023
Peterson N Perry DC

Salter-Harris II fractures of the distal tibia affect children frequently, and when they are displaced present a treatment dilemma. Treatment primarily aims to restore alignment and prevent premature physeal closure, as this can lead to angular deformity, limb length difference, or both. Current literature is of poor methodological quality and is contradictory as to whether conservative or surgical management is superior in avoiding complications and adverse outcomes. A state of clinical equipoise exists regarding whether displaced distal tibial Salter-Harris II fractures in children should be treated with surgery to achieve anatomical reduction, or whether cast treatment alone will lead to a satisfactory outcome. Systematic review and meta-analysis has concluded that high-quality prospective multicentre research is needed to answer this question. The Outcomes of Displaced Distal tibial fractures: Surgery Or Casts in KidS (ODD SOCKS) trial, funded by the National Institute for Health and Care Research, aims to provide this high-quality research in order to answer this question, which has been identified as a top-five research priority by the British Society for Children’s Orthopaedic Surgery.

Cite this article: Bone Joint J 2023;105-B(5):471–473.


The Bone & Joint Journal
Vol. 106-B, Issue 6 | Pages 582 - 588
1 Jun 2024
Bertram W Howells N White SP Sanderson E Wylde V Lenguerrand E Gooberman-Hill R Bruce J

Aims

The aim of this study was to describe the prevalence and patterns of neuropathic pain over one year in a cohort of patients with chronic post-surgical pain at three months following total knee arthroplasty (TKA).

Methods

Between 2016 and 2019, 363 patients with troublesome pain, defined as a score of ≤ 14 on the Oxford Knee Score pain subscale, three months after TKA from eight UK NHS hospitals, were recruited into the Support and Treatment After Replacement (STAR) clinical trial. Self-reported neuropathic pain and postoperative pain was assessed at three, nine, and 15 months after surgery using the painDETECT and Douleur Neuropathique 4 (DN4) questionnaires collected by postal survey.


The Bone & Joint Journal
Vol. 98-B, Issue 10_Supple_B | Pages 11 - 15
1 Oct 2016
Konan S Haddad FS

Aims. Medial unicompartmental knee arthroplasty (UKA) is associated with successful outcomes in carefully selected patient cohorts. We hypothesised that severity and location of patellofemoral cartilage lesions significantly influences functional outcome after Oxford medial compartmental knee arthroplasty. Patients and Methods. We reviewed 100 consecutive UKAs at minimum eight-year follow-up (96 to 132). A single surgeon performed all procedures. Patients were selected based on clinical and plain radiographic assessment. All patients had end-stage medial compartment osteoarthritis (OA) with sparing of the lateral compartment and intact anterior cruciate ligaments. None of the patients had end-stage patellofemoral OA, but patients with anterior knee pain or partial thickness chondral loss were not excluded. There were 57 male and 43 female patients. The mean age at surgery was 69 years (41 to 82). At surgery the joint was carefully inspected for patellofemoral chondral loss and this was documented based on severity of cartilage loss (0 to 4 Outerbridge grading) and topographic location (medial, lateral, central, and superior or inferior). Functional scores collected included Oxford Knee Score (OKS), patient satisfaction scale and University College Hospital (UCH) knee score. Intraclass correlation was used to compare chondral damage to outcomes. Results. All patients documented significant improvement in pain and improved functional scores at mid-term follow-up. There were four revisions (mean 2.9 years, 2 to 4; standard deviation (. sd). 0.9) in this cohort, three for tibial loosening and one for femoral loosening. There was one infection that was treated with debridement and insert exchange. The mean OKS improved from 23.2 (. sd. 7.1) to 39.1 (. sd. 6.9); p < 0.001. The cohort with central and lateral grade 3 patellofemoral OA documented lower mean satisfaction with pain (90, . sd.  11.8) and function (87.5, . sd. 10.3) on the patient satisfaction scale. On the UCH scale, patients reported significantly decreased mean overall scores (7.3, . sd. 1.2 vs 9, . sd. 2.3) as well as stair climb task (3.5, . sd. 0.3 vs 5, . sd. 0.1) when cartilage lesions were located centrally or laterally on the PFJ. Patients with medial chondral PFJ lesions behave similar to patients with no chondral lesions. Conclusion. Topographical location and severity of cartilage damage of the patella can significantly influence function after successful Oxford medial UKA. Surgeons should factor this in when making their operative decision, and undertake to counsel patients appropriately. Cite this article: Bone Joint J 2016;98-B(10 Suppl B):11–15


