Early functional outcome after lateral UKA is sensitive to postoperative lower limb alignment

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

Unicompartmental knee replacement (UKR) is one of the effective interventions for the treatment of symptomatic knee osteoarthritis. Moreover, it has multiple advantages over total knee arthroplasty (TKA), including reduced intraoperative blood loss, decreased risk of transfusion, and faster recovery. This study aimed to discuss critical technical considerations regarding UKR and some of the controversies and updates.

METHODS

We conducted a review to provide an overview of the controversies and technical considerations about UKR in several aspects. Only peer-reviewed articles were included, up to December 2023 using PubMed, Google Scholar, ERIC, and Cochrane database for systematic reviews databases.

RESULT

UKR is associated with superior patient-reported clinical and functional outcomes, as well as shorter hospital stays, fewer postoperative complications, and revealed favorable outcomes in patients' return to sport. The choice between mobile- and fixed-bearing prostheses depends, in part, on the surgeon's preference. The mobile-bearing UKR is a less constrained prosthesis and can potentially result in less wear, but it is more technically demanding. While no significant difference between mobile-bearing versus fixed-bearing prostheses, cementless is superior to cemented design. Furthermore, UKR can be a good alternative for high tibial osteotomy (HTO) and still can be considered after a failed HTO. Lastly, recent reviews have shown a revision rate comparable to that of TKA. This is probably influenced by Improved comprehension of the best indications, patient selection criteria, as well as of the design, materials, and technological advances.

CONCLUSION

UKR treatment for unicompartmental knee osteoarthritis is secure and effective. Based on clinical and functional outcomes, decreased morbidity and mortality, and cost-effectiveness, long-term studies suggest that UKR is superior to TKA. Further investigation in this area is warranted.

Effect of lower limb alignment on outcome after lateral unicompartmental knee arthroplasty: a retrospective study

PURPOSE

The objective of this study was to investigate the correlation between lower limb alignment and patient outcomes after lateral unicompartmental knee arthroplasty (LUKA).

METHODS

In this retrospective study, the information of 51 patients who underwent lateral UKA was collected after an average of 27months of follow-up (13 to 60 months). Evaluation indicators include the AKS and WOMAC score. The Kellgren-Lawrence grade is used to evaluate the severity of osteoarthritis, while the hip-knee-ankle (HKA) angle is utilized to measure the valgus angle of lower limb alignment.

RESULT

Patients with postoperative valgus (≥ 3°) alignment had the best outcomes, while those with varus (≤-3°) alignment had the worst outcomes (p < 0.001). Furthermore, it was noted that patients with preoperative mild valgus (≤ 4°) alignment had worse postoperative outcomes than those with severe valgus (≥ 7°) alignment (p < 0.05). The study also revealed a positive correlation between postoperative valgus and WOMAC scores (p < 0.001), whereas a negative correlation was observed between the change in valgus angle and WOMAC scores (p = 0.005).

CONCLUSION

During follow-ups, we found that lower limb alignment seems to be an independent predictor of postoperative outcomes. It is recommended that more than 3° of valgus alignment should be maintained after LUKA. Surgeons performing lateral UKA should be cautious of overcorrecting alignment, particularly in patients with preoperative mild valgus alignment.

Fixed-Bearing Unicompartmental Knee Arthroplasty of the Lateral Compartment: A Series of 246 Cases

Background

Isolated osteoarthritis of the lateral compartment of the knee is less common than that of the medial compartment, resulting in significantly fewer lateral unicompartmental knee arthroplasties (UKAs) being performed. This study aimed to evaluate results of a fixed-bearing UKA for the treatment of lateral compartment osteoarthritis of the knee.

Methods

A prospectively collected cohort of 255 patients undergoing fixed-bearing UKA of the lateral compartment using the Triathlon PKR (Stryker, Warsaw, IND) implant with a minimum 2-year follow-up was reviewed. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, radiographic alignment, complications, reoperations, and revisions were recorded. Patient factors and pre- and post-surgical alignment were assessed for their association with a minimum important change (MIC) of the total WOMAC score.

Results

A total of 246 implants with a mean follow-up of 6.6 years (2-10.8 years) were included (4% lost to follow-up). The total WOMAC score increased from 61.3 ± 3.5 to 85.3 ± 7.5, exceeding the MIC in 215 patients (88%). Exceeding the MIC was not associated with age, body mass index, or alignment. The 5-year implant revision rate was 1.6% (3/187).

Conclusions

The fixed-bearing Stryker Triathlon PKR implant for lateral UKA resulted in good clinical outcomes with a low revision rate at midterm follow-up. Body mass index, age, and pre- and post-surgical alignment did not correlate with the clinical outcome. Long-term follow-up is necessary to determine if the clinical improvement and low revision rate can be maintained.

