Medium term results of per-operative knee arthroscopy in confirming suitability for unicompartmental arthroplasty

IntroductionThe status of the lateral compartment of the knee is a determining factor in the long-term outcome of medial unicompartmental arthroplasty (UKA). Various methods of assessing the lateral compartment have been used including stress radiography, radioisotope bone scanning, magnetic resonance imaging and visualisation at the time of surgery. Arthroscopy is another means of directly assessing the integrity of the articular cartilage and the meniscus in the lateral compartment.PurposeThis study aims to show that per-operative arthroscopy is a safe and effective means of deciding whether to proceed with UKA or convert to total knee arthroplasty (TKA).MethodWe have used arthroscopy of the lateral compartment to assess suitability for UKA in 151 knees over 8 years.ResultsAt time of arthroscopy 34 knees underwent a change of surgical plan from UKA to TKA (22.5%). There has been one revision to TKA and 2 bearing exchanges for dislocation.ConclusionImmediate per-operative arthroscopy is a reliable method for assessing the suitability of a knee for UKA, in particular the lateral compartment.     

Fixed bearing lateral unicompartmental knee arthroplasty—Short to midterm survivorship and knee scores for 101 prostheses

BackgroundIsolated unicompartmental knee arthritis is less common laterally than medially. Lateral unicompartmental knee arthroplasty (UKA) constitutes only 1% of all knee arthroplasty performed. Use of medial UKA is supported by several published series showing good long-term survivorship and patient satisfaction, in large patient cohorts. Results of lateral UKA however have been mixed. We present the short and mid-term survivorship and 5-year clinical outcome of 101 lateral UKAs using a single prosthesis.MethodsOver a 9 year period, 100 patients who satisfied inclusion criteria underwent a lateral fixed-bearing unicompartmental arthroplasty. American Knee Society (AKSS), Oxford Knee (OKS) and modified Western Ontario McMaster Universities Arthritis Index (WOMAC) scores were completed preoperatively and at 1, 2 and 5 years postoperatively. Kaplan–Meier survival analysis was used to determine the 2-year and 5-year survivorship, using revision for any cause as end point.ResultsSurvivorship was 98.7% and 95.5% at 2 and 5 years respectively. 1 knee was revised for subsidence of the tibial component and 1 knee for progression of medial compartment osteoarthritis. Of a possible 35 knees in situ at 5 year follow-up, 33 knees were fully scored. Median AKSS, OKS and modified WOMAC scores were 182, 41, and 16 respectively.ConclusionsThe mid-term survivorship and outcome scores at 5-years suggest that lateral unicompartmental knee arthroplasty provides a valuable alternative to total joint replacement in selected patients with isolated lateral tibio-femoral arthritis at mid-term follow-up.Level II evidence.     

In vivo kinematic comparison before and after mobile-bearing unicompartmental knee arthroplasty during high-flexion activities

BackgroundMany patients who undergo unicompartmental knee arthroplasty (UKA) have an expectation that their knee flexion would increase following its replacement. Additionally, the survival rate of mobile-bearing UKA (MB-UKA) is high. However, the effect on the patient's kinematics remains unknown. This study aimed to clarify the kinematic effect of MB-UKA knees during high-flexion activities by comparing the in vivo kinematics before and after surgery.MethodsA squatting motion was performed under fluoroscopic surveillance in the sagittal plane before and after MB-UKA. To estimate the spatial position and orientation of the knee, a two-dimensional/three-dimensional registration technique was used. The femoral rotation and varus–valgus angle relative to the tibia and anteroposterior (AP) translation of the medial and lateral side of the femur on the plane perpendicular to the tibial mechanical axis in each flexion angle were evaluated.ResultsRegarding the varus–valgus angle, the preoperative knees indicated a significant varus alignment compared with the postoperative knees from 10° to 60° of flexion. There were no significant differences in the femoral rotation angle, AP translation, and kinematic pathway before and after MB-UKA in the mid-flexion of the range of motion.ConclusionThere were differences between the varus–valgus knee kinematics before and after MB-UKA, from 10 to 60° of flexion, but no difference from midrange of flexion to deep flexion. In addition, the rotational knee kinematics before and after MB-UKA was not significantly different.     