The Bone & Joint Journal
Vol. 103-B, Issue 6 | Pages 1088 - 1095
1 Jun 2021
Banger M Doonan J Rowe P Jones B MacLean A Blyth MJB

Aims

Unicompartmental knee arthroplasty (UKA) is a bone-preserving treatment option for osteoarthritis localized to a single compartment in the knee. The success of the procedure is sensitive to patient selection and alignment errors. Robotic arm-assisted UKA provides technological assistance to intraoperative bony resection accuracy, which is thought to improve ligament balancing. This paper presents the five-year outcomes of a comparison between manual and robotically assisted UKAs.

Methods

The trial design was a prospective, randomized, parallel, single-centre study comparing surgical alignment in patients undergoing UKA for the treatment of medial compartment osteoarthritis (ISRCTN77119437). Participants underwent surgery using either robotic arm-assisted surgery or conventional manual instrumentation. The primary outcome measure (surgical accuracy) has previously been reported, and, along with secondary outcomes, were collected at one-, two-, and five-year timepoints. Analysis of five-year results and longitudinal analysis for all timepoints was performed to compare the two groups.


The Bone & Joint Journal
Vol. 103-B, Issue 4 | Pages 672 - 680
1 Apr 2021
Clement ND Scott CEH Murray JRD Howie CR Deehan DJ

Aims

The aim of this study was to assess the quality of life of patients on the waiting list for a total hip (THA) or knee arthroplasty (KA) during the COVID-19 pandemic. Secondary aims were to assess whether length of time on the waiting list influenced quality of life and rate of deferral of surgery.

Methods

During the study period (August and September 2020) 843 patients (THA n = 394, KA n = 449) from ten centres in the UK reported their EuroQol five dimension (EQ-5D) scores and completed a waiting list questionnaire (2020 group). Patient demographic details, procedure, and date when listed were recorded. Patients scoring less than zero for their EQ-5D score were defined to be in a health state “worse than death” (WTD). Data from a retrospective cohort (January 2014 to September 2017) were used as the control group.


The Bone & Joint Journal
Vol. 102-B, Issue 11 | Pages 1511 - 1518
1 Nov 2020
Banger MS Johnston WD Razii N Doonan J Rowe PJ Jones BG MacLean AD Blyth MJG

Aims

The aim of this study was to compare robotic arm-assisted bi-unicompartmental knee arthroplasty (bi-UKA) with conventional mechanically aligned total knee arthroplasty (TKA) in order to determine the changes in the anatomy of the knee and alignment of the lower limb following surgery.

Methods

An analysis of 38 patients who underwent TKA and 32 who underwent bi-UKA was performed as a secondary study from a prospective, single-centre, randomized controlled trial. CT imaging was used to measure coronal, sagittal, and axial alignment of the knee preoperatively and at three months postoperatively to determine changes in anatomy that had occurred as a result of the surgery. The hip-knee-ankle angle (HKAA) was also measured to identify any differences between the two groups.


The Bone & Joint Journal
Vol. 103-B, Issue 2 | Pages 329 - 337
1 Feb 2021
MacDessi SJ Griffiths-Jones W Harris IA Bellemans J Chen DB

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).

Methods

A radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type.


