Revision of Unicompartmental to Total Knee Arthroplasty: Does the Unicompartmental Implant (Metal-Backed vs All-Polyethylene) Impact the Total Knee Arthroplasty?

BACKGROUND: The aim of this study is to investigate differences in implant requirement, outcomes, and re-revision when total knee arthroplasty (TKA) was performed following unicompartmental knee arthroplasties (UKAs) with metal-backed (MB) compared to all-polyethylene (AP) tibial components. METHODS: Retrospective study of 60 UKAs converted to 60 TKAs at mean 7.3 years (0.1 to 17) after implantation in 55 patients (mean age, 64 [49-83]; 44% male): 44 MB and 16 AP. TKA implant requirement was investigated in addition to mode of failure, Oxford Knee Score, and TKA survival at mean 5.4 years (0.5 to 17). RESULTS: Progression of osteoarthritis was the commonest mode of failure in MB UKAs (P = .03) and unexplained pain in AP (P = .011) where revisions were performed earlier (4.8 ± 3.2 vs 8.2 ± 4.5, P = .012). In 56 of 60 (93%) cases, unconstrained TKA implants were used. The use of standard cruciate-retaining TKAs without augments or stems was less likely following MB UKA compared to AP (12 of 38 [32%] vs 10/14 [71%], P = .013). Specifically MB UKA implants were associated with more tibial stem use (P = .04) and more use of cruciate-substituting polyethylene (P = .05). There was no difference in the use of constrained implants. Multivariate analysis showed tibial resection depth to predict stem requirement. Seven were re-revised giving 7-year TKA survival: from MB UKA 70.3 (95% CI, 47.0 to 93.6) and from AP UKA 87.5 (95% CI, 64.6 to 100; P = .191). CONCLUSION: MB UKA implants increase the chances of a complex revision requiring tibial stems and cruciate substitution but reduce the chances of early revision compared to AP UKA which often fail early with pain.

Ten-year survival and patient-reported outcomes of a medial unicompartmental knee arthroplasty incorporating an all-polyethylene tibial component.

INTRODUCTION: Biomechanical studies have suggested that proximal tibial strain is elevated in UKAs incorporating all-polyethylene tibial components with concern that this leads to premature failure. This study reports minimum 10-year outcomes for a UKA incorporating an all-polyethylene tibial component to determine whether these concerns were realised. MATERIALS AND METHODS: 109 fixed bearing UKAs (97 patients, mean age 68 (range 48-87), 54/97 (56%) female) with all-polyethylene tibial components were followed up for ≥ 10 years with Oxford Knee Scores, Forgotten Joint Scores and Kaplan-Meier analysis. 106/109 implants were 7 mm, 3 were 9.5 mm. RESULTS: Ten-year survival was 85.5% (78.6-92.4 95% CI) with the end-point failure for any reason. Unexplained pain was the commonest mode of failure (6/17) followed by lateral compartment osteoarthritis (5/17) and tibial subsidence/loosening (4/17). Revision rate was highest at 2-5 years due to revisions for unexplained pain. Ten-year survival was worse in patients < 65 years old (p = 0.035), in those with BMI > 30 (p = 0.017) and in those with postoperative increases in medial tibial sclerosis (p < 0.001 log-rank). Implant malalignment was not significantly associated with failure. Radioisotope bone scans in 16 patients all remained "hot" at mean 6.1 years (range 2.1-11.5). Relative risk of failure in patients < 65 years was 2.9 (1.2-7.0 95% CI) and when BMI > 30 was 2.9 (1.2-6.9 95% CI). In those with intact UKAs at 10 years, mean Oxford Knee Score was 34.8 ± 10.7, Forgotten Joint Score was 37.9 ± 26.7 and 96% were satisfied with their knee. CONCLUSION: The high rate of early failure between 2 and 5 years in this all-polyethylene tibial component UKA did not persist in the long term. Though medial proximal tibial metabolic changes appear to persist they are not necessarily symptomatic. BMI > 30 and age < 65 years were significant risk factors for revision.

Changes in Bone Density in Metal-Backed and All-Polyethylene Medial Unicompartmental Knee Arthroplasty.

BACKGROUND: Proximal tibial strain in medial unicompartmental knee arthroplasty (UKA) may alter bone mineral density and cause pain. The aims of this retrospective cohort study were to quantify and compare changes in proximal tibial bone mineral density in metal-backed and all-polyethylene medial UKAs, correlating these with outcome, particularly ongoing pain. METHODS: Radiographs of 173 metal-backed and 82 all-polyethylene UKAs were analyzed using digital radiograph densitometry at 0, 1, 2, and 5 years. The mean grayscale of 4 proximal tibial regions was measured and converted to a ratio: the GSRb (grayscale ratio b), where GSRb>1 represents relative medial sclerosis. RESULTS: In both implants, GSRb reduced significantly to 1 year and stabilized with no differences between implants. Subgroup analysis showed less improvement in Oxford Knee Score in patients whose GSRb increased by more than 10% at 1 year (40/255) compared with patients whose GSRb reduced by more than 10% at both 1 years (8.2 vs 15.8, P=.002) and 5 years (9.6 vs 15.8, P=.022). Patients with persistently painful UKAs (17/255) showed no reduction in GSRb at 1 year compared with a 20% reduction in those without pain (P=.05). CONCLUSIONS: Bone mineral density changes under medial UKAs are independent of metal backing. Medial sclerosis appears to be associated with ongoing pain.