Mild Valgus Alignment After Lateral Unicompartmental Knee Arthroplasty Led to Lower Functional Results and Survivorship at Mean 8-Year Follow-Up

BACKGROUND

In medial unicompartmental knee arthroplasty (UKA), the best results and the highest survivorship are found by mild undercorrection of varus deformities. In lateral UKA, the desirable amount of valgus undercorrection has not yet been determined. The purposes of this study were to present the results of a consecutive series of lateral UKAs and to investigate the effect of postoperative limb alignment on them.

METHODS

A total of 161 lateral UKA were reviewed. Outcomes studied included range of motion (ROM), Knee Society Score (KSS), University of California Los Angeles Activity Score, Tegner Activity Scale, Forgotten Joint Score, visual analogue scale (VAS) for pain, and survivorship. Patients were divided into two groups according to postoperative alignment: group A (hip-knee-ankle ≥184°, 79 UKA) and group B (hip-knee-ankle <184°, 82 UKA).

RESULTS

At a mean follow-up of 8 years (range, 2-18), ROM (P < .01); KSS-C (P < .01); KSS-F (P < .01); VAS (P < .01) improved from baseline. No differences were noted in postoperative ROM, VAS, University of California Los Angeles, Tegner Activity Scale, and Forgotten Joint Score between groups. Group A showed higher postoperative clinical and functional KSS (P < .01) and higher survivorship (96.2 versus 91.5%, P = .01) than group B.

CONCLUSION

Mild valgus alignment (3° or less) after lateral UKA is linked to lower clinical and functional scores and lower survivorship compared to moderate valgus (over 4°) at mean 8-year follow-up. More undercorrection of the coronal deformity in lateral UKA compared to medial UKA is desirable to get the best results.

Preoperative Condition of the Patellofemoral Joint Does Not Negatively Impact Surgical Outcomes of Lateral Unicompartmental Knee Arthroplasty in the Short Term

The relationship between patellofemoral joint (PFJ) degeneration and clinical outcomes following lateral unicompartmental knee arthroplasty (UKA) has not been well described thus far. This study aimed to investigate the relationship between the preoperative PFJ condition and postoperative outcomes and the changes in lower-limb and PFJ alignment after lateral UKA. This was a retrospective study including 54 patients (mean age 72.9 years) who underwent lateral UKA for isolated lateral knee osteoarthritis at our institution between March 2013 and January 2019. The Oxford Knee Score (OKS), the Knee Society Score-Knee (KSSK), and Knee Society Score-Function (KSSF), the degree of degeneration, tilting angle and lateral shift of the PFJ, and the hip-knee-ankle angle (HKA) were evaluated pre- and postoperatively. The average follow-up period was 2.8 (range 1-6.1) years. There was a significant improvement in the OKS, KSSK, and KSSF after lateral UKA. Preoperative degeneration of the PFJ did not correlate with the recovery of clinical scores. The degeneration, tilting angle, and lateral shift of the PFJ did not significantly progress following lateral UKA. The HKA was improved after lateral UKA, and there was no correlation between the HKA change and PFJ condition. Postoperative severe valgus knee alignment was associated with a greater tilting angle. Preoperative degeneration of the PFJ did not have a negative impact on postoperative outcomes, and no short-term changes in the degeneration, tilting angle, and lateral shift of the PFJ were observed. Correction of knee-joint alignment did not have a negative impact on the condition of the PFJ.

Midterm Survivorship of Robotic-Assisted Lateral Unicompartmental Knee Arthroplasty

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) is a popular alternative to total knee arthroplasty (TKA) for patients with isolated lateral compartment osteoarthritis. Few studies have investigated outcomes following robotic-assisted lateral UKA. The purpose of this study is to evaluate mid-term survivorship and patient-reported outcomes of robotic-assisted lateral UKA.

METHODS

A retrospective case series was conducted on all robotic-assisted lateral UKAs performed by a single surgeon between 2013 and 2019. Patient demographics, surgical variables, and Kozinn and Scott criteria were collected. Implant survivorship was estimated using the Kaplan-Meier method with all-cause reoperation and conversion to TKA as endpoints. Participating patients were assessed for patient satisfaction and the Forgotten Joint Score-12. Correlations between patient demographics and patient outcome scores were investigated.

