Introduction. Bicompartmental knee replacement (BKR) may be an alternative to total knee arthroplasty (TKA) for degenerative disease limited to two knee compartments. Most commonly, BKA is a combination of medial compartment and patellofemoral compartment resurfacing. In contrast to TKA, BKA preserves the uninvolved compartment and cruciate ligaments possibly leading to advanced stability and more physiologic knee kinematics. Robotic-assisted systems for unicompartmental knee arthroplasty have shown to provide improved component positioning with dynamic ligament balancing that may improve outcomes of BKA. The purpose of this study was to evaluate the short-term outcomes of patients undergoing BKA at a single institution by a single surgeon using a robotic-assisted system. Methods. A search of the institution's joint registry was conducted to identify patients that underwent robotic-assisted BKA of the patellofemoral compartment and the medial or lateral compartment between December 2009 and April 2012. All medical records were analyzed for patient demographics and comorbidities. The patients were evaluated preoperatively and at 6,12 months and then annually. The patients were contacted by phone when recent follow-up was not available. The radiographic assessment was also undertaken. The orientation of the tibial and femoral implants was assessed radiologically postoperatively. We examined the clinical results with the Oxford Knee Score (OKS). Results. A total number of 29 patients (30 BKR) with a mean age of 63.6 years (range 39 to 82) were identified who received a patellofemoral resurfacing in combination with medial (25, 83%) or lateral (5, 17%) compartment resurfacing. The mean BMI was 33.7 kg/m. 2. (range, 21.5 to 51.8), median Charlson comorbidity index score was 0, median American Society of Anaesthesiologists' (ASA) classification was 3. The mean length of surgery was 40.2 minutes (range, 23 to 151). At a mean follow-up of 15 months (range, 2 to 54), 3 patients (10%, 2 patellofemoral and lateral compartment, 1 patellofemoral and medial compartment) underwent arthroscopic debridement of loose cement fragments following BKA. One patient (3%, patellofemoral and lateral compartment) received manipulation under anesthesia and botulinum neurotoxin injections into the hamstrings for postoperative flexion contracture and another patients (3%, patellofemoral and medial compartment) underwent open lateral retinacular release. There were no component revisions noted during the follow-up period. The preoperative oxford knee score improved from 26.4 to 33. Discussion. Our analysis shows the bicompartmental knee replacement using robotics is a viable option when two out of three components are involved

There is great contemporary interest to provide treatments for knees with medial or medial plus patellofemoral arthritis that allow retention of the cruciate ligaments and the natural lateral compartment. Options for bicompartmental arthroplasty include custom implants, discrete compartmental implants and monoblock off-the-shelf implants. Each approach has potential benefits. The monoblock approach has the potential to provide a cost-efficient off-the-shelf solution with relatively simple surgical instrumentation and procedure. The purpose of this study was to determine if monoblock bicompartmental knee arthroplasty shows evidence of retained cruciate ligament function and clinical performance more similar to unicompartmental arthroplasty than total knee arthroplasty. Nine females and one male patient were enrolled in this IRB approved study. Each subject received unilateral bicompartmental knee arthroplasty an average of 2.6 years (2.0 to 3.6 years) prior to this study. Subjects averaged 65 years (58–72 years) and 28 BMI (25–31) at the time of surgery. Mean outcome scores at the time of study were 97/95 for the Knee Society knee/function score, 16.4 Oxford score, 6.5 UCLA Activity score and 137 degrees range of motion. Subjects were observed using dynamic fluoroscopy during lunge, kneeling and step-up/down activities. Subjects also received CT scans of the knee in order to create bone/implant composite shape models. Model-image registration techniques were used to determine 3D knee kinematics (Figure 1). Knee angles were quantified using a flexion-abduction-rotation Cardan sequence and condylar translations were determined from the lowest point on the condyle with respect to the transverse plane of the tibial segment. Maximum knee flexion during lunge and kneeling activities averaged 112°±8° and 125°±7°, respectively. Tibial internal rotation averaged 10°±6° and 12°±10° for the lunge and kneeling activities. For both deeply flexed postures, the medial condyle was 1 mm anterior to the AP center of the tibia while the lateral condyle was 11 mm and 13 mm posterior to the tibial center. For the step-up/down activity, tibial internal rotation increased an average of 2° from 5° to 75° flexion, but was quite variable (Figure 2). Medial condylar translations averaged 4 mm posterior from 5° to 25° flexion, followed by 6 mm anterior translation from 25° to 80° flexion (Figure 3). All knees showed posterior condylar translation from extension to early flexion. An important potential benefit to any bicompartmental arthroplasty treatments is retention of the cruciate ligaments and maintenance of more natural knee function. The knees in this study showed excellent or good clinical outcomes and functional scores, and relatively activity high levels. There was no evidence of so-called paradoxical anterior femoral translation during early flexion, indicating retained integrity of the natural AP stabilizing structures. Weight-bearing deep flexion during lunge and kneeling activities was comparable to previously reported unicompartmental and well-performing total knee arthroplasty subjects. Kinematics were quite variable between subjects. Monoblock bicompartmental arthroplasty appears to permit functional retention of the cruciate ligaments, consistent with functionally stable knees. Further efforts should focus on the specific surgical placement of off-the-shelf bicompartmental implants to optimize knee function and provide consistent knee mechanics