Trabecular Metal Use in Paprosky Type 2 and 3 Acetabular Defects: 5-Year Follow-Up.

BACKGROUND: The reconstructive challenge of achieving a stable acetabulum in revision total hip arthroplasties in the presence of major osteolytic lesions has led to debate about the most appropriate surgical strategy to minimize implant-related failures. Trabecular metal (TM) implants have become popular but ongoing surveillance of their performance is required. METHODS: We reviewed the clinical and radiological outcome of a consecutive series of 52 patients (55 hips) who had undergone revision total hip arthroplasty for Paprosky type 2 or 3 acetabular defects with TM revision acetabular shells between 2002 and 2008. RESULTS: Four implant failures occurred (2 infections and 2 dislocations). Eleven patients from this cohort died (representing 12 hips) before the 5-year follow-up period giving us a follow-up of 78.2%. Implant survival at 5 years was 92% (95% confidence interval: 80.2%-96.9%). There were no cases of radiological loosening. The mean Oxford hip score was 34 (range, 5-48) at a mean follow-up of 63 months (range, 34-105 months). CONCLUSIONS: We conclude that the use of TM revision shells for complex acetabular reconstruction yields satisfactory results.

Short Term Recovery of Function following Total Knee Arthroplasty: A Randomised Study of the Medial Parapatellar and Midvastus Approaches.

This pilot double blind randomised controlled study aimed to investigate whether the midvastus (MV) approach without patellar eversion in total knee arthroplasty (TKA) resulted in improved recovery of function compared to the medial parapatellar (MP) approach. Patients were randomly allocated to either the MV approach or the MP approach. Achievements of inpatient mobility milestones were recorded. Knee kinematics, muscle strength, Timed Up and Go, WOMAC, and daily step count were assessed before and up to six months after surgery. Cohen's effect size d was calculated to inform the sample size in future trials. Twenty-eight participants (16 males, 12 females) participated. Patient mobility milestones such as straight leg raise were achieved on average 1.3 days (95% CI -3.4 to 0.7, d = 0.63) earlier in the MV group. Knee extensor strength at 6 weeks after surgery was higher (95% CI -0.38 to 0.61, d = 0.73) in the MV group. No trends for differences between the groups were observed in knee kinematics, TUG, WOMAC, or step count. Our results suggest a short term advantage in the first 6 weeks after surgery of the MV approach over the MP approach, but a larger study is required to confirm these findings. This trial is registered with NCT056445.

Revision hip arthroplasty for late instability secondary to polyethylene wear.

We evaluated the outcome of revision arthroplasty for polyethylene wear presenting as late dislocation. The computerized databases at two institutions were reviewed to identify all patients presenting with first time dislocation five or more years after total hip arthroplasty. Records and radiographs were then evaluated, and patients whose late dislocation occurred in the presence of greater than two millimeters of polyethylene liner wear with no other etiology for dislocation were identified. There were 22 patients with a mean age of 57.8 years at primary procedure. The average time from initial arthroplasty to dislocation was 9.0 years. Revision surgery to address polyethylene wear and instability was performed at a mean of 11.1 years (range 5.8 to 23 years). Revision surgery restored stability to eighteen patients (eighty-two percent). Polyethylene wear can and is associated with late dislocation after hip arthroplasty. Exchange of polyethylene lining of a metal backed implant or revision of the all polyethylene acetabular component can successfully address late instability in the majority of patients.

Femoral perforation complicating contemporary uncemented hip arthroplasty.

This case series reports on 4 patients in whom intraoperative penetration of the femoral cortex occurred and went unrecognized on routine postoperative radiographs. This case series highlights some important points. Femoral cortex penetration can and does occur with uncemented hip arthroplasty and is likely to occur when surgical exposure is difficult and inadequate (such as in patients with severe obesity) or some form of proximal femoral deformity exists (such as patients with achondroplasia). Extra diligence should be exercised to avoid this complication in the high-risk patients, and adequate 2-plain radiographs may need to be ordered intraoperatively if such complication is suspected.

Isolated acetabular polyethylene exchange through the anterolateral approach.

Isolated exchange of an acetabular liner, in the presence of a well-fixed acetabular component, has become an established method for the management of polyethylene wear. Various experienced adult-reconstruction surgeons have noted a high incidence of instability following isolated liner exchange. We report the results of isolated liner exchange in 35 patients with polyethylene wear and osteolysis (16 patients) or polyethylene wear and instability (19 patients) with a minimum follow-up of 2 years. Isolated liner exchange was performed through an anterolateral approach in all cases. Postoperative dislocation occurred in 2 of the 35 patients (6%), both with polyethylene wear and osteolysis. Isolated liner exchange was successful in addressing instability in all 19 patients who presented with polyethylene wear and dislocation. Isolated acetabular liner exchange performed through an anterolateral approach carries an acceptable dislocation rate.

Living with digital imaging.

Increasingly orthopaedic departments are using digital radiology and imaging systems. We review the technical features of a digital radiology system for the orthopaedic surgeon. The pros and cons of digital and computed radiology are discussed. Hardware and software requirements for storage, retrieval, manipulation, and display of digital images are reviewed. The potential benefits to the clinician and the patient are outlined.