Introduction. Ideally, a patient receiving a unicondylar knee replacement will have fully functional anterior and posterior cruciate ligaments. When at least one of the cruciate ligaments is not fully functional, femoral and tibial implant contact position can potentially increase along the anterior-posterior (AP) axis. Where unicondylar implant wear testing typically uses AP resistance assuming fully functional cruciate ligaments, the authors used reduced AP resistance intended to simulate deficient cruciate ligaments. Methods. Optetrak Logic® Uni (Exactech Inc, Gainesville, FL USA) unicondylar test specimens featuring an all-UHMWPE tibial component and a cobalt chromium femoral component were used in this study. The system has a semi-constrained articular geometry. Testing was conducted at an independent testing facility (EndoLab GMBH, Thansau, Rosenheim, Germany). A four-station knee simulator was used (EndoLab knee simulator) with two unicondylar knee implants per station, giving a total of eight test specimens. Two different tibial fixation designs (keeled and peg) with identical articulating surfaces were tested. Tibial test specimens were 6 mm in thickness. Unloaded soak controls were stored in distilled water at 37°C. The test was conducted according to ISO 14243–1: 2009 [1]. Test specimens were immersed in calf serum (PAA GmBH, Cölbe, LOT B00111-5126) with a protein content of 20 g/l. Custom polyurethane molds allowed for individual component measurement. Per the ISO 14243-1, a 7% medial offset was incorporated into the set-up. The unicondylar knee implants were set at neutral position in extension. Tibial rotational restraint was 0.36 Nm/° and zero when the test specimen was within ± 6° of the reference position. This test was conducted with an AP resistance of 9.3N/mm to maximize AP displacement and simulate deficient cruciate ligaments. Typical unicondylar knee wear testing is conducted with an AP resistance of 44N/mm, which assumes functional cruciate ligaments. Results. Wear data was separated by component design (keeled and peg) as well as for medial and lateral placement [Table 1]. There was no significant difference between lateral components but there was for medial components. This difference could be due to the small sample size. Contact area of the UHMWPE tibial components was elliptical, with the longer portion along the AP axis. Mean wear rates were comparable to historical unicondylar knee systems tested at the same laboratory using the standard AP resistance (i.e., 44 N/mm). Discussion/Conclusion. This study demonstrated using an AP resistance 9.3 N/mm to simulate the presence of deficient cruciate ligaments in a unicondylar knee wear test produced similar wear rates and greater AP displacement when compared to testing using an AP resistance of 44 N/mm, which assumes functioning ligaments. This being said, design and material information about historical unicondylar knee systems tested are not known, so a direct comparison cannot be made. Performing unicondylar knee wear tests with reduced AP resistance could provide realistic wear information for devices implanted in patients without fully functioning cruciate ligaments

Aim: Our goal was to evaluate the short term result of medial unicondylar arthroplasty in a valgus knee and to determine the reason for medial compartment osteoarthritis (OA) in a valgus knee. Material and method: Between 1997–2001 312 unicondylar arthroplasties have been carried out at our department. 8 were lateral the others were all medial. Of the 304 medial 10 were done for a valgus knee. We examined the pre- and postoperative mechanical and anatomical axis. We rated the knees using the American Knee Society Knee Score on avarage at 5 years follow-up. Intra- and postoperative complications, revisions are noted. Results: All of the knees had an anatomical axis of increased valgus. The mechanical axis differed, from 3 degrees of varus to 4 degrees of valgus. 8 of the patients rated the result excellent or good. 1 had an acceptable result, 1 had a revision. Conclusion: Medial compartment OA can develop in a knee with an anatomical axis in valgus, and a mechanical axis of varus. It can be succesfully treated with medial unicondylar arthroplasty. The results are similar to medial unicondylar arthroplasty in a varus knee