Introduction. It is well known that total knee arthroplasty (TKA) does not preserve normal knee kinematics. This outcome has been attributed to alteration of soft-tissue balance and differences between the geometry of the implant design and the normal articular surfaces. Bicompartmental knee arthroplasty (BKA) has been developed to replace the medial and anterior compartments, while preserving the lateral compartment, the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL). In a previous study, we reported that unicompartmental knee arthroplasty did not significantly change knee kinematics and attributed that finding to a combination of preservation of soft-tissue balance and minimal alteration of joint articular geometry (Patil, JBJS, 2007). In the present study, we analyzed the effect of replacing trochlear surface in addition to the medial compartment by implanting cadaver knees with a bicompartmental arthroplasty design. Our hypothesis was that kinematics after BCKA will more closely replicate normal kinematics than kinematics after TKA. Methods. Eight human cadaveric knees underwent kinematic analysis with a surgical navigation system. Each knee was evaluated in its normal intact state, then after BKA with the Deuce design (Smith & Nephew, Memphis, TN), then after ACL sacrifice, and finally after implanting a PCL-retaining TKA (Legion, Smith & Nephew). Knees were tested on the Oxford knee rig, which simulates a quadriceps-driven dynamic deep knee bend. Tibiofemoral rollback and rotation and patellofemoral shift and tilt were recorded for each condition and compared using repeated measures ANOVA for significance. Results. Statistically significant differences were noted in femoral rollback between TKA and Intact conditions but not between Intact and BKA or between Intact and BKA without ACL. Statistically significant differences were noted in tibiofemoral rotation between TKA and Intact conditions but not between Intact and BKA or between Intact and BKA without ACL. No significant differences in patellar lateral shift or lateral tilt were found among the four conditions tested. Discussion & Conclusion. BKA prostheses that preserve the ACL and PCL allow for more normal knee kinematics than does conventional TKA. Our results supported our primary hypothesis that a bicompartmental approach would not significantly alter knee kinematics. These results also imply that replacement of the medial compartment and trochlear surface are not major factors contributing to altered knee function. The results that we observed may not necessarily apply to other BKA designs and should therefore not be extrapolated beyond the prosthesis designs in this study. Additionally, the current study was designed to only evaluate kinematics, and we can not make conclusions regarding implant wear, fixation, durability, ideal patient selection, and reproducibility of successful clinical outcomes. Lastly, the current study was undertaken using relatively normal cadaveric knees whereas in vivo arthroplasty is typically reserved for arthritic knees that are often affected by contracture and/or deformity. We therefore believe that clinical studies with well-defined measures of success need to be conducted before far-reaching conclusions can be drawn regarding the utility of these implants in clinical practice

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) has been shown to have many benefits over conventional Total Knee Arthroplasty (TKA), but has also been shown to be technically difficult. In fact, technical error is the most common cause of premature failure in UKA. Bicompartmental arthroplasty (BKA) has the potential to perform like TKA with the benefits of UKA. We describe the initial experience with customized alignment guides and implants for UKA and BKA, manufactured based upon preoperative CT scan.

