Abstract
We studied the mechanisms of extension lag after knee surgery. The position of the patella was measured by using the method of Insall-Salvati.
Subjects: There were four groups of subjects. Group I consisted of 17 knees of non-surgically treated rheumatoid arthritis (RA), Group II was 21 knees of surgically treated RA: 9 synovectomies and 12 total knee replacements (TKR) ; Group III and IV were two controls: 274 non-surgically treated knees having various knee diseases and 16 TKR knees having osteoarthritis (OA) .
Results: 1) The patellar height of the non-surgically treated RA knees tended to decrease; 2) there was a temporary increase in the patellar height just after surgery in the surgically treated RA knees; 3) there was no correlation between patellar height and aging; and 4) TKR OA knees showed no change in patellar height after surgery.
Conclusion: The course of the non-surgically treated RA knee showed a tendency for the patellar height to decrease due to knee contracture. In the case of the patellar tendon being released by synovectomy or TKR, there was a temporary increase in patellar height which caused extension lag. However, as this temporary increase became less, the extension of the surgically treated knees improved.
