R a d i o l o g y C a s e R e p o r t s 1 2 ( 2 0 1 7 ) 5 4 9 e5 5 1
Available online at www.sciencedirect.com
ScienceDirect journal homepage: http://Elsevier.com/locate/radcr
Case Report
Radiological difficulty in identifying unicompartmental knee replacement dislocation Mr Oruaro Adebayo Onibere MBBS, MRCSa,*, Mr Iain Stevenson MBChB, FRCS Tr & Orthb, Mr Fraser Jonathan Gill MBChB, FRCEM, FRCSc a
Trauma and Orthopaedic Department, Dr Gray's Hospital, Elgin IV30 1SN, UK Trauma and Orthopaedic Department, Aberdeen Royal Infirmary, Aberdeen, UK c Emergency Medicine Department, Aberdeen Royal Infirmary, Aberdeen, UK b
article info
abstract
Article history:
Unicondylar knee replacement is a relatively common elective orthopedic procedure but is
Received 17 February 2017
not often seen in the Emergency Department setting. Familiarity with normal clinical and
Received in revised form
radiological appearances is difficult to gain. Dislocation of the mobile bearing component
20 February 2017
“spacer” is a known complication of unicondylar knee replacements, and these patients
Accepted 6 March 2017
will initially present to the accident and Emergency Department. In this setting, an accu-
Available online 21 April 2017
rate and prompt diagnosis is necessary to appropriately manage the patient's condition. There is normally a radiological challenge in identifying dislocated mobile bearings on
Keywords:
plain radiographs. These patients may need to have further imaging, such as a computer
Unicompartmental knee
tomographic scan to identify the dislocated mobile bearing.
replacement Dislocation
Crown Copyright © 2017 Published by Elsevier Inc. on behalf of under copyright license from the University of Washington. This is an open access article under the CC BY-NC-ND
Radiographs
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
Case
Partial knee replacements “unicondylar arthroplasties” are a relatively commonly performed orthopedic elective procedure. The Oxford unicompartmental knee is comprised of 2 metallic components, separated by a mobile polyethylene bearing, which acts as a mobile spacer between the metallic femoral and tibial components which are normally fixed to the bone with bone cement. The aim of these mobile bearings is to reduce polyethylene wear and to improve the congruity between the articulating surfaces [1].
We present a case of a 47-year-old man who is from Barnsley and was in Aberdeen for work. He was performing an activity as part of his normal employment and suffered a relatively innocuous valgus and external rotation injury to his right knee. He had previously had an uncomplicated right Oxford unicompartmental knee replacement performed in January 2013 in Chesterfield. He was otherwise fit and well, with no allergies and no preceding problems with his knee after his operation and before his presentation to our department.
Competing Interests: The authors have declared that no competing interests exist. * Corresponding author. E-mail address: [email protected] (O.A. Onibere). http://dx.doi.org/10.1016/j.radcr.2017.03.002 1930-0433/Crown Copyright © 2017 Published by Elsevier Inc. on behalf of under copyright license from the University of Washington. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
550
R a d i o l o g y C a s e R e p o r t s 1 2 ( 2 0 1 7 ) 5 4 9 e5 5 1
Fig. 1 e Anteroposterior radiograph of dislocated mobile bearing (white arrow).
Fig. 3 e Postoperative anteroposterior radiograph with well-placed mobile bearing.
At time of presentation to our Emergency Department, he was unable to weight bear and fully extend his right knee with range of movement of 20-50 degrees. Distal neurovascular examination was normal. A hard object was palpable on the subcutaneous medial aspect of his knee joint, and radiographs performed revealed a dislocated spacer which could be difficult to spot on plain radiographs (Figs. 1 and 2). This was evident from the abnormal position of the wire within the spacer as otherwise the polyethylene spacer is radiolucent. Early evidence of patellofemoral and lateral compartment
osteoarthritis was incidentally noted. The original operation note was transferred from Chesterfield which showed he had large 4-mm meniscal bearing initially inserted. The following day he underwent operative intervention in the form of removal of dislocated spacer and washout with insertion of a new 3-mm meniscal bearing as perioperatively, it was thought the 4-mm spacer may have “overstuffed” the compartment (Figs. 3 and 4). There were no signs of infection clinically. He was discharged to Barnsley a few days later.
