There has been significant interest in day-case and rapid discharge pathways for unicompartmental knee replacements (UKR). Pathways to date have shown this to be a safe and feasible option; however, no studies to date have published results of rapid-discharge pathways using the NAVIO robotic system. To date there is no published experience with rapid discharge UKR patients using the NAVIO robotic system. We report an initial experience of 11 patients who have safely been discharged within 24 hours. With the primary goal of investigating factors that led to rapid discharge and a secondary goal of evaluating the safety of doing so.

All patients were discharged within 24 hours; there were no post-operative complications and no readmissions to hospital. The mean length of stay was 16.9 hours (SD=7.3), with most patients seen once on average by physiotherapy. Active range of motion at 6 weeks was 0.7o to 130.5 o, with all patients mobilising independently. The average 6-month post-operative Oxford Knee Score was 43.5 out of 48. There were no readmission or complications in any of our patients.

This initial feasibility study identified that patients could be safely discharged within 24 hours after UKR using the NAVIO robotic system. With growing uptake of robotic procedures, with longer operative durations than traditional procedures, it is essential to ensure a rapid discharge to reduce healthcare cost whilst ensuring that patients are discharged home in a safe manner.

In recent years, reduction in the length of stay in patients undergoing UKA has gained considerable interest. This has led to development of ‘fast-track' and even day-case protocols aimed at decreasing length of stay (LOS), enhancing post-operative recovery and decreasing post-operative morbidity. One potential barrier to faster discharge and patient recovery is the need for post-operative haemoglobin checks and allogenic blood transfusion; which has been shown to increase LOS. Allogenic blood transfusion itself is not without risk, including immunological reactions, transfusion associated lung injury, infection and transmission of disease, thus reducing blood loss and the need for transfusion is imperative. Currently there is a knowledge gap regarding post-operative transfusion need and blood loss following UKA. We aimed to investigate blood loss and transfusion rates following UKA. Our primary aim was to evaluate the extent of post-operative transfusion need following UKA and identify which patients are at higher risk of needing transfusion.

Following institutional approval, a retrospective analysis of all patients undergoing unicompartmental knee arthroplasty (UKA) at our level one academic university hospital was conducted. Operative records of all patients undergoing primary UKA were reviewed between March 2016 and March 2019. Patients' pre-operative haemoglobin and haematocrit, BMI, co-morbidities, application of tourniquet, tourniquet time, administration of Tranexamic Acid, need for post-operative blood transfusion, hospital length of stay, complications and re-admission were all recorded. Blood loss was estimated using the post-operative haematocrit.

A total number of 155 patients were included. There were 70 females (45%) and 85 males (55%). The mean age was 66±10 years. Median pre-op blood volume was 4700mls (IQR; 4200–5100). Median blood loss was 600 mls (IQR; 400–830). Mean pre-op Haemoglobin was 135±14g/L and mean post-op Haemoglobin was 122±13g/L. No patient had a post-op Haemoglobin under 80g/L (Range 93–154). No patients in our study needed transfusion. A further comparison group of high-blood loss and low-blood loss patients was included in analysis. High-blood loss patients were defined as those losing greater than 20% of their pre-operative blood volume whilst low-blood loss patients were defined as those losing ≤20% of their blood volume. Results of these groups are presented in Table 3. No significance was found between the two groups in patient's demographics and in terms of intra-operative factors including TXA usage (p=0.68) and tourniquet time (p=0.99). There was no difference in terms of post-operative complications (p=1.0), length of stay (p=0.36) or readmission rates (p=0.59).

The results of our study indicated that post-operative haemoglobin and haematocrit check proved unnecessary in all of our patients and could have been omitted from post-operative routines. We conclude that routine post UKA check of haemoglobin and haematocrit can be avoided and be saved for special circumstances depending on patient's physiology.

In light of recent regulatory initiatives, medical devices now require additional clinical evidence to prove their safety and efficacy. At the same time, patients' own assessment of their devices' function and performance has gained in importance. The collection of these data allows for a more comprehensive picture of clinical outcomes and complications following total knee arthroplasty (TKA).

