title: Tunnel enlargement 5 years after anterior cruciate ligament reconstruction: a radiographic and functional evaluation.
abstract: OBJECTIVE
  The aetiology and clinical significance of enlargement of bone tunnels following anterior cruciate ligament (ACL) reconstruction remains controversial. This phenomenon has been attributed to biological factors and mechanical factors. We wanted to study the amount of femoral and tibial tunnel enlargement 5 years post-ACL reconstruction. By standardizing the type of femoral fixation, we also wanted to determine whether the type of tibial fixation had any bearing to the amount of tibial tunnel enlargement.
  
  
  METHODS
  All patients who underwent arthroscopic hamstring autograft ACL reconstruction between January 2000 and December 2000 were identified. All grafts were fixed with close-looped endobutton proximally. The grafts were fixed on the tibial side with staples or bioabsorbable interference screws. At a minimum of 5 years after surgery, these patients were recalled. They were assessed with Lysholm knee, Tegner activity and the IKDC Subjective and Objective forms and a KT-1000 arthrometer. The diameter of the bone tunnels and tunnel positions in the anterior-posterior and lateral radiographs were measured using digital callipers by a two blinded researchers.
  
  
  RESULTS
  We found that the femoral tunnel enlarged more than the tibial tunnel. At 5 years, the mean tibial tunnel enlargement was 2.46 mm and the mean femoral tunnel enlargement was 3.23 mm. All 54 patients had endobutton femoral fixation. Of them, 34 patients had tibial graft fixation with staples (extracortical fixation) and 20 patients had tibial graft fixation with bioabsorbable interference screws (aperture fixation). The mean enlargement as measured by the two independent observers in the extracortical group was 1.98 mm (24.7 %)* and 1.51 mm (18.2 %)**compared to 3.27 mm (40.4 %)* and 2.92 mm (30.0 %)** in the aperture fixation group. This difference in tibial tunnel enlargement between the groups was significant (p < 0.001, mean difference 1.29 mm). However, this was not correlated with any significant difference in clinical outcome at 5 years.
  
  
  CONCLUSIONS
  We, like some authors, have shown that the use of interference screws in tibial fixation despite being aperture fixation actually has a greater amount of tibial enlargement. This lends weight to the biological theory to tunnel enlargement.
authors: Department of Orthopaedic Surgery, Changi General Hospital, 2, Simei Street 3, Singapore, 529889, Republic of Singapore, davelyh@singnet.com.sg.
authors: Lee Yee Han
authors: LY
authors: Dave
authors: Ong Kee
authors: OK
authors: Leong
authors: Sarina Abdul
authors: SA
authors: Karim
authors: Chang Haw
authors: CH
authors: Chong
mesh_terms: D000293:Adolescent; D000328:Adult; D059549:Anterior Cruciate Ligament Reconstruction / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D001863:Bone Screws / Q000009:adverse effects*; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D011859:Radiography; D012189:Retrospective Studies; D013977:Tibia / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D016896:Treatment Outcome; D055815:Young Adult