Fat pad adhesion to partially torn anterior cruciate ligament: a cause of knee locking

Isolated damage to the ACL was found on arthroscopic examination of 51 patients who had symptomatic knees. There were 47 male and 4 female patients. The average age of the patients was 26.5 years, ranging from 13 to 43 years. Twenty-four of the patients had isolated partial tears of the ACL, and 27 had isolated complete tears. The purpose of this study was to examine the clinical patterns and arthroscopic findings in these two groups. On examination, 12 patients were found to have locked knees. An additional six patients gave a history of knee locking. All 18 of these patients were clinically suspected of having meniscal damage; however, only partial and complete ACL tears were found at arthroscopy. Of these 18 patients who had locking knees, 15 had a partial tear of the ACL and 3 had a complete tear. Locking was involved primarily in the group with partial ACL tears (15 of 24); only 3 of the 27 patients who had complete tears described locking. Of the 12 patients who had locked knees on examination, all were found to have fibrosis and adhesions of the fat pad and the synovium adjacent to the ACL stump. All 12 of these patients had a partial tear of the ACL. The fibrosis and adhesions were histologically documented in 10 of those 12 patients. The three patients who had partial ACL tears and histories of locking were not observed to have adhesions of synovium to the fat pad, but did have an entrapped remnant of ACL between the tibial plateau and femoral condyle.(ABSTRACT TRUNCATED AT 250 WORDS)