Osteoporosis is a commonly encountered problem affecting outcomes after total knee arthroplasty(TKA). The current gold standard for diagnosing osteoporosis is bone mineral density(BMD) as measured by DEXA. This requires radiation exposure and is routinely performed at the hip, spine and radius. TKA affects the bone quality around the knee. A tool to diagnose the quality of bone at the knee joint without requiring radiation exposure would be extremely beneficial and reduce costs. We aim to investigate the diagnostic strength of subjective assessment of bone quality by an orthopaedic surgeon against the gold standard, bone mineral density measured by DEXA.
We prospectively enrolled 31 patients undergoing unilateral TKA. All patients undergoing bilateral and revision TKA were excluded. All patients underwent BMD by DEXA preoperatively. Intraoperatively, based on the bone quality, a single surgeon graded the bone on a VAS scale from 0 – 10, with 10 being the strongest bone. The surgeon was blinded to the BMD results. We divided the patients into 3 groups; normal, osteopenic and osteoporotic depending on the T score in the ipsilateral femoral neck. We correlated this T score with the VAS scale scoring. On the VAS scale we used a cutoff of 4 to define osteoporosis and 8 to define normal bone. We then tested the diagnosing power of these cutoffs in identifying osteoporotic and normal bones respectively.
The spearman correlation co-efficient for VAS scale and BMD as measured by T score is 0.954 (p<0.001).
Surgeon conclusion of osteoporosis (VAS 4 and below) :
The diagnostic accuracy was 93.55%, sensitivity was 71.43%, specificity was 100%, positive predictive value was 100% and negative predictive value was 92.31%.
Surgeon conclusion of osteopenia or osteoporosis (VAS 7 and below) :
The diagnostic accuracy was 77.42%, the sensitivity was 70.83%, specificity 100%, positive predictive value 100% and negative predictive value 50%.
Intraoperative surgeon assessed bone quality has a strong correlation with BMD measured by DEXA. A VAS score of 4 or below has a 100 % specificity and positive predictive value along with a high negative predictive value and diagnostic accuracy for diagnosing osteoporosis. This can be used as a tool in diagnosing osteoporosis, eliminating the need for additional tests and radiation exposure. A VAS score of 7 and below has a 100 % specificity and positive predictive value for diagnosing osteopenia or osteoporotic bone. This may help identify normal bone, aiding the surgeon make better decisions regarding the implant fixation choice – cementless versus cemented.