Aims. The aim of this study was to determine the risk of tibial eminence avulsion intraoperatively for bi-unicondylar knee arthroplasty (Bi-UKA), with consideration of the effect of implant positioning, overstuffing, and sex, compared to the risk for isolated medial unicondylar knee arthroplasty (UKA-M) and bicruciate-retaining total knee arthroplasty (BCR-TKA). Methods. Two experimentally validated finite element models of tibia were implanted with UKA-M, Bi-UKA, and BCR-TKA. Intraoperative loads were applied through the condyles, anterior cruciate ligament (ACL), medial collateral ligament (MCL), and lateral collateral ligament (LCL), and the risk of fracture (ROF) was evaluated in the spine as the ratio of the 95. th. percentile maximum principal elastic strains over the tensile yield strain of proximal tibial bone. Results. Peak tensile strains occurred on the anterior portion of the medial sagittal cut in all simulations. Lateral translation of the medial implant in Bi-UKA had the largest increase in ROF of any of the implant positions (43%). Overstuffing the joint by 2 mm had a much larger effect, resulting in a six-fold increase in ROF. Bi-UKA had ~10% increased ROF compared to UKA-M for both the male and female models, although the smaller, less dense female model had a 1.4 times greater ROF compared to the male model. Removal of anterior bone akin to BCR-TKA doubled ROF compared to Bi-UKA. Conclusion. Tibial eminence avulsion fracture has a similar risk associated with Bi-UKA to UKA-M. The risk is higher for smaller and less dense tibiae. To minimize risk, it is most important to avoid overstuffing the joint, followed by correctly positioning the medial implant, taking care not to narrow the bone island anteriorly. Cite this article: Bone Joint Res 2022;11(8):575–584

Aims. Bi-unicondylar arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL)-preserving alternative to total knee arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA. Methods. Bi-UKA subjects (n = 22) were measured on an instrumented treadmill, using standard gait metrics, at top walking speeds. Age-, sex-, and BMI-matched healthy (n = 24) and primary TKA (n = 22) subjects formed control groups. TKA subjects with preoperative patellofemoral or tricompartmental arthritis or ACL dysfunction were excluded. The Oxford Knee Score (OKS) and EuroQol five-dimension questionnaire (EQ-5D) were compared. Bi-UKA, then TKA, were performed on eight fresh frozen cadaveric knees, to investigate knee extensor efficiency under controlled laboratory conditions, using a repeated measures study design. Results. Bi-UKA walked 20% faster than TKA (Bi-UKA mean top walking speed 6.7 km/h (SD 0.9),TKA 5.6 km/h (SD 0.7), p < 0.001), exhibiting nearer-normal vertical ground reaction forces in maximum weight acceptance and mid-stance, with longer step and stride lengths compared to TKA (p < 0.048). Bi-UKA subjects reported higher OKS (p = 0.004) and EQ-5D (p < 0.001). In vitro, Bi-UKA generated the same extensor moment as native knees at low flexion angles, while reduced extensor moment was measured following TKA (p < 0.003). Conversely, at higher flexion angles, the extensor moment of TKA was normal. Over the full range, the extensor mechanism was more efficient following Bi-UKA than TKA (p < 0.028). Conclusion. Bi-UKA had more normal gait characteristics and improved patient-reported outcomes, compared to matched TKA subjects. This can, in part, be explained by differences in extensor efficiency. Cite this article: Bone Joint Res 2021;10(11):723–733