单髁置换术应用于骨关节炎合并前交叉韧带缺失的三维有限元研究

目的采用有限元方法比较前交叉韧带(anterior cruciate ligament,ACL)完整与缺失的骨关节炎患者单髁关节置换(unicompartmental knee arthroplasty,UKA)术后膝关节生物力学特性,分析ACL缺失对膝关节单髁置换术后的运动和应力的影响。方法根据膝关节CT、MRI图像,建立有限元模型。采用逆向工程技术重建活动衬垫单髁假体,加载入该正常膝关节三维有限元模型。在不同屈膝角度(0°、30°、60°、90°、120°)加载载荷,观察在ACL完整(ACL-intact,ACLI)和缺失(ACL-deficiency,ACLD)情况下,膝关节的最大接触压和位移程度。结果 UKA-ACLI与UKA-ACLD模型在膝关节屈膝各角度,各部位(外侧股骨软骨、胫骨软骨、半月板、股骨假体、胫骨假体、衬垫)最大应力无明显差异,ACLD模型在膝关节屈膝0°和30°位前后位移明显大于ACLI模型,在膝关节屈膝0°位股骨相对内旋减小,在膝关节屈膝30°位股骨相对外旋增加。结论标准位置假体植入情况下,ACL缺失并不会导致UKA术后应力异常增大,会导致在膝关节伸直位时位移增加。     

Rotational alignment errors can occur in unicompartmental knee arthroplasty if anatomical landmarks are misused: A preoperative CT scan analysis

BackgroundAccurate implant positioning, including rotation, is essential for successful unicompartmental knee arthroplasty (UKA). This study defined the rotational error that would result in medial UKA when using the medial edge of the tibial tubercle (TT) rather than the medial tibial spine for determining tibial component rotation, and in lateral UKA when aligning the anterior edge of the sagittal tibial cut with the lateral edge of the patellar tendon.MethodsPreoperative computed tomography (CT) scans were reviewed in 88 knees undergoing medial (n = 71) and lateral (n = 17) UKAs. In medial UKA, the angle between a line along the long axis of the medial tibial spine and a line drawn to the medial edge of the TT was measured. In lateral UKA, the angular relationship between the longitudinal axis of the lateral tibial spine and the lateral edge of the patellar tendon was measured.ResultsIn medial UKA, an average angular error of 9.6° of external rotation could result if the medial edge of the TT is used to set tibial implant rotation. In lateral UKA, the error of the sagittal tibial cut was an average of 7.1° of excessive external rotation if it is referenced on the lateral edge of the patellar tendon.ConclusionsThe preoperative CT scan analysis showed that using the medial edge of the TT and lateral edge of the patellar tendon to set tibial implant rotation may result in excessive external rotation in medial and lateral UKAs, which could result in kinematic mismatch, suboptimal contact areas and rotational malalignment.     

The natural history of radiolucencies following cemented unicompartmental knee arthroplasty at 7 years

IntroductionRadiolucent lines (RLLs) following unicompartmental knee arthroplasty (UKA) can be concerning as aseptic loosening remains a cause of failure in UKA. The aim of our study was to report on the history of RLLs surrounding the components in a cemented medial compartment fixed-bearing UKA as well as the long-term functional outcomes in this group of patients.Material and methodsIn this retrospective consecutive case-series, twenty-eight patients (37 knees) were treated with medial, fixed-bearing cemented unicompartmental knee arthroplasty. At average final follow-up of 7.1 years, 36 knees were available for review. Radiographs were taken at six weeks, one year, and final follow up. RLLs were measured using a novel modification to the Knee Society scoring (KSS) system.ResultsAt six-weeks, we identified RLLs in 26 tibias and two femurs out of 37 total knees. At one-year, four additional tibias and both femurs showed some progression of their radiolucencies but were < 2 mm total. At final follow-up, 31 of the 36 tibias (86.1%) and five of the 36 femurs (13.9%) had any RLLs. On the tibial side, RLLs were most common in medial/lateral and anterior/posterior aspects of the tibial tray with few found centrally. On the femoral side, the posterior femoral cut accounted for the most RLLs of any zone at all time points. KSS averaged 93.8 at final follow-up and none of the patients required revision surgery.ConclusionRLLs are common following cemented, fixed-bearing UKA. Many seem to progress slowly up to one year but not thereafter. There does not appear to be any association between the presence of these radiolucencies and long-term follow-up function in this group of patients.     