RESULTS

In total, 120 lateral UKAs were identified, 84 of which met inclusion criteria, with a mean follow-up of 4.0 years (range 2.0-7.0). Five-year survivorship was 92.9% (95% confidence interval [CI] 84.5-96.7) with all-cause reoperation as the endpoint, and 100% (95% CI 95.0-100) with conversion to TKA as the endpoint. One patient was converted to TKA after the 5-year mark, resulting in a 6-year survival for conversion to TKA of 88.9% (95% CI 44.9-98.5). Average Forgotten Joint Score-12 score was 82.7/100, and patient satisfaction 4.7/5. Mean coronal plane correction was 2.5° ± 1.9° toward the mechanical axis. Neither final postoperative alignment nor failure to meet classic Kozinn and Scott criteria for UKA resulted in differences in patient-reported outcomes.

CONCLUSION

The current study demonstrates high mid-term survivorship and excellent patient-reported outcomes with robotic-assisted lateral UKA. Robotic-assisted lateral UKA is a viable treatment option for isolated lateral compartment arthritis even in patients who do not meet classic indications.

Cemented Lateral Unicompartmental Knee Replacement: A retrospective single centre independent series

Background

Unicompartmental knee replacement (UKR) has functional and economic benefits when compared with total knee replacement, however it is technically demanding and may be associated with higher failure rates. The primary aim of this independent series study was to evaluate the survival of lateral UKRs implanted in our institution and their clinical outcomes. The secondary outcome was to compare the results of mobile and fixed-bearing prostheses.

Methods

This is a retrospective series study of 183 cemented lateral UKRs implanted in 170 patients, for advanced isolated lateral compartment arthritis, under the care of two senior surgeons. Fixed or mobile-bearing prostheses were used according to the surgeon's preference. Kaplan Meier analysis was used to evaluate prosthesis survival with the endpoint being revision for any reason. A subgroup analysis of survival was also done for each bearing type. Functional outcomes were evaluated using the Oxford knee score (OKS) at final follow-up.

Results

This series included 103 Fixed-bearing and 80 mobile-bearing prostheses. Median follow-up was 6.9 years. 9 knees required revision. The commonest reason for revision was progression of arthritis to the medial compartment. Dislocation was the commonest cause of revision in the mobile-bearing group. Survival at 10 years was 91.9% with no significant difference ( p = 0.083) between bearing types (fixed-bearing 93.8% and mobile-bearing 90.6%). The OKS were comparable in both groups, the mean OKS was 44/48.

Conclusion

Good survival and functional outcomes can be achieved using cemented lateral UKRs with both bearing types. There was a trend towards superior outcomes in the fixed-bearing group.

External rotation of the tibial component should be avoided in lateral unicompartmental knee arthroplasty

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) leads to good clinical outcomes for isolated lateral osteoarthritis. However, the impact of the tibial component position on postoperative outcomes in lateral UKA is yet to be determined.

PURPOSE

This study investigated the influence of tibial component malposition on clinical outcomes in lateral UKA.

MATERIALS

This was a retrospective study of 50 knees (mean age 73.5 years) who underwent lateral UKA between September 2013 and January 2019. The Oxford Knee Score (OKS), Knee Society Score - Knee (KSSK), and Knee Society Score - Function (KSSF) were evaluated. The coronal alignment, posterior slope of tibial component, tibial component rotation relative to Akagi's line (angle α), and femoral anteroposterior (AP) axis (angle β) were measured postoperatively. The average follow up period was 2.3 (range, 1-4.9) years.

RESULTS

Clinical scores were significantly improved after lateral UKA. The mean coronal alignment was 0.9° ± 3.2° varus (range, 9.1° varus to 5.5° valgus), the mean posterior slope was 6.8° ± 3.8° (range, 0.8° to 14.8°). The mean α and β angles, were 4.1° ± 5.8° (range, -9.7° to 16.5°) and 6.7° ± 7.1° (range, -7.0° to 20.5°) external rotation. The angle α had significant negative correlations with postoperative OKS (r = -0.36), KSSK (r = -0.28), and KSSF (r = -0.39), and angle β had significant negative correlations with postoperative OKS (r = -0.34) and KSSK (r = -0.46).

CONCLUSION

Excessive external rotation of the tibial component could negatively influence the postoperative outcomes of lateral UKA.

Lateral Unicompartmental Knee Arthroplasty

Lateral unicompartmental knee arthroplasty affords excellent functional results and implant survivorship for properly selected patients. More high-quality studies are necessary to determine whether expanded indications for medial unicompartmental knee arthroplasty also apply to lateral unicompartmental knee arthroplasty. Operative adjuncts such as robotics, custom implants, and navigation technology hold promise in minimizing the technical burden and unfamiliarity of lateral unicompartmental knee arthroplasty. Improvements in lateral-specific implants may translate to operational efficiency and improved outcomes, but few lateral-specific implants currently exist. Mobile-bearing devices have increased rates of failure due to bearing dislocation, and further studies are warranted to evaluate this complication with newer designs. Future registry and cohort studies should show medial unicompartmental knee arthroplasty and lateral unicompartmental knee arthroplasty separately to allow for better understanding of the nuances and technical differences between these uniquely different procedures.