Aims: To determine the kneeling ability in 3 groups of patients who have undergone either Unicondylar, Primary, or Revision knee arthroplasty. Methods: A questionnaire was designed to determine the kneeling ability of patients who have undergone knee arthroplasty surgery. The ‘Kneeling’ questionnaire along with a Western Ontario and MacMaster Osteoarthritis Index (WOMAC) questionnaire was sent to 191 patients of whom, 27 have had Unicondylar, 105 had Primary and 59 Revision knee arthroplasty. Results: The mean follow-up time for assessment for each of the 3 groups of patients were; Unicondylar = 3.32 years, Primary = 5.30 years and Revision = 5.06 years. The mean total WOMAC scores for the 3 groups were; Unicondylar = 13.96, Primary = 22.10, and Revision = 38.67. The percentage of patients who underwent knee arthroplasty that found it impossible to kneel were; Unicondylar = 18%, Primary = 36% and Revision = 66%. The commonest reasons why patients found kneeling difficult were; pain and stiffness around the knee prosthesis, fear of harming the prosthesis and sensory deficit around the knee. Visual Analogue Pain scores for kneeling in the 3 patient groups were, Unicondylar = 5.6, Primary = 7.12, Revision = 9.18. A minimum of 30% of patients in each of the 3 groups reported their daily lives were moderately-severely affected due to their difficulty in kneeling following knee arthroplasty. At least 60% of the patients in each group reported they would like to have better kneeling ability. Conclusion: Unicondylar knee arthroplasty patients have better WOMAC scores and find kneeling easier than patients who have undergone Primary knee arthroplasty (p< 0.01). The Primary group have better WOMAC scores and find kneeling easier than the Revision group (p< 0.001). Kneeling is considered important in patients who have undergone knee arthroplasty. Poor kneeling ability in patients may restrict their daily activities

Aim of the Study: Evaluation of differences in pro-prioception, gait analysis, electromyography in consideration of clinical results in patients with unicondylar and bicondylar knee arthroplasty. Material and Methods: 17 patients with mean age of 62.5 years were examined after a mean time of 21.5 months after unicondylar knee arthroplasty and compared with 15 patients with a mean age of 67 years and a mean time of 31.9 months after bicondylar knee arthroplasty. For clinical examination the Knee Society, Hospital for Special Surgery and Patella Score were used. Proprioception was examined using the Balance test. In addition each patient was examined by gait analysis with three-dimensional-kinematics and force plate. M. rectus femoris, M. vastus medialis/lateralis, M. semiten-dinosus, M. biceps femoris, M. tibialis anterior and M. gastrocnemius were examined by electromyography. Results: There were neither significant deviations in demographic data, clinical scores, electromyography results (except M. vastus lateralis), gait analysis nor in proprioception. Conclusion: There were no deviations in any clinical or functional results in patients with unicondylar and bicon-dylar knee arthroplasty. Because of the uncertain long term results of unicondylar knee arthroplasty in respect of loosening and development of contralateral osteoarthritis, bicondylar knee arthroplasty can be approved

One of the advantage in using unicondylar prosthesis seems to be the preservation of the bone stock, which allows most often easily revision to a total knee replacement if required. The purpose of the study was to compare the patients outcome after revision of unicondylar prosthesis with a group of patients who have received total knee replacement primarily. Material and Method: 28 patients after revision unicondylar prosthesis (group A) and 28 patients after primary total knee replacement (group B) were included in the study. The two groups were matched according to age, sex, weight, height, type of prosthesis and follow-up time. The patients’ evaluation was based on the Knee-Society-Score and the WOMAC-score. X-rays of the knee were taken in the AP weight bearing and lateral view. Results: In group A the average follow-up time was 55±15 months and in group B 56±13 months. The knee-score showed 71.8±18 and 80.4±10.4 points and the function-score 56.1±15 and 62±19 points for group A and group B respectively without any statistical difference. The subjective assessment according to the WOMAC score showed difference in the functional outcome. A better range of motion of 110±11° was noticed for group B in comparison with group A 102±8° (p=0.004). The revised patients required a significantly higher poly-ethylene-inlay (12.9±3mm) compared to the primarily implanted ones (10.3±3mm) (p=0.004). Discussion: Based on our findings revision of unicondylar to total knee replacement provides comparable results to primarily implanted total knee arthroplasty and should be considered for the treatment of unicompartmetal osteoarthritis even in younger patients, where a revision operation during lifetime is more likely. Despite the difference regarding the height of the inlay of 3mm, adequate bone stock was still found in order to implant an unconstraint type of knee prosthesis. The impaired functional outcome seems to be related to the fact of the reoperation and a significant longer history of osteoarthritis for group A in comparison with group B