The Bone & Joint Journal
Vol. 102-B, Issue 10 | Pages 1297 - 1302
3 Oct 2020
Kurosaka K Tsukada S Ogawa H Nishino M Nakayama T Yoshiya S Hirasawa N

Aims

Although periarticular injection plays an important role in multimodal pain management following total hip arthroplasty (THA), there is no consensus on the optimal composition of the injection. In particular, it is not clear whether the addition of a corticosteroid improves the pain relief achieved nor whether it is associated with more complications than are observed without corticosteroid. The aim of this study was to quantify the safety and effectiveness of cortocosteroid use in periarticular injection during THA.

Methods

We conducted a prospective, two-arm, parallel-group, randomized controlled trial involving patients scheduled for unilateral THA. A total of 187 patients were randomly assigned to receive periarticular injection containing either a corticosteroid (CS group) or without corticosteroid (no-CS group). Other perioperative interventions were identical for all patients. The primary outcome was postoperative pain at rest during the initial 24 hours after surgery. Pain score was recorded every three hours until 24 hours using a 100 mm visual analogue scale (VAS). The primary outcome was assessed based on the area under the curve (AUC).


The Bone & Joint Journal
Vol. 102-B, Issue 4 | Pages 434 - 441
1 Apr 2020
Hamilton DF Burnett R Patton JT MacPherson GJ Simpson AHRW Howie CR Gaston P

Aims

There are comparatively few randomized studies evaluating knee arthroplasty prostheses, and fewer still that report longer-term functional outcomes. The aim of this study was to evaluate mid-term outcomes of an existing implant trial cohort to document changing patient function over time following total knee arthroplasty using longitudinal analytical techniques and to determine whether implant design chosen at time of surgery influenced these outcomes.

Methods

A mid-term follow-up of the remaining 125 patients from a randomized cohort of total knee arthroplasty patients (initially comprising 212 recruited patients), comparing modern (Triathlon) and traditional (Kinemax) prostheses was undertaken. Functional outcomes were assessed with the Oxford Knee Score (OKS), knee range of movement, pain numerical rating scales, lower limb power output, timed functional assessment battery, and satisfaction survey. Data were linked to earlier assessment timepoints, and analyzed by repeated measures analysis of variance (ANOVA) mixed models, incorporating longitudinal change over all assessment timepoints.


The Bone & Joint Journal
Vol. 102-B, Issue 1 | Pages 117 - 124
1 Jan 2020
MacDessi SJ Griffiths-Jones W Chen DB Griffiths-Jones S Wood JA Diwan AD Harris IA

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).

Methods

We conducted a randomized superiority trial comparing patients undergoing TKA assigned to KA within a restrictive safe zone or MA. Optimal knee balance was defined as an intercompartmental pressure difference (ICPD) of 15 psi or less using a pressure sensor. The primary endpoint was the mean intraoperative ICPD at 10° of flexion prior to knee balancing. Secondary outcomes included balance at 45° and 90°, requirements for balancing procedures, and presence of tibiofemoral lift-off.


The Bone & Joint Journal
Vol. 101-B, Issue 8 | Pages 941 - 950
1 Aug 2019
Scott CEH MacDonald DJ Howie CR

Aims

The EuroQol five-dimension (EQ-5D) questionnaire is a widely used multiattribute general health questionnaire where an EQ-5D < 0 defines a state ‘worse than death’ (WTD). The aim of this study was to determine the proportion of patients awaiting total hip arthroplasty (THA) or total knee arthroplasty (TKA) in a health state WTD and to identify associations with this state. Secondary aims were to examine the effect of WTD status on one-year outcomes.

Patients and Methods

A cross-sectional analysis of 2073 patients undergoing 2073 THAs (mean age 67.4 years (sd 11.6; 14 to 95); mean body mass index (BMI) 28.5 kg/m2 (sd 5.7; 15 to 72); 1253 female (60%)) and 2168 patients undergoing 2168 TKAs (mean age 69.3 years (sd 9.6; 22 to 91); BMI 30.8 kg/m2 (sd 5.8; 13 to 57); 1244 female (57%)) were recorded. Univariate analysis was used to identify variables associated with an EQ-5D score < 0: age, BMI, sex, deprivation quintile, comorbidities, and joint-specific function measured using the Oxford Hip Score (OHS) or Oxford Knee Score (OKS). Multivariate logistic regression was performed. EQ-5D and OHS/OKS were repeated one year following surgery in 1555 THAs and 1700 TKAs.