Fixed bearing, all-polyethylene tibia, lateral unicompartmental arthroplasty - A final outcome study with up to 28 year follow-up of a single implant

BACKGROUND

Lateral unicompartmental arthroplasty (UKA) constitutes only 5-10% of all unicompartmental replacements performed. Whilst the short and medium term benefits are well documented, there remains concern regarding the higher revision rate when compared with total knee replacement. We report the long term clinical outcome and survivorship of a large series of lateral UKA.

PATIENTS AND METHODS

Between 1974 and 1994, 71 patients (82 knees) underwent a lateral fixed-bearing St Georg Sled UKA. Prospective data was collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), with later introduction of the Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan Meier survival analysis was used, with revision, or need for revision, as end point. 85% of the patients were female. No patients were lost to follow-up.

RESULTS

Functional knee scores improved post-operatively up to 10 years, at which point they demonstrated a steady decline. Survivorship was 72% at 15 years, and 68% at 20 and 25 years. Nineteen knees were revised, with progression of disease in another compartment the commonest reason. There were two revisions due to implant fracture. In patients aged over 70 years at time of index procedure, 81% died with a functioning prosthesis in situ.

CONCLUSION

This represents the longest follow-up of a large series of lateral UKA. Results of this early design of fixed bearing UKA demonstrate satisfactory long term survivorship. In elderly patients, further intervention is rarely required. More contemporary designs or techniques may show improved long term survivorship in time.

Predictors of Satisfactory Outcomes With Fixed-Bearing Lateral Unicompartmental Knee Arthroplasty: Up to 7-year Follow-Up

BACKGROUND

There is little literature available examining factors that may predict functional recovery after lateral unicompartmental knee arthroplasty (UKA). The purpose of this study was to report short to mid-term effectiveness and evaluate predictors of better outcome following lateral UKA.

METHODS

We retrospectively reviewed 248 patients (260 knees) who underwent lateral UKA from January 2013, with a mean 5-year follow-up. The primary outcome measures comprised the Hospital for Special Surgery (HSS) score and patient satisfaction. Multivariate regression analyses were implemented to investigate associations between these factors with a satisfactory outcome. Implant survival was estimated by Kaplan-Meier analysis.

RESULTS

Complete follow-up was available for 186 patients (198 knees). At last follow-up, the HSS scores were changed from 52.1 (range, 38-80) preoperatively to 85.6 (range, 61-98) (P < .001), The OKS improved from 22.8 (range, 16-32) preoperatively to 42.7 (range, 30-47) postoperatively (P < .01). The 5-year survival was 99.5%. The multivariate analysis showed that the following factors tended to obtain a satisfactory outcome: higher proportion of ASA class I (P < .001), diagnosis of primary OA (P = .007), postoperative limb alignment (P = .007), and higher preoperative HSS score (P = .019). Patients with valgus 9°-12° reported the highest HSS scores among different subgroups (P < .001).

CONCLUSION

Following lateral UKA, postoperative outcomes were satisfactory in patients with lower ASA scores, diagnosis with primary OA, higher preoperative HSS scores and those with postoperative valgus alignment. It is important to understand these correlations to help appropriate patient selection to obtain optimal function after lateral UKA.

Robotic-assisted surgery in medial unicompartmental knee arthroplasty: does it improve the precision of the surgery and its clinical outcomes? Systematic review

There is a high prevalence of knee osteoarthritis that affects only the medial tibiofemoral compartment. In this group of patients with severe disease, the medial unicompartmental knee arthroplasty (UKA) is an excellent choice. However, this technique has a great learning curve due to the lower tolerance of improper positioning and alignment. In this context, the robotic-assisted surgery (RAS) arises as an option to improve the accuracy and secondarily enhance the clinical outcomes related to the UKA. The objective in this study is to determine if there are significant advantages with the use of RAS over conventional surgery (CS). In the systematic review of the literature, classification of the results in three main subjects: (A) precision and alignment; (B) functional results and clinical parameters; (C) survivorship. We found 272 studies, of which 15 meet the inclusion and exclusion criteria. There is mostly described that RAS significantly improves the accuracy in position (80-100% of planned versus performed P < 0.05), alignment (2-3 times less error variance P < 0.05) and selection of the proper size of the implants (69.23% of correct size femoral implants versus 16.67% using CS P < 0.0154). Recently, there is mild evidence about benefits in the early rehabilitation and post-operative pain, but in all studies reviewed, there is no advantages of RAS in the long-term functional evaluation. There is no strong literature that supports a longer survival of the prothesis with RAS, being the longest mean follow-up reported of 29.6 months. RAS is a useful tool in increasing the precision of the medial UKA implant placement. However, there is still a lack of evidence that properly correlates this improvement in accuracy with better clinical, functional and survival results.

