Anterior Cruciate Ligament Deficiency is Not Always a Contraindication for Medial Unicompartmental Knee Arthroplasty: A Retrospective Study in Nondesigner’s Japanese Hospital

BackgroundAn intact anterior cruciate ligament (ACL) is thought to be prerequisite for successful unicompartmental knee arthroplasty (UKA), but recent studies reported successful midterm results of UKA in ACL-deficient (ACLD) knees. We hypothesized that ACLD is not always a contraindication for medial UKA when preoperative radiographs showed typical anteromedial knee patterns.MethodsFrom April 2012 to March 2016, 401 Oxford mobile-bearing UKAs in 282 patients were retrospectively identified from our database. Patients whose ACL was severely damaged, but preoperative X-rays showed typical anteromedial osteoarthritis patterns, were categorized into the ACLD group. From intraoperative data, those whose ACL was intact were categorized into the ACL functional (ACLF) group. There were 32 and 369 knees in the ACLD and ACLF groups, respectively, and mean follow-up periods were 66.1 and 63.8 months for the ACLD and ACLF groups, respectively. We compared the postoperative clinical outcome and component survivorship, with an endpoint of component revision, between ACLD groups and ACLF groups.ResultsIn both groups, the Oxford knee score, Knee Society score, Tegner activity score, and knee range of motion in extension were improved after surgery. The UKA component survival rate at five years was 100% in the ACLD group and 98.9% in the ACLF group. There were no significant differences between the groups.ConclusionMid-term clinical outcomes of Oxford mobile-bearing UKA in ACLD knees were similar to those in ACLF knees. ACL deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs.     

Is Mobile-Bearing Medial Unicompartmental Knee Arthroplasty Appropriate for Asian Patients With the Risk of Bearing Dislocation?

BackgroundMobile-bearing unicompartmental knee arthroplasty (UKA) is an attractive operation for medial unicompartmental knee arthritis, but unexpected bearing dislocation is a drawback. Bearing dislocation occurs more frequently in Asians, whose lifestyle involves deeper knee flexion than Westerners. This study investigated whether mobile-bearing medial UKA is appropriate for Asians by analyzing (1) the rate of bearing dislocation and (2) the results of patients with bearing dislocation.MethodsWe retrospectively reviewed 531 consecutive mobile-bearing medial UKA in the previous 15 years, including 22 patients with bearing dislocation who had at least 2 years of follow-up. The entire patient cohort was divided into 2 groups: the symmetrical bearing (187 knees) and the anatomic bearing (344 knees) groups. In the anatomic bearing group, patients who underwent surgery using the conventional phase III (283 knees) vs the Microplasty (61 knees) instrumentation systems were compared.ResultsThe overall incidence of bearing dislocation was 4.1% (22/531). Patients with the symmetrical bearing displayed a relatively high dislocation rate of 9.6% (18/187), which significantly decreased to 1.1% (4/344) after changing to the anatomic bearing (P < .001). In the anatomic bearing group, the dislocation rate with the conventional phase III system was 1.4% (4/283). There were no bearing dislocations in the Microplasty system group (0%, 0/61) after at least 2 years of follow-up.ConclusionAlthough mobile-bearing medial UKA was reported to have a high incidence of bearing dislocation in Asians, this frequency of dislocation is drastically decreased by bearing design and implantation system improvements. We consider mobile-bearing medial UKA appropriate for Asians.     

