Ambient theatre temperature and cement setting time in total knee arthroplasty.

BACKGROUND: Polymethylmethacrylate cement is used in total knee arthroplasty and plays a significant role in the success of the procedure. Temperature variation is known to influence cement setting time in vitro. Our aim is to evaluate the relationship between ambient theatre temperature and cement setting time in vivo. METHODS: Theatre temperature and cement setting time were prospectively recorded during 683 total knee arthroplasties over 8 years using a single cement and vacuum mixing system (Simplex with tobramycin). Setting time was defined as the time until a scalpel blade could not indent the cement surface. RESULTS: Mean temperature was 18.92°C (SD 1.16) and setting time 13.08 min (SD 1.92). A moderate inverse relationship exists between ambient temperature and setting time (Pearson's R = -0.423); however, potential setting times within a given temperature range varied considerably (<19°C: 8-19.1 min, 19-20°C: 7-18 min and >20°C: 7.5-16 min), suggesting that temperature alone cannot reliably predict setting time. CONCLUSION: Our data support the current understanding of bone cement properties in vivo and suggest that surgeons should be mindful in regards to unpredictable cement setting time and optimal theatre environment.

The effect of knee prosthesis design on tibiofemoral biomechanics during extension tasks following total knee arthroplasty.

BACKGROUND: Determine whether the tibiofemoral motion and electromyographic activity of the knee differs in patients with a medial pivot implant, compared to those with cruciate-retaining and posterior-stabilised designs, during knee extension after Total Knee Arthroplasty (TKA). METHODS: An observational study was conducted on a cohort of patients that had undergone TKA for a minimum of 12 months prior. Three matched groups (n = 18) were categorised based on implant type: medial-pivot (MP), posterior-stabilised (PS) and cruciate-retaining (CR). Kinematics, with motion analysis (Vicon, USA) and surface electromyography (Delsys, USA) were assessed during step-ascent and walking tasks. RESULTS: All groups displayed a similar amount of knee extension in both tasks. They also paradoxically produced an average mean internal rotation movement during knee extension in both the step-ascent and walking tasks. The only significant difference was found in the step-ascent task, in which the MP group produced a larger absolute amount of rotation than the CR implant group (P = 0.007), but neither group differed from the PS implant group. The groups did not differ in rotation during the walking task (P > 0.05). The MP group displayed significantly (P < 0.01) greater knee extensor activation during the step-ascent than the PS group. CONCLUSION: The MP design was only significantly different to another implant design for the step-ascent task. Patients with either knee implant types were not strictly limited to producing the traditional "screw-home" mechanism, defined by external rotation during extension. Furthermore, comparison with the non-implant contralateral limb suggested that rotation is not necessarily dictated by implant design.

Evaluation of Nitinol Staples for the Lapidus Arthrodesis in a Reproducible Biomechanical Model.

While the Lapidus procedure is a widely accepted technique for treatment of hallux valgus, the optimal fixation method to maintain joint stability remains controversial. The purpose of this study is to evaluate the biomechanical properties of new shape memory alloy (SMA) staples arranged in different configurations in a repeatable first tarsometatarsal arthrodesis model. Ten sawbones models of the whole foot (n = 5 per group) were reconstructed using a single dorsal staple or two staples in a delta configuration. Each construct was mechanically tested non-destructively in dorsal four-point bending, medial four-point bending, dorsal three-point bending, and plantar cantilever bending with the staples activated at 37°C. The peak load (newton), stiffness (newton per millimeter), and plantar gapping (millimeter) were determined for each test. Pressure sensors were used to measure the contact force and area of the joint footprint in each group. There was a statistically significant increase in peak load in the two staple constructs compared to the single staple constructs for all testing modalities with P values range from 0.016 to 0.000. Stiffness also increased significantly in all tests except dorsal four-point bending. Pressure sensor readings showed a significantly higher contact force at time zero (P = 0.037) and contact area following loading in the two staple constructs (P = 0.045). Both groups completely recovered any plantar gapping following unloading and restored their initial contact footprint. The biomechanical integrity and repeatability of the models was demonstrated with no construct failures due to hardware or model breakdown. SMA staples provide fixation with the ability to dynamically apply and maintain compression across a simulated arthrodesis following a range of loading conditions.

Femoral Bone Plug in Total Knee Replacement.

The intramedullary alignment guides used in total knee replacement disrupt the intramedullary vessels, resulting in greater postoperative blood loss. The use of an autologous bone plug to seal the intramedullary femoral canal has been shown to be effective in reducing postoperative bleeding. The authors present a simple technique to create a bone plug from the anterior chamfer femoral cut to perfectly seal the intramedullary canal of the femur.

Anterior Longitudinal Osteotomy of the Greater Trochanter in Total Hip Arthroplasty.

The extra-articular impingement of the greater trochanter against the ileum is an underrated cause of early dislocation in total hip arthroplasty. In this preliminary study, the authors assess the effectiveness of an anterior longitudinal osteotomy of the greater trochanter for preventing dislocation. A total of 115 patients underwent a total hip arthroplasty through a posterolateral approach. All patients underwent clinical and radiological follow-up at 1, 3, and 6 months. No dislocation was reported. All patients demonstrated fast recovery of range of motion and walking. No trochanter fractures were observed. The osteotomy of the greater trochanter is an effective surgical technique that decreases anterior impingement and consequently lowers the dislocation rate in primary total hip arthroplasty. [Orthopedics. 2015; 38(8):490-493.].

Polyurethane scaffold for the treatment of partial meniscal tears. Clinical results with a minimum two-year follow-up.

PURPOSE: to evaluate the safety and effectiveness of the polyurethane meniscal scaffold through clinical examination, MRI and arthroscopic second look, over a minimum two-year follow-up. METHODS: between 2009 and 2011, 19 patients underwent meniscal scaffold implantation in our department (medial meniscus in 16 cases lateral meniscus in two cases, and bilateral in one case). All the patients were clinically evaluated preoperatively, and at 6, 12, and 24 months after surgery using Lysholm score, Tegner score, and VAS. Ten patients were studied with MRI, and nine patients were evaluated arthroscopically. RESULTS: no adverse reactions to the implant were observed. The clinical scores showed a significant improvement at 6 months and increased progressively over time. On MRI studies, the implants showed a clear hyperintense signal, sometimes irregular, and the chondral surface was preserved in all cases. At arthroscopic second look in the first months after surgery, the scaffold size was unchanged and the scaffold appeared light yellowish in color and well integrated into the surrounding tissues. At arthroscopic second look at 12 and 24 months the scaffold was found to have an irregular morphology and to be slightly reduced in size. CONCLUSIONS: polyurethane meniscal scaffold is a good alternative to a collagen scaffold, but a longer follow-up is needed to evaluate the scaffold degradation and chondral coverage. LEVEL OF EVIDENCE: level IV, therapeutic case series.