Anterior Cruciate Ligament Injury and Reconstruction


Abstract
An anterior cruciate ligament injury is an important sports injury. Failure to reconstruct a torn ACL usually leads to both an inability to satisfactorily participate in vigorous activities and the gradual deterioration of the knee function. Arthroscopic reconstructive surgery has become the standard of care for the majority of patients. The search for ideal graft is still elusive. Quadrupled hamstring tendon autograft and allografts have recently gained popularity. The standard for postoperative care and rehabilitation has been challenged in the literature, with reports of better results with accelerated protocols leading to earlier return to sporting activity.1
Keywords: anterior cruciate ligament injury, arthroscopic reconstruction, postoperative rehabilitation.
Case report
Mr N, a 21 year old student, alleged sports injury 2 years ago while playing football. He complained of pain and instability while walking on uneven surface. He was tackled from behind and twisted his knee. He also noted a popping sound while falling down to the ground. He developed an immediate swelling of his right knee and unable to resume the game. He sought an outpatient treatment and was put on long leg backslab for six weeks duration. He tried to return to sporting activity three months later but noticed that the knee would give way while turning and the knee would swell up after the game. He claimed no history of locking.
He was referred to arthroscopy and sports injury unit HKL for further evaluation and management. A thorough physical examination was performed. On examination, he was a well built man with normal gait. There was no deformity of the right knee but there was evidence of wasting of vastus medialis oblique muscle. There was mild effusion of the right knee. There was no joint line tenderness. The range of motion of the right knee were normal. An anterior drawer test revealed a positive sign (Grade 2 laxity) which was confirmed by Lachman’s test. There was no posterior sagging. Pivot shift test and dial test were negative and there were no laxity of medial and lateral collateral ligament. A clinical diagnosis of anterior cruciate ligament (ACL) injury was made. The patient was advised for anterior cruciate ligament reconstruction with hamstring autograft .
The procedure was done under general anaesthesia. An examination under anaesthesia was performed and confirmed the clinical findings. The patient was placed in supine position with the operated leg on the arthroscopic leg holder. The other leg was abducted, flexed at the hip and knee and placed in a padded support out of the surgical field.
Hamstring tendon graft harvest was performed through a vertical skin incision centered over the tibial insertion of the pes anserine tendons. The sartorius fascia was exposed by sharp and blunt dissection. The conjoined tibial insertion of gracilis and semitendinosus tendons was detached from the tibia by making an inverted L-shaped incision through the sartorius fascia. Blunt scissors dissection was used to free the tendon from the undersurface of the sartorius fascia. The fascial bands were also released with blunt and sharp dissection. Running whipstitch sutures were placed in the end of the gracilis and semitendinosus tendons. A slotted tendon stripper was used to harvest the tendons. The tendons were harvested by flexing the knee to 90 degrees and advancing the tendon stripper parallel to the tendon by a slow, steady, rotating motion.
A graft preparation board was used to prepare the graft. Residual muscle fibers on the proximal end of both tendons were removed. The two tendons were cut to the same length, and the proximal end of each tendon was tubularized with a running, baseball-style whipstitch of a No. 2 nonabsorbable suture. The tendons were folded into two to make a quadrupled graft. The diameter of the graft is measured to the nearest 0.5 mm by use of a 0.5-mm incremental sizing tubes. Cutting the tendons to a length of 22-24 cm will usually ensure that the sutured portions of each tendon will lie within the tibial tunnel. The graft was then pre-tensioned to 10 lbs.
An anteromedial portal at the level of the inferior pole of the patella adjacent to the medial border of the patellar tendon was created for instrumentation and viewing of the medial wall of the lateral femoral condyle. A high anterolateral portal at the level of the inferior pole of the patella adjacent to the lateral border of the patellar tendon is used for the routine viewing portal. A routine diagnostic arthroscopy was performed, and associated meniscal and chondral injuries were treated appropriately. The remaining anterior cruciate ligament stump was identified and was preserved. The tibial tunnel was prepared using the tibial aimer set at 45 to 55 degrees. The tip of the tibial aimer was placed intraarticularly through the anteromedial portal and positioned at the center of the remaining ACL stump. An appropriate size cannulated reamer was used to drill the tibial tunnel through a guide wire. An endoscopic femoral aimer was placed through the tibial aimer and a guide wire was drilled through it. A microfracture awl was passed through the accessory medial portal and used to mark the starting point for the femoral tunnel under arthroscopic guidance. The 2.7-mm drill-tipped guide wire was drilled out through the soft tissues of the lateral thigh. A closed-end femoral socket was drilled with the appropriately sized, calibrated endoscopic 0.5-mm drill bit. A loop of No. 5 nonabsorbable suture was inserted into the eyelet of the passing pin, and the ends of the suture are passed out of the lateral thigh. The loop of No. 5 suture was passed into the joint and positioned at the entrance to the femoral tunnel.