Abstract. Objectives. There is renewed interest in bi-unicondylar arthroplasty (Bi-UKA) for patients with medial and lateral tibiofemoral osteoarthritis, but a spared patellofemoral compartment and functional cruciate ligaments. The bone island between the two tibial components may be at risk of tibial eminence avulsion fracture, compromising function. This finite element analysis compared intraoperative tibial strains for Bi-UKA to isolated medial unicompartmental arthroplasty (UKA-M) to assess the risk of avulsion. Methods. A validated model of a large, high bone-quality tibia was prepared for both UKA-M and Bi-UKA. Load totalling 450N was distributed between the two ACL bundles, implant components and collateral ligaments based on experimental and intraoperative measurements with the knee extended and appropriately sized bearings used. 95th percentile maximum principal elastic strain was predicted in the proximal tibia. The effect of overcuts/positioning for the medial implant were studied; the magnitude of these variations was double the standard deviation associated with conventional technique. Results. For all simulations, strains were an order of magnitude lower than that associated with bone fracture. Highest strain occurred in the spine, under the anteromedial ACL attachment, adjacent to transverse overcut of the medial component. Consequently, Bi-UKA had little effect on strain: <10% increases were predicted when compared to UKA-M with equivalent medial cuts/positioning. However, surgical overcutting/positional variation that resulted in loss of anteromedial bone in the spine increased strain. The biggest increase was for lateral translation of the medial component: 44% and 42% for UKA-M and Bi-UKA, respectively. Conclusions. For a large tibia with high bone quality, Bi-UKA with a well-positioned lateral implant had no tangible effect on the risk of tibial eminence avulsion fracture compared to UKA-M. Malpositioning of the medial component that removes bone from the anterior spine could prove problematic for smaller tibiae. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Aims. There has been a recent resurgence in interest in combined partial knee arthroplasty (PKA) as an alternative to total knee arthroplasty (TKA). The varied terminology used to describe these procedures leads to confusion and ambiguity in communication between surgeons, allied health professionals, and patients. A standardized classification system is required for patient safety, accurate clinical record-keeping, clear communication, correct coding for appropriate remuneration, and joint registry data collection. Materials and Methods. An advanced PubMed search was conducted, using medical subject headings (MeSH) to identify terms and abbreviations used to describe knee arthroplasty procedures. The search related to TKA, unicompartmental (UKA), patellofemoral (PFA), and combined PKA procedures. Surveys were conducted of orthopaedic surgeons, trainees, and biomechanical engineers, who were asked which of the descriptive terms and abbreviations identified from the literature search they found most intuitive and appropriate to describe each procedure. The results were used to determine a popular consensus. Results. Survey participants preferred “bi-unicondylar arthroplasty” (Bi-UKA) to describe ipsilateral medial and lateral unicompartmental arthroplasty; “medial bi-compartmental arthroplasty” (BCA-M) to describe ipsilateral medial unicompartmental arthroplasty with patellofemoral arthroplasty; “lateral bi-compartmental arthroplasty” (BCA-L) to describe ipsilateral lateral unicompartmental arthroplasty with patellofemoral arthroplasty; and tri-compartmental arthroplasty (TCA) to describe ipsilateral patellofemoral and medial and lateral unicompartmental arthroplasties. “Combined partial knee arthroplasty” (CPKA) was the favoured umbrella term. Conclusion. We recommend bi-unicondylar arthroplasty (Bi-UKA), medial bicompartmental arthroplasty (BCA-M), lateral bicompartmental arthroplasty (BCA-L), and tricompartmental arthroplasty (TCA) as the preferred terms to classify CPKA procedures. Cite this article: Bone Joint J 2019;101-B:922–928