Background: Unicondylar knee arthroplasty (UKA) are being expanded to include younger patients with more active lifestyles because of its minimally invasive nature. Prior to expanding this role, it is important to examine mode of failure and implication of conversion to TKA in the low demand elderly patients. Aim: To ascertain the modes of early failure of unicondylar knee Arthroplasty and assess whether the conversion to TKA improved the functional scores, range of motion, pain, and patient satisfaction. Method: A retrospective study to evaluate the results of 14 revision procedures after failed unicompartmental knee arthroplasty (UKA). Patients’ operative charts were reviewed. Details of modes of failure, technical difficulty of revision including exposure, component removal, and management of bone loss were noted. Post operative functional outcome was assessed using WOMAC osteoarthritis index and SF-36. Result: Total of 106 primary unicondylar knee arthroplasty procedures was performed between 2003 and 2007 in our institution. Oxford unicondylar implant was used in all patients. 13.21% of these were revised to total knee replacement. Revisions were performed 4 months to 36 months after the primary procedure; 86% of these were required within the first 12 months. The average time to failure was 15.6 months. The modes of failure were aseptic loosening (4), progression of osteoarthritis (2), instability (3), infection (2), dislocated insert (1) and persistent pain after UKA (2). Tibia insert exchange was done in one patient and the rest were converted to primary Scorpio and PFC components. Three of the patients had significant defect in femoral condyle. Fourteen percent of cases required femoral stem extension or metal wedge augmentation. Nine of the 14 knees (64%) were followed up for an average of 15 months. The mean WOMAC and SF-36 scores at latest follow up were 33.33 and 63.79 respectively. Conclusion: Despite the advantage of minimally invasive UKA, early failure can occur in the face of good surgical technique. The higher long-term success rate claimed by implant manufacturer is challengeable and patient should be informed during consent

The introduction of unicondylar knee prostheses has allowed the preservation of the non-diseased compartment of the knee whilst replacing the diseased or damaged compartment. However, as is well known, there is concern that the body’s biological reaction to ultra-high molecular weight polyethylene (UHMWPE) wear particles leads to bone resorption and subsequent loosening and failure of the joint. Also, in some cases, delamination of the UHMWPE tibial bearing surface has been found to occur leading to failure of these conventional joints. Therefore new material combinations have been investigated within the laboratory. The unicondylar knee that was tested consisted of CoCrMo tibial and femoral components between which a mobile Pitch-based carbon fibre reinforced polyetheretherketone (CFR-PEEK OPTIMA®) meniscal bearing was mounted. The joints were supplied by INVIBIO Ltd. Tribological tests were performed on these knees using the Durham six station knee wear simulator and the Durham friction simulator II. In both cases the loading and motion were similar to the standard walking cycle. On the six station wear machine five stations applied both the loading and motion and were the active stations and one applied loading only as it was used as the loaded soak control station. Approximately every 500,000 cycles, the wear of the CFR-PEEK meniscal bearings was assessed gravimetrically (using a Mettler Toledo AX 205 balance, accurate to 0.01 mg) and the loaded soak control was used to take account of any change in weight due to lubricant absorption. The joints were tested to five million cycles (equivalent to approximately five years in vivo) with diluted new-born calf serum as the lubricant which gave a protein content of 17 gl-1. At periods throughout the wear test the surface topography was measured on the Zygo NewView 100 non-contacting profilometer. Friction tests were performed at the beginning and the end of the wear test. The average volumetric wear rate of the medial and lateral components was found to be 1.70 and 1.02 mm3/million cycles respectively (range 0.66 – 2.73 and 0.59 – 2.45 mm3/million cycles respectively). This is lower than the reported wear rate of metal-on-UHMWPE unicondylar knee joints (6.69 and 2.98 mm3/million cycles for the medial and lateral components respectively) [. 1. ]. The surface topographical analysis of the CFR-PEEK bearings showed a reduction in surface roughness and also a change to more negative skewness (i.e. more valleys than peaks) which may aid in lubrication. Before and after wear testing the joints were found to be operating in the boundary/mixed lubrication regime. The Pitch-based CFR-PEEK unicondylar knee joints performed well in these wear tests. They gave lower volumetric wear rates than metal-on-UHMWPE uni-condylar knee prostheses. The friction tests showed that at physiological viscosities, these joints operate in the boundary/mixed lubrication regime. These results show that this novel joint couple may potentially be an alternative solution for the reduction of wear and osteolysis. The authors wish to thank INVIBIO Ltd for funding this research

Introduction. Unicondylar knee replacement (UKR) surgery is proven long term results in its benefit in medial compartment OA. However, its results are sensitive to component alignment with poor alignment leading to early failure. The advent of computer navigation has resulted in improved mechanical alignment, but little has been published on the outcomes of navigated UKR surgery. We present the results of 253 consecutive Computer Assisted UKR's performed by a single surgeon. Objective. Assess clinical and radiological outcomes of Computer Assisted Unicondylar Knee Replacement at 5 years follow-up. Methods. Between August 2003 and June 2007, 253 UKR's were performed by a single surgeon using the Stryker Knee navigation system. Pre-operative Knee Society Scores (KSS) were recorded. The UKR's consisted of 98 oxford UKR's and 155 MG UKR's. Tourniquet time, time to straight leg raise and time to discharge was also recorded. All patients had post op KSS scores and long leg standing radiographs. Data regarding revision surgery was also collected. Results. Pre-op mean KSS scores was 54 (24–62) and post-op scores were a mean of 89 (75–100). 92% percent of femoral components were aligned at 90+/− 4 degrees from neutral in the coronal plane whilst eighty nine percent of tibial components were aligned at 90+/− 4 degrees from neutral in the coronal plane. Mean tourniquet time was 53 minutes whilst 98% of patients had SLR at 24hours. Only two percent of patients had an overall valgus alignment of their limb at the end of the procedure on long leg radiographs. 1% of the UKRs underwent revision for loosening of the femoral component. 1 oxford UKR was revised for progression of patello-femoral disease. One MG UKR was revised for unexplained pain. Conclusion. Our single surgeon series of Computer Assisted UKR demonstrates favourable outcomes in the medium term with 98% survival at 5 years. Computer Assisted UKR allows accurate and reproducible alignment of the tibial and femoral component. We recommend the use of Computer Navigation in performing Unicondylar Knee Replacements