Relevance of the Tibial Slope on Functional Outcomes in ACL-Deficient and ACL Intact Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BackgroundExcessive posterior tibial slope in medial unicompartmental knee arthroplasty (UKA) has been implicated in early failure. The purpose of this study was to evaluate the relationship between preoperative posterior tibial slope and postoperative slope of the implant (PSI) on outcomes in patients with anterior cruciate ligament (ACL) intact and ACL-deficient knees after fixed-bearing medial UKA.MethodsPatients who underwent a medial UKA between 2002 and 2017 with a minimum 3-year follow-up were included. Preoperative posterior tibial slope and postoperative PSI were measured. Outcomes measures included Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales, Lysholm, and VR-12. Failure was defined as conversion to total knee arthroplasty.ResultsOf 241 knees undergoing UKA, 131 patients (70 women, 61 men; average age of 65 ± 10 years (average BMI of 27.9 ± 4) were included. For all patients, survivorship was 98% at 5 years and 96% at 10 years with a mean survival time for UKA was 15.2 years [95% CI: 14.6-15.7]. No failure had a PSI >7°. There were no superficial or deep infections. There were no significant differences in outcome scores between the ACL intact and the ACL-deficient group; therefore, the data were combined for analysis. At mean 8-year follow-up, KOOS pain scores were better in patients with PSI ≤7° (87 ± 16) than those with PSI >7° (81 ± 15). 76% of patients with PSI ≤7° reached the Patient Acceptable Symptom State for KOOS pain; whereas, 59% of patients with PSI >7° reached PASS for KOOS pain (P = .015).ConclusionPatients with postoperative posterior slope of the tibial implant >7° had significantly worse postoperative pain, without conversion to TKA, and with maintenance of high function. In ACL deficient and intact knees, nonrobotically-assisted, fixed-bearing medial UKA had a 96% survivorship at 10 years.     

Fixed-Bearing Medial Unicompartmental Knee Arthroplasty in Patients Younger Than 55 Years of Age at 4-19 Years of Follow-Up: A Concise Follow-Up of a Previous Report

BackgroundUnicompartmental knee arthroplasty (UKA) is an effective alternative to total knee arthroplasty (TKA) in isolated unicompartmental disease; however, mid-term to long-term results in young patients are unknown. The purpose of this study is to determine the mid-term outcomes of fixed-bearing medial UKA in patients less than 55 years of age.MethodsSeventy-seven fixed-bearing medial UKAs in patients less than 55 years of age (mean 49.9, range 38-55) from a previously published report were retrospectively reviewed at a mean follow-up of 11.2 years (range 4.1-19.2).ResultsEleven knees were converted to TKA (14.3%) at 0.7-13.8 years postoperatively. The indications for revision included 7 for unexplained pain (9.1%), 2 for grade 4 arthritic progression (1 isolated lateral and 1 lateral and patellofemoral compartments; 2.6%), 1 for polyethylene wear (1.3%), and 1 for femoral component loosening (1.3%). Predicted survivorship free from component revision was 90.4% (95% confidence interval 86.9-93.9) at 10 years and 75.1% (95% confidence interval 66.2-84.0) at 19 years. The mean Knee Society Score improved from a mean of 51.9-88.6 points (P < .001). Of the 52 knees with 4-year minimum radiographs, 3 (5.8%) developed isolated grade 4 patellofemoral arthritis that was asymptomatic, and no knees had evidence of component loosening or osteolysis.ConclusionFixed-bearing medial UKA is a durable option for young patients with unicompartmental arthritis, with good clinical outcomes at mid-term follow-up. Unexplained pain was the most common reason for revision to TKA.     

A Comparison of Mobile and Fixed-Bearing Unicompartmental Knee Arthroplasty at a Minimum 10-Year Follow-up

Background

The long-term survivorship and functional outcomes of the mobile-bearing (MB) compared to the fixed-bearing (FB) unicompartmental knee arthroplasty (UKA) implant design remain a topic of debate. The aim of the current study was to compare the survivorship and functional outcomes of MB and FB UKA at a minimum 10-year follow-up.

Impact of Polyethylene Thickness on Clinical Outcomes and Survivorship in Medial Mobile-Bearing Unicondylar Knee Arthroplasty