Combined Partial Knee Arthroplasty (CPKA) is a promising alternative to Total Knee Arthroplasty (TKA) for the treatment of multi-compartment arthrosis. Through the simultaneous or staged implantation of multiple Partial Knee Arthroplasties (PKAs), CPKA aims to restore near-normal function of the knee, through retention of the anterior cruciate ligament and native disease-free compartment. Whilst PKA is well established, CPKA is comparatively novel and associated biomechanics are less well understood. Clinically, PKA and CPKA have been shown to better restore knee function compared to TKA, particularly during fast walking. The biomechanical explanation for this superiority remains unclear but may be due to better preservation of the extensor mechanism. This study sought to assess and compare extensor function after PKA, CPKA, and TKA. An instrumented knee extension rig facilitated the measurement extension moment of twenty-four cadaveric knees, which were measured in the native state and then following a sequence of arthroplasty procedures. Eight knees underwent medial Unicompartmental Knee Arthroplasty (UKA-M), followed by patellofemoral arthroplasty (PFA) thereby converting to medial Bicompartmental Knee Arthroplasty (BCA-M). In the final round of testing the PKA implants were removed a posterior-cruciate retaining TKA was implanted. The second eight received lateral equivalents (UKA-L then BCA-L) then TKA. The final eight underwent simultaneous Bi-Unicondylar Arthroplasty (Bi-UKA) before TKA. Extensor efficiencies over extension ranges typical of daily tasks were also calculated and differences between arthroplasties were assessed using repeated measures analysis of variance. For both the medial and lateral groups, UKA demonstrated the same extensor function as the native knee. BCA resulted in a small reduction in extensor moment between 70–90° flexion but, in the context of daily activity, extensor efficiency was largely unaffected and no significant reductions were found. TKA, however, resulted in significantly reduced extensor moments, leading to efficiency deficits ranging from 8% to 43% in flexion ranges associated with downhill walking and the stance phase of gait, respectively. Comparing the arthroplasties: TKA was significantly less efficient than both UKA-M and BCA-M over ranges representing stair ascent and gait; TKA showed a significant 23% reduction compared to BCA-L in the same range. There were no differences in efficiency between the UKAs and BCAs over any flexion range and TKA efficiency was consistently lower than all other arthroplasties. Bi-UKA generated the same extensor moment as native knee at flexion angles typical of fast gait (0–30°). Again, TKA displayed significantly reduced extensor moments towards full extension but returned to the normal range in deep flexion. Overall, TKA was significantly less efficient following TKA than Bi-UKA. Recipients of PKA and CPKA have superior functional outcomes compared to TKA, particularly in relation to fast walking. This in vitro study found that both UKA and CPKA better preserve extensor function compared to TKA, especially when evaluated in the context of daily functional tasks. TKA reduced knee extensor efficiency by over 40% at flexion angles associated with gait, arguably the most important activity to maintain patient satisfaction. These findings go some way to explaining functional deficiencies of TKA compared to CPKA observed clinically

Numerous fluoroscopic studies of total knee arthroplasty (TKA) kinematics have shown that many contemporary TKA designs exhibit abnormal tibiofemoral translations during activities like gait and stair climbing. One reason for these abnormal motions is the absence of the anterior cruciate ligament (ACL) in the vast majority of knees with TKA. The purpose of this study was to analyze knee kinematics during gait and stair activities in patients with a new design of TKA, incorporating a lateral compartment which is fully congruent in extension, but lax in flexion approximating the function of the anterior cruciate ligament. Our goal was to determine if such ACL-substitution results in more normal weight-bearing kinematics during gait and stair activities. Thirteen ACL-substituting TKAs (AS knees) in 8 patients were observed using fluoroscopy during treadmill gait (1 m/s) and stair stepping. Model-image registration was used to determine the 3D knee kinematics. These kinematics were compared with those from 5 knees with posterior cruciate preserving TKA (PCL Group) and 7 knees with ACL-intact bi-unicondylar arthroplasties (bi-UNI Group). AS Group subjects were 12±6 months post-op. Control groups (PCL Group/bi-UNI Group) subjects were 72±6/15±6 months post-op. During gait, the AS knees showed 1.6±0.4mm medial condyle posterior translation from heel strike to the middle of stance phase and 2.6±0.3mm posterior translation during swing phase. A similar pattern was observed in the bi-UNI knees. The lateral condyle translated posteriorly 2.1±0.2mm from heel strike to terminal stance phase, similar to the PCL knees and the bi-UNI knees. The center of rotation was predominantly lateral (19% lateral) from heel strike to mid-stance and then moved medially (16% medial) in swing phase. AS knees showed 3.4°±2.4°of internal tibial rotation from mid-stance to terminal stance, similar to the bi-UNI knees. During the stair activity, medial/lateral condylar AP translation in the AS Group was 1.6±0.1mm/2.0±0.3mm from extension to flexion, similar to the bi-UNI knees. The AS knees showed 5.9°±2.4° of internal tibial rotation from 20° to 80° during stair activity, similar to the bi-UNI knees. Substitution of the ACL by a lateral compartment which is conforming in extension may provide more natural stability and function with knee arthroplasty. Medial condylar translations and axial rotations were similar to those observed in ACL-intact bi-unicondylar knees. Gait kinematics were similar to those reported for healthy natural knees [Koo S and Andriacchi TP, J Biomechancs, 2008]. The long-term success of TKA depends not only on kinematic factors, such as those reported here, but also on polyethylene wear and patellar complications. A longer-term clinical study will be required to determine if ACL-substituting TKA represents an overall functional and clinical improvement compared to more traditional designs

Aims

The metabolic equivalent of task (MET) score examines patient performance in relation to energy expenditure before and after knee arthroplasty. This study assesses its use in a knee arthroplasty population in comparison with the widely used Oxford Knee Score (OKS) and EuroQol five-dimension index (EQ-5D), which are reported to be limited by ceiling effects.