Introduction and Aims: We present a review of the long-term results of custom-made massive unicondylar femoral replacement for reconstruction following tumor excision, and compare the functional outcome of this procedure with prosthetic distal femoral replacement. Method: Using our centre’s endoprosthetic database we identified and analysed all cases of massive unicondylar femoral replacement performed at our unit (group 1). Patients were evaluated for function, (Musculoskeletal Tumour Society System), and for stability (adapted from Oxford Knee Score). An age and sex-matched cohort of patients who had undergone distal femoral replacements for similar pathologies, and in who the follow-up was of a comparable time period (group 2) was evaluated in an identical manner. Statistical analysis was performed on the results. Results: Twelve cases of massive unicondylar replacement have been performed between 1990 and 2001, for a variety of malignant and benign tumors. There have been no incidences of infection, aseptic loosening or tumor recurrence. One patient has died of metastatic disease and another has undergone revision to distal femoral replacement for osteoarthritis. Of the remaining 10 patients, nine were available for assessment. Each of the two groups consisted of five males and four females, with mean age 48 years in group 1 and 49 years in group 2. The average follow-up since surgery in both groups was 10 years. The mean MSTS and stability scores of group 1 were 83% and 3.9 respectively, and 71% and 3.2 for group 2; the difference in scores between groups was statistically significant (p< 0.02). Conclusion: With stringent case selection criteria, the custom-made massive unicondylar femoral replacement produces a good outcome, with functional results significantly better than distal femoral replacement. This may be because a substantial proportion of the knee joint with at least one cruciate and one collateral ligament are kept intact, thus facilitating enhanced proprioception

Introduction and Aims: A significant proportion of patients currently undergoing total knee arthroplasty have uni-compartmental disease. Unicondylar knee replacement (UKA) offers the benefits of less bone resection and better soft tissue retention. However, knee kinematic changes after UKA have not been established. Method: A significant proportion of patients currently undergoing total knee arthroplasty have uni-compartmental disease. Unicondylar knee replacement (UKA) offers the benefits of less bone resection and better soft tissue retention. However, knee kinematic changes after UKA have not been established. Results: In the normal knee, knee flexion was accompanied by femoral rollback and tibial internal rotation. Similar patterns of rollback and rotation were seen after UKA. Surprisingly, resecting the ACL did not affect rollback or tibial rotation. However, tibial rotation was significantly different and was more variable after TKA. This suggests that loss of the ACL may not be the major cause of abnormal kinematics after TKA. Conclusion: Abnormal kinematics have been previously reported after TKA. However, UKA appeared to maintain normal kinematics. This study reported kinematic advantages to UKA, in addition to less bone resection and better recovery

Introduction: We present a review of the long-term results of custom-made massive unicondylar femoral replacement for reconstruction following tumour excision, and compare the functional outcome of this procedure with prosthetic distal femoral replacement. Method: Using our centre’s endoprosthetic database we identified and analysed all cases of massive unicondylar femoral replacement performed at our unit (group 1). Patients were evaluated for function, (Musculoskeletal Tumour Society System), and for stability (adapted from Oxford Knee Score). An age and sex-matched cohort of patients who had undergone distal femoral replacements for similar pathologies, and in who the follow-up was of a comparable time period (group 2) was evaluated in an identical manner. Statistical analysis was performed on the results. Results: Twelve cases of massive unicondylar replacement have been performed between 1990 and 2001, for a variety of malignant and benign tumours. There have been no incidences of infection, aseptic loosening or tumour recurrence. One patient has died of metastatic disease and another has undergone revision to distal femoral replacement for osteoarthritis. Of the remaining ten patients, nine were available for assessment Each of the two groups consisted of 5 males and 4 females, with mean age 48 years in group 1 and 49 years in group 2. The average follow-up since surgery in both groups was 10 years. The mean MSTS and stability scores of group 1 were 83% and 3.9 respectively, and 71% and 3.2 for group 2; the difference in scores between groups was statistically significant, (p< 0.02). Conclusion: With stringent case selection criteria, the custom-made massive unicondylar femoral replacement generally produces a good outcome, with functional results significantly better than distal femoral replacement. This may be because a substantial proportion of the knee joint with at least one cruciate and one collateral ligament are kept intact, thus facilitating enhanced proprioception

