Validation of varus stress radiographs for anterior cruciate ligament and posterolateral corner knee injuries: A biomechanical study.
OBJECTIVE
The purpose of this study was to determine the effect of isolated anterior cruciate ligament (ACL) insufficiency on the radiographic varus stress test, and to provide reference data for the increase in lateral compartment opening under varus stress for a combined ACL and PLC injury.


METHODS
Ten cadaveric lower extremities were fixed to a jig in 20° of knee flexion. Twelve Newton-meter (Nm) and clinician-applied varus loads were tested, first with intact knee ligaments, followed by sequential sectioning of the ACL, fibular collateral ligament (FCL), popliteus tendon and the popliteofibular ligament (PFL). Lateral compartment opening was measured after each sequential sectioning.


RESULTS
Maximum increase in lateral compartment opening for an isolated ACL deficient knee was 1.06mm with mean increase of 0.52mm (p=0.021) for the clinician-applied load. Mean increase in lateral compartment opening in an ACL and FCL deficient knee compared to the intact knee was 1.48mm (p<0.005) and 1.99mm (p<0.005) for the 12-Nm and clinician-applied loads, respectively, increasing to 1.94mm (p<0.005) and 2.68mm (p<0.005) with sectioning of the ACL and all PLC structures.


CONCLUSIONS
Anterior cruciate ligament deficiency contributes to lateral compartment opening on varus stress radiographs though not sufficiently to confound previously established standards for lateral ligament knee injuries. We did not demonstrate the same magnitude of lateral compartment opening with sectioning of the PLC structures as previously reported, questioning the reproducibility of varus stress radiographic testing among institutions. Clinicians are cautioned against making surgical decisions based solely on current standards for radiographic stress examinations.
Naval Medical Center San Diego, Department of Orthopaedic Surgery, Suite 112, 34800 Bob Wilson Drive, San Diego, CA 92134, United States. Electronic address: lucas.s.mcdonald.mil@mail.mil.
Lucas S
LS
McDonald
Naval Health Clinic New England, Orthopaedics Clinic, 43 Smith Road, Newport, RI 02841, United States.
Robert A
RA
Waltz
Naval Medical Center San Diego, Department of Orthopaedic Surgery, Suite 112, 34800 Bob Wilson Drive, San Diego, CA 92134, United States.
Joseph R
JR
Carney
Naval Medical Center San Diego, Department of Orthopaedic Surgery, Suite 112, 34800 Bob Wilson Drive, San Diego, CA 92134, United States.
Christopher B
CB
Dewing
Naval Medical Center San Diego, Department of Orthopaedic Surgery, Suite 112, 34800 Bob Wilson Drive, San Diego, CA 92134, United States.
Joseph R
JR
Lynch
Naval Medical Center San Diego, Department of Radiology, 34800 Bob Wilson Drive, San Diego, CA 92134, United States.
Dean B
DB
Asher
Naval Medical Center San Diego, Department of Orthopaedic Surgery, Suite 112, 34800 Bob Wilson Drive, San Diego, CA 92134, United States.
Dustin J
DJ
Schuett
Naval Medical Center San Diego, Department of Orthopaedic Surgery, Suite 112, 34800 Bob Wilson Drive, San Diego, CA 92134, United States.
Lance E
LE
LeClere
D000070598:Anterior Cruciate Ligament Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D002102:Cadaver; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D016474:Weight-Bearing
Anterior cruciate ligament (ACL); Posterolateral corner (PLC); Stress radiographs; Varus instability