INTRODUCTION. There is strong current interest to provide reliable treatments for one- and two-compartment arthritis in the cruciate-ligament intact knee. An alternative to total knee arthroplasty is to resurface only the diseased compartments with discrete compartmental components. Placing multiple small implants into the knee presents a greater surgical challenge than total knee arthroplasty, and it is not certain natural knee mechanics can be maintained. The goal of this study was to compare functional kinematics in cruciate-intact knees with either medial unicondylar (mUKA), mUKA plus patellofemoral (mUKA+PF), or bi-unicondylar (biUNI) arthroplasty using discrete compartmental implants with preparation and placement assisted by haptic robotic technology. METHODS. Nineteen patients with 21 knee arthroplasties consented to participate in an I.R.B. approved study of knee kinematics with a cruciate-retaining multicompartmental knee arthroplasty system. All subjects presented with knee OA, intact cruciate ligaments, and coronal deformity ranging from 7° varus to 4° valgus. All subjects received multicompartmental knee arthroplasty using haptic robotic-assisted bone preparation an average of 13 months (6–29 months) before the study. Eleven subjects received mUKA, five subjects received mUKA+PF, and five subjects received biUKA. Subjects averaged 62 years of age and had an average body mass index of 31. Combined Knee Society Pain/Function scores averaged 102 ± 28 preoperatively and 169 ± 26 at the time of study. Knee range of motion averaged −3° to 120° preoperatively and −1° to 129° at the time of the study. Knee motions were recorded using video-fluoroscopy while subjects performed step-up/down, kneeling and lunging activities. The three-dimensional position and orientation of the implant components were determined using model-image registration techniques (Fig. 1). The AP locations of the medial and lateral condyles were determined by computing a distance map between the femoral condyles and the tibial articular surfaces. RESULTS. Knee kinematics during maximum flexion kneeling and lunging showed tibial internal rotation, and posterior lateral condylar translation for all three treatments (Fig. 2). All knees showed femoral external rotation and posterior condylar translation with flexion during the step activity (Fig. 3). In all three activities, knees with mUKA and mUKA+PF arthroplasty showed the most femoral external rotation and posterior translation, and knees with biUKA showed the least. DISCUSSION. Knees with tricompartmental arthroplasty usually sacrifice one or both cruciate ligaments and also exhibit kinematics which differ from the normal knee. In particular, tibiofemoral rotations are almost always significantly less than the normal knee, and often the femur translates forward with flexion over some portion of the motion arc. In contrast, knees with accurately-placed uni- or bi-compartmental arthroplasty exhibited stable knee kinematics consistent with intact and functioning cruciate ligaments. The patterns and magnitudes of tibiofemoral motion were more similar to natural knees in the mUKA and mUKA+PF groups than commonly has been observed in knees with total knee arthroplasty. These results demonstrate the potential to restore or maintain closer-to-normal knee kinematics by retaining intact structures and compartments. Knees with an intact lateral compartment had kinematics closer to normal than those where both tibiofemoral compartments were diseased/replaced