Change in the weight-bearing line ratio of the ankle joint and ankle joint line orientation after knee arthroplasty and high tibial osteotomy in patients with genu varum deformity

PURPOSE

Several studies reported that excessive correction of severe genu varum deformity with total knee arthroplasty or high tibial osteotomy (HTO) could result in ankle joint pain and osteoarthritis progression. However, few studies have evaluated the change in the weight-bearing-line (WBL) ratio of the ankle joint after knee arthroplasty or HTO in patients with genu varum deformities. This study aimed to investigate the change in the WBL ratio of the ankle joint and ankle joint line orientation after knee arthroplasty or HTO in patients with genu varum deformities.

METHODS

We retrospectively evaluated 40 patients (mean age, 69.9 ± 8.0 years) with genu varum deformities of > 5° and underwent knee arthroplasty or HTO. Three radiologic parameters, including (1) the hip-knee-ankle (HKA) angle, (2) WBL ratio of the ankle joint, and (3) ankle joint line orientation relative to the ground (AJLO-G), were assessed using pre-operative and post-operative orthoradiographs. A paired t test was used to evaluate post-operative changes in the three parameters. Correlations between the change in HKA angle and that in the WBL ratio of the ankle joint and AJLO-G were analyzed.

RESULTS

The mean HKA angle significantly decreased post-operatively (10.6° ± 5.3° to 1.1° ± 3.4°; P < 0.001). The WBL ratio of the ankle joint increased from 35.8% ± 15.2% to 53.0% ± 17.4% (P < 0.001), with a lateral shift of the mechanical axis. The AJLO-G decreased with valgization of ankle orientation (7.8° ± 4.8° to 0.4° ± 3.8°; P < 0.001). The change in the HKA angle was significantly correlated with that in the AJLO-G (correlation coefficient = 0.716; P < 0.001) but not with the change in the WBL ratio of the ankle joint.

CONCLUSION

Knee arthroplasty and HTO corrected the genu varum deformity, which influenced the lateral shift of the WBL of the ankle joint and valgization of the ankle joint line orientation.

Does Unicompartmental Knee Replacement Offer Improved Clinical Advantages Over Total Knee Replacement in the Treatment of Isolated Lateral Osteoarthritis? A Matched Cohort Analysis From an Independent Center

BACKGROUND

The purpose of this study is to compare the functional and radiographic results, perioperative complications, satisfaction rate, and mid-term survivorship after unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) for the treatment of lateral compartmental knee osteoarthritis (LCKO).

METHODS

Between March 2007 and September 2017, we identified 35 patients with primary TKAs and 121 patients with lateral UKAs (LUKAs) for LCKO with a minimum follow-up of 2 years (mean 5.3 years, range 2-12.4). The matched variables were age, gender, operation side, body mass index, American Society of Anesthesiologist grade, initial diagnosis, osteoarthritis grade in lateral compartment, and follow-up time. All patients were assessed using the Oxford Knee Score, Hospital for Special Surgery score, range of motion, length of hospital stay, satisfaction, and complications. Survivorship of UKA and TKA implants was also compared.

RESULTS

At last follow-up, LUKA had a significantly better postoperative Oxford Knee Score, Hospital for Special Surgery score, range of motion, shorter length of hospital time, and higher satisfaction rate than matched TKA group. There were significant differences regarding patellar tendon injury (P = .043), superficial wound infection (P = .028), patellar snapping or impingement (P = .047), and stiffness (P < .001). Five-year survivorships free from revision were similar in both groups (99.2% vs 97.1%, P = .347).

CONCLUSION

LUKA for LCKO demonstrated more favorable 5-year results in comparison with TKA. Furthermore, LUKA achieved comparable mid-term survivorship and was less likely to suffer from wound infection and knee stiffness, although not overall surgical complications.

