Introduction. A tibial insert with choices in size, thickness, and posterior slope is proposed to improve ligament balancing in total knee arthroplasty. However, increasing posterior slope, or the angle between the distal and proximal insert surfaces, will redistribute ultra-high molecular weight polyethylene (UHMWPE) thickness in the sagittal plane, potentially affecting wear. This study used in-vitro testing to compare wear for a standard cruciate-retaining tibial insert (STD) and a corresponding 6° sloped insert (SLP), both manufactured from direct-compression molded (DCM) UHMWPE. Our hypothesis was slope variation would have no significant effect on wear. Methods. Two of each insert (STD and SLP) were tested on an Instron-Stanmore knee simulator with a force-control regime. The gait cycle and other settings followed ISO 14243-1 and -2, except for reference positions. The STD insert was tilted 6° more than the SLP insert to level the articular surfaces. Wear was gravimetrically measured at intervals according to strict protocol. Results. No statistical difference (p=0.36) in wear rates was found for the STD (9.5 ±1.8 mg/Mc)) and SLP (11.4 ±0.5 mg/Mc) inserts. Discussion. The overall wear rate measured was higher than previously published rates for implants similar to the STD inserts. This may result from increased shear loads due to the shift in reference position and 6° slope. This is the first time the effect of tibial insert slope on wear has been evaluated in-vitro. For inserts made from DCM UHMWPE with a slope limited to 6°, this test suggests altering tibial insert slope has an insignificant effect on wear

Introduction. In valgus knees, ligament balance remain difficult when implanting a total knee arthroplasty (TKA), this leads some authors to systematically propose the use of constrained devices. Others prefer reserving higher constraints to cases where it is not possible to obtain final satisfactory balance: less than 5 of residual frontal laxity in extension in each compartment, and a tibiofemoral gap difference not in excess to 3mm between flexion and extension. The goal of the study was to assess if is possible to establish preoperative criteria that can predict a constrained design prosthetic implantation at surgery. Materials and Methods. A consecutive series of 93 total knee prostheses, implanted to treat a valgus deformity of more than 5 was retrospectively analysed. Preoperatively, full weight bearing long axis AP views A-P were performed: hip knee angle (HKA) averaged 195 (186 to 226), 36 knees had more than 15 of valgus, and 19 others more than 20 of valgus. Laxity was measured by stress radiographies with a TelosTM system at 100 N. Fifty-two knees had preoperative laxity in the coronal plane of more than 10. Fourteen knees had more than 5 laxity on the convex (medial) side, 21 knees had more than 10 laxity on the concave (lateral) side. Statistical assessment, using univariate analysis, identified the factors that led, at surgery, to an elevated constraint selection level; these factors of independence were tested by multivariate analysis. Logistical regression permitted the classification of the said factors by their odds ratios (OR). Results. High-constraints prostheses (CCK type) were used in 26 out of 93 TKA, the other TKA were regular posterostabilized (PS) prostheses. Statistically, the preoperative factors that led to the choice of a constrained prosthesis were: (1) valgus severity as measured by HKA (PS = (PS = 193, CCK = 198), (2) increased posterior tibial slope (PS = 4.8, CCK = 6.5), (3) low patellar height (using Blackburne and Peel index PS = 0.89, CCK = 0.77), (4) severity of laxity in valgus (PS = 2.3, CCK = 4.3). Among all these factors, the only independent one was laxity in valgus (convex side laxity) (p = 0.0008). OR analysis showed a two-fold increased probability of implanting an elevated constraints prosthesis for each one degree increment of laxity in valgus. Discussion. This study demonstrated that it was not the valgus angle severity but rather the convex medial side laxity that increased the frequency of constrained prostheses implantation. Other factors, as a low patellar height or an elevated posterior tibial slope, when associated, potentiate this possible prosthetic switch (to higher constraints) and should make surgeons aware, in these situations, of encountering difficulties when establishing ligament balance

Introduction:. Bicondylar tibial plateau fractures are serious periarticular injuries. We investigated outcomes in injuries managed with Ilizarov external fixators. Methods:. We retrospectively reviewed bicondylar tibial plateau fractures treated with Ilizarov fixators in a major trauma centre from 2008–2012. Radiological parameters were measured from standardised weight-bearing radiographs. A subset (n=34) had patient-related outcome measures. Results:. Of 80 injuries, all fractures united. Two developed septic arthritis and one osteomyelitis. 76.3% were graded a good-excellent outcome (Rasmussen radiological score). 30.3% had evidence of osteoarthritis (Kellgren Lawrence>1). Neither parameter correlated significantly with lower functional scores. Referrals from neighbouring hospitals had longer times to surgery, which associated with increased condylar widening (p=0.0214) and posterior tibial slope (p=0.0332). Risk of developing osteoarthritis correlated with lower joint line congruency angle (JLCA) (p=0.0017) and increased articular step-off (p=0.0008) on initial radiographs. 3 patients have progressed to total knee arthroplasty. Discussion and Conclusion:. This is the largest study of bicondylar tibial plateau fractures treated by Ilizarov fixation. Rates of septic arthritis and osteomyelitis compare with previously reported rates, with no cases of non-union. Over 76% achieved good-excellent radiological outcome, compared with 63–96% in studies of internal fixation. Achieving normal JLCA and smooth articular surface at the time of fixation reduce risk of developing osteoarthritis