These trends have led researchers to search for new methods of acquiring, interpreting and disseminating patient-reported outcome measurements (PROMs). The current study assesses the feasibility of a digital platform for collecting PROMs that was recently adapted for TKA patients. It sought to determine patient engagement, survey completion rates, and satisfaction with this platform.

Eighty-two patients (mean age, 63.7 years, 59% females) scheduled for TKA were enrolled from one US and six UK sites between January 12, 2018 and April 30, 2018. Patients were supplied with a mobile application (app) that collects a variety of PROMs, including four domains based on the Patient-Reported Outcome Information System (PROMIS™): physical function, depression, pain interference and pain behavior. The platform electronically administers questionnaires using computer-adaptive tests (CATs), which reduce the burden on patients by tailoring follow-up questions to account for their previous answers. Satisfaction with the app was assessed in subset of patients who evaluated its ease-of-use (n=45), likelihood that they would recommend it to family/friends (n=35), and whether they successfully used the information it provided during their recovery (n=31). These scores were taken on a 1 to 10 (worst to best) scale.

Patients demonstrated regular engagement with the platform, with 73% using the app at least once a week. Weekly engagement remained high throughout the seven-week post-operative period (Figure 1). There was a 69% completion rate of all PROMIS™ CAT surveys during the study. The four PROMIS™ CAT domains had similar survey completion rates (Figure 2). The subset of patients queried regarding their satisfaction with the app gave it favorable mean scores for ease-of-use (8.8), likelihood to recommend to a family member or friend (8.1), and their success at using its information to improve their recovery (7.4).

Initial results support this digital platform's potential for successfully and efficiently collecting large volumes of PROMs. Patients reported high levels of engagement and satisfaction.

For any figures or tables, please contact authors directly.

There has been a lot of focus on the value of anatomic tunnel placement in ACL reconstruction, and the relative merits of single and double bundle grafts. Multiple cadaveric and animal studies have compared the effects of tunnel placement and graft type on knee biomechanics. 45 patients who underwent ACL reconstruction were included into our study. Femoral tunnel position was analysed by two independent doctors using the radiographic quadrant method as described by Bernard et al., and the mean values calculated. Forty-one of these patients completed a KOOS questionnaire. The mean ratio ‘a’ was 26.57% and mean ratio ‘b’ was 30.04% as compared to 24.8% (+/− 2.2%) and 28.5% (+/− 2.5%) respectively quoted by Bernard et.al, as the ideal tunnel position. Only twenty-three of these femoral tunnels were in the anatomic range. Analysis of forty-one KOOS surveys (23 anatomic, 18 non-anatomic) revealed no significant difference in total score or subscales between the anatomic and non-anatomic groups (p= >0.05). Our study suggests that the ideal tunnel position, as described by Bernard et.al. may not be ideal and fixed.

Unicompartmental knee replacement (UKR) is technically challenging, but has the advantage over total knee replacement (TKR) of conserving bone and ligaments, preserving knee range of movement and stability. Computer navigation allows for accurate placement of the components, important for preventing failures secondary to mal-alignment. Evidence suggests an increase in failure rates beyond 3 degrees of coronal mal-alignment.

Our previous work has shown superior functional scores in those patients having undergone UKR, when compared with those having had TKR. However, to a certain extent, this is likely to be due to differences in the two cohorts. Those selected for UKRs are likely to be younger, with less advanced and less widespread degenerative disease. It is almost inevitable, therefore, that functional outcomes will be superior. We aimed to compare the functional and radiological outcomes of UKR vs TKR in a more matched population.