The Bone & Joint Journal
Vol. 101-B, Issue 4 | Pages 461 - 469
1 Apr 2019
Lädermann A Schwitzguebel AJ Edwards TB Godeneche A Favard L Walch G Sirveaux F Boileau P Gerber C

Aims

The aim of this study was to report the outcomes of different treatment options for glenoid loosening following reverse shoulder arthroplasty (RSA) at a minimum follow-up of two years.

Patients and Methods

We retrospectively studied the records of 79 patients (19 men, 60 women; 84 shoulders) aged 70.4 years (21 to 87) treated for aseptic loosening of the glenosphere following RSA. Clinical evaluation included pre- and post-treatment active anterior elevation (AAE), external rotation, and Constant score.


The Bone & Joint Journal
Vol. 100-B, Issue 4 | Pages 468 - 474
1 Apr 2018
Kirzner N Zotov P Goldbloom D Curry H Bedi H

Aims

The aim of this retrospective study was to compare the functional and radiological outcomes of bridge plating, screw fixation, and a combination of both methods for the treatment of Lisfranc fracture dislocations.

Patients and Methods

A total of 108 patients were treated for a Lisfranc fracture dislocation over a period of nine years. Of these, 38 underwent transarticular screw fixation, 45 dorsal bridge plating, and 25 a combination technique. Injuries were assessed preoperatively according to the Myerson classification system. The outcome measures included the American Orthopaedic Foot and Ankle Society (AOFAS) score, the validated Manchester Oxford Foot Questionnaire (MOXFQ) functional tool, and the radiological Wilppula classification of anatomical reduction.


The Bone & Joint Journal
Vol. 99-B, Issue 5 | Pages 640 - 646
1 May 2017
Matsumoto T Takayama K Ishida K Hayashi S Hashimoto S Kuroda R

Aims

The aim of this study was to compare the post-operative radiographic and clinical outcomes between kinematically and mechanically aligned total knee arthroplasties (TKAs).

Patients and Methods

A total of 60 TKAs (30 kinematically and 30 mechanically aligned) were performed in 60 patients with varus osteoarthritis of the knee using a navigation system. The angles of orientation of the joint line in relation to the floor, the conventional and true mechanical axis (tMA) (the line from the centre of the hip to the lowest point of the calcaneus) were compared, one year post-operatively, on single-leg and double-leg standing long leg radiographs between the groups. The range of movement and 2011 Knee Society Scores were also compared between the groups at that time.


The Bone & Joint Journal
Vol. 100-B, Issue 1 | Pages 50 - 55
1 Jan 2018
Kono K Tomita T Futai K Yamazaki T Tanaka S Yoshikawa H Sugamoto K

Aims

In Asia and the Middle-East, people often flex their knees deeply in order to perform activities of daily living. The purpose of this study was to investigate the 3D kinematics of normal knees during high-flexion activities. Our hypothesis was that the femorotibial rotation, varus-valgus angle, translations, and kinematic pathway of normal knees during high-flexion activities, varied according to activity.

Materials and Methods

We investigated the in vivo kinematics of eight normal knees in four male volunteers (mean age 41.8 years; 37 to 53) using 2D and 3D registration technique, and modelled the knees with a computer aided design program. Each subject squatted, kneeled, and sat cross-legged. We evaluated the femoral rotation and varus-valgus angle relative to the tibia and anteroposterior translation of the medial and lateral side, using the transepicodylar axis as our femoral reference relative to the perpendicular projection on to the tibial plateau. This method evaluates the femur medially from what has elsewhere been described as the extension facet centre, and differs from the method classically applied.