The loop of No. 5 suture was retrieved from the femoral tunnel and pulled out of the tibial tunnel. The No. 2 flipping suture and No. 5 passing suture were passed through the loop of the No. 5 suture and pulled out the lateral thigh. Under arthroscopic visualization, the EndoButton and the attached hamstring tendon graft were passed across the joint and into the femoral socket by use of the No. 5 passing suture. The No. 2 flipping suture was pulled in a proximal direction, parallel to the femoral tunnel, and the EndoButton will be felt to flip against the lateral femoral cortex.
A constant tension was applied to the opposite end of the graft while the bioabsorbable screw was inserted into the tibial tunnel. The stability and range of motion of the knee were checked. Graft tension and impingement were assessed with the arthroscope. A closed drain suction was inserted into anteromedial portal and secured with an anchor suture. Postoperatively, a cryocuff was applied for the next 48 hours. The patient was instructed to do static quadriceps exercise, knee mobilisation exercise, gastrosoleus exercise, ankle exercise and straight leg raising exercise for the first 2 week post surgery. The patient was discharged on day three postoperatively with an extension brace.
He was seen in the clinic 2 weeks later and the wound was inspected. The patient was allowed knee flexion with the brace up to 90 degrees. He was taught closed chain exercises and strengthening exercises. The strengthening exercise includes quadriceps isometrics, quadricep-hamstring co-contraction, straight leg raises and an active knee extension. Balance and proprioceptive training were also taught. An aerobic conditioning exercise was started at 6 weeks. The exercises include stationary bike (adjust to protect patellofemoral joint), elliptical machine, pool exercises. Walking, stair climbing exercise and ski machine were started at 12 weeks postoperatively. Straight running was allowed at 6 months and he was allowed to return to full sport at 9 months.

Discussion
The anterior cruciate ligament (ACL) is the most common totally disrupted ligament of the knee.2It has been estimated that more than 80,000 ACL tears occur in the United States each year and that 50,000 of these are surgically reconstructed at an annual cost of approximately $8.5 million.3 The anterior cruciate ligament is composed of longitudinally oriented bundles of collagen tissue arranged in fascicular subunits within larger functional bands. The ligament is 31 to 35 mm in length and 31.3 mm2 in cross section. Microscopically, the interlacing fibrils (150 to 250 nanometre in diameter are grouped into fibers (1 to 20 um in diameter). The ligament is surrounded by synovium, thus making it extrasynovial. The ACL consists of two individual fiber bundles, named for their insertion points on the tibial footprint. The larger anteromedial (AM) bundle inserts anteromedially on the tibial side and originates more proximally on the femoral side than the posterolateral (PL) bundle, which is posterolateral relative to AM bundle. The tibial attachment site is larger and more secure than the femoral site. It is attached in a fossa in front of and lateral to anterior tibial spine. The anterior bundle goes forward to the level of transverse meniscal ligament. The primary blood supply to the ligament is from the middle geniculate artery, which pierces the posterior capsule and enters the intercondylar notch near the femoral attachment. Additional supply comes from the retropatellar fat pad via the inferior medial and lateral geniculate arteries. This source plays a more important role when the ligament is injured. The osseous attachments of the anterior cruciate ligament contribute little to its vascularity.4The posterior articular nerve, a branch of the tibial nerve, innervates the anterior cruciate ligament. Histological study has revealed nerve fibers of the size most consistent with transmitting pain in the intrafascicular spaces. Mechanoreceptors also have been identified on the surface of the ligament, mostly at the insertions of the ligament (especially femoral), well beneath the external synovial sheath.5
Studies indicate that the AM bundle tightens in flexion while the PL bundle relaxes; in extension, the PL bundle tightens while the AM bundle relaxes. What is unusual about the workings of the two bundles is the way their insertion points on the femur relate to each other in flexion and extension. In extension, their insertion points are vertical to each other, but with the knee in 90 degrees flexion, the insertion points are horizontal to each other. Likewise, the bundles themselves shift from parallel orientation in extension to crossed orientation in flexion.