BackgroundThe thickness of the polyethylene bearing in medial unicondylar knee arthroplasty (UKA) is determined by the depth of the tibial resection, degree of correctable deformity, and balance of the knee. The purpose of this study is to evaluate whether polyethylene thickness in medial mobile-bearing UKA impacts clinical outcomes and survivorship.MethodsA retrospective review from 2004 to 2017 identified patients who underwent a primary mobile-bearing medial UKA with 2-year minimum follow-up or revision. A total of 2305 patients (3030 knees) met inclusion criteria. Patients were divided in 2 groups: thin bearing (group 1): 3-mm or 4-mm bearing and thick bearing (group 2): ≥ 5 mm. The thin group consisted of 2640 knees (87%), whereas the thick group had 390 knees (13%). Preoperative and postoperative demographics, range of motion, Knee Society scores, complications, and reoperations were evaluated.ResultsMean follow-up was 5.2 years (range, 0.5 to 12.6). There was no significant difference between groups in postoperative range of motion or Knee Society scores (P > .05). Manipulations were performed in 1.3% of patients and not significantly different between groups. The all-cause revision rate for group 1 was 4.02% and group 2 was 4.58% (P = .6). Revision rates for tibial aseptic loosening were significantly higher in group 2 (1.8%) than those in group 1 (0.7%) (P = .04). There was no significant difference in failure rates between groups for tibial collapse or fracture, femoral aseptic loosening, arthritic progression, bearing dislocation, or other cause of revision.ConclusionThis study demonstrated that thicker bearings in medial UKA increased the risk of tibial aseptic loosening, but not all-cause failures or clinical outcomes.     

Activity Level Does Not Affect Survivorship of Unicondylar Knee Arthroplasty at 5-Year Minimum Follow-Up

BackgroundPatients are often cautioned against a high level of activity after knee arthroplasty. The purpose of this study was to report on implant survivorship and outcomes of high-activity patients compared with low-activity patients after unicondylar knee arthroplasty (UKA).MethodsWe identified 487 patients (576 knees) who underwent UKA with the Oxford mobile bearing knee (Zimmer Biomet, Warsaw, IN) with a 5-year minimum follow-up. Patients were divided into 2 groups: low activity (LA) (University of California Los Angeles ≤6) and high activity (HA) (University of California Los Angeles ≥7). Preoperative and postoperative range of motion, Knee Society scores, complications, and reoperations were evaluated.ResultsMean follow-up was 9 years (range, 4 to 13.1). The HA group had significantly more male patients, were younger, and had higher knee society clinical scores and knee society functional scores preoperatively. The HA group had significantly higher improvements in Knee Society scores and pain postoperatively. Revisions were performed in 8.4% of the LA group and 6.2% of the HA group (P = .43). At our mean of 9-year follow-up, there was 94.0% survival for the HA group and 92.1% for the LA group (P = .6085).ConclusionsHighly active patients had no increased risk of revision after UKA with the Oxford mobile bearing knee at 5-year minimum follow-up.     

Impact of Proximal Tibial Varus Anatomy on Survivorship After Medial Unicondylar Knee Arthroplasty

BackgroundPrecise indications for medial unicondylar knee arthroplasty (UKA) continue to be defined. It is unclear if patients who have proximal tibia vara should be considered candidates for UKA. The purpose of this study was to evaluate the impact of proximal tibial varus alignment on outcomes after UKA.MethodsA retrospective review identified 2,416 patients (3,029 knees) who underwent mobile-bearing medial UKA with 2-year minimum follow-up or revision. Preoperative radiographs were evaluated, and medial proximal tibial angle (mPTA) was measured. Patients were grouped into two groups as follows: mPTA <80 degrees and mPTA ≥80 degrees. Analyses were performed on the impact of mPTA on clinical outcomes, all-cause revisions, and tibial failures.ResultsAt a mean follow-up of 5 years (range, 0.5 years to 12.8 years), there was not a statistically significant difference in clinical outcomes nor increased risk for all-cause revision or tibial failure in patients who had an mPTA <80°. Mean mPTA in patients who had tibial failures was 82.5° and not significantly different than those who did not have a tibial failure (82.9°) (P = .289). Tibial failure rate in knees with an mPTA <80° was 2.2% and not significantly different than knees with an mPTA ≥80° at 1.4% (P = .211). The all-cause revision rate in knees with an mPTA <80° was 5.8% and was not significantly different than knees with an mPTA ≥80° at 4.9% (P = .492).ConclusionPatients who have tibia vara are not at increased risk for tibial related or all-cause failure in medial UKA. This data may allow surgeons to increase their indications for medial UKA.     