Robotic-Assisted Unicompartmental Knee Arthroplasty: State-of-the Art and Review of the Literature

BACKGROUND

Unicompartmental knee arthroplasty is a successful treatment for unicompartmental knee osteoarthritis that has lower complication rates, faster recovery, and a more natural feeling knee compared to total knee arthroplasty. However, long-term survival has been a persistent concern. As more surgeon-controlled variables have been linked to survival, interest in robotic-assisted surgery has continued to grow.

METHODS

A review and synthesis of the literature on the subject of robotic-assisted unicompartmental knee arthroplasty was performed.

RESULTS

We present the driving factors behind the development of robotic-assisted techniques in unicompartmental knee arthroplasty and the current state-of-the art. The ability of surgeons to achieve intraoperative targets with robotic assistance and the outcomes of robotic-assisted surgery are also described.

CONCLUSION

Robotic-assisted surgery has become increasingly popular in unicompartmental knee arthroplasty, as it allows surgeons to more accurately and reproducibly plan and achieve operative targets during surgery. Cost remains a concern, and it remains to be seen whether robotic-assisted surgery will improve long-term survivorship after unicompartmental knee arthroplasty.

Clinical Outcomes and Survivorship of Lateral Unicompartmental Knee Arthroplasty: Does Surgical Approach Matter?

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) has been shown to be an effective procedure to treat isolated lateral compartment osteoarthritis with excellent long-term survivorship. Whether a medial parapatellar approach or a lateral parapatellar approach is superior in lateral UKA is unknown. The purpose of this study was to determine if there is a difference in intermediate-term clinical outcomes in patients undergoing lateral UKA through a lateral vs medial parapatellar approach.

METHODS

We retrospectively reviewed a consecutive series of 65 patients who underwent lateral UKA with a minimum of 2-year follow-up. Fifty-two patients (80%) had a lateral approach and 13 (20%) a medial parapatellar approach. Patient demographics, preoperative and postoperative radiographic findings, need for revision surgery, Knee Society Score, and range of motion were assessed.

RESULTS

Overall survivorship was 94% at a mean of 82 months; with the sample size available for study, there was no difference in survivorship between the groups. There was no difference in Knee Society Score or revision to total knee arthroplasty (5% vs 7%, P = 1.000) between the medial and lateral approach groups. Comparatively, the lateral approach group did have significantly greater postoperative flexion (123.6° vs 116.5°, P = .006) and greater improvement in flexion from preoperative measurements (3.0 vs -8.0°, P = .010).

CONCLUSION

Although our sample size was small, we could not demonstrate a difference in revision rates or clinical outcome scores when comparing a lateral or a medial approach with lateral UKA at intermediate-term follow-up. A lateral approach did have greater postoperative flexion, but its clinical significance remains undetermined.

Lateral unicompartmental knee replacement: a systematic review of reasons for failure

PURPOSE

Currently, individual studies lack the power to successively illustrate different failure modes; therefore, we undertook a systematic review to examine lateral unicompartmental knee replacement (lat UKR) failure modes. Furthermore, we compared early with midterm and late failures and fixed-bearing with mobile-bearing implants.

METHODS

A search using the databases of PubMed, EMBASE, Cochrane, and annual registries was performed to search for failed lat UKRs. Studies were included when they reported more than four failures, described failure modes and were minimum level IV studies. Data was analysed based on overall failure modes, fixed- vs. mobile bearing and early (<5 years) vs. midterm (5-10 years) vs. late failures (>10 years).

RESULTS

Fourteen cohort studies and two registry-based studies were included. A total of 336 overall failures, 87 time-dependent failures, and 175 implant-specific failures were identified. The main overall causes of failure were osteoarthritis (OA) progression (30%) and aseptic loosening (22%). These were followed by less common causes such as instability (7%), unexplained pain (5%), infection (5%), polyethylene wear (5%), and bearing dislocation (5%). Bearing dislocation was the most common early failure (29%) and also the most common failure among mobile-bearing implants (27%). In midterm and late failures, OA progression had the highest rates (59% and 78% respectively) and was also the most common type of failure in fixed-bearing implants (44%).

CONCLUSIONS

Progression of OA and aseptic loosening are the major overall failure modes in lat UKR. Bearing dislocation was the main failure mode in early years and in mobile-bearing implants, whereas OA progression caused most failures in late years and in fixed-bearing implants.

LEVEL OF EVIDENCE

Systematic Review of minimum level IV studies.

Medial vs lateral unicompartmental knee arthrroplasty: clinical results

Unicompartmental Knee Arthroplasty (UKA) is a common procedure for the management of isolated osteoarthritis. UKA is considered less invasive compared to total knee arthroplasty, associated with less operative time, blood loss and faster recovery. Isolated lateral osteoarthritis is a relatively uncommon clinical problem, with an incidence about ten times lower than the medial compartment. In fact, lateral UKA are about 5-10% of the total amount of the UKAs. In addition, it's historically considered more challenging and with poorer results. The aim of this paper was to compare current indications, modes of failure, survivorship and clinical results of medial and lateral UKA by a narrative review of the latest literature.

