Rare Asymptomatic Posterior Dislocation of Mobile Bearing Insert in Unicondylar Knee Arthroplasty: A Case Report
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CASE REPORT
Rare Asymptomatic Posterior Dislocation of Mobile Bearing Insert in Unicondylar Knee Arthroplasty: A Case Report Ramneek Mahajan1 · Varun Khanna1 · Piyush Suresh Nashikkar1 · Anchit Uppal1 Received: 10 March 2020 / Accepted: 21 August 2020 / Published online: 8 September 2020 © Indian Orthopaedics Association 2020
Abstract Dislocation of polyethylene insert is a common complication of mobile bearing uniconylar knee arthroplasty (UKA). Dislocation, when occurs is common in anterior, lateral or medial direction. The authors report a case of posterior dislocation in which patient remained asymptomatic and the dislocation was detected in a routine follow-up radiograph done at 18 months after surgery. UKA was subsequently converted into total knee arthroplasty and patient had a stable knee at two years followup with no signs of loosening or instability. Posterior meniscal bearing dislocation may remain asymptomatic and continued examination with high index of suspicion is needed to disclose such complications in the absence of symptoms. Keywords Unicondylar knee arthroplasty · Replacement · Bearing dislocation · Posterior · Asymptomatic
Introduction Bearing dislocation is one of the earlier occurring complications of mobile-bearing (MB) Oxford uniconylar knee arthroplasty (UKA) with reported incidence rates between 0 and 5.3% [1]. A fully congruent MB polyethylene (poly) insert, used in Oxford UKA, closely approximates normal knee kinematics. Theoretically, it has a lesser risk of component loosening and low wear potential but carries risk of dislocation. Dislocation, when it occurs, is usually anterior and rarely occurs in other direction [2–4] We report a case of rare posterior dislocation of the MB insert as an incidental finding during a regular 18 months follow-up of a case of medial Oxford UKA. Index surgery was done in our institute which is a tertiary care hospital, by a high volume joint replacement surgeon (RM). Consent
* Varun Khanna Ramneek Mahajan [email protected] Piyush Suresh Nashikkar [email protected] Anchit Uppal [email protected] 1
Max Institute of Musculoskeletal Sciences,Max Smart Super Speciality Hospital, Mandir marg, Press Enclave Road, Saket, New Delhi 110017, India
of the patient was taken before sending this case report for publication. A 57 years old, obese female (BMI 29.3 kg/mt2) presented in out-patient department (OPD) in October, 2017 with complaints of bilateral knee pain with pain in the left knee confined only over the medial portion of the knee. A detailed clinical and radiological evaluation suggested tricompartmental osteoarthritis of right knee and medial compartment arthritis of left knee (Fig. 1a, b). After medical evaluation and anesthetic clearance patient underwent total knee arthroplasty (THA) for right side and UKA for left side. Intra-operatively during UKA trial, size 7 poly gave a stable articulation and knee was well balanced in coronal plane with no signs of dislocation of insert. Extra small femoral and AA size tibial component was
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