A Comprehensive Evaluation of Lateral Unicompartmental Knee Arthroplasty Short to Mid-Term Survivorship,and the Effect of Patient and Implant Characteristics: An Analysis of Data From the Dutch Arthroplasty Register

BackgroundThe rarity of lateral unicompartmental knee arthroplasty (UKA) results in a lack of large cohort studies and understanding. The aim of this study is to comprehensively evaluate survivorship of lateral UKA with registry data and compare this to medial UKA.MethodsLateral (n = 537) and medial UKAs (n = 19,295) in 2007-2017 were selected from the Dutch Arthroplasty Register. Survival analyses were performed with revision for any reason as primary endpoint. Adjustments were made for patient and implant characteristics. Stratified analyses according to patient and implant characteristics were performed. Reasons and type of revision were grouped according to laterality and bearing design.ResultsThe 5-year revision rate was 12.9% for lateral UKA and 9.3% for medial UKA. Multivariable regression analyses showed no significant increased risk for revision for lateral UKA (hazard ratio 0.87, 95% confidence interval 0.66-1.15). Stratified analyses showed that the effect of patient characteristics on revision was comparable between lateral and medial UKA; however, the use of mobile-bearing design for lateral UKA was associated with increased revision rate. Progression of osteoarthritis was the main reason for revision on both sides accompanied by tibia component loosening for medial UKA. Reasons and type of revision varied depending on bearing design.ConclusionSimilar survivorship of lateral and medial UKA was reported. Specifically, there is a notable risk for revision when using mobile-bearing designs for lateral UKA. Failure modes and type of revision depends on laterality and bearing design. These findings emphasize that surgical challenges related to anatomy and kinematics of the lateral and medial knee compartment need to be considered.     

Satisfactory Outcomes of All-Poly Fixed Bearing Unicompartmental Knee Arthroplasty for Avascular Osteonecrosis Versus Osteoarthritis: A Comparative Study With 10 to 22 Years of Follow-up

BackgroundWhile good mid-term results for treating spontaneous knee osteonecrosis (SPONK) with unicompartmental knee arthroplasty (UKA) have been reported, concerns remain about implant survival at long-term. This study aimed to compare outcomes and survivorship of UKA for SPONK vs osteoarthritis at a minimum of 10 years.MethodsThis case-control study included medial UKA for femoral SPONK operated between 1996 and 2010 with a minimum 10-year follow-up (n = 47). Each case was matched with a medial UKA for osteoarthritis based on body mass index (BMI), gender, and age. Knee Society Score (KSS), complications and radiological (loosening) data were collected at the last follow-up. Kaplan-Meier survivorship analysis was performed using revision implant removal as endpoint.ResultsThe mean follow-up was 13.2 years (range 10 to 21 years). Mean age and BMI were 72.9 ± 8.4 years and 25.5 ± 3.6 Kg/m² in SPONK group. At last follow-up, knee and function KSS were 89.5 ± 12 and 79 ± 18 in SPONK group vs 90 ± 15 (P = .85) and 81.7 ± 17 (P = .47) in control group. Complications and radiological results showed no significant differences. The survival rate free from any revision was 85.1% at last follow-up in SPONK group and 93.6% in control group (P = .23). The leading cause for revision was aseptic tibial loosening (57.1%) in SPONK group. The 15-year survival estimate was 83% in SPONK group.ConclusionSatisfactory clinical outcomes at long-term after UKA for femoral SPONK were observed, similar to those after UKA for osteoarthritis, despite a higher risk of tibial loosening in the SPONK group. No symptomatic femoral loosening leading to a revision was observed.Level of EvidenceIV.     

Does preoperative patellofemoral joint state affect medial unicompartmental arthroplasty survival?