The anterior cruciate ligament is the primary restraint to anterior tibial displacement, accounting for approximately 85% of the resistance to the anterior drawer test when the knee is at 90 degrees of flexion and neutral rotation. At full extension, it provides 75% of resistance. Deep medial collateral ligament is a major secondary restraint to anterior translation. Selective sectioning of the anterior cruciate ligament has shown that the anteromedial band is tight in flexion, providing the primary restraint, whereas the posterolateral bulky portion of this ligament is tight in extension. The posterolateral bundle provides the principal resistance for hyperextension. Tension in the anterior cruciate ligament is least at 30 to 40 degrees of knee flexion. The anterior cruciate ligament also functions as a secondary restraint on tibial rotation and varus-valgus angulation at full extension. The ultimate tensile strength of the ACL is 2160 ± 157 N and the linear stiffness is 242 ± 28 N/mm.6
Injury of the ACL is most commonly associated with with valgus and external rotation, hyperextension, deceleration and rotational knee movement. Often the history is of non-contact deceleration, jumping or cutting action. The patient often describes the knee as having been hyperextended accompanied by an audible pop. Frequently the swelling develops immediately or few hours after the surgery indicating haemarthrosis. The patient usually unable to continue the game. Subsequently the patient usually complained of instability and pain.
The anterior drawer, Lachman, pivot shift, and arthrometer (e.g., KT-1000) tests are the most common methods used to make this assessment. Even though the anterior drawer test is commonly described as a means with which to assess anterior cruciate ligament laxity, it can be an unreliable measure of anterior knee laxity.7When a patient has an acute injury, hamstring spasms and flexion of the knee to 90° cause pain that makes it difficult to perform an accurate examination. Secondary stabilizers of the knee (the osseous contour of the joint, the posterior meniscal horns, and the medial collateral ligament) may also interfere with the ability to obtain a true assessment of anterior knee translation. Usually, the result of the anterior drawer test is abnormal when secondary restraints are also injured. For these reasons, the Lachman test is more sensitive than the anterior drawer test for detecting anterior cruciate ligament insufficiency. Furthermore, biomechanical studies have revealed that there is greater strain in the anterior cruciate ligament at 30° of flexion than there is at 90° of flexion.8
A positive pivot-shift test represents the subluxation-reduction phenomenon associated with a knee in which the anterior cruciate ligament is functionally deficient. The tibia is subluxated relative to the femur in extension and is reduced in flexion. When the knee has a deficient anterior cruciate ligament, the femur is subluxated relative to the tibia by gravity and the iliotibial band lies anterior to the instant center of rotation of the knee. As the knee is flexed to approximately 20° to 25°, the pivot shift phenomenon occurs as the knee reduces.9 The test result is graded as 1+ (glide), 2+ (jump), or 3+ (transient lock). This test is better than the anterior drawer or Lachman test for defining anterior cruciate ligament insufficiency, and a positive result is considered indicative of anterior cruciate ligament deficiency. It is especially useful for determining if anterior laxity will be clinically relevant. Therefore, the pivot shift test is the most helpful for defining the extent of an injury to the anterior cruciate ligament, especially when it is performed with the patient under anaesthesia. It is important to note that this examination is quite painful. An anxious and tensed patient may gives a negative result. An arthrometer could be used as an adjunct to define pathologic anterior translation. More than 3 mm of anterior translation on arthrometric testing suggests anterior cruciate ligament deficiency.10These devices also are useful for documentation of surgical results both intraoperatively and postoperatively.
Radiographic studies also are useful in diagnosis of anterior cruciate ligament injuries. Plain radiographs often are normal; however, a tibial eminence fracture indicates an avulsion of the tibial attachment of the anterior cruciate ligament. The Segond fracture, or avulsion fracture of the lateral capsule, is pathognomonic of an anterior cruciate ligament tear. MRI is the most helpful diagnostic radiographic technique. It is the most appropriate screening tool before therapeutic arthroscopy. It is preferable to diagnostic arthroscopy in most patients because it avoids the surgical risks of arthroscopy.11
The natural history of ACL deficient knee is still controversial. The ACL has limited ability to heal. Untreated isolated ACL rupture and resultant abnormal force distribution can lead to progressive knee deterioration. In chronic ACL injury, proinflammatory cytokines such as interleukin-1 and tumor necrosis factor α are elevated whereas protective inflammatory proteins such as interleukin receptor antagonist protein are markedly decreased. Gender and intercondylar notch have been implicated in ACL injury.12The notch index is the ratio of width of inter condylar notch to the width of distal femur at the level of the popliteal groove measured on a tunnel view radiograph of the knee. The normal intercondylar notch ratio was 0.231 ± 0.044.
