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Background Extensor mechanism disruption (EMD) combined with periprosthetic joint infection (PJI) after total knee arthroplasty are life-changing complications. The literature suggests many eventually receive above-knee amputation and lose ambulatory function. An alternative is modular knee fusion (KF), but little is known about its outcomes and biomechanical function. We report early term results on a case series of patients. Methods A retrospective review was conducted of patients who underwent 2-stage reconstruction with modular KF for combined EMD and PJI. Patient-reported outcomes at 1 year after arthrodesis and complications of surgery were recorded. Biomechanical analysis was conducted on 6 patients >1 year after surgery to measure gait speed and balance. Results Fifteen patients received a modular KF. At the most recent follow-up visit (average 25.7 months), 12 patients had their modular KFs in place and were ambulatory while 2 had died. Six patients used a walker; 4, a cane; and 2, unassisted. Gait analysis of 6 of these patients showed variation in patterns and speed. Balance was better than historical controls treated with above-knee amputation. Average Knee Injury and Osteoarthritis Outcome Score Junior was 76 ± 11. Conclusion Modular KF for EMD and PJI can result in successful outcomes in terms of preventing additional operations and maintaining ambulation. While speed is variable, physical testing shows this method for limb salvage may allow patients to ambulate with a gait aid although further studies are needed to evaluate midterm and long-term results.

Background Polyethylene liner dissociation is an uncommon complication of hip replacement. Dissociation has been associated with particular acetabular component designs. This study reviewed acetabular liner dissociations in a specific modular cup with a Morse taper locking mechanism that has not been previously reported. Methods The senior author performed 655 primary total hip arthroplasties with one particular design of acetabular component using Class A polyethylene liners and metal head articulation. Cases with revision surgery performed for acetabular liner dissociation were reviewed. Results Seven of 655 patients with this cup underwent revision surgery for a dissociated liner. Liner dissociation occurred at a mean of 73 months postoperatively. Patients presented with new-onset hip pain or squeaking, 4 of which developed symptoms acutely. Two patients treated with polyethylene liner exchange into the same cup required a second revision surgery for recurrent dissociation. Conclusion Polyethylene liner dissociation is an infrequent but possible complication associated with modular acetabular components using a Morse taper locking. Providers should be vigilant with long-term follow-up of patients with this acetabular system for patient complaints of catching or squeaking. Patients treated for liner dissociation should not have a new liner placed into the same acetabular shell given the risk for further dissociation.

Introduction: Management of periprosthetic infection in total hip arthroplasties is challenging, especially when there is severe loss of proximal femoral bone stock. When a 2-stage approach is used, either a static or an articulating spacer may be considered. Static spacers leave the patient with a flail leg, which can be very difficult with massive bone loss. The purpose of this study is to report a novel technique for articulating antibiotic spacers and report our results. Materials and Methods: We describe a technique for an articulating hip spacer in the setting of a large amount of proximal femoral bone loss using a locked intramedullary nail, modular femoral body, and an all-polyethylene constrained acetabular component. This technique allowed for mobilization of the patient without a flail leg. Four patients underwent 2-stage reconstruction, and the case series is reported here. Results: No complications occurred due to the spacer, and in all cases, a second reconstruction was later carried out after treatment with intravenous antibiotics. Three of 4 patients did well after 2-stage reconstruction, with 1 patient ultimately requiring an amputation. Discussion: We feel this technique improves upon previously reported large spacers due to the stability and maintenance of leg length. Conclusion: This technique offers a modular solution to address massive bone loss of the proximal femur in the face of periprosthetic joint infection.