One contested contraindication to medial unicompartmental knee arthroplasty (UKA) has been status of the patellofemoral joint. Surgeons have avoided UKA when the patellofemoral joint has radiographic evidence of arthritic changes. However, recent studies advocate ignoring patellofemoral joint status when considering UKA. The purpose of this study was to compare the failure rate of mobile-bearing, medial UKA in patients with and without preoperative radiographic evidence of patellofemoral joint degeneration. Preoperative radiographs from a random selection of 503 patients (638 knees) treated with UKA for anteromedial osteoarthritis were assessed by an observer blinded to clinical outcome. The patellofemoral joint was graded using the modified Altman classification from 0 to 3 with 0 being no evidence of changes and 3 being severe, and identified 396 grade 0, 168 grade 1, 65 grade 2, and 9 grade 3 knees. At 1- to 7-year follow-up, there have been 17 revisions for overall survivorship of 97.3%. Kaplan-Meier analysis predicted 97.9% survival in knees with patellofemoral joint disease and 93.8% survival in knees without patellofemoral joint disease at 70 months (P=.1). Failure requiring revision occurred in 3.5% (14/396) of grade 0 knees, 1.2% (2/168) of grade 1, 1.5% (1/65) of grade 2, and 0% (0/9) of grade 3. No survival difference was noted between knees with medial or lateral patellofemoral joint disease (P=.1). No knees were revised for progression of disease in the patellofemoral joint or anterior knee pain. In light of this investigation and the work of others, preoperative radiographic changes in the patellofemoral joint can be safely ignored when considering patients for medial UKA without compromising survivorship.     

Varus-Valgus Constrained Implants With a Mobile-Bearing Articulation: Results of 367 Revision Total Knee Arthroplasties

BackgroundVarus-valgus constrained (VVC) implants are used for compromised ligamentous stability in revision total knee arthroplasties (TKAs). Mobile-bearing VVC implants may reduce rotational forces; yet, limited clinical data exist. The purpose of this study is to report mid-term risk of re-revision, complications, and clinical outcomes with a mobile-bearing VVC implant.MethodsThree hundred thirty-seven patients (367 TKAs) who underwent revision TKA with a mobile-bearing VVC implant between 1999 and 2013 at a single institution were reviewed. Mean age at revision was 67 years. Mean follow-up was 4 years. The main indications for revision were aseptic loosening in 158 cases (43%), reimplantation after 2-stage exchange arthroplasty in 120 (33%), instability in 61 (17%), and other in 28 (7%). Clinical outcomes were assessed by Knee Society Scores, and survivorship was analyzed with death as the competing risk.ResultsThe 5-year cumulative incidences of any re-revision or re-revision for aseptic loosening were 9% and 3%, respectively. Twenty-six knees (7%) were re-revised: 15 for infection, 6 for aseptic loosening, and 5 for other causes. There were 17 cases of irrigation and debridement, 10 cases of manipulations under anesthesia, and 9 cases of periprosthetic fractures. There were no bearing “spin-outs.” The mean Knee Society Scores improved from 45 preoperatively to 77 at most recent follow-up (P < .001).ConclusionThe functional improvement and 5-year cumulative incidence of revision of a mobile-bearing VVC implant demonstrated acceptable outcomes with no unique complications related to the mobile-bearing construct. Additional follow-up will be needed to determine long-term implant survivorship.     

The mid-term clinical results of the phase 3 Oxford unicompartmental knee arthroplasty: a 6- to 8-year follow-up

Unicompartmental knee arthroplasty (UKA) is widely performed in the United Kingdom for the management of patients with symptomatic osteoarthritis of the medial compartment of the tibiofemoral joint. A limited number of papers have presented the findings of mid-term clinical and survival data with sufficiently large patient numbers following mobile-bearing UKA. The purpose of this study was to present the 6- to 8-year follow-up data on a series of 230 minimally invasive medial Oxford Phase 3 mobile-bearing UKAs in our institution. Data on surgical procedure, postoperative rehabilitation requirement, complications, revision procedures and Oxford Knee Score (OKS), Short Form-12 (SF-12) and visual analogue scale (VAS) pain scores were analysed. The results indicated that the majority of patient’s recoveries were uneventful, with 96% experiencing no postoperative complications. The mean OKS, VAS pain and SF-12 scores indicated good functional outcomes and acceptable perceived general health for this age group. Twenty-one patients underwent revision surgery, indicating a survival rate of 85% (95% CI: 0.76–0.91) during the 6- to 8-year follow-up period. The most frequently cited indication for revision was due to progression of osteoarthritis to the lateral component. To conclude, this series indicated that the mobile-bearing Oxford UKA provides good clinical outcomes at 6- to 8-year follow-up, with minimal requirement for postoperative rehabilitation, few complications and an acceptable survivorship in the mid-term.     