Unicondylar knee arthroplasty in the UK National Health Service: An analysis of candidacy, outcome and cost efficacy

The viability of unicondylar knee arthroplasty (UKA) as a stand-alone or temporising option for the management of gonarthrosis is a topic of considerable contention. Despite recent advances in prosthesis design and surgical technique, as well as mounting evidence of long-term survivorship, UKA remains infrequently used, accounting for just 8–15% of all knee arthroplasties. Instead this group is more typically managed using total knee arthroplasty (TKA). For UKA to warrant increased usage the candidacy for UKA must be prevalent, the outcome must be equivalent or superior to that of TKA, and the costs should be comparatively low. Here we address three issues regarding UKA: 1) a prospective assessment of the proportion of knees needing arthroplasty that are candidates for UKA; 2) retrospective outcome measures comparing TKA, UKA and controls; and 3) an estimation of the difference in costs between TKA and UKA from a hospital perspective. We show in a series of 200 knees that candidacy for UKA is widespread; representing 47.6% of knees. Furthermore, we also show for the first time, that not only is UKA functionally superior to TKA (based on Total Knee Questionnaire (TKQ) scores), but scores in medial and lateral UKA knees do not differ significantly from normal, non-operative age- and sex-matched knees (t = 1.14 [38], p = 0.163; and t = 1.16 [38], p = 0.255 respectively). Finally, we report that UKA offers a substantial cost saving over TKA (£1761 per knee) indicating that UKA should be considered the primary treatment option for unicompartmental knee arthritis.     

Is postoperative flexion angle genuinely better in unicompartmental knee arthroplasty than in total knee arthroplasty? A comparison between the knees in the same patients

BackgroundThe aim of this retrospective study was to clarify if unicompartmental knee arthroplasty (UKA) can acquire a greater postoperative flexion angle than total knee arthroplasty (TKA) in the same individuals after adjusting for the preoperative flexion angle and if the preoperative flexion angle correlates with the change in flexion postoperatively.MethodsThirty-five patients between 2011 and 2017 who had undergone simultaneous TKA on one knee and UKA on the other knee were included in the study. Range of motion was measured preoperatively and at one year after the surgery. The relationship between the pre- and postoperative flexion angles was evaluated.ResultsUKA can acquire approximately 10° greater flexion postoperatively when compared to TKA, even after adjustment for the preoperative flexion angle. The preoperative flexion angle is strongly and negatively correlated with the change in flexion angle in both the TKA and UKA knees. A preoperative knee with a smaller flexion angle will gain greater flexion postoperatively, whereas a preoperative knee with a greater flexion angle tends to lose flexion angle. The thresholds of gain/loss are estimated as 123° and 135° in TKA and UKA knees, respectively.ConclusionsThese results provide an evidence that the UKA can acquire a greater postoperative flexion angle than the TKA and valuable information for patients who demand a deep postoperative flexion angle.     

Clinical outcomes and patient satisfaction following revision of failed unicompartmental knee arthroplasty to total knee arthroplasty are as good as a primary total knee arthroplasty

BackgroundWith unicompartmental knee arthroplasty (UKA) being increasingly performed for medial compartment osteoarthritis (OA) of the knee, revision total knee arthroplasty (TKA) for failed UKA is expected to increase. Our primary aim is to evaluate patients in our tertiary institution who underwent revision of failed UKA to TKA to compare their pre-operative clinical scores (patient-reported outcome measures, PROMs) to those of primary TKA.MethodsRetrospective review of our institutional arthroplasty registry between 2001 and 2014 was performed. We identified 70 patients who underwent revision of UKA to TKA. The revision UKA to TKA patients was matched with 140 patients who underwent primary TKA for OA in terms of preoperative demographics, gender, age at time of surgery, body mass index (BMI), primary surgeon, and PROMs. Intra-operative data and postoperative complications or re-revision surgeries performed were reviewed.ResultsIn the revision UKA to TKA group, more stems, augments or constrained implants were used compared to primary TKA. A greater proportion of patients with metal-backed UKA revision to TKA required stems, augments or constrained implants as compared to all-polyethylene UKA revision to TKA, but not a significant proportion (P = 0.250). At two years postoperatively, there were no significant differences observed between the groups in terms of patient satisfaction and PROMs.ConclusionsThis study showed similar outcomes following revision of failed UKA to TKA and primary TKA. There were significant improvements in PROMs for revision UKA to TKA, which is comparable to that of primary TKA.     