Fig. 2 e Lateral radiograph of dislocated mobile bearing (white arrow).
Fig. 4 e Postoperative lateral radiograph with well-placed mobile bearing.
R a d i o l o g y C a s e R e p o r t s 1 2 ( 2 0 1 7 ) 5 4 9 e5 5 1
Discussion Dislocation of the mobile bearing is a recognized but rare complication of the Oxford unicompartmental knee when used to replace the medial compartment, occurring in less than 0.6% of patients. The risk of dislocation increases to 10% when used to replace the lateral compartment. Dislocation commonly occurs through a significant twisting injury, resulting in immediate severe localized pain with or without loss in knee motion [2]. Dislocated bearing inserts are usually found on the anterior, medial, or lateral side of the intracapsular area. However, posterior dislocation of a polyethylene bearing to the extra-articular area after unicompartmental knee arthroplasty has also been reported [3]. There have been several cases of missed dislocated mobile bearing from unicondylar knee replacement on initial radiographic examination [2,4]. Recognition of this diagnosis on plain radiographs and prompt referral to the Orthopaedic Department will greatly improve the chances of a successful
551
outcome and decrease the chances of a long-term negative outcome with regards to the life and performance of the unicondylar arthroplasty.
references
[1] Hamelynk KJ. History of mobile bearing knee replacement systems. Orthopedics 2006;29:7e12. [2] Woodacre T, Marshall M, Awad A, Isaac D. Chronic asymptomatic dislocation of the bearing in an Oxford unicompartmental knee replacement. BMJ Case Rep 2012;2012:1e3. [3] Jeong JH, Kang H, Ha YC, Jang EC. Incarceration of a dislocated mobile bearing to the popliteal fossa after unicompartmental knee arthroplasty. J Arthroplasty 2012;27(2):323.e5e7. [4] Thavarajah D, Davies A. A dislocated mobile bearing from a unicondylar knee replacementda complication not to be missed. Ann R Coll Surg Engl 2010;92(1):W8e9.
Available online at www.sciencedirect.com
ScienceDirect journal homepage: http://Elsevier.com/locate/radcr
Case Report
Radiological difficulty in identifying unicompartmental knee replacement dislocation Mr Oruaro Adebayo Onibere MBBS, MRCSa,*, Mr Iain Stevenson MBChB, FRCS Tr & Orthb, Mr Fraser Jonathan Gill MBChB, FRCEM, FRCSc a
Trauma and Orthopaedic Department, Dr Gray's Hospital, Elgin IV30 1SN, UK Trauma and Orthopaedic Department, Aberdeen Royal Infirmary, Aberdeen, UK c Emergency Medicine Department, Aberdeen Royal Infirmary, Aberdeen, UK b
article info
abstract
Article history:
Unicondylar knee replacement is a relatively common elective orthopedic procedure but is
Received 17 February 2017
not often seen in the Emergency Department setting. Familiarity with normal clinical and
Received in revised form
radiological appearances is difficult to gain. Dislocation of the mobile bearing component
20 February 2017
“spacer” is a known complication of unicondylar knee replacements, and these patients
Accepted 6 March 2017
will initially present to the accident and Emergency Department. In this setting, an accu-
Available online 21 April 2017
rate and prompt diagnosis is necessary to appropriately manage the patient's condition. There is normally a radiological challenge in identifying dislocated mobile bearings on
Keywords:
plain radiographs. These patients may need to have further imaging, such as a computer
Unicompartmental knee
tomographic scan to identify the dislocated mobile bearing.
replacement Dislocation
Crown Copyright © 2017 Published by Elsevier Inc. on behalf of under copyright license from the University of Washington. This is an open access article under the CC BY-NC-ND
Radiographs
license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
Case
Partial knee replacements “unicondylar arthroplasties” are a relatively commonly performed orthopedic elective procedure. The Oxford unicompartmental knee is comprised of 2 metallic components, separated by a mobile polyethylene bearing, which acts as a mobile spacer between the metallic femoral and tibial components which are normally fixed to the bone with bone cement. The aim of these mobile bearings is to reduce polyethylene wear and to improve the congruity between the articulating surfaces [1].