Eight Hundred Twenty-Five Medial Mobile-Bearing Unicompartmental Knee Arthroplasties: The First 10-Year US Multi-Center Survival Analysis

Background

FDA approval for the Oxford phase III device was approved for use in the United States in 2004. This study seeks to provide the first long-term, large patient sample size, Oxford phase III multi-site survivorship study in the United States, investigating patient reported outcomes of pain and function, while also providing an in-depth analysis of causes for revision, and finally addressing recent advancements that can help aid the unicompartmental knee arthroplasty (UKA) process and further improve partial knee survivorship.

Midterm Results of Medial Unicompartmental Knee Arthroplasty Performed in Patients With Lateral Meniscus Abnormalities on Preoperative MRI Without Symptoms Related to Lateral Meniscus

BackgroundThe purpose of the present study was to compare the functional outcomes of medial unicompartmental knee arthroplasty (UKA) between patients with lateral meniscal abnormalities (LM [+] group) on the preoperative magnetic resonance imaging and those without lateral meniscal pathology (LM [–] group) and to evaluate the effect of a lateral meniscus lesion on functional outcomes after minimal 5 year follow-ups of medial UKA.MethodsThe outcomes of 66 knees (LM (+) group) were compared with the outcomes of 59 knees (LM (?) group) with a mean follow-up period of 75 months (range 60-93 months). The clinical outcomes were examined including the KS object/function score, Knee Injury and Osteoarthritis Outcome score, lateral side pain, and squatting ability at the last follow-up. The radiological parameters (mechanical axis and component position) were compared at the final follow-up visit.ResultNo significant intergroup difference was found in terms of the KS object/function score, Knee Injury and Osteoarthritis Outcome score, presence of lateral side pain, and squatting ability. On the radiographic evaluation, there was no statistical difference in the position of the implant and mechanical axis between the two groups. After the surgery, the LM (+) group showed a tendency of slight varus alignment in the postoperative radiography.ConclusionThe results of UKA for medial unicompartmental knee osteoarthritis were excellent regardless of preoperative lateral meniscal pathology in the magnetic resonance imaging, if the patients had no symptoms related to the lateral meniscus lesion.     

Comparison of Long-Term Survival Analysis Between Open-Wedge High Tibial Osteotomy and Unicompartmental Knee Arthroplasty

BackgroundTo compare unicompartmental knee arthroplasty (UKA) and open-wedge high tibial osteotomy (OWHTO) in a long-term follow-up propensity score matching analysis.MethodsPatients who underwent UKA or OWHTO for unilateral medial unicompartmental osteoarthritis (OA) between 2004 and 2010 were included. The ROM, HSS score, KS score, WOMAC score, forgotten joint score, OA progression in patellofemoral and lateral compartments, and survivorship were compared within ten years of follow-up between 67 UKA and 67 OWHTO patients after propensity score matching for age, gender, body mass index, range of motion, and osteoarthritis (OA) grade.ResultsAt the last follow-up, there were no significant differences between the two groups in clinical outcomes, but the WOMAC score showed better results after UKA (13.1 in UKA vs 18.9 in OWHTO, P = .011). The OA progression also showed no significant difference between the two groups. After a 10-year follow-up, the survival rate was higher in UKA patients (96.2%) than in OWHTO patients (87.7%), with no statistical difference (P = .06).ConclusionUKA showed better clinical outcomes and OA progressions than OWHTO. The survival rate presented a superiority of 8.5% for the UKA group in the 10-year follow-up, without significant difference.     