Objective. To investigate the reasons for revision of Oxford Unicondylar Knee Replacement (UKR). Does insert size used relate to requirement for revision?. Methods. We retrospectively reviewed the cases needing revision from a single surgeon consecutive series of 209 ‘Oxford’ UKRs. 10 cases required early (within 2 years) revision. The reasons for revision were investigated. A comparison of cases requiring revision by insert size implanted was made. Results. 10 cases required revision. 2 patients suffered from Sjorgens Syndrome which was undiagnosed at the time of primary surgery and underwent revision for ongoing pain, 2 cases fractured the tibia beneath the implant, 2 were revised for sepsis, and 3 cases were revised for ongoing pain without obvious cause. 1 case was revised for tibial component loosening. A significantly greater proportion of cases in which a size 6 insert was used required revision (4 of 11), compared with size 4 (1 of 44)(p=0.001) or size 5 (0 of 28)(p=0.002), and also compared with size 3 (3 of 31)(p=0.005). In cases where a size 3 insert is measured with this prosthesis, one option is to take a further tibial cut to rather use a size 6 insert. Given the five-fold increase in likelihood for requiring revision found in our series, we would recommend against this step. Conclusion. In conclusion we report a successful series of Oxford unicondylar knees taking early revision surgery as the endpoint. We recommend caution when considering a further cut when initial measurement suggests a size 3 insert, as in our series size 6 inserts showed a 5 fold increase in revision rate when compared to size 3

Utilisation of unicondylar knee arthroplasty (UKA) has been limited due in part to high revision rates. Only 8% of knee arthroplasty surgeries completed in England and Wales are UKAs. It is reported that the revision rate at 9 years for Total Knee Arthroplasty (TKA) was 3% compared to 12% for UKAs. In the last decade semi active robots have been developed to be used for UKA procedures. These systems allow the surgeon to plan the size and orientation of the tibial and femoral component to match the patient's specific anatomy and to optimise the balancing the soft tissue of the joint. The robotic assistive devices allow the surgeon to execute their plan accurately removing only ‘planned’ bone from the predefined area. This study investigates the accuracy of an imageless navigation system with robotic control for UKA, reporting the errors between the ‘planned’ limb and component alignment with the post-operative limb and component alignment using weight bearing long leg radiographs. We prospectively collected radiographic data on 92 patients who received medial UKA using an imageless robotic assisted device across 4 centres (4 surgeons). This system is CT free, so relies on accurate registration of intra-operative knee kinematic and anatomic landmarks to determine the mechanical and rotational axis systems of the lower limb. The surface of the condylar is based on a virtual model of the knee created intra-operatively by ‘painting’ the surface with the tip of a tracked, calibrated probe. The burring mechanism is robotically controlled to prepare the bone surface and remove the predefined volume of bone. The study shows the 89% of the patients' post-operative alignment recorded by the system was within 30 of the planned coronal mechanical axis alignment. The RMS error was 1.980. The RMS errors between the robotic system's implant plan and the post-operative radiographic implant position was; femoral coronal alignment (FCA) 2.6o, tibial coronal alignment (TCA) 2.9o and tibial slope (TS) 2.9o. In conclusion, the imageless robotic surgical system for UKA accurately prepared the bone surface of the tibia and femur which resulted in low errors when comparing planned and achieved component placement. This resulted in a high level of accuracy in the planned coronal mechanical axis alignment compared to that measured on post-operative radiographs