The treatment options available include nonoperative management, repair of the anterior cruciate ligament (either isolated or with augmentation), and reconstruction with either autograft or allograft tissues or synthetics. Nonoperative treatment is a viable option for a patient who is willing to make lifestyle changes and avoid the activities that cause recurrent instability. It may include a short period of immobilization, bracing, a progressive rehabilitation program, and regular follow-up evaluations. An early range of motion is the goal in order to prevent arthrofibrosis.
Acute repair is appropriate when a bony avulsion occurs with the anterior cruciate ligament attached. Anterior cruciate ligament avulsions usually occur from the tibial insertion. The avulsed bone fragment often can be replaced and fixed with sutures or passed through transosseous drill holes or screws placed through the fragment into the bed.
Reconstructive surgery for ACL insufficiency includes extraarticular and intraarticular procedures. Extraarticular procedures generally create a restraining band on the lateral side of the knee, extending from the lateral femoral epicondyle to the Gerdy tubercle in a line parallel with the anterior cruciate ligament. However, these procedures were associated with high failure rate when used alone.13 Currently, extraarticular procedures are used primarily in conjunction with an intraarticular reconstruction.
The advances made in arthroscopy have led to the development of arthroscopic techniques for anterior cruciate ligament reconstruction. The results were improved dramatically with increased understanding of technical issues of graft selection, placement, tensioning, and fixation as well as of postoperative rehabilitation. The procedures usually delayed until after the patient has recovered from the initial injury. Resolution of inflammation around the knee and return of full motion reduce the incidence of postoperative knee stiffness.
The graft selection includes autografts, allografts and synthetic grafts. Autografts have the advantages of low risk of adverse inflammatory reaction and virtually no risk of disease transmission. As a biological graft, an autograft undergoes revascularization and recollagenization, but initially a 50% loss of graft strength occurs after implantation. Therefore, it is desirable to begin with a graft stronger than the tissue to be replaced. The most common current graft choices are bone–patellar tendon–bone graft and the quadrupled hamstring tendon graft. The bone–patellar tendon–bone graft usually is an 8- to 11-mm-wide graft taken from the central third of the patellar tendon, with its adjacent patella and tibial bone blocks. This graft's attractive features include its high ultimate tensile load (approximately 2300 N), its stiffness (approximately 620 N/mm), and the possibility for rigid fixation with its attached bony ends. However, it is complicated by an anterior knee pain which can last up to six weeks. The use of the hamstring tendon graft has increased in recent years because of its relatively low donor site morbidity. The ultimate tensile load of a quadrupled hamstring tendon graft reported to be as high as 4108 N. This quadruple-stranded graft also provides a multiple-bundle replacement graft that may better approximate the function of the two-bundle anterior cruciate ligament. Disadvantages of this soft-tissue graft include the concern over tendon healing within the osseous tunnels and the lack of rigid bony fixation. The hamstring tendon graft regenerate but it often heals in a non-anatomic position more proximally on the medial tibial plateau. A meta-analysis of patellar tendon autograft as compared with allograft revealed significantly better results in term of the rate of graft rupture and the performance of a hop test in association with the use of autograft.14
Allografts are a good choice when there are limitations in a patient's own tissue availability. Patellar tendon, hamstring tendon, and even Achilles tendon allografts can be used as ACL graft tissues and are inserted and fixed with the same techniques that are used for autografts. Allograft has the advantage of causing less perioperative surgical pain and morbidity. The disadvantages include slower incorporation rate, the possibility for disease transmission, increased residual laxity and slightly reduced strength compared with autogenous reconstructions. The dilemma with allografts is that they can't be 100% sterilized without altering or even destroying the tensile strength of the graft tissue. Currently the preferred allograft treatment technique is a fresh frozen graft; the tissue is harvested, cleaned and then frozen in liquid nitrogen.