High Failure Rates for Unicompartmental Knee Arthroplasty in Morbidly Obese Patients: A Two-Year Minimum Follow-Up Study

BackgroundSeveral recent studies have recommended offering unicompartmental knee arthroplasty (UKA) to all patients regardless of body mass index (BMI). The aim of this investigation was to evaluate the proposition that UKA can indeed be offered to the morbidly-obese and super-obese (morbidly-obese, BMI ≥ 40 kg/m²) without compromising results or survivorship.MethodsWe retrospectively reviewed mobile-bearing medial UKA procedures performed at our facility from January 2012 to May 2015 with a minimum of 2-year follow-up. The study cohort was divided into patients with morbid obesity (BMI ≥ 40 kg/m²) and those without morbid obesity (BMI < 40 kg/m²). A detailed medical record review was performed. Extracted outcome data included the frequency of (1) major revision procedures (components revised), (2) minor secondary procedures (components not revised), (3) infection procedures, and (4) recommendations for revision.ResultsWe found 152 patients (190 knees) who met criteria for inclusion. Mean follow-up duration was 3.4 years (range: 2.0-6.8 years). Major revision surgery occurred more frequently in the morbid-obesity UKA group (15.7% vs 3.0%, P < .01). Rates of minor secondary surgery and infection were comparable for both groups. Most failures in the morbid-obesity UKA group (85.7%) were due to disease progression involving other compartments or mobile-bearing instability.ConclusionWe found the rate of early major revision surgery in morbidly-obese patients undergoing UKA to be over 5-times greater than that of other patients. Failure was predominantly due to disease progression in other compartments or mobile-bearing instability. Further study is warranted and needed before expanding UKA indications to the morbidly-obese population.     

Oxford medial unicompartmental arthroplasty for focal spontaneous osteonecrosis of the knee

Background?Spontaneous osteonecrosis of the knee (SONK) is a distinct clinical condition occurring in patients without any associated risk factors. There is controversy as to the best method of treatment, and the available literature would suggest that patients with SONK have a worse outcome than those with primary osteoarthrosis when arthroplasty is performed.

We assessed the outcome of medial unicompartmental knee arthroplasty (UKA) using the Oxford prosthesis for end-stage focal spontaneous osteonecrosis of the knee (SONK; Ahlbäck grades III & IV).

Patients and methods?We assessed 29 knees (27 patients) with spontaneous osteonecrosis of the knee using the Oxford Knee Score. 26 knees had osteonecrosis of the medial femoral condyle and 3 had osteonecrosis of the medial tibial plateau. All had been operated on using the Oxford Medial Unicompartmental Knee Arthroplasty (UKA). This group was compared to a similar group (28 knees, 26 patients) who had undergone the same arthroplasty, but because of primary osteoarthrosis. Patients were matched for age, sex and time since operation. The mean length of follow-up was 5 (1–13) years.

Results?There were no implant failures in either group, but there was 1 death (from unrelated causes) 9 months after arthroplasty in the group with osteonecrosis. The mean Oxford Knee Score in the group with osteonecrosis was 38, and it was 40 in the group with osteoarthrosis.

Interpretation?Use of the Oxford Medial UKA for spontaneous focal osteonecrosis of the knee is reliable in the short to medium term, and gives results similar to those obtained when it is used for patients with primary osteoarthrosis.     

Outcomes of unicompartmental knee arthroplasty stratified by body mass index

Patients who have high body mass indices can have disabling medial compartment knee osteoarthritis, which might benefit from unicompartmental knee arthroplasty (UKA). The purpose of this study was to compare clinical and radiographic outcomes of UKAs in patients with body mass indices (BMIs) greater and less than 35 kg/m². Thirty-four patients (40 knees) had BMIs of 35 kg/m² or greater, whereas the remaining 33 patients (40 knees) had BMIs below 35 kg/m², with 2-year minimum follow-up. In the high-BMI group, 5 knees were revised to total knee arthroplasty, compared with none in the lower BMI group. Knee Society scores were lower in the surviving high-BMI knees. All surviving components were radiographically stable. The results suggest that UKA should be approached with caution in patients who have high BMIs.