We present a case of a 47-year-old man who is from Barnsley and was in Aberdeen for work. He was performing an activity as part of his normal employment and suffered a relatively innocuous valgus and external rotation injury to his right knee. He had previously had an uncomplicated right Oxford unicompartmental knee replacement performed in January 2013 in Chesterfield. He was otherwise fit and well, with no allergies and no preceding problems with his knee after his operation and before his presentation to our department.
Competing Interests: The authors have declared that no competing interests exist. * Corresponding author. E-mail address: [email protected] (O.A. Onibere). http://dx.doi.org/10.1016/j.radcr.2017.03.002 1930-0433/Crown Copyright © 2017 Published by Elsevier Inc. on behalf of under copyright license from the University of Washington. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
550
R a d i o l o g y C a s e R e p o r t s 1 2 ( 2 0 1 7 ) 5 4 9 e5 5 1
Fig. 1 e Anteroposterior radiograph of dislocated mobile bearing (white arrow).
Fig. 3 e Postoperative anteroposterior radiograph with well-placed mobile bearing.
At time of presentation to our Emergency Department, he was unable to weight bear and fully extend his right knee with range of movement of 20-50 degrees. Distal neurovascular examination was normal. A hard object was palpable on the subcutaneous medial aspect of his knee joint, and radiographs performed revealed a dislocated spacer which could be difficult to spot on plain radiographs (Figs. 1 and 2). This was evident from the abnormal position of the wire within the spacer as otherwise the polyethylene spacer is radiolucent. Early evidence of patellofemoral and lateral compartment
osteoarthritis was incidentally noted. The original operation note was transferred from Chesterfield which showed he had large 4-mm meniscal bearing initially inserted. The following day he underwent operative intervention in the form of removal of dislocated spacer and washout with insertion of a new 3-mm meniscal bearing as perioperatively, it was thought the 4-mm spacer may have “overstuffed” the compartment (Figs. 3 and 4). There were no signs of infection clinically. He was discharged to Barnsley a few days later.
Fig. 2 e Lateral radiograph of dislocated mobile bearing (white arrow).
Fig. 4 e Postoperative lateral radiograph with well-placed mobile bearing.
R a d i o l o g y C a s e R e p o r t s 1 2 ( 2 0 1 7 ) 5 4 9 e5 5 1
Discussion Dislocation of the mobile bearing is a recognized but rare complication of the Oxford unicompartmental knee when used to replace the medial compartment, occurring in less than 0.6% of patients. The risk of dislocation increases to 10% when used to replace the lateral compartment. Dislocation commonly occurs through a significant twisting injury, resulting in immediate severe localized pain with or without loss in knee motion [2]. Dislocated bearing inserts are usually found on the anterior, medial, or lateral side of the intracapsular area. However, posterior dislocation of a polyethylene bearing to the extra-articular area after unicompartmental knee arthroplasty has also been reported [3]. There have been several cases of missed dislocated mobile bearing from unicondylar knee replacement on initial radiographic examination [2,4]. Recognition of this diagnosis on plain radiographs and prompt referral to the Orthopaedic Department will greatly improve the chances of a successful
551
outcome and decrease the chances of a long-term negative outcome with regards to the life and performance of the unicondylar arthroplasty.
references
[1] Hamelynk KJ. History of mobile bearing knee replacement systems. Orthopedics 2006;29:7e12. [2] Woodacre T, Marshall M, Awad A, Isaac D. Chronic asymptomatic dislocation of the bearing in an Oxford unicompartmental knee replacement. BMJ Case Rep 2012;2012:1e3. [3] Jeong JH, Kang H, Ha YC, Jang EC. Incarceration of a dislocated mobile bearing to the popliteal fossa after unicompartmental knee arthroplasty. J Arthroplasty 2012;27(2):323.e5e7. [4] Thavarajah D, Davies A. A dislocated mobile bearing from a unicondylar knee replacementda complication not to be missed. Ann R Coll Surg Engl 2010;92(1):W8e9.