Ninety-two patients having had one hundred consecutive computer navigated UKRs were reviewed both clinically and radiographically. The Smith & Nephew Accuris fixed-bearing modular prosthesis was used in all cases, with the ‘Brainlab’ navigation system. For our comparative group we identified patients who had actually undergone navigated TKR several years ago, but who, in retrospect, would have now been offered a UKR in line with our current practice. These patients were identified following review of pre-operative radiographs and operation notes, confirming degenerative disease confined mainly to one compartment of the knee, in the absence of any concern as to the integrity of the anterior cruciate ligament. This sub-group of patients were also assessed clinically and radiographically. Mean follow-up for the UKR group was 25 months, (range 8–45.) For our TKR sub-group, nineteen patients were identified. Average length of stay for the UKR group was 3.7 days, (range 2 to 7,) and for the TKR group this was 5.2 days, (range 3 to 10.)

Functional scores (Oxford Knee Score) were good to excellent for the majority of patients in both groups, although they were significantly better in the UKR group. Mean Oxford Knee Score in the UKR group was 7.5, (0–48, with 0 being best.) Mean score in the TKR sub-group was 12.1. (p = 0.02)

Reliably comparing TKR with UKR is difficult, due to the fundamental differences in the two groups. We have endeavoured to match these two cohorts as best possible, in order to compare the outcomes of both. Our use of computer navigation in both groups allows for accurate prosthesis placement. When measuring component position, there were no ‘outliers,’ outside of the widely accepted three degrees of deviation.

We propose that, with the correct patient selection, UKR gives a better functional outcome than TKR. Longer-term follow-up of our UKR group is required to monitor the onset of progressive arthrosis in other joint compartments, although our early results are very encouraging. Furthermore, we advocate the use of computer navigation to firstly allow for more accurate component positioning, and secondly to make challenging UKR surgery less technically demanding.

Computer navigation has the potential to revolutionise orthopaedic surgery, although according to the latest 7^th Annual NJR Report, only 2% of the 5 800 unicompartmental knee replacements (UKRs) performed in 2009 were carried out using ‘image guidance.’ The report also states an average 3-year revision rate for UKRs of 6.5%. Previous NJR data has shown that this figure rises up to 12% for certain types of prosthesis. We suspect that a significant proportion of these revisions are due to failure secondary to component malpositioning. We therefore propose that the use of computer navigation enables a more accurate prosthesis placement, leading to a reduction in the revision rate for early failure secondary to component malpositioning. Our early results of one hundred consecutive computer navigated UKRs are presented and discussed.

Ninety-two patients having had one hundred consecutive computer navigated UKRs were reviewed both clinically and radiographically. The Smith & Nephew Accuris fixed-bearing modular prosthesis was used in all cases, with the ‘Brainlab’ navigation system. Pre-operative aim was neutral tibial cut with three degrees posterior slope. Post-operative component alignment was measured with PACs web measuring tools. Patients were scored clinically using the Oxford Knee Score.

Our patient cohort includes 54 male knees and 46 female knees. Average age is 66.6yrs. Average length of stay was 3.7 days, (range 2–7.) With respect to the tibial component, average alignment was 0.7° varus, and 2.32° posterior slope. All components were within the acceptable 3 degrees deviation. Functional scores are very satisfactory, with an overall patient satisfaction rate of 97%.

To date, only one UKR has required revision. This was due to ongoing medial pain due to medial overhang, not related to computer navigation. There was one superficial infection, with full resolution following a superficial surgical washout, debridement and antibiotics. Unlike complications reported in the NJR, we report no peri-prosthetic fractures or patella tendon injuries.

Our results demonstrate accurate prosthesis placement with the use of computer navigation. Furthermore, clinical scores are highly satisfactory. Our current revision rate is 1% at a mean of 27 months post-op. Although longer-term follow-up of our group is required, our results compare very favourably to statistics published in the NJR, (average 3-year revision rate 6.5%.) The only major differences appear to be the type of prosthesis used and the use of computer navigation. It is our proposal that computer navigation reduces the number of revisions required due to component malpositioning and subsequent failure. Furthermore, we believe that this challenging surgery is made easier with the use of computer navigation. We expect our longer-term results to show significant benefits of computer navigation over conventional techniques.