Comparison of medial and lateral posterior femoral condyle articular cartilage wear patterns

Background

While degenerative changes to the articular cartilage of the anterior and distal portions of the femoral condyles have been well studied in the literature, the changes that occur on the posterior femoral condyle are not as clear. The purpose of this study was to assess the difference in articular cartilage thickness between the medial and lateral posterior femoral condyles in knees undergoing unicompartmental knee arthroplasty.

Unicompartmental knee arthroplasty for spontaneous osteonecrosis of the medial tibial plateau

Background

There have been very few reports on isolated medial tibial plateau osteonecrosis, and the condition has not been clearly described. Unicompartmental knee arthroplasty (UKA) may be an appropriate treatment method for this condition. The aims of this study were to report our experience of using mobile-bearing knee implants for osteonecrosis of the medial tibial plateau and to discuss the etiology and treatment of this type of osteonecrosis.

Single photon emission computed tomography in planning unicompartmental knee arthroplasty. A prospective study examining the association between scan findings and intraoperative assessment of osteoarthritis

The aim of this study was to determine the relationship between preoperative single photon emission computed tomography (SPECT) scan findings and intraoperative assessments of knee osteoarthritis (OA) in patients undergoing tibiofemoral unicompartmental knee arthroplasty (UKA). Fifty knees in 46 patients undergoing UKA were investigated preoperatively with a SPECT scan to confirm unicompartmental disease. There were 38 men and 12 women in the cohort with an average age of 63 years (range 44-78). The SPECT scan uptake in each compartment of the knee was graded by a single radiologist and these findings were compared with intraoperative assessments of OA (size and grade of lesion), made by two experienced surgeons, blinded to the scan findings. Significant association was demonstrated between scan findings and OA in all compartments of the knee (p<0.05), and this was strongest in the medial compartment and weakest in the patellofemoral compartment and lateral tibial plateau. We conclude that SPECT scan is a useful imaging modality in the planning of medial tibiofemoral UKA to confirm unicompartmental disease. The lower degree of association between scan findings and OA encountered in the patellofemoral compartments and lateral tibial plateau indicates that greater vigilance should be exercised in the intraoperative assessment of these areas.     

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

BackgroundLateral 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 MethodsBetween 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.ResultsFunctional 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.ConclusionThis 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.     

Medial meniscus extrusion as a predictor for a poor prognosis in patients with spontaneous osteonecrosis of the knee

BackgroundRisk factors for the progression of spontaneous osteonecrosis of the knee (SONK) remain unclear. The purpose of this study was to investigate the association between magnetic resonance imaging (MRI) findings of the meniscus and the prognosis of SONK.MethodsA total of 78 consecutive patients (female 85%; mean age 75.6 ± 7.2 years old) diagnosed with SONK were included. Of these, 30 patients did not receive surgery within 1 year from the onset of SONK (conservative group), while the remaining 48 patients underwent unicompartmental knee arthroplasty due to worsening of symptoms (UKA group). Using MRI findings obtained within 3 months of the onset, we compared the types of meniscus tear and medial meniscus extrusion between the conservative group and UKA group. We performed a receiver operating characteristics (ROC) analysis to estimate the cut-off value.ResultsPatients in the UKA group showed greater medial meniscus extrusion (absolute value, 4.2 mm ± 1.9 vs. 2.8 mm ± 1.2, P = 0.001; relative percentage of extrusion (RPE), 45.7% ± 21.5 vs. 30.7% ± 12.9, P = 0.001) and a higher prevalence of radial tear (P = 0.021) than those in the conservative group. In the multivariate analysis, RPE remained a relevant independent factor (P = 0.035) for future UKA. An ROC analysis found that the cut-off point of RPE was 33% (sensitivity, 81.2%; specificity, 63.3%).ConclusionRPE was a predictor of the prognosis of patients who underwent UKA within 1 year after the onset of SONK. Our results suggest that patients with RPE ≥ 33% are at high risk for progression.     

