A New Arthroscopic Technique to Determine Anterior-Inferior Glenoid Bone Loss: Validation of the Secant Chord Theory in a Cadaveric Model
Received 20 November 2008; accepted 23 May 2009.
Purpose
The accuracy of a previously described method using the glenoid bare spot (GBS) as a reference point was compared with a new method using the secant chord theory (SCT), which relies on the circular geometry of the inferior glenoid to calculate bone loss.
Methods
In 7 embalmed cadaveric shoulders a digital image of the glenoid face was used to calculate the area of the best-fit circle of the inferior glenoid. Osteotomy templates from the 3-o'clock to 6-o'clock position were created to make a simulated anterior-inferior bone defect of 12.5% and 25% of the area of the circle. Measurements were taken with an arthroscopic probe from 2 simulated posterior portal positions (9 and 10 o'clock) by use of 2 techniques—SCT and GBS—in the intact, 12.5% loss, and 25% loss states.
Results
In the intact state, measurements showed a mean SCT loss of 4.1% and GBS loss of 4.4%. In the 12.5% loss state, mean percent bone loss with GBS was 23.1% compared with 14.8% with SCT (P = .0001) at the 10-o'clock portal and 22.2% compared with 15.9% (P = .006) at the 9-o'clock portal. In the 25% loss state, mean percent bone loss with GBS was 31.5% compared with 26.6% with SCT (P = .002) at the 10-o'clock portal and 30.4% compared with 28.9% (P = .48) at the 9-o'clock portal.
Conclusions
The SCT is shown to be a more accurate method of determining glenoid bone loss in an arthroscopic model; however, additional mathematic calculations are necessary. As shown in the intact state, there is an inherent small error of approximately 4% when arthroscopically determining bone loss.
Clinical Relevance
The technique may aid the clinician in quantifying glenoid bone loss and help determine when bone augmentation may be advisable.
aDepartment of Orthopedic Surgery, Rush University Medical Center, Chicago, Illinois, U.S.A.
bDivision of Sports Medicine, Rush University Medical Center, Chicago, Illinois, U.S.A.
cShoulder and Elbow Section, Rush University Medical Center, Chicago, Illinois, U.S.A.
dDepartment of Orthopaedic Shoulder, Knee and Sports Surgery, Naval Medical Center San Diego, San Diego, California, U.S.A.
Address correspondence and reprint requests to Alvin J. Detterline, M.D., Towson Orthopaedic Associates, Ruxton Professional Center, 8322 Bellona Ave, Ste 100, Baltimore, MD 21204-2012, U.S.A.
The views expressed in this article are those of the authors and do not reflect the official policy or position of the Department of the Navy, Department of Defence, or the United States government.
ABSTRACT