Computer navigation has the potential to revolutionise orthopaedic surgery. It is widely accepted that component malalignment and malrotation leads to early failure in knee arthroplasty. We aimed to assess the use and reliability of computer navigation in both total (TKR) and unicompartmental (UKR) knee replacement surgery.

We analysed 40 consecutive UKRs and 40 consecutive TKRs. All procedures were carried out with the Brain-LAB navigation system and all were carried out by one consultant orthopaedic surgeon. Preoperative aim was neutral tibial cuts with 3 degrees posterior slope. Coronal and sagittal alignment of tibial components were measured on postoperative radiographs. Patients were also scored clinically with regards to function and pain.

In the TKR group, mean tibial coronal alignment was 0° (range 1 to −2.) Mean sagittal alignment was 2° posterior slope (range 0 to 4.) In the UKR group, mean tibial coronal alignment was 0.55° (range 0 to −3.) Mean sagittal alignment was 2.1° posterior slope (range 0 to 4°.) Clinical outcome scores were very satisfactory for the majority of patients, with far superior functional scores in the UKR group.

Our results demonstrate very accurate placement of the prosthesis in both the TKR and UKR group with computer navigation. There is a very narrow range with no outliers, (all within +/−3 degrees of desired alignment.) Functional outcome scores are good. We advocate the use of computer navigation in unicompartmental as well as total knee replacment surgery, in order to minimise early failures.

Reconstructive knee arthroplasty in patients with limb deformity can be a daunting and complex task. These patients are often younger and so post traumatic osteoarthritis poses a real challenge. In view of their relative youth, bone preservation would be favourable; however accurate implantation of components is essential. Formulation of a well calculated plan and accurate execution is essential for successful surgery.

We report on a novel method which combines 3D CT joint analysis and computer navigation to define the deformity present pre-operatively and determine whether the proposed reconstruction is feasible. If the reconstructive surgery is feasible, an accurate calculation the correction required is performed. The planned surgery is executed using computer aided navigation surgery.

Eight patients have benefited from the technique. Four patients presented with isolated medial compartment osteoarthritis and intact anterior cruciate ligament. These patients underwent 3D CT joint analysis and computer assisted navigation surgery to accurately implant unicondylar knee replacements.

Four Patients presented with two or three compartment disease. These patients underwent similar 3D CT analysis and navigated Total Knee Replacement.

The series demonstrates the merits of 3D CT joint analysis to accurately define deformity and therefore determine pre-operatively feasibility of corrective surgery proposed. The technique is then complimented by computer assisted navigation surgery to ensure the proposed surgical plan is accurately executed.

Over 80% of patients are satisfied following total knee arthroplasty (TKA). Female gender was one of the factors found to be a predictor of poorer satisfaction. The landmarks commonly used to achieve correct rotation of the femoral component are the posterior condylar axis, the transepicondylar axes (TEA) & the anteroposterior axis (Whiteside’s line) of the distal femur. The design features of most conventional jig based TKA instrumentation assumes a constant relationship of 3 degrees external rotation between the posterior condylar axis & the epicondylar axis. However during TKA using computer assisted navigation, we observe that these rotational landmarks do not have a constant relationship & there is wide variation among the arthritic population & between the male & female rotational profile. We hypothesise no consistent relationship between the posterior condylar axis, the TEA & the anteroposterior axis of the distal femur.

125 Computerised Tomography (CT) scans of the knee were performed using a 3D helical CT scanner in subjects who did not have any pre-existing clinical & radiological evidence of knee arthritis. CT slices 3 mm in thickness were obtained over the distal femur from the level of the proximal pole of the patella. Standard protocols were established for identifying the bony landmarks & taking measurements. The posterior condylar axis, the TEA & the anteroposterior axis were constructed. The condylar twist angle (CTA), the posterior condy-lar angle (PCA) & the angles made by the TEA & the line perpendicular to the anteroposterior axis were then measured using the PACSWEB digital measurement tools. The data was analysed to determine the consistency of the angular relationship between the reference axes using the STATA data analysis & statistical software. Linear regression was used to investigate any differences in the angle measurements between genders.