Survivorship and patient satisfaction of robotic-assisted medial unicompartmental knee arthroplasty at a minimum two-year follow-up

BACKGROUND

Successful clinical outcomes following unicompartmental knee arthroplasty (UKA) depend on lower limb alignment, soft tissue balance and component positioning, which can be difficult to control using manual instrumentation. Although robotic-assisted surgery more reliably controls these surgical factors, studies assessing outcomes of robotic-assisted UKA are lacking. Therefore, a prospective multicenter study was performed to assess outcomes of robotic-assisted UKA.

METHODS

A total of 1007 consecutive patients (1135 knees) underwent robotic-assisted medial UKA surgery from six surgeons at separate institutions between March 2009 and December 2011. All patients received a fixed-bearing metal-backed onlay implant as tibial component. Each patient was contacted at minimum two-year follow-up and asked a series of five questions to determine survivorship and patient satisfaction. Worst-case scenario analysis was performed whereby all patients were considered as revision when they declined participation in the study.

RESULTS

Data was collected for 797 patients (909 knees) with average follow-up of 29.6months (range: 22-52months). At 2.5-years of follow-up, 11 knees were reported as revised, which resulted in a survivorship of 98.8%. Thirty-five patients declined participation in the study yielding a worst-case survivorship of 96.0%. Of all patients without revision, 92% was either very satisfied or satisfied with their knee function.

CONCLUSION

In this multicenter study, robotic-assisted UKA was found to have high survivorship and satisfaction rate at short-term follow-up. Prospective comparison studies with longer follow-up are necessary in order to compare survivorship and satisfaction rates of robotic-assisted UKA to conventional UKA and total knee arthroplasty.

Different optimal alignment but equivalent functional outcomes in medial and lateral unicompartmental knee arthroplasty

INTRODUCTION

Several differences in kinematics, functional outcomes and alignment exist between medial and lateral unicompartmental knee arthroplasty (UKA). Therefore, the purpose of this study was (1) to compare functional outcomes between both procedures with the hypothesis that both have equivalent outcomes and (2) to assess the role of preoperative and postoperative alignment on functional outcomes in both procedures.

METHODS

Patients who underwent UKA were included when overall function - using Western Ontario and McMaster Universities Arthritis (WOMAC) score - and joint awareness - using Forgotten Joint Score (FJS) - were available preoperatively and at minimum two-year follow-up. A total of 143 medial UKA and 36 lateral UKA patients reported outcomes at mean 2.4-years follow-up (range 2.0 to 5.0year).

RESULTS

Preoperatively and postoperatively, no differences were seen between medial and lateral UKA in overall function (89.8±11.7 vs. 90.2±12.4, respectively, p=0.855) and joint awareness (71.2±24.5 vs. 70.9±28.2, respectively, p=0.956). With neutral postoperative alignment (-1° to three degrees), less joint awareness was noted following medial UKA than lateral UKA (72.6±22.6 vs. 55.3±28.5, p=0.024). With undercorrection (three degrees to seven degrees), however, following lateral UKA less joint awareness (85.3±19.5 vs. 68.2±26.8, p=0.020) and better functional outcomes (96.0±5.4 vs. 88.5±11.6, p=0.001) were noted than medial UKA.

CONCLUSION

Equivalent functional outcomes were noted between medial and lateral UKA at short-term follow-up but different optimal alignment angles seem to exist for both procedures.

LEVEL OF EVIDENCE

Level III therapeutic study.

Patients with isolated lateral osteoarthritis: Unicompartmental or total knee arthroplasty?

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are both reliable treatment options for patients with isolated lateral osteoarthritis (OA). However, studies comparing both procedures are scarce. Aims of this study were to (I) compare short-term functional outcomes following lateral UKA and TKA and (II) assess the role of patient characteristics on outcomes as measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

METHODS

In this retrospective cohort study, 82 patients (48 undergoing lateral UKA and 34 undergoing TKA) were identified that presented with lateral OA and completed the WOMAC. Independent t-tests were used to compare outcomes following lateral UKA and TKA.