Introduction. Traditional Total Knee Arthpolasty (TKA) replaces all 3 compartments of the knee for patients diagnosed with OA. There might be functional benefit to replacing only damaged compartments, and retaining the normal ligamentous structures. There is a long history of performing multi-compartment arthroplasty with discrete components. Laskin reported in 1976 that good pain relief and acceptable clinical results were achieved at two years in patients with bi-unicondylar knee replacement [Laskin 1976]. Other authors also have reported on bi-unicompartmental knee arthroplasty achieving successful clinical outcomes [Stockley 1990; Confalonieri 2005]. Banks et al. reported that kinematics of bi-unicompartmental arthroplasties during gait demonstrated some of the basic features of normal knee kinematics [Banks 2005]. These reports suggest that a modular approach to resurfacing the knee can be successful and achieve satisfactory clinical and functional results. Objective. The primary objective of this study is to compare the functional outcomes of three patient groups treated for osteoarthritis. Methods. Subjects received either a modular, multicompartment knee arthroplasty (MKA) implanted with robotic-arm assistance(MAKO Surgical Corp., Fort Lauderdale, FL), a computer assisted TKA (TKA CAS) or a TKA implanted using traditional manual instrumentation (TKA T). Patients that were eligible to receive a TKA were randomly selected to receive computer assisted or traditional surgical technique and blinded to the type of TKA surgical technique utilized. We report post-operative functional outcomes including Range of Motion (ROM), Timed-up and go(TUG), and Quad strength at time intervals of 2 weeks, 6 weeks, 3 months and 6 months. The TUG test is a validated measure of patient mobility where a patient is asked to stand up from a chair, walk three meters turn around and sit back down [Boonstra, 2008]. The Quad strength assessment is measured with a hand held dynamometer (Lafayette Instruments, Lafayette, IN) while patient was seated with leg at 90 degrees flexion. The patient is asked to extend their knee while a physical therapist provides resistive forces to maintain static knee flexion. All tests were administered by one physical therapist. Results. Patients that underwent MKA saw significant increase in ROM post-operatively when compared to TKA CAS patients (P<0.009) and TKA T patients (p<0.003), Figure 1. Patients that underwent MKA also saw an increase in Quad Strength, however this was only statistically significant between the MKA and TKA CAS groups, (P<0.04), Figure 2. Patients that underwent MKA saw a reduction in TUG which indicated an improved mobility post-operatively, Figure 3. The reduced TUG was only statistically significant for MKA patients compared to TKA T patients (P<0.005). There was no statistical significance seen between the two TKA groups for any functional measure. Discussion. Initial findings do indicate a short term improvement in functional outcomes for MKA patients when compared to TKA patients. Additional data clinical and functional data is being collected and enrollment is continuing for this study

Total knee arthroplasty (TKA) has evolved over the past 40 years to a point where it now is a routine treatment with fairly predictable outcomes. However, TKA is an end-stage treatment which frequently is used when only one or two compartments in the knee are damaged. Ideally, treatments for earlier stage and isolated disease would be available to provide the same high level of outcome predictability, but provide for isolated treatment of the affected compartments, greater levels of postoperative physical activity and the shorter convalescence demanded by younger, more active, and often employed patients. One approach to a compartment-by-compartment treatment regime is the utilization of discrete condylar unicompartmental prostheses and a patellofemoral prosthesis in any combination. This approach has been practiced in some European clinics for decades with good reported outcomes. However, it remains a major surgical challenge to optimally place multiple discrete arthroplasty components using conventional tools and small incisions. This lecture will present a detailed overview of a unified approach to minimally invasive, modular knee arthroplasty using haptic robotic instrumentation and implants designed specifically for robotic installation in a customized modular treatment regime. Haptic robotics provide a ‘virtual cutting guide’ capability permitting precise sculpturing of bone surfaces using near-zero-visibility minimally invasive incisions. The use of a single-multifunctional tool eliminates many of the instrument trays commonly needed for these procedures. The surgeon has complete control in manipulating the bone cutting tool within the desired bone-removal area, but the haptic robotics prohibit the cutting tool from removing bone outside the planned bone removal volume. Precise bone sculpturing has the potential to minimize bone removal and optimize the alignment and fixation of the prosthetic components. Haptic robotic cutting tools obviously can be used with off-the-shelf prosthetic components, but this approach would fail to fully take advantage of the precision surfaces that can be achieved using robot assisted bone sculpting. Instead, a purpose built system of modular knee components can be defined that work in any combination (medial or lateral unicompartmental, bi-unicondylar, medial or lateral plus patellofemoral, or tricompartmental), require minimum bone removal, can be placed through very small incisions, give great flexibility to customize implant placement to fit the patient’s anatomy, and take advantage of the types of fixation features which easily are created with a robotically controlled bone cutting device. The current treatment implementation and implant design will be presented. Clinical results for unicompartmental procedures and in vitro results for multiple-compartment procedures will be presented and discussed

Aims

Joint registries classify all further arthroplasty procedures to a knee with an existing partial arthroplasty as revision surgery, regardless of the actual procedure performed. Relatively minor procedures, including bearing exchanges, are classified in the same way as major operations requiring augments and stems. A new classification system is proposed to acknowledge and describe the detail of these procedures, which has implications for risk, recovery, and health economics.