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

INTRODUCTION. Bicompartmental knee arthroplasty (BKA) is an alternative to total knee arthroplasty (TKA) for degenerative joint disease when present in only two compartments. BKA spares the cruciate ligaments and preserves bone in the healthy compartment, possibly leading to better knee kinematics and clinical outcomes when compared to TKA. While BKA is a technically demanding procedure when performed with manual instrumentation, robotic assistance allows for accurate implant placement and soft tissue balancing of the joint. Robotic unicompartmental knee arthroplasty (UKA) has shown favorable clinical outcomes and survivorship at short term (2 year) follow up compared to manual UKA. The purpose of this study is to evaluate the short term functional outcomes and survivorship of patients undergoing robotically assisted BKA. METHODS. 45 patients (48 knees) were identified in an initial and consecutive single surgeon series receiving robotically assisted BKA to correct disease in the medial and patellofemoral compartments. As part of an IRB approved study, every patient in the series was contacted at a minimum two year (±2 months) follow up and asked a series of questions to determine implant survivorship and functional outcomes (using the patient portion of the Knee Society Score). 9 patients were lost to follow up and 1 patient was deceased. 35 patients (38 knees) at a minimum two year follow up enrolled in the study for an enrollment rate of 79%. There are 22 male patients and 13 female patients; the average age at time of surgery is 67.0 ± 6.8 and the average BMI is 29.5 ± 4.6. Five patients in this series also qualified for a 5 year follow up assessment. RESULTS. Only 1 BKA was reported as revised to a TKA at two year follow up. The revision was reported by the patient due to severe pain and occurred 25 months after the index BKA procedure. The patient did not return to the same surgeon for the revision procedure. The average pre-operative Knee Society Function Score was 58.1 ± 9.9 (n=18) and improved at 2 years post-operatively to 81.5 ± 15.9 (n = 36) (p<0.001). Of the 5 patients contacted at a minimum 5 year follow up, there were no reported revisions. CONCLUSIONS. Robotically assisted BKA shows good survivorship and functional outcomes at a short term 2 year follow up. This procedure may be a viable option to patients with only two diseased compartments, as sparing of healthy bone and cruciates may improve overall kinematics and outcomes of the joint. This study remains ongoing to include a larger cohort and longer follow up

INTRODUCTION. Bicompartmental knee arthroplasty (BKA) is an alternative to total knee arthroplasty (TKA) for degenerative joint disease when present in only two compartments. BKA spares the cruciate ligaments and preserves bone in the healthy compartment, possibly leading to better knee kinematics and clinical outcomes when compared to TKA. While BKA is a technically demanding procedure when performed with manual instrumentation, robotic assistance allows for accurate implant placement and soft tissue balancing of the joint. Robotic unicompartmental knee arthroplasty (UKA) has shown favorable clinical outcomes and survivorship at short term (2 year) follow up compared to manual UKA. The purpose of this study is to evaluate the short term functional outcomes and survivorship of patients undergoing robotically assisted BKA. METHODS. 45 patients (48 knees) were identified in an initial and consecutive single surgeon series receiving robotically assisted BKA to correct disease in the medial and patellofemoral compartments. As part of an IRB approved study, every patient in the series was contacted at a minimum two year (±2 months) follow up and asked a series of questions to determine implant survivorship and functional outcomes (using the patient portion of the Knee Society Score). 9 patients were lost to follow up and 1 patient was deceased. 35 patients (38 knees) at a minimum two year follow up enrolled in the study for an enrollment rate of 79%. There are 22 male patients and 13 female patients; the average age at time of surgery is 67.0 ± 6.8 and the average BMI is 29.5 ± 4.6. Five patients in this series also qualified for a 5 year follow up assessment. RESULTS. Only 1 BKA was reported as revised to a TKA at two year follow up. The revision was reported by the patient due to severe pain and occurred 25 months after the index BKA procedure. The patient did not return to the same surgeon for the revision procedure. The average pre-operative Knee Society Function Score was 58.1 ± 9.9 (n=18) and improved at 2 years post-operatively to 81.5 ± 15.9 (n = 36) (p<0.001). Of the 5 patients contacted at a minimum 5 year follow up, there were no reported revisions. CONCLUSIONS. Robotically assisted BKA shows good survivorship and functional outcomes at a short term 2 year follow up. This procedure may be a viable option to patients with only two diseased compartments, as sparing of healthy bone and cruciates may improve overall kinematics and outcomes of the joint. This study remains ongoing to include a larger cohort and longer follow up