RESULTS

Mean follow-up was 2.8 years (range: 2.0 - 5.0 years). Preoperatively, no differences between lateral UKA and TKA were seen (50.1±13.5 and 53.3±17.1, respectively, p=0.551). Postoperatively, lateral UKA patients reported better overall outcomes than TKA (90.5±11.7 vs. 81.8±17.9, p=0.017). Subgroup analysis showed better outcomes following lateral UKA than TKA in patients younger than 75 years (92.1±9.9 vs. 81.3±19.6, p=0.014) and in females (91.6±9.9 vs. 81.0±18.2, p=0.014).

CONCLUSION

These findings indicate that lateral UKA has superior short-term functional outcomes compared to TKA in patients with isolated lateral OA. Better outcomes were especially seen in younger patients and females. These findings may help orthopedic surgeons choose treatment for patients presenting with lateral OA and optimize treatment for individual patients.

Current state of computer navigation and robotics in unicompartmental and total knee arthroplasty: a systematic review with meta-analysis

Recently, there is a growing interest in surgical variables that are intraoperatively controlled by orthopaedic surgeons, including lower leg alignment, component positioning and soft tissues balancing. Since more tight control over these factors is associated with improved outcomes of unicompartmental knee arthroplasty and total knee arthroplasty (TKA), several computer navigation and robotic-assisted systems have been developed. Although mechanical axis accuracy and component positioning have been shown to improve with computer navigation, no superiority in functional outcomes has yet been shown. This could be explained by the fact that many differences exist between the number and type of surgical variables these systems control. Most systems control lower leg alignment and component positioning, while some in addition control soft tissue balancing. Finally, robotic-assisted systems have the additional advantage of improving surgical precision. A systematic search in PubMed, Embase and Cochrane Library resulted in 40 comparative studies and three registries on computer navigation reporting outcomes of 474,197 patients, and 21 basic science and clinical studies on robotic-assisted knee arthroplasty. Twenty-eight of these comparative computer navigation studies reported Knee Society Total scores in 3504 patients. Stratifying by type of surgical variables, no significant differences were noted in outcomes between surgery with computer-navigated TKA controlling for alignment and component positioning versus conventional TKA (p = 0.63). However, significantly better outcomes were noted following computer-navigated TKA that also controlled for soft tissue balancing versus conventional TKA (mean difference 4.84, 95 % Confidence Interval 1.61, 8.07, p = 0.003). A literature review of robotic systems showed that these systems can, similarly to computer navigation, reliably improve lower leg alignment, component positioning and soft tissues balancing. Furthermore, two studies comparing robotic-assisted with computer-navigated surgery reported superiority of robotic-assisted surgery in controlling these factors. Manually controlling all these surgical variables can be difficult for the orthopaedic surgeon. Findings in this study suggest that computer navigation or robotic assistance may help managing these multiple variables and could improve outcomes. Future studies assessing the role of soft tissue balancing in knee arthroplasty and long-term follow-up studies assessing the role of computer-navigated and robotic-assisted knee arthroplasty are needed.

The Role of Preoperative Patient Characteristics on Outcomes of Unicompartmental Knee Arthroplasty: A Meta-Analysis Critique

BACKGROUND

In 1989, Kozinn and Scott introduced strict exclusion criteria for unicompartmental knee arthroplasty (UKA). Because outcomes have improved with modern techniques and implants, these criteria have now been challenged. Therefore, the goal was to assess the role of these criteria on (1) functional outcomes and (2) revision rates of medial UKA. The hypothesis was that, with modern surgical techniques and implants, these traditional exclusion criteria are no longer strict contraindications for UKA.

METHODS

Databases of PubMed, EMBASE, and Cochrane and annual registries were searched for studies comparing UKA results in subgroups: age (young vs old), gender (male vs female), body mass index (obese vs nonobese), present vs absent patellofemoral osteoarthritis, and intact vs deficient anterior cruciate ligament.

RESULTS

Thirty-one comparative cohort studies (7 level II and 24 level III/IV studies) and 6 registries reported outcomes in 17,147 patients and revision rates in 285,472 patients. Females had inferior functional outcomes compared to males (odds ratio [OR], 4.03; 95% CI, 1.77-6.30). Furthermore, younger patients (in studies: OR, 1.52; 95% CI, 1.06-2.19; in registries: OR, 2.09; 95% CI, 1.70-2.57) and females (OR, 1.13; 95% CI, 1.06-1.21) had increased likelihood for revision. No increased likelihood for inferior outcomes or revisions was detected in patients with obesity, preoperative patellofemoral osteoarthritis, or anterior cruciate ligament deficiency.

CONCLUSION

Findings of increased revision risk in younger patients and increased revision risk with inferior outcomes in females give a more nuanced perspective on historical criteria, such that surgical decision-making may be based on UKA outcome data for subgroups rather than strict exclusion criteria.