From January 2017 to April 2019, 80 patients with ACL rupture were treated surgically in our department:44 males and 36 females. The age ranged from 19 to 58 years old, with an average of 37.68±9.13 years old. The time of injury ranged from 3 days to 12 months. There were 56 patients with a history of 3 months, 31 males and 25 females, with an average age of 37.70±9.47 years. There were 24 patients with a history of more than 3 months, 13 males and 11 females, with an average age of 37.63±8.46 years. All patients were injured in one knee:27 cases on the left and 53 cases on the right. X-ray film, magnetic resonance imaging and bone mineral density were measured in both knees routinely after admission. Case selection criteria: 1. only ACL rupture (including meniscus tear) was found, excluding posterior cruciate ligament and collateral ligament rupture; 2. there was no history of knee joint trauma or surgery; 3. there was joint instability and a positive Lachman test or anterior drawer test; and 4. cases of primary osteoporosis (postmenopausal osteoporosis and senile osteoporosis) were excluded.
There is a standardized database reference for the bone mineral density T value of the lumbar vertebrae and hip joint, but there is no database comparison for the local bone mineral density of the knee joint. In this study, we compared the bone mineral density (g/cm2) of the affected knee joint with that of the healthy knee joint. The results were statistically analysed by paired t tests. The measuring instrument was American Norland XR-36 dual energy X-ray absorptiometry.
Selection of operative methods
In this study, patients were grouped according to the degree of decrease in local bone mineral density before the operation: the density of the affected knee was not significantly lower than that of the healthy side (normal bone mineral density group), the local bone mineral density of the affected knee was lower than 70% of the healthy side (low bone mineral density group), and the local bone mineral density of the affected knee decreased but not by more than 30% of the healthy side. If tunnel cutting or screw splitting and tunnel enlargement or screw pull-out occurred during the operation, the fixation mode was adjusted in time according to the situation: an additional plate with a loop was used for suspension fixation at the outer entrance of the tunnel, and if the tunnel was obviously enlarged, it was necessary to carry out artificial bone grafting.
Extrusion fixation method
After successful anaesthesia, the patient was placed in the supine position, and the affected limb was placed in the 90°flexion position. Routine disinfection and towel laying were performed. An anterior medial L-shaped incision was made under the tibial tubercle of the knee, the semitendinosus tendon and gracilis tendon were cut, the muscle was removed, and the tendon line was woven at both ends. At the level of the knee joint space, an opening of 8 mm was made on both sides of the patellar ligament to the articular cavity, which was disposed into the arthroscope from the lateral entrance, additionally, the intercondylar fossa was cleared, and the scar tissue and residual ACL were removed. The tibial end of the ACL was located with a guide needle, and the tibia of the corresponding diameter was drilled to open the tibial tunnel. Then, the femoral footprint of the ACL was located with a guide needle, and the femur drill was used to open the femoral tunnel by approximately 35 mm. The braided tendon was introduced with the guide needle, and the knee was flexed by 20°. Reverse traction was implemented at both ends of the femur and tibia to maintain a certain tension, and passive movement of the affected knee was carried out to provide appropriate tension of the tendon. The femoral tunnel was fixed with a 25 mm long polylactic acid hydroxyapatite screw. The tibial tunnel was fixed with a tibial fixation wing and a 25 mm long polyetheretherketone screw (both screws and wings were produced by Smith & Nephew). The knee was moved passively, and the anterior drawer test was performed. If the knee joint was stable and the autologous tendon tension was moderate, then suturing and pressure bandaging were performed. If screw splitting or tendon cutting occurred during the operation, the mode of fixation was adjusted to suspension fixation. If the tunnel was enlarged or screws were pulled out due to osteoporosis during the operation, adjustment to suspension fixation could be carried out. Alternatively, on the basis of extrusion fixation, a loop steel plate was added to the outer entrance of the tunnel to carry out suspension fixation. If the tunnel was obviously enlarged, it was necessary to carry out artificial bone grafting.
Suspension fixation method
Harvesting of the transplanted tendon and the cleaning process of the joint cavity were carried out in the same manner as the extrusion fixation method. After the joint cavity was cleaned, the guide needle was used to locate the tibial attachment of the ACL, and the tibia was drilled to expand the tibial tunnel. Then, the femoral footprint of the ACL was located, and the femur was drilled and enlarged by approximately 35 mm in a long tunnel. The guide needle was introduced into the autologous tendon, which was pulled at both ends of the tunnel to provide a certain tension; passive movement of the affected knee was carried out, providing the autologous tendon with the appropriate tension. A plate with a loop (Smith & Nephew) was used, the loop was cut, the tendon traction line was passed through both of the plate holes outside the thigh, and the plate was pushed forward to make sure the plate was adhered to the femoral cortex; multiple knots were made on the surface of the plate so that the plate was firmly stuck at the outer entrance of the femoral tunnel to achieve suspension fixation. The outer entrance of the tibial tunnel was also suspended and fixed with a plate with a loop. The affected knee was moved passively again, and the anterior drawer test was performed. If the knee was stable and the tension of the transplanted tendon was moderate, the knee was sutured and bandaged under pressure.
After the operation, a local cold compress was applied, the affected limb was raised, hinge braces were worn, and isometric contraction training of the quadriceps femoris and hamstring muscles was performed every day. One to two weeks after the operation, the affected limb was locked in a completely straight position, and the use of double crutches was supported until complete loading. Passive flexion and extension could be performed daily starting 3 to 4 weeks after the operation, reaching knee flexion ≥120°. Five to eight weeks after the operation, the affected knee joint could be actively moved to reach 90° of knee flexion, and semi-squatting exercises could be used to improve muscle strength. Starting at the 9th week after the operation, forward uniform speed running and backward running could be carried out.
Postoperative follow-up and evaluation of the curative effect
The patients were followed 1 month, 2 months, 3 months, 6 months and 12 months after the operation. All patients were examined by the anterior drawer test and Lachman test. Patients with suspension fixation were re-examined by X-ray, and squeeze fixation did not need to be photographed because the screw was not visible. The function of the knee joint was evaluated by the IKDC scale score and Lysholm knee joint scale score.
The data of this study were analysed by the statistical software SPSS 19.0, and the measurement data were expressed as the mean ± standard deviation. Paired t-tests were used to compare the bone mineral density of both knee joints and the functional score of the affected knee before and after the operation. Group t-tests were used to compare the decreasing degree of bone mineral density within 3 months and more than 3 months. P <0.05 was considered statistically significant.