Quantifying the immediate post-implantation strain field of cadaveric tibiae implanted with cementless tibial trays: A time-elapsed micro-CT and digital volume correlation analysis during stair descent.

Primary stability, the mechanical fixation between implant and bone prior to osseointegration, is crucial for the long-term success of cementless tibial trays. However, little is known about the mechanical interplay between the implant and bone internally, as experimental studies quantifying internal strain are limited. This study employed digital volume correlation (DVC) to quantify the immediate post-implantation strain field of five cadaveric tibiae implanted with a commercially available cementless titanium tibial tray (Attune, DePuy Synthes). The tibiae were subjected to a five-step loading sequence (0-2.5 bodyweight, BW) replicating stair descent, with concomitant time-elapsed micro-CT imaging. With progressive loads, increased compression of trabecular bone was quantified, with the highest strains directly under the posterior region of the tibial tray implant, dissipating with increasing distance from the bone-implant interface. After load removal of the last load step (2.5BW), residual strains were observed in all of the five tibiae, with residual strains confined within 3.14 mm from the bone-implant interface. The residual strain is reflective of the observed initial migration of cementless tibial trays reported in clinical studies. The presence of strains above the yield strain of bone accepted in literature suggests that inelastic properties should be included within finite element models of the initial mechanical environment. This study provides a means to experimentally quantify the internal strain distribution of human tibia with cementless trays, increasing the understanding of the mechanical interaction between bone and implant.

Outcome following total knee replacement in patients with a previous patellectomy.

Although patellectomy is a rarely performed surgical procedure, patients may still progress to develop osteoarthritis of the tibiofemoral compartments leading to total knee replacement surgery. Due to the mechanical disadvantage of a previous patellectomy, it has previously been suggested that a prosthesis with more constraint should be used, however, there are conflicting reports in the literature. We aimed to assess the effects of stability following total knee replacement in patellectomised knee with revision as a primary endpoint. We reviewed the outcome of 25 total knee replacements in our institution in patients with a previous patellectomy. Ten were posterior stabilised and 15 minimally stabilised (including those with a 'deep dish'). Five of the patients in the minimally stabilised group underwent revision surgery, and 3 of these were early revision due to instability. None of the patients in the posterior stabilised group underwent revision. We conclude that when a total knee replacement is performed in a patient with a previous patellectomy a posterior stabilised implant should be used.

Patellectomy for osteoarthritis: a new tension preserving surgical technique to reconstruct the extensor mechanism with retrospective review of long-term follow-up.

BACKGROUND: The management of severe patellofemoral arthritis in young patients remains a significant problem. For many, patellofemoral replacement is not a desirable option. Current surgical techniques for patellectomy disrupt the extensor lever arm causing weakness. We describe a new technique that maintains the extensor mechanism tension and a case series showing good results for patella-only arthritis at a mean follow-up of 11 years. METHODS: Eight patellectomies were performed using a new surgical technique in patients with a mean age of 38 years, and an average follow-up of 11 years (range 8-16 years). Patients were followed up using a pain visual analogue scale, Lysholm knee score and patient-reported outcome measures. RESULTS: All patients experienced pain relief following surgery. Those with patella-only arthritis had better outcomes than patients who had patella and trochlea disease. All patients had either full or near full extension. Lysholm scores were better in patients who had disease confined to the patella. CONCLUSION: We believe patellectomy with this tension-preserving technique has a role for the management of anterior knee pain secondary to severe patella-only arthritis in young patients where arthroplasty is not desirable.

Staged venous thromboemolic events prophylaxis with low-molecular-weight heparin followed by aspirin is safe and effective after arthroplasty.

BACKGROUND: The rate of fatal pulmonary embolism (PE) following hip and knee arthroplasty has remained unchanged despite the use of low-molecular-weight heparin (LMWH) and oral antithrombotic agents. Concerns regarding bleeding and wound complications resulted in the introduction of a staged chemoprophylaxis protocol at our institution in 2002. We hypothesized that staged chemoprophylaxis using LMWH in hospital followed by aspirin after discharge was safe and effective for the prevention of venous thromboembolic events (VTE). METHODS: Data were retrospectively collected on all patients undergoing hip and knee arthroplasty between 2002 and 2012. For VTE prophylaxis, LMWH was administered to all patients following surgery until discharge. Aspirin was prescribed from discharge until 6 weeks following surgery. Complications were recorded in a database. Patients suspected of having a VTE were investigated with bilateral lower limb duplex ultrasound and computerized tomography-pulmonary angiogram. RESULTS: The 11-year results of this protocol used in 9035 patients with a mean age 62 years (range 20-95) and follow-up at 6 weeks demonstrate an overall symptomatic VTE rate of 2.55% and overall PE rate of 1.28%. The overall fatal PE rate is 0.03% (unicompartmental knee arthroplasty 0.07-0.96%, total knee arthroplasty 0.19% and total hip arthroplasty 0%) and the all-cause mortality is 0.07%. The wound complication rate is low. CONCLUSION: Staged chemoprophylaxis using LMWH followed by aspirin is a safe and effective thromboprophylactic regime that is associated with a very low rate of fatal PE and all-cause mortality.

Injury to the infrapatellar branch of the saphenous nerve in anterior cruciate ligament reconstruction: comparison of horizontal versus vertical harvest site incisions.

PURPOSE: Damage to the infrapatellar branch of the saphenous nerve (IPBSN) has been described for knee arthrotomy and arthroscopy. The true incidence of damage to this structure during anterior cruciate ligament (ACL) reconstruction has not been reported. Furthermore, the traditional vertical incision for central patellar tendon harvesting runs perpendicular to the course of this nerve. Therefore, a horizontal incision to avoid this potential complication was developed. TYPE OF STUDY: Case series. METHODS: A retrospective comparative study of ACL reconstructions was performed in 76 patients with central third patellar tendon as graft with a minimum of 2 years follow-up. Forty-two patients had a horizontal incision and 34 patients had a vertical incision. A questionnaire was used to evaluate function, satisfaction, and evidence of IPBSN damage. RESULTS: There was no difference between the 2 groups with regard to scar length, pain at rest, and pain with activity. Patients with a horizontal incision were more satisfied with the cosmetic appearance of their scar (P < .004). Twenty patients (59%) with a vertical incision had evidence of damage to the IPBSN as opposed to 18 patients (43%) with a horizontal incision. CONCLUSIONS: Although technically slightly more difficult, a horizontal incision may be a useful option for ACL graft harvesting to provide a more satisfactory scar with less risk of IPBSN damage. Regardless of the incision used, damage to the IPBSN is a potential complication and patients should be counseled of this preoperatively. LEVEL OF EVIDENCE: Level IV.