Background: In a recent publication from the National Joint Registry it was suggested that prosthesis type influenced patient satisfaction at one year following knee arthroplasty. In this report Unicondylar Replacement (UKR) was associated with lower levels of patient satisfaction when compared to cemented TKR. The unicondylar group did however have a significantly lower Oxford Knee Score (OKS) than the TKR group and this occurred irrespective of patient age. A common perception is that UKR is only offered to patients with lesser disease, with a decreased clinical profile. This may explain their higher levels of dissatisfaction as the overall change in their OKS from pre to post operation would be relatively smaller than for TKR. Aim: We hypothesised that patients listed for UKR have less severe disease and therefore a lower preoperative OKS when compared to TKR. Methods: After sample size calculation we retrospectively analysed 76 patients who underwent either UKR or TKR under the care of a single surgeon. OKS was recorded at a dedicated pre-assessment clinic. The decision to offer UKR was based on clinical and radiological criteria as outlined by the Oxford group. Results: There were 38 patients in either group. The mean pre-operative OKS was 39.5 (26–56, SD 7.6) in the UKR group and 41.6 (31–51, SD 5.7) in the TKR group. There was no statistical difference between these two groups (p=0.18). Discussion: Patients listed for knee replacement have significant pain and functional impairment. In our population those suitable for UKR have similarly severe symptoms to those who do not meet the criteria for UKR and are only eligible for TKR. It remains unclear why patients undergoing UKR should be less satisfied when they have better post operative patient reported outcome scores. It emphasizes the need for careful patient selection and counselling in patient undergoing UKR

Background. Current analysis of unicondylar knee replacements (UKR) by national registries is based on the pooled results of medial and lateral implants. Using data from the National Joint Registry for England and Wales (NJR) we aimed to determine the proportion of lateral UKR implanted, their survival and reason for failure in comparison to medial UKR. Methods. By combining information on the side of operation with component details held on the NJR we were able to determine implant laterality (medial vs. lateral) for 32,847 of the 35,624 (92%) UKR registered before December 2010. Kaplan Meier plots, Life tables and Cox' proportion hazards were used to compare the risk of failure for lateral and medial UKRs after adjustment for patient and implant covariates. Results. 2,052 (6%) UKR were inserted on the lateral side of the knee. The rates of survival at 5 years were 93.1% (95%CI 92.7 to 93.5) for medial and 93.0% (95%CI 91.1% to 94.9%) for lateral replacements (p=0.49). The rates of failure remained equivalent after adjustment for patient age, gender, ASA grade, indication for surgery and implant type using Cox's proportional hazards (HR=0.87, 95%CI 0.68 to 1.10, p=0.24). For medial implants covariates found to influence the risk of failure were patient age (p< 0.001) and ASA grade (p=0.04). Age similarly influenced the risk of failure for lateral UKRs. Implant design (Mobile versus Fixed bearing) did not influence the risk of failure in either the medial or lateral compartment. Aseptic loosening/lysis and unexplained pain were the main reasons for revision in both groups. Conclusion. The mid-term survival of medial and lateral UKRs are equivalent. This supports the on-going use of pooled data by registries for the reporting on unicondylar outcomes in the future

Summary Statement. Uptake of robotically-assisted orthopaedic surgery may be limited by a perceived steep learning curve. We quantified the technological learning curve and 5 surgeries were found to bring operating times to appropriate levels. Implant positioning was as planned from the outset. Introduction. Compared to total knee replacement, unicondylar knee replacement (UKR) has been found to reduce recovery time as well as increase patient satisfaction and improve range of motion. However, contradictory evidence together with revision rates concern may have limited the adoption of UKR surgery. Semi-active robotically-assisted orthopaedic tools have been developed to increase the accuracy of implant position and subsequent mechanical femorotibial angle to reduce revision rates. However, the perceived learning curve associated with such systems may cause apprehension among orthopaedic surgeons and reduce the uptake of such technology. To inform this debate, we aimed to quantify the learning curve associated with the technological aspects of the NavioPFS™ (Blue Belt Technologies Inc., Pittsburgh, USA) with regards to both operation time and implant accuracy. Methods. Five junior orthopaedic trainees volunteered for the study following ethical permission. All trainees attended the same initial training session and subsequently each trainee performed 5 UKR surgeries on left-sided synthetic femurs and tibiae (model 1146–2, Sawbones-Pacific Research Laboratories Inc, Vashon, WA, USA). A few days lapsed between surgeries, which were all completed in a two week window. Replica Tornier HLS Uni Evolution femoral and tibial implants (Tornier, France) were implanted without cementation. Each surgery was videoed and timings taken for key operation phases, as well as the overall operative time. A ball point probe with four reflective spherical markers attached was used to record the position of manufactured divots on the implant, which allowed the 3D position of the implant to be compared to the planned position. Absolute translational and rotational deviations from the planned position were analysed. Results. Total surgical time decreased significantly with surgery number (p < 0.001) from an initial average of 85 minutes to 48 minutes after 5 surgeries. All stages, except the cutting tool set up, demonstrated a significant difference in operative time with increasing number of surgeries performed (all p < 0.05) with the cutting phase decreasing from 41 to 23 minutes (p < 0.001). The translational and rotational accuracy of the implants did not significantly vary with surgery number. Discussion and Conclusion. The accuracy in implant position obtained by trainee surgeons on synthetic bones were similar to published data for experienced orthopaedic surgeons on other systems on cadavers. Whilst cadaver operations increase the complexity of operation, this should not theoretically affect the robotic system in preventing innaccurate implantation. Moreover, the fact that this accuracy was obtainable on the first surgery clearly demonstrates the system's ability in ensuring accurate implantation. Five surgeries dramatically reduced the total operative time, and moreover, the trend suggests that more surgeries would further decrease the total operation time. It was not the intention of the study to compare absolute trainee times on synthetic bones to surgeons with cadavers, but the learning curve of the protocol and technology suggests a halving of the operation time after 5 sessions would not be unrealistic