Medial/central PF arthritis and functionally stable ACL deficiency do not compromise outcomes of fixed-bearing medial UKA

BackgroundThere is limited published data assessing functional scores and patient satisfaction following unicompartmental knee arthroplasty (UKA) in patients with patellofemoral (PF) arthritis or anterior cruciate ligament (ACL) deficiency. The purpose of this study was to determine whether medial/central PF arthritis or functionally stable ACL deficiency compromise outcomes of fixed-bearing medial UKA at a minimum follow-up of 2 years. The hypothesis was that equivalent outcomes can be achieved in patients with substantial medial/central PF arthritis or with functionally stable ACL deficiency.MethodsThe authors studied a consecutive series of 229 patients (240 knees) at 36.9 ± 6.3 months after receiving fixed-bearing medial UKA. Patients completed pre- and post-operative (2 years) clinical outcome questionnaires for Oxford Knee Score (OKS), EQ-5D, Knee injury and Osteoarthritis Outcome Score Physical Function Short Form (KOOS-PS), University of California, Los Angeles (UCLA) activity score, and Forgotten Joint Score (FJS). Multivariable analyses were performed to determine associations between clinical scores, patient demographics, PF arthritis and functionally stable ACL deficiency.ResultsOf the 240 knees, 125 (54%) had substantial medial/central PF arthritis and 21 (9%) functionally stable ACL deficiency. Multivariable analyses revealed no association between outcomes and medial/central PF arthritis, but knees with functionally stable ACL deficiency were associated with better KOOS-PS (β = 8.99, p = 0.012).ConclusionFixed-bearing medial UKA grants satisfactory outcomes at 2 years even in knees with substantial medial/central PF arthritis or functionally stable ACL deficiency. Longer-term prospective studies with larger cohorts are needed to confirm these promising findings regarding outcomes in patients traditionally contraindicated for medial UKA.     

Finite element analysis of the influence of the posterior tibial slope on mobile-bearing unicompartmental knee arthroplasty

BackgroundThe most common modes of failure reported in unicompartmental knee arthroplasty (UKA) in its first two decades were wear on the polyethylene (PE) insert, component loosening, and progressive osteoarthritis in the other compartment. The rates of implant failure due to poor component positioning in patients who have undergone UKA have been reported. However, the effect of the posterior tibial slope on the biomechanical behavior of mobile-bearing Oxford medial UKA remains unknown.MethodsWe applied finite element (FE) analysis to evaluate the effects of the posterior tibial slope in mobile-bearing UKA on the contact stresses in the superior and inferior surfaces of PE inserts and articular cartilage as well as the forces exerted on the anterior cruciate ligament (ACL). Seven FE models for posterior tibial slopes of −1°, 1°, 3°, 5°, 7°, 9°, and 11° were developed and analyzed under normal-level walking conditions based on this approach.ResultsThe maximum contact stresses on both the superior and inferior surfaces of the PE insert decreased as the posterior tibial slope increased. However, the maximum contact stress on the lateral articular cartilage and the force exerted on the ACL increased as the posterior tibial slope increased.ConclusionsIncreasing the tibial slope led to a reduction in the contact stress on the PE insert. However, a high contact stress on the other compartment and increased ACL force can cause progressive osteoarthritis in the other compartment and failure of the ACL.     

Ten year survivorship after cemented and uncemented medial Uniglide® unicompartmental knee arthroplasties

BackgroundResults of knee replacement registries have shown that unicompartmental knee arthroplasty (UKA) has a significantly higher revision and failure rate than current state-of-the-art TKA. The aim of this prospective study is to evaluate the long-term outcomes and to calculate the 10 year survival of knees with medial osteoarthritis treated with Uniglide® UKA.MethodsTwo hundred thirty-four patients were assessed by an independent clinical observer using the American Knee Society Clinical Rating System, a validated outcome measure. Kaplan–Meier analysis was used to calculate the 10 year survival rates using revision surgery for any cause as the end point.ResultsThere were no revisions due to progression of lateral osteoarthritis or polyethylene failure. There were one traumatic and three non-traumatic bearing dislocations and two revisions due to aseptic loosening of the tibial component. One joint was revised for traumatic ligament rupture, one for synovitis from bearing impingement, one due to femoral component mal-positioning and one for infection.A total of 10 cases were revised due to failures for any cause in the 61 patients withdrawn because they had died, thus giving a cumulative survival rate at 10 years of 95.57%. The knee (function) score showed an increase from 33.4 (54.7) pre-operatively to 94 (83.4) points post-operatively. The average range of motion increased from 107 to 122° (p < 0.01).ConclusionBased on our findings we believe that the Uniglide® unicompartmental knee prosthesis offers a safe and effective solution for the treatment of medial compartment osteoarthritis.     