Synthetic grafts are being researched and developed to create the perfect ACL replacement. A newer synthetic augmentation graft, a series of woven polymer fibers with similar mechanical properties to ligaments, is under study in Europe. This material is biocompatible and apparently serves as a scaffold to allow native tissue to gradually grow in over 3-4 years. It slowly weakens over time which gives the new biologic tissue a progressive load stimulus that allows it to adapt and strengthen to its ultimate maturity.
The placement of the graft is important in reproducing the function of an intact anterior cruciate ligament. Error in the femoral sites is more critical due to proximity to the center of axis of knee motion. Femoral tunnel that is too anterior will result in lengthening of the intraarticular distance between tunnels with knee flexion. This will results in loss of flexion or stretching of the graft that may results in graft failure. The placement on the side wall of the lateral condyle of the femur at 1 o’clock position reproduces the femoral attachment site of the anterior cruciate ligament and provides rotational stability.
Double bundle reconstruction shows better rotational stability as compared with single bundle reconstruction.15,16 Markolf et al demonstrated that single bundle reconstruction is sufficient to restore intact knee kinematics during pivot-shift manoeuvres and that overtensioning of the graft in double-bundle reconstructions can reduce the rotation to less than that of the intact knee.17
The placement of the tibial tunnel is also important for clinical outcome. Studies of current techniques have suggested that placement of the tibial tunnel in the posterior portion of the anterior cruciate ligament footprint is important in order to avoid notch impingement. Many surgeons use the posterior cruciate ligament, the medial tibial eminence, and the free edge of the anterior horn of the lateral meniscus to guide tunnel placement, but there continue to be large variations in the orientation of the tibial tunnel. Computer navigation has been proposed as a way to optimize accurate tunnel placement in anterior cruciate ligament reconstruction. A randomized controlled trial comparing manual and computer-guided placement of the tibial tunnel showed no significant differences between the two groups.18
Rehabilitation of the reconstructed knee is critical for the successful return to risky cutting and jumping activities. The goal of rehabilitation after anterior cruciate ligament surgery is to restore normal joint motion and strength while protecting the ligament graft. General principles of postoperative rehabilitation of ACL reconstruction include reduction of swelling, mobilisation, strengthening exercises, proprioception and kinetic chain exercises. Early restoration of full extension is important. Studies showed that there is no substantial advantage for continuous passive motion (CPM) use except for a possible decrease in pain.19,20,21
Electrical muscle stimulation does not significantly decrease muscle atrophy in patients after anterior cruciate ligament surgery. It also does not have any long-term strengthening effect. However it is useful for muscle reeducation if the patient has a poor quadriceps set. The early emphasis of strengthening is on the hamstrings, which function in concert with the anterior cruciate ligament to prevent anterior translation of the tibia. Also, their strengthening does not stress the graft. Patella mobilisation is important in preventing stiffness and helps to stimulate the healing.
Early weight bearing is allowed immediately. It may decrease patellofemoral pain. No study demonstrated a potentially worse outcome when bracing was not used. Importantly, no increase in postoperative injuries, increased pain, decreased range of motion, or increased knee laxity was found in the control groups that were not braced following surgery. Several studies showed that postoperative bracing was not necessary following ACL reconstruction.22
A closed kinetic chain (CKC) exercises are prescribed early in the rehabilitation program. CKC exercises are performed where the foot is fixed and cannot move. The foot remains in constant contact with the surface, usually the ground or the base of a machine. These exercises are typically weight bearing exercises, where an athlete or patient uses their own body weight and/ or external weight. When external weight is added, it is usually rested across the back of the shoulders or the front of the chest. Examples of these exercises would be the Squat (both front and back), Leg Press, Lunges, Power Clean, and Snatch. CKC exercises concentrates on a co-contraction of the quadriceps, hamstrings, hip flexors, soleus, and gastrocnemius muscles. An open chain exercises could be safely added at 6 weeks postoperatively without risk of increased knee laxity and with the added potential of improved quadriceps strength and better return to sports.23ACL rehabilitation protocols slowly evolved from a 12-month time frame to a generally accepted 6-month time frame for return to sports. Beynnon et al concluded that accelerated rehabilitation for 19 weeks did not result in deleterious effects compared with a 32-week program.24


Conclusion
ACL reconstruction is indicated for active patients with unstable knees following an ACL rupture. Great variability exists in the practice of ACL reconstruction, including the timing of reconstruction, surgical technique, and postoperative protocol. The graft choices are wide and variable but generally have the same outcome. Accelerated rehabilitation protocol has led to earlier return to sporting activity.
References
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