For patients suffering from osteoarthritis confined to one compartment of the knee joint, a successful unicondylar knee arthroplasty (UKA) has demonstrated an ability to provide pain relief and restore function while preserving bone and cruciate ligaments that a total knee arthroplasty (TKA) would sacrifice. Long-term survival of UKA has traditionally been inconsistent, leading to decreased utilisation in favour of alternative surgical treatment. Robot-assisted UKA has demonstrated an ability to provide more consistent implantation of UKA prosthesis, with the potential to increase long-term survivorship. This study reports on 65 patients undergoing UKA using an image-free, handheld robotic assistive navigation system. The condylar surface was mapped by the surgeon intra-operatively using a probe to capture a 3-dimensional representation of the area of the knee joint to be replaced. The intra operative planning phase allows the surgeon to determine the size and orientation of the femoral and tibial implant to suit the patients’ anatomy. The plan sets the boundaries of the bone to be removed by the robotic hand piece. The system dynamically adjusts the depth of bone being cut by the bur to achieve the desired result. The planned mechanical axis alignment was compared with the system's post-surgical alignment and to post-operative mechanical axis alignment using long leg, double stance, weight bearing radiographs. All 65 knees had knee osteoarthritis confined to the medial compartment and UKA procedures were completed using the handheld robotic assistive navigation system. The average age and BMI of the patient group was 63 years (range 45–82 years) and 29 kg/m. 2. (range 21–37 kg/m. 2. ) respectively. The average pre-operative deformity was 4.5° (SD 2.9°, Range 0–12° varus). The average post-operative mechanical axis deformity was corrected to 2.1° (range 0–7° varus). The post-operative mechanical axis alignment in the coronal plane measured by the system was within 1° of intra-operative plan in 91% of the cases. 3 out of 6 of the cases where the post-operative alignment was greater than 1° resulted due to an increase in the thickness of the tibia prosthesis implanted. The average difference between the ‘planned’ mechanical axis alignment and the post-operative long leg, weight bearing mechanical axis alignment was 1.8°. The average Oxford Knee Score (old version) pre and post operation was 38 and 24 respectively, showing a clinical and functional improvement in the patient group at 6 weeks post-surgery. The surgical system allowed the surgeons to precisely plan a UKA and then accurately execute their intra operative plan using a hand held robotically assisted tool. It is accepted that navigation and robotic systems have a system error of about 1° and 1mm. Therefore, this novel device recorded accurate post-operative alignment compared to the ‘planned’ post-operative alignment. The patients in this group have shown clinical and functional improvement in the short term follow up. The importance of precision of component alignments while balancing existing soft-tissue structures in UKA has been documented. Utilisation of robotic-assisted devices may improve the accuracy and long-term survivorship UKA procedure

Introduction. With the introduction of minimally invasive surgery techniques and improved polyethylene wear properties, there has been a renewed interest in Unicondylar Knee Replacements (UKR). Customized, Individually Made (CIM) UKR have been in the market for some time, and have shown to provide improved coverage and fit. The purpose of this study was to assess clinical and patient-reported outcomes utilizing CIM-UKR prostheses. Methods. A prospectively recruited cohort of 118 patients was implanted with 120 CIM-UKR (110 medial/10 lateral) at multiple centers across the US. Patients were diagnosed with uni-compartmental osteoarthritis of the medial or lateral compartment. Patients with compromised cruciate or collateral ligaments or having a varus/valgus deformity <15. °. were excluded. Patients were assessed for Knee Society Knee and Function Scores, WOMAC & ROM pre-operatively (120 patients), at 6-weeks post-op (119), 6-months post-op (71 optional visit), 1 year post-op (113) and 2 years post-operatively (96). For the 3 and 4 year post-operative time points, patients were contacted to report on any possible adverse events. Results. Range-of-motion was improved from 120. °. pre-operatively to 131. °. at 2 years post-op. Patients demonstrated marked improvements from baseline scores across all domains. All patients have passed their 2-year follow up visit to date. Average KSS Knee Scores significantly improved from their preoperative levels to 95 at the 2-years follow-up visit. KSS Function domain scores significantly improved from pre-operative levels to 91 at the 2 year time-point. Similar improvements were noted in the WOMAC score, which was reported to be 89 at the 2 year time point. Average VAS Pain scores at the 2 year visit was 1.3. To date, at an average follow-up of 3.1 years there have been 2 patients revised for tibial loosening and an additional 2 patients have been revised for disease progression in the other compartments of the knee. Discussion. There are a multitude of studies of off-the-shelf mobile and fixed-bearing UKR. The 2-year follow up data collected on CIM-UKR compares favorably to both published scores as well as revision rates for off-the-shelf implants

