This was one-year prospective study conducted from January to December 2009 at a tertiary-care hospital in Southern India. Informed written consent was taken from all the patients. Institutional ethical clearance was obtained for this study. All patients with chronic ACL injury who underwent primary arthroscopic ACL-R using tripled hamstring tendon autograft were included in the study. Patients with associated medial or lateral collateral ligament injury or those undergoing revision ACL-R were excluded from the study. The graft was fixed to the tibial tunnel by Interference Screw (IFS) or Suture Disc (SD) and to the femoral tunnel by IFS, SD, Cross-Pin (CP) or Endo-button CL (Smith & Nephew). The reamed diameters of the tibial and femoral tunnels were noted. Post-operatively immediate accelerated physiotherapy protocol was followed in all patients to mobilize the knee joint. Closed chain exercises and isometric muscle strengthening exercises were started by 2^nd post-operative day. Full weight-bearing walking was started from 2^nd post-operative day. Patients were followed up at two weeks, six weeks, three months, six months and at one year. Patients were expected to achieve 90 range of motions at two weeks follow-up. Isokinetic and isotonic exercises were started at three months post-operatively and return to sports was allowed after six months. CT scan measurements of the femoral and tibial tunnels using Philips MX 8000 multislice CT scanner was done at one year follow-up [Table/Fig-1&2]. The slice thickness was 1 mm. Transosseous tibial tunnel diameter was measured at four levels; axial section at plateau and midpoint and sagittal section at plateau and midpoint. Femoral tunnel measurements were also done at four points; the axial section at notch, middle and the end of the tunnel and the coronoal image in the middle of the tunnel. The average of these tunnel diameters was tabulated. The widening of the tibial and femoral tunnels in different methods of fixation at 12 months follow-up was compared using paired sample test. The statistical analysis was done using SPSS version 17 software. A p-value of < 0.05 was considered significant.

[Table/Fig-1]:

CT scan measurement of tibial tunnel.

[Table/Fig-2]:

CT scan measurement of femoral tunnel.

A total of 63 patients were included in the study of which 58 (92%) were males and 5 (8%) were females. The age group varied from 18 to 43 years with mean age of 29.1 ± 5.9 years. Of the 63 patients, fixation of graft to the tibial tunnel was performed with IFS in 34 patients (54%) and SD in 29 patients (46%). On the femoral side, fixation of graft was performed using IFS in 11 patients (17%), SD in 30 patients (47.6%), Endobutton CL in 5 patients (7.9%) and CP in 17 patients (27%) [Table/Fig-3]. Average follow-up period was 12 months in different methods of fixation. The tibial tunnel widening at one year follow-up was 1.680 ± 1.08794 (19.37%) and 1.517 ± 0.94834 mm (17.39%) by IFS and SD methods respectively [Table/Fig-4]. This was found to be statistically significant (p<0.05) [Table/Fig-5]. Femoral tunnel widening at one year follow-up was 1.294 ± 0.231, 1.809 ± 0.912, 1.320 ± 0.238, 1.779 ± 0.889 mm by IFS, SD, EB, and CP methods respectively [Table/Fig-6]. Tunnel widening was found to be statistically significant (p<0.05) by all the methods. However, widening following SD method of fixation was highly significant (p<0.001) in comparison with other methods [Table/Fig-7].

[Table/Fig-3]:

Fixation method.

[Table/Fig-4]:

Tibial tunnel widening at one year.

[Table/Fig-6]:

Femoral tunnel widening at one year.

Despite its recognition, there is a paucity of knowledge about the origin and natural history of bone tunnel widening. The hamstring autograft used in ACL-R heals in three phases inside the tunnel by three major histological changes; the maturation of fibrous tissue, the new bone formation and the bone remodelling. The aetiology of tunnel widening is still not well understood. A complex interplay of biologic and mechanical factors probably contributes to tunnel widening. Biologic factors include immune-mediated increased cytokine levels or the inflammatory response caused by synovial fluid leakage within the bone tunnel. Mechanical factors include the types of graft, various methods of fixation and rehabilitation protocols [4].

CT is a standard method to measure the bone tunnel enlargement. Compared to X-ray, geometric factors like knee positioning differences or exposing distance from film surface do not influence the CT images. According to Hoher et al., suspensory graft fixation resulted in significantly greater longitudinal graft motion, known as the “bungee effect” while an aperture fixation correlates with transverse graft motion known as the “wind shield-wiper effect”. Transverse motion of the graft is directly proportional to the distance between the fixation points, with maximum transverse motion at the tunnel aperture. Suspensory methods of fixation are associated with increased tunnel widening by causing more graft micro-motion than aperture fixation [13].

Peyrache et al., noted an increase in tunnel diameter at 3 months post-operatively and no changes between 3 months and 2 years and decreases after 3 years post-operatively [4]. Hence, we decided to observe tunnel widening at 12 months follow-up with CT scan measurements compared with reamed diameter. In our study, we observed femoral and tibial tunnel widening in all methods of fixation which correlates with other studies [14,15]. The tibial tunnel measurements increased by 19.73% and 17.39% in IFS and SD method respectively, both of which were statistically significant. The femoral tunnel measurements increased by 16.75% in IFS, 22.24% in SD, 16.1% in EB, and 21.91% in cross pin fixation methods. Tunnel widening was significant in all methods of fixation. The femoral tunnel widening was more in cross pin fixation method compared to Endobutton CL group. This is comparable to another study which concluded that transfixation pin system fixation caused greater femoral tunnel enlargement compared to extra-cortical fixation methods [16]. Tunnel widening following SD method of fixation was statistically very highly significant compared to other methods of fixation.

Femoral tunnel and tibial tunnel widening varies with different methods of fixation and was maximum with suture disc method compared to others at one year follow-up after ACL-R.