Defining Normal Postoperative Magnetic Resonance Imaging After Total Knee Arthroplasty
Defining Normal Postoperative Magnetic Resonance Imaging After Total Knee Arthroplasty
The aim of this study was to describe the postoperative "baseline" magnetic resonance imaging
 (MRI) appearance of the ipsilateral thigh musculature after total knee arthroplasty (TKA).
 The secondary aim was to describe baseline muscle enzyme levels under the same clinical
 scenario. Neither of these measures have been reported previously.
-  In 2016, 3 sentinel cases of presumed local anesthetic-induced myotoxicity were reported
 after TKA with associated continuous adductor canal block (CACB) analgesia. The
 diagnosis was made based on its consistency with animal and human descriptions of local
 anesthetic myotoxicity, including: a) exposure to local anesthetic, b) delayed symptom
 onset after a period of normal recovery, c) rapid development of profound muscle
 flaccidity, and d) complete to partial recovery of motor function after weeks to months.
 MRIs obtained in these patients showed diffuse intra- and inter-muscular edema
 (inflammation) of the ipsilateral thigh, which was believed to support the presumptive
 diagnosis. However, because baseline MRI appearance of upper leg muscles has never been
 described for this clinical scenario, it is possible that the MRI scans represented
 "normal, baseline" appearance.

 -  This case series intended to prospectively describe postoperative MRI appearance in a
 cohort of asymptomatic volunteer patients that underwent uncomplicated TKA/CACB. In
 addition, because obtaining biomarkers of muscle injury might also be a reasonable
 diagnostic step, we sought to measure preoperative and postoperative creatine
 phosphokinase (CPK) and aldolase levels.

 -  MRI scans were read by 5 board-certified musculoskeletal radiologists masked to the
 study's purpose. Grading was done using a standard grid that facilitated systematic
 evaluation of various regions within the upper leg. At least 3 of 5 radiologists were
 required to declare edema as present within a given region of the leg.

 -  Only those volunteer patients that presented a normal postoperative course, i.e., had no
 unexpected leg muscle weakness, were entered into the study. As such, the MRI and muscle
 enzyme analysis results had no impact on the volunteer patients' clinical outcome or
 management. This was a prospective, observational/descriptive case series. There was no
 control group and we did not intend to investigate issues of cause-and-effect.
Inclusion Criteria:

 -  Scheduled for unilateral primary TKA with CACB

 -  TKA and early recovery was uncomplicated (no evidence of unexpected leg weakness)

 Exclusion Criteria:

 -  Contraindication to spinal anesthesia or adductor canal-based analgesia

 -  History of muscle wasting or related disease

 -  History of autoimmune disorders that may affect muscles

 -  History of neurologic condition affecting the lower extremities

 -  Contraindications to MRI