Unicondylar knee arthroplasty (UKA) is a treatment for osteoarthritis when the disease only affects one compartment of the knee joint. The popularity in UKA grew in the 1980s but due to high revision rates the usage decreased. A high incidence of implant malalignment has been reported when using manual instrumentation. Recent developments include surgical robotics systems with navigation which have the potential to improve the accuracy and precision of UKA. UKA was carried out using an imageless navigation system – the Navio Precision Freehand Sculpting system (Blue Belt Technologies, Pittsburgh, USA) with a medical Uni Knee Tornier implant (Tornier, Montbonnot Saint Martin, France) on nine fresh frozen cadaveric lower limbs (8 males, 1 females, mean age 71.7 (SD 13.3)). Two users (consultant orthopaedic surgeon and post doctoral research associate) who had been trained on the system prior to the cadaveric study carried out 4 and 5 implants respectively. The aim of this study was to quantify the differences between the planned and achieved cuts. A 3D image of the ‘actual’ implant position was overlaid on the planned implant image. The errors between the ‘actual’ and the planned implant placement were calculated in three planes and the three rotations. The maximum femoral implant rotational error was 3.7° with a maximum RMS angular error of 2°. The maximum femoral implant translational error was 2.6mm and the RMS translational error across all directions was up to 1.1mm. The maximum tibial implant rotational error was 4.1° with a maximum RMS angular error was 2.6°. The maximum translational error was 2.7mm and the RMS translational error across all directions was up to 2.0mm. The results were comparable to those reported by other robotic assistive devices on the market for UKA. This technology still needs clinical assessment to confirm these promising results

NavioPFS™ is a hand-held robotic technology for bone shaping that employs computer control of a high-speed bone drill. There are two control modes – one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. The unicondylar knee replacement (UKR) application uses the image-free approach in which a mix of direct and kinematic referencing is used to define all parameters relevant for planning. After the bone cutting plan is generated, the user freely moves the NavioPFS handpiece over the bone surface, and carves out the parts of the bone targeted for removal. The real-time control loop controls the depth or speed of cut, thus resulting in the planned bone preparation. This experiment evaluates the accuracy of bone preparation and implant placement on cadaveric knees in a simulated clinical setting. Three operators performed medial UKR on two cadaver specimens (4 knees) using a proprietary implant design that takes advantage of the NavioPFS approach. In order to measure the placement of components, each component included a set of 8 conical divots in predetermined locations. To establish a shared reference frame, a set of four fiducial screws is inserted in each bone. All bones were cut using a 5 mm spherical bur. Exposure Control was the primary mode of operation for both condylar cuts – although the users utilised Speed Control to perform some of the more posterior burring activities and to prepare the peg holes. Postoperatively, positions of conical divots on the femoral and tibial implants and on the respective four fiducial screws were measured using a Microscribe digitising arm in order to compare the final and the planned implant position. All implants were placed within 1.5 mm of target position in any particular direction. Maximum translation error was 1.31 mm. Maximum rotational error was 1.90 degrees on a femoral and 3.26 degrees on a tibial component. RMS error over all components was 0.69mm/1.23 degrees. This is the first report of the performance of the NavioPFS system under clinical conditions. Although preliminary, the results are overall in accordance with previous sawbones studies and with the reports from comparable semi-active robotic systems that use real time control loop to control the cutting performance. The use of NavioPFS in UKR eliminates the need for conventional instrumentation and allows access to the bone through a reduced incision. By leveraging the surgeon's skill in manipulating soft tissues and actively optimising the tool's access to the bone, combined with the precision and reproducibility of the robotic control of bone cutting, we expect to make UKR surgery available to a wider patient population with isolated medial osteoarthritis that might otherwise receive a total knee replacement. In addition to accurate bone shaping with a handheld robotically controlled tool, NavioPFS system for UKR incorporates a CT-free planning system. This approach combines the practical advantages of not requiring pre-operative medical images, while still accurately gathering all key information, both geometric and kinematic, necessary for UKR planning