125 CT scans of the knee were performed in 111 patients (60 males [65 knees] & 51 females [60 knees]). The mean age was 45 years (SD, 15 years). The results showed no significant difference between the rotational axes of the distal femur between men & women (CTA male(SD): female(SD): 5.9(1.6): 6.3(2.0) [p=0.317], PCA male(SD): female(SD): 2.3(1.5): 2.5(1.9) [p=0.648]). The results also showed it would be inappropriate to assume a constant relationship of 3 degress external rotation between the posterior condylar axis & the epicondylar axes (PCA mean (SD) 2.39(1.70) [p< 0.001], CTA mean (SD) 6.11(1.81) [p< 0.001]).

Our study suggests no significant difference between the rotational reference axes of the distal femur between men & women. Furthermore, most jig-based systems result in 3 degress external rotation of the femoral component. Our results show this is not consistent & may be responsible for the pain in 20% of patients post TKA because of abnormal patellar tracking.

Restoration of the position of the prosthetic joint line to the same level as the natural joint line, is a challenging problem in primary and revision knee arthroplasty and there is no reliable method for achieving this objective. We hypothesise that there is a constant ratio between the inter-epicondylar distance and the distance from this interepicondylar line to the joint line.

We analysed one hundred Computerised Tomography (CT) scans of the knee in the non arthritic population to study this relationship. The inter-epicondylar distance and the perpendicular distance from this inter-epicondylar line to the joint line was measured using both the clinical and surgical epicondylar axes for each knee as described in previous literature.

The results showed that using the clinical epicondylar axis the inter-epicondylar distance was 3 times the perpendicular distance from the inter-epicondylar line to the joint line (the median and mean ratio 3.0, Standard Deviation ±0.21). Using the surgical epicondylar axis the inter-epicondylar distance was 3.3 times the perpendicular distance from the inter-epicondylar line to the joint line (the median and mean ratio 3.3, SD ±0.25).

Landmarks such as inferior pole of patella or fibular head have been used to estimate the joint line position, but these methods have been shown to be unreliable. Our method will give an accurate estimate of the position of the joint line from the clinical epicondylar axis distance. This distance is easily calculated when using Computer Navigation for the surgery in both the primary and revision setting and the modern software programmes for Computer Assisted TKR should be modified accordingly. We conclude that the position of the joint line from the inter-epicondylar line is one-third of the inter-epicondylar distance which is valuable especially when there is significant bone loss at the tibio-femoral articulation.

The purpose of this study was to analyse the effects of two different biomechanical configurations on the tensile properties of equine patellar tendons. The study looked at a comparison of straight untwisted patellar tendons and double stranded, twisted specimens. The aim was to attempt a more anatomical Anterior Cruciate Ligament configuration when performing reconstruction using the patellar tendon.

Thirty four specimens were harvested and each sample group consisted of a pair of equine ligaments taken from the same animal. The first of the pair served as an ‘untwisted, straight ligament’ control group and the second as the ‘twisted, double stranded test group’. The ligament dimensions were measured for each specimen and the specimen was mounted on an Instron Series 4411© tensile testing machine and tensile load was applied until failure.

Results showed a clearly statistically significant reduction in the tensile properties (p< 0.005) of the twisted double stranded specimens which was against our original hypothesis. The results indicated that the twisted double stranded ligaments had only 65% of the tensile strength of their untwisted counterparts. Similar reductions were demonstrated when calculating energy to yield point and load at zero point yield stress. The results also demonstrated a significant reduction in the stiffness (Young’s Modulus) between the two test configurations.

The application of a double stranded twist to the patellar tendon confers no advantage in terms of tensile property of the ligament. In fact the application of such a model may cause significant reduction in strength and stiffness of the construct which may lead to early failure of the ACL patellar tendon autograft.