Readmissions and mortality after outpatient vs inpatient unicompartmental knee arthroplasty in Denmark – A propensity score matched study of 5,384 procedures

BackgroundLimited nationwide data on the development of outpatient unicompartmental knee arthroplasty (UKA) practice and patient safety exist. The primary objective of this study on patients receiving a medial or lateral UKA was to investigate 7-, 30- and 90-day readmission risk and 90-day mortality in outpatient vs inpatient surgeries. Secondary to investigate the nationwide development of outpatient UKA surgery in 2014–2018.MethodsIncluded patients received a medial or lateral UKA in the period January 1, 2014 to December 31, 2018 in any Danish hospital. Data were collected from the Danish National Patient Register. The cohort consisted of 1,059 outpatient and 4,325 inpatient surgeries, hereof 5,182 medial and 202 lateral UKA. After propensity score matching (1:1) 1,057 patients were included in each group.ResultsWe found a 7-day readmission risk of 1.5 % vs 1.4 % (p = 0.8), 30-day readmission risk of 2.6 % vs 3.2 % (p = 0.3), and 90-day readmission risk of 4.2 % vs 4.8 % (p = 0.4) after outpatient vs inpatient UKA. Similar results were found after matching. We found no significant differences in 90-day mortality for the unmatched or matched cohorts. The amount of outpatient UKA surgeries in Denmark increased from 86 in 2014 to 214 in 2018.ConclusionOutpatient medial or lateral UKA seem to be as safe as inpatient UKA on a nationwide basis.     

Preoperative varus deformity of the knee affects the intraoperative joint gap in unicompartmental knee arthroplasty

BackgroundIt is generally believed that contraction of the soft tissue structures on the medial side may occur in the knee with severe varus deformity. However, the relationship between the severity of varus deformity of the knee and the intraoperative soft tissue balance in unicompartmental knee arthroplasty (UKA) has not been well reported thus far.MethodsOne hundred and three consecutive medial UKAs were enrolled. After the femoral trial prosthesis was placed, the component gap was measured at 10° (extension) and 120° (flexion) of flexion using a UKA tensor. The pre-osteotomy gap was then calculated from the thickness of the bone cut. Paired Student’s t-test was used to compare the component gap, as well as the pre-osteotomy gap, in extension and those in flexion. The relationship between the preoperative Hip-Knee-Ankle (HKA) angle and the pre-osteotomy gap was analysed using Pearson’s correlation coefficient and simple linear regression analysis.ResultsThe component gap in extension was significantly smaller than that in flexion while the pre-osteotomy gap in extension was significantly wider than that in flexion. There was a positive correlation between the severity of varus deformation in preoperative knee and the pre-osteotomy gap in extension, while there was no correlation between the preoperative HKA angle and the pre-osteotomy gap in flexion.ConclusionsThe tension of the medial tightness does not correlate with the degree of preoperative varus deformity in UKA.     

Unicompartmental knee arthroplasty: an intermediate report of survivorship after the introduction of a new system with analysis of failures

We describe the outcome of a series of 66 consecutive porous coated low contact stress (LCS) unicompartmental knee arthroplasty (UKA) cases performed in 52 patients for osteoarthritis (OA) by a single surgeon. Both survival, using the endpoint of revision for any cause, and knee function, using the Oxford knee score (OKS) as a validated outcome measure, were established in a retrospective review. At an average postoperative follow-up period of 5.9 years (range 5.1-6.6), there were 8 knees in patients who had died and 58 knees in those who were still living. We established the status of all knees, and prosthesis survival at 5 years was 89.7% (95% confidence interval, 81.6% to 97.7%). Technical errors were responsible for four of six failures and included progression of lateral compartment OA due to overcorrection, a medial tibial stress fracture due to poor pin placement, and a case where cement was required and poor cementing technique lead to early tibial component loosening. In the remaining 52 knees, the average preoperative OKS had improved significantly (p<0.0001) from 37.0 (range, 17-49) to a postoperative score of 20.5 (range, 13-32). We conclude that the functional results following UKA compare favourably to total knee arthropasty (TKA); however, the survivorship of this series does not match that of published reports of TKA. The introduction of a new system of UKA includes the risk of early failures due to surgeon error, even when a surgeon is competent in UKA